A preparation system and method for xylitol crystals

Abstract

The present invention relates to a preparation system and preparation method of xylitol crystals, the preparation system includes a blending tank, a decoloring tank, an ion exchange column, a nanofiltration system, a first evaporator, a first crystallization kettle, a first centrifuge, a hot air drying tank, a first fluidized drying bed, a primary mother liquor storage tank, a second evaporator, a second crystallization kettle, a second centrifuge, a second fluidized drying bed, a two-crystal sugar dissolving tank, a secondary mother liquor storage tank, a third evaporator, a third crystallization kettle, a third centrifuge, a third fluidized drying bed and a three-crystal sugar dissolving tank, the first centrifuge is also connected to the primary mother liquor storage tank, the second centrifuge is also connected to the secondary mother liquor storage tank, the two-crystal sugar dissolving tank is connected to the blending tank, the three-crystal sugar dissolving tank is connected to the primary mother liquor storage tank, the blending tank stores the xylitol hydrogenation liquid raw material used for preparing xylitol crystals, and the output of the discharge port of the first fluidized drying bed is the prepared xylitol crystals. The present invention improves the particle size of the xylitol crystals and prolongs the agglomeration cycle of the xylitol crystals.

Description

Technical Field

[0001] The invention belongs to the technical field of xylitol preparation, and particularly relates to a xylitol crystal preparation system and a preparation method. Background Art

[0002] The existing xylitol production process uses corn cobs as raw materials and prepares xylitol crystals through steps such as hydrolysis, hydrogenation, decolorization, ion exchange, concentration, crystallization, centrifugation and drying. The crystallization process is the key to determining the quality and yield of xylitol products, and plays a decisive role in the morphology, purity, bulk density, particle size distribution and agglomeration properties of the crystal products.

[0003] The driving force of the xylitol crystallization process mainly comes from the thermodynamic non-equilibrium characteristics of the crystallization system. The thermodynamic properties of crystallization such as solubility, metastable zone and induction period have a great influence on the selection of crystallization methods and crystallization yield. At present, the commonly used crystallization methods in industry are evaporation crystallization and cooling crystallization. For the crystallization process of xylitol, due to its large solubility, evaporation crystallization and cooling crystallization have been well applied.

[0004] However, whether it is evaporation crystallization or cooling crystallization, due to unreasonable process operation parameters, or adding crystal seeds based on experience, there is a lack of theoretical and factual basis for the timing of adding crystal seeds, resulting in a long crystallization process of xylitol, serious secondary nucleation, a high proportion of fine powder, and large differences between products in different batches. The crystallization process is unstable, which ultimately leads to the xylitol product being prone to agglomeration. For example, the patent with publication number CN1736970A discloses a method for refining and crystallizing xylitol. By optimizing the crystallization process rotation speed, crystal seed amount, crystal seed particle size, cooling rate and other factors, although xylitol crystals with centralized and adjustable particle size are obtained, it is impossible to achieve a 3-6% crystal seed addition amount in actual production, which limits the application of the process in production. For example, the patent with publication number CN102731252A discloses a method for crystallizing xylitol or maltitol. Although a small amount of anti-caking agent is added during the crystallization process to effectively alleviate the crystal agglomeration phenomenon, it is not clear whether the addition of the anti-caking agent will affect the product quality, and the relevant standards do not allow the use of the method of adding anti-caking agents.

[0005] Therefore, from the perspective of industrial feasibility, optimizing crystallization process parameters, reducing secondary nucleation and controlling product particle size distribution have become important measures to avoid or alleviate the agglomeration of xylitol crystals. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a system and method for preparing xylitol crystals, which can improve the particle size of xylitol crystal products and extend the agglomeration period of xylitol crystal products.

