Catalytic ethylation of glycerol and a consecutive tert-butylation of glycerol ethyl ethers over heterogeneous catalysts

摘要

Abstract The goal of the present work was to enhance the degree of alkylation of glycerol to ethyl-butyl ethers at a maximum use of bioethanol as an alkylation agent. While being less reactive, ethanol is renewable. On the other hand, the non-renewable isobutylene is more reactive. Etherification of bioglycerol with bioethanol was studied over H-beta zeolite catalysts and over ion-exchange resins in acidic form. Selectivity to di- and triethyl ethers of glycerol over H-beta zeolite at 200?°C after 8?h was up to 49%, while over Purolite catalyst at 180?°C (at the upper limit of its thermal stability) only 14%. Recycling the formed diethyl ether, as a by-product of glycerol ethylation, can significantly increase the yield of di- and triethyl ethers. To increase the yield of the desired di- and tri-alkyl ethers, a consecutive tert-butylation of the remaining hydroxyl groups of glycerol by isobutylene at mild reaction conditions was used (over ion-exchange resin Purolite or Amberlyst 35 as catalysts at a reaction temperature 80?°C). The best results of tert-butylation have been obtained over Purolite CT 169 DR (dry form) at 80?°C after 8?h. The overall selectivity to diethyl, triethyl, di-tert-butyl, tri-tert-butyl, and mixed diethyl-tert-butyl and ethyl-di-tert-butyl ethers of glycerol was 93.3%. Comparable results were obtained over Amberlyst 35 dry catalyst as well. The alkylation was carried out in two steps. The first step was ethylation of glycerol at 200?°C over zeolite catalyst, and the second one was tert-butylation of the products of ethylation over ion-exchange resins as catalysts at 80?°C. The mixture of di- and tri-alkyl ethers with very low concentration of mono-ethers can be potentially used as oxygenate additives to diesel fuels.Graphical abstract