Note: Chevron, Energy Technology Company, 100 Chevron Way, Richmond, California 94802-0627 Reference EPFL-ARTICLE-200588doi:10.1021/cr8002642 URL: http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/cr8002642 URL: http://pubs.acs.org/doi/pdfplus/10.1021/cr8002642 Record created on 2014-08-14, modified on 2017-05-12

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

The kaleidoscopic applications of zeolite catalysts (zeo-catalysts) in petrochemical processes has been considered as one of the major accomplishments in recent decades. About twenty types of zeolite have been industrially applied so far, and their versatile porous architectures have contributed their most essential features to affect the catalytic efficiency. This review depicts the evolution of pore models in zeolite catalysts accompanied by the increase in industrial and environmental demands. The indispensable roles of modulating pore models are outlined for zeo-catalysts for the enhancement of their catalytic performances in various industrial processes. The zeolites and related industrial processes discussed range from the uni-modal micropore system of zeolite Y (12-ring micropore, 12-R) in fluid catalytic cracking (FCC), zeolite ZSM-5 (10-R) in xylene isomerization and SAPO-34 (8-R) in olefin production to the multi-modal micropore system of MCM-22 (10-R and 12-R pocket) in aromatic alkylation and the hierarchical pores in FCC and catalytic cracking of C4 olefins. The rational construction of pore models, especially hierarchical features, is highlighted with a careful classification from an industrial perspective accompanied by a detailed analysis of the theoretical mechanisms.

Recent advances of pore system construction in zeolite-catalyzed chemical industry processes

Jet turbine fuels have not been completely replaced by biomass-derived fuels due, in part, to the lack of the aromatic and cycloalkane hydrocarbons in bio-jet fuels. Such molecules play a critical role in traditional jet fuels for combustion characteristics and material compatibility. To date, this problem has been addressed by blending bio-jet fuel with traditional petroleum-based oils. In order to produce a 100% biomass-derived jet fuel, a suitable bioresource is needed for synthesizing aromatic and cycloalkane fuel compounds. Lignin, the only biomass component rich in aromatic benzene ring structures, is currently underutilized for low-value heat or treated as process waste because of its high chemical resistance. In this review, a four-step pathway of pretreatment, depolymerization, hydrodeoxygenation (HDO), and alkylation to convert lignin into jet-fuel-range aromatic hydrocarbons and cycloalkanes is explored. While many studies about these processes can be found in the literature for biomass and bio-derived molecules, the purposes of those studies were often for something other than lignin valorization. For example, pretreatment processes focus on cellulose and hemicellulose as desired products while lignin is handled as a waste. Most HDO studies focus on the upper phase of bio-oil which contains primarily water and phenolic monomers, ignoring the bottom phase which contains the larger, main components from depolymerization. Many alkylation studies used single, pure components; by comparison, the feedstocks from HDO of lignin-derived bio-oil are mixtures of varying complexity. This review of each process can be used to guide pathway integration and optimization.

Producing jet fuel from biomass lignin: Potential pathways to alkyl-benzenes and cycloalkanes

Alkylations of benzene with dodecene and/or chloromethanes in the chloroaluminate room temperature ionic liquid modified with HCl as catalysts have been investigated. Different product distributions and enhanced activity, were respectively observed for these two alkylation reactions. This may be attributed to the superacidity of the ionic liquid induced by the presence of HCl.

Alkylations of benzene in room temperature ionic liquids modified with HCl

Xylene isomerization and aromatic alkylation in zeolites NU-87, SSZ-33, β, and ZSM-5: molecular dynamics and catalytic studies

Alkylation of benzene with propene has been investigated on a series of H-Beta zeolites with different Si/Al ratio: 10, 35 and 66, using different techniques such as FTIR, 13 C NMR and catalytic testing. It has been shown that H-Beta zeolite (Si/Al ratio=10) is a very active catalyst for this reaction with propene, but it leads also to fast oligomerization even at lower reaction temperatures. 13 C NMR experiments have demonstrated for the first time that the reaction of alkylation is already complete at −80°C on these catalysts. Dealuminated H-Beta zeolites are less active but lead to less aromatic by-products (especially n -propylbenzene) and the deactivation due to the coke formation is reduced. The high ratio of benzene/propene favors the formation of cumene and suppresses the oligomerization of propene. Triisopropylbenzene (TIPB) can also be formed at low temperatures ( 130°C). The present work reveals that the alkylation of benzene by propene occurs via an Eley–Rideal type mechanism. The apparent activation energy for this reaction has been determined and shows to decrease as the Si/Al ratio of H-Beta zeolites increases. The relatively low apparent activation energies obtained for this reaction on a series of H-Beta zeolites studied suggests that it exists a diffusion step of reactants and products between the silanols of the Beta zeolite.

S Siffert

Papers

Alkylation of benzene by propene on a series of Beta zeolites: toward a better understanding of the mechanisms