[0007] The present invention is achieved by providing a system for preparing xylitol crystals, comprising a blending tank, a decolorizing tank, an ion exchange column, a nanofiltration system, a first evaporator, a first crystallization kettle, a first centrifuge, a hot air drying tank and a first fluidized drying bed which are sequentially connected through pipelines, and also comprising a primary mother liquor storage tank, a second evaporator, a second crystallization kettle, a second centrifuge, a second fluidized drying bed and a two-crystal sugar dissolving tank which are sequentially connected through pipelines, and also comprising a secondary mother liquor storage tank, a third evaporator, a third crystallization kettle, a third centrifuge, a third fluidized drying bed and a three-crystal sugar dissolving tank which are sequentially connected through pipelines, wherein the solid material discharge port of the first centrifuge is connected to the feed port of the hot air drying tank through a pipeline, the liquid material discharge port of the first centrifuge is connected to a feed port of the primary mother liquor storage tank through a pipeline, and the liquid material discharge port of the first centrifuge is connected to a feed port of the primary mother liquor storage tank through a pipeline. The solid material discharge port of the second centrifuge is connected with the feed port of the second fluidized drying bed through a pipeline, the liquid material discharge port of the second centrifuge is connected with the feed port of the secondary mother liquid storage tank through a pipeline, the two-crystal sugar dissolving tank is provided with a water inlet for purified water, the two-crystal sugar dissolving tank is also provided with a discharge port connected with a feed port of the blending tank through a pipeline, the three-crystal sugar dissolving tank is also provided with a water inlet for purified water, the three-crystal sugar dissolving tank is also provided with a discharge port connected with a feed port of the primary mother liquid storage tank through a pipeline, a feed pipe for hydrogenated liquid is also provided on the blending tank, the blending tank stores xylitol hydrogenated liquid raw materials used for preparing xylitol crystals, the blending tank is used to evenly mix the xylitol hydrogenated liquid raw materials with the two-crystal sugar solution transported from the two-crystal sugar dissolving tank, and the output of the discharge port of the first fluidized drying bed is the prepared xylitol crystals.

[0008] Furthermore, the preparation system also includes a liquid xylitol storage tank, and a discharge port of the third centrifuge is connected to a feed port of the liquid xylitol storage tank through a pipeline.

[0009] The present invention is implemented in this way, and also provides a method for preparing xylitol crystals, the preparation method using the above-mentioned xylitol crystal preparation system, the preparation method comprising the following steps:

[0010] Step 1: In the blending tank 1, the xylitol hydrogenated liquid raw material and the disaccharide solution are blended in a certain ratio, and then sequentially subjected to decolorization treatment in a decolorization tank, impurity removal treatment in an ion exchange column, filtration treatment in a nanofiltration system, and evaporation and concentration treatment in a first evaporator to obtain a xylitol concentrate. In this step, the xylitol concentrate is required to have a refractive index of 78-82%, a temperature of 90-100° C., and a conductivity of <20 μs / cm.

[0011] Step 2: The xylitol concentrated liquid enters the first crystallization kettle through a pipeline, and a certain amount of initial xylitol concentrated liquid is first introduced into the first crystallization kettle, and the vacuum degree of the first crystallization kettle is controlled to be -0.095 MPa and the temperature is kept constant at 65°C. When crystals just begin to precipitate in the first crystallization kettle, an appropriate amount of xylitol seed crystals are added to stimulate crystallization, and a certain amount of xylitol concentrated liquid is added to the first crystallization kettle at the same time, and crystallization is carried out while stirring for 7 to 12 hours; at the end of the crystallization, steam is introduced to raise the system temperature to 66 to 68°C and then maintained for a certain time to obtain xylitol sugar paste; in this step, the ratio of the initial feed liquid to the additional feed liquid is 1:0.8 to 1.5, the stirring speed is set to variable frequency stirring, the timing of adding xylitol seed crystals is set to observe that the number of particles is less than 50 from the window of the first crystallization kettle, and the maintenance time after the temperature is raised at the end of the crystallization is 0.5 to 2.0 hours.

