GB1585369A - Process for separating a monosaccharide from an oligosaccharide by selective adsorption - Google Patents

Description

(54) PROCESS FOR SEPARATING A MONOSACCHARIDE FROM AN OLIGOSACCHARIDE BY SELECTIVE ADSORPTION (71) We, UOP INC., a corporation organized under the laws of the State of Delaware, United States of America, of Ten UOP Plaza, Algonquin & Mt.

Prospect Roads, Des Plaines, Illinois, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the solid-bed adsorptive separation of sugars.

More specifically it concerns the separation of a monosaccharide from a mixture comprising a monosaccharide and an oligosaccharide.

It is well known that certain crystalline aluminosilicates can be used to separate different hydrocarbon types or isomers from mixtures thereof. For example, it is known to use a type A zeolite to separate normal paraffins from branched-chain paraffins, or to use type X or type Y zeolites to separate olefinic hydrocarbons from paraffinic hydrocarbons. Similarly, adsorbents comprising X and Y zeolites are used to separate alkyl-trisubstituted benzene isomers; also alkyl-tetrasubstituted monocyclic aromaticisomers; also alkyl-substituted naphthalenes. Probably the most extensively used hydrocarbon isomer separation processes are those which separate para-xylene from a mixture of C5 aromatics by means of particular zeolites which selectively adsorb para-xylene.

In contrast, the present invention relates to the separation of sugars. It is based on the discovery that adsorbents comprising X or Y zeolites, especially those containing one or more selected cations at the exchangeable cationic sites, exhibit adsorptive selectivity for a monosaccharide with respect to an oligosaccharide. The process has particular utility in separating one or more monosaccharides from one or more oligosaccharides found in a starch syrup, such as the corn syrup formed by the partial hydrolysis of starch, generally in the presence of mineral acids or enzymes, and consisting of mixtures of glucose, maltose and higher saccharides. A portion of the glucose in corn syrup may be isomerized with an isomerizing enzyme to produce a high-frustose corn syrup which typically contains 40-45% fructose, 50 55 /O glucose and 510% higher saccharides or oligosaccharides, by weight. By charging such corn syrups to the process of the present invention it is possible to obtain an extract stream containing a monosaccharide in a higher concentration than that found in the feed mixture and a raffinate stream containing an oligosaccharide in a higher concentration than that found in the feed mixture. Both products can be used in the food industry not only for their sweetening power but because of such properties as their viscosity, hygroscopicity, and their retarding effect on the crystallization of sugar. More specifically one or both products may be used in confectionery and bakery products, in the canning of fruits and vegetables and in beverages.

According to the present invention there is provided a process for obtaining from a feed mixture comprising a monosaccharide and an oligosaccharide a first, moncsaccharide-enriched component (i.e. one having a high monosaccharide/oligo- saccharide ratio relative to the ratio in the feed mixture) and a second; oligow saccharide-enriched component (i.e. one having a high oligosaccharide/monosaccharide ratio relative to the ratio in the feed mixture), which process comprises contacting the feed mixture at adsorption conditions with an adsorbent comprising X or Y zeolite in order selectively to adsorb the monosaccharide and to separate the feed mixture thereby into the first component which is adsorbent-extracted- and the second component as raffinate.

In a preferred embodiment the invention provides a process of this type com prising the steps of: (a) contacting the feed mixture at adsorption conditions with an adsorbent comprising an X or Y zeolite containing at exchangeable cationic sites cations of at least one type selected from ammonium cations and cations of non transition metals of Groups I and II of the Periodic Table, thereby selectively adsorb ing the monosaccharide; (b) removing from the adsorbent a raffinate stream comprising the oligosaccharide; (c) contacting the adsorbent at desorption conditions with a desorbent material to effect the desorption of the monosaccharide from the adsorbent; and, (d) removing from the adsorbent an extract stream comprising the mono saccharide.

In the process of the present invention, a monosaccharide is the basic extract component and an oligosaccharide is the basic raffinate component. The desorbent material may be any material capable of desorbing such an extract component from the adsorbent. Although it is possible by the process of this invention to produce a high-purity monosaccharide product or a high-purity oligosaccharide product (or both) at high recoveries, it will be appreciated that an extract component is never completely adsorbed by the adsorbent, nor is a raffinate component completely non adsorbed by the adsorbent. Therefore, varying amounts of raffinate component can appear in the extract stream and, likewise, varying amounts of extract component can appear in the raffinate stream. The extract and raffinate streams then are further distinguished from each other and from the feed mixture by the ratio of the concentrations of an extract component and a raffinate component appearing in the particular stream. More specifically, the ratio of the concentration of a monosaccharide to that of a less selectively adsorbed oligosaccharide 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 oligosaccharide to that of the more selectively adsorbed monosaccharide will be highest in the raffinate stream, next highest in the feed mixture, and the lowest in the extract stream.

