System and method for producing high quality xylitol crystals

Abstract

The present invention relates to a system and method for producing high-quality xylitol crystals. The system includes a conditioning tank, a heat exchanger, a decolorization tank, an ion exchange system, a microporous filter, a first evaporator, a first crystallization tank, a first centrifuge, a fluidized drying tank, a xylitol dissolving tank, a second evaporator, a second crystallization tank, a second centrifuge, a hot air drying tank, and a cold air fluidized bed, which are connected in sequence through a pipe, the first centrifuge is further connected to the conditioning tank through a pipe, the second centrifuge is further connected to the xylitol dissolving tank through a pipe, the conditioning tank is provided with a supply port for xylitol hydrogenation liquid, the xylitol dissolving tank is further provided with a water supply port for purified water, and the material from the cold air fluidized bed is the xylitol crystal product. The present invention adds water to the initially produced xylitol crystals at a certain ratio to dissolve them to obtain a higher purity xylitol solution, and recrystallizes the xylitol solution to produce xylitol crystals with a higher pH and better flavor.

Description

Technical Field

[0001] The present invention belongs to the technical field of xylitol production, and particularly relates to a system and method for producing high-quality xylitol crystals.

Background Art

[0002] Currently, the industrial production of xylitol mainly involves hydrolyzing agricultural fiber waste containing hemicellulose with dilute acid, neutralizing, decolorizing, concentrating, and crystallizing the hydrolysis solution to obtain xylose crystals. Next, the xylose crystals are dissolved to form a xylose solution with a certain concentration, hydrogenated and reduced to xylitol, and finally, through steps such as ion exchange, vacuum concentration, cooling crystallization, and centrifugal drying, xylitol crystals are obtained, using chemical hydrogenation. In order to improve the yield of the xylitol product, the centrifuged mother liquor is often mixed with the hydrogenation solution. As a result, there are 4-6% of miscellaneous sugars and sugar alcohols in the mixed solution. These miscellaneous sugars and sugar alcohols have little effect on the crystallization process of xylitol, but they lower the pH value of the product and ultimately bring a significant difference in the flavor of the product.

[0003] In the production process of xylitol, there are two main factors that affect the pH of the product. One is the ion exchange process. In the cation exchange column and anion exchange column of the xylitol solution, H + and OH - are respectively exchanged, and due to the difference in the exchange amounts of the cation exchange column and the anion exchange column, the pH of the finally produced xylitol crystals is different. The other is that due to the difference in the components of the xylitol concentrate, there is a significant difference in the pH of the xylitol crystals. The acidity coefficients (pKa) of miscellaneous sugars such as glucose and xylose are smaller than that of xylitol, as shown in Table 1 below. Therefore, when a certain amount of miscellaneous sugars is present in the xylitol concentrate, as shown in Table 2 below, the pH of the produced xylitol crystals is lower and the flavor difference is greater.

[0004]

Table 1

[0005]

Table 2

[0006] Currently, there are mainly two methods to increase the pH of xylitol crystals. One method is to add strong alkali resin or mixed layer resin after the ion exchange process, such as in Patent Publication No. CN109438184A and Patent Publication No. CN110894180A. Another method is to add a small amount of alkali solution to the ion exchange solution, such as in Patent Publication No. CN112661796A. Both methods aim to increase the pH of xylitol crystals by increasing the pH of the xylitol concentrate. The route of this process is simple and clear, and there are corresponding technical effects, but it does not essentially solve the problems of the low pH of xylitol produced by the conventional process and the large difference in flavor.

[0007] Therefore, considering this problem existing in the conventional production process of xylitol, it is very important to search for a method to increase the pH of xylitol crystals and improve the flavor from the essential properties that affect the low pH and large flavor difference of xylitol crystals.

Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a system and a method for producing high-quality xylitol crystals, which can add water to the initially produced xylitol crystals at a certain ratio to dissolve them, obtain a xylitol solution with higher purity, recrystallize this xylitol solution, and produce xylitol crystals with a higher pH and better flavor. This system can significantly increase the pH of xylitol crystals, stably maintain the pH over a long period of time, and effectively improve the flavor of xylitol crystals.

