IE45056B1 - Process for separating ketose-aldose mixtures by selective adsorption - Google Patents

Abstract

abstract A process for separating components of a feed mixture comprising a ketose and an aldose which process comprises contacting the mixture at adsorption conditions with an adsorbent comprising a crystalline aluminosilicate selected from the X and Y zeolites and containing one or more selected cations at the exchangeable cationic sites, thereby selectively adsorbing one of said components and thereafter recovering the same. Preferably the adsorbed component will be recovered by contacting the adsorbent with a desorbent material.

Description

The present invention relates to a process for separating a ketose or an aldose from a feed mixture comprising a ketose and an aldose as components.

It is well known in the separation art that crystalline alluminosilicates can be used to separate certain hydrocarbon types from mixtures thereof, such as the separation of normal paraffins from branched-chain paraffins and the separation of olefinic hydrocarbons from paraffinic hydrocarbons. The X and Y zeolites have been employed in processes to separate individual hydrocarbon isomers. Thus, adsorbents comprising X and Y zeolites are used to separate alkyl-trisubstituted benzene isomers (U.S. Patent 3,114,782): to separate alkyltetrasubstituted monocyclic aromatic isomers (U.S. Patent 3,864,416); and to separate specific alkylsubstituted naphhalenes (in U.S. Patent 3,668,267). Perhaps the most extensively used processes are those for separating paraxylene from a mixture of Cg aromatics. (U.S. Patents Nos. 3,558,730; 3,558,732; 3,626,020; 3,663,638 and 3,734,974).

We have now found that such an adsorption process can be applied to the separation of non-hydrocarbons and more specifically to the separation of monosaccharides. We have discovered that adsorbents comprising certain zeolites containing cations of one or more selected species at the exchangeable cationic sites exhibit adsorptive selectivity for a ketose with respect to an aldose, while certain other cationic-exchanged zeolites exhibit selectivity for an aldose with respect to a ketose, thereby making separation of a ketose (or aldose) from a mixture comprising a ketose and an aldose by solid-bed selective adsorption possible. The invention may in.particular be used for separating fructose from a mixture comprising fructose and glucose.

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 sweetness 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 intravenously, whereas, glucose is not suitable for intravenous feeding. Although fructose exists widely in nature, the methods for isolating high-purity fructose are more difficult than the primary method for obtaining high-purity glucose. High-purity glucose is readily manufactured from starch by hydrolysis with mineral acids at elevated temperature followed by refining and crystallization, while one method of obtaining high-purity fructose involves hydrolysis of sucrose, separation of an insoluble lime20 fructose complex, acidification of the complex with acids that form insoluble calcium salts, removal of cation and anion contaminants, concentration of the resulting solution, and finally crystallization 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 derivatives of glucose and chloride addition compounds of glucose, but these have not been practicable.

It is accordingly a broad objective of the present invention to provide a process for separating a ketose or an aldose from a feed mixture containing a ketose and an aldose as components to produce ketose and aldose product streams containing higher concentrations of the ketose and aldose, respectively, than.were contained in the feed mixture. More specifically it is an objective cf the invention 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.

According to the present invention there is provided a process for separating a ketose or an aldose from a feed mixture comprising a ketose and an aldose as components, which comprises contacting the feed mixture at adsorption conditions with an adsorbent comprising either} (1) an X zeolite containing at exchangeable cationic sites sodium, potassium, barium and/or strontium cations, or (2) a Y zeolite containing at exchangeable cationic sites ammonium, sodium, potassium, calcium, strontium and/or barium cations, thereby selectively adsorbing one of said components to leave a raffinate comprising the other, and thereafter contacting the adsorbent containing the adsorbed component with a desorbent and recovering the resultant desorbed component.

In order to separate the ketose selectively the feed mixture is contacted with an adsorbent comprising an X zeolite containing at exchangeable cationic sites sodium, - 4- barium and/or strontium cations, or comprising an X zeolite containing at exchangeable cationic sites barium and potassium cations or barium and strontium cations, or comprising a Y zeolite containing at exchangeable cationic sites ammonium/ sodium, potassium, calcium, stronium and/or barium cations.