The so-called "simple sugars" or monosaccharides are those sugars which upon hydrolysis do not break down into smaller simpler sugars. One may further classify monosaccharides as aldoses or ketoses, depending upon whether they are hydroxy aldehydes or hydroxy ketones, and by the number of carbon atoms in the molecule.

Most common and well known are probably the hexoses. Common ketohexoses are fructose (levulose) and sorbose; common aldohexoses are glucose (dextrose), mannose and galactose. The oligosaccharides are simple polysaccharides containing a small known number of constituent monosaccharide units. An oligosaccharide that breaks up upon hydrolysis into two monosaccharide units is called a disaccharide, examples being sucrose, maltose and lactose. Those giving three such units are trisaccharides, of which raffinose and melezitose are examples. Di-, tri- and tetrasaccharides comprise practically all of the oligosaccharides. The term "polysaccharide" includes oligosaccharides but usually it refers to carbohydrate materials of much higher molecular weight, namely, those that are capable of breaking up on hydrolysis into a large number of monosaccharide units. Typical polysaccharides are starch, glycogen, cellulos and pentosans.

Feed mixtures which can be charged to the process of the present invention are those comprising a monosaccharide and an oligosaccharide, preferably aqueous solutions of one or more monosaccharides and one or more oligosaccharides. The concentration of solids in the solutions may range from 0.5 Wt.% to 50 wt.% or more but is preferably from 5 to 35 wt.%. The monosaccharide may be an aldose or a ketone or both. If more than one monosaccharide is present they may have the same number of carbon atoms per molecule or a different number of carbon atoms per molecule.

The oligosaccharide will usually be one or more disaccharides but it could also be one or more higher oligosaccharides or a mixture of one or more disaccharides and one or more higher oligosaccharides. Starch syrups such as corn syrup are examples of feed mixtures which can be charged to the process. Corn syrup produced in this manner will typically contain 25 to 75 wt.% solids comprising 90 to 95% glucose and 5 to 10% maltose and higher oligosaccharides. A portion of the glucose in this corn syrup may be isomerized with an isomerizing enzyme to produce a high-fructose corn syrup, typically comprising 40--450/, fructose, 5055% glucose and 510% oligosaccharides, which can also be charged to the process.

In adsorptive separation processes which are generally operated continuously at substantially constant pressures and temperatures selected 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 displacing the desorbent material in a following adsorption cycle. Secondly, desorbent materials must not reduce or destroy the critical selectivity of the adsorbent for an extract component with respect to a raffinate component. Desorbent materials should be easily separable from both the raffinate stream and the extract stream. It is contemplated that at least a portion of the desorbent material will be separated from the extract and the raffinate streams by distillation but other separation methods may also be employed, alone or in combination with distillation. Since the raffinate and extract products are foodstuffs intended for human consumption, desorbent materials should also be non-toxic. Finally, desorbent materials should be readily available and therefore reasonable in cost. It has been found that water satisfied these criteria and is the preferred desorbent material for use in the process of the invention.

A dynamic testing apparatus can 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 may consist 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 equipment is used to operate the chamber at a constant predetermined pressure. Quantitative and qualitative analytical equipment such as refractometers, polarimeters and chromatogranhs can be attached to the outlet line of the chamber and used to detect quantitatively or determine qualitatively 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 systems. 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 tracer and of a particular ketose or aldose, or both. all diluted in desorbentj is injected for a duration of several minutes. Desorbent flow is resumed, and the tracer and the ketose and aldose are eluted as in a liquid-solid chromatographic operation. The effluent can be analyzed on-stream or alternatively effluent samples can be collected periodically and later analyzed separately bv analytical equipment and traces of the envelopes or corresponding component peaks developed.

From information derived from the test, adsorbent performance can be rated in terms of void volume retention volume for an extract of a raffinate comnonent. 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 interval 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 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 characterized by the width of the peak envelopes at half intensity. 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 racer peak envelope and the disappearance of an extract component which has just been desorbed. This distance is again the volume of desorbent pumped during this time interval.

To further evaluate promising adsorbent systems and to translate this type of data into a practical separation process requires actual testing of the best system in a continuous counter-current liquid-solid contacting device. The general operating principles of such a device have been previously described and are found in U.S.

