CEST2025

Biomass gasification (thermal decomposition in the presence of limited amount of oxygen) and production of a gaseous mixture of mainly CO, H2 and CO2 (syngas) was discovered at the beginning of the 17th century and syngas was already used in internal combustion engines and street lighting systems towards the end of the 18th century. Following the discovery of Fischer-Tropsch process at the beginning of the 20th century, the development of various routes for chemical catalytic synthesis of fuels and chemicals from syngas bloomed during the last century. The biological conversion of syngas came to the forefront only recently, following important advances within the biotechnology discipline. It was just at the beginning of the 21st century that the scientific community experienced exponential growth in research studies dealing with biological conversion of syngas to mainly alcohols, organic acids and methane. This thermochemical biomass conversion combined with the gas fermentation route for production of low-value products like fuels can be considered competitive and advantageous compared to the thermochemical/catalytic route when small-scale installations are concerned. Production of higher value products via the carboxylate platform is also a promising, and certainly worth investigating route. The presentation will summarize the status of the technology and will highlight recent advances within syngas bio-transformations for addressing the main process challenges, i.e. the low solubility of the gaseous substances and the relatively low growth rates of the microbes. As a case study, the presentation will focus on syngas and CO2 biomethanation in trickle bed reactors from lab-scale to pilot-scale. We will show how the scale and different reactor geometry and operating conditions may affect the efficiency of syngas biomethanation, and how modelling of variable volumetric mass transfer coefficient may result in the optimal up-scaling of a rather complex reactor system. Predicting and controlling the volumetric mass transfer coefficient is valuable, not only for maximizing the mass transfer rate, but also for preventing inhibition phenomena. Temperature, pressure, reactor geometry and gas and liquid flow rates can be adjusted to secure maximum efficiency of the gas fermentation process. The presented approach and modelling tool may be adjusted to different reactors and microbial systems, and thus it can be very useful for designing new as well as revisiting established processes in the field.