Note: Descriptions are shown in the official language in which they were submitted.
llS164~
The field of art to which this invention per-
tains is the solid-bed adsorptive separation of monosac-
charides. More specifically the invention relates to a
process for separating one component from a mixture com-
prising a ketose and an aldose which process employs an
adsorbent comprising a crystalline aluminosilicate which
selectively adsorbs either the ketose or the aldose from
the feed mixture.
It is well known in the separation art that cry-
stalline aluminosilicates can be used to separate cer-
tain hydrocarbon types from mixtures thereof, such as the
separation of normal paraffins from branched-chain paraf-
fins and the separation of olefinic hydrocarbons from
paraffinic hydrocarbons. The X and Y zeolites have been
employed in processes to separate individual hydrocar-
bon isomers. Thus, adsorbents comprising X and Y zeolites
are used to separate alkyl-trisubstituted benzene`isomers
(U.S. Patent 3,114,782); to separate alkyl-tetrasubsti-
tuted monocyclic aromatic isomers (U.S. Patent 3,864,416);
and to separate specific alkyl-substituted naphthalenes
(in U.S. Patent 3,668,267). Perhaps the most extensively
used processes are those for separating paraxylene from
a mixture of C8 aromatics. (U.S. Patents Nos. 3,558,730;
3,558,732; 3,626,020; 3,663,638; and 3,734,974).
In contrast, our invention relates to the sep-
aration of non-hydrocarbons and more specifically to the
separation of monosaccharides. We have discovered that
adsorbents comprising certain zeolites containing one or
more selected cations at the exchangeable cationic sites
exhibit adsorptive selectivity for a ketose with respect
to an aldose, while certain other cationic-exchanged zeo-
lites e~hibit selectivity for an aldose with respect to
,. ~
mab/, ~
~5:16~4
a ketose, thereby making separation of a ketose (or al-
dose) from a mixture comprising a ketose and an aldose
by solid~bed selective adsorption possible. In a speci-
fic embodiment our process is directed to separating
fructose from a mixture comprising fructose and ~lucose.
Fructose is considered to be the most soluble
and the sweetest of the sugars. Relative to sucrose
having a sweetness of 1.0, fructose has a relative sweet-
ness of about 1.4 while that of glucose is 0.7. The
literature indicates that one of the uses of fructose in
pure form is as a source of calories for patients who
must be fed intervenously, whereas glucose is not suitable
for intervenous feeding. While fructose exists widely in
nature, the methods for isolating high-purity fructose
are, however, more difficult than the primary method for
obtaining high-purity glucose. High-purity glucose is
readily manuEactured from starch by hydrolysis with min-
eral acids at elevated temperature followed by refining
and crystallization, while one method of obtaining high-
purity fructose involves hydrolysis of sucrose, separa-
tion of an insoluble lime-fructose complex, acidification
of the complex with acids that form insoluble calcium
salts, removal of cation and anion contaminants, concen-
tration of the resulting solution, and finally crystal-
lization of fructose. Extensive studies have been made
on the production of fructose by hydrolysis of fructose-
bearing polysaccharides extracted from the Jerusalem
artichoke. Several methods of separating glucose from
invert sugar, leaving fructose, have also been attempted,
such as formation of insoluble benzidine dèrivatives of
glucose and sodium chloride addition compounds of glucose,
but these have not been practicable.
It is accordingly a broad object of the pre-
sent invention to provide a process for separating the
ketose and aldose from a feed mixture containing both
components to produce ketose and aldose product streams
containing higher concentrations of the ketose and al-
dose, respectively, than were contained in the feed mix-
ture. More specifically it is an objective of the in-
vention to provide a process for producing concentrates
- of the fructose and the glucose from a feed mixture,
such as an invert sugar solution or a high fructose corn
syrup, containing the two components.
Accordingly, the present invention is directed
to a process for separating components of a feed mixture
comprising a ketose ànd an aldose which process comprises
contacting said mixture at adsorption conditions with an
adsorbent comprising a crystalline aluminosilicate selec-
ted from
(1) an X zeolite containing at exchangeable
cationic sites a cation selected from the group consist-
ing of sodium, potassium, barium and strontium, and
(2) a Y zeolite containing at exchangeable
cationic sites at least one cation selected from the
group consisting of ammonium, sodium, potassium , calcium,
strontium, barium and combinations thereof,
thereby selectively adsorbing one of said com-
ponents, and thereafter contacting the adsorbent con-
taining the adsorbed component with a desorbent and re-
covering the resultant desorbed component.
In another embodiment of the invention the feed
mixture is contacted with an adsorbent comprising a X
zeolite containing at exchangeable cationic sites a
ab~ C
115~6~
cation selected from the group consisting of sodium,
barium and strontium thereby selectively adsorbing the
ketose and thereafter recovering the ketose by desorp-
tion.
In a further embodiment the feed mixture is
contacted with an adsorbent comprising a X zeolite con-
taining at exchangeable cationic sites a cation pair
selected from the group consisting of barium and potas-
sium and barium and strontium thereby selectively adsor-
bing the ketose and thereafter recovering the ketose
by desorption.
In a still further embodiment, the feed mlx-
ture is contacted at adsorptlon conditions with an ad-
sorbent comprising a ~ zeolite containing potassium
cations at exchangeable cationic sites, thereby selec-
tively adsorbing the aldose and thereafter recovering
the aldose by desorption.
In still another embodiment the feed mixture
is contacted with an adsorbent comprising a Y zeolite
containing at exchangeable cationic sites at least one
cation selected from the group consisting of ammonium,
sodium, potassium, calcium, strontium, barium and com-
binations thereof; thereby selectively adsorbing the
ketose and thereafter recovering the ketose by desorp-
tion.
