Performance Investigation of Membranes Suitable for Osmotic Membrane Pressure Actuators
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Polybenzimidazole (PBI) membrane performance having hydrocarbons mixed with the feed water was investigated. Forward osmosis (FO) and pressure retarded osmosis (PRO) experiments were performed with different ratios of hydrocarbons. The membranes performed well under these conditions. The results did not conclusively indicate that there is a relationship between the hydrocarbon ratio and the water or salt permeability. It appeared that the contact between the water and the membrane surface is an important factor contributing to water permeation. The results indicated that exposure to hydrocarbons possibly increases the membrane s salt retention. It was also found that hydrocarbons possibly cause swelling of the membrane. This was done by measuring thickness before and after exposure under different circumstances. In experiments conducted in PRO mode pressure was generated on the draw side when hydrocarbons were mixed together with water in the feed. PRO experiments using pure water in the feed were performed at different pressure differences. The results showed no linear relationship between water flux and pressure difference. FO experiments using pure water in the feed were carried out to test the effect of temperature on the trans-membrane water and salt flux. It was found that both water and salt flux increase with temperature. The PBI membrane s thermal stability was investigated using thermogravimetric analysis. It was heated to temperatures just short of 600 °C with very little loss of mass. The membrane morphology was characterized by SEM, and its hydrophilic properties demonstrated by attempted contact angle measurements.