JPS5838160B2 - Method for improving fructose crystal yield by pH adjustment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for improving fructose crystal yield by adjusting the pH of an aqueous fructose solution containing glucose as an impurity, comprising: a) an aqueous fructose solution containing glucose as an impurity and at least about 90% dry matter; wherein the fructose content of the dry material is at least about 90% by weight; b) adjusting the pH of the solution to within the range of 4.5 to 5.5; d) adding fructose seed crystals to said solution; e) causing the resulting mass to be supersaturated with respect to fructose; and new fructose crystals substantially form. f) lowering the temperature of the mass at a controlled rate to increase the crystal size of the seed crystals without causing any The present invention relates to a method for improving the yield of fructose crystals by adjusting the pH of a fructose solution, which comprises a step of separating fructose crystals from the above-mentioned aggregate when the fructose crystals are present.

The large crystals thus obtained are easily separated from the solution by centrifugation.

The crystals are free-flowing and easily handled.

The fructose obtained by the process of the invention is of very homogeneous crystal size and is extremely pure.

Crystallizing fructose from aqueous solutions presents many technical difficulties because of the very high solubility of fructose in water.

In addition, conventional crystallization methods using evaporation techniques are not a problem due to the low thermal stability of fructose.

As the demand for fructose has increased tremendously in recent years,
The ability to produce high-purity, large-crystal, and therefore mechanically easy-to-process fructose in an economically advantageous manner by a simple crystallization process from aqueous solutions represents a significant advance in this field.

All these benefits are obtained by the method of the present invention.

According to the invention, fructose is crystallized from an aqueous solution by adding to the aqueous solution a small amount of fructose crystals of as uniform size as possible as a crystal component and growing the size of the seed crystals.

Keeping the new crystal shape or the distance between seed crystals appropriately short,
and can be prevented by accurately controlling the temperature during complete crystallization.

The distance between the seeds is determined by the ratio of the seed crystal volume to the total solution volume.

The volume of the solution is increased continuously or stepwise as the crystallization operation progresses in order to maintain the desired distance between the seed crystals.

The present invention relates to the crystallization of fructose from aqueous solutions to obtain crystals with an average crystal size of 200 to 600 microns.

In particular, the invention relates to the crystallization of fructose from an aqueous solution with a dry matter content of about 90 wt.

the dry matter content is in the range of 90 to 94% by weight;
The aqueous fructose solution with a purity of fructose in the range of 90 to 99% by weight is manufactured by Asco Di.
Asko J, Melaja US Patent No. 3
．． It is obtained by separating fructose from glucose by the method disclosed in No. 692, No. 582.

Until now, fructose has been crystallized from methanol.

On the other hand, when fructose is crystallized from water, the difficulty is due to the high solubility of fructose and its low thermal stability.

The viscosity of concentrated aqueous solutions of fructose is very high, and the viscosity cannot be reduced by increasing temperature because fructose is unstable at the high temperatures required to substantially reduce the viscosity.

Under these circumstances, very small crystals are produced that are uneconomical to separate from solution.

Furthermore, drying large quantities of small crystals is difficult.

Because of all the above-mentioned difficulties, experts in this field
Crystallization of fructose from aqueous solution is practically impossible on commercially attractive criteria.

Due to the poor thermal stability of fructose, the usual crystallization by evaporation is out of the question, and the crystallization is carried out, according to the method of the invention, by lowering the temperature of the solution and possibly also by evaporation.

One object of the present invention is to crystallize fructose from an aqueous solution as crystals of a size that are easily separated from the solution by centrifugation.

Another object of the present invention is to successfully crystallize fructose as crystals of sufficiently large size that they are free-flowing, in which case their handling, such as weighing and packaging, is simplified. That's true.

Another object of the invention is to crystallize fructose which is very uniform in crystal size and also very pure.

Fructose crystallized from methanol has hitherto been mainly used by the pharmaceutical industry, which has been satisfied with very small crystals with dimensions clearly below 0.15 μm.

