On the Isolation of Single Basic Amino Acids with Electrodialysis for the Production of Biobased Chemicals

Abstract

Amino acids from biobased feeds are an interesting feedstock for the production of biobased chemicals from cheap protein sources, as amino acids already have the required functionalities. Amino acids are zwitterionic molecules whose charge is determined by the surrounding pH. This makes the use of an electrical field as driving force for their separation, as in membrane electrodialysis (ED), attractive. Electrodialysis with commercially available ion exchange membranes was applied for the isolation of the basic amino acids L-lysine (Lys) and L-arginine (Arg) as a mixture and further separation of Arg from 1,5 pentanediamine (PDA), which is obtained from the enzymatic conversion of Lys. Electrodialysis experiments for the separation of PDA from Arg are carried out at three different pH values: 12.5 (PDA 0 /Arg −0.5 ), 10.9 (PDA +0.5 /Arg 0 ), and 10.0 (PDA +1.5 / Arg 0 ). Owing to the sensitivity of the charge of the amino acids with respect to pH changes, experiments at constant pH (using acid or base dosing or using a buffer in the feed solution) are carried out as well. Control of the pH significantly improves the performance of the process. The separation of PDA from Arg at pH = 10.0, when PDA has an average net charge of +1.5, resulted in the highest recovery (63%) at the highest current efficiency (83%) and significantly low energy consumption (3 kWh/ kg). Depending on the conditions, pure streams of amino acids, either Arg (at pH = 12.5) or PDA (pH = 10.9) could be obtained, which shows the strength of the concept of enzymatic conversion combined with electrodialysis for the fractionation of amino acids for biorefinery applications.

Mixed matrix membranes for process intensification in electrodialysis of amino acids

“…Current is not only used for amino acid transport, but part of it is used for water splitting to produce the necessary ions for charge transport. The occurrence of water splitting has not only an influence on the current efficiency but also on the total recovery and product purity as the charge of the amino acids is strongly dependent on the surrounding pH . Retro‐migration of the amino acids through the MMM as described for the electrodialysis with ultrafiltration membranes for the separation of peptides is, however, not likely to occur due to the coupling of the prepared MMM with an AEM, which would retain positively charged amino acids from migrating towards the cathode.…”

“…The effective membrane area used was 44.2 cm 2 . The process was assessed based on amino acid flux, current efficiency, energy consumption and GABA retention . Additionally, the conversion of Glu to GABA relative to the amount of Glu transported from feed to receiving 1 stream was determined.…”

“…Electro‐membrane processes have been successfully applied for the isolation of amino acids and peptides with different charge behavior with respect to pH . For example, electro‐membrane filtration, a technology that combines conventional membrane filtration with electrophoresis was developed and applied for the separation of bioactive peptides .…”

“…To solve the problem, enzymatic modification is considered to introduce prominent differences in the charge behavior of the molecules involved and at the same time leading to a product that is interesting for biorefinery applications . The combination of electrodialysis and enzymatic conversion to modify the charge behavior of the amino acids was proven to be successful for their isolation …”

“…38,39 The combination of electrodialysis and enzymatic conversion to modify the charge behavior of the amino acids was proven to be successful for their isolation. 22,23,38,40 Integration of enzymatic conversion and subsequent separation into one single unit operation would lead to further intensification of the process. An attractive approach is the use of mixed matrix membranes as platform for enzymatic reactions.…”