Fractional Utilization Emission Reduction System of Water-rich Solvent for Preparation of Terephthalic Acid

Abstract

The invention discloses a water-rich solvent graded utilization emission reduction system for preparing terephthalic acid, which includes multiple units such as oxidation reaction, rectification and dehydration, oxidation and refining filtration, solvent stripping, and multi-effect distillation. Through the optimized allocation of materials, the use of water-rich solvents with different grades of acetic acid concentrations in grades can greatly reduce the amount of fresh water and reduce the organic matter content in the discharge liquid under the premise of ensuring product quality and effective use of reaction heat. The technical key lies in: (1) The dehydration unit is equipped with a three-stage rectification tower, and the water-rich solvent produced by each unit in the oxidation and refining process is refluxed into the rectification tower at each level according to the concentration matching rules, and the water-rich solvent obtained by rectification is in accordance with the concentration requirements of different acetic acid They are respectively used for oxidation filter washing, refining filter washing, exhaust gas spraying, etc.; (2) Use the low-pressure steam produced by the system to perform multi-effect distillation on the discharge liquid, fully recover the acetic acid in the discharge liquid, and reduce the consumption of acetic acid in the system.

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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