Removal of oxygenates in aqueous phase product of F-T process by catalytic hydrogenation over Ru catalyst
CHEN Lungang, LIU Yong, DING Mingyue, ZHANG Xinghua, LI Yuping, ZHANG Qi, WANG Tiejun, MA Longlong
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Removal of oxygenates in aqueous phase product of Fischer-Tropsch (F-T) process was studied by the catalytic hydrogenation over supported Ru catalysts. The catalytic performance of several Ru catalysts supported on different metal oxides such as ZrO2, TiO2, SiO2 and γ-Al2O3 was investigated. In the catalytic hydrogenation processes, aldehydes, ketones and esters are more readily to be transformed than carboxylic acid and alcohol. The Ru/ZrO2 and Ru/TiO2 catalysts exhibited excellent hydrogenation activity, and under the conditions of 200℃, 9.8 MPa pressure and 3.0 h-1 WHSV, the carboxylic acids, aldehydes, alcohols, ketones and esters all are transformed to C1—C6 alkanes with overall conversion of above 92%. However, the Ru/Al2O3 catalyst displays the lowest activity towards alcohols with below 30% of conversion at the same conditions, although other oxygenates, including carboxylic acids, aldehydes, ketones and esters, are transformed with considerable conversion of above 87%, indicating that the Ru/Al2O3 catalyst was of selectivity for the conversion of oxygenates and the most of alcohols can not be transformed. The results from H2-TPR and NH3-TPD reveal that the synergy between metal and alumina is conductive to the hydrogenation of carboxylic acids and inhibits the hydrogenation-decarbonylation of alcohols. On the contrary, the catalysts with weak metal-support interaction and low acidity improve the hydrogenation activity for carboxylic acids and alcohols. However, there was a good stability of 400 h for Ru/Al2O3 catalyst, although the degeneration of catalytic activity was also observed after running 400 h. The results from X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2 physisorption show that the change of textural and structural properties is the key factors for activity degeneration of Ru/Al2O3 catalyst, because of the transformation of γ-alumina to boehmite and of the great decrease of surface area from 197 m2·g-1 to 21 m2·g-1 and loss of porosity.