In order to separate the aldose seledtively the feed mixture is contacted with an adsorbent comprising an X xeolite containing potassium cations at exchangeable cationic sites.

The invention may be carried out step-wise by (a) contacting the feed mixture with the adsorbent to selectively absorb one component (ketose or aldose); (b) removing from the adsorbent the resulting raffinate stream comprising the other component; (c) contacting the adsorbent with a desorbent material to effect the desorption of the absorbed component from the adsorbent; and, (d) removing from the desorbent the resulting extract stream comprising said absorbed component.

Preferably the step-wise- process employs simulated moving-bed counter current flow ’(see O.S. Patent 2,985,589) which comprises the steps of: (a) maintaining net fluid flow in a single direction through a column of the absorbent which column contains at least three zones in which different operational functions occur and which are serially interconnected, with the terminal zones of said column also being connected to provide a closed loop with continuous cyclic film through said zones; (b) maintaining in said column an absorption zone comprising the adsorbent located between a feed inlet point at the upstream boundary and a raffinate outlet point at the downstream boundary; (c) maintaining immediately upstream from the adsorption zone a purification zone comprising the adsorbent located between an extract outlet point at the upstream boundary and the feed inlet point at the downstream boundary; (d) maintaining immediately upstream from said purification zone a desorption zone defined by the adsorbent located between a desorbent inlet point at the upstream boundary of said zone^the extract outlet point at the downstream boundary; (e) passing the feed mixture into the adsorption zone via the feed inlet point at adsorption conditions to effect the selective adsorption of one component (i.e. ketose or aldose) by the adsorbent in the adsorption sone and withdrawing a raffinate output stream comprising the non-adsorbed component from the adsorption zone via the raffinate outlet point; (f) passing the desorbent into the desorption zone via the desorbent inlet point at desorption conditions to effect the displacement of the adsorbed compound from the adsorbent in the desorption zone; (g) withdrawing an-extract output stream comprising adsorbed component and desorbent material from the desorption zone via the extract outlet point; (h) passing at least a portion of the extract output stream to a separation means and therein separating at least a portion of the desorbent material to produce a product stream comprising the selectively adsorbed component and having a reduced concentration of desorbent material; and (i) periodically advancing through the column of adsorbent, in a downstream direction with respect to fluid flow in the column, the points selected as ths feed inlet point, raffinate outlet point, desorbent inlet point, and extract outlet point, whereby there is achieved the shifting of the adsorption, purification and desorption zones through the adsorbent.

The following explanation of various terms used in the specification will be useful in making clear the operation of the 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 compound that is more selectively adsorbed by the adsorbent while a - 6 ,/ \· >β raffinate component is a compound or type of compound 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 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 I a portion of the raffinate stream from 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 containing, 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 -7component is never completely adsorbed by the adsorbent, nor is a raffinate component completely non-adsorbed by the adsorbent. Therefore, varying amounts of a raffinate component can appear in the extract stream and,likewise, varying amounts of an extract component can appear in the raffinate stream 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 concentrations of an extract component and a raffinate component appearing in the particular stream. More 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 nonselective 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 interstitial void spaces between’adsorbent particles. The selective pore volume and the non-selective void volume are generally expressed in volumetric quantities and are of importance in -8S5056 determining the proper flow rates of fluid required to be passed into an operational zone for efficient operations to take place for a given quantity of adsorbent. When adsorbent passes into an operational zone (hereinafter defined and described) employed in one embodiment of this process,its non-selective void volume together with its selective pore volume carries fluid into that zone. The non-selective 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-selective 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 2one 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 components. The selective pore volume of an adsorbent can in certain instances adsorb portions of raffinate material from the fluid surrounding the adsorbent since in certain instances there is 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 charged to the process of the invention will be those comprising a ketose and an aldose 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 -9OSS feed mixture will contain one ketose and one aldose each in concentrations of from .0.5 to 30 wt.%, more preferably from 1 to 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 fhe 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 selectivity of the adsorbent for an extract component with respect to a raffinate component. It should be easily Separable from the feed mixture -10*ΰ0 8β that is passed into the process, preferably by distillation.

