Note: Descriptions are shown in the official language in which they were submitted.
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"FATTY ACID SEPARATION"
BACKGROUND OF THE INVENTION
Field of the Invention
The field of art to which this invention pertains is the
sol;d bed adsorptive separation oF Fatty acids. More specifically,
the invention relates to a process for separating fatty acids which
process employs an adsorbent comprising particular polymers which
selectively adsorb one fatty acid from a feed mixture containing
more than one fatty acid.
Descript _n of the Prior Art
It is known in the separation art that cer~ain crys~al-
line aluminosilicates can be used to separate certa;n esters of fatty
acids from mixtures thereof. For example, in U.S. Patent Nos.
4,048,205; 4,049,688 and 4,066,6779 there are claimed processes ~or
the separation of esters of fatty acids of various degrees of unsat-
urat;on from mixtures of esters of saturated and unsaturated fatty
acids. These processes use adsorbents comprising an X or a Y zeolite
conta;n;ng a selected cation at the exchangeable cationic sites.
In contrast, this invention relates to the separation o-f
certain fatty acids rather than fatty acid esters. We have discovered
that adsorbents comprising nonionic hydrophobic insoluble crosslinked
polystyrene polymers exhibit adsorptive selectivity for one fatty
acid with respect to another fatty acid, thereby making separation
of such fatty acids by solid bed selective hdsorption possible.
In one specific embodiment, our process is a process for separating stearic
acid from palmitic acid. In another specific embodiment, our process is
a process for separating oleic acid from linoleic acid. Substantial
uses of fatty acids are in the plasticizer ancl surface active agent
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fields. uel~v~ s or ral~y a~as ar~ ul Y~IU~ in compounding lubri-
cating oil~ as a lubricant ~or the tex~ile and molding trade, in special
lacquers, as a water-proofing agent, in the cosmetic and pharmaceutical
fields, and in biodegradable detergents.
SUMMARY OF THE INVENTION
-
In brief summary, our invention is in one embodiment a process
for separating a first fatty acid selected from the group consisting of
stearic acid and oleic acid from a mix~ure comprising the first fatty
acid and a second fatty acid selected from the group consisting of
palmitic acid and linoleic acid, which process comprises contacting at
adsorption conditions that mixture with an adsorbent comprising a non-
ionic hydrophobic insoluble crosslinked polystyrene polymer having adsorp-
tive selectivity for the f;rst fatty acid, thereby selectively adsorbing
the first fatty acid, wherein when the first ac;d is stearic acid then
the second acid is palmitic acid and wherein when the first acid is oleic acid
then the second acid is linoleic actd,
In yet another embodlment, our ;nvention is a process for separat-
ing a first fatl;y acid selected from the group consisting of stearic acid and
oleic acid frûm a mixture comprising the first fatty acid and a second fatty
acid selected from the group consistlng of palmitic acid and linoleic acid,
wherein, wb~n, the first acid is stearic acid then the second acid is
palmitic acid and wherein when the first acid is oleic acid ^then the second
acid is linoleic ~cid, which process employs an adsorbent fomprising a
non~onic hydrophobic insoluble cross-linked polystryene polymer, which
process cbmprises the steps of: (a) main~aining net fluid flow through
a column of the adsorbent in a sinyle direction, which column contains at
least three zones having separate operat;onal functions occurring therein
and being serially interconnected with the terminal zones of said column
connected to provide a continuous connection of the zones; (b) maintaining an
adsorption zone in the column, the zone defined by the adsorbent located
bet~een a feed inputstream at an upstream boundary of the ~one and a
--2--
raffinate output stream at a downstream boundary of the zone; k)
maintaining a purification zone i~nediately upstream from the adsorp-
tion zone, the purification zone defined by the adsorbent located
between an ex~ract output stream at an upstream boundary of the
purification ~one and the feed input stream at a downs~ream boundary
of the purification zone; (d) maintaining a desorpt;on zone immedi-
ately upstream from the purification zone, the desorption zone
defined by the adsorbent located between a desorbent input stream at
an upstream boundary of the zone and the extract output stream at a
downstream boundary of ~he zone; (e) pass;ng the ~eed mixture into
the adsorption zone at adsorption conditions to effect the selective
adsorption of the first fatty acid by the adsorbent in
the adsorption zone and withdrawing a raffinate output stream com~
prising the second fatty acid from the adsorption zone;
(f) passing a desorbent material into the desorption zone at desorp-
: tion conditions to effect the displacement of the first
fatty acid from the adsorbent in the desorption zone; (g) withdrawing
an extract ou~put stream comprising the first fatty acid
and desorbent material from the desorption zone; (h) passing at least
a portion of the extract output stream to a separation means and
therein separating at separation conditions at least a portion of the
desorbent material; and (i) periodically advancing through the column
of adsorbent in a downstream direction with respect to fluid flow in
the adsorption zone the feed ;nput stream, raffinate output stream,
desorbent input stream, and extract output stream to effect the shift-
ing of zones through the adsorbent and the production of extract out-
put and raffinate output streams.
