A method for preparing crystalline xylitol

Abstract

The present application relates to a kind of preparation methods of crystalline xylitol, including xylose dissolving, hydrogenation hydrogenation, decolorization, chromatographic separation, ion exchange, evaporation concentration, vacuum crystallization, centrifugal separation, drying and screening after obtaining the desired crystalline xylitol.The present application is by controlling the conversion rate of xylose in the process of hydrogenation hydrogenation from 99.8% to 95%, while the hydrogenation reaction time is changed from 2 hours to 1 hour, then the obtained xylitol solution is treated by decolorization and chromatographic separation, the content of xylitol in chromatographic extract is improved, and the desired crystalline xylitol is obtained by further refining treatment of chromatographic extract;And chromatographic raffinate is recycled for xylose hydrogenation hydrogenation process, and is fully utilized.

Description

Technical Field

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

[0002] Currently, xylitol is primarily produced by adding hydrogen to xylose under high-temperature, high-pressure conditions, followed by subsequent refining to produce crystalline xylitol. During the hydrogenation process, the conversion rate of xylose to xylitol gradually decreases due to the continuous reduction of substrate. While xylose conversion can reach 95% in just one hour, it also takes another hour to reach 95% to 99.8%. Low conversion efficiency in the later stages of the reaction reduces energy efficiency, creating bottlenecks in the production process and lowering overall production capacity, indirectly increasing the cost of xylitol production. Another xylitol production method involves hydrogenating low-purity xylose solution to produce xylitol, followed by chromatographic separation. This method produces numerous byproducts. However, this method suffers from a high number of products, a complex production process, and low efficiency. Furthermore, it fails to consider the cost of hydrogenation. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing crystalline xylitol, by controlling the conversion rate of xylose in the hydrogenation process from 99.8% to 95%, and at the same time shortening the hydrogenation reaction time from 2 hours to 1 hour, and then subjecting the obtained xylitol solution to decolorization and chromatographic separation to increase the xylitol content in the chromatographic extract, and then refining the chromatographic extract to obtain the desired crystalline xylitol; and the chromatographic extract is recycled and used in the xylose hydrogenation process, so as to be fully utilized.

[0004] The present invention is achieved by providing a method for preparing crystalline xylitol, comprising the following steps:

[0005] Step 1: Dissolve xylose in a xylose dissolving tank to obtain xylose solution. If conditions permit, add 2.0 ml of chromatographic raffinate to the xylose dissolving tank. 3 ~3.0m 3 When the chromatographic residual liquid is insufficient, it is replaced with drinking water. The refractive index of the xylose solution is tested to be between 50% and 60%. The steam valve is opened to heat the xylose dissolving tank to 50-70°C.

[0006] Step 2, hydrogenation: The xylose solution with qualified refractive index is pumped into the hydrogenation reactor for hydrogenation reaction. After hydrogenation, the xylose becomes xylitol. The pressure of the hydrogenation reaction is controlled at 8.0MPa to 10.0MPa. The temperature of the material during the entire hydrogenation reaction is ≤140°C. The hydrogenation reaction time is 50min to 60min. When the xylose conversion rate is controlled at 95%, the obtained xylitol solution is discharged to the next process.

[0007] Step 3: Decolorization: The xylitol solution is pumped into a decolorization tank via a centrifugal pump. The temperature of the xylitol solution is raised to 60-80°C using a plate heat exchanger. Activated carbon is added to the decolorization tank for decolorization. After decolorization, a decolorized liquid is obtained. The light transmittance of the decolorized liquid is tested. When the light transmittance is ≥95%, the material is discharged to the next process.

[0008] Step 4, chromatographic separation: The decolorized liquid enters the chromatographic system for chromatographic treatment to obtain a chromatographic extract and a chromatographic residual liquid. The feed flow rate of the chromatographic system is 8000L / h to 12000L / h, and the feed temperature is 40 to 60°C. The xylitol content in the chromatographic extract is tested online. When the xylitol content in the chromatographic extract is ≥98%, the chromatographic extract enters the next process. When the xylitol content in the chromatographic extract is <98%, the chromatographic extract material is refluxed for further chromatographic separation treatment, and the operating parameters of the chromatographic system are adjusted; the chromatographic residual liquid is refluxed to the xylose dissolution tank in step 1 for utilization;

[0009] The chromatographic extract is then sequentially subjected to ion exchange treatment, evaporation concentration treatment, vacuum crystallization treatment, centrifugal separation treatment, drying and screening treatment to obtain the desired crystalline xylitol.

