General Characteristics of PE Production Processes

Some general aspects of technical PE production should be discussed before entering the detailed discussion of the individual processes. 

The heat of polymerization of ethylene is 93.6kJ mol (3.34 kj g ). As the specific heat capacity of ethylene is 2.08 J °C g , the temperature rise in the gas phase is 16 °C per 1% conversion (ATadiabatic = 1600°C). If the temperature in the reactor exceeds 300 °C, ethene decomposition to carbon, hydrogen, and methane starts. This decomposition is even more exothermic = — 120kJ mol ) and is very 

Eor all these reasons heat removal and reliable temperature control are key factors in all technical ethylene polymerization processes to ensure an economical and safe process. The different processes may chose different ways to limit or remove the reaction heat (e.g., by limited conversion per reactor pass, cooling of unreacted monomer, large surface area for heat exchange) in all concepts heat management is a key aspect of the reactor design. 

Ethylene polymerization is very demanding with respect to the required ethylene quality. The detrimental effects of the various impurities that may be found in technical ethene qualities can be grouped into four main categories  

1) Inert impurities (CH4, C2H6, N2) These substances do not react and do not interact with the catalyst. However, in the efficient recycling systems of a technical PE plant these inerts would accumulate and dilute the process stream. Such dilution would lead to reduced reaction rates and to a less effective usage of the reactor volume. 

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