Methods for D-allulose crystallization

Abstract

This invention relates to the field of crystallization, specifically to a method for crystallizing D-allulose. The method includes: (1) mixing a concentrated D-allulose solution, D-allulose seed crystals, and ethanol to obtain a mixture; (2) pre-crystallizing and cooling crystallizing the mixture under intermittent ultrasonic waves to obtain a slurry; and (3) performing solid-liquid separation on the slurry to obtain D-allulose crystals and a mother liquor. This method offers high crystallization yield, a suitable crystallization rate, uniform product particles that are not prone to clumping, a simple and safe preparation process, low cost, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of crystallization, and more specifically to a method for crystallizing D-allulose. Background Technology

[0002] With the global spread of chronic diseases such as obesity, diabetes, and hypertension, the "three highs" (high blood pressure, high blood sugar, and high cholesterol) in the diet, "healthy intake" of sugar has become a new health challenge. The development and application of low-calorie sweeteners is one of the most effective approaches. Allulose, with a sweetness equivalent to 70% of sucrose and calories equivalent to 0.3% of sucrose, can serve as a sucrose substitute in the food and pharmaceutical industries. D-Allulose has the effect of controlling obesity and diabetes, and can significantly inhibit weight gain and abdominal fat accumulation. D-Allulose is classified as a conventional carbohydrate substitute.

[0003] However, D-allulose is extremely water-soluble, making crystallization difficult. Spray drying causes it to deliquesce easily, resulting in poor quality. Therefore, developing a suitable crystallization process is crucial for the development of the allulose industry.

[0004] Currently, the commonly used aqueous crystallization technology for D-allulose generally follows three approaches. The first is to adjust the supersaturation of the crystallization solution by regulating the relationship between temperature and solubility, as disclosed in CN201780066740.7. The second is to continuously reduce the water content in the crystallization mother liquor through evaporation, thereby increasing the crystallization yield, as disclosed in CN201910876767.3. The third is a two-step crystallization process: first, crystallization is performed through concentration; when the concentration of the concentrated crystallization mother liquor is too high, crystallization is then carried out at a lower temperature, as disclosed in CN201911015344.9 and CN201680069967.2. However, these methods suffer from problems such as difficulty in controlling the crystallization rate, leading to uneven particle size, easy clumping, low evaporation area and efficiency, and low yield.

[0005] In addition, conventional crystallization techniques have several disadvantages. First, the D-allulose concentrate itself contains a small amount of gas, which affects mass transfer at the microscale, thus reducing the crystallization yield. Second, the high viscosity of the liquid makes it difficult for D-allulose molecules to contact the surface of the seed crystals, thus affecting the crystallization rate. Third, high viscosity also reduces the speed of molecular motion at the microscale, further decreasing the crystallization rate of D-allulose. Fourth, conventional stirring creates dead zones in the container, where crystals tend to agglomerate, affecting product quality and yield, and posing a risk of clogging pipelines. Furthermore, the crystallization time is generally long, typically requiring more than 120 hours.

[0006] Therefore, there is a need to develop a method for preparing D-allulose that has a high crystallization yield, a suitable crystallization rate, uniform product particles that are not prone to clumping, a simple and safe preparation process, low cost, and is environmentally friendly and does not use harmful organic reagents. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide a method for D-allulose crystallization. This method has a high crystallization yield, a suitable crystallization rate, uniform product particles that are not prone to clumping, a simple and safe preparation process, low cost, and is environmentally friendly.

[0008] To achieve the above objectives, the present invention provides a method for D-allulose crystallization, the method comprising:

[0009] (1) Mix D-allulose concentrate, D-allulose seed crystals and ethanol to obtain a mixture;

[0010] (2) Under the intermittent presence of ultrasound, the mixture is pre-crystallized and cooled to crystallize, to obtain a slurry;

[0011] (3) The slurry is subjected to solid-liquid separation to obtain D-aloxose crystals and mother liquor.

[0012] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0013] 1. The method of the present invention can achieve a high crystallization yield and a suitable crystallization rate, which can significantly shorten the crystallization time, making the product particles uniform and less prone to clumping, thus improving the quality of the crystallized product.

