Note: Descriptions are shown in the official language in which they were submitted.
129Z9~
"PROCESS FOR SEPARATING PSICOSE FROM ANOTHER KETOSE"
_______________________________________________ _
FIELD OF THE INVENTION
_ ________ _ ___ _ _____
The field of art to which this invention pertains is the
solid bed adsorptive separation of a ketose, psicose, from
other ketoses and aldoses. More specifically, the invention
relates to a process for separating psicose from a mixture
comprising psicose, fructose and one or more additional
ketoses, and/or aldoses which process employs an adsorbent
comprising a calcium-exchanged Y-type zeolite to selectively
adsorb psicose from the feed mixture.
BACKGROUND OF THE INVENTION
___ _ ______________________
The use of crystalline aluminosilicates in non-
hydrocarbon separations is known, e.g., to separate specific
monosaccharides or classes of monosaccharides from
carbohydrate feed mixtures. A specific example of a class
separation is given in U.S. Patent 4,024,331 disclosing the
separation of ketoses from a mixture of ketoses and aldoses
using a type X zeolite. Specific monosaccharides such as
glucose and fructose are isolated from a feed mixture
containing the same by an adsorptive separation process using
an X zeolite as taught in U.S. Patent 4,442,285.
This invention is particularly concerned with the
separation of a ketose, psicose, from another ketose,
fructose, mixed with the aldoses mannose and glucose.
Heretofore, no feasible method for commercially separating
psicose from the other products of isomerization of aldose
sugars, e.g., glucose, was available. Therefore, enzymatic
means rather than simple isomerization methods have been used
129291~8
for the production of fructose, because the enzymatic route
minimizes the production of psicose. A means for separating
psicose from fructose, and other ketoses and aldoses, has now
been discovered and this enables the use of simpler, less
costly isomerization methods can be used to produce fructose.
There are two isomerization routes known for obtaining
fructose from glucose, namely by the reaction of weak alkali
on glucose and the reaction of hot pyridine on glucose. See
Chemistry of the Carboh_drates Pigman et al Academic Press
________ ____________ ___
Inc. NY, NY 1948, pages 41, 126-7. Similarly, isomerization
of galactose by either of the isomerization techniques
referred to above will produce a mixture of aldoses, talose
and galactose and a mixture of ketoses, sorbose and tagatose
and may be separated by means here disclosed. Furthermore,
there is considerable interest in the various L-sugars, which
are believed to be low in calories and possibly non-
metabolized, which cannot be made enzymatically, but only by
1somerization routes such as those mentioned above. This
invention applies to the L-sugars as well as D-sugars, and is
seen to be an advantageous method for obtaining L-fructose,
free of contamination by L-psicose.
Data related to potential adsorbents for the separation
of mannose from other monosaccharides is set forth in U.S.
Patent 4,471,114, Shenman et al., Se~t./84. This patent contains data related to the
use of a Y type faujasite exchanged with calcium cations as
an adsorbent for the separation of mannose from glucose and
other monosaccharides.
The separation of mannose from glucose is the subject of
British Patent No. 1,540,556., Dec./77. There the adsorbent is a
cation exchange resin in salt form, preferably calcium form.
Neuzil et al. U.S. Patent 4,340,724, July/82 teaches the separation by
adsorption of a ketose from an aldose with a Y zeolite
exchanged with NH4, Na, K, Ca, Sr, Ba and combinations at the
ion exchangeable sites or an X zeolite exchanged with Ba, Na
or Sr and combinations thereof.
2988
The separation of psicose from other ketoses is stated
in U.S. Patent 4,096,036 to be possible with ion exchange
resins capable of complexing with a polyol at a first
temperature and dissociating the complex at a second
temperature in a thermal parametric pumping apparatus.
SUMMARY OF THE INVENTION
____________ _ __________
It is accordingly an objective of the present invention
to provide a process for the separation of a ketose from a
feed mixture which is the alkaline- or pyridine-catalyzed
isomerization product of an aldohexose or aldopentose using a
Y type zeolite with calcium cations at cation exchanged
sites.
