Regeneration and long-term stability of surfactant-modified zeolite for removal of volatile organic compounds from produced water

We report the results of laboratory-scale evaluation of a produced-water treatment system. The system used surfactant-modified zeolite (SMZ) to strip the volatile organic compounds benzene, toluene, ethylbenzene, and p-, m- and o-xylene (BTEX) from produced water generated as a byproduct of oil and gas recovery. We used laboratory column studies to (1) investigate how different airflow rates impact regeneration of BTEX-saturated SMZ and (2) perform long-term tests to determine the chemical and physical stability of SMZ in a produced-water treatment system. Varying the airflow rate from 1.3 to 10 pore volumes (PV) per minute did not significantly affect BTEX removal rates. Rather, BTEX removal was controlled by the total number of PV that passed through the SMZ bed, suggesting only minor kinetic effects on regeneration. BTEX sorption and SMZ regeneration profiles varied little over 50 sorption/regeneration cycles. Each cycle consisted of BTEX sorption from 100 PV of produced water followed by regeneration with approximately 2000 PV of air. A weakly decreasing trend was observed for the BTEX distribution coefficients (K-d), indicating only a small loss in sorption affinity after 50 cycles. The sorption affinity for BTEX was maintained even though 24% of the original surfactant was washed off the SMZ by 5000 PV of produced water. The hydraulic conductivity of the SMZ decreased by roughly 30% after 50 cycles. Most of the hydraulic conductivity loss was likely caused by particle attrition. The results suggest that SMZ is a viable sorbent for removal of volatile organics from oil- and gas-field wastewaters. (c) 2007 Elsevier Inc. All rights reserved.