[0009] The present invention is achieved as follows. It includes a harmonic tank, a heat exchanger, a decolorization tank, an ion exchange system, a microporous filter, a first evaporator, a first crystallization kettle, a first centrifuge, a fluidized drying layer, a xylitol dissolution tank, a second evaporator, a second crystallization kettle, a second centrifuge, a hot air drying tank, and a cold air fluidized layer, which are sequentially communicated through pipes. Each of the first centrifuge and the second centrifuge is provided with a liquid discharge port. The liquid discharge port of the first centrifuge communicates with one supply port of the harmonic tank through a pipe, and the liquid discharge port of the second centrifuge communicates with one supply port of the xylitol dissolution tank through a pipe. The harmonic tank is provided with a supply port for the material to be treated, the xylitol dissolution tank is further provided with a water supply port for purified water, the cold air fluidized layer is provided with a discharge port, the material to be treated is a xylitol hydrogenation solution, and the material discharged from the discharge port of the cold air fluidized layer is a xylitol crystal product, thus providing a system for manufacturing high-quality xylitol crystals.

[0010] The technical problem to be solved by the present invention is further Manufacture of xylitol concentrate: The xylitol hydrogenation solution and the first centrifuge mother liquor sent from the first centrifuge are mixed in a certain ratio and uniformly mixed to obtain a mixed liquid material. The mixed liquid material is sequentially subjected to heat exchange by a heat exchanger, decolorization by a decolorization tank, ion exchange by an ion exchange system, filtration by a microporous filter, and evaporation by a first evaporator to obtain a xylitol concentrate with a concentration of 1200 - 1400 g / L and a purity of 94 - 96%. This is step 1. Crystallization of xylitol concentrate: The xylitol concentrate is cooled and crystallized in the first crystallization kettle for 8 - 12 h. The obtained xylitol paste is separated by a first centrifuge and dried by a fluidized drying layer to obtain xylitol crude crystals. The first centrifuge mother liquor obtained by separation by the first centrifuge is recycled to the harmonic tank through a pipe and mixed with the xylitol hydrogenation solution for reuse. In this step, the purity of the xylitol crude crystals is 98.5 - 99.8% and the pH < 5.0, and the purity of the first centrifuge mother liquor is 88 - 92%. This is step 2. Dissolution and recrystallization of xylitol crude crystals: The xylitol crude crystals are sent to a xylitol dissolution tank and dissolved with purified water added to the xylitol dissolution tank. Then, they are mixed in a certain ratio and uniformly blended with the second centrifugal mother liquor sent from the second centrifuge to obtain a xylitol dissolution mixture. The xylitol dissolution mixture is concentrated by a second evaporator, crystallized by a second crystallization kettle, centrifuged by a second centrifuge, hot air dried by a hot air drying tank, and cold air dried by a cold air fluidized bed to obtain a high-quality xylitol crystal product. The second centrifugal mother liquor obtained by separation using the second centrifuge is recycled to the xylitol dissolution tank through a pipeline and mixed with the xylitol crude crystal dissolution solution for reuse. In this step, the purity of the high-quality xylitol crystal product is >99.8% and the pH > 6.0. Step 3 is included to provide a method for producing high-quality xylitol crystals.

[0011] Compared with the prior art, in the system and method for manufacturing high-quality xylitol crystals of the present invention, the hydrogenated solution is uniformly mixed with the first centrifugation mother liquor to obtain a mixed liquid material. The mixed liquid material is purified and concentrated in a heat exchanger, a decolorization tank, an ion exchange system, a microporous filter, and a first evaporator to obtain a xylitol concentrate. The xylitol concentrate is crystallized in a first crystallization kettle by a specific process to obtain a xylitol paste. The first centrifugation mother liquor obtained by separating the xylitol paste with a high-speed first centrifuge is recycled to a conditioning tank. After the obtained crude xylitol crystals are dried in a first fluidized bed, purified water is added and dissolved in a xylitol dissolution tank, and uniformly mixed with the second centrifugation mother liquor by a second centrifuge and sent to a second evaporator for concentration. After the xylitol solution is concentrated in the second evaporator, the xylitol solution is recrystallized in a second crystallization kettle, and then separated by a second centrifuge to obtain crystalline xylitol and a second centrifugation mother liquor. The second centrifugation mother liquor is recycled to the xylitol dissolution tank, and the crystalline xylitol is dried in a hot air drying tank and a cold air fluidized bed to obtain a high-quality xylitol crystal product. The xylitol product manufactured by the present invention has a further increased purity, better pH stability of the xylitol crystals, and its pH is maintained at 6.0 or higher even after being left for one month. Also, regarding the sweetness of the xylitol product manufactured by this method, the sweet aftertaste is improved, tooth erosion and numbness are reduced, and the flavor of the product is significantly improved.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0013] To more clearly illustrate the technical problems to be solved, the technical solutions and the advantageous effects of the present invention, the present invention will be described in more detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used for the purpose of explaining the present invention and are not intended to limit the present invention.

