A facile and greener synthesis of butylene carbonate via CO2 utilisation using a novel copper–zirconia oxide/graphene catalyst

The cumulative CO2 emissions in the atmosphere are causing serious changes in climate via global warming because of continuous burning of fossil fuel. However, the scientific community has identified the means to alleviate the environmental burden through carbon capture and storage, and utilisation of CO2 for synthesis of value added chemicals. The latter greener approach for utilising CO2 as a C1 feedstock for organic chemical synthesis is extremely beneficial not only for the chemical industry but also for contributing to limit its emissions. The direct synthesis of butylene carbonate (BC) through cycloaddition reaction of CO2 to butylene oxide (BO) is of a great commercial interest. BC is an excellent reactive intermediate material used in industry for the production of surfactant, plasticisers, polymers and can also be used as a solvent for wood binder resins, degreasing, paint remover, lubricants and the foundry, sand binders as well as lithium battery because of its high polarity property. Several reaction routes have been attempted for BC production, e.g. phosgene, oxidative carboxylation, direct synthesis using homogeneous catalyst and direct synthesis using a heterogeneous catalyst. The latter being the most attractive route due to the inexpensive raw material, ease of catalyst recovery and avoidance of corrosive reagents, such as phosgene. In the present work, a facile and environmentally benign method has been developed for the synthesis of highly efficient graphene-inorganic heterogeneous catalyst, represented as Cu–Zr/GO inorganic composite. The graphene-inorganic heterogeneous catalyst has been characterised using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and nitrogen adsorption/desorption method (for measuring BET surface area and pore size distribution). Copper-zirconia/graphene inorganic composite catalyst (Cu–Zr–GO) as heat treated at 723 K exhibited high catalytic activity as compared to other reported heterogeneous catalysts in the absence of any organic solvent with 71% yield of BC, and 87% selectivity towards BO at the reaction conditions of 423 K, 80 bar in 12 h. The use of Box-Behnken Design (BBD) from Response Surface Methodology (RSM) has been employed to investigate the single and interactive effect of several independent reaction variables that include temperature, pressure, catalyst loading, heat treatment and time, on the conversion of BO and yield of BC. Two quadratic regression models have been developed representing an empirical relationship between each reaction response and all the independent variables. The predicted models have been validated statistically and experimentally, where very high agreement has been observed between predicted and experimental results with approximate relative errors of ±1.25% for BO conversion and ± 0.75% for BC yield. Acknowledgments We acknowledge the financial support from London South Bank University and The British University in Egypt.