Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2013
Publication Date: 2/3/2014
Citation: Dorado, C., Mullen, C.A., Boateng, A.A. 2014. H-ZSM5 Catalyzed co-pyrolysis of biomass and plastics. ACS Sustainable Chemistry & Engineering. 2(2):301-311.
Interpretive Summary: In an effort to increase U.S. energy independence as well as reduce greenhouse gas emissions, the Renewable Fuels Standard Program calls for 36 billion gallons of renewable fuel to be combined with transportation fuel by 2022. Of these 36 billion gallons, 21 billion gallons must come from advanced and cellulosic based sources. Biomass, such as crop residues, herbaceous grasses and woody materials, are the largest cellulosic based source available and can be readily converted to liquids, known as bio-oil, by rapid heating in the absence of oxygen, otherwise known as fast pyrolysis. Bio-oil from these cellulosic sources is not miscible with current petroleum based fuels due to high water and oxygen content. These undesirable properties can be combated by the use of catalysts, in combination with fast pyrolysis, that are selective for converting cellulosic biomass into oils that are more compatible with current petroleum derived fuels. Catalysts used in this manner quickly become deactivated by the accumulation of carbon and oxygen based compounds on the catalyst; this could be alleviated by increasing the amount of hydrogen rich carbon molecules being reacted. Agricultural plastic waste could serve as a source for this hydrogen rich carbon and its participation in catalytic fast pyrolysis with cellulosic biomass would serve as a method for agricultural plastic waste removal from the environment. The products of the catalytic fast pyrolysis of individual biomass components, individual plastics and mixtures of biomass and plastic were compared. The presence of plastics in particular mixtures with biomass showed an increase in the amount of desired products that are compatible with petroleum based fuels. The results of this work will be useful to those designing pyrolysis based biorefineries and those addressing the issue of agricultural plastic waste disposal.
Technical Abstract: This study aims at addressing two important problems vital to agriculture, disposal of agricultural plastics and production of drop-in fuels from biomass via co-pyrolysis of both feedstocks. Mixtures of biomass (switchgrass, cellulose, xylan and lignin) and plastic (polyethylene terephthalate (PET), polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE) and polystyrene (PS)) were subjected to catalytic fast pyrolysis, (CFP) at 650 oC in the presence of H-ZSM5. A micro pyrolyzer coupled with GC/MS (py-GC/MS) was utilized to evaluate desired mixes and product distribution. Yields of the aromatic compounds typically observed as catalytic pyrolysis products including toluene, ethylbenzene, p-xylene, o-xylene, naphthalene and 2-methylnaphthalene and their sum, were tracked. The products from CFP of mixtures of biomass and plastic were compared with that of biomass alone, plastic alone and the calculated arithmetic sum of yield values expected if there was no chemical interaction between the two feedstocks. The latter provides insights as to whether a synergetic effect occurred that enhanced the selectivity to aromatics of the blend or just the additive sum of the individual products. It was found that in several cases conversion enhancement occurred for the mixture, with the aliphatic polymers (PE and PP) and PET generally providing the biggest increase in total aromatic yields. Positive changes in selectivity for the production of individual aromatic compounds were also observed in the blends compared with the biomass or plastics alone.