CN1373117A

CN1373117A - Process for purifying hihg-content o-methylbenzoic acid

Info

Publication number: CN1373117A
Application number: CN 02112684
Authority: CN
Inventors: 陆守纯
Original assignee: Chemical Plant No7 Taixing City
Current assignee: Chemical Plant No7 Taixing City
Priority date: 2002-02-21
Filing date: 2002-02-21
Publication date: 2002-10-09
Anticipated expiration: 2022-02-21
Also published as: CN1156431C

Abstract

A process for purifying high-content o-methylbenzoic acid includes adding the raw o-methylbenzoic acid to water, heating, adding alkali, reaction to obtain o-methylbenzoate, dissolving it in water to obtain solution A, adding another solvent to extract the water insoluble liquid impurities, separating, adding activated carbon to solution A for decolouring it, cooling, filtering, adding acid, reaction to separate out o-methylbenzoic acid powder, recrystallizing in water, solid-liquid separation, and drying the solid.

Description

Method for purifying high-content o-methylbenzoic acid

Technical Field

The invention relates to a purification method of high-content o-methylbenzoic acid, which is a purification method for purifying, deodorizing and whitening an o-methylbenzoic acid crude product.

Background

The unpurified crude o-methylbenzoic acid is a product obtained by carrying out air homogeneous phase oxidation, gas phase oxidation or electrochemical oxidation on o-xylene, and then rectifying or directly cooling and crystallizing, wherein solid impurities, liquid impurities,phthalic acid, o-methylbenzaldehyde and the like in the product cannot be removed in rectification due to similar boiling points, so that the product quality is directly influenced, and therefore the crude o-methylbenzoic acid has the following defects: low purity, instability, large color difference of appearance, bad smell, and easy agglomeration during storage.

Disclosure of Invention

The invention aims to overcome the defects of the crude o-methylbenzoic acid product, and provides a method for purifying high-content o-methylbenzoic acid, which comprises the following steps: the crude o-methylbenzoic acid reacts with the alkali solution to become o-methylbenzoate dissolved in an alkaline or neutral aqueous solution. Extracting with extractant to remove liquid impurities insoluble in alkaline or neutral aqueous solution, decolorizing and whitening with activated carbon, adding acid for acid precipitation, recrystallizing, and drying to obtain the final product. The key of the method for purifying the high-content o-methylbenzoic acid is as follows: (1) the solid impurities of benzoic acid and phthalic acid in the crude o-toluic acid have high solubility in an aqueous solution and can be removed during recrystallization. (2) Impurities which affect the color of the product are absorbed by the activated carbon in the o-methyl benzoate solution. (3) The liquid impurities in the crude o-methylbenzoic acid are removed in the o-methylbenzoate solution by using an extracting agent.

The purification method of the high-content o-methylbenzoic acid comprises the following steps:

1. adding the crude o-methylbenzoic acid into the solution water, and adding alkali. The alkali can be one of inorganic alkali such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassiumbicarbonate and the like, and liquid and solid can be heated to 80-105 ℃ to promote reaction. The method comprises the following steps of (1) controlling the pH value of o-methylbenzoic acid and solvent water to be 1: 5-10 (weight ratio), controlling the pH value to be 6-8, enabling the o-methylbenzoic acid to be changed into o-methylbenzoate, completely dissolving the o-methylbenzoic acid into the solvent water (called solution A for short), adding solution A into a liquid-liquid separator, cooling, adding an extracting agent, fully stirring, standing, and enabling liquid impurities which are not dissolved in the solution A to be extracted by the extracting agent (called solution B for short). And separating the solution A from the solution B according to different densities. The weight ratio of the extracting agent to the solution A is 1: 5-15, and the density of liquid impurities is almost equal to that of water, so that the difference between the density of the extracting agent and the density of water is at least 0.1, and the extracting agent is a solution which has a density below 0.9 or above 1.1 and a boiling point below 150 ℃ and is insoluble in most solvents soluble in water, such as benzene, toluene, xylene, diethyl ether, chloroform and the like.

