CN112592766A

CN112592766A - Method for separating by-products generated in biodiesel production process

Info

Publication number: CN112592766A
Application number: CN202011318932.2A
Authority: CN
Inventors: 张秋兰; 罗萍; 王义永; 许建
Original assignee: Changzhou Jintan Weige Biological Technology Co ltd
Current assignee: Changzhou Jintan Weige Biological Technology Co ltd
Priority date: 2020-11-23
Filing date: 2020-11-23
Publication date: 2021-04-02

Abstract

The invention provides a method for separating byproducts generated in the production process of biodiesel, wherein the byproducts generated in the production process of the biodiesel mainly comprise glycerol, salt and grease. The soap is converted into acid oil and salt by adding an acid solution, so that the aim of separating glycerin from the soap and simultaneously obtaining a byproduct salt is fulfilled. In the process, the methanol can be recovered by distillation and recycled; the recovered acid oil can be used as a raw material for producing biodiesel.

Description

Method for separating by-products generated in biodiesel production process

Technical Field

The application belongs to the technical field of fatty acid methyl ester separation and purification, and particularly relates to a method for separating byproducts generated in a biodiesel production process.

Background

With the increasing consumption of energy, non-renewable energy sources such as petroleum, diesel oil and natural gas are not enough to meet the requirements of people. The biodiesel is used as a substitute fuel for replacing the non-renewable mineral energy sources, and has the characteristics of good environmental protection performance, good engine starting performance, good fuel performance, wide raw material source, renewability and the like.

Fatty acid methyl ester, also called biodiesel, is a long carbon chain higher fatty acid monoalkyl ester prepared by ester exchange process of animal and vegetable oil or oil and methanol. The fatty acid monoalkyl esters have biodegradability, high flash point, no toxicity, low VOC content, excellent lubricating property and solubility, and are also important raw materials for producing biodegradable fine chemical products with high added value. Has wide application in the aspects of energy, chemical intermediates, surfactants and the like, and reduces the dependence on petroleum products. The vigorous development of the biodiesel has important strategic significance on economic sustainable development, energy source replacement promotion, environmental pressure reduction and urban atmospheric pollution control.

The biodiesel can be prepared by ester exchange reaction of oil and fat, namely triglyceride and low-carbon alcohol, wherein the reaction product comprises fatty acid ester, monoglyceride, diglyceride, glycerol, alcohol and unreacted triglyceride, and the biodiesel can be obtained by separation, wherein the fatty acid ester is mainly the fatty acid ester, and the monoglyceride and diglyceride are also contained in small amount.

The preparation method of biodiesel can be divided into an acid catalysis method, a base catalysis method, an enzyme catalysis method and a supercritical method. Wherein, the acid-base catalysis method is the most widely used method for producing biodiesel at home at present.

CN1412278A discloses an acid catalytic method, which is a method for preparing biodiesel by using high-acid-value waste animal and vegetable oil, and the method is carried out by using sulfuric acid as a catalyst according to the procedures of raw material dehydration, esterification, ester exchange, phase splitting and decoloration, wherein the raw material is dehydrated under vacuum at 60-100 ℃, then the addition amount of the sulfuric acid is 2-6% at 40-85 ℃, the esterification and ester exchange reaction is carried out for 6 hours, a fatty acid methyl ester phase is separated, and the biodiesel is obtained by decoloring with activated clay at 90-125 ℃.

The acid catalysis has the problems of low reaction speed and generation of a large amount of waste acid and waste water.

The reaction rate of the alkali catalyst method is faster than that of the acid catalyst method, but if the content of free fatty acid in the fat is large, fatty acid soap is generated by directly using the alkali catalyst, in which case the amount of the alkali catalyst must be excessive, which makes it difficult to separate the fatty acid ester layer from the glycerin layer.

During the production of fatty acid methyl esters, neutral glycerides are converted to methyl esters during transesterification and glycerol and soap are produced as by-products. The mixture formed by the soap and the grease can not enter the subsequent dealcoholization and rectification sections, but is discharged together with the glycerol to become crude glycerol with lower value. The existing crude glycerol treatment method is to use an acid solution to acidify crude glycerol, and then to distill the crude glycerol at the lower layer after gravity settling to obtain refined glycerol. The method has the defects that about 35 percent of grease and a large amount of salt still remain in the crude glycerin which is only settled by gravity after acidification, and the grease and the salt remain in the kettle liquid after distillation and are treated in a solid waste form; and the acidified crude glycerol has high saponification equivalent and cannot be used for producing medicinal and food-grade glycerol with the content of 99.5 percent or more. Therefore, the separation method commonly used at present not only reduces the yield of unit raw materials and the economic benefit of byproducts, but also increases the solid waste treatment burden of manufacturers.

