Biodiesel and preparation method thereof

Abstract

The invention relates to the technical field of biodiesel, and particularly discloses biodiesel and a preparation method thereof. The preparation method of the biodiesel comprises the following steps: mixing kitchen waste oil, methanol, an organic solvent and gemini quaternary ammonium salt modified montmorillonite, adding free lipase, carrying out heat preservation reaction at 40-60 DEG C, adding methanol and gemini quaternary ammonium salt modified montmorillonite, carrying out heat preservation reaction again, and purifying the reaction liquid to obtain the biodiesel. By adding the gemini quaternary ammonium salt modified montmorillonite and improving the process, not only can the free lipase be recycled, but also the biodiesel conversion rate can be improved, so that the efficient utilization of resources is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of biodiesel, and specifically discloses biodiesel and a preparation method thereof. Background Art

[0002] Biodiesel is a clean renewable energy source and one of the most promising development directions to address the greenhouse effect, environmental pollution, energy shortage and other issues. At present, the preparation methods of biodiesel mainly include chemical catalysis, bioenzyme method and supercritical method. Among them, the bioenzyme method has received increasing attention due to its mild reaction conditions, no pollution byproducts, wide adaptability of raw materials, and compliance with the development direction of green chemistry. According to the physical form of the enzyme, the lipase used in the preparation of biodiesel by the bioenzyme method can be divided into immobilized lipase and free lipase. Compared with immobilized lipase, free lipase has the advantages of no need for complex immobilization steps, lower production cost and faster reaction rate, but the disadvantage is that the reuse rate of free lipase is low. Summary of the invention

[0003] In view of the defect of low recycling rate of lipase when free lipase is used to prepare biodiesel in the prior art, the present invention provides a method for preparing biodiesel with recycling free lipase and high conversion rate of target product by adding montmorillonite modified by gemini quaternary ammonium salt and improving the process.

[0004] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for preparing biodiesel, the method comprising the following steps: S1. Mixing waste cooking oil, methanol, an organic solvent and gemini quaternary ammonium salt-modified montmorillonite, adding free lipase, and reacting at 40°C to 60°C to obtain a primary ester exchange solution; S2. Methanol and gemini quaternary ammonium salt-modified montmorillonite are added to the primary ester exchange solution, and the reaction is heated at 40 ℃ ~ 60 ℃ to obtain a secondary ester exchange solution; S3. Purifying the secondary ester by liquid exchange to obtain the biodiesel; Wherein, the structural formula of the gemini quaternary ammonium salt is: .

[0005] The present invention uses waste cooking oil as a raw material, free lipase as a catalyst, and performs esterification and transesterification reactions with methanol in an organic solvent, and provides a method for preparing biodiesel in which lipase can be recycled without reducing the conversion rate of the target product. Compared with immobilized lipase, free lipase has the advantages of higher catalytic activity, lower cost and more flexible reaction conditions, but low reuse rate. The present invention provides a method for preparing biodiesel in which the number of free lipase cycles can reach 11 to 14 times and the biodiesel conversion rate can reach 86.2% to 91.6% by introducing gemini quaternary ammonium salt-modified montmorillonite and process improvement. The present invention plays an important role in promoting the development of circular economy and efficient utilization of resources.

[0006] The gemini quaternary ammonium salt modified montmorillonite in the present invention has the following functions: 1. It has a certain catalyst function, cooperates with free lipase, and jointly catalyzes the ester exchange reaction of waste cooking oil and methanol; 2. It can adsorb and slowly release methanol: at the beginning of the reaction, the gemini quaternary ammonium salt modified montmorillonite can adsorb methanol to avoid the damage of methanol to lipase; as the reaction time prolongs, when the concentration of methanol in the system changes, the adsorbed methanol is released to promote the forward progress of the reaction; 3. The organic modified montmorillonite can improve the lipophilicity and has a certain emulsification property, which is conducive to better mixing of oil and alcohol and improving the reaction rate; 4. The modified montmorillonite can stabilize the three-dimensional structure of lipase through electrostatic action or hydrogen bonding, and improve its temperature resistance and stability in organic solvents; 5. The gemini quaternary ammonium salt modified montmorillonite can adsorb a certain amount of reaction inhibitory byproducts (such as glycerol) to promote the forward progress of the ester exchange reaction.