[0010] Furthermore, the ion exchange treatment refers to:

[0011] Step 5, ion exchange: The chromatographic extract enters the ion exchange system for ion exchange treatment to obtain a xylitol exchange liquid. The ion exchange system includes a positive column and a negative column that are interconnected. The feed valve of the positive column is adjusted to adjust the flow rate of the chromatographic extract to 8000L / h to 12000L / h. The quality control of the xylitol exchange liquid is as follows: transmittance ≥ 95%, pH value 4.0 to 7.5, conductivity ≤ 50μs / cm. After that, the xylitol exchange liquid is sent to the coarse filtration system for coarse filtration treatment. The pressure difference of the coarse filtration treatment is 0.2MPa to 0.3MPa.

[0012] The evaporation concentration process refers to:

[0013] Step 6, evaporation and concentration: the xylitol exchange liquid is introduced into an evaporation device for evaporation to obtain xylitol massecuite, the evaporation device includes a triple-effect evaporator. During the evaporation process, the vacuum degree of the first effect is -0.02MPa to -0.1MPa, the material temperature is 100-120°C, the vacuum degree of the second effect is -0.05MPa to -0.07MPa, the material temperature is 90-100°C, and the vacuum degree of the third effect is -0.085MPa to -0.095MPa, the material temperature is 55-65°C, and the refractive index of the material is between 75% and 83%;

[0014] The vacuum crystallization treatment refers to:

[0015] Step 7, vacuum crystallization: xylitol sugar paste is input into a vacuum crystallization kettle for vacuum crystallization treatment to obtain xylitol crystalline sugar, the vacuum degree of the vacuum crystallization kettle is controlled between -0.085 and -0.095 MPa, and the temperature is quickly lowered to a crystallization temperature of 55 to 65°C. During the crystallization process, the material temperature is kept in the range of 55 to 75°C. After the crystallization is completed, the jacket steam valve of the crystallization aid tank on the vacuum crystallization kettle is opened, and the jacket temperature is controlled to be close to the material temperature in the vacuum crystallization kettle at this time, that is, the material temperature ±5°C, and then the vacuum in the vacuum crystallization kettle is removed through the vacuum unloading valve. The vacuum crystallization kettle discharge valve is opened to discharge the obtained xylitol crystalline sugar through the crystallization aid tank to the next process.

[0016] Furthermore, the centrifugal separation process refers to:

[0017] Step 8, centrifugal separation: The xylitol crystal sugar is input into the centrifuge for centrifugal separation to obtain xylitol centrifugal sugar, the centrifugation time is controlled at 25min to 40min, and the xylitol centrifugal sugar is sent to the next process through a screw conveyor;

[0018] The drying and screening process refers to:

[0019] Step 9, drying and screening: The centrifuged xylitol sugar is sequentially conveyed to a hot air boiling dryer and two vibrating fluidized bed dryers for drying to obtain xylitol crystals, and then sent to a screening machine for screening to obtain the desired crystalline xylitol.

[0020] Furthermore, the drying process includes boiling drying, hot air drying and cold air drying, wherein:

[0021] Boiling drying: Xylitol centrifugal sugar is transported to the pre-drying tank for boiling drying, and the air supply temperature is controlled at 75-85℃;

[0022] Hot air drying: The xylitol centrifugal sugar after boiling drying is transported to the hot air vibrating fluidized bed dryer for hot air drying. The hot air temperature of the hot air vibrating fluidized bed dryer is controlled at 40-60°C. By adjusting the inlet and outlet air volumes, the material layer forms a boiling state in the hot air vibrating fluidized bed dryer and moves forward at a uniform speed.

[0023] Cold air drying: The xylitol centrifugal sugar after hot air drying is put into the cold air vibrating fluidized bed dryer for cold air drying. The dehumidified cold air is used to reduce the material temperature. The cold air inlet and outlet volume of the cold air vibrating fluidized bed dryer is controlled to make the material layer form a boiling state in the machine and move forward at a uniform speed to ensure that the discharge temperature is between 15 and 40 °C.

[0024] Furthermore, the screening process refers to: selecting screens with different apertures according to actual production needs to screen the xylitol crystals obtained after the drying process to obtain the desired crystalline xylitol, with a material flow rate of 0 to 3 t / h.