In addition, the national standard and the European Union standard related to the finished product biodiesel have strict requirements on the content of free glycerol in the biodiesel, and the maximum value of the content is 0.02 percent, so that the problem that the glycerol generated in the reaction process is effectively separated and utilized is urgently needed to be solved in the field.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a method for separating byproducts generated in the production process of biodiesel.

The technical scheme adopted by the invention for solving the technical problems is as follows: a process for separating the by-products generated during the production of biologic diesel oil, such as glycerin, salt and oil, is disclosed. The soap is converted into acid oil and salt by adding an acid solution, so that the aim of separating glycerin from the soap and simultaneously obtaining a byproduct salt is fulfilled. In the process, the methanol can be recovered by distillation and recycled; the recovered acid oil can be used as a raw material for producing biodiesel.

Specifically, the invention provides a method for separating glycerol, salt and grease generated in the production process of biodiesel, which comprises the following steps:

s1: adding an acidic solution into a biodiesel byproduct containing glycerol, soap, grease and methanol to adjust the pH value of the byproduct system to 5-6; preferably, the acid solution is an aqueous solution of strong acid or medium strong acid such as hydrochloric acid, sulfuric acid, phosphoric acid and the like, the addition amount is 1-10% of the mass of the byproduct mixture, and the preference is that

More preferably, the acid solution is a hydrochloric acid solution with a mass concentration of 3-3.5%;

s2: stirring and heating the mixture system obtained in the step S1 to 40-60 ℃, and acidifying the soap in the process to form salt and acid oil;

s3: carrying out suction filtration on the salt and grease mixed solution obtained in the step S2, and separating to obtain salt and filtrate; preferably, the negative pressure used for suction filtration is-0.065 to-0.085 MPa; after suction filtration, washing residual glycerin and grease in the salt layer with methanol for a few times so as to remove the residual glycerin and grease, and separating to obtain high-purity salt; the salt obtained by separation is usually potassium salt or sodium salt, and is determined according to the alkali used for preparing the biodiesel by an acid-base catalysis method; in the present invention, it is preferred that the salt is a potassium salt;

s4: distilling the filtrate separated in the step S3 at normal pressure and low temperature, recovering methanol, and preferably recycling the recovered methanol;

preferably, the normal pressure and low temperature refer to the standard atmospheric pressure of 102.325KPa, and the low temperature is preferably

S5: reducing the pressure of the residual material obtained in the step S4 to 100-120 ℃, preferably 110 ℃, dealcoholizing to obtain a mixture containing glycerol and acidic oil, then separating the glycerol and the acidic oil through centrifugation, wherein the upper layer is the acidic oil and enters a raw material tank; the lower layer is crude glycerol; because no soap and methanol exist in the mixture, the separation degree of the glycerol and the acid oil is higher, so that the saponification equivalent of the glycerol is greatly reduced; preferably, the reduced pressure means-0.1 MPa.

Further preferably, in the above method, the step S4 recycles the recovered methanol to the step S3 for salt washing; the content of the methanol obtained by low-temperature distillation and recovery is reduced along with the increase of the application times, and the content of the methanol is generally reduced by about 0.5 percent in each application; the redundant methanol enters a methanol tower to prepare high-purity methanol for an esterification and ester exchange section; here, the reduction of about 0.5% in the methanol content means that the methanol content in the recovered methanol at the time of dealcoholization at low temperature is reduced by 0.5% as compared with that before washing the residue (salt).

Further preferably, the step S5 dealcoholizes the material remaining in the step S4 to 110 ℃ at-0.1 MPa, and obtains a mixture containing glycerol and acidic oil.

Further preferably, in the above method, the biodiesel byproduct containing glycerin, soap, grease, and methanol in step S1 is a byproduct generated by the production of biodiesel by an acid-base catalysis method. Preferably, the by-product is an alcoholic glycerol mixture separated after the transesterification process in the preparation of fatty acid methyl esters. Wherein the esterification step, the transesterification step, and the step of separating the alcoholic glycerin mixture in the process of preparing fatty acid methyl ester are conventional methods in the art, such as methods disclosed in patent documents CN101696372B, CN102676306A, etc.

Further preferably, the biodiesel by-product containing glycerin, soap, grease and methanol in the step S1 has an oil content of

Soap content

Content of Glycerol

Preferably, the methanol content is not less than 40%, more preferably, the methanol content is

When the content of the methanol in the by-product is lower than 40 percent, a proper amount of methanol can be added according to the proportion.

The fatty acid methyl ester and the biodiesel can be replaced mutually, and the meaning of the designation is the same.

