Ultrathin membranes composed of branched polyethylenimine and poly[(o-cresyl glycidyl ether)-co-formaldehyde] for primary recovery of itaconic acid

Efficient primary recovery of building-block chemicals produced by microbial processes, such as biobased itaconic acid, is a key step for environmentally sustainable and economically feasible manufacturing processes. Ultrathin membranes have the potential to address these challenges. Here, ultrathin membranes composed of branched polyethylenimine and poly[(o-cresyl glycidyl ether)-co-formaldehyde] were fabricated using a facile spin coating procedure, and the composition of the casting solution was adjusted to improve the separation performance. The structural properties of the ultrathin membranes (intrinsic porosity, thickness, surface morphology, chemistry, charge, and wettability) were investigated and linked to the separation performance. By increasing the content of polyethylenimine in the casting solution, the transport rate of itaconic acid across the membranes increased up to 40 times. Membranes with a 4:1 mass ratio of polyethylenimine to poly[(o-cresyl glycidyl ether)-co-formaldehyde] reactive groups were selected, and their ability to recover itaconic acid from synthetic solutions and recombinant Pichia pastoris culture supernatant in diffusion-based mode was demonstrated. Experiments with pure solutions of supernatant components demonstrated that the membranes were equally selective for itaconic acid and potential cultivation byproducts and at least 7-times more selective for itaconic acid than culture medium components. Experiments with synthetic complex solutions and culture supernatant confirmed the high selectivity for itaconic acid: the separation performance was similar for complex and pure itaconic acid solutions, despite the significant difference in the complexity of these solutions. This study is the basis for a new technology to recover microbially produced building-block chemicals.