[0014] 2. The method of this invention is simple and safe in preparation, operates under mild conditions, and uses commonly used and widely available equipment. Furthermore, the reagents used are environmentally friendly, low in cost, and easily scaled up industrially. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] This invention provides a method for D-allulose crystallization, the method comprising:

[0017] (1) Mix D-allulose concentrate, D-allulose seed crystals and ethanol to obtain a mixture;

[0018] (2) Under the intermittent presence of ultrasound, the mixture is pre-crystallized and cooled to crystallize, to obtain a slurry;

[0019] (3) The slurry is subjected to solid-liquid separation to obtain D-aloxose crystals and mother liquor.

[0020] According to the present invention, a preferred method for obtaining 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 D-allulose concentrate.

[0021] The purified D-allulose solution has a purity of not less than 98.5% by weight (e.g., 98.5% by weight, 98.6% by weight, 98.7% by weight, 98.8% by weight, 98.9% by weight, or 99% by weight).

[0022] The D-allulose solution to be purified can be any one or a mixture of two or three materials obtained from natural extraction, enzymatic synthesis, or chemical synthesis. For example, the D-allulose solution to be purified can be obtained from fructose through the catalytic conversion of D-allulose 3-epimerase.

[0023] The purification method can employ continuous ion exchange chromatography and simulated moving bed separation technology.

[0024] According to the present invention, in order to further ensure a high crystallization yield and a suitable crystallization rate, and to further ensure that the obtained product particles are uniform and do not clump, preferably, the concentration of the D-allulose concentrate is 800-900 g / L (for example, it can be 800 g / L, 820 g / L, 840 g / L, 850 g / L, 870 g / L, 880 g / L, or 900 g / L), more preferably 840-860 g / L, and even more preferably 850 g / L.

[0025] It is understandable that "purity" and "concentration" are different concepts. In actual production, solutions containing D-allulose often contain other sugars or alcohols (dry matter) in addition to D-allulose. Purity refers to the ratio of the weight of 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 to the total weight of the solution.

[0026] The concentration equipment is not subject to any particular restrictions, but in order to facilitate operation during industrial scale-up and lower the threshold for process technology scale-up, single-effect, double-effect, triple-effect, and quadruple-effect concentration equipment can be used.

[0027] According to the present invention, in order to avoid the caramelization reaction caused by excessively high local temperature during the concentration process of D-allulose, which would lead to browning of the concentrate and result in the final D-allulose crystals being yellow, it is preferable that the temperature during the concentration process be controlled not higher than 50°C (for example, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C).

[0028] According to the present invention, the concentration method can be a conventional choice in the art, but preferably, the concentration method is vacuum concentration. It is understood that in vacuum concentration, the lower the concentration pressure, the better, but taking into account cost and ease of operation, the concentration pressure is based on the principle of achieving rapid concentration of the purified D-allulose solution at a lower temperature.

[0029] According to the present invention, preferably, the amount of ethanol used is 1-5 L relative to 1 L of D-allulose concentrate. The inventors of the present invention have discovered that when the amount of ethanol meets the range described above, while reducing the amount used and making full use of ethanol, it is also possible to further ensure a high crystallization yield and a suitable crystallization rate, and further ensure that the obtained product particles are uniform and do not clump together.

[0030] According to the present invention, preferably, the amount of D-allulose seed crystals used relative to 1L of a mixture of D-allulose concentrate and ethanol is 1-50g (e.g., 1g, 5g, 10g, 20g, 30g, 40g, 50g), more preferably 10-30g, and even more preferably 20g. The inventors of the present invention have discovered that when the amount of D-allulose seed crystals meets the range described above, the crystallization rate is suitable, which not only avoids product agglomeration but also enables a high crystallization yield to be obtained in a shorter time.

[0031] According to the present invention, preferably, the total time for pre-crystallization and cooling crystallization is 40-50 hours (for example, it can be 40 hours, 41 hours, 42 hours, 43 hours, 44 hours, 45 hours, 46 hours, 47 hours, 48 ​​hours, 49 hours, or 50 hours).

