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

A technology of mixing xylene and p-xylene, which is applied in crystallization purification/separation, chemical instruments and methods, purification/separation of hydrocarbons, etc., can solve the problems of high energy consumption, and achieve the reduction of refrigeration energy consumption, energy consumption reduction, The effect of good technical effects

CN101941883AActive Publication Date: 2011-01-12CHINA PETROLEUM & CHEM CORP +1
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Patent Information

Authority / Receiving Office
CN · China
Patent Type
Applications(China)
Current Assignee / Owner
Publication Date
2011-01-12

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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.
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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...

Examples

Embodiment 1

[0015] The method for separating p-xylene from mixed xylenes described in the present invention.

[0016] Such as figure 1 Described, the mixed xylene a from raw material tank 1 contains 90% p-xylene, and temperature is 25 ℃, and flow rate is 1116kg / h, after cooling through heat exchanger 2 and heat exchanger 3, in first stage crystallizer 4 The crystallization is carried out in the crystallizer, and the operating temperature is 4°C. The magma b in the crystallizer 4 is separated from the solid and liquid by the first solid-liquid separator 5 to obtain high-purity p-xylene crystals c and crystallization and filtration mother liquor f. Paraxylene crystal c is melted in heat exchanger 6, and the paraxylene of 20% by weight is washed as washing solution e to the crystal in the first solid-liquid separator 5, and the paraxylene of 80% by weight is used as paraxylene product d enters the product tank 7, and the crystallization and filtration mother liquor f is divided into two str...

Embodiment 2

[0018]Existing method for separating p-xylene from mixed xylenes

[0019] According to the operating condition of embodiment 1, adopt as figure 2 The result of the method for separating p-xylene by mixed xylene crystallization is listed in Table 1.

[0020] Can find out by comparative example, the method for separating p-xylene by mixed xylene of the present invention has effectively reduced the energy consumption of crystallization separation process, and the cooling capacity of recovery comes from the crystallization clear mother liquor and the crystallization filtration mother liquor of the second stage crystallizer, Among them, the crystal clear mother liquor does not need solid-liquid separation, so the energy consumption of the solid-liquid separator is reduced. The overflow of the crystal clear mother liquor also prolongs the residence time of p-xylene crystals in the crystallizer, and promotes the growth of p-xylene crystals. , which is beneficial to improve the puri...