[0007] Montmorillonite is a natural clay mineral with a 2:1 layered silicate structure consisting of two layers of silicon-oxygen tetrahedral sheets (Si-O) with a layer of aluminum-oxygen octahedral sheets (Al-O) in between. It has a high negative charge and has a cation exchange capacity and layer expansion capacity. In the present invention, organic ions are introduced into the interlayer space of montmorillonite, which increases the interlayer spacing while changing the polarity of the montmorillonite sheet surface, thereby improving the affinity for organic solutions and the adsorption capacity for methanol.

[0008] Preferably, the preparation method of the gemini quaternary ammonium salt comprises the following steps: adding triethylamine to an alcohol solution of 1,3-dibromopropane, and performing a quaternization reaction at 80° C. to 85° C. to obtain the gemini quaternary ammonium salt.

[0009] Preferably, the molar ratio of triethylamine to 1,3-dibromopropane is 2:1 to 2.5:1; and / or The reaction time of the quaternization reaction is 6h~8h.

[0010] Preferably, the preparation method of the gemini quaternary ammonium salt modified montmorillonite comprises the following steps: mixing a montmorillonite suspension with a gemini quaternary ammonium salt solution to obtain a mixed suspension, and reacting under ultrasonic and microwave conditions for 2h to 4h to obtain the gemini quaternary ammonium salt modified montmorillonite.

[0011] The mass ratio of the gemini quaternary ammonium salt to montmorillonite in the mixed suspension is 3.5:10 to 5:10; The mass concentration of the montmorillonite suspension is 38 g / L to 45 g / L; The mass concentration of the gemini quaternary ammonium salt solution is 40g / L-50g / L.

[0012] Preferably, the power of the ultrasound is 600W~800W; The power of the microwave is 450W~600W.

[0013] Preferably, in step 1, the molar ratio of the waste cooking oil to methanol is 1:1.5 to 1:2; In step 1, the mass ratio of the methanol to the gemini quaternary ammonium salt modified montmorillonite is 1:3-1:6; In step 1, the mass ratio of the free lipase to the kitchen waste oil is 2.5:100 to 4:100; In step 1, the insulation reaction time is 2h~3h.

[0014] Preferably, the molar ratio of the waste cooking oil to the methanol in step 2 is 1:1.1 to 1:1.6.

[0015] Preferably, in step 2, the mass ratio of the methanol to the gemini quaternary ammonium salt-modified montmorillonite is 1:1.5-1:3; In step 2, the insulation reaction time is 2h~4h.

[0016] Preferably, the organic solvent comprises at least one of petroleum ether or n-hexane.

[0017] In a second aspect, the present invention further provides a biodiesel, which is prepared by the biodiesel preparation method provided in the first aspect.

[0018] The biodiesel provided by the present invention has low production cost and relatively simple preparation process, realizes high-value utilization of waste kitchen oil and recycling of free lipase, and plays a positive role in improving the recycling rate of waste oil in my country, improving the waste oil recovery system, and promoting green and low-carbon production of biodiesel industry. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] In the present invention, frying oil recycled free of charge in the local catering market in Shijiazhuang City, Hebei Province is selected as the raw material oil of the waste kitchen oil. After filtering to remove food residues and insoluble impurities, degumming, decolorization, washing, drying and other pretreatments are performed, and the acid value is 14.4 mg KOH / g and the average molar mass is 842 g / mol. The waste kitchen oil recorded in the embodiments of the present invention is obtained by the above-mentioned pretreatment of the recycled waste kitchen oil raw material oil.

[0021] The free lipase in the present invention is purchased from Qingdao Weilan Biotechnology Co., Ltd., and FM-10 lipase (CAS No. 9001-62-1) with an enzyme activity of 10000U / g is used as an example for illustration; The boiling range of petroleum ether selected in the present invention is 60°C to 90°C.

