CN1850944A - Method for synthesizing biodiesel - Google Patents

Abstract

The invention discloses a method for synthesizing biodiesel. The method is as follows: adding alcohol and an alkali catalyst to animal and vegetable oils, the reaction temperature is 25-45°C, stirring and reacting; layering, the upper layer is a biodiesel layer, and the lower layer is a glycerol layer The biodiesel layer is separated, alcohol and alkali catalyst are added, the reaction temperature is 25-45° C., and the reaction is stirred; layers are separated, the upper layer is an alcohol glycerol layer, and the lower layer is a biodiesel layer; biodiesel is separated. The present invention utilizes animal and vegetable oils to synthesize biodiesel in a two-step process under alkali catalysis, and the reaction temperature is low. The upper alcohol glycerin layer in the second step can be added to the first step to react as a raw material to save the catalyst, and the reaction yield is high, generally exceeding 97 %; The conversion rate is high, generally exceeding 99%.

Description

A kind of synthetic method of biodiesel

Technical field

The invention relates to the technical field of new energy utilization, in particular to a method for synthesizing biodiesel from animal and vegetable oils.

Background technique

Biodiesel is a new type of bioenergy that has developed rapidly in recent years and will become an important part of sustainable energy in the future. Biodiesel can be used as a substitute for high-quality petroleum diesel. It is an environmentally friendly green fuel and has far-reaching economic and social benefits. In 1983, American scientist Graham Quick first used the methyl ester of linseed oil in the engine, burned it for 1000 hours, and defined the renewable fatty acid monoester as biodiesel. Fatty acid monoesters mainly refer to methyl, ethyl or propyl esters of fatty acids from animals and plants. Biodiesel is a new type of renewable energy, and it is an ideal substitute for petroleum resources. At present, developed countries such as Europe, America and Japan have raised the development of biodiesel to a strategic level. In 2004, the EU's biodiesel production was 3 million tons, and the United States was 1 million tons. According to EU law, the share of biodiesel must account for 2% of petroleum energy in 2005, 5.75% in 2010, and 20% in 2020. From 2009 onwards, 1% biodiesel must be added to all mineral diesel in the EU, and 1.75% from 2010.

Traditional diesel engines can directly use 100% biodiesel without modification. In Germany, cars produced by Mercedes-Benz, BMW, Volkswagen and Audi can run on biodiesel without engine modification. Blends of biodiesel and mineral diesel are also available, and the US sells diesel products blended with 20% biodiesel.

On January 18, 2003, Xu Kuangdi, president of the Chinese Academy of Engineering, proposed at the "Seminar on the Development of Biodiesel Plant Raw Materials in my country" that the large-scale production of biodiesel, an alternative liquid fuel based on domestic raw materials, is of great importance to enhance my country's oil security. strategic significance. my country passed and implemented the "Renewable Energy Law of the People's Republic of China" on February 28, 2005, and biodiesel was clearly included in it.

At present, the industry mainly uses animal and vegetable oils as raw materials to synthesize biodiesel by alkali catalysis, the reaction temperature is 50-60°C, the amount of methanol added is 6 times the molar amount of oil, and the reaction time is about 1 hour. This one-step method of catalyzing biodiesel synthesis requires high initial acid value and water content of animal and vegetable oils. Due to the high reaction temperature, the energy consumption is high. At the same time, the alkali catalyst is easy to saponify neutral oil at high temperature, which reduces the catalytic efficiency. And product yield, because European and American standards have strict restrictions on the content of triglycerides in biodiesel, the conversion rate of triglycerides in the traditional one-step catalytic process generally does not exceed 97%, and the yield does not exceed 95%.

Contents of invention

In order to solve the deficiencies in the above-mentioned prior art, the object of the present invention is to provide an efficient method for synthesizing biodiesel from animal and vegetable oils, which has higher conversion rate, higher yield and more energy saving.

The invention relates to a method for synthesizing biodiesel in a two-step method using animal and vegetable oils under the action of alkali catalysis at normal temperature (25-45°C). The excess alcohol in the second step reaction is added to the first step reaction to save catalyst costs. When used, the conversion rate of triglyceride can reach more than 99%, and the yield of biodiesel exceeds 97%.