[0032] According to the present invention, in order to further ensure a high crystallization yield and a suitable crystallization rate, and to further ensure that the obtained product particles are uniform and do not clump, the pre-crystallization conditions preferably include: a stirring speed of 50-150 rpm (e.g., 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm), a temperature of 45-55℃ (e.g., 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃), and a time of 5-10 h (e.g., 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h). More preferably, the stirring speed of the pre-crystallization is 90-120 rpm. The inventors of this invention discovered in their research that by using the conditions described above, especially the stirring rate described above, and by combining intermittent ultrasonic waves, it is possible to avoid the crystal particles from breaking due to rapid stirring, and to avoid the crystal particles from clumping due to local oversaturation caused by slow stirring.

[0033] According to the present invention, in order to further ensure a high crystallization yield and a suitable crystallization rate, and to further ensure that the obtained product particles are uniform and do not clump, the preferably preferred conditions for the cooling crystallization include: cooling at a rate of 1-1.5℃ / h (e.g., 1℃ / h, 1.1℃ / h, 1.2℃ / h, 1.3℃ / h, 1.4℃ / h, 1.5℃ / h) to 22-28℃ (e.g., 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃) and maintaining the temperature at 22-28℃, with a stirring rate of 50-150 rpm (e.g., 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm). Cooling crystallization is generally completed in 35-40 hours. More preferably, the stirring rate for the cooling crystallization is 90-120 rpm. Stirring occurs both during the cooling process and while the temperature has reached and is maintained at the target temperature. It is understood that cooling can bring the mixture to a supersaturated state, thereby promoting crystallization. The inventors of this invention have discovered in their research that using the conditions described above, particularly the cooling rate, avoids excessively drastic changes in conditions, promoting crystallization while preventing the crystalline product from agglomerating.

[0034] According to the present invention, although the objective of the invention can be achieved by intermittent ultrasonic waves, in order to further ensure a high crystallization yield and a suitable crystallization rate, and to further ensure that the obtained product particles are uniform and do not clump, the preferred method of providing ultrasonic waves is: ultrasonication for 10-60 seconds (e.g., 10S, 20S, 30S, 40S, 50S, 60S, 70S, 80S, 90S, 100S, 110S, 120S) every 10-120s ...). S, 60S), continue for 1-10 minutes (e.g., 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min), then turn off the ultrasound and maintain it for 60-180 minutes (e.g., 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, 180 min). Repeat the ultrasound and ultrasound-off operation until pre-crystallization and cooling crystallization are completed. The power of the ultrasound is 100-1000 W / m. 3 Mixture (e.g., 100W / m) 3 Mixed material, 200W / m 3 Mixed material, 300W / m 3 Mixed material, 400W / m 3 Mixed material, 500W / m 3 Mixed material, 600W / m 3 Mixed material, 700W / m 3 Mixed material, 800W / m 3 Mixed material, 900W / m 3 Mixed material, 1000W / m 3 (Mixture). More preferably, the method of providing ultrasound is as follows: ultrasound is performed for 15-40 seconds every 15-40 seconds, and this is continued for 3-7 minutes. Then, the ultrasound is turned off and maintained for 90-120 minutes. The operation of ultrasound and turning off the ultrasound is repeated until the pre-crystallization and cooling crystallization are completed. The power of the ultrasound is 300-500 W / m. 3 Mixture. For example, sonicate for 20 seconds every 20 seconds, continue for 5 minutes, then turn off the sonication and maintain it for 120 minutes. Repeat the sonication and sonication-off operation until pre-crystallization and cooling crystallization are completed. The power of the sonication is 400 W / m. 3 Mixture.

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

[0036] According to the present invention, preferably, after solid-liquid separation, the D-allulose crystals are dried. The drying method can be a conventional choice in the art, but for more efficient drying of the D-allulose crystals to remove any liquid that may still be present, preferably, the drying is selected from 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 portion of the mother liquor, returning it to be mixed with the purified D-allulose solution, and concentrating them together;

[0038] The amount of the mother liquor is such that, after being returned to the purified D-allulose solution and mixed, the purity of the resulting material is not less than 98.5% by weight.

