Bio/catalytic synthesis of methacrylic acid
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Methacrylic acid was synthesized from the bio-based substrates citric acid, itaconic acid, and 2-hydroxyisobutyric acid. Hydrotalcite, a solid base catalyst, was employed to form methacrylic acid through decarboxylation of itaconic acid and citric acid. The effect of varying temperatures, catalyst mass, residence times and substrate concentrations on methacrylic acid concentration and yield was determined. Comparing yields of methacrylic acid in each series of reactions resulted in finding an optimum substrate to catalyst mass ratio where methacrylic acid yield reaches to its highest value (9.6 g-substrate/g-catalyst and 22.7% yield for citric acid, 6.4 g/g and 22.9% yield for itaconic acid). Catalyst reusability experiments resulted higher methacrylic acid yields. Methacrylic acid was also formed from 2-hydroxyisobutyric acid in a single-step dehydration reaction. Among these three substrates, the highest yield of methacrylic acid (71.48 %) was achieved at 275 °C and a 1 minute residence time using 2-hydroxyisobutyric acid and subcritical water.