Patent 2,985,589. A specific laboratory-size apparatus utilizing these principles is described in U.S. Patent 3,706,812.

Adsorbents to be used in the process of this invention are certain specific crystalline aluminosilicates or molecular sieves having a cage structure in which the alumina and silica tetrahedra are intimately connected in an open three dimensional network to form cage-like structures with window-like pores of preferably about 8 A free diameter. The tetrahedra are cross-linked by the sharing of oxygen atoms with spaces between the tetrahedra occupied by water molecules prior to partial or total dehydration of this zeolite. The dehydration of the zeolite results in crystals interlaced with cells having molecular dimensions and thus the crystalline aluminosilicates are often referred to as "molecular sieves"..

In hydrated form, the crystalline aluminosilicates generally encompass those zeolites represented by the Formula 1 below: Formula 1.

M,O:Al,Os:wSiO2:yH2O where "M" is a cation which balances the electrovalence of the aluminum-centred tetrahedra and which is 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 form can be represented in terms of mole oxides as shown in Formula 2 below: Formula 2.

(0.9 + 0.2)M2nO A1,0,:(2.51+ 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/AI2OS 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 initially prepared, the cation "M" is usually pre dominantly sodium, and the zeolite is therefore referred to as a sodium-X zeolite.

The eolite in the hydrated or partially hydrated form can be similarly represented in terms of mole oxides as in Formula 3 below: Formula 3.

(0.9 1+ 0.2)M2,,,O:Al2O:wSiO2:yH2O 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 about 6, and "y" is a value up to about 9 depending upon the identity of "M" and the degree of dehydration of the crystal. The SiO2/AI2OS mole ratio for Y zeolites can thus be from about 3 to about 6. Like the X zeolite, the cation "M" may be one or more of a variety of cations but, as the Y zeolite is initially prepared, the cation "M" is also usually predominantly sodium and is therefore 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 by which the sodium 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.

The term "base material" as used herein shall refer to a material containing X or Y zeolite which can be used to make the adsorbents to be used in our process.

The zeolite will typically be present in the base material in amounts ranging from 75 wt.% to 98 wt.% of the base material, based on volatile-free composition (compositions after calcining at 9000C). The remainder of the base material will generally be amorphous material such as silica, alumina or silica-alumina mixtures or compounds, such as clays. The base material can be in the form of particles such as extrudates, aggregates, tablets, macrospheres or granules having a desired particle size range. The adsorbent used will preferably have a particle size range of about 1640 mesh (Standard U.S. Mesh). Examples of suitable base materials are "Molecular Sieves 13X" and "SK-40" (available from the Linde Company, Tonawanda, New York).

The first material contains X zeolite while the latter material contains.Y zeolite.

The preferred adsorbents for use in the present process comprise an X or a Y zeolite containing at exchangeable cationic sites cations of at least one type selected from ammonium cations and cations of non-transition metals of Groups I and II of the Periodic Table. Particularly preferred, because of their higher selectivities for a monosaccharide with respect to an oligosaccharide, are X or Y zeolites containing barium cations at the exchangeable cationic sites. Preferably the X or Y zeolites will be essentially completely exchanged with the selected cation or cations. A zeolite is deemed to be essentially completely exchanged when the residual content of the initial cation is less than 2 wt.%.

The adsorbent may be employed in the form of a dense compact fixed bed which is alternately contacted with the feed mixture and desorbent materials. In the simplest embodiment 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, and any conventional apparatus employed in static bed, fluid-solid contacting may be used.

Counter-current moving-bed or simulated moving-bed counter-current flow systems are preferred. In the moving-bed or simulated moving-bed processes the adsorption and desorption operations are continuously taking place which allows both continuous product of an extract and a raffinate stream and the continual use of feed and desorbent streams. One preferred embodiment of this process utilizes what is known in the art as the simulated moving-bed counter-current flow system. The operating principles and sequence of such a flow system are described in U.S. Patent 2,985,589.

In such a system it is the progressive movement, or cyclic advancement, of multiple liquid access points down an adsorbent chamber that simulates the upward movement of adsorbent contained in the chamber. Usually, 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 is the movement of the liquid occupying the void volume of the packed bed of adsorbent, so that counter-current contact is maintained.

The active liquid access points effectively divide the adsorbent chamber into separate zones, each of which has a different function, and it is generally necessary to use at least three separate operational zones, the first being an adsorption zone (located between the feed inlet stream and the raffinate outlet stream), the second being a purification zone, immediately upstream of the adsorption zone (and defined as the adsorbent between the extract outlet stream and the feed inlet stream), and the third being the desorption zone, which is immediately upstream of the purification zone (and comprises the adsorbent between the desorbent inlet and the extract outlet stream).

