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

摘要

Cellulose upgrading with methanol (MeOH) to produce fuel-range alcohols involves the formation of alpha,beta-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 H-2 flow over CuMgAlOx has been elucidated. Isotopic C-13-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 P-Hydrogen and P-1,P-2-PDO, but has a 1.3 reaction order with respect to P-MeOH. C-O scission is 1(st) order in P-Hydrogen and has low/near-zero reaction orders with respect to P-1,P-2-PDO and P-MeOH. Direct C-C scission has a 0.8-0.7 reaction order with respect to P-Hydrogen, P-1,P-2-PDO and P-MeOH. 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 P-Hydroxyacetone, while C-O scission and retro aldol condensation rates do not. C-C coupling is observed to occur with other alpha,beta-diols and primary monoalcohols, but not with alpha,omega-diols or secondary monoalcohols.