US3928062A

US3928062A - Method for obtaining anhydrous fructose crystals

Info

Publication number: US3928062A
Application number: US435525A
Authority: US
Inventors: Toshio Yamauchi
Original assignee: Dai Ichi Kogyo Seiyaku Co Ltd
Current assignee: DKS Co Ltd
Priority date: 1973-02-12
Filing date: 1974-01-22
Publication date: 1975-12-23
Anticipated expiration: 1992-12-23
Also published as: GB1407785A; DE2406663B2; AU6545674A; DE2406663A1; FR2217421B1; JPS49102853A; JPS5239901B2; FR2217421A1

Abstract

Anhydrous fructose crystals are obtained from a supersaturated fructose solution in water by seeding anhydrous crystals into the solution, concentrating and/or cooling the solution while maintaining the sugar concentration and temperature in the liquid phase within a certain range, and then recovering the anhydrous fructose crystals from the massecuite.

Description

United States Patent Yamauchi Dec. 23, 1975 METHOD FOR OBTAINING ANHYDROUS 2.588.449 3/1952 Young 127/30 FRU CRYSTALS 3.513.023 5/1970 Kusch 127/58 3.607.392 9/1971 Lauer.... 127/58 X Inventor: Toshlo Yamauchi, Kyoto, Japan 3,684.574 8/1972 Km l27/46 A [73] Assignec. Dai ichi gy Seiyaku Ltd, 3.883.365 5/1975 Forsberg 127/60 Kyoto, Japan [22] Filed: Jan. 22, [974 Primary Examiner-Morris O. Wolk Assistant Examiner-Sidney Marantz [2]] Appl' 435525 Attorney, Agent, or Firm-James C. Haight [30] Foreign Application Priority Data Feb. 12. 1973 Japan 48-l77l8 57 ABSTRACT US- Cl. Anhydrous fructose crysals are btained from a su- 2 127/62 persaturated fructose solution in water by seeding anlnthydrous crystals ino the solution concentrating and. [58] Field of l27/30, 46 R, 46 A, 58. [or cooling the solution while maintaining h sugar 127/60 62 concentration and temperature in the liquid phase within a certain range, and then recovering the anhy- [56] Rdmnces Cmd drous fructose crystals from the massecuite.

UNITED STATES PATENTS 2.007.971 7/1935 Jackson l27/58 x Claims, 2 Drawing Figures 6 7 8 H g: 94 I a I E 90 I g5 k F g 86 f T 4 A" A I 82 e c )0 .10 JJ' 10 I! 6f li-mpcmfurr (0 US. Patent Dec. 23, 1975 Sheet 2 of 2 3,928,062

FIG. 2

- QQ F QME xfiva Emperafu re (6) METHOD FOR OBTAINING ANHYDROUS FRUCTOSE CRYSTALS This invention relates to a method for obtaining anhydrous fructose crystals from an aqueous solution containing fructose. More particularly, it relates to the method whereby anhydrous fructose crystals are obtained economically and in a high yield from an aqueous solution containing fructose.

It has been well known that crystalline fructose occurs in the forms of anhydrous fructose, the hemihydrate or the dihydrate. Since the hemihydrate or dihydrate generally crystallizes out more easily than anhydrous fructose, it is difficult to obtain crystalline anhydrous fructose from the aqueous solution containing fructose by crystallization. This can be explained by the fact that the metastable range of a supersaturated solution of fructose in which the growth of existing crystals can take place without the formation of additional crystal nuclei is relatively narrow and the range lies close to the supersaturating point of the hemihydrate. This therefore makes it difficult to crystallize anhydrous crystalline fructose out from the aqueous solution. The formation of the hemihydrate or dihydrate crystals makes the massecuite of the crystallizing process pasty so that further growth of crystals is greatly retarded.

The dihydrate and the anhydrous fructose melt at 21.3C and l02-l04C respectively, while the hemihydrate does not have any definite melting point. Thus, it is apparent that the anhydrous crystals are more advantageous than the hemihydrate or the dihydrate for various purposes because the dihydrate will melt even during transportation, packaging, or other handling processes thereof, especially in the summer.