In some instances an optional, fourth, buffer zone may be utilized, which comprises a portion of adsorbent between the raffinate outlet stream and the desorbent inlet stream.

The cyclic advancement of the input and output streams through the fixed bed of adsorbent can be accomplished by utilizing a manifold system of valves or 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 the disc valve are well known in the literature.

Normally, the extract stream will pass into a separation means wherein at least a portion of the desorbent material can be separated to produce an extract product containing a reduced concentration of desorbent material, while the raffinate output stream will also be passed to a separation means wherein at least a portion of the desorbent material is separated 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. The U.S.

Patent No. 2,985,589 gives further explanation of the simulated moving-bed countercurrent process flow scheme.

Liquid-phase operation is preferred for the present process because of the lower temperature requirements and because of the higher yields of extract product that can be obtained relative to vapor-phase operation. Adsorption conditions generally include a temperature of from 20 C. to 2000 C., with 200 to 1000 C. being preferred, and a pressure of from atmospheric to 35 atmospheres, with from atmospheric to 18 atms. being preferred. Desorption conditions generally include the same ranges of temperatures and pressures.

EXAMPLE.

Selectivity indexes for eight adsorbents, for glucose with respect to maltose, and for fructose with respect to maltose, were obtained using the pulse-test apparatus and procedure previously described. Of the eight adsorbents two comprised X zeolites and six comprise Y zeolites. The two adsorbents comprising X zeolites were prepared bv essentially completely ion exchanging two portions of Linde (Registered Trade Mark) 13X Molecular Sieves with K and Ba cations respectively, and the six adsorbents comprising Y zeolites were prepared by essentially completely exchanging six portions of Linde SK-40 with Ba, Sr, Ca, Cs, Na, and NH4 cations respectively.

These eight adsorbents are hereinafter referred to as K-X, Ba-X, Ba-Y, Sr-Y, Ca-Y, Cs-Y, Na-Y and NH4-Y zeolite adsorbents. All adsorbents had a particle size range of approximately 2040 U.S. Mesh. The adsorbents were tested in a 70 cc coiled column maintained at 550C. and 3.5 atm. gauge pressure and using pure water as the desorbent material. The sequence of operations for each test was as follows.

Desorbent (water) was continuously run through the column containing the adsorbent at a nominal liquid hourly space velocity (LHSV) of about 1.0. At a convenient time the flow of desorbent material was stopped, a 4.7 cc sample of 10 wt.% fructose in water was injected into the column via a sample loop, and the flow of desorbent material 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 in water was similarly run, as was a third pulse of 10 wt.% maltose in water .Thus for each adsorbent tested three peak traces were developed, one for glucose, one for fructose and one for maltose. As part of the pulse test for any adsorbent the void volume of the adsorbent is usually determined by injecting into the adsorbent bed a feed pulse containing a tracer, such as a paraffin, which is almost totally non-adsorbed by the adsorbent. When a tracer is used the retention volume for an extract or a raffinate component is calculated by measuring the distance from time zero or the reference point to the midpoint of the extract or raffinate component peak and subtracting the distance representing the void volume of the adsorbent obtained by measuring the distance from the same reference point to the midpoint of the tracer peak. Selectivities for an adsorbent for one component with respect to another are the quotients obtained by dividing the respective retention volumes which were obtained in this manner. For this example, however, it was found that maltose was in effect a tracer, that is, that it was as non-adsorbed as any separate tracer component tried. Thus the retention volumes for components for the tests of this example were calculated by measuring the distances from time zero to the midpoints of the respective component peaks without subtracting the distance from the same reference point to a tracer component which would have represented the adsorbent void volume. Retention volumes for the tests of this example are therefore referred to as "gross retention volumes" and selectivity indexes were calculated using the gross retention volumes determined in this manner. Thus "retention volumes are "selectivities" are calculated from pulse-test data when a separate tracer component is used in the pulse-test procedure and "gross retention volumes" and "selectivity indexes" are calculated from pulse-test data when no separate tracer component is used in the pulse-test procedure. Gross retention volumes and selectivity indexes for the pulse tests are shown in Table No. 1 below: TABLE No. 1 Gross Retention Volumes and Selectivity Indexes for Various Adsorbents for Glucose and Fructose with Respect to Maltose Gross Retention Volumes @ Selectivity Indexes Test Adsorbent Glucose Fructose Maltose Glucose/Maltose Fructose/Maltose 1 K-X 36.7 31.0 29.9 1.23 1.04 2 Ba-X 56.4 68.3 47.6 1.19 1.43 3 Ba-Y 56.6 68.8 49.2 1.15 1.40 4 Sr-Y 55.5 68.8 51.0 1.09 1.35 5 Ca-Y 51.8 64.4 48.7 1.06 1.32 6 Cs-Y 53.9 54.7 48.8 1.10 1.12 7 Na-Y 53.2 56.8 52.8 1.01 1.08 8 NH4-Y 51.8 58.9 48.6 1.06 1.21 Since all selectivity indexes for all eight tests are greater than 1.0, these pulse tests illustrate the ability of these adsorbents to preferentially adsorb, in the presence of water as a desorbent material, a monosaccharide over an oligosaccharide thus making our process possible. The highest selectivity indexes were obtained in Tests 2 and 3 with Ba-X and Ba-Y zeolite adsorbents respectively, thus illustrating why these adsorbents are preferred for use in our process. The lowest selectivity indexes were obtained in Test 7 with the Na-Y zeolite adsorbent.