The large crystalline fructose crystallized by the method of the invention is in fact a new product.

Since the demand for fructose has increased significantly in recent years, it was desirable to produce highly pure, large crystalline, and therefore mechanically easy to handle fructose in an economically advantageous manner by a simple crystallization method from aqueous solution. The ability to do so represents a significant advance in this field.

Another advantage compared to crystallization from methanol is that
The resulting product is completely free of methanol, a toxic substance.

The above objects of the present invention are achieved by the method of the present invention by first providing an aqueous fructose solution having a dry matter content of greater than about 90 wt. Ru.

The temperature of the fructose solution in this first stage is the temperature at which the solution is saturated with fructose, for example about 58°C to 65°C.

Fructose is then crystallized from this aqueous solution by adding to the solution a small amount of fructose crystals of as uniform a size as possible as a crystal component, and growing the size of these seed crystals while at the same time preventing the formation of new crystals. .

This keeps the spacing between the seeds reasonably short and the temperature during complete crystallization between 1.1 and 1.1 for fructose.
This is achieved by precise control to maintain an optimal supersaturation in the range of 2.

It was established that as the average distance between crystals increases, the risk of new crystal formation also increases.

Similarly, as the degree of supersaturation increases above the above-mentioned optimum range, the risk of new crystal formation increases.

Continuously or stepwise increasing the volume of the solution while proceeding with crystallization is another essential feature of the method of the invention.

If the crystallization is carried out in several steps, ie as two or more consecutive steps, the rate of formation of small crystals is substantially reduced.

When crystallization is carried out in two or more steps,
Each step may be carried out in a separate crystallizer, in which case the volume of the crystallizer increases with each step due to the increased volume of solution.

Alternatively, the crystallization in several steps may be carried out in the same crystallizer whose volume is equal to the solution volume of the last step.

Based on the sugar aggregate, addition of 2 to 4 volumes of a low molecular weight organic solvent, such as methanol, ethanol or isopropanol, reduces the viscosity of the solution as well as the solubility of fructose.

In this way, crystallization and centrifugation of fructose crystals is improved.

It is another essential feature of the process of the invention that the pH of the fructose solution is adjusted in the range from 45 to 5.5 before evaporation, if evaporation is carried out, and before crystallization. .

In the prior art literature, little attention has been paid to the importance of tightly controlling pH during the fructose crystallization process, and the indicated p
It is clear that the H range varied widely.

For example, the method of the Jackson patent (US Pat. No. 2,007,971) pointed to a pH range of 6-7.

This range was found to be too high due to the rapid formation of colored degradation products at the above pH and the conversion of fructose to glucose as well as mannose that occurs in neutral or alkaline fructose solutions.

Austrian Patent No. 489 to Kusch et al.
, 610 indicates a wide pH range from 3.5 to 8.0.

U.S. Pat. No. 2,949,389 to J. Murtaugh et al.
Indicates that the H range is 4.0 or less.

The above proposal is consistent with the findings obtained with applicant's dilute fructose solutions.

During the development of the process of the invention, it was observed that the crystal yield in some cases was much lower than expected.

As a result of the research, a pH range of 30 to 4.0, which was initially considered to be the most advantageous for minimizing fructose degradation and shrimping at high temperatures, based on applicant's research in the prior art, was found to be It was found that the pH range was not favorable for crystallization of solutions containing fructose.

21 Sapranov (A, Sapranov): S
acharnaja Pr-omyslennost
, 9 (1968) p. 19 and Kato et al.: Ag
r. Biol. Chem, 33, (1969), No. 93
After a review of the literature, including 9 pages, Applicants have drawn the conclusion that fructose degradation at elevated temperatures is minimal if the pH is maintained within the range of 3.2 to 3.6.

The present inventors also investigated the reaction rate constant (k: min-1) of the fructose decomposition reaction at 60°C using a 10 g/100-pure fructose solution in order to follow up the results of A. Sapranobu. However, as shown in FIG. 12, the pH was 3. 6 had the lowest value of k.