[0039] According to the present invention, in order to further improve the crystallization yield, preferably, the remaining mother liquor is returned to be mixed with the D-allulose solution to be purified and purified together.

[0040] According to a particularly preferred embodiment of the present invention, D-allulose crystallization is carried out according to the following method:

[0041] (1) The D-allulose solution to be purified was 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.

[0042] Take the purified D-allulose solution as described above and concentrate it under reduced pressure at a temperature not exceeding 50°C until the concentration is 845-855 g / L to obtain D-allulose concentrate.

[0043] Take the D-allulose concentrate as described above and mix it with ethanol (2-3L of ethanol relative to 1L of D-allulose concentrate). Add D-allulose seed crystals (15-25g of D-allulose seed crystals relative to 1L of the mixture of D-allulose concentrate and ethanol) to the mixture and stir to make the D-allulose seed crystals evenly dispersed to obtain a mixture.

[0044] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 380-420W / m. 3 Mix the materials and set the ultrasonic treatment to be performed every 18-22 seconds for 18-22 seconds. Continue this for 4-6 minutes, then turn off the ultrasonic treatment and maintain it for 115-120 minutes. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0045] The pre-crystallization conditions include: a stirring rate of 95-105 rpm, a temperature of 49-51℃, and a time of 6.5-7.5 h. After pre-crystallization, cooling crystallization begins. The cooling crystallization conditions include: cooling at a rate of 1.2-1.3℃ / h to 24-26℃ and maintaining that temperature, with a stirring rate of 95-105 rpm during the cooling crystallization process. Cooling crystallization lasts for 37-40 h, after which a slurry is obtained.

[0046] (3) The slurry is centrifuged to obtain D-allulose crystals and mother liquor, and the D-allulose crystals are vacuum dried and weighed.

[0047] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being 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 further purified.

[0048] The present invention will be described in detail below through embodiments. In the following embodiments and test examples,

[0049] The ultrasonic circulating extractor, model GCXZ-2B, was purchased from Beijing Hongxianglong Biotechnology Co., Ltd.

[0050] The vacuum drying oven, model DZF-6050, was purchased from Shanghai Bozheng Industrial Co., Ltd.

[0051] The centrifugal filter, model SSC300, was purchased from Yongle Machinery Equipment Manufacturing Co., Ltd.

[0052] Allulose standard was purchased from Shanghai Lizhi Biotechnology Co., Ltd.

[0053] Example 1

[0054] This invention provides a method for illustrating the crystallization of D-allulose.

[0055] (1) The D-allulose solution to be purified was purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.8% by weight.

[0056] Take the purified D-allulose solution as described above, and concentrate it under reduced pressure in a triple-effect concentrator at 49°C until the concentration is 850 g / L, to obtain D-allulose concentrate.

[0057] Take 17.6L of the D-allulose concentrate as described above and mix it with 44L of ethanol (2.5L of ethanol relative to 1L of D-allulose concentrate). Add 352g of D-allulose seed crystals (20g of D-allulose seed crystals relative to 1L of the mixture of D-allulose concentrate and ethanol) to the mixture and stir to make the D-allulose seed crystals evenly dispersed to obtain the mixture.

[0058] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 400W / m. 3 Mix the materials and set the ultrasonic treatment to 20 seconds every 20 seconds. Continue this for 5 minutes, then turn off the ultrasonic treatment and maintain it for 120 minutes. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0059] The pre-crystallization conditions included a stirring rate of 100 rpm, a temperature of 50°C, and a time of 7 hours. After pre-crystallization, cooling crystallization commenced. The cooling crystallization conditions included a cooling rate of 1.2°C / h, cooling to 25°C and maintaining that temperature, with a stirring rate of 100 rpm during the cooling crystallization process. Cooling crystallization lasted for 37 hours, after which a slurry was obtained.

[0060] (3) The slurry is centrifuged to obtain D-allulose crystals and mother liquor, and the D-allulose crystals are vacuum dried and weighed.

[0061] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being 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 further purified.

[0062] Example 2

[0063] This invention provides a method for illustrating the crystallization of D-allulose.

