Note: Descriptions are shown in the official language in which they were submitted.
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FRACTIONATION OF ALKYL CARBOXYLATE MIXTURES
Technical Field
The field of this invention is the separation of alkyl
fatty ~C~-C26) carboxylate mixture to obtain fractions of
lesser degree of unsaturation and of higher degree of un-
;~ 5 saturation (i.e. separating such mixture according to degree
~ of unsaturation). The separated fractions are useful, for
i example, as chemical intermediates in the manufacture of
fatty chemical derivatives.
; Fractional distillation is the most common method now
being used commercially to separate alkyl fatty carboxylate
mixtures. This unit operation separates primarily on the
basis of chain length. While it may provide very slight
separation on the basis of unsaturation with conventional
equipment, adequate separation would re~uire a very large
number of theoretical stages.
Fractional solvent crystallization, which is used to
separate fatty acids on the basis of unsaturation, is not
economic for alkyl fatty carboxylates. Temperatures of
minus 50F to minus 70F and lower would have to be used,
~; 20 the crystals would be very fragile, and there would be a
mutual solubility between unsaturate components; this provides
v a very expensive process for a substantially incomplete
separation.
~` Urea adduction is another uneconomic process for
separating alkyl fatty carboxylates. This consists, for
example, of admixing the mixture to be separated with urea
and acetone and cooling whereby the urea forms a crystal cage
around the highest melting point component (usually the
saturates~. Recovery of separated fraction from the adduct
is difficult. Moreover, this process is ~
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not as effective for separating one unsaturate from
another. Furthermore, this process is difficult to
adapt to continuous operation.
Background Art
Neuzil et al U.S. 4,048,205 and Neuzil et al U.S.
4,049,688 and Logan et al U.S. Patent 4,210,594 issued
July 1, 1980 disclose the fractionation of alkyl fatty
carboxylate mixtures using synthetic crystalline
aluminosilicates (zeolites). These crystalline
alu~inosilicate adsorbents typically contain up to
about 25% amorphous aluminosilicate, e.g., clay. The
`, process of the invention herein differs, for example,
in the adsorbent which is advantageous over the
crystalline adsorbents from the standpoints of
versatility (in that, with the adsorbent herein, the
same equipment and packing is advantageously used for
separation of alkyl carboxylates and triglycerides
- this is not true for crystalline zeolites) and flex-
'! ibility (in that various ratios of surface-silicon
~ 20 atoms to aluminum atoms and various surface areas are
- readily available for the adsorbent herein - there is
substantially less choice for crystalline zeolites).
Lubsen et al U.S. Patent 4,189,442, issued February
19, 1980 discloses the fractionation of alkyl fatty
carboxylate mixtures utilizing macroreticular strong
acid cation exchange resin adsorbents. Tbe invention
;~ herein differs, for example, in utilizing an adsorbent
different from that disclosed in the Lubsen patent and
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advantageous over the adsorbent disclosed in the Logan
patent from the standpoints of flexibility, capacity,
cost, and of being inorganic rather than organic in
~ature.
It is known on an analytical scale to separate
alkyl fatty carboxylate mixtures utilizing silica
gel treated with silver nitrate. See Chemistry and
Industry 24, pp. 1049-50 (June 1962). The adsorbent
there has the disadvantage of having a short life cycle
in that the silver nitrate is leached out since it is
not chemically attached. The adsorbent used herein has
no such short life cycle problem.
British 1,476,511 (complete specification published
June 16, 1977) which corresponds to German 2,335,890,
assigned to Henkel, discloses using an aluminosilicate
clay as an acidic catalyst to polymerize multiple
unsaturated components of a mixture of esters of fatty
acids and distilling to separate unpolymerized material
from polymerized material. Such process has the disad-
vantage of producing unuseful polymerized material. The
process of the instant invention is carried out without
significant polymerization occurring.
Lam et al, "Silver Loaded Aluminosilicate As a
Stationary Phase for the Liquid Chromatographic
Separation of Unsaturated Compounds", J. Chromatog.
; Sci. 15 (7), 234-8 (1977) discloses the analytical
(chromatographic) separation of bromophenacyl carboxy-
lates on the basis of unsaturation utilizing silvered,
surface aluminated silica gel adsorbents of micropar-
ticulate particle size (which particle size is not
readily handled in a non-analytical commercial context
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and can result in significant loss due to suspension
of particles in solvent. The process of the instant
invention differs at least in the feedstock and the
adsorbent particle size.
The invention herein involves fractionating alkyl
fatty (C6-C26) carboxylate mixture according to
degree of unsaturation utilizing selected solvent(s)
and selected surface aluminated silica gel adsorbent.
It comprises the steps of:
(a) contacting a solution of said mixture in solvent
with surface aluminated silica gel adsorbent to
selectively adsorb alkyl carboxylate of higher deqree
of unsaturation and to leave in solution in solvent a
fraction of said mixture enriched in content of alkyl
carboxylate of lesser degree of unsaturation,
(b) removing solution of fraction enriched in content
of alkyl carboxylate of lesser degree of unsaturation
from contact with adsorbent which has selectively
adsorbed alkyl carboxylate of higher degree of
unsaturation,
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(c) contacting adsorbent which has selectively adsorbed
alkyl carboxylate of higher degree of unsaturation with
solvent to cause desorption of adsorbed alkyl carboxy-
late and provide solution in solvent of fraction
S enriched in content of alkyl carboxylate of higher
degree of unsaturation,
(d) removing solution of fraction enriched in content
of alkyl carboxylate of higher degree of unsaturation
from contact with adsorbent.
The feed (sometimes called feedstock) is a mixture
of alkyl carboxylates with different degrees of unsatur-
ation in the carbon chain in the carboxylic acid moiety
(a mixture of alkyl carboxylate of higher degree of
unsaturation with alkyl carboxylate of lesser degree of
unsaturation) which is tok be separaed into fractions
of higher degree of unsaturation and lesser degree of
unsaturation. Alkyl carboxylates in the feed have alkyl
containing one to four carbon atoms and carboxylic acid
moiety with a carbon chain containing from 6 to 26
carbon atoms.
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; The feed is dissolved in particular solvent ( the
adsorption vehicle). The solution which is formed is
contacted with particular surface aluminated silica gel
adsorbent. Alkyl carboxylate of higher degree of unsatu-
ration is selectively adsorbed on such adsorbent, and
a fraction of the mixture which is enriched (compared to
the feed) in content of alkyl carboxylate of lesser degree
of unsaturation is left in solution in solvent.
Solution in solvent of the fraction which is
enriched in content of alkyl carboxylate of lesser degree
of unsaturation is removed from contact with the
adsorbent which has selectively adsorbed alkyl carboxylate
of higher degree of un~aturation; this solution is
denoted a raffinate. Fraction enriched in content of
alkyl carboxylate of lesser degree of unsaturation can
readily be recovered from the raffinate as described
later.
The adsorbent which has selectively adsorbed thereon
alkyl carboxylate of higher degree of unsaturation is
~ contacted with particular solvent (the desorbent) to
i 20 cause desorption of adsorbed alkyl carboxylate and
' provide a solution in the solvent of fraction enriched
, (¢ompared to the feed) in content of alkyl carboxylate
of higher degree of unsaturation.
Solution in solvent of fraction enriched in content
of alkyl carboxylate of higher degree of unsaturation
is removed from contact with the adsorbent which has
undergone desorption of alkyl carboxylate; this solution
- is denoted an extract. Fraction enriched in content of
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alkyl carboxylate of higher degree of unsaturation
can be readily recovered from the extract as described
later.
Preferred is a process where the solvent which is
used to dissolve feed for selective adsorption (that is,
the adsorption vehicle), and the solvent which is
used as the vehicle for desorption (that is, the
desorbent) have the same composition. Such process is
conveniently referred to herein as a one solvent process.
Preferably, such one solvent process is carried out
continuously utilizing a simulated moving bed unit
operation.
Less preferred is a process where the solvent which
is used as the dissolving phase during adsorption and
the solvent which is used as the vehicle for desorption
have different compositions. This process is conveniently
referred to herein as a two solvent process.
In general, the solvent(s) utilized herein (whether
in a one solvent-process or in a two solvent process) is
(are) characterized by a solubility parameter (on a 25C
basis) ranging from about 7.0 to about 15.0, a solubility
parameter dispersion component (on a 25C basis) ranging
from about 7.0 to about 9.0, a solubility parameter polar
component (on a 25C basis) ranging from 0 to about 6.0
and a solubility parameter hydrogen bonding component (on
` a 25C basis) ranging from 0 to about 11.5.
The surface aluminated silica gel adsorbent for
the process herein is a synthetic amorphous alumino-
;~ silicate cation exchange material. It is homogeneous
with respect to silicon atoms but not with respect to
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aluminum atoms; aluminum atoms are present essentially
entirely at the surface of the adsorbent (i.e., they
are associated with surface-silicon atoms) and are
considered to be essentially completely in the form of
aluminate moieties.
The adsorbent is derived from silica gel having
a surface area of at least about 100 square meters per
gram. The adsorbent is further characterized by a ratio
of surface-silicon atoms to aluminum atoms ranging from
about 3:1 to about 20:1, a moisture content less than about
10~ by weight, and a particle size ranging from about 200
mesh to about 20 mesh.
The adsorbent has cation substituents selected from
; the group consisting of cation substituents capable of
fo`rming ~ complexes and cation substituents not capable of
forming ~ complexes and combinations of these.
The adsorbent is formed by first treating particular
silica gel with aluminate ion; then, if necessary, adjusting
the cation content (e.g. by providing a selected level of
cation substituents capable of forming ~ complexes); and
adjusting the moisture content. Particle size can also be
adjusted.
The solvent~s) (that is, the adsorption vehicle and
;i the desorbent, whether in a one solvent process or a twosolvent process), the ratio of surface-silicon atoms to
` aluminum atoms in the adsorbent, and the level of cation sub-
~ stituents capable of forming ~ complexes (which level can
r range from none at all up to 100% of exchange capacity) are
; selected to provide selectivity during adsorption and satis-
factory desorption of adsorbed alkyl carboxylate.
~i Processing is carried out without significant poly-
;- merization of alkyl carboxylate occurring.
. The invention herein contemplates one stage processing
~, as well as processing in a plurality of stages. One stage
processing is suitable for separating a mixture into two
fractions. Multistage processing is suitable for separating
a mixture into more than two ~ractions.
