Hydrogenation and hydrodeoxygenation of difurfurylidene acetone to liquid alkanes over Raney Ni and the supported Pt catalysts

Highlights: • The C₈−C₁₄ alkane yield of 82.9% was obtained in the two-step hydrogenation/HDO process. • Protonation effect from methanol solvent increased F₂A conversion in the two-step process. • The rate-determining step was acyl C=O bond hydrogenation in the first step of F₂A hydrogenation. • The acidic centers from SiO₂−ZrO₂ activated the acyl and oxygen atoms of intermediates. • Acidity of SiO₂−ZrO₂ and Pt active centers of 1 wt%Pt/SiO₂−ZrO₂ resulted stable HDO performance. - Abstract: Direct HDO process for difurfurylidene acetone dimer (F₂A) conversion to liquid alkanes (C₈−C₁₄) at 260 °C in a batch reactor was investigated over different material supported 1 wt%Pt catalysts, including SAPO-11, HZSM-5, SiO₂−Al₂O₃, MCM-22, and home-made SiO₂−ZrO₂. C₈−C₁₄ alkanes of 55.8% was obtained over the optimized 1 wt%Pt/SiO₂−ZrO₂ due to its proper pore size of 9.0 nm and moderate acidic centers, together with more than 10% carbon yield of the oxygenated hydrocarbons, including C₁₁−C₁₃ chain alcohols & ketones and the hydrogenated F₂A dimers with furan ring (H-F₂A dimers). To improve the liquid alkane yield, a two-step process for F₂A conversion was also investigated, which included low-temperature hydrogenation at 50 °C over Raney Ni catalyst in a batch reactor and the subsequent high-temperature hydrodeoxygenation (HDO) at 280 °C over 1 wt%Pt/SiO₂−ZrO₂ in a fixed-bed reactor. The selectivity of 1,5-di(tetrahydro-2-furanyl)-3-pentanol (II-c) was the highest of 83.0% among the hydrogenated intermediates of H-F₂A dimers due to the protonation effect of methanol as the solvent and the hydrogenation of C=C bonds by Ni active centers. In the same time, the high content of this saturated alcohol H-dimer of II-C increased the solubility and stability of the intermediates in methanol solvent. High carbon yield of C₈−C₁₄ alkanes of 82.9%(mol) was obtained after oxygen atom removal from H-F₂A dimers via. the second-step HDO reaction. Long time operation showed the stability of 1 wt%Pt/SiO₂−ZrO₂ as HDO catalyst, deduced from the steady phase structure, acidity of SiO₂−ZrO₂ support and Pt active centers by catalyst characterization.