Method for removing impurity molecules in lignocellulose hydrolysate through ultrafiltration membrane

Abstract

The invention relates to the field of lignocellulose biomass pretreatment, and discloses a method for removing impurity molecules in lignocellulose hydrolysate by an ultrafiltration membrane, which comprises the following steps: S1, corncob dilute acid pretreatment, S2, corncob acid hydrolysate pretreatment by an ultrafiltration method, S3, analysis method, and S4, ultrafiltration process data processing. The PES10 ultrafiltration membrane can effectively decolorize the lignocellulose acid hydrolysate, few entrapped mixed sugars and inorganic salts, the recovery rate of fermentable sugars after ultrafiltration treatment is 70%-80%, about 20% of sugars are left in the trapped fluid, the trapped fluid is washed and filtered to reduce the loss of the sugars so as to improve the total recovery rate of the sugars, and the cost is reduced. The decolorization effect of the organic ultrafiltration membrane with the molecular weight cutoff of 10kDa is optimal, so that the hydrolysate can be pretreated through ultrafiltration before entering the bipolar membrane electrodialysis device.

Description

Technical Field

[0001] The invention relates to the field of lignocellulose biomass pretreatment, in particular to a method for removing impurity molecules in lignocellulose hydrolyzate using an ultrafiltration membrane. Background Art

[0002] When using lignocellulosic biomass as raw material for fermentation, pretreatment is required to hydrolyze the polysaccharides into monosaccharides. There are many pretreatment methods, such as acid hydrolysis, alkaline hydrolysis, microbial degradation, ionic liquid, steam explosion, etc. At present, acid hydrolysis is the most studied and widely used pretreatment method.

[0003] After acid hydrolysis, there will be a large amount of acid remaining in the hydrolyzate. The traditional method is to add calcium hydroxide to the hydrolyzate to an alkaline state to neutralize the excess acid and achieve the detoxification effect. However, the large amount of calcium sulfate precipitate produced in this process needs to be removed by centrifugation. The whole process is cumbersome to operate, and solid waste is generated, polluting the environment. Therefore, researchers use sodium hydroxide instead of calcium hydroxide to neutralize the excess acid in the hydrolyzate, but this will lead to a high concentration of sodium sulfate in the hydrolyzate, and produce a large osmotic pressure on bacteria during subsequent fermentation, thereby inhibiting bacterial growth. Therefore, the presence of sodium sulfate in the acid hydrolysis of lignocellulose will hinder the smooth progress of fermentation, and efforts should be made to remove it or reduce its content.

[0004] Common desalination methods include ion exchange resin, nanofiltration, electrodialysis and bipolar membrane electrodialysis. When using ion exchange resin, the regeneration of the resin requires a large amount of acid, alkali and manpower, and the resin will adsorb sugar in the hydrolyzate, causing sugar loss. When desalination is performed by nanofiltration using molecular sieving and charge repulsion effects, it is difficult to completely separate sugar and sodium sulfate because their molecular weights are relatively close. Either the sugar retention rate is very high or the salt permeability is very high. In recent years, the use of electrodialysis for desalination has gradually attracted people's attention. As a green separation technology, bipolar membrane electrodialysis performs the desalination process under relatively mild conditions. It converts salt into corresponding acids and bases without introducing other impurity ions, does not produce excess waste, and can achieve the recycling of acids and bases, which is more advantageous in comparison.

[0005] However, the composition of lignocellulose hydrolysate is complex. In addition to mixed sugars and small molecular inhibitors, there are also macromolecular substances such as pigments and water-soluble lignin. When directly used for bipolar membrane electrodialysis treatment, it will cause obvious membrane pollution, thereby affecting the performance of the membrane and the desalination effect. Therefore, it is necessary to pretreat the hydrolysate to remove macromolecular substances. Summary of the invention

[0006] The organic ultrafiltration membrane with a molecular weight cutoff of 10 kDa in the present invention has the best decolorization effect, so the hydrolyzate can be pre-treated by ultrafiltration before entering the bipolar membrane electrodialysis device.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for removing impurity molecules in lignocellulose hydrolysate by ultrafiltration membrane, the method comprising the following steps:

