Adsorption of lignosulfonates onto clay minerals and their effectiveness as a sacrificial agent

Abstract

Surfactant adsorption on reservoir rock surface is a fundamental issue in surfactant based enhanced oil recovery. Reservoirs contain a significant amount of clays that results in large surface areas, thus causing a large portion of the surfactant to be adsorbed. Sacrificial agent (SA) is meant to be sacrificed, hence serving as a shield that protects the formation of rock by adsorbing into active adsorption site and prevents the subsequent surfactant to be adsorbed onto the surface. Despite the promising initial results, the suitability of numerous available types of lignosulfonate (LS) in the vast market as SA has yet to be investigated. Having that said, the objectives of this study are to determine the readiness of four LS types to adsorb onto clay minerals based on their functional groups, to investigate the adsorption capability and to define the effective method (mixture or pre-treatment), as well as to identify the underlying mechanism responsible for the effectiveness to reduce cetyl trimethyl ammonium bromide (CTAB) adsorption. The most commonly used method to measure adsorption refers to the depletion method, where the concentration before and after adsorption are measured. Adsorption data obtained from the depletion method can be modelled into adsorption model to describe the adsorption process. Four types of LS, which are sodium LS (SLS), ammonium LS (ALS), magnesium LS (MLS), and calcium LS (CLS), were compared in terms of functional group, adsorption capability, and adsorption model to determine their readiness to adsorb onto kaolinite and montmorillonite. Different LS types, concentration, contact time, and model of adsorption were among the parameters tested with different brine salinity and pH. Both mixture and pre-treatment methods were investigated in depth to identify the underlying mechanism responsible to effectively reduce CTAB adsorption. A major finding from this study is that the functional groups in LS, such as (a) hydroxyl group in phenolic and aliphatic, (b) methyl and methylene, (c) aromatic, (d) sulfonic acids and stretching aliphatic, and (e) CHx bending out plane, were involved in the adsorption process onto kaolinite and montmorillonite. The mechanism appeared to be driven by electrostatic forces. SLS displayed the highest readiness to adsorb onto kaolinite and montmorillonite, which adhered to the following sequence SLS>ALS>CLS>MLS. Higher LS concentration and salinity led to higher adsorption, especially with the change of monovalent salt to divalent salt. Nonetheless, pH had no impact on adsorption. This signifies that pH modification may be ignored when using LS as SA. Equilibrium and kinetic adsorptions adhered to the Freundlich model and the pseudo-second order, respectively. Electrostatic forces, cation-p interaction, hydrophobic interaction, and cation bridging had a crucial role in the adsorption mechanism of LS with kaolinite and montmorillonite. The SLS as SA had successfully reduced CTAB adsorption via pre-treatment method. The effective underlying mechanism revealed in this study is SLS as SA that displayed high adsorption readiness, along with cation bridging assistance from divalent salt and reversed surface charge. As high as 50% CTAB reduction was recorded in the experimental work. As such, this study concludes that SLS is suitable to function as SA to reduce cationic adsorption onto kaolinite and montmorillonite. Pre-treatment is an effective way to reduce CTAB adsorption.