Modeling aqueous-phase hydrodeoxygenation of sorbitol over Pt/SiO2-Al2O3

In this paper, we investigated the effects of temperature, hydrogen partial pressure, and sorbitol concentration on the aqueous-phase hydrodeoxygenation (APHDO) of sorbitol over a bifunctional 4 wt % Pt/SiO2-Al2O3 catalyst in a trickle bed reactor. APHDO involves four fundamental reactions: (1) hydrogenation; (2) dehydration; (3) C-C bond cleavage by dehydrogenation and decarbonylation; and (4) C-C bond cleavage by dehydrogenation and retro-aldol condensation. The main deoxygenation routes are decarbonylation and alcohol dehydration. Retro-aldol condensation plays a critical role in reducing the carbon number of the products. The key products in this system are C1-C6 n-alkanes, primary and secondary alcohols, and carbon dioxide. As shown in this paper, the reaction conditions can dramatically change the product selectivity for APHDO of biomass-derived feedstocks (e. g., sorbitol). A sorbitol hydrodeoxygenation reaction network was generated that predicts all of the 43 experimentally measured species. The reaction network consists of 4804 reactions and produces a total of 1178 distinct chemical species. The associated material balance equations were solved numerically to model the experimentally observed species as a function of temperature, concentration, and pressure. The model concentrations fit well the experimentally measured values, demonstrating that the model was accurately able to model the reaction families and capture the salient features of the experimental observations. The trend observed in this paper can be used for the optimization of reactors and new catalysts to selectively make targeted products by hydrodeoxygenation of biomass-derived feedstocks.