System and method for producing xylitol crystals

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 cobs as raw material and obtains xylitol crystals through steps such as hydrolysis, hydrogenation, decolorization, ion exchange, concentration, crystallization, centrifugation and drying. Among them, 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 property of the crystal products.

[0003] The dynamics of xylitol crystallization process is 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. At present, the crystallization methods commonly used in industry are evaporation crystallization and temperature-reducing crystallization, and for 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, so that the xylitol crystallization process takes a long time, the secondary nucleation phenomenon is serious, the proportion of fine powder is relatively high, and the product difference between different batches is relatively large, the crystallization process is unstable, and finally the xylitol product is prone to caking. For example, the patent with publication number CN1736970A discloses a method for purifying and crystallizing xylitol, which optimizes the rotation speed, seed crystal amount, seed crystal grain size, cooling rate and other factors in the crystallization process to obtain xylitol crystals with a grain size that can be intensively adjusted, but in actual production, the amount of seed crystals added cannot be 3-6%, which limits the application of this process in production. For example, patent publication number CN102731252A discloses a method for crystallizing xylitol or maltitol, in which a small amount of an anti-caking agent is added during the crystallization process to effectively alleviate the caking phenomenon of crystals. However, it is unclear whether the addition of the anti-caking agent affects the quality of the product, and the relevant standards do not permit the adoption of the method of adding an anti-caking agent.

[0005] Therefore, from the perspective of industrial feasibility, reducing the secondary nucleation phenomenon and controlling the particle size distribution of the product by optimizing the parameters of the crystallization process are 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, which 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 achieves the following: A system for producing xylitol crystals, comprising: The present invention further includes a first mother liquor storage tank, a second evaporator, a second crystallization tank, a third centrifuge, a third fluidized drying bed, and a second crystallization sugar dissolving tank, which are sequentially connected through piping, and 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 through piping, and a solid discharge port of the first centrifuge is connected to a supply port of the hot air drying tank through piping, a liquid discharge port of the first centrifuge is connected to one supply port of the first mother liquor storage tank through piping, a solid discharge port of the second centrifuge is connected to one supply port of the second fluidized drying bed through piping, and a liquid discharge port of the second centrifuge is connected to one supply port of the first mother liquor storage tank through piping. The second crystallization sugar dissolving tank is connected to a supply port of the second mother liquor storage 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 an outlet port connected to one of the supply ports of the blending 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 an outlet port 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 for producing 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 twice-crystallization sugar dissolving tank, and the discharge from the outlet of the first fluidized drying bed is the finished xylitol crystallized product.

[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 has been achieved as follows: A method for producing xylitol crystals, comprising: The xylitol crystal manufacturing system is used, 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 steps are sequentially performed: decolorization in a decolorization tank, impurity removal in an ion exchange column, filtration in a nanofiltration system, and evaporation and concentration in a first evaporator to obtain a xylitol concentrated liquid with a refractive index of 78-82%, a temperature of 90-100°C, and a conductivity of <20μs / cm; Step 2: introducing a certain amount of initial xylitol concentrate into the first crystallization tank through a pipe; specifically, first, introducing a certain amount of initial xylitol concentrate into the first crystallization tank; controlling the vacuum of the first crystallization tank at -0.095MPa and maintaining the temperature at 65°C; when crystal precipitation begins in the first crystallization tank, adding an appropriate amount of xylitol seed crystals to stimulate crystallization; supplementing the first crystallization tank with a certain amount of xylitol concentrate; crystallizing for 7-12 hours while stirring; at the end of crystallization, introducing steam to increase the temperature of the system to 66-68°C and keeping the temperature for a certain period of time to obtain a xylitol sugar paste; the ratio of the starting liquid raw material and the supplementary liquid raw material is 1:0.8-1.5; the stirring speed is set to a variable speed; the timing of adding the xylitol seed crystals is the time when the particle number <50 is observed through the observation window of the first crystallization tank; and the keeping time after the final warming of the crystallization is 0.5-2.0 hours. Step 2: Separating the xylitol sugar paste obtained by the first centrifuge to obtain crystalline xylitol and primary mother liquor, respectively; Entering the primary mother liquor into the primary mother liquor storage tank through the pipe for temporary storage; Drying the crystalline xylitol in the hot air drying tank, and drying with cold air in the first fluidized drying bed to obtain the finished xylitol crystallized product; Concentrating the primary mother liquor through the second evaporator, crystallizing in the second crystallizing pot, and centrifuging in the second centrifuge in sequence to obtain twice-crystallized sugar and secondary mother liquor, respectively; Entering the secondary mother liquor into the secondary mother liquor storage tank through the pipe for temporary storage; Drying the twice-crystallized sugar in the second fluidized drying bed, and then entering the twice-crystallized sugar dissolving tank for dissolving; Adding purified water to dissolve the twice-crystallized sugar to obtain twice-crystallized sugar solution; Entering the twice-crystallized sugar solution into the blending tank through the pipe for mixing with the xylitol hydrogenated liquid raw material for blending; Step 3: The method for producing xylitol crystals further includes the step 4 of concentrating the second mother liquor obtained in the step 2 with a third evaporator, crystallizing the second mother liquor with a third crystallizer, and centrifuging the second mother liquor with a third centrifuge to obtain triple crystallized sugar and tertiary mother liquor, respectively, drying the triple crystallized sugar in a third fluidized drying bed, and then dissolving the triple crystallized sugar in a triple crystallized sugar dissolving tank, adding purified water to dissolve the triple crystallized sugar, obtaining a triple crystallized sugar solution, and transferring the triple crystallized sugar solution to a primary mother liquor storage tank through a pipe to mix with the primary mother liquor, recover and reuse the solution, and store the tertiary mother liquor as liquid xylitol. Effect of the Invention