Since the raffinate and extract products are foodstuffs intended for human consumption, desorbent materials should also be nontoxic. Finally, desorbent materials should be readily available and therefore reasonable in cost. Water satisfies these criteria 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 adsorption 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, (Β), for one component as compared to another component. The selectivity, (Β), 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 equilibrium conditions. Relative selectivity is shown as Equation 1 below.

Equation 1 Selectivity = (B) = [vol. percent C/vol. percent DR [vol. percent 'c/vol. percent D]^, 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. Where selectivity as between two components approaches 1-there is no preferential adsorption of one component by the adsorbent with respect to the -11/£ 3 0 S G other. When comparing the selectivity by the adsorbent of one component C over component D, a value of (B) larger than 1 indicates preferential adsorption of component C within the adsorbent. A value of (B) less than 1 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 less than 1 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 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 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 volume 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 -124 5 0 5 5 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 ketose 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 tha 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. Xt 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, (Β), 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. -13The 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 disappearance 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 Cq Aromatics by Adsorption by A. J. deRosset, R. W. Neuzil, D. J. Porous, and D. If. Rosback presented at the American Chemical Society, Los Angeles, California, March 28 through April 2, 1971.

Adsorbents to be used in the process of this invention are 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 electrochemical attraction between a ketose and the adsorbent on the one hand and between an aldose and the adsorbent on the other, rather than on physical size differences in the molecules.

Iri hydrated form, the crystalline aluminosilicates -14 Formula 1 · M2/n0:Al203:wSiO2:yH20 where M is a cation which balances the electrovalence of the aluminum-centered tetrahedra and which is generally referred to as an exchangeable cationic site, n represents the valence of the cation, w represents the moles of Si02, 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)M2/n0:Al203:(2.5+0.5)Si02: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 Sii^/AljO^ 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 predominantly sodium and the zeolite is therefore referred to as a sodium-X zeolite. Depending upon the purity of the reactants used to make the zeolite, other cations mentioned above may be present, however, as impurities. -15The Υ zeolite in the hydrated or partially hydrated form can be similarly represented in terms of mole oxides as in Formula 3 below: Formula 3 (0.9t0.2)M2/n0:Al203:wSiO2:yH2^ 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 9 depending upon the identity of M and the degree of hydration of the crystal. The Sit^/A^Oj mole ratio for Ϋ zeolites can thus be from about 3 to about 6. The cation l-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, ths cation M is also usually predominately sodium. A Y zeolite containing predominately sodium cations at the exchangeable cationic sites 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, 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 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. -164 5 0 5 6 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 incomplete 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 forming or agglomerating the hard crystalline particles of the zeolite.

.Normally the base material will be in the form of particles such as extrudates, aggregates, tablets, pills, macrospheres, or granules produced by grinding any of the above to a desired particle size range. The adsorbent used in our process will preferably have a particle size range of 16-60 mesh, and more preferably 30 to 50 mesh (Standard U.S. Mesh). A figure of 40 mesh may also be mentioned. 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. -17viQS® It has been discovered that X and Y zeolites containing specified 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 cationic sites while others are essentially completely exchanged with selected cation pairs. A zeolite is deemed to be essentially completely exchanged when the residual sodium content of the zeolite after ion exchange is less than 2 wt.% Na^O. Specifically we have found that the adsorbents comprising an X zeolite containing at exchangeable cationic sites sodium cations or barium cations or strontium cations all possess selectivity for a ketose with respect to an aldose. Other adsorbents having similar selectivity are X zeolites containing the cation pair batium and potassium or the cation pair barium and strontium at exchangeable cationic sites, A zeolite X adsorbent containing barium and potassium at the exchangeable cationic sites will preferably have a weight ratio of barium to potassium within the range from 1:1 to 100:1 and more preferably within the range of from 1:1 to 10:1 A zeolite X adsorbent containing barium and strontium at the exchangeable cationic sites will preferably have a weight ratio of barium to strontium within the range of from 1:1 to 15:1.and more preferably from 5:1 to 15:1.