[0008] S1. Dilute acid pretreatment of corn cobs

[0009] The crushed corn cobs were acid-hydrolyzed in an autoclave under the action of 20 g / L sulfuric acid, and the hydrolysis conditions were: solid-liquid ratio 1:10, 121°C, 2 h; after the hydrolysis, they were filtered using 325-mesh gauze to obtain a filtrate and a filter residue, respectively. In order to avoid the loss of sugar, the filter residue was washed with a small amount of deionized water, and the liquid after washing was added to the filtrate so that the volume of the filtrate was consistent with the volume of the liquid before hydrolysis; then, the obtained corn cob acid hydrolyzate was adjusted to pH 8.0 with 10 mol / L sodium hydroxide solution to remove the divalent metal cations present, including Mg 2+ With Ca 2+ , then the hydrolyzate is filtered with filter paper to remove impurities, and the hydrolyzate after impurities removal is used for the next step of ultrafiltration treatment;

[0010] S2. Pretreatment of corncob acid hydrolyzate by ultrafiltration

[0011] The corncob hydrolyzate was pretreated by ultrafiltration. The cross-flow ultrafiltration device used was composed of a feed tank with an insulation jacket, i.e., 5 L, a feed pump, and a spiral membrane assembly, including a MWCO of 10 kDa and an effective membrane area of ​​0.3 m 2 It consists of a water bath with a circulating pump. During the ultrafiltration process, a temperature sensor installed in the feed tank is used to monitor the temperature, and the feed temperature is controlled by a circulating water bath. The cross-flow velocity is measured by a rotor flowmeter and adjusted by the frequency converter of the pump. The transmembrane pressure is adjusted by a ball valve and the frequency converter of the pump. The feed liquid is treated in a concentration mode, the permeate is collected by a measuring cylinder, and the retained liquid is returned to the feed tank for circulation. When the remaining volume of the feed tank is close to the dead volume of the equipment, that is, 700mL, the concentration is stopped. The ultrafiltration operating conditions are: cross-flow velocity 5L / min, constant transmembrane pressure 5bar, feed temperature 22-25℃; every time 100 / 200mL of permeate is collected, the filtration time is recorded and the permeate flux is calculated.

[0012] S3. Analytical methods

[0013] The pigment content of corncob hydrolyzate before and after ultrafiltration was measured by the absorbance of the sample at 420nm, i.e. A 420Representative, measured by UV-9000S ultraviolet visible spectrophotometer, the higher the pigment content, the darker the color, the greater the absorbance value, the concentration of glucose, xylose, arabinose and acetic acid in the sample is detected by high performance liquid chromatography, i.e. HPLC;

[0014] S4. Ultrafiltration process data processing

[0015] For the ultrafiltration process, the parameters of permeate flux, permeability and apparent retention rate are worthy of attention. The specific calculation formula is as follows;

[0016] Apparent retention rate:

[0017]

[0018] Where C F , C P and C R are the sugar concentration or pigment concentration in the feed, permeate and retentate, i.e., A 420 or conductivity, for batch filtration, the average sugar concentration in the retentate is calculated according to Equation 1.2;

[0019] Permeate flux:

[0020]

[0021] Membrane permeability:

[0022]

[0023] Irreversible fouling of membrane:

[0024]

[0025] Where V P is the permeate volume, i.e. L, and A is the effective area of ​​the membrane, i.e. 0.3m 2 , t is the filtration time, i.e. h, AP is the transmembrane pressure, i.e. bar, L P,b and L P，a are the membrane permeabilities before and after filtration, respectively;

[0026] Before each treatment of the feed solution, the permeation flux was measured with deionized water, i.e., J P，b After treating the feed liquid, it was first rinsed with 2L deionized water for 10min to remove reversible pollutants, and then the permeation flux was measured with deionized water under the same conditions, that is, J P，a , combine formula 1.4 and 1.5 to calculate the irreversible fouling of the membrane after filtering the feed liquid;

