GB2382038A

GB2382038A - Melt crystallization of sugars and sugar alcohols

Info

Publication number: GB2382038A
Application number: GB0222387A
Authority: GB
Inventors: Heikki Heikkila; Mirja Lindroos; Marco Giulietti; Marcelo Seckler; Joachin Ulrich; Sandra Peters-Erjawetz; Uta Luedecke
Original assignee: Danisco Sweeteners Oy
Current assignee: Danisco Sweeteners Oy
Priority date: 2001-09-28
Filing date: 2002-09-26
Publication date: 2003-05-21
Anticipated expiration: 2022-09-26
Also published as: GB2382038B; FI20011907A0; GB0222387D0; FI20011907A

Abstract

The present invention relates to a process for the crystallization of at least one component of a multi-component system, wherein a liquid system containing at least two components selected from sugar and sugar alcohol compounds is subjected to a melt layer crystallization to cause crystallization of at least one of said sugar or sugar alcohol components on a cooled surface, and the resulting crystals are recovered from the remaining liquid system.

Description

Melt crystallization of sugars and sugar alcohols The present invention relates to a process for the crystallization of at least one sugar or sugar alcohol component of a multi-component system containing at least two components selected from sugars and sugar alcohols. This invention may be used for the crystallization of melts for example when one of the components is to be separated from the melt, or when the melt is to be purified or fractionated.

Sugars and sugar alcohols are widely used in the food and pharmaceutical industries. Many of the sugars and sugar alcohols are directly or indirectly obtained from natural biological sources and their'production very often includes crystallization as the final step in the production process in order to provide a pure product or composition. Such a crystallization process may be e. g. an evaporation or boiling crystallization, a cooling crystallization, a melt crystallization, spray drying or a precipitation. The sugars and sugar alcohols are usually separated and purified using e. g. centrifuging, ion exchange, chromatographic or filtration methods, including membrane filtration.

Solid layer melt crystallization has been used in the prior art for processing of various substances. Solid layer melt crystallization has also been used for the separation of mixtures of organic compounds. The applications range from the separation of isomers to the isolation of chemicals from tar and from the production of pure carboxylic acids to the purification of monomers, Solid layer melt crystallization has been found to be efficient when separating azeotropic mixtures or compounds which are difficult to separate by distillation because of boiling points being very close to each other, as well as when purifying thermally unstable compounds.

Solid layer melt crystallization has been used e, g. for fractionating of milk fat. CA 2,115, 472 discloses a method using melt crystallization for purification of lactides, including separation of optically active forms thereof.

Purification of caprolactam by solid layer melt crystallization is described in an article "Purification by solid layer melt crystallization", J. Ulrich and M. Neumann, Journal of Thermal Analysis, Vol. 48 (1997) p. 527-533.

The publication"Die Schmelzkristallisation von organischen Stoffen und ihre grosstcchnischen Anwendung", S. RiMer and R. Steiner, Chem.-Ing.-Tech. 57 (1985) No. 2, p. 91-102 discloses a solid layer melt crystallization method for the separation e. g. of m-xylene and p-xylene and the purification of monochloroacetic or benzoic acid. The amount of p-xylene in the melt in the method was 70 % before the separation and about 99 % after the separation.

US 5,755, 975 discloses a method of separating substances from a liquid mixture by solid layer melt crystallization. The crystal layer formed contains less impurities than the liquid mixture in the beginning (0,102 % and 0,6 % respectively based on 100 % by weight of N-vinylpyrrolidone in the example).

I Solid layer melt crystallization has not been used in the prior art for sugars and sugar alcohols.

Sugars can be produced e. g. from biomasses by hydrolysis and the sugar thus obtained may be further reduced to sugar alcohols, e. g. by hydrogenation. These processes usually provide mixtures of sugars and/or sugar alcohols and many of these mixtures are hexose-pentose or hexitol-pentitol mixtures. Separation of sugar and/or sugar alcohol mixtures is complicated. Crystallization is a common way to separate sugars and/or sugar alcohols, but production of pure crystallized products from low purity solutions is difficult. The conventional crystallization processes are slow and their energy consumption is relatively high. The solutions are often viscous and heat transfer is slow in the solutions Heat transfer in a solution or melt is fairly long due to the long distance to the cooling surface, which slows down the mass transfer in the process. Examples of sugar and sugar alcohol crystallizations are indicated below : US 5,951, 777 and US 6,086, 681 disclose methods for pre-purifying a low purity xylose solution by supersaturated crystallization e. g. in order to obtain sufficiently pure xylose for the actual crystallization. High supersaturation is used and the crystals are recovered essentially by nucleation.

