CN1908121A - Method of preparing biologic diesel oil from high acid value vegetable oil catalyzed by p-toluenesulfonic acid - Google Patents

Abstract

The invention discloses a method for preparing biodiesel from high acid value vegetable oil by catalyzing p-toluenesulfonic acid, belonging to the technical field of biodiesel. The present invention uses high acid value vegetable oil with an acid value of 5-200 mgKOH/g as a raw material, uses p-toluenesulfonic acid as a catalyst, and carries out transesterification reaction with high acid value vegetable oil and methanol to prepare biodiesel. The single factor test of dosage and alcohol-oil ratio, and the orthogonal experiment of catalyst dosage, alcohol-oil ratio and time finally determined that the reaction conditions were 60°C-75°C, and the catalyst dosage was 0.5% of the raw material high acid value vegetable oil. %-3%, the mass ratio of alcohol to oil is 1:1-1:3, the reaction time is 2-4h, when the high-acid-value vegetable oil with an acid value of 5-100mgKOH/g is used as raw material, after thin film evaporation treatment, then Alkali-catalyzed treatment, supplementary treatment of transesterification of triglycerides in the product. The biodiesel product yield of the invention is greater than 94.10%, the purity is greater than 91.79%, and the acid value is less than 3mgKOH/g.

Description

Method for preparing biodiesel catalyzed by p-toluenesulfonic acid from high acid value vegetable oil

technical field

The invention discloses a method for preparing biodiesel from high acid value vegetable oil by catalyzing p-toluenesulfonic acid, belonging to the technical field of biodiesel.

Background technique

Biodiesel is a renewable diesel alternative fuel obtained by converting vegetable oil and recycled animal and vegetable oil. ASTM (American Society for Testing and Materials) D6751 defines biodiesel as "long carbon chain fatty acid ester, one molecule of alcohol and one molecule of long carbon chain fatty acid are connected to the two ends of the ester bond respectively. Crude oil or refined vegetable oil contains three ester bonds, which cannot It's called biodiesel, and biodiesel can be methyl ester, ethyl ester, isopropyl ester, or whatever."

All kinds of animal and vegetable oils are not suitable to be directly used as alternative fuels, because the molecular weight of oil is about 4 times that of petroleum diesel, and the viscosity is about 11-17 times that of petroleum diesel. When grease is directly used as fuel, there are many disadvantages such as high viscosity, poor injection effect, incomplete combustion, easy carbon deposition and unsatisfactory emission performance.

Oil molecules are mostly straight-chain fatty acid glycerides with 14-20 carbon atoms. After the oil and fatty alcohol are transesterified to form biodiesel, the average relative molecular weight of the product drops to about 1/3 of the molecular weight of the oil, which is close to being composed of 15 hydrocarbon chains. The average relative molecular weight of petroleum diesel has similar physical and chemical properties to petroleum diesel.

The performance comparison of biodiesel and petroleum diesel is shown in Table 1.

Table 1 Performance comparison of biodiesel and petroleum diesel nature biodiesel Petroleum Diesel Cold filtration point of summer products (°C) Cold filtration point of winter products (°C) Density (g/ml, 20°C) Closed flash point (°C) Kinematic viscosity (mm ² /s, 40°C) Cetane number calorific value (MJ /kg) combustion efficiency (diesel oil = 100%) (%) sulfur content (W, %) oxygen content (V, %) water hazard level -10-200.88＞1004～6≥5632104＜0.001101 0-200.83602～4≥4935100＜0.202 Biodegradation rate after three weeks (%) 98 70

As a fuel for diesel engines, biodiesel has many advantages, such as good environmental protection performance, storage and transportation performance, excellent lubricating performance, good engine low-temperature starting performance, and good combustion performance. These advantages make it more and more popular as a potential alternative fuel. more and more attention.

