The Future Role of Hydrogen in Petrochemistry and Energy Supply DGMK Conference October 4-6, 2010, Berlin, Germany

Selective Hydrogenation Processes in Steam Cracking M. Bender, M.-K. Schroeter, M. Hinrichs, P. Makarczyk BASF SE, Ludwigshafen, Germany

Abstract Hydrogen is the key elixir used to trim the quality of olefinic and aromatic product slates from steam crackers. Being co-produced in excess amounts in the thermal cracking process a small part of the hydrogen is consumed in the “cold part” of a steam cracker to selectively hydrogenate unwanted, unsaturated hydrocarbons. The compositions of the various steam cracker product streams are adjusted by these processes to the outlet specifications. This presentation gives an overview over state-of-art selective hydrogenation technologies available from BASF for these processes.

Introduction Today, steam cracking of paraffinic hydrocarbons is a main source for the basic olefinic and aromatic hydrocarbon streams in petrochemistry. These hydrocarbon streams are further processed into mostly petrochemical products. The product spectrum ranges from polymers like polyolefins and polystyrene, to intermediates like ethylene oxide and propylene oxide that are used to produce more complex chemical products further downstream.

Ethylene production is almost exclusively based on steam cracking and for propylene steam cracking is still the predominant source before other available technologies. For the production of heavier C4 and aromatic hydrocarbons, however, the picture turns in favour of refinery processes like fluid-catalytic cracking (FCC) and catalytic reforming, respectively.

Key to economically processing these basic hydrocarbon streams into chemical products is a sufficient purity, mainly being characterized by the absence of multi-unsaturated compounds, such as acetylenes, dienes, or related species. In steam cracking these compounds originate from side reactions typically in the range of a few percent of the main product compounds. They are unwanted in the product streams of steam crackers. Due to their high specific reactivity they would interfere negatively with the main reactions of the (mostly catalytic) downstream chemical processes, for instance the polymerization of an olefin. Also, in significant concentrations they tend to form gums and would thereby limit storability and transportability of the various hydrocarbon slates.

Selective hydrogenation processes elegantly remove these multi-unsaturated impurities by converting them into the corresponding main component of the respective product stream, e.g. turning unwanted acetylene into the desired compound ethylene in the presence of a large amount of the latter. The selectivity challenge in these processes goes well beyond not passing the sweet spot of 100% acetylene conversion into ethylene. The process mustn’t convert any of the already existing ethylene in the matrix either. Similar challenges exist for selective hydrogenation processes for the higher hydrocarbon streams in a steam cracker.

This paper presents BASF’s Selectivity Optimized SELOP® Technologies for Selective Hydrogenation of the various hydrocarbon streams in steam crackers. Catalysts and process technologies are available from BASF offering world-class performance for each of these hydrogenation processes.

DGMK-Tagungsbericht 2010-3, ISBN 978-3-941721-07-4 69