Selective hydrogenolysis of glycerol to propylene glycol by using Cu:Zn:Cr:Zr mixed metal oxides catalyst

• Hydrogeneolysis of glycerol to propylene glycol using a novel Cu:Zn:Cr:Zr catalyst.
• Zn and Zr improved catalyst activity and selectivity towards propylene glycol.
• Hydrogenolysis of crude and pure glycerol with 80 wt% solution was also carried out.
• Pure and crude glycerol resulted into 97 and 90% of propylene yield, respectively.
• The catalyst is reusable.

Hydrogeneolysis of glycerol to propylene glycol has high interest due to cost and ease of availability of glycerol. In this study, Cu:Zn:Cr:Zr based catalyst was used for selective hydrogeneolysis of glycerol to propylene glycol. It was observed that incorporation of zinc and zirconium in Cu:Cr catalyst matrix improved glycerol conversion and propylene glycol selectivity. This improvement is due to increases in acidity which is confirmed by NH3-TPD and Cu dispersion in the catalyst matrix which is measured by CO-chemisorption. XRD results confirmed the presence of active metallic Cu in the reduced catalyst. The liquid phase reaction was carried out with 80 wt% of glycerol solution at 240 °C, with 4 MPa of hydrogen pressure and 3 wt% catalyst loading. The novel catalyst Cu:Zn:Cr:Zr with the elemental molar ratio of 3:2:1:3 gave 100% of pure glycerol conversion and 97% of propylene glycol selectivity. The effects of temperature, hydrogen pressure, glycerol concentration and speed of agitation were studied for reaction optimization. A hydrogenolysis of crude glycerol obtained from biodiesel process, was also carried out under similar reaction condition to yield 90% of propylene glycol. Kinetic study was delineated and reaction followed the pseudo first order with respect to glycerol. The apparent activation energy was found to be 31.7 kcal/mol. The catalyst has good reusability up to four runs.

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