[0012] Step 3: subjecting the xylitol massecuite obtained in step 2 to separation treatment in a first centrifuge to obtain crystalline xylitol and a primary mother liquor respectively, the primary mother liquor enters a primary mother liquor storage tank through a pipeline for temporary storage, the crystalline xylitol is dried in a hot air drying tank and dried by cold air in a first fluidized drying bed to obtain a xylitol crystal product; the primary mother liquor is sequentially concentrated in a second evaporator, crystallized in a second crystallization kettle, and centrifuged in a second centrifuge to obtain discrystal sugar and a secondary mother liquor respectively, the secondary mother liquor enters a secondary mother liquor storage tank through a pipeline for temporary storage; the discrystal sugar enters a discrystal sugar dissolving tank for dissolution treatment after being dried in the second fluidized drying bed, purified water is input to dissolve the discrystal sugar to obtain a discrystal sugar dissolved solution, the discrystal sugar dissolved solution enters a blending tank through a pipeline to be mixed and blended with the xylitol hydrogenated liquid raw material.

[0013] Step 4: The secondary mother liquor obtained in step 2 is sequentially concentrated by a third evaporator, crystallized by a third crystallizer, and centrifuged by a third centrifuge to obtain tricrystalline sugar and tertiary mother liquor, respectively. The tricrystalline sugar is dried by a third fluidized drying bed and then enters a tricrystalline sugar dissolving tank for dissolution. Purified water is input to dissolve the tricrystalline sugar to obtain a tricrystalline sugar dissolved solution. The tricrystalline sugar dissolved solution enters a primary mother liquor storage tank through a pipeline and is blended with the primary mother liquor and then recycled and reused. The tertiary mother liquor is stored in the form of liquid xylitol.

[0014] Compared with the prior art, the preparation system and preparation method of the xylitol crystals of the present invention have the following characteristics: xylitol crystals with larger particle size and more concentrated particle size distribution can be prepared, wherein, in the prepared xylitol crystals, the proportion of xylitol particles above 30 mesh can be increased by more than 30%; at the same time, the results of small package samples show that the agglomeration period of the xylitol crystal product is increased from 45 days to more than 100 days. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the principle of a preferred embodiment of a system for preparing xylitol crystals of the present invention;

[0016] Figure 2 Schematic diagram of particle size distribution of xylitol crystals prepared in various examples and comparative examples. DETAILED DESCRIPTION

[0017] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] Please refer to Figure 1 As shown, a preferred embodiment of the system for preparing xylitol crystals of the present invention comprises a blending tank 1, a decolorizing tank 2, an ion exchange column 3, a nanofiltration system 4, a first evaporator 5, a first crystallization kettle 6, a first centrifuge 7, a hot air drying tank 8 and a first fluidized drying bed 9 which are sequentially connected through pipelines, and also comprises a primary mother liquor storage tank 10, a second evaporator 11, a second crystallization kettle 12, a second centrifuge 13, a second fluidized drying bed 14 and a two-crystal sugar dissolving tank 15 which are sequentially connected through pipelines, and also comprises a secondary mother liquor storage tank 16, a third evaporator 17, a third crystallization kettle 18, a third centrifuge 19, a third fluidized drying bed 20 and a three-crystal sugar dissolving tank 21 which are sequentially connected through pipelines. The direction indicated by the arrow in the figure is a schematic diagram of the flow direction of the materials in the system.

[0019] Among them, the solid material discharge port of the first centrifuge 7 is connected to the feed port of the hot air drying tank 8 through a pipeline, and the liquid material discharge port of the first centrifuge 7 is connected to a feed port of the primary mother liquid storage tank 10 through a pipeline. The solid material discharge port of the second centrifuge 13 is connected to the feed port of the second fluidized drying bed 14 through a pipeline, and the liquid material discharge port of the second centrifuge 13 is connected to the feed port of the secondary mother liquid storage tank 16 through a pipeline. The two-crystal sugar dissolving tank 15 is provided with a water inlet for purified water, and the two-crystal sugar dissolving tank 15 is also provided with a discharge port connected to a feed port of the blending tank 1 through a pipeline. The three-crystal sugar dissolving tank 21 is also provided with a water inlet for purified water, and the three-crystal sugar dissolving tank 21 is also provided with a discharge port connected to a feed port of the primary mother liquid storage tank 10 through a pipeline. A feeding pipe for hydrogenated liquid is also provided on the blending tank 1. The blending tank 1 stores the raw material of xylitol hydrogenated liquid used for preparing xylitol crystals. The blending tank 1 is used to evenly mix the raw material of xylitol hydrogenated liquid with the disaccharide solution delivered from the disaccharide dissolving tank 15. The output of the discharge port of the first fluidized drying bed 9 is the prepared xylitol crystals.

