Pretreatment of Oilfield Produced Water using Ionic Liquids for Dissolved Air Floatation

Abstract

Energy consumption is rising due to population increase and industry development. There will be an increase of nearly 66% of energy consumption related to fossil fuel such as oil and gas between 2003 and 2030 from 7.6*1013 to 12.6*1013 kilowatt-hours worldwide. With the increase in the production of oil and gas, a larger amount of produced water (PW) will be generated. Produced water poses a risk to the environment, because it contains persistent toxic and carcinogenic constituents. The dissolved air floatation (DAF) process is the most widely used technique in the world for produced water treatment. In order to reach better experimental results, different coagulants are added as a pretreatment process. In this research, as a pretreatment to the DAF process, three similarly structured ionic liquids (n-methylpyridinium tosylate, 1,3-dimethylimidazolium tosylate, and 1-benzyl-3-methylimidazolium tosylate) were used to improve the efficiency of treatment. An orthogonal experimental design (OED) with different factors and levels was designed to determine the most effective ionic liquid, the best operation conditions, and the influence strength order of different factors. Two blank columns were designed for error estimate. Range analysis and variance analysis (ANOVA) were used to understand factor influence and determine the best operating conditions. The results of the experiments indicate that, with the same operation conditions (concentration, speed, and reflux ratio), 1-benzyl-3-methylimidazolium tosylate had the highest oil and turbidity removal efficiency when compared to the other two ionic liquids. According to range analysis and variance analysis (ANOVA), the three ionic liquids have the same influential order for the three factors considered with an ionic liquid concentration influence greater than that of both speed (RPM) and the reflux ratio (RR). The best operating conditions for the three ionic liquids were 300 mg/l for ionic liquid concentration, 200 for RPM, and 20% for RR, respectively. At the best operating conditions, the percentages of the removal of oil content were 75.4% ± 0.7% for n-methylpyridinium tosylate, 71.0% ± 0.2% for 1,3-dimethylimidazolium tosylate, and 81.6% ± 0.3% for 1-benzyl-3-methylimidazolium tosylate, respectively.