Working with CO2

CO₂ is produced in processes that convert fossil fuel to energy or chemicals. Reducing CO₂ emissions during the chemical conversions occurring in these processes is at the heart of both chemical engineering and the global challenge of climate change. We can ask why processes emit CO₂ and what the minimum amount of CO₂ a process needs to emit is. This quantification of minimum CO₂ emissions allows actual processes to be systematically compared and improved against that minimum target. It is essential to view the process as a System, as the choice of chemistry, catalysts, and operating conditions of the individual unit operations impact the CO₂ emissions of the system. In this talk, I will use XTL as a case study and explain how the gasification - Fischer Tropsch synthesis system can be viewed as a Carnot engine that supplies the work required for the chemical transformations. The reaction temperatures of the gasification-synthesis system determine the efficiency of the Carnot engine and it is these inefficiencies that lead to increased CO₂ emissions from the process.

The concept of the Thermodynamic Attainable Region (AR^T) in Gibbs Free Energy – Enthalpy space is introduced. The insights that can be gained from this approach, both from a broader system's view as well as the more detailed view of unit processes, reactor and catalyst development and operation are explored. The results from the AR^T have guided our development of simple, robust XTL processes which have been demonstrated at various scales.

Looking to the future, CO₂ will be used as a feed for manufacturing commodities, such as detergents, lubricants, and plastics, and chemicals for storage of renewable energy. We can extend the AR^T approach to the chemistry, design, and operation of CO₂ utilization systems.