A method for producing fatty acids using fatty acid monomethyl esters

Abstract

The application relates to a method for preparing fatty acid by using fatty acid monomethyl ester, which comprises the following steps: 1) reacting fatty acid monomethyl ester with water by heating in the presence of a catalyst composed of p-toluenesulfonic acid and sulfuric acid to generate fatty acid and methanol; and 2) promoting the reaction to be completed by adding water and removing methanol. According to the application, a small amount of catalyst can be used to catalyze the hydrolysis of fatty acid monomethyl ester to obtain fatty acid under normal pressure, the reaction rate is fast, high yield and high-purity fatty acid can be obtained, the process for preparing fatty acid by using fatty acid monomethyl ester is simple, the catalyst and methanol can be recycled, and the process cost is greatly reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fatty acid preparation, and particularly relates to a method for preparing fatty acid by using fatty acid monomethyl ester. BACKGROUND

[0002] Fatty acid is an important chemical raw material, and is one of basic raw materials of surfactants. A variety of anionic, nonionic, cationic and amphoteric surfactants can be prepared by taking it as a starting material, and are widely applied to the industries of light and textile, washing, rubber, cosmetics, plastic, papermaking, medicine, food, petroleum, synthetic fiber, leather making, ore dressing, machinery and the like, and the demand is increasing day by day.

[0003] In the prior art, hydrolysis of triglyceride (i.e. hydrolysis of oils and fats of plant and animal origin) has become the main source of fatty acid production. The oil hydrolysis method can be divided into batch method and continuous method according to operation mode, can be divided into catalysis-free and catalysis (using acid, alkali, enzyme and the like) according to whether there is a catalyst, and can be divided into low pressure (170-190 DEG C, 0.8-1.2 MPa), medium pressure (230 DEG C, 2.5 MPa) and high pressure (250-260 DEG C, 5.5-6.0 MPa) hydrolysis method according to operation pressure. At present, the low pressure batch hydrolysis method is mainly used in China, but this method has problems of high energy consumption, long hydrolysis time, unstable process, poor product quality and the like.

[0004] In order to prepare fatty acid by hydrolysis of fatty acid alkyl ester, especially fatty acid monomethyl ester, the prior art hinders the establishment of equilibrium by evaporating formed methanol from the reaction mixture, and this method works at low pressure such as ambient pressure, at a temperature range of, for example, 70 to 150 DEG C, as a result of these low reaction temperatures, it is necessary to catalytically accelerate the reaction in order to obtain the required high conversion on the basis of industrial standard reaction time and residence time. However, the method for preparing fatty acid by using fatty acid methyl ester in the prior art uses a large amount of catalyst, and the preparation process is complex, thereby resulting in high cost of preparing fatty acid. SUMMARY

[0005] The technical problem to be solved by the present application is to solve the deficiency that the method for preparing fatty acid by using fatty acid monomethyl ester in the prior art uses a large amount of catalyst, and the preparation process is complex, thereby resulting in high cost of preparing fatty acid, and thus a method for preparing fatty acid by using fatty acid monomethyl ester is provided.

[0006] The technical scheme adopted by the present application to solve the technical problem is:

[0007] The method for preparing fatty acid by using fatty acid monomethyl ester comprises the following steps:

[0008] 1) reacting fatty acid monomethyl ester with water by heating in the presence of a catalyst composed of p-toluene sulfonic acid and sulfuric acid to produce fatty acid and methanol;

[0009] 2) promoting the reaction to completion by adding water and removing methanol.

[0010] Preferably, the reaction mixture is heated at 95-100°C.

[0011] Preferably, after the reaction is completed, the reaction solution is allowed to stand and cool to separate into an upper layer and a lower layer, the lower layer containing the catalyst is discharged, and the upper layer is distilled to obtain fatty acid.

[0012] Preferably, before the upper layer is distilled, the upper layer is washed with water, and the washed water solution is mixed with the lower layer to obtain a water solution containing the catalyst for reuse.

