System and method for refining xylitol fermentation liquid

Abstract

The present invention relates to a system for purifying xylitol fermentation liquid, comprising a fermentation tank, a post-fermentation tank, a ceramic membrane filter, a nanofiltration membrane filter, an activated carbon filter, an ion exchange column, an evaporation tank, a crystallization tank, a centrifuge, and a dryer, which are connected through piping. The post-fermentation tank is used to store the fermentation liquid obtained in the fermentation tank and allow it to stand to obtain a supernatant fermentation liquid. The ceramic membrane filter, the nanofiltration membrane filter, the activated carbon filter, and the ion exchange column are used to remove impurities from the supernatant fermentation liquid to obtain a xylitol ion exchange liquid. The evaporation tank and the crystallization tank are used to evaporate and crystallize the xylitol ion exchange liquid to obtain a xylitol sugar paste. The centrifuge is used to separate the xylitol sugar paste to obtain xylitol crystals. The dryer is used to dry the xylitol crystals to obtain xylitol crystals. The present invention also discloses a method using the system. The present invention can significantly reduce the amount of activated carbon used, increase the pH of the liquid material, significantly reduce the conductivity, and reduce the load of the subsequent ion exchange process.

Description

[Technical field]

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

[0002] Xylitol is a type of five-carbon sugar alcohol. Currently, industrial production is mostly carried out by chemical hydrogenation of xylitol. Although the reaction conditions for biological conversion are mild, there are still some technical bottlenecks. Currently, biological production of xylitol generally involves using biomass resources such as corn cobs and straw as raw materials and hydrolyzing them with acid to obtain hemicellulose hydrolyzate. The hydrolyzate after acid hydrolysis has a low xylose concentration and cannot be used directly as a raw material for biological fermentation, so the raw hydrolyzate needs to be concentrated, and evaporation is the common method. During this process, sugars, proteins and other substances in the raw material may cause the Maillard reaction, causing the raw liquid material to darken in color. If the raw material produced by this process is fermented, the color of the final fermentation liquid will become darker, which will cause major problems in the subsequent purification process of the fermentation liquid. Patent publication number CN108949839A describes high-purity xylitol and a method for producing the same, in which the fermentation liquid is sterilized, decolorized, ion-exchanged, concentrated, crystallized and dried to finally obtain a xylitol crystal product. The decolorization process uses activated carbon, and the amount of activated carbon added is 20%, which is about 100 times the amount added by chemical method, making the industrial production cost too high and generating a large amount of waste carbon. Summary of the Invention [Problem to be solved by the invention]

[0003] The technical problem to be solved by the present invention is to provide a system and method for purifying xylitol fermentation liquid, which ensures decolorization and light transmittance, significantly reduces the amount of activated carbon used, improves the pH of the liquid material, significantly reduces the conductivity, and reduces the load in the subsequent ion exchange. [Means for solving the problem]

[0004] The present invention is achieved as follows: A system for purifying a xylitol fermentation liquid is provided, comprising a fermentation tank, a post-fermentation tank, a ceramic membrane filter, a nanofiltration membrane filter, an activated carbon filter, an ion exchange column, an evaporation tank, a crystallization tank, a centrifuge, and a dryer, which are sequentially connected via piping, in which the post-fermentation tank is used to store the xylitol fermentation liquid obtained in the fermentation tank, leave it to stand, and separate it to obtain a precipitate and a supernatant fermentation liquid, respectively, the ceramic membrane filter, the nanofiltration membrane filter, the activated carbon filter, and the ion exchange column are sequentially used to filter the supernatant fermentation liquid to remove impurities, and obtain a xylitol ion-exchange liquid, the evaporation tank and the crystallization tank are used to evaporate and crystallize the xylitol ion-exchange liquid to obtain a xylitol sugar paste, the centrifuge is used to separate the xylitol sugar paste to obtain xylitol crystals and a mother liquor, respectively, and the dryer is used to dry the xylitol crystals to obtain a purified xylitol crystal product.