[0022] Example 1 This embodiment provides a method for preparing biodiesel. In the method, gemini quaternary ammonium salt-modified montmorillonite is first prepared, and then the prepared gemini quaternary ammonium salt-modified montmorillonite is used to prepare biodiesel.

[0023] The preparation method of gemini quaternary ammonium salt modified montmorillonite is as follows: (1) Preparation of Gemini Quaternary Ammonium Salts A certain amount of anhydrous ethanol was added to a flask equipped with a reflux condenser, and triethylamine and 1,3-dibromopropane were added in a molar ratio of 2.4:1. The quaternization reaction was carried out at 80°C. After reacting for 8 hours, the mixture was cooled to room temperature, and the ethanol was removed by vacuum distillation to obtain a light yellow viscous substance. The substance was then washed three times with petroleum ether and ethyl acetate (volume ratio of 1:1), and a white solid was obtained by suction filtration. The solid was dried in vacuo to obtain the target product. The target product contains two quaternary ammonium salts N + The characteristic peaks indicate that the target product is a gemini quaternary ammonium salt, and its structural formula is: .

[0024] (2) Preparation of Gemini quaternary ammonium salt modified montmorillonite First, the montmorillonite is washed with distilled water, dried, ground through a 100-mesh sieve, added to distilled water, heated in a 60° C. water bath and mechanically stirred until uniformly dispersed, to obtain a montmorillonite suspension with a mass concentration of 40 g / L; the gemini quaternary ammonium salt prepared above is added to distilled water, stirred at 60° C. to dissolve it, to obtain a gemini quaternary ammonium salt solution with a mass concentration of 45 g / L.

[0025] The above-mentioned gemini quaternary ammonium salt solution and montmorillonite suspension were mixed to obtain a mixed suspension, which was stirred at 300 rpm for 20 min and then transferred to an ultrasonic / microwave device for reaction. The reaction conditions were set as follows: ultrasonic power 750 W, microwave power 500 W, and reaction time 3 h. After the reaction, the obtained product was centrifugally cleaned, vacuum dried, and ground through a 100-mesh sieve to obtain gemini quaternary ammonium salt modified montmorillonite.

[0026] Wherein, the mass ratio of the gemini quaternary ammonium salt to montmorillonite in the mixed suspension is 4:10.

[0027] In addition, this embodiment provides a method for preparing biodiesel, and the preparation method comprises the following steps: S1. Take 10.1kg (12mol) of waste cooking oil, 0.58kg (18mol) of methanol, 50.5L of petroleum ether and 2.9kg of gemini quaternary ammonium salt-modified montmorillonite, mix them evenly and continue stirring for 20min, add 0.4kg of FM-10 lipase, and keep the reaction at 40℃ and 100rpm for 3h to obtain the initial ester exchange solution; S2. Add 0.61 kg (19.2 mol) of methanol and 1.23 kg of gemini quaternary ammonium salt-modified montmorillonite to the primary ester exchange solution prepared above, and keep the reaction at 60 ° C and 100 rpm for 2 h to obtain a secondary ester exchange solution; S3. The secondary ester exchange liquid is centrifuged at 3000rpm for 30min to obtain an oil phase, an aqueous phase and a precipitate; the oil phase is taken, allowed to stand for stratification, and the crude biodiesel is separated according to the density difference, and the crude biodiesel is purified to obtain biodiesel; the upper layer of the aqueous phase contains lipase, which is sequentially passed through ceramic membranes with pore sizes of 50nm and 20nm, concentrated, dried under reduced pressure, and the free lipase is recovered for the next round of biodiesel preparation.

[0028] Example 2 This embodiment provides a method for preparing biodiesel. In the method, gemini quaternary ammonium salt-modified montmorillonite is first prepared, and then the prepared gemini quaternary ammonium salt-modified montmorillonite is used to prepare biodiesel.

