Simultaneous etherification of isobutene with ethanol and 1-butanol over ion-exchange resins

Abstract

The simultaneous liquid-phase etherification of isobutene with ethanol and 1-butanol to give ethyl tert-butyl ether (ETBE) and butyl tert-butyl ether (BTBE) has been studied, at temperatures in the range of 315-353 K and at 2.5 MPa, over six commercial acidic macroreticular ion-exchange resins as catalysts. The initial alcohol to isobutene molar ratio was varied in the range of 0.5-5.5 and the initial ethanol to 1-butanol molar ratio in the range of 0.5-2.0. Strongly acidic catalysts with a rigid polymer backbone structure enhance reaction rate. This fact, along with the reduced side reactions extent, makes Amberlyst¿ 35 the most promising catalyst, among the tested ones, for the studied simultaneous etherification process. Irrespectively of the used catalyst, initial ETBE synthesis reaction rate is hardly sensitive to the variation of the ethanol to 1‐butanol molar ratio, whereas initial BTBE synthesis reaction rate strongly diminishes at high ethanol concentration. Preferential adsorption of ethanol over 1‐butanol on the catalysts active sites has been detected. As expected, both etherification reaction rates increase at increasing isobutene concentration. At 353 K, the highest temperature, both etherification rates are affected by internal mass transfer resistances due to diffusion limitations even when small catalyst beads are used. The simultaneous process has been compared to the individual syntheses of ETBE and BTBE and it has been found that the isobutene selectivity towards ethers is enhanced in the simultaneous system.