[0005] Furthermore, the ion exchange column includes an anion exchange column and a cation exchange column.

[0006] The present invention is achieved as follows: The purification system for the xylitol fermentation liquid is used, Step 1: Using corn cobs as raw material, remove impurities, rinse, and acid decompose to obtain a fermentation liquid material, concentrate the fermentation liquid material until the xylose concentration is >500g / L, and then ferment using genetically modified bacteria to obtain a xylitol fermentation liquid, and allow the xylitol fermentation liquid to stand to obtain a precipitate and a supernatant fermentation liquid, respectively; Step 2: filtering the supernatant fermentation liquid through a ceramic membrane to obtain a ceramic membrane discharge liquid material that does not contain bacteria and large particle impurities, and the parameters of the process are a feed temperature of 36°C to 48°C and a filtration pressure of 0.2MPa to 0.4MPa; Step 3: sending the ceramic membrane discharge liquid material to a nanofiltration filter, filtering through the nanofiltration membrane to separate impurity molecules with a molecular weight of >400 Da, and obtaining a nanofiltrate with a light transmittance of 20%-40%, and the feed temperature in the nanofiltration is 36°C-48°C and the filtration pressure is 2.5MPa-3.3MPa; Step 4: After the obtained nanofiltrate is filtered through activated carbon, it is subjected to ion exchange treatment in the order of cation exchange column and anion exchange column to obtain a xylitol ion exchange liquid, and the amount of activated carbon used is set to 0.5% to 1.0% and the conductivity of the ion exchange liquid is set to <20 μs / cm; and step 5 of concentrating the xylitol ion exchange liquid by evaporation until the refractive index is 78% to 82%, then lowering the temperature to crystallize the liquid to obtain a xylitol sugar paste, centrifuging the sugar paste to obtain xylitol crystals and a mother liquor, and drying the xylitol crystals to obtain a purified xylitol crystal product. Effect of the Invention

[0007] Compared with the prior art, the system and method for purifying xylitol fermentation liquid of the present invention have the following features: 1. After treatment with this process, the light transmittance of the bleached area reaches 90% or more.

[0008] 2. Improve the pH of the treated liquid material, adsorb some ions and obviously reduce the conductivity, thus reducing the load in the subsequent ion exchange.

[0009] 3. The xylitol crystal products produced by primary crystallization meet the requirements of national standards, with regular and smooth crystal surface and high purity. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing the principle of a preferred embodiment of a purification system for xylitol fermentation liquid of the present invention. FIG. [Diagram 2] FIG. 1 is a schematic diagram of the flow of the purification system and method for xylitol fermentation liquid of the present invention. [Diagram 3] 1 is an HPLC purity analysis spectrum of the xylitol crystal product prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In order to clarify the technical problems, technical solutions and advantageous effects of the present invention, the present invention will be described in more detail below with reference to the drawings and examples. Note that the specific examples described herein are only for the purpose of interpreting the present invention and are not intended to limit the present invention.

[0012] 1 and 2, a preferred embodiment of the purification system for xylitol fermentation liquid of the present invention is shown, and the system includes a fermentation tank 1, a post-fermentation tank 2, a ceramic membrane filter 3, a nanofiltration membrane filter 4, an activated carbon filter 5, an ion exchange column 6, an evaporation tank 7, a crystallization tank 8, a centrifuge 9, and a dryer 10, which are connected in series via piping. The arrows in the figures indicate the flow direction of materials within the system.

[0013] The post-fermentation tank 2 is used to store the xylitol fermentation liquid obtained in the fermentation tank 1, and then leave it to stand and stratify it to obtain a precipitate and a supernatant fermentation liquid A. The ceramic membrane filter 3, the nanofiltration membrane filter 4, the activated carbon filter 5, and the ion exchange column 6 are used to sequentially filter the supernatant fermentation liquid A to remove impurities and obtain a xylitol ion exchange liquid, the evaporation tank 7 and the crystallization tank 8 are used to evaporate and crystallize the xylitol ion exchange liquid to obtain a xylitol sugar paste, the centrifuge 9 is used to separate the xylitol sugar paste to obtain xylitol crystals and mother liquor, and the dryer 10 is used to dry the xylitol crystals to obtain a refined xylitol crystal B product.