[0029] The preparation method of gemini quaternary ammonium salt modified montmorillonite is as follows: (1) Preparation of Gemini Quaternary Ammonium Salts A certain amount of anhydrous ethanol was added to a flask equipped with a reflux condenser, and triethylamine and 1,3-dibromopropane were added in a molar ratio of 2.1:1. The quaternization reaction was carried out at 85°C. After reacting for 6 hours, the mixture was cooled to room temperature, and the ethanol was removed by vacuum distillation to obtain a light yellow viscous substance. The substance was then washed three times with petroleum ether and ethyl acetate (volume ratio of 1:1), and a white solid was obtained by suction filtration. The solid was dried in vacuo to obtain the target product. The target product contains two quaternary ammonium salts N + The characteristic peaks indicate that the target product is a gemini quaternary ammonium salt, and its structural formula is: .

[0030] (2) Preparation of Gemini quaternary ammonium salt modified montmorillonite First, the montmorillonite is washed with distilled water, dried, ground through a 200-mesh sieve, added to distilled water, heated in a 60° C. water bath and mechanically stirred until uniformly dispersed, to obtain a montmorillonite suspension with a mass concentration of 45 g / L; the gemini quaternary ammonium salt prepared above is added to distilled water, stirred at 60° C. to dissolve it, to obtain a gemini quaternary ammonium salt solution with a mass concentration of 50 g / L.

[0031] The above-mentioned gemini quaternary ammonium salt solution and montmorillonite suspension were mixed to obtain a mixed suspension, which was stirred at 300 rpm for 20 min and then transferred to an ultrasonic / microwave device for reaction. The reaction conditions were set as follows: ultrasonic power 600 W, microwave power 600 W, and reaction time 2 h. After the reaction, the obtained product was centrifugally cleaned, vacuum dried, and ground through a 200-mesh sieve to obtain gemini quaternary ammonium salt modified montmorillonite.

[0032] Wherein, the mass ratio of the gemini quaternary ammonium salt to montmorillonite in the mixed suspension is 3.5:10.

[0033] In addition, this embodiment provides a method for preparing biodiesel, and the preparation method comprises the following steps: S1. Take 10.1kg (12mol) of waste cooking oil, 0.77kg (24mol) of methanol, 45.5L of n-hexane and 4.6kg of gemini quaternary ammonium salt-modified montmorillonite, mix them evenly and continue stirring for 20min, add 0.25kg of FM-10 lipase, and keep the reaction at 60℃ and 150rpm for 2h to obtain the initial ester exchange solution; S2. Add 0.42 kg (13.2 mol) of methanol and 0.63 kg of gemini quaternary ammonium salt-modified montmorillonite to the primary ester exchange solution prepared above, and heat and react at 40 ° C and 150 rpm for 3 h to obtain a secondary ester exchange solution; S3. The secondary ester exchange liquid is centrifuged at 3000rpm for 30min to obtain an oil phase, an aqueous phase and a precipitate; the oil phase is taken, allowed to stand for stratification, and the crude biodiesel is separated according to the density difference, and the crude biodiesel is purified to obtain biodiesel; the upper layer of the aqueous phase contains lipase, which is sequentially passed through ceramic membranes with pore sizes of 50nm and 20nm, concentrated, dried under reduced pressure, and the free lipase is recovered for the next round of biodiesel preparation.

[0034] Example 3 This embodiment provides a method for preparing biodiesel. In the method, gemini quaternary ammonium salt-modified montmorillonite is first prepared, and then the prepared gemini quaternary ammonium salt-modified montmorillonite is used to prepare biodiesel.

[0035] The preparation method of gemini quaternary ammonium salt modified montmorillonite is as follows: (1) Preparation of Gemini Quaternary Ammonium Salts A certain amount of anhydrous ethanol was added to a flask equipped with a reflux condenser, and triethylamine and 1,3-dibromopropane were added in a molar ratio of 2.5:1. The quaternization reaction was carried out at 85°C. After reacting for 6 hours, the mixture was cooled to room temperature, and the ethanol was removed by vacuum distillation to obtain a light yellow viscous substance. The substance was then washed three times with petroleum ether and ethyl acetate (volume ratio of 1:1), and a white solid was obtained by suction filtration. The solid was dried in vacuo to obtain the target product. The target product contains two quaternary ammonium salts N + The characteristic peaks indicate that the target product is a gemini quaternary ammonium salt, and its structural formula is: .

