Showing papers by "Sushil Adhikari published in 2009"
TL;DR: In this article, the authors reviewed different generation methods, catalysts and operating conditions used to produce hydrogen using glycerol as a substrate, including steam reforming, autothermal reforming, aqueous-phase reforming and supercritical water reforming.
256 citations
TL;DR: In this article, the authors discussed thermodynamic limits of the synthesis gas upgrading process and concluded that to get optimum H2 yields, with negligible CH4 and coke formation, upgrading syngas is best practiced at a temperature range of 900-1100 K.
Abstract: Hydrogen yields in the syngas produced from non-catalytic biomass gasification are generally low. The hydrogen fraction, however, can be increased by converting CO, CH4, higher hydrocarbons, and tar in a secondary reactor downstream. This paper discusses thermodynamic limits of the synthesis gas upgrading process. The method used in this process is minimization of Gibbs free energy function. The analysis is performed for temperature ranges from 400 to 1300 K, pressure of 1–10 atm (0.1–1 MPa), and different carbon to steam ratios. The study concludes that to get optimum H2 yields, with negligible CH4 and coke formation, upgrading syngas is best practiced at a temperature range of 900–1100 K. At these temperatures, H2 could be possibly increased by 43–124% of its generally observed values at the gasifier exit. The analysis revealed that increasing steam resulted in a positive effect. The study also concluded that increasing pressure from 1 to 3 atm can be applied at a temperature >1000 K to further increase H2 yields.
97 citations
TL;DR: In this article, the activation energy and reaction order for the glycerol steam reforming reaction over Ni/CeO2 catalyst were 103.4 kJ/mol and 0.233, respectively.
Abstract: As a result of skyrocketing prices, environmental concerns and depletion associated with fossil fuels, renewable fuels are becoming attractive alternatives. In this respect, the demand for biodiesel has increased tremendously in recent years. Increased production of biodiesel has resulted in a glut of glycerol that has reduced the demand for this once valuable commodity. Consequently, finding alternative uses for glycerol is a timely proposition. One alternative is producing renewable hydrogen from this cheap commodity. Only a handful of studies have been conducted on producing hydrogen from glycerol. Previous studies have mainly focused on finding effective catalysts for glycerol steam reforming. This paper extends previous knowledge by presenting kinetic parameters in relation to glycerol steam reforming over Ni/CeO2 and a reactor modeling. The study found that the activation energy and the reaction order for the glycerol steam reforming reaction over Ni/CeO2 catalyst were 103.4 kJ/mol and 0.233, respectively.
62 citations
TL;DR: In this paper, the experimental results of the water−gas shift reaction over supported nickel catalysts in comparison to thermodynamic equilibrium composition at the same reaction conditions were discussed, and the effects of different supports on the performance of H2 production over nickel-supported catalysts were also evaluated at both low and high temperatures.
Abstract: This paper discusses the experimental results of the water−gas shift reaction over supported nickel catalysts in comparison to thermodynamic equilibrium composition at the same reaction conditions. The effects of different supports on the performance of H2 production over nickel-supported catalysts are also evaluated at both low and high temperatures. Ceria-promoted nickel catalyst supported on powder alumina (Ni/CeO2−Al2O3) demonstrated excellent performance. The catalyst was not stable at low temperature (250 °C) but showed good stability at high temperature (450 °C). At 450 °C, with a catalyst loading of 0.05 g, CO/S (S = steam) ratio of 1:3, and gas hourly space velocity (GHSV) ≈ 200 L h−1 gcat−1, the activity of Ni/CeO2−Al2O3 was 95% with a H2 yield of 52% and a H2 selectivity of 73%.
51 citations
TL;DR: The adsorption of glycerol was increased by removing the functional groups from the carbon surface at high temperatures under N2 atmosphere, and was decreased by increasing surface functional groups through HNO3 oxidation.
Abstract: The removal of glycerol by adsorption from biodiesel washwaters has been studied at room temperature using various adsorbent materials, including activated carbons, clay minerals, and natural and synthetic zeolites. Activated carbon exhibited the best adsorption for glycerol among the examined materials. Glycerol adsorption isotherms are obtained on activated carbons after treatment under different conditions. The Langmuir isotherm coefficients and the first‐order desorption kinetic parameters for glycerol on a coconut activated carbon were determined by fitting the experimental data. The adsorption of glycerol was increased by removing the functional groups from the carbon surface at high temperatures under N2 atmosphere, and was decreased by increasing surface functional groups through HNO3 oxidation. Compared with water, glycerol tends to adsorb more favourably on a hydrophobic carbon surface than on a hydrophilic one.
23 citations