As used herein, the term "selectivity" in the phrase
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"selectively adsorb" describes the ability of the adsorbent
to preferentially adsorb a component or components. In
practice, the component(s~ which is (are) preferentially
adsorbed, is (are) rarely ever the only component(s) adsorbed.
For example, if the feed contains one part of a first
component and one part of a second component, and 0.8 parts
of the first component and 0.2 parts of the second component
are adsorbed, the first component is selectively adsorbed.
The magnitude of the selective adsorption is expressed
herein in terms of relative selectivity, that is, the ratio
of two components in the adsorbed phase (extract) divided by
the ratio of the same two components in the unadsorbed phase
(raffinate). In other words, relative selectivity as used
herein is defined by the following equation:
[Concentration M/Concentration N]A
Selectivity =
[Concentration M/Concentration N]U
where M and N are two components of the feed represented in
volume or weight percent and the subscripts A and U
represent the adsorbed and unadsorbed phases respectively.
When the selectivity is 1.0, there is no preferential
adsorption of one component over the other. A selectivity
larger than 1.0 indicates preferential adsorption of component
M; in other words, the extract phase is enriched in M and
the raffinate phase is enriched in N. The farther removed
the selectivity is from 1.0, the more complete the
'~ separation.
The amount selectively adsorbed per unit volume of
adsorbent in a batch equilibrium test (mixing of feed
~ 30 dissolved in solvent with adsorbent for up to one hour or
;~ until no further change in the chemical composition of the
liquid phase occurs) is the static capacity of the adsorbent.
An advantage in static capacity indicates a potential
;~ advantage in dynamic capacity. Dynamic capacity is the
production rate in continuous operation in apparatus of
predetermined size to obtain predetermined purity product(s).
The term "capacity" as used herein means both static and
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dynamic capacity unless the context indicates.otherwise.
Separating "according-to degree of unsaturation" is
used herein to mean separating an alkyl ¢arboxylate mixture
(containing alkyl carboxylates with different degrees of
unsaturation) to provide first fraction.enriched in alkyl
carboxylate of higher degree of unsaturation and second
fraction enriched in alkyl carboxylate of.lesser.degree of
unsaturation. The more double bonds in the carbon chain in
the carboxylic acid moiety, the higher is..the degree of
10 unsaturation. ~hus, ester of triunsaturated (three double
bonds in the carbon chain in the carboxylic acid moiety)
fatty acid has a higher degree.of unsaturation than.ester of
. diunsaturated (two.double bonds in the carbon chain in the
carboxylic acid moiety) fatty acid which in turn has a
higher degree of unsaturation.than ester of monounsaturated
(one double bond in the carbon chain in the carboxylic acid
moiety) fatty acid which in turn has a higher degree of
unsaturation than ester of saturated (no-double-bonds in the
. carbon chain in th.e carboxylic acid.moiety) fatty acid.
The meaning of the terms"alkyl carboxylate of higher
degree of unsaturation" and "alkyl carboxylate of lesser
degree of unsaturation" as used herein depends on the context,
that is the particular separatinn to which the invention is
being applied. The alkyl carboxylate of higher degree of
~: 25 unsaturation can include more than one alkyl carboxylate and
;~ can include alkyl carboxylates with different degrees of
unsaturation. Likewise the alkyl carboxylate of lesser degree
: of unsaturation can include more than one alkyl carboxylate
and can include alkyl carboxylates with different degrees of
unsaturation. The alkyl carboxylate of higher degree of
. unsaturation has to include the alkyl carboxylate of highest
degree of unsaturation, and the alkyl carboxylate of lesser
degree of unsaturation has to include the alkyl carboxylate
. of lowest degree of unsaturation. The alkyl carboxylate of
lesser degree of unsaturation includes ester of saturated
fatty acid, if such is present in the mixture being separated.
In a multistage process, the alkyl carboxylate of higher
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degree of unsaturation in one stage can be different from
; the alkyl carboxylate of higher degree of unsaturation in
another s~age and the-alkyl carboxylate of lesser degree of
unsaturation in one stage can be different from-the alkyl
s carboxylate of lesser degree of unsaturation in-another
stage. For example, in a two stage process where the feed
to the first stage comprises methyl linolenate, methyl
linoleate, methyl oleate and methyl stearate and the feed
to the second stage is fraction obtained on stripping solvent
from raffinate from the first stage, in the first stage
the alkyl carboxylate of higher degree of unsaturation might
be methyl linolenate and methyl linoleate and the alkyl
carboxylate of lesser degree of unsaturation might be methyl
oleate and methyl stearate, and in the second stage the alkyl
carboxylate of higher degree of unsaturation might be methyl
oleate and the alkyl carboxylate of lesser degree of
unsaturation might be methyl stearate.
The terms "alkyl carboxylate" and "alkyl fatty
carboxyiate" are used interchangeably herein.
The term "solvent" as used herein refers both to
solvent blends (i.e., solvents consisting of a plurality of
, constituents) and to pure compounds (i.e., solvents
consisting of a single constituent) unless the context
' indicates otherwise.
` 25 The terms "solubility parameter", "solubility parameter
` dispersion component"j "solubility parameter polar component"
and "solubility parameter hydrogen bonding component" as used
herein are defined by equations 6-10 at page 891 of-Kirk-
Othmer, Encyclopedia of Chemical Technolog~, 2nd Edition,
Supplement Volume, published by Interscience Publishers
(John Wiley & Sons) New York, 1971. Values herein for
solubility parameter, solubility parameter dispersion
component, solubility parameter polar component and solubility
parameter hydrogen bonding component are for solvents at
3s 25C (i.e., they are on a 25C basis). As on page 891, the
symbols u~ D"~ " ~p", and " ~H" are used herein to
refer respectively to "solubility parameter", "solubility
parameter dispersion component","solubility parameter polar
component", and "solubility parameter hydrogen bonding
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- 12 -
component". For many solvents the ~alues for ~D~ ~p~ and
~H are given in Table I which-directly follows page 891 and
the value for ~ is calculated using equation ~6~ on page 891.
For solvents consisting of a plurality of constituents, the
S values for "~D~ p" and "~H" are calculated by summing
the corresponding values for the constituents multiplied by
their volume fractions and the value for "~" i6 calculated
using equation (6) on page 891.
The "surface area" of the silica gel is measured by
the B.E.T. nitrogen adsorption technique described in
Brunauer, Emmett and Teller, J. Am. Chem. Soc. 60, p. 309
;s (1938).
The term "surface-silicon atom" as used herein means
a silicon atom attached to only three other silicon atoms
: 15 by Si-O bonds.
' Determination of the ratio of surface-silicon atoms
to aluminum atoms in the surface aluminated sili¢a gel
adsorbent is readily carried out by determining the number
! of surface-silicon atoms assuming the presence of 8 silicon
atoms per square nanometer of surface area-(the figure of
8 silicon atoms per square nanometer af surface area is
Y~ found, for example, in Iler, R.K. The Colloid Chemistry of
Silica and Silic-ates, Cornell University Press, Ithaca,
New York 1955, p. 58) of the silica gel from which the
~` 25 adsorbent is derived and determining the number of aluminum
atoms, for example, utilizing elemental analysis, and cal-
; culating.
The term "cation substituents" means the exchangeable
cations associated with the adsorbent. The "cation sub-
stituents ¢apable of forming ~ complexes" are cation sub-
stituents capable of attracting and holding unsaturated
materials (the greater the degree of unsaturation, the
, greater the attracting and holding power) by formation of a
~ particular kind of chemisorption bonding known as ~ bonding.
s~ 35 The "cation substituents not capable of forming ~ complexes"
do not have significant ability to form such chemisorption
bonds. The formation of ~ complexes is considered to involve
two kinds of bonding: (1) overlap between occupied ~
molecular orbital of an unsaturate and an unoccupied d orbital
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or dsp-hybrid orbital of a metal and (2) o~e~lap between an
unoccupied antîbonding ~* molecuiar orbital of the
unsaturate and one of the occupied metal d or dsp-hybrid
orbitals tsometimes referred to as "back bonding"). This
complexing is described, for example, in Chem. Revs. 68,
pp. 785-806 (1968).
The term "adsorbent surface area" as used hereinafter
in defining silver substituents level is also measured by ;-
the B.E.T. nitrogen adsorption technique referred to above
and is measured on the adsorbent after silvering and moisture
adjustment.
The level of silver substituents is referred to here-
inafter in terms of millimoles/100 square meters of
adsorbent surface area. This is determined by determining
the amount of silver (e.g. by elemental microanalysis or
utilizing X-ray fluorescence), by obtaining the adsorbent
surface area as described above and calculating.
The term "moisture content" as used herein in relation
to the adsorbent means the water present in the particles
Of adsorbent according to measurement by Karl Fischer
titration or by determining weight loss on ignition at 400C
for 2 - 4 hours. The moisture content values presented
herein are-percentages by weight.
Détailed Description
~: 25 The alkyl carboxylates in the feed have the formula
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R O R
: in which R is aliphatic chain which contains ~rom 5 to 25
carbon atoms and is saturated (no double bonds in the
j r.
aliphatic chain) or unsaturated (containing, for example,
up to 5 double bonds in the aliphatic chain) and in which
-- Rl is an alkyl chain containing from 1 to 4 carbon atoms.
Alkyl carboxylates in the feed herein can be, for
example, methyl caproate, methyl caprylate, methyl caprate,
methyl laurate, ethyl laurate, methyl myristate, methyl
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- 14 -
myristoleate, methyl palmitate, ethyl palmitate, methyl
palmitoleate, methyl stearate, ethyl stearate, propyl
stearate, isopropyl stearate, butyl stearate, methyl oleate,
ethyl oleate, propyl oleate, isopropyl oleate, ~utyl oleate,
methyl linoleate, ethyl linoleate, methyl linolenate,ethyl
linolenate, methyl eleostearate, methyl arachidate, methyl
gadoleate, methyl arachidonate, methyl behenate, methyl
erucate, ethyl erucate, methyl clupanodonate, methyl
lignocerate, methyl nisinate and methyl shibate.
