A solid-phase preparation method of sulfonated chitosan membrane and application thereof in catalytic preparation of biodiesel

Abstract

The application discloses a solid-phase preparation method of sulfonated chitosan membrane and application of the sulfonated chitosan membrane in catalytic biodiesel preparation, and the sulfonated chitosan membrane is prepared by the following steps: chitosan powder is suspended in a dispersant in which a sulfonating agent is dissolved to perform a sulfonating reaction, sulfonated chitosan powder is obtained through solid-liquid separation, the sulfonated chitosan powder is dissolved in a membrane solvent to prepare a casting membrane liquid, the casting membrane liquid is naturally cast on a glass surface to form a membrane, and the sulfonated chitosan membrane is obtained after drying and removing the membrane solvent. The sulfonated chitosan membrane is added into a mixed solution of fatty acid and methanol, and after stirring and heating for a period of time, the sulfonated chitosan membrane is taken out, and biodiesel is obtained after removing methanol from the solution. The sulfonated chitosan membrane prepared by the application has the advantages of fast mass transfer rate, high catalytic efficiency and easy separation, and under the conditions of an alcohol / oil ratio of 10:1, a reaction temperature of 65 DEG C, a catalyst dosage of 5wt%, and a reaction time of 3h, the esterification rate reaches 92.29%. Under the same conditions, the esterification rates of powdered chitosan and commercially available macroporous ion exchange resin are 57.73% and 33.0% respectively.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing sulfonated chitosan membrane by solid phase and its application in catalyzing the preparation of biodiesel. BACKGROUND

[0002] Biodiesel is a kind of fuel oil which is obtained by transesterification of fatty acid triglyceride with methanol or ethanol. Biodiesel can be prepared by physical method, enzymatic method or chemical method. However, the enzymatic method is difficult to realize industrial production due to high price and long reaction time. The strong acid or strong base catalysts are used in the synthesis of biodiesel. Although the strong acid or strong base catalysts have high catalytic efficiency, they have some problems such as difficult separation of catalyst, large amount of acid wastewater, strong corrosion of equipment, etc. The resin type solid acid / base catalysts solve the problem of difficult separation of traditional strong acid / base catalysts, but they also have some problems such as slow mass transfer rate, low catalytic efficiency and long reaction time.

[0003] Chitosan is a kind of natural high molecular polysaccharide, which has good biocompatibility and biodegradability. Meanwhile, the amino group at C2 position and the hydroxyl group at C3 and C6 position of chitosan can be sulfonated with different sulfonating agents to prepare sulfonated chitosan with acidity. More importantly, chitosan has good ductility and film-forming property, which can be prepared into powder sulfonated chitosan and film sulfonated chitosan. At present, the sulfonation research of chitosan mainly focuses on two aspects: sulfonation method of chitosan and application of sulfonated chitosan. Commonly used sulfonating agents of chitosan include concentrated sulfuric acid, chlorosulfonic acid and sulfur trioxide, which mainly sulfonate the hydroxyl group at C3 and C6 position. However, the sulfonation process has strict reaction condition control, and the reaction temperature and the amount of sulfonating agent need to be strictly controlled. In addition, the sulfonation rate is difficult to control, and the product separation is difficult. There are also some compounds containing sulfonic acid groups, such as 1,3-propanesultone and 3-chloro-2-hydroxypropanesulfonic acid sodium, which are used as sulfonating agents to sulfonate the amino group at C2 position. The reaction conditions of this kind of sulfonation reaction are mild and controllable. However, this kind of sulfonation reaction mainly adopts liquid phase reaction method, for example, chitosan and 1,3-propanesultone are dissolved in acetic acid aqueous solution to form a homogeneous solution, and then the sulfonation reaction is carried out under reflux. Since the sulfonated chitosan can also be dissolved in acetic acid solution, the separation and collection of sulfonated chitosan are difficult. The existing method is to remove the unreacted 1,3-propanesultone by dialysis, and then obtain the sulfonated chitosan powder by freeze-drying. Therefore, the liquid phase preparation method of sulfonated chitosan has high energy consumption and low efficiency. The application research of sulfonated chitosan mainly focuses on the antibacterial effect on bacteria such as Escherichia coli and Staphylococcus aureus, and there is no report on the direct use as a solid acid catalyst for esterification reaction and biodiesel synthesis. The water produced in the esterification reaction can reduce the stability of sulfonated chitosan as a solid acid catalyst, which may be the reason why sulfonated chitosan is not applied to catalyze esterification reaction.

