Alkene Metathe­sis for Propy­lene Pro­duc­tion over W-based Cat­a­lysts: Insights from Multi-Functional Cat­a­lysts and Met­al­la­cy­clobu­tanes

2014 Spring Symposium

Christo­pher P. Nicholas

Abstract — Tung­sten oxide sup­port­ed on sil­i­ca is an effi­cient cat­a­lyst for olefin metathe­sis used in indus­tri­al process­es since the 1960s. Sev­er­al ele­ments point to iso­lat­ed met­al cen­ters as the active sites, and from the Chau­vin mech­a­nism, it is rea­son­able to expect that car­bene species are involved, pos­si­bly bear­ing an oxide lig­and in the metal’s lig­and sphere. Owing to the strate­gic impor­tance of olefins as build­ing blocks for the world chem­i­cal indus­try, devel­op­ment of effi­cient process­es is of utmost rel­e­vance. More specif­i­cal­ly, tai­lored het­ero­ge­neous cat­a­lysts with known structure–activity rela­tion­ships may improve life­times and have high­er num­bers of active sites.

With our col­lab­o­ra­tors, we have been study­ing tung­sten hydride sup­port­ed on alu­mi­na pre­pared by the sur­face organometal­lic chem­istry method as an active pre­cur­sor for metathe­sis process­es at low tem­per­a­ture and pres­sure. Taoufik, et​.al. showed that eth­yl­ene can be con­vert­ed to propy­lene at very high selec­tiv­i­ties of 99% via a tri-func­tion­al mech­a­nism involv­ing dimer­iza­tion, iso­mer­iza­tion and cross-metathe­sis of eth­yl­ene and the pro­duced 2-butene. Recent­ly, via a con­tact time study we revealed that the dimer­iza­tion of eth­yl­ene to 1-butene is the pri­ma­ry and also the rate lim­it­ing step in this reac­tion and results in deac­ti­va­tion of the cat­a­lyst due to a side reac­tion like olefin poly­mer­iza­tion pro­duc­ing car­bona­ceous deposits on the cat­a­lyst.

With that knowl­edge, we have also inves­ti­gat­ed per­for­mance of the cat­a­lyst in the pres­ence of eth­yl­ene and butenes. At low tem­per­a­ture (120 °C) in the cross-metathe­sis of eth­yl­ene and 2-butene, the cat­a­lyst deac­ti­vates notably with time on stream. How­ev­er, at 150 °C, the cat­a­lyst was sta­ble with time and there­by gave a high pro­duc­tiv­i­ty in propy­lene. The ratio of eth­yl­ene to trans-2-butene was also stud­ied, and the W-H/Al2O3 cat­a­lyst is sta­ble and high­ly selec­tive to propy­lene even at sub-sto­i­chio­met­ric eth­yl­ene ratios.

Sur­pris­ing­ly, we have also been able to obtain propy­lene in high yields from butene only feeds. 1-butene and 2-butene are both able to be con­vert­ed into propy­lene at high­er selec­tiv­i­ty than expect­ed due to iso­mer­iza­tion and metathe­sis occur­ring simul­ta­ne­ous­ly. Then, by study­ing isobutene / 2-butene cross-metathe­sis, we observed that the cat­alyt­ic cycle involv­ing the less ster­i­cal­ly hin­dered tungsta­cy­clobu­tane inter­me­di­ate gov­erns the con­ver­sion rate of the cross-metathe­sis reac­tion for propy­lene pro­duc­tion from butenes and/or eth­yl­ene.


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Christopher_P_NicholasBiog­ra­phy — Chris joined UOP in 2006 after earn­ing a Ph.D. from North­west­ern Uni­ver­si­ty and work­ing in the Hard Mate­ri­als Cen­ter of Excel­lence at Sig­ma-Aldrich. He has worked in the Catal­y­sis and Explorato­ry Research depart­ments and is cur­rent­ly focused on New Mate­ri­als Research. Chris is an inven­tor or co-inven­tor on 30+ US and for­eign patents and coau­thor of 13 peer reviewed jour­nal arti­cles and a book chap­ter. He has been involved with the Chica­go Catal­y­sis Club since grad­u­ate stu­dent days and is cur­rent­ly serv­ing as the Pro­gram Chair for the Chica­go Catal­y­sis Club. Chris’ research inter­ests encom­pass the gamut of inor­gan­ic and cat­alyt­ic tech­nolo­gies rang­ing from mate­ri­als syn­the­sis to char­ac­ter­i­za­tion to cat­a­lyst and process devel­op­ment. He has par­tic­u­lar­ly enjoyed under­stand­ing the rela­tion­ship between homo­ge­neous and het­ero­ge­neous cat­a­lysts.