Title : Study of kinetics and mechanisms of catalytic pyrolysis of biomass components by using linear free energy relationships and TPD MS
Abstract:
The conversion of biomass into chemicals and fuels is the most promising avenue being considered by countries to help them reach their renewable energy and feedstock goals and move from hydrocarbon-based chemicals to bio-based chemicals. Non-food biomass is considered to be a feedstock of crucial importance. Currently, the only industrially feasible and “green” technology for conversion of such biomass is heterogeneous catalysis. It is crucial to have a precise understanding of the catalytic transformation mechanisms of main components of biomass on the surfaces of metal oxides.
In this study, we used TPD MS to investigate the pyrolysis of fatty acids on various oxide surfaces. Detailed and targeted kinetic studies for reacting series of fatty acids C2-C18 and triglycerides on the surfaces of nanosized CeO2, CeO2/SiO2, SiO2, γ-Al2O3, Al2O3/SiO2 and TiO2/SiO2 have been investigated by the Linear Free Energy Relationships (LFERs) principle and temperature-programmed desorption mass spectrometry. Fourier transform infrared spectroscopy (FTIR) has also been used to investigate the structure of fatty acids complexes on the oxide surfaces. Two reaction pathways of fatty acids conversion were found to be dominant—ketenization to form alkyl ketenes and ketonization to form dialkyl ketones. The kinetic parameters (Tmax, n, E≠, ν0, and dS≠) of ketonization and ketenization were calculated. The first order of ketonization reaction was confirmed by using the Arrhenius Plot method and by investigating the effect of the degree of the surface coverage on the reaction rate. Taft correlation "structure-reactivity" for fatty acids ketonization on the surface of CeO2/SiO2 nanocomposites, has been found. Based on these results modified concerted mechanism of the ketonization has been proposed. It was found that the activation energy of ketenization decreases in the order SiO2>Al2O3>TiO2/SiO2>Al2O3/SiO2, and the activation energy of ketonization decreases in the order Al2O3>CeO2/SiO2. CeO2 and Al2O3/SiO2 are suitable catalysts for ketonization and ketenization respectively. These catalytic materials provide excellent performance with very low temperature conversions and high selectivities.
