Progress 05/01/06 to 12/30/07
Outputs
OUTPUTS: Results were not promising. This non-confidential report is the only dissemination of the project results and findings outside of MTR. PARTICIPANTS: P.I./Project Manager: Dr. Ingo Pinnau, MTR's Director of Materials and Membrane Development since 1991. Other Key Contributor: Ms. Sylvie Thomas, Research Engineer in MTR's Materials and Membrane Development group since 2005. TARGET AUDIENCES: Our work, though unsuccessful, was targeted at improving the economics of ethanol production from corn by developing a cost-effective membrane-based process for the separation and purification of zein, a high-value corn protein and co-product of ethanol production. The primary target audiences were thus corn-based ethanol producers, and zein consumers. The major potential uses for zein include textiles, zein-based plastics, inks and adhesives. PROJECT MODIFICATIONS: The overall objective of the Phase I program was to develop a membrane with the same rejection properties as a previously developed polyamide-polyether membrane, but with a higher flux when operated with zein solutions. Many membranes with different polyamide-polyether selective layer thicknesses and composite membrane configurations were made and tested for separation performance. No membrane test gave us the required combination of high water/ethanol flux, high zein rejection and low sugar rejection. Membrane fouling in short-term longevity testing exacerbated the membrane performance problems. Our disappointing results with the initial polyamide-polyether membranes led us to consider other types of membranes that night be successful in the zein application. Polyamide materials seemed promising as candidates for use in zein separation membranes because of their good water permeance and excellent rejection rates, even for small molecules. We decided to evaluate one commercial reverse osmosis (RO) membrane and one commercial ultrafiltration (UF) membrane with polyamide selective layers to determine their zein and sugar rejection levels. In order to function in the RO and UF markets, membrane materials must show high salt rejection rates, and we therefore suspected that RO and UF membranes would show very good zein rejection rates. The RO membrane selected was the Hydranautics polyamide membrane, ESPA3. The UF membrane we chose was the Filmtec nanofiltration membrane, NF270. The two commercial membranes exhibited moderate flux coupled with excellent zein rejection; however, ethanol and sugar rejection were very significant, which is not suitable for recovery of zein at a high purity. We also tried two other types of membranes in this study: a zein composite membrane and a hydroxycellulose membrane; neither one could provide the target performance combinations. The series of experiments carried out on this project seem to confirm that there is a tradeoff between high water/ethanol flux, high zein rejection and low ethanol/sugar rejection for the membrane materials tested. Unfortunately, none of the membranes tested during the study could provide the rigorous performance combination required for economical separation of zein.
Impacts
Outcome: Flux-rejection tradeoffs in membrane performance for zein separation. The series of experiments carried out on this project seem to confirm that there is a tradeoff betwen high water/ethanol flux, high zein rejection and low ethanol/sugar rejection for the membrane materials tested. Unfortunately, none of the membranes tested during the study could provide the rigorous performance combination required for economical separation of zein. Outcome: We do not intend to continue work on membrane-based zein separation from bioethanol process streams. The goal of this project was to improve the economics of ethanol production from corn by developing a cost-effective process for the separation and purification of zein, a high-value corn protein and co-product of ethanol production. Specifically, we intended to develop selective, high-flux ultrafiltration membranes that would allow isolation of high-purity zein in dry-grind ethanol plants. The co-product would have generated additional income for the plant, thus contributing to lower net production costs. The key innovation in the proposed zein separation process was a zein-rejecting, sugar permeable membrane. Prior to the project, a polyamide-polyether composite membrane had been developed at MTR that met these rejection and permeability targets. However, the ethanol/water flux of the membrane was too low to make the membrane separation process economical. The overall objective of the Phase I program was to develop a membrane with the same rejection properties as the polyamide-polyether composite membrane, but with a higher flux when operated with zein solutions. Many membranes with different selective layer thicknesses and composite membrane configurations were made and tested for separation performance. No membrane test gave us the required combination of high water/ethanol flux, high zein rejection and low sugar rejection. Membrane fouling in short-term longevity testing only exacerbated the membrane performance problems. Tests were also carried out using membranes with selective layers of other polymers; none could provide the target performance combinations. The zein/sugar rejection combinations and flux/fouling results were discouraging enough to any future commercialization effort that we consider it highy unlikely that an economic membrane process for zein separation can be developed with current membrane materials.
Publications
- No publications reported this period
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