Heretofore, it has been already known that anhydrous fructose crystals may be obtained by crystallizing from an aqueous methanolic or ethanolic solution of fructose. However, the use of such organic solvents is undesirable not only from an economical point of view, but the resulting crystals and the mother liquor contain the solvent used which must be completely removed prior to the consumption. An object of the present invention is to provide a method for obtaining anhydrous fructose crystals from an aqueous solution containing fructose.

Another object is to provide a method for crystallization of anhydrous fructose in which the crystals are separated out from the aqueous solution thereof without using any organic solvent. Further objects will be apparent from the description which follows:

According to the present invention, it has now been found that anhydrous fructose crystals can be obtained from aqueous solutions of fructose in high yields without forming the hemi-or dihydrate crystals if the crystallization is carried out within a certain range of fructose concentration and temperature.

It has been also found that this range lies within the supersaturation area a below the point at which the hemihydrate begins to crystallize out. If a supersaturated solution falling within such range is seeded with crystals of anhydrous fructose and then the equilibrium between the liquid-solid phases of the system is shifted to a direction in which the degree of supersaturation of the liquid phase is enhanced, crystallization of anhydrous fructose may be achieved very satisfactorily.

The present invention will be better understood from the following detailed description taken in conjunction with the accompanying drawing.

In the drawing, FIG. I is a graph showing the range of fructose concentration in the liquid phase and the temperature thereof within which the crystallization of anhydrous fructose crystals takes place in accordance with the present invention.

FIG. 2 is a graph which typically shows the change of the concentration-temperature relationship in a few embodiments of the present invention.

In accordance with the present invention, the concentration and the temperature of the starting fructose solution in water are adjusted to a point within the range defined by points A, B, C and D in FIG. 1. The solution is seeded with a small amount of anhydrous fructose crystals and then concentrated and/or cooled under moderate stirring within said range so that crystallization of anhydrous fructose takes place. This crystallization step may be carried out in several manners as shown in FIG. 2. The starting point is shown at a. When the solution is concentrated under reduced pressure while maintaining substantially constant temperature, the anhydrous fructose crystallizes out as the concentration rises to a point at b. In like manner, the crystallization may take place as the temperature lowers to a point at 0 while maintaining substantially constant concentration by cooling and concentrating the solution simultaneously, or as both the temperature and the concentration lower from a point at e to point f by simultaneous cooling of the solution while concentrating under reduced pressure at a lower speed of evaporation than in the above case. Cooling under atmospheric pressure without concentrating may also be employed. In this case the fructose concentration and the temperature lower from point a to point g. The foregoing procedures may be employed alone or in combination thereof depending upon the situation to give a satisfactory results.

In FIG. I, the range within which the crystallization of the present invention must be carried out is defined by points A, B, C and D. As shown in the figure, A, B, C and D locate at temperatures of 25C, 60C, 25C and 60C, and at concentrations of 83%, 95.5%, 8 l% and 89.7% respectively. Preferably, the crystallization is carried out within the range defined by points G, H, C and D wherein G and H locate at temperatures of 25C and 60C, and at concentrations 82.6% and 94% respectively.

Now referring to FIG. 2, details of the crystallizing step of the present invention are given with respect to the following four typical embodiments thereof:

I. Crystallization by concentrating under reduced pressure at a constant temperature (a b) This procedure is similar to the conventional crystallizing method for sucrose or glucose. The starting fructose solution at a whose fructose concentration and temperature are c and 1,, respectively is concentrated to b at which the fructose concentration rises to 0,, while maintaining the initial temperature r,,. The concentration of fructose in the resulting massecuite is maintained within the metastable range by removing appropriate amounts of water from the system. During the procedure, rapid concentration should be avoided as it causes formation of pseudocrystals.

2. Crystallization by cooling and concentrating at constant level of fructose (a c).

The starting fructose solution at a is gradually cooled from temperature I to I, while a sufficient amount of water is evaporated under reduced pressure from the solution to maintain a constant level of the initial fructose concentration c,,. The rate of temperature-fall is preferably such that the increase of crystallization speed becomes linear to the operation time and is between 0.2 to C, more preferably 03C per hour. The rate above 15C per hour will cause the formation of pseudocrystals and is, therefore, undesirable.