Earl Jackson's U. S. Bureau o
f Standards Research Paper
According to RP 611,1933, the stability of fructose exceeds its maximum at pH 3.3.

Earl Jackson is 2-10 per 100 yards.
Based on the study of solutions with a concentration of g, it was concluded that the concentration of the solution does not affect the degradation of fructose.

In fact, fructose can be dissolved in neutral or alkaline solutions (p
H6 and above), and difructose and its anhydride are produced along with other degradation products at low states below 3.

Surprisingly, it has now also been found that the pH range 4.5 to 5.5 provides the most advantageous pH range for crystallizing fructose from concentrated aqueous solutions.

That is, pH 3. In the range of 5 to 5, the higher the pH, the more fructose crystals of desired size were obtained within a shorter crystallization time.

Therefore, the crystal yield of fructose reached its maximum around pH 5, as shown in FIG. 13.

During the course of the above studies, it became clear that the influence of pH on the formation of undesired difructose and difructose anhydride increases in highly concentrated fructose solutions.

That is, when a concentrated solution of fructose is left at 60°C for 40 hours and the amount of difructozan produced is examined, as shown in Figure 14, the production of fructose anhydride (difructozan) increases at pH 4 or below, and increases at higher pH. Difructozan production was low.

This difructozan is formed when two fructose molecules release two water molecules in an acidic solution to form a dianhydride, but its formation occurs in a concentrated solution with a small amount of water. easy.

This is also clear from the fact that more difructozan is produced in the 90% fructose solution than in the 80% solution in FIG.

Therefore, when using a high-concentration fructose solution as in the present invention, attention must be paid to the formation of difructozan, but from this point as well, the pH
4. It was found that around 5 to 5.5 is good.

It was also shown that the relative amounts of the seven major degradation products change as pH changes, that water is liberated when difructose anhydride is formed, and that concentrated fructose solutions (>90% solids) at pH 3. It has also been found that more than 10% of fructose is converted to difructose within 10 hours when held at a temperature of 60°C.

Furthermore, it is believed that difructose and difructose anhydride are the actual crystallization inhibitors.

Minimum fructose degradation is experienced when carrying out the process of the invention at a pH of 4.5 to 5.5, preferably 5.0.

This increases the yield of fructose crystals with the desired size dimensions between 200 and 600 μm within a shorter crystallization time.

The total crystallization time is reduced, e.g. from 180 to 120 hours, and the yield of crystalline fructose is reduced from pH 3 to
The dry matter in the solution increased to 45-50% compared to 30-35% dry matter within the range of 4.

A detailed description of the method of the invention is provided below.

We describe a two-step crystallization carried out in two separate crystallizers.

The process is the crystallization of fructose from an aqueous solution with a dry matter content of about 90 to 94% by weight and a purity of about 90 to 99% with respect to fructose and the impurity being glucose.

As a result, crystals are obtained with a crystal size of 300 to 500 μm and a crystal weight of 45 to 55 weight units of dry weight, as determined by the sieve test defined below.

The purity of the finished product is higher than 99.5% with respect to fructose.

The next step in the above method involves adjusting the pH of the aqueous solution as described in the previous section.

The pH of the solution should be adjusted to within the range 4.5 to 5.5, and preferably to pH 5.Q.

This may be done, for example, by adding an aqueous solution of Na 2 CO s.

A suitable alternative method can be arranged with anion exchangers.

The latter method involves preparing a fructose solution by using an anion exchanger before fructose is separated from glucose by the method of Melaya's patent, ie, U.S. Pat. No. 3,692,582. It's convenient to get.

Step 1: (a) Fill the crystallizer/161 with the aqueous solution of fructose mentioned in the previous section, and the temperature is controlled at a level such that the solution is saturated with fructose (temperature = 58
to 65°C).

(b) in the above solution a small amount of fructose crystals of maximum uniformity in size are added as the crystal component, either 5 to 10 μm crystals suspended in isopropanol, or larger crystals, e.g. in the dry state; 80 to 1
Add 00μ door crystals.

