Method for Crystallizing D-psicose

Abstract

The present invention relates to the field of chemical purification, and particularly to a method for crystallizing D-psicose. The method comprises: (1) mixing a D-psicose concentrate with D-psicose seeds to obtain a mixture; (2) subjecting the mixture to pre-crystallization and cooling crystallization in the intermittent presence of dry gas to obtain a slurry; (3) performing solid-liquid separation on the slurry to obtain D-psicose crystals and mother liquor. The D-psicose concentrate can be obtained by a method of catalytic conversion of fructose by D-psicose 3-epimerase. This method can achieve a high crystallization yield, with uniform product particles that do not form lumps, a simple preparation process, and environmental friendliness, without using organic solvents and requiring a short crystallization time.

Description

Technical Field

[0001] The present invention relates to the field of chemical purification, and particularly to a method for crystallizing D-allulose. Background Art

[0002] The sweetness of D-allulose is equivalent to 70% of sucrose, and the calorie is equivalent to 0.3% of sucrose. Its volume characteristics and taste are similar to those of sucrose, and it can be used as a substitute for sucrose in the food and pharmaceutical industries. D-allulose can significantly inhibit weight gain and abdominal fat accumulation, and can maintain glucose tolerance and insulin sensitivity by exporting the nucleus of hepatic glucokinase, achieving the effects of controlling obesity and diabetes. However, the research on allulose in the Chinese market started relatively late, and there is no industrialization report yet. The market for this sugar is broad.

[0003] The currently commonly used D-allulose crystallization technologies generally include the following several technical methods. The first method is the one disclosed in CN201811470319.5. This method adds organic solvents to reduce free water and promote crystal precipitation. However, this technology has a large consumption of organic solvents, high costs, high risks, and problems such as residues of organic reagents. The second method is to adjust the supersaturation by changing the relationship between temperature and solubility, such as the method disclosed in CN202011237164.8. In this process, water cannot be discharged in time. As crystals precipitate, the supersaturation of the mother liquor decreases, and the crystallization yield completely depends on the initial supersaturation of the mother liquor. If the supersaturation is too large, the crystallization rate is difficult to control, the crystal particles are non-uniform, and the product quality is poor; if the supersaturation is too small, the yield will inevitably decrease. The third method is the one disclosed in CN201910876767.3. By continuously reducing the water content in the crystallization mother liquor to maintain an appropriate supersaturation, but through heating and evaporation, the evaporation area is only the liquid surface area of the crystallization mother liquor, with low evaporation efficiency and low yield; in addition, during the heating process, the high-viscosity crystallization mother liquor has slow heat transfer and low yield, and the part in contact with the heating components in the container is prone to browning, affecting the product quality. The fourth method is two-step crystallization, such as the method disclosed in CN201680069967.2. This method first conducts concentration crystallization, and then cools the crystallization when the concentration of the concentrated crystallization mother liquor is relatively high. This process combines the technical advantages of the second and third methods to a certain extent, but ultimately cannot avoid the problems of small evaporation area, low heat transfer efficiency, and easy browning.

[0004] Therefore, there is an urgent need to develop a preparation method for D-allulose with a high crystallization yield, uniform and non-agglomerated crystal products, and a simple, safe, and environmentally friendly preparation process. Summary of the Invention

[0005] The object of the present invention is to overcome the above problems existing in the prior art, and to provide a method for crystallizing D-allulose, which can achieve a high crystallization yield, with uniform and non-agglomerated product particles, a simple preparation process and environmental friendliness, without using organic solvents and requiring a short crystallization time.

[0006] To achieve the above object, the present invention provides a method for crystallizing D-allulose, which comprises:

[0007] (1) Mixing a D-allulose concentrate with D-allulose crystal seeds to obtain a mixed material;

[0008] (2) Subjecting the mixed material to pre-crystallization and cooling crystallization in the intermittent presence of absolutely dry gas to obtain a slurry;

[0009] (3) Separating the solid and liquid of the slurry to obtain D-allulose crystals and mother liquor.

[0010] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0011] 1. By using the method of the present invention, the crystallization yield is high, the crystallization time is short and the rate is appropriate, so that the obtained crystalline product particles are uniform and non-agglomerated, and the product quality is high.