[0020] The preparation system further comprises a liquid xylitol storage tank 22 , and a discharge port of the third centrifuge 19 is connected to a feed port of the liquid xylitol storage tank 22 through a pipeline.

[0021] Please refer to Figure 1As shown, the present invention also discloses a method for preparing xylitol crystals, the method using the aforementioned xylitol crystal preparation system, the method comprising the following steps:

[0022] Step 1: In the blending tank 1, the xylitol hydrogenated liquid raw material and the disaccharide solution are blended in a certain ratio, and then sequentially subjected to decolorization treatment in the decolorization tank 2, impurity removal treatment in the ion exchange column 3, filtration treatment in the nanofiltration system 4, and evaporation and concentration treatment in the first evaporator 5 to obtain a xylitol concentrate. In this step, the xylitol concentrate is required to have a refractive index of 78-82%, a temperature of 90-100°C, and a conductivity of <20μs / cm.

[0023] Step 2, the xylitol concentrated liquid enters the first crystallization kettle 6 through the pipeline, and a certain amount of initial xylitol concentrated liquid is first introduced into the first crystallization kettle 6, and the vacuum degree of the first crystallization kettle 6 is controlled to be -0.095MPa and the temperature is kept constant at 65°C. When crystals just begin to precipitate in the first crystallization kettle 6, an appropriate amount of xylitol seed crystals are added to stimulate crystallization, and a certain amount of xylitol concentrated liquid is added to the first crystallization kettle 6 at the same time, and crystallization is carried out while stirring for 7-12 hours; at the end of the crystallization, steam is introduced to increase the system temperature to 66-68°C and then maintained for a certain time to obtain xylitol sugar paste; in this step, the ratio of the initial feed liquid to the additional feed liquid is 1:0.8-1.5, the stirring speed is set to variable frequency stirring, the timing of adding xylitol seed crystals is set to observe that the number of particles is less than 50 from the window of the first crystallization kettle 6, and the maintenance time after the temperature is increased at the end of the crystallization is 0.5-2.0h.

[0024] Step 3: After the xylitol massecuite obtained in step 2 is separated by the first centrifuge 7, crystalline xylitol and primary mother liquor are obtained respectively. The primary mother liquor enters the primary mother liquor storage tank 10 through a pipeline for temporary storage. The crystalline xylitol is dried by the hot air drying tank 8 and the cold air drying by the first fluidized drying bed 9 to obtain a xylitol crystal product. The primary mother liquor is concentrated by the second evaporator 11, crystallized by the second crystallization kettle 12, and centrifuged by the second centrifuge 13 in sequence to obtain disintegrated sugar and secondary mother liquor respectively. The secondary mother liquor enters the secondary mother liquor storage tank 16 through a pipeline for temporary storage. After the disintegrated sugar is dried by the second fluidized drying bed 14, it enters the disintegrated sugar dissolving tank 15 for dissolution treatment. Purified water is input to dissolve the disintegrated sugar to obtain a disintegrated sugar dissolved solution. The disintegrated sugar dissolved solution enters the blending tank 1 through a pipeline to be mixed and blended with the xylitol hydrogenated liquid raw material.

[0025] Step 4: The secondary mother liquor obtained in step 2 is sequentially subjected to concentration treatment in the third evaporator 17, crystallization treatment in the third crystallizer 18, and centrifugation treatment in the third centrifuge 19 to obtain three-crystal sugar and three-crystal mother liquor respectively. After the three-crystal sugar is dried in the third fluidized drying bed 20, it enters the three-crystal sugar dissolving tank 21 for dissolution treatment, and purified water is input to dissolve the three-crystal sugar to obtain a three-crystal sugar dissolved solution. The three-crystal sugar dissolved solution enters the primary mother liquor storage tank 10 through a pipeline and is blended with the primary mother liquor for recycling and reuse, and the tertiary mother liquor is stored in the form of liquid xylitol.

