(521i) Optimization of Process Parameters for Solketal Synthesis Using Microwave Reactor: Catalytic Activity and Reactor Energy Model

During biodiesel production, a huge quantity of glycerol is produced as a byproduct. To utilize effectively the surplus glycerol, it is essential to convert glycerol to value-added product. The use of microwave (MW) assisted chemistry shows the effects such as short reaction times, clean and improved product yields, and less waste generation. Glycerol acetalization is an acid-catalyzed reaction of glycerol with aldehyde or ketone. In the present work, MW energy has been used for solketal synthesis using modified sulfated zirconia (Zr-S-400, Zr₆₀₀-S-400, and Zr₆₀₀-S-600) as a catalyst. To improve the surface area, pore diameter, and acidity of the catalyst, pre and post-thermal treatment was imparted to sulfated zirconia. Catalysts were characterized by BET, FTIR, SEM, and XRD techniques. To maximize the conversion of glycerol reaction temperature (40-56C), the concentration of doped (Mn & Ni) and un-doped catalyst, the acidity of the catalyst (0.5-1M) was optimized (at a constant microwave power of 250W) by Box-Behnken design (BBD) using Design-Expert Version 11 (Stat-Ease, Inc. Minneapolis). Reaction mixture was analyzed by Thin Layer Chromatography (TLC) and confirmed by Gas Chromatography-Mass Spectrophotometer (GCMS). At optimized conditions, maximum conversion (93%) was obtained with Zr-S-400 (surface are:13.25 m²/g) catalyst though it had a lesser surface area compared to Zr₆₀₀-S-600 (surface area:18.81 m²/g). FTIR results indicated that post-thermal treatment of the catalyst (Zr₆₀₀-S-400, and Zr₆₀₀-S-600) at a higher temperature (600^°C) showed the decomposition of zirconium sulfate, which might have reduced the activity of the catalyst and resulted lower conversion. Scale-up of the laboratory experiments with the utilization of MW as a CSTR was also performed. From model equations, it was found that with time volumetric flow rate should be increased to control the reactor volume. Maximum value obtained 122.45 at the rate constant value (113 min^-1) and 93.26% conversion was achieved for this case.