The invention has the beneficial effects that:

(1) in the process of preparing fatty acid methyl ester, the steps of acidification and filtration are added to the byproduct mixture after the ester exchange procedure, so that the glycerol with low saponification equivalent weight is obtained and can be used for producing refined glycerol with the content of 99.5 percent or more.

(2) The acidic oil impurities and salt residues separated from the byproducts by the method are extremely low, and the acidic oil impurities and salt residues can be directly doped into the raw oil for producing methyl ester, so that the value produced by unit raw material is greatly improved.

(3) And methanol is used for washing the filter cake for multiple times in the filtering process, so that the residue of the grease in the filter cake is effectively reduced, and the high-purity potassium salt is obtained and can be used for the production of downstream fertilizers.

(4) The methanol consumed by the method can be recycled by distillation and recycled, and the aim of separating byproducts under the condition of extremely low consumption cost is fulfilled.

(5) The method can be widely applied to large-scale fatty acid methyl ester production process, and the production benefit of enterprises is improved.

Description of the drawings:

FIG. 1 shows the steps of preparing fatty acid methyl esters and separating glycerol, salts and fats produced during the biodiesel production process using the method of the present invention.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.

As shown in the attached FIG. 1, the by-product in this example refers to the alcohol-containing glycerol mixture separated after the transesterification process in the process of preparing biodiesel by acid-base catalysis known in the art.

Example 1: a method for separating by-products generated in the production process of biodiesel:

(1) weighing 420g of the byproduct mixture (oil content: 31.02%, soap content: 10.1%, glycerin: 17%, methanol: 42 wt.%), adding 13.3g (3.16% by mass) of hydrochloric acid, adjusting the pH value of the mixture system to 5, stirring for 4min, and heating to 40 ℃;

(2) carrying out filter pressing on the mixed solution at-0.065 to-0.085 MPa for 1min for 49s, cleaning the salt obtained by filter pressing with a small amount of methanol, drying and weighing to obtain 17.9g of salt;

(3) dealcoholizing the filtrate to 90 ℃ at normal pressure to obtain 173.3g of methanol (content: 97.3%);

(4) dealcoholizing the residual filtrate to 110 ℃ under the vacuum degree of-0.1 MPa, pouring the kettle liquid into a separating funnel for layering, separating glycerol and acid oil, wherein the acid oil on the upper layer is 140.6g, and the acid value is 11.9; the lower layer was 91g of glycerol, having a glycerol content of 82.2% and a saponification equivalent of 67 mmol/100 g.

Example 2: a method for separating by-products generated in the production process of biodiesel:

(1) weighing 426g of the byproduct mixture (oil content: 31.02%, soap content: 10.1%, glycerin: 17%, methanol: 42 wt.%), adding 14.8g (3.47% by mass) of hydrochloric acid, adjusting the pH value of the mixture system to 5, stirring for 4min, and heating to 40 ℃;

(2) carrying out filter pressing on the mixed solution at-0.065 to-0.085 MPa for 1min for 52s, cleaning the salt obtained by filter pressing with a small amount of methanol, drying and weighing to obtain 19.5g of salt;

(3) dealcoholizing the filtrate at normal pressure to 90 ℃ to obtain 172.6g of methanol (the content is 97.0%);

(4) dealcoholizing the residual filtrate to 110 ℃ under the vacuum degree of-0.1 MPa, pouring the kettle liquid into a separating funnel for layering, separating glycerin and grease, wherein the upper layer of acidic oil is 144.4g, and the acid value is 15.1; the lower layer was 91.2g of glycerin, having a glycerin content of 83.6% and a saponification equivalent of 70m mol/100 g.

Example 3: a method for separating by-products generated in the production process of biodiesel:

(1) weighing 426g of the byproduct mixture (oil content: 31.02%, soap content: 10.1%, glycerin: 17%, methanol: 42 wt.%), adding 17.0g (4% by mass) of sulfuric acid, adjusting the pH value of the mixture system to 6, stirring for 4min, and heating to 60 ℃;

(2) carrying out filter pressing on the mixed solution at-0.065 to-0.085 MPa, cleaning the salt obtained by filter pressing with a small amount of methanol, drying and weighing to obtain 19.5g of salt;

(3) dealcoholizing the filtrate to 85 ℃ at normal pressure to obtain 173.5g of methanol (content: 97.5%);

(4) dealcoholizing the residual filtrate to 120 ℃ under the vacuum degree of-0.1 MPa, pouring the kettle liquid into a separating funnel for layering, separating glycerin and grease, wherein the upper layer of acidic oil is 143.4g, and the acid value is 15.1; the lower layer was 91.2g of glycerin, the glycerin content was 83.6%, and the saponification equivalent was 70mmol/100 g.