2. And adding the separated solution A into a reaction kettle, heating to 80-150 ℃, adding activated carbon, boiling for 10-20 min, cooling and filtering. The weight ratio of the activated carbon to the solution A is 1: 300-600.

3. And adding the filtered solution A into a reaction kettle, adding acid while stirring, controlling the pH value to be 1-6, completely separating out the o-methylbenzoic acid powder, heating to 90-100 ℃, stirring, cooling, carrying out solid-liquid separation, and drying to obtain white crystals, namely the high-content o-methylbenzoic acid finished product. The acid can be one of inorganic acids such as hydrochloric acid, phosphoric acid, nitric acid, and sulfuric acid.

The reaction formula of adding alkali into o-methylbenzoic acid is as follows:

example (c):

the method for the acid addition reaction of the o-methyl benzoate comprises the following steps:

example (c):

the advantages are that: 1. the o-methylbenzoic acid product purified by the method disclosed by the invention is low in smell, few in impurities and high in product content, can reach 99.8% (by an HPLC (high performance liquid chromatography) external standard method), is snow white in color, is needle-shaped, and is not easy to agglomerate when stored. 2. The purification method has simple process and universal and simple equipment, has low requirement on the semi-finished product rectified in the previous procedure, does not need repeated rectification, thereby saving energy and improving the productivity of the rectification section.

Detailed Description

Example 1:

(1) adding 120Kg of crude o-methylbenzoic acid (85% of front fraction content of a rectification slice is yellow and has mucus) into a reaction kettle, adding 600Kg of water, adding 1: 5 (weight ratio) of o-methylbenzoic acid to solution water, adding alkali NaOH while stirring, heating while adding alkali, heating to 80 ℃ to control pH to be 6.5 to prepare a solution A, putting the solution A into a liquid-liquid separator while hot, cooling to normal temperature, adding 144Kg of toluene, stirring vigorously for 1h, and standing. Toluene: solution a 1: 5 (weight ratio).

(2) Standing for 1h, separating the lower layer solution A, adding into a reaction kettle (recovering the upper layer toluene solution B), heating to 80 deg.C, adding 2.4Kg of activated carbon, boiling the activated carbon and solution A at a ratio of 1: 300 for 15min, cooling, and filtering.

(3) Adding the filtered solution A into a reaction kettle, adding hydrochloric acid while stirring, controlling the pH to be 2, heating the hydrochloric acid to 85 ℃, stirring and cooling to normal temperature, performing solid-liquid separation, discharging after wastewater treatment, and drying needle-like white o-methylbenzoic acid crystals to obtain a high-purity product with the content of 99.6% (HPLC external standard method).

Example 2:

(1) adding 120Kg of crude o-methylbenzoic acid (white and non-sticky liquid with the front fraction content of rectification slicing of 95%) into a reaction kettle, adding 840Kg of water, adding 1: 7 (weight ratio) of o-methylbenzoic acid to solvent water, adding alkali KOH, heating while stirring, adding alkali, heating to 90 ℃ to control pH to be 7, preparing a solution A, putting the solution A into a liquid-liquid separator while hot, cooling to normal temperature, adding 120Kg of dimethylbenzene, stirring vigorously for 1h, and standing. Xylene to solution a was 1 to 8 (weight ratio).

(2) Standing for 1h, separating the lower layer solution A, adding into a reaction kettle (recovering the upper layer xylene solution B), heating to 90 deg.C, adding 2.4Kg of activated carbon, boiling for 20min, cooling, and filtering.

(3) Adding the filtered solution A into a post-reaction kettle, adding the prepared dilute sulfuric acid while stirring, controlling the pH to be 4, heating to 90 ℃, stirring and cooling to normal temperature, performing solid-liquid separation, discharging after wastewater treatment, and drying needle-like white o-methylbenzoic acid crystals to obtain a high-purity product with the content of 99.9% (HPLC external standard method).

