The global annual production of adipic acid is currently three million tonnes. It is mainly derived from fossil oil and the byproduct, nitrous oxide, is a very powerful greenhouse gas. The production is, thus, anything but sustainable. Emma Karlsson, a PhD student at Industrial biotechnology at Chalmers, is on the track to find a sustainable solution for adipic acid production.
-If we should succeed in moving towards a bioeconomy, where we are not dependent on fossil raw materials, we need to develop bio-based production alternatives. The fuel sector is important, but so is the chemical sector. Within BioBuF we work to find other, more sustainable ways to produce chemicals. If the production of adipic acid could be made sustainable this would be at least a little step towards saving the world, says Emma Karlsson.
Adipic acid is used as raw material for nylon which, in turn, is used for many purposes: textiles, rugs, car upholstery, shoes etc. The byproduct, nitrous oxide (or laughing gas) is 300 times more potent than carbon dioxide as greenhouse gas.
-Depending on chosen production method, the emissions of greenhouse gases can be reduced with as much as 95 percent, says Emma Karlsson.
Her research aims at finding a way to produce adipic acid from forest residues, such as branches, roots and tops, as raw material. In literature, there are several metabolic pathways proposed to convert sugar released from cellulose to adipic acid. These work in theory, but if they also work in practice is a different matter. In order for it to work there must exist microorganisms allowing the enzymatic reactions required in the selected metabolic pathway. In addition, the microorganism must tolerate an environment with an increasing concentration of adipic acid as the conversion progresses.
Emma Karlsson has chosen one metabolic pathway to focus her work on. Now it is important to find sufficiently effective enzymes to perform all chemical steps. One problem is that most enzymes are yet unknown. Therefore, Emma Karlsson looks at what type of chemical reaction that is required and, thereafter, if an enzyme exist that perform the same type of reaction on a similar substance. This is to evaluate if it would also work on the substance she wants to convert, or if the enzyme could be modified to obtain the function wanted. In the metabolic pathway chosen by Emma Karlsson there were, initially, four enzymatic steps, and only one was known. By changing the order of the reactions she has now, on paper, found enzymes to all conversion steps but one.
The second part of the project is about finding suitable microorganisms into which these enzymes could, genetically, be inserted. In a screening study, she grew several different species in a broad range of adipic acid concentrations to investigate which of these species that also exhibit tolerance to high concentration levels. The result showed that one yeast, Candida viswanathii, also grew relatively unimpeded, despite increasing concentrations of adipic acid. Currently, Emma Karlsson is performing a more controlled cultivation study with specific focus on this specie cultivated in fermentors.
-Once we have found an efficient way to convert sugar to adipic acid it is time to scale up the process. If adipic acid production is to be a reality in the future, this will require cultivations in bioreactors with capacities of hundreds of thousands litres, and to reach this we still have some work to do.