The present invention is a process for separating a
ketose from a feed mixture comprising the ketose and at least
one other monosaccharide selected from the group consisting
of ketopentoses and ketohexoses. More specifically, the
process comprises contacting at adsorption conditions a
monosacchar~de compr~sing a mixture of psicose, fructose and
one or more monosaccharides with an adsorbent comprising a
type Y zeolite containing calcium cations at the exchangeable
cat10nic sites, selectively adsorbing psicose and fructose,
removing the nonadsorbed portion of the feed mixture from
contact with the adsorbent, and thereafter recovering an
extract containing the psicose and fructose by desorption at
desorption conditions. The fructose can be separated from
the psicose by contacting the extract containing psicose and
fructose with a second bed of Y-type zeolite exchanged by
calcium at the exchangeable s1tes, selectively adsorbing the
psicose and recovering the fructose in the raffinate. The
psicose may be recovered by desorption at desorpt10n
conditions with water as desorbent.
Alternatively, the psicose may be selectively adsorbed
in the first step to produce a raffinate contain1ng fructose
1~2~88
and other monosaccharides in the original feed mixture. The
psicose can be recovered by desorption under desorption
conditions with water as desorbent. Subsequently, the
raffinate phase containing non-absorbed fructose can again be
contacted with a Ca-exchanged Y zeolite, the fructose being
selectively adsorbed by the zeolite, and recovered as one
product by desorption with water. Other objectives and
embodiments of the present invention relate to specific feed
mixtures, adsorbents, desorbent materials, operating
conditions and flow configurations, all of which are
hereinafter disclosed in the following discussion of the
present invention.
_ESCRIPTION OF THE DRAWING_____________ _ __ ______
Figure 1 provides a graphical representation of
relative concentration of specified sugars versus retention
volume for the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
____________________ ________________
At the outset the definitions of various terms used
through the specification will be useful in making clear the
operation, objects and advantages of this process.
A "feed mixture" is a mixture containing one or more
extract components and one or more raffinate components to be
separated by this 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 component that is more
selectively adsorbed by the adsorbent while a "raffinate
component" is a component that is less selectively adsorbed.
The term "desorbent material" shall mean generally a material
lZ9Z9813
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, from the separation process are passed to separation
means, typically fractionators or evaporators, where at least
a portion of desorbent material is separated to produce an
extract product and a raffinate product. The term "extract
product" and "raffinate product" mean products produced by
the process containing, respectively, an extract component
and a raffinate component in higher concentrations than those
found in the extract stream and the raffinate stream.
The adsorbent materials of this invention comprise type
Y crystalline aluminosilicates having calcium cations at
cation exchange sites. The type Y crystalline
aluminosilicates or zeolites can be further classified as
faujasites. As in the general case of all zeolites, these
crystalline compounds are described as a three-dimensional
network of fundamental structural units consisting of
silicon-centered SiO4 and aluminum-centered A104 tetrahedra
interconnected by a mutual sharing of apical oxygen atoms.
The space between the tetrahedra is occupied by water
molecules and subsequent dehydration or partial dehydration
results in a crystal structure interlaced with channels of
lZ9Z98~
molecular dimension. Zeolites are more fully described and
defined in U.S. Patents 2,883,244 and 3,~30,007 respectively-
The Y zeolites inthe hydrated or partially hydrated form can be represented in
terms of mole oxides as shown in Formula 1 below, in which
"M" is a cation having a valence up to 3, "n" is the valence
of "M", "w" is a value from 3 to 6 and "y" is a value up to
9, depending on the identity of "M" and the degree of
hydration of the crystal:
Formula 1
________
(o-9+o~2~M2/no:Al2o3 wsio2 yH2o
The electrovalence of the tetrahedra is balanced by the
cation "M" of the above equation which occupies exchangeable
cation~c sites in the zeolite. These cations which after
initial preparation are predominantly sodium may be replaced
with other cat10ns by ion exchange methods well known to
those having ordinary skill in the field of crystalline
aluminosilicates. Such methods are generally performed by
contacting the zeolite or an adsorbent material containing
the zeolite with an aqueous solution of the soluble salt of
the cation or cations desired to be placed upon the zeolite.