In a step-wise embodiment, the invention in-
volves: (a) contacting the feed mixture with the adsor-
bent to thereby selectively adsorb one component (ketose
or aldose); (b) removing from the adsorbent a raffinate
stream comprising the other component; ~c) contacting
said adsorbent with a desorbent material to effect the
desorption of the adsorbed component from
- 4
mabj
~lSl~
said adsorbent; and, (d) removing from said desorbent an l'extract"
stream comprising said adsorbed component.
Preferably the step-wise process comprises the steps
of: (a) maintaining net fluid flow through a column of said
adsorbent in a single direction, which column contains at
least three zones having separate operational functions occurring
therein and being serially interconnected with the terminal
zones of said column connected to provide a conti.nuous connection
of said zones; (b) maintaining an adsorption zone in said column,
said zone defined by the adsorbent located between a feed input
stream at an upstream boundary of said zone and a raffinate out--
put stream at a downstream boundary of said zone; (c) maintaining
a purification zone immediately upstream from said adsorption
zone, said purification zone defined by the adsorbent located
between an extract output stream at an upstream boundary of said
purification zone and said feed input stream at a downstream
boundary of said purification zone; (d) maintaining a desorption
zone immediately upstream from said purification zone, said
desorption zone defined by the adsorbent located between a
desorbentinput stream at an upstream boundary of said zone and
said extract output stream at a downstream boundary of said zone;
(e) passing said feed mixture into said adsorption zone at
adsorption conditions to effect the selective adsorption of one
component (ketose or aldose) by said adsorbent in said adsorption
zone and withdrawing a raffinate output stream comprising the
non-adsorbed component from said adsorption zone; (f) passi.ng a
desorbent material into said desorption zone at desorption con-
ditions to effect the displacement of the adsorbed compound ~rom
115~6~4
the adsorbent in said desorption zone; (g) withdrawing an
extract output stream comprising adsorbed component and desorbent
material from said desorption zonei (h) passing at least a
portion of said extract output stream to a separation means and
therein separating at least a portion of said desorbent material
to produce an extract product stream having a reduced concen-
tration of desorbent material; and, (i) periodically advancing
through said column of adsorbent, in a downstream direction with
respect to fluid flow in said adsorption zone, the feed input
stream, raffinate output stream, desorbent input stream, and
extract output stream to effect the shifting of zones through
said adsorbent and the production of extract output and raffinate
output streams.
Other objectives and embodiments of our invention
encompass details about feed mixtures, adsorbents, desorbent
materials and operating conditions all of which are herein-
after disclosed in the following discussion of each of the
facets of the present invention.
The definitions of various terms used throughout the
specification will be useful in making clear the operation,
objects and advantages of our process.
A feed mixture is a mixture containing one or more
extract components and one or more raffinate 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 com-
pound that is more selectively adsorbed by the adsorbent while a
11516~
"raffinate component'1 is a compound or type of compowld that is
less selectively adsorbed. In this process, when a ketose is
an extract component, an aldose is a raffinate component, and
vice versa. The term "desorbent material" shall mean generally
a material capable of desorbing 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 through 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 adsorbent. The composition of the
extract stream,likewise, can vary from essentially 100%
desorbent material to essentially 100% extract components. At
least a portion of the extract stream and preferably at least
a portion Of the raffinate stream frorn the separation process
are passed to separation means, typically fractionators, where
desorbent material is separated to produce an extract product
and a raffinate product. The terms "extract product" and
"raffinate product" mean products produced by the process con-
taining, 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
to produce a high purity ketose product or aldose product (or
both) at high recoveries, it will be appreciated that an extract
~lS~6~
component is never completely adsorbed by the adsorbent, nor is
a raffinate component completely non-adsorbed by the adsorbent.
Therefore, varyin~ amounts of a raffinate component can appear
in the extract stream and,likewise, vaxying amounts of an extract
component can appear in the raffinate stream depending upon
the process operating conditions employed. The extract and
raffinate streams then are further distinguished from each
other and from the feed mixture by the ratio of the concen-
trations of an extract component and a raffinate component
appearing in the particular stream. ~lore specifically, the ratio
of the concentration of a ketose for example, to that of a less
selectively adsorbed aldose will be lowest in the raffinate
stream, next highest in the feed mixture, and the highest in
the extract stream. Likewise, the ratio of the concentration
of a less selectively adsorbed aldose to that of the more
selectively adsorbed ketose 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
defined as the volume of the adsorbent which selectively adsorbs
an extract component from the feed mixture. The term "non-
selective void volume" of the adsorbent is the volume of the
adsorbent which does not selectively retain an extract component
from the feed mixture. This volume includes the cavities of
the adsorbent which contain no adsorptive sites and the inter-
stitial void spaces betweenadsorbent particles. The selective
pore volume and the non-selective void volume are generally
expressed in volumetric quantities and are of importance in
~1516~
determininy 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 (hereinaf-ter 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 void volume is utilized
in determining the amount of fluid which should pass into the
same zone in a counter-current direction to the adsorbent to
displace the fluid present in the non-se]ective void 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 into the
zone by the adsorbent. Since this net entrainment is a fluid
present in non-selective void volume of the adsorbent, it in
most instances comprises less selectively retained feed compo-
nents. The selective pore volume of an adsorbent can in certain
instances adsorb portions of raffinlte material from the fluid
surrounding the adsorbent since in certain instances there is
competition between extract material and raffinate material
for adsorptive sites within the selective pore volume. If a
large quantity of raffinate material with respect to extract
material surrounds the adsorbent, raffinate material can be
competitive enough to be adsorbed by the adsorbent.
Feed mixtures which can be charged to the process of
the invention will be those comprising a ketose and an aldose
and more specifically and preferably will be aqueous solutions
of a ketose and an aldose. While the feed mixture may contain
more than one ketose and more than one aldose, typically the
~lS~
feed mixture will contain one ketose and one aldose each in
concentrations of from about 0.5 wt.% to about 30 wt.~ and more
preferably from about 1 to about 15 wt.%. The process may be
used to separate a ketopentose from an aldopentose but more
typically will be used to separate a ketohexose from an aldohexose.