The feed into a one stage process-or into the first
stage of a multistage process is readily obtained, for
example, by alcoholysis of naturally occurring triglyceride
(e.g., by reaction of naturally occurring fats and oils with
excess methanol in the presence of sodium methoxide). Very
important fee~s are obtained by methanolysis of cottonseed
oil, soybean oil, regular safflower oil, high oleic safflower
oil, sunflower oil and tallow~ Feeds containing methyl esters
are the most important commercially. One group of important
feeds comprises by weight (total alkyl carboxylate basis)
from 0% to about 60% methyl linolenate, from about 2% to
about 80% methyl linoleate, from about 5% to about 75% methyl
oleate, and from about l~ to about 35% methyl stearate;
such feeds often also comprise by weight (total alkyl carboxy-
late basis) from about 5~ to about 30% methyl palmitate.
It is desirable for the feed to be essentially free
of impurities which can foul (i.e. deactivate) the
adsorbent thereby causing loss of fractionating performance.
Such impurities are not alkyl carboxylates as defined above
and are materials which would be preferentially adsorbed and
not desorbed thereby inactivating adsorption sites. When
the feed is produced by alcoholysis of triglyceride, feed
purity is readily obtained by clean-up of triglyceride prior
to the alcoholysis reaction, and by reacting (and purify-
ing, if necessary) to minimize free fatty acid level and
other impurites. Clean-up of triglyceride to remove
impurities such as gums, free fatty acids, color bodies,
odor bodies, etc. is accomplished by numerous techniques
known in the art, such as alkali refining, bleaching with
Fuller's Earth or other active adsorbents, vacuum-steam
~S7~3 ~2
-15 - ..
stripping.to remove odor bodies, etc.
In a one solvent process, the feed is usually
introduced into the adsorbing unit without sol~ent and is
dissolved in solvent already in the unit, introduced, for
example, in a previous cycle to cause desorption. -If
desired, however, the feed in a one solvent process can be
dissolved in solvent prior to introduction into the
adsorbing unit or the feed can be raffinate or extract from
a previous stage comprising alkyl carboxylate mixture
dissolved in solvent. In a two solvent process, the feed
is p~eferably dissolved in the solvent constituting the
vehicle for adsorption prior to introduction into the
adsorbing unit.
Turning now to the solvents useful herein for a one
solvent process (where the same solvent composition performs
the dual role of being.the dissolving-phase during
adsorption and the vehicle for desorption), these are
preferably characterized by ~ ranging from about 7.0 to
about 10.5, ~D ranging from about 7.0 to about 9.0, ~p
ranging from about 0.2 to about 5.1 and ~H ranging from
about 0.3 to about 7.4. More preferred solvents for use
in a one solvent process herein are characterized by ~
ranging from about 7.4 to about 9 0~ ~D ranging from about
7.25 to about 8.0, ~p ranging from about 0.5 to about 3.0
and ~H ranging from.about 0.7 to about 4Ø
One important group of solvents for a one solvent
process includes those consisting essentially by volume of
from 0% to about 90% C5-Clo saturated hydrocarbon (that is,
saturated hydrocarbon with from S to 10 carbon atoms) and
from 100% to about 10% carbonyl group containing compound
selected from the group consisting of (a) ester having the
formula
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R2-C-O-CH2-R3 wherein R2 is hydrogen or alkyl chain
containing one or two carbon atoms and R3 is hydrogen or
alkyl chain containing one to three carbon atoms and (b)
ketone having the formula
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R4-~-R4 wherein each R4 is the same or di~ferent and is
alkyl chain containing 1 to 5 carbon atoms. ~xa~ples of
suitable hydrocarbons are pentane, hexanej heptane, octane,
nonane, decane, isopentane and cyclohexane. Examples of
s esters suitable for use in or as the solvent-are methyl formate,
methyl acetate, ethyl acetate, methyl propionate,-propyl
formate and butyl formate. Examples of ketones suitable
for use in or as the solvent are acetone, methyl ethyl ketone,
methyl isobutyl ketone and diethyl ketone.
Another important group of solvents for a one solvent
process are dialkyl ethers containing l to 3 carbon atoms in
each alkyl group and blends of these with the hydrocarbon,
ester and ketone solvents set forth above. Specific examples
of solvents within this group are diethyl ether and diiso-
propyl ether.
Yet another important group of solvents for a one
solvent process are blends of Cl 3 alcohols (e.g. from about
5% to about 40% by volume alcohol) with the hydrocarbon,
ester and ketone solvents set forth above. Specific
examples of solvents within this group are blends of
methanol or ethanol with hexane.
Very preferably, the solvent for a one solvent process
comprises ethyl acetate with blending with hexane being
utilized to weaken the solvent and blending with ethanol being
utilized to strengthen the solvent.
In most continuous one solvent processes envisioned
within the scope of the invention, the solvent is
introduced into the process in a desorbing zone and-sufficient
solvent remains in the process to perform at a downstream
location the dissolving function for adsorption.
The solvent to feed ratio for a one solvent process
generally ranges on a volume basis from about 4:1 to about
100:1 and preferably ranges from about S:l to about 40:1.
We turn now to the solvents useful herein for a two
solvent process (where different solvent compositions are
used as the dissolving phase during adsorption and as the
vehicle for desorption).
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For a two ~olvent process herein, the solvents for
use as the dissolving phase during adsorption, i.e., as
the adsorption ~ehicle, are preferably characterized by ~
ranging from about 7.3 to about 14.9, ~D ranging from about
7.3 to about 9.0, ~p ranging from 0 to about 5.7 and ~H
ranging from 0 to about 11Ø More preferred solvents for
the adsorption vehi¢le for a two solvent process-herein are
characterized by ~ ranging from about 7.3 to about 9 0~ ~D
ranging from about 7.3 to about 8.0, ~p ranging from 0 to
about 2.7 and ~ ranging from 0 to about 3.6. Very
H
preferably, the solvent for the adsorption vehicle in a
two solvent process herein is hexane or a blend consisting
essentially of hexane and up to about 15% by volume ethyl
acetate or diisopropyl ether.
For a two solvent process herein, the solvents for use
as the vehicle for desorption, i.e., as the desorbent, are
preferably characterized by ~ ranging from about 7.4 to
about 15.0 and at least 0.1 greater than the ~ of the
adsorption vehicle, ~D ranging from about 7.3 to about 9.0,
~p ranging from about 0.3 to about 6.0 and at least 0.3
greater than the ~p of the adsorption vehicle, and ~H
ranging from about 0.5 to about 11.5 and at least 0.5
greater than the ~H of the adsorption vehicle. More preferred
solvents fox the desorbent for a two soivent process herein
are characterized by a ~ ranging from about 7.4 to about
10.0, ~D ranging from about 7.3 to about 8.0, Cp ranging
from about 0.5 to about 4.0, and ~H ranging from about 0.5
to about 6.0 and having ~ , ~p and ~H~ respectively, greater
than the ~, ~p and ~H of the adsorption vehicle by at least
the amounts stated above. Important desorbents for use in
a two solvent process herein include: ethyl acetate; blends
consisting essentially of ethyl acetate and up to about 80%
by volume hexane; blends consisting essentially of ethyl
acetate and up to about 25~ by volume methanol or ethanol;
and diisopropyl ether. Very preferably, the solvent for
the desorbent in a two solvent process herein comprises
ethyl acetate.
It is preferred both in a one solvent process herein
.~
,
- ~ ,
.: , '
~ ~7C~
- 18 -
and in a two solvent process herein to avoid use of
halogenated hydrocarbon solvents as these shorten adsorbent
life.
We turn now in detail to the adsorbent for use herein.
It is defined the same regardless of whether it is used in
a one solvent process or in a two solvent process.
The bonding of aluminate groups to surface-silicon
atoms of the silica gel from which adsorbent herein is derived
to provide the adsorbent herein characterized by aluminum
atoms present essentially entirely in anionic moieties at
the surface is-indicated by following chemical structure
which i9 believed to represent anionic sites in such adsorbent:
l l
-Si - O Al OH
-si- `
wherein the silicon atoms which are depicted are surface-
silicon atoms. The cation substituents are associated with
such anionic sites to provide electrostatic neutrality.
The characterization of the adsorbent herein in
terms of surface area of the silica gel from which it is
derived ~silica gel starting material) is important to
obtaining appropriate capacity. If silica gel starting
material is utilized with a surface area less than the
aforestated lower limit of about 100 square meters per gram,
capacity becomes quite low. Preferably, the adsorbent
herein is derived from silica gel having a surface area of at
least about 300 square meters per gram. Silica gel starting
materials are known with surface axeas as high as 800 square
meters per gram.
i ~
'~
~ . .
" llS7l3 ~2
-- 19 --
The characte~ization of the adsorbent herein in terms
of ratio of surface-silicon atoms to aluminum atoms is impor-
tant in relation to selectivity. The lower limit of about
3:1 is related to the chemical structure of the adsorbents
S llerein; in such structure,- aluminate moiety is associated with
three silicon atoms. The upper limit of about 20:1 has been
selected t.o provide sufficient adsorbing power to obtain
selectivity in some fractionation envisioned. In most
instances in important applications of this invention, the
adsorbent prefera~ly is characterized by a ratio of surface-
silicon atoms to aluminum atoms ranging from about 3:1 to
about 12:1.
We turn now to the cation substituents of the
adsorbent.
The cation.substituen.ts capable o forming ~ complexes
are preferably selected from the group consisting of silver
(in a valence state of 1), copper (in a valence state of 1),
platinum (in a valence state of 2), palladium (in a valence
state of 2)~and combinations-of these.
The cation substituents not capable of forming ~
complexes are preferably selected from the group consisting
of cation substituents from Groups lA and IIA of the
Periodic Table and zinc cation substituents and
combinations of these and very preferably are selected
2S from the group consisting of sodium, potassium, barium,
calcium, magnesium and zinc substituents and combinations
of these.
Most preferably, the adsorbent has cation sub-
stituents selected ~rom the group consisting of silver
substituents in a valence state of one and sodium
substituents and combinations of these.
Preferably, cation substituents such as hydrogen,
which cause deter.ioration of the adsorbent structure
(e.g. by stripping aluminum therefrom) or which foster
significant polymerization, should be avoided or kept
at a minimum.
Fractionations are envisioned herein utilizing
adsorbent with no cation substituents capable of forming
Xl
.
.
