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Abstract
This work investigated activated carbon monolith catalysts as a substitute for conventional packed bed reactors in furfural hydrogenation reactions. Comparing the powder, granular and monolith forms of Pd catalyst for furfural hydrogenation, monolith was the only catalyst that did not show external mass transfer resistance for both hydrogen and furfural, which contributed to a lower activity loss for this catalyst. Adding acetic acid to the reaction medium, an impurity of crude furfural, did not affect the conversion of furfural in presence of Pd on activated carbon monolith. Selective hydrogenation of furfural using bi-metal Pd-Cu and Pd-Fe on activated carbon monolith was studied. Adding a second metal to Pd shifted the selectivity of the catalyst from 2-methylfuran and 2-methyltetrahydrofuran to furfuryl alcohol and tetrahydrofurfuryl alcohol over the range of tested temperatures and pressures. A high space time yield of 272 g/Lcat/h tetrahydrofurfuryl alcohol and 143 g/Lcat/h furfuryl alcohol was achieved using Pd-Fe/ACM at 180 °C, 300 psig and liquid hourly space velocity of 15.38 h-1. Selective hydrogenation of furfural to 5-hydroxy-2-pentanone over Pd-TiO2 was also studied. TiO2 added weak acid sites to Pd catalyst resulting in furan ring opening and formation of 5-hydroxy-2-pentanone. The highest space time yield of 140 g/Lcat/h and selectivity of 39% was achieved for 5-hydroxy-2-pentanone in a short residence time at 180 °C and 300 psig. A kinetic model was developed for hydrogenation of furfural over Pd-TiO2 using a two-site Langmuir-Hinshelwood mechanism. The reaction constants of 1.925, 0.506, 0.269 and 0.973 mol/gcat.h for consumption of furfural, formation of 2-methylfuran, formation of tetrahydrofurfuryl alcohol and formation of 5-hydroxy-2-pentanone were calculated from the model, respectively.