On the other hand it has been found that an adsorbent comprising anX zeolite containing potassium at the exchangeable cationic sites is suitable for use in our process by virtue of its selectivity for an aldose with respect to a ketose. Such -18adsorbent may be manufactured by essentially completely ion exchanging Molecular Sieves 13X (Na-X zeolite) with potassium cations (typically with a KC1 solution), washing the exchanged material with water to remove excess ion exchange solution and drying the adsorbent to less than 10 percent weight loss on ignition (fOI) at 900°C.

Further, it has been discovered that adsorbents 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 combinations thereof are suitable for use in our process because of their selectivity for a ketose with respect to an aldose. Preferably, the zeolites will be essentially completely exchanged with the selected cation or cations. A particularly preferred adsorbent is a base material comprising Y zeolite and amorphous material containing calcium cations at the exchangeable cationic sites.

There is a surprising lack of predictability regarding the suitability cf adsorbents for use in our process. Many adsorbents comprising X or Y zeolites and amorphous material in fact exhibit no selectivity for either a ketose or an aldose and are therefore not suitable for use ii-. the process. For instance, a Y zeolite containing ammonium cations at exchangeable cationic sites-exhibits selectivity for a ketose with respect to an aldose, but a Y zeolite containing hydrogen cations at the exchangeable cationic sites exhibits no selectivity for either a ketose or an aldose.

An X zeolite containing potassium at the exchangeable cationic sites appears unique among the X zeolites in its -194S0SS ability to selectively adsorb an aldose with respect to a ketose.. An adsorbent comprising either a cesium-exchanged X or Y zeolite exhibits selectivity for neither an aldose nor a ketose. A potassium-exchanged Y zeolite, unlike the potassiumexchanged X zeolite, also exhibits selectivity for a ketose with respect to an aldose. Adsorbents comprising X zeolites containing 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 zeolite containing magnesium exhibits selectivity for neither a ketose nor an aldose. Of those suitable adsorbents comprising Y zeolites containing Ca, Sr, or 3a cations at exchangeable cationic sites, we have discovered 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. The 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 -20of the invention the adsorbent is employed in the form of a single static bed in which case the process is only semicontinuous. 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 movingbed processes the adsorption and desorption operations are continuously taking place which allows both continuous production of an extract and a raffinate stream and the continual use of feed and desorbent streams. 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 progressive movement of multiple liquid access points down an adsorbent chamber that simulates the upward movement of adsorbent contained in the chamber. Only four of the access lines are active at any one 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 -21that 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 active liquid access points effectively divide the adsorbent chamber into separate sones, 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 adsorbent located between the feed inlet stream and the raffinate outlet stream. - In this sone, the feed stock 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 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 -22desorption of any raffinate material adsorbed within the selective 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 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 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 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 23SQ3S 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 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 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 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 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 arrahge'ment 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-? at least a portion of the desorbent 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 the desorbent is removed to produce a desorbent stream which can be reused in the process and a raffinate product containing a reduced concentration of desorfcent. 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 generally Include a temperature in the range of from 2O°C to 2OO°C., preferably 2O°C. to 100°C., and a pressure in the range of from atmospheric to 35 atmospheres absolute, preferably from atmospheric to 17.5 atmospheres to ensure liquid phase operation. Desorption 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 spirit 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 -254sos® comprising X zeolites. More specifically the adsorbent comprising the A zeolite was Linde 5A Molecular Sieves (a calciumexchange A zeolite-Linde is a Registered Trade Mark), the adsorbent.comprising a Y zeolite was prepared by essentially completely non-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, Ba, Ba+K and Ba+Sr. - All adsorbents had a particle size range of approximately 20-40 O.S. Mesh. (Ha-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 55°C. and 4.4 atmospheres absolute pressure, and using pure water as the desorbent material. The sequence.of operations for each test was as follows: Desorbent material (water) was continuously run through the columm containing the adsorbent at a nominal liquid hourly space velocity {LHSVj of about 1.0. At a convenient time desorbent flow was stopped, a 4.7 cc sample of 10 wt.S 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.S 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 -26or the reference point to the midpoint of the glucose peak and subtracting 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 fdr 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 FRUCTOSE, CC.