Example 4: a method for separating by-products generated in the production process of biodiesel:

(1) weighing 420g of the byproduct mixture (oil content: 31.02%, soap content: 10.1%, glycerin: 17%, methanol: 42 wt.%), adding 21g (5% by mass) of phosphoric acid, adjusting the pH value of the mixture system to 5.5, stirring for 5min, and heating to 50 ℃;

(2) carrying out filter pressing on the mixed solution at-0.065 to-0.085 MPa to finish filter pressing, cleaning the salt obtained by filter pressing with a small amount of methanol, drying and weighing to obtain 18.9g of salt;

(3) dealcoholizing the filtrate to 85 ℃ at normal pressure to obtain 173.3g of methanol (the content is 97.3%);

(4) dealcoholizing the residual filtrate to 100 ℃ under the vacuum degree of-0.1 MPa, pouring the residue into a separating funnel for layering, separating glycerol and acidic oil, wherein the upper layer of acidic oil is 142.6g, and the acid value is 11.9; the lower layer was 92g of glycerol, having a glycerol content of 82.2% and a saponification equivalent of 67 mmol/100 g.

Comparative example 1: a method for separating by-products generated in the production process of biodiesel:

(1) weighing 432g of the byproduct mixture (oil content: 31.02%, soap content: 10.1%, glycerin: 17%, methanol: 42 wt.%), adding 13.8g (3.2% by mass) of hydrochloric acid, adjusting the pH value of the mixture system to 5, stirring, and pouring into a separating funnel; (3) standing for 45min, wherein the upper layer contains 235.8g of alcohol acid oil, and the lower layer contains 206.6g of crude alcohol glycerol; (4) after dealcoholization, 136g of acidic oil and 131.3g of crude glycerin were distilled at-0.1 MPa to 240 ℃ to obtain 86g of refined glycerin having a glycerin content of 85.6% and a large amount of salt remaining in the pot liquid, and having a saponification equivalent of 103m mol/100 g.

In light of the foregoing description of the preferred embodiments according to the present application, it is to be understood that various changes and modifications may be made without departing from the spirit and scope of the invention. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.

Claims

1. A method for separating glycerin, salt and grease generated in the production process of biodiesel is characterized by comprising the following steps:

s1: adding an acidic solution into a biodiesel byproduct containing glycerol, soap, grease and methanol to adjust the pH value of the byproduct system to 5-6;

s2: stirring and heating the mixture system obtained in the step S1 to 40-60 ℃ to form salt and acid oil;

s3: carrying out suction filtration on the mixed solution containing the salt and the acidic oil obtained in the step S2, and separating to obtain a potassium salt and a filtrate;

s4: distilling the filtrate separated in the step S3 at normal pressure and low temperature, and recovering methanol;

s5: and (3) dealcoholizing the residual material in the step (S4) under reduced pressure to 100-120 ℃, separating the glycerol and the acidified oil by centrifuging the obtained mixture containing the glycerol and the acidified oil, wherein the upper layer is the acidic oil, and the lower layer is the crude glycerol.

2. The method according to claim 1, wherein the acidic solution in step S1 is an aqueous solution of hydrochloric acid, sulfuric acid, and phosphoric acid, and the amount of acid added is 1-10% of the mass of the byproduct mixture.

3. The method of claim 1, wherein the pressure used for the suction filtration in step S3 is-0.065 MPa to-0.085 MPa.

4. The method according to claim 1, wherein after the suction filtration in step S3, the glycerin and the oil and fat remaining in the salt layer are washed with methanol in small amounts and a plurality of times to obtain a high-purity potassium salt.

5. The method of claim 1, wherein the normal pressure and low temperature of step S4 are normal atmospheric pressure,

6. the method of claim 1, wherein the methanol recovered in step S4 is recycled to the salt washing stage of step S3 for use, the excess methanol is fed to a methanol column, and the high purity methanol is used in the esterification and transesterification stage.

7. The method of claim 1, wherein the step S5 dealcoholizes the residue of the step S4 at-0.1 MPa to 110 ℃ to obtain a mixture comprising glycerol and acidic oil.

8. The method of claim 1, wherein the methanol is recovered and recycled in step S4, wherein the methanol content is reduced to about 0.5% by weight of the recovered methanol during the low temperature dealcoholization for each recycle.

9. The method according to any one of claims 1 to 8, wherein the biodiesel byproduct containing glycerin, soap, grease and methanol in step S1 is a byproduct generated in biodiesel production by an acid-base catalysis method.

10. The method according to any one of claims 1 to 8, wherein the biodiesel by-product containing glycerin, soap, grease and methanol in step S1 has an oil content of

Soap content

Glycerol