[0012] 2. The method of the present invention is not limited by the initial supersaturation of the crystallization mother liquor. Moreover, it can be carried out without using organic solvents, with low cost, simple process, safety and environmental friendliness, and has good industrialization prospects. Detailed Embodiments

[0013] The endpoints and any values disclosed herein are not limited to the exact range or value, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0014] The present invention provides a method for crystallizing D-allulose, which comprises:

[0015] (1) Mixing a D-allulose concentrate with D-allulose crystal seeds to obtain a mixed material;

[0016] (2) Subjecting the mixed material to pre-crystallization and cooling crystallization in the intermittent presence of absolutely dry gas to obtain a slurry;

[0017] (3) Separating the solid and liquid of the slurry to obtain D-allulose crystals and mother liquor.

[0018] It is understandable that the absolutely dry gas is not air without water molecules, but a gas with a water content much lower than the humidity of conventional air. Moreover, the absolutely dry gas is a gas that does not react with the mixture. For example, the absolutely dry gas can be at least one of air, nitrogen, and carbon dioxide with a water content much lower than the humidity of conventional air.

[0019] According to the present invention, preferably, the method for obtaining a D-allulose concentrate includes: purifying the D-allulose solution to be purified to obtain a purified D-allulose solution, and concentrating the purified D-allulose solution to obtain a D-allulose concentrate; wherein, the purity of the purified D-allulose solution is not less than 98.5% by weight (for example, it can be 98.5% by weight, 98.6% by weight, 98.8% by weight, 99% by weight).

[0020] Among them, the D-allulose solution to be purified can be any one or a mixture of two or three of the materials obtained by natural extraction, enzymatic synthesis, or chemical synthesis. For example, the D-allulose solution to be purified can be converted from fructose by catalysis with D-allulose 3-epimerase.

[0021] Among them, the purification method is not particularly limited and can be a conventional choice in the art as long as it can ensure that the purity of the purified D-allulose solution is not less than 98.5% by weight. For example, the purification method can adopt ion exchange chromatography or simulated moving bed separation technology.

[0022] According to the present invention, the concentration of the D-allulose concentrate is not particularly limited and can be selected within a relatively wide range. However, in order to further ensure a high crystallization yield in a short time and make the crystal particles more uniform and not easily agglomerated, preferably, the concentration of the D-allulose concentrate is 700 - 850 g / L (for example, it can be 700 g / L, 720 g / L, 750 g / L, 780 g / L, 800 g / L, 830 g / L, 850 g / L), more preferably 780 - 830 g / L, and even more preferably 800 g / L.

[0023] It is understandable that the "purity" and "concentration" mentioned are different concepts. Since in actual production, in the solution containing D-allulose, in addition to containing D-allulose, it often also contains other sugars or alcohols (dry matter). Purity refers to the ratio of the weight of D-allulose in the solution containing D-allulose to the total weight of all dry matter in the solution; while concentration refers to the ratio of the sum of the weights of all sugars and alcohols in the solution containing D-allulose to the total weight of the solution.

[0024] Among them, the equipment for concentration is not particularly limited. However, for ease of operation during industrial scale-up and to lower the threshold for process technology scale-up, single-effect, double-effect, triple-effect, and quadruple-effect concentration equipment can be used for the concentration equipment.

[0025] According to the present invention, to avoid caramelization reaction caused by excessively high local temperature during the concentration of D-allulose, resulting in browning of the concentrated solution and ultimately yellow color of the prepared D-allulose crystals, preferably, the temperature during the concentration process should be controlled not to exceed 50 °C (for example, it can be 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C).

[0026] According to the present invention, the method for concentration is not particularly limited and can be a conventional choice in the art. Preferably, the method for concentration is vacuum concentration. It can be understood that in vacuum concentration, generally, the lower the concentration pressure, the better. However, considering cost and operational simplicity, the concentration pressure should be such that the purified D-allulose solution can be concentrated relatively quickly at a lower temperature.

[0027] According to the present invention, the dosage of the D-allulose crystal seeds can be selected within a relatively wide range. However, to further ensure a high crystallization yield within a short time and make the crystallization particles more uniform and less likely to agglomerate, preferably, relative to 1 L of the D-allulose concentrated solution, the dosage of the D-allulose crystal seeds is 1 - 50 g (for example, it can be 1 g, 5 g, 10 g, 20 g, 30 g, 40 g, 50 g), more preferably 10 - 30 g, and even more preferably 20 g.