3. Crystallization by cooling first in combination with concentrating at constant level of fructose then cooling alone (d e f).

This is a modification of the above procedure (2), and the initial stage d e is carried outjust as same as the above procedure (2). When the solution reaches point e, the apparent viscosity of the massecuite increases remarkably so that the speed of further evaporation becomes too slow to maintain the equilibrium between the amount of evaporating water and the fall of the fructose level in the massecuite caused by the growth of crystals. At this point, the procedure enters the second stage wherein cooling alone is continued at the same rate of temperature-fall (02 to lC/hour) under reduced pressure. During this stage (e f), the speed of crystal growth becomes slower than in the first stage (d e). However the crystallization of this stage may well be employed on a commercial scale.

4. Crystallization by cooling alone (a g).

This procedure may be conducted by simply cooling the solution under atmospheric pressure.

The selection of the above-described procedures l to (4) depends in part on the type of crystallization apparatus and the' instrumentation thereof, but substantially the same yield can be achieved using any one of them. The procedures 1 to (3) above are different from the procedure (4) in that the fructose level in the mother liquor from which the resulting crystals have been separated is kept to a higher or the same, or slightly lower levels than that of the starting solution. This enables the use of each mother liquor for recovering a second or further crops as such. In contrast, the fructose level in the mother liquor resulting from procedure (4) necessarily decreases proportionally to the yield of crystals. Therefore, the mother liquor must be concentrated to the starting level at a certain point for obtaining a second or further crops. Thus, the former three procedures are more advantageous than the latter.

The starting fructose solutions which may be employed in practising the present invention include those obtained from inversion of sucrose or from isomerization of glucose. When these starting fructose solutions have a sugar concentration and temperature falling within the range shown in FIG. 1, the solutions may be subjected to the crystallization of the present invention as such. Otherwise the concentration and the temperature of the solution must be brought into said range by conventional means such concentration, dilution, heating or cooling. If the fructose proportion in the total sugar content thereof is less than 88%, it is necessary to increase the fructose proportion to greater than 88%. This can be accomplished in a conventional manner by removing other sugars from the mixture.

In a specific embodiment of the present invention, the solution preferably contains from 83 to 95.5% (dry basis) of total sugar comprising 88 to 99% of fructose. Though the higher concentration of sugar is generally more preferable as the starting solution for crystallization, concentrations greater than 90%, particularly 92 to 95% make the evaporation speed decrease greatly because of their high viscosity. Therefore, a higher evaporation temperature such as to C and a longer period of time are required for the concentration thereof. These severer conditions sometimes cause oxidation or decomposition of fructose and result in coloration or a decrease in purity of the final product. For such reasons, relatively low concentrations such as less than 90% are preferable for the present invention. Adjustment of pH, for example, pH at 3.9 5.7 by the addition of food-grade hydrochloric acid is also effective to prevent deterioration.

If a specific concentration of sugar, for example 90%, is given, suitable conditions and procedures for the crystallization may be sought by making reference to FIG. 1. First, it will be easily understood that the initial temperature must be from 45 to 60C. If 60C has been chosen as the initial temperature, then the abovementioned procedure (I) wherein the temperature of 60C is maintained, or procedure (2) wherein the 90% of sugar concentration is maintained can be taken into consideration. Similarly, procedure (3) can be also be taken into consideration when the starting solution has the sugar concentration of 90% and the initial temperature of 55C. In this case, the solution is concentrated and cooled while maintaining the constant concentration of 90% in the first stage, then is cooled without concentration. It must be noted that the initial temperature close to the line A B of FIG. I is not preferable because the system will easily depart from the critical range which results in the formation of pseudocrystals or hemihydrate. Thus a temperature below 50C is not preferable in the above case and the starting solution is subjected to the crystallization step. For example, the solution having a sugar concentration of 90% and an initial temperature of 55C is charged in a vacuum crystallization vessel while maintaining the temperature at 55ilC and the pH at 4.5i0.3. The crystallization vessel is installed with heating and cooling means, and a rotary stirring-wing therein. The stirring is controlled to such extent that it is not sufficient to cause any crushing or growing crystals or generation of heat.

The solution is allowed to standfor a certain period of time, for example, for 20 to 30 minutes to stabilize the system, and then seeded with l to 4% by weight of seed crystals based on the weight of the charged solution. The seed crystals preferably have a particle size of I00 I50 mesh (Tyler, 0.06 0.1 mm). The addition of seed crystals may be achieved using a form of massecuite which was previously prepared by suspending the crystals in the fructose solution. The resulting solution is gradually cooled and concentrated under reduced pressure in accordance with the aforementioned procedure (2). Addition of seed crystals often brings fine air-bubbles into the solution. These bubbles retard the growth of crystals and heat-transfer between the vessel and the solution. Removal of these bubbles may easily be accomplished by conventional means such as evacuation. For example, the crystallization vessel is evacuated to 80 to 60mm Hg, the bubbles are removed for to minutes from the massecuite as the result ing foams disappear on the surface of the solution. The degree of evacuation should be controlled to such extent that the foams do not overflow by watching the level from the viewing window. The significance of crystallization by concentrating under reduced pressure resides in that it prevents a decrease of sugar concentration resulting from the crystallization, maintains crystallization in the metastable supersaturation range and increases the speed and the yield of the crystallization.

The rate of temperature-fall is 1 to 4 hours/C, pref erably 2.5 to 3 hours/C. The preferable degree of vacuum is to 60mm Hg, although it varies with the temperature and fructose concentration.

Thus, the crystals begin to grow without forming pseudo-crystals when the temperature begins to fall. The speed of growth is inversely proportional to the speed of temperature-fall and is directly proportional to the speed of concentration. Therefore the amount of 20 crystals formed may increase linearly to the time.

As the crystallization proceeds, the massecuite becomes very viscous. When the yield of crystals reaches higher than 50%. it is almost a mud and transfer or separation of massecuite becomes difficult. In this case the mother syrup of the second crop or fresh fructose solution may be added to reduce the viscosity and to ease centrifugation. The syrup is added at the final stage of the crystallization step after adjusting its sugar concentration to the same or a slightly higher level than the massecuite at the same temperature. 10 to parts by weight of the syrup per 100 parts by weight of massecuite are suitable for this purpose. Then the massecuite is taken from the crystallization vessel and centrifuged. The centrifuge is provided with ajacket and is warmed at a temperature of 30 to 50C. This makes the separation of syrup easier, especially in winter. The separation may easily be accomplished by a conventional means. The resulting crystals are washed with small amounts of warm water (30 45C) 2 to 3 times to remove syrup remaining on the crystal surfaces. 5 to 10 parts of water are preferable to wash 100 parts of crystals. The crystals thus prepared are then dried preferably at a temperature of 50 to 60C under reduced pressure below 100mm Hg whereby free-flowing anhydrous fructose crystals are obtained. Yield of the first crop of crystals ranges from 40 to 50 parts per 100 parts by weight of fructose in the starting solution. The

crystals melt at 101 104C and have an optical purity of 100%.

Alternatively, the aforementioned procedure (4) (a g) may be applied to the same starting solution. As can be seen from FIG. 1, a temperature between 45C and C is preferable for the fructose solution. Therefore, the temperature and pH are adjusted at 58C and at 3.9 to 5.7 respectively. The solution is seeded with l to 4% of anhydrous fructose crystals mesh/Tyler). After seeding, the solution is stirred slowly for 10 to 20 minutes to disperse seeds uniformly. The temperature is reduced by cooling at a rate of 1 to 02C per hour. As the crystallization proceeds, the massecuite becomes viscous as well. Crystallization is stopped when the yield of crystals reaches 45 to 50% for 20 to 25 hours at which point the temperature has fallen to 30 to 35C. Separation of the resulting massecuite is carried out by centrifuging and the resulting crystals are washed with water and dried as the aforementioned manner.

From the foregoing description, it will be easily understood that other procedures can be utilized to crystallize anhydrous fructose from fructose solutions within the range in FIG. 1. Without further elaboration,

it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

EXAMPLES Two crystallization vessels of each 1000 ml and 2000 ml capacity were used. They have a jacket for cooling or warming and a stirring means (rotary wing). They are tolerable to vacuum.

