Characteristics of catalysts for enhanced green production of distillates and chemicals in bio-oil from catalytic dehydration of bio-ethanol

Abstract

The dehydration of ethanol to gasoline and C6–C8 hydrocarbons has been made possible by using a HZSM-5 zeolite due to its proper acid property and shape selectivity. HZSM-5 had been also used as a support of phosphorous- (P), antimony- (Sb), and bismuth- (Bi) oxides for ethanol dehydration, which mainly gave high gasoline in oil. Since the moderate pore size of HZSM-5 limits the production of heavier biofuels in the distillate ranges (namely, kerosene and gas oil), therefore, in this work, the zeolites, HY and HBeta, with a larger pore size were employed, aiming to produce larger hydrocarbons. HZSM-5 was also used for comparison. Moreover, Group 5A oxides (P-, Sb-, and Bi oxides) were also doped onto the zeolites at 5 wt.% of elemental loading, expectedly to further enhance the production of distillate-range products. The results from the experiments carried out at 500 °C showed that, regardless of the type of loaded oxides, the distillate production was primarily governed by the channel opening size of zeolites, but the yield also depended on other parameters such as acid strength, and the complexity of the pore channel. HZSM-5 tended to produce high contents of large hydrocarbons ( $${\text{C}}_{9}^{ + }$$ ) whereas HBeta and HY tended to produce high amounts of C6–C8 hydrocarbons, especially benzene, and toluene. HBeta and HY gave high selectivity of p-xylene in mixed xylenes. Furthermore, oxygenates were produced in a trace amount using the parent zeolites, but their formation was significantly enhanced with using oxide-promoted catalysts, especially when HY was used as the support. In addition, Group 5A oxides doped on HBeta and HY can increase the oil yield. The content of distillates in bio-oil was also more greatly enhanced by Sb x O y and Bi x O y than by P x O y , promoted on HBeta and HY, possibly due to the promoter loading that created new stronger Bronsted acid sites. Generally speaking, high production of distillates in bio-oil preferably requires a support that possesses high strength of Bronsted acid sites in a large channel opening with low tortuosity of channel structure. Furthermore, the selected promoter should offer a new type of acid sites on the catalyst.