7~Z
- 20 -
~ complexes (e.g. together with a weak ~olvent as the
adsorption vehicle). Such adsorbent functions by a
physical adsorption mechanism to preferentially adsorb
more unsaturated alkyl carboxylate. Preferably, however,
the adsorbent utilized has cation substituents capable
of forming ~ complexes as at least some of-its cation
substituents; these adsorbents function by a combination
of physical adsorption and the type of chemical adsorption
known as ~ complexing to preferentially adsorb more
unsaturated alkyl carboxylate.
Very preferably, the adsorbent has a level of
silver substituents greater than about 0.05 millimoles/
100 square meters of adsorbent surface area. The upper
limit on silver is found in a fully silver exchanged
adsorbent with a ratio of surface-silicon atoms to
aluminum atoms of about 3:1 and is about 0.44 milli-
moles/100 square meters of adsorbent surface area. Most
preferably, the adsorbent has a silver level ranging
from about 0.10 millimoles/100 s~uare meters of adsorbent
surface area to about 0.35 millimoles/100 square meters of
adsorbent surface area. Amount of silver is readily
measured utilizing X-ray fluorescence or elemental micro-
analysis.
The ratio of surface-silicon atoms to aluminum
atoms and the level of cation substituents capable of
forming ~ complexes interrelate, and the selection of these
governs adsorbing power and therefore selectivity. These
also have an effect on capacity.
The ratio of surface-silicon atoms to aluminum atoms
selected sets the maximum amount of cation substituents
capable of forming ~ complexes that can be introduced. This
is because the cation substituents are held by the negative
charges associated with aluminum atoms in anionic moieties,
with a monovalent cation substituent being held by the
charge associated with a single aluminum atom and a
divalent cation substituent being held by the charges
associated with two aluminum atoms.
~a
.
i7J~ ~Z
- 21 -
With the silica gel starting material surface area held
constant, and with the level of cation substituents capable
of forming ~ complexes being held at the same percentage
of exchange capacity, as the ratio of surface-silicon atoms
~o aluminum atoms is increased, the adsorbing power and
capacity decreases. With the silica gel starting material
surface area held constant and with the ratio of surface-
silicon atoms to aluminum atoms held constant, increasing the
level of cation substituents capable of forming ~ complexes
results in increasing adsorbing power and capa~ity. With the
ratio of surface-silicon atoms to aluminum atoms held constant
and the level of cation substituents capable of forming ~
complexes held constant, using adsorbent derived from silica
gel of increased surface area increases capa~ity.
The moisture content is important in the adsorbent be-
cause too much moisture causes the adsorbent to be oleophobic
(water occupies pores of the adsorbent preventing feed from
reaching solid surface of the adsorbent). The less the
moisture content is, the greater the adsorbing power and
capacity. The upper limit of about 10% by weight moisture
content has been selected so that the adsorbent will perform
with at least mediocre efficiency. Preferably, the moisture
content in the adsorbent is less than about 4% by weight.
The adsorbents herein generally have particle sizes
ranging from about 200 mesh to about 20 mesh (U.S. Sieve Series).
Use of a particle size less than about 200 mesh provides
handling problems and can result in loss of adsorbent as a
result of very small particles forming a stable suspension in
solvent. Use of a particle size greater than about 20 mesh
results in poor mass transfer. For a continuous process,
particle sizes of about 80 mesh to about 30 mesh (U.S. Sieve
Series) are preferred: using particle sizes larger than
about 30 mesh reduces resolution and causes diffusion (mass
transfer) limitations and using particle sizes less than
about 80 mesh results in high pressure drops. Preferably, there is
'î'~
~i7Ct ~2
- 22 -
naerow particle size disteibution within the aforestated
ranges to provide good flow properties.
We turn now to the preparation of the adsorbent.
Tbe silica gel starting material is selected on
the basis of surface area and particle size. As indic-
ated above, the surface area must be at least about 100
square meters per gram. The particle size must be at
least about 200 mesh since the adsorbent has a particle
size approximately the same as the particle size of the
silica gel particles which are reacted to provi~e the
adsorbent. Thus, microparticulate silica gels are unac-
ceptable for use in producing the adsorbent herein.
Silica gel starting materials including particles with
a size greater than 20 mesh are readily made useful,
for example, by sieving out larger particles if only
some are present or by size-reducing and sieving if
a substantial part of the particles is too large.
Preferred silica gel starting materials are sold under
the tradenames Silica Gel 100 and Geduran~ (both are
manuactured by E. Merck and Company) and Grade 59
Silica Gel (manufactured by the Davison Chemical
~ivision of W.R. Grace). Silica Gel 100 and Geduran
are obtainable in particle size of 35-70 mesh. Grade
59 Silica Gel is obtainable in a particle size of 3-8
mesh and must undergo size reduction and sieving.
The aluminate ion can be furnished by using a
water soluble aluminate or a source thereof (in other
words, the aluminate can be formed in situ). Preferred
water-soluble aluminate reactants are sodium aluminate
and potassium aluminate. Aluminate is suitably formed
....
,
---` h~ 2
23
in situ, for example, by reacting ca~ionic aluminum ~e.g.,
~rom aluminum nitrate) with sodium hydroxide, or by
reacting aluminum metal with sodium hydroxide.
The reaction involving aluminate ion and silica gel is
suitably carried out-as follows: Firstly, an aqueous
solution of aluminate ion (or precursors thereof) is
contacted with selected silica gel. The amount of aluminate
ion is selected to provide the desired ratio of surface-
silicon atoms to aluminum atoms. Reaction temperatures
range, for example, from about 15C to about 100C and
reaction times range, for example, from about 1 to about 48
hours. In one useful process, reaction is carried out at
room temperature. In another useful process, boiling water
(100C) is used as the reaction medium. Reaction is carxied
out to obtain the desired surface alumination. After the
surface alumination is completed, it is desirable to wash
the product, e.g. with distilled water, to remove excess
aluminum salts.
Lam et al, cited above, suggest the following reaction
equation: _ _ -1
3 Si - o~ + ~1 ] ~ ~-Si ~ +3~0
If the surface alumination reaction described above
does not provide the proper cation substituents in the
selected level, a cation exchange is carried out.
The cation exchange to provide a selected level of cation
substituents capable of forming ~ complexes is readily
carried out by contacting the aluminated material with a
sufficient amount of cation that is desired to be introduced~
When it is desired to introduce silver substituents to provide
cation substituents capable of forming ~ complexes, the
exchange is carried out in aqueous medium. Suitable sources
of silver include silver nitrate which is preferred and
X
7~-~2
- 24 -
silver fluoride, silver chlorate and silver perchlorate.
When the level of cation desired to be introduced is sub-
stantially less than 100% of exchange capacity, reaction is
preferably carried out in a stirred tan~ and a slight excess
of cation (preferably 105 - 115~ of stoichiometric) is
desirably used. When the level of cation desired to be
introduced approaches 100~ of exchange capacity, reaction is
preferably carried out in a packed column and a large excess
(preferably 200% of stoichiometric) is used. Unreacted
cation is readily washed from the product.
The moisture content is readily adjusted with conventional
drying methods. For example, drying i8 readily carried out
using vacuum or an oven (e.g. a forced draft oven). Drying
is carried out to obtain the desired moisture level, e.g.,
by drying at a temperature of 100C-110C for 15-20 hours.
The particle size of the adsorbent is preferably
adjusted by adjusting the particle size of ~he silica gel
starting material, for example, by sieving (screening) to
obtain a narrow size distribution of particles within the
aforedescribed range and by size reducing when such is
appropriate. Particle size of adsorbent is readily controlled
in this manner because particle size of the aluminated
reaction product is essentially the same as that of the
silica gel reactant. Less preferably, sieving or size-
reduction can be carried out on aluminated reaction productor even on reaction product subsequent to cation treatment.
Turning now to the instant fractionation process, the
selection of solvent(s), ratio of surface-silicon atoms to
aluminum atoms in the adsorbent and level of cation sub-
stituents capable of forming ~ complexes are interrelatedand depend on the separation desired to be obtained. The
lower the ratio of surface-silicon atoms to aluminum atoms
in the adsorbent is, the greater the adsorbing power is. The
higher the level of cation substituents capable of forming
~ complexes is, the greater the adsorbing power and the
greater the resistance to desorption. The lower the solubil-
ity parameter and solubility parameter polar and hydrogen
bonding components of the solvent utilized as the dissolving
phase during adsorption are, the more adsorbing power a
~1 .
: ' ~
,
.
- 25 -
particular adsorbent is able to exert. The higher the
solubility parameter and the solubility parameter polar and
hydrogen bonding components of the solvent utilized as the
vehicle for desorption are, the more the.desorbing power.
The higher the.degree of unsaturation of the fraction
desired to be separated is, the higher the solubility para-
meter and solubility parameter polar and hydrogen bonding
components of the solvent that can be used for adsorbing and
that is required for desorbing and the.higher the ratio of
surface-silicon atoms to aluminum atoms and the lower the
level of cation substituents capabie of forming ~ complexes
in the adsorbent that can be.used for adsorbing and which will
allow desorbing.
When a particular adsorbent has been selected, the
solvent.used during adsorbing should have a solubility para-
meter and solubility parameter components sufficiently low to
obtain selectivity, and the solvent used for desorbing should
have a solubility parameter and solubility parameter components
sufficiently.high to obtain desorption.
~hen a particular solvent or particular solvents has
(have) been selected, an adsorbent is selected with a ratio
of surface-silicon atoms to aluminum atoms sufficiently low
and a level of cation substituents capable of forming ~
complexes sufficiently high to provide desired.selectivity
during adsorption.and with a ratio.of surface-silicon atoms
to aluminum atoms sufficiently high and a level of cation
substituents capable of forming ~ complexes sufficiently low
to allow desorption of all or desired portion of adsorbed
alkyl carboxylate during the desorbing step.
We turn now to the conditions of temperature and
pressure for the instant fractionation process. The tempera-
ture utilized during adsorbing and during desorbing can be
the same and generally range from about 20 to 150C. A
preferred temperature range to be used when the feed is a
mixture of alkyl carboxylates having fatty carboxylic acid
moieties with aliphatic chains having from 12 to 20 carbon
atoms, is about 50 to about 80C. Lower temperatures within
the above described broad range are preferably utilized when
- 26 -
the solvent comprises ketone. The pressures utilized during
adsorbing and desorbing can be the same and generally are
those pressures encountered in packed bed processing, e.g.,
ranging from atmospheric (14.7 psia)-to about 500 psia. For
a simulated moving bed process as described hereafter, the
pressures utilized preferably range from about 30 psia to
about 120 psia or are as prescribed by the desired flow rate.
For a batch process, sufficient residence time should
be provided to obtain appropriate yields and purities,
usually 15 minutes to 20 hours. The rates for continuous
processing are a function of the size of the equipment, the
resolving ability of the adsorbent-solvent pair, and the
desired yield and purity.
The fractionation process herein as described above
provides a "raffinate" and an "extract". The raffinate
contains fraction which is enriched in content of alkyl
carboxylate of lesser degree of unsaturation. It comprises
alkyl carboxylate which was weakly attracted by the adsorbent,
dissolved in solvent. The extract contains fraction enriched
in content of alkyl carboxylate of higher degree of unsatura-
tion. It comprises alkyl carboxylate which was more strongly
attracted by the adsorbent, dissolved in solvent. The fractions
can be recovered from the raffinate and from the extract by
conventional separation processes such as by stripping
solvent with heat and vacuum.
We turn now to apparatus for a one solvent process herein
and its operation.
For batch processing, the one solvent process herein is
readily carried out in e~uipment conventionally used for
adsorptions carried out batchwise. For example, such
processing can be carried out utilizing a column containing
adsorbent and alternately (a) introd~cing feed dissolved in
solvent to obtain selective adsorption and (b) introducing
solvent to obtain desorption of adsorbed fraction.
For continuous processing, the one solvent process herein
is readily carried out in conventional continuous adsorbing
apparatus and is preferably carried out by means of a
simulated moving bed unit operation. A simulated moving bed
;i76~ ~2
- 27 -
unit operation and apparatus for such useful herein is
described in Broughton et al U.S. Patent No. 2,985,589.
For a simulated moving bed embodiment of this invention,
preferred apparatus includes: ~a) at least four columns
connected in series, each containing a bed or adsorbent;
~b) liquid access lines communicating with an inlet line
to the first column, with an outlet line from the last
column, and with the connecting lines between successive
columns; (c) a recirculation loop including a variable speed
pump, to provide communication between the outlet line from
the last column and the inlet line to the first column; and
(d) means to regulate what flows in or out of each liquid
access line.
Such preferred simulated moving bed apparatus is
operated so that liquid flow is in one direction and so that
countercurrent flow of adsorbent is simulated by manipulation
of what goes into and out of the liquid access lines. In one
embodiment, the apparatus is operated so that four functional
zones are in operation. The first of the functional zones
is usually referred to as the adsorption zone. This zone is
downstream of a feed inflow and upstream of a raffinate out-
flow. In the adsorption zone, there is a net and selective
adsorption of alkyl carboxylate of higher degree of unsatura- -
tion and a net desorption of solvent and of alkyl carboxylate
2S of lesser degree of unsaturation. The second of the
functional zones is usually referred to as the purification
zone. It is downstream of an extract outflow and upstream of
the feed inflow and just upstream of the adsorption zone. In
the purification zone, alkyl carboxylate of higher degree of
unsaturation which has previously been desorbed is preferen-
tially adsorbed and there is a net desorption of solvent and
of alkyl carboxylate of lesser degree of unsaturation. The
third of the functional zones is referred to as the desorption
zone. It is downstream of a solvent inflow and upstream of
extract outfl~w and just upstream of the purification zone.
In the desorption zone, there is a net desorption of alkyl
carboxylate of higher degree of unsaturation and a net
adsorption of solvent. The fourth functional zone is usually
X .,
. . .
- 28 -
referred to as the bu~fer zone. It is downstrea~ o the
raffinate outflow and upstream of the solvent inflow and
just upstream of the desorption zone. In the buffer zone,
alkyl carobxylate of lesser degree of unsaturation is adsorbed
and solvent is desorbed. The various liquid access lines
are utilized to provide the feed inflow between the
purification and adsorption zones, the raffinate outflow
between the adsorption and buffer zones, solvent-inflow be-
tween the buffer and desorption zones and extract outflow
between the desorption and purification zones. The liquid
flow is manipula*ed at predetermined time periods and the
speed of the pump in the recirculation loop is varied con-
current with such manipulation so that the inlet points (for
feed and solvent) and the outlet points (for raffinate and
extract) are moved one position in the direction of liquid
flow (in a downstream direction) thereby moving the afore-
described zones in the direction of liquid flow and
simulating countercurrent flow of desorbent.
In another embodiment of simulated moving bed operation,
a plurality of successive desorption zones is utilized (in
place of a single desorption zone) with solvent being
introduced at the upstream end of each desorption zone and
extract being taken off at the downstream end of each
desorption zone. It may be advantageous to use different
solvent inlet temperatures and/or different so-lvents for
different desorption zones.
In another embodiment of simulated moving bed processing,
raffinate is taken off at a plurality of locations along
the adsorption zone.
Less preferred continuous simulated moving bed apparatus
than described above is the same as the apparatus described
above except that the recirculation loop is omitted. The
buffer zone can also be omitted.
In the operation of the above described simulated moving
bed processes, the relative number of columns in each zone to
optimize a process can be selected based on selectivities and
resolution revealed by pulse testing coupled with capacity
and purity requirements. A factor in selecting the number
. .
:
" '
~ '
` ,, ; .
.
.
5'~ ~2
- 29 -
of columns in the adsorption zone is ~he percentage of the
feed to be adsorbed. The purity of the extract and raffinate
streams is a function of the number of columns in the
adsorption zone. The longer the adsorption zone is ~the
more columns in it), that is, the further removed the feed
inlet is from the raffinate outlet, the purer the raffinate
is .
In the operation of the above described simulated moving
bed processes, the time interval between manipulations of
liquid flow should be sufficient to allow a substantial
propor~ion-of alkyl carboxylate of ~igher degree of unsatura-
tion to stay in the adsorption zone and a substantial
proportion of alkyl carboxylate of lesser degree of
unsaturation to leave.
We turn now to apparatus for the two solvent process
herein and its operation.
Such two solvent process is preferably carried out using
a column loaded with adsorbent. The feed and the solvent
constituting the adsorption vehicle are run through the
column until a desired amount of feed is adsorbed. Then,
the desorbing solvent is run through the column to cause
desorption of adsorbed material.
Such two solvent process is less preferably carried out,
for example, in a batch mixing tank containing the adsorbent.
The feed together with solvent constituting the adsorption
vehicle is added into the tank. Then mixing is carried out
until a desired amount of adsorption occurs. Then liquid
is drained. Then desorbing solvent is added and mixing is
carried out until the desired amount of desorption occurs.
Then solvent containing the desorbed alkyl carboxylate is
drained.
We turn now in more detail to the multistage process
referred to generally above.
Multistage processing can involve the following. The
feedstock to be separated is processed in a first stage to
obtain first extract containing fraction enriched (compared
to the feedstock) in content of alkyl carboxylate of higher
degree of unsaturation and first raffinate containing fraction
~1~57~ ~2
- 30 -
enriched (compared to the feedstock) in content of alkyl
carboxylate of lesser degree of unsaturation and depleted
(compared to the feedstock) in content of alkyl carboxylate
of higher degree of unsaturation. The first raffinate or first
extract, preferably the alkyl carboxylate fraction obtained
by essentially completely removing solvent from first
raffinate or first extract, is processed in the second stage
to obtain second extract containing fraction enriched in
content of alkyl carboxylate of higher degree of unsaturation
(compared to the feed to the second stage~ and sçcond
raffinate enriched (compared to the feed to the second stage)
in content of alkyl carboxylate of lesser degree of
unsaturation and depleted (compared to feed to the second
stage) in content of alkyl carboxylate of higher degree of
unsaturation. To the extent succeèding stages are used, each
succeeding stage has as its feed raffinate or extract from
the preceding stage, preferably alkyl carboxylate fraction
obtained by essentially completely removing solvent from
such.
We turn now to some important applications of the
instant process.
One application is a process in which the alkyl
~arboxylate feed mixture comprises a mixture of methyl ester
of polyunsaturated fatty acid, methyl ester of monounsaturated
fatty acid and methyl ester of saturated fatty acid and in
which alkyl carboxylate of higher degree of unsaturation
comprises methyl ester of polyunsaturated fatty acid. Feeds
for this application can be derived, for example, from
regular safflower oil, high oleic safflower oil, soybean oil
or sunflower oil. Processing of the feeds derived from
regular safflower oil and sunflower oil gives a product
containing a very high percentage of methyl linoleate.
Another application is a process in which the alkyl
carboxylate feed mixture comprises a mixture of methyl ester
of monounsaturated fatty acid and methyl ester of saturated
fatty acid and in which alkyl carboxylate of higher degree of
unsaturation comprises methyl ester of monounsaturated fatty
acid. Feeds for this application can be fraction obtained,
: ;
: '' ' `
,
.
~s~ z
- 31 -
for example, from raffinate from a first stage of a two
stage process in which the feed to the first stage is
derived from high oleic safflower oil or soybean oil or sun-
flower oiI. This gives product containing a very high
percentage of methyl oleate.
StilI another application is a process in which the
alkyl carboxylate feed mixture comprises a mixture of methyl
ester of triunsaturated fatty acid and methyl ester of di-
unsaturated fatty acid and in which the alkyl carboxylate
of higher degree of unsaturation is methyl ester of tri-
unsaturated fatty acid. A feed for this application can be
derived, e.g., from soybean oil.
We turn now to advantages of the process herein.
Significant advantages result from the chemical
composition and structure of the adsorbent herein. Firstly,
such adsorbent is made from materials which are readily
commercially available in large amounts. Secondly, flexibility
in adsorbent composition is readily provided in that silica
gels with different surface areas are readily available and
in that a predetermined ratio of surface-silicon atoms to
aluminum atoms is readily obtained. Thirdly, level of cations
capable of forming ~ complexes can be readily regulated by
selecting the ratio of surface-silicon atoms to aluminum
atoms. Fourthly, any cations capable of forming ~ complexes
are situated at the surface of the adsorbent where such are
availabie to provide adsorbing power thereby providing
efficient usage of such cations (e.g. silver).