Other embodiments of our invention encompass details about
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feed mixtures, adsorbents, desorbents, desorbent materials and
operating conditions, all of which are hereinafter disclosed in
the following discussion of each of the facets of the prPsent invention.
DESCRIPTION OF THE INVENTION
At the outset the defin;t;ons of various ~er~s used through-
out the specification will be useful in making clear the operation,
objects and advantages of our process.
A "feed m;xture" is a mixture containing one or more extract
components and one or rnore ra~finate components to be separated by our
process. The term "feed stream" indicates a stream of a feed mixture
which passes to the adsorbent used in the process.
An "extract component" is a compound or type of compound
that is more selectively adsorbed by the adsorbent while a "raffinate
csmponen'L" is a compound or type of rompound that is less selectively
adsorbed. In this process a first fatty acid is an extract com-
ponent and a second fatty acid is a raffinate component. The term
"desorbent material" shall mean generally a material capable of desorb-
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~ ~ ~ ...................................... . .
ing an extract component. The term "desorbent stream" or "desorbent
input stream" indicates the stream through which desorbent material
passes to the adsorbent. The term "raffinate stream" or "raffinate
output stream" means a stream ~hrough which a raffinate component is
removed from the adsorbent. The composition of the raffinate stream
can vary from essentially 100~ desorbent material to essentially 100%
raffinate components. The term "extract stream" or "extract output
stream" shall mean a stream through which an extract material which
has been desorbed by a desorbent material is removed from the adsor-
bent. The composition of the extract stream, likewise, can vary from
essentially 100% desorbent material to essentially 100% extract com-
ponents. At least a portion of the extract stream and preferably at
least a portion of the raffinate stream from the separation process
are passed ts separation means, typically fractiona~ors? where at
least a portion of desorbent material is separated to produce an ex-
tract product and a raffinate product. The terms "extract product"
and "raffinate product" mean products produced by the process contain-
;ng, respectively, an extract component and a raffinate component in
higher concentrations than those found in the extract stream and the
raffinate stream. Although it is possible by the process of this inven-
tion to produce a high purity, first fatty acid product or a
second fatty acid product (or both) at high recoveries, it will be
appreciated that an extract component is never completely adsorbed by
the adsorbent, nor is a raffinate component completely non-adsorbed by
the adsorbent. Therefore, varying amounts of a raffinate component can
appear in the extract stream and, likewise, varying amounts of an extract
component can appear in the raffinate stream. The extract and raffinate
streams then are further distinguished from each uther and from the feed
~i~17~;~
m;xture by the ratio of the concentrations of an extract component
and a raffinate component appeariny in the particular stream. More
specifically, the ra~io of the concentration of a first fatty
acid to ~hat of a less selectively adsorbed second fatty acid
will be lowest in the raffinate stream, next hi~hest in the feed
mixture, and the highest in the extract stream. Likewise, the ratio
of the concentration of a less selectively adsorbed first fatty
acid to that of a more selectively adsorbed second fatty acid
will be highest in the raffinate stream, next highest in the feed
mixture, and the lowest in the extract stream.
The -term "selective pore volume" of the adsorbent is de-
fined as the volume of the adsorbent which select;vely adsorbs an
extract component from the feed mixture. The term "non-selective
void volume" of ~he adsorbent is the volume of the adsorbent whioh
does not selectively retain an extract component from the feed mix-
ture. This volume includes the cavities of the adsorbent which con-
tain no adsorptive sites and the interstitial void spaces between
adsorbent particles. The selective pore volume and the non-selective
void volume are generally expressed in volumetric quantities and are
of importance in determinin~ the proper flow rates of fluid required
to be passed into an operational zone for efficient operations to take
place for a given quantity of adsorbent. When adsorbent "passes" into
an operational zone (hereinafter defined and described) employed in
- one embodiment of this process its non-selective void volume together
with its selective pore volume carries fluid into that zone. The non-
selective ~oid volume is utilized in determining the amount of fluid
which should pass into the same zone in a countercurrent direction to
the adsorbent to displa~e the fluid present in the non-selectiYe void
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~ !L76~
volume. If the fluid flow rate passing into a zone is smaller than
the non-selective void volume rate of adsorbent material passing
into that zone, there is a net entrainment of liquid intn the zone
by the adsorbent. Since this net entrainmen~ is a fluid present in
non-selective void volume of the adsorbent, it in most instances
comprises less selectively retained feed components. The selective
pore volume of an adsorbent can in certain instances adsorb portions
of raffinate material from the fluid surrounding the adsorbent since
in certain instances there is competi$ion between extract material
and raffinate material for adsorptive sites within the selective
pore volume. If a large quantity of raf~inate material with respect
to extract material surrounds the adsorbent, raffinate material can
be competitive enough to be adsorbed by the adsorbent.
