Modified SAPO-34 for dehydration of bio-ethanol to light olefins in comparison with KOH-trezted HZSM-5

Abstract

Light olefins (especially, ethylene and propylene) are primarily used for the production of petrochemicals. In recent years, with the shortage of petroleum, the high demands of light olefins, and the increase in the price of naphtha feedstock, the production of light olefins from renewable resources has received wide attention. SAPO-34 and HZSM-5 catalysts were proven to be a potential catalyst for the catalytic dehydration of bio-ethanol to light olefins; however, they must be operated at the moderate acid strength with appropriate distribution of acid sites in order to produce a high composition of propylene in the gas product, because too strong acidity might lead to propylene transformation to aromatics and fast deactivation of the catalyst. In this research the reaction was carried out in an isothermal fixed bed reactor. The temperature was controlled at 400 ºC, and the liquid hourly space velocity (LHSV) was fixed at 0.5 h¯¹. The purpose of this research was to study the promoting effect of acidic oxides of germanium, gallium, tin, and antimony mixed with a SAPO-34 catalyst. The loading was varied as 3% and 5% by weight. The results revealed that the composition of ethylene decreased whereas that of propylene significantly increased with the loading percentage for all tested catalysts. It was found that the loading amount of 5% SnO₂ on SAPO-34 gave the highest composition of propylene in the gas. In addition, the catalytic performance of HZSM-5 catalysts treated with 0.1 M, 0.5 M, and 0.9 M of KOH solution were investigated as well. As a result, the treatment 0.1 M of KOH with HZSM-5 catalyst was the optimal one for the propylene production. Thus, the oxides on SAPO-34 and alkaline treatment with HZSM-5 can help to enhance the composition of propylene from bio-ethanol dehydration.