[0014] As shown in FIG. 1, a preferred embodiment of the system for producing high-quality xylitol crystals according to the present invention includes a conditioning tank 1, a heat exchanger 2, a decolorization tank 3, an ion exchange system 4, a microporous filter 5, a first evaporator 6, a first crystallization kettle 7, a first centrifuge 8, a fluidized drying layer 9, a xylitol dissolution tank 10, a second evaporator 11, a second crystallization kettle 12, a second centrifuge 13, a hot air drying tank 14, and a cold air fluidized layer 15, which are sequentially communicated through pipes. Liquid discharge ports are provided in each of the first centrifuge 8 and the second centrifuge 13. The liquid discharge port of the first centrifuge 8 communicates with one supply port of the conditioning tank 1 through a pipe, and the liquid discharge port of the second centrifuge 13 communicates with one supply port of the xylitol dissolution tank 10 through a pipe. A supply port for the material to be treated is provided in the conditioning tank 1, a water supply port for purified water E is further provided in the xylitol dissolution tank 10, and a discharge port is provided in the cold air fluidized layer 15. The material to be treated is the xylitol hydrogenation liquid A, and the material discharged from the discharge port of the cold air fluidized layer 15 is the xylitol crystal B product.

[0015] The first centrifuge mother liquor C is discharged from the liquid discharge port of the first centrifuge 8, and the second centrifuge mother liquor D is discharged from the liquid discharge port of the second centrifuge 13. The conditioning tank 1 is used to uniformly mix the xylitol hydrogenation liquid A and the first centrifuge mother liquor C to obtain a mixed liquid material.

[0016] The present invention further discloses a method for producing high-quality xylitol crystals, which includes the following steps.

[0017] Step 1: Production of xylitol concentrate Mix xylitol hydrogenation liquid A and the first centrifugal mother liquor C sent from the first centrifuge 8 at a certain ratio and mix them uniformly to obtain a mixed liquid material. Perform heat exchange on the mixed liquid material by the heat exchanger 2, decolorization by the decolorization tank 3, ion exchange by the ion exchange system 4, filtration by the microporous filter 5, and evaporation treatment by the first evaporator 6 in sequence to obtain a xylitol concentrate with a concentration of 1200 - 1400 g / L and a purity of 94 - 96%.

[0018] Step 2: Crystallization of xylitol concentrate Cool the xylitol concentrate in the first crystallization kettle 7 for 8 - 12 h to crystallize it. Separate the obtained xylitol paste by the first centrifuge 8 and dry it by the fluidized drying layer 9 to obtain crude xylitol crystals. The first centrifugal mother liquor C obtained by separation using the first centrifuge 8 is recycled to the mixing tank 1 through a pipeline, and is mixed with xylitol hydrogenation liquid A for reuse. In this step, the purity of the crude xylitol crystals is 98.5 - 99.8% and the pH < 5.0, and the purity of the first centrifugal mother liquor C is 88 - 92%.

[0019] Step 3: Dissolution and recrystallization of crude xylitol crystals Send the crude xylitol crystals to the xylitol dissolution tank 10, dissolve them with purified water added to the xylitol dissolution tank 10, and then mix them uniformly with the second centrifugal mother liquor D sent from the second centrifuge 13 at a certain ratio to obtain a xylitol dissolution mixed liquid. Perform concentration on the xylitol dissolution mixed liquid by the second evaporator 11, crystallization by the second crystallization kettle 12, centrifugation by the second centrifuge 13, hot air drying by the hot air drying tank 14, and cold air drying by the cold air fluidized layer 15 to obtain high-quality xylitol crystal B products. The second centrifugal mother liquor D obtained by separation using the second centrifuge 13 is recycled to the xylitol dissolution tank 10 through a pipeline and mixed with the crude xylitol crystal dissolution liquid for reuse. In this step, the purity of the high-quality xylitol crystal B products is > 99.8% and the pH > 6.0.

