CRE: Addressing resource sustainability, environmental and life science challenges
Exploiting the Synergies Between Catalysis and Neoteric Solvents for Sustainable CRE: Opportunities and Challenges
The modern day refining industry relies primarily on fossil fuel (such as petroleum, natural gas and coal) based feedstock. There exist several megaton catalytic processes (such as the homogeneous hydroformylation of higher olefins, epoxidation of light olefins and p-xylene oxidation to produce terephthalic acid) that produce essential chemicals for everyday life but present major sustainability challenges with respect to reducing environmental footprints and enhancing energy efficiency. To meet the increasing demand for such chemicals, via either fossil-based feedstock or plant-based biomass, requires the development of novel sustainable processes. This talk will highlight the role and promise of new types of benign solvents, with emphasis on gas-expanded liquids (GXLs), for developing sustainable catalytic processes.
A gas-expanded liquid (GXL) phase is formed by dissolving a compressible gas such as CO2 or a light olefin into the traditional liquid phase (the resulting liquid phase is termed CO2-expanded liquid or CXL when CO2 is used as the expansion gas).1 This talk will address the various unique ways in which GXL media have been exploited to develop greener catalytic process concepts for O2 and H2O2-based oxidations, hydroformylations and ozonolysis.2 The demonstrated advantages include process intensification at mild conditions by increasing dissolution of the limiting reagent (gaseous reactants such as O2 or syngas or light olefins) in the GXL reaction phase;3 enhancing inherent safety by suppression of flammable vapors;2 and waste mitigation by reduced usage of organic solvents and by suppression of side reactions that generate undesired byproducts such as CO2.4
Specific examples of novel process concepts to be discussed include the highly selective hydroformylation of higher olefins at mild conditions employing soluble polymer-attached Rh catalysts that are easily retained in solution while the product is isolated by membrane filtration;5 a novel homogeneous ethylene oxide process virtually eliminating CO2 formation as a byproduct;6 and a one-step spray reactor concept to overcome gas-liquid transport limitations for the inherently safe formation of polymer-grade terephthalic acid from p-xylene at high yields and purity. The significant role of quantitative sustainability analyses to benchmark novel technology concepts against conventional processes will be discussed.7 Such comparative analyses not only guide research and development but are also essential for making informed business decisions about the practical viability of alternate technologies.