Biomethanation of syngas, kinetic study and pilot scale implementation

Overview & Synopsis

In a context of circular economy, the energetic valorisation of heterogeneous and woody waste in the form of syngas thanks to pyro-gasification is a promising strategy at the territorial scale. The obtained syngas, composed mainly of N2, H2, CO and CO2 can then be upgraded into methane by biomethanation. Biomethanation is the biological conversion of H2 and CO or CO2 into methane. This allows to improve the calorific value of syngas and to take advantage of the important natural gas grid and infrastructures already existing in France and in Europe. However, the biomethanation of syngas is a recent technology that raises research issues. In particular, the transfer of the gaseous substrate to the micro-organisms acting as catalysts and situated in the liquid phase is one of the major limitations of the process and must be optimized. On the other hand, it has been observed that CO present in large quantities in syngas could have inhibitory effects on certain groups of microorganisms. Finally, minor compounds (H2S, NH3, tars...) of syngas could also cause inhibition phenomena on microorganisms. To address these issues, a 12 L pressure reactor operating continuously at 4 bars and 55°C was set up. Good performances were obtained, with a maximum productivity of 1 NLCH4/Lreactor/h with conversion rates higher than 80% for CO and H2. Moreover, the inhibition by CO was characterized, showing the high tolerance of the microbial consortium. Finally, a bibliographical study associated with batch tests allowed to identify pollutants in syngas which inhibit certain groups of microorganisms, and which would need to be purified upstream of the process.