[0014] The ion exchange column 6 includes a cation exchange column 61 and an anion exchange column 62 .

[0015] Furthermore, with reference to both Figs. 1 and 2, the present invention provides a method for purifying a xylitol fermentation liquid, which uses the above-mentioned purification system for a xylitol fermentation liquid and includes the following steps 1 to 6. Step 1: Using biomass resources such as corn cobs as raw materials, impurities are removed, rinsed, and treated with acid decomposition to obtain a fermentation liquid material. The fermentation liquid material is concentrated until the xylose concentration is >500g / L, and then fermented using genetically modified bacteria to obtain xylitol fermentation liquid A. The xylitol fermentation liquid A is allowed to stand to obtain a precipitate and a supernatant fermentation liquid, respectively. The fermentation liquid material has a solid content of 10% to 13%, a conductivity of 14000μs / cm to 16000μs / cm, and a pH of 6.0 to 6.8. The precipitate is treated separately.

[0016] Step 2: The supernatant fermentation liquid is filtered through a ceramic membrane to obtain a ceramic membrane discharge liquid material that does not contain bacteria and large particle impurities. The process parameters for this step are the feed temperature of 36°C to 48°C and the filtration pressure of 0.2MPa to 0.4MPa.

[0017] Step 3: The ceramic membrane discharged liquid material is sent to the nanofiltration filter, filtered through the nanofiltration membrane, and the impurity molecules with molecular weight >400Da are fractionated to obtain a nanofiltrate with a light transmittance of 20%-40%, and the feed temperature in nanofiltration is 36℃-48℃, and the filtration pressure is 2.5MPa-3.3MPa.

[0018] Step 4: The obtained nanofiltrate is filtered through activated carbon, and then subjected to ion exchange treatment in the cation exchange column 61 and the anion exchange column 62 in this order to obtain a xylitol ion exchange liquid, with the amount of activated carbon used being 0.5% to 1.0%, and the conductivity of the ion exchange liquid being <20 μs / cm.

[0019] Step 5: The xylitol ion exchange liquid is evaporated and concentrated until the refractive index reaches 78% to 82%, then the temperature is lowered to crystallize, obtaining a xylitol sugar paste, which is centrifuged to obtain xylitol crystals and mother liquor, and the xylitol crystals are dried to obtain the purified xylitol crystal B product.

[0020] Step 6: The mother liquor is mixed with the xylitol ion exchange liquid and concentrated for recovery and use.

[0021] The system and method for purifying xylitol fermentation liquid of the present invention will be further described below with reference to specific examples. Example 1

[0022] A first embodiment of the system and method for purifying xylitol fermentation liquid of the present invention includes the following steps.

[0023] Step 11: Production of xylitol fermentation liquid Using biomass resources such as corn cobs as raw materials, impurities were removed, rinsed, and hydrolyzed with acid to obtain a fermentation liquid material. The fermentation liquid material was then subjected to further steps such as impurity removal and decolorization, and concentrated until the xylose concentration reached >500g / L. It was then fermented with genetically modified bacteria to obtain a xylitol fermentation liquid with a solid content of 11%, a conductivity value of 16000μs / cm, and a pH of 6.2. In addition to the fermentation microorganisms, the fermentation liquid contained impurities such as large particles of corn syrup, and the fermentation liquid was dark in color and had a light transmittance of 0%.

[0024] Step 12: 6L of xylitol fermentation liquid was filtered through a ceramic membrane. The membrane unit was used to separate bacteria and large particle impurities of >50nm. In the process, the average throughput was 2L / h, the filtration pressure was 0.2MPa, the liquid temperature was 45℃, the conductivity value of the liquid after treatment was reduced to 13460μs / cm, and the pH of the liquid was 6.4.