The following tables show details of crystallization conditions and the results of each example. As shown in the tables, crystallization in Examples 1 to 5 was carried out by cooling and concentrating simultaneously (procedure 2 or 3; a c or d e j). Examples 6 to 8 illustrate the crystallization by concentrating at a constant temperature (procedure 1, a b), and Exam ple 9 illustrates the crystallization by cooling alone (procedure 4, a g). Table 2 shows changes of the concentration and/or temperature during the operation in detail.

Table l Ex.l Ex.2 Ex Ex.4 Ex.5 Ex.6 Ex.7 Ex.8 Ex.9

Purity of fructose.& by weight 98.8 98.8 92.6 98.8 98.8 98.8 94.8 98.8 94.8 Sugar concentrationF/v by weight. 88.5 89.9 88.8 86.9 90.0 87.0 83.8 87.9 91.5 dry basis Charged quantity. g 778 1000 1493 1329 1600 1017 1006 1000 1445 Amount of seed crystals'flr 3.46 3.80 3.4 1.7 1.70 1.7 1.7 1.7 1.7 lnitial tcmpcrature.C 55 56 54 45 50 47 35 40 58 Final temperature,C 47 46.2 46.5 39 45 47 35 40 32 Rate of temperature-fa|l,C/hour 0.336 0.343 0.351 0.33 1.0 0.88 Operation time. hours 25 29.5 26 20 imposs- 25 23 imposs- 26 ible 8 ible 7 I Yield 01 crystals".% 46 48.3 49 64.4 57.2 45.5 56 Purity of crystalsfil 100 100.5 100.1 100 100 I00 I00 Melting point.C 102.6 101.5 103.3 104.1 101.7 103.7 101.7 Particle size. mm 0.15 0.17 0.18 0.23 0.2 0.18 02 Fructose content in the mother 1iquor.% 97.4 97.2 86.1 96.7 97.0 92.6 91.7

Table l-continued Ex.l Ex.2 Ex.3 Ex.4 Ex.5 Ex.6 Ex.7 Exit Ex.9 Type of stirring rotary rotary rotary rotary rotary rotary rotary rotary rotary Note assayed by optical rotation and rufracllon Table 2 Example I 2 3 4 5 Tlme Concn.7r Temp.C Concnft Temp.C Concn9l TempC Concn.% Tcmp.C Concnffit Temp.C

0 88.5 55.0 89.9 56.0 88.8 54.0 86.9 45.0 90.0 50.0 2 89.0 54.5 90.0 55.5 88.9 53.5 87.0 44.2 90.4 50.0 4 89.2 53.6 89.8 55.1 88.8 53.0 86.6 43.9 90.3 49.0 6 89.1 52.6 89.7 54.5 88.6 52.4 86.5 43.4 90.6 47.0 8 88.7 52.2 89.8 54.0 89.2 51.7 86.3 42.8 90.4 45.0 10 88.7 51.5 89.9 53.2 88.8 51.0 86.3 42.2 Discontinued 12 88.5 50.8 89.7 52.4 88.6 50.4 86.0 41.7 14 88.3 50.3 89.6 52.5 88.7 49.9 85.9 41.1 16 88.4 49.5 89.8 51.0 89.0 49.3 85.8 40.5 18 88.8 49.1 89.5 50.2 88.8 48.7 85.8 39.8 20 88.7 48.4 89.4 49.5 88.5 48.1 22 88.6 47.8 89.3 49.0 88.8 47.4 24 88.3 47.4 88.8 48.1 88.6 46.9 26 89.0 47.2 28 88.8 46.5 Finishing 88.2 47.0 88.9 46.2 88.7 46.5 85.8 39.0 point hours) (29 hours) (26 hours) (20 hours) Example 6 7 B 9 Time Concnfil Temp.C Concnfif Temp.C Concn.% Temp.C Concn.% Temp.C