[0027] The series resistance model is used to analyze the resistance type that causes membrane fouling at the end of filtration. At the end of liquid filtration, the total resistance, i.e., R tot, including the resistance of the membrane itself, namely R m , the resistance caused by reversible pollution, that is, R rf and the resistance caused by irreversible pollution, namely R irf , the model is expressed as:

[0028]

[0029] Where μ is the viscosity of the permeate, i.e. Pas;

[0030] According to the permeation flux of the feed liquid at the end of filtration, R is calculated using formula 1.6 tot The value of

[0031] Before treating the feed liquid, the permeation flux was measured with deionized water, i.e., J P，b , there is only the resistance of the membrane itself, and R is calculated according to formula 1.6 m :

[0032]

[0033] After the filtration of the feed liquid is completed, it is rinsed with deionized water to remove reversible pollutants. At this time, when the permeation flux is measured with deionized water, that is, J P，a , R rf = 0, there are only the resistance of the membrane itself and the resistance caused by irreversible pollution, and formula 1.6 is derived into:

[0034]

[0035] Calculate R according to formulas 1.7 and 1.8 irf , according to R tot =R m +R rf +R irf Further calculation of R rf , by analyzing the proportion of each resistance to the total resistance, the type of pollutant causing membrane fouling can be determined.

[0036] Preferably, in step S2, before each treatment of the feed liquid, the permeation flux of the deionized water is measured under the same operating conditions.

[0037] Preferably, in step S2, after treating the feed liquid, it is first rinsed with 2L of deionized water for 10 minutes to remove reversible pollutants, and then the permeation flux of deionized water is measured under the same conditions to calculate the permeability and irreversible contamination of the membrane.

[0038] Preferably, in step S2, after each ultrafiltration, the ultrafiltration membrane is first rinsed with deionized water at 30°C, and then further cleaned with NaOH solution, i.e., pH 10-12, if necessary, to control the permeability change of the membrane before and after use to be within 5%.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The PES10 ultrafiltration membrane of the present invention can effectively decolorize the lignocellulose acid hydrolyzate, and retain less mixed sugars and inorganic salts. The recovery rate of fermentable sugars after ultrafiltration treatment is between 70% and 80%, indicating that about 20% of the sugar is retained in the retained liquid. In order to reduce the loss of sugar, the retained liquid is subjected to a diafiltration operation to improve the total recovery rate of sugar;

[0041] 2. The organic ultrafiltration membrane with a molecular weight cutoff of 10 kDa in the present invention has the best decolorization effect, so the hydrolyzate can be pre-treated by ultrafiltration before entering the bipolar membrane electrodialysis device. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of cross-flow filtration in the concentration mode of the present invention;

[0043] Figure 2 Graphs showing changes in membrane flux (A) and permeability (B) in different ultrafiltration batches of the present invention;

[0044] Figure 3 It is a graph showing the ratio of each resistance to the total resistance in different ultrafiltration batches of the present invention;

[0045] Figure 4 It is the retention rate diagram of the ultrafiltration of the present invention for sugars (A) and conductivity and pigments (B). DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] A method for removing impurity molecules in lignocellulose hydrolysate by ultrafiltration membrane, the method comprising the following steps:

[0048] S1. Dilute acid pretreatment of corn cobs

[0049] The crushed corn cobs were acid-hydrolyzed in an autoclave under the action of 20 g / L sulfuric acid, and the hydrolysis conditions were: solid-liquid ratio 1:10, 121°C, 2 h; after the hydrolysis, they were filtered using 325-mesh gauze to obtain a filtrate and a filter residue, respectively. In order to avoid the loss of sugar, the filter residue was washed with a small amount of deionized water, and the liquid after washing was added to the filtrate so that the volume of the filtrate was consistent with the volume of the liquid before hydrolysis; then, the obtained corn cob acid hydrolyzate was adjusted to pH 8.0 with 10 mol / L sodium hydroxide solution to remove the divalent metal cations present, including Mg 2+ With Ca 2+ , then the hydrolyzate is filtered with filter paper to remove impurities, and the hydrolyzate after impurities removal is used for the next step of ultrafiltration treatment;