[0025] Compared with the prior art, the preparation method of crystalline xylitol of the present invention has the following characteristics:

[0026] 1. Reduce hydrogenation reaction time by 50% and improve the production efficiency of related practitioners;

[0027] 2. Improved energy and equipment utilization efficiency;

[0028] 3. Use chromatography technology to purify xylitol and improve the quality of the prepared crystalline xylitol product. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The figure is a schematic diagram of the principle of a preferred embodiment of the method for preparing crystalline xylitol of the present invention. DETAILED DESCRIPTION

[0030] 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 with reference to 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.

[0031] Please refer to Figure 1 As shown, a preferred embodiment of the method for preparing crystalline xylitol of the present invention comprises the following steps:

[0032] Step 1: Dissolve xylose in a xylose dissolving tank to obtain xylose solution. If conditions permit, add 2.0 ml of chromatographic raffinate to the xylose dissolving tank. 3 ~3.0m 3 When the chromatographic residual liquid is not enough, use drinking water to replace it, check that the refractive index of the xylose solution is between 50 and 60%, open the steam valve to heat the xylose dissolving tank, and heat the xylose solution in the xylose dissolving tank to 50-70°C.

[0033] Step 2, hydrogenation: The xylose solution with qualified refractive index is pumped into the hydrogenation reactor for hydrogenation reaction. After hydrogenation, the xylose becomes xylitol. The pressure of the hydrogenation reaction is controlled at 8.0MPa~10.0MPa. The temperature of the material during the entire hydrogenation reaction is ≤140°C. The hydrogenation reaction time is 50min~60min. When the xylose conversion rate is controlled at 95%, the obtained xylitol solution is discharged into the next process.

[0034] Step 3: Decolorization: The xylitol solution is pumped into a decolorization tank via a centrifugal pump. The temperature of the xylitol solution is raised to 60-80°C using a plate heat exchanger. Activated carbon is added to the decolorization tank for decolorization. After decolorization, a decolorized liquid is obtained. The light transmittance of the decolorized liquid is tested. When the light transmittance is ≥95%, the material is discharged to the next process.

[0035] Step 4, Chromatographic Separation: The decolorized liquid enters the chromatography system for chromatography treatment to obtain a chromatography extract and a chromatography residue. The chromatography system includes a delivery pump, a chromatography column, a sulfate-type chromatography resin, and a control system. The chromatography system has a feed flow rate of 8000L / h to 12000L / h, a feed temperature of 40-60°C, and elution is performed using purified water at 60-80°C. The xylitol content in the chromatography extract is tested online. When the xylitol content in the chromatography extract is ≥98%, the chromatography extract enters the next process. When the xylitol content in the chromatography extract is <98%, the chromatography extract material is refluxed for further chromatography separation treatment, and the operating parameters of the chromatography system are adjusted; the chromatography residue is refluxed to the xylose dissolution tank in step 1 for use.

[0036] Step 5, ion exchange: The chromatographic extract enters the ion exchange system for ion exchange treatment to obtain xylitol exchange liquid. The ion exchange system includes a positive column and a negative column that are interconnected. The feed valve of the positive column is adjusted to adjust the flow rate of the chromatographic extract to 8000L / h~12000L / h. The quality control of the xylitol exchange liquid is as follows: transmittance ≥95%, pH value 4.0~7.5, conductivity ≤50μs / cm. After that, it is sent to the coarse filtration system for coarse filtration treatment. The pressure difference of the coarse filtration treatment is 0.2MPa~0.3MPa.

[0037] Step 6, evaporation and concentration: the xylitol exchange liquid is introduced into an evaporation device for evaporation treatment to obtain xylitol sugar paste, the evaporation device includes a triple-effect evaporator. During the evaporation process, the vacuum degree of the first effect is -0.02MPa to -0.1MPa, the material temperature is 100-120°C, the vacuum degree of the second effect is -0.05MPa to -0.07MPa, the material temperature is 90-100°C, the vacuum degree of the third effect is -0.085MPa to -0.095MPa, the material temperature is 55-65°C, and the refractive index of the material is between 75% and 83%.

[0038] Step 7, vacuum crystallization: xylitol sugar paste is input into a vacuum crystallization kettle for vacuum crystallization treatment to obtain xylitol crystalline sugar, the vacuum degree of the vacuum crystallization kettle is controlled between -0.085 and -0.095 MPa, and the temperature is quickly lowered to a crystallization temperature of 55 to 65°C. During the crystallization process, the material temperature is kept in the range of 55 to 75°C. After the crystallization is completed, the jacket steam valve of the crystallization aid tank on the vacuum crystallization kettle is opened, and the jacket temperature is controlled to be close to the material temperature in the vacuum crystallization kettle at this time, that is, the material temperature ±5°C, and then the vacuum in the vacuum crystallization kettle is removed through the vacuum unloading valve. The vacuum crystallization kettle discharge valve is opened to discharge the obtained xylitol crystalline sugar through the crystallization aid tank to the next process.

