Xylitol crystal production system and production method

Abstract

The present invention relates to a system and method for producing xylitol crystals, the system comprising a blending tank, a decolorization tank, an ion exchange column, a nanofiltration system, a first evaporator, a first crystallization tank, a first centrifuge, a hot air drying tank, a first fluidized drying bed, a first mother liquor storage tank, a second evaporator, a second crystallization tank, a second centrifuge, a second fluidized drying bed, a second crystallization sugar dissolving tank, a second mother liquor storage tank, a third evaporator, a third crystallization tank, a third centrifuge, a third fluidized drying bed, and a third crystallization sugar dissolving tank, the first centrifuge is connected to the first mother liquor storage tank, the second centrifuge is connected to the second mother liquor storage tank, the second crystallization sugar dissolving tank is connected to the blending tank, and the third crystallization sugar dissolving tank is connected to the first mother liquor storage tank, the blending tank stores a xylitol hydrogenation liquid raw material used to produce xylitol crystals, and the discharge from the outlet of the first fluidized drying bed is the finished xylitol crystals. The present invention improves the particle size of xylitol crystals and extends the time it takes for the xylitol crystals to caking.

Description

[Technical Field]

[0001] The present invention relates to the technical field of xylitol production, and in particular to a system and method for producing xylitol crystals. [Background technology]

[0002] Conventional xylitol production technology uses corn cob as raw material and obtains xylitol crystals through steps such as hydrolysis, hydrogenation, decolorization, ion exchange, concentration, crystallization, centrifugation, and drying. Among these, the crystallization process is the key to determining the quality and yield of xylitol products, and plays a determining role in the morphology, purity, stack density, particle size distribution, and caking properties of the crystalline products.

[0003] The dynamics of xylitol crystallization process are mainly due to the thermodynamic non-equilibrium characteristics of the crystal system, and the crystal thermodynamic properties such as solubility, metastable region and induction period have a relatively large impact on the selection of crystallization method and crystal yield. Currently, the commonly used crystallization methods in industry are evaporation crystallization and temperature-reducing crystallization, and in the crystallization process of xylitol, due to its high solubility, evaporation crystallization and temperature-reducing crystallization are both widely used.

[0004] However, regardless of whether it is evaporation crystallization or cooling crystallization, due to the unreasonableness of the process operation parameters or the addition of seed crystals based on experience, there is a lack of theoretical and factual basis for the timing of adding seed crystals. ohAs a result, the xylitol crystallization process takes a long time, the secondary nucleation phenomenon is severe, the proportion of fine powder is relatively high, and the product batch-to-batch variation is relatively large, the crystallization process is unstable, and ultimately the xylitol product is prone to caking. For example, Patent Publication No. CN1736970A discloses a method for purifying and crystallizing xylitol, optimizing factors such as rotation speed, seed crystal amount, seed crystal particle size, and cooling rate during the crystallization process to obtain xylitol crystals with a concentrated and adjustable particle size. However, in actual production, the seed crystal addition amount cannot be increased to 3-6%, thereby limiting the application of this process to manufacturing. Also, Patent Publication No. CN102731252A discloses a method for crystallizing xylitol or maltitol, adding a small amount of an anti-caking agent during the crystallization process effectively alleviates the caking phenomenon of the crystals. However, it is unclear whether the addition of an anti-caking agent affects the quality of the product, and the relevant specifications do not permit the addition of an anti-caking agent.

[0005] Therefore, from the viewpoint of industrial feasibility, optimizing the parameters of the crystallization process to reduce the secondary nucleation phenomenon and control the particle size distribution of the product is one of the important measures to avoid or mitigate the caking of xylitol crystals. Summary of the Invention [Problem to be solved by the invention]

[0006] The technical problem to be solved by the present invention is to provide a system and method for producing xylitol crystals that can improve the particle size of the finished xylitol crystals and extend the solidification period of the finished xylitol crystals. [Means for solving the problem]