[0028] According to the present invention, to further ensure a high crystallization yield within a short time and make the crystallization particles more uniform and less likely to agglomerate, preferably, the temperature of the dry gas is 30 - 60 °C (for example, it can be 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C), and the water content is 0.5 - 1.5 wt% (for example, it can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%); more preferably, the temperature of the dry gas is 40 - 50 °C, and the water content is 0.8 - 1 wt%; even more preferably, the temperature of the dry gas is 45 °C, and the water content is 0.9 wt%.

[0029] According to the present invention, although the object of the present invention can be achieved by adopting the method in which the absolutely dry gas intermittently exists as described above, preferably, the method for providing the absolutely dry gas includes: dispersing and introducing the absolutely dry gas from the bottom of the mixture. The inventors of the present invention found in the research that when the absolutely dry gas is introduced from the bottom of the mixture, the absolutely dry gas can make more sufficient contact with the mixture, so that a higher crystallization yield can be obtained within a shorter crystallization time, and the obtained crystal particles are more uniform. Among them, in order to make the introduced absolutely dry gas as dispersed as possible and make as uniform contact with the mixture as possible, an absolutely dry gas distributor can be arranged at the bottom of the mixture to introduce the absolutely dry gas.

[0030] According to the present invention, in order to further ensure obtaining a higher crystallization yield within a shorter time, and making the crystallization particles more uniform and not easy to agglomerate, preferably, the method for providing the absolutely dry gas includes: introducing the absolutely dry gas once every 5 - 30 min (for example, it can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min), and maintaining the introduction for 5 - 30 s (for example, it can be 5 s, 10 s, 15 s, 20 s, 25 s, 30 s), repeating the operations of introducing and not introducing until the end of pre-crystallization and cooling crystallization; more preferably, the method for providing the absolutely dry gas includes: introducing the absolutely dry gas once every 10 - 20 min, and maintaining the introduction for 10 - 20 s, repeating the operations of introducing and not introducing until the end of pre-crystallization and cooling crystallization. For example, introducing the absolutely dry gas once every 15 min, and maintaining the introduction for 15 s, repeating the operations of introducing and not introducing until the end of pre-crystallization and cooling crystallization.

[0031] According to the present invention, preferably, relative to 1 L of the allulose concentrate, the introduction rate of the absolutely dry gas is 0.1 - 1 L / min, and more preferably 0.3 - 0.7 L / min.

[0032] The inventors of the present invention further found in the research that by adopting the above-mentioned method of dispersing and intermittently introducing the absolutely dry gas from the bottom of the mixture, when introducing the gas, the absolutely dry gas can push the liquid and crystal particles in the mixture to tumble and mix, avoiding agglomeration of the crystal particles, and the absolutely dry gas can also take away part of the moisture in the mixture, increasing the solid content ratio in the material within a controllable range. In the repeated cycle of introducing - not introducing, a steady increase in crystals is achieved, not only ensuring the crystallization yield, but also avoiding agglomeration caused by a large amount of crystals precipitating in a short time.

[0033] According to the present invention, in order to further ensure a high crystallization yield within a relatively short time and make the crystal particles more uniform and less likely to agglomerate, preferably, the conditions for pre-crystallization include: the temperature is 35 - 55 °C (for example, it can be 35 °C, 40 °C, 45 °C, 50 °C, 55 °C), the time is 50 - 60 h (for example, it can be 50 h, 52 h, 55 h, 57 h, 60 h), and the stirring rate is 50 - 150 rpm (for example, it can be 50 rpm, 70 rpm, 90 rpm, 100 rpm, 120 rpm, 135 rpm, 150 rpm). More preferably, the temperature for pre-crystallization is 40 - 50 °C.

[0034] According to the present invention, in order to further ensure a high crystallization yield within a relatively short time and make the crystal particles more uniform and less likely to agglomerate, preferably, the conditions for cooling crystallization include: cooling at a cooling rate of 0.8 - 1.5 °C / h (for example, it can be 0.8 °C / h, 1 °C / h, 1.2 °C / h, 1.3 °C / h, 1.5 °C / h), cooling to 22 - 28 °C (for example, it can be 22 °C, 24 °C, 25 °C, 26 °C, 28 °C) and maintaining the temperature at 22 - 28 °C, the stirring rate is 50 - 150 rpm (for example, it can be 50 rpm, 70 rpm, 90 rpm, 100 rpm, 120 rpm, 135 rpm, 150 rpm), and the time for cooling crystallization is 15 - 30 h. Among them, during the cooling process and during the process where the temperature has dropped to the target temperature and is maintained at this temperature, stirring is carried out, and the total time of these two processes is 15 - 30 h. It can be understood that cooling can make the mixture in a supersaturated state, thus promoting crystallization. The inventors of the present invention found in the research that by using the above-mentioned conditions, especially the cooling rate condition, it avoids too drastic changes in conditions, and while promoting crystallization, it can also avoid agglomeration of the crystallization product.