[0004] In view of the above background, the present application provides a solid phase preparation method of sulfonated chitosan film and a method for catalyzing fatty acid esterification to prepare biodiesel. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art, and to sulfonate chitosan by solid phase synthesis, and then to prepare sulfonated chitosan film to catalyze fatty acid esterification to prepare biodiesel.

[0006] The technical scheme adopted by the present application is as follows:

[0007] The solid phase preparation method of sulfonated chitosan film is characterized by two steps of sulfonation and film forming in the preparation process, and the specific process is as follows:

[0008] S1: mix and dissolve the sulfonating agent and dispersant liquid to form a sulfonating agent / dispersant solution; then add chitosan and the sulfonating agent / dispersant solution into a reactor, stir, and make the chitosan suspended and dispersed in the dispersant liquid. Stir and heat to a certain temperature, and make the chitosan react with the sulfonating agent for a certain time;

[0009] S2: after the reaction is completed, perform suction filtration to obtain sulfonated chitosan solid, and wash the sulfonated chitosan solid with a detergent to remove residual dispersant;

[0010] S3: transfer the sulfonated chitosan to a surface dish, place it in a forced air oven for drying, and obtain sulfonated chitosan powder.

[0011] S4: weigh the sulfonated chitosan powder, add a film solvent, stir and dissolve to form a casting solution of the sulfonated chitosan, and stand for 1 h for defoaming;

[0012] S5: pour the casting solution into a glass surface dish, and allow it to naturally flow and form a film;

[0013] S6: place it in a 65℃ oven for drying for 5 h, and remove the sulfonated chitosan film from the surface dish after the film solvent is volatilized.

[0014] Further, in step S1, the sulfonating agent is 1,3-propanesultone, and the dispersant is an organic solvent that can dissolve 1,3-propanesultone but cannot dissolve chitosan, which can be at least one of C1-C5 alkyl alcohol, ester, ether or ketone, and isopropanol is preferred. The deacetylation degree of the chitosan used is 50%-95%, and the molecular weight is 50 kDa-500 kDa. The molar ratio of chitosan monomer to 1,3-propanesultone is 1:1-1:9, preferably 1:6; the amount of dispersant is 1.5-3 ml / g of chitosan, preferably 2 ml / g of chitosan; the sulfonation reaction temperature is 60℃-85℃, preferably 80℃, and the sulfonation reaction time is 1 h-18 h, preferably 12 h.

[0015] Further, in step S2, the detergent used is isopropanol. The sulfonated chitosan is washed with isopropanol multiple times, and the washing liquid is detected by gas chromatography to confirm that the 1,3-propanesultone is completely washed out.

[0016] Further, in step S3, the drying temperature of the sulfonated chitosan is 60℃-80℃, and the drying time is 5 h-24 h.

[0017] Further, in step S4, the film solvent used is a 10-30% mass fraction methanol or ethanol aqueous solution, and the mass of the sulfonated chitosan is 1wt%-10wt% of the mass of the film solvent, preferably 5wt%.

[0018] The application discloses a sulfonated chitosan membrane piece applied to catalysis of preparation of biodiesel oil, and is characterized by the following preparation process: in a reactor, fatty acid, methanol and the sulfonated chitosan membrane piece are added, stirring and heating to a reaction temperature, after a certain reaction time, the sulfonated chitosan membrane piece is taken out, and after removal of methanol in the solution, a biodiesel oil product is obtained. Sampling is performed, and the acid value of the product is determined according to a known method, and the esterification rate is calculated.

[0019] Further, the sulfonated chitosan membrane piece is applied to catalysis of the preparation of biodiesel oil, the alcohol / oil ratio is 15:1-1:1, preferably 10:1, the sulfonated chitosan membrane piece is used in an amount of 1wt%-10wt% of the mass of the fatty acid, preferably 5wt%, the reaction temperature is 55°C-65°C, preferably 65°C, and the reaction time is 1h-10h.

[0020] By adopting the technical scheme, the application has the following beneficial effects:

[0021] 1. The sulfonated chitosan is used as a solid acid catalyst for esterification. Chitosan is cheap and easy to obtain, has good biocompatibility and biodegradability, the sulfonated chitosan is used for catalyzing esterification, the catalyst has low use cost, and the used chitosan catalyst is easy to degrade and does not pollute the environment.