[0007] The present invention is achieved as follows: A system for producing xylitol crystals, comprising: The system includes a blending tank, a decolorization tank, an ion exchange column, a nanofiltration system, a first evaporator, a first crystallization tank, a first centrifuge, a hot air drying tank, and a first fluidized drying bed, which are sequentially connected via piping; a first mother liquor storage tank, a second evaporator, a second crystallization tank, a second centrifuge, a second fluidized drying bed, and a second crystallization sugar dissolving tank, which are sequentially connected via piping; a second mother liquor storage tank, a third evaporator, a third crystallization tank, a third centrifuge, a third fluidized drying bed, and a third crystallization sugar dissolving tank, which are sequentially connected via piping; a solids outlet of the first centrifuge is connected via piping to a supply port of the hot air drying tank; a liquids outlet of the first centrifuge is connected via piping to one supply port of the first mother liquor storage tank; a solids outlet of the second centrifuge is connected via piping to a supply port of the second fluidized drying bed; and a liquids outlet of the second centrifuge is connected via piping to a supply port of the second fluidized drying bed. The second-crystallization sugar dissolving tank is also provided with a discharge port that is connected to one of the supply ports of the blending tank via a pipe, the second-crystallization sugar dissolving tank is provided with a purified water supply port, the second-crystallization sugar dissolving tank is also provided with a discharge port that is connected to one of the supply ports of the first mother liquor storage tank via a pipe, the third-crystallization sugar dissolving tank is also provided with a purified water supply port, the third-crystallization sugar dissolving tank is further provided with a discharge port that is connected to one of the supply ports of the first mother liquor storage tank via a pipe, the blending tank is further provided with a hydrogenated liquid supply pipe, the blending tank stores a xylitol hydrogenated liquid raw material used to produce xylitol crystals, the blending tank is a uniform mixture of the xylitol hydrogenated liquid raw material and the twice-crystallized sugar solution sent from the second-crystallization sugar dissolving tank, and the discharge from the discharge port of the first fluidized drying bed is the finished xylitol crystals.

[0008] Furthermore, the manufacturing system further includes a liquid xylitol storage tank, and one outlet of the third centrifuge is connected to one supply inlet of the liquid xylitol storage tank via a pipe.

[0009] The present invention achieves the following: A method for producing xylitol crystals, comprising: The xylitol crystal manufacturing system is used, In the blending tank 1, the xylitol hydrogenated liquid raw material and the twice-crystallized sugar solution are blended in a certain ratio, and then the following processes are carried out in order: decolorization in the decolorization tank, impurity removal in the ion exchange column, filtration in the nanofiltration system, and evaporation and concentration in the first evaporator. sugar content Step 1: obtaining a xylitol concentrate of 78-82%, temperature 90-100°C, and conductivity <20 μs / cm; The xylitol concentrate is introduced into the first crystallizer via a pipe. Specifically, a certain amount of initial xylitol concentrate is introduced into the first crystallizer. The vacuum in the first crystallizer is controlled at -0.095 MPa, and the temperature is maintained at 65°C. When crystals begin to precipitate in the first crystallizer, an appropriate amount of xylitol seed crystals is added to stimulate crystallization. A certain amount of xylitol concentrate is then replenished into the first crystallizer. Crystallization is carried out for 7-12 hours with stirring. At the end of the crystallization, steam is introduced to raise the temperature of the system to 66-68°C and maintain the temperature for a predetermined time to obtain xylitol sugar paste. In this step, the ratio of the starting liquid material to the replenished liquid material is 1:0.8-1.5, the stirring speed is variable, and the timing for adding the xylitol seed crystals is the point when the particle number is observed through the observation window of the first crystallizer. Temperature increase The subsequent incubation time is 0.5 to 2.0 hours. Step 2: Separating the xylitol sugar paste obtained in step 2 using a first centrifuge to obtain crystalline xylitol and primary mother liquor, which are then transferred via a pipe to a primary mother liquor storage tank for temporary storage; Drying the crystalline xylitol in a hot air drying tank and drying with cold air in a first fluidized drying bed to obtain a finished xylitol crystallized product; Concentrating the primary mother liquor in a second evaporator, crystallizing in a second crystallizer, and centrifuging in a second centrifuge to obtain twice-crystallized sugar and secondary mother liquor, which are then transferred via a pipe to a secondary mother liquor storage tank for temporary storage; Drying the twice-crystallized sugar in a second fluidized drying bed, then transferring it to a twice-crystallized sugar dissolving tank for dissolution, adding purified water to dissolve the twice-crystallized sugar, obtaining a twice-crystallized sugar solution, which is then transferred via a pipe to a blending tank for mixing with a xylitol hydrogenated liquid raw material for blending; Step 3: The method for producing xylitol crystals further includes step 4, wherein the second mother liquor obtained in step 2 is concentrated using a third evaporator, crystallized using a third crystallizer, and centrifuged using a third centrifuge to obtain triple-crystallized sugar and tertiary mother liquor, respectively; the triple-crystallized sugar is dried in a third fluidized drying bed, and then transferred to a triple-crystallized sugar dissolving tank for dissolution; purified water is added to dissolve the triple-crystallized sugar to obtain a triple-crystallized sugar solution; the triple-crystallized sugar solution is transferred to a first mother liquor storage tank via a pipe, mixed with the first mother liquor, recovered and reused; and the tertiary mother liquor is stored as liquid xylitol. [Effects of the Invention]