[0039] Step 8, centrifugal separation: The xylitol crystal sugar is input into a centrifuge for centrifugal separation to obtain xylitol centrifugal sugar. The centrifugal time is controlled at 25 minutes to 40 minutes. The xylitol centrifugal sugar is sent to the next process through a screw conveyor.

[0040] Step 9, drying and screening: The centrifuged xylitol sugar is sequentially conveyed to a hot air boiling dryer and two vibrating fluidized bed dryers for drying to obtain xylitol crystals, and then sent to a screening machine for screening to obtain the desired crystalline xylitol.

[0041] The drying process includes boiling drying, hot air drying and cold air drying, wherein,

[0042] Boiling drying: Xylitol centrifugal sugar is transported to the pre-drying tank for boiling drying, and the air supply temperature is controlled at 75-85℃;

[0043] Hot air drying: The xylitol centrifugal sugar after boiling drying is transported to the hot air vibrating fluidized bed dryer for hot air drying. The hot air temperature of the hot air vibrating fluidized bed dryer is controlled at 40-60°C. By adjusting the inlet and outlet air volumes, the material layer forms a boiling state in the hot air vibrating fluidized bed dryer and moves forward at a uniform speed.

[0044] Cold air drying: The xylitol centrifugal sugar after hot air drying is put into the cold air vibrating fluidized bed dryer for cold air drying. The dehumidified cold air is used to reduce the material temperature. The cold air inlet and outlet volume of the cold air vibrating fluidized bed dryer is controlled to make the material layer form a boiling state in the machine and move forward at a uniform speed to ensure that the discharge temperature is between 15 and 40 °C.

[0045] The screening process refers to: selecting screens of different apertures according to actual production needs to screen the xylitol crystals obtained after drying to obtain the required crystalline xylitol, with a material flow rate of 0 to 3 t / h.

[0046] The preparation method of the crystalline xylitol of the present invention further comprises a packaging process, namely, step 10, packaging: the crystalline xylitol after screening is packaged according to customer requirements.

[0047] The preparation method of the crystalline xylitol of the present invention is further illustrated below by means of specific examples.

[0048] Example 1

[0049] The first embodiment of the method for preparing crystalline xylitol of the present invention comprises the following steps:

[0050] Step 11: Add 3.0 ml of purified water to the xylose dissolving tank. 3 , open the steam valve to raise the water temperature to 50-70℃. Put 6t of crystalline xylose into the xylose dissolving tank. After the xylose is completely dissolved, check the refractive index to be 50-60% before sending it to the next process.

[0051] Step 12: The xylose solution with qualified refractive index is pumped into the hydrogenation reactor for hydrogenation reaction. The pressure of the hydrogenation reaction is controlled at 8.0MPa-10.0MPa, the temperature of the material during the entire reaction process is ≤140°C, the reaction time is 50min-60min, and the xylose conversion rate is controlled at 95% before discharging.

[0052] Step 13: The xylitol solution is pumped into a decolorization tank via a centrifugal pump. The temperature of the xylitol solution is raised to 60-80°C using a plate heat exchanger. An appropriate amount of activated carbon is added to the decolorized solution for decolorization. The decolorized solution is tested for light transmittance. When the light transmittance is ≥95%, the material can be discharged.

[0053] Step 14: The decolorized liquid enters the chromatography system for chromatography treatment to obtain a chromatography extract and a chromatography residual liquid, which are then chromatographically separated using a sulfate-type chromatography resin. The feed flow rate of the chromatography system is 8000L / h to 12000L / h, the feed temperature is 40 to 60°C, and elution is carried out using purified water at 60 to 80°C. The xylitol content in the chromatography extract is tested online. When the xylitol content in the chromatography extract is ≥98%, the chromatography extract enters the next process. When the content of the chromatography extract is <98%, the chromatography extract material is refluxed for further chromatography separation, and the operating parameters of the chromatography system are adjusted; the remaining chromatography liquid is refluxed to the xylose dissolving tank in step 1 for use.