RETENTION VOL. OF GLUCOSE, CC.

SELECTIVITY (B) TEST ADSORBENT 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 Ng-X Both were relatively unadsorbed 6 Ca-X Both vzere 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 10 Ba-K-X 16.4 7.5 2.19 11 Ba-Sr-x 21.3 4.2 5.0 -27¢5033 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 1.42) 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 glucose were relatively unadsorbed with the Mg-X, Ca-X and Ca-A adsorbents used in the presence of water for Tests 5, 5 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 comprising 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. -28The adsorbents used for Tests 10 and 11 were X zeolites containing at exchangeable cationic sites the cation pairs Ba and K, and Ba and Sr, respectively. The Ba-K-X - adsorbent used in Test 10 exhibited selectivity for fructose with respect to glucose, while the K-X adsorbent used in Test 2 did not, but the selectivity of the Ba-K-X adsorbent was not as high as that of the Ba-X adsorbent used in Test 9. The BaSr-X adsorbent used in Test 11 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.

EXAMPLE II To assure that fructose could be separated from an actual mixture containing fructose and glucose a solution containing 20 wt.% each of fructose and glucose in water was pulse-tested over a 440 cc. bed of adsorbent comprising bear iumexchanged X zeolite contained in a column having a 1.27 cm· inside diameter and''2.28 m. in height. The adsorbent was the same as that used·in Test 9 of Example I above and the same operating 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 desorbant material flow was resumed. The effluent was analyzed by both refractive index and polarimetry, and with this combination 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 (which used the same adsorbent), are shown in Table 2. -29iSQ53 TABLE 2 Selectivity Comparison with Ba-X Adsorbent TEST RETENTION VOL. OF FRUCTOSE, CC. RETENTION VOL. OF SELECTIVITY, GLUCOSE, CC. (B) 5 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 10 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 obtained by conducting pulse tests with ten different adsorbents. 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 Ba cations. These ten adsorbents are hereinafter referred to as NH4-Y, H-Y, Na-Y, K-Y, Cs-Y, Mg-Υ, 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 X, with the exception that -30after the pulse containing 10 wt.% glucose was run, a pulse of deuterium 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. Retention 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 NH^-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 sone while still permitting an extract component to be removed with reasonable amounts of desorbent material from adsorbent in the desorption zone. The H-Y 2eolite 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 1.0. -31Λ50 56 Both the Mg-Y zeolite used for Test 6 and the Ca-X adsorbent used for Test 8 exhibited no selectivity for glucose or fructose since both eluted simultaneously. The Sr-Y zeolite 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 respect to water of all the adsorbents tested, indicating that larger amounts of desorbent material (water) 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 X5 these reasons the Ca-Y zeolite adsorbent is the preferred adsorbent for the process of this invention. -32 $- QJ P to 3: TJ (/) c P c to GJ Φ JQ ω ί- O Ο a tn ff TJ r— < ίΰ in O ff O 4-> •r— P 5- U «3 Φ 5> o. Ul 4- ω O as in x: Φ P •r“ 4-» •r- ϊ > QJ r— <Λ 4-1 o (J -P dJ a (—» ff Φ 5- U- S-. O Ll. -a Q) 4-1 ff aj V) o υ ff CO o co >> >> >» r~‘ tn tn in ff 3 ff O O o Φ Qj φ c ff c rt* iff .to P P P r-“ c— ff ff ε ε ε •Γ- in ω tn Ό •ff ff CJ OJ o Φ P P P ff ff o 3 r— Φ Φ Φ Φ Φ Φ ω (Λ tn o O O P P P o O a ff ff 3 J- ί- 5- LL· ο. U- “ff ff ff C ff c <0 fO 03 Φ Φ Φ (/) (Λ tn o o O υ o o ο ff ff LO LQ r^ co J © >· LU ti ac a tol O P Φ tn cr Ll. _l QJ «X υ tn X u O P H *> u l·- ff 5— X H~» J— to a z LL· κ-r UJ QJ tn o PEAK I u ff r— © -C P O CQ r-.