[0010] Compared with the prior art, the system and method for producing xylitol crystals of the present invention have the following advantages: It can produce xylitol crystals with larger particle diameters and a more concentrated particle size distribution, and the proportion of xylitol particles of 30 mesh or larger in the produced xylitol crystals is increased by more than 30%. Furthermore, the results of small-package samples show that the solidification period of the finished xylitol crystals is extended from 45 days to more than 100 days. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating the principle of a preferred embodiment of the xylitol crystal production system of the present invention. [Figure 2] FIG. 1 is a schematic diagram showing the particle size distribution of xylitol crystals produced in each Example and Comparative Example. DETAILED DESCRIPTION OF THE INVENTION

[0012] In order to make the technical problems, technical solutions and beneficial effects of the present invention clearer and more obvious, the present invention will be described in more detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to illustrate the present invention and are not used to limit the present invention.

[0013] 1, a preferred embodiment of the xylitol crystal production system of the present invention includes a blending tank 1, a decolorization tank 2, an ion exchange column 3, a nanofiltration system 4, a first evaporator 5, a first crystallization tank 6, a first centrifuge 7, a hot air drying tank 8, and a first fluidized drying bed 9, which are connected in series via piping; a first mother liquor storage tank 10, a second evaporator 11, a second crystallization tank 12, a second centrifuge 13, a second fluidized drying bed 14, and a second crystallization sugar dissolving tank 15, which are connected in series via piping; and a second mother liquor storage tank 16, a third evaporator 17, a third crystallization tank 18, a third centrifuge 19, a third fluidized drying bed 20, and a third crystallization sugar dissolving tank 21, which are connected in series via piping. The arrows in the figure indicate the direction of material flow in the system.

[0014] Here, the solids discharge port of the first centrifuge 7 is connected via piping to the supply port of the hot air drying tank 8, and the liquids discharge port of the first centrifuge 7 is connected via piping to one supply port of the primary mother liquor storage tank 10. The solids discharge port of the second centrifuge 13 is connected via piping to the supply port of the second fluidized drying bed 14, and the liquids discharge port of the second centrifuge 13 is connected via piping to the supply port of the secondary mother liquor storage tank 16. The second crystallization sugar dissolution tank 15 is provided with a purified water inlet and a discharge port that is connected via piping to one supply port of the blending tank 1. The third crystallization sugar dissolution tank 21 is also provided with a purified water inlet and a discharge port that is further connected via piping to one supply port of the primary mother liquor storage tank 10. The blending tank 1 is further provided with a supply pipe for the hydrogenated liquid, and stores the xylitol hydrogenated liquid raw material used to produce xylitol crystals. The blending tank 1 is a uniform mixture of the xylitol hydrogenated liquid raw material and the twice-crystallized sugar solution sent from the twice-crystallized sugar dissolution tank 15. The discharge from the outlet of the first fluidized drying bed 9 is the finished xylitol crystals.

