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Extraction method for reducing emission of chemical oxygen demand (COD) in pure terephthalic acid (PTA) wastewater

An extraction method and wastewater technology, applied in the direction of extraction water/sewage treatment, natural water treatment, chemical instruments and methods, etc., can solve the problems of hazards, reverse osmosis membrane swelling side effects affecting membrane life, PX removal is rarely mentioned, etc. To achieve the effect of COD emission reduction

Active Publication Date: 2015-03-11
浙江化安安全技术研究院有限公司
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Problems solved by technology

After the wastewater is extracted with PX, about 100ppm of PX will remain in the wastewater. If these PX are not removed, they will have a strong swelling side effect on the reverse osmosis membrane and affect the life of the membrane, and these PX will affect the bacteria in the subsequent biochemical sewage station. There are also hazards, but the removal of these residual PX is rarely mentioned in the literature

Method used

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  • Extraction method for reducing emission of chemical oxygen demand (COD) in pure terephthalic acid (PTA) wastewater

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0017] This implementation example includes the following two steps:

[0018] In the first step, the extraction agent n-propyl acetate and PTA waste water are sent to the extraction tower at a mass ratio of 1:4, the waste water flow rate is 2.0t / h, the PTA waste water is added from the bottom, and the extractant is added from the top, and the extraction tower is a packed tower , the efficiency is equivalent to 3-4 theoretical equilibrium stages, the operating temperature of the tower is 38-45°C, and the oil phase from the top of the extraction tower is sent to the PTA dehydration tower;

[0019] In the second step, the water phase discharged from the top of the extraction tower enters from the top of the stripping tower, nitrogen gas is introduced into the bottom of the stripping tower, and the mass ratio of nitrogen to water is 1:16, and the water discharged from the bottom of the stripping tower goes to the sewage treatment station. The gas is sent to the PTA dehydration tow...

Embodiment 2

[0024] With the same raw material in example 1, carry out experiment in the similar mode in example 1, just the extraction agent of the 1st step changes n-butyl acetate into, the 2nd step stripping tower air inlet and the mass ratio of influent change into 1 :20. As a result, the COD of PTA wastewater was reduced from 3050mg / L to 901mg / L, a reduction of 70%; after air stripping, the residual extractant in water was reduced from 6000mg / kg to 13mg / kg.

Embodiment 3

[0026] With the same raw material in example 1, carry out experiment in the similar mode in example 1, just the extraction agent of the 1st step changes isobutyl acetate into, and the mass ratio of the 2nd step air stripper air inlet and influent is changed into 1 :20. As a result, the COD of PTA wastewater was reduced from 3134mg / L to 992mg / L, a reduction of 68%; after air stripping, the residual extractant in water was reduced from 6470mg / kg to 40mg / kg.

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Abstract

The invention discloses an extraction method for reducing emission of chemical oxygen demand (COD) in pure terephthalic acid (PTA) wastewater. The method includes that a solvent is firstly used for extracting and removing a large amount of organic carboxylic acid of benzoic acid, p-toluic acid, p-carboxyl benzyl alcohol, p-carboxybenzaldehyde and terephthalic acid, and then a gas stripping method is used to remove a residual extracting agent in the wastewater so that COD concentration in the wastewater is greatly reduced; simultaneously, organic carboxylic acid which is extracted into an extracting agent phase returns to a PTA device with the extracting agent, and the p-toluic acid, the p-carboxyl benzyl alcohol, the p-carboxybenzaldehyde and the terephthalic acid in the organic carboxylic acid are finally converted into PTA products through the PTA device so that a large quantity of useful organic substances in the wastewater are recycled, and economic benefits are increased; and outlet gases of a gas stripping tower, which carry the extracting agent, are returned to the PTA device so that the extracting agent is recycled, and consumption of the extracting agent is low. The extraction method is high in efficiency, low in consumption and capable of reducing emission of COD, reducing loads of sewage treatment stations and partially achieving resource utilization of the wastewater.

Description

technical field [0001] The invention relates to a method for reducing the COD discharge of PTA wastewater, which is from the wastewater discharged in the production process of terephthalic acid. Background technique [0002] Purified Terephthalic Acid (PTA) is the main raw material for the production of polyester fibers and resins. Currently, it is mainly produced by air oxidation of p-Xylene (PX). During the production of PTA, a large amount of wastewater is discharged, and 2 to 3 tons of wastewater are discharged for every ton of PTA produced. PTA wastewater is an acidic wastewater with a COD concentration of 2500-8000 mg / L. The wastewater contains acetic acid, benzoic acid, p-toluic acid, p-carboxybenzyl alcohol, p-carboxybenzaldehyde, terephthalic acid, isophthalic acid, Organic acids such as phthalic acid, trimellitic acid, fluorenone dicarboxylic acid, etc. PTA wastewater is currently generally treated by anaerobic + aerobic biochemical methods. Obviously, reducing ...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C02F9/04C07C51/265C07C63/26C02F1/26C02F1/24C02F103/36
Inventor 谢刚徐海波王献忠
Owner 浙江化安安全技术研究院有限公司
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