Gypsum based catalysts for the catalytic synthesis of glycerol carbonate / Nor Ain Syuhada Zuhaimi

Faculty of Industrial Sciences and Technology

Thesis (Master of Science (Industrial Chemistry)) -- Universiti Malaysia Pahang – 2017

Bibliography : p. 104-117

Synthesis of glycerol carbonate from glycerol has attracted the interest from many researchers across the world due to their interesting chemical properties. However, the tremendous growth of biodiesel have make drop of glycerol’s price due to the excessive production of glycerol. Therefore, researchers find it necessary to tune this chemical into a value added compound such as glycerol carbonate. In this study, the catalytic carbonylation of glycerol with urea in the presence of treated commercial gypsum and red gypsum as catalyst are reported for the first time. Gypsum (CaSO4•2H2O) is one of the waste materials produced from advanced material industrial processing plant. Red gypsum is an unwanted by-product from titanium dioxide manufacturing industry. The effects of physical and chemical pre-treatment procedures on both gypsums were investigated. To obtain the catalyst structure-activity relationship, the treated catalysts were characterised by means of several characterisation techniques (i.e., XRD, TGA, BET surface area, SEM, CO2–TPD, NH3–TPD and Hammett test). Tunable physicochemical properties of gypsum based catalysts were successfully prepared by varying the pre-treatment techniques, which later on contributed to the variation of catalytic activity toward glycerol carbonate formation from glycerol. The highest catalytic activity obtained was for catalyst consisting β-CaSO4 phase where it produced 83.6% yield of glycerol carbonate for commercial gypsum and 87.4% for red gypsum, respectively. The presence of Ca2+ acts as Lewis acid sites while (SO4)2- acts as conjugate basic sites in gypsum based catalysts is responsible for the catalytic activity. Optimisation for the red gypsum catalyst showed that the suitable parameters for catalytic testing were 150 °C, 340 rpm and 0.25 g (1.81 wt%) with 4 h reaction time respectively. Gypsum catalyst is easily recoverable and reusable for subsequent cycles of reaction. Similar physico-chemical properties of fresh and used catalyst were confirmed through XRD and SEM. Besides, the mechanistic pathway of glycerol carbonate was confirmed through the formation of glycerol carbamate as intermediate compound which was further established through time on-stream analysis study using 13C NMR and ATR–FTIR, respectively. The study clearly supports conversion of waste into wealth while promising proper disposal of waste to produce value added product.