[0064] (1) The D-allulose solution to be purified was purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.6% by weight.

[0065] Take the purified D-allulose solution as described above, and concentrate it under reduced pressure in a triple-effect concentrator at 50°C until the concentration is 840 g / L, to obtain D-allulose concentrate.

[0066] Take 20L of the D-allulose concentrate as described above and mix it with 20L of ethanol (the amount of ethanol used is 1L relative to 1L of D-allulose concentrate). Add 200g of D-allulose seed crystals (the amount of D-allulose seed crystals used is 10g relative to 1L of the mixture of D-allulose concentrate and ethanol) to the mixture and stir to make the D-allulose seed crystals evenly dispersed to obtain the mixture.

[0067] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 300W / m. 3 Mix the materials and set the ultrasonic treatment to 15 seconds every 15 seconds. Continue this for 3 minutes, then turn off the ultrasonic treatment and maintain it for 90 minutes. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0068] The pre-crystallization conditions included a stirring rate of 90 rpm, a temperature of 45°C, and a time of 5 hours. After pre-crystallization, cooling crystallization commenced. The cooling crystallization conditions included a cooling rate of 1°C / h until the temperature reached 22°C, which was then maintained at 22°C, with a stirring rate of 90 rpm during the cooling crystallization process. Cooling crystallization continued for 35 hours, after which a slurry was obtained.

[0069] (3) The slurry is centrifuged to obtain D-allulose crystals and mother liquor, and the D-allulose crystals are vacuum dried and weighed.

[0070] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being 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 further purified.

[0071] Example 3

[0072] This invention provides a method for illustrating the crystallization of D-allulose.

[0073] (1) The D-allulose solution to be purified was purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0074] Take the purified D-allulose solution as described above, and concentrate it under reduced pressure in a triple-effect concentrator at 40°C until the concentration is 860 g / L, to obtain D-allulose concentrate.

[0075] Take 20L of the D-allulose concentrate as described above and mix it with 100L of ethanol (the amount of ethanol used is 5L relative to 1L of D-allulose concentrate). Add 600g of D-allulose seed crystals (the amount of D-allulose seed crystals used is 30g relative to 1L of the mixture of D-allulose concentrate and ethanol) to the mixture and stir to make the D-allulose seed crystals evenly dispersed to obtain a mixture.

[0076] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 500W / m. 3 Mix the materials and set the ultrasonic treatment to 40 seconds every 40 seconds. Continue this for 7 minutes, then turn off the ultrasonic treatment and maintain it for 120 minutes. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0077] The pre-crystallization conditions included a stirring rate of 120 rpm, a temperature of 55°C, and a time of 10 h. After pre-crystallization, cooling crystallization began. The cooling crystallization conditions included a cooling rate of 1.5°C / h, cooling to 28°C, and maintaining the temperature at 28°C, with a stirring rate of 120 rpm during the cooling crystallization process. Cooling crystallization lasted for 40 h, after which a slurry was obtained.

[0078] (3) The slurry is centrifuged to obtain D-allulose crystals and mother liquor, and the D-allulose crystals are vacuum dried and weighed.

[0079] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being 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 further purified.

[0080] Example 4

[0081] This invention provides a method for illustrating the crystallization of D-allulose.

[0082] (1) The D-allulose solution to be purified was purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0083] Take the purified D-allulose solution as described above, and concentrate it under reduced pressure in a triple-effect concentrator at 35°C until the concentration is 800 g / L, to obtain D-allulose concentrate.

[0084] Take 20L of the D-allulose concentrate as described above and mix it with 20L of ethanol (the amount of ethanol used is 1L relative to 1L of D-allulose concentrate). Add 20g of D-allulose seed crystals (the amount of D-allulose seed crystals used is 1g relative to 1L of the mixture of D-allulose concentrate and ethanol) to the mixture and stir to make the D-allulose seed crystals evenly dispersed to obtain a mixture.