[0022] 2. The sulfonated chitosan is made into a membrane piece and applied to catalyze esterification. Chitosan has good ductility and film-forming property, and the sulfonated chitosan has good water solubility. Water is generated in the esterification reaction, when the sulfonated chitosan in powder form is used as a catalyst for esterification, the stability of the sulfonated chitosan is poor, the sulfonated chitosan is dissolved in the reaction system in the reaction process, the catalyst is difficult to recover, and the reaction system is polluted. The sulfonated chitosan is made into a membrane piece, the hydrothermal stability of the catalyst is improved. Compared with the sulfonated chitosan in powder form, the sulfonated chitosan membrane piece has three advantages when applied to catalyze esterification: 1) high stability, not easy to be dissolved in water, and maintaining the membrane piece form in the whole reaction process; 2) large contact area with the reaction system, fast mass transfer rate, and high catalytic efficiency; 3) easy to be separated from the reaction system, not needing centrifugation or pressure filtration, and being directly taken out from the reaction system; and 4) the sulfonated chitosan membrane piece has certain water absorption, and the water binding capacity of the sulfonated chitosan membrane piece can promote the esterification reaction to proceed in a positive direction, and improve the esterification rate.

[0023] Under the conditions of an alcohol / oil ratio of 10:1, a reaction temperature of 65°C, a catalyst dosage of 5wt%, and a reaction time of 3h, the esterification rate catalyzed by the sulfonated chitosan membrane piece reaches 92.3%, and the esterification rates catalyzed by the chitosan in powder form and the macroporous ion exchange resin are 54.8% and 33.0% respectively.

[0024] 3.The present application uses 1,3-propane sultone as a sulfonating agent to modify chitosan by solid phase synthesis.Compared with traditional sulfonating reagents (such as concentrated sulfuric acid, chlorosulfonic acid and sulfur trioxide), 1,3-propane sultone as a sulfonating agent has milder reaction conditions and safer operation, and different acid contents of sulfonated chitosan can be obtained by controlling the reaction conditions.Compared with the liquid phase preparation method of dissolving chitosan in acetic acid aqueous solution, the solid phase preparation method suspends chitosan powder in a dispersant for sulfonation reaction, thereby eliminating the steps of freeze-drying and washing to remove acetic acid, reducing energy consumption and reducing waste liquid discharge. DETAILED DESCRIPTION

[0025] The present application will be further described below in conjunction with specific examples, but the scope of protection of the present application is not limited thereto.

[0026] Example 1

[0027] A three-necked flask was charged with 22.68g of methanol and soybean oil fatty acid according to an alcohol / oil molar ratio of 10:1, a condensing device was installed, stirring was started, the stirring speed was 300rmp, and the reaction temperature was heated to 65℃. After 9h of reaction, the reaction was cooled to room temperature, and the oil phase was analyzed by titration. The initial acid value of the fatty acid was 180.54mgKOH / g, and the acid value after 9h of reaction was 163.02mgKOH / g. The esterification rate of the fatty acid was calculated to be 9.70%.

[0028] Example 2

[0029] A certain amount of commercially available strong acid ion exchange resin LS-51 was weighed, soaked in 4%hydrochloric acid for 2h, washed with deionized water for several times until the washing liquid was neutral, and dried in an oven at 105℃ for 8h.

[0030] A three-necked flask was charged with 22.68g of methanol and soybean oil fatty acid according to an alcohol / oil molar ratio of 10:1, a condensing device was installed, stirring was started, the stirring speed was 300rmp, and the reaction temperature was heated to 65℃. After 9h of reaction, the reaction was cooled to room temperature, and the oil phase was analyzed by titration. The initial acid value of the fatty acid was 180.54mgKOH / g, and the acid value after 9h of reaction was 163.02mgKOH / g. The esterification rate of the fatty acid was calculated to be 9.70%.

[0031] Example 3

[0032] Take 4g of chitosan with 95% deacetylation degree in a three-necked flask, add 40g of isopropyl alcohol as dispersant, mix, dissolve and prepare sulfonating agent / dispersant solution, add 18.18g of 1,3-propanesultone as sulfonating reagent (molar ratio of chitosan monomer to 1,3-propanesultone is 1:6) to it, react at 80°C for 12h. After the reaction is completed, the product is suction filtered, and the unreacted 1,3-propanesultone is washed away with isopropyl alcohol to obtain a light yellow powder solid. The sulfonated chitosan is sent to a 65°C oven and dried to constant weight to obtain a sulfonated chitosan catalyst.

