Title : Tuning acidity in metal organic frameworks-based catalysts for enhanced production of Butyl Butyrate as a biofuel additive
In an attempt to optimize the production of biofuel additives from biomass-derived components, different structures of metal organic frameworks (MOFs) were synthesized to serve as catalysts for the esterification reaction of butyric acid with butanol to produce a green fuel additive, butyl butyrate. The thrust of this study is to understand at a fundamental level the relations between the structure, properties and catalytic performance of champion materials that confer upon them the capacity to function as efficient esterification catalysts. For this purpose, a variety of MOFs were synthesized and fully characterized by X-ray diffraction, electron microscopy, Brunauer–Emmett–Teller (BET) measurements and thermogravimetric analysis. Their acid density was evaluated using back titrations. All prepared MOFs were efficiently used as catalysts of the liquid-phase esterification reaction for the production of butyl butyrate. Interestingly, 91% conversion was achieved by employing one of the most acidic members as a heterogeneous catalyst, which is very close to the 96% conversion obtained by the conventional homogeneous liquid catalyst H2SO4. This exceptional rate was attributed to its superior acid density which was found to be the key factor to high conversion. All MOFs were easily separated from the reaction medium, recycled, and reused without significant loss in activity after at least four cycles. XRD analysis and acidity test of the recycled MOFs confirmed that their acidity and crystallinity were retained. With this knowledge, catalytic conversion rates and efficiencies of MOFs can be engineered from a laboratory prototype and optimized by tuning the functional groups of the organic linkers to serve as effective catalysts for the production of fine chemicals such as biofuels.