Carbon-Negative production of Hydrogen through Sulfur Intermediates

Chemical fuel production from biomass represents one method for decarbonizing the global energy infrastructure. However, current technologies have significant drawbacks that limit application to select feedstocks. For example, the endothermic steam-reforming process is limited to gasified low-sulfur feedstocks that have thus far precluded the economic utilization of municipal solid wastes (MSW) among other sources of biomass. The use of elemental S is one potential method to utilize these organic wastes for H2 production through the high-temperature and exothermic production of hydrogen sulfide (H2S) and carbon disulfide (CS2) gasses as chemical intermediates. These reduced sulfur species are thermodynamically unstable with respect to their oxygen-analogs, which indicates that usable chemical energy may be derived from their oxidation. When biomass is dehydrogenated with S at lower temperatures, the formation of CS2 is suppressed and sulfurized biochar is produced. In this work, we describe and analyze a possible cyclic route to producing H2 from these species through the use of well-known chemical reactions operating in continuous fashion using cellulose as an example molecule. This “sulfur-reforming” process and additional steps may allow for the economical valorization of currently unutilized organic matter in MSW that may be contributing to environmental harm. If the sulfurized biochar is left sequestered, such as through use as a soil-amendment, and if the electrical energy is sourced from renewables, this process may be considered carbon-negative.