[0085] (2) An ultrasonic circulating extractor is used. The ultrasonic probe is inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 100W / m. 3 Mix the materials and set the ultrasonic treatment to 10 seconds every 10 seconds. Continue this for 1 minute, then turn off the ultrasonic treatment and maintain it for 60 minutes. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0086] The pre-crystallization conditions included a stirring rate of 50 rpm, a temperature of 45°C, and a time of 5 hours. After pre-crystallization, cooling crystallization commenced. The cooling crystallization conditions included a cooling rate of 1.5°C / h, cooling to 25°C and maintaining that temperature, with a stirring rate of 50 rpm during the cooling crystallization process. Cooling crystallization continued for 40 hours, after which a slurry was obtained.

[0087] (3) The slurry is centrifuged to obtain D-allulose crystals and mother liquor, and the D-allulose crystals are vacuum dried and weighed.

[0088] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being 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 further purified.

[0089] Example 5

[0090] This invention provides a method for illustrating the crystallization of D-allulose.

[0091] (1) The D-allulose solution to be purified was purified by simulated moving bed separation technology to obtain a purified D-allulose solution with a purity of 98.5% by weight.

[0092] Take the purified D-allulose solution as described above, and concentrate it under reduced pressure in a triple-effect concentrator at 30°C until the concentration is 900 g / L, to obtain D-allulose concentrate.

[0093] Take 20L of the D-allulose concentrate as described above and mix it with 100L of ethanol (the amount of ethanol used is 5L relative to 1L of D-allulose concentrate). Add 1000g of D-allulose seed crystals (the amount of D-allulose seed crystals used is 50g relative to 1L of the mixture of D-allulose concentrate and ethanol) to the mixture and stir to make the D-allulose seed crystals evenly dispersed to obtain a mixture.

[0094] (2) An ultrasonic circulating extractor is used, with the ultrasonic probe inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 1000W / m. 3 Mix the materials and set the ultrasonic treatment to 60 seconds every 120 seconds. Continue this for 10 minutes, then turn off the ultrasonic treatment and maintain it for 180 minutes. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed.

[0095] The pre-crystallization conditions included a stirring rate of 150 rpm, a temperature of 55°C, and a time of 10 hours. After pre-crystallization, cooling crystallization commenced. The cooling crystallization conditions included a cooling rate of 1.5°C / h, cooling to 25°C and maintaining that temperature, with a stirring rate of 150 rpm during the cooling crystallization process. Cooling crystallization continued for 40 hours, after which a slurry was obtained.

[0096] (3) The slurry is centrifuged to obtain D-allulose crystals and mother liquor, and the D-allulose crystals are vacuum dried and weighed.

[0097] A portion of the mother liquor is returned to be mixed with the purified D-allulose solution and concentrated together; wherein the amount of the mother liquor is such that, after being 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 further purified.

[0098] Example 6

[0099] D-allulose crystallization was carried out according to the method of Example 1, except that during pre-crystallization and cooling crystallization, sonication was maintained for 20 seconds every 20 seconds, i.e., the sonication was not turned off and was maintained.

[0100] Comparative Example 1

[0101] D-allulose crystallization was carried out according to the method of Example 1, except that ultrasound was not provided during pre-crystallization and cooling crystallization.

[0102] Comparative Example 2

[0103] Take 17.6 L of the purified D-allulose solution obtained in Example 1, and crystallize D-allulose according to CN201910876767.3. Record the time required to obtain the same weight of D-allulose crystals as obtained in Example 1, which is 120 h.

[0104] Test case

[0105] The purity, crystallinity, and particle uniformity of the D-allulose crystals obtained in Examples 1-6 and Comparative Examples 1-2 were tested, and the presence of agglomeration or clumping in the crystals was observed. The results are shown in Table 1. The obtained crystals refer to the D-allulose crystals obtained after solid-liquid separation of the slurry and drying, i.e., before the mother liquor was returned.

