Climate change is a chemical problem and chemistry and chemical engineering can provide some of the solutions. What kind of chemistry should we be doing? Two of our speakers at GRIPS 2022, Anthony J. Ryan and Rachael H. Rothman, try to answer this question with their article on Nature.com
Two of the speakers at Global Research & Innovation in Plastics Sustainability (GRIPS) 2022, Prof. Tony Ryan and Rachel Rothman, have written an article on Engineering Chemistry to Meet COP26 Targets, looking at the solutions chemistry and chemical engineering can provide in alleviating the impacts of climate change. You can find an excerpt of it below:
On the American prairie under no-till cropping, 1 hectare of land produces on average 4 tonnes of cereal and 9 tonnes of straw or stover. The field carbon dioxide budget is 30 tonnes per ha per yr: 10 tonnes turnover in plant and soil respiration (burning carbohydrate to drive metabolic processes) while 20 tonnes are fixed into carbohydrate (6 in the harvested food and 14 in the agricultural waste). Of the fixed carbon dioxide in the waste, 2 tonnes move to the soil pool and 12 tonnes are currently returned to the atmosphere.If we were to collect just 20% of the agricultural waste worldwide, this would provide 4 gigatonnes of biomass carbohydrate: more than the feedstock needs of the entire petrochemicals industry. All that has to be done is to turn that biomass feedstock into C1–C4 and C6 feedstocks (with a C efficiency of 33%); we could then turn to the Fischer–Tropsch process3 and catalytic cracking4 to produce all the chemical products we need. The entirety of the chemicals industry could be carbon neutral. Every organic chemical released into the environment could be made from this year’s carbon dioxide and when it ultimately degrades back to carbon dioxide it wouldn’t have added anything to the pool because it came from the pool.
So what do we need to do? Clearly there’s a lot of biochemistry and fermentation technology needed; cellulose and lignin are not the easiest things to ferment. There is a role for chemists, biochemists and chemical engineers in designing enzymes, separation technologies and processes. One of the issues with making specialty chemicals from bio-feedstocks is the diversity of the feedstock. Heterogeneity might not be a problem in fabric conditioners, but it could be when it comes to making an excipient in a drug formulation. Taking the feedstock back to short hydrocarbons gets us over these biorefinery problems.
Once we’ve produced methanol, ethanol, propanol and butanol by fermentation, there are a number of routes to the chemicals we need. Dehydration to ethene, propene and butene feeds directly into conventional chemistry already run in large chemical plants and the molecular diversity that results. But we also need to develop new synthetic methods to build large and elaborate compounds directly from the alcohols and use the power of molecular mode lling to help us to design these processes and molecules rather than go via the traditional hit-and-miss routes.
There is nothing stopping us from doing all of this now. There are biorefining textbooks, fermentation technologies are a part of the undergraduate syllabus, and the dehydration of alcohols to alkenes is covered at high school. But when would we want to do it? Life cycle assessment (LCA) can tell us when it makes sense to use energy to convert biomass into a petrochemical feedstock rather than using a conventional fossil feedstock. What we must avoid is emitting more carbon dioxide by biomass conversion than we would by continuing to use the fossil feedstock. The whole system must be considered in this analysis to avoid unintended consequences and detrimental environmental impacts (other than carbon) — it is all too easy to make a decision on part of a system, then to realize it wasn’t actually a very good idea for the planet after all. LCA and whole-system analysis must therefore be a key part of research and knowing how to perform an LCA must become an intrinsic part of a chemist’s education.
Read the article in full here.