The amount of seed crystals (m,) is determined by the size of seed crystals (d,) according to the following formula:
It depends on the amount of finished crystals (M) and the desired crystal size (D).

:(C) The supersaturation of the solution with respect to fructose is then increased by lowering the temperature, and by planned control of the temperature the highest crystallization rate is obtained without the formation of a certain amount of interfering new crystals.

The above temperature schedules depend on the purity and dry matter content of the solution used for crystallization, and these plans are worked out on the basis of experiments for various cases.

The supersaturation of the mother liquor is determined by samples taken at specified intervals to check the accuracy of the above plan and, if necessary, to modify it during the crystallization.

Optimal supersaturation for fructose is about 1.1 to 1
．． It was found to be within the range of 2.

The cooling schedule is preferably calculated to maintain supersaturation within the above range during crystallization.

(d) Crystallization takes about 50 hours, after which the temperature of the mass is between 25 and 35°C, again depending on the type of solution used.

At the end of the crystallization process, the amount of crystals is approximately 50% by weight more than the dry matter content of the mass.

Step 2: The ready mass obtained in the previous step is added to the crystallizer 4I and, before charging, the mother liquor is saturated or slightly unsaturated with respect to fructose. Simultaneously fill with fresh solution whose temperature is controlled to a level that produces a mixture that is saturated.

After filling, fine-tune the temperature.

After that, the same operations as steps (C) and (d) in step 1 are performed.

At the end of the above operation, the fructose crystals are separated from the liquid by centrifugation.

The centrifuge of choice is of the type used for sugar recovery.

Due to the high viscosity of the aggregates, high centrifugal forces are required.

A preferred device has a drum diameter of 106.7 to 121.
91 m, and rotation speed 1400 to 1800
It has rpm.

In a typical operation, a 106.7 Cr/L centrifuge is charged with 120 to 250 K9 fructose crystal mass.

Wash the crystals with water (1-211/batch).

When the fructose crystals leave the centrifuge, their residual water content is approximately 1.5%.

Centrifugation time for each batch is 10 to 14 minutes including filling, centrifugation and draining.

The throughput of this type of centrifuge (diameter 10-6.7 mm, basket height 600 mm) is between 250 and 500 mm.
K9/hour.

Horizontal cylindrical tanks with a diameter of 2 to 2.7 m are used as crystallizers and rivers.

Tanks should be well insulated externally to prevent heat loss.

The tank has a through shaft on which a spiral-shaped refrigeration pipe is placed.

The rotational speed of the shaft is 0.75 to 1.5 rpm.

The frozen area is approximately 2.5 m2/m3. Volume of crystallizer (
length) increases from step to step by the final crystal size of the step as follows: where V is the volume of crystallizer I, V is the volume of crystallizer, and d and d are are steps 1 and 2 respectively
is the final crystal size at .

This arrangement provides for indirect temperature control, controlling the temperature of the water circulating in the refrigeration pipes, and the large refrigeration area allows for a small temperature difference between the mass and the frozen water (2 to 7 ℃).

Direct temperature control methods can also be used if desired.

Crystallization is also facilitated by evaporating water from the mass, for example by blowing dry, warm air over the surface of the mass.

The table below gives numerical values for effective crystallization.

Instead of two separate crystallizers I and 1, a single crystallizer can be used.

The crystallization can also be carried out in more than two steps, for example in 3 or 4 steps, or even more steps, with a number of crystallizers corresponding to the number of steps, or only one crystallizer. equipment may be used.

Alternatively, it is also possible to use a combination of the two methods indicated above, for example a three-step method, in which step 1
and step 2 can be carried out in the same crystallizer, and step 3 can be carried out in a separate crystallizer.

If one crystallizer is used for several steps, its volume must correspond to the solution volume of the last step carried out in it.

In such a case, the crystallizer may, for example, comprise a vertical shaft on which a helical freezing pipe rests.