FI 104738 discloses a method for a cooling crystallization of fructose from a viscous solution wherein the initial fructose concentration is fairly high, i. e. at least 90 %. Heat and mass transfer is improved by mixing.

Isomalt is a two-component sugar alcohol which has been commercially produced in crystalline form by solidification as a mixture in a special equipment which provides a combination of vacuum evaporation, crystallization and drying (Carbohydrates in Industrial Synthesis, Edited by M. A. Clarke, Verlag Dr. Albert Bartens KG, Berlin, 1992, page 48).

In FI 103120 different crystal forms of lactitol are obtained by selecting the temperature and concentration of an aqueous lactitol solution.

Chromatographic methods have been widely used in the separation of sugars and sugar alcohols, e. g. glucose and fructose. The components can be separated into a fairly pure form ( > 90 %) and then crystallized. However, obtaining a very high purity by chromatographic methods is difficult with good economy. Large amounts of eluent are needed, which is costly and may include costly recovery methods, e. g. evaporation.

Naturally occurring invert sugar is a mixture of fructose and glucose. Fructose can also be produced for example by isomerizing glucose into fructose. By this way it is possible to obtain a mixture of fructose and glucose that contains no more than about 50 % fructose. However, a higher content of fructose is often needed in the commercial use, and therefore glucose has to be removed from the liquid. In Patent FI 88933 fructose and glucose have been produced from sucrose with an enzymatic hydrolysis. Glucose and fructose fractions were separated using a

continuous process with a chromatographic simulated moving bed method.

0 GB 1539553 discloses a method for the chromatographic recovery of a fructose-rich fraction from isomerized starch conversion syrup using an ion exchange resin column. GB 2087400 discloses a method for producing a syrup having a high fructose concentration by isomerising glucose syrup and crystallizing glucose by cooling the liquid and separating the crystallization product.

US 6,217, 754 discloses a process for the manufacture of a starch hydrolysate with high dextrose content wherein the raw saccharified hydrolysate is separated by nanofiltration for recovery of glucose.

AU-A-87047/98 describes methods of manufacturing a maltose-rich syrup. Glucose is removed

from the mixture either by transforming the glucose into gluconic acid and then removing the 1 9 acid with an ion exchange resin or by transforming the glucose into ethanol which is then C > eliminated by evaporation.

Many of the conventional methods of separating sugars and sugar alcohols require quite a high purity of the material which is to be crystallized and the result is not always satisfactory. Many of them also have a high energy consumption and slow heat and mass transfer. There is thus a need for an effective and fast method of crystallizing especially for separating and/or purifying sugars and/or sugar alcohols.

I It has now been found that melt layer crystallization can be used for the purification and/or separation of sugars and/or sugar alcohols.

The process according to the present invention enables separation and/or purification of at least one component of a multi-component system by crystallizing at least one of the components. A multi-component system is intended to mean a system containing two ore more distinct compounds. The process according to the invention is defined in the appended claims.

According to the invention a liquid system containing at least two liquid components selected from sugar and sugar alcohol compounds is subjected to a melt layer crystallization to cause crystallization of at least one of the sugar or sugar alcohol components on a cooled surface. Said component can be separated in a purer form on the cooled surface containing crystals of the component. The crystallized layer may contain some of the other components of the liquid system. The recovered crystalline layer may be used in further processes.

It is also possible to use the process of the present invention in order to enrich one of the components in the liquid system. The purified mother liquid which has an enriched content of the non-crystallized component (s) may be used as such for further processing. Another advantage of the invention is that it enables separation and/or purification of melts of two or more sugars or sugar alcohols also when the amounts of the components in the melt are fairly large. Thus, the process is not limited to the purification of systems wherein the impurity comprises only a very minor component of the melt. However, there are also combinations of

sugars and/or sugar alcohols which form co-crystals or crystal mixtures and where the crystals thus do not provide a pure product but which may still be a useful product for some purposes.