Furthermore, the process herein is characterized by
a long adsorbent life cycle. Firstly, there is no problem
of cations capable of forming ~ complexes being leached from
the adsorbent as there is with silver nitrate treated silica
gel ad~orbents. This is because the cations are attached in
the adsorbent herein by electrostatic interaction. Secondly,
there is no fouling of the adsorbent with impurities. Thirdly,
the adsorbent has physical strength such that it does not
break down into smaller pieces.
Moreover, processing is carried out without any
significant amount of polymerization so that there is no
problem of disposing of polymer by-product.
,,
.,
~ .:
.:. :
~ .
~LS7~-~2
- 32 -
Furthermore, the process herein is carried out without
the adsorbent handling and loss problems which can be
associated with use of microparticulate-partlcle size
adsorbents.
Furthermore, the adsorbent herein has a high capacity
for adsorbing alkyl carboxylates compared to resin adsorbents.
This means higher throughput rates or smaller equipment size
and reduction in usage of active cations (e.g. silver).
Furthermore, the adsorbent herein is advantageous over
resin adsorbents and crystalline zeolite adsorbents ~rom
the standpoint of flexibility and is advantageous over resin
adsorbents in being inorganic in nature.
Furthermore, with the adsorbe~t herein, contrary to
the case with crystalline zeolite adsorbents, the same equip-
ment and adsorbent are appropriatel~ used to separate alkylcarboxylate mixtures and triglyceride mixtures.
The invention is illustrated in the following specific
examples.
In Examples I-III below, "pulse tests" are run to
determine the ~uality of separation that can be obtained in
one solvent processing with selected adsorbents and solvents.
The apparatus consists of a column having a length of 120 cm.
and an inside diameter of 1 cm. and having inlet and outlet
ports at its opposite ends. The adsorbent is dispersed in
solvent and then introduced into the column. The column is
packed with about 100 cc. of adsorbent on a wet packed basis.
The column is in a temperature controlled environment. A
constant flow pump i-s used to pump liquid through the column
at a predetermined flow rate. In the conducting of the tests,
the adsorbent is allowed to come to e~uilibrium with the
particular solvent and feed by passing a mixture of the
solvent and feed through the column for a predetermined period
of time. The adsorbent is then flushed with solvent un~il a
5 milliliter fraction contains a negligible amount of feed.
At this time, a pulse of feed containing a known amount of
docosane tracer is injected, via a sample coil, into the
solvent inflow. The pulse of feed plus tracer is thereby
caused to flow through the column with components first being
~1
:
.
` `~
i~iS7~3 ~2
adsorbed by ~he adsorbent and then caused to be desorbed by
the solvent. E~ual volume effluent samples are collected,
and alkyl carboxylate therefrom is analyzed by gas
chromatography. From these analyses, elution concentration
curves for tracer and alkyl carboxylate components are
obtained (concentration in milligrams per milliliter is
plotted on the y axis and elution volume in milliliters is
plotted on the x axis). The distance from time zero (the
time when the pulse of feed plus tracer is introduced) to the
peak of a curve is the elution Yolume. The difference be-
tween the elution volume for an alkyl carboxylate component
and the elution volume for the tracer is the retention
volume of that alkyl carboxylate component. The relative
selectivity of one ester component over another (when the
selected adsorbent and solvent are utilized) is the ratio of
their respective retention volumes.
In Example IV, pilot plant test apparatus (sometimes
referred to as a demonstration unit) is utilized. The
apparatus is operated according to the continuous simulated
moving bed unit operation mentioned above to carry out a one
solvent process. The apparatus comprises fourteen columns
which are connected in series in a loop to permit the process
liquid to flow in one direction. Each column has a length
of 24 inches and an inside diameter of 9/10 of an inch and
i5 loaded with about 237 cc of adsorbent (wet packed basis).
Each column is equipped with two four-position valves (top
and bottom) connected to four inlet and four outlet conduits.
When a valve is closed, liquid flows only toward the column
downstream of the valve. By selecting between the eight open
positions (four at top and four at bottom), feed can be caused
to be introduced to the system (e.g. position 1), solvent can
be caused to be introduced to the system (e.g. position 2), a
raffinate stream can be removed from the system (e.g. position
3) or an extract stream can be removed from the system (e.g.
position 4). Backflow check positions are located in each
of the bottom valves. These are used to isolate zones of
the system from backflow; i.e., isolate the high pressure in-
let (solvent) from the low pressure outlet. Operation is as
. . ,~ ~
- 34 -
follows: At any time, the apparatus constitutes a single
stage. It is operated with three working zones (adsorption,
purification and desorption). One backflow control valve
is always in closed position to eliminate backflow between
s the solvent inlet and the low pressure outlet. No recircu-
lation is used. The fourteen columns are apportioned between
the adsorption, purification and desorption zones with a
selected number of-columns-in series comprising each zone.
Feed is introduced into the first column of the adsorption
zone and is dissolved in solvent and is contacted with
adsorbent. As liquid flows downstream through the adsorption
zone, alkyl carboxylate component~s) of higher degree of
unsaturation is (are) selectively adsorbed leaving raffinate
enriched in alkyl carboxylate of lower degree of unsaturation.
In the purification zone, non-adsorbed components are forced
from the adsorbent and are thus forced downstream toward
the feed point. The extract is removed at the inlet to the
purification zone and is enriched in adsorbed components.
The solvent is added at the inlet to the desorption zone
and causes desorption of adsorbed component(s) from the
adsorbent for removal downstream at the extract point. ~t
selected intervals a controller advances the flow pattern
(into and out of columns) one column (in other words, the
controller manipulates valves so that raffinate outflow, feed
inflow, extract outflow and solvent inflow points each
advance one step, that is, to the next liquid access point
in the direction of liquid flow) to "step forward" to keep
pace with the liquid flow. Fourteen "steps" constitute a
cycle. The "step time" is chosen such as to allow the non-
adsorbed components to advance faster than the feed pointand reach the raffinate point. The adsorbed alkyl carboxy-
late moves slower than the feed point and falls behind to
the extract point.
In Example V below, a test is run to demonstrate
selection of solvents for a two solvent process once a
particular adsorbent has been selected. The apparatus
utilized is the same as that utilized in the runs of
Examples I-III, and as in Examples I-III the column is packed
,
- 35 -
with about 100 cc of adsorbent (wet packed basis). The
following procedure is utilized. A plurali~y of solvents
is utilized successively, each being of progressively in-
creasing desorbing power. The initial s~lvent is pumped
through the column at 5 ml/minute with the column temperature
being 50C. 2.0 gms of feed (0.1 gram docosane tracer and
1.9 gms alkyl carboxylate mixture) is dissolved in 10 ml of
the initial solvent. Flow through the column is stopped,
and the 10 ml of initial solvent with feed dissolved therein
is injected into the column entrance. Flow of initial solvent
is then restarted and effluent sample collection is begun.
After ap~roximately two col D volumes of the initial
solvent is pumped into the column, the solvent is changed
and approximately two column volumes of the second solvent
is pumped into the column. The solvent is successively
changed after two-column volumes of a-solvent is pumped until
all the solvents being tested have been pumped into the
column. Eluant samples are ~ollected, and the-alkyl carboxy-
late therefrom is analyzed by gas chromatography.
We turn now to the Examples I-V which are generally
described above.
EXAMPLE I
This example involves pulse testing to determine solvent
and adsorbent combinations useful for continuous simulated
moving bed processing for various fractionations of safflower
methyl ester feedstock (containing, by weight, 8.0% methyl
palmitate, 2.5% methyl stearate, 13.0% methyl oleate, and
76.5% methyl linoleate).
Six runs are carried out.
In each run, the pulse consists of 0.5 ml solvent, 0.1
gm docosane tracer and 0.4 gm of the above described
safflower methyl ester feedstock.
In Run 1 and in Run 2, the adsorbent has the following
characteristics: It is derived from silica gel having a
surface area of 470 square meters per gram. It is also
characterized by a ratio of surface-silicon atoms to aluminum
atoms of 4.97:1, a moisture content less than 2% by weight,
and a particle size of 35-70 mesh (U.S. Sieve Series). It
7~3~2
- 36 -
contains 0.3~ millimoles of silver lin the form of ~ation
substituents in a valence state of lJ per 100 square meters
of adsorbent surface area. The silver substituents make up
97.6% of the exchangeable cations. The remainder of the
exchangeable cations are sodium substituents. The surface
area of the final adsorbent is 366 square meters per gram.
The-adsorbent for Runs 1 and 2 is made as follows:
Grade 59 Silica Gel (3-8 mesh U.S. Sieve Series) is gently
crushed, and a fraction with particle size range of 35-70
mesh is recovered~ lOOO grams of such fraction and 2 liters
of distilled wa~er are charged into a 5.0 liter, 3-neck,
fluted flask fitted with a mechanical stirrer, a pH electrode,
and an addition funnel. The mixture is agitated to form a
homogeneous slurry. The pH of the slurry is adjusted to 9.5
with 10% aqueous sodium hydroxide solution. Then a freshly
prepared solution of sodium aluminate (112.2 gm) in distilled
water (2.0 liters) is added. The slurry is stirred 10 hours `
at room temperature (about 20C). Then stirring is stopped
and the mixture is allowed to stand overnight. The
resulting product is poured into a glass chromatographic
column and washed free of unreacted aluminate with dist~illed
water (1-2 ml per minute). Then, the material in the column
is treated with a solution of silver nitrate (a two-fold molar
equivalent of silver based on the aluminate reagent) in
distilled water. Flow rate of the silver exchange solution
is about 0.5 ml/minute. The solid is then washed with
distilled water to remove excess silver nitrate, suction
filtered to remove bulk water, and dried in a forced draft
oven (105-110C) overnight.
In Run 3 and in Run 4, the adsorbent has the following
characteristics: It is derived from silica gel having a
surface area of 346 square meters per gram. It is also
characterized by a ratio of surface-silicon atoms to aluminum
atoms of 5.06:1, a moisture content less than 2% by weight,
and a particle size of 35-70 mesh (U.S. Sieve Series). It
contains 0.25 millimoles of silver (in the form of cation
substituents in a valence state of 1) per 100 square meters
of adsorbent surface area. The silver substituents make up
:
:'
- 37 -
94.3% of the exchangeable cations. The remainder of the
exchangeable cations are sodium substituents. The surface
area of the final adsorbent is 339 square meters per gram.