In each of these alternative methods, the pH of the fructose solution introduced into the crystallizer must be within the range between pH 4 and pH 5, preferably between 4.5 and 5.5.

The accompanying drawing shows a diagram of a two-step crystallization with two crystallizers.

This diagram shows 87.5% fructose and 4.5% glucose.
% and from a factory-scale crystallization of fructose from a solution containing 8 g of water.

In the drawings, Figure 1 shows the total amount of fructose and the amount of fructose crystallized in the above system in tons as a function of time, and the total crystallization time is 110 hours, and Figure 2 shows the amount of fructose crystallized in the above system. Temperature in °C as a function of time
Figure 3 shows the amount of fructose crystallized in the above system as a function of time in percent, and Figure 4 shows the crystal size of fructose in the above system in μm as a function of time. Figures 5A to 5H are illustrations of the conditions used in a preferred embodiment of the method of the invention, Figure 6 is a continuous crystallizer, and Figures A and 7 Figure B schematically shows the formation of difructose and water at 60°C in a fructose solution containing 90% solids during storage over 12 hours at a pH varying from 1.9 to 5.0; Figure 8 is a graph illustrating the improved yield obtained by the present invention and Figure 9 is a graph of the degradation products of fructose obtained at a pH below about 4 in concentrated fructose solutions stored at elevated temperatures. 10 is a graph showing the correlation between pH, difructose content and yield of fructose crystals, and FIG. 11 is a graph showing the effect on difructose level and yield of fructose crystals. FIG. 3 is another graph showing the influence of pH.

The illustrations in Figures 1 to 4 are divided into five sections.

That is, filling of crystallizer I, crystallization in crystallizer I (referred to as preliminary crystallization), filling of crystallizer (2), crystallization in crystallizer (2), and centrifugation.

In FIG. 1, curve A shows the total amount of fructose in the system, and curve B shows the amount of fructose crystallized.

The point O marked in the drawing is the point at which the solution begins to be charged into the crystallizer I.

The fifth section of the illustrations in Figures 1-4 relates to centrifugation of solutions containing crystals.

As previously indicated, the centrifugation time for a single fill of a typical centrifuge requires 10 to 14 minutes for a complete cycle of fill, centrifuge, and drain.

In the illustrated method, two centrifuges (each with a throughput of 250 to 500 Kp/hr) were used continuously until the crystals were separated from the entire batch.

The total amount of crystals was 20 tons.

It is for this reason that each of the figures shows a time span of about 20 hours for the centrifugation operation.

With respect to Figures 3 and 4, the curves show a slight decrease in the amount of fructose crystals and crystal size, which occurs at the beginning of centrifugation, and which occurs during the centrifugation process. and especially the effects of losses that occur during cleaning of the crystal to remove solution adhering to the crystal.

Regarding the transition from step 1 (Crystallizer I) to Wangcheng 2 (Crystallizer River), at this time a new solution of the same nature as the starting solution is added and a small part of the fructose crystals dissolves (Fig. ), the temperature increases (Figure 2), the amount of crystals calculated as a percentage of the total mass decreases substantially (Figure 3), and the average crystal size becomes slightly smaller (Figure 4).

The above method in which the addition of a new solution is carried out at the transition from step 1 to step 2 is such that the new solution is added continuously up to the end of step 1, and in that case, when moving to step 2, further addition of the new solution is performed. It may be changed so that it is not added.

The process is carried out in two steps but in one crystallizer as follows: Step 1: Fructose 8 in the crystallizer 7. 5%, glucose 4.5% and water 8%, the temperature is so high (65° C.) that the solution is unsaturated with respect to fructose.

The amount of solution is such that it, together with the fructose crystals added as a crystal component, constitutes a mass in which about 15 by weight of the dry matter content is present as crystals.

The solution is cooled to saturation point and the required amount of crystalline component (the crystal size is approximately 100 μm) is added.

For example, if the amount of solution is 900Kp (there are 8
30K9 dry matter is present), 150KP of crystalline components with a size of 100 μm are added.