Before considering feed mixtures which can be charged to
the process of our invention brief reference is first made to the
terminology and to the general production of fatty acids. The fatty
acids are a large group of aliphatic monocarboxylic acids, many of
which occur as glycerides (esters of glycerol) in natural fats and
oils. Although the term "fatty acids" has been restricted by some to
the saturated acids of the acetic acid series, both normal and branched
chain, it is now generally used, and is so used herein, to include also
related unsaturated acids, certain substituted acids, and e~en aliphatic
acids containing al;cyclic substituents. The naturally occurring fatty
acids with a few exceptions are higher straight chain unsubstituted
~5 acids containing an even number of carbon atoms. The unsaturated fatty
acids can be divided, on the basis of the number of double bonds in the
hydrocarbon chain, into monoethanoid, diethanoid, triethanoid, etc. (or
monoethylenic, etc.) Thus the term "unsaturated fatty acid" is a ~eneric
7~i7
term for a fatty acid having at least one double bond, and the term
"polyethanoid fatty acid" means a fatty acid having more than one
double bond per molecule. Fatty acids are typically prepared from
glyceride fats or oils by one of several "splitting" or hydrolytic
processes. In all cases the hydrolysis reaction may be summarized
as the reaction of a fat or oil with water to yield fatty acids plus
glycerol. In modern fatty acid plants this process is carried out
by continuous high pressure, high temperature hydrolysis of the fat.
Starting materials most commonly used for the production of fatty
acids include coconut oil, palm oil, inedible animal fats, and the
commonly used vegetable oils, soybean oil~ cottonseed oil and corn oil.
The composition of the fatty acids obtained from the "spl;tter" is
dependent on the fat or oil from which they were made. As detailed
data for ~he fatty acid composition of fats have accumulated over a
wide range of rnaterial, it has become more and more apparent that
natural fats tend to align themselves, by their component acids, in
groups according to their biological origin. Moreover, it has become
clear that the fats of the simplest and most primitive organisms are
usually made up from a very complex mixture of fatty acids whereas as
biological development has proceeded, the chief romponent acids of the
fats of the higher organisms have become fewer in number. In the
animal kingdom this change in type is remarkably consistent and culmin-
ates, in the fats of the higher land animals, in fats in which oleic,
palmitic and stearic acids are the only major components. All fats of
aquatic origin contain a wide range of combined fatty acids, mainly of
the unsaturated series. On passing from fats of aquatic to those of
land animals there is also a marked simplification in the composition
of the mixed fatty acids, most of the unsaturated acids, except oleic
'7~7
acid. disappear. The final result is that in most of the higher land
animals the major componen~ acids of the fats are restr;cted to oleic,
palmitic and stearic and, morPover, that about 60-65% of the acids
belong to the C18 series, saturated or unsaturated. Thus the compo-
sition cf the fatty acids obta;ned from the "splitter" can vary widely
depending upon the fat or oil charged to the "spl;tter". Rarely will
the composition of the fatty acid mixture nbtained from the "splitter"
be ideal or even satisfactory for most uses. Hence fractionation is
used almost universally to prepare prsducts more desirable for spec;fic
end uses than the mixtures obtained from the "splitter". Fractionation
according to molecular weight is usually accomplished in fractional dis-
i tillation. ~here is somewhat of a di ff erence in.the volatility of any
two fatty acids ofdifferentchainlength~ andin practice,theutility sf
fractional distillation is enhaneed by the absence of odd-membered
1~ acids in the natural fats, so that 2 carbon atoms is nearly always the
minimum difference in chain ~ength of the fatty acids present in a
mixture. Fract'ionating columns in such operation are sometimes ~apable
of producing fatty acids of 95% purity or better from the viewpoin~ of
chain length depending on the chain length in question. It is not pos-
sible~ however, to separate unsaturated fatty acids from each other or
. froms~t~r~ted fatty acids or to separate certain saturated fatty ac;ds
; from each other by commercial fractional distillation when all have the
same cha~n length or minimum differen~e in chain length.
Our process is directed to separating certain mixtures of these
, fatty acids; more specifically, it is directed to separating a f;rst
fatty acid from a mixture comprising a first fatty acid and a second fatty
acid, wherein when the first fatty acid is stearic acid then the second
fatty acid is palmitic acid and where~n when the first fatty acid is
oleic acid then the second fatty acid is linoleic acid.
~ . ..... .
An example of a typical feed mixture is known as "tall oil fatty acids"
and comprises abnut 1 vol. % of palmitic acid, 2 vol. % stearic acid, 51
vol. ~ oleic acid, 45 vol. % linoleic acid and 4 vol. % others. Feed
mixtures which can be charged to our process may contain, in addition
to fatty ac;ds, a diluent material that is not adsorbed by the adsor-
bent and which is preferably separable from the extract and raffinate
output streams by fractional d;stillat;on. When a diluent is
employed the concentrat;on of d;luent in the mixture of diluent and
fatty acids may be from a few vol. % up to about 90 vol. X.