[0026] In step 1, the nanofiltration membrane size of the nanofiltration system 4 is 300-800 Da.

[0027] In step 2, the first crystallization kettle 6 is a vacuum evaporation crystallization kettle, and the speed of the variable frequency stirring process is gradually reduced from 90 rpm to 10 rpm. The window size of the first crystallization kettle 6 is 1 cm 2 The number of xylitol crystal particles in the window was observed using a 10×10 microscope. Xylitol seed crystals were added to stimulate the system to crystallize. The seed crystal addition ratio was 0.0004-0.0008%, and the seed crystal particle size was 80-100 mesh.

[0028] In step 2, after the xylitol massecuite is separated by the first centrifuge 7, it is sprayed with an ethanol solution with a concentration of 80-100% for 5-10 seconds to remove the moisture in the crystalline xylitol to the greatest extent.

[0029] In step three, the hot air temperature of the hot air drying tank 8 is selected to be 75-85°C.

[0030] The preparation system of xylitol crystals of the present invention is further described below through specific examples.

[0031] Example 1

[0032] The first embodiment of the method for preparing xylitol crystals of the present invention comprises the following steps:

[0033] Step 11, the xylitol hydrogenated liquid and the disaccharide solution are blended in a certain ratio, and then sequentially subjected to activated carbon decolorization treatment in the decolorization tank 2, ion exchange treatment in the ion exchange column 3, 400Da nanofiltration membrane system 4 and first evaporator 5 to obtain a xylitol concentrate with a refractive index of 79%, a temperature of 95°C and a conductivity of 1.958μs / cm.

[0034] Step 12, firstly, 10 tons of xylitol concentrate are introduced into the first crystallization kettle 6, and further concentrated at -0.095 MPa, until the system temperature drops to about 65°C, and 20 fine crystals are observed in the window of the first crystallization kettle 6, then 0.0005% of xylitol seed crystals are added to stimulate crystallization, and at the same time, 10 tons of xylitol concentrate are added to the crystallization tank, and the system temperature is maintained at -0.095 MPa and 65°C, and the crystallization is stirred at an initial speed of 90 rpm. After crystallization for 7 hours, steam is introduced to raise the system temperature to 67°C, and then 67°C is maintained to continue crystallization for 0.5 hours to obtain xylitol sugar paste.

[0035] Step 13, the obtained xylitol massecuite is separated and treated 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 cold air dried by the first fluidized drying bed 9 to obtain a xylitol crystal product. The primary mother liquor is further crystallized at -0.095MPa and 65°C in the second crystallization kettle 12 after being concentrated by the second evaporator 11, and then centrifuged by the second centrifuge 13 to obtain discrystal sugar and secondary mother liquor respectively. After the discrystal sugar is dried by the second fluidized drying bed 14, it enters the discrystal sugar dissolving tank 15 and is dissolved into a discrystal sugar dissolving solution, which is then transported to the blending tank 1 for blending with the xylitol hydrogenated liquid. The secondary mother liquor is concentrated by the third evaporator 17, crystallized by the third crystallization kettle 18, and centrifuged by the third centrifuge 19 to obtain tricrystal sugar and tertiary mother liquor respectively. The tertiary mother liquor is stored in the liquid xylitol storage tank 22. After being dried in the third fluidized drying bed 20, the tricrystalline sugar enters the tricrystalline sugar dissolving tank 21 for dissolution to obtain a tricrystalline sugar dissolved solution. The tricrystalline sugar dissolved solution enters the primary mother liquor storage tank 10 through a pipeline and is blended with the primary mother liquor for recycling.

[0036] The prepared xylitol crystal product was sieved to obtain a particle size distribution of the xylitol crystal product as shown in Table 1 below.

[0037] Table 1 Particle size distribution of xylitol crystal product prepared in Example 1

[0038]

[0039] The agglomeration period of the small package sample of xylitol crystals prepared in Example 1 was actually measured to be 105 days.