Several crystallization runs may be performed to provide the final product either as the combined crystallized compounds or as the purified remaining liquid.

A melt can be defined as a material that is solid at ambient conditions and is heated until it becomes a molten liquid (Handbook of Industrial Crystallization, ed. A. S. Myerson, 1993, Butterworth-Heinemann). Melts can be pure materials or they may be mixtures of materials. A homogenous melt with more than one component can also be called a solution, although it is usually referred to as a melt.

I In the present description a liquid solution of two or more components is defined as a melt. The melt may contain further crystallizable components and also a solvent component. A solvent, on the other hand, is defined as a component which is in liquid form at ambient conditions and which does not crystallize on the cooled surface under the conditions of the present process.

Solid layer crystallization from a melt, i. e. melt layer crystallization is a process where crystals are formed on a cooled surface from a melt. At least one of the components of the melt is crystallized as a crystal layer perpendicular to the surface.

The liquid system used in the present invention consists of at least two components These two components are sugars or sugar alcohols. The melt layer crystallization according to the present invention may be used for crystallization of a large variety of sugars or sugar alcohols. The liquid system may also contain an aqueous or an organic solvent as a further component. The system can contain organic or inorganic compounds as impurities deriving from the preceding production process or from the raw materials. The sugar or sugar alcohol compounds may be dissolved in the solvent. The process is, however, operated in such a way that the water or organic solvent does not crystallize in the process.

Crystalline sugars and sugar alcohols are usually produced by crystallizing from their melts which may contain water or alcohol as solvents. Poor heat transfer is a problem encountered in the conventional methods using large crystallizers. The crystallizing melts often have a very high viscosity. Crystallization of a pure sugar or sugar alcohol may be very slow. Seed crystals

are often needed in order to initiate crystallization. A conventional crystallization requires several apparatuses, evaporators, boiling crystallizers, cooling crystallizers, centrifuges, driers, which consume time and energy and are technically complicated. Conventional crystallization processes are often batch processes and difficult to control to satisfaction.

The present invention is based on the use of conventional solid layer melt crystallization techniques which are well known to those skilled in the art and which are therefore not described herein in detail. A basis of the separation is believed to be the difference in the melting points and, or solubilities of the substances. A cooled surface contacted with the melt of two or more components generally causes the higher melting and/or less soluble component to solidify n the surface and to form coherent layers. Lower melting and'or more soluble components enrich in the remaining melt. The liquid system preferably has a temperature which is just sufficient for retaining the melt in a liquid form. The solid layer comprises a crystallization surface having a temperature which is lower than the temperature of the liquid system. The crystallization may be repeated at least once and preferably several times for improving the separation and/or purification.

The melt crystallization can be performed in a static as well as in a dynamic mode. Melt crystallization from a stagnant melt is usually called static melt crystallization. In a static crystallization process the surface on which the crystals are formed is positioned in the stagnant melt within a vessel. The heat transfer and mass transport to the surfaces take place by natural convection. Static processes are usually carried out in modified multitube or plate-type heat exchangers. Static melt crystallization requires only a relatively small temperature difference between the melt and the coolant as a result of the low growth rates.

Layer growth from a forced flowing melt is referred to as dynamic melt crystallization. In a dynamic process the melt is circulated through the crystallizer or the melt may be mechanically mixed. The melt flows over the surface of the cooled surface. Dynamic crystallization processes are effected by forced convection of the melt or by moving the cooled surface. Modified heat exchangers can also be used in dynamic or static melt crystallization. The melt crystallization equipment is preferably a static heat exchanger type and the remaining melt is drained out of the equipment after the crystallization. The process according to the invention may be performed as a continuous or as a batch process.

The crystallization on a solid layer is preferably improved by pre-application thereon of a primary layer of seed crystals of the sugar and/or sugar alcohol component which is to be crystallized. The crystals may comprise different crystal forms of said component or mixtures of the solidified components and it may also contain amorphous components of the same. A primary layer can be created by freezing the attached residual liquid of the last remelting process to serve as a starter (nuclei) of the next process cycle.

