Chemical and Technical Aspects of the Synthesis of Chlorohydrins from Glycerol

In the synthesis of biodiesel via the transesterification of vegetable oils, 10 wt % of glycerol is obtained as byproduct. This means that, by increasing the biodiesel production, the glycerol availability also increases and its cost goes down more and more. In order to consume the large amount of glycerol derived from biodiesel production in a profitable way, only two strategies are possible: (i) use glycerol as raw material to produce fuel additives and (ii) use glycerol as raw material to produce commodities. In the present work, we have briefly considered the first aspect while focusing, in particular, on the second opportunity by reviewing the production of chlorohydrins by glycerol hydrochlorination with HCl. Chlorohydrins are important intermediates in the production of epichlorohydrin used to produce epoxy–resins. The advantages of producing chlorohydrins by starting from glycerol instead of propene—that is, the classical route—will be discussed. The glycerol hydrochlorination reaction is catalyzed by carboxylic acids, and in this work, we describe (i) the reaction conditions normally adopted; (ii) the behavior of different catalysts proposed in the literature (concerning activity and selectivity); (iii) the reaction mechanism; (iv) the kinetic laws, reported by different authors, along with the related parameters; and (v) the role of mass transfer. A brief discussion on the best reactors for performing the reaction and some information about the different processes used to produce epichlorohydrin starting from glycerol will also be reported. Some catalysts, other than carboxylic acids, have also been briefly reviewed, although they have not been used in industrial plants until recently.