After the desired degree of exchange takes places, the sieves
are removed from the aqueous solution, washed and dried to a
desired water content. By such methods, the sodium cations
and any nonsodium cations which might be occupying
exchangeab1e sites as impurities in a sodium-Y zeolite can be
partially or essentially completely replaced with other
cations. It is essential that the zeolite used in the
process of my invention contains calcium cations at
exchangeable cationic sites.
Typically, adsorbents used in separative processes
contain zeolite crystals and amorphous material~ The zeolite
,~
~'~P~
1~?2~8~
will typically be present in the adsorbent in amounts ranging
from about 75 wt. ~ to about 98 wt. % based on volatile free
composition. The remainder of the adsorbent will generally
be amorphous material such as silica, 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 zeolite (for example,
intentionally incomplete purification of either zeolite
during its manufacture), or it may be added to relatively
pure zeolite, but in either case its usual purpose is as a
binder to aid in forming or agglomerating the hard
crystalline particles of the zeolite. Normally, the
adsorbent will be in the form of particles such as
extrudates, aggregates, tablets, macrospheres or granules
having a desired particle size range. The adsorbent used in
the subject process will preferably have a particle size
range of about 16-40 U.S. mesh (420 to 1190 microns). It has
been found that Y zeolite with calc~um cations and amorphous
btnders possess the selectiv~ty and other necessary
requirements previously discussed and is therefore suitable
for use in the instant process.
Certain carbohydrates or so-called simple sugars are
classified as monosaccharides. These monosaccharides are
hydroxyaldehydes or hydroxyketones containing one ketone or
aldehyde unit per molecule and two or more alcohol
functionalities. Thus monosaccharides are classified as
aldoses or ketoses on the basis of their carbonyl unit.
Ketoses and aldoses are further classified by their carbon
skeleton length. Accordingly, five-carbon and six-carbon
monosaccharides receive the respective names of pentoses and
hexoses. Well-known aldohexoses include glucose, mannose and
galactose. Arabinose, ribose and xylose are well-known
aldopentoses. Examples of common ketohexoses are fructose,
psicose and sorbose. Ribulose and xylulose are common
8 lZ9Z988
ketopentoses. This invention is a process for separating
psicose from other ketopentoses and ketohexoses.
Consequently, feed mixtures which can be utilized in the
process of this invention will comprise a mixture of psicose
and at least one other ketose. Potential feed mixtures can
be found in isomerization products of D-glucose and L-
glucose. Such mixtures will usually contain significant
quantities of such monosaccharides as psicose, fructose,
glucose, mannose and small quantities of polysaccharides,
such as DP 4+, i.e. having a degree of polymerization of four
and greater. The feed mixtures whether derived from natural
sources or isomerization, will also contain quantities of
lesser known monosaccharides. A typical feed mixture for
this invention will contain psicose, fructose, mannose,
glucose and polysaccharides in respective proportions, based
on weight percent of solids, ranging from 0.5 to 90 wt. ~.
In addition, there may be up to 10 wt. % solids of other
lesser known sugars.
Although it 1s not clear what properties of the
adsorbent are responsible for the separation herein
described, it appears that it cannot be attributed to pore
size selectivity alone. Since psicose and fructose are
separated from sugar molecules of similar size, it appears
that steric factors as well as electrostatic attraction
action play an important role in the separation. While it is
not possible to conclusively set forth the molecular
interaction responsible for the adsorption, one possible
explanation is a combination of cation attraction which
varies the orientation of specific sugar molecules to the
pore opening on the adsorbent. This varied orientation can
provide a suitable dispos1t1on of the particular structural
configuration corresponding to certain sugar molecules which
coincides with the shape of the adsorbent pore openings as
altered by the presence of specific cations. Therefore, both
electrostatic interaction as well as physical and
lZ9Z~
stoichiochemical considerations may provide the mechanism for
this separation.