[0033] In a three-necked flask, add 22.68g of methanol, add soybean oil fatty acid according to an alcohol / oil molar ratio of 10:1, install a condensing device, turn on the stirring, and the stirring speed is 300rmp. Add the powdered sulfonated chitosan acid catalyst (the mass of the catalyst is 5wt% of the mass of the oleic acid), wait for the temperature to reach 65°C again, and react for 9h. After the reaction is completed, cool to room temperature, centrifuge the reaction product, the centrifugation time is 5min, and the rotation speed is 8000rmp. The upper layer is the oil phase containing biodiesel (fatty acid methyl ester), and the lower layer is the solid gel containing water and sulfonated chitosan. Analyze the upper oil phase by titration method, the initial acid value of the fatty acid is 179.21mgKOH / g, and the acid value after 9h of reaction is 20.12mgKOH / g. The esterification rate of the fatty acid is calculated to be 88.77%.

[0034] Example 4

[0035] The preparation of sulfonated chitosan is referred to Example 3, the only difference is that the amount of 1,3-propanesultone is changed to 27.27g (molar ratio of chitosan monomer to 1,3-propanesultone is 1:9).

[0036] In a three-necked flask, add 22.68g of methanol, add soybean oil fatty acid according to an alcohol / oil molar ratio of 10:1, install a condensing device, turn on the stirring, and the stirring speed is 300rmp. Add the powdered sulfonated chitosan acid catalyst (the mass of the catalyst is 5wt% of the mass of the oleic acid), wait for the temperature to reach 65°C again, and react for 9h. After the reaction is completed, cool to room temperature, centrifuge the reaction product, the centrifugation time is 5min, and the rotation speed is 8000rmp. The upper layer is the oil phase containing biodiesel (fatty acid methyl ester), and the lower layer is the solid gel containing water and sulfonated chitosan. Analyze the upper oil phase by titration method, the initial acid value of the fatty acid is 179.21mgKOH / g, and the acid value after 9h of reaction is 20.12mgKOH / g. The esterification rate of the fatty acid is calculated to be 88.77%.

[0037] Example 5

[0038] The preparation of sulfonated chitosan is referred to Example 3.

[0039] Take the above powder sulfonated chitosan 2 g, add 20 g water and 20 g ethanol, stirring 30 min, configuration into 5% wt sulfonated chitosan casting solution, standing defoaming 1 h. Pour the casting solution into a glass surface dish, let it flow naturally, send into a 65 °C oven, dry 5 h, wait until the solvent evaporates, take the sulfonated chitosan film from the surface dish.

[0040] In a three-necked flask, add 22.68 g of methanol, add soybean oil fatty acid according to the alcohol oil molar ratio of 10:1, install the condensing device, open the stirring, the stirring speed is 300 rmp, heat to the reaction temperature 65 °C. Cut the chitosan film into appropriate size, add the sulfonated chitosan acid catalyst in the form of film (the catalyst mass is 5% wt of the mass of oleic acid), wait for the temperature to reach 65 °C again, react for 8 h. After the reaction is completed, cool to room temperature, take out the sulfonated chitosan film, analyze the oil phase by titration method, the initial acid value of the fatty acid is 180.87 mgKOH / g, the acid value after 8 h reaction is 6.8 mgKOH / g, the esterification rate of the fatty acid is calculated to be 96.11%.

[0041] Example 6

[0042] The preparation of sulfonated chitosan is referred to Example 3, the only difference is that the amount of 1,3-propane sultone is changed to 9.09 g (the molar ratio of chitosan monomer to 1,3-propane sultone is 1:3).

[0043] The preparation of sulfonated chitosan film is referred to Example 5.

[0044] In a three-necked flask, add 22.68 g of methanol, add soybean oil fatty acid according to the alcohol oil molar ratio of 10:1, install the condensing device, open the stirring, the stirring speed is 300 rmp, heat to the reaction temperature 65 °C. Cut the chitosan film into appropriate size, add the sulfonated chitosan acid catalyst in the form of film (the catalyst mass is 5% wt of the mass of oleic acid), wait for the temperature to reach 65 °C again, react for 8 h. After the reaction is completed, cool to room temperature, take out the sulfonated chitosan film, analyze the oil phase by titration method, the initial acid value of the fatty acid is 180.87 mgKOH / g, the acid value after 8 h reaction is 6.8 mgKOH / g, the esterification rate of the fatty acid is calculated to be 96.11%.

