Adsorption and desorption of water-soluble naphthenic acid in simulated offshore oilfield produced water

Abstract

The removal of water-soluble organics compounds in oilfield produced water (OPW) is currently one of the biggest challenges to meet the environmental legislation, as conventional remediation focuses mainly on removing solids and the dispersed oil fraction. Naphthenic acids (NAs) are present in significant amounts in water-soluble organics compounds; therefore, this work milestone is to properly understand the adsorption process by using an acutely recalcitrant O2-NA as WSO model. For this, a comprehensive screening of commercial adsorbents and waste was tested for NAs remediation, assessing also the influence of adsorbent properties and functionalities. Afterwards, there were selected the resins MN 202 and L 493 as adsorbents to further evaluate the regeneration and other variables such as temperature, pH and salt content, focusing on on-site offshore conditions. The initial screening and the equilibrium data suggest that characteristics such as surface area, pore diameter, and ionic form have a great influence on the adsorption process. Furthermore, the adsorption mechanisms involve anion exchange and hydrophobic interactions, showing a transition between multilayer to monolayer adsorption with the increase of the adsorbent dosage and the kinetics, while increasing NA encourages pore diffusion, resulting in irreversible adsorption. The use of eluents, while avoiding irreversible adsorption, allows recovering the adsorbent, improving the process feasibility at the targeted conditions.