(171e) Distributed Reforming of Bio-Oil for Hydrogen Production

With the world's energy demands rapidly increasing, it is necessary to look to sources other than fossil fuels, preferably those that minimize greenhouse emissions. One such renewable source of energy is biomass, which has the added advantage of being a near-term source of hydrogen. Over 500 million tons of biomass could be available in the U.S. at less than $50/ton, which can be converted to 50 million tons of hydrogen [1]. The challenges for the variety of feedstocks that will be used include handling and drying, regional and seasonal availability and variability, and the impurities that could be generated and have an impact on conversion technology and hydrogen purity. Processes must be feedstock flexible, and minimize costs for feedstock collection, transport, and processing.

While there are several potential routes to produce hydrogen from biomass thermally, given the near-term technical barriers to hydrogen storage and delivery, distributed technologies such that hydrogen is produced at or near the point of use are attractive. One such route is to first produce bio-oil via fast pyrolysis of biomass close to its source to create a higher energy-density product, then ship this bio-oil to its point of use where it can be reformed to hydrogen and carbon dioxide. This route is especially well suited for smaller-scale reforming plants located at hydrogen distribution sites such as filling stations. There is also the potential for automated operation of the conversion system [2].

This research addresses the challenge of distributed hydrogen production with the target of producing hydrogen at $3.80/kg by 2012 [3]. A system has been developed for volatilizing bio-oil with manageable carbon deposits using ultrasonic atomization and by modifying bio-oil properties, such as viscosity, by blending or reacting bio-oil with methanol. Non-catalytic partial oxidation of bio-oil is then used to achieve significant conversion to CO with minimal aromatic hydrocarbon formation by keeping the temperature at 650°C or less and oxygen levels low. The non-catalytic reactions occur primarily in the gas phase. However, some nonvolatile components of bio-oil present as aerosols may react heterogeneously. The product gas is passed over a packed bed of precious metal catalyst where further reforming as well as water gas shift reactions are accomplished completing the conversion to hydrogen [4].

The approach described above requires significantly lower catalyst loadings than conventional catalytic steam reforming due to the significant conversion in the non-catalytic step. The goal is to reform and selectively oxidize the bio-oil and catalyze the water gas shift reaction without catalyzing methanation or oxidation of CO and H2, thus attaining equilibrium levels of H2, CO, H2O, and CO2 at the exit of the catalyst bed.

The results of experiments performed in a laboratory scale vertical reactor have shown that this process shows great promise as CO yields of over 50 % have been observed in the non-catalytic partial oxidation step and equilibrium yields of H2 (~80 %) have been observed after the catalytic step. The experimental results are being used to develop a process flow diagram (including mass and energy balance) for the process to determine whether the economic target discussed above is feasible. The results and conclusions of the efforts to develop this process will be discussed.

References

(1) Milbrandt A., A Geographic Perspective on the Current Biomass Resource Availability in the United States; National Renewable Energy Laboratory: Golden, CO, TP-560-39181, 2005.

(2) Czernik, S.; Elam, C.; Evans R.; and Milne, T., in Thermal and Chemical Biomass Conversion; Bridgwater, A.V. and Boocock D.G.B., eds.; CPL Press: Newbury, UK, 2006; pp.1752-1761.

(3) U.S. Department of Energy: Hydrogen, Fuel Cells and Infrastructure Technologies Program; Multi-Year Research, Development and Demonstration Plan, Section 3.1 Hydrogen Production; U.S. Department of Energy: Office of Energy Efficiency and Renewable Energy: Washington, D.C, 2006.

(4) Evans, R.J.; Czernik, S.; French, R.; and Marda, J.; Distributed Bio-Oil Reforming, DOE Hydrogen Program FY2006 Annual Progress Report, 2006.