Mixed matrix for process intensification in electrodialysis of amino acids

Amino acids are valuable intermediates in the biobased economy for the production of chemicals. Electro-membrane processes combined with enzymatic modification have been investigated as an alternative technology for the fractionation of a mixture of amino acids with almost identical charge behavior. Up to now, the modification and subsequent separation were performed in two separate reactors. An interesting approach is the integration of both unit operations into one single device using mixed matrix membranes (MMMs) as platform for enzymatic conversio

On the isolation of single acidic amino acids for biorefinery applications using electrodialysis

\u3cp\u3eElectrodialysis using commercially available ion exchange membranes was applied for the isolation of l-glutamic acid (Glu) and l-aspartic acid (Asp) from a mixture of amino acids. Based on the differences in their isoelectric points, Glu and Asp, being negatively charged at neutral pH, can be separated from neutral and basic amino acids. Outstanding recoveries for Glu and Asp of around 90% and 83%, respectively, were obtained. The further separation of Glu from Asp with electrodialysis is enabled with an enzymatic modification step where Glu is converted into γ-aminobutyric acid (GABA) with the enzyme glutamic acid α-decarboxylase (GAD) as the catalyst. Negatively charged Asp is separated from uncharged GABA at neutral pH conditions with a current efficiency of 70% and a recovery of 90%. Higher current efficiencies and lower energy consumption can be obtained when adjusting the current in time. This opens the route to successful isolation of amino acids for biorefinery applications using an integrated process of enzymatic conversion and separation with electrodialysis.\u3c/p\u3

Layer-by-Layer Modification of Cation Exchange Membranes Controls Ion Selectivity and Water Splitting

The present study investigates the possibility of inducing monovalent ion permselectivity on standard cation exchange membranes, by the layer-by-layer (LbL) assembly of poly(ethyleneimine) (PEI)/poly(styrenesulfonate) (PSS) polyelectrolyte multilayers. Coating of the (PEI/PSS)N LbL multilayers on the CMX membrane caused only moderate variation of the ohmic resistance of the membrane systems. Nonetheless, the polyelectrolyte multilayers had a substantial influence on the monovalent ion permselectivity of the membranes. Permselectivity comparable to that of a commercial monovalent-ion-permselective membrane was obtained with only six bilayers of polyelectrolytes, yet with significantly lower energy consumption per mole of Na+ ions transported through the membranes. The monovalent ion permselectivity stems from an increased Donnan exclusion for divalent ions and hydrophobization of the surface of the membranes concomitant to their modification. Double-layer capacitance obtained from impedance measurements shows a qualitative indication of the divalent ion repulsion of the membranes. At overlimiting current densities, water dissociation occurred at membranes with PEI-terminated layers and increased with the number of layers, while it was nearly absent for the PSS-terminated layers. Hence, LbL layers allow switching on and turning off water splitting at the surface of ion exchange membranes.The authors from Germany acknowledge support through the German Research Foundation (DFG) grant - SFB 985 "Functional Microgels and Microgel Systems". M.C. Marti-Calatayud is grateful to the Universitat Politecnica de Valencia for his postgraduate (Ref.: 2010-12) and visiting scientist grant (PAID-00-12). M. Wessling appreciates financial support from the Alexander-von-Humboldt Foundation.Abdu, S.; Martí Calatayud, MC.; Wong, JE.; García Gabaldón, M.; Wessling, M. (2014). Layer-by-Layer Modification of Cation Exchange Membranes Controls Ion Selectivity and Water Splitting. ACS Applied Materials and Interfaces. 6(3):1843-1854. https://doi.org/10.1021/am4048317S184318546