[0025] Step 13: Ceramic membrane discharge The liquid material was decolorized by filtering through a nanofiltration membrane. A nanofiltration membrane with a cutoff of >400 Da was used in this process. The processing temperature was 45°C, the filtration pressure was 3.3 MPa, and the throughput was about 6 L / h. After being decolorized by nanofiltration, the liquid material had an optical transmittance increase from 0% to 33%, a pH increase to 6.8, and a conductivity value decrease to 7588 μs / cm.

[0026] Step 14: After the treatment in step (2), the secondary decolorization treatment was carried out by adding 0.5% activated carbon powder to the system and filtering with activated carbon. Conditions: Decolorization at 60°C for 2 hours. The secondary decolorization liquid has a pH of 6.9, a conductivity value of 6865μs / cm, and a light transmittance of 92.4% for the liquid material.

[0027] Step 15: The secondary decolorization liquid treated in (3) is subjected to an ion exchange process to carry out ion exchange treatment, and the conductivity of the discharged material is controlled to <50 μs / cm during the ion exchange, and the yield is improved stepwise by water pushing.

[0028] Step 16: The liquid material discharged from the ion exchange was evaporated and concentrated until the refractive index reached 82%, and then the liquid material was crystallized by cooling, centrifuged and dried to obtain xylitol crystals.

[0029] The HPLC analysis of the produced xylitol crystals showed that the product had a purity of 99.71% and a white appearance. Microscopic observation showed that the crystals had a prismatic shape, the crystal surfaces were regular and smooth, and the fine crystals were rarely adsorbed on the surfaces of the large particles. The remaining indicators all met the requirements of the national standard. Figure 3 shows the HPLC purity analysis spectrum of the xylitol crystal product. (Example 2) Testing of nanofiltration membranes of various fractions

[0030] Methodology for selection and testing of nanofiltration membranes for decolorization of xylitol fermentation broth The decolorization effect was tested using nanofiltration membranes with cutoff pore sizes of 200 Da, 400 Da, and 600 Da, respectively, and a comprehensive evaluation was performed in two aspects: the decolorization effect of the liquid material and the amount of activated carbon added in the subsequent secondary decolorization, to select a nanofiltration membrane with an appropriate pore size.

[0031] (1) 30 L of liquid material discharged from the ceramic membrane was divided into three equal parts of 10 L each. The liquid material discharged through the ceramic membrane had a light transmittance of 0% and a pH of approximately 6.47.

[0032] (2) Decolorization test using nanofiltration membrane with a cutoff of 200 Da 10L of liquid material was placed in the nanofiltration device, the processing pressure was 3.3MPa, the throughput was about 4L / h, and the temperature of the liquid material was 45℃. The light transmittance of the nanofiltered liquid material was about 48%. The yield of this process is <50%. After processing with a 200Da nanofiltration membrane, the light transmittance of the liquid material increased to 96% after adding 0.5% activated carbon.

[0033] (3) Decolorization test using nanofiltration membrane with a cutoff of 400 Da 10L of liquid material was placed in the nanofiltration device, the processing pressure was 3.3MPa, the throughput was about 6L / h, and the temperature of the liquid material was 45℃. The light transmittance of the nanofiltered liquid material was about 35%. The yield of this process is >90%. After processing with a 400Da nanofiltration membrane, the light transmittance of the liquid material increased to 92% when 0.5% activated carbon was added for processing.

[0034] (4) Decolorization test using nanofiltration membrane with a cutoff of 600 Da 10L of liquid material was placed in the nanofiltration device, the processing pressure was 3.3MPa, the throughput was about 6L / h, and the temperature of the liquid material was 45℃. The light transmittance of the nanofiltered liquid material was about 17.06%. The yield of this process is >90%. After processing with the 600Da nanofiltration membrane, the light transmittance of the liquid material increased to more than 90% when about 2% activated carbon was added for processing.