[0036] (2) Preparation of Gemini quaternary ammonium salt modified montmorillonite First, the montmorillonite is washed with distilled water, dried, ground through a 200-mesh sieve, added to distilled water, heated in a 60° C. water bath and mechanically stirred until uniformly dispersed, to obtain a montmorillonite suspension with a mass concentration of 38 g / L; the gemini quaternary ammonium salt prepared above is added to distilled water, stirred at 60° C. to dissolve it, to obtain a gemini quaternary ammonium salt solution with a mass concentration of 40 g / L.

[0037] The above-mentioned gemini quaternary ammonium salt solution and montmorillonite suspension were mixed to obtain a mixed suspension, which was stirred at 300 rpm for 20 min and then transferred to an ultrasonic / microwave device for reaction. The reaction conditions were set as follows: ultrasonic power 800 W, microwave power 450 W, and reaction time 4 h. After the reaction, the obtained product was centrifugally cleaned, vacuum dried, and ground through a 200-mesh sieve to obtain gemini quaternary ammonium salt modified montmorillonite.

[0038] Wherein, the mass ratio of the gemini quaternary ammonium salt to montmorillonite in the mixed suspension is 5:10.

[0039] In addition, this embodiment provides a method for preparing biodiesel, and the preparation method comprises the following steps: S1. Take 10.1kg (12mol) of waste cooking oil, 0.67kg (21mol) of methanol, 48.5L of petroleum ether and 2.0kg of gemini quaternary ammonium salt-modified montmorillonite, mix them evenly and continue stirring for 20min, add 0.31kg of FM-10 lipase, and keep the reaction at 50℃ and 150rpm for 3h to obtain the initial ester exchange solution; S2. Add 0.52 kg (16.2 mol) of methanol and 1.55 kg of gemini quaternary ammonium salt-modified montmorillonite to the primary ester exchange solution prepared above, and heat and react at 50 ° C and 150 rpm for 3 h to obtain a secondary ester exchange solution; S3. The secondary ester exchange liquid is centrifuged at 3000rpm for 30min to obtain an oil phase, an aqueous phase and a precipitate; the oil phase is taken, allowed to stand for stratification, and the crude biodiesel is separated according to the density difference, and the crude biodiesel is purified to obtain biodiesel; the upper layer of the aqueous phase contains lipase, which is sequentially passed through ceramic membranes with pore sizes of 50nm and 20nm, concentrated, dried under reduced pressure, and the free lipase is recovered for the next round of biodiesel preparation.

[0040] Comparative Example 1 This comparative example provides a method for preparing biodiesel, which is basically the same as the method provided in Example 1, except that: (1) in this comparative example, neither gemini quaternary ammonium salt nor gemini quaternary ammonium salt-modified montmorillonite is prepared; (2) when preparing biodiesel, the "gemini quaternary ammonium salt-modified montmorillonite" in Example 1 is replaced with an equal amount of "montmorillonite", and the remaining steps and parameters are the same as in Example 1.

[0041] Effect example (1) Biodiesel conversion rate In the present invention, the conversion rate of biodiesel in Examples 1-3 and Comparative Example 1 is measured, and the specific formula is shown in Formula 1.

[0042]

[0043] The results of the determination of the biodiesel conversion rates in Examples 1-3 and Comparative Example 1 are shown in Table 1 below.

[0044] Table 1

[0045] As shown in Table 1, the biodiesel conversion rate in the technical solution provided by the embodiment of the present invention is 86.2%~91.6%. In the preparation method provided by Comparative Example 1, the biodiesel conversion rate is significantly lower than that of Example 1. The reasons may be that (1) montmorillonite has not been modified by gemini quaternary ammonium salt. Although montmorillonite has a certain adsorption effect on methanol, its adsorption capacity is significantly lower than that of montmorillonite modified by gemini quaternary ammonium salt, and it cannot well achieve the effect of adsorption-slow release of methanol; (2) because montmorillonite cannot well adsorb methanol, the excessive methanol at the beginning of the reaction will have an adverse effect on lipase; (3) montmorillonite has not been modified by gemini quaternary ammonium salt, and has no catalytic effect on the process of preparing biodiesel by ester exchange reaction of kitchen waste oil and methanol, and cannot play a synergistic catalytic role with lipase; (4) montmorillonite has not been organically modified and has no emulsification, which is not conducive to better mixing of oleyl alcohol, so the reaction rate is lower than that of Example 1; (5) the adsorption effect of montmorillonite on the reaction product glycerol is weakened, which is not conducive to the forward progress of the ester exchange reaction.