[0020] Specifically, in Step 1, the temperature of the xylitol concentrate is 90 - 100 °C.

[0021] Specifically, in Step 2, in the cooling crystallization by the first crystallization kettle 7, xylitol seed crystals are added. The addition ratio of the xylitol seed crystals is 0.001 - 0.002%, the mesh of the xylitol seed crystals is 60 - 120 mesh, and the temperature of the system when adding the xylitol seed crystals is 64 - 66°C.

[0022] Specifically, in Step 3, in the crystallization by the second crystallization kettle 12, xylitol seed crystals are added. The addition ratio of the xylitol seed crystals is 0.001 - 0.002%, the mesh of the xylitol seed crystals is 60 - 120 mesh, and the temperature of the system when adding the xylitol seed crystals is 64 - 66°C.

[0023] Hereinafter, the system and method for producing high-quality xylitol crystals of the present invention will be further described by specific examples. <Example 1>

[0024] The first embodiment of the method for producing high-quality xylitol crystals of the present invention includes the following steps.

[0025] Step 11: The xylitol hydrogenation liquid A and the first centrifugal separation mother liquid C are mixed at a certain ratio, and the mixed liquid is sequentially purified and concentrated by the heat exchanger 2, the decolorization tank 3, the ion exchange system 4, the microporous filter 5, and the first evaporator 6 to obtain a xylitol concentrated liquid with a temperature of 100°C, a concentration of 1200 g / L, and a purity of 94%.

[0026] Step 12: Maintain the vacuum degree of the first crystallization kettle 7 at -0.095 MPa, further evaporate the xylitol concentrate. When the temperature of the first crystallization kettle 7 drops to 65 °C, add 0.001% of xylitol seed crystals (80 - 100 mesh), maintain the system at 65 °C, and evaporate for 8 h for crystallization. Finally, perform centrifugal separation using the first centrifuge 8 and fluidized drying using the fluidized drying layer 9 to obtain xylitol crude crystals with a purity of 99.5% and a pH of 4.87. At the same time, perform centrifugal separation using the first centrifuge 8 to obtain the first centrifugal separation mother liquor C with a purity of 90% and recycle it to the mixing tank 1.

[0027] Step 13: After adding purified water to dissolve the above xylitol crude crystals with a purity of 99.5%, mix them with the second centrifugal separation mother liquor D to obtain a second mixed solution with a xylitol content of 98.2%. Concentrate the second mixed solution to a concentration of 1350 g / L in the second evaporator 11, put it into the second crystallization kettle 12, maintain the vacuum degree of the second crystallization kettle 12 at -0.095 MPa, maintain the temperature at 65 °C, add 0.001% of xylitol seed crystals (80 - 100 mesh), and evaporate for 8 h for crystallization. Finally, perform centrifugal separation using the second centrifuge 13, hot air drying using the hot air drying tank 14, and cold air drying using the cold air fluidized layer 15 to obtain a xylitol crystal B product with a purity of 99.97%. In addition, recycle the second centrifugal separation mother liquor D obtained by performing centrifugal separation using the second centrifuge 13 to the xylitol dissolution tank 10.

[0028] According to the method described in the Chinese Pharmacopoeia, measure the acidity of the produced xylitol crystal B. Using new ultrapure water, prepare a xylitol solution at a ratio of 10 g of crystal : 20 ml of water and measure it. As a result, the pH of the xylitol solution in this example was 6.06. After leaving the obtained xylitol crystal B at room temperature for one week and measuring it by the same method, the pH of the xylitol solution was 6.03. After leaving the xylitol crystal at room temperature for one month and measuring it by the same method, the pH of the xylitol solution was 6.01.

[0029] Test and evaluate the flavor of the xylitol crystals produced in Example 1, and obtain the results shown in Figure 2. <Example 2>

[0030] The second example of the method for producing high-quality xylitol crystals of the present invention includes the following steps.

