Stabilization of Carbon Dioxide Foam by a Low Concentration of Cetyltrimethylammonium Bromide-Grafted Nano-Faujasite Zeolite. Part 1: Experimental Study

Abstract

In this work, we are introducing an innovative technique to enhance the CO2 foam stability by using a nanofoam stabilizer that reduces the surfactant concentrations below the critical micelle concentration (CMC). The core structure of our foam stabilizer consists of faujasite zeolite nanoparticles (FAU) that are grafted with cationic surfactant, cetyltrimethylammonium bromide (CTAB). The prepared nanomaterials were fully characterized by an array of characterization techniques to gain insight into their surface properties and stability. Then, the foamability and foam stabilization properties of the CTAB, compared with the physically mixed CTAB and neat FAU nanoparticles, and CTAB-grafted FAU nanoparticle systems were evaluated at various surfactant concentrations based on initial foam volume, half-life, liquid holdup, surface shear viscosity, and bubble sizes. Furthermore, the CO2 foