Liquid–liquid-mediated extraction of metals from crude oils using tetramethylammonium hydroxide pentahydrate ionic liquid

Abstract

This study investigated efficacy of tetramethylammonium hydroxide pentahydrate in extraction of trace metals from Nigerian crude oils. Samples were collected from Belema, Ogoni and Imo oil fields. Metal extraction was done at 30–70 °C, while analysis done using atomic absorption spectrophotometry. Recovery analysis results showed 92.85–96.77% recoveries, confirming reliability of results. Total metal concentrations followed the order: Ni > Pb > Cu > Mn > Cr > Cd. Single factor analysis of variance results showed that F < F critical (0.07 < 3.68), indicating null hypothesis acceptance. Hierarchical cluster result indicated chemical affinity/similar sources. T-test results at 95% confidence interval indicated significant differences. Metal removal efficiency decreased with increased temperature from 30 to 70 °C, indicating exothermic process. Thermodynamic parameter values (ΔH°) for Cd, Cr, Cu, Mn, Ni, and Pb are −19.64, −16.64, −13.62, −13.47, −6.93, and −5.51 KJmol⁻¹, respectively, confirming exothermic reactions. Values of ΔS° for Cd, Cr, Cu, Mn, Ni and Pb are −50.46, −40.77, −26.80, −29.11, −19.99, and −1.31, respectively, indicating decreased randomness at liquid/liquid interface during the extraction, and unfavorable extraction at higher temperatures. ΔG° at the various temperatures indicated negative values, indicating feasible and spontaneous extraction. Conclusively, metal distribution in the oils followed similar trend, metal extraction efficiency decreased with increased temperature, and thermodynamic parameter values indicated possible metal extraction process.

Keywords:

• atomic absorption spectrophotometry
• crude oil
• extraction process
• metal
• thermodynamic parameters
• tetramethylammonium hydroxide pentahydrate