[0035] According to the present invention, preferably, the solid-liquid separation is selected from at least one of centrifugal separation and filtration separation. It can be understood that the solid-liquid separation can also be a combination of centrifugal separation and filtration separation.

[0036] According to the present invention, after solid-liquid separation, the D-allulose crystals can also be dried. Among them, the method of drying can be a conventional choice in the art, preferably at least one of fluidized bed drying and vacuum drying.

[0037] According to the present invention, in order to further improve the crystallization yield, preferably, the method further includes: taking a part of the mother liquor, returning it to be mixed with the purified D-allulose solution, and concentrating them together; wherein, the amount of the part of the mother liquor is such that after returning it to be mixed with the purified D-allulose solution, the purity of the obtained material is not less than 98.5% by weight.

[0038] According to the present invention, in order to further improve the crystallization yield, preferably, the remaining part of the mother liquor is returned to be mixed with the D-allulose solution to be purified, and they are purified together.

[0039] In a particularly preferred embodiment of the present invention, the D-allulose crystallization is carried out according to the method described as follows:

[0040] (1) The D-allulose solution to be purified is purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of not less than 98.5% by weight.

[0041] Take the purified D-allulose solution as described above, and under the condition of not higher than 50 °C, it is concentrated under reduced pressure by a triple-effect concentration device to a concentration of 790 - 810 g / L to obtain a D-allulose concentrate.

[0042] Take the D-allulose concentrate as described above, and mix it with D-allulose crystal seeds (the dosage of the D-allulose crystal seeds is 18 - 22 g relative to 1 L of the D-allulose concentrate), and stir it to make the D-allulose crystal seeds more evenly dispersed to obtain a mixture.

[0043] (2) Place the mixture in a crystallization tank provided with a dry gas distributor at the bottom, and introduce dry gas from the bottom of the crystallization tank once every 14 - 16 min and keep introducing it for 14 - 16 s, and repeat the operations of introducing and not introducing until the pre-crystallization and cooling crystallization are completed. Among them, the temperature of the dry gas is 44 - 46 °C, and the water content is 0.85 - 0.95% by weight; relative to 1 L of the allulose concentrate, the introduction rate of the dry gas is 0.4 - 0.6 L / min.

[0044] Among them, the conditions for pre-crystallization include: temperature of 44 - 46 °C, time of 50 - 55 h, and stirring rate of 105 - 110 rpm. After the pre-crystallization is completed, it enters the cooling crystallization. The conditions for cooling crystallization include: cooling rate of 0.8 - 0.9 °C / h, cooling to 24 - 26 °C and maintaining at 24 - 26 °C, and stirring rate of 105 - 110 rpm. The cooling crystallization lasts for 28 - 30 h, and after the completion, a slurry is obtained.

[0045] (3) Centrifuge the slurry in a centrifuge filter to obtain D-allulose crystals and mother liquor, and vacuum-dry the D-allulose crystals in a vacuum drying oven and weigh them.

[0046] Part of the mother liquor is returned to be mixed with the purified D-allulose solution, and they are concentrated together; wherein, the amount of the part of the mother liquor is such that after it is returned to be mixed with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight, and the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified, and the purification continues.

[0047] The present invention will be described in detail below through examples. In the following examples and test examples:

[0048] The triple-effect concentration equipment is purchased from Zhejiang Kemei Pharmaceutical Machinery Co., Ltd.;

[0049] The vacuum drying oven, model DZF-6050, is purchased from Shanghai Bosheng Industry Co., Ltd.;

[0050] The centrifugal filter, model SSC300, is purchased from Yongle Machinery Equipment Manufacturing Co., Ltd.;

[0051] The allulose standard product is purchased from Shanghai Aladdin Reagent Co., Ltd.

[0052] Example 1

[0053] To illustrate the method for D-allulose crystallization provided by the present invention

[0054] (1) The D-allulose solution to be purified is purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0055] Take the purified D-allulose solution as described above, and under the condition of 45°C, use a triple-effect concentration equipment for vacuum concentration until the concentration reaches 800 g / L to obtain a D-allulose concentrate.