In a process according to present invention a crystal layer is formed on a cooled surface.

Various kinds of cooling apparatus may be used for the present invention. It is important that the temperature of the melt remains sufficiently high in order to prevent any crystallization from taking place in the melt itself. After the crystallization the sugar and/or sugar alcohol component which is to be purified is removed from the liquid system in the form of crystals on the cooled surface. The recovered crystals have a purity of the component which is higher than the purity of the component in the liquid system.

The process according to this invention may also be used to enrich the melt in respect of at least one of the components. The sugar and/or sugar alcohol component which is to be purified is retained in liquid form and the other sugar and/or sugar alcohol component is removed from the liquid system in the form of crystals on the cooled surface. The crystals have a concentration of the removed component which is higher than the concentration of the removed component in the liquid system. The component (s) remaining in the melt are concurrently enriched. If a melt is to be purified by this method it is essential that the crystallized sugar or sugar alcohol remains intact on the cooled surface when the run off is removed.

Conventional post-crystallization purification processes, such as washing and sweating may be used, if the crystallized sugar or sugar alcohol needs to be further purified. The crystallized sugar may be removed from the surface by dissolving, melting or scraping.

In sweating the temperature is increased to the temperature close to the melting point of the pure material in order to melt the material partially. Impurities drain out of the pores of the crystalline material and from the boundary layer adhering to the crystalline surface. Sweating is a temperature driven process. Washing on the other hand removes the impurities on the surface of the crystal.

The present invention is preferably used for separating and purifying mixtures wherein the sugars and/or sugar alcohols are different combinations of sucrose, ketoses, aldoses, hexoses, pentoses, (including ketohexoses, ketopentoses, ketotetroses, aldohexoses, aldopentoses and aldotetroses), hexitols and pentitols. Deoxy sugars and deoxy sugar alcohols as well as aldobioses and aldobitols are also included in the terms sugar and sugar alcohol. Such

combinations may contain hexoselhexose, pentose/pentose, hexoselpentose, hexitol/hexitol, pentitol/pentitol, hexitol/pentitol, hexose/hexitol, hexosefpentitol, pentose/hexitol, pentose/pentitol, hexo$e/hexose/pentose or hexose/pentose/pentose or the like. The sugar and sugar alcohol may crystallize in the D and/or L forms. Sugars can be crystallized in a-and p- anomeric forms and as pyranose or furanose ring structure. The melt may also contain other impurities deriving from the production process.

In a preferred embodiment the at least two sugar and/or sugar alcohol components are glucose and fructose or glucose and sorbitol. In the present process it is also useful to separate a mixture of glucose and xylose deriving from the hydrolysis of biomasses, e. g. in the production of xylose from wood. Another embodiment comprises a mixture of arabinose and mannose or a mixture of arabinose, mannose and xylose which may also be obtained from biomasses. Other useful components are mannose and mannitol, such mixtures deriving from an incomplete reduction of mannose. A mixture of xylitol and xylose deriving from an incomplete hydrogenation of xylose is also a useful two-component system for the present invention.

In another embodiment the two sugar and/or sugar alcohol components are sorbitol and maltitol deriving from the reduction of starch hydrozylate, where a mixture of glucose and maltose has first been obtained from starch. It is also useful to separate a mixture of 1-0-a-D- glucopyranosyl- D-mannitol (1, I-GPM) and 6-0-a-D-glucopyranosyl-D-sorbitol (1,6-GPS) deriving from the hydrogenation of isomaltulose or a mixture of arabinitol and xylulose obtained e. g. microbiologically from glucose. Yet another useful two-component liquid system contains arabinitol and xylitol deriving e. g. from the biochemical production of xylitol. Other useful liquid systems may contain sorbitol and mannitol or maltitol and maltotritol.

The melting points of some of the above mentioned compounds are shown below. The solubilities of most of the sugars and sugar alcohols are also found in the literature or they may be determined experimentally.