[0050] S2. Pretreatment of corncob acid hydrolyzate by ultrafiltration

[0051] The corncob hydrolyzate was pretreated by ultrafiltration. The cross-flow ultrafiltration device used was composed of a feed tank with an insulation jacket, i.e., 5 L, a feed pump, and a spiral membrane assembly, including a MWCO of 10 kDa and an effective membrane area of ​​0.3 m 2 The ultrafiltration process consists of a water bath with a circulating pump. During the ultrafiltration process, a temperature sensor installed in the feed tank is used to monitor the temperature, and the feed temperature is controlled by a circulating water bath. The cross flow velocity is measured by a rotor flowmeter and adjusted by the frequency converter of the pump. The transmembrane pressure is adjusted by a ball valve and the frequency converter of the pump. The feed liquid is treated in a concentrated mode, the permeate is collected by a measuring cylinder, and the retentate is returned to the feed tank for circulation. Figure 1 As shown, the concentration was stopped when the remaining volume of the feed tank was close to the dead volume of the equipment, i.e., 700 mL. The ultrafiltration operating conditions were: cross flow rate 5 L / min, constant transmembrane pressure 5 bar, feed temperature 22-25 °C. Every time 100 / 200 mL of permeate was collected, the filtration time was recorded and the permeate flux was calculated.

[0052] S3. Analytical methods

[0053] The pigment content of corncob hydrolyzate before and after ultrafiltration was measured by the absorbance of the sample at 420nm, i.e. A 420 Representative, measured by UV-9000S ultraviolet visible spectrophotometer, the higher the pigment content, the darker the color, the greater the absorbance value, the concentration of glucose, xylose, arabinose and acetic acid in the sample is detected by high performance liquid chromatography, i.e. HPLC;

[0054] S4. Ultrafiltration process data processing

[0055] For the ultrafiltration process, the parameters of permeate flux, permeability and apparent retention rate are worthy of attention. The specific calculation formula is as follows;

[0056] Apparent retention rate:

[0057]

[0058] Where C F , C P and C R are the sugar concentration or pigment concentration in the feed, permeate and retentate, i.e., A 420 Or conductivity, for batch filtration, the average sugar concentration in the retentate is calculated according to formula 1.2.

[0059] Permeate flux:

[0060]

[0061] Membrane permeability:

[0062]

[0063] Irreversible fouling of membrane:

[0064]

[0065] Where V P is the permeate volume, i.e. L, and A is the effective area of ​​the membrane, i.e. 0.3m 2 , t is the filtration time, i.e. h, ΔP is the transmembrane pressure, i.e. bar, L P,b and L P,a are the permeabilities of the membrane before and after filtration, respectively.

[0066] Before each treatment of the feed solution, the permeation flux was measured with deionized water, i.e., J P,b After treating the feed liquid, it was first rinsed with 2L deionized water for 10min to remove reversible pollutants, and then the permeation flux was measured with deionized water under the same conditions, that is, J P,a , combine formula 1.4 and 1.5 to calculate the irreversible fouling of the membrane after filtering the feed liquid.

[0067] The series resistance model is used to analyze the resistance type that causes membrane fouling at the end of filtration. At the end of liquid filtration, the total resistance, i.e., R tot， Including the resistance of the membrane itself, that is, R m , the resistance caused by reversible pollution, that is, R rf and the resistance caused by irreversible pollution, namely R irf , the model is expressed as:

[0068]

[0069] Where μ is the viscosity of the permeate, i.e. Pas.

[0070] According to the permeation flux of the feed liquid at the end of filtration, R is calculated using formula 1.6 tot The value of .

[0071] Before treating the feed liquid, the permeation flux was measured with deionized water, i.e., J P,b , there is only the resistance of the membrane itself, and R is calculated according to formula 1.6 m :

[0072]

[0073] After the filtration of the feed liquid is completed, it is rinsed with deionized water to remove reversible pollutants. At this time, when the permeation flux is measured with deionized water, that is, J P,a , R rf = 0, there are only the resistance of the membrane itself and the resistance caused by irreversible pollution, and formula 1.6 is derived into:

[0074]

[0075] Calculate R according to formulas 1.7 and 1.8 irf , according to R tot =R m +R rf +R irf Further calculation of R rf , by analyzing the proportion of each resistance to the total resistance, the type of pollutant causing membrane fouling can be determined.

