Due to the inflated petroleum and natural gas price, the synthesis of liquid fuels from coal via the Fischer-Tropsch (FT) synthesis has received large interest. In this process, liquid and gaseous hydrocarbons and oxygenates are produced by the catalytic hydrogenation of CO in a bubbling bed reactor. Typically, the H₂/CO molar ratio of the FT reactor feedstock is around 2, which is much higher compared to the ratio obtained from the syngas of modern gasifiers such as GE (~0.67) or Shell (~0.5) gasifiers. Current technology uses water gas shift (WGS) reactors to make up this H₂ deficit. However, the WGS process generates a H₂/CO₂ mixture, where the CO₂ separation process is energy intensive.

The syngas chemical looping (SCL) or Syngas Redox process developed at Ohio State University converts the energy of a gaseous fuel into a pure hydrogen. The gaseous fuel can be coal derived syngas, unconverted gaseous FT products, or mixtures thereof. In the process, iron oxide particles are first reduced with the gaseous fuel in a reactor converting the gas in a mixture of CO₂ and H₂O. As condensing the water, a rich CO₂ stream is obtained, and no further CO₂ separation steps are required. Subsequently, the reduced iron particles are partially oxidized with steam in a second reactor, where hydrogen is produced in the process. The Hydrogen can be mixed with a clean syngas stream to obtain a suitable H₂/CO gas mixture for production of liquid fuels thorough a FT process.

This study discusses the synergy between the SCL system and the FT process for the production of liquid fuels. The hydrogen stream from the SCL is used to increase the H₂/CO ratio from the gasifier outlet. The inherent CO₂ separation in the SCL system requires no additional CO₂ separation processes. Unconverted FT products are processed in the SCL system to produce H₂ improved the system selectivity towards a single product. As a result, improved system efficiency as well as selectivity towards liquid fuels can be achieved. Results show that the combination of a SCL looping with a FT process can enhance the production of liquid fuels such as diesel up to 30%. Experiments in a fixed bed of looping particles are performed to demonstrate the concept. Several cycles of reduction and oxidation of the looping particles were carried out. Particles showed good activity though the cycles delivering, after condensing the excess steam, a pure stream of hydrogen. The effect of the reducing gas composition on the hydrogen outlet was investigated. In this study, the catalytic effect of the reduced looping particles on carbon deposition is also investigated. Results show that the addition of small quantities of carbon dioxide to the SCL gas feedstock reduces the carbon deposition generated by the catalytic effect of the looping particles.