Elucidation of reaction network and kinetics between cellulose-derived 1,2-propanediol and methanol for one-pot biofuel production?

Green Chemistry Pub Date: 2021-12-09 DOI: 10.1039/D1GC03650E

Abstract

Cellulose upgrading with methanol (MeOH) to produce fuel-range alcohols involves the formation of α,β-diols like 1,2-propanediol (1,2-PDO) that can undergo C–C scission, C–O scission, and C–C coupling with MeOH. In this work, the reaction network for conversion of 1,2-PDO and MeOH in H2 flow over CuMgAlOx has been elucidated. Isotopic 13C-MeOH studies show that C–C coupling with 1,2-PDO produces 2,3-butanediol (14% selectivity) and 1,2-butanediol (5.3%), while 1,2-ethanediol (3.3%) forms from retro aldol condensation of a C–C coupling intermediate. Products observed from dehydrogenation, direct C–C scission, and C–O scission of 1,2-PDO include hydroxyacetone (44%), ethanol (15.2%), 1-propanol (5.5%) and 2-propanol (6%). C–C coupling is zero-order with respect to PHydrogen and P1,2-PDO, but has a 1.3 reaction order with respect to PMeOH. C–O scission is 1st order in PHydrogen and has low/near-zero reaction orders with respect to P1,2-PDO and PMeOH. Direct C–C scission has a 0.8–0.7 reaction order with respect to PHydrogen, P1,2-PDO and PMeOH. Dehydrogenation and C–C coupling have the lowest apparent activation energies of 45.6 and 47.2 kJ mol?1, respectively, while all other pathways have apparent activation energies at least 15 kJ mol?1 higher. Cofeed experiments with formaldehyde show that the rate determining step in C–C coupling is associated with the nucleophilic attack by 1,2-PDO. C–C coupling, direct C–C scission and esterification rates increase with PHydroxyacetone, while C–O scission and retro aldol condensation rates do not. C–C coupling is observed to occur with other α,β-diols and primary monoalcohols, but not with α,ω-diols or secondary monoalcohols.

Graphical abstract: Elucidation of reaction network and kinetics between cellulose-derived 1,2-propanediol and methanol for one-pot biofuel production
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