[0015] The production system further includes a liquid xylitol storage tank 22, and one outlet of the third centrifuge 19 is connected to one supply inlet of the liquid xylitol storage tank 22 via a pipe.

[0016] Furthermore, as shown in FIG. 1, the present invention further discloses a method for producing xylitol crystals, which uses the xylitol crystal production system, and includes the following steps:

[0017] Step 1: In the blending tank 1, the xylitol hydrogenated liquid raw material and the twice-crystallized sugar solution are blended in a certain ratio, and then the following processes are carried out in sequence: decolorization in the decolorization tank 2, impurity removal in the ion exchange column 3, filtration in the nanofiltration system 4, and evaporation and concentration in the first evaporator 5, to obtain a xylitol concentrate with a concentration of 78-82%, a temperature of 90-100°C, and a conductivity of less than 20 μs / cm.

[0018] Step 2: The xylitol concentrate is introduced into the first crystallizer 6 via a pipe. Specifically, a certain amount of the initial xylitol concentrate is first introduced into the first crystallizer 6. The vacuum in the first crystallizer 6 is controlled at -0.095 MPa, and the temperature is maintained at 65°C. When crystal precipitation begins in the first crystallizer 6, an appropriate amount of xylitol seed crystals is added to stimulate crystallization. A certain amount of xylitol concentrate is then replenished into the first crystallizer 6, and crystallization is continued for 7-12 hours with stirring. At the end of crystallization, steam is introduced to raise the temperature of the system to 66-68°C and maintain the temperature for a predetermined period to obtain a xylitol sugar paste. In this step, the ratio of the starting liquid material to the replenished liquid material is 1:0.8-1.5, the stirring speed is variable, and the timing for adding the xylitol seed crystals is determined when the particle count is less than 50 observed through the observation window of the first crystallizer 6. Temperature increase The subsequent warming time is 0.5 to 2.0 hours.

[0019] Step 3: The xylitol sugar paste obtained in Step 2 is separated in the first centrifuge 7 to obtain crystalline xylitol and primary mother liquor. The primary mother liquor is transferred via a pipe to the primary mother liquor storage tank 10 for temporary storage. The crystalline xylitol is dried in the hot air drying tank 8 and then dried with cold air in the first fluidized drying bed 9 to obtain the finished xylitol crystals. The primary mother liquor is concentrated in the second evaporator 11, crystallized in the second crystallizer 12, and centrifuged in the second centrifuge 13 to obtain the second-crystallized sugar and secondary mother liquor. The secondary mother liquor is transferred via a pipe to the secondary mother liquor storage tank 16 for temporary storage. The second-crystallized sugar is dried in the second fluidized drying bed 14, then transferred to the second-crystallized sugar dissolution tank 15 for dissolution. Purified water is added to dissolve the second-crystallized sugar, obtaining the second-crystallized sugar solution. The second-crystallized sugar solution is transferred via a pipe to the blending tank 1 and mixed with the xylitol hydrogenated liquid raw material for blending.

[0020] Step 4: The secondary mother liquor obtained in Step 2 is concentrated in a third evaporator 17, crystallized in a third crystallization vessel 18, and centrifuged in a third centrifuge 19 to obtain triple-crystallized sugar and tertiary mother liquor. The triple-crystallized sugar is dried in a third fluidized drying bed 20, then transferred to a triple-crystallized sugar dissolution tank 21 for dissolution. Purified water is added to dissolve the triple-crystallized sugar, obtaining a triple-crystallized sugar solution. The triple-crystallized sugar solution is transferred via a pipe to a primary mother liquor storage tank 10, where it is mixed with the primary mother liquor and recovered for reuse. The tertiary mother liquor is stored as liquid xylitol.

[0021] In step 1, the size of the nanofiltration membrane of the nanofiltration system 4 is 300 to 800 Da.