[0056] Take 1875 L of the D-allulose concentrate as described above and mix it with 37.5 kg of D-allulose crystal seeds (that is, the dosage of the D-allulose crystal seeds is 20 g relative to 1 L of the D-allulose concentrate), and stir to make the D-allulose crystal seeds more evenly dispersed to obtain a mixture.

[0057] (2) Place the mixture in a crystallization tank equipped with a dry gas distributor at the bottom, and introduce dry gas from the bottom of the crystallization tank every 15 minutes and keep introducing it for 15 seconds. Repeat the operations of introducing and not introducing until the pre-crystallization and cooling crystallization are completed. Among them, the temperature of the dry gas is 45°C, which is air with a water content of 0.9% by weight; the introduction speed of the dry gas is 0.5 L / min relative to 1 L of the allulose concentrate.

[0058] Among them, the conditions for pre-crystallization include: temperature of 45°C, time of 55 h, and stirring rate of 100 rpm. After pre-crystallization, cooling crystallization is carried out. The conditions for cooling crystallization include: cooling rate of 0.8°C / h, cooling to 25°C and maintaining at 25°C, and stirring rate of 100 rpm. The cooling crystallization lasts for 30 h, and after completion, a slurry is obtained.

[0059] (3) Centrifuge the slurry in a centrifuge filter to obtain D-allulose crystals and mother liquor, and vacuum-dry the D-allulose crystals in a vacuum drying oven and weigh them.

[0060] Return a part of the mother liquor to be mixed with the purified D-allulose solution and concentrate them together; among them, the amount of the part of the mother liquor is such that after returning it to be mixed with the purified D-allulose solution, the purity of the obtained material is not less than 98.5% by weight, and the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and continue the purification.

[0061] Example 2

[0062] Used to illustrate the method for crystallizing D-allulose provided by the present invention

[0063] (1) Purify the D-allulose solution to be purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0064] Take the purified D-allulose solution as described above and carry out vacuum concentration at 40°C using a triple-effect concentration device until the concentration reaches 780 g / L to obtain a D-allulose concentrate.

[0065] Take 1923 L of the D-allulose concentrate as described above and mix it with 19.23 kg of D-allulose crystal seeds (that is, the dosage of the D-allulose crystal seeds is 10 g relative to 1 L of the D-allulose concentrate), and stir to make the D-allulose crystal seeds more evenly dispersed to obtain a mixture.

[0066] (2) Place the mixture in a crystallization tank equipped with a dry gas distributor at the bottom, and introduce dry gas from the bottom of the crystallization tank every 20 min and keep introducing it for 20 s, and repeat the operations of introducing and not introducing until the pre-crystallization and cooling crystallization are completed. Among them, the temperature of the dry gas is 40°C, which is air with a water content of 0.8% by weight; the introduction rate of the dry gas is 0.3 L / min relative to 1 L of the allulose concentrate.

[0067] Among them, the conditions for pre-crystallization include: temperature of 40 °C, time of 60 h, and stirring rate of 50 rpm. After pre-crystallization, cooling crystallization is carried out. The conditions for cooling crystallization include: cooling rate of 1 °C / h, cooling to 28 °C and maintaining at 28 °C, and stirring rate of 50 rpm. The cooling crystallization lasts for 15 h. After completion, a slurry is obtained.

[0068] (3) Centrifuge the slurry in a centrifuge filter to obtain D-psicose crystals and mother liquor, and vacuum dry the D-psicose crystals in a vacuum drying oven and weigh them.

[0069] Return a part of the mother liquor to be mixed with the purified D-psicose solution and concentrate them together; among them, the amount of the part of the mother liquor is such that after returning it to be mixed with the purified D-psicose solution, the purity of the obtained material is not less than 98.5% by weight. The remaining mother liquor is returned to be mixed with the D-psicose solution to be purified and continue the purification.

[0070] Example 3

[0071] Used to illustrate the method for crystallizing D-psicose provided by the present invention

[0072] (1) Purify the D-psicose solution to be purified by simulated moving bed separation technology to obtain a purified D-psicose solution with a purity of 98.5% by weight.

[0073] Take the purified D-psicose solution as described above, and carry out vacuum concentration at 45 °C using a triple-effect concentration device until the concentration reaches 830 g / L to obtain a D-psicose concentrate.

