2017 Spring Symposium
Mark Deimund, ExxonMobil Research and Engineering Company, Annandale, NJ
Abstract – Two zincosilicate molecular sieves (CIT-6 and Zn-MCM-41) were synthesized and ion-exchanged with nickel, allowing them to act as catalysts for the oligomerization of propylene into C3n products (primarily C6 and C9 species). For performance comparison to aluminosilicate materials, two zeolites (high-aluminum beta and zeolite Y) were also nickel exchanged and utilized in the oligomerization reaction.
CIT-6 and the high-aluminum zeolite beta (HiAl-BEA) both have the *BEA framework topology, allowing for comparison between the zinc and aluminum heteroatoms when exchanged with nickel, as the former gives two framework charges per atom, while the latter gives only one. Ni-CIT-6 and Ni-Zn-MCM-41 enable the comparison of a microporous and a mesoporous zincosilicate. The Ni2+ ion exchanged onto zeolite Y has been previously reported to oligomerize propylene and is used here for comparison.
Reaction data are obtained at 180°C and 250°C, atmospheric pressure, and a WHSV = 1.0 h-1 in a feed stream consisting of 85mol% propylene, with the balance inert. At these conditions, all catalysts are active for propylene oligomerization, with steady-state conversions ranging from 3-16%. With the exception of Ni-HiAl-BEA, all catalysts exhibit higher propylene conversions at 250°C than 180°C. Both *BEA topology materials exhibit similar propylene conversions at each temperature, but Ni-HiAl-BEA is not as selective to C3n products as Ni-CIT-6. Zincosilicates demonstrate higher average selectivities to C3n products than the aluminosilicates at both reaction temperatures tested. Hexene products other than those expected by simple oligomerization are also present, likely formed by double-bond isomerization catalyzed at acid sites.
Additionally, both of the aluminosilicate materials catalyzed cracking reactions, forming non-C3n products. The reduced acidity of the zincosilicates relative to the aluminosilicates likely accounts for the higher C3n product selectivity of the zincosilicates. Zincosilicates also exhibited higher linear-to-branched hexene isomer ratios when compared to the aluminosilicates. The mesoporous zincosilicate exhibits the best reaction behavior (including C3n product selectivity: approximately 99% at both temperatures for Ni-Zn-MCM-41) of the catalytic materials tested here.
From Deimund, MA, et al. ACS Catal., 2014, 4 (11), pp 4189–4195. DOI: 10.1021/cs501313z
Biography – Originally from Oklahoma City, Oklahoma, Mark attended Texas A&M University where he earned his undergraduate degree in chemical engineering. He then attended the University of Cambridge for his MPhil, conducting research into the formation of protein deposits in brain cells as a means to better understand the onset of Alzheimer’s and other neurodegenerative diseases. Upon completion of this degree, he began his PhD work at the California Institute of Technology in the area of molecular sieve synthesis and reaction testing under Professor Mark E. Davis. Currently, he works as a researcher at ExxonMobil Research and Engineering Company in Annandale, NJ.