CONICET | Buscador de Institutos y Recursos Humanos

The reaction of hydrogenolysis of glycerol was studied in a trickle-bed three phase reactor. A thermodynamic study of possible reactions was performed. A feasible reaction network at the reaction conditions was thus written, made up of 9 reactions, including glycerol hydrogenolysis, hydrogenations and dehydrations. The phase equilibrium properties of the feedstock at the reactor inlet conditions were verified, in order to assess the relative concentration of the three phases. At all reaction conditions it was found that three phases, solid, liquid and gas, coexisted in the reactor, and that the flow pattern of the system was "trickling". Two catalysts were tested in the reaction test of hydrogenolysis of glycerol to 1,2-propanediol, copper chromite and Cu/Al2O3. The catalysts were further characterized by ICP, nitrogen sortometry, XPS, XRD, TPR and pyridine-TPD. The catalysts were quite different in composition, acidity and other physicochemical properties. In spite of these differences a similar behavior in reaction was seen. The average reaction rate per unit catalyst mass was found to be practically constant at different varying conditions. The results pointed out to the possible presence of mass transfer limitations and therefore all resistances of the system were estimated with the aid of measured and estimated properties. This study indicated that the resistance to mass transfer of hydrogen from the gas phase to the liquid phase dominated the overall kinetics of the reactor. The overall pellet resistance by diffusion and reaction was estimated to be the smallest (RDR= 5 s). The liquid-solid resistance (RSL = 23-40 s) had an intermediate value. Hydrogen G-L mass transfer resistance was found to be the highest (RG-L = 50-280 s) and thus controlled the overall reaction rate. Operation conditions were varied in different ranges (temperature 210-250 C; pressure 8-20 bar and LHSV 1.9-5.63 h-1). It was found that when the temperature was increased the selectivity to 1,2-propanediol was also increased and that a maximum existed at 230 C (97 %). At higher temperatures selectivity was decreased and different compounds were also produced, with varying nature and amount depending on the catalyst acidity. When the pressure was increased the selectivity to 1,2-propanediol was also increased, up to a value of 97% at 14 bar. Higher pressures did not modify this selectivity value.

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