[0040] Example 2

[0041] The second embodiment of the method for preparing xylitol crystals of the present invention comprises the following steps:

[0042] Step 21, the xylitol hydrogenated liquid and the disaccharide solution are blended in a certain ratio, and then sequentially subjected to activated carbon decolorization treatment in the decolorization tank 2, ion exchange treatment in the ion exchange column 3, 400Da nanofiltration membrane system 4 and first evaporator 5 to obtain a xylitol concentrate with a refractive index of 80%, a temperature of 95°C and a conductivity of 1.744μs / cm.

[0043] Step 22, firstly, 10 tons of xylitol concentrate are introduced into the first crystallization kettle 6, and further concentrated at -0.095 MPa, until the system temperature drops to about 65°C, and 25 fine crystals are observed in the window of the first crystallization kettle 6, then 0.0005% of xylitol seed crystals are added to stimulate crystallization, and at the same time, 10 tons of xylitol concentrate are added to the crystallization tank, and the system temperature is maintained at -0.095 MPa and 65°C, and crystallization is performed at an initial speed of 90 rpm with variable frequency stirring. After crystallization for 8 hours, steam is introduced to raise the system temperature to 66.5°C, and then 66.5°C is maintained to continue crystallization for 0.8 hours to obtain xylitol sugar paste.

[0044] Step 23, the obtained xylitol massecuite is separated and treated 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 cold air dried by the first fluidized drying bed 9 to obtain a xylitol crystal product. The primary mother liquor is further crystallized at -0.095MPa and 65°C in the second crystallization kettle 12 after being concentrated by the second evaporator 11, and then centrifuged by the second centrifuge 13 to obtain discrystal sugar and secondary mother liquor respectively. After the discrystal sugar is dried by the second fluidized drying bed 14, it enters the discrystal sugar dissolving tank 15 and is dissolved into a discrystal sugar dissolving solution, which is then transported to the blending tank 1 for blending with the xylitol hydrogenated liquid. The secondary mother liquor is concentrated by the third evaporator 17, crystallized by the third crystallization kettle 18, and centrifuged by the third centrifuge 19 to obtain tricrystal sugar and tertiary mother liquor respectively. The tertiary mother liquor is stored in the liquid xylitol storage tank 22. After being dried in the third fluidized drying bed 20, the tricrystalline sugar enters the tricrystalline sugar dissolving tank 21 for dissolution to obtain a tricrystalline sugar dissolved solution. The tricrystalline sugar dissolved solution enters the primary mother liquor storage tank 10 through a pipeline and is blended with the primary mother liquor for recycling.

[0045] The prepared xylitol crystal product was sieved to obtain a particle size distribution of the xylitol crystal product as shown in Table 2 below.

[0046] Table 2 Particle size distribution of xylitol crystal product prepared in Example 2

[0047]

[0048] The agglomeration period of the small package sample of xylitol crystals prepared in Example 2 was actually measured to be 112 days.

[0049] In order to better describe the beneficial effects brought by the present invention, further explanation is given below in conjunction with comparative examples.

[0050] Comparative Example

[0051] The comparative example of the present invention comprises the following steps:

[0052] Step 31, directly blending the xylitol hydrogenated liquid with the first centrifuged mother liquor in a certain ratio, and then sequentially subjecting them to activated carbon decolorization, ion exchange and triple-effect evaporation 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.

[0053] In step 32, 7 tons of xylitol concentrate are first introduced into the crystallization tank, and further concentrated at -0.095 MPa. When the system is cooled to about 65°C, a large number of fine crystals (>50) are observed in the window of the crystallization tank. At this time, 0.0005% of xylitol seed crystals are added to stimulate crystallization. At the same time, 13 tons of xylitol concentrate are added to the crystallization tank. The system temperature is maintained at -0.095 MPa and 65°C. The crystallization is stirred at a constant speed of 90 rpm for 8 hours to obtain xylitol syrup.

