Chemical Looping Reforming Using Transition Metal Carbides

Abstract

Scientists around the world have concluded, with 95% probability, that the levels of CO2 have increased due to human activity over the past 50 years [1]. Consequently, humanity has been seeking solutions to lower greenhouse gas emissions. In an effort to reduce emission the use of hydrogen (H2) for energy generation has great appeal because it reduces the CO2 emission into the atmosphere and has H2O as its main product. Currently, H2 is mainly produced from steam reforming which is a thermal process where steam is used to convert hydrocarbons into a stream mainly composed of H2 and CO (syngas). However, this process still consumes excessive amounts of energy due to its endothermicity and as a result there are still some emission related to fuel combustion. Additionally, it is also important to consider that in its currently state, the production of H2 via steam reforming is currently a fossil fuel dependent technology. Consequently, alternative technologies that can lower carbon emissions have to be considered in this scenario. Chemical Looping Reforming (CLR) is an alternative method for hydrogen production where the nature of the reactions makes the process autothermal and enables it to achieve higher efficiency by controlling the amount of reactive gas entering the system. However, CLR has not been implemented at commercial level yet and it still relies on the use of steam. Additionally, it needs further material improvement in terms of oxygen carrier to overcome problems related to carbon deposition, sintering and attrition, for example. This work presents a new process for CLR where transition metal oxides are studied as oxygen carries and then reduced to transition metal carbides, differing from the traditional process, producing syngas. The Carbide Chemical Looping Reforming (CCLR), as it was named, was studied thermodynamically under equilibrium conditions to allow the identification of possible candidates for the process, among 9 different transition metal species studied. Tungsten was used in the experimental measurements and the results confirmed the thermodynamic predictions. This work provides the primary information of the original technology which can serve as basis for further improvement and development of the process.