Purification method for acetic acid synthesized by low pressure methanol carbonylation

Abstract

This invention relates to a method for purifying methanol carbonyl synthesized acetic acid at low pressure, comprising: flash distill the reaction solution containing catalyst in the flash evaporator to produce the gas-phase crude acetic acid with impurities, produce wet acetic acid with impurities by lightness-removing column distillation, then send the wet acetic acid to the dehydration column for further dehydration and impurities removing, use the current method to further purify the dehydrated and impurities removed acetic acid to be acceptable high-grade product, wherein the gas phase is cooled at the top of the dehydration column and sent to a second distillation decanter, which separates the liquid to be a low-density phase mainly comprising of water and acetic acid and a high-density phase mainly comprising of methyliodide and methyl acetate; the gas phase is cooled at the top of the said lightness-removing column and then sent to the first distillation decanter which separates the liquid to be a low-density phase mainly comprising of water and acetic acid and a high-density phase mainly comprising of methyliodide and methyl acetate, decant the high-density phase produced by the second distillation decanter to the first distillation decanter.This method is characterized of simplified method and purification energy consumption decreasing.

Description

technical field [0001] The present invention relates to a kind of method of low-pressure methanol carbonylation acetic acid, and this acetic acid is prepared by carrying out carbonylation to methanol in the presence of a catalyst containing Group VIII metals, more specifically, the present invention relates to the purification method of preparing high-purity acetic acid, Wherein, in the preparation process of acetic acid generated by carbonylation reaction catalyzed by rhodium, the impurities of methyl acetate and methyl iodide contained in the product are reduced, and the energy consumption required for purifying acetic acid is significantly reduced at the same time. Background technique [0002] Acetic acid is an important chemical intermediate and solvent for chemical reactions. The largest use is vinyl acetate monomer (VAM), which accounts for 40% of its production, and VAM can be used to make protective coatings, adhesives and plastics. The production of purified terep...

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Problems solved by technology

The effect of two aspects makes the content of entering and removing light tower (2) methyl acetate and iodomethane significantly increase, and methyl acetate content is at 5~6% (wt), and iodomethane content is at 35~50% (wt), makes this The concentration of methyl acetate and methyl iodide in the gas phase inside the tower increases, and the methyl acetate and methyl iodide in the fluid flowing back from the top of the tower also increase significantly, resulting in the initial product acetic acid extracted from the light removal tower (2). Although the water content decreases, methyl acetate The amount of methyl iodide and methyl iodide obviously increases, has caused the discharge of dehydration tower (3) and the feed stream containing methyl acetate and methyl iodide to increase, especially methyl acetate and methyl iodide content increase in the tower top reflux, has caused The tower product is polluted by methyl acetate and methyl iodide, so under the premise of changing the catalyst, the process of purifying acetic acid also needs new improvements

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