Some countries and regions in the United States, Europe, and Asia have begun to establish commercial biodiesel production bases, and biodiesel has been widely used as an alternative fuel. Europe is the most used biodiesel, and its share has accounted for 5% of the refined oil market. In 2003, the biodiesel production in European countries exceeded 1.76 million tons. It is estimated that by 2010, the biodiesel production in European countries will reach 8.3 million tons.

So far, foreign countries have developed a variety of production processes for preparing biodiesel, the most important one is the transesterification method. Transesterification, also known as alcoholysis, belongs to chemical production, which is to replace the alcohol in glyceride with another alcohol to obtain free fatty acid ester. However, due to the complexity of the esterification process to generate fatty acid methyl esters and the difficulty in recycling catalysts, at present, some people have begun to study the bioenzymatic synthesis of biodiesel, that is, transesterification with animal fats and low-carbon alcohols through lipase to prepare The corresponding fatty acid methyl and ethyl esters. Although the enzymatic method has the advantages of mild conditions, small amount of alcohol, and no pollution discharge, it also has disadvantages such as low conversion rate, short service life of the enzyme, and the difficult-to-recover by-product glycerol is toxic to the immobilized enzyme. The technology of "engineering microalgae" (that is, microalgae constructed through genetic engineering technology) developed by American scientists has also opened up a new way for biodiesel production.

At present, the most commonly used method for preparing biodiesel at home and abroad is the chemical method, that is, the transesterification method. For the transesterification method, the catalyst used in the transesterification reaction is a key technology. Among the traditional esterification catalysts, the most widely used catalysts are acids, bases and molecular sieves, but each catalyst has its own advantages and disadvantages. When sodium hydroxide is used as a catalyst, the transesterification reaction is mild and the reaction time is short; the alkali-catalyzed transesterification is irreversible like saponification, the yield exceeds 90%, and can be carried out at room temperature. However, bases as catalysts have higher requirements on raw materials, and generally refined oil is required to synthesize biodiesel. If frying oil is used as a raw material, due to its high content of free fatty acids, it is easy to cause saponification reaction, resulting in emulsification of the reaction system, difficulty in separation, and reduction of reaction yield.

On the contrary, the use of concentrated sulfuric acid as a catalyst has lower requirements on raw materials and will not cause saponification reaction, but its disadvantages are that the reaction requires higher temperature and longer time, and there are many side reactions caused by oxidation, and the product has deep color and strong Corrosion reaction equipment and residual liquid pollute the environment; and the acid-catalyzed transesterification reaction is reversible, with high energy consumption and low yield. The use of heterogeneous catalysts in the transesterification reaction will increase the yield of biodiesel.

Contents of the invention

The purpose of the present invention is to provide a method for preparing biodiesel from high-acid-value vegetable oil with p-toluenesulfonic acid catalysis, adopting solid acid catalysis technology to catalyze the transesterification reaction of high-acid-value vegetable oil, and the addition of catalyst, fatty acid and methanol The factors that restrict the reaction yield, such as the proportioning ratio, temperature, time, etc., are systematically studied to determine the best synthetic process route.

The technical scheme of the present invention: use high-acid-value vegetable oil with an acid value of 140-200 mgKOH/g as a raw material, use p-toluenesulfonic acid as a catalyst, and perform transesterification reaction with high-acid-value vegetable oil and methanol to obtain a primary product of biodiesel; The reaction conditions are as follows: the temperature is 60-75° C., the amount of catalyst p-toluenesulfonic acid is 0.5%-3% of the raw material high acid value vegetable oil quality, the alcohol-oil mass ratio is 1:1-1:3, and the reaction time is 2-4h; the first product is then subjected to thin film evaporation treatment. The thin film evaporation conditions are: the vacuum degree is less than 10Pa, the temperature is 150-200°C, when the acid value of the high acid value vegetable oil raw material is 100-200mgKOH/g, after the thin film evaporation treatment , to obtain pure biodiesel;

Or when the acid value of the high-acid value vegetable oil raw material is 5-100mgKOH/g, after the film evaporation treatment, and then undergo an alkali-catalyzed treatment, the triglyceride in the product is transesterified, and the alkali-catalyzed treatment condition is to add a high acid value Use 0.5%-3% NaOH or sodium methoxide as catalyst, add methanol with 0.3 times the mass of high acid value vegetable oil, react at 65-80°C for 3 hours, then dehydrate and demethanol to obtain pure biodiesel .