0 87.0 47.0 83.8 35.0 87.9 40.0 91.5 58.0 2 87.2 46.9 85.3 34.8 88.5 39.9 91.4 56.4 4 87.8 46.8 86.2 34.9 89.0 39.9 90.8 54.0 6 88.2 47.0 86.1 34.9 89.8 40.0 90.1 52.4 8 88.3 47.1 85.9 35.0 89.7 40.0 89.0 50.8 10 88.4 47.0 85.3 35.0 (7 hours) 88.5 49.9 12 88.6 47.2 85.0 35.1 Discontinued 89.6 49.3 14 89.1 47.2 85.4 35.1 87.3 48.8 16 88.4 47.2 85.6 35.1 86.7 48.5 18 88.1 47.1 84.8 35.2 86.0 47.7 20 88.3 47.1 84.8 35.1 85.1 45.0 22 88.3 47.1 84.9 35.0 84.4 41.6 24 88.4 47.0 84.1 37.0 26 Finishing 87.8 47.0 85.0 35.0 83.8 32.0 point (25 hours) (24 hours) (27 hours) The starting fructose solutions used in Examples 1, 2, 4 to 6 and 8 were prepared from fructose made by inversion of sucrose. Examples 7 and 9 illustrate the crystallization of third crop using mother liquor of a Example 1 from which the first crop (Example I) and the second crop have been separated.

The starting solution of Example 3 was prepared by adding a sufficient amount of glucose to the fructose used in Example I to make a 92.6% fructose content. This fructose content corresponds to that of the mother liquor obtained in Example 7. This fact suggests that the mother liquor may be used repeatedly for the crystallization of further crops in the same manner as the first crop without any additional treatment.

Examples 5 and 8 illustrate examples wherein the crystallization took place in part outside the range of FIG. 1. In these examples, a large amount of pseudocrystals appeared within 3 to 4 hours and the massecuite became too viscous to continue the crystallizatron.

As can be seen from the foregoing examples, crystallization of the anhydrous fructose can satisfactorily be accomplished only when the crystallization takes place within the range defined by A, B, C and D. preferably by G, H, C and D, in FIG. 1. The range above line A B in FIG. 1 is believed to be that in which the crystallization of fructose hemihydrate will take place. The range defined A, B, C and D is that in which the seed crystals can grow without formation of additional nuclei. In FIG. 1, line E F is the extended saturation curve of fructose in water reported by R. F. Jackson, J. Phys. Chem. 56, 1092-1096 1952.

It has been also found that the yield and the time required are not influenced by the purity of starting fructose, size or shape of seed crystals, or the quantity thereof, but mainly depend on the evaporation speed of water from the massecuite. Furthermore, it has been found that the crystals grow almost linearly to the evaporation speed. Therefore, the crystallization vessel used for earring out the present invention is preferably installed with means to control the sugar concentration of the massecuite and the degree of vacuum during the operation, and has a good heat-transfer coefficient.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

What is claimed is:

l. A process for obtaining anhydrous fructose crystals without the formation of fructose hemihydrate or fructose dihydratc crystals from an aqueous solution of fructose. which comprises:

a. seeding anhydrous fructose crystals into a metastable supersaturated solution of fructose in water having an initial sugar concentration of less than 92% (dry basis) of total sugar comprising 88-99% fructose and a temperature of 2560 C. located at a point within the range defined by points G, H, C and D in FIG. 1 of the accompanying Drawing;

h. simultaneously crystallizing anhydrous fructose from said solution and concentrating said solution by evaporation under reduced pressure at a rate sufficient to shift the equilibrium between the solid and liquid phases of the resultant system in a direc tion which increases the degree of supersaturation of the liquid phase within said range to continuously crystallize anhydrous fructose from said metastable supersaturated solution without the formation of hemihydrate or dihydrate crystals; and recovering anhydrous fructose crystals from the resultant mother liquor having a fructose concentration within said range.

2. A process according to claim I, wherein the concentrating is carried out at a substantially constant temperature.

3. A process according to claim 1, wherein said fructose solution is the mother liquor from a previous crystallization cycle.

4. A process according to claim 1, further comprising adding 10-30 parts by weight of a fresh fructose solution or the mother liquor from a previous crystallization cycle to I00 parts by weight of the massecuite at the final stage of crystallization before separation of said crystals.