The temperature is lowered to a value (50 to 55° C.) that reaches the optimum environment for crystal growth, including the optimum supersaturation in the range of 1.1 to 1.2, and the temperature is kept constant. .

Because fructose constantly leaves the solution due to crystallization, more solution must be constantly added to the mass in order to keep the environment unchanged.

The degree of supersaturation must remain within the above optimum range.

When the crystal grows, the crystal area also grows and the most of the fructose that crystallizes in unit time increases.

This is the reason for constantly accelerating the rate of solution addition according to a pre-established schedule.

When the crystallizer is full, stop adding the solution.

Step 2: This step is first a cryo-crystallization of the same type as described in step (C) of the previously described method.

The mass is then cooled to 50 to 55° C. until the temperature reaches a point at which the amount of crystals is about 50 by weight of the total dry weight of the mass.

Reference to FIG. 5 serves to further explain the considerations set out in steps 1 and 2 above.

The weight of the mass in tons of dry matter, the temperature, the proportion of crystals to the total mass, the size of the crystals, the rate of crystallization, the purity of the mother liquor, the supersaturation and the change in the dry matter content of the mother liquor each follow the entire process. Described by a curve.

The crystallizer should be completely filled at the end of step 1 and the supersaturation with respect to fructose should be between 1.1 and 1.
It will be appreciated that optimal crystallization conditions are maintained during step 2 by lowering the temperature of the mass to maintain it within a range of 2.

The crystallizer is a tank of the same type as that described in connection with the first method.

A pump with adjustable output was used to add the solution, and a scheduling mechanism was coupled thereto to effect the solution addition at a rate that was varied depending on the desired schedule.

? The table below gives numerical values for effective crystal crossing.

Table 2 307 rL3 39.5 tons of dry material 100 μm to 500 l1rrL Time 120 hours Amount of crystals recovered 19 tons = 49 weight percent of the fructose contained in the initial solution.

As seed crystals in the crystallization according to the method of the invention, crystal masses taken from previous intentional steps of crystallization may be used.

As seed crystals, for example, the crystal mass remaining after centrifugation in the method of the invention may be used.

References to tons in this specification and claims refer to metric tons.

When the crystalline size of fructose is referred to in the text and claims, it is referred to as the standard method for measuring sugar crystalline size, as defined by the International Commission for Uniform Methods for the Analysis of Sugars.
the International Committee
on for Unifrm Methods fSu
It was determined from the dry sample by the Grist test or from the final product by the Grist test, which was temporarily adopted by gar analysis).

The above method is described in De Whatley (Ed.) Sugar Analysis I.
The CUMSA Method, Elsvier, New York 1964, pages 94, 95 and 96.

During the crystallization operation, the crystal size of the crystals in the syrup was determined by microscopic examination.

As used herein and in the claims, the term "supersaturation" refers to the following formula: supersaturation P, T S/W = sugar/water ratio for solution of purity P and temperature T; S1/W1=Sugar for saturated solution of purity P and temperature T/
As the "supersaturation coefficient" expressed by the ratio of water, (sugar = fructose), Claas
defined by the equations of en and Holven (Honig
P. : Principles of Sugar
technology, vol. 11, Elsevier
．． New York 1959, p. 232).

Continuous crystallization can be carried out in a crystallizer similar to that used in batch crystallization.

However, in the continuous crystallization method, the volume of the crystallizer is 29 m3 = 4 2.9 tons, and the size of the crystals obtained is such that the crystallizer is divided into sections by walls, and each section is provided with temperature control and fructose solution. It is advisable to install a separate device for the addition.

There are holes in the dividing wall through which the mass flows continuously from one section to the other.

Each section may also be a separate device, in which case the mass flows from one crystallizer to another.

These crystallizers may be of the same size or of different sizes.

A typical continuous crystallizer is shown in Figure 6 and works as follows: From a feed tank equipped with an agitator, a quantity of seed crystals suspended in a saturated fructose solution is added to the crystallizer. Add continuously or in portions to the first section of the dispenser.