[0022] In step 2, the first crystallization vessel 6 is a vacuum evaporation crystallization vessel, and in the variable speed stirring process, the rotation speed is gradually reduced from 90 rpm to 10 rpm, and the size of the observation window of the first crystallization vessel 6 is 1 cm. 2 The particle number of xylitol crystals in the observation window was observed under a 10x10 microscope. Xylitol seed crystals were added to stimulate the crystallization of the system, and the seed crystal addition rate was 0.0004-0.0008%, and the particle size of the seed crystals was 80-100 mesh.

[0023] In step 2, the xylitol sugar paste is separated in the first centrifuge 7, and then washed for 5 to 10 seconds by spraying it with an ethanol solution having a concentration of 80 to 100%, thereby removing the maximum amount of moisture from the crystalline xylitol.

[0024] In step 3, the temperature of the hot air in the hot air drying tank 8 is set to 75 to 85°C.

[0025] The system for producing xylitol crystals of the present invention will be further described below by way of specific examples. Example 1

[0026] A first embodiment of the method for producing xylitol crystals of the present invention comprises the following steps:

[0027] Step 11: The xylitol hydrogenated solution and the twice-crystallized sugar solution were mixed in a certain ratio, and then the mixture was subjected to activated carbon decolorization treatment in the decolorization tank 2, ion exchange treatment in the ion exchange column 3, and treatment in the 400 Da nanofiltration membrane system 4 and the first evaporator 5, to obtain a concentrated xylitol solution with a refractive index of 79%, a temperature of 95°C, and a conductivity of 1.958 μs / cm.

[0028] Step 12: First, 10 tons of xylitol concentrate was introduced into the first crystallization vessel 6 and further concentrated at -0.095 MPa. The system temperature was lowered to approximately 65°C. When 20 fine crystal grains were observed through the observation window of the first crystallization vessel 6, 0.0005% xylitol seed crystals were added to stimulate crystallization, and 10 tons of xylitol concentrate was added to the crystallization tank. The system was maintained at -0.095 MPa, the temperature was kept constant at 65°C, and the initial rotation speed was 90 rpm. After 7 hours of crystallization, steam was introduced to raise the system temperature to 67°C. Then, the temperature was maintained at 67°C and crystallization continued for 0.5 hours, yielding a xylitol sugar paste.

[0029] Step 13: The resulting xylitol sugar paste was separated in the first centrifuge 7 to obtain 8.7 tons of crystalline xylitol and 10.5 tons of primary mother liquor. The crystalline xylitol was dried in the hot air drying tank 8 with hot air at 80°C and then dried in the first fluidized drying bed 9 with cold air to obtain a finished xylitol crystallized product. The primary mother liquor was concentrated in the second evaporator 11 and further crystallized in the second crystallizer 12 at -0.095 MPa and 65°C. The resulting mixture was centrifuged in the second centrifuge 13 to obtain twice-crystallized sugar and secondary mother liquor. The twice-crystallized sugar was dried in the second fluidized drying bed 14 and then dissolved in the twice-crystallized sugar dissolution tank 15 to produce twice-crystallized sugar solution, which was then sent to the blending tank 1 to be blended with the xylitol hydrogenated liquid. The secondary mother liquor was concentrated in a third evaporator 17, crystallized in a third crystallization vessel 18, and centrifuged in a third centrifuge 19, to obtain triple-crystallized sugar and tertiary mother liquor. The tertiary mother liquor was stored in a liquid xylitol storage tank 22. The triple-crystallized sugar was dried in a third fluidized drying bed 20, then transferred to a triple-crystallized sugar dissolving tank 21 for dissolution, yielding a triple-crystallized sugar solution. The triple-crystallized sugar solution was then transferred via piping to a primary mother liquor storage tank 10, mixed with the primary mother liquor, and recovered for reuse.

[0030] The produced xylitol crystals were sorted, and the particle size distribution of the obtained xylitol crystals is shown in Table 1 below.

[0031] [Table 1]

[0032] The caking period of the small packaged sample of xylitol crystals produced in Example 1 was actually measured and found to be 105 days. Example 2

[0033] A second embodiment of the method for producing xylitol crystals of the present invention comprises the following steps:

[0034] Step 21: The xylitol hydrogenated solution and the twice-crystallized sugar solution are mixed in a certain ratio, and then the mixture is subjected to activated carbon decolorization treatment in the decolorization tank 2, ion exchange treatment in the ion exchange column 3, and treatment in the 400 Da nanofiltration membrane system 4 and the first evaporator 5, to obtain a concentrated xylitol solution with a refractive index of 80%, a temperature of 95°C, and a conductivity of 1.744 μs / cm.

