Catalytic conversion of glycerol to olefins over modified ZSM-5 zeolite catalysts
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Date
2014
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Publisher
Universiti Teknologi Malaysia
Abstract
Glycerol, an alcohol and oxygenated chemical byproduct from biodiesel production, has enormous potential to be converted into higher value-added fuels and chemicals. Due to the alarming excessive production of glycerol worldwide that have triggered environmental concerns, and the importance of olefins in the industry, it is therefore essential to explore the process of glycerol-to-olefin (GTO) in greater depth. This is mainly due to the fact that no dedicated study concerning GTO has been performed. In this present research, the activity and yield towards light olefin in the glycerol steam reforming process was tested and analyzed using zeolite ZSM-5 catalysts modified with selected metals across the periodic table and characterized using X-Ray Diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier Transform Infrared Spectroscopy (FTIR), Temperature Programmed Desorption (TPD) and Temperature Programmed Reduction (TPR). Then GTO process involving the best performing catalyst, Cu/ZSM-5, yielding light olefin of 16.3% was further optimized using Response Surface Methodology (RSM) to obtain the most optimum operating condition. The best olefin selectivity and yield were 22.87% and 17.68%, respectively. Multi-Response Objective Genetic Algorithm (MRO-GA) was then performed to give optimum olefin selectivity of 22.06% and yield of 17.84% at the following optimum conditions: T=923K, WHSV=116.54hr-1 and glycerol concentration=26.91%. The reaction kinetic analysis revealed fractional positive values for the order of reaction for products whilst calculated reaction activation energy was 51.88 kJ/mol and pre-exponential constant was 3720.9 mmol.m-2s-1. A reaction model and the reaction mechanism consisting 18 reactions on the catalyst acid surface single-site based on Langmuir-Hinshelwood model were then generated. Thermodynamic analysis was also carried out to investigate the trend of light olefin yield as a function of temperature, pressure and glycerol to water ratio (GWR). The thermodynamic analysis revealed that light olefin formation is minute and occured at temperatures between 873 to 1073K for various GWR. The effect of co-feeding with CO2 shows more encouraging results towards light olefin formation. At thermoneutral point, optimum C2H4 production occurred at 778.44 K (GWR 2:1 and P=1 Bar). In conclusion, GTO offers viable, sustainable and environmental friendly technology for green olefins production from renewable resources, and concerted efforts should be geared to explore its potential
Description
Thesis (PhD. (Chemical Engineering))
Keywords
Zeolite catalysts, Glycerin—Biotechnology, Alkenes—Analysis