Production of Hydrogen from Post-consumer Wastes

At present, the commercial production of hydrogen is essentially carried out by catalytic steam reforming of hydrocarbons: natural gas and naphtha. However, the instability of the prices of natural gas makes the use of other raw materials increasingly attractive. This research focuses on the development of a technology for producing hydrogen from alternative resources, specifically from two types of waste post-consumer materials: plastics and “trap grease”. The concept proposed for plastics is a two-stage process: fast pyrolysis to convert polymers to a gas/vapor stream of monomers and other low-molecular weight compounds followed by catalytic steam reforming of this gas to yield hydrogen and carbon oxides. “Trap grease”, a waste material recovered from traps on sewer lines, does not require a depolymerization step and can be directly steam reformed to produce hydrogen. To prove the process concept, we employed a two-stage micro-scale reactor interfaced with a molecular-beam massspectrometer. Samples of plastics were pyrolyzed in the bottom part of the reactor then the created gases and vapors were steam reformed in a fixed bed of a commercial catalyst located in the upper part of the reactor. The product gas was analyzed by mass spectroscopy. Preliminary tests showed that at process conditions similar to those used for reforming natural gas, polymers were almost completely converted to hydrogen and carbon oxides. “Trap grease”, after washing and filtering, was catalytically steam reformed in a 2”-diameter fluidized bed reactor using the same commercial nickel catalyst. At 850°C, using steam-to-carbon ratio 5, and with a space velocity of 1000 h, hydrogen was produced with a yield of 25 g per 100 g of grease during 135 hours of continuous testing. This yield could be increased to over 28 g H2/100 g grease (85% of the stoichiometric potential) if CO were further converted by water-gas shift. 1 Proceedings of the 2002 U.S. DOE Hydrogen Program Review NREL/CP-610-32405