Desorbent materials used in various prior art a~sorptive
separat;on processes vary depending upon such factors as ~he type of
operation employed. In the swing bed system in which ~he select;vely
adsorbed ~eed component is removed from the adsorbent by a purge
stream desorbent selection is not as critical and desorbent mat~rials
compris;ng gaseous hydrocarbons such as methane; ethane, e~c., or
other types of ~3ases such as nitrogen or hydrogen may be used at
elevated temperatures or reduced pressures or both to effectively
purge the adsorbed feed component from the adsorbent. However, in
adsorptive separation processes which are generally operated contin-
uously at substantially constant pressures and temperatures to insure
liquid phase, the desorbent material must be judic;ously selected to
satisfy many criteria. First, the desorbent material should displace
an extract component from the adsorbent with reasonable mass flow rates
withuut itself being so strongly adsorbed as to unduly prevent an
extract component from displacing the desorbent material in a following
adsorption cycle. Expressed in tenms of the selectiYity ~hereinafter
discussed in more detail)9 it is preferred that the adsorbent be more
selective for all of the extract components with respect to a raffinate
, _ ___.___
'7
component than it is for the desorbent material with respect ~o a
raffinate component. Secondly, desorbent materials must be compati-
ble with the particular adsorbent and the particular feed mixture.
More specifically, they must not reduce or destroy the critical sel-
ectivity of the adsorbent for an extract component with respect to
a raffinate component. Desorbent materials should addi~ionally be
substances which are easily separable from the feed mixture that is
passed into the process. Both the raffinate stream and the extract
stream are removed from the adsorbent in admixture with desorbent
material and without a method of separating at least a portion of the
desorbent material the purity of the extract product and the raff;-
nate product would no~ be very high, nor would the desorbent material
be available for reuse in the process. It is therefore contemplated
that any desorbent material used in th;s process will preferably have
a substantially different average boiling point than that of the feed
mixture to allow separation of at least a por~ion of desorbent mate-
rial from feed components in the extract and raffinate streams by sim-
ple fractional distillation ~hereby permitting reuse of desorbent
material in the process. The term "substantially different" as used
herein shall mean that the difference between the average boiling points
between the desorbent material and the feed mixture shall be at least
about 5C. The boiling range of the desorbent material may be higher
or lower than that of the feed mixture. Finally, desorbent materials
should also be materials which are readily available and therefore
reasonable in cost. In the preferred isothermal, ;sobaric, liquid
phase operation of the process of our invention? we ha~e found parti-
cular1y effective desorbent materials compr~sing one o~ the mixtures
176~
in the group of mixtures comprising acetonitrile and methanol;
acetonitrile, tetrahydrofuran and water; acetone and water; dimethyl
acetamide and water; methanol and water; dimethyl formamide and water;
quarternary methyl ammonium hydroxide, water and methanol; and quarter-
nary propyl ammonium hydroxide.
The prior art has also recognized that certain characteristics
of adsorbents are highly desirable, if not absolutely necessary, to
the successful operation of a selective adsorption process. Such
characteristics are equally important ~o this process. Among such
characteristics are: adsorptive capacity for some volume of an
extract component per volume of adsorbent; the selective adsorption
of an extract componen~ with respect to a raffinate component and the
desorbent materialj and sufficiently fast rates of adsorption and
desorp~ion o~ an extract component to and from the adsorbent. Capa-
city of the adsorbent for adsorbing a specific volume of an extract
component is, of course, a necessity; without such capac;ty the
adsorbent is useless for adsorptive separation. Furthermore, the
higher the adsorbent's capacity for an extract component the better
is the adsorbent. Increased capacity of a particular adsorbent makes
it possible to reduce the amount of adsorbent needed to separate an
extract component of known concentration contained in a particular
charge rate of feed m;xture. A reduction in the amount of adsorbent
requ;red for a specific adsorptive separation reduces the cost of the
scparation process. It is important that the good initial capacity of
2~ the adsorbent be maintained during actual use in the separation pro-
cess over some economically desirable life. The second necessary ad-
sorbent characteristic is the ability of the adsorbent to separate
components of the feed, or, in other words, that the adsorbent possess
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adsorptive selectivity, (B), ~or one component as compared to another
component. Relative selectivity can be expressed not only for one
feed component as compared to another but can also be expressed be-
tween any feed mixture component and the desorbent material. The
selectivity, (B), as used throughout th;s spec;fication is defined as
the ratio of the two components of the adsorbed phase over the ratio
of the same two components in ~he unadsorbed phase at equilibrium
conditions. Relative selectivity is shown as Equation 1 below:
Equation 1
Selectivity = (B) = Evl- percent C!vol. percent
vol. percent Clvol. percent D U
where C and D are two components of the feed represented in volume
percent and the subscr;p~s A and U represent the adsorbed and unadsorbed
phases respectively. The equ;librium conditions were detenm;ned when
the feed passing over a bed of adsorbent did not change compos;tion
after contacting the bed of adsorbent. In other words, there was no
net transfer of material occurring between the unadsorbed and adsorbed
phases. Where select;v;ty of two components approaches 1.0 there is no
preferential adsorption of one component by the adsorbent with respect
to the other; they are both adsorbed ~or non-adsorbed) to about the same
degree with respect to each o~her. As the (B) becomes less than or
greater than 1.0 there is a preferent;al adsorption by the adsorbent for
one component with respect to the other. When comparing the selectivity
by the adsorbent of one component C over component D, a (B) larger than
1.0 indicates preferential adsorption of component C within the adsorbent.
