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Chemicals from Paraffin Hydrocarbons
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
In the partial oxidation reaction (Arutyunov, 2007), methane and other hydrocarbon derivatives in natural gas react with a limited amount of oxygen (typically from air) that is not enough to completely oxidize the hydrocarbon derivatives to carbon dioxide and water. With less than the stoichiometric amount of oxygen available, the reaction products contain primarily hydrogen and carbon monoxide (and nitrogen, if the reaction is carried out with air rather than pure oxygen), and a relatively small amount of carbon dioxide and other compounds. Subsequently, in a water-gas shift reaction, the carbon monoxide reacts with water to form carbon dioxide and more hydrogen. 2CH4+O2→2CO+2H2(partialoxidationofmethane)CO+H2O→CO2+H2(water-gasshift)
Hydrogen Production from Biomass
Published in Vladimir Strezov, Hossain M. Anawar, Renewable Energy Systems from Biomass, 2018
() Water gas shift reaction: CO + H2O⇌H2+ CO2 () Dry reforming of tar: CnHm(tar)+CO2→ CO + H2 () Cracking of tar: CnHm(tar)→ C + H2
Future Fuels
Published in Arumugam S. Ramadhas, Alternative Fuels for Transportation, 2016
Fast pyrolysis takes place at higher temperatures; a rapid heating process in which water vapor is produced that is condensed to a dark brownish liquid bio-oil. The yield of bio-oil depends upon proper choice of reactor configuration; biomass feedstock particle size, and heat and mass transfer rate. Fast pyrolysis produced bio-oils can be easily transported. Moreover, small pyrolysis can be installed where sufficient amounts of biomass are available for fast pyrolysis. This bio-oil is steam reformed to hydrogen and carbon monoxide. The water–gas shift reaction is used to convert the reformed gas into hydrogen. The pressure swing adsorption is used to purify the product. The yield from the gasification process is higher than the pyrolysis process. Moreover, the yield increases with steam to sample ration in the reaction. Jong (2008) assumed the typical reaction for biohydrogen production is given as: CH1.98O0.76+1.24H2O→CO2+2.23H2.
Morphology and Growth Region Analysis of Carbon Nanotubes Growth in Water-Assisted Flame Synthesis
Published in Combustion Science and Technology, 2023
N. Hamzah, M. F. Mohd Yasin, M. T. Zainal, M. Mohd Sies, M. Z. Mohd Yusop, C. T. Chong, N.A. Mohd Subha, M. S. Rosmi Rosmi
The chemical effect of water vapor in a high-temperature environment also plays a critical role in reducing the formation of an amorphous carbon layer, as shown in Figure 7. Two main mechanisms that are responsible for the ACLT reduction are the regulation of carbon supply through modification of gas-phase reaction and the etching effect of water on the amorphous carbon surface (Cho, Schulz, Shanov 2014; Hata et al. 2004; Heras and Viscido 1988; Vander Wal 2002). Addition of water vapor to the methane fuel increases the concentration of water around 22% within the CNT growth region, as shown in Figure 2d. Water as a component in water-gas shift reaction reduces the carbon source precursors such as CO by directing the reaction equilibrium toward the formation of CO2 and H2 through the law of mass action (Turns 2000; Vander Wal 2002). The shift in the reaction significantly reduces the carbon supply that in turn reduces the formation rate of the amorphous carbon layer. FESEM images in Figure 7 illustrate the reduction in ACLT from the conventional to the water-assisted synthesis. There are two main possible reaction paths of the water vapor etching process on the amorphous carbon surface, as shown in Figure 7. First, the etching of a amorphous carbon surface can occur on the surface of the catalyst through dissociation of water molecules on the catalyst surface to hydrogen (H+) and hydroxide (OH−) ions. The hydroxide ions readily gasifies amorphous carbon to form CO and reduces the overall thickness of the amorphous carbon layer (Bartholomew 1982; Heras and Viscido 1988; Little 2003; Vander Wal 2002). Second, water is an effective oxidizing agent for the carbon precipitate at around 800°C through the water-gas reaction, C(s) + H2O(g) → CO(g) + H2(g) (Yoshihara, Ago, Tsuji 2007; Yu et al. 2006). Since the growth region temperatures are fixed around 800°C, the carbon supply regulation through the water-gas reaction is highly probable. By considering the flame structure in Figure 2d, a higher water concentration within the CNT growth region for flame 4 indicates a more dominant etching effect of water on the surface of the catalyst particle compared to that in flame 1. Overall, the present observation on the flame characteristics and amorphous carbon layer thickness indicates the effect of water vapor on the reduction of amorphous carbon layer thickness through regulation of carbon supply and a variant of water etching effects within the growth region.