[0076] In this embodiment: in step S2, before each treatment of the feed liquid, the permeation flux of the deionized water is measured under the same operating conditions.

[0077] In this embodiment: in step S2, after the feed liquid is treated, it is first rinsed with 2L of deionized water for 10 minutes to remove reversible pollutants, and then the permeation flux of the deionized water is measured under the same conditions to calculate the permeability and irreversible contamination of the membrane.

[0078] In this embodiment: in step S2, after each ultrafiltration, the ultrafiltration membrane is first rinsed with deionized water at 30°C, and then the membrane is further cleaned with a NaOH solution, i.e., a pH of 10-12, if necessary, to control the change in membrane permeability before and after use to be within 5%.

[0079] When the actual feed of corncob acid hydrolysate is treated by bipolar membrane electrodialysis technology, the presence of macromolecules such as pigments in the feed must be taken into account, because these macromolecules will deposit on the surface of the ion exchange membrane to increase the resistance of the membrane stack, reduce the effective area of ​​the membrane, thereby increasing energy consumption and reducing current efficiency. Considering the high price of ion exchange membranes, in order to avoid irreversible pollution and shorten the service life, an attempt was made to pre-treat the corncob acid hydrolysate by ultrafiltration before it entered the bipolar membrane electrodialysis device to remove pigments. In this experiment, a PES10 ultrafiltration membrane with a molecular weight cutoff of 10kDa was selected to pre-treat the corncob acid hydrolysate for decolorization. The operating conditions were: cross-flow rate 5L / min, constant transmembrane pressure 5bar, and feed temperature 22-25℃.

[0080] It should be noted that the first batch of acid hydrolysis, i.e., Run 0, uses 20 g / L dilute sulfuric acid, pH 0.75, which is prepared from concentrated sulfuric acid. The sulfuric acid solution recovered from the first batch of corn cob acid hydrolyzate after ultrafiltration and bipolar membrane electrodialysis is used for the second batch of acid hydrolysis, i.e., Recycle 1, after adjusting the pH. By analogy, the sulfuric acid recovered from the previous batch is used for the next batch of acid hydrolysis, i.e., Recycle 2 and the fourth batch, i.e., Recycle 3. Each batch of corn cob acid hydrolyzate needs to be decolorized by ultrafiltration. Figure 2 As shown in A, when VRR, i.e., volume reduction ratio, increases from 1.0 to 1.5, the membrane flux decreases rapidly, indicating that the macromolecular substances in the corncob acid hydrolyzate form a filter cake layer at the beginning of ultrafiltration, and then the membrane flux continues to decrease slowly with the increase of VRR until the end of ultrafiltration. Figure 2 As shown in Figure B, with the increase of the number of cycles, the average flux of the ultrafiltration process decreases. In addition to the decline in the performance of the membrane itself, it is also related to the instability of the operating temperature. For example, the initial permeability of the membrane in the Recycle 1 and Recycle 2 batches, i.e., L P,b , which is significantly lower than Run 0 and Recycle 3 batches. The ultrafiltration process of the first two batches was carried out at 22-23℃, and the ultrafiltration process of the last two batches was carried out at 25℃. The increase in the feed temperature can significantly increase the membrane permeability and permeability. After the ultrafiltration, the membrane permeability of the Run 0-Recycle 3 batches decreased by 60%, 49%, 54% and 52%, respectively. Among them, the feed volume of the Recycle 1 batch ultrafiltration was 3L, which was less than that of other batches, namely 4L, so the permeability decreased the least. The degree of permeability decrease represents the strength of the irreversible pollution. The irreversible pollution of the Run 0 ultrafiltration batch is the most serious. With the increase in the number of cycles, the degree of irreversible pollution decreases, which is related to the proportion of irreversible pollution resistance, namely R irf / R tot , the decrease is consistent, such as Figure 3 shown.