The object of the present invention is achieved through the following technical solutions: a synthetic method for biodiesel, comprising the steps:

(1) Alcohol and alkali catalyst are added to animal and vegetable oils, the reaction temperature is 25-45°C, and the reaction is stirred at 300-400r/min for 0.5-2 hours; static layering or centrifugal layering, the upper layer is biodiesel layer, the lower layer It is a glycerol alcohol layer; the added amount of the alcohol is 20-30% of the weight of the animal and vegetable oil; the added amount of the alkali catalyst is 0.5-1.6% of the weight of the animal and vegetable oil.

(2) Separate the biodiesel layer, add alcohol and alkali catalyst, the reaction temperature is 25-45°C, and react for 0.5-2 hours under stirring at a speed of 300-400r/min; , after layering, the upper layer is the alcohol glycerin layer, and the lower layer is the biodiesel layer; the upper alcohol glycerin layer is added to the next batch of animal and vegetable oil as a reaction raw material, which can save catalyst and alcohol, and the lower biodiesel is evaporated to recover alcohol, and then in 60～90 DEG C, wash with the hot water (80～90 DEG C) that accounts for 5～10% of biodiesel weight, obtain biodiesel; The addition amount of described alcohol is 22～35% of animal and vegetable oil weight; 0.5-1.6% by weight of vegetable oil.

In order to better realize the present invention, the animal and vegetable oils include soybean oil, blended oil, palm oil, lard oil or rapeseed oil and the like. The alcohol includes methanol or ethanol, etc., and the alkali catalyst is first dissolved in the alcohol, and then added to the animal and vegetable oil. The alkali catalyst includes sodium hydroxide or potassium hydroxide and the like.

Particularly preferred scheme, in described step (1), alcohol addition is 22～25% of animal and vegetable oil weight, and alkali catalyst addition is 0.8～1.4% of animal and vegetable oil weight; In described step (2), alcohol addition is 25-30% of the weight of the animal and vegetable oil; the amount of the alkali catalyst is 0.8-1.4% of the weight of the animal and vegetable oil. The reaction temperature is 30-40°C.

If potassium hydroxide is used as the alkali catalyst, it is particularly preferred that the amount of potassium hydroxide added be 1.0 to 1.4% of the weight of the animal and vegetable oil; %.

The conversion rate of triglyceride in the present invention is analyzed by gas chromatography. The purpose of water washing is to remove residual glycerin and catalysts in biodiesel products. The alcohol of the follow-up first step reaction can use the supernatant liquid of the second step reaction as a reactant, saving alcohol consumption. In the step (2), the upper alcohol glycerin layer is added as a raw material to the next batch of animal and vegetable oils to be reacted, and the first step (1) reaction is carried out to save alcohol consumption. Because the reaction temperature is low, the saponification of neutral oil is less, the product yield is high, generally exceeding 97%; because the step (2) has a lot of alcohol excess, so the reaction conversion rate is very high, generally exceeding 99%.

Compared with the prior art, the present invention has the following advantages and beneficial effects: the present invention adopts a two-step method to synthesize biodiesel, the reaction temperature is low, and the energy saving is 20-50% compared with the traditional process. The upper alcohol glycerol layer in the second step can be added to the first step reaction as a raw material to save catalyst, and the reaction yield is high, exceeding 97%; the conversion rate is high, exceeding 99%.

Detailed ways

The present invention will be further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

Example 1

Two-step synthesis of biodiesel:

The first step of reaction: Take 100g of edible blend oil, add 25g of methanol, 1g of sodium hydroxide (dissolved in methanol), and react in the reactor at 25°C for 1 hour at a stirring speed of 300r/min. Static stratification, the upper layer is the biodiesel layer, and the lower layer is the glycerol methanol layer. The second step reaction: take the upper biodiesel layer, add 27g of methanol, 1g of sodium hydroxide (dissolved in methanol), and react in a reactor at 25°C for 1 hour at a stirring speed of 300r/min. Use a separatory funnel to stand for stratification. Because there is more methanol, the upper layer is a methanol-glycerin layer after the layering, and the lower layer is a biodiesel layer. The biodiesel in the lower layer was evaporated and recovered methanol with a rotary evaporator at an absolute pressure of 60 kPa at 60° C., and washed twice at 80° C. with hot water (80° C.) accounting for 10% of the weight of the biodiesel to obtain biodiesel. Calculate the yield by weighing after drying. The conversion of triglycerides was analyzed by gas chromatography. The upper methanol glycerol layer is added as a raw material to the next batch of 100g edible blending oil to be reacted to carry out the first step reaction, saving the alkali catalyst. The product yield of the two-step method is 97.8%, and the conversion rate of triglyceride is 99.2%.