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CO CM CM ΓΙΟ CM t CO CO I ο γγο to >I -. tZ) >I ro co s co n I tn gS®5'3 EXAMPLE IV This example illustrates the ability of the process of the invention to separate a ketose from an aldose when operated in a preferred embodiment which utilizes a continuous, simulated-moving bed, counterourrent-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). Briefly the apparatus consists essentially of 24 adsorbent chambers each having about 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. The valve has inlet and outlet ports which direct the flow of feed and desorbent material to 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 chambers, 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 moving 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 -34input 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 material 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 subsequently 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 chromatographic 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, deter20 mining this quantity as a percentage of the fructose fed to the unit over a known period of time and subtracting this percentage from 100 percent. The operating pressure for the tests was 10.2 atms., gauge, and the operating temperatures were 50°C. and 75°C., respectively, for Tests 1 and 2. The fructoae purity (as a percent of total sugars present) of the extract output stream, and the fructose yield, are shown below in Table 4. -35- TABLE 4 EXTRACT STREAM FRUCTOSE PURITY, % FRUCTOSE YEILD, % TEST represent EXAMPLE V The results of Tests 1 and 2 above do not necessarily the optimums that might be achieved.

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 IHand 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 523 glucose, 42% fructose and 6% higher saccharides. The operating temperature was 50°C. 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.) TABLE 5-.

TEST EXTRACT STREAM FRUCTOSE PURITY, % FRUCTOSE YIELD, % 97 10 94 49 92 55 87 83 84 88 80 90 -36By way of illustration, analysis of the extract and the raffinatie streams at one point on the fructose purity-yield curve, 85% fructose yield point, were as shown in Table 6 below.

TABLE 6 Extract and Raffinate Stream Analysis at the 85% Yield Point EXTRACT STREAM RAFFINATE STREAM % Fructose 88.3 10.7 % Glucose 11.7 79.5 10 % Higher Saccharides Trace 9.8 % Sugars 14.9 13.3 Again, the results of the tests above do not necessarily represent the optimums that might be achieved.

Claims (23)

1. CLAIMS:1. A process for separating a ketose or an aldose from a feed mixture comprising a ketose and an aldose as components thereof, which comprises contacting the feed mixture at adsorption conditions with an adsorbent comprising either, (1) an X zeolite containing at exchangeable cationic sites sodium, potassium, barium and/or strontium cations, or (2) a Y zeolite containing at exchangeable cationic sites ammonium, sodium, potassium, calcium, strontium and/or barium cations, thereby selectively adsorbing one of said components to leave a raffinate comprising the other, and thereafter contacting the adsorbent containing the adsorbed component with a desorbent and recovering the resultant desorbed component.

2. A process as claimed in claim 1, wherein the adsorbent used comprises an X zeolite containing at exchangeable cationic sites sodium, barium or strontium cations, thereby selectively adsorbing the ketose.

3. A process as claimed in claim 1, wherein the adsorbent used comprises a Y zeolite containing at exchangeable cationic sites ammonium, sodium, potassium, calcium, strontium or barium cations, thereby selectively adsorbing the ketose.

4. A process as claimed in claim 1, wherein the adsorbent used comprises an X zeolite containing at exchangeable cationic sites barium and potassium cations or barium and strontium cations, thereby selectively adsorbing the ketose.

5. A process an claimed in claim 1, wherein the adsorbent used comprises an X zeolite containing potassium cations at exchangeable cationic sites, thereby selectively adsorbing the aldose.

6. A process as claimed in any of claims 1 to 5, wherein the adsorption conditions include a temperature of from 20 to 200°C. and a pressure of from atmospheric to 35 - 38 atmospheres .absolute.

7. A process as claimed in any of claims 1 to 6, wherein the adsorption and desorption are effected in the liquid phase.

8. - A process as claimed in any or claims 1 to 7, wherein the desorbent is water.