[0054] Step 15: The decolorized liquid enters the ion exchange system for ion exchange treatment to produce a xylitol exchange liquid. The feed valve of the anodic column is adjusted to a flow rate of 8,000 to 12,000 L / h. After the material reaches the anodic column, it is pumped to the anionic column. The xylitol exchange liquid is quality-controlled to achieve a transmittance of ≥95%, a pH of 4.0 to 7.5, and a conductivity of ≤50 μs / cm. The xylitol exchange liquid is then fed to the coarse filtration system for coarse filtration. The xylitol exchange liquid is passed through a 1-micron pore size cardboard filter to remove insoluble matter from the ion exchange liquid. The pressure differential is between 0.2 MPa and 0.3 MPa.

[0055] Step 16: The xylitol exchange liquid is introduced into an evaporation device for evaporation to obtain xylitol sugar paste. The evaporation is carried out using a triple-effect evaporator. During the evaporation process, the vacuum degree of the first effect is -0.02 MPa to -0.1 MPa, the material temperature is 100-120° C., the vacuum degree of the second effect is -0.05 MPa to -0.07 MPa, the material temperature is 90-100° C., the vacuum degree of the third effect is -0.085 MPa to -0.095 MPa, the material temperature is 55-65° C., and the refractive index of the material is between 75% and 83%.

[0056] Step 17, crystallization process: control the vacuum degree of the vacuum crystallization kettle between -0.085 and -0.095 MPa, quickly cool it to the crystallization temperature of 55 to 65 ° C. During the crystallization process, keep the material temperature in the range of 55 to 75 ° C. After the crystallization is completed, open the jacket steam valve of the crystallization tank on the vacuum crystallization kettle, and control the jacket temperature to be close to the material temperature in the vacuum crystallization kettle at this time, that is, the material temperature ± 5 ° C. Then, remove the vacuum in the vacuum crystallization kettle through the vacuum discharge valve, open the vacuum crystallization kettle discharge valve through the crystallization tank, and discharge the obtained xylitol crystalline sugar to the next process.

[0057] Step 18: The centrifugation time of the material is controlled at 25 to 40 minutes, and the centrifuged xylitol sugar is sent to the next process through a screw conveyor.

[0058] Step 19: After the centrifugal material has been dried by boiling, hot air, and cold air, it is sent to a screening machine for screening. The material flow rate is 0-3 t / h. Screens of different apertures are selected for screening according to actual production needs.

[0059] Step 20: Packaging the sieved crystalline xylitol according to customer requirements.

[0060] Example 2

[0061] The second embodiment of the method for preparing crystalline xylitol of the present invention comprises the following steps:

[0062] Step 21: Add 2.0 ml of purified water to the xylose dissolving tank. 3 , open the steam valve to raise the water temperature to 50-70℃. Put 5t of crystalline xylose into the xylose dissolving tank. After the xylose is completely dissolved, check the refractive index to be 50-60% before sending it to the next process.

[0063] Step 22: inject the qualified xylose solution into the hydrogenation reactor for hydrogenation reaction. The pressure of the hydrogenation reaction is controlled at 8.0MPa-10.0MPa, the temperature of the material during the entire reaction process is ≤140°C, the reaction time is 50min-60min, and the xylose conversion rate is controlled at 95% before discharging.

[0064] Step 23: The xylitol solution is pumped into a decolorization tank via a centrifugal pump. The temperature of the xylitol solution is raised to 60-80°C using a plate heat exchanger. An appropriate amount of activated carbon is added to the decolorized solution for decolorization. The decolorized solution is tested for light transmittance. When the light transmittance is ≥95%, the material can be discharged.

[0065] Step 24: The decolorized liquid enters the chromatography system for chromatography treatment to obtain a chromatography extract and a chromatography residual liquid, which are then chromatographically separated using a sulfate-type chromatography resin. The feed flow rate of the chromatography system is 8000L / h to 12000L / h, the feed temperature is 40 to 60°C, and elution is carried out using purified water at 60 to 80°C. The xylitol content in the chromatography extract is tested online. When the xylitol content in the chromatography extract is ≥98%, the chromatography extract enters the next process. When the content of the chromatography extract is <98%, the chromatography extract material is refluxed for further chromatography separation treatment, and the operating parameters of the chromatography system are adjusted; the remaining chromatography liquid is refluxed to the xylose dissolving tank in step 1 for use.

