On the kinetics of multiphase etherification of glycerol with isobutene

The etherification of the hydroxyl groups of glycerol with isobutene successively forms mono-ethers (ME), di-ethers (DE) and tri-ether (TE) of glycerol, which are desired fuel additives. The initial rates of each step in the consecutive etherification were measured independently under various concentrations and temperatures. The initial rate of ME synthesis from glycerol and isobutene was independent of the initial composition due to the invariant concentrations of reactants in the reaction phase. Adding ME to the glycerol-isobutene reaction was observed to accelerate the glycerol conversion by enhancing the solvation of isobutene in glycerol. Rate expressions in the form of power-law with parameters regressed from initial rates measured separately for each etherification step were found to be unable to predict the kinetics of complex reaction where all reaction steps coexisted together. This signifies significant interaction of reactions and competitive adsorption of reactants. Glycerol etherification with isobutene under high conversions where all reactions and reactants exist simultaneously was carried out to obtain kinetic data containing the interactions between different reactions. Thereafter a model considering phase separation and competitive adsorption was proposed and correlated with the initial rates and kinetic data under high conversions. The model was capable to describe all observed kinetics.