Melting points'C Arabinitol 102-103 Merck Index 12th ed. (1996) Arabinose 160 Fructose 103-105 Anhydrous a-glucose 146 Anhydrous -glucose 150 Glucose monohydrate 83-86 1, 1-GPM (anhydrous) 162 1,6-GPS 165,5-168, 5 Xylitol 92-96 Xylose 145 Maltitol 146-147 Mannitol 165-168 Mannose 133 Sorbitol'92-96 Melting points from Z. Bubnik, P. Kadlec, D. Urban, M. Bruhns, Sugar Technologists Manual 8 ed. , Bartens, 1995, Berlin, except for arabinitol.

In a preferred embodiment of the invention the liquid system consists essentially of glucose and fructose dissolved in water. The fractionation of invert sugar provides an especially preferred technical embodiment of the invention. The glucose is removed from the liquid system and the glucose concentration in the crystal layer is higher than the glucose concentration in the melt.

Glucose has a melting point of about 146 C and fructose has a melting point of about 103- 105 oe. The weight ratio of fructose to glucose in the initial liquid system may be 1: 99-99 : 1, but the present invention enables the separation and purification also if the weight ratio is 30: 70 - 70 : 30. The weight ratio of fructose to glucose in the mother liquid after crystallization is 40: 60-60 : 40, preferably 45: 55-55 : 45.

The present invention also relates to a process wherein the sugar and/or sugar alcohol obtained from the process according to the invention is processed further by purification and/or separation processes. Such processes are e. g. crystallization, chromatographic processes, ion exchange, filtration and membrane filtration.

The separated and/or purified sugar and/or sugar alcohol may also be processed further to provide an edible or pharmaceutical product. The crystalline or liquid sugar and/or sugar alcohol or a mixture of those obtained from the process according to the invention may be incorporated in confectionery, bakery products, cereals, desserts, jams, beverages, soft drinks, chocolate, marzipan, table top sweeteners, chewing gum, ice cream, and dietetic products as

well as in health care, oral hygiene and pharmaceutical products. The solid product of the process may be milled or granulated and/or it may be used as such. The product of the process may also be mixed with other compounds in the conventional way. Usually the product is dissolved and crystallized or used as a solution.

The invention is now illustrated with a few examples.

Example I The purification of a mixture of glucose and fructose resembling invert sugar was performed in a layer crystallizer containing a covered jacketed beaker glass and a cooled tube and a thermometer therein as well as thermostats for controlling the temperature. Before the actual purification a mixture (with a saturation temperature of 30 C) containing water (70 g), glucose (95.1 g, melting point 146 oC (a-anhydride)) and fructose (77.8 g, mp. 103-105 C) was molten and tempered at 40 C for 8 h in a glass, double jacketed beaker (feed tank), which was temperature controlled by a thermostat.

For the crystallization procedure the beaker was set to 32 C in order to keep the melt in a molten condition. A cooled tube made of stainless steel was placed into the beaker to provide a solid layer for the crystallization. In order to initiate the crystallization of glucose on the cooled surface a primary layer was produced by dipping the tube into a glucose-water suspension and drying the primary layer by heating up the tube. The temperature differences between the cooled surface and liquid melt used in the crystallization were 15 C, 20 C, 25 C, 30 C and 35 C. The crystallization lasted for 72 h. Subsequent to the solid/liquid separation process, a draining of the residual melt, the glucose crystals were remolten and collected as product.

The crystallization led to the growth of compact, stable crystal layers of glucose. The growth rate of the layer was about 1. 6 x 10. 9 m/s. The concentration of glucose in the crystal layer was 75 to 82 % on DS. The concentration of glucose in the residual melt was about 45 to 50 % on DS.

Example 2 The crystallization was carried out in the same way as in Example 1, except for the primary layer which was produced by dipping the tube into a glucose-water suspension and adhering

glucose crystals additionally. The temperature differences between surface and melt were 20 C, 25 C, 30 C, 35 C, 40 C and 50 C.

The crystallization led to the growth of soft crystal layers in the case of growth rates higher than about 3 x 10-9 mls. The concentration of glucose in the crystal layer was 71 to 84 % on DS. The concentration of glucose in the residual melt was about 45 to 50 % on DS. The optimum temperature difference was 35 C in respect of the degree of separation.

