High-temperature averaging process

The high-temperature solution process is state-of-the-art for the production of ethylene homopolymers as well as ethylene/1-olefin copolymers with a wide range of average molecular mass and copolymer composition [15]. This process is performed in a CSTR or in a cascade of two reactors, like the low-temperature process. Only the downstream equipment is different. The diluent is an aliphatic hydrocarbon such as cyclohexane, n-hexane, or a Cg-Cio alkane fraction. Homogeneous catalyst and co-catalyst are fed into the polymerization reactor mixed with solvent. Ethylene, hydrogen to regulate average molecular mass, and the comonomer are injected either as a gas or as a liquid. Temperature can be con-... 

For commercial purposes, the high temperature polymerization processes appear to be favoured. In one process, polymerization is conducted in liquid sulphur dioxide. The polymer separates and gravitates to the base of the reactor, from which it is continuously removed. The material is then extruded and chopped. The average molecular weight (Mn) of commercial polymer is 250 000-350 000. 

The first large-scale commercial oxychlorination process for vinyl chloride was put on-stream in 1958 by The Dow Chemical Company. This plant, employing a fixed-tube reactor containing a catalyst of cupric chloride on an active carrier, produced 1,2-dichloroethane from ethylene. The high temperatures involved in the reaction were moderated by a suitable diluent. The average heat output from the reaction is 116 kJ/mol (50,000 Btu/lb mol). 

The importance of the first three of these factors has already been discussed. The temperature factor would include the cost of insulation plus the increase in metal thickness necessary to counteract the poorer structural properties of metals at high temperatures. Zevnik and Buchanan17 have developed curves to obtain the average cost of a unit operation for a given fluid process. They base their method on the production capacity and the calculation of a complexify factor. The complexity factor is based on the maximum temperature (or minimum temperature if the process is a cryogenic one), the maximum pressure (or minimum pressure for vacuum systems) and the material of construction. It is calculated from Equation 2 ... 

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