The use of an adsorbent comprising either an X-zeolite containing sodium, potassium, barium and/or strontium cations at exchangeable cationic sites or a Y-zeolite containing ammonium, sodium, potassium, calcium, strontium and/or barium cations at exchangeable cationic sites for the separation of a ketone or analdose from a mixture containing a ketose and an aldose by selective adsorption of one of these two components followed by its desorption using a desorbent is described and claimed in our copending G.B. Patent Application No. 22240/77 (Serial No. 1574915).

Claims (16)

WHAT WE CLAIM IS:-

1. A process for obtaining from a feed mixture comprising a monosaccharide and an oligosaccharide a first component having a high monosaccharide/oligosaccharide ratio relative to the ratio in the feed mixture and a second component having a high oligosaccharide/monosaccharide ratio relative to the ratio in the feed fixture, which process comprises contacting the feed mixture at adsorption condition with an adsorbent comprising X or Y zeolite in order selectively to adsorb the monosaccharide and to separate the feed mixture thereby into the first component, which is adsorbent-extracted, and the second component as raffinate.

2. A process as claimed in claim 1 wherein the adsorbent contains at exchangeable cationic sites cations of at least one type selected from ammonium cations and cations of non-transition metals of Groups I and II of the Periodic Table.

3. A process as claimed in claim 1 or claim 2 wherein the first and second components are obtained by:- (a) contacting the feed mixture at adsorption conditions with an adsorbent comprising an X or a Y zeolite containing at exchangeable cationic sites cations of at least one type selected from ammonium cations and cations of non-transition metals of Groups I and II of the Periodic Table, thereby selectively adsorbing the monosaccharide; (b) removing from the adsorbent a raffinate stream comprising the oligosaccharide; (c) contacting the adsorbent at desorption conditions with a desorbent material to effect the desorption of the monosaccharide from the adsorbent; and (d) removing from the adsorbent an extract stream comprising the monosaccharide.

4. A process as claimed in any one of claims 1 to 3 wherein the adsorbent comprises X or Y zeolite having barium cations at the exchangeable cationic sites.

5. A process as claimed in any preceding claim wherein contact of the feed mixture with the adsorbent is effected at a temperature in the range from 200C to 2000C and a pressure in the range from atmospheric to 35 atmospheres.

6. A process as claimed in any preceding claim wherein the feed mixture is contacted in the liquid phase with the adsorbent.

7. A process as claimed in any preceding claim wherein the monosaccharide comprises a ketohexose and/or an aldohexose.

8. A process as claimed in claim 7 wherein the ketohexose is fructose.

9. A process as claimed in claim 7 wherein the aldohexose is glucose.

10. A process as claimed in any preceding claim wherein the oligosaccharide comprises a disaccharide.

11. A process as claimed in claim 10 wherein the disaccharide is maltose or sucrose.

12. A process as claimed in any of claims 3 to 11 wherein the desorbent material is water.

13. A process as claimed in any preceding claim wherein the adsorbent is of particulate form having a particle size of from 16 to 40 Standard United States Mesh and comprises the zeolite together with an amorphous material, the zeolite constituting from 75% to 98% by weight of the volatiles-free adsorbent.

14. A process as claimed in claim 1 wherein the adsorbent is one substantially as hereinbefore described in any one of Tests 1 to 8 set forth in the specific Example.

15. A monosaccharide-enriched component obtained by a process as claimed in any preceding claim.

16. An oligosaccharide-enriched component obtained by a process as claimed in any one of claims 1 to 14.