[0066] Step 25: The decolorized liquid enters the ion exchange system for ion exchange treatment to produce a xylitol exchange liquid. The feed valve of the anodic column is adjusted to a flow rate of 8,000 to 12,000 L / h. After the material reaches the anodic column, it is pumped to the anionic column. The xylitol exchange liquid is quality-controlled to ensure a transmittance of ≥95%, a pH of 4.0 to 7.5, and a conductivity of ≤50 μs / cm. The xylitol exchange liquid is then fed to the coarse filtration system for coarse filtration. The xylitol exchange liquid is passed through a 1-micron pore size cardboard filter to remove insoluble matter from the ion exchange liquid. The pressure differential is between 0.2 MPa and 0.3 MPa.

[0067] Step 26: The xylitol exchange liquid is introduced into an evaporation device for evaporation to obtain xylitol massecuite. The evaporation is carried out using a triple-effect evaporator. During the evaporation process, the vacuum degree of the first effect is -0.02 MPa to -0.1 MPa, the material temperature is 100 to 120° C., the vacuum degree of the second effect is -0.05 MPa to -0.07 MPa, the material temperature is 90 to 100° C., the vacuum degree of the third effect is -0.085 MPa to -0.095 MPa, the material temperature is 55 to 65° C., and the refractive index of the material is between 75% and 83%.

[0068] Step 27, crystallization process: control the vacuum degree of the vacuum crystallization kettle between -0.085 and -0.095 MPa, quickly cool it to the crystallization temperature of 55 to 65 ° C. During the crystallization process, keep the material temperature in the range of 55 to 75 ° C. After the crystallization is completed, open the jacket steam valve of the crystallization aid tank on the vacuum crystallization kettle, and control the jacket temperature to be close to the material temperature in the vacuum crystallization kettle at this time, that is, the material temperature ± 5 ° C. Then, remove the vacuum in the vacuum crystallization kettle through the vacuum discharge valve, open the vacuum crystallization kettle discharge valve through the crystallization aid tank, and discharge the obtained xylitol crystalline sugar to the next process.

[0069] Step 28: The centrifugation time of the material is controlled at 25 to 40 minutes, and the centrifuged xylitol sugar is sent to the next process via a screw conveyor.

[0070] Step 29: After the centrifugal material has been dried by boiling, hot air, and cold air, it is sent to a screening machine for screening. The material flow rate is 0-3 t / h. Screens of different apertures are selected for screening according to actual production needs.

[0071] Step 30: Packaging the sieved crystalline xylitol according to customer requirements.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 1 is that no chromatographic separation step is provided. The preparation method of crystalline xylitol in Comparative Example 1 comprises the following steps:

[0074] Step D1: Add 3.0 ml of purified water to the xylose dissolving tank. 3 , open the steam valve to raise the water temperature to 50-70℃. Put 6t of crystalline xylose into the xylose dissolving tank. After the xylose is completely dissolved, check the refractive index to be 50-60% before sending it to the next process.

[0075] Step D2: The xylose solution with qualified refractive index is pumped into the hydrogenation reactor for hydrogenation reaction. The pressure of the hydrogenation reaction is controlled at 8.0MPa-10.0MPa, the temperature of the material during the entire reaction process is ≤140°C, the reaction time is 110min-120min, and the xylose conversion rate is controlled at 99.8% before discharging.

[0076] Step D3: The xylitol solution is pumped into a decolorization tank via a centrifugal pump. The temperature of the xylitol solution is raised to 60-80°C using a plate heat exchanger. An appropriate amount of activated carbon is added to the decolorized solution for decolorization. The decolorized solution is tested for light transmittance. When the light transmittance is ≥95%, the material can be discharged.

[0077] Step D4: The decolorized liquid enters the ion exchange system for ion exchange treatment to produce a xylitol exchange liquid. The feed valve of the anodic column is adjusted to a flow rate of 8,000 to 12,000 L / h. After the material reaches the anodic column, it is pumped to the anionic column. The xylitol exchange liquid is quality-controlled to ensure a transmittance of ≥95%, a pH of 4.0 to 7.5, and a conductivity of ≤50 μs / cm. The xylitol exchange liquid is then fed to the coarse filtration system for coarse filtration. The xylitol exchange liquid is passed through a 1-micron pore size cardboard filter to remove insoluble matter from the exchange liquid. The pressure differential is 0.2 to 0.3 MPa.