At the same time, a fructose solution (saturated or slightly unsaturated, since its temperature is very high for fructose) is continuously added at a controlled rate to the first section of the crystallizer.

In the section, the mass is cooled to a certain temperature so that the crystals grow at the highest rate without noticeable formation of new crystals.

A similar fructose solution is added at a controlled rate to the mass flowing into the second section, and the temperature is lowered again in the same manner as in the first section.

No seeds are added to this section or to the next section.

The number of consecutive sections can vary, and the operating range of each section depends on their number and size.

The characteristic figures following the operation of a continuous crystallizer, divided into 5 sections and with similar delays in each step (20 to 30 hours), are shown in Table 3 below.

The processing capacity of this crystallizer is approximately 140Kp of fructose crystals.
/ It was time.

Figures 7A and 7B show the effect of a change in pH within the range of pH 1.9-5.0 on the amount of difructose and water produced during storage of concentrated fructose solutions at a temperature of 60°C. shows.

Difructose was analyzed by thin layer chromatogram;
Water, on the other hand, was measured by the Karl Fischer method.

Fructose is rapidly converted to difructose and its anhydride at pH 1.9, but at pH 5. At 0, the amount of difructose produced is minimal.

Similarly, a substantial amount of water is liberated when difructose anhydride is produced, which is shown in Figure 7B.

Figure 8 summarizes yield data from several crystallization processes carried out within the pH range of 3.5 to 5.0.

The six measurements shown in the graph within the range of 3.5 to 4.0 were obtained in commercial production experiments, which indicate a wide variation in yield and relatively low levels.

Four measurements within the range of 4.5 to 5.0 indicate small variations and high yields varying from about 40 to about 45%.

Figure 9 shows unidentified degradation products of fructose.
Typical thin layer chromatography durams designated as l61, 2, 4, 5, 6, 7 and 8 are shown.

Spot /l63 is fructose.

Rapid production of difructose tends to reduce the purity and concentration of fructose in solution and thus inhibit fructose crystallization and reduce crystal yield.

Furthermore, there appears to be another strong influence on crystallization caused by the presence of difructose and its anhydride, which appears to actually inhibit crystallization.

Figure 10 shows data collected from 53 samples;
The data shows the yield improvement obtained by adjusting the pH of the fructose solution to about pH 5.

The overall yield before centrifugation, drying and sieving is 2-3 cents higher.

The upper graph shows the yield as a percentage of the original fructose content for each sample.

Sample 16 and subsequent samples show that the pH of the samples was adjusted to about pH5.

The bottom graph of Figure 10 each shows the difructose profile in each sample, and the difructose levels were determined by thin layer chromatography.

FIG. 11 provides data showing the effect of difructose level on crystalline fructose yield.

As is known from the data, there is a correlation between high difructose content and low yield of fructose crystals.

Adjust the pH of the fructose solution to approximately pH before starting the crystallization operation.
When adjusted to 5, the difructose content of the liquid is kept below 3, and usually below 1.5.

Heretofore and hereafter, when referring to the pH of fructose solutions, the pH of the solution was measured after diluting a portion of the sample to about 50% dry matter.

Example I A fructose solution was prepared using the Melaya method (U.S. Pat. No. 3,699).
2,5 8 2) and crystallized using the two-step crystallization method described above.

The crystals are summarized in Table 1 above.

The solution before pH adjustment contained 75 parts by weight of dry matter.

The 98 pounds of dry material was fructose and the solution had a pH of 3.6.

The pH of the above solution was adjusted to 3.5 with Na2CO3 before the evaporation step.
It was prepared by adding K as an aqueous solution.

The adjusted pH was 5.0 (measured after diluting 1 part to about 50% dry matter).

After evaporation of the dry substance to 92.5 weight cake, the solution 31rr
L3 was crystallized and the total crystallization time was 110 hours (Step 1 = 50 hours and Step 2 = 60 hours).

