Supported Ionic Liquid-Phase (SILP) Membrane Reaction Systems for Industrial Homogeneous Catalysis

Abstract

To reduce the energy consumption and CO2 emissions in the chemical industry, process intensification is an essential concept. In this study, a monolithic membrane reactor has been developed combining heterogenized homogeneous catalysts with in-situ product removal, based on a project funded by the European Commission with 6 million Euros (ROMEO). Two prominent and industrially relevant large-scale reactions have been employed as case studies: water-gas shift and hydroformylation of 1-butene. The catalyst system of the former was based on ruthenium complexes dissolved in the ionic liquid 1-butyl-2,3 dimethylimidazolium chloride ([C4C1C1Im]Cl) immobilized on γ-alumina-rich monoliths. A facilitated transport membrane was applied to selectively remove CO2 from the reactor zone to enhance the reaction rate of the equilibrium-driven reaction and to facilitate downstream processing. The catalyst system has been successfully immobilized on monoliths and sustained activity for more than 300 h time on stream without membrane functionality. A feasibility performance test of the membrane reactor presented similar activity but has not shown any gas enrichment in the retentate/permeate streams yet, which was attributed to a possible pinhole in the membrane. The latter reaction, the hydroformylation of 1-butene, has been performed with Rh-biphephos complexes dissolved in the ionic liquid 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([C2C1Im][NTf2]) and immobilized on a silicon carbide monolith showing high activity and regioselectivity towards the liner aldehyde, n-pentanal. However, the consecutive reaction lead to the formation of heavies, high-boiling aldol condensation products, which accumulated in the ionic liquid and pore structure hampering the activity. By applying an alternative liquid phase, comprised of melted bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, the formation and accumulation was efficiently suppressed over 1500 h time on stream while keeping the high catalyst regioselectivity and increasing the turnover frequency up to 570 mol1−butene mol−1 Rh h−1. The performance test conducted with addition of a polydimethylsiloxane (PDMS) membrane presented an increase in aldehydeto-alkene ratio by a gas-enrichment factor of 2.2 in the permeate stream compared to the retentate stream. In conclusion, the monolithic membrane reactor has been developed and applied successfully, demonstrating its strong potential. The structured, monolithic reactor enables a scalable and versatile platform for process intensification for both case reactions, as well as other important industrial gas-phase processes.