[0031] Step 21: Xylitol hydrogenation liquid A and the first centrifugation mother liquor C are mixed at a certain ratio, and the mixed solution is sequentially purified and concentrated by a heat exchanger 2, a decolorization tank 3, an ion exchange system 4, a microporous filter 5, and a first evaporator 6 to obtain a xylitol concentrated solution with a temperature of 90 °C, a concentration of 1400 g / L, and a purity of 94%.

[0032] Step 22: The vacuum degree of the first crystallization kettle 7 is maintained at -0.095 MPa, and the xylitol concentrated solution is further evaporated. When the temperature of the first crystallization kettle 7 drops to 64 °C, 0.001% of xylitol seed crystals (100 - 120 mesh) are added, and the system is maintained at 64 °C and evaporated for 12 h for crystallization. Finally, centrifugation is performed by a first centrifuge 8 and fluidized drying is performed by a fluidized drying layer 9 to obtain xylitol crude crystals with a purity of 99.6% and a pH of 4.90. At the same time, centrifugation is performed by the first centrifuge 8 to obtain the first centrifugation mother liquor C with a purity of 89.5% and recycle it to the mixing tank 1.

[0033] Step 23: After adding purified water to dissolve the above xylitol crude crystals with a purity of 99.6%, it is mixed with the second centrifugation mother liquor D to obtain a second mixed solution with a xylitol content of 98.4%. The second mixed solution is further concentrated to a concentration of 1380 g / L by a second evaporator 11, put into a second crystallization kettle 12, the vacuum degree of the second crystallization kettle 12 is maintained at -0.095 MPa, the temperature is maintained at 65 °C, 0.001% of xylitol seed crystals (100 - 120 mesh) are added, and it is evaporated for 10 h for crystallization. Finally, centrifugation is performed by a second centrifuge 13, hot air drying is performed by a hot air drying tank 14, and cold air drying is performed by a cold air fluidized layer 15 to obtain a xylitol crystal B product with a purity of 99.97%. In addition, the second centrifugation mother liquor D obtained by centrifugation using the second centrifuge 13 is recycled to the xylitol dissolution tank 10.

[0034] The acidity of xylitol crystal B produced according to the method described in the Japanese Pharmacopoeia was measured. Using fresh ultrapure water, a xylitol solution was prepared at a ratio of 10 g of crystals to 20 ml of water and measured. As a result, the pH of the xylitol solution in this example was 6.12. After leaving the obtained xylitol crystal B at room temperature for one week and measuring it by the same method, the pH of the xylitol solution was 6.08. After leaving the xylitol crystal at room temperature for one month and measuring it by the same method, the pH of the xylitol solution was 6.05.

[0035] The flavor of the xylitol crystal produced in Example 2 was tested and evaluated, and the results shown in Figure 2 were obtained. <Example 3>

[0036] The third example of the method for producing high-quality xylitol crystals of the present invention includes the following steps.

[0037] Step 31: Xylitol hydrogenation liquid A and the first centrifugation mother liquor C are mixed at a certain ratio to obtain a mixed solution with a xylitol content of 96%. The mixed solution is sequentially purified and concentrated by a heat exchanger 2, a decolorization tank 3, an ion exchange system 4, a microporous filter 5, and a first evaporator 6 to obtain a xylitol concentrated solution with a temperature of 95°C and a concentration of 1350 g / L.

[0038] Step 32: Maintain the vacuum degree of the first crystallization kettle 7 at -0.095 MPa, further evaporate the xylitol concentrated solution. When the temperature of the first crystallization kettle 7 drops to 66°C, add 0.002% of xylitol seed crystals (60 - 80 mesh), maintain the system at 66°C and evaporate for 10 h for crystallization. Finally, perform centrifugation by the first centrifuge 8 and fluidized drying by the fluidized drying layer 9 to obtain xylitol crude crystals with a purity of 99.7% and a pH of 4.99, and perform centrifugation by the first centrifuge 8 to obtain the first centrifugation mother liquor C with a purity of 92% and recycle it to the mixing tank 1.