[0078] Step D5: The xylitol exchange liquid is introduced into an evaporation device for evaporation to obtain xylitol massecuite. The evaporation is carried out using a triple-effect evaporator. During the evaporation process, the vacuum degree of the first effect is -0.02 MPa to -0.1 MPa, the material temperature is 100 to 120° C., the vacuum degree of the second effect is -0.05 MPa to -0.07 MPa, the material temperature is 90 to 100° C., and the vacuum degree of the third effect is -0.085 MPa to -0.095 MPa, the material temperature is 55 to 65° C., and the refractive index of the material is between 75% and 83%.

[0079] Step D6, crystallization process: control the vacuum degree of the vacuum crystallization kettle between -0.085 and -0.095 MPa, quickly cool it to the crystallization temperature of 55 to 65 ° C. During the crystallization process, keep the material temperature in the range of 55 to 75 ° C. After the crystallization is completed, open the jacket steam valve of the crystallization aid tank on the vacuum crystallization kettle, and control the jacket temperature to be close to the material temperature in the vacuum crystallization kettle at this time, that is, the material temperature ± 5 ° C. Then, remove the vacuum in the vacuum crystallization kettle through the vacuum discharge valve, open the vacuum crystallization kettle discharge valve through the crystallization aid tank, and discharge the obtained xylitol crystalline sugar to the next process.

[0080] Step D7: The centrifugation time of the material is controlled at 25 to 40 minutes, and the centrifuged xylitol sugar is sent to the next process via a screw conveyor.

[0081] Step D8: After the centrifugal material has been dried by boiling, hot air, and cold air, it is sent to a screening machine for screening. The material flow rate is 0-3 t / h. Screens of different apertures are selected for screening according to actual production needs.

[0082] Step D9: Packaging the sieved crystalline xylitol according to customer requirements.

[0083] The hydrogenation reaction time and hydrogenation energy cost of each embodiment and comparative example 1 are compared to obtain the following Table 1.

[0084] Table 1 Comparison of hydrogenation reaction time and hydrogenation energy cost of each embodiment and comparative example 1

[0085] Hydrogenation reaction time (min) Hydrogenation energy cost (yuan / t) Example 1 50～60 280～350 Example 2 50～60 280～350 Comparative Example 1 110～120 400～500

[0086] As can be seen from Table 1, the xylose hydrogenation reaction time of the present invention is about one hour shorter than that of Comparative Example 1, and the hydrogenation energy cost is saved by about half.

[0087] 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 scope of protection of the present invention.

Claims

1. A method for preparing crystalline xylitol, characterized in that: The steps include: Step 1: Dissolve xylose in a xylose dissolving tank to obtain xylose solution. If conditions permit, add 2.0 ml of chromatographic raffinate to the xylose dissolving tank. 3 ~3.0m 3 When the chromatographic residual liquid is insufficient, it is replaced with drinking water. The refractive index of the xylose solution is tested to be between 50% and 60%. The steam valve is opened to heat the xylose dissolving tank to 50-70°C. Step 2, hydrogenation: The xylose solution with qualified refractive index is pumped into the hydrogenation reactor for hydrogenation reaction. After hydrogenation, the xylose becomes xylitol. The pressure of the hydrogenation reaction is controlled at 8.0MPa to 10.0MPa. The temperature of the material during the entire hydrogenation reaction is ≤140°C. The hydrogenation reaction time is 50min to 60min. When the xylose conversion rate is controlled at 95%, the obtained xylitol solution is discharged to the next process. Step 3: Decolorization: The xylitol solution is pumped into a decolorization tank via a centrifugal pump. The temperature of the xylitol solution is raised to 60-80°C using a plate heat exchanger. Activated carbon is added to the decolorization tank for decolorization. After decolorization, a decolorized liquid is obtained. The light transmittance of the decolorized liquid is tested. When the light transmittance is ≥95%, the material is discharged to the next process. Step 4, chromatographic separation: The decolorized liquid enters the chromatographic system for chromatographic treatment to obtain a chromatographic extract and a chromatographic residual liquid. The feed flow rate of the chromatographic system is 8000L / h to 12000L / h, and the feed temperature is 40 to 60°C. The xylitol content in the chromatographic extract is tested online. When the xylitol content in the chromatographic extract is ≥98%, the chromatographic extract enters the next process. When the xylitol content in the chromatographic extract is <98%, the chromatographic extract material is refluxed for further chromatographic separation treatment, and the operating parameters of the chromatographic system are adjusted; the chromatographic residual liquid is refluxed to the xylose dissolution tank in step 1 for utilization; The chromatographic extract is then sequentially subjected to ion exchange treatment, evaporation concentration treatment, vacuum crystallization treatment, centrifugal separation treatment, drying and screening treatment to obtain the desired crystalline xylitol.

