Dry Reforming of Methane (DRM) is one of the enabling processes that converts two greenhouse gases (Carbon dioxide and Methane) to syngas (a mixture of carbon monoxide and hydrogen). Syngas is an important precursor that is used to produce liquid hydrocarbons (or ultra clean fuels) and many other value added chemicals (methanol, Dimethylether, Acetic acid etc). In comparison to the conventional reforming technologies (Steam reforming and Partial Oxidation), the main benefit of this process is that it utilizes carbon dioxide, whereas the other processes require steam and oxygen to be used as oxidant. Equations 1-3 presents the stoichiometric equations for the three reforming technologies:
Dry Reforming (DRM):
Partial Oxidation (POX):
Steam Reforming (SRM):
Although DRM provides a very attractive route towards utilization of CO2, its successful industrial implementation faces several process limitations. These limitations include high endothermicity of the reaction, low quality of the syngas yield ratio (not suitable for direct use for Fischer Tropsch reaction) and the deactivation of catalyst due to large quantity of carbon formation. Due to the severity of these limitations, DRM is still a grey area that has attracted incredible amount of research both in terms of process advancement (in the way the reaction is carried out) and in terms of the catalytic systems (towards the development of catalyst that are more stable and sustain carbon formation). In our previous publications (Challiwala et al. 2017  and Shaik et al. 2018 ), we have demonstrated a different pathway that synergises the benefit of the three reforming technologies, which not only reduces the energy requirements from the overall process, but also targets reduction in the carbon formation during combined reaction. In the present work, we have developed a novel processes that systematically handles the formation of carbon and enhances the CO2 utilization in the overall process.
For the preliminary assessment using thermodynamic calculations, equilibrium compositions were evaluated from the solution of overall Gibbs Free Energy (GFE) of the system as shown in equation (4) below:
More detailed calculation philosophy with fugacity coefficient calculation using equation of state solution are given in our previous work in .
For the experimental proof of concept, we conducted all the tests using Micromeritics 2920 Autochem II instrument. We used a commercial Nickel based catalyst to carry out the reaction for our novel reactor configuration termed as carbon generator (CARGEN). For this, we used a mixed gas comprising ofand the evolving gas from the CARGEN reactor after the reaction was analysed using a Residual Gas Analyser (RGA) to instantaneously monitor the composition.
The novel process reported in this study, our aim is to produce both syngas and solid carbon, in contrast to conventional approach which targets only the formation of syngas. We propose to utilize a combination of two reactors (rather than one reactor in DRM), with one focussed on production of solid carbon (also known as CARGEN) and the other focussed on production of syngas via combined reforming reaction. The benefit of this process that we have proved from both our thermodynamics calculations and experimental proof of concept indicated significant reduction in energy requirements (about 50% of DRM) in addition to significantly high levels of CO2 conversions (at least 65% CO2 conversion). As it is already known that the syngas yield ratio (H2: CO) obtained from the DRM process is not more that 1:1, the major benefit of this process is that the syngas yield ratio can be tuned as per the process requirements up to 3:1 due to the flexibility in operation provided by the two reactor setup proposed in this work. Due to significant merits obtained from this work, this process was recognized as one of the patentable outcomes from the Qatar National Research Fund (QNRF) Exceptional project. As a part of our continuous efforts in identifying the possibilities for overcoming the challenges associated with DRM process, this work provided a very interesting pathway for CO2 utilization.
1. Challiwala, M.S., et al., A combined thermo-kinetic analysis of various methane reforming technologies: Comparison with dry reforming. Journal of CO2 Utilization, 2017. 17(Supplement C): p. 99-111.