[0039] Step 33: After adding purified water to the above-mentioned xylitol crude crystals with a purity of 99.7% and dissolving them, they were mixed with the second centrifugation mother liquor D to obtain a second mixed solution with a xylitol content of 98.4%. The second mixed solution was further concentrated to a concentration of 1400 g / L in the second evaporator 11, put into the second crystallization kettle 12, the vacuum degree of the second crystallization kettle 12 was maintained at -0.095 MPa, the temperature was maintained at 66 °C, 0.002% of xylitol seed crystals (60 - 80 mesh) were added, and evaporation was carried out for 10 h for crystallization. Finally, centrifugation was carried out by the second centrifuge 13, hot air drying was carried out by the hot air drying tank 14, cold air drying was carried out by the cold air fluidized bed 15, and xylitol crystal B products with a purity of 100% were obtained. Also, centrifugation was carried out by the second centrifuge 13 to obtain the second centrifugation mother liquor D, which was recycled to the xylitol dissolution tank 10.

[0040] According to the method described in the Chinese Pharmacopoeia, the acidity of the xylitol crystal B produced was measured. Using new ultrapure water, a xylitol solution was prepared at a ratio of 10 g of crystals : 20 ml of water, and the measurement results showed that the pH of the xylitol solution in this example was 6.09. After leaving the obtained xylitol crystal B at room temperature for one week and measuring it by the same method, the pH of the xylitol solution was 6.07. After leaving the xylitol crystal at room temperature for one month and measuring it by the same method, the pH of the xylitol solution was 6.05.

[0041] The flavor of the xylitol crystals produced in Example 3 was tested and evaluated, and the results shown in Figure 2 were obtained.

[0042] To further explain the improvement effect of the present invention, the following comparative experiments were carried out. Comparative Example 1

[0043] The first comparative example of the method for producing xylitol crystals of the present invention includes the following steps.

[0044] Step D11: The xylitol hydrogenation liquid A and the first centrifugation mother liquor C were mixed at a certain ratio to obtain a mixed solution with a xylitol content of 94%. The mixed solution was sequentially purified and concentrated by a heat exchanger 2, a decolorization tank 3, an ion exchange system 4, a microporous filter 5, and a first evaporator 6 to obtain a xylitol concentrated solution with a temperature of 95°C and a concentration of 1300 g / L.

[0045] Step D12: The vacuum degree of the first crystallization kettle 7 was maintained at -0.095 MPa, and the xylitol concentrated solution was further evaporated. When the temperature of the first crystallization kettle 7 dropped to 64°C, 0.001% of xylitol seed crystals (80 - 100 mesh) were added, and the system was maintained at 64°C and evaporated for 10 h for crystallization. Finally, centrifugation by a first centrifuge 8 and fluidized drying by a fluidized drying layer 9 were carried out to obtain xylitol crystals with a purity of 99.8%, and at the same time, centrifugation by the first centrifuge 8 was carried out to obtain a first centrifugation mother liquor C with a purity of 90%, which was recycled to the mixing tank 1.

[0046] According to the method described in the Chinese Pharmacopoeia, the acidity of the produced xylitol crystals was measured. Using fresh ultrapure water, a xylitol solution was prepared at a ratio of 10 g of crystals : 20 ml of water and measured. As a result, the pH of the xylitol solution in this example was 5.02. After the obtained xylitol crystals were left at room temperature for one week and measured by the same method, the pH of the xylitol solution was 4.85. After the xylitol crystals were left at room temperature for one month and measured by the same method, the pH of the xylitol solution was 4.64.

[0047] The flavor of the xylitol crystals produced in Comparative Example 1 was tested and evaluated, and the results shown in Figure 2 were obtained. Comparative Example 2

[0048] The second comparative example of the method for producing xylitol crystals of the present invention includes the following steps. Step D21: Xylitol hydrogenation liquid A and the first centrifugation mother liquor C were mixed at a certain ratio to obtain a blended solution with a xylitol content of 94.5%. The blended solution was sequentially purified and concentrated by a heat exchanger 2, a decolorization tank 3, an ion exchange system 4, a microporous filter 5, and a first evaporator 6 to obtain a xylitol concentrated solution with a temperature of 100 °C and a concentration of 1200 g / L.