The adsorbent for Runs 3 and 4 is made the same as
that for Runs 1 and 2 except that Silica Gel 100 is used
instead of Grade 59 Silica Gel and except that alumination
is carried out for 4 hours at 80C.
In Run 5 and in Run 6, the adsorbent has the following
characteristics: It is derived from silica gel having a
surface area of 346 square meters per gram. It is also
characterized by a ratio of surface-silicon atoms to
aluminum atoms of 11.4:1, a moisture ¢ontent less than 2
by weight, and a particle size of 35-70 mesh (U.S. Sieve
Series). It contains 0.13 millimoles of silver (in the form
of cation substituents in a valence state of 1) per 100 m
of adsorbent surface area. The silver substituents make up
78.3% of the exchangeable cations. The remainder of exchange-~
able cations are sodium substituents. The surface area of
the final adsorbent is 245 square meters per gram.
The adsorbent for Runs 5 and 6 is made the same as
that for Runs 3 and 4 except 43.4 gms of sodium aluminate
is used and except for the silvering procedure. For silvering,
the product of the reaction of silica gel and sodium aluminate
is transferred to a reaction vessel, and a solution of silver
nitrate (82.8 grams) in distilled water is added. This
mixture is stirred for 10-20 minutes and left standing
overnight at room temperature. The exchange liquor is then
removed by suction filtration and the solid is washed until
wash effluent contains no detectable silver ion. Dewatering
and drying is carried out the same as for the adsorbent
for Runs 1 and 2.
The solvent for Runs 1 and 3 consists by volume of 60
hexane and 40% ethyl acetate (for this solvent blend: ~ =
7.66; ~D = 7.46; ~p = 1.04; ~H = 1.40). The solvent for
35 Runs 2, 4 and 6 consists by volume of 100% ethyl acetate
( ~= 8.85; ~D = 7~70; ~p = 2.60; ~ = 3.50). The solvent
for Run 5 consists by volume of 40% hexane and 60% ethyl
acetate (for this solvent blend: ~ = 7.85; ~D = 7.54; ~P =
1.56; ~H = 2.10).
!` ':, :
.
.
. -; ' `' ~
;7~3 ~2
- 38 -
Each Qf the runs is carried out at 50C.
In each run: Solvent is pumped continuously through
the column at a rate of 5 ml per minute. At time zero, a
sample pulse as described above is introduced by means of the
sample coil into the solvent flow. The equal volume samples
that are collected are each 5 ml.
In Run 1, retention volumes are obtained as follows:
for methyl palmitate, 0 for methyl stearate, 0 for methyl
oleate, 30 ml; for methyl linoleate, 125 ml.
In Run 1, relative selectivities are obtained as
follows: for methyl oleate/methyl stearate, ~ ; for methyl
linoleate/methyl stearate, ~ ; for methyl linoleate/meth~l
oleate, 4.17.
In Run 2, retention volumes are obtained as follows:
for methyl palmitate, 0; for methyl stearate, 0; for methyl
oleate, 20 ml; for methyl linoleate, 85 ml.
In Run 2, relative selectivities are obtained as
follows: for methyl olcate/methyl stearate, ~ ; for methyl
linoleate/methyl stearate, x ; for methyl linoleate/methyl
oleate, 4.25.
In Run 3, retention volumes are obtained as follows:
for methyl palmitate, 10 ml; for methyl stearate, 10 ml;
for methyl oleate, 30 ml; for methyl linoleate, 110 ml.
In Run 3, relative selectivities are obtained as
follows: for methyl palmitate/methyl stearate, 1.00; for
methyl olea~e/methyl stearate, 3.00; for methyl linoleate/
methyl stearate, 11.00; for methyl linoleate/methyl oleate,
3.67.
In Run 4, retention volumes are obtained as follows:
for methyl palmitate, 5 ml; for methyl stearate, 5 ml; for
methyl oleate, 20 ml; for methyl linoleate, 75 ml.
In Run 4, relative selectivities are obtained as
follows: for methyl palmitate/methyl stearate, 1.00; for
methyl oleate/methyl stearate, 4.00; for methyl linoleate/
methyl stearate, 15.00; for methyl linoleate/methyl oleate,
3.75.
In Run 5, retention volumes are obtained as follows:
for methyl palmitate, 5 ml; for methyl stearate, 5 ml; for
~, .
.
- 39 -
methyl oleate, 10 ml; for methyl linoleate, 20 ml.
In Run 5, relative selectivities are obtained as
follows: for methyl palmitate/methyl stearatej 1.00; for
methyl oleate/methyl stearate, 2.00; for methyl linoleate/
methyl stearate, 4.00; for methyl linoleate/methyl oleate,
2.00.
In Run 6, retention volumes are obtained as follows:
for methyl palmitate, 0; for methyl stearate, 0; for
methyl oleate, 5 ml; for methyl linoleate, 10 ml.
In Run 6, relative selectivities are obtained as
follows: for methyl oleate/methyl stearate, ~ ; for methyl
linoleate/methyl stearate, ~ ; for methyl linoleate/methyl
oleate, 2.00.
The above runs indicate that to obtain one fraction
enriched in methyl linoleate and other fraction enriched
in the other components in simulated moving bed processing,
the adsorbent best utilized out of those tested is the
adsorbent of Runs 1 and 2 and the solvent can be either the
solvent of Run 1 or the solvent of Run 2. The abo~e runs
indicate that to obtain one fraction enriched in unsaturates
and other fraction enriched in saturates, the adsorbent best
utilized out of those tested is the adsorbent of Runs 1 and
2 and the solvent can be either the solvent of Run 1 or the
solvent of Run 2. The different splits are accomplished by
apportioning the columns in the simulated moving bed
processing differently amongst the four zones. To provide a
fraction enriched in methyl linoleate but not in methyl oleate,
fewer columns are used in the adsorption zone than are used
to provide a fraction enriched in both methyl oleate and
methyl palmitate.
EXAMPLE II
This example involves pulse testing to determine solvent
and adsorbent combination useful for fractionation of soybean
methyl ester feedstock (that is, methyl ester mixture derived
from soybean oil and containing, by weight, 12.5% methyl
palmitate, 3.8~ methyl stearate, 23.1% methyl oleate, 53.4%
methyl linoleate, and 7.2% methyl linoleate).
Two runs are carried out.
'~,'i~i
: : -
:.
:
.
.:
~;71~42
- 40 -
In each run, the pulse consists of 0.5 ml solvent,
~.1 gm docosane tracer and 0.4 gm of thb above-described
soybean methvl ester feedstock.
In both the runs, the adsorbent has the following
characteristics: ~t is derived from-silica gel having a
surface area of 346 square meters per gram. It is also
characterized by a ratio of surface-silicon atoms to
aluminum atoms of 6.4:1, a moisture content less than 2%
by weight, and a particle size of 35-70 mesh (U.S. Sieve
Series). It contains sodium substituents as all of its
cation substituents.
The adsorbent is made as follows: Silica Gel 100
(35-70 mesh U.S. Sieve Series~ is utilized. 1000 grams of
the silica gel and 2 liters of distilled water are charged
into a 5.0 llter, 3-neck, fluted flask fitted with a
mechanical stirrer, a pH electrode, and an addition funnel.
The mixture is agitated to form a homogeneous slurry. The
pH of the slurry is adju~ted to 9.5 with 10% aqueous sodium
hydroxide solution. Then a freshly prepared solution of
sodium aluminate (108.6 gm) in distilled water (2.0 liters)
is added. The slurry is stirred 10 hours at room temperature
(about 20C). Then sitrring is stopped and the mixture is
allowed to stand overnight. The resulting product is poured
into a glass chromatographic column and washed free of un-
reacted aluminate with distilled water (1-2 ml per minute).
Washing is continued until the pH of the effluent is about 9Ø
The solid is suction filtered to remove bulk water and then
dried in a forced-draft oven (105-110C) overnight.
The solvent for Run 1 consists by volume of 99% hexane
and 1~ ethyl acetate (for this solvent blend: ~ ~ 7 30; ~D =
7.30; ~p = 0 03; ~H = 0 04)- The solvent for ~un 2 consists
by volume of 97~ hexane and 3% ethyl acetate (for this solvent
blend: ~ = 7.31; ~D = 7.31; ~p = 0.08; ~H = 0.11).
Each of the runs is carried out at 50C.
In each run: Solvent is pumped continuously through
the column at a rate of 5 ml per minute. At time zero, a
sample pulse as described above is introduced by means of the
sample coil into the solvent flow. The equal volume samples
that are collected are each 5 ml.
r
~1 .
~57a~z
- 41 -
In ~un 1, retention volumes are obtained as follows:
for methyl palmitate, 135 ml; for methyl stearate, 135 ml;
for methyl oleate, 145 ml; for methyl linoleate, 170 ml;
for methyl linolenate, 185 ml.
In Run 1, relative selectivities are obtained as follows:
for methyl palmitate/methyl stearate, 1.00; for methyl
oleate/methyl stearate, 1.07; ~or methyl linoleate/methyl
stearate, 1.26; for methyl linolenate/methyl stearate, 1.37;
for methyl linoleate/methyl oleate 1.17; for methyl linolenate/
methyl oleate, 1.~8; and for methyl linolenate/methyl
linoleate, 1.09.
In Run 2 f retention volumes are obtained as follows:
for methyl palmitate, 55 ml; for methyl stearate, 55 ml;
for methyl oleate, 55 ml; for methyl linoleate, 60 ml; for
methyl linolenate, 65 ml.
In Run 2, relative selectivities are obtained as follows:
for methyl palmitate/methyl stearate, 1.00; for methyl
oleate/methyl stearate, 1.00; for methyl linoleate/methyl
stearate, 1.09; for methyl linolenate/methyl stearate, 1.18;
for methyl linoleate/methyl oleate, 1.09; for methyl
linolenate/methyl oleate, 1.18; for methyl linolenate/methyl
linoleate, 1.08.
These runs indicate that fraction enriched in methyl
linolenate can be obtained using the adsorbent of Example II
and the solvent consisting by volume of 99% hexane and 1
ethyl acetate.
EXAMPLE III
This example involves pulse testing to determine solvent
and silvered adsorbent combination useful to fractionate soy-
bean methyl ester feedstock to produce one fraction enriched
in methyl linolenate and depleted in other components and
other fraction depleted in methyl linolenate and enriched in
other components.