Although it is possible by the process of this invention
to produce high purity products, it will be appreciated that
an extract component is never completely adsorbed by the
adsorbent, nor is a raffinate component completely unadsorbed
by the adsorbent. Therefore, small amounts of a raffinate
component can appear in the extract stream, and likewise,
small amounts of an extract component can appear in the
raffinate stream. The extract and raffinate stream then are
further distinguished from each other and from the feed
mixture by the ratio of the concentrations of an extract
component and a specific raffinate component, both appearing
in the particular stream. For example, the ratio of
concentration of the more selectively adsorbed to the
concentration of less selectively adsorbed sugars will be
highest in the extract stream, next highest in the feed
mixture, and lowest in the raffinate stream. Likewise, the
rat10 of the less selectively adsorbed sugars to the more
selectively adsorbed will be highest in the raffinate stream,
next highest in the feed mixture, and the lowest in the
extract stream.
Desorbent materials used in various prior art adsorptive
separation processes vary depending upon such factors as the
type of operation employed. In the swing bed system, in
which the selectively adsorbed feed component is removed from
the adsorbent by a purge stream, desorbent selection is not
as critical. However, in adsorptive separation processes
which are generally operated continuously at substantially
constant pressures and temperatures to ensure liquid phase,
the desorbent material must be judiciously selected to
satisfy many criteria. First, the desorbent material 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
- - 1 o lZ9Z98~3
displacing the desorbent material in a following adsorption
cycle. Expressed in terms of the selectivity, it is
preferred that the adsorbent 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. Secondly, desorbent material must be compatible
with the particular adsorbent and the particular feed
mixture. More specifically, they must not reduce or destroy
the critical selectivity of the adsorbent for an extract
component with respect to a raffinate component.
Additionally, desorbent materials should not chemically react
with or cause a chemical reaction of either an extract
component or a raffinate component. Both the extract stream
and the raffinate stream are typically removed from the
adsorbent in admixture with desorbent material and any
chemical reaction involving a desorbent material and an
extract component or a raffinate component would reduce the
purity of the extract product or the raffinate product or
both. Since both the raffinate stream and the extract stream
typically contain desorbent material, desorbent materials
should additionally be substances which are easily separable
from the feed mixture that is passed into the process.
Without a method of separating at least a portion of the
desorbent material present in the extract stream and the
raffinate stream, the concentration of an extract component
in the extract product and the concentration of a raffinate
component in the raffinate product would not be very high,
nor would the desorbent material be available for reuse in
the process. It is contemplated that at least a portion of
the desorbent material will be separated from the extract and
the raffinate streams by distillation or evaporation, but
other separation methods such as reverse osmosis may also be
employed alone or in combination with distillation or
evaporation. Since the raffinate and extract products are
foodstuffs intended for human consumption, desorbent material
Zg~
ll
should also be non-toxic. Finally, desorbent materials
should also be materials which are readily available and
therefore reasonable in cost. Suitable desorbents for this
separation comprise water and ethanol or mixtures thereof.
The prior art has recognized that certain
characteristics of adsorbents and desorbents are highly
desirable, if not absolutely necessary, to the successful
operation of a selective adsorption process. Such
characteristics are equally important to 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 component with respect to
a raffinate component and the desorbent material; and
sufficiently fast rates of adsorption and desorption of an
extract component to and from the adsorbent.
Capacity of the adsorbent for adsorbing a specific
volume of an extract component is, of course, a necessity;
without such capacity the adsorbent is useless for adsorptive
separation. Furthermore, the higher the adsorbent's capacity
20 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 extrac~ component of known concentration contained in a
particular charge rate of feed mixture. A reduction in the
25 amount of adsorbent required for a specific adsorptive
separation reduces the cost of a separation process. It is
important that the good initial capacity of the adsorbent be
maintained during actual use in the separation process over
some economically desirable life.
