Thermodynamic and kinetic studies of a catalytic process to convert glycerol into solketal as an oxygenated fuel additive

Glycerol is a byproduct of biodiesel industry and can be converted into high value-added applications. The heterogeneous ketalization of glycerol with acetone was conducted over a solid acid catalyst of Amberlyst-35 in a batch reactor. The thermodynamics and kinetics of the ketalization reaction for the synthesis of solketal were investigated. The reaction equilibrium constants were determined experimentally in the temperature range of 293-323 K, with which the following standard molar properties ( at 298 K) were obtained: Delta H-0 = -30.1 +/- 1.6 kJ mol 1 1, Delta G(0) = -2.1 +/- 0.1 kJ mol (1), Delta S-0 = -0.1 +/- 0.01 kJ mol (1) K-1. Effects of various experimental conditions ( stirring speed, catalyst addition amount, pressure, temperature, moisture content and the feed composition) on the reaction kinetics ( glycerol conversion and solketal yield vs. time) were also investigated in this work. A two-parameter kinetic law based on a Langmuir-Hinshelwood rate expression was used. The activation energy of the overall ketalization reaction was determined to be 55.6 +/- 3.1 kJ mol (1). The obtained solketal could be synthesized from renewable resources like bioglycerol and biomass derived acetone, and seem to be a good candidate for different applications such as fuel additive and in pharmaceutical industries. The work is an important step for further development of a technology for the continuous synthesis and separation of solketal from glycerol and acetone. (C) 2013 Elsevier Ltd. All rights reserved.