The yield is 21 tons, which is equal to 49% of dry matter as fructose crystals.

Example 1 A fructose solution was prepared and crystallized as described in Example I.

The pH was adjusted to 4.4% before evaporation. Adjusted to 5.1 by adding 9 Kp.

The solution was evaporated to 92.5% dry matter.

Fructone content was 97.0% of dry matter.

Crystallization was carried out in two steps and the time was 50 hours + 70 hours.

The final filling temperature was 38.9℃, and the yield was 21 tons,
That is, there were 49 tons of dry matter as fructose crystals.

Example ■ A fructose solution was prepared and crystallized as in Examples ■ and ■.

The pH was adjusted to 4.9 and the solution was 92.5 on dry matter.
evaporated to %.

Fructose content was 97% of dry matter.

Crystallization was performed in two steps for 60 hours + 70 hours.

The final temperature was 35.5°C. The yield was 20 tons, or 48 tons of dry matter as crystalline fructose.

EXAMPLE 1 A fructose solution was prepared and crystallized as described in Examples I-■.

The pH was adjusted to 4.5 and the solution was evaporated to 92.5%.

The fructose content was 96 moss.

Crystallization was carried out for 60+70 hours and the yield was 44 pounds of dry material as fructose crystals.

Example ■ A fructose solution was prepared as described in the previous example,
And it crystallized.

The pH was adjusted to 5.5 and the solution was evaporated to 92.4%.

Fructose content was 96 g.

Crystallization was carried out for 60 to 70 hours and the yield was 43% of dry material as fructose crystals.

[Brief explanation of the drawing]

Figure 1 shows the total amount of fructose and the amount of fructose crystallized in tons as a function of time in the method of the present invention; the total crystallization time is 110 hours, and Figure 2 shows the temperature of the fructose solution as a function of time. Figure 3 shows the amount of fructose crystallized in the process of the invention in percent as a function of time, and Figure 4 shows the amount of fructose crystallized in the process of the invention in degrees Celsius as a function of time. Figures 5A to 5H are illustrations of the conditions used in one preferred embodiment of the process of the invention, and Figure 6 is a continuous crystallization diagram. Figures 7A and 7B show the formation of difructose and water at 60°C in a fructose solution containing 90% solids during storage for 12 hours at pH varying from 1.9 to 5.0. FIG. 8 is a graph showing the yield improvement obtained by the present invention, and FIG. 9 is a graph showing the degradation products of fructose obtained when the pH of a concentrated fructose solution stored at high temperature is about 4 or less. FIG. 10 is an illustration of a typical chromatogram, and is a graph showing the correlation between pH, difructose content and yield of fructose crystals;
Figure 11 is another graph showing the effect of pH on difructose levels and yield of fructose crystals, and Figure 12 is a graph showing the reaction rate constant and pH for the fructose decomposition reaction.
FIG. 13 is a graph showing the relationship between the yield of fructose crystals and pH, and FIG.
Figure 4 is a graph showing the relationship between a certain amount of difructozan production and pH.

Claims (1)

[Scope of Claims] 1. A method for obtaining fructose crystals from an aqueous fructose solution containing glucose as an impurity, comprising: a) an aqueous fructose solution having a pH of 4. b) the fructose content of the dry material is at least about 90% by weight;
adjusting H in the range from 4.5 to 5.5; C) bringing the solution to a temperature at which the solution is saturated with respect to fructose; d) adding fructose seeds to the solution; e) reducing the temperature of the aggregate at a controlled rate so as to supersaturate the aggregate with respect to fructose and increase the crystal size of the seed crystals without substantially forming new fructose crystals; Then, at a similarly controlled rate, the fructose solution of b) is continuously or stepwise replenished to the above aggregate, and f) the fructose crystals are added when the crystal size is within the range of about 200 to 500 μm. A method for improving fructose crystal yield by adjusting the pH of a fructose solution, the method comprising the step of separating fructose from the aggregate.