Improved Reverse Osmosis Membranes for Treating Produced Water

Abstract

Abstract For many years, reverse osmosis (RO) elements have been used in the treatment of produced water, including at several sites in California. The RO reduces salts and organics in the produced water to a level that allows for disposal or reuse. The RO elements used to treat produced water are similar in chemistry and construction to the conventional seawater RO membrane. But compared to seawater, the characteristics of produce water are unique and varied. The conventional seawater membrane comes with pressure and temperature limitations that restrict its ability to treat a wide range of produced waters. Specifically, conventional membranes have a temperature limit and a pressure limit. Only a portion of the produce waters needing treatment fall within the membrane's temperature and pressure limitations. Many produced waters, including produce waters associated with SAGD, require membranes that can accommodate higher temperatures up to 60 C. Other produced waters may allow for treatment at ambient temperatures but their higher salinities above 60,000 mg/l TDS require RO membrane to overcome high osmotic pressures and operate at feed pressures up to 1800 psi. In recent years, membrane manufacturers have enhanced their exiting RO elements to address the challenges associated with the treatment of unique industrial streams such as produced water. Specifically, new, more robust element construction allow designers to push beyond the normal limits of temperature and pressure. One such element allows for operation at temperatures up to 90 C while a second, ultra high-pressure RO (UHPRO), can concentrate the total dissolved salts (TDS) up to 120,000 ppm (12%) while operating at pressures up to 1,800 psi (124 bar). These unique elements can be used to increase the overall efficiency of the treatment facility by reducing the cost of brine disposal and maximizing water recovery. This paper will show how these new elements perform when operated beyond conventional pressure and temperature limits - including how individual ion passage and water permeability are affected at extreme conditions. This paper will share element performance data from laboratory and pilot studies. The data will be used as a basis for new designs at the extreme conditions associated with produced water treatment.