~5 A (B) less than 1.0 would ;ndicate that component D is preferentially
adsorbed leav;ng an unadsorbed phase richer in component C and an adsorbed
phase r;cher in component D. Ideally desorbent mater;als should have a
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select;v;ty equal to about 1 or slightly less than 1 with respect to
all extract components so that all of the ex~ract components can be
desorbed as a class with reasonable flow rates of desorbent ma~erial
and so that extract components can displace desorbent material in a
subsequent adsorption step. Wh;le separation of an extract component
from a raffinate component is theoretically possible when the selec-
tivity of the adsorbent for the extract component with respect to the
raffinate component is greater than 1, it ;s preferred that such
selectiv;ty approach a value of 2. Like relative volat;l;ty, the
higher the selectivity the easier the separation is to perform.
Higher select;v;ties penmit a smaller amount of adsorbent to be used.
The third ;mportant characteristic is the ra~e of exchange of the
extract component of the feed m;xture mater;al or, in other words~
the relative rate of desorption of the extract component. Th;s char-
acterist;c relates directly to the amount of desorbent material that
must be employed in the process to recover the extract component from
the adsorbent; faster rates of exchange reduce the amount of desorbent
material needed to remove the extract component and therefore permit a
reduction in the operating cost of the process. ~lith faster rates of
exchange, less desorbent material has to be pumped through the process
and separated from the extract stream for reuse in the process.
A dynamic testing apparatus is employed to test various
adsorbents with a particular feed mixture and desorbent material to
measure the adsorbent characteristics of adsorptive capacity, selecti-
vity and exchange rate. The apparatus consists of an adsorbent chamber
comprising a helical column of approximately 70 cc volume havlng inlet
and outlet portions at opposite ends of the chamber. The chamber is
contained within a temperature control means and, in addition, pressure
~81~76~7
control equipment ;s used to operate the chamber at a constant pre-
determined pressure. Quantitative and qualitative analytical equip-
ment such as refractometers, polarimeters and chromatographs can be
attached to the outlet line of the chamber and used to detect quanti-
tati~ely or determ;ne qualitatively one or more components in the
effluent stream leaYing the adsorbent chamber. A pulse test, performed
using this apparatus and the following general procedure, is used to
determine selectivities and other data for various adsorbent systems.
The adsorbent is filled to equ;librium with a particular desorbent
material by passing the desorbent material through the adsorbent cham-
ber. At a convenient time, a pulse of feed containing known concentra-
tions of a tracer and of a particular extract component or of a
raffinate component or both all diluted in desorbent is injected for a
duration of several minutes. Desorbent flow is resumed, and the tracer
and the extract component or the raffinate component (or both) are
eluted as in a liguid-solid chromatographic operation. The effluent
can be analyzed onstream or alternatively eFfluent samples can be col-
lected periodically and la~er analyzed separately by analytical equip-
~ent and traces of the envelopes of corresponding component peaks
developed.
-- From information derived from the test adsorbent performance
can be rated in terms of void volume, retention volume for an extract
or a raffinate component, selectivity for one component with respect to
the other, and the rate of desorption of an extract component by the
desorbent. The retention volume of an extract or a raffinate component
may be characterized by the distance between the center of the peak
envelope of an extract or a raffinate compon~nt and the peak envelope
of the tracer component or some o~her known reference point. It is
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'76~
expressed in terms of the volume in cubic cent;meters of desorbent
pumped during this time interval represented by the distance between
the peak envelopes. Selectivity, (B), for an extract component w;th
respect to a raff;nate component may be characterized by the ratio
of the distance between the center of the extract camponent peak
envelope and the tracer peak envelope ~or other reference point) to
the corresponding distance between lthe center of the raffinate compo-
nent peak envelope and the tracer peak envelope. The rate of exchange
of an extract component with the desorbent can generally be charac-
terized by the width of the peak envelopes at half intensity. The
narrower the peak width the faster the desorption rate. The desorp-
tion rate can also be characteri~ed by the distance between the
center of the ~tracer peak envelope and ~he disappearance of an extract
component which has just been desorbed. This distance is again the
volume of desorbent pumped during this time interval.
To further evalua~te promising adsorbent systems and ~o
translate this type of data into a practical separation process
requires actual testing of the best system in a continuous counter-
current liquid-solid contacting device. The general operating opera-
ting principles of such a device have been previously described
and are found in Broughton U.S. Patent 2,985,589. A specific
laboratory size apparatus utilizing these principles is described in
deRosset etal.,U.S.Patent 3,706,812. The equipment romprjSes
multiple adsorbent beds with a number of access lines attached to dis-
tributors within the beds and terminating at a rotary distributing
valve. At a given valve position. feed and desorbent are being
introduced through two of the lines and the raffinate and extract
streams are being withdrawn through two more. All rema~ning access
-16-
~i81~6~
lines are inactive and when the position of the distributing valve
is advanced by one index all active positions will be advanced by
one bed. This simulates a condition in which the adsorbent
physically moves in a direction countercurrent to the liquid flow.
