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: ΔH0 = −30.1 ± 1.6 kJ mol−1, ΔG0 = −2.1 ± 0.1 kJ mol−1, ΔS0 = −0.1 ± 0.01 kJ mol−1K−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.