阅读说明：本技术 一种基于催化反应精馏耦合技术的酯化-水解法提纯乳酸的工艺流程 (Esterification-hydrolysis method lactic acid purification process flow based on catalytic reaction rectification coupling technology ) 是由 曾作祥 王莹 徐菊美 孙莉 薛为岚 李莎婷 于 2020-06-29 设计创作，主要内容包括：本发明公开了一种基于催化反应精馏耦合技术的酯化-水解法提纯乳酸的工艺流程。该方法首先让低浓度乳酸粗产品与异戊醇在酯化反应精馏塔中发生逆流接触,进行反应精馏得到乳酸异戊酯。富含乳酸异戊酯的塔底产品被送到提纯塔,得到高纯度乳酸异戊酯。高纯度乳酸异戊酯在水解反应精馏塔中进行水解,在塔底得到高纯度乳酸并将富含异戊醇的塔顶产品送入回收塔进行循环利用。本发明具有分离效率高、运行成本低选择性好等优点。(The invention discloses a technological process for purifying lactic acid by an esterification-hydrolysis method based on a catalytic reaction rectification coupling technology. The method comprises the steps of firstly enabling a low-concentration lactic acid crude product to be in countercurrent contact with isoamyl alcohol in an esterification rectifying tower, and carrying out reactive rectification to obtain isoamyl lactate. The tower bottom product rich in isoamyl lactate is sent to a purification tower to obtain high-purity isoamyl lactate. Hydrolyzing the high-purity isoamyl lactate in a hydrolysis reaction rectifying tower, obtaining high-purity lactic acid at the bottom of the tower, and sending the tower top product rich in isoamyl alcohol into a recovery tower for recycling. The invention has the advantages of high separation efficiency, low operation cost, good selectivity and the like.)

1. A technological process for purifying lactic acid by an esterification-hydrolysis method based on a catalytic reaction rectification coupling technology is characterized in that: the method adopts a catalytic reaction rectification technology, comprises an esterification reaction rectifying tower, an isoamyl lactate purifying tower, a hydrolysis reaction rectifying tower, a dehydrating tower and a solvent recovery tower, takes silica gel loaded sodium bisulfate and ion exchange resin as esterification and hydrolysis reaction catalysts respectively, and comprises the following steps: (1) the low-concentration lactic acid crude product and isoamylol are in countercurrent contact in an esterification rectifying tower filled with silica gel supported sodium bisulfate catalyst to generate esterification reaction, and the tower bottom product rich in isoamyl lactate is sent into a purifying tower; (2) obtaining high-purity isoamyl lactate at the top of the purification tower and feeding the high-purity isoamyl lactate into a hydrolysis rectifying tower; (3) hydrolyzing isoamyl lactate under the catalysis of ion exchange resin to obtain a high-purity lactic acid product at the bottom of the tower, and feeding the product at the top of the tower into a dehydration tower; (4) sending the mixture of isoamyl alcohol and isoamyl lactate obtained from the bottom of the dehydration tower into a solvent purification tower, and sending the isoamyl alcohol obtained from the top of the purification tower into an esterification rectifying tower for recycling; the catalyst loading was 50% of the tray liquid hold-up.

2. The method according to claim 1, wherein the process conditions of the esterification rectifying tower are as follows: 0.3-1.0 bar, 2-8 reaction section theoretical plates, 2-4 rectification section theoretical plates, 3-6 stripping section theoretical plates, 3-5 th theoretical plates for feeding the lactic acid crude product, 4-12 th theoretical plates for feeding the isoamyl alcohol, and the molar ratio of alcohol acid feeding is (1-2): 1.

3. the method as claimed in claim 1, wherein the process conditions of the hydrolysis reaction rectifying tower are as follows: under normal pressure, 2-26 theoretical plates of a reaction section, 2-4 theoretical plates of a rectification section, 3-6 theoretical plates of a stripping section, 3-5 theoretical plates of isoamyl lactate feeding position, 4-30 theoretical plates of water feeding position and (2-15): 1 molar ratio of water ester feeding.

4. The method according to claim 1, wherein the method is applied to a crude lactic acid product with a lactic acid mass fraction of 25-45%.

Technical Field

The invention relates to a technological process for purifying lactic acid by an esterification-hydrolysis method based on a catalytic reaction rectification coupling technology, belongs to a chemical separation process, and is suitable for purifying lactic acid in a low-concentration lactic acid crude product.

Background

Lactic acid, also known as a-hydroxypropionic acid, is a naturally occurring organic carboxylic acid, and has wide applications in the fields of food, medicine, chemical industry, and the like, and particularly has been a hotspot of research in recent years as a raw material for synthesizing biodegradable plastics, and has a good development and utilization prospect.

The methods for industrially producing lactic acid mainly include fermentation, chemical synthesis and enzymatic method. The fermentation method is a main production mode of lactic acid due to the advantages of cheap and easily available raw materials, good safety, high economic benefit and the like. The cost of separation and purification of lactic acid in fermentation liquor is relatively high, and the conventional methods comprise crystallization, solvent extraction, adsorption, ion exchange, membrane separation, reactive distillation and the like. For example, CN 109206310A proposes a method for extracting D-lactic acid from a D-calcium lactate fermentation broth, but the method adopts concentrated sulfuric acid for acidolysis, and has the problems of environmental pollution, equipment corrosion and the like.

