Across-phase biomass pyrolysis stoichiometry, energy balance, and product formation kinetics

Authors: LEBLANC, JEFFREY - City College Of New York; Uchimiya, Sophie; RAMAKRISHNAN, GIRISH - State University Of New York (SUNY); CASTALDI, MARCO - City College Of New York; ORLOV, ALEXANDER - State University Of New York (SUNY)

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2016
Publication Date: 7/25/2016
Citation: LeBlanc, J., Uchimiya, M., Ramakrishnan, G., Castaldi, M.J., Orlov, A. 2016. Across-phase biomass pyrolysis stoichiometry, energy balance, and product formation kinetics. Energy and Fuels. 30:6537-6546.

Interpretive Summary: Pyrolysis and other high-temperature conversion of agricultural wastes to value-added products have received considerable interests in the past decades. However, fundamental technological knowledge, including the reaction stoichiometry and pathways is absent, making real-world utilization of the technology a challenge. This work offers a new method to predict the value of pyrolysis products based on the reaction kinetics, i.e., the amount of intermediates and products formed as a function of time. This new methodology will allow stakeholders to convert wastes to energy/bio-products for specific end-products including the fertilizers and growth enhancers.

Technical Abstract: Predictive correlations between reactions occurring in the gas-, liquid- and solid-phases are necessary to economically utilize the thermochemical conversion of agricultural wastes impacting the food, water, and energy nexus. On the basis of an empirical mass balance (99.7%), this study established the overall reaction stoichiometry (C33.4H45.9O20.3N0.2S0.1 = 0.5C10.0H28.5O11.2N0.1S0.1 + 1.7H2O + 0.1H2 + 1.1CH4 + 0.02C2H4 + 0.06C2H6 + 2.2CO2 + 2.1CO + 0.28C18H9.1O0.9N0.1) and energy balance for the slow pyrolysis of lignocellulosic pecan shell waste biomass at 10 ºC min-1 up to 500 ºC. In situ thermogravimetry-gas chromatography and Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) were used to link gas-, liquid-, and solid-phase nonisothermal reaction kinetics. Gaussian fit-based deconvolution of individual gaseous product formation rates (hydrogen, methane, carbon monoxide, carbon dioxide, ethylene, and ethane in mg min-1) suggested the relationships between (1) evolved methane and increased aromaticity/energy density of char product at 300-500 ºC, and (2) evolved carbon dioxide and decarboxylation of char product near 400 ºC. Partial least square (PLS) calibrations were obtained between (1) DRIFTs monitoring of the surface functional groups in the solid phase (transition from pecan shell to char) and (2) CO, CO2, CH4, C2H6, C2H4, and tar formation profiles in the gas/condensable phase. Established across-phase PLS calibrations can be used to predict biochar’s surface chemistry based on the fingerprint of volatile products, and vise versa. These new thermodynamic (reaction stoichiometry and energy balance) and kinetic (deconvolution of specific gas formation rates and PLS) predictive methodologies will facilitate the nexus of food, water (designing of biochar soil amendment), and energy (optimization of syngas and bio-oil composition) enabling sustainable agriculture.