[0035] Step 22: First, 10 tons of xylitol concentrate was introduced into the first crystallization vessel 6 and further concentrated under -0.095 MPa. The system temperature was lowered to approximately 65°C. When 25 fine crystal grains were observed through the observation window of the first crystallization vessel 6, 0.0005% xylitol seed crystals were added to stimulate crystallization, and 10 tons of xylitol concentrate was added to the crystallization tank. The system was maintained at -0.095 MPa, the temperature was kept constant at 65°C, and the initial rotation speed was 90 rpm. After 8 hours of crystallization, steam was introduced to raise the system temperature to 66.5°C. Then, the system was maintained at 66.5°C and crystallization continued for 0.8 hours, yielding a xylitol sugar paste.

[0036] Step 23: The resulting xylitol sugar paste was separated in the first centrifuge 7 to obtain 8.6 tons of crystalline xylitol and 10.6 tons of primary mother liquor. The crystalline xylitol was dried in the hot air drying tank 8 with hot air at 80°C and then dried in the first fluidized drying bed 9 with cold air to obtain a finished xylitol crystallized product. The primary mother liquor was concentrated in the second evaporator 11 and further crystallized in the second crystallizer 12 at -0.095 MPa and 65°C. It was then centrifuged in the second centrifuge 13 to obtain twice-crystallized sugar and secondary mother liquor. The twice-crystallized sugar was dried in the second fluidized drying bed 14 and then dissolved in the twice-crystallized sugar dissolution tank 15 to produce twice-crystallized sugar solution, which was then sent to the blending tank 1 to be blended with the xylitol hydrogenated liquid. The secondary mother liquor was concentrated in a third evaporator 17, crystallized in a third crystallization vessel 18, and centrifuged in a third centrifuge 19, to obtain triple-crystallized sugar and tertiary mother liquor. The tertiary mother liquor was stored in a liquid xylitol storage tank 22. The triple-crystallized sugar was dried in a third fluidized drying bed 20, then transferred to a triple-crystallized sugar dissolving tank 21 for dissolution, yielding a triple-crystallized sugar solution. The triple-crystallized sugar solution was then transferred via piping to a primary mother liquor storage tank 10, mixed with the primary mother liquor, and recovered for reuse.

[0037] The produced xylitol crystals were sorted, and the particle size distribution of the obtained xylitol crystals is shown in Table 2 below.

[0038] [Table 2]

[0039] The caking period of the small packaged sample of xylitol crystals produced in Example 2 was actually measured and found to be 112 days.

[0040] To better illustrate the beneficial effects of the present invention, a comparative example will be further described below. Comparative Example

[0041] The comparative example of the present invention includes the following steps.

[0042] Step 31: The xylitol hydrogenation liquid and the primary centrifuged mother liquor were directly mixed in a certain ratio, and then decolorized with activated carbon, ion-exchanged, and evaporated in triple-effect fashion to obtain a concentrated xylitol liquid with a refractive index of 80.5%, a temperature of 95°C, and a conductivity of 2.063 μs / cm.

[0043] Step 32: First, 7 tons of xylitol concentrate was introduced into the crystallization tank and further concentrated at -0.095 MPa. The temperature of the system was lowered to about 65°C. When a large amount of fine crystal grains (>50) was observed through the observation window of the crystallization tank, 0.0005% xylitol seed crystals were added to stimulate crystallization, and 13 tons of xylitol concentrate was added to the crystallization tank. The system was maintained at -0.095 MPa, the temperature was kept constant at 65°C, and the mixture was stirred at a constant speed of 90 rpm for 8 hours to crystallize, obtaining xylitol sugar paste.