Additional details on the above-mentioned nonionic adsorbent testing apparatus
and adsorbent evaluation tPchn;ques may be found in the paper
"Separation of C~ Aromatics by Adsorption" by A.J. deRosset9 R.W.
Neuzil, D.J. Korous, and D.H. Rosback presented at the American
Chemical Society, Los Angeles9 California, March 28 through April 2,
1971.
Adsorbents to be used in the process of this invention will
comprise nonionic hydrophobic insoluble crosslinked polystyrene polymers,
preferably ~hose manufactured by the Rohm and Haas Company and sold
under the trade name l'Amberlite". The types of Amberlite polymers
known to be eFfective for use by this invention are referred to in
Rohm and ~laas Company literature as Amberlite XAD-2 and Amberlite
XAD-4, and described in the literature as "hard, insoluble spheres
of high surface, porous polymer". The various types of Amberlite
polymeric adsorbents differ in physical properties such as porosity
volume, surface area, average pore d;ameter, skeletal density and
nominal mesh sizes. Applications for Amberlite polymer;c adsorbents
suggested in the Rohm and Haas Company literature include decolorizing
pulp mill bleaching effluent, decolorizing dye wastes and pesticide
removal from waste effluent. There is, of course, no hint in the
2~ literature to our surprising discovery of the effectiv2ness of Amberlite
polymeric adsorbents in the separation of monoethanoid fatty acids from
diethanoid fatty acids.
A fundamental superiority of the Amberlite polymeric adsor-
-17-
6i~
bents over crystalline aluminosilicates is that the former, unlike
the latter, may be used for the direct separation of fa~ty acids
without first converting the fatty acids to their corresponding
esters. The processes of the aforementioned prior art patents are
applicable only to esters of fat~y acids because the free carboxylic
group of a fatty ac;d chemically reacts with the crystalline alumino-
s;licates used by those processes. The adsorbent of this invention
exhibits no such reactivity and, therefore, the process of this
invention is uniquely suitable for the separation of fatty acids.
The adsorbent may b~ employed in the form of a dense
compact fixed bed which is alternatively contacted w;th the feed mix-
ture and desorbent materials. In the simplest embodiment of the
invention the adsorbent is employed in the fcrm of a single static
bed in which case the process is only semi-oontinuous. In ano~her
embod;ment a set of two or more static beds may be employed in fixed
bed contacting with appropriate valving so that ~he feed mixture is
passed through one or more adsorbent beds while the desorbent materials
can be passed through one or more of the other beds in the set. The
flow of feed mixture and desorben~ materials may be either up or down
through the desorbent. Any of the conventional apparatus employed in
static bed fluid-solid oontacting may be used.
Countercurrent moving bed or simulated movin~ bed counter-
current flow systems, however, have a much greater separation
efficiency than fixed adsorbent bed systems and are therefore preferred.
In the moving bed or simulated moving bed processes the adsorption and
desorption operations are continuously taking place which allows both
continuous production of an extract and a raffinate stream and the
continual use of feed and desorbent streams. One preferred embodiment
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of this process utilizes what is known in the art as the simulated
moving bed countercurrent flow system. The operating principles and
sequence of such a flow system are described in U.S. Patent 2,98~,589
incorporated herein by reference thereto. In such a system it is
the progressive movement of multiple liquid access points down an
adsorbent chamber that simulates the upward movement of adsorbent
contained in the chamber. Only four of the access lines are active
at any one timei the feed input stream, desorbent inlet stream, raf-
finate owtlet stream, and extract outlet stream access lines.
~oincident with this simulated upward movement of the solid adsorbent
is the movement of the liquid occupying the void volume of the packed
bed of adsorbent. So that countercurrent contact is maintained, a
liquid flow down the adsorbent chamber may be provided by a pump. As
an ac~ive liquid access point moves through a cycle, that is, from
the top of the chamber to the bottom, the chamber circulation pump
moves through different zones which requ;re different flow rates. A
programmed flow controller may be provided to set and regulate these
flow rates.
The active liqu;d access points effectively divided the
adsorbent chamber into separate zunes, each of which has a different
function. In this embodiment of our process it is generally necessary
that three separate operational zones be present in order for the
process to take place although in some instances an optional fourth
zone may be used.
The adsorption zone, 7one 1, is defined as the adsorbent
located between the feed ;nlet stream and the raffinate outlet stream.
In this zone, the feedstock contacts the adsorbent, an extract compo-
nent is adsorbed, and a raffinate stream is withdrawn. Since the
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76'~
general flow through zone 1 is from the feed stream which passes into
the zone to the raffinate stream which passes out of the zone, the
flow in this zone is considered to be a downstream direction when pro-
ceeding from the feed inlet to the raffinate outlet streams.