Well known ketohexoses are fructose (levulose) and sorbose;
well known aldohexoses are glucose (dextrose), mannose and
galactose while lesser-known aldohexoses are gulose, talose,
allose, altrose, and idose. Preferred feed mixtures containing
hexoses will be aqueous solutions of invert sugar formed when
sucrose is hydrolyzed by acidic materials into equi-molar
amounts of fructose and glucose. Other preferred feed mixtures
will be aqueous solutions of high fructose (typically about
40-45%) corn syrup produced by the enzymatic isomerization of
glucose solutions.
The desorbent used in the process of the invention
should satisfy several criteria. First, it should displace
an extract component from the adsorbent with reasonable mass
flow rates without itself being so strongly adsorbed as to
unduly prevent an extract component from displacing the desorbent
material in a following adsorption cycle. It should also be
more selective for all of the extract components with respect
to a raffinate component than it is for the desorbent material
with respect to a raffinate component. It must be compatible
with the particular adsorbent and the particular feed mixture.
It must not reduce or destroy the critical selectivit~ of the
adsorbent for an extract component with respect to a raffinate
component. It should be easily separable from the feed mixture
--10--
1~S~64~
that is passed into the process, preferably by distillation.
Since the raffinate and extract products are oodstuffs intended
for human consumption, desorbent materials should also be non-
toxic. Finally, desorbent materials should be rea~ily availahle
and therefore reasonable in cost. Water satisfies these cri-
teria and is a suitable desorbent material for the present
process.
It is known that certain characteristics of adsorbents
are necessary to the successful operation of a selective ad-
sorption process. Among such characteristics are: adsorptive
capacity for some volume of an extract component per volume of
adsorbent; also sufficiently fast rates of adsorption and
desorption. Another necessary characteristic is the ability of
the adsorbent to separate components of the feed; in other words,
that the adsorbent possess adsorptive selectivity, (B), for one
component as compared to another component. The selectivity,
(B), as used throughout this specification is defined as the
ratio of the two components of the adsorbed phase over the ratio
of the same two components in the unadsorbed phase at equilibiium
conditions. Relative selectivity is shown as Equation 1 below.
~quation 1
Selectivity = (B) = [vol. percent C/vol. percent D]A
[vol. percent C/vol. percent D]u
where C and D are two components of the feed represented in
volume percent and the subscripts A and U represent the adsorbed
and unadsorbed phases respectively. T~here selectivity as be-
tween two components approaches 1.0 there isno preferential
adsorption of one component by the adsorbent with respect to the
-11-
~5~4~
other, When comparing the selectivity by the adsorbent of one
component C over component D, a value of (B) larger than ].0
indicates preferential adsorption of component C within the
adsorbent. A value of (B) less than 1.0 would indicate that
component D is preferentially adsorbed leaving an unadsorbed
phase richer in component C and an adsorhed phase richer in
component D. Ideally,desorbent materials should have a selec-
tivity equal to about 1 or less than l with respect to all
extract components so that all of the extract components can
be extracted as a class and all raffinate components cleanly
rejected into the raffinate stream. While separation oE an
extract component from a raffinate component is theoretically
possible when the selectivity of the adsorbent for the extract
component with respect to the raffinate component is greater than
1, it is preferred that such selectivity approach a value of 2.
Like relative volatility, the higher the selectivity the easier
the separation is to perform.
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,
selectivity and exchange rate. Such an apparatus may consist
of an adsorbent chamber of approximately 70 cc volurne having
inlet and outlet at opposite ends, temperature and pressure
control equipment to assure a constant predetermined pressure,
analytical equipment such as refractometers, polarimeters and
chromatographs to determine quantitatively or qualitatively one
or more components in the effluent stream leaving the chamber.
A pulse test using this apparatus will determine selectivities
-12-
~15~644
and other data for various adsorbent systems. The adsorbent is
filled to equilibrium with a particular desorbent material. At
a convenient time, a pulse of feed containing known concentrations
of a tracer and of a particular ketose or aldose, or both, all
diluted in desorbent, is injected for a duration of several
minutes. Desorbent flow is resumed, and the tracer and the ke-
tose and aldose are eluted as in a liquid-solid chromatographic
operation. The effluent is analyzed to determine 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, capacity
index for an extract component, selectivity for one component
with respect to the other, and the rate of desorption of an
extract component by the desorbent. The capacity index of an
extract component may be characterized by the distance between
the center of the peak envelope of the extract component and the
peak envelope of the tracer component or some other known
reference point. It is expressed in terrns of the volume in
cubic centimeters of desorbent pumped during this time interval
represented by the distance between the peak envelopes. Selecti-
vity, (B), for an extract component with respect to a raffinate
component may be characterized by the ratio of the distance be-
tween the center of the extract component peak envelope and the
tracer peak envelope (or other reference point) to the corresponding
distance between the center of the raffinate component peak
envelope and the tracer peak envelope. The rate of exchange of
an extract component with the desorbent can generally be charac-
teri~ed by the width of the peak envelopes at half intensity.
-13--
~l~5~4
The narrower the peak width the faster the desorption rate.
The desorption rate can also be characterized by the distance
between the center of the tracer peak envelope and the disap-
pearance of an extract component which has just been desorbed.
This distance is again the volume of desorbent pumped during
this time interval.
Adsorbent systems can also be evaluated by actual
testing in a continuous countercurrent liquid-solid contacting
device, such as described in U.S. Patents 2,985,589 and 3,706,812.
Additional details on adsorbent evaluation techniques may be
found in the paper "Separation of C8 Aromatics by Adsorption"
by ~. J. deRosset, R. W. Neuzil, D. J. Korous, and D. l~. Roshack
presented at the American Chemical Society, Los Angeles, Califor-
nia, March 28 through April 2, 1971.
