Retrieving Oil and Recycling Surfactant in Surfactant-Enhanced Soil Washing

Abstract

How to simultaneously realize retrieving oil and recycling surfactant in the remediation of leaked oil-polluted soil by means of surfactant-enhanced soil washing is still a significant challenge. Here, we reported for the first time a novel CO2-switchable anionic surfactant, 11-dimethylamino-undecyl sulfate sodium salt (DUSNa), to retrieve leaked oil and recycle surfactant simultaneously in the process of oil-polluted sand remediation by DUSNa-enhanced soil washing. Because a CO2-switchable tertiary amine group had been incorporated into a traditional anionic surfactant of sodium alkyl sulfate to form DUSNa, DUSNa was readily converted into its inactive form of DUS upon CO2 treatment, leading to complete oil/water phase separation from a DUSNa-stabilized oil-in-water emulsion. The formed DUS was insoluble in both the oil and the water, but was suspended or precipitated in the lower aqueous phase, allowing subsequent retrieval of almost surfactant-free oil. Recycling of DUSNa was enabled by its recovery from DUS by treatment with N2 or NaOH. Upon CO2 treatment, both around 92.1% of the oil and around 90.8% of the DUSNa at least could be retrieved and recycled over three cycles of DUSNa-enhanced soil washing.

Advanced Switchable Molecules and Materials for Oil Recovery and Oily Waste Cleanup

“…[40] More recently, Xu et al reported a novel CO 2 -switchable anionic surfactant based on a sulfate salt surfactant (i.e., 11-dimethylaminoundecyl sulfate sodium salt, DUSNa) for the oil-contaminated soil remediation (Figure 3b). [41] The authors claimed that the recovery ratio of mineral oil was around 92.1-94.1%, whereas the residual oil on "clean" sands only counted for 2.8-3.2% of the original amount, or less than 0.17% in the aspect of the total mass. Furthermore, the total organic content (TOC) and chemical oxygen demand (COD) in the process water were measured at less than 40 mg L −1 after treatment, indicating excellent decontamination of the process water as well.…”

“…Reproduced with permission. [41] Copyright 2018, American Chemical Society.…”

“…Since the CO 2 response is a subphase of the pH response, which relies on the change of molecular amphiphilicity during the protonation/deprotonation process, [10h] these CO 2 -responsive Residual oil on sands: < 0.17% (to the total mass); TOC, COD < 40 mg L −1 . [41] surfactants must have at least one state carrying electro-charges, e.g., the interfacial-active fatty acid is anionic (deprotonated). Therefore, the presence of dissolved ions in the process water, especially multivalent ions such as Ca 2+ and Mg 2+ , could negatively impact the switchability and as a result, the performance of the responsive surfactants.…”

Effect of selenium‐position on the redox responsivity of isomeric selenium‐containing anionic surfactants

“…Increasingly, more and more people are waking up to that, surfactants are useful in some certain steps, after which they become a liability (Liu et al, 2006). For example, surfactant-enhanced soil washing (SESW) (Ceschia et al, 2014;Xu et al, 2018) is one of the most versatile remediation techniques. In the process of SESW, both the oil-water interfacial tension and the oil-soil attraction are reduced by surfactants.…”

“…However, the water insoluble organic contaminants are solubilized or emulsified by surfactants, making it difficult to separate the contaminants from the SESW eluents. It is believed that switchable or stimuli-responsive surfactants may solve this problem (Ceschia et al, 2014;Xu et al, 2018). The reason for this is that switchable surfactants could reversibly interconvert between active and inactive forms under an applicable stimulus.…”