Example 2

The first step of reaction: Take 500g of palm oil, add 100g of methanol, 3g of sodium hydroxide (dissolved in methanol), and react in a reactor at 40°C for 1.5 hours at a stirring speed of 400r/min. Centrifugal layering, the upper layer is the biodiesel layer, and the lower layer is the glycerol methanol layer. The second step reaction: take the upper biodiesel layer, add 115g of methanol, 3g of sodium hydroxide (dissolved in methanol), and react in a reactor at 40°C for 1 hour at a stirring speed of 400r/min. Use a separatory funnel to stand for stratification. Because there is more methanol, the upper layer is a methanol-glycerin layer after the layering, and the lower layer is a biodiesel layer. The biodiesel in the lower layer was evaporated and recovered methanol with a rotary evaporator at an absolute pressure of 60 kPa at 60° C., and washed twice at 90° C. with hot water (90° C.) accounting for 6% of the weight of the biodiesel to obtain biodiesel. Calculate the yield by weighing after drying. The conversion of triglycerides was analyzed by gas chromatography. The upper methanol glycerol layer is added to the next batch of 500g palm oil to be reacted as a raw material to carry out the first step reaction and save the alkali catalyst. The product yield of the two-step method is 98.6%, and the conversion rate of triglyceride is 99.5%.

Example 3

The first step reaction: take 1000g of lard, add 300g of methanol, 14g of potassium hydroxide (dissolved in methanol), and react in a reactor at 45°C for 2 hours at a stirring speed of 350r/min. Use a centrifuge to centrifuge the layers, the upper layer is the biodiesel layer, and the lower layer is the glycerol methanol layer. The second step reaction: take the upper biodiesel layer, add 350g of methanol, 10g of potassium hydroxide (dissolved in methanol), and react in a reactor at 45°C for 2 hours at a stirring speed of 350r/min. Centrifuge the layers with a centrifuge (centrifugation conditions: at a speed of 3000r/min, centrifugation time 10min), because there is more methanol, the upper layer is a methanol glycerol layer after layering, and the lower layer is a biodiesel layer. The biodiesel in the lower layer was evaporated with a rotary evaporator at 60° C. to recover methanol at an absolute pressure of 60 kPa, and washed twice at 80° C. with hot water (80° C.) accounting for 8% of the weight of the biodiesel to obtain biodiesel. Calculate the yield by weighing after drying. The conversion of triglycerides was analyzed by gas chromatography. The upper methanol glycerol layer is added as a raw material to the next batch of 1000g lard to be reacted to carry out the first step reaction, saving the alkali catalyst. The product yield of the two-step method is 97.8%, and the conversion rate of triglyceride is 99.4%.

Example 4

The first step reaction: take 5000g soybean oil, add 1000g ethanol, 40g sodium hydroxide (dissolved in ethanol), and react in a reactor at 35°C for 0.5 hours at a stirring speed of 300r/min. Use a centrifuge to centrifuge the layers, the upper layer is the biodiesel layer, and the lower layer is the glycerol ethanol layer. The second step reaction: take the upper biodiesel layer, add 1500g of ethanol, 40g of sodium hydroxide (dissolved in ethanol), and react in a reactor at 35°C for 0.5 hours at a stirring speed of 300r/min. Centrifuge the layers with a centrifuge (centrifugation conditions: at a speed of 3000r/min, centrifugation time 10min), because there is more ethanol, after layering, the upper layer is the ethanol glycerol layer, and the lower layer is the biodiesel layer. The lower layer of biodiesel was evaporated and recovered ethanol with a rotary evaporator at an absolute pressure of 60 kPa at 65° C., and washed twice with 5% hot water (85° C.) accounting for the weight of the biodiesel at 70° C. to obtain biodiesel. Calculate the yield by weighing after drying. The conversion of triglycerides was analyzed by gas chromatography. The upper ethanol glycerol layer is added as a raw material to the next batch of 5000g soybean oil to be reacted to carry out the first step reaction, saving the alkali catalyst. The product yield of the two-step method is 97.8%, and the conversion rate of triglyceride is 98.5%.

