New processes for the selective production of 1-octene

Linear alpha-olefins, especially 1-hexene and 1-octene, are key components for the production of LLDPE and the demand for 1-hexene and 1-octene increased enormously in recent years. To meet this demand several processes were developed in the last decade to produce 1-hexene and 1-octene selectively. Here we review the new processes for 1-octene production based on homogeneous catalysts. Sasol's coal-based high temperature Fischer-Tropsch technology produces an Anderson-Schulz-Flory distribution of hydrocarbons with high alpha-olefin content and the desired alkenes, including 1-heptene and 1-octene, are separated by distillation. In this case, as in the SHOP process, 1-octene constitutes only a minor part of the total yield. Nowadays other technologies are being applied or considered for on-purpose 1-octene production: hydroformylation of 1-heptene, the telomerization of 1,3-butadiene, and ethene tetramerization. 1-Heptene can be converted in three steps to 1-octene: (1) hydroformylation of 1-heptene to octanal, (2) hydrogenation of octanal to 1-octanol, and (3) dehydration of 1-octanol to 1-octene. This process was commercialized by Sasol. Dow commercialized a process based on butadiene. Telomerization of butadiene with methanol in the presence of a palladium catalyst yields 1-methoxy-2,7-octadiene, which is fully hydrogenated to 1-methoxyoctane in the next step. Subsequent cracking of 1-methoxyoctane gives 1-octene and methanol for recycle. Recently highly active and stable phosphine based systems were reported that show particularly good performance for the industrially attractive feedstock, the C-4 cut of the paraffin cracker. 1-Hexene can be obtained by ethene trimerization by a family of catalysts based mainly on Cr. High selectivity to 1-hexene can be achieved thanks the propensity of the chromium based catalyst to form 7-membered ring metallacycles. Sasol has found catalyst systems that allow the formation of a 9-membered metallacycle in large proportion relative to 7-membered ring formation, yielding 1-octene. (C) 2010 Elsevier B.V. All rights reserved.