The second necessary adsorbent characteristic is the
ability of the adsorbent to separate components of the feed;
or, in other words, that the adsorbent possess adsorptive
selectivity, for one component as compared to another
component. Relative selectivity can be expressed not only
35 for one feed component as compared to another, but can also
~ 8 8
12
be expressed between any feed mixture component and the
desorbent material. The selectivity, (B), is defined as the
ratio of the two components of the adsorbed phase divided by
the ratio of the same two components in the unadsorbed phase
at equilibrium conditions, as shown in Equation 1, below:
Equation 1
_____
Selectivity = (B) = twt. percent C/wt. percent_D]A
[wt. percent C/wt. percent D]U
where C and D are two components of the feed represented in
weight percent and the subscripts A and U represent the
adsorbed and unadsorbed phases respectively. The equilibrium
conditions are determined when the feed passing over a bed of
adsorbent does not change composition after contacting the
bed of adsorbent. In other words, there is no net transfer
l~ of material occurring between the unadsorbed and adsorbed
phases. Where selectivity of the adsorbent for 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 other. As the (B)
becomes less than or greater than 1.0, there is a
preferential 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. A (B) less than 1.0 would
indicate that component D is preferentially adsorbed leaving
an unadsorbed phase richer in component C and an adsorbed
phase richer in component D. Ideally, desorbent materials
should have a selectivity equal to about 1 or slightly less
than 1 with respect to all extract components so that all of
l~Z~88
the extract components can be desorbed as a class with
reasonable flow rates of desorbent material and so that
extract components can displace desorbent material in a
subsequent adsorption step. While separation of 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
just slightly greater than 1.0, it is preferred that such
selectivity be reasonably greater than 1Ø Like relative
volatility, the higher the selectivity the easier the
separation is to perform. Higher selectivities permit a
smaller amount of adsorbent to be used.
The third important characteristic is the rate of
exchange of the extract component of the feed mixture
material, or, in other words, the relative rate of desorption
of the extract component. This characteristic 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 mater~al needed to remove the extract component and
therefore permit a reduct~on in the operating cost of the
process. With 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.
The adsorption-desorption operations may be carried out
in a dense fixed bed which is alternatively contacted with a
feed mixture and a desorbent material in which case the
process will be only semi-continuous. In another embodiment,
generally referred to as a swing bed system, a set of two or
more static beds of adsorbent may be employed with
appropriate valving so that a feed mixture can be passed
through one or more adsorbent beds of a set while a desorbent
material can be passed through one or more of the other beds
in a set. The flow of a feed mixture and a desorbent
material may be either up or down through an adsorbent in
l;~9Z98B
such beds. Any of the conventional apparatus employed in
static bed fluid-solid contacting may be used.
Countercurrent moving bed or simulated moving bed flow
systems, however, have a much greater separation efficiency
S than fixed bed systems and are therefore preferred. In the
moving bed or simulated moving bed processes, the retention
and displacement operations are continuously taking place
which allows both continuous production of an extract and a
raffinate stream and the continuous use of feed and
displacement fluid streams. One preferred embodiment of this
process utilizes what is known in the art as the simulated
moving bed countercurrent flow system. In such a system, it
is the progressive movement of multiple liquid access points
down a molecular sieve 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, desorbent inlet stream,
raffinate outlet stream, and extract outlet stream access
lines. Coincident with this simulated upward movement of the
solid adsorbent ~s 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 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 act;ve liquid access points effectively divide the
adsorbent chamber into separate zones, each of which has a
different function. In this embodiment of this 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.
lZ9Z988
The adsorption zone, zone 1, is defined as the adsorbent
located between the feed inlet stream and the raffinate
outlet stream. In this zone, the feedstock contacts the
adsorbent, an extract component is adsorbed, and a raffinate
stream is withdrawn. Since the 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 in a downstream direction when
proceeding from the feed inlet to the raffinate outlet
streams.
Immediately upstream with respect to ftuid 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 desorption of any raffinate material adsorbed within the
select~ve pore volume of the adsorbent or adsorbed on the
surfaces 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 bounday, 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 zone 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 streams. The function
of the desorption zone is to allow a desorbent material which
passes into this zone to displace the adsorbed material
produced by contact with feed in zone 1 1n 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.
lZ~Z988
16
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 raffinate stream passing out of zone
1 and into zone 4 can be prevented from passing into zone 3,
thereby contaminating the extract stream removed from zone 3.