[0081] Calculate the different types of resistance in the ultrafiltration process and the proportion of each resistance to the total resistance. Figure 3 As shown in the figure, in all ultrafiltration batches, the reversible resistance accounts for the highest proportion, and is much higher than the resistance of the membrane itself and the irreversible resistance. This shows that reversible pollution is the main type of membrane pollution during the ultrafiltration treatment of corn cob acid hydrolysate, which is caused by concentration polarization or the formation of a gel layer on the membrane surface and can be removed after water washing. At the same time, we found that with the increase in the number of cycles, the proportion of reversible resistance increases successively, and the proportion of irreversible resistance decreases successively, which shows that the content of substances causing irreversible pollution in corn cob acid hydrolysate has decreased, or it is related to the difference in the acidolysis of the recycled sulfuric acid solution.

[0082] The main purpose of using ultrafiltration to pretreat corncob acid hydrolyzate is to remove the pigments, but at the same time, the retention of fermentable sugars and salts should be avoided as much as possible. Figure 4 As shown, except for cellobiose with a slightly larger molecular weight, the retention rates of glucose, xylose and arabinose vary in the range of 11%-15%, 7%-9% and 8%-12% respectively, the retention rate of salt is only about 14%, but the retention rate of pigments is as high as 73%-80%.

[0083] In summary, the PES10 ultrafiltration membrane can effectively decolorize the lignocellulose acid hydrolyzate, and retain less mixed sugars and inorganic salts. The recovery rate of fermentable sugars after ultrafiltration treatment is between 70% and 80%, indicating that about 20% of the sugars are retained in the retentate. In order to reduce the loss of sugars, the retentate is subjected to a filtration operation to increase the total recovery rate of sugars. The organic ultrafiltration membrane with a molecular weight cutoff of 10 kDa in the present invention has the best decolorization effect, so the hydrolyzate can be pretreated by ultrafiltration before entering the bipolar membrane electrodialysis device.

