Search

Surfactant losses by adsorption to rock surfaces make surfactant-based enhanced oil recovery economically less feasible. We investigated polyacrylate (PA) as a sacrificial agent in the reduction of anionic surfactant adsorption with focus on calcite surfaces by using quartz crystal microbalance with dissipation monitoring. It was found that the adsorption of the anionic surfactant alcohol alkoxy sulfate (AAS) followed a Langmuir adsorption isotherm, and the adsorbed amount reached saturation above its critical micellar concentration. Adsorption of PA was a much slower process compared to AAS adsorption. Increasing the calcium ion concentration also increased the amount of AAS adsorbed as well as the mass increase rate of PA adsorption. Experimental results combined with density functional theory calculations indicated that calcium cation bridging was important for anionic surfactant AAS and PA adsorption to calcite surfaces. To effectively reduce the amount of surfactant adsorption, it was needed to preflush with PA, rather than by a simultaneous injection. Preflushing with 30 ppm of PA gave a reduction of AAS adsorption of 30% under high salinity (HS, 31,800 ppm) conditions, compared to 8% reduction under low salinity (LS, 3180 ppm) conditions. In the absence of PA, the amount of adsorbed AAS was reduced by already 50% upon changing from HS to LS conditions. Lower calcium ion concentrations, as under LS conditions, contributed to this observation. On different mineral surfaces, PA reduced the AAS adsorption in the order of alumina > calcite > silica. These results offer important insights into mitigating surfactant adsorption using PA polyelectrolyte as sacrificial agent and contribute to improved flooding strategies with reduced surfactant loss. [ABSTRACT FROM AUTHOR]

Adsorption behavior of surfactants to rock surfaces is an important issue in oil recovery, especially in the process of surfactant flooding. The surfactant loss through adsorption to rock surfaces makes such process economically less feasible. Here, we investigated the adsorption behavior of anionic surfactants (alcohol alkoxy sulfate, AAS) onto silica with quartz crystal microbalance with dissipation monitoring. The results demonstrated that the surfactant adsorption followed the Langmuir adsorption isotherm. Up to solution pH 10, surfactant adsorption slightly increased with increasing pH. The higher pH leads to more anionic surface sites for binding with an anionic surfactant with the help of a calcium cation bridging. The amount of anionic surfactant binding also increases with increasing calcium ion concentration up to 50 mM. It was found that sodium ions were able to exchange calcium ions near the silica surface, which would reduce the affinity for surfactant adsorption. The effect of the polyanion polystyrene sulfonate (PSS) on the anionic AAS adsorption was investigated to learn the possible competitive adsorptions. Indeed, this was found. Upon addition of 50 ppm PSS to a 0.05 wt% AAS containing solution, the adsorption of AAS was reduced by about 85 %. The obtained results show the interplay of different interacting species affecting the overall degree of anionic surfactant adsorption to silica surfaces. Optimal tuning of the process conditions according to these results will contribute to a more efficient use of anionic surfactants in enhanced oil recovery. [ABSTRACT FROM AUTHOR]

We have investigated the conditions of colloidal stability of silica nanoparticles smaller than 100 nm for their applications in enhanced oil recovery (EOR), especially pertaining to chemical flooding processes. Using zeta sizer and dynamic light scattering techniques, the stability of silica nanoparticle (SNP) dispersions has been investigated by variation of the pH, composition of salt solutions, addition of surfactants and polyelectrolytes. Such conditions can be encountered in oil reservoirs. It was found that changing pH from 5 to 10 had a negligible effect on the size of SNPs, whereas its zeta potential increased with increasing pH. Aggregation of SNPs is a partially reversible process for low degrees of aggregation in 500 mM NaCl, whereas observed strong aggregation in 1000 mM NaCl was irreversible. A critical aggregation concentration (CAC) was defined for the different salts investigated, above which the SNP dispersion became unstable at a fixed pH of 9.5. The CAC for NaCl was approximately 200 times higher than for CaCl 2 and MgCl 2. Our observations could not be explained completely by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Therefore, we have included non-DLVO interactions such as cation bridging, hydration forces, and steric effects. The additional presence of anionic alcohol alkoxy sulfate (AAS) surfactant slightly destabilized the SNP solution, but by the addition of polyacrylate (PA) was effectively stabilized. With increasing PA concentration, the CAC for both CaCl 2 and MgCl 2 increased. Upon addition of 100 ppm PA, the CAC increased by a factor of five compared to the situation in the absence of PA. Reducing the solution pH below 8.5, SNP can be stabilized in higher salinity in the presence of PA. The obtained results contribute to a better fundamental understanding of the SNP stability mechanism and a guide to optimize the SNP injection process with EOR chemicals. [ABSTRACT FROM AUTHOR]

We report an advanced treatment method for phosphoric acid recovery from leached sewage sludge ash. Layer-by-layer (LbL) polyelectrolyte deposition has been used as a tool to modify and convert a hollow ultrafiltration membrane into a nanofiltration (NF) LbL membrane for H 3 PO 4 recovery. To build the LbL membrane, poly(styrenesulfonate) PSS was chosen as polyanion, while three different polycations were used: a permanently charged polyelectrolyte, poly(diallyldimethylammonium chloride), PDADMAC; a pH-dependent charged polyelectrolyte poly(allylamine hydrochloride), PAH; and a PAH modified with guanidinium groups (PAH-Gu). Based on detailed surface characterizations (AFM, XPS and Zeta-potential) it was concluded that both charge density and pH-responsiveness of the polycations are key parameters to control the final membrane surface structure and transport properties. The surface properties of LbL-coated membranes were correlated with the membrane filtration performance, when exposed to the real leached sewage sludge ash solution. The highest permeability was recorded for (PDADMAC/PSS) 6 , a result that was rationalized on its loose, and possibly less interpenetrated, structure, followed by (PAH-Gu/PSS) 6 characterized by a more dense, compact layer. H 3 PO 4 recovery was the highest in the case of (PDADMAC/PSS) 6 , but the retention of multivalent metals (Fe3+ and Mg2+) was low, leading to a more contaminated permeate. The opposite trend was observed for (PAH-Gu/PSS) 6, resulting in a less metal-contaminated, but also a less H 3 PO 4 -concentrated permeate. Our LbL-modified membranes were found to improve the permeability and H 3 PO 4 recovery compared to a commercially available acid-resistant NF membrane. Image 1 • Layer-by-layer NF membranes recover H 3 PO 4 from leachate sewage sludge ash. • Permeability: LbL-coated membranes > commercial acid-resistant NF membranes. • Type of polycation in LbL coatings affects separation properties. • Largest H 3 PO 4 recovery for permanent polycation, but low Fe3+ and Mg2+ retention. • Weaker polycation with guanidinium moiety: less metal and less H 3 PO 4 in permeate. [ABSTRACT FROM AUTHOR]