[0046] (2) Recycling performance of free lipase After the FM-10 lipase in Examples 1-3 and Comparative Example 1 is recovered, the recovered FM-10 lipase is put into a new round of preparation of biodiesel from waste kitchen oil according to the preparation method provided in each Example or Comparative Example. When the biodiesel yield is lower than 85%, the number of cycles of FM-10 lipase recycling is counted, and the specific statistical results are shown in Table 2 below.

[0047] Table 2

[0048] As shown in Table 2, the FM-10 lipase in the technical solution provided by the embodiment of the present invention can be recycled for 11 to 14 times after being recovered, and the biodiesel yield is still not less than 85%. However, the biodiesel conversion rate in the preparation method provided in Comparative Example 1 is less than 40%, and the enzyme activity of the FM-10 lipase after recovery is greatly reduced, and it does not have the potential for reuse.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing biodiesel, characterized in that: The preparation method comprises the following steps: S1. Mixing waste cooking oil, methanol, an organic solvent and gemini quaternary ammonium salt-modified montmorillonite, adding free lipase, and reacting at 40°C to 60°C to obtain a primary ester exchange solution; S2. Methanol and gemini quaternary ammonium salt-modified montmorillonite are added to the primary ester exchange solution, and the reaction is heated at 40 ℃ ~ 60 ℃ to obtain a secondary ester exchange solution; S3. Purifying the secondary ester by liquid exchange to obtain the biodiesel; Wherein, the structural formula of the gemini quaternary ammonium salt is: 。 2. The method for preparing biodiesel according to claim 1, characterized in that: The preparation method of the gemini quaternary ammonium salt comprises the following steps: adding triethylamine to an alcohol solution of 1,3-dibromopropane, and performing a quaternization reaction at 80° C. to 85° C. to obtain the gemini quaternary ammonium salt.

3. The method for preparing biodiesel according to claim 2, characterized in that: The molar ratio of triethylamine to 1,3-dibromopropane is 2:1 to 2.5:1; and / or The reaction time of the quaternization reaction is 6h~8h.

4. The method for preparing biodiesel according to claim 1, characterized in that: The preparation method of the gemini quaternary ammonium salt modified montmorillonite comprises the following steps: mixing a montmorillonite suspension with a gemini quaternary ammonium salt solution, and reacting the mixture under ultrasonic and microwave conditions for 2h to 4h to obtain the gemini quaternary ammonium salt modified montmorillonite.

5. The method for preparing biodiesel according to claim 4, characterized in that: The power of the ultrasound is 600W-800W; and / or The power of the microwave is 450W~600W.

6. The method for preparing biodiesel according to claim 1, characterized in that: In step 1, the molar ratio of the waste cooking oil to methanol is 1:1.5 to 1:2; and / or In step 1, the mass ratio of the methanol to the gemini quaternary ammonium salt modified montmorillonite is 1:3 to 1:6; and / or In step 1, the mass ratio of the free lipase to the waste cooking oil is 2.5:100 to 4:100; and / or In step 1, the insulation reaction time is 2h~3h.

7. The method for preparing biodiesel according to claim 1, characterized in that: The molar ratio of the waste cooking oil to the methanol in step 2 is 1:1.1 to 1:1.

6.

8. The method for preparing biodiesel according to claim 1, characterized in that: In step 2, the mass ratio of the methanol to the gemini quaternary ammonium salt modified montmorillonite is 1:1.5 to 1:3; and / or In step 2, the insulation reaction time is 2h~4h.

9. The method for preparing biodiesel according to claim 1, characterized in that: The organic solvent includes at least one of petroleum ether and n-hexane.

10. A biodiesel, characterized in that: The biodiesel is prepared by the method for preparing the biodiesel according to any one of claims 1 to 9.

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