CN100344732C - Method of making biodiesel oil by subcritical methanol phase solid acid alkali catalytic oil fat ester exchange - Google Patents

Abstract

The present invention relates to a method for preparing biologic diesel oil by solid acid-base catalysis grease of a subcritical methanol phase in the form of ester exchange. Vegetable oil and methanol are added into an autoclave by the mol ratio of 1: 3 to 60, and solid catalyst with the grease volume of 2 to 10 wt% is added. The reaction temperature is controlled in 130 to 180DEG. C, the reaction pressure is 1 to 8MPa, and the reaction time is 5 to 50 minutes. The catalyst is separated from an obtained product after the reaction by centrifugation or filtration, the reaction product is stratified by still standing, an upper layer is the mixture of methanol and fatty acid methyl ester, and the fatty acid methyl ester which is the biologic diesel oil is obtained by distilling the methanol. A lower layer is the mixture of methanol and glycerol, and the glycerol is obtained by distilling the methanol. The present invention has the advantages of low reaction temperature and pressure, little equipment investment and short reaction time.

Description

Method for producing biodiesel by subcritical methanol phase solid acid-base catalyzed oil transesterification

technical field

The invention relates to the field of renewable energy, belongs to the green chemical process, and is a method for producing biodiesel by subcritical methanol phase solid acid-base catalyzed transesterification of grease and methanol.

Background technique

Biodiesel refers to substances derived from biological products that can be used as fuel for diesel engines, including cracking products of animal and vegetable oils or fatty acid esters obtained by transesterification of animal and vegetable oils with short-chain alcohols. Biodiesel has the characteristics of renewable, complete combustion, low exhaust pollution, easy biodegradation, and harmless to human body. The research and application of biodiesel is of great significance for coping with the oil crisis, improving fuel safety, and transitioning fuel varieties after oil resources are exhausted. At present, the application of biodiesel mainly has the following four methods: direct mixed use, microemulsion, pyrolysis, and transesterification. The transesterification method is to transesterify triglycerides with low molecular weight alcohols (methanol or ethanol) to generate fatty acids. Esters, which can be used alone or blended with regular diesel in any existing model of engine without modification, are the main development direction of biodiesel.

At present, biodiesel production is mainly based on chemical and biological methods, that is, the transesterification reaction of triglyceride and methanol is realized through liquid acid-base homogeneous catalysis, such as ZL98811443. Complex, long reaction time, separation of catalysts and saponification products, and post-treatment produces a large amount of sewage. Aiming at problems such as the pollution of liquid acid-base catalysts, Cao Weiliang prepared biodiesel through solid acid-base catalyzed transesterification of oil and methanol in CN200410038292.4 patent application, no sewage discharge, no pollution to the environment, but because the reactant methanol and oil are insoluble , plus the catalyst phase, the mass transfer between phases is difficult during the reaction, so the reaction process is relatively long, and the reaction time is 3 to 15 hours. The biological method uses biological enzymes to catalyze transesterification, such as ZL03119600.4, which catalyzes the transesterification of oil and methanol through biological enzymes. The reaction conditions are mild, the environment is friendly, the reaction process is simple and easy to control, and the enzyme can be reused, etc., but the reaction speed is slow. Biological enzymes are toxic and expensive.

The supercritical methanol system has a mutual solubility between methanol and oil, which solves the problem of mass transfer between phases, and the transesterification reaction changes from a heterogeneous reaction to a homogeneous reaction, so the reaction speed is significantly increased and the reaction time is shortened. Ayhan Demirbas et al. conducted a study on the transesterification process of six vegetable oils and methanol in the supercritical methanol phase. The reaction temperature exceeded 240-300°C, and the methanol-to-fat molar ratio exceeded 40. The reaction time was 5 minutes. The yield of fatty acid methyl esters It has exceeded 90% (Energy Conversion and Management, 2002(43): 2349～2356). Wang Cunwen of Wuhan Institute of Chemical Technology also applied for the patent CN200410013430.3 on supercritical preparation of biodiesel in 2004. The transesterification reaction was carried out at 220-400°C and 8-25 MPa, and the reaction time was 4-30 minutes. There is no catalyst for the transesterification reaction of supercritical methanol phase methanol and oil, but the reaction is carried out under high temperature and high pressure conditions, which requires high equipment and is difficult to industrialize.