9. A process as claimed in any of claims 1 to 8, wherein the ketose and aldose are hexoses.

10. A process as claimed in claim 9, wherein the ketose is fructose and the aldose is glucose.

11. A process as claimed in any of claims 1 to 10, wherein the feed mixture comprises an aqueous solution.

12. A process as claimed in claim 11, wherein the I feed mixture comprises an invert sugar solution.

13. A process as claimed in claim 11, wherein the feed mixture comprises a high-fructose corn syrup.

14. A process as claimed in any of claims 11 to 13, wherein the ketose and aldose are present in the feed mixture in concentrations of from 0.5 to 30 wt.%.

15. A process as claimed in any of claims 11 to 13, wherein the ketose and aldose are.present in the feed mixture in concentrations of from 1 to 15 wt.%.

16. A process as claimed in any of claims 1 to 15, wherein the adsorbent has a particle size of from 16 to 60 mesh (Standard U.S. Mesh).

17. A process as claimed in any of claims 1 to 16, wherein the adsorbent has been prepared by ion-exchange treatment of a base material which comprises from 75 to 98 wt.% zeolite (volatile-free).

18. A process as claimed in any of claims 1 to 17, wherein the adsorbent possesses a residual sodium content of less than 2 wt.% ^£0.

19. A process as claimed in any of claims 1 to 18, wherein the procedure of simulated moving bed countercurrect 4S0SS flow is used comprising. (a) maintaining a net fluid flow in a single direction through a column of the adsorbent, which column contains at least three serially-interconnected zones, each having a different 5 operational function occurring therein, with the terminal zones of said column being connected to provide a closed loop with continuous cyclic flow through said zones; (b) maintaining in said column an adsorption zone comprising the adsorbent located between a feed inlet point at the up10 stream boundary and a raffinate outlet point at the downstream boundary; (c) maintaining immediately upstream of said adsorption zone a purification zone comprising the adsorbent located between an extract outlet point at the upstream boundary and the feed 15 inlet point at the downstream boundary; (d) maintaining immediately up-stream of said purification zone a desorption zone comprising the adsorbent located between a desorbent inlet point at the upstream boundary and the extract outlet point at the downstream boundary;

20. (e) passing the feed mixture into the adsorption zone via the feed inlet point and therein selective adsorbing the one component, and withdrawing from the adsorption zone via the raffinate outlet point a raffinate output stream comprising the other component; 25 (f) passing the desorbent into the desorption zone at the desorbent inlet point and displacing from the adsorbent therein the one component which had been selectively adsorbed thereon in a previous cycle; (g) withdrawing from the desorption zone via the extract outlet 30 point an extract output stream comprising desorbent and the selectively adsorbed one component^ (h) passing at least a portion of the extract output stream to a separation means and therein separating at least a portion 40 4 3 of the desorbent material and producing a product stream comprising the selectively adsorbed component; and (i) periodically advancing through the column of adsorbent, in a downstream direction with respect to fluid flow in thd column, the points selected as the feed inlet point, raffinate outlet point, desorbent inlet point, and extract outlet point whereby there is achieved the shifting of the adsorption purification and desorption zones through said adsorbent20. A process as claimed in claim 19, vzherein at least a portion of the raffinate output stream is passed to a separation means and at least a portion of the desorbent is separated therein to produce a raffinate product having a reduced concentration of desorbent.

21. A process as claimed in claim 19 or 20, wherein a buffer zone is maintained immediately upstream from said desorption zone and comprising adsorbent located between the desorbent inlet point at the downstream boundary and the raffinate outlet point at the upstream boundary.

22. An adsorption/desorption process for separating an aldose or a ketose from a feed mixture comprising a ketose and an aldose, carried out substantially as herein before described.

23. A process in which aldose or ketose is selectively adsorbed from a mixture of an aldose and a ketose, which process comprises contacting said mixture with an adsorbent which is selective for the aldose or the ketose and which comprises (i) one or more X zeolites containing at cationic sites therein one or more of sodium, potassium, barium and strontium cations and/or (ii) one or more Y zeolites containing at cationic sites therein one or more of ammonium, sodium, potassium, calcium, strontium and barium cations, thereby producing an adsorbed aldose or ketose component and a non-adsorbed component comprising whichever of the aldose and ketose the material for which the adsorbent is not a