[0074] Take 1765 L of the D-psicose concentrate as described above and mix it with 52.68 kg of D-psicose crystal seeds (that is, the dosage of the D-psicose crystal seeds is 30 g relative to 1 L of the D-psicose concentrate), and stir to make the D-psicose crystal seeds more evenly dispersed to obtain a mixture.

[0075] (2) Place the mixture in a crystallization tank equipped with a dry gas distributor at the bottom, and introduce dry gas from the bottom of the crystallization tank once every 10 min and keep introducing it for 10 s. Repeat the operations of introducing and not introducing until the pre-crystallization and cooling crystallization are completed. Among them, the temperature of the dry gas is 50 °C, which is air with a water content of 1% by weight; relative to 1 L of the psicose concentrate, the introduction rate of the dry gas is 0.7 L / min.

[0076] Among them, the conditions for pre-crystallization include: temperature of 50 °C, time of 50 h, and stirring rate of 150 rpm. After pre-crystallization, cooling crystallization is carried out. The conditions for cooling crystallization include: cooling rate of 1.5 °C / h, cooling to 22 °C and maintaining at 22 °C, and stirring rate of 150 rpm. The cooling crystallization lasts for 20 h. After completion, a slurry is obtained.

[0077] (3) Centrifuge the slurry in a centrifuge filter to obtain D-allulose crystals and mother liquor. Vacuum dry the D-allulose crystals in a vacuum drying oven and weigh them.

[0078] Return a part of the mother liquor to be mixed with the purified D-allulose solution and concentrate them together; among them, the amount of the part of the mother liquor is such that after returning it to be mixed with the purified D-allulose solution, the purity of the obtained material is not less than 98.5% by weight. Return the remaining mother liquor to be mixed with the D-allulose solution to be purified and continue the purification.

[0079] Example 4

[0080] Used to illustrate the method for crystallizing D-allulose provided by the present invention

[0081] (1) Purify the D-allulose solution to be purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0082] Take the purified D-allulose solution as described above and carry out vacuum concentration at 35 °C using a triple-effect concentration device until the concentration reaches 700 g / L to obtain a D-allulose concentrate.

[0083] Take 1923 L of the D-allulose concentrate as described above and mix it with 1.923 kg of D-allulose crystal seeds (i.e., the dosage of the D-allulose crystal seeds is 1 g relative to 1 L of the D-allulose concentrate), and stir to make the D-allulose crystal seeds more evenly dispersed to obtain a mixture.

[0084] (2) Place the mixture in a crystallization tank equipped with a dry gas distributor at the bottom, and introduce dry gas from the bottom of the crystallization tank every 5 min and keep introducing it for 5 s. Repeat the operations of introducing and not introducing until the pre-crystallization and cooling crystallization are completed. Among them, the temperature of the dry gas is 30 °C, which is air with a water content of 0.5% by weight; the introduction rate of the dry gas is 0.1 L / min relative to 1 L of the allulose concentrate.

[0085] Among them, the conditions for pre-crystallization include: temperature of 35°C, time of 50 h, and stirring rate of 135 rpm. After pre-crystallization, cooling crystallization is carried out. The conditions for cooling crystallization include: cooling rate of 0.8°C / h, cooling to 25°C and maintaining at 25°C, and stirring rate of 135 rpm. The cooling crystallization lasts for 30 h. After completion, a slurry is obtained.

[0086] (3) Centrifuge the slurry in a centrifuge filter to obtain D-allulose crystals and mother liquor. Vacuum-dry the D-allulose crystals in a vacuum drying oven and weigh them.

[0087] Return a part of the mother liquor to be mixed with the purified D-allulose solution and concentrate them together; among them, the amount of the part of the mother liquor is such that after returning it to be mixed with the purified D-allulose solution, the purity of the obtained material is not less than 98.5% by weight. Return the remaining mother liquor to be mixed with the D-allulose solution to be purified and continue the purification.

[0088] Example 5

[0089] Used to illustrate the method for crystallizing D-allulose provided by the present invention

[0090] (1) Purify the D-allulose solution to be purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0091] Take the purified D-allulose solution as described above and carry out vacuum concentration at 45°C using a triple-effect concentration device until the concentration reaches 850 g / L to obtain a D-allulose concentrate.

