Produced water treatment using microemulsion formulated with vegetable oil-based surfactant

Abstract

The presence of produced water is common in oil production. In certain production stages, the volume of produced water exceeds that of oil. Pretreatment is necessary before the disposal or reinjection of produced water into wells because it is harmful to the environment owing to the high oil and grease contents (OGC), salinity, and other factors. This study proposes a produced water treatment using microemulsions (ME) with vegetable oil-based surfactants (S), with the aim of reducing two main factors, OGC and salinity. The decision to use a vegetable oil-based surfactant as an alternative to a petroleum-based surfactant was made to reduce the negative effects of the overall process on the environment. Coconut soap, the surfactant used in the formulated ME, was selected after testing a variety of vegetable oil-based surfactants. The other components used in the ME formulation were 2-butanol as a co-surfactant (C), pine oil as the oil phase, and saline water at 2 % NaCl as the water phase. The ME point used in the water treatment was defined by D-optimal mixture planning, composed of 85 % C/S, 2.5 % oil phase, and 12.5 % water phase, with a C/S ratio of 10. In addition, we used a complete factorial experimental design with combinations of three variables (time, temperature, and microemulsion percentage), and repetition of the central point to select the greatest reduction in OGC and salinity. According to the results, OGC reduction values ranged from 89.15 % to 95.43 %, with the real OGC values ranging from 16.98 mg·L−1 to 7.15 mg·L−1. These values are within the limits established by environmental agencies, CONAMA, US EPA, and the OSPAR Commission, for the disposal of produced water in the sea. In addition, salinity reduction varied from 38.02 % to 46.8 %, with real salinity decreasing from 36,223.53 mg·L−1 to 31,217.65 mg·L−1. Therefore, it can be said that using a vegetable oil-based and biodegradable surfactant in the microemulsion formulation for the treatment of produced water is as effective in the reduction of OGC and salinity as petroleum-based surfactants, which are more harmful to the environment.