Mesoporous carbon xerogel material for the adsorption of model naphthenic acids: structure effect and kinetics modelling

ABSTRACT

The study examined the preparation, characterization and the use of carbon xerogel (CX) material for the adsorption of three model naphthenic acids (NAs); such as, heptanoic acid (HPA), 5-cyclohexanepentanoic acid (CHPA), and 5-phenylvaleric acid (PVA). CX was synthesized by sol–gel method from resorcinol and formaldehyde. The characterization results showed that CX was a mesoporous material with large surface area (573 m²/g) and high pore volume (1.55 cm³/g), which was mainly composed of carbon (93.20%) and oxygen (6.71%). Adsorption studies revealed that PVA, the NA having an aromatic ring was adsorbed more easily by CX (87 mg/g) due to π–π interactions, followed by HPA (65 mg/g) and CHPA (61 mg/g). In addition, by studying the effect of solution pH, the result confirmed that repulsion greatly hindered the adsorption of HPA onto CX at pHs above that of the pH_PZC and at lower pHs attractive electrostatic forces promoted adsorption. Adsorption kinetics fitted the pseudo-first-order model, which suggested that physisorption was most likely the means of adsorption. For the intraparticle diffusion model, the rate of film diffusion was higher than the rate of pore diffusion for each model compound regardless of their structure. Accordingly, this confirmed that pore diffusion was the rate-limiting step, although film diffusion still maintained a significant role in the rate of diffusion. In general, CX exhibited excellent adsorption performance due to its highly mesoporous character so it could be used as a passive treatment method in tailing ponds for removal of organic matters.

GRAPHICAL ABSTRACT

KEYWORDS:

• Adsorption
• carbon xerogel
• naphthenic acids
• kinetics
• unconventional oil process water

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support for this research was provided by a research grant from Natural Sciences and Engineering Research Council of Canada (NSERC) Senior Industrial Research Chair (IRC) in Oil Sands Tailings Water Treatment through the support by Syncrude Canada Ltd., Suncor Energy Inc., Canadian Natural Resources Ltd., Imperial Oil, Teck Resources Ltd., EPCOR Water Services, Alberta Innovates, and Alberta Environment and Parks. Moreover, as a part of the University of Alberta’s Future Energy Systems research initiative, this research was made possible in part thanks to funding from the Canada First Research Excellence Fund.