Purification of Produced Water by Solvents to Enhance Oil Recovery and Reuse Separated Droplets

In crude oil production, large volumes of produced water are generated as a highly polluting waste byproduct. On average, at least two barrels of produced water are generated for every barrel of oil. This water contains oil traces in stable and complex emulsions. To purify it, a method is proposed based on breaking these emulsions using solvents that induce the coalescence of oil droplets, facilitating their separation from the water. The method has two main objectives: (1) To identify the characteristics a solvent must have to effectively break oil emulsions according to the Hansen solubility parameter (HSP) model. (2) To select, from 40 solvents of different chemical families, the most suitable ones based on efficiency, low toxicity, industrial availability, and cost. The experimental procedure included the following steps: (1) Contacting the solvent with produced water containing 150 ppm of oil under agitation. (2) Allowing the mixture to rest until a layer of recovered oil formed. (3) Spectrophotometric analysis of the residual oil. Three distinct HSP solubility spheres were identified, within which the most effective solvents were xylene (99.4% recovery), cyclohexane (99.5% recovery), and tetrahydrofuran (100% recovery). Their high efficiency not only facilitated oil separation but also made the recovered oil suitable for commercialization.