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Hydrogen or syn gas production from glycerol using pyrolysis and steam gasification processes



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Glycerol is a waste by-product obtained during the production of biodiesel. Biodiesel is one of the alternative fuels used to meet our energy requirements and also carbon dioxide emission is much lesser when compared to regular diesel fuel. Biodiesel and glycerol are produced from the transesterification of vegetable oils and fats with alcohol in the presence of a catalyst. About 10 wt% of vegetable oil is converted into glycerol during the transesterification process. An increase in biodiesel production would decrease the world market price of glycerol. The objective of this work is to produce value added products such as hydrogen or syn gas and medium heating value gas from waste glycerol using pyrolysis and steam gasification processes. Pyrolysis and steam gasification of glycerol reactions was carried out in an Inconel®, tubular, fixed bed down-flow reactor at atmospheric pressure. The effects of carrier gas flow rate (30mL/min-70mL/min), temperature (650oC-800oC) and different particle diameter of different packing material (quartz - 0.21-0.35mm to 3-4mm; silicon carbide – 0.15 to 1mm; Ottawa sand – 0.21-0.35mm to 1.0-1.15mm) on the product yield, product gas volume, composition and calorific value were studied for the pyrolysis reactions. An increase in carrier gas flow rate did not have a significant effect on syn gas production at 800oC with quartz chips diameter of 3-4mm. However, total gas yield increased from 65 to 72wt% and liquid yield decreased from 30.7 to 19.3wt% when carrier gas flow rate decreased from 70 to 30mL/min. An increase in reaction temperature, increased the gas product yield from 27.5 to 68wt% and hydrogen yield from 17 to 48.6mol%. Also, syn gas production increased from 70 to 93 mol%. A change in particle size of the packing material had a significant increase in the gas yield and hydrogen gas composition. Therefore, pyrolysis reaction at 800oC, 50mL/min of nitrogen and quartz particle diameter of 0.21-0.35mm were optimum reaction parameter values that maximise the gas product yield (71wt%), hydrogen yield (55.4mol%), syn gas yield (93mol%) and volume of product gas (1.32L/g of glycerol). The net energy recovered at this condition was 111.18 kJ/mol of glycerol fed. However, the maximum heating value of product gas (21.35 MJ/m3) was obtained at 650oC, 50mL/min of nitrogen and with a quartz packing with particle diameter of 3-4mm. The steam gasification of glycerol was carried out at 800oC, with two different packing materials (0.21-0.35mm diameter of quartz and 0.15mm of silicon carbide) by changing the steam to glycerol weight ratio from 0:100 to 50:50. The addition of steam to glycerol increased the hydrogen yield from 55.4 to 64mol% and volume of the product gas from 1.32L/g for pyrolysis to 1.71L/g of glycerol. When a steam to glycerol weight ratio of 50:50 used for the gasification reaction, the glycerol was completely converted to gas and char. Optimum conditions to maximize the volume of the product gas (1.71L/g), gas yield of 94wt% and hydrogen yield of 58mol% were 800oC, 0.21-0.35mm diameter of quartz as a packing material and steam to glycerol weight ratio of 50:50. Syn gas yield and calorific value of the product gas at this condition was 92mol% and 13.5MJ/m3, respectively. The net energy recovered at this condition was 117.19 kJ/mol of glycerol fed. The steam gasification of crude glycerol was carried out at 800oC, quartz size of 0.21-0.35mm as a packing material over the range of steam to crude glycerol weight ratio from 7.5:92.5 to 50:50. Gasification reaction with steam to glycerol weight ratio of 50:50 was the optimum condition to produce high yield of product gas (91.1wt%), volume of gas (1.57L/g of glycerol and methanol), hydrogen (59.1mol%) and syn gas (79.1mol%). However, the calorific value of the product gas did not change significantly by increasing the steam to glycerol weight ratio.



Pyrolysis, Steam Gasification, Hydrogen, Syn Gas and Medium heating value gas



Master of Science (M.Sc.)


Chemical Engineering


Chemical Engineering


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