Chemical and Biochemical Engineering Seminar - Working with CO2

Diane Hildebrandt, Distinguished Professor of Future Energy. Joint appointment in the African Energy Leadership Centre, Wits Business School, and Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, South Africa.

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 how much they need to emit. It will be shown that process CO2 emissions are a consequence of the material, energy, and work balances across a process. Quantifying the minimum process CO2 emissions allows actual processes to be systematically compared and improved against this 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 overall CO2 emissions of the system.

The X-To-Liquids (XTL) process will be used as a case study to illustrate the approach used. We will define the Carnot temperature for a reaction and explore the consequences of operating at temperatures other than the Carnot temperature on process efficiency. We will further show that the gasification - Fischer Tropsch synthesis system can be viewed as a Carnot engine that supplies the work required for the chemical transformations that occur in XTL.

In the future, CO2 could be used as a feed for manufacturing commodities such as detergents, lubricants, plastics, and chemicals for renewable energy storage. We will extend the approach to consider the implications of CO2 as a feed on the process material, energy, and work balances and hence on the process design.