Surplus glycerol from biodiesel production can be transformed to valuable fuel additives through etherification with isobutene [1, 2]. Our previous work has studied the kinetics and thermodynamics of this reaction [3, 4]. Previous design studies have also appeared [5-7]. In the present work, we propose a novel process design and address its optimization.
The proposed process starts with a continuous stirred tank reactor to carry out the etherification reaction. Fresh glycerol is used to extract mono-ethers from the reaction product and is recycled back to the reactor. The raffinate of the extraction is washed by water to remove residual glycerol, and then is fed to a distillation column to separate isobutene. Dimers of isobutene are taken out of the system via a side stream, and the desired di-ethers and tri-ether of glycerol are obtained at the bottom of the distillation column. The glycerol in the waste water is recycled after steaming out water in another distillation column. This process avoids steaming out a large amount of high boiling point materials appearing in the Behr and Obendorf process . Also “pure” glycerol ethers are obtained, which can not only be mixed with biodiesel as well as in the Di Serio et al. process , but also be added to gasoline and diesel.
Rigorous models were developed for the various units and then connected to form a plant wide model. An optimization problem was formulated to minimize the cost of production of the glycerol di-ethers and tri-ether. The resulting mixed-integer nonlinear programming (MINLP) problem enables simultaneous determination of key design variables including number of column trays, feed tray location of column, volume of reactor, process flowrates etc. The optimization problem was solved in gPROMS.
 J.F. Izquierdo, M. Montiel, I. Palés, P.R. Outón, M. Galán, L. Jutglar, M. Villarrubia, M. Izquierdo, M.P. Hermo, X. Ariza. Fuel additives from glycerol etherification with light olefins: State of the art. Renew Sust Energ Rev, 2012, 16, 6717-6724.
 V. Cruz, S. Hernandez, M. Martín, I. E. Grossmann. Integrated synthesis of biodiesel, bioethanol, isobutene, and glycerol ethers from algae. Ind Eng Chem Res, 2014, 53, 14397-14407.
 J. Liu, B. Yang, C. Yi. Kinetic study of glycerol etherification with isobutene. Ind Eng Chem Res, 2013, 52, 3742-3751.
 J. Liu, Y. Yuan, Y. Pan, Z. Huang, B. Yang. Liquid–liquid equilibrium for systems of glycerol and glycerol tert-butyl ethers. Fluid Phase Equilibr, 2014, 365, 50-57.
 P.G. Vijai, P. Berwyn. Glycerine ditertiary butyl ether preparation. Patent: 5476971, 1995.
 A. Behr, L. Obendorf. Development of a process for the acid catalyzed etherification of glycerine and isobutene forming glycerine tertiary butyl ethers. Eng Life Sci, 2002, 2, 185-189.
 M. Di Serio, L. Casale, R. Tesser, E. Santacesaria. New process for the production of glycerol tert-butyl ether. Energ Fuel, 2010, 24, 4668-4672.