Date

2021-2-12

Author

Göktürk, Sevil

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Today, intensive studies are carried out on alternative energy sources that will replace fossil fuels due to its limited sources, soaring of prices and negative effects on people and environment. Hydrogen energy offers a solution to minimize these problems as a clean and renewable energy carrier. One of the most important applications of hydrogen is its use in fuel cell-derived vehicles. However, the implementation of hydrogen in the transport sector is limited by the difficulty of storage and the lack of infrastructure for its distribution. On-board hydrogen generation is a great solution to overcome these limitations, particularly by allowing hydrogen produced from renewable sources to be fed directly into the fuel cell without itself being stored. Bio-glycerol is one of the most attractive biomass-derived oxygenated compounds since its utilization in hydrogen production through steam reforming process is economically viable and environmentally friendly. In addition, theoretically one mole of glycerol produces 7 moles of hydrogen gas. Bio-glycerol is produced as a by-product of 10% by weight of biodiesel synthesis produced by transesterification of vegetable oils or animal fats, allowing it to be used as a lowcost raw material in a large supply of renewable materials. Generally, metal-loaded mesoporous supports are used to achieve higher hydrogen yield in steam reforming of glycerol. In this study, silica aerogel was used for the first time as a catalyst support in the steam reforming of glycerol. To activate the silica aerogel, various types and amounts of metal precursors were loaded onto the silica aerogel by wet-impregnation or co-precipitation methods. According to the characterization results, all catalysts are mesoporous and in crystal forms with Lewis dominant acid sites. The activities of the catalysts were tested in a conventional fixed-bed quartz reactor in the presence of a constant weight of catalyst at constant carrier gas flow rate, atmospheric pressure, and various reaction parameters. According to the experimental results, the increase in water/glycerol molar ratio resulted in an increase in H2 yield, furthermore, H2 yield increased first and then decreased slightly at elevated temperatures consistent with the equilibrium line. In addition, the increase in the metal amount increased the H2 yield, while the catalyst synthesis method and loaded-metal types affected the H2 yield in various ways. In particular, Ni-Ru containing bimetallic catalysts showed greater activity among the catalysts used in the reaction. As a result of the experiments, the highest activity was achieved at 550oC, atmospheric pressure, water-glycerol feed flow rate of 0.9 ml/h and 30 ml/min of Ar flow rate with the W/G molar ratio of 9 in the presence of 0.15 g catalyst. Under these conditions, the highest H2 yield was obtained as 84.5%, with coke deposition as 0.06 gc/gcath -1 in the presence of 10Ni-2Ru/SA catalyst.

Subject Keywords

Glycerol, Hydrogen, Steam Reforming, Mesoporous Materials, Silica Aerogel

URI

https://hdl.handle.net/11511/89722

Collections

Graduate School of Natural and Applied Sciences, Thesis