One run is carried out.
The pulse is the same as that used in Example II.
The adsorbent has the following characteristics: It is
derived from silica gel having a surface area of 346 square
meters per gram. It is also characterized by a ratio of
surface-silicon atoms to aluminum atoms of 6.4:1, a moisture
,Y~
~LS7~ ~2`
- 42 -
content less than 2% by weight, and a particle size of 35-50
mesh (U.S. Sieve Series). It contains 0.27 millimoles of
silver ( in the form of cation substituents in a ~alence state
of 1) per 100 square meters of adsorbent surface area. The
silver substituents make up 67.6~ of the exchangeable cations.
The remainder of the exchangeable cations are sodium sub-
stituents. The surface area of the final adsorbent is 233
square meters per gram.
The adsorbent is made up the same as the adsorbent for
Runs 5 and 6 of Example I except for the following differences.
Silica Gel 100 is screened to provide a 35-50 mesh fraction
for reaction. 108.6 gms of sodium aluminate is used in the
surface aluminating reaction. 156 gms of silver nitrate is
used in the silvering procedure.
The solvent consists by volume of 30% ethyl acetate and
70~ hexane (for this solvent blend: ~ = 7~53~ ~D = 7.42, ~p =
0.78, ~H = 1.05).
The run is carried out at 50C.
In the run, solvent is pumped continuously through the
column at a rate of 5 ml per minute. At time zero, a sample
pulse as described above is introduced by means of the sample
coil into the solvent flow. The equal volume samples that
are collected are each 5 ml.
In the run, retention volumes and selectivities are
obtained indicating fractionation on the basis of unsatura-
tion wherein the ester of triunsaturated fatty acid is the
alkyl carboxylate of higher degree of unsaturation. In other
words the run indicates the adsorbent - solvent combination
tested is advantageously used to obtain one fraction enriched
in methyl linolenate and other fraction enriched in the other
alkyl carboxylates.
EXAMPLE IV
This example illustrates separation of a mixture of
methyl oleate and methyl linoleate to provide one fraction
enriched in methyl oleate and a second fraction enriched in
methyl linoleate. The run is carried out in the demonstration
unit as described above.
The feed composition consists by weight of 25% methyl
!~ ~`'`
-
'
~ ~76~ ~Z
- 43 -
oleate and 75% methyl linoleate.
The adsor~ent is the same as thàt used in Example III.
The solvent consists by volume of 20% ethyl acetate
and 80% hexane (for this solvent blend: ~ = 7~43~ ~D = 7.38,
~p = 0.52, and ~H = 0 70
The controller and the valves of the demonstration unit
are set so that the adsorption zone includes 4 columns, the
purification zone includes 4 columns and the desorption zone
includes 6 columns.
The step time (the interval at which the flow pattern
is advanced one column) is 7 minutes. The feed rate is 1.25
ml per minute. The solvent introduction rate is 42.63 ml
per minute. The extract flow rate is 13.88 ml per minute.
The raffinate flow rate is 30.00 ml per minute.
The temperature of operation is 50C.
The raffinate obtained consists ttotal fatty acid ester
basis) by weight of 97.80~ methyl oleate and 2.20~ methyl
linoleate. The extract obtained consists (total fatty acid
ester basis) by weight of 0.70~ methyl oleate and 99.30%
methyl linoleate.
The above indicates separation according to degree of
unsaturation.
The adsorbent particle size used presents no signi-
ficant handling or loss (because of suspension in solvent)
problems. There is no significant leaching of silver. There
is no fouling of adsorbent with impurities. No polymers are
detected in the product. The same equipment and adsorb~nt
is readily used for separating triglyceride mixtures.
When in the run of Example IV, the process is operated
using 16 columns and so that the adsorption zone includes
5 columns, the purification zone includes 5 columns and the
desorption zone includes 6 columns, the raffinate (total fatty
acid ester basis) consists of 100% methyl oleate and the
extract stream (total fatty acid ester basis) consists of
100~ methyl linoleate.
When in the run of Example IV, the feed instead consists
of the safflower methyl ester feedstock of ExampIe I, there
is separation to provide one fraction enriched in methyl
ester of polyunsaturated fatty acid and other fraction enriched
,~ ,
.
7~3 ~2
- 44 -
in methyl ester of saturated fatty acid and methyl ester of
monounsaturated fatty acid.
When in the run of Example IV, the feed consists instead
by weight of (a) 25% ethyl oleate and 75% ethyl linoleate
or (b) 25% propyl oleate and 75% propyl linoleate or (c)
25% butyl oleate and 75% butyl linoleate, fractionation
according to degree of unsaturation is obtained.
When in the-run of Example IV, an equivalent amount of
copper or platinum or palladium is substituted for the
silver substituents of the adsorbent, results are obtained
indicating attainment of fractionation according to degree
of unsaturation.
When in the run of Example IV, an equivalent amount
of potassium, barium, calcium, magnesium or zinc
substituents is substituted for the sodium substituents
of the adsorbent, results are obtained indicating
fractionation according to degree of unsaturation.
When a solvent consisting by volume of 15% acetone
and 85% hexane (for this solvent blend: ~ = 7 40~ ~D = 7 35'
~p = 0 77' ~H = 0.51) is substituted in Example IV for the
hexane/ethyl acetate solvent, fractionation according to
degree of unsaturation is obtained.
When a solvent consisting by volume of 65~ hexane and
35~ diethyl ether (for this solvent blend: ~ = 7 30~ ~D =
7.23, ~p = 0 49~ ~H = 0.88) is substituted in Example IV
for the hexane/ethyl acetate solvent, fractionation
according to degree of unsaturation is obtained.
When a solvent consisting by volume of 10% ethanol
;~.l~i
~;7~ ~Z
- 45 ~-
and 90~ hexane (for this solvent blend: ~ = 7.41,
~ = 7.34, ~p s 0.43, ~ = 0.95) is substituted in Example
IV for the hexane/ethyl acetate solvent, fractionation
according to degree of unsaturation is obtained.
When Amberlyst~ XN1010 ~a macroreticular strong acid
cation exchange resin sold by Rohm & Haas) with an equiv-
alent amount of silver to that used in Example IV is sub-
stituted for the adsorbent in Example IV, the fractionation
obtained is significantly less complete.
When Zeolite X or Zeolite Y or silvered Zeolite X
or silvered Zeolite Y is substituted as the adsorbent
in Example IV, the same equipment and adsorbent is not
appropriately used for separation of methyl esters and
triglycerides.
EXAMPLE V
The alkyl carboxylate mixture for fractionation is
derived from soybean oil and consists by weight o~ 12.5%
methyl palmitate, 3.8% methyl stearate, 23.1% methyl
oleate, 53.4% methyl linoleate, and 7.2% methyl linolenate.
The adsorbent is from the same batch as that used in
Runs 1 and 2 of Example I.
The solvent used irst consists by volume of 100%
hexane (6= 7 30~ D = 7 30~ p = ~ H = ); this solvent
is denoted solvent I below. The solvent used second
consists by volume of 9o% hexane and 10% ethyl acetate
(for this solvent blend: ~ = 7 35~ D = 7.34,6p = 0.26,
~H = 0 35); this solvent is denoted Solvent II below. The
solvent used third consists by volume of 50% hexane and 50%
ethyl acetate (for this solvent blend: ~ = 7.81,6D = 7 50
~p = 1.30, ~H = 1.75); this solvent is denoted Solvent III
below. The solvent used fourth consists by volume of 100
ethyl acetate ( ~= 8.85, ~D = 7 70~ ~p = 2.60,
,
, ,
' ~ ' ':~., ,
,:
-
~70~Z
- 46 -
~H = 3 50); this solvent is denoted Solvent IV ~elow. The
solvent used fifth consists by volume of 100~ methanol
( ~ i 14.5, ~D = 7 4- ~p = 6.0, ~H = 10.9); This solvent
is denoted Solvent V below.
The test is carried out at 50C.
Solvent I is pumped through the "pulse test" column
described above at 5.0 ml/minute. With flow stopped, a
"pulse" containing 2.0 grams (95% soybean methyl ester
described above and 5% C22 linear hydrocarbon tracer)
dissolved in 10 ml of Solvent I is injected into the column
entrance. Flow of Solvent I is then restarted, and eluant
sample collection begins. After approximately two column
volumes of Solvent I are pumped, the solvent is changed to
Solvent II, then to Solvent III, etc., with approximately
two column volumes of each solvent being pumped in succession
after the above described feed injection. Eluant samples
are collected and analyzed.
The table below presents data for this run. In the
table: 16=0 stands for methyl palmitate, 18=0 stands for
methyl stearate 18=1 stands for methyl oleate, 18=2 stands
for methyl linoleate, and 18=3 stands for methyl linoleate.
The values given opposite each solvent represent the alkyl
carboxylate composition eluted with that particular solvent.
TAsLE
SEPARATION OF SOYBEAN METHYL
ESTERS IN A TWO SOLVENT PROCESS
Solvent %16=0 %18=0~18=1 %18=2 %18=3
I 73.15 26.85 --- --- ---
II --- --- 33.32 66.68 ---
30 III --- --- --- 25.80 74.2
V _ _ _ _ _ _ _ _ _
i~
,, -.: , . ,
-:
7~3 ~2
- 47 -
The above data indicates that with the selected
adsorbent: Saturates are best separated from unsaturates
using hexane as the adsorption vehicle and 50/50 hexane/ethyl
acetate as the desorbent. To provide fraction free of
methyl linolenate, hexane can be the adsorbent and 90/10
hexane/ethyl acetate the desorbent. To provide fraction
enriched in methyl linolenate and depleted-in other
components, the adsorbing solvent should be 90/10 hexane/
ethyl acetate and the desorbent should be 50/50 hexane/
ethyl acetate. To separate polyunsaturates, the adsorbing
solvent should contain by volume between 0 and 10% hexane
(with the remainder ethyl acetate) and the desorbent should
be 50/50 hexane/ethyl acetate. Other solvents and blends
can be substituted provided there is similarity of
solubility parameters and solubility parameter components.
While the foregoing describes certain preferred
embodiments of the invention, modification will be readily
apparent to those skilled in the art. Thus, the scope of
the invention is intended to be defined by the following
claims.
1~
; ' ~'
.