[0084] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0085] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for removing impurity molecules from lignocellulose hydrolysate by ultrafiltration membrane, characterized in that: The method comprises the following steps: S1. Dilute acid pretreatment of corn cobs The crushed corn cobs were acid-hydrolyzed in an autoclave under the action of 20 g / L sulfuric acid, and the hydrolysis conditions were: solid-liquid ratio 1:10, 121°C, 2 h; after the hydrolysis, they were filtered using 325-mesh gauze to obtain a filtrate and a filter residue, respectively. In order to avoid the loss of sugar, the filter residue was washed with a small amount of deionized water, and the liquid after washing was added to the filtrate so that the volume of the filtrate was consistent with the volume of the liquid before hydrolysis; then, the obtained corn cob acid hydrolyzate was adjusted to pH 8.0 with 10 mol / L sodium hydroxide solution to remove the divalent metal cations present, including Mg 2+ With Ca 2+ , then the hydrolyzate is filtered with filter paper to remove impurities, and the hydrolyzate after impurities removal is used for the next step of ultrafiltration treatment; S2. Pretreatment of corncob acid hydrolyzate by ultrafiltration The corncob hydrolyzate was pretreated by ultrafiltration. The cross-flow ultrafiltration device used was composed of a feed tank with an insulation jacket, i.e., 5 L, a feed pump, and a spiral membrane assembly, including a MWCO of 10 kDa and an effective membrane area of ​​0.3 m 2 It consists of a water bath with a circulating pump. During the ultrafiltration process, a temperature sensor installed in the feed tank is used to monitor the temperature, and the feed temperature is controlled by a circulating water bath. The cross-flow velocity is measured by a rotor flowmeter and adjusted by the frequency converter of the pump. The transmembrane pressure is adjusted by a ball valve and the frequency converter of the pump. The feed liquid is treated in a concentration mode, the permeate is collected by a measuring cylinder, and the retained liquid is returned to the feed tank for circulation. When the remaining volume of the feed tank is close to the dead volume of the equipment, that is, 700mL, the concentration is stopped. The ultrafiltration operating conditions are: cross-flow velocity 5L / min, constant transmembrane pressure 5bar, feed temperature 22-25℃; every time 100 / 200mL of permeate is collected, the filtration time is recorded and the permeate flux is calculated. S3. Analytical methods The pigment content of corncob hydrolyzate before and after ultrafiltration was measured by the absorbance of the sample at 420nm, i.e. A 420 Representative, measured by UV-9000S ultraviolet visible spectrophotometer, the higher the pigment content, the darker the color, the greater the absorbance value, the concentration of glucose, xylose, arabinose and acetic acid in the sample is detected by high performance liquid chromatography, i.e. HPLC; S4. Ultrafiltration process data processing For the ultrafiltration process, the parameters of permeate flux, permeability and apparent retention rate are worthy of attention. The specific calculation formula is as follows; Apparent retention rate: Where C F , C P and C R are the sugar concentration or pigment concentration in the feed, permeate and retentate, i.e., A 420 or conductivity, for batch filtration, the average sugar concentration in the retentate is calculated according to Equation 1.2; Permeate flux: Membrane permeability: Irreversible fouling of membrane: Where V P is the permeate volume, i.e. L, and A is the effective area of ​​the membrane, i.e. 0.3m 2 , t is the filtration time, i.e. h, ΔP is the transmembrane pressure, i.e. bar, L P,b and L P,a are the membrane permeabilities before and after filtration, respectively; Before each treatment of the feed solution, the permeation flux was measured with deionized water, i.e., J P,b After treating the feed liquid, it was first rinsed with 2L deionized water for 10min to remove reversible pollutants, and then the permeation flux was measured with deionized water under the same conditions, that is, J P,a , combine formula 1.4 and 1.5 to calculate the irreversible fouling of the membrane after filtering the feed liquid; The series resistance model is used to analyze the resistance type that causes membrane fouling at the end of filtration. At the end of liquid filtration, the total resistance, i.e., R tot , including the resistance of the membrane itself, namely R m , the resistance caused by reversible pollution, that is, R rf and the resistance caused by irreversible pollution, namely R irf , the model is expressed as: Where μ is the viscosity of the permeate, i.e. Pas; According to the permeation flux of the feed liquid at the end of filtration, R is calculated using formula 1.6 tot The value of Before treating the feed liquid, the permeation flux was measured with deionized water, i.e., J P,b , there is only the resistance of the membrane itself, and R is calculated according to formula 1.6 m : After the filtration of the feed liquid is completed, it is rinsed with deionized water to remove reversible pollutants. At this time, when the permeation flux is measured with deionized water, that is, J P,a , R rf = 0, there are only the resistance of the membrane itself and the resistance caused by irreversible pollution, and formula 1.6 is derived into: Calculate R according to formulas 1.7 and 1.8 irf , according to R tot =R m +R rf +R irf Further calculation of R rf , by analyzing the proportion of each resistance to the total resistance, the type of pollutant causing membrane fouling can be determined.

2. The method for removing impurity molecules from lignocellulose hydrolysate by using an ultrafiltration membrane according to claim 1, characterized in that: In step S2, before each treatment of the feed solution, the permeation flux of the deionized water is measured under the same operating conditions.

3. The method for removing impurity molecules from lignocellulose hydrolysate by using an ultrafiltration membrane according to claim 1, characterized in that: In step S2, after treating the feed liquid, it is first rinsed with 2L of deionized water for 10 minutes to remove reversible pollutants, and then the permeation flux of deionized water is measured under the same conditions to calculate the permeability and irreversible contamination of the membrane.

4. The method for removing impurity molecules from lignocellulose hydrolysate by using an ultrafiltration membrane according to claim 1, characterized in that: In step S2, after each ultrafiltration, the ultrafiltration membrane is first rinsed with deionized water at 30°C, and then further cleaned with NaOH solution, i.e., pH 10-12, if necessary, to control the permeability change of the membrane before and after use to be within 5%.

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