BACKGROUND

The present disclosure is directed to new catalyst compositions for the oligomerization of light alkenes, especially gaseous alkenes, e.g., ethene, propene, butenes and pentenes, to their respective higher molecular weight hydrocarbon derivatives. The longer chain higher molecular weight hydrocarbons have a greater value than the lighter alkenes.

More efficient utilization of petroleum and gas reserves is an important strategy for the deployment of future energy generation. Shale gas has become an increasingly important source of natural gas in the United States, and the U.S. government's Energy Information Administration predicts that by 2040, approximately 70 percent of the United States' natural gas supply will come from shale gas. The transformation of shale gas to transportation fuels, fine chemicals and additives is one of the strategies to utilize the shale gas reserves to their highest value.

Light alkene oligomerization is a promising pathway to synthesize higher molecular weight hydrocarbons for transportation fuels and additives. Solid acids including supported phosphoric acid, acid resins, amorphous silica-alumina, and zeolites have been used in industrial oligomerization processes, with MFI framework zeolites garnering the most attention for these reactions due to its resistance to coke formation and high selectivity to linear olefins with high cetane number. MFI zeolites in their aluminosilicate composition are also known as ZSM-5. ZSM-5 is used in the Mobil Olefins to Gasoline and Distillate (MOGD) process, and there are several patents from the 1980s associated with this process.

Zeolites contain tetrahedral silicon atoms linked by oxygen, forming charge-neutral crystalline structures. The isomorphous substitution of trivalent aluminum atoms into the crystalline structure for tetravalent silicon introduces a negative charge imbalance that can be compensated by protons, which act as Brønsted acid sites for catalysis. Zeolites, molecular sieves, and related microporous and mesoporous materials have the ability to control the access of reactants and products, based on their size and shape, to catalytically active sites within the pores of these materials. Thus, they can preferentially contain only those transition states that can be stabilized while excluding others. These phenomena have been described as concepts of shape selectivity and size exclusion and are considered to be a hallmark of zeolite catalysis.

Oligomerization can also be accompanied by an undesired cracking (β-scission) reaction to form smaller hydrocarbons from oligomers. High selectivity is strived for by preferentially slowing cracking reactions relative to oligomerization. However, the selectivity of this reaction is insensitive to the strength of the solid acid since β-scission is the microscopic reverse reaction of oligomerization, thus stabilization of intermediates or transition states affects these pathways to the same extent. Other synthetic variables that may affect the product distribution of olefin oligomerization in zeolites include local aluminum proximity and the interplay between crystal size and bulk aluminum content.

There is a need for improved catalysts for use in alkene dimerization and oligomerization reactions that provide improved selectivity while also enabling acceptable conversion rates.

