# Purification of Produced Water by Solvents to Enhance Oil Recovery and Reuse Separated Droplets
###### Abstract  
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.  
produced water; purification of produced water; oil; petroleum; complex emulsions; solvents; Hansen solubility parameters; xylene; cyclohexane; tetrahydrofuran 2020  
31 January 20253 February 202  
The treatment of produced water to remove residual oil typically involves primary separation, secondary separation, and, in some cases, a final cleaning treatment. Produced water enters primary treatment with up to 1000 ppm of oil and exits with concentrations between 100 ppm and 200 ppm. In secondary treatment, the water enters with concentrations of 100-200 ppm and exits with oil levels reduced to between 10 ppm and 40 ppm. Following secondary treatment, current environmental regulations can generally be met in most oil-producing regions. However, future trends, as exemplified by Norway's regulations for oil platforms, aim to achieve zero harmful discharges--an objective that remains unattainable with the current technology [2].  
The state-of-the-art final cleaning treatments currently available in the industry can reduce the residual oil content to approximately 15 ppm, a level that is still far from the desired goal of complete elimination.  
In the industry, various traditional techniques are used for treating produced water, but their results are not optimal, as they do not achieve 100% efficiency or even values close to it. For this reason, new methods are being researched; however, they are currently developed only at the laboratory level. These methods also are not sufficiently effective and, in some cases, even lead to additional environmental problems.  
The next two sections briefly outline a significant number of methods, including both those commonly used in the industry and those proposed at the laboratory level. To keep the text concise, only their names are mentioned, along with a few characteristics and/or drawbacks that make them insufficiently suitable.