[0092] Take 1923 L of the D-allulose concentrate as described above and mix it with 96.15 kg of D-allulose crystal seeds (that is, the dosage of the D-allulose crystal seeds is 50 g relative to 1 L of the D-allulose concentrate), and stir to make the D-allulose crystal seeds more evenly dispersed to obtain a mixture.

[0093] (2) Place the mixture in a crystallization tank equipped with a dry gas distributor at the bottom. From the bottom of the crystallization tank, introduce dry gas once every 30 min and keep introducing it for 30 s. Repeat the operations of introducing and not introducing until the pre-crystallization and cooling crystallization are completed. Among them, the temperature of the dry gas is 60°C, which is air with a water content of 1.5% by weight; the introduction rate of the dry gas is 1 L / min relative to 1 L of the allulose concentrate.

[0094] Among them, the conditions for pre-crystallization include: temperature of 55 °C, time of 50 h, and stirring rate of 120 rpm. After pre-crystallization, cooling crystallization is carried out. The conditions for cooling crystallization include: cooling rate of 1.5 °C / h, cooling to 25 °C and maintaining at 25 °C, and stirring rate of 120 rpm. The cooling crystallization lasts for 25 h, and after completion, a slurry is obtained.

[0095] (3) Centrifuge the slurry in a centrifuge filter to obtain D-allulose crystals and mother liquor, and vacuum-dry the D-allulose crystals in a vacuum drying oven and weigh them.

[0096] Return a part of the mother liquor to be mixed with the purified D-allulose solution and concentrate them together; among them, the amount of the part of the mother liquor is such that after returning it to be mixed with the purified D-allulose solution, the purity of the obtained material is not less than 98.5% by weight. The remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and continue the purification.

[0097] Comparative Example 1

[0098] Perform D-allulose crystallization according to the method of Example 1, except that in pre-crystallization and cooling crystallization, no dry gas is introduced.

[0099] Comparative Example 2

[0100] Perform D-allulose crystallization according to the method of Example 1, except that the dry gas is replaced with ordinary air.

[0101] Comparative Example 3

[0102] Take 18.75 L of the purified D-allulose solution obtained in Example 1 and perform D-allulose crystallization according to the method disclosed in CN202011237164.8, and record the time required for the purified D-allulose solution to start preparing for crystallization from entering the crystallization container to the completion of crystallization and the material leaving the crystallization container, which is 120 h.

[0103] Test Example 1

[0104] Detect the purity, crystallization rate, and particle uniformity of the D-allulose crystals obtained in Examples 1-5 and Comparative Examples 1-3, and observe whether there are cavities or caking phenomena in the crystals. The results are shown in Table 1. Among them, the obtained crystals refer to the D-allulose crystals after solid-liquid separation of the slurry and drying of the D-allulose crystals, that is, the D-allulose crystals obtained when the mother liquor has not been returned yet.

[0105] Among them, the detection method of purity is as follows: Using D-psicose standard product, prepare D-psicose standard solution (10.0 mg / mL), and successively dilute it into solutions with concentrations of 10.0 mg / mL, 8.0 mg / mL, 6.0 mg / mL, 4.0 mg / mL, 2.0 mg / mL, 1.0 mg / mL, 0.5 mg / mL, and 0.25 mg / mL. Use a high-performance liquid chromatography system to measure the peak area of the D-psicose standard solution. Taking the peak area (the average value of 3 parallel samples) as the ordinate and the solution concentration as the abscissa, plot a standard curve, and quantitatively analyze the D-psicose crystals in Examples 1-5 and Comparative Examples 1-3 according to the standard curve. The chromatographic conditions are as follows: The Agilent 1260 series high-performance liquid chromatography system includes a G 1311C quaternary pump, a G 1316A column oven, a G 1329B automatic injection system, and a G 1236A differential refractive index detector. The chromatographic column is a Luna 5u NH2 100A chromatographic column (250 mm × 4.6 mm, 5 μm). The mobile phase is acetonitrile: water = 70:30 (volume ratio), the flow rate is 1 mL / min, the column temperature is 30 °C, a differential refractive index detector is used, and the injection volume is 10 μL. All samples are filtered through a 0.45 μm microfiltration membrane before injection.

[0106] Among them, the calculation method of the primary crystallization yield is: crystallization yield = (mass of D-psicose crystals) / (volume of D-psicose concentrated solution * concentration) * 100%.