[0013] Preferably, the fatty acid part of the fatty acid monomethyl ester contains 6-10 carbon atoms; further, the fatty acid monomethyl ester is preferably at least one of hexanoic acid monomethyl ester, octanoic acid monomethyl ester, and decanoic acid monomethyl ester.

[0014] Preferably, the mass ratio of p-toluene sulfonic acid to sulfuric acid is 1:1-2:1, preferably 1:1.

[0015] Preferably, in step 1), the catalyst is used in an amount of at least 0.1wt% of the fatty acid monomethyl ester, preferably 0.1wt%-0.3wt%.

[0016] Preferably, in step 1), the molar ratio of water to fatty acid monomethyl ester is 1:0.2-1:0.5, preferably 1:0.3.

[0017] Preferably, a rotameter is used to control the flow rate of the added water, so that the amount of added water is equal to the amount of water consumed during the reaction.

[0018] The present application has the following advantages:

[0019] The present application can catalyze the hydrolysis of fatty acid monomethyl ester to produce fatty acid at normal pressure with a small amount of catalyst, and the reaction rate is fast, and high yield and high purity fatty acid can be obtained. The process of the present application for preparing fatty acid from fatty acid monomethyl ester is simple, and the catalyst and methanol can be recycled, greatly reducing the process cost. DETAILED DESCRIPTION

[0020] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0021] The technical solutions of the present application will be described in detail below with reference to the embodiments.

[0022] Example 1

[0023] The present embodiment provides a method for preparing hexanoic acid using hexanoic acid monomethyl ester, comprising the following steps:

[0024] 1) adding 5421 kg of hexanoic acid monomethyl ester and 1500 kg of water into a reactor with a rectifying tower, and adding 8132 g of catalyst under stirring to form a reaction mixture; the catalyst is a mixture of p-toluenesulfonic acid and sulfuric acid with a mass ratio of 1:1; the reaction mixture is heated to 95-100°C to make the fatty acid monomethyl ester react with water to produce fatty acid and methanol;

[0025] 2) removing methanol through the rectifying tower during the reaction, and timely adding water to the reaction system; the flow rate of the added water is controlled by a rotor flowmeter, so that the amount of added water is equal to the consumption of water during the reaction; when no methanol is produced, the reaction is stopped, and the reaction time is 1 hour;

[0026] 3) allowing the reaction liquid to stand and cool to separate into two layers, discharging the lower aqueous solution with the catalyst, and washing the upper solution with clean water twice; the upper solution after washing contains hexanoic acid and a small amount of unreacted hexanoic acid monomethyl ester, and the yield of hexanoic acid is 98.5% by analysis; the upper solution after washing is distilled to obtain hexanoic acid with a content of 99.5%, and the aqueous solution after washing the upper solution is mixed with the lower aqueous solution to obtain an aqueous solution with catalyst for reuse.

[0027] Example 2

[0028] The present embodiment provides a method for preparing octanoic acid using octanoic acid monomethyl ester, comprising the following steps:

[0029] 1) adding 2637 kg of octanoic acid monomethyl ester and 1500 kg of water into a reactor with a rectifying tower, and adding 5274 g of catalyst under stirring to form a reaction mixture; the catalyst is a mixture of p-toluenesulfonic acid and sulfuric acid with a mass ratio of 2:1; the reaction mixture is heated to 95-100°C to make the octanoic acid monomethyl ester react with water to produce octanoic acid and methanol;

[0030] 2) removing methanol through the rectifying tower during the reaction, and timely adding water to the reaction system; the flow rate of the added water is controlled by a rotor flowmeter, so that the amount of added water is equal to the consumption of water during the reaction; when no methanol is produced, the reaction is stopped, and the reaction time is 1.2 hours;

[0031] 3) Let the reaction solution stand and cool to separate into two layers, release the lower aqueous solution with catalyst, and wash the upper solution with water twice. The upper solution after washing contains hexanoic acid and a small amount of unreacted octanoic acid monomethyl ester. The yield of octanoic acid is 98.9% by analysis. The upper solution after washing is distilled to obtain octanoic acid with a content of 99.7%. The aqueous solution after washing the upper solution is mixed with the lower aqueous solution to obtain an aqueous solution with catalyst for reuse.