I~mediately upstream with respect to fluid flow in zone 1
;s the puri~ication zone, zone 2. The purification zone ;s defined
as the adsorbent between the extract outlet stream and the feed inlet
stream. The basic operations tak;ng place in zone 2 are ~he displace-
ment from the non-selective void volume of the adsorbent of any
raffinate material carried into zone 2 by the shift;ng of adsorbent
into this zone and the desorption of any raffinate material adsorbed
within the selective pore volume of the adsorbent or adsorbed on the
surfaces of the adsorben~ particles. Purification is achieved by
passing a portion of extract stream material leaving zone 3 into zone
2 at zone 2's upstream boundary, the extract outlet stream, to effect
the displacement of raffinate material. The flow of material in zone
2 is in a downstream direction from the extract outlet stream to the
feed inlet stream.
mediately upstream of zone 2 wi~h respect to the fluid
flowing in zone 2 is the desorption zone or zone 3. The desorption
zone is defined as the adsorbent between the desorbent inlet and the
extract outlet stream. The function of the desorption zone is to
allow a desorbent material which passes into this zone to displace the
extract component wh;ch was adsorbed upon the adsorbent during a
previous contact with feed in zone 1 in a prior cycle of operation.
The flow of fluid in zone 3 is essentially in the same direction as
that of zones 1 and 2.
In some instances an optional buffer zone, zone 4, may be
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1181 ~
utilized. This zone, defined as the adsorbent between the raffinate
outlet stream and the desorbent inle~ stream, if used, is located
immediately upstream with respect to the fluid flow to zone 3. Zone
4 would be utilized to conserve the amount of desorbent utilized in
the desorption s~ep since a portion of the raffinate stream which ls
removed from zone 1 can be passed into zone 4 ~o displace desorbent
material present in that zone out of that zone into the~ desorption
zone. Zone 4 will contain enough adsorbent so that raffinate mate-
rial present in the raffinate stream passing out of zone 1 and into
æone 4 can be prevented from passing into zone 3 thereby contaminating
extract stream rcmoved from zone 3. In the ;nstances which the fourth
operational zone is not utilized the raffina~e stream passed from
70ne 1 to zone 4 must be carefully monitored in order that the flow
directly from zone 1 to zone 3 can be stopped when ~here is an appre-
1B ciable quantity of raffinate material present in the raffinate stream
passing from zone 1 into zone 3 so that the extract outlet stream is
not contaminatled.
A cyclic advancement of the input and output streams through
the fixed bed Df adsorbent can be accomplished by utilizing a manifold
system in which the valves ~n the manifold are operated in a sequential
manner to effect the shifting of the input and output streams thereby
allowing a flow of fluid with respect to solid adsorbent in a counter-
current manner. Another mode of operation whish can effect the counter-
current flow of solid adsorbent with respect to fluid involves the use
2~ of a rotating disc valve in which the input and output streams are con-
nected to the valve and the lines through which feed input~ extract
output, desorbent input and raffinate output streams pass are advanced
in the same direction through the adsorbent bed. Both the manifold
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~81i767
arrangement and disc valve are known in the art. Specifically rotary
disc valves which can be ut;l ked in this operation can be found in
U.S. Patents 3,040,777 and 3,422,848. Both of the aforementioned
patents disclose a rotary type connection valve in which the suitable
advancement of the various input and output streams from fixed
sources can be achieved without difficulty.
In many instances, one operational zone will contain a
much larger quantity of adsorbent than some other operational zone.
For instances, in some operations the buffer zone can contain a minor
amount of adsorbent as compared to the adsorbent required for the
adsorption and purification zones. It can also be seen that ;n
instances in which desorbent is used which can easily desorb extract
material from the adsorbent that a relatively small amount of adsor-
bent will be needed in a desorption zone as compared to the adsorbent
needed in the buffer zone or adsorption zone or purification zone or
all of them. Since it is not required that the adsorbent be located
in a single column, the use of multiple chambers or a series of col-
umns is within the scope of the invention.
It is not necessary that all of the input or output streams
be simultaneously used, and in fact, in many instances some of the
streams can be shut off while others effect an ;nput or output of mate-
rial. The apparatus which can be utili7ed to e ffect ~he process of
this invention can also contain a series of individual beds connected
by connecting conduits upon which are placed input or output taps to
which the various input or output streams can be attached and alternately
and periodically shifted to effect continuous operation. In some in-
stances, the connecting conduits can be connected to transfer taps which
during the normal operations do not function as a conduit through which
~L~ '7
material passes into or out of the process.
It is contemplated that at least a port;on of the extract
output stream will pass into a separation means wherein at least a
portion of the desorbent material can be separated to produce an ex-
tract product containing a reduced concentration of desorbent
material. Preferably, but not necessary to the operat;on of the pro-
cess, at least a portion of the raffinate output stream will also be
passed to a separation means where;n at least a portion of the desorbent
material can be separated to produce a desorbent stream which can be
reused in the process and a raffinate product containing a reduced
concentration o~ desorbent material. The separa~ion means will typically
be a fract;onation column, the design and operation of which is well-
known to the separation art.
Reference can be made to D.B. Broughton U.S. Patent
2,985,589, and to a paper entitled "Continuous Adsorpt;ve Processing--
A New Separation Technique" by D.B. Broughton presented at the 34th
Annual Meeting of the Society of Chemical Engineers at Tokyo~ Japan on
April 2, 1969, both incorporated herein by reference, for further
explana~ion of the simulated mo~ing bed countercurrent process flow
scheme.