[0107] The detection method of particle uniformity is as follows: Use 40-mesh and 60-mesh sieves to determine the proportion of the weight of D-psicose with a particle size in the range of 40-60 meshes in the total mass of D-psicose crystals. The higher this proportion, the better the uniformity.

[0108] Table 1

[0109]

[0110] It can be seen from the results in Table 1 that Examples 1-5 adopting the technical solution of the present invention have higher crystallization rates and purities, and the obtained crystal particle size distributions are relatively uniform, and the occurrence of cavities or caking phenomena in the crystals is avoided, and the effects of Examples 1-3 are better. The crystallization rates and crystal particle size distributions of Comparative Examples 1-3 are not uniform, and obvious caking and cavities exist in the crystals. Moreover, it can be seen from the results of Example 1 and Comparative Examples 1 and 3 that adopting the technical solution of the present invention can obtain a higher crystallization rate in a shorter time, so it can greatly shorten the time and improve the efficiency.

[0111] In addition, by adopting the technical solution of the present invention, a high crystallization rate can be obtained without using organic reagents, the production process is relatively safe, the pollution and residue of organic reagents can be avoided, and it is environmentally friendly. Moreover, the process is simple, the cost is low, and it has good industrialization prospects.

[0112] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for crystallizing D-psicose, characterized in that, The method includes: (1) Mixing a D-psicose concentrate with D-psicose seeds to obtain a mixture; (2) Performing pre-crystallization and cooling crystallization on the mixture in the intermittent presence of a bone-dry gas to obtain a slurry; The bone-dry gas is at least one of air, nitrogen, and carbon dioxide with a water content far lower than the humidity of conventional air, and the water content of the bone-dry gas is 0.5 - 1.5% by weight; The method for providing the bone-dry gas includes: introducing the bone-dry gas once every 5 - 30 min and maintaining the introduction for 5 - 30 s, repeating the operations of introduction and non-introduction until the end of pre-crystallization and cooling crystallization; The temperature of the pre-crystallization is 44 - 46 °C; The conditions for the cooling crystallization include: cooling at a cooling rate of 0.8 - 1.5 °C / h, cooling to 22 - 28 °C and maintaining the temperature at 22 - 28 °C, with a stirring rate of 50 - 150 rpm, and the time for cooling crystallization is 15 - 30 h; (3) Separating the solid and liquid of the slurry to obtain D-psicose crystals and mother liquor.

2. The method according to claim 1, wherein, The method for obtaining the D-psicose concentrate includes: purifying a D-psicose solution to be purified to obtain a purified D-psicose solution, and concentrating the purified D-psicose solution to obtain a D-psicose concentrate; Among them, the purity of the purified D-psicose solution is not less than 98.5% by weight.

3. The method according to claim 1, wherein The concentration of the D-psicose concentrate is 700 - 850 g / L; And / or, relative to 1 L of the D-psicose concentrate, the dosage of the D-psicose seeds is 1 - 50 g.

4. The method according to claim 1, wherein The concentration of the D-psicose concentrate is 780 - 830 g / L; And / or, relative to 1 L of the D-psicose concentrate, the dosage of the D-psicose seeds is 10 - 30 g.

5. The method according to claim 1, wherein The temperature of the bone-dry gas is 30 - 60 °C; And / or, the method for providing the bone-dry gas includes: dispersedly introducing the bone-dry gas from the bottom of the mixture; And / or, relative to 1 L of the psicose concentrate, the introduction rate of the bone-dry gas is 0.1 - 1 L / min.

6. The method according to claim 1, wherein, The temperature of the bone-dry gas is 40 - 50 °C, and the water content is 0.8 - 1% by weight; And / or, the method for providing the bone-dry gas includes: introducing the bone-dry gas once every 10 - 20 min and maintaining the introduction for 10 - 20 s, repeating the operations of introduction and non-introduction until the end of pre-crystallization and cooling crystallization.

7. The method according to claim 1, wherein The conditions for the pre-crystallization further include: the time is 50 - 60 h, and the stirring rate is 50 - 150 rpm.

8. The method according to claim 2, wherein, The method further includes: taking a part of the mother liquor, returning it to be mixed with the purified D-psicose solution, and concentrating them together; Among them, the amount of a part of the mother liquor is such that after returning it to be mixed with the purified D-psicose solution, the purity of the obtained material is not less than 98.5% by weight.

9. The method according to claim 8, wherein Returning the remaining part of the mother liquor to be mixed with the D-psicose solution to be purified, and purifying them together.

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