2. The method for preparing crystalline xylitol according to claim 1, wherein: The ion exchange treatment refers to: Step 5, ion exchange: The chromatographic extract enters the ion exchange system for ion exchange treatment to obtain a xylitol exchange liquid. The ion exchange system includes a positive column and a negative column that are interconnected. The feed valve of the positive column is adjusted to adjust the flow rate of the chromatographic extract to 8000L / h to 12000L / h. The quality control of the xylitol exchange liquid is as follows: transmittance ≥ 95%, pH value 4.0 to 7.5, conductivity ≤ 50μs / cm. After that, the xylitol exchange liquid is sent to the coarse filtration system for coarse filtration treatment. The pressure difference of the coarse filtration treatment is 0.2MPa to 0.3MPa. The evaporation concentration process refers to: Step 6, evaporation and concentration: the xylitol exchange liquid is introduced into an evaporation device for evaporation to obtain xylitol massecuite, the evaporation device includes a triple-effect evaporator. During the evaporation process, the vacuum degree of the first effect is -0.02MPa to -0.1MPa, the material temperature is 100-120°C, the vacuum degree of the second effect is -0.05MPa to -0.07MPa, the material temperature is 90-100°C, and the vacuum degree of the third effect is -0.085MPa to -0.095MPa, the material temperature is 55-65°C, and the refractive index of the material is between 75% and 83%; The vacuum crystallization treatment refers to: Step 7, vacuum crystallization: xylitol sugar paste is input into a vacuum crystallization kettle for vacuum crystallization treatment to obtain xylitol crystalline sugar, the vacuum degree of the vacuum crystallization kettle is controlled between -0.085 and -0.095 MPa, and the temperature is quickly lowered to a crystallization temperature of 55 to 65°C. During the crystallization process, the material temperature is kept in the range of 55 to 75°C. After the crystallization is completed, the jacket steam valve of the crystallization aid tank on the vacuum crystallization kettle is opened, and the jacket temperature is controlled to be close to the material temperature in the vacuum crystallization kettle at this time, that is, the material temperature ±5°C, and then the vacuum in the vacuum crystallization kettle is removed through the vacuum unloading valve. The vacuum crystallization kettle discharge valve is opened to discharge the obtained xylitol crystalline sugar through the crystallization aid tank to the next process.

3. The method for preparing crystalline xylitol according to claim 2, wherein: The centrifugal separation process refers to: Step 8, centrifugal separation: The xylitol crystal sugar is input into the centrifuge for centrifugal separation to obtain xylitol centrifugal sugar, the centrifugation time is controlled at 25min to 40min, and the xylitol centrifugal sugar is sent to the next process through a screw conveyor; The drying and screening process refers to: Step 9, drying and screening: The centrifuged xylitol sugar is sequentially conveyed to a hot air boiling dryer and two vibrating fluidized bed dryers for drying to obtain xylitol crystals, and then sent to a screening machine for screening to obtain the desired crystalline xylitol.

4. The method for preparing crystalline xylitol according to claim 3, wherein: The drying process includes boiling drying, hot air drying and cold air drying, wherein, Boiling drying: Xylitol centrifugal sugar is transported to the pre-drying tank for boiling drying, and the air supply temperature is controlled at 75-85℃; Hot air drying: The xylitol centrifugal sugar after boiling drying is transported to the hot air vibrating fluidized bed dryer for hot air drying. The hot air temperature of the hot air vibrating fluidized bed dryer is controlled at 40-60°C. By adjusting the inlet and outlet air volumes, the material layer forms a boiling state in the hot air vibrating fluidized bed dryer and moves forward at a uniform speed. Cold air drying: The xylitol centrifugal sugar after hot air drying is put into the cold air vibrating fluidized bed dryer for cold air drying. The dehumidified cold air is used to reduce the material temperature. The cold air inlet and outlet volume of the cold air vibrating fluidized bed dryer is controlled to make the material layer form a boiling state in the machine and move forward at a uniform speed to ensure that the discharge temperature is between 15 and 40 °C.

5. The method for preparing crystalline xylitol according to claim 3, wherein: The screening process refers to: selecting screens of different apertures according to actual production needs to screen the xylitol crystals obtained after drying to obtain the required crystalline xylitol, with a material flow rate of 0 to 3 t / h.

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