Example 3 The crystallization was carried out as in Example 1, except for the primary layer which was produced by dipping the tube into a glucose-water suspension, then drying and roughening the primary layer by grinding. The temperature differences used were 10 C, 15 C, 20 C and 25 C.

The crystallization led to the growth of compact, stable but rough crystal structures with growth rates at about 2. 5 x 10. 9 mls. The concentration of glucose in the crystal layer was 70 to 82 % on DS. The optimum temperature difference was 20 C in respect of the degree of separation.

Example 4 A mixture of mannitol (32.5 g, mp. 165-168 C) and sorbitol (32. 5 g, mp. 92-96 oc) in water (35.0 g) was molten and tempered at 80 C. The sugar alcohols were separated in a static crystallization mode using the equipment described in Example 1. The melt was held at a temperature of about 75 C and the cooled tube had a temperature of about 60 C. After 10 hours a layer of mannitol had accumulated on the cooled surface and was removed. The mannitol crystals were purified by sweating to provide a final mannitol purity of 95 %.

Example 5 A mixture of mannitol (14.0 g, mp. 165-168 C) and sorbitol (56.0 g, mp. 92-96 C) in water (30.0 g) was molten and tempered at 80 C. The sugar alcohols were separated in a static crystallization mode using the equipment described in Example 1. The melt was held at a temperature of about 68 C and the cooled tube had a temperature of about 40 C After 10 hours a layer of mannitol had accumulated on the cooled surface and was removed.

Example 6 A mixture of mannitol (50.0 g, mp. 165-168 C) and sorbitol (150.0 g, mp 92-96 C) in water (118.0 g) was molten and tempered at 80 C. The sugar alcohols were separated in a static crystallization mode using the equipment described in Example I. The primary layer was produced by dipping the tube into a mannitol suspension and adhering mannitol crystals additionally. The melt was held at a temperature of about 55 C and the cooled tube had temperatures of about 5, 10, 15,20, 25,30, 35 and 40 oC. The growth rate of the mannitol layer was 2 - 4. 5 X 10-8 mls. After 21 hours a layer of mannitol had accumulated on the cooled surface and was removed. The concentration of mannitol in the crystal layer was 57,54, 58,64, 78,78, 85 and 91 % on DS respectively. The concentration of mannitol in the residual melt was 22 to 20 %.

Another series of experiments with the same mannitol/sorbitol mixture was carried out without the primary layer. The melt was held at a temperature of about 55 C and cooled tube had temperatures of about 10, 15,25 and 30 C. The growth rate of the mannitol layer was 2-4. 5 x 10-8 m/s. After 21 hours a layer of mannitol had accumulated on the cooled surface and was removed. The concentration of mannitol in the crystal layer was 53,61, 77 and 86 % on DS respectively.

Example 7

A mixture of maltitol (170. 0 g, mp. 146-147 C) and sorbitol (30. 0 g, mp. 92-96 C) in water (80. 0 g) was molten and tempered at 85 C. The sugar alcohols were separated in a static crystallization mode using the equipment described in Example I. The primary layer was produced by dipping the tube into a maltitol suspension and adhering maltitol crystals additionally. The melt was held at a temperature of about 80 C and the cooled tube had temperatures of about 5,10, 15,20, 25 and 30 C. The growth rate of the maltitol layer was 7- 10x 10-9 m/s. After 99 to 117.5 hours a layer of maltitol had accumulated on the cooled surface and was removed. The concentration of maltitol in the crystal layer was > 99.8, 99, > 99.8, 98.5, > 99.8 and 99.1 % on DS respectively. The concentration of maltitol in the residual melt was 83 %.

The present invention has been illustrated in detail by the above crystallization processes, and especially by the separation of glucose from a mixture of glucose and fructose. It is evident to those skilled in the art that similar suitable combinations of sugars and sugar alcohols exist, as mentioned in the specification, wherein at least one component of a mixture will crystallize more readily than the other.

