Petroleum xylene and coal tar xylene both contain a considerable amount of p-xylene. Because the boiling point difference between p-xylene and m-xylene is only 0.75℃, distillation separation cannot be used. At present, the method developed at home and abroad is low temperature crystallization separation. Adsorption separation method and complex separation method. Low temperature crystallization separation method uses the melting point difference of xylene isomers for separation. The main method is low-temperature fractional crystallization with mature technology, which is dominant in xylene separation. However, this method has huge equipment, limited by the melting point of p-xylene, and the recovery rate is low, only 60-70%. Adsorption separation is a new method developed in 1970s. Compared with cryogenic crystallization, this method has the advantages of low investment, low total production cost, high yield and purity of p-xylene, and may replace cryogenic crystallization. ?
The raw material toluene undergoes transalkylation reaction in transalkylation reactor to produce xylene and benzene. In the isomerization reactor, mixed xylene isomerizes part of meta-xylene to generate para-xylene. After the light fraction is removed in the stabilizer, the reactant is mixed with xylene from the transalkylation section and enters the C9 fraction removal tower, and the mixed xylene with high p-xylene content is obtained at the top of the tower, and the bottom of the tower is above C9. The mixed xylene obtained from the top of the stabilizer enters the adsorption and separation section, and the p-xylene is adsorbed by the non-molecular sieve solid adsorbent, and desorbed to obtain the p-xylene product with a purity of 99.9%, and m-xylene is also a by-product. In addition, there is hydrogen fluoride-boron trifluoride extraction method.
Reference link: p-xylene _ Baidu Encyclopedia
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