(337bh) Biomass Utilization for a Sustainable Decarbonization Strategy

Decarbonization strategies are needed to reduce the threats posed by the increasing amount of atmospheric carbon. Two of the decarbonization strategies that are explored here use biomass for carbon capture plus storage and as feedstock for high-value materials. The use of biomass as carbon capture and storage helps in bypassing the substantial entropy penalty of carbon dioxide removal from the atmosphere. Here, we proposed the use of waste biomass torrefaction as a means to convert the accumulated carbon dioxide by biomass into stable solid carbon material that can be buried underground. Using a Monte Carlo model to evaluate the mass, energy, and economics of the Biomass Torrefaction and Burial (BTB) process, we determined that 95% of the scenarios cost less than $200 per ton of CO₂ equivalent captured. The energy requirement per ton of CO₂ equivalent removed by the BTB process is also 50 times less than conventional direct air capture technology.

The second decarbonization strategy can be achieved by the creation of a sustainable circular economy that can reduce the dependence on fossil fuel feedstocks for production of high-value materials, such as high-performing plastic. This requires the ability to produce high-performing biodegradable polymers from renewable resources, such as biomass. Lignin is one of the abundant components of biomass that can be depolymerized into stable lignin-derived intermediates, such as alkyl-substituted monophenols, which can undergo selective hydrogenation into alkyl-substituted cyclohexanone for a feedstock for these high-performing polymers. Due to the broad range of potential lignin-intermediates, it is critical to develop a process to study the various functionality in these lignin-derived intermediates. While selective hydrogenation of monophenols has been widely studied, achieving high selectivity towards the desired product while maintaining high reaction activity in a continuous flow process remains a challenge.

In this work, we demonstrated the ability to achieve high selectivity (>95%) at high conversion (>90%) towards various alkyl-substituted cyclohexanone via liquid phase hydrogenation in an up-flow packed bubble column reactor using a Pd/γ-Al₂O₃ catalyst. The reaction performance was quantified through conversion and selectivity studies using hydrogenation of phenol, p-cresol, and p-propyl-phenol in the flow reactor system under various space velocities and hydrogen partial pressure. In addition, reaction performance is presented as a function of the variation of alkyl groups and operating parameters. The results from this study provide new evidence for the ability to process complex lignin-derived materials under mild conditions into valuable feedstocks for high-performing polymers.