Key Takeaways & Executive Findings
- •• • SDS-Na2SiO3 composite microemulsion achieved 92.47% oil removal efficiency, outperforming single-surfactant systems (86.33% for SDS, 87.45% for AOS), demonstrating enhanced performance for hazardous waste remediation. • • Optimal single-surfactant formulations were determined: SDS microemulsion (SDS:alcohol:NaCl = 2.72%:13.21%:2.17%) and AOS microemulsion (SDS:alcohol:NaCl = 2.72%:15.41%:2.17%), providing precise formulation guidelines for industrial application. • • The composite microemulsion could be recycled up to 5 times while meeting national secondary utilization standards, indicating significant cost reduction potential for large-scale operations. • • AOS-Na2SiO3 composite exhibited superior salt resistance, whereas SDS-Na2SiO3 showed better alcohol resistance, enabling tailored selection based on specific field conditions (e.g., salinity, cosurfactant availability).
Abstract
Shale gas extraction generates hazardous oily sludge, necessitating effective in-situ treatment. Microemulsion technology offers low energy consumption, cost efficiency, and high oil removal without heating. This study investigates single-surfactant microemulsions using sodium dodecyl sulfate (SDS) and alpha-olefin sulfonate (AOS), and composite microemulsions with sodium silicate (Na2SiO3). Phase behavior and effects of surfactant, alcohol, and salt concentrations on oil removal were examined. Optimal single formulations achieved removal rates of 86.33% for SDS (SDS:alcohol:NaCl = 2.72%:13.21%:2.17% mass ratio) and 87.45% for AOS (SDS:alcohol:NaCl = 2.72%:15.41%:2.17%). SDS microemulsions showed superior phase stability despite slightly lower removal efficiency. Composite SDS-Na2SiO3 microemulsion achieved 92.47% oil removal, outperforming single systems, and could be recycled five times while meeting national secondary reuse standards. AOS-Na2SiO3 exhibited better salt resistance, whereas SDS-Na2SiO3 showed better alcohol resistance. This work provides a novel approach for in-situ oily sludge treatment.
1. Introduction
Oily sludge from shale gas drilling platforms is a hazardous waste stream characterized by complex composition and recalcitrant contaminants. Conventional treatment methods such as incineration, pyrolysis, or solvent extraction often entail high energy consumption, secondary pollution, or limited oil recovery. Microemulsion-based washing has emerged as a promising alternative due to its low energy footprint, ambient-temperature operation, and high oil removal efficiency. However, single-surfactant microemulsions often exhibit limited elution capacity and poor recyclability, hindering their industrial deployment.
This study addresses these bottlenecks by developing composite microemulsions incorporating sodium silicate (Na2SiO3) as a builder. The authors systematically evaluated phase behavior and oil removal performance of SDS- and AOS-based microemulsions, both alone and in combination with Na2SiO3. The results demonstrate that the SDS-Na2SiO3 composite achieves a 92.47% oil removal rate, surpassing single-surfactant systems, and retains efficacy over five reuse cycles. These findings provide a technically viable and cost-effective solution for in-situ oily sludge treatment, offering a pathway toward sustainable waste management in shale gas operations.
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HE Linglin, LIAO Song, ZHAO Ziyu, ZHAO Mengting, GAO Wen, WANG Wei, LIU Shengyu (2026). Preparation of Microemulsion and Its In-Situ Oil Removal Performance on Oily Sludge from Shale Gas Drilling Platforms. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202604015
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Frequently Asked Questions
What is the optimal formulation for the SDS-Na2SiO3 composite microemulsion, and how does it compare to single-surfactant systems in terms of oil removal efficiency?
The SDS-Na2SiO3 composite microemulsion achieved an oil removal efficiency of 92.47%, which is significantly higher than the 86.33% and 87.45% obtained with SDS and AOS single-surfactant microemulsions, respectively. The optimal single-surfactant formulations were SDS:alcohol:NaCl = 2.72%:13.21%:2.17% and AOS:alcohol:NaCl = 2.72%:15.41%:2.17% (mass ratios). The composite system's superior performance is attributed to the synergistic effect of Na2SiO3, which enhances interfacial activity and oil displacement.
How many times can the composite microemulsion be recycled without significant loss in performance, and what are the implications for operational costs?
The SDS-Na2SiO3 composite microemulsion can be recycled up to 5 times while still meeting national secondary utilization standards for treated sludge. This recyclability reduces chemical consumption and waste generation, directly lowering operational costs for large-scale field applications. After five cycles, the oil removal efficiency likely decreases, necessitating replenishment or regeneration of the microemulsion.
What are the relative salt and alcohol tolerances of the AOS-Na2SiO3 and SDS-Na2SiO3 composite microemulsions, and how does this affect their applicability in different shale gas drilling environments?
AOS-Na2SiO3 composite microemulsion exhibits better salt resistance than SDS-Na2SiO3, while SDS-Na2SiO3 shows better alcohol resistance. This means that in high-salinity environments, AOS-based systems are more stable, whereas in systems requiring higher cosurfactant (alcohol) concentrations, SDS-based systems are preferable. Field operators should select the appropriate formulation based on the specific ionic strength and cosurfactant requirements of the oily sludge matrix.
What is the impact of NaCl and alcohol concentration on the phase behavior and oil removal efficiency of the microemulsions?
Increasing NaCl and alcohol concentrations induces phase transitions from lower-phase to upper-phase microemulsions. Oil removal efficiency initially increases with rising concentrations, reaches an optimum, and then declines before stabilizing. This trend is critical for process optimization: operating near the optimal salinity and alcohol content maximizes oil recovery, while deviations can lead to phase separation or reduced efficiency.
How does the SDS-Na2SiO3 composite microemulsion compare to conventional thermal or solvent-based methods in terms of energy consumption and environmental impact?
Microemulsion-based washing operates at ambient temperature and pressure, eliminating the need for energy-intensive heating or high-pressure equipment. This results in significantly lower energy consumption and reduced carbon footprint compared to thermal desorption or incineration. Additionally, the microemulsion components are biodegradable and can be recycled, minimizing secondary waste. The high oil removal efficiency (92.47%) and recyclability (5 cycles) further enhance its environmental and economic viability.
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