Fundamental Science Needs for Waste to Chemical Conversion: Fundamental Challenges and Opportunities in Catalyst Design Christopher W. Jones Georgia Institute of Technology School of Chemical & Biomolecular Engineering School of Chemistry and Biochemistry February 29, 2016

Waste Feedstocks Municipal solid waste (e.g. garbage, food waste, etc.) Agricultural solid waste (e.g. corn stover, pine bark, etc.) Fermentation broths Landfill waste Polymer waste Stranded gas (e.g. methane) Carbon dioxide

Feedstock Conversion to Processable Fluids Solid feedstocks must be converted to liquids or gases for further catalytic processing – gasification or liquefaction Each feedstock brings a unique mix of impurities Separation/fractionation can remove some impurities Impurities inevitably will remain – impact of specific impurities on catalytic performance is crucial Polymer waste, stranded gas, and CO 2 unique from other feeds – hydrocarbon rich and relatively pure

Conventional Catalytic Processing Majority of chemical catalysts developed for processing organic liquids, vapors and gases > 100 years of development = highly developed catalysts Processing done in large centralized facilities, can solve some economic challenges by operating on large scale Solid catalysts dominate, some molecular and biocatalysts for specific conversions, typically of highly purified feedstocks

Catalytic Processing for Waste Feedstocks Ag waste, Muni waste, Landfill waste – complex mixtures likely to be converted to: (i) liquid media by liquefaction (ii) gas/vapor media by gasification (iii) mixed liquid/gas/vapor by pyrolysis Liquid media produced likely to be aqueous or have an aqueous component Fermentation broths available as aqueous liquid media Aqueous medium conversions very important to waste feedstock conversion

Today’s Chemical Catalysts Catalysts today optimized for: (i) large scale processes at centralized facilities (ii) organic hydrocarbon media (iii) relatively clean feedstocks (iv) typically single-step conversions, each step has an associated catalyst

Catalyst Needs for Conversion of Waste Feedstocks (1) Catalysts that can operate at smaller scales in non-centralized facilities with variable feedstocks -- catalysts that are more active and operate at lower temperatures Catalysts that offer enhanced selectivity -- convert only specific molecules in mixtures -- convert only specific bonds/groups in polyfunctional molecules Catalysts that operate in aqueous media -- nearly all chemical catalysts have been developed and optimized for operation in organic media or the gas phase Catalysts that are tolerant of salts in aqueous liquid media

Catalyst Needs for Conversion of Waste Feedstocks (2) Catalysts that can break down large polymer chains (biomass, synthetic polymers, etc.) Catalysts that can create new building blocks, typically by creation of new carbon-carbon bonds Catalysts that can remove heteroatoms, such as (chiefly) oxygen, nitrogen, sulfur, phosphorous -- includes catalysts that can operate by hydrogenation using dihydrogen, or transfer hydrogenation using suitable donors -- includes catalysts that remove heteroatoms without an external hydrogen source, for example via production of water, ammonia, hydrogen sulfide, elemental sulfur, etc.

Fundamental Catalysis Science Questions (1) How do we create new types of catalysts and active sites that operate (one or more): -- in aqueous and aqueous/organic mixed media -- at low temperatures -- with higher activity (enabling lower temperatures) -- with extraordinary molecular, or functional group, or atomic selectivity (e.g. convert specific alcohol in a polyalcohol) How do typical impurities in new waste feedstocks interact with catalyst surfaces and specifically active sites? Can we pair active sites in productive ways in a single catalyst to allow for new transformations?

Fundamental Catalysis Science Questions (2) Can we pair active sites in productive ways in a single catalyst to allow for new transformations? -- cooperative reactions, cascade reactions, eliminating separation steps How do aqueous media (water, salts, etc.) affect chemical adsorption and reaction on surfaces? -- how do these species affect intrinsic constants describing elementary steps (k, K, etc.)? Basic science of solid-liquid interfaces is probably the biggest need, IMO. -- new/improved tools probing the interface -- interface will be dynamic – can we capture complex adsorption/desorption dynamics

Closing Thoughts Conventional waste feedstocks not strongly considered here: (i) CO 2 (ii) stranded gas Of non-traditional wastes as potential feedstocks, most likely to be gasified or liquefied to produce aqueous/organic mixtures or already are liquids (fermentation broths, ag waste, muni waste, landfill, etc.) Polymeric wastes are unique from the above: (i) relatively clean, homogeneous feed (ii) not likely an aqueous product (iii) closest to conventional hydrocarbon feeds for which we already have catalysts and processes