Membranes in the biobased economy: electrodialysis of amino acids for the production of biochemicals

The depletion of fossil fuels, increasing oil prices and CO2 emissions, rise the need for green alternatives for the production of energy, fuels and chemicals. Emerging sustainable technologies based on renewable resources promote the shift of conventional refineries toward biorefinery concepts. Biomass feedstocks can be used for the production of such bioenergy, biofuels and biobased chemicals. Amino acids that can be obtained from cheap protein sources (e.g. side streams from the production of biotransportation fuels from rapeseed oil) are interesting as chemical intermediates as amino acids already have the functionalities (i. e. –N and –O) required for the production of chemicals. In such feeds, the amino acids are usually present as a mixture and need to be isolated for further processing. ED is an electro-membrane process that uses an electrical potential difference over the membrane as driving force for the selective extraction of ions from solutions. It can also be used in biorefinery applications to separate e.g. amino acids due to the differences in their charge behavior with respect to pH. However, only fractionation of the amino acids into three main groups (basic, acidic and neutral) can be obtained in practice. Within the scope of this PhD Thesis, a novel approach that combines enzymatic modification, for instance by using an amino acid specific decarboxylase which removes the acidic group of the corresponding amino acid changing its charge behavior, is applied to basic, acidic and neutral amino acids. In this way intermediate building blocks for chemicals are produced and isolation of single amino acids could be achieved. The approach was validated for the separation of complex biobased mixtures. Finally, mixed matrix membranes as support for enzyme immobilization were prepared and successfully integrated in the electrodialysis stack achieving enzymatic conversion and separation in one single unit operation. A preliminary cost evaluation indicated the directions to further optimize the process, focusing on increasing amino acid flux through the membrane and decreasing the cost of the membranes to make this approach cost effective. Altogether gives this work a high value as a contribution to promote the shift of conventional refinery toward a biobased economy.