[0045] Example 7

[0046] The preparation of sulfonated chitosan is referred to Example 3.

[0047] The preparation of sulfonated chitosan film is referred to Example 5.

[0048] In a three-necked flask, 22.68 g of methanol was added, and soybean oil fatty acid was added according to an alcohol to oil molar ratio of 10:1, a condensing device was installed, stirring was turned on, and the stirring speed was 300 rpm. The reaction temperature was heated to 65°C. The chitosan film was cut into an appropriate size, and the film-shaped sulfonated chitosan acid catalyst (the catalyst mass was 5% of the mass of the oil acid) was added. The temperature was again allowed to reach 65°C, and the reaction was allowed to proceed for 3 h. After the reaction was completed, the temperature was cooled to room temperature, the sulfonated chitosan film was taken out, and the oil phase was analyzed by titration. The initial acid value of the fatty acid was 180.87 mgKOH / g, and the acid value after 3 h of reaction was 13.95 mgKOH / g. The esterification rate of the fatty acid was calculated to be 92.29%.

[0049] Example 8

[0050] The sulfonated chitosan was prepared, as described in Example 3.

[0051] The sulfonated chitosan film was prepared, as described in Example 5.

[0052] In a three-necked flask, 22.68 g of methanol was added, and soybean oil fatty acid was added according to an alcohol to oil molar ratio of 10:1, a condensing device was installed, stirring was turned on, and the stirring speed was 300 rpm. The reaction temperature was heated to 65°C. The chitosan film was cut into an appropriate size, and the film-shaped sulfonated chitosan acid catalyst (the catalyst mass was 5% of the mass of the oil acid) was added. The temperature was again allowed to reach 65°C, and the reaction was allowed to proceed for 3 h. After the reaction was completed, the temperature was cooled to room temperature, the sulfonated chitosan film was taken out, and the oil phase was analyzed by titration. The initial acid value of the fatty acid was 180.87 mgKOH / g, and the acid value after 3 h of reaction was 13.95 mgKOH / g. The esterification rate of the fatty acid was calculated to be 92.29%.

[0053] Example 9

[0054] The sulfonated chitosan was prepared, as described in Example 3.

[0055] The sulfonated chitosan film was prepared, as described in Example 5.

[0056] In a three-necked flask, 22.68 g of methanol was added, and soybean oil fatty acid was added according to an alcohol to oil molar ratio of 10:1, a condensing device was installed, stirring was turned on, and the stirring speed was 300 rpm. The reaction temperature was heated to 65°C. The chitosan film was cut into an appropriate size, and the film-shaped sulfonated chitosan acid catalyst (the catalyst mass was 5% of the mass of the oil acid) was added. The temperature was again allowed to reach 65°C, and the reaction was allowed to proceed for 3 h. After the reaction was completed, the temperature was cooled to room temperature, the sulfonated chitosan film was taken out, and the oil phase was analyzed by titration. The initial acid value of the fatty acid was 180.87 mgKOH / g, and the acid value after 3 h of reaction was 13.95 mgKOH / g. The esterification rate of the fatty acid was calculated to be 92.29%.

[0057] Example 10

[0058] Preparation of sulfonated chitosan, see Example 3.

[0059] Preparation of sulfonated chitosan film, see Example 5.

[0060] In a three-necked flask, 22.68 g of methanol was added, soybean oil fatty acid was added according to the alcohol oil molar ratio of 10:1, the condensing device was installed, the stirring was turned on, the stirring speed was 300 rpm, and the heating was turned on to heat to the reaction temperature of 65℃. The sulfonated chitosan film was cut into appropriate size, the film-shaped sulfonated chitosan acid catalyst (the catalyst mass was 3wt% of the mass of the oleic acid) was added, the temperature was waited to reach 65℃ again, and the reaction was carried out for 8h. After the reaction was completed, the temperature was cooled to room temperature, the sulfonated chitosan film was taken out, the oil phase was analyzed by titration method, the initial acid value of the fatty acid was 177.98 mgKOH / g, the acid value was 26.57 mgKOH / g after the reaction for 8h, and the esterification rate of the fatty acid was calculated to be 85.07%.

[0061] Table 1 Parameters and effects of Examples 1-10

[0062]

[0063] Note: PCS-X represents that the molar ratio of 1,3-propane sulfonate lactone to chitosan monomer in the preparation process of sulfonated chitosan is 1:X; the catalyst dosage is based on the mass of fatty acid.