[0010] Compared with the prior art, the system and method for producing xylitol crystals of the present invention have the following features: It can produce xylitol crystals with a larger particle size and a more concentrated particle size distribution, and the proportion of xylitol particles of 30 mesh or more in the produced xylitol crystals is increased by more than 30%. In addition, 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 description of the drawings]

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

[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 in this specification are only used to explain the present invention and are not used to limit the present invention.

[0013] As shown in Fig. 1, a preferred embodiment of the xylitol crystal manufacturing 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 through piping, and further includes 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 through piping, and further includes 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 through piping. The direction indicated by the arrow in the figure indicates the flow direction of materials in the system.

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

[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 piping.

[0016] In addition, as shown in FIG. 1, the present invention further discloses a method for producing xylitol crystals, the method using the xylitol crystal production system, and the method 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 sequentially carried out: 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 <20 μs / cm.

[0018] Step 2: The xylitol concentrate is fed into the first crystallization tank 6 through a pipe. Specifically, a certain amount of initial xylitol concentrate is fed into the first crystallization tank 6. The vacuum in the first crystallization tank 6 is controlled at -0.095MPa, and the temperature is kept at 65℃. When crystallization begins in the first crystallization tank 6, an appropriate amount of xylitol seed crystals is added to stimulate crystallization. Then, a certain amount of xylitol concentrate is replenished into the first crystallization tank 6, and crystallized for 7-12 hours while stirring. At the end of the crystallization, steam is introduced to increase the temperature of the system to 66-68℃ and keep it at that temperature for a certain period of time to obtain xylitol sugar paste. In this step, the ratio of the starting liquid raw material to the replenishment liquid raw material is 1:0.8-1.5, the stirring speed is set to a variable speed, the timing for adding xylitol seed crystals is the point at which the particle number <50 is observed through the observation window of the first crystallization vessel 6, and the incubation time after the final warming of the crystallization vessel is 0.5-2.0 hours.

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

[0020] Step 4: The second mother liquor obtained in step 2 is concentrated by the third evaporator 17, crystallized by the third crystallizer 18, and centrifuged by the third centrifuge 19 to obtain triple crystallized sugar and tertiary mother liquor. The triple crystallized sugar is dried in the third fluidized drying bed 20, then dissolved in the triple crystallized sugar dissolving tank 21, and purified water is added to dissolve the triple crystallized sugar to obtain the triple crystallized sugar solution. The triple crystallized sugar solution is fed through the pipe to the first mother liquor storage tank 10, mixed with the first 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 kettle 6 is a vacuum evaporation crystallization kettle, 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 kettle 6 is 1 cm 2 The particle number of xylitol crystals in the observation window is observed under a 10x10 microscope, xylitol seed crystals are added to stimulate the crystallization of the system, the addition rate of seed crystals is 0.0004-0.0008%, and the grain size of the seed crystals is 80-100 mesh.

