Recent advances in glycerol hydrochlorination: Impact of reaction temperature, hydrogen chloride solubility and reaction intermediates

A homogeneously catalyzed gas–liquid process, glycerol hydrochlorination was studied in a semibatch reactor with gaseous hydrogen chloride (HCl) as a continuous phase and acetic acid as homogeneous catalyst. Several experiments were conducted varying the temperature in the jacket of the reactor in the range 70–115 °C and the catalyst mole fraction between 0 and 15 mol-%. The effects of HCl on the kinetics was investigated by changing the partial pressure of HCl in the range 0.25–1 atm by diluting HCl with inert gas, while the absolute pressure of the reactor was remained constant at atmospheric pressure. The experiments revealed new information about this particular reaction system. Considerable changes in the reactor temperature occurs, temperature changes close to 20 °C, which are an effect of the absorption process of gaseous HCl. The HCl uptake in the liquid phase exhibits a strange behavior at the beginning of the reaction, associated to the appearance of water and the temperature change during the experiments. The experiments also revealed that a part of the catalyst is transformed into esters in the presence of glycerol and 3-chloro-1,2-propanediol (α-MCP), particularly at high catalyst concentrations. These esters were detected and an improved gas-chromatographic method was developed to analyze these quantitatively. In long run, the esters are converted back to the original catalyst, acetic acid, as the reaction stops because of lack of glycerol. The information provided by the experiments in this work gives better understanding of the reaction mechanism and thus they are the basis for a rational design of glycerol hydrochlorination reactors.