Water-rich solvent classification utilization emission reduction system for preparing terephthalic acid

Abstract

The invention discloses a water-rich solvent classification utilization emission reduction system for preparing terephthalic acid, which comprises a plurality of units, such as oxidation reaction, rectification dehydration, oxidation and purification filtration, solvent stripping, multi-effect distillation and the like. According to the system, through the optimized configuration of materials, water-rich solvents with different levels of acetic acid concentration are classified and utilized, and on the premise of ensuring product quality and effectively utilizing the reaction heat, the use amount of fresh water is greatly reduced and the organic matter content in a discharged liquid is reduced. The key technology lies in that: (1) a dehydration unit is provided with a three-stage rectifying column, the water-rich solvent produced by each unit in the oxidation and refining process is re-circulated to the rectifying columns according to a concentration matching rule, and the water-rich solvents obtained by rectification are respectively used for oxidation filter washing, refining filter washing, exhaust gas spraying and the like as required by different acetic acid concentrations; (2) self-produced low-pressure steam of the system is utilized for multi-effect distillation of the discharged liquid, thereby fully recovering acetic acid in the discharged liquid, and reducing systemacetic acid consumption.

Description

technical field [0001] The invention relates to the technical field of clean production, in particular to an emission reduction system for graded utilization of water-rich solvents used for preparing terephthalic acid. Background technique [0002] Terephthalic acid (Pure Terephthalic Acid, PTA) is the main raw material of chemical fibers and polyester bottle flakes, which is prepared by the liquid-phase air oxidation method of p-xylene (PX), and its process mainly includes the following units: [0003] Step 1: Air oxidation, the oxidation reaction uses a stirred tank or a bubble column reactor. Under the three-way catalytic condition of cobalt, manganese and bromine, the phenylcyclomethyl group of the PX molecule is combined with oxygen to produce terephthalic acid, and a small amount of unreacted PX is transformed into the impurity p-carboxybenzaldehyde (4-CBA). The oxidation reaction is strongly exothermic and the heat of reaction is removed from the reactor by evaporati...

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Problems solved by technology

[0014] In summary, the drawbacks of the existing PTA process that adopts the direct distillation of oxidation reaction tail gas are that the content of acetic acid in the liquid obtained from the distillation is high, resulting in a large loss of acetic acid in the discharge liquid. The existence of non-condensable gases in the tail gas also reduces the separation efficiency of rectification. Therefore, it is urgent to propose a new rectification tower operation scheme and discharge liquid acetic acid recovery technology to solve the above difficult problems

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