Selective C-C and C-O hydrogenolysis of sugar polyols to C2-C3 polyols or partially dehydroxylated products
Résumé
Catalytic hydrogenolysis of sugar-derived polyols (e.g. sorbitol, xylitol, erythritol) in aqueous solution is likely to become an interesting route in the production of chemicals from renewables1. Both cleavage of C-C bonds and C-O bonds can occur. Smaller C2-C3 polyols or less oxygenated compounds with limited C-C bond cleavage may be obtained. In these processes, selectivity is a major issue due to the multitude and sequential steps, which result in a mixture of products. Also, the production of C2-C3 polyols (i.e. ethylene glycol (EG), propylene glycol (PG), and glycerol (GL)) by C-C cleavage is known to be favored in basic media; it would be interesting to develop a base-free process. In this contribution, we report the evaluation of catalysts and operating conditions in a series of batch experiments in order to achieve maximum yields towards desired products.
We have demonstrated in this work that Ru catalysts supported on oxide modified active carbon are selective for the hydrogenolysis of C-C bonds without excessive addition of a base. Results from C-O hydrogenolysis on Re-modified Rh and Ir catalysts have shown that the carbon length of the polyol can be an important factor, as dehydration reactions in the early stages generate less reactive intermediates. In both cases, specific interactions between the catalysts and the polyoxygenated substrates could explain the selectivity.