Contents of the invention

The purpose of the present invention is to provide a method for producing biodiesel with short reaction time and mild reaction conditions.

The study on the supercritical phase behavior of methanol and oil found that with the change of the ratio of methanol to oil, the critical point of the system also changed. Table 1 shows the results of the mutual solubility point and critical point of the methanol/soybean oil binary system.

Table 1 Determination of mutual solubility point and critical point of methanol/soybean oil binary system Methanol/grease (mole) 268 217 161 108 54 Miscibility temperature (°C) 124.8 124.9 124.5 137.9 136.0 Mutual solution pressure (MPa) 1.01 0.61 0.59 0.86 0.90 Critical temperature (℃) 248.3 249.6 251.6 271.7 314.0 Critical pressure (MPa) 8.44 8.64 8.76 10.66 13.31

It can be seen from Table 1 that during the process of reducing the mass ratio of methanol to soybean oil from 268:1 to 54:1, the critical temperature of the mixture rose from 248.3°C to 314.0°C, and the critical pressure also changed from 8.67MPa to 13.31Mpa. As the amount of methanol decreases, the critical temperature and critical pressure become higher and higher, so usually when the molar ratio is 40, the supercritical methanol phase transesterification reaction temperature should be much higher than 300°C. At the same time, in the process of thermodynamic research, it is also found that methanol and oil are already miscible at 120-140°C, and the pressure does not exceed 1Mpa at this time. At this point, if the transesterification reaction between methanol and oil is carried out, the problem of mass transfer between phases has been solved.

The invention combines the low-temperature catalytic activity of solid acid and alkali with the mutual solubility characteristics of methanol and oil in the subcritical methanol phase, and complements each other's advantages. It not only solves the problem of high pressure and high temperature in the non-catalytic reaction process of supercritical methanol phase, but also solves the problem of conventional reactions. In the process, the problem of interphase mass transfer caused by the immiscibility of methanol and oil can be solved, and the transesterification reaction between methanol and oil can be completed quickly at a lower temperature.

The specific operation steps of the present invention are as follows: using vegetable oil as a raw material, biodiesel is prepared in the subcritical methanol phase through solid acid-base catalyzed methanol and grease for transesterification reaction, and the specific steps include:

(1), vegetable oil and methanol are added into the autoclave with a molar ratio of 1:3 to 60, and a solid catalyst with a grease content of 2 to 10 wt% is added to control the reaction temperature at 130 to 180°C, the reaction pressure at 1 to 8 MPa, and the reaction time 5 to 50 minutes;

(2), after the reaction is finished, the product obtained in (1) is centrifuged or filtered to separate the catalyst, and the reaction product is allowed to stand for stratification. The upper layer is a mixture of methanol and fatty acid methyl ester, and methanol is distilled to obtain fatty acid methyl ester, which is biodiesel. The lower layer is methanol Mixture with glycerol, methanol is distilled to give glycerol.

The vegetable oil mentioned above refers to soybean oil, rapeseed oil, rice bran oil, castor oil, peanut oil, sunflower oil or various waste edible oils.

The solid catalyst as described above is a solid acid catalyst or a solid base catalyst.

The solid acid catalyst mentioned above is SO ^4- /ZrO ₂ , SO ^4- /ZrO ₂ -TiO ₂ , ZrSO ₄ or H-type molecular sieve.

The above-mentioned solid base catalyst is ZnO, MgO, K ₂ CO ₃ /Al ₂ O ₃ or KF/Al ₂ O ₃ .

The inventive method mainly has the following characteristics:

1. Subcritical methanol phase Methanol and oil are miscible, which solves the problem of mass transfer between phases, greatly shortens the reaction time and improves production capacity;

2. The reaction temperature is reduced through solid acid-base catalysis, which solves the problem of high temperature and high pressure in the supercritical methanol phase reaction process and reduces equipment investment;

3. There is no pollution problem caused by liquid acid-base catalysis, which belongs to green environmental protection technology.

