对二甲苯的发展现状分析及其对环境的影响.ppt

Analysis and influence of paraxylene on living environment 认识PX 对发展的建议 NI MU 需求与矛盾 关于PX Start from here... About p-Xylene p-Xylene is an aromatic hydrocarbon based on benzene with two methyl substituents with the chemical formula C8H10 or C6H4(CH3)2. The “p” stands for para, identifying the location of the methyl groups as across from one another. It is an isomer of xylene. Other isomers include o-xylene and m-xylene. The boiling point of p-xylene is 138.35 °C (281 °F) and the melting point is 13.2 °C (56 °F).[1] p-Xylene is used on a large scale for the manufacture of terephthalic acid for polyester. Its polymer is known as parylene. p-Xylene is produced by catalytic reforming of petroleum naphtha as part of the BTX aromatics (benzene, toluene and the xylene isomers) extracted from the catalytic reformate. The p-xylene is then separated out in a series of distillation, adsorption or crystallization and reaction processes from the m-xylene, o-xylene and ethylbenzene. Its melting point is the highest among this series of isomers, but simple crystallization does not allow easy purification due to the formation of eutectic mixtures.It is also highly flammable. Technology development and process improvement Paraxylene is currently manufactured by crystallization and adsorption processes. The Pascagoula plant uses the patented hybrid adsorption/crystallization technology to produce paraxylene. This process is characterized by the use of adsorption technology to produce a medium-purity paraxylene feedstock stream that goes into a low-temperature crystallization plant to produce crystals. These crystals are centrifuged and melted to produce high purity paraxylene. Paraxylene is primarily used as a basic raw material in the manufacture of terephthalic acid (TPA), purified terephthalic acid (PTA) and dimethyl-terephthalate (DMT). TPA, PTA and DMT are used to manufacture polyethylene terephthalate (PET) saturated polyester polymers. Polyesters are used to produce fibers and