Adsorbents to be used in the process of this invention
include crystalline aluminosilicate cage structures in which the
alumina and silica tetrahedra are intimately connected in an
open three dimensional network. The crystalline aluminosilicates
are often referred to as "molecular sieves" particularly when
the separation which they effect is dependent essentially upon
differences between the sizes of the feed molecules. In the
process of this invention, however, the term "molecular sieves"
is not strictly suitable since the separation of a ketose from
an aldose is apparently dependent on differences in electro-
chemical attraction between a ketose and the adsorbent on the
one handand between an aldose and the adsorbent on the other,
rather than on physical size differences in the molecules.
In hydrated form, the crystalline aluminosilicates
-14-
llS~6~4
generally encompass those zeolites represented by the Formula
1 below:
Formula 1
M2/nO :A1203 :wsio2 :yH20
where "M" is a cation which balances the electrovalence o~ the
aluminum-centered ~etrahedra and which i.s generally referred to
as an exchangeable cationic site, "n" represents the valence
of the cation, "w" represents the moles of SiO2, and "y"
represents the moles of water. The generalized cation "M"
may be monovalent, divalent or trivalent or mixtures thereof.
The X zeolite in the hydrated or partially hydrated
~orm can be represented in terms of mole oxides as shown in
Formula 2 below:
Formula 2
(0.9+0.2)M2/nO:A1203:(2.5+0.5)SiO2;yH20
where "M" represents at least one cation having a valence of
not more than 3, "n" represents the valence of "M", and '~y" is
a value up to about 9 depending upon the identity of "M" and
the degree of hydration of the crystal. As noted from Formula 2
the SiO2/A1203 mole ratio of X zeolite is 2.5+0.5. The cation
"M" may be one or more of a number of cations such as a hydrogen
cation, an alkali metal cation, or an alkaline earth cation,
or other selected cations, and is generally referred to as an
exchangeable cationic site. As the X zeolite is initially
prepared, the cation "M" is usually predominately sodium and
the zeolite is therefore referred to as a sodium-X zeolite. De-
pending upon the purity of the reactants used to make the zeolite,
other cations mentioned above may be present, however, as impurities.
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~5~;4~
The Y zeolite in the hydrated or partially hydrated
form can be similarly represented in terms of mole oxides as in
Formula 3 below:
Formula 3
(o.g+o~2)M2/no:Al2o3:wsio2 y~2o
where "M" is at least one cation having a valence not more than
3, "n" represents the valence of "M", "w" is a value greater than
about 3 up to 6, and "y" is a value up to about ~ depending
upon the identity of "M" and the degree of hydration of the
crystal. The SiO2/A1203 mole ratio for Y zeolites can thus
be from about 3 to about 6. The cation "M" may be one or more
of several cations as in the case of the X-zeolite but, as the
Y zeolite is initially prepared, the cation "M" is also usually
predominately sodium. A Y zeolite containing predominately
sodium cations at the exchangeable cationic sites is therefor
referred to as a sodium-Y zeolite.
Cations occupying exchangeable cationic sites in the
zeolite may be replaced with other cations by well known ion
exchange methods, for example by contacting the zeolite, or a
base material containing the zeolite, with an aqueous solution
of a soluble salt of the cation or cations desired to be placed
upon the zeolite. After the desired degree of exchange takes
place the sieves are removed from the aqueous solution, washed,
and dried to a desired water content. By such methods the sodlum
cations and any non-sodium cations which might be occupying
exchangeable sites as impurities in a sodium~X or sodium-Y
zeolite can be partially or essentially completely replaced
with other cations.
-16-
The term "base material" as used herein shall refer to a
material containing X or Y zeolite which can be used to make
the special adsorbents described below. The zeolite will
typically be present in the base material in amounts ranging
from about 75 wt. % to about 98 wt. % of the base material based
on volatile free composition. Volatile free compositions are
generally determined after the base material has been calcined
at 900 C. in order to drive off all volatile matter. The
remainder of the base material will generally be amorphous
material such as silica, alumina or silica-alumina mixtures or
compounds, such as clays, which material is present in intimate
mixture with the small particles of the zeolite material. This
amorphous material may be an adjunct of the manufacturing
process for X or Y zeolite (for example, intentionally incom-
plete purification of either zeolite during its manufacture)
or it may be added to relatively pure X or Y zeolite, but in
either case its usual purpose is as a binder to aid in formlng
or agglomerating the hard crystalline particles of the zeolite.
Normally the base material will be in the form of particles
Z0 such as extrudates, aggregates, tablets, pills, macrospheres,
or granules produced by grinding any of the above to a desired
particle size range. The adsorbent to be used in our process
will preferably have a particle size range of about 16-60
mesh, and more preferably about 30 to about 50 mesh (Standard
U.S. Mesh), Examples of suitable base materials which can be
used to make the adsorbents employed in our process are
"Molecular Sieves 13X" and "SK-40" both of which are available
from the Linde Company, Tonawanda, New York. The first material
contains X zeolite, while the latter material contains Y
zeolite.
1~5~6~4
It has heen diseovered that X and Y zeolites con-
taining speeified cations at the exchangeable cationic sites
possess the requirements previously discussed and are therefore
suitable for use in the process. Some of the suitable zeolites
contain essentially a single cation species at the exchangeable
cationie sites while others are essentially completely exchanged
with selected eation pairs. A zeolite is deemed to be essentially
eompletely exehanged when the residual sodium eontent of the
zeolite after ion exchange is less than about 2 wt.% Na20. Spe-
eifieally we have found that the adsorbents comprising an X
zeolite eontaining at exchangeable cationic sites sodium
cations or barium eations or strontium eations all possess
seleetivity for a ketose with respec~ to an aldose. Other
adsorbents having similar selectivity are X zeolites containing
the eation pair ba~ium and potassium or the cation pair barium
and strontium at exehangeable cationie sites. A zeolite X
adsorbent eontaining barium and potassium at the exchangeable
eationie sites will preferably have a weight ratio of barium to
potassium within the range from about 1:1 to about 100:1 and
more preferably within the range of from about 1:1 to ahout 10:1.
