Optimization of sulfate removal from injection water using multi-walled carbon nanotubes by response surface methodology

Abstract

One of the major operators' concerns in the injected water into oil reservoirs is the water source itself because sulfate scale formation occurs during waterflooding due to the incompatibility of injected and produced waters. In this work, multiwalled carbon nanotubes (MWCNTs) were prepared by chemical vapor deposition of condensate-gas at 1000 °C and oxidized with an acid mixture at 115 °C for 2 h and then applied as adsorbent for sulfate-removal. Variables Effects such as temperature, adsorbent dose, time and stirring speed, and their interactions during the adsorption were determined and optimized by response surface methodology (RSM) via central composite factorial design (CCF). The experimental data were examined by variance analysis (ANOVA) and fitted to a second-order polynomial equation. The optimum conditions were initial concentration = 800 mg/L, adsorbent dose = 0.14447 g, pH = 7, and temperature = 74.21 °C, 530 rpm during 240 min, and maximum sulfate-removal of 96% was achieved. Isotherm models were investigated to describe the sulfate-adsorption data and a higher suitable to the Langmuir isotherm was found. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The thermodynamic parameters indicated that adsorption was spontaneous and endothermic. Overall, MWCNTs are promising adsorbents for water treatment and have great potential application in oilfields to reduce scale ion content from the source.

Keywords:

• Injection water
• maximum adsorption capacity
• sulfate ion
• carbon nanotubes
• chemically enhanced oil recovery

Disclosure statement

No conflict of interest has been reported by the authors.