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Reducing coke formation and extending lifetime of the HZSM-5 catalyst via co-pyrolysis of high density polyethylene with switchgrass(Panicum virgatum) Frankie Lazauskas, Drexel University, Department of Biodiversity, Earth, and Environmental Sciences


Background: PyrolysisThermochemical decomposition of organic matter in the absence of oxygen which can produce solid, liquid, and gas productsBiomass fast pyrolysis oil is a complex mixture of many oxygenated hydrocarbons and water (Acids, esters, ketones, aldehydes, sugars, furans, phenols, 15-30% water)Other issues with biomass pyrolysis oil include its high acidity, low heating value, thermal instability, and high oxygen/low hydrogen content(compared to petroleum oil)


Background: Catalytic Fast Pyrolysis(CFP)Same as fast pyrolysis, except products pass over a reactive catalyst bedOften a zeolite catalyst, such as HZSM-5, that selectively makes deoxygenated aromatic hydrocarbonsCFP of biomass creates coke while losing H, this coke formation eventually leads to deactivation of the catalyst3

Background: Agricultural Plastic WasteMany different plastics used for agricultural needs such as hay bale covers, pesticide/insecticide containers, transportation/storage of crops, etc.521 million pounds of agricultural plastic waste every year in the U.S alone with about 70% being polyethyleneDisposal SolutionsIncineration, burial, and landfills come with many environmental concernsSimply recycling them can be difficult/expensive(toxins from pesticides)Co-pyrolysis feedstock


ObjectiveHow does addition of HDPE affect product formation?Does addition of HDPE have an effect on coke formation and the lifetime of the catalyst?5

Materials & MethodsCDS pyrolyzer(CDS Pyroprobe 5250-T) and external reactor(CDS 5250-TR)Agilent GC/MS(6890N)Quartz tube with ~1mg of sample(Switchgrass, HDPE, and 1:1 mixture) stuffed with quartz wool to prevent loss of sample


Materials & MethodsPyrolysis done at 650C with either 30 sample or 60 sample runsGases transferred to external reactor and passed over HZSM-5 bed with ~15mg of catalyst at 500CProducts then analyzed by GC/MS


Materials & MethodsSpent catalyst with quartz wool removed post-runQuartz wool separated from spent catalystSpent catalyst heated to 650C, weight loss recorded for determining coke formation on HZSM-58

Results: Coke Formation9




Results: HZSM-5 Lifetime and Product Formation (Switchgrass Alone)10BTEX is the sum of the aromatic compounds Benzene, Toluene, Ethylbenzene, p-Xylene, and o-Xylene.

Results: HZSM-5 Lifetime and Product Formation (HDPE Alone)11

Results: HZSM-5 Lifetime and Product Formation (1:1 Mix of HDPE and Switchgrass)12

Results: Deactivation of HZSM-5Production of acetic acid increased as more sample was run over HZSM-5 for all switchgrass runsNo acetic acid detected in any of the HDPE runsOnly 1 out of 4 of the mixed runs showed any acetic acid production(highest value ~12)


ConclusionsAddition of HDPE reduces coke formation which helps to delay deactivation of HZSM-5HDPE increased yield of stable aromatic hydrocarbons compared to biomass alone with a synergistic effect(1:1 ratio showed consistently higher yields)


Future Directions Understanding chemical pathways for the observed synergistic effect in mixed samples testing of other biomass/plastic combinationsDifferent/smaller ratios of plastic to biomass, how much plastic is needed to still utilize this effects?Potential options for external reactor that is compatible with Shimadzu GC/MS models could mitigate many of the maintenance issues that hindered this project

Acknowledgements Special thanks to Dr. Akwesi Boateng, Dr. Charles Mullen, Tom Coleman and the entire pyrolysis team!