Example 3:

(1) adding 120Kg of crude o-methylbenzoic acid (81% of the front fraction content of the rectification slices is yellow and black sticky matter) into a reaction kettle, adding 1200Kg of water, adding 1: 10 (weight ratio) of o-methylbenzoic acid to solvent water, adding sodium carbonate, stirring, heating, adding alkali, heating to 100 ℃ to control pH to be 8, preparing a solution A, putting the solution A into a liquid-liquid separator while hot, cooling to normal temperature, adding 95Kg of benzene, stirring vigorously for 1h, and standing. Benzene: solution a was 1: 15 (weight ratio).

(2) Standing for 1h, separating the lower layer solution A, adding into a reaction kettle (recovering the upper layer benzene solution B), heating to 70 deg.C, adding 2.2Kg of activated carbon, boiling the solution A at a ratio of 1: 600 for 10min, cooling, and filtering.

(3) Adding the filtered solution A into a reaction kettle, adding the prepared dilute nitric acid while stirring, controlling the pH to be 5, heating the nitric acid to 100 ℃ after adding the nitric acid, stirring and cooling to normal temperature, carrying out solid-liquid separation, discharging after treating wastewater, and drying needle-like white o-methylbenzoic acid crystals to obtain a high-purity product with the content of 99.4% (HPLC external standard method).

Claims

1. A method for purifying high-content o-methylbenzoic acid is characterized by comprising the following steps:

(1) adding the crude o-methylbenzoic acid into solution water, adding alkali, heating to 80-105 ℃ to promote reaction, and controlling the pH to be 6-8 to ensure that the o-methylbenzoic acid is changed into o-methylbenzoate which is completely dissolved in the solvent water (referred to as solution A for short);

(2) adding the hot solution A into a liquid-liquid separator, cooling to normal temperature, adding an extracting agent to extract liquid impurities (solution B for short) which are insoluble in the solution A, standing, and carrying out liquid-liquid separation on the solution A, B according to different densities;

(3) adding the separated solution A into a reaction kettle, heating to 70-90 ℃, adding activated carbon for decolorization, heating to boil for 15-20 min, cooling, filtering to remove impurities insoluble in the solution A, adding acid into the solution A to control the pH value to be 1-6, separating out the o-methylbenzoic acid powder in the solution, adding thermal recrystallization, carrying out solid-liquid separation, and drying the solid crystal to obtain a high-content o-methylbenzoic acid finished product.

2. The method for purifying high-content o-methylbenzoic acid according to claim 1, which is characterized in that: the weight ratio of the o-methylbenzoic acid to the solvent water is 1: 5-10.

3. The method for purifying high-content o-methylbenzoic acid according to claim 1, which is characterized in that: the weight ratio of the extracting agent to the solution A is 1: 5-15.

4. The method for purifying high-content o-methylbenzoic acid according to claim 1, which is characterized in that: the weight ratio of the activated carbon to the solution A is 1: 300-600.

5. The method for purifying high-content o-methylbenzoic acid according to claim 1, which is characterized in that: adding the crude o-methylbenzoic acid into an alkali solution for reaction, wherein the alkali can be one of inorganic bases such as sodium hydroxide or potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate.

6. The method for purifying high-content o-methylbenzoic acid according to claim 1, which is characterized in that: extracting the liquid impurities insoluble in alkaline or neutral solution water with an extractant which is an organic solvent having a density below 0.9 or above 1.1, a boiling point below 150 ℃, insoluble in water and miscible with most solvents.

7. The method for purifying high-content o-methylbenzoic acid according to claim 1 or 6, which is characterized in that: the extractant can be one of benzene, xylene, o-xylene, diethyl ether, etc.

8. The method for purifying high-content o-methylbenzoic acid according to claim 1, which is characterized in that: adding acid into the o-methylbenzoate solution for reaction, wherein the acid can be one of inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid.