Ethylene gasification

Two examples are an ethylene plant and a coal gasification plant. 

The technology of gasification is under active development in both equipment and process design to reduce capital costs, and in the chemistry of the process to improve yields and obtain more favorable gas ratios. The latter includes the use of catalysts to enhance the process and to promote the formation of specific products, such as methane or ethylene for increased thermal efficiency or for feedstocks for chemical synthesis. 

One can envisage the future production of liquid fuels and commodity chemicals in a biorefinery Biomass is first subjected to extraction to remove waxes and essential oils. Various options are possible for conversion of the remaining biofeedstock, which consists primarily of lignocellulose. It can be converted to synthesis gas (CO + H2) by gasification, for example, and subsequently to methanol. Alternatively, it can be subjected to hydrothermal upgrading (HTU), affording liquid biofuels from which known transport fuels and bulk chemicals can be produced. An appealing option is bioconversion to ethanol by fermentation. The ethanol can be used directly as a liquid fuel and/or converted to ethylene as a base chemical. Such a hiorefinery is depicted in Fig. 8.1. 

When ethane is cracked to ethylene and hydrogen, there is a volume expansion and thus, by the Le Chatelier s Principle, the pyrolysis is favoured by lowering the pressure. In practice this is achieved by adding large volumes of steam so as to lower the partial pressure of the hydrocarbons. Steam addition also has the advantage of removing coke by steam gasification ... 

Derivation (1) Air oxidation of ethylene followed by hydration of the ethylene oxide formed (2) ace-toxylation (3) from carbon monoxide and hydrogen (synthesis gas) from coal gasification (4) Oxirane process. 

Gasification of a carbonaceous deposit formed on a radiantly heated ethylene steam cracker pyrolysis tube, in water vapour, at 721-1056°C was chemically controlled. Oxidation rates were linear between 10-85% burn off and increased proportionally with water vapour partial pressure (38-362 mm Hg). The activation energy and pre-exponential factor were 57 Real mole-l and 3.6 x 10 mg cm min" respectively. Gasification was catalysed by inorganic impurities entrained in the deposit and was promoted by hydrogen and butane. 

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