Cellulose Acetate Membrane
Project ID: 1526
Principal Investigator: Saied Delagah
Research Topic: Desalination and Water Treatment
Priority Area Assignments: 2013 (Advanced Water Treatment)
Funded Fiscal Years: 2013
Today, cellulose acetate desalting membranes make up a significant percentage of the desalting membranes in use at desalting plants around the country. Although it is well established that the intrinsic transport properties of cellulose acetate (CA) membranes can exceed 99.5 percent salt rejection, this has not been the case in practice. This is due to irregularities with the CA polymer. If feed water at 3,500milligrams per liter (mg/L) is desalted with a CA membrane with 95 percent salt rejection, the product would be 175 mg/L. If a superior CA membrane existed with 99.5 percent salt rejection, the product would be 17 mg/L. Also, CA membranes currently operate at a small range in pH. Development of a CA membrane that is operated at an increased pH range improves overall desalting costs by lowering pretreatment chemical costs. The Yuma Desalting Plant, which is a CA-based membrane plant, would benefit greatly from a CA membrane that is both capable of operating at higher pHs and is able to have superior performance than commercially available membranes.
To date, the ongoing study is showing tremendous results in displaying a superior CA membrane with increased salt rejection. The research question that is looked at being answered in this study is: Is it possible to make relatively minor modification(s) during the synthesis of the polymer to achieve a superior CA membrane?
Need and Benefit
The cellulose acetate membranes commercially available today are deficient in both salt rejection and flux compared to what is possible. For example, increased salt rejection is supported by data from the literature:
Riley, R.L., H.K. Lonsdale, C.R. Lyons, and U. Merten, J. Appl.Polym. Sci., 11, 2143-2158 (1967).
in this study multiple layers of CA thin films were overlaid on each other resulting in improved salt rejection from the low values of 94.4% to improved values of 99.0%. Indeed, this paper reports a salt rejection on one membrane sample tested of 99.81% compared with 99.83%. Although this approach would not result in a viable membrane because of low flux, high pressure and other reasons, the experiments demonstrate that salt "leaks" through imperfections in the single thin film that makes up the commercial membranes. There is room for significant improvement. A lower pressure CA membrane with high flux is desirable to lower energy costs for desalting. By using the investigator's knowledge of solvent deposition, the novel CA polymer can be deposited onto substrates resulting in this superior membrane.
Advances in this area would result in increased water supply for the needed regions of the American West. The Yuma desalting plant has used CA membranes for its operation and improvements to the CA membrane will reduces operation and maintenance costs including energy costs of the plant along with reducing the carbon footprint of the plant by having modified CA membranes that are superior in performance characteristics than what is available commercially today.
Independent Peer Review
The following documents were reviewed by qualified Bureau of Reclamation employees. The findings were determined to be achieved using valid means.
Cellulose Acetate Bulletin (final, PDF,
By Saied Delagah
R&D Bulletin completed on February 10, 2015