In the instances in which the fourth operational zone is not
utilized, the raffinate stream passing from zone 1 to zone 4
must be carefully 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 contaminated.
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 1n 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 mode of operation which can
effect the countercurrent flow of solid adsorbent with
respect to fluid involves the use of a rotating disc valve in
3~ 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
lZ9Z~8~
17
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 instance, 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 in instances in which desorbent is
used which can easily desorb extract material from the
adsorbent, that a relatively small amount of adsorbent 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 columns is within the scope of the
invention.
It ~s 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 input or output of material. The apparatus which
can be utilized to effect the 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 alternatively and periodically shifted to effect
continuous operation. In some instances, the connecting
conduits can be connected to transfer taps which during the
normal operations do not function as a conduit through which
material passes into or out of the process.
It is contemplated that at least a portion of the
extract output stream will pass into a separatlon means
wherein at least a portion of the desorbent material can be
129Z988
18
separated to produce an extract product containing a reduced
concentration of desorbent material. Preferably, but not
necessary to the operation of the process, at least a portion
of the raffinate output stream will also be passed to a
separation means wherein at least a portion of the desorbent
material can be separated under separating conditions to
produce a desorbent stream which can be reused in the process
and a raffinate product containing a reduced concentration of
desorbent material. The separation means will typically be a
fractionation column or an evaporator, the design and
operation of either being 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 Adsorptive
Processing--A New Separation Technique" by D. B. Broughton
lS presented at the 34th Annual Meeting of the Society of
Chemical Engineers at Tokyo, Japan, on April 2, 1969,
for further
explanation of the simulated moving bed countercurrent
process flow scheme.
Although both liqu~d and vapor phase operations can be
used in many adsorptive separation processes, liquid-phase
operation is required for this process because of the lower
temperature requirements and because of the higher yields of
extract product that 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 200C with about 20C to about 100C
being preferred and a pressure range of from about
atmospheric to about 500 psig with from about atmospheric to
whatever pressure is required to ensure liquid phase being
preferred. Desorption conditions will include the same range
of temperatures and pressures as used for adsorption
conditions.
The size of the units which can utilize the process of
this invention can vary anywhere from those of pilot plant
~A
l~Z9~8
19
scale (see for example U.S. Patent 3,706,812 to de Rosset et
al) to those of commercial scale and can range in flow rates
from as little as a few cc an hour up to many thousands of
gallons per hour.
Another embodiment of a simulated moving bed flow system
suitable for use in the process of the present invention is
the cocurrent high efficiency simulated moving bed process
disclosed in U.S. Patent 4,402,832 to Gerhold.
A dynamic testing apparatus may be 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. The
apparatus consists of an adsorbent chamber of approximately
70 cc volume having inlet and outlet portions at opposite
ends of the chamber. The chamber is contained within a
temperature control means and, in addition, pressure control
equ~pment is used to operate the chamber at a constant
predetermined pressure. Chromatographic analysis equipment
can be attached to the outlet line of the chamber and used to
detect qualitatively or determine quantitatively one or more
components in the effluent stream leaving 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 systéms.
The adsorbent is filled to equilibrium with a particular
desorbent material by passing the desorbent material through
the adsorbent chamber. At a convenient time, a pulse of feed
containing known concentrations of a non-adsorbed
polysaccharide tracer maltrin-DP4+, aldoses, and other trace
sugars, all diluted in desorbent, is injected for a duration
of several minutes. Desorbent flow is resumed, and the
tracer and the aldoses are eluted as in a liquid-solid
chromatographic operation. The effluent is collected in
fractions and analyzed using chromatographic equ1pment and
129298~3
traces of the envelopes of corresponding component peaks
developed.
From information derived from the test, adsorbent
performance can be rated in terms of 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 component and the
peak envelope of the tracer component or some other known
reference point. It is expressed in terms of the volume in
cubic centimeters of desorbent pumped during this time
lnterval represented by the distance between the peak
envelopes. Selectivity, (B), for an extract component with
respect to a raffinate component may be characterized by the
ratio of the distance between the center of the extract
component peak envelope and the tracer peak envelope (or
other reference point) to the corresponding d1stance 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 characterized
by the width of the peak envelopes at half intensity. The
narrower the peak width the faster the desorption rate.