A zeolite X adsorbent eontaining barium and strontium at the
exehangeable cationic sites will preferahly have a weight ratio
of barium to strontium within the range of from about 1:1 to
about 15:1 and more preferably from about 5:1 to ahout 15:1.
On the other hand it has been found that an adsorbent
eomprising anX zeolite eontaining potassium at the exchangeable
eationie sites is suitable for use in our proeess by virtue of
its seleeti~lity for an aldose with respeet to a ketose. Such
-18-
~S.16~4
adsorbent may be manufactured by essentially completely ion
exehanging "Moleeular Sieves 13X" (Na-X zeolite) with potassium
cations (typically with a KCl solution), washing the exchanged
material with water to remove excess ion exehange solution and
drying the adsorbent to less than about 10 pereent weight
loss on ignition (LOI) at 900C.
Further, it has been discovered that adsorbents com-
prising a Y zeolite eontaining at exehangeable eationie sites
at least one eation seleeted from the group eonsisting of ammonium,
sodium, potassium, ealcium, strontium, barium and combinations
thereof are suitable for use in our process beeause of their
selectivity for a ketose with respect to an aldose. Preferably,
the zeolites will be essentially eompletely exchanged with the
seleeted cation or cations. A partieularly preferred adsorbent
is a base material eomprising Y zeolite and amorphous material
eontaining ealeium eations at the exehangeable eationie sites.
There is a surprising lack of predietability regarding
the suitability of adsorbents for use in our process. Many
adsorbents comprising X or Y zeolites and amorphous material
in faet exhibit no selectivity for either a ketose or an aldose
and are therefore not suitable for use in the process. For
instanee, a Y zeolite eontaining ammonium cations at exehangeable
eationie sites exhibits seleetivity for a ketose with respeet
to an aldose, but a Y zeolite containing hydrogen eations at
the exchangeable cationic sites exhibits no selectivity for
either a ketose or an aldose.
An X zeolite containing potassium at the exchangeable
cationie sites appears unique among the X zeolites in its
--19--
~L5 ~6~
ability to selectively adsorb an aldose with respect to a
ketose. An adsorbent comprising either a cesium-exchanged X
or Y ~eolite exhibits selectivity for neither an aldose nor a
ketose. A potassium-exchanged Y zeolite~ unlike the potassium-
exchanged X zeolite, also exhibits selectivity for a ketose with
respect to an aldose. Adsorbents comprising Y zeolites con-
taining at exchangeable cation sites either barium or strontium
or barium and strontium or barium and potassium cations exhibit
selectivity for a ketose with respect to an aldose, while
adsorbents comprising X zeolites containing at exchangeable
cationic sites either calcium or magnesium exhibit selectivity
for neither an aldose nor a ketose.
Considering adsorbents comprising Y zeolites containing
at exchangeable cation sites cations of metals of Group IIA of
the Periodic Table of Elements, those containing calcium,
strontium or barium all exhibit selectivity for a ketose with
respect to an aldose but a Y ~eolite containing magnesium
exhibits selectivity for neither a ketose nor an aldose. Of
those suitable adsorbents comprising Y zeolites containing Ca,
Sr, or Ba cations at exchangeable cationic sites, we have dis-
covered that an adsorbent comprising a Y zeolite containing Ca
cations at such sites is much superior to adsorbents containing
Sr or Ba cations at the same sites. l`he reasons why some
adsorbents are acceptable for use in our process while others
are not is not fully understood at the present time.
The adsorbent may be employed in the form of a dense
compact fixed bed which is alternatively contacted with the
feed mixture and desorbent materials. In the simplest embodiment
-20-
6~4
of the invention the adsorbent is employed in the form of a
single static bed in which case the process is only semi-
continuous~ In another embodiment a set of two or more static
beds may be employed in fixed-bed contacting with appropriate
valving so that the 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 desorbent materials may be either up or down
through the desorbent. Any of the conventional apparatus employed
in static bed fluid-solid contacting may be used.
Countercurrent moving-bed or simulated moving-bed
countercurrent 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 pro-
duction of an extract and a raffinate stream and the continual
use of feed and desorbent streams. The operating principles
and sequence of the simulated moving-bed countercurrent flow
system are described in U.S. Patent 2,985,589. In such a system
it is the pro~ressive 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 time; the feed input stream, desor-
bent inlet stream, raffinate outlet stream, and extract outlet
stream access lines. Coincident 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
-21-
~SJ.644
that countercurrent contact is maintained, a li~uid flow down
the adsorbent chamber may be provided by a pump. As an active
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 require different flow rates.
A programmed flow controller may be provided to set and regulate
these flow rates.
The active liquid access points effectively divide
the adsorbent chamber into separate zones, 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, zone 1, is defined as the ad-
sorbent located between the feed inlet stream and the raffinate
outlet stream. In this zone, the feed stock contacts the
adsorbent, an extract component is adsorbed, and a raffinate
stream is withdrawn. Since the general flow through zone ] 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 proceeding from
the feed inlet to the raffinate outlet streams.
Immediately upstream with respect to fluid flow in
zone 1 is the purification zone, zone 2. The purification zone
is defined as the adsorbent between the extract outlet stream
and the feed inlet stream. The basic operations taking place
in zone 2 are the displacement, from the non-selective void
volume of the adsorbent, of any raffinate material carried into
zone 2 by the shifting of adsorbent into this zone and the
il~l64~
desorption of any raffinate material adsorbed within the
selective pore volume of the adsorbent or adsorbed on the sur-
faces of the adsorbent 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.
