Experimental Investigation of Hydrogen Production from Glycerin Reforming

A series of tests were performed to investigate reforming of reagent-grade propane-1,2,3-triol, (C3H8O3) commonly called glycerin, to produce a H2 rich gas. Effects of the operating parameters, oxygen to carbon ratio, steam to carbon ratio, and temperature, were determined using a factorial experimental design. A mathematical model defining the effect of the three parameters was derived and used to improve the hydrogen yield. From the range of experimental conditions, it was concluded that the oxygen to carbon ratio, as well as the interaction between oxygen to carbon ratio and temperature had the most important effects on H2 yield. A 4.5 mol quantity of hydrogen was produced per mole of glycerin at experimental conditions of oxygen to carbon ratio of 0, steam to carbon ratio of 2.2, and temperature of 804 °C. This is 65% of the maximum theoretical H2 yield, and 90% of the H2 yield predicted by thermochemical equilibrium. A 1.4 mol quantity of CO was also produced per mole of glycerin, presenting the potential for additional production of 1.4 mol H2/mol glycerin. A water gas shift reactor was added to the process and operated at 369 °C, producing a final yield of 5.3 mol H2/mol glycerin, 75% of the maximum stoichiometric hydrogen yield. Crude glycerin obtained from biodiesel production was finally tested (without the water gas shift reactor) as a feed and compared with reagent-grade glycerin results. The initial crude glycerin hydrogen yield, 4.4 mol H2/mol glycerin, was almost identical to that of reagent-grade glycerin, but carbon formation and coking increased the pressure drop through the catalyst bed causing the test to be terminated. Possible contaminants, chloride and sodium cations, present in crude glycerin as byproducts of biodiesel synthesis were added to reagent-grade glycerin and tested in the reformer, producing results similar to those observed for the crude glycerin reforming test.