[0106] The purity was determined as follows: A D-allulose standard solution (10.0 mg / mL) was prepared using D-allulose standards and subsequently diluted to 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. The peak area of ​​the D-allulose standard solution was determined using high-performance liquid chromatography (HPLC). A standard curve was plotted with the peak area (average of three parallel samples) on the ordinate and the solution concentration on the abscissa. The D-allulose crystals in Examples 1-6 and Comparative Examples 1-2 were then quantitatively analyzed based on the standard curve. The chromatographic conditions were as follows: The Agilent 1260 series high-performance liquid chromatography system included a G 1311C quaternary pump, a G 1316A column oven, a G 1329B autosampler, and a G 1236A differential detector. The column was a Waters Sugar-PakI (10 μm, 6.5 mm × 300 mm); the column temperature was 80 °C, the RID detection temperature was 55 °C, the mobile phase was water, and the flow rate was 0.4 mL / min. All samples were filtered through a 0.45 μm microfiltration membrane before injection.

[0107] The method for calculating the primary crystallization rate is as follows: Crystallization yield = (mass of D-allulose crystals) / (volume of D-allulose concentrate * concentration) * 100%.

[0108] The method for detecting particle uniformity is as follows: using 40-mesh and 60-mesh sieves, determine the proportion of the weight of D-allulose with a particle size in the range of 40-60 mesh to the total mass of D-allulose crystals. The higher the proportion, the better the uniformity.

[0109] Table 1

[0110]

[0111] As can be seen from the results in Table 1, Examples 1-6 using the technical solution of the present invention exhibit higher crystallinity and purity, and the obtained crystal particle size distribution is more uniform, avoiding the occurrence of agglomeration or clumping in the crystals. Examples 1-3 show even better results. Comparative Examples 1-2 show uneven crystallinity and crystal particle size distribution, with obvious agglomeration and clumping in the crystals. Furthermore, the results of Examples 1, 6, and Comparative Example 1 demonstrate that the technical solution of the present invention can achieve a higher crystallinity in a shorter time, thus significantly reducing time and improving efficiency.

[0112] Furthermore, the preparation process using the technical solution of this invention is simple, the operating conditions are mild, the equipment is commonly used and widely available, the reagents used are environmentally friendly and low in cost, and it has good prospects for industrialization.

[0113] 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 inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for crystallizing D-allulose, characterized in that, The method includes: (1) The D-allulose solution to be purified was 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. Take the purified D-allulose solution as described above and concentrate it under reduced pressure at a temperature not exceeding 50°C until the concentration is 845-855 g / L to obtain D-allulose concentrate. Take the D-allulose concentrate as described above and mix it with ethanol. The amount of ethanol used is 2-3L relative to 1L of D-allulose concentrate. Add D-allulose seed crystals to the mixture. The amount of D-allulose seed crystals used is 15-25g relative to 1L of the mixture of D-allulose concentrate and ethanol. Stir the mixture to make the D-allulose seed crystals evenly dispersed to obtain a mixture. (2) An ultrasonic circulating extractor is used. The ultrasonic probe is inserted below the liquid surface of the mixture, and the ultrasonic power is adjusted to reach 380-420W / m. 3 Mix the materials and set the ultrasonic treatment to be performed every 18-22 seconds for 18-22 seconds. Continue this for 4-6 minutes, then turn off the ultrasonic treatment and maintain it for 115-120 minutes. Repeat the ultrasonic treatment and turn off the ultrasonic treatment until the pre-crystallization and cooling crystallization are completed. The pre-crystallization conditions include: a stirring rate of 95-105 rpm, a temperature of 49-51℃, and a time of 6.5-7.5 h. After pre-crystallization, cooling crystallization begins. The cooling crystallization conditions include: cooling at a rate of 1.2-1.3℃ / h to 24-26℃ and maintaining the temperature at 24-26℃, with a stirring rate of 95-105 rpm during the cooling crystallization process. The cooling crystallization lasts for 37-40 h, after which a slurry is obtained. (3) The slurry is centrifuged to obtain D-allulose crystals and mother liquor, and the D-allulose crystals are vacuum dried.

2. The method according to claim 1, wherein, The method further includes: taking a portion of the mother liquor, returning a portion of the mother liquor to mix with the purified D-allulose solution, and concentrating them together; wherein the amount of the portion of the mother liquor is such that after returning it to mix with the purified D-allulose solution, the purity of the resulting material is not less than 98.5% by weight.

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