Claims

1. A process for the crystallization of at least one component of a multi-component system, characterized in that a liquid system containing at least two components selected from sugar and sugar alcohol compounds is subjected to a melt layer crystallization to cause crystallization of at least one of said sugar or sugar alcohol components on a cooled surface, and the resulting crystals are recovered from the remaining liquid system.

2. The process according to claim 1, wherein said system contains a further component which is an aqueous or an organic solvent.

3. The process according to claim 1, wherein said liquid system has a temperature which is just sufficient for retaining said liquid system in a liquid form and said surface comprises a crystallization surface having a temperature which is lower than the temperature of said liquid system.

4. The process according to claim 3, wherein one of said sugar and/or sugar alcohol components is to be purified and is removed from said liquid system in the form of crystals on said surface, said crystals having a purity of said component which is higher than the purity of said component in said liquid system.

5. The process according to claim 3, wherein one of said sugar and/or sugar alcohol components is to be purified and is retained in liquid form and the other sugar and/or sugar alcohol component is removed from said liquid system in the form of crystals on said surface, said crystals having a concentration of said removed component which is higher than the concentration of the removed component in said liquid system.

6. The process according to claim 1, wherein crystallization on said surface is improved by preapplication thereon of a primary layer of seed crystals of said sugar and/or sugar alcohol component which is to be removed.

7. The process according to claim 1, wherein said melt layer crystallization is performed in a dynamic or a static mode.

8. The process according to claim 1, wherein said melt layer crystallization is repeated at least once and preferably several times for improving the separation, purification and/or yield.

9. The process according to claim 1, wherein the crystals on said surface are purified by sweating.

10. The process according to claim 1, wherein said sugars and/or sugar alcohols arc selected from sucrose, ketoses, aldoses and alditols.

11. The process according to claim 1, wherein said sugars and/or sugar alcohols are

hexose/hexose, pentose/pentose, hexose/pentose, hexitollhexitol, pentitol/pentitol, hexitol/ pentitol, hexose/hexitol, hexose/pentitol, pentose/hexitol, pentose/pentitol, hexose/hexose/ pentose, hexose/pentose/pentose.

12. The process according to claim 1, wherein said at least two sugar and/or sugar alcohol components are selected from the following ; glucose and fructose ; glucose and sorbitol; glucose and xylose; sorbitol and maltitol ; sorbitol and mannitol ; mannose and mannitol ; xylitol and xylose; maltitol and maltotriol, I-O-a-D-glucopyranosyl-D-mannitol (I, l-GPM) and 6-0-a-D- glucopyranosyI-D-sorbitoI (1, 6-GPS); arabinose and mannose; arabinitol and xylulose ; arabinitol and xylitol; arabinose, mannose and xylose; glucose, mannose and xylose ; and glucose, xylose and arabinose.

13. The process according to claim 7, wherein said sugar and/or sugar alcohol components are dissolved in water.

14. The process according to claim !, wherein said liquid system consists essentially of glucose and fructose dissolved in water and wherein the glucose concentration in said crystal layer is higher than the glucose concentration in said solution.

15. The process according to claim 14, wherein the weight ratio of fructose to glucose in the initial liquid system is 1: 99-99 : 1, preferably 30 : 70-70 : 30.

16. The process according to claim 14, wherein the weight ratio of fructose to glucose in the

mother liquid after crystallization is 40: 60-60 : 40, preferably 45: 55-55 : 45.

17. The process according to claim I wherein the resulting purified or separated sugar and/or c sugar alcohol is preceded by and/or followed by another purification and/or separation process

18. The process according to claim 17 wherein said other process comprises a crystallization, chromatographic separation, ion exchange, filtration and/or membrane filtration process.

19. The process according to claim 1, wherein the resulting separated and/or purified sugar and/or sugar alcohol is processed further to provide an edible, health care, oral hygiene and/or pharmaceutical product.

20. The process according to claim 19 wherein said crystalline or liquid sugar and/or sugar alcohol is incorporated in a confectionery or bakery product, a cereal, dessert, jam, beverage, soft drink, chocolate, marzipan, table top sweetener, chewing gum, ice cream or dietetic product or in a pharmaceutical product.

21. A process for crystallizing at least one component from a multi-component system substantially as described herein with reference to any of the Examples.