[0023] In step 2, the xylitol sugar paste is separated by a 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 moisture from the crystalline xylitol to the maximum extent.

[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 with reference to 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 liquid and the twice-crystallized sugar solution are mixed in a certain ratio, and then the mixture is sequentially 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 xylitol concentrated liquid with a refractive index of 79%, a temperature of 95°C, and a conductivity of 1.958 μs / cm.

[0028] Step 12: First, introduce 10 tons of xylitol concentrate into the first crystallization tank 6, and further concentrate at -0.095MPa. When the temperature of the system is lowered to about 65℃, and 20 fine crystal grains are observed through the observation window of the first crystallization tank 6, add 0.0005% xylitol seed crystals to stimulate crystallization, and replenish 10 tons of xylitol concentrate into the crystallization tank, maintain the system at -0.095MPa, keep the temperature constant at 65℃, and set the initial rotation speed at 90rpm to stir the crystals at a variable speed. After 7h of crystallization, introduce steam to raise the temperature of the system to 67℃, and then maintain the temperature at 67℃ and continue crystallization for 0.5h to obtain xylitol sugar paste.

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

[0030] The produced xylitol crystal finished product was sorted, and the particle size distribution of the obtained xylitol crystal finished product is shown in Table 1 below.

[0031] [Table 1]

[0032] The caking period of the small packaged samples of xylitol crystals produced in Example 1 was actually measured and was 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 liquid and the twice-crystallized sugar solution are mixed in a certain ratio, and then the mixture is sequentially 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 xylitol concentrated liquid with a refractive index of 80%, a temperature of 95°C, and a conductivity of 1.744 μs / cm.

[0035] Step 22: First, introduce 10 tons of xylitol concentrate into the first crystallization tank 6, and further concentrate at -0.095 MPa. When the temperature of the system is lowered to about 65°C and 25 fine crystal grains are observed through the observation window of the first crystallization tank 6, add 0.0005% xylitol seed crystals to stimulate crystallization, and replenish 10 tons of xylitol concentrate into the crystallization tank, maintain the system at -0.095 MPa, keep the temperature constant at 65°C, and set the initial rotation speed at 90 rpm to stir the crystals at a variable speed. After 8 hours of crystallization, introduce steam to increase the temperature of the system to 66.5°C, and then maintain the temperature at 66.5°C to continue crystallization for 0.8 hours, to obtain xylitol sugar paste.

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

[0037] The produced xylitol crystal finished product was sorted, and the particle size distribution of the obtained xylitol crystal finished product is shown in Table 2 below.

[0038] [Table 2]

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

[0040] In order to better illustrate the beneficial effects of the present invention, comparative examples are 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 centrifugation mother liquor were directly mixed in a certain ratio, and then decolorized with activated carbon, ion-exchanged and evaporated in triple-effect order to obtain a xylitol concentrate with a refractive index of 80.5%, a temperature of 95°C and a conductivity of 2.063 μs / cm.

[0043] Step 32: First, introduce 7 tons of xylitol concentrate into the crystallization tank and further concentrate at -0.095MPa. When the temperature of the system is lowered to about 65℃ and a large amount of fine crystal grains (>50) are observed through the observation window of the crystallization tank, add 0.0005% xylitol seed crystals to stimulate crystallization, and replenish the crystallization tank with 13 tons of xylitol concentrate. Maintain the system at -0.095MPa, keep the temperature constant at 65℃, and stir at a constant speed of 90 rpm for 8 hours to crystallize and obtain xylitol sugar paste.

[0044] Step 33: The obtained xylitol sugar paste was separated by 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 collected and reused in the hydrogenation liquid preparation step.

[0045] The produced xylitol crystal finished product was sorted, and the particle size distribution of the obtained xylitol crystal finished product is shown in Table 3 below.