5. A process according to claim I, further comprising centrifuging the resultant massecuite at 3050 C., washing the resultant crystals with warm water and drying the washed crystals at 5060 C. under reduced pressure.

6. A process according to claim 1., wherein the concentrating is carried out with gradual cooling at the rate of 0.2-1 .5 C. per hour such that the resultant increase in crystallization speed becomes a linear function of the operation time.

7. A process according to claim 6, wherein said cooling is at the rate of about 0.3 C. per hour.

8. A process according to claim I, wherein said fructose solution has a sugar concentration of less than by weight and a pH of 3.9-5.7.

9. A process according to claim 8, wherein said fructose solution is seeded with l-4% by weight of seed crystals having a particle size of lOO-SOO mesh (Tyler) and then evacuated to remove air bubbles therefrom.

10. A process according to claim 9, wherein the concentrating is carried out at a pressure of l060mm Hg.

Claims

1. A PROCESS FOR OBTAINING ANHYDROUS FRUCTOSE CRYSTALS WITHOUT THE FORMATION OF FRUCTOSE HEMIHYDRATE OR FRUCTOSE DIHYDRATE CRYSTALS FROM AN AQUEOUS SOLUTION OF FRUTOSE, WHICH COMPRISES: A. SEEDING ANHYDROUS FRUCTOSE CRYSTALS INOT A METASTABLE SUPERSATURATED SOLUTION OF FRUCTOSE IN WATER HAVING AN INITIAL SUGAR CONCENTRATION OF LESS THAN 92% (DRY BASIS) OF TOTAL SUGAR COMPRISING 88-99% FRUCTOSE AND A TEMPERATURE OF 25*-60*C. LOCATED AT A POINT WITHIN THE RANGE DEFINED BY POINTS G, H, C AND D IN FIG. 1 OF THE ACCOMPANYING DRAWING; B. SIMULTANEOUSLY CRYSTALLIZING ANHYDROUS FRUCTOSE FROM SAID SOLUTION AND CONCENTRATING SAID SOLUTION BY EVAPORATION UNDER REDUCED PRESSURE AT A RATE SUFFICIENT TO SHIFT THE EQUILIBRIUM BETWEEN THE SOLID AND LIQUID PHASES OF THE RESULTANT SYSTEM IN A DIRECTION WHICH INCREASES THE DEGREE OF SUPERSATURATION OF THE LIQUID PHASE WIHTIN SAID RANGE TO CONTINUOUSLY CRYSTALLIZE ANHYDROUS FRUCTOSE FROM SAID METASTABLE SUPERSATURATED SOLUTION WITHOUT THE FORMATION OF HEMIHYDRATE OR DIHYDRATE CRYSTALS; AND C. RECOVERING ANHYDROUS FRUCTOSE CRYSTALS FROM THE RESULTANT MOTHER LIQUOR HAVING A FRUCTOSE CONCENTRATION WITHIN SAID RANGE.

2. A process according to claim 1, wherein the concentrating is carried out at a substantially constant temperature.

4. A process according to claim 1, further comprising adding 10-30 parts by weight of a fresh fructose solution or the mother liquor from a previous crystallization cycle to 100 parts by weight of the massecuite at the final stage of crystallization before separation of said crystals.

5. A process according to claim 1, further comprising centrifuging the resultant massecuite at 30*-50* C., washing the resultant crystals with warm water and drying the washed crystals at 50*-60* C. under reduced pressure.

6. A process according to claim 1, wherein the concentrating is carried out with gradual cooling at the rate of 0.2*-1.5* C. per hour such that the resultant increase in crystallization speed becomes a linear function of the operation time.

7. A process according to claim 6, wherein said cooling is at the rate of about 0.3* C. per hour.

8. A process according to claim 1, wherein said fructose solution has a sugar concentration of less than 90% by weight and a pH of 3.9-5.7.

9. A process according to claim 8, wherein said fructose solution is seeded with 1-4% by weight of seed crystals having a particle size of 100-500 mesh (Tyler) and then evacuated to remove air bubbles therefrom.

10. A process according to claim 9, wherein the concentrating is carried out at a pressure of 10-60mm Hg.