Development of environmentally benign green processes for utilization of carbon dioxide to synthesize value-added compounds using heterogeneous catalysis is desirable. One such proposed process is the cycloaddition of styrene oxide with carbon dioxide to synthesize styrene carbonate, synthesis of which has been well studied using various homogenous catalysts. The aim of the current work was to develop an active, selective and reusable heterogeneous catalyst for the cycloaddition of carbon dioxide to styrene oxide. Various solid catalysts such as 0.1% Li/MgO, calcined hydrotalcite (CHT), La–Zr mixed oxide (1:3 La/Zr), 0.1% La/MgO and ZrO2 were employed for cycloaddition of carbon dioxide to styrene oxide. Carboxylation of styrene oxide with carbon dioxide is enhanced by catalysts having both strong basic sites and weak acidic sites. Lanthanum–zirconia mixed oxide was prepared by combustion method using different compositions and evaluated for this reaction. La/Zr ratio of 1:3 was found to be the best among all studied and gave 90% conversion of styrene oxide with 100% selectivity of styrene carbonate at moderate temperature and pressure conditions in 3 h. The catalyst was characterized by various techniques to understand its textural properties. The catalyst was reused over three cycles without any loss of activity. The optimum reaction conditions were obtained by studying all process parameters in a laboratory batch stirred tank reactor (speed of agitation-1000 rpm, catalyst loading-2 × 10−2 g/cm3, 0.01 mol styrene oxide, DMF as solvent (total volume 30 mL), CO2 pressure-2.5 MPa, 130 °C). A detailed mathematical model was developed using Langmuir–Hinshelwood-Hougen–Watson mechanism in the absence of any transport resistances. The activation energy was calculated as 19.1 kcal/mol. The process is green and clean.
Clean Technologies and Environmental Policy – Springer Journals
Published: Dec 26, 2017
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