Hydrogenolysis of Glycerol

Michele Besson, Laurent Djakovitch, Pierre Gallezot, Catherine Pinel, Alain 

Institut de recherches sur la catalyse et I environnement de Lyon, UMR 5256 — CNRS- Universite de Lyon, 2 avenue Albert Einstein, 69626 Villeurbanne Cedex, 

Biomass is a renewable resource from which various useful chemicals and fuels can be produced. Glycerol, obtained as a co-product of the transesterification of vegetable oils to produce biodiesel, is a potential building block to be processed in biorefineries (1,2). Attention has been recently paid to the conversion of glycerol to chemicals, such as propanediols (3, 4), acrolein (5, 6), or glyceric acid (7, 8). 

Propylene glycol, i.e., 1,2-propanediol (1,2-PDO), is an important commodity chemical. It is used as biodegradable functional fluids and as precursors for the syntheses of unsaturated polyester resins and pharmaceuticals (9-10). Propylene glycol is currently produced from petroleum-derived propylene via oxidation to propylene oxide and subsequent hydrolysis (9, 11). However, the rising cost of propylene provides an incentive to find a substitute to propylene for this 

Several supported metalhc catalysts were evalrrated for the selective hydrogenolysis of glycerol. Initially, the reactions were performed tmder acidic conditions in order to promote the formation of 1,3-PDO. Rutheniirm-based catalysts were found to be the most active catalysts but significant amount of tmdesired products resulted from C-C cleavages were detected. On the contrary, Rh/C catalysts were found selective to C-O cleavages. As far as the selectivity to 1,3-PDO was concerned, we previously reported that the addition of iron salts in the medium improved the l,3-PDO/l,2-PDO selectivity (11). A systematic study on the influence of additives was therefore carried out in the present investigation. Mineral and organic acids were evaluated for this purpose (Table 35.1). 

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Dasari, M.A., Kiatsimkul, P., Sutterlin, W.R., Suppes, G.J. (2005) Low-Pressure Hydrogenolysis of Glycerol to Propylene Glycol. Applied Catalysis A General, 281,225-231. 

Figure 35.2 Influence of lanthanide salts addition on the hydrogenolysis of glycerol.

The hydrogenolysis of glycerol was studied over a large range of pH in order to determine the optimal pH value at which the higher reaction rate and selectivity to 1,2-PDO are obtained. Selected results are summarized in Table 35.2. In the presence of Rh/C and under neutral conditions (pHi = 5.5), a low conversion of glycerol was achieved (< 4%) after 48 h. The main product was 1,2-PDO, but EG, 1-propanol, ethanol and 1,3-PDO were also detected. Increasing the initial pH from 5.5 to 12.0 had beneficial effects both on the conversion and selectivity. The selectivity to EG decreased from 13% under neutral condition to less than 1% while the selectivity toward the desired 1,2-PDO increased from 52% to 96%. 

Scheme 35.3 Proposed routes for the catalytic hydrogenolysis of glycerol.

In conclnsion, it was shown that the hydrogenolysis of glycerol in the presence of heterogeneous rhodium-based catalysts yielded mainly either 1,2-, or 1,3-propane diol. Many parameters influenced the activity and the selectivity of the catalysts, particnlarly the presence of metal additives and the initial pH value. 1,2-propanediol can be obtained nearly quantitatively at high pH. Further woik is currently under progress in order to optimize this reaction. 

Many systems have been described for the hydrogenolysis of glycerol, yielding mainly 1,2-propanediol. Copper chromite-based catalysts seem to be the better performing ones. Unfortunately, most of the data available is of a descriptive nature and a fundamental understanding of the catalyst is often missing. 

Maris, E.P. and Davis, RJ. 2007. Hydrogenolysis of Glycerol Over Carbon-Supported Ru and Pt Catalysts../. Catal., 249, 328-337. 

In contrast, selective hydrogenolysis of glycerol to 1,3-propanediol by means of chemo catalysis is still a challenging task. Although several attempts do exist with, for example, Pt/W03/Zr02 or Ir-ReOx/Si02 catalysts [48, 49], the enzyme-catalyzed route using bacterial strains is more efficient [42] and has been commercialized (see Table 2.2.1). 

Bienholz A, Blume R, Knop-Gericke A, Giergsdies F, Behrens M, Claus P. Prevention of catalyst deactivation in the hydrogenolysis of glycerol by Ga203-modified copper/zinc oxide catalysts. J Phys Chem C. 2011 115 999-1005. 

Hydrogenolysis of Glycerol and Tetrahydrofurfuryl Alcohol (THFA) Using Rh-MOj,-... 

Hydrogenolysis of glycerol to 1,2- and 1,3-propanediols (PrD) seems to be simple judging from the reaction formula as below (1, 2) because the hydrogenolysis of C-O bonds apparently means the dissociation of C-O bonds and insertion of hydrogen atoms. 

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