[0054] Step 33, separating the obtained xylitol massecuite by high-speed centrifuge to obtain 8.8 tons of xylitol crystals and 10.2 tons of primary centrifugal mother liquor, and drying the xylitol crystals by hot air drying at 88° C. and cold air drying to obtain a xylitol product; the primary centrifugal mother liquor is directly recycled for the hydrogenated liquid blending step.

[0055] The prepared xylitol crystal product was sieved to obtain a particle size distribution of the xylitol crystal product as shown in Table 3 below.

[0056] Table 3 Particle size distribution of xylitol crystal products prepared in comparative example

[0057]

[0058] The agglomeration period of the small package sample of xylitol crystals prepared in the comparative example was actually measured to be 45 days.

[0059] Compared with the comparative example, Example 1 and Example 2 obtained xylitol crystal products with larger particles and narrower particle size distribution by reducing the recycling of xylitol mother liquor, adding a nanofiltration system to remove low molecular weight impurities, optimizing the crystallization process, and using alcohol washing in the centrifugal process, and the agglomeration cycle of the xylitol crystal products was significantly improved. The comparative data are shown in Table 4 and Figure 2 shown.

[0060] Table 4 Comparison of test data of xylitol crystal products of various embodiments and comparative examples

[0061]

[0062] From the above table, it can be concluded that in the comparison item of the proportion of 30 mesh, the xylitol crystal product of Example 1 is 40% higher than that of the comparative example, and the xylitol crystal product of Example 2 is 36% higher than that of the comparative example. In addition, the agglomeration period of the xylitol crystal products of Examples 1 and 2 is significantly higher than that of the comparative example.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A system for preparing xylitol crystals, characterized in that: The invention comprises a blending tank, a decolorizing tank, an ion exchange column, a nanofiltration system, a first evaporator, a first crystallization kettle, a first centrifuge, a hot air drying tank and a first fluidized drying bed which are sequentially connected through pipelines, and also comprises a primary mother liquor storage tank, a second evaporator, a second crystallization kettle, a second centrifuge, a second fluidized drying bed and a two-crystal sugar dissolving tank which are sequentially connected through pipelines, and also comprises a secondary mother liquor storage tank, a third evaporator, a third crystallization kettle, a third centrifuge, a third fluidized drying bed and a three-crystal sugar dissolving tank which are sequentially connected through pipelines, wherein the solid discharge port of the first centrifuge is connected to the feed port of the hot air drying tank through a pipeline, the liquid discharge port of the first centrifuge is connected to a feed port of the primary mother liquor storage tank through a pipeline, and the solid discharge port of the second centrifuge is connected to a feed port of the primary mother liquor storage tank through a pipeline. The second centrifuge is connected with the feed port of the second fluidized drying bed through a pipeline, the liquid discharge port of the second centrifuge is connected with the feed port of the secondary mother liquor storage tank through a pipeline, the two-crystal sugar dissolving tank is provided with a water inlet for purified water, the two-crystal sugar dissolving tank is also provided with a discharge port connected with a feed port of the blending tank through a pipeline, the three-crystal sugar dissolving tank is also provided with a water inlet for purified water, the three-crystal sugar dissolving tank is also provided with a discharge port connected with a feed port of the primary mother liquor storage tank through a pipeline, a feed pipe for hydrogenated liquid is also provided on the blending tank, the blending tank stores xylitol hydrogenated liquid raw materials used for preparing xylitol crystals, the blending tank is used to evenly mix the xylitol hydrogenated liquid raw materials with the two-crystal sugar solution transported from the two-crystal sugar dissolving tank, and the output of the discharge port of the first fluidized drying bed is the prepared xylitol crystals.

2. The system for preparing xylitol crystals according to claim 1, characterized in that: The preparation system further comprises a liquid xylitol storage tank, and a discharge port of the third centrifuge is connected to a feed port of the liquid xylitol storage tank through a pipeline.

