DEVELOPMENT OF METAL ORGANIC FRAMEWORK CATALYST FOR CONVERSION OF GLYCEROL TO VALUABLE CHEMICALS

Abstract

Value addition of the excess (~10 wt.%) glycerol obtained from the biodiesel industry has gain significant attention due to the overall economic viability of the biodiesel plant globally. Among the various glycerol conversion process proposed in the previous decades, conversion of glycerol to propylene glycol (PG) is very promising due to the very high commercial value of PG. During last two decades, various noble and non-noble metal catalysts have been developed and their performance are examined. However, the information related to the application of a newly proposed hybrid material i.e Metal organic frameworks (MOFs) and MOFs derived catalyst for the conversion of glycerol is very limited. In this study, highly active MOFs and modified MOFs such as MOF-5, Cu/MOF-5, Cu-BDC, Cu-BDC/MgO and catalysts derived from MOFs precursors were developed. For Cu-BDC/MgO catalyst, copper to magnesium weight ratio was varied from (0.7-9) in the catalyst. Solvothermal and direct mixing methods were used to develop the MOFs and modified MOFs catalysts. MOFs derived material was synthesis by atomic layer deposition followed by the solvothermal method. Solvothermal method was found to be more effective for the synthesis of MOFs. The physico-chemical properties of the catalysts were characterized by various techniques such as specific surface area (BET), X-ray diffraction (XRD) study, scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) and thermogravimetric analysis(TGA). Characterization results confirmed very higher specific surface area (>1000 m2/g) of MOF-5 and Cu-BDC catalyst.. However, for modified MOFs catalyst with different metal guest molecules the surface area (~244 m2/g) was reduced significantly. The catalytic activity of all synthesized catalysts were determined in a high-pressure autoclave as well as in high pressure continuous fixed bed reactor at various reaction conditions. The results obtained in both the reactors were compared. Effect of various reaction parameters such as catalyst loading and feed concentration were examined to maximize the glycerol conversion and propyleneglycol selectivity. The results demonstrated that, Cu1.8Mg1.2-BDC catalyst derived from Cu-BDC-MOF was the most active and selective for propylene glycol formation. The maximum glycerol conversion of ~78% with very high selectivity (~93%) to PG (1,2-propanediol) was obtained in liquid phase reaction at 220oC and at 4.5 MPa pressure after 12 h of reaction. However, in the continuous reactor the similar results were obtained at mild reaction condition.