Detailed ways

Example 1:

(1) Take 90 ml of soybean oil and put it into the autoclave, add 9 g of K ₂ CO ₃ /Al ₂ O ₃ catalyst, control the reaction temperature to 140°C, inject methanol through the high-pressure plunger pump until the system pressure is 2 MPa, then add Methanol is about 160 milliliters, the molar ratio is about 1:42, and the reaction time is 20 minutes;

(2), after the reaction is finished, the product obtained in (1) is filtered to separate the catalyst, the reaction product is left to stand and layered, the upper layer is a mixture of methanol and fatty acid methyl ester, distilled methanol to obtain fatty acid methyl ester, that is, biodiesel, and the lower layer is methanol and glycerin mixture, methanol was distilled to obtain glycerol.

Example 2:

(1), take 150 milliliters of rapeseed oil and put it into the autoclave, add 10 grams of SO ^4- /ZrO ₂ -TiO ₂ catalyst, control the reaction temperature at 150°C, inject methanol through a high-pressure plunger pump until the system pressure is 3MPa, at this time Add about 100 ml of methanol, the molar ratio is about 1:16, and the reaction time is 30 minutes;

(2), after the reaction is finished, the product obtained in (1) is centrifuged to separate the catalyst, and the reaction product is left to stand for stratification. The upper layer is a mixture of methanol and fatty acid methyl ester, and methanol is distilled to obtain fatty acid methyl ester, which is biodiesel. The lower layer is methanol and glycerin. mixture, methanol was distilled to obtain glycerin.

Example 3:

(1) Take 200ml of peanut oil and put it into the autoclave, add 5g of KF/Al ₂ O ₃ catalyst, control the reaction temperature at 180°C, inject methanol through a high-pressure plunger pump until the system pressure is 6Mpa, then add about 50ml of methanol , the molar ratio is about 1:6, and the reaction time is 40 minutes;

(2), with embodiment 1.

Example 4:

(1), take 180 milliliters of rice bran oil and put it into the autoclave, add 18 grams of ZnO catalyst, control the reaction temperature at 160 ° C, inject methanol through a high-pressure plunger pump until the system pressure is 4Mpa, add about 70 milliliters of methanol at this time, and the molar ratio is about is 1:9, and the reaction time is 8 minutes;

(2), with embodiment 1.

Example 5:

(1), take 120 milliliters of sunflower oil and put into the autoclave, add 6 grams of SO ^4- /ZrO ₂ catalyst, control the reaction temperature at 150°C, inject methanol through a high-pressure plunger pump until the system pressure is 7Mpa, then add methanol about 130 milliliter, the molar ratio is about 1: 26, and the reaction time is 50 minutes;

(2), with embodiment 1.

Claims (5)

1, a kind of subcritical methanol phase solid acid alkali catalytic stearic exchange system method of bio-diesel oil is characterized in that comprising the steps:

(1) vegetables oil and methyl alcohol are added autoclave with the ratio of mol ratio 1: 3～60, add the solid catalyst of oil quantity 2～wt10%, 130～180 ℃ of control reaction temperature, reaction pressure 1～8MPa, 5～50 minutes reaction times;

(2) product that after reaction finishes (1) is obtained is centrifugal or filter to isolate catalyzer, reaction product standing demix, upper strata are methyl alcohol and fatty acid methyl ester admixture, and it is biofuel that distillating carbinol obtains fatty acid methyl ester, lower floor is the mixture of methyl alcohol and glycerine, and distillating carbinol obtains glycerine.

2, the method for claim 1 is characterized in that described vegetables oil is soybean oil, rapeseed oil, Rice pollard oil, Viscotrol C, peanut oil, Trisun Oil R 80 or discarded edible oil.

3, the method for claim 1 is characterized in that solid catalyst is solid acid catalyst or solid base catalyst.

4, method as claimed in claim 3 is characterized in that described solid acid catalyst is ZrSO ₄Or H type molecular sieve.

5, method as claimed in claim 3 is characterized in that described solid base catalyst is ZnO, MgO, K ₂CO ₃/ Al ₂O ₃Or KF/Al ₂O ₃