Immediately upstream of æone 2 with 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 which 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 utilized. This zone, defined as the adsorbent between
the raffinate outlet stream and the desorbent inlet 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 step since a portion of
the raffinate stream which is removed from zone 1 can be passed
into zone 4 to displace desorbent material present in that zone
out of that zone into the desorption zone. Zone 4 will contain
enough adsorbent so that raffinate material present in the
-23-
~1516~
raffinate stream passing out of zone 1 and into zone 4 can be
prevented from passing into zone 3 thereby contaminating extract
stream removed from zone 3. In the instances in which the
fourth operational zone is not utilized the raffinate stream
passed from zone 1 to zone 4 must be care~ully monitored in
order that the flow directly from zone 1 to zone 3 can be
stopped when there is an appreciable quantity of raffinate
material present in the raffinate stream passing from zone 1
into zone 3 so that the extract outlet stream is not contaminat-
ed.
A cyclic advancement of the input and output streams
through the fixed bed of adsorbent can be accomplished by
utilizing a manifold system in which the valves in 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 counterCurrent manner.
Another modeof operation which can effect the countercurrent
flow of solid adsorbent with respect to fluid involves the
use of a rotating disc valve in which the input and output
streams are connected 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 arrangement and disc valve
are known in the art. Specifically rotary disc valves which
can be utilized in this operation can be found in U.S. Patents
3,040,777 and 3,422,848.
It is contemplated that at least a portion of the
extract output stream will pass into a separation means wherein
-24-
~5~6~9,
at least a portion of the desorhent is removed to produce an
extract product containing a reduced concentration of desorbent.
Preferably at least a portion of the raffinate output stream
will also be passed to a separation means wherein at least a
portion of thedesorbent is removed to produce a desorbent stream
which can be reused in the process and a raffinate product con-
taining a reduced concentration of desorbent. The separation
means will typically be a fractionation column.
Although both liquid and vapor phase operations can
be used in many adsorptive separation processes, liquid-phase
operation is preferred for the present process because of the
lower temperature requirements and higher yields of extract
product that can be obtained. Adsorption conditions will
include a temperature range of from about 20C. to about 200C.
with about 20C. to about 100C. being preferred and a pressure
range of from about atmospheric to about 35 atmospheres absolute,
with from about atmospheric to about 17.5 atmospheres being
preferred to insure liquid phase. ~esorption conditions will
include the same range of temperatures and pressures as used
for adsorption conditions.
The following examples are presented to illustrate
the unique selectivity relationships that makes the process
of the invention possible, and are not intended to unduly
restrict the scope and spirlt of the claims attached hereto.
EXAMPLE I
..
This example presents retention volume and selectivity
results obtained by pulse tests with eleven adsorbents, one
comprising an A zeolite, one comprising a Y zeolite, and nine
~S~6~
comprising X zeolites. More specifically the adsorbent com-
prising the A zeolite was Linde 5A Molecular Sieves (a calcium-
exchange A zeolite), the adsorbent comprising a Y zeolite was
pr0pared by essentially Gompletely ion-exchanging Linde SK-40
with potassium and the adsorbents comprising X zeolite were
portions of Linde 13X Molecular Sieves essentially completely
exchanged with the cations of metals K, Cs, Mg, Ca, Sr, sa,
Ba+K and Ba+Sr. All adsorbents had a particle size range of
approximately 20-40 U.S. Mesh. (Na-X = unexchanged 13X sieves.)
The general pulse-test apparatus and procedure have
been previously described. The adsorbents were tested in a 70
cc.coiled column maintained at 55C. and 4.4 atmospheres
absolute pressure, and using pure water as the desorhent material.
The sequence of operations for each test was as follows: De-
sorbent material (water) was continuously run through the columm
containing the adsorbent at a nominal liquid hourly space ve-
locity (LHSV) of about 1Ø At a convenient time desorbent
flow was stopped, a 4.7 cc sample of 10 wt.% fructose in water
was injected into the column via a sample loop, and the desorbent
flow was resumed. The emergent sugar was detected by means of
a continuous refractometer detector and a peak envelope trace
was developed. Another pulse containing 10 wt.% glucose was
similarly run. A saturated water solution of benzene was also
injected to serve as a tracer from which the void volume of
the adsorbent bed could be determined. Thus for each adsorbent
tested three peak traces were developed, one for glucose, one
for fructose and one for benzene. The retention volume for
glucose is calculated by measuring the distance from time zero
-26-
~L~Sl~i44
or the reference point to the midpoint of the glucose peak
and subtractin~ the distance representing the void volume of
the adsorbent obtained by measuring the distance from the same
reference point to the mid-point of the benzene peak. For
some adsorbents both the fructose and glucose peaks were
essentially on top of the benzene peak envelope indicating
that both monosaccharides were relatively unadsorbed by the
particular adsorbents in the presence of water. The selectivity
of an adsorbent for fructose with respect to glucose is the
quotient obtained by dividing the fructose retention volume by
the glucose retention volume. The results for these tests are
shown in Table No. 1 below.
Table No. 1
Selectivities of Various Adsorbents
for Fructose with Respect to Glucose
RETENTION VOL. OF RETENTION VOL. OF SELECTIVITY
TEST ADSORBENT FRUCTOSE, CC. GLUCOSE, CC. (B)
1 Na-X 7.1 5.0 1.42
2 K-X 11.9 21.6 0.55
3 K-Y 10.8 4.9 2.21
4 Cs-X Both were relatively unadsorbed
5 Mg-X Both were relatively unadsorbed
6 Ca-X Both were relatively unadsorbed
7 Ca-A Both were relatively unadsorbed
8 Sr-X 8.0 1.3 6.15
9 Ba-X 27.1 9.6 2.82
10Ba-K-X 16.4 7.5 2.19
11Ba-Sr-X 21.3 4.2 5.0
The adsorbents used for tests 1 through 4 were
three X zeolites and one Y zeolite each containing at the
exchangeable cationic sites cations of metals from Group IA
of the Periodic Table of Elements. The K-X adsorbent used for
test 2 had a "selectivity" of 0.55 (for fructose with respect
to glucose), and therefore actually exhibited selectivity
for glucose with respect to fructose. The Na-X adsorbent used
for test 1 (selectivity of ' 42) and the K-Y adsorbent used
for test 3 (selectivity of 2.21) both exhibited selectivity for
fructose with respect to glucose, while the Cs-X adsorbent used
in Test 4 exhibited relative selectivity for neither.
