The need of establishment of biohydrogen purification techniques is due the fact that biohydrogen production will be completely transformed into industrial scale soon or later. For biohydrogen process development to be commercially feasible, all the process involved, including purification should be low cost, practical and efficient; particularly when the biohydrogen production is technically challenging. In any case, carbon dioxide and other gaseous impurities are usually evolved during hydrogen production, and highly purified hydrogen is desirable in fuel cells application and other hydrogenation processes. Particularly, is critical to achieve high purity of hydrogen especially in a fuel cell application where it requires 99.9% only hydrogen. This paper reviews four main principle methods that are suitable for biohydrogen mixed gases, namely cryogenic separation, absorption, adsorption and membrane separation. The comparison based on their strengths and weaknesses, regarding the rate and yield of hydrogen, energy requirement and efficiency in terms of hydrogen selectivity, recovery and purity for fuel cell application. Cryogenic separation is among the earliest technique used for hydrogen purification. Though, due to the low temperature requirement, cryogenic separation is least preferred as gas separation is energy intensive and costly. Cyrogenic separation is commonly combine with membrane separation. It was also acknowledged that the membrane separation technique is widely used for biohydrogen purification. Most of research mostly in advancement of the membrane for high selectivity for hydrogen and low selectivity for carbon dioxide.Another method, pressure swing adsorption (PSA) is one of commonly used in conventional hydrogen purification. The hydrogen purity produced by PSA was higher than absorption but the cost to operate it is the same at the expense of low hydrogen recovery. Also, chemical absorption of hydrogen separation from mixed gaseous mixture is discussed due to its simplicity of operation and possible to operate using existing common absorber.
Tallow mainly consists of triglycerides, whose major constituents are derived from stearic, palmitic and oleic acids, and its usage reduces production cost of soap, adds lather stability and hardness to soap. Laundry soaps were produced with variation on amount of tallow (sourced from cow, sheep and goat) and labelled as A, B, C, D and E formulations. The respective tallows were characterized in terms of saponification value and acid value and determined to be 192.14 and 2.24mg KOH/g (cow tallow); 200.56 and 2.38mgKOH/g (sheep tallow) and 197.75 and 1.96 mgKOH/g (goat tallow). The physicochemical properties of soap which determine its area of usage and cleansing properties were determined. The properties considered in this work were hardness, moisture content, foam capacity, pH, free acidity content, and total fatty matter. The hardness, moisture content, foam capacity, pH, free acidity content and total fatty matter of the produced soaps were determined and ranged between mild-deep penetration level; 11-21%; 1-9cm; 8-10.5; 0.16-0.82% and 40-86% respectively. From the comparative analysis, soap made from sheep tallow has the lowest penetration level (with formulations B and E), lowest free acidity content of 0.16% (with formulation A), highest total fatty matter of 86% (using formulation E), highest foam height of 9cm (with formulation A), lowest moisture content of 11% (with formulation A) and mild alkalinity of 8 (with formulations A, B and E). These results showed that the soaps produced from sheep tallow are the best in terms of hardness, lather and skin friendliness, due to its high degree of longer carbon chain lengths of fatty acids. These values satisfy the standard limit set for good quality laundry soap by National Agency for Food and Drug Administration and Control and Encyclopaedia of Industrial Chemical Analysis, respectively.
Thermodynamic equilibrium analysis of ethanol steam reforming was carried out by direct minimization of Gibbs free energy method using Aspen Plus (V8.8). Equilibrium compositions of each species were analysed for temperatures ranging from 873 to 1173K, steam-to-ethanol molar ratios (S/C) of 2:1 -6:1 and pressure at 1atm. Due to high temperature and reduction of CO2, there is shift in equilibrium which resulted to increase in hydrogen formation. The predominant reactions which contributed to the increase in hydrogen formation are incomplete ethanol steam reforming, ethanol decomposition, methane steam reforming and water-gas shift reaction, which in turn make H2/CO ratio significant, with regard to steam-to-ethanol feed ratio of 6. Methane formation is negligible when the reforming is operated between 1093K and 1173K for all the steam-to-ethanol molar feed ratios. This implies that higher carbon deposition (4.17×10-23 kmol/s) observed at 1173K with respect to steam-to-ethanol molar feed ratio 2 could be due to methane decomposition, Boudouard reaction and CO2 reduction. However, the least rate of carbon deposition is 2.48×10-23 kmol/s relating to feed ratio 6 at 1173K, which implies that high carbon formation is significant at temperature above 1173K and steam-to-ethanol molar feed ratio 2. In view of the high H2/CO ratio attained within the considered temperatures (873-1173K) and steam-to-ethanol molar feed ratio of 6, the syngas is recommended to be used for electricity generation via solid oxide fuel cell.
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