(532o) Elucidation of Reaction Kinetics between Supercritical Methanol and Cellulose-Derived 1,2-Propanediol for Biofuel Production
AIChE Annual Meeting
2022
2022 Annual Meeting
Catalysis and Reaction Engineering Division
Poster Session: Catalysis and Reaction Engineering (CRE) Division
Wednesday, November 16, 2022 - 3:30pm to 5:00pm
Supercritical methanol depolymerization and hydrodeoxygenation (SCM-DHDO) of cellulose over CuMgAl catalysts results in the formation of C2-10 monoalcohols with >98% conversion. α,β-Diols are observed as the major products at low reaction times, and methanol (MeOH) incorporation is detected in all liquid products. The selectivity to C5+ alcohols cannot be improved without a better understanding of the reactions between α,β-diols and MeOH. In this work, we performed kinetic experiments at 300 °C and 1000 psig in a packed bed reactor with an observed intermediate from cellulose: 1,2-propanediol (1,2-PDO). Isotopic 13C-MeOH studies show that 1,2-PDO dehydrogenates to hydroxyacetone, which then undergoes C-C coupling with MeOH to form 2,3-butanediol and 1,2-butanediol. 1,2-PDO also undergoes C-O scission to form 1-propanol and 2-propanol, and C-C scission to form ethanol. Dehydrogenation and C-C coupling have the lowest apparent activation energies of 45.6 and 47.2 kJ/mol, while all other pathways are least 15 kJ/mol higher. From partial pressure experiments, C-C coupling was found to have a zero-order dependence on PHydrogen and P1,2-PDO, but is 1st order with respect to PMeOH. C-O scission has a 1st order dependence on PHydrogen but has near-zero reaction orders with respect to P1,2-PDO and PMeOH. Cofeed experiments with formaldehyde and hydroxyacetone show that the rate determining step in C-C coupling is the nucleophilic attack by 1,2-PDO on MeOH. We conclude that the selectivity to C-C coupling at low conversions can be increased by carrying out the reaction at lower temperatures (280 â 300 °C), higher PMeOH, and lower PHydrogen and PMeOH. Lastly, we demonstrate that C-C coupling can occur between other α,β-diols and primary monoalcohols, but not with α,Ï-diols or secondary monoalcohols. These advances in quantifying the fundamental kinetics involved in biomass conversion with supercritical MeOH will allow for higher selectivity to desired C5+ alcohols and better process design.
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