The adsorbents used for Tests 5, 6, 8 and 9 were X
zeolites containing at exchangeable cationic sites cations of
metals from Group IIA of the Periodic Table of Elements, while
the adsorbent used for TeSt 7 was a calcium-exchanged A zeolite.
Both fructose and g~ucose were relatively unadsorbed with the
Mg-X, Ca-X and Ca-A adsorbents used in the presence of water
for Tests 5, 6 and 7 respectively, but both the Sr-X and Ba-X
adsorbents used in Tests 8 and 9, respectively, exhibited
selectivity for fructose with respect to glucose. While not
definitely established, it is believed that adsorbents com-
prising X zeolites containing at the exchangeable cationic
sites a Group IIA cation generally become less acidic as one
moves downward from Period 3 to Period 6 of the Periodic Table
of Elements in selecting the Group IIA cation. Thus adsorbents
comprising Ca- or Mg-exchanged X zeolites are unsuitable for
use in the present process because they are more acidic, while
adsorbents comprising a Ba- or Sr-exchanged X zeolite are
suitable for use in our process because less acidic.
-28-
1644
The adsorbents used for Tests 10 and ll were X zeo-
lites containing at exchan~eable cationic sites the cation
pairs Ba and K, and Ba and Sr, respectively. The Ba-K-X
adsorbent used in Test lO exhibited selectivity for fructose
with respect to glucose, while the K-X adsorbent used in Test
2 did not, but the selectivity of the sa-K-x adsorbent was not
as high as that of the Ba-X adsorbent used in Test 9. The Ba-
Sr-X adsorbent used in Test ll exhibited fructose-to-glucose
selectivity less than the Sr-X adsorbent used in Test 8 but
higher than the Ba-X adsorbent used in Test 9.
EX~MPLE II
To assure that fructose could be separated from an
actual mixture containing fructose and glucose a solution con-
taining 20 wt.~ each of fructose and glucose in water wa~
pulse-tested over a 440 cc. bed of adsorbent comprisin~ barium-~
exchanged X zeolite contained in a column having a 1.27 cm-
inside diameter and 2.28 m. in heiyht. The adsorbent was the
same as that used in Test 9 of Example I above and the same
operatin~ temperature and pressure as those of Example I were
employed. Water as the desorbent material was first passed
over the adsorbent, then the pulse of feed was injected, and then
desorbent material flow was resumed. The effluent was analyzed
by both refractive index and polarimetry, and with this combina-
tion quantitative rather than qualitative determinations of
the fructose and glucose in the effluent were determined. The
larger sample sizes required for these analyses was the reason
for using a column larger than that used in Example I. The
results obtained from this example, along with those of Test 9
of Example I twhich used the same adsorbent), are shown in Table 2.
-29-
~15~44
TABLE 2
Selectivity Comparison with Ba-X Adsorbent
RETENTION VOL. OF RETENTION VOL. OF SELECTIVITY,
TEST FRUCTOSE, CC. GLUCOSE, CC. (~)
Example II 105. 35 3.0
Test 9 of
Example I 27.1 9.6 2.82
The selectivity obtained when the fructose and glucose
were processed together is considered to be substantially the
same as that obtained when they were processed separately.
EXAMPLE III
This example presents glucose and fructose peak
widths and retention volumes and selectivities for fructose
with respect to glucose and with respect to water which were
lS obtained by conducting pulse tests with ten different adsor-
bents. Of the ten adsorbents, one comprised an X zeolite, and
nine comprised Y zeolites. More specifically the adsorbent
comprising X zeolite was a portion of Linde 13X Molecular
Sieves which had been essentially completely exchanged with Ca
cations and the nine adsorbents comprising Y zeolite were nine
portions of Linde SK-40 which had been essentially completely
ion exchanged with hydrogen, ammonium, Na, K, Cs, Mg, Ca,
Sr, and ~a cations. These ten adsorbents are hereinafter
referred to as NI14-Y, ~I-Y, Na-Y, K-Y, Cs-Y, Mg-Y, Ca-Y, Ca-X,
Sr-Y and Ba-Y zeolite adsorbents. All adsorbents had a particle
size range of approximately 20-40 U.S. Mesh.
The adsorbents were tested in a 70 cc.coiled column
maintained under the same conditions as in Example I, and using
the same procedure as in Example I, with the exception that
-30-
~5:16/~4
after the pulse containing 10 wt.% glucose was run, a pulse
of deuter.ium oxide was injected. Deuterium oxide has a different
index of refraction than does water; thus deuterium oxide can
be detected with the refractometer in the same way as is done
for the sugars. For each adsorbent tested four peak traces
were developed, one for glucose, one for fructose, one for
deuterium oxide and one for benzene. ~etention volumes for
glucose, fructose and water, and also for deuterium oxide
were obtained by the method described in Example I. The
results for these pulse tests are shown in Table No. 3.
