Multi-stage crystallization method for producing p-xylene

Abstract

The invention relates to a multi-stage crystallization method for producing p-xylene. The problems of high energy consumption, serious scaling of a precooler and difficulty in crystal washing in the prior art are mainly solved. According to the technical scheme, the method comprises the following steps: feeding mixed xylene raw materials into a raw material intermediate tank; causing overflow mother liquor in a crystal slurry tank to flow out of the upper part and enter a primary crystallizer for crystallization, causing concentrated crystal slurry to flow out of the lower part, performing separation to obtain filtered mother liquor and p-xylene crystals by using a solid-liquid separator, causing the filtered mother liquor to enter the primary crystallizer for crystallization, performing separation on the crystal slurry in the primary crystallizer to obtain p-xylene crystals and primary crystallized-filtered mother liquor by using the solid-liquid separator, and heating and melting the p-xylene crystals in a melting tank; dividing the primary crystallized-filtered mother liquor into two jets, performing separation on crystal slurry in a secondary crystallizer to obtain p-xylene crystals and secondary crystallized-filtered mother liquor, and returning the p-xylene crystals into the crystal slurry tank. According to the method, the problems are well solved; the method can be used for p-xylene crystallization production.

Description

technical field [0001] The present invention relates to a multistage crystallization method for producing p-xylene. Background technique [0002] Paraxylene is an important raw material for the polyester industry, mainly used to produce purified terephthalic acid (PTA) or purified dimethyl terephthalate (DMT), and then produce polyester (PET) from PTA and DMT, and separate Mixed xylene is the main production method of p-xylene. Mixed xylenes are mainly composed of p-xylene, m-xylene, o-xylene and ethylbenzene. The difference between the boiling points of each component is small, but the difference in melting point is large. The crystallization method can be used to separate p-xylene. [0003] Patent US5498822 discloses a crystallization method for separating p-xylene. In this method, the raw material of mixed xylene is pre-cooled by a precooler, and then a high-purity p-xylene product is obtained by separating through a single-stage crystallization process. In the actual c...

AI Technical Summary

Problems solved by technology

[0005] The technical problem to be solved by the present invention is the problems of high energy consumption, serious fouling of the precooler and difficult crystal washing in the existing crystallization method for producing p-xylene, and a new multi-stage crystallization method for producing p-xylene is provided method, which has the advantages of low energy consumption, light fouling of the precooler, and easy washing of crystals

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