[0064] The content described in the specification is only a list of forms of the implementation of the inventive concept, and the protection scope of the present application should not be regarded as limited to the specific forms stated in the examples.

Claims

1. A solid-phase preparation method for sulfonated chitosan membranes used in the catalytic preparation of biodiesel, characterized in that... The preparation process includes two steps: sulfonation and film formation. The specific preparation steps are as follows: S1: Mix and dissolve the sulfonating agent and dispersant liquids to prepare a sulfonating agent / dispersant solution. Then add chitosan to the solution and stir to suspend and disperse the chitosan in the solution. Stir and heat simultaneously to allow the chitosan and sulfonating agent to undergo a sulfonation reaction for a period of time. S2: After the reaction is complete, filter to obtain sulfonated chitosan solid, and wash the sulfonated chitosan solid thoroughly with detergent to remove residual dispersant, and then dry to obtain sulfonated chitosan product; S3: Add the sulfonated chitosan product obtained in step S2 to the membrane solvent, stir and dissolve to prepare a casting solution of sulfonated chitosan, and let it stand to remove bubbles; S4: Pour the casting solution into a glass petri dish, allow it to flow and form a film naturally, then dry it until the film solvent evaporates, and remove the sulfonated chitosan film from the petri dish. In step S1, the sulfonating agent is 1,3-propanesulfonate lactone, and the dispersant liquid is an organic solvent that can dissolve 1,3-propanesulfonate lactone but cannot dissolve chitosan, selected from at least one of C1-C5 alkyl alcohols, esters, ethers or ketones.

2. The solid-phase preparation method of sulfonated chitosan membrane for catalytic preparation of biodiesel as described in claim 1, characterized in that... In step S1, the dispersant liquid is isopropanol.

3. The solid-phase preparation method of sulfonated chitosan membrane for catalytic preparation of biodiesel as described in claim 1, characterized in that... In step S1, the degree of deacetylation of chitosan is 50%-95%, and the molecular weight is 50kDa-500kDa.

4. The solid-phase preparation method of sulfonated chitosan membrane for catalytic preparation of biodiesel as described in claim 1, characterized in that... In step S1, the molar ratio of chitosan monomer to 1,3-propanesulfonic acid lactone is 1:1 to 1:9; the mass ratio of dispersant liquid to chitosan is 10:1; the sulfonation reaction temperature is 60℃-85℃, and the sulfonation reaction time is 1h-18h.

5. The solid-phase preparation method of sulfonated chitosan membrane for catalytic preparation of biodiesel as described in claim 4, characterized in that... In step S1, the molar ratio of chitosan monomer to 1,3-propanesulfonate lactone is 1:6; the sulfonation reaction temperature is 80℃, and the sulfonation reaction time is 12h.

6. The solid-phase preparation method of sulfonated chitosan membrane for catalytic preparation of biodiesel as described in claim 1, characterized in that... In step S2, the detergent used is isopropanol.

7. The solid-phase preparation method of sulfonated chitosan membrane for catalytic preparation of biodiesel as described in claim 1, characterized in that... The membrane solvent used in step S3 is a 10-30% methanol aqueous solution or a 10-30% ethanol aqueous solution, and the mass of sulfonated chitosan is 1wt%-10wt% of the mass of the membrane solvent.

8. The solid-phase preparation method of sulfonated chitosan membrane for catalytic preparation of biodiesel as described in claim 7, characterized in that... In step S3, the mass of sulfonated chitosan is 5 wt% of the mass of the membrane solvent.

9. A sulfonated chitosan membrane for catalytic preparation of biodiesel, prepared by the method according to any one of claims 1 to 8.

10. The application of the sulfonated chitosan membrane as described in claim 9 in the preparation of catalytic biodiesel.

11. The application as described in claim 10, characterized in that... Fatty acids, methanol, and sulfonated chitosan membranes are mixed, stirred, and heated to the reaction temperature. After a certain reaction time, the sulfonated chitosan membranes are removed, and the solution is de-methanoled to obtain the biodiesel product.

12. The application as described in claim 11, characterized in that... The methanol-to-fatty acid ratio is 15:1-1:1; the amount of sulfonated chitosan film used is 1wt%-10wt% of the fatty acid mass; the reaction temperature is 55℃-65℃, and the reaction time is 1h-10h.

13. The application as described in claim 12, characterized in that... The methanol-to-fatty acid ratio was 10:1; the amount of sulfonated chitosan film used was 5 wt% of the fatty acid mass; the reaction temperature was 65℃.

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