The invention provides a method for purifying lactic acid by adopting a catalytic reaction rectification technology, which comprises the steps of firstly catalytically synthesizing lactate from a low-concentration lactic acid crude product and alcohol in an esterification reaction rectification tower, separating the lactate from impurity acid or an esterified product of the impurity acid by utilizing the characteristic of relatively high volatility of the esterified product, and then carrying out catalytic hydrolysis on the lactate in a hydrolysis reaction rectification tower to obtain high-purity lactic acid.

Disclosure of Invention

The invention adopts esterification hydrolysis reaction rectification coupling technology to purify lactic acid, and mainly comprises the following steps:

(1) rectification process of esterification reaction

In an esterification rectifying tower, a crude lactic acid product is added from the upper part of a reaction section, isoamylol is added from the lower part of the reaction section, a selected catalyst is a silica gel supported sodium bisulfate catalyst, the two phases are in countercurrent contact in the rectifying tower, a water phase containing a small amount of impurities is obtained at the tower top, and an oil phase containing a large amount of isoamyl lactate, a small amount of impurity acid, water and isoamylol is obtained at the tower bottom. And (3) feeding the product at the bottom of the tower into a purification tower, obtaining impurity acid at the bottom of the purification tower, and obtaining high-purity isoamyl lactate at the top of the tower. Sending the high-purity isoamyl lactate into a hydrolysis reaction rectifying tower.

(2) Hydrolysis reaction rectification process

Adding the high-purity isoamyl lactate obtained in the step (1) from the upper part of the reaction section of the hydrolysis reaction rectifying tower, adding water from the lower part of the reaction section, obtaining the high-purity lactic acid at the bottom of the tower by adopting an ion exchange resin catalyst, and sequentially feeding the tower top product into a dehydrating tower and a solvent recovery tower to recycle isoamylol.

The mass fraction of lactic acid in the crude product of lactic acid is 25-45%.

The technological conditions of the esterification rectifying tower are as follows: 0.3-1.0 bar, 2-8 reaction section theoretical plates, 2-4 rectification section theoretical plates, 3-6 stripping section theoretical plates, 3-5 th theoretical plates for feeding the lactic acid crude product, 4-12 th theoretical plates for feeding the isoamyl alcohol, and the molar ratio of alcohol acid feeding is (1-2): 1.

the technological conditions of the hydrolysis reaction rectifying tower are as follows: under normal pressure, 2-26 theoretical plates of a reaction section, 2-4 theoretical plates of a rectification section, 3-6 theoretical plates of a stripping section, 3-5 theoretical plates of isoamyl lactate feeding position, 4-30 theoretical plates of water feeding position and (2-15): 1 molar ratio of water ester feeding.

The invention has the advantages that: the process flow of esterification, hydrolysis, rectification and coupling is adopted, and the method has good economic benefit for purifying the low-concentration lactic acid crude product. The solid catalyst is adopted, so that the problem of equipment corrosion caused by using concentrated sulfuric acid is avoided, and the catalyst is easy to recycle.

Drawings

FIG. 1 is a process flow diagram of esterification hydrolysis reaction rectification coupling of lactic acid purification

In the figure, T1 is an esterification rectifying tower, T2 is an isoamyl lactate purifying tower, T3 is a hydrolysis rectifying tower, T4 is a dehydrating tower, and T5 is an isoamyl alcohol recovery tower. The method comprises the following steps of 1, 2, 3, 4 and 5, 6, 7, 8, 13 and 13, wherein the raw solvent is isoamyl alcohol fresh solvent, the raw product is lactic acid, the product is the bottom product containing a large amount of isoamyl lactate, the product is the top product containing a large amount of water, the raw product is high-purity isoamyl lactate, the raw product is impurity acid, the target product is high-purity lactic acid, the raw product is the aqueous solution of isoamyl alcohol containing impurities, the raw product is water, the raw product is the mixture of isoamyl alcohol and isoamyl lactate, the raw product is 12, isoamyl.

Fresh isoamyl alcohol solvent 1, recovered isoamyl alcohol solution 13 and crude lactic acid product 2 enter a T1 tower from the lower part and the upper part of a reaction section respectively to perform catalytic esterification reaction, after rectification and separation of the products, a part of water phase 5 at the tower top enters a tower T2, a product 3 at the tower bottom enters a T2 tower, after rectification and separation, isoamyl lactate 6 with high purity at the tower top enters a tower T3, material flow 5 and material flow 2 are subjected to hydrolysis reaction and rectification in a tower T3, a product 9 at the tower top enters a T4 tower to be dehydrated, a product 11 at the tower bottom enters a T5 tower to perform isoamyl alcohol recovery, and a product 13 at the tower top enters a tower T1 to be recycled. High-purity lactic acid is obtained at the bottom of the T3 tower.

Detailed Description