material that would otherwise be buried , burned or lost into the atmosphere ; it also returns the waste into a chemical that would otherwise be made from fossil resources . Guaiacol is a major constituent of lignin and one strain of soil bacteria can break this down into its central metabolic intermediates . “ The interesting thing for us is that , if it can do that , we can harness that process and divert it into the production of other industrial chemicals ,” Wallace said . The target molecule was adipic acid . Over two million tonnes / year of this are produced worldwide , more by some estimates and 86 % of it is used as an intermediate in making polyamide 6,6 . This is made from fossil resources and the “ quite frankly unacceptable ” manufacturing process pumps out 10 % of all of the anthropogenic emissions of the GHG nitrous oxide . “ We thought engineering biology could provide a really good example of how we could tackle these sort of environmental problems through IB ,” said Wallace . The process chosen , put simply , harnesses the mechanisms present in the soil bacteria to demethylate guaiacol and produce catechol . Using a second enzyme , referred to as Cat A , oxidatively cleaves catechol into muconic acid , which is then reduced , using another enzyme , to yield adipic acid . The methodology the team used to create the enzyme is essentially the same as in any synthetic biology project at the university , Wallace noted . The DNA that encodes the enzyme that does the chemistry is synthesised , put into a bacterial cell and grown in the presence of a substrate . After a series of optimisations , large quantities of adipic acid were isolated from a single batch . About 0.6 g / L can now be made in a single flask in water in one hour , without any GHGs being emitted .
PTA to vanillin
In the second project , the waste source was a higher profile one : plastic waste . Terephthalic acid , a precursor to PET , is a microbial feedstock that can be transformed into other industrial products using synthetic biology . The pathway also harnesses a mechanism found in soil bacteria . Terephthalic acid is oxidised into a diol intermediate , decarboxylated using a decarboxylase from the same enzyme and reduced using another enzyme from soil bacteria . Finally , the molecule is selectively methylated using another enzyme to produce the common flavour and cosmetic molecule vanillin .
PET can itself be depolymerised to terephthalic acid using enzymes , Wallace added . To date , a method has been developed in which the material is fed to bacteria , achieving 70 % conversion on a scale of 1 g / L in a single-flask reaction that occurs in water , at room temperature in less than 24 hours . “ We think the use of plastic waste is a novel carbon feedstock for the industrial bioeconomy that will grow and grow ,” Wallace said . Further projects with IBioIC will take this further in the coming years .
Gone fishing
A very different source of material for use in making adipic acid is waste from the fishing industry . This is a pressing issue for the whole world , said Nikos Tsipias , research lead at Impact Solutions , an independent testing laboratory for plastic products . About 35 % of the fish produced worldwide is wasted for various reasons , according to an FAO study
Sugar beet and forestry are huge potential sources of biomass in Scotland
64 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981