The examples shown below are intended to further
illustrate the process of this invention and are not to be
construed as unduly limiting the scope and spirit of said
process. The examples present test results for various
adsorbent and desorbent materials when using the above
3~ dynamic testing apparatus.
Example I
In this example a pulse test was run using a Y type
zeolite having Ca+~ ions at cation exchange sites to
lZ~Z~88
21
determine the separation of psicose from a carbohydrate
mixture containing the same. The calcium exchanged Y type
zeolite of this example was bound in an organic binder and
had an average bulk density of 0.71 gm/ml. The adsorbent was
packed in a 8.4 mm diameter column having a total volume of
70 cc. The feed mixture cons;sted of 10 ml of the
carbohydrate mixture in a solution containing 20% of solids.
The mixture composition is given in Table 1.
Table 1
_______
Wt. % Dry_Solids
D-Fructose 28.11
D-Mannose 6.62
D-Glucose 56.06
D-Psicose 4.42
DP4+ 1.59
The exper1ment began by pass1ng a water desorbent
through the column at a flow rate of 1.32 cc/min. and a
temperature of 65C. At a convenient time, 10 ml of feed was
injected 1nto the column after wh1ch flow of desorbent was
immediately resumed. Figure 1 provides a graphical
representation of the adsorbent's retention of the ps1cose
and other sugars.
A consideration of the average midpoint for each
concentration curve reveals a good separation of psicose from
the other feed mixture components. Psicose is clearly the
most selectively retained component. Moreover, fructose is
also selectively retained from among the remaining
components, and may be separated by the Ca-Y adsorbent in the
same or a different adsorbent bed. From the data obta1ned
from this experiment the select1vities of Table 2 were
calculated.
- lZ~298~
22
Table 2
Selectivity
____
Psicose/Fructose 3.76
Psicose/Mannose 6.33
Psicose/Glucose 18.25
Fructose/Mannose 1.68
Fructose/Glucose 4.84
These selectivities clearly establish the achievement of a
high degree of separation for psicose and also a satisfactory
degree of separation for fructose from the remaining
components of the feed, which can be accomplished in a second
pass over the same Ca-Y adsorbent or another Ca-Y bed.
Example II
____ __
In this example, an aqueous feed, as described below in
Table 3, was separated in a countercurrent flow, simulated
mov~ng bed system described above in which the adsorbent was
a calcium-exchanged Y zeolite and the desorbent was water.
The valve cycle was l hour, the temperature was 65C and the
ratio of adsorbent to feed, A/F, was 0.9. The feed was
obtained by the isomerization of L-glucose at 37C and a pH
of 10.6 for 48 hours.
1;~92988
23
Table 3 - Feed Analysis
_______ ____ _ _ ___ ___
Feed Wt. % Dry Solids
L-Glucose 62.5
L-Fructose 28.3
L-Mannose 4.7
L-Psicose 3.6
Unknown 0.6
In the first stage, most of the fructose and psicose were
separated from the remaining components in the extract
stream, as will be seen from the product analysis in Table 4,
below. The extract from the first stage, consisting of
highly pure L-fructose and L-psicose was then treated in a
column containing calcium-exchanged Y fau~asite. The L-
psicose, be~ng more strongly adsorbed by the ~eolite, was
found in the extract stream whlle the L-fructose was
obtained, free of L-psicose, in the raffinate stream with
minor amounts of other components at a purity of 94.6X.
Table 4 - Product Analysis
First Stage _ _ _ _ _ Second Sta~e
_____
Extract Raffinate Extract Raffinate
L-Glucose 0.5 80.6 0.0 0.5
L-Mannose 3.3 5.4 3.4 3.0
L-Fructose 88.9 10.0 73.9 94.6
L-Psicose 3.8 0.6 14.2
Other 3.5 0.1 8.5 1.9
