Capturing the gigaton problem of CO2 emissions

Jennifer Wilcox drives a Volt and charges it with electricity generated from PV at her home. She often commutes on her bike 30 miles from Half Moon Bay to campus.

Her efforts don’t stop there.

With 300 million people in India not yet hooked up to electricity, and coal and natural gas the most-used energy sources on the planet, Wilcox investigates carbon capture, or how to separate CO₂ from power plant emissions and other sources to mitigate climate change.

Wilcox is also the author of Carbon Capture, published in April.

The textbook focuses on mechanical and chemical engineering methods for “above ground” capture of CO₂. (Storage methods, on the other hand, are mostly below ground, the domain of geologists and geophysicists.)  

“This comprehensive textbook…has arrived at a pivotal moment,” Robert Socolow of Princeton University said in a review. “Wilcox’s book will usher a new generation of students into this critical field.”

What prompted the book?
When I arrived here four years ago, I created a course on carbon capture and storage with Sally Benson (professor of energy resources engineering and director of the Global Climate and Energy Project). I realized then that the massive scale of carbon dioxide emissions— ~30 gigatons (30 billion tons) annually worldwide—is a bigger problem than we can really fathom.

Carbon capture has the potential to play a big role in the move to a more sustainable energy future. Because it involves chemical engineering, which is my expertise, this is an area where I can contribute.

The textbook provides a skill set for the next generation of chemists and chemical engineers. Although primarily aimed at this audience, the textbook takes an interdisciplinary approach and may be used by students in many disciplines. Finding solutions to global warming and energy challenges will require social scientists, physicists, Earth scientists, chemists, mathematicians, engineers and behavior change specialists. It will take a different kind of thinking.

Is carbon capture currently in use? What is the history of carbon capture? Is carbon capture already happening?

Carbon capture and storage is a somewhat new field, but carbon capture has been used since the early 1900s to purify CO₂ for use as a chemical feedstock and for carbonated beverages like soda.

“Amine scrubbing” is the current state-of-the-art technology. This involves pumping the chemical amine solvent down through a tall tower directly at the power plant site, while simultaneously blowing the flue gas containing CO₂ in the opposite direction, up the tower. The CO₂ forms a chemical bond with amine. Then, the solution is pumped through a second tower where heat is added to break the chemical bonds. This results in a pure stream of CO₂ that is captured and may be used for carbonated beverages or other uses.

As for capturing carbon dioxide for the purpose of keeping it out of the atmosphere, there are only pilot projects at the moment.

I’m not convinced that at the scale of gigatons (of carbon dioxide) amine scrubbing is the best solution. It’s an energy inefficient process, and the amine-based solvent is volatile, hazardous and corrosive.

What will move the field forward?

The textbook includes fundamental concepts and equations, and discusses the most advanced carbon capture technologies, including absorption, adsorption and membrane separation technologies. I encourage students to take the next steps through end-of-chapter challenges that explore current limitations. Maybe a student will have a passion for improving the efficiency of one of the chemical processes and spend his or her career making it happen.

One-step carbon capture and storage might be possible in the future, and I examine some scenarios for that in the book. Here’s an example: To generate energy, we oxidize fossil sources like coal or natural gas, releasing heat plus CO₂ and H₂O. What if we reversed this combustion process using wind or solar as the energy source and turned the CO2 and water back into a hydrocarbon that could be stored as a fuel? This could be a game-changing approach. Fuel is a market that could match the gigatons of CO2 we generate on an annual basis. The problem is that water and CO2 are very stable molecules, from which we’ve already harnessed the energy from oxidation of hydrocarbons. Logically, the wind and solar energy would be used directly, but when these resources are stranded far from the grid, this fuel conversion process might be an interesting approach to consider.

How did you approach writing your first textbook?

It was pretty intense. There was a tremendous amount of material I had to learn in just a few years. I wanted the book to come out soon enough for use in the classroom while the topic was of global interest.

I kind of treated the effort like a marathon by breaking it up into small steps and accomplishing achievable goals one at a time. As a marathon runner you have moments in a race where you feel like you can’t or won’t continue, but then you find the strength within yourself and you push through. It can be very rewarding. Also, throughout the writing process I received a lot of support from the scientific community. Many folks from Stanford, faculty and postdocs, reviewed several chapters. My students helped with the images and tables for the book also. 

Did your research focus change based on what you learned in writing the book?

 The research that I carry out related to carbon capture is primarily focused on adsorption and membrane technologies. This text is based largely on the fundamentals behind separation processes and the materials and their properties used for carbon capture. When I update the textbook, I plan to funnel in more of my own research efforts and ideas.

Carbon Capture is available at amazon.com and at the Stanford Bookstore in the textbook section.