[0046] [Table 3]

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

[0048] Compared with the comparative example, in Example 1 and Example 2, the crystallization process is optimized by omitting the recycling of xylitol mother liquor and adding the removal of low molecular weight impurities by a nanofiltration system. The centrifugal process is performed using methods such as alcohol washing, which results in a finished xylitol crystal with larger particles and a narrower particle size distribution, and the solidification period of the finished xylitol crystal is 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 ratio 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 is obviously 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 apparatus 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 method further includes a first mother liquor storage tank, a second evaporator, a second crystallization vessel, a second centrifuge, a second fluidized drying bed, and a second crystallization sugar dissolution tank, which are connected in series through piping; 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 through 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 twice-crystallized sugar dissolving tank is provided with a purified water inlet, and the twice-crystallized sugar dissolving tank is also provided with an outlet communicating with one of the supply inlets of the blending tank via a pipe; The triple crystallized sugar dissolving tank is also provided with a purified water inlet, the triple crystallized 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 for producing xylitol crystals, and the blending tank uniformly mixes the xylitol hydrogenated liquid raw material and the twice crystallized sugar solution sent from the twice crystallized 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 as described in claim 1, further comprising 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.

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 a decolorization process is performed in a decolorization tank, an impurity removal process is performed in an ion exchange column, a filtration process is performed in a nanofiltration system, and an evaporation and concentration process is performed in a first evaporator to obtain a xylitol concentrated liquid having a refractive index of 78-82%, a temperature of 90-100°C, and a conductivity of <20 μs / cm; Step 2 is to feed the xylitol concentrate into the first crystallization vessel through a pipe; specifically, first, a certain amount of initial xylitol concentrate is introduced into the first crystallization vessel, the vacuum degree of the first crystallization vessel is controlled to -0.095 MPa, and the temperature is kept at 65°C; when crystal precipitation begins in the first crystallization vessel, an appropriate amount of xylitol seed crystals is added to stimulate crystallization, and a certain amount of xylitol concentrate is replenished into the first crystallization vessel, and crystallization is performed for 7-12 hours while stirring; at the end of crystallization, steam is introduced to increase the temperature of the system to 66-68°C and keep the temperature for a certain period of time to obtain a xylitol sugar paste; the ratio of the starting liquid raw material to the replenishment liquid raw material is 1:0.8-1.5, the stirring speed is set to a variable speed, the timing of adding the xylitol seed crystals is the time when the particle number <50 is observed through the observation window of the first crystallization vessel, and the keeping time after the final warming of the crystallization is 0.5-2.0 hours; Step 2 is separated by the first centrifuge to obtain crystalline xylitol and primary mother liquor, and the primary mother liquor is transferred to the primary mother liquor storage tank through a pipe for temporary storage; the crystalline xylitol is dried in the hot air drying tank, and then dried in the first fluidized drying bed through cold air to obtain the finished xylitol crystallized product; the primary mother liquor is concentrated by the second evaporator, crystallized by the second crystallizing pot, and centrifuged by the second centrifuge to obtain the twice-crystallized sugar and the secondary mother liquor, and the secondary mother liquor is transferred to the secondary mother liquor storage tank through a pipe for temporary storage; the twice-crystallized sugar is dried in the second fluidized drying bed, and then transferred to the twice-crystallized sugar dissolving tank for dissolving; the twice-crystallized sugar is dissolved by adding purified water to dissolve the twice-crystallized sugar, and the twice-crystallized sugar solution is obtained; the twice-crystallized sugar solution is transferred to the blending tank through a pipe for mixing with the xylitol hydrogenated liquid raw material for blending; and step 4, the second mother liquor obtained in step 2 is concentrated by a third evaporator, crystallized by a third crystallizer, and centrifuged by 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, then put into a triple crystallized sugar dissolving tank to dissolve, purified water is added to dissolve the triple crystallized sugar, obtain a triple crystallized sugar solution, the triple crystallized sugar solution is put into a primary mother liquor storage tank through a pipe, mixed with the primary mother liquor, recovered and reused, and the tertiary mother liquor is stored as liquid xylitol.

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

5. In step 2, the first crystallization kettle is a vacuum evaporation crystallization kettle, 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 kettle is 1 cm ２ The system and method for producing xylitol crystals according to claim 1, 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 the crystallization of the system; the addition rate of the seed crystals is 0.0004-0.0008%; and the grain size of the seed crystals is 80-100 mesh.

6. The method for producing xylitol crystals according to claim 1, characterized in that in step 2, the xylitol sugar paste is separated using a first centrifuge, and then sprayed with an ethanol solution having a concentration of 80 to 100% for 5 to 10 s to wash the xylitol crystals, thereby removing moisture from the xylitol crystals to the maximum extent.

7. The method for producing crystals of xylitol according to claim 1, characterized in that 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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