The Calculation For The Production Process Of Para-xylene With An Annual Output Of 0.5 Million Tons

Paraxylene is one of the basic organic materials for the petrochemical industry, which has been widely used in chemical industry, including synthetic fabrics, synthetic resins, pesticides, plastics, medicine and other fields. Paraxylene is mainly used to produce PTA or DMT. In recent years, with the rapid development of polyester industry, consumpion of PX has soared, which fulled by the increased consumption of PTA. PX import dependecce rate has been staying at a high level. The growth rate of domestic supply can not meet with demands. With the rapid expansion of PX production capacity in china in the next few years, to advance the clean and highly effecitive synthetic industry development in PX industry will be an important subject of the sustainable development for polyester industry in the future.The paper compelted process design from practical purposes. By comparing various schemes, we finally select an environmental, economical and highly efficient process routes. We have completed the unit process simulation all-process simulation, material balance calculation and energy balance calculation by Aspen Plus software. The main results are as follows:(1) Raw materials, as the starting point of the process, the rational selection of which remains to be the key factor to reduce waste by the higly effective use of resources. The paper determines the raw material and product program by consulting the literature data. This article illustrates a schme to produce para xylene by using excess capacity of methyl alcohol and BTX aromatics as raw material, with an annual output of 0.5 million tons, and benzene and o-xylene as by-product.Through the comprehensive comparison of process scheme, the paper adpot coproduction technology of disproportionation and transalkylation-alkylate-isomerization to produce PX. The technological process can help optimize material to realize product variety and cleanliness, which include four units, BTX aromaticsseparation, Toluene disproportionation and alkylation, Toluene alkylation with methanol, and Isomerization. The technological process realizes circulating utilization of methanol, hydrogen and BTX aromatics.(2) Based on the mass balance calculation, we determine the raw material consumption, the yields of main products and by-producs and quality index. We determine such index as the circulating volume and loss rate of hydrogen, methanol and toluene. We determine the equipment of logistics input or output and composition of equipment. We determine the positions, quantity and composition of the wastewater and emission discharge so as to put forward suggestions to treat wastes. Material balance provides a basis for energy balance.Material consumption:BTX aromatics,795960 tons/year, Methyl alcohol,150500 tons/year, Hydrogen,720.28 tons/year.The main/by-product actual output:Para xylene,505300 tons/year,99.99%(wt%); Benzene,155300 tons/year, above 91%(wt%); O-xylene,153700 tons/year,99.90%(wt%); Wastewater,82000 tons/yaer. Toxic emission; Components include Ethylene, Dimethylmethane, Ethane, Methyl alcohol, Eethane, a little Xylene. The toxic emission can meet with environmeantal demands.(3) Distribution of flow energy in the column, reactor, gas-liquid separation, and compressor is calculated by means of energy balance. We calculated the heat duty of equipment for the purpose of equipment selection and size determination in the future.Above all we have completed the basic work for processing system design and then we will complete drawing process flow diagram and determing the size of equipment by collecting data of material balance and energy balance, which provides basic data for later design.