[0044] Step 33: The obtained xylitol sugar paste was separated using a high-speed centrifuge to obtain 8.8 tons of xylitol crystals and 10.2 tons of primary centrifugal mother liquor. The xylitol crystals were dried with hot air at 88°C and then dried with cold air to obtain the finished xylitol product. The primary centrifugal mother liquor was directly recovered and reused in the hydrogenated liquid preparation step.

[0045] The produced xylitol crystals were sorted, and the particle size distribution of the obtained xylitol crystals is shown in Table 3 below.

[0046] [Table 3]

[0047] The caking period of the small packaged sample of xylitol crystals produced in the comparative example was actually measured and found to be 45 days.

[0048] Compared with the comparative examples, in Examples 1 and 2, the crystallization process was optimized by eliminating the recycling of xylitol mother liquor and adding a nanofiltration system to remove low-molecular-weight impurities. By using methods such as alcohol washing during the centrifugation process, the resulting xylitol crystals had larger particles and a narrower particle size distribution, and the caking cycle of the finished xylitol crystals was significantly improved. The comparative data are shown in Table 4 and Figure 2.

[0049] [Table 4]

[0050] From the above table, it is clear that in the comparison item of the percentage of 30 mesh or more, the xylitol crystal finished product of Example 1 is 40% higher than the comparative example, and the xylitol crystal finished product of Example 2 is 36% higher than the comparative example. In addition, the solidification period of the xylitol crystal finished products of Example 1 and Example 2 was significantly longer than that of the comparative example.

[0051] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. 1. A system for producing xylitol crystals, comprising: The system includes a blending tank, a decolorization tank, an ion exchange column, a nanofiltration system, a first evaporator, a first crystallization vessel, a first centrifuge, a hot air drying tank, and a first fluidized drying bed, which are connected in series via piping; The system further includes a primary mother liquor storage tank, a second evaporator, a second crystallization vessel, a second centrifuge, a second fluidized drying bed, and a second crystallization sugar dissolving tank, which are connected in series via piping; The system includes a second mother liquor storage tank, a third evaporator, a third crystallization vessel, a third centrifuge, a third fluidized drying bed, and a third crystallization sugar dissolving tank, which are connected in series via piping; a solid discharge port of the first centrifuge communicates with a supply port of a hot air drying tank via a pipe; a liquid discharge port of the first centrifuge communicates with one supply port of a first mother liquor storage tank via a pipe; a solid discharge port of the second centrifuge communicates with a supply port of a second fluidized drying bed via a pipe; and a liquid discharge port of the second centrifuge communicates with a supply port of a second mother liquor storage tank via a pipe; The double-crystallization sugar dissolution tank is provided with a purified water inlet, and the double-crystallization sugar dissolution tank is also provided with an outlet communicating with one of the supply ports of the blending tank via a pipe; The triple crystallization sugar dissolving tank is also provided with a purified water inlet, the triple crystallization sugar dissolving tank is further provided with an outlet communicating with one of the inlets of the primary mother liquor storage tank via a pipe, the blending tank is further provided with a hydrogenated liquid supply pipe, the blending tank stores the xylitol hydrogenated liquid raw material used to produce xylitol crystals, and the blending tank uniformly mixes the xylitol hydrogenated liquid raw material and the twice-crystallized sugar solution sent from the twice-crystallization sugar dissolving tank; A system for producing xylitol crystals, characterized in that the discharge from the discharge outlet of the first fluidized drying bed is finished xylitol crystals.

2. 2. The system for producing xylitol crystals according to claim 1, further comprising a liquid xylitol storage tank, wherein one outlet of the third centrifuge is connected to one supply inlet of the liquid xylitol storage tank via a pipe.