The NH4-Y zeolite adsorbent used for Test 1 exhibited
a good selectivity of 6.5 for fructose with respect to glucose
and an acceptable -- although somewhat low -- selectivity of
0.71 for fructose with respect to water. Preferred selectivities
for an extract component with respect to a desorbent material
are from about 1.0 to about 1.5 so that an extract component
can readily displace desorbent material from the adsorbent in
the adsorption zone while still permitting an extract component
to be removedwith reasonable amounts of desorbent material from
adsorbent in the desorption zone. The H-Y zeolite used for
Test 2 exhibited selectivity for neither fructose nor glucose
in the presence of water; both eluted simultaneously. Both
the Na-Y zeolite adsorbent used for Test 3 and the K-Y zeolite
adsorbent used for Test 4 exhibited fructose selectivity with
respect to glucose, although less than that obtained with the
NH4-Y adsorbent, but the Cs-Y zeolite adsorbent used for Test
5 exhibited selectivity for neither. Fructose selectivities
with respect to water for the Na-Y and the K-Y zeolite adsorbents
were again less than 1Ø
-31-
~15:~64~
Both the Mg-Y zeolite used for Test 6 and the Ca-x
adsorbent used for Test 8 exhibited no selectivity for ylucose
or fructose since both eluted simultaneously. The Sr-Y æeolite
and the Ba-Y zeolite used for Tests 9 and 10 respectively
both exhibited acceptable selectivity for fructose, but they
also exhibited the highest selectivity for fructose with res-
pect to water of all the adsorbents tested, indicating that
larger amounts of desorbent material (watex) would be required
to desorb the extract component fructose. The best overall
performance as measured by the pulse test was obtained with the
Ca-Y zeolite adsorbent used for Test 7. This adsorbent has
the best selectivity for fructose with respect to glucose, an
ideal selectivity for fructose with respect to water, and peak
widths which indicate reasonably fast transfer rates. For
these reasons the Ca-Y zeolite adsorbent is the preferred
adsorbent for the process of this invention.
-32-
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EXAMPLE IV
_
~his example illustrates the ability of the process
of the invention to separate a ketose from an aldose when operat-
ed in a preferred embodiment which utilizes a continuous,
simulated-moving bed, countercurrent-flow system. Specifically
the example presents test results obtained when a synthetic
blend of 16.5 wt.% each of fructose and glucose in water was
processed using a barium-exchanged X zeolite adsorbent of
approximately 20-40 U.S. Mesh particle size range and water as
a desorbent material in a pilot-plant-scale testing apparatus
(described in U.S. Patent 3,706,816). ~riefly the apparatus
consists essentially of 24 adsorber,t chambers each havinq ahout-
18.8 cc. volume. The individual adsorbent chambers are serially
connected to each other with small-diameter connecting piping,
and to a rotary-type valve with separate piping. ~he valve has
inlet and outlet ports which direct the flow of feed and desor-
bent material t~ the chambers, and extract and raffinate streams
from the chambers. By manipulating the rotary valve and main-
taining given pressure differentials and flow rates through
the various lines passing into and out of the series of chamber.s,
a simulated countercurrent flow is produced. The adsorbent
remains stationary while fluid flows throughout the serially
connected chambers in a manner which when viewed from any
position within the adsorbent chambers is steady countercurrent
flow. The movir,g of the rotary valve is done in a periodic
shifting manner to allow a new operation to take place in the
adsorbent beds located between the active inlet and outlet
ports of the rotary valve. Attached to the rotary valve are
-34-
~15~6~4
input lines and output lines through which fluids flow to and
from the process. The rotary valve contains a feed input line
through which passes a feed mixture containing an extract and
a raffinate component, an extract stream outlet line through
which passes desorbent material in admixture with an extract
component, a desorbent material inlet line through which passes
desorbent ma~erial and a raffinate stream outlet line through
which passes a raffinate component in admixture with desorbent
material. Additionally, a flush material inlet line is used
for the purpose of flushing feed components from lines which
had previously contained feed material and which will subse-
quently contain a raffinate or extract output stream. The
flush material employed is desorbent material which then
leaves the apparatus as part of the extract and raffinate output
streams. The raffinate and extract output streams were collected
and analyzed for fructose and glucose concentrations by chroma-
tographic analysis, but no attempt was made to remove desorbent
material from them. Fructose yield was determined by calculating
the amount of fructose "lost" to the raffinate stream, deter-
mining this quantity as a percentage of the fructose fed to
the unit over a known period of time and subtractin~ this
percentage from 100 percent. The operating pressure for the
tes~s was 10.2 atms., gauge, and the operating temperatures
were 50C. and 75C. r respectively, for Tests 1 and 2. The
fructose purity (as a percent of total sugars present) of the
extract output stream, and the fructose yield, are shown below
in Table 4.
llS16~4
TABLE 4
EXTRACT STREAM
TEST FRUCTOSE PURITY, % FRUCTOSE YEILD,
1 80 60
2 80 71
The results of Tests 1 and 2 above do not necessarily
represent the optimums that might be achieved.
EXAMPLE V
-
In this example the procedure of Example IV was
essentially repeated but using a Ca-Y zeolite adsorbent to
separate a ketose from an aldose. Specifically the example
presents test results obtained when a water solution of corn
syrup was processed using the Ca-Y zeolite adsorbent described
in Example IIIand using deionized water as a desorbent material.
The feed was processed as a 50% sugar solution in
water. The solids content of the feed was 52~ glucose, 42~
fructose and 6% higher saccharides. The operating temperature
was 60C. The fructose purities (as a percent of total sugars
present) of the extract output stream, and the fructose yields,
are shown below in Table 5. (Pressure used was 10.5 atms. gauge.)
TA~LE 5
EXTRACT STREAM
TEST FRUCTOSE PURITY, % FRUCTOSE YIELD, '~
1 97 10
2 94 49
3 92 65
4 87 83
84 88
6 80 90
-36-
6~
By way of illustration, analysis of the extract and
the raffinate streams at one point on the fructose purity-yield
curve, 85% fructose yield point, were as shown in Table 6 below.
TABLE 6
5Extract and Raffinate Stream Analysis
at the 85% Yield Point
EXT~CT STREAM RAFFINATE STREAM
~ Fructose 88.3 10.7
% Glucose 11.7 79.5
% Higher Saccharides Trace 9.8
% Sugars 14.9 13.3
Again, the results of the tests above do not necessarily
repreeent the optimums that might be achieved.
