Glycerol Chlorination in Gas-Liquid Semibatch Reactor: An Alternative Route for Chlorohydrins Production

In the present paper, an alternative synthetic way to obtain chlorohydrins, that are commercial products from glycerol feedstock is presented. This synthetic route to transform glycerol into these high-value chemicals involves the use of gaseous HCl and glycerol in the presence of a carboxylic acid, as catalyst, in order to obtain, as main product, alpha gamma-dichlorohydrin. Monochlorohydrins are also obtained as intermediates reaction products. As shown in a previous work some catalysts are selective in the production of the desired product, while others give monochlorohydrins as the main products. We attempted to correlate the selectivity shown by different carboxylic acids to their pK(a), but this correlation seems not of general validity and it still remains a problem to correlate the catalytic behavior with the molecular structure of the catalyst. At this purpose, in this work we have investigated the behavior of a homologous chlorinated series of catalysts, such as the following: acetic, monochloroacetic, dichloroacetic, and trichloroacetic acid, focusing in particular the attention on both activity and selectivity shown by each catalyst. A kinetic model, based on a reliable mechanism, developed in a previous work but implemented for the HCl gas liquid partition has been used for interpreting all the kinetic runs. Then, the obtained kinetic constants have been elaborated by using the Taft equation in the attempt to correlate chemical structure of the catalyst and the activity.