Enhance glycerol conversion through co-etherification with isobutene and tert-butanol

Abstract

tert-Butyl glycerol ethers obtained from etherification of glycerol with isobutene or tert-butanol are desirable fuel additives. While glycerol etherification with isobutene has high glycerol conversion and yield to the desired ethers, it undergoes intricate interphase mass-transfer and the rate is restricted by the low reactant concentration resulting from phase separation. On the contrary, although glycerol etherification with tert-butanol avoids phase separation, the conversion and yield are relatively low due to equilibrium limitation and/or the inhibition from the produced water. We proposed to etherify glycerol with isobutene and tert-butanol simultaneously (co-etherification) to enhance glycerol conversion. Multiphase chemical equilibrium was calculated to explore the phase states of reaction mixtures as well as the equilibrium conversions and yields under a wide range of conditions. The co-etherification was then demonstrated on NKC-9 catalyst, which validated that the solvation function of tert-butanol to the glycerol-isobutene mixture improved the glycerol conversion rate (up to twice). Isobutene addition raised glycerol conversion and yield to the poly-substituted ethers comparing with the etherification with tert-butanol. Co-etherification (G:IB:TBA = 1:3:1) yielded 0.573 poly-substituted ethers at 353 K, while the yield was only 0.069 in the G-TBA etherification (G:TBA = 1:4). Moreover, the presence of tert-butanol effectively hindered the undesired isobutene dimerization.