(539g) Development of Advanced Membranes for Produced Water Treatment
Produced water (PW) is oily water that is co-produced during oil and gas exploration and production. In the United States, PW accounted for 88% of the total volume of exploration and production material brought to the surface by the oil and gas industry in 2007. The total volume of PW generated from most of the nearly 1 million actively producing oil and gas wells in the United States in 2007 was estimated to be about 21 billion barrels (bbl). Therefore, identifying and implementing appropriate beneficial uses for PW should provide overwhelming benefits for local communities and ecosystems and provide oil and gas companies with flexible, cost-saving water management options. Conventional wastewater treatment technologies such as coagulation, flocculation, air flotation and gravity separation normally cannot meet the high purity requirements for discharge of PW. There is a growing tendency to use membrane technology for PW treatment. Although membranes can treat PW, their widespread use is hindered by a decline in permeate flux experienced as a result of fouling.
We have developed an approach to control membrane fouling during filtration of PW and to provide a chemical-free strategy to reverse foulant accumulation. Commercial, regenerated cellulose (RC) ultrafiltration membranes were surface modified by growing block copolymer nanolayers from the membrane surfaces by surface-initiated atom transfer radical polymerization (ATRP). By controlling both the chemical and environmentally responsive conformational properties of these polymer layers at the nano-scale, we limit foulant accumulation on these membranes and provide an easy, chemical-free way to remove any attached foulants. Membranes were modified by grafting poly(N-isopropylacrylamide) (PNIPAAm)-block-poly(oligoethylene glycol methacrylate) (PPEGMA) nanolayers from the membrane surfaces. The dual functionality provided by this block copolymer system yields fouling resistant and temperature responsive membranes for the treatment of produced water. The temperature responsive block (PNIPAAm) makes it possible for the membranes to self-clean during the filtration of produced water. Initiator grafting density and average molecular weight of both the PNIPAAm and PPEGMA nanolayers were used as independent variables to optimize the performance of the surface modified membranes. The initiator grafting density was varied by changing the initiator concentration during the membrane activation step. Polymerization time was used as an independent variable to increase the average molecular weight of both PNIPAAm and PPEGMA. The performance of the modified membranes was tested by carrying out water flux measurements using both dead-end and cross-flow filtration experiments.