Hydrogenolysis of Aqueous Glycerol over Raney Nickel Catalyst: Comparison of Pure and Biodiesel By-Product

The hydrogenolysis of pure and biodiesel byproduct glycerol in the presence of Raney nickel catalyst using an autoclave was studied. The effects of stirring speed, temperature, amount of catalyst, H-2 pressure, and glycerol content on the conversion of glycerol, the yield of liquid products, and the selectivity of 1,2-propanediol were investigated, and the results were compared to chemically pure glycerol and crude glycerol from biodiesel production. All the experimental results obtained from the use of crude glycerol from biodiesel production were close to those Obtained from the use of chemically pure glycerol. The highest conversion of glycerol (80%) was achieved under the conditions of 35 g catalyst L-1 solution, 20% glycerol content, 40 bar H-2 pressure, 400 rpm stirring speed, and 230 degrees C temperature for the chemically pure glycerol. In order to reach the highest liquid products yield (95%) and the 1,2-propanediol selectivity (54%), the catalyst amount was decreased from 35 g catalyst L-1 solution to 7 g catalyst L-1 solution while the other conditions were unchanged. On the other hand, the highest conversion of glycerol (74%) and the highest selectivity of 1,2-propanediol (50%) for the crude glycerol were obtained under the same reaction conditions with those obtained in the use of chemically pure glycerol while the liquid products yield was 74% under the reaction conditions of 21 g catalyst/L solution, 20% glycerol content, 40 bar H-2 pressure, 400 rpm stirring speed, and 200 degrees C temperature. According to the obtained results, increasing the temperature and amount of catalyst led to the increase in the glycerol conversion and decrease in the liquid products yield and in the 1,2-propanediol selectivity. The glycerol conversion decreased and the liquid products yield and the 1,2-propanediol selectivity increased with the increasing hydrogen pressure.