Although both liquid and vapor phase operations can be used
in many adsorptive separation processes, liquid-phase operation is
preferred for this process because of the lower temperature requirements
and because of the higher yields of extract product than can be
obtained with liquid-phase operation over those obtained with vapor-
phase operation. Adsorption conditions will include a temperature range
of from about 20C. to about 200~C. with about 20C. to about 100C.
being more preferred and a pressure range of from about atmospheric to
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7~-7
about 500 psig ~345n kPa gauge) w~th from about a~mospheric to about
250 psig (1725 kPa gauge) being more preferred to ensure liquid phase.
Desorption conditions will include the same range of tempera~ures and
pressures as used for adsorption conditions.
The size of the units which can util ke the process of
this invention can vary anywhere from those of pilot plant scale
(see for example our assignee's U.S. Patent 3,706,~12, ineorporated
herein by reference) to those of commercial scale and can range in
flow rates fron as little as a few cc an hour up to ~any thousands
of gallons per hour.
The ~ollowing examplearépresented to illustrate 1:he
selectivity relationsh;p that makes the process o~ our in~ention pos-
sible. The example is not ~ntended to unduly res~rict the scope and
spirit o~ claims attached hereto.
1~ ~, .
Thi5 example presents selectivities ~or two Amberlite
polymeric adsorbents, comprising Amberlite XAD-2 and Amberlite XAD-4,
for oleic acid with respect to a linoleic acid.
The feed mixture comprised the desorbent used in the pulse test in ques-
tion and Tall-oil fatty acids in a ratio of desbrbent to Tall-oil fatty
~cids of 90:10. The Tall-~il fatty acids had the following composition:
Fatt~ Acids
Palmitic (C160)
S Stearic (Cl8~) 2
Ole;c (C181) 5~
Linoleic ~C182) 45
All others 4
Retention volumes and selectivities were obtained using
~ 1 ~3il~7~i~7
the pulse test apparatus and procedure previously described. Spec-
ifically, the adsorbents were tested in a 70 cc helical coiled column
using the following sequence of operations for each pulse test.
Desorbent material was continuously run through ~he column containing
the adsorbent at a nominal liquid hourly space veloc;ty (LHSV) of
about 1Ø A void volume was determined by observing the volume of
desorbent reguired to fill the packed dry column. At a convenient
time the flow of desorbent material was stopped, and a 10 cc sample
of feed mixture was injected into the column via a sample loop and
the flow of desorben~ material was resumed. Samples of the effluent
were automatically collected in an automatic sample collector and
later analyzed by chromatographic analysis. From the analysis of
these samples peak envelope concentrations were developed for ~he feed
mixture components. The retention volume for the fatty acids werP
calculated by measuring the distances from time zero on the reference
po;nt to the respective midpoints of the fatty acids and subtracting
the distance representing the void volume of the adsorbent. The
selectivities of an adsorbent for oleic ac;d with respect
to linoleic acid in the presence of a desorbent material are
in the quotients obtained by divid;ng the retention volume for the
oleic acid by the retention volume for the linoleic
acid. The results for these pulse tests are shown in Table No. 1.
-25-
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c~ . ~D ~D ~ ~ æ o o ~ cn
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-26-
L'76''~
Figure 1 is an example of a graphical presentation of the
results of one of the pulse tests the data from which is also set
forth in Table 1. This pulse test was conducted at 90C. with Amberlite
XAD-2 adsorbent and 85% dimethylformamide-15~ water desorbent. As
shown in Figure 1 linoleic acid was eluted
first and then oleic acid.
Table 1 and Figure 1 show that oleic acid is
more strongly adsorbed than lino7eic acid, particularly for
certain desorbent mixture combinations when used for the separation
of fatty acids having 18 carbon atoms per molecule. Furthermore, the
separations achieved for many of these combinations are substantial,
as exempli~ied in Figure 1, and clearly o~ commercial feasibility.
~7-
EXAMPLE II
This example presents the results of using Amberlite
XAD-2 for separating stear;c acid from about a 50-50 mlxture of
stearic and palmitic acids diluted in desorbent in a ratio of desor-
bent ~o acid mixture of 90 10. The desorbent used was 85 wt. %
dimethyl formamide and 15 wt. ~ water.
Data was obtained using the pulse te t appara~us and
procedure previously described at a temperature of 90C. Specifi-
cally, the adsorbent was placed in a 70 cc helical coiled column
and the following sequence of operations was used. Desorbent mate-
rial was continuously run upflow through the column containing the
adsorbent at a flow rate of 1.2 ml/min. At a convenient time the
flow of desorben~ material was stopped, and a 10 cc sample of feed
mixture was injec~ed into the column via a sample loop and the flow
of desorbent material was resumed. Samples of the effluent were
automatically collected in an automatic sample collector and later
analyzed by chromatographic analysis.
Figure 2 is a graphical presentation of the results of the
pulse tests. Figure 2 shows that stearic acid is more strongly
adsorbed than palmitic acid, particularly for the desorbent mixture
used. Furthermore, the separation achieved for this combination was
- substantial and clearly of commercial feasibility.
-2~-