3. A method for preparing xylitol crystals, characterized in that: The preparation method uses the xylitol crystal preparation system as claimed in claim 1 or 2, and the preparation method comprises the following steps: Step 1: In a blending tank 1, the xylitol hydrogenated liquid raw material and the disaccharide solution are blended in a certain ratio, and then sequentially subjected to decolorization treatment in a decolorization tank, impurity removal treatment in an ion exchange column, filtration treatment in a nanofiltration system, and evaporation and concentration treatment in a first evaporator to obtain a xylitol concentrate. In this step, the xylitol concentrate is required to have a refractive index of 78-82%, a temperature of 90-100° C., and a conductivity of <20 μs / cm; Step 2, the xylitol concentrated liquid enters the first crystallization kettle through the pipeline, firstly, a certain amount of initial xylitol concentrated liquid is introduced into the first crystallization kettle, the vacuum degree of the first crystallization kettle is controlled to be -0.095MPa, and the temperature is kept constant at 65°C, and when crystals just begin to precipitate in the first crystallization kettle, an appropriate amount of xylitol seed crystals are added to stimulate crystallization, and at the same time, a certain amount of xylitol concentrated liquid is added to the first crystallization kettle, and crystallization is carried out while stirring for 7-12 hours; at the end of crystallization, steam is introduced to raise the system temperature to 66-68°C and then maintained for a certain time to obtain xylitol sugar paste; in this step, the ratio of initial feed liquid to supplementary feed liquid is 1:0.8-1.5, the stirring speed is set to variable frequency stirring, the timing of adding xylitol seed crystals is set to observe that the number of particles is less than 50 from the window of the first crystallization kettle, and the maintenance time after heating at the end of crystallization is 0.5-2.0h; Step 3: subjecting the xylitol massecuite obtained in step 2 to separation treatment in a first centrifuge to obtain crystalline xylitol and a primary mother liquor respectively, the primary mother liquor enters a primary mother liquor storage tank through a pipeline for temporary storage, the crystalline xylitol is dried in a hot air drying tank and dried by cold air in a first fluidized drying bed to obtain a xylitol crystal product; the primary mother liquor is sequentially concentrated in a second evaporator, crystallized in a second crystallization kettle, and centrifuged in a second centrifuge to obtain discrystal sugar and a secondary mother liquor respectively, the secondary mother liquor enters a secondary mother liquor storage tank through a pipeline for temporary storage; the discrystal sugar enters a discrystal sugar dissolving tank for dissolution treatment after being dried in the second fluidized drying bed, purified water is input to dissolve the discrystal sugar to obtain a discrystal sugar dissolved solution, the discrystal sugar dissolved solution enters a blending tank through a pipeline to be mixed and blended with the xylitol hydrogenated liquid raw material; Step 4: The secondary mother liquor obtained in step 2 is sequentially concentrated by a third evaporator, crystallized by a third crystallizer, and centrifuged by a third centrifuge to obtain tricrystalline sugar and tertiary mother liquor, respectively. The tricrystalline sugar is dried by a third fluidized drying bed and then enters a tricrystalline sugar dissolving tank for dissolution. Purified water is input to dissolve the tricrystalline sugar to obtain a tricrystalline sugar dissolved solution. The tricrystalline sugar dissolved solution enters a primary mother liquor storage tank through a pipeline and is blended with the primary mother liquor and then recycled and reused. The tertiary mother liquor is stored in the form of liquid xylitol.

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

5. The system and method for preparing xylitol crystals according to claim 1, characterized in that: In step 2, the first crystallization kettle is a vacuum evaporation crystallization kettle, and the speed of the variable frequency stirring process is gradually reduced from 90 rpm to 10 rpm. The window size of the first crystallization kettle is 1 cm 2 The number of xylitol crystal particles in the window was observed using a 10×10 microscope. Xylitol seed crystals were added to stimulate the system to crystallize. The seed crystal addition ratio was 0.0004-0.0008%, and the seed crystal particle size was 80-100 mesh.

6. The method for preparing xylitol crystals according to claim 1, characterized in that: In step 2, after the xylitol massecuite is separated by the first centrifuge, it is sprayed with an ethanol solution with a concentration of 80-100% for 5-10 seconds to remove the moisture in the crystalline xylitol to the greatest extent.

7. The method for preparing xylitol crystals according to claim 1, characterized in that: In step three, the hot air temperature of the hot air drying tank is selected to be 75-85°C.

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