Summary:

Researchers at The Ohio State University have developed a highly efficient chemical looping process that utilizes cyclic redox reactions of metal oxide (MO) particles with gaseous fuels (like syngas and natural gas) and steam to produce hydrogen. Named as SynGas Redox (SGR), the process as developed is a marked improvement over the conventional Steam-Iron process to produce hydrogen.

MO + CO/H₂/CH₄ <-> M + CO₂ + H₂O
M + H₂O <-> MO + H₂

The primary metal oxide in SGR is Fe₂O₃ which is converted to Fe on reaction with syngas. The reactor design allows for a complete conversion of syngas to a mixture of carbon dioxide and water, exiting the reactor using the same high pressure of the gasifier. Upon condensation of water, a relatively pure stream of carbon dioxide is produced which is ready for sequestration. The iron oxide is regenerated in a second reactor, the design of which is also optimized for maximum conversion of steam to hydrogen.

The process has been demonstrated on a bench scale reactor with significant success, including detailed ASPEN simulations. The process has also been optimized (and integrated) for syngas derived from a commercially available dry feed bituminous coal gasifier. Close to 75% of the coal HHV (high heating value) can be converted to hydrogen HHV, suggesting a much higher efficiency than the conventional coal gasification-water gas shift route to hydrogen. Preliminary cost analysis suggests a significant reduction in the cost of hydrogen as compared to the SMR (steam methane reforming) process for natural gas. The process can be further adapted to Coal-To-Liquids(CTL) plants to utilize by-products from the Fischer-Tropsch reactor, resulting in a higher (over 10%) yield of liquid fuels and a significant reduction in operational costs by handling carbon dioxide separation more efficiently. Additionally, optimizing iron oxide particles has led to the development of strong particles durable at high temperatures, demonstrated to maintain full oxygen transfer capacity over a 100 cycles of reduction and oxidation.

Potential Applications:

• Centralized large scale hydrogen production: Uses in oil refining, ammonia manufacture
• Coal to Liquid (CTL) plants
• Suitable for making Fe particles which can be used for hydrogen storage and producing electricity via fuel cells

Advantages:

• Integrated CO₂ separation, with no costly separation techniques. Provides ready to sequester CO₂ stream by design, offering several environmental benefits
• Fuel flexibility, allowing for all kinds of gaseous carbonaceous fuels such as syngas, producer gas, natural gas, and fuel cell exhaust
• Can help tailor H₂/CO ratio of syngas to any desired level
• High hydrogen production efficiency (80-90%)
• Over 15% costs savings over traditional processes
• Easily adaptable for integration with CTL plants, resulting in cost reductions
• Produces low cost Fe₂O₃ composite particles, shown to undergo more that 100 redox cycles without loss in activity