[0032] Example 3

[0033] This example provides a method for preparing decanoic acid using decanoic acid monomethyl ester, comprising the following steps:

[0034] 1) Add 5238 kg of decanoic acid monomethyl ester and 1500 kg of water to a reaction kettle with a rectifying column, and add 5238 g of catalyst under stirring to form a reaction mixture; the catalyst is a mixture of p-toluenesulfonic acid and sulfuric acid with a mass ratio of 1.5:1. Heat the reaction mixture to 95-100°C to react decanoic acid monomethyl ester with water to produce decanoic acid and methanol;

[0035] 2) Remove methanol by the rectifying column during the reaction, and supplement water to the reaction system in time. The flow rate of the supplemented water is controlled by a rotor flow meter to make the amount of water added equal to the amount of water consumed during the reaction. Stop the reaction when no methanol is produced, and the reaction time is 1.5 hours;

[0036] 3) Let the reaction solution stand and cool to separate into two layers, release the lower aqueous solution with catalyst, and wash the upper solution with water twice. The upper solution after washing contains hexanoic acid and a small amount of unreacted decanoic acid monomethyl ester. The yield of decanoic acid is 98.6% by analysis. The upper solution after washing is distilled to obtain decanoic acid with a content of 99.5%. The aqueous solution after washing the upper solution is mixed with the lower aqueous solution to obtain an aqueous solution with catalyst for reuse.

[0037] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the content in the specification, and must be determined by the scope of the claims.

Claims

1. A method for producing a fatty acid using a fatty acid monomethyl ester, characterized by, The method comprises the following steps: 1) reacting fatty acid monomethyl ester with water at 95-100 DEG C by heating in the presence of a catalyst composed of p-toluene sulfonic acid and sulfuric acid to produce fatty acid and methanol; the mass ratio of p-toluene sulfonic acid to sulfuric acid is 1:1-2:1, and the catalyst is used in an amount of at least 0.1 wt% of the weight of fatty acid monomethyl ester; 2) promoting the reaction to completion by adding water and removing methanol.

2. The method for producing fatty acids using fatty acid monomethyl esters according to claim 1, characterized by, After the reaction is completed, the reaction liquid is allowed to stand and cool to separate into two layers, the lower aqueous layer with catalyst is discharged, and the upper layer is distilled to obtain fatty acid.

3. The method of preparing fatty acids using fatty acid monomethyl esters according to claim 2, characterized by, Before distilling the upper layer, the upper layer is washed with water, and the aqueous solution after washing is mixed with the lower aqueous layer to obtain an aqueous solution with catalyst for reuse.

4. The method for producing fatty acids using fatty acid monomethyl esters according to claim 1, characterized by, The fatty acid part of the fatty acid monomethyl ester contains 6-12 carbon atoms.

5. The method of preparing fatty acids using fatty acid monomethyl esters according to claim 4, characterized by, The fatty acid monomethyl ester is at least one of hexanoic acid monomethyl ester, octanoic acid monomethyl ester and decanoic acid monomethyl ester.

6. The method of preparing fatty acids using fatty acid monomethyl esters according to claim 1, characterized by, The mass ratio of p-toluene sulfonic acid to sulfuric acid is 1:

1.

7. The method of preparing fatty acids using fatty acid monomethyl esters according to claim 1, characterized by, The catalyst is used in an amount of 0.1-0.3 wt% of the weight of fatty acid monomethyl ester.

8. The method of preparing fatty acids using fatty acid monomethyl esters according to claim 1, characterized by, In step 1), the molar ratio of water to fatty acid monomethyl ester is 1:0.2-0.

5.

9. The method of preparing fatty acids using fatty acid monomethyl esters according to claim 8, characterized by, In step 1), the molar ratio of water to fatty acid monomethyl ester is 1:0.

3.

10. The method of preparing fatty acids using fatty acid monomethyl esters according to claim 1, characterized by, The flow of added water is controlled by a rotor flow meter so that the amount of added water is equal to the amount of water consumed during the reaction.