[0049] Step D22: The vacuum degree of the first crystallization kettle 7 was maintained at -0.095 MPa, and the xylitol concentrated solution was further evaporated. When the temperature of the first crystallization kettle 7 dropped to 65 °C, 0.002% of xylitol seed crystals (100 - 120 mesh) were added, and the system was maintained at 65 °C and evaporated for 8 h for crystallization. Finally, centrifugation was performed by a first centrifuge 8 and fluidized drying was performed by a fluidized drying layer 9 to obtain xylitol crystals with a purity of 99.75%. At the same time, centrifugation was performed by the first centrifuge 8 to obtain a first centrifugation mother liquor C with a purity of 91% and recycled to the blending tank 1.

[0050] According to the method described in the Chinese Pharmacopoeia, the acidity of the produced xylitol crystals was measured. Using fresh ultrapure water, a xylitol solution was prepared at a ratio of 10 g of crystals: 20 ml of water and measured. As a result, the pH of the xylitol solution in this example was 5.04. After the obtained xylitol crystals were left at room temperature for one week and measured by the same method, the pH of the xylitol solution was 4.81. After the xylitol crystals were left at room temperature for one month and measured by the same method, the pH of the xylitol solution was 4.68.

[0051] The flavor of the xylitol crystals produced in Comparative Example 2 was tested and evaluated, and the results shown in Figure 2 were obtained. Comparative Example 3

[0052] The third comparative example of the method for producing xylitol crystals of the present invention includes the following steps.

[0053] Step D31: Xylitol hydrogenation liquid A and the first centrifugation mother liquor C were blended at a certain ratio to obtain a blended liquid with a xylitol content of 96%. The blended liquid was sequentially purified and concentrated by a heat exchanger 2, a decolorization tank 3, an ion exchange system 4, a microporous filter 5, and a first evaporator 6 to obtain a xylitol concentrated liquid with a temperature of 92°C and a concentration of 1400 g / L.

[0054] Step D32: The vacuum degree of the first crystallization kettle 7 was maintained at -0.095 MPa, and the xylitol concentrated liquid was further evaporated. When the temperature of the first crystallization kettle 7 dropped to 66°C, 0.001% of xylitol seed crystals (100 - 120 mesh) were added, and the system was maintained at 66°C and evaporated for 12 h for crystallization. Finally, centrifugation by a first centrifuge 8 and fluidized drying by a fluidized drying layer 9 were performed to obtain xylitol crystals with a purity of 99.7%. At the same time, centrifugation by the first centrifuge 8 was performed to obtain the first centrifugation mother liquor C with a purity of 92% and recycled to the blending tank 1.

[0055] According to the method described in the Chinese Pharmacopoeia, the acidity of the produced xylitol crystals was measured. Using fresh ultrapure water, a xylitol solution was prepared at a ratio of 10 g of crystals : 20 ml of water and measured. As a result, the pH of the xylitol solution in this example was 5.03. After the obtained xylitol crystals were left at room temperature for one week and measured by the same method, the pH of the xylitol solution was 4.90. After the xylitol crystals were left at room temperature for one month and measured by the same method, the pH of the xylitol solution was 4.73.

[0056] The flavor of the xylitol crystals produced in Comparative Example 3 was tested and evaluated, and the results shown in Figure 2 were obtained.

[0057] The measurement results of the pH and the flavor evaluations of the xylitol crystals produced in the above Examples and Comparative Examples are summarized and shown in Table 3 and FIG. 2. As can be seen from Table 3, in any of Examples 1 to 3, the pH is 6.0 or higher, and after standing for one month, the decrease in the pH of the xylitol crystals is within 0.1. On the other hand, in Comparative Examples 1 to 3, the pH is only about 5.0, and after standing for one month, the decrease in the pH of the xylitol crystals is 0.3 or higher. From these data, the pH of the xylitol crystals can be clearly and stably lowered by the recrystallization method. Also, as can be seen from the flavor radar chart in FIG. 2, the characteristics preferred by consumers, such as the sweetness and sweet aftertaste of the xylitol crystal products produced in Examples 1 to 3, are all better than those of the Comparative Examples. Also, the unfavorable attributes such as tooth erosion and numbness are all lower than those of the Comparative Examples, indicating that the flavor of the xylitol crystals produced using the method of the present invention has been significantly improved.