[0035] (5) Comparing the decolorization effect of membranes with pore sizes of 200 Da, 400 Da, and 600 Da, the decolorization effect and the amount of activated carbon added were combined, and the nanofiltration membrane with a pore size of 400 Da had the best effect, a higher yield, and a lower amount of activated carbon added.

[0036] The above is merely a preferred embodiment of the present invention, and is not intended to limit the present invention. All modifications, equivalent replacements, improvements, etc. made without departing from the spirit and principles of the present invention are intended to be included in the patent scope of the present invention.

Claims

1. A method for purifying a xylitol fermentation liquid using a purification system for a xylitol fermentation liquid, comprising: The purification system includes a fermentation tank, a post-fermentation tank, a ceramic membrane filter, a nanofiltration membrane filter, an activated carbon filter, an ion exchange column, an evaporation tank, a crystallization tank, a centrifuge, and a dryer, which are connected in series via piping; The post-fermentation tank is used to store the xylitol fermentation liquid obtained in the fermentation tank, leave it to stand, and separate it to obtain the sediment and the supernatant fermentation liquid, respectively. The ceramic membrane filter, the nanofiltration membrane filter, the activated carbon filter, and the ion exchange column are successively used to filter the supernatant fermentation liquid to remove impurities, and obtain a xylitol ion exchange liquid; The evaporation tank and the crystallization tank are used to evaporate and crystallize the xylitol ion exchange liquid to obtain a xylitol sugar paste; The centrifuge is used to separate the xylitol sugar paste to obtain xylitol crystals and mother liquor respectively. The dryer is used for drying the xylitol crystals to obtain a purified xylitol crystal product; The ion exchange column includes an anion exchange column and a cation exchange column; The method for purifying the xylitol fermentation liquid includes the steps of: Step 1: Using corn cobs as a raw material, remove impurities, rinse, and perform acid decomposition to obtain a fermentation liquid material, concentrate the fermentation liquid material until the xylose concentration is >500 g / L, and then ferment using a genetically modified bacterium to obtain a xylitol fermentation liquid, and allow the xylitol fermentation liquid to stand to obtain a precipitate and a supernatant fermentation liquid, respectively; Step 2: filtering the supernatant fermentation liquid through a ceramic membrane to obtain a ceramic membrane discharge liquid material that does not contain bacteria and large particle impurities, and the process parameters of step 2 are a supply temperature of 36°C to 48°C and a filtration pressure of 0.2MPa to 0.4MPa; Step 3: sending the ceramic membrane discharged liquid material to a nanofiltration filter, filtering through the nanofiltration membrane to separate impurity molecules with a molecular weight of >400 Da, and obtaining a nanofiltrate with a light transmittance of 20%-40%, and the feed temperature in the nanofiltration is 36°C-48°C, and the filtration pressure is 2.5MPa-3.3MPa; Step 4: filtration of the obtained nanofiltrate with activated carbon, followed by ion exchange treatment in a cation exchange column and an anion exchange column in this order to obtain a xylitol ion exchange liquid, with the amount of activated carbon used being 0.5% to 1.0% and the conductivity of the ion exchange liquid being less than 20 μs / cm; and step 5, concentrating the xylitol ion-exchanged liquid by evaporation until the refractive index is 78%-82%, then lowering the temperature to crystallize the xylitol sugar paste, centrifuging the sugar paste to obtain xylitol crystals and mother liquor, and drying the xylitol crystals to obtain a purified xylitol crystal product. A method for purifying a xylitol fermentation liquid, characterized in that in step 1, the fermentation raw liquid material has a solid content of 10% to 13%, a conductivity of 14,000 μs / cm to 16,000 μs / cm, and a pH of 6.0 to 6.

8.

2. 2. The method for purifying a xylitol fermentation liquid according to claim 1, further comprising step 6 of concentrating the mixture of the mother liquor and the xylitol ion exchange liquid for recovery and utilization.

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