3. A method for producing xylitol crystals, comprising: The system for producing xylitol crystals according to claim 1 or 2 is used, Step 1: In a blending tank 1, a xylitol hydrogenated liquid raw material and a twice-crystallized sugar solution are blended in a certain ratio, and then the following steps are sequentially performed: decolorization in a decolorization tank, impurity removal using an ion exchange column, filtration using a nanofiltration system, and evaporation and concentration using a first evaporator, to obtain a xylitol concentrate having a refractive index of 78-82% sugar content, a temperature of 90-100°C, and a conductivity of less than 20 μs / cm; The xylitol concentrate is introduced into the first crystallization vessel through a pipe. A certain amount of the initial xylitol concentrate is first introduced into the first crystallization vessel. The vacuum of the first crystallization vessel is controlled at -0.095 MPa, and the temperature is maintained at 65°C. When crystal precipitation begins in the first crystallization vessel, xylitol seed crystals are added to stimulate crystallization, and a certain amount of xylitol concentrate is replenished into the first crystallization vessel. Crystallization is carried out for 7 to 12 hours with stirring. At the end of the crystallization, steam is introduced to raise the temperature of the system to 66 to 68°C and maintain the temperature for a predetermined time to obtain a xylitol sugar paste. In step 2, the ratio of the starting liquid material to the replenished liquid material is 1:0.8 to 1.5, the stirring speed is set to a variable speed, and the timing for adding the xylitol seed crystals is determined when the particle count is less than 50, as observed through the observation window of the first crystallization vessel. The observation window size of the first crystallization vessel is 1 cm2. The particle count is measured using a 10x10 microscope, and the incubation time after the final heating of the crystallization is 0.5-2.0 hours. Step 3: The xylitol sugar paste obtained in step 2 is separated by a first centrifuge to obtain crystalline xylitol and primary mother liquor, which are transferred via a pipe to a primary mother liquor storage tank for temporary storage; the crystalline xylitol is dried in a hot air drying tank and then dried with cold air in a first fluidized drying bed to obtain a finished xylitol crystallized product; the primary mother liquor is concentrated by a second evaporator, crystallized by a second crystallizer, and centrifuged by a second centrifuge to obtain twice-crystallized sugar and secondary mother liquor, which are transferred via a pipe to a secondary mother liquor storage tank for temporary storage; the twice-crystallized sugar is dried in a second fluidized drying bed, then transferred to a twice-crystallized sugar dissolving tank for dissolution, and purified water is added to dissolve the twice-crystallized sugar to obtain a twice-crystallized sugar solution, which is transferred via a pipe to a blending tank for mixing with a xylitol hydrogenated liquid raw material for blending; and (4) subjecting the secondary mother liquor obtained in step 2 to a concentration process using a third evaporator, a crystallization process using a third crystallization vessel, and a centrifugation process using a third centrifuge to obtain triple-crystallized sugar and a tertiary mother liquor, respectively; drying the triple-crystallized sugar in a third fluidized drying bed, then dissolving it in a triple-crystallized sugar dissolution tank; adding purified water to dissolve the triple-crystallized sugar, thereby obtaining a triple-crystallized sugar solution; and transferring the triple-crystallized sugar solution through a pipe to a primary mother liquor storage tank, mixing it with the primary mother liquor, recovering and reusing it; and storing the tertiary mother liquor as liquid xylitol.

4. 4. The method for producing xylitol crystals according to claim 3, wherein in step 1, the molecular weight cutoff size of the nanofiltration membrane of the nanofiltration system is 300 to 800 Da.

5. In step 2, the first crystallization vessel is a vacuum evaporation crystallization vessel, and in the variable speed stirring process, the rotation speed is gradually reduced from 90 rpm to 10 rpm during 7 to 12 hours, and the size of the observation window of the first crystallization vessel is 1 cm. ２ The method for producing xylitol crystals according to claim 3, characterized in that the particle number of xylitol crystals in the observation window is observed under a 10x10 microscope, xylitol seed crystals are added to stimulate crystallization of the system, the addition rate of the seed crystals is 0.0004 to 0.0008 mass%, and the particle size of the seed crystals is such that they can pass through an 80 to 100 mesh sieve.

6. The method for producing xylitol crystals according to claim 3, characterized in that in step 2, the xylitol sugar paste is separated using a first centrifuge, and then sprayed with an ethanol solution for 5 to 10 seconds to wash the xylitol crystals, thereby removing as much water as possible from the xylitol crystals.

7. 4. The method for producing xylitol crystals according to claim 3, wherein in step 3, the temperature of the hot air in the hot air drying tank is set to 75 to 85°C.

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