Hydrogen production from glycerin reforming

Abstract

Following a factorial experimental design, a series of tests were performed to investigate the effects of operating parameters; oxygen to carbon ratio (O/C), steam to carbon ratio (SIC) and temperature (T), on reforming glycerin to a H2 rich gas. A mathematical model defining the effect of those three variables was derived., and used for improving the reaction hydrogen yield. From the range of experimental conditions tested it was concluded that OIC, as well as the interaction between OIC and temperature had the most important effects on H2 yield. 4.5 mole of hydrogen were produced per mole of glycerin at experimental conditions of O/C=1, S/C=2.2, and T=804°C. This is 65% of the maximum theoretical yield, and 90% of the yield predicted by thermochemical equilibrium. 1.4 moles of carbon monoxide per mole of glycerin were also produced., presenting a potential for an additional 1.4 mole hydrogen per mole glycerin. A water gas shift reaction was then used., and its operating temperature optimized, in order to convert the reformate gas CO into hydrogen by combining it with water. Results were satisfying, with a final yield of 5.3 moles H2 I mole glycerin, which is 75% of the maximum stoichiometric hydrogen yield. Crude glycerin, obtained from biodiesel production, was finally tested (without a water gas shift) as a feed to compare it with pure glycerin used throughout the tests. The initial results were very encouraging, almost identical to those of pure glycerin, but carbon formation quickly became a problem. Possible contaminants causing the coking may include methanol, chloride and sodium cations, and free fatty acids, all present in crude glycerin as byproducts of biodiesel synthesis.