The optimized reaction conditions of the transesterification reaction are: temperature 75°C, catalyst p-toluenesulfonic acid addition amount is 2% of raw material high acid value vegetable oil, alcohol-oil mass ratio is 1:1, and reaction time is 2h.

Beneficial effects of the present invention: due to poor catalytic effect of sulfuric acid for high-acid value vegetable oils, long reaction time, and high requirements for equipment, a large amount of waste water is generated during the reaction. Based on the characteristics of catalyzing the esterification of triglycerides, a method for preparing biodiesel from high acid value vegetable oils was established.

The raw material for the synthetic biodiesel selected in the present invention is vegetable oil with high acid value. The recycling of high-acid value vegetable oil solves the raw material problem of biodiesel, reduces the cost of biodiesel, makes waste resources, and has positive significance for improving the ecological environment.

The invention adopts p-toluenesulfonic acid solid catalyst to catalyze the reaction for the first time, has outstanding catalytic performance, the catalyst is easy to separate from the product, does not cause acid waste water pollution, has little environmental pollution, and is one of the environment-friendly catalysts.

In 2001, 40% of my country's crude oil was imported, which is a serious challenge to oil safety, and the balance between supply and demand of diesel oil will be one of the focal issues of my country's oil market development in a long time in the future. Vigorously developing biodiesel can partially alleviate the tight supply of diesel in my country, and help partially replace imported products, save foreign exchange, and will make a significant contribution to national energy security. In addition, the planting of oil crops and the development of biodiesel are also of positive significance to the adjustment of my country's agricultural industrial structure and the improvement of farmers' income.

70%-80% of the price of biodiesel lies in the cost of raw materials, and the use of high acid value vegetable oil greatly reduces the cost of biodiesel. For the calculation of the price of biodiesel, factors such as low exhaust emissions on the consumer side, no adverse impact on the environment in the event of an oil spill, and reduced engine overhaul times are considered, combined with the production side from a systematic point of view. Considering its comprehensive price, biodiesel is cheaper than petroleum diesel. The industrialization of biodiesel synthesized from high acid value vegetable oil is beneficial to the development and application of biodiesel in my country.

Detailed ways

The influence of embodiment 1 temperature on reaction

Weigh about 40 g of high acid value vegetable oil samples, and react under the conditions of 5% p-toluenesulfonic acid catalyst, alcohol-oil mass ratio of 1:2, and reaction time of 3 h. Investigate the influence of temperature on the reaction, as shown in Table 2:

The influence of table 2 temperature on reaction temperature °C Yield% 50607580 076.0091.4491.22

No reaction at 50°C, slow reaction at 60°C, rapid reaction above 75°C. This is because as the temperature increases, the activity of the reactants increases and the reaction speed increases, which leads to an increase in the esterification rate. However, due to the excess amount of methanol in the reaction system, there is an optimal reaction temperature for the transesterification reaction, and the temperature is low. It will slow down the reaction and reduce the rate of esterification. If the temperature is too high, the volatilization of methanol will be accelerated, and the volume concentration of methanol in the liquid phase will be reduced, which will also lead to a decrease in the rate of esterification. Therefore, in the actual operation process, a temperature of 75°C can be selected for condensing and reflux, which not only does not have a great impact on the reaction speed, but also effectively reduces energy consumption.