[0058]

Table 3

[0059] The above are only preferred embodiments of the present invention and do not limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention are intended to be included within the protection scope of the present invention.

Claims

1. A system for producing high-quality xylitol crystals, comprising: A conditioning tank, a heat exchanger, a decolorization tank, an ion exchange system, a microporous filter, a first evaporator, a first crystallization kettle, a first centrifuge, a fluidized drying layer, a xylitol dissolution tank, a second evaporator, a second crystallization kettle, a second centrifuge, a hot air drying tank, and a cold air fluidized layer, which are sequentially connected in communication via pipes. Each of the first centrifuge and the second centrifuge is provided with a liquid discharge port. The liquid discharge port of the first centrifuge communicates with one supply port of the conditioning tank via a pipe, and the liquid discharge port of the second centrifuge communicates with one supply port of the xylitol dissolution tank via a pipe. The conditioning tank is provided with a supply port for the material to be processed, the xylitol dissolution tank is further provided with a water supply port for purified water, the cold air fluidized layer is provided with a discharge port, the material to be processed is a xylitol hydrogenation solution which is a xylitol solution obtained by hydrogenating xylose, and the material discharged from the discharge port of the cold air fluidized layer is a xylitol crystal product. A system characterized by this.

2. A method for producing high-quality xylitol crystals, comprising: Production of xylitol concentrate: A xylitol hydrogenation solution which is a xylitol solution obtained by hydrogenating xylose and the first centrifuge mother liquor sent from the first centrifuge are mixed in a certain ratio and uniformly mixed to obtain a mixed liquid material. The mixed liquid material is sequentially subjected to heat exchange by a heat exchanger, decolorization by a decolorization tank, ion exchange by an ion exchange system, filtration by a microporous filter, and evaporation by a first evaporator to obtain a xylitol concentrate with a temperature of 90 - 100°C, a concentration of 1200 - 1400 g / L, and a purity of 94 - 96%. Step 1; Crystallization of xylitol concentrate: The xylitol concentrate is cooled and crystallized in the first crystallization kettle for 8 - 12 h, and the obtained xylitol paste is separated by a first centrifuge and dried by a fluidized drying layer to obtain xylitol crude crystals. The first centrifuge mother liquor obtained by separation by the first centrifuge is recycled to the conditioning tank via a pipe and mixed with the xylitol hydrogenation solution for reuse. In this step, the purity of the xylitol crude crystals is 98.5 - 99.8% and the pH < 5.0, and the purity of the first centrifuge mother liquor is 88 - 92%. Step 2; Dissolution and recrystallization of xylitol crude crystals: The xylitol crude crystals are sent to a xylitol dissolution tank and dissolved with purified water added to the xylitol dissolution tank. Then, they are mixed in a certain ratio with the second centrifugal mother liquor sent from the second centrifuge to obtain a uniformly mixed xylitol dissolution mixture. The xylitol dissolution mixture is concentrated by a second evaporator, crystallized by a second crystallization kettle, centrifuged by a second centrifuge, hot-air dried by a hot-air drying tank, and cold-air dried by a cold-air fluidized bed to obtain a high-quality xylitol crystal product. The second centrifugal mother liquor obtained by separation by the second centrifuge is recycled to the xylitol dissolution tank through a pipeline and mixed with the xylitol crude crystal dissolution solution for reuse. In this step, the purity of the high-quality xylitol crystal product is >99.8% and the pH > 6.

0. Step 3, including this, is a method characterized by this.

3. In step 2, in the cooling crystallization where crystallization is carried out by lowering the temperature, xylitol seed crystals are added. The addition ratio of the xylitol seed crystals is 0.001 - 0.002%, the mesh of the xylitol seed crystals is 60 - 120 mesh, and the temperature of the system when adding the xylitol seed crystals is 64 - 66°C. The method for producing high-quality xylitol crystals according to claim 2, characterized by this.

4. In step 3, in the crystallization by the second crystallization kettle, xylitol seed crystals are added. The addition ratio of the xylitol seed crystals is 0.001 - 0.002%, the mesh of the xylitol seed crystals is 60 - 120 mesh, and the temperature of the system when adding the xylitol seed crystals is 64 - 66°C. The method for producing high-quality xylitol crystals according to claim 2, characterized by this.

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