Method for preparing p-xylene by separating and crystallizing mixed xylenes

Abstract

The invention relates to a method for preparing p-xylene by separating and crystallizing mixed xylenes, and mainly solves the problem of large energy consumption in a crystal separating process in the prior art. To well solve the problem, the invention adopts the following technical scheme of preparing the p-xylene by separating and crystallizing the mixed xylenes that: p-xylene crystal I and crystallization filtered stock I are obtained by crystallizing mixed xylenes in a primary crystallizer and separating crystal mush; the crystal I is melted by heat exchange, is partially returned to a first solid-liquid separator, and partially enters a product tank; the crystallization filtered stock I is separated into two streams, one stream returns to the crystallizer, and the other stream entersa pulping tank; one part of crystal mush in the primary crystallizer is cleared so as to obtain clear crystallization stock I which enters the pulping tank; p-xylene crystal II and crystallization filtered stock II are obtained by separating the crystal mush in a secondary crystallizer by a second solid-liquid separator; the crystal II enters the pulping tank, and separated after mixed heat exchange so as to obtain p-xylene crystal III and crystallization filtered stock III; the crystal III is melted by heat exchange, is partially returned to a third solid-liquid separator to be used as cleaning solution, and partially enters the product tank; the crystallization filtered stock II is separated into two streams, one stream returns to the secondary crystallizer, and the other stream enters the pulping tank; the crystallization filtered stock II and the mixed xylenes are subject to heat exchange and enter a stock tank; and the clear crystallization stock II and the mixed xylenes are subjected to heat exchange and enter the stock tank. The method can be used in p-xylene industrial production.

Description

technical field [0001] The invention relates to a method for separating p-xylene from mixed xylene crystallization. Background technique [0002] P-xylene 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 US 6565653 discloses a crystallization method for preparing high-purity p-xylene. The raw material contains at least 50% or 60% p-xylene. When the method uses the crystallization method to produce p-xylene, a part of p-xylene is obtained through single-stage crystallization , ano...

AI Technical Summary

Problems solved by technology

[0004] The technical problem to be solved by the present invention is the problem of large energy consumption in the existing method for separating p-xylene by crystallization of mixed xylenes, and a new method for separating p-xylene by crystallization of mixed xylenes is provided

Images