The impact of embodiment 2 catalyst dosage on reaction

The mass ratio of alcohol to oil was 1:2 and the temperature was 80°C for 3 hours to investigate the effect of different amounts of catalyst p-toluenesulfonic acid (0.5%, 2%, 3%, 5%) on the reaction yield. As in Table 3:

The influence of table 3 catalyst dosage on reaction Catalyst addition (%) Yield (%) 0.5235 92.4094.0892.5291.36

It can be seen from the table above that the influence of the amount of catalyst on the reaction yield and viscosity is not obvious, and the amount of catalyst can be 0.5%-3% of the raw oil.

The influence of embodiment 3 alcohol oil ratio on reaction

The catalyst addition was 3%, and the reaction was carried out at 75°C for 3 hours to investigate the influence of different alcohol-oil mass ratios (1:0.5, 1:1, 1:2, 1:3) on the reaction yield. As shown in Table 4:

The impact of table 4 alcohol-oil ratio on reaction Alcohol to Oil Ratio (w/w) Yield (%) 1:0.51:11:21:3 66.5493.1089.6087.86

It can be seen from the above table that with the change of methanol concentration, the esterification rate also increases correspondingly. Among them, when the mass ratio of methanol to oil is 1:1, the increase rate of esterification rate is the largest. Considering economic factors comprehensively, adopt Excess methanol not only has little effect on improving the esterification rate, but also leads to an increase in cost. Therefore, in the actual application process, the mass ratio of methanol to acidified oil should be 1:1 to 1:3 as the best.

The influence of embodiment 4 reaction times on reaction

The effect of different time (1.5h, 2h, 2.5h, 3h) on the reaction yield was investigated under the conditions of 3% catalyst addition, 75°C temperature and 1:2 mass ratio of alcohol to oil. As shown in Table 5:

The impact of table 5 reaction time on reaction time (h) Yield (%) 1.522.53 87.5093.8091.7692.58

It can be seen from the table that in the initial stage, with the prolongation of the reaction time, the yield increased rapidly, but after the reaction time exceeded 2h, the yield gradually tended to a stable value and decreased slightly. As can be seen from the table, the transesterification process has been basically completed within 2 hours after the reaction started, but when the reaction time exceeds 2.5 hours, the reaction equilibrium has been reached, and continuing to increase the reaction time cannot promote the chemical equilibrium to the right. The increase of fatty acid methyl ester will lead to the progress of side reactions, etc., thereby reducing the reaction esterification rate. Moreover, the properties of the product fuel will be reduced, so the occurrence of side reactions should be avoided. The reaction time should be controlled within 2h to 3h.

Embodiment 5 Orthogonal experiments optimize transesterification reaction conditions

On the basis of single factor experiment, with the yield of biodiesel as the index, an orthogonal experiment was carried out to seek the best process conditions. In the orthogonal experiment, three factors including catalyst dosage, alcohol-to-oil ratio and reaction time were considered, and the reaction temperature was fixed at 75°C. 40g of acidified oil samples were weighed each time for experiment.

According to the results of the single factor experiment, the three factors of catalyst dosage, alcohol-oil ratio and reaction time were selected as independent variables, and three levels were selected for each, and the response surface analysis was carried out with the reaction yield as the response value.

Factor: A-catalyst dosage, 0.5%-3%;

The amount of B-alcohol added, 1:0.5-1:2;

C-reaction time: 2h-4h;

Indicator: Y-yield rate

Table 6 Factor and level table A B C Level 1 Level 2 Level 3 0.523 1:0.51:11:2 234

The transformed experimental scheme and experimental results are shown in Table 7.

Table 7 Orthogonal experiment result table Experiment number _{x1 x2 x3} Y ₁ 123456789 111222333 123123123 312231123 75.0093.8884.2392.1293.7892.1285.0094.1089.90

The range analysis of the yield rate is shown in the table below:

Table 8 Yield range analysis Yield k1k2k3R 253.11278.02269.06.56 252.12281.76266.2514.76 271270.45258.6811.77

From the results of the orthogonal experiment:

Factors affecting the yield, according to the order of the primary and secondary factors of the extreme difference, is B>C>A, that is, the factors affecting the yield are in order: alcohol-oil ratio>time>catalyst addition, and the optimal level combination can be obtained as : A2B2C1

Considering comprehensively, the addition amount of catalyst p-toluenesulfonic acid is 2% of the raw oil, the mass ratio of alcohol to oil is 1:1, the reaction temperature is 75°C, and the reaction time is 2h as the production process conditions.

Embodiment 6 verification test

According to the results of the orthogonal test, the addition of the catalyst p-toluenesulfonic acid is selected as 2% of the feedstock oil, the mass ratio of alcohol to oil is 1:1, the reaction temperature is 75°C, and the reaction time is 2h as the production process conditions. Under this condition, biological The yield of diesel oil is 94.10%, and the viscosity is 14.35mPa.s.

Its purity was measured by thin-layer chromatography, using a mixed solvent of n-hexane, ether, and acetic acid with a volume ratio of 80:20:2 as a developing solvent. The thin plate after development and color development is scanned under the conditions of a light beam (5) of 0.2×0.2 mm, a reference wavelength of 700 nm, and a sample absorption wavelength of 550 nm.

In the formula: the mass percentage content of M _ME methyl ester

M ₁ , M ₂ , M ₃ ... the mass percentage of each component in the obtained product

The area of each spot is obtained: 2762, 25, 159, 25, 38, which are substituted into the formula:

That is, the product purity is: 91.79%.

Example 7

When high-acid-value vegetable oil with an acid value of 5-100mgKOH/g is used as the raw material, after thin-film evaporation treatment, it is subjected to alkali-catalyzed treatment to transesterify the triglyceride in the product. The alkali-catalyzed treatment condition is to add high-acid-value vegetable oil raw material 0.5%-3% NaOH or sodium methoxide as a catalyst, the amount of the catalyst is adjusted according to the acid value of the raw material oil, add methanol with 0.3 times the quality of the high acid value vegetable oil raw material, and react for 3 hours at a temperature of 65-80°C, Then dehydrate and remove methanol to obtain pure biodiesel.

Claims (2)

1. A preparation method for biodiesel, which is characterized in that the high acid value vegetable oil with acid value at 5-200mgKOH/g is a raw material, adopts p-toluenesulfonic acid as a catalyst, and carries out transesterification with high acid value vegetable oil and methyl alcohol Reaction to obtain the primary product of biodiesel; the reaction conditions are a temperature of 60-75°C, the amount of catalyst p-toluenesulfonic acid added is 0.5%-3% of the quality of the raw material high acid value vegetable oil, and the mass ratio of alcohol to oil is 1:1-1 : 3, the reaction time is 2-4h; the first product is then subjected to film evaporation treatment, and the film evaporation conditions are that the vacuum degree is less than 10Pa, and the temperature is 150-200°C; when the acid value of the high acid value vegetable oil raw material is 100-200mgKOH/g , after thin film evaporation treatment, the pure biodiesel can be obtained; Or when the acid value of the high-acid value vegetable oil raw material is 5-100mgKOH/g, after the film evaporation treatment, and then undergo an alkali-catalyzed treatment, the triglyceride in the product is transesterified, and the alkali-catalyzed treatment condition is to add a high acid value Use 0.5%-3% NaOH or sodium methoxide as catalyst, add methanol with 0.3 times the mass of high acid value vegetable oil, react at 65-80°C for 3 hours, then dehydrate and demethanol to obtain pure biodiesel . 2. the preparation method of biodiesel according to claim 1 is characterized in that transesterification reaction condition is temperature 75 ℃, the addition of catalyzer p-toluenesulfonic acid is 2% of raw material high acid value vegetable oil quality, alcohol oil The mass ratio is 1:1, and the reaction time is 2h.