Acetylene Hydrogenation Process Design

Two different process configurations are now used to remove acetylene from ethylene. The choice of these depends on how the cracked hydrocarbon gases are separated following desulfurization and drying  

Both procedures work well. The choice between them is determined by the process supplied by the contracting compaity. However, the two types of palla-diutn/alumina catalyst used are very different and are not interchangeable. 

Operating problems with palladium eatalysts have been associated with increasingly high volumes of acetylene in the process gas, whieh is a result of increased steam cracking severity to improve ethylene yields. Both front-end and tail-end reactors now include several adiabatic beds, with interbed cooling, to control reaction and remove the excessive heat evolved as acetylene is hydrogenated. 

Significant hydrogenation of ethylene can occm- if the gas is not efficiently cooled or the catalyst is not very selective. This is referred to as ethylene loss. Catalyst selectivity is also important to minimize the formation of green oil polymers, which wastes ethylene and causes operating problems. Some process designs have included tube-cooled adiabatic catalyst reactors to cope with high acetylene coneentrations, but they have not been very popular. 

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C4 cuts from catalytic cracking contain little butadiene and acetylenic compounds. Hence they can be used directly for isobutene separation processes, but require prior hydrogenation to obtain 1-butene. By contrast, steam cracked effluents must systematically undergo hydrogenation pretreatmcnL This is necessary to eliminate the compounds liable to cause highly exothermic side-polymerizations, and to form gums that disturb the operation of the catalyst systems, solvents and adsorbents used in steps designed to produce the different C4 olefins. 

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