(156b) Hydrogen Form Biomass: A Novel Application of Catalytic Membrane Reactors
Hydrogen as a fuel is an important example of a non-fossil energy carrier, which can be produced from various renewable and non-renewable sources. Today, more than 95% of H2 is produced from carbonaceous materials, and is mainly utilized as a chemical feedstock for various industries, such as the petrochemical and food sectors. In addition, increasing demand for energy, and the growing concern about the green-house gas emissions is increasing the hydrogen's share in the energy market.
Abundantly available everywhere in the world, biomass is an attractive and comparatively inexpensive renewable energy source for H2 production. Gasification, coupled with water gas-shift (WGS) reaction, is the process most commonly used for converting biomass to H2. It involves, first, reacting the biomass with steam and/or air in a gasifier to produce syngas. The syngas must then be cooled down to remove its contaminants, and further reacted with steam in dual WGS reactors to maximize its H2 content. Finally, the gas stream exiting the WGS reactors must be treated further in separation units to produce pure H2 to be used in power generation applications. As such, the process is very energy-intensive.
In this study, a process intensification in which gas clean-up, the WGS reaction, and H2 separation are all integrated into one system, has been investigated. It includes a novel reactor/separator system, termed the "one-box" process. The heart of this process is a membrane reactor that combines the WGS reaction with hydrogen separation into a single unit, thus eliminating the need for the two separate WGS reactors and a distinct purification section. Another advantage of the WGS-membrane reactor under study is that it uses impurity-resistant carbon molecular sieve membrane and a Co/Mo/Al2O3 catalyst, both of which show particularly high tolerance for H2S and NH3, that are the common impurities in the syngas. In fact, the catalyst requires sulfur to remain active. This eliminates the need for gas clean-up upstream of the WGS reactor, which saves energy and simplifies significantly the process design.
The project's focus has been on the experimental investigations in order to prove the feasibility of using the "one-box" approach for H2 production from biomass-derived syngas, and to validate the mathematical model developed. Experimental studies are carried out to determine the catalytic WGS reaction kinetics and the rate parameters. The system performance is investigated for a range of pressures and steam sweep ratios, which produces higher CO conversion and H2 purity than that of a traditional packed-bed reactor. An isothermal mathematical model is used to further investigate the design features of the proposed process.