Amino acids (AAs) are interesting raw materials for the chemical industry due to the chemical functionalities they have. This makes them very similar to conventional petrochemicals and provides the possibility to save process steps, extra reagents and energy.
They may be obtained as a mixture after hydrolysis of potentially inexpensive proteins obtained from agricultural or biofuel rest streams, but separation is needed to be able to carry out further transformations into the desired products. Electrodialysis (ED) is a promising method for this purpose, but its efficiency is limited by the similar charge behavior of certain AAs. So specific conversion that changes charge behavior is desired, and if the conversion could lead to useful products, an in-situ product formation and separation process of AAs could be designed.
In this thesis, enzymes are preferred to convert AAs due to their high selectivity. L-lysine decarboxylase and L-glutamate α-decarboxylase are applied to convert basic and acidic AAs, respectively. L-serine decarboxylase and L-phenylalanine ammonia-lyase are employed in one reaction system to convert neutral AAs. All these enzymes are specific and their conversion products have a different charge behavior compared to the other AAs in the mixture. Therefore they can be used to aid the separation of AAs.
On the other hand, chemical conversions can also be considered. In this research, the conversion of L-glutamic acid (Glu) to L-pyroglutamic acid (pGlu) is specific with the presence of L-aspartic acid (Asp). The formation of pGlu can be performed under aqueous or melt conditions. After the conversion, pGlu can be separated utilizing its high solubility After separation, pGlu can be hydrolyzed to Glu under both acidic and basic conditions. Thus the separation of acidic AAs, Asp and Glu, was achieved. However, under melt conditions more Asp and Glu were recovered, and the Asp obtained was of higher purity.
In conclusion, this thesis shows that specific conversion of AAs with similar charge behaviors can be used as a means to aid their separation by ED or where reactions lead to differences in solubility behavior. Such a biorefinery route contributes to the use of biomass as the feedstocks for chemical production, bringing benefits in reducing the requirement of fossil fuels, avoiding the use of extreme reaction conditions, and reducing the need of extra chemicals and capital cost.