Example 5

The first step of reaction: Take 5000g of rapeseed oil, add 1200g of methanol, 50g of potassium hydroxide (dissolved in methanol), and react in a reactor at 30°C for 1 hour at a stirring speed of 300r/min. Use a centrifuge to centrifuge the layers, the upper layer is the biodiesel layer, and the lower layer is the glycerol methanol layer. The second step reaction: take the upper biodiesel layer, add 1400g ethanol, 50g sodium hydroxide (dissolved in methanol), and react in a reactor at 30°C for 1 hour at a stirring speed of 300r/min. Centrifuge the layers with a centrifuge (centrifugation conditions: at a speed of 3000r/min, centrifugation time 10min), because there is more methanol, the upper layer is a methanol glycerol layer after layering, and the lower layer is a biodiesel layer. The biodiesel in the lower layer was evaporated and recovered methanol with a rotary evaporator at an absolute pressure of 60kPa at 60°C, and washed twice with 10% hot water (80°C) of the weight of the biodiesel at 60°C to obtain biodiesel. Calculate the yield by weighing after drying. The conversion of triglycerides was analyzed by gas chromatography. The upper methanol glycerol layer is added as a raw material to the 5000g rapeseed oil to be reacted in the next batch to carry out the first step reaction and save the alkali catalyst. The product yield of the two-step method is 99.2%, and the conversion rate of triglyceride is 99.5%.

As described above, the present invention can be preferably carried out.

Claims (10)

1, a kind of method for synthesizing biological fuel-oil is characterized in that comprising the steps:

(1) add pure and mild alkaline catalysts in the vegetable and animals oils, temperature of reaction is 25～45 ℃, and stirring reaction is 0.5～2 hour under 300～400r/min rotating speed; Standing demix or centrifugal layering, upper strata are bio-diesel layer, and lower floor is the glyceryl alcohol layer; Described pure addition is 20～30% of a vegetable and animals oils weight; The alkaline catalysts addition is 0.5～1.6% of a vegetable and animals oils weight;

(2) isolate bio-diesel layer, add pure and mild alkaline catalysts, temperature of reaction is 25～45 ℃, reacts 0.5～2 hour under 300～400r/min rotating speed stirs; Standing demix or centrifugal layering, the upper strata is pure glycerin layer after the layering, lower floor is a bio-diesel layer; Alcohol glycerin layer in upper strata is added to as reaction raw materials in the vegetable and animals oils of next batch, and lower floor's biofuel reclaims alcohol through evaporation, and then at 60～90 ℃, 5～10% hot water washing with accounting for biofuel weight obtains biofuel; Described pure addition is 22～35% of a vegetable and animals oils weight; The alkaline catalysts consumption is 0.5～1.6% of a vegetable and animals oils weight.

2, a kind of biofuel synthetic method according to claim 1, it is characterized in that: described vegetable and animals oils comprises soybean oil, mixed oil, plam oil, lard or rapeseed oil.

3, a kind of method for synthesizing biological fuel-oil according to claim 1 is characterized in that: described alcohol is methyl alcohol or ethanol.

4, a kind of method for synthesizing biological fuel-oil according to claim 1, it is characterized in that: described alkaline catalysts is dissolved in the alcohol earlier, and then adds in the vegetable and animals oils.

5, a kind of method for synthesizing biological fuel-oil according to claim 1, it is characterized in that: described alkaline catalysts comprises sodium hydroxide or potassium hydroxide.

6, a kind of method for synthesizing biological fuel-oil according to claim 1 is characterized in that: pure addition is 22～25% of a vegetable and animals oils weight in the described step (1), and the alkaline catalysts addition is 0.8～1.4% of a vegetable and animals oils weight.

7, a kind of method for synthesizing biological fuel-oil according to claim 1 is characterized in that: pure addition is 25～30% of a vegetable and animals oils weight in the described step (2); The alkaline catalysts consumption is 0.8～1.4% of a vegetable and animals oils weight.

8, a kind of method for synthesizing biological fuel-oil according to claim 1 is characterized in that: described temperature of reaction is 30～40 ℃.

9, a kind of method for synthesizing biological fuel-oil according to claim 5 is characterized in that: described potassium hydroxide addition is 1.0～1.4% of a vegetable and animals oils weight.

10, a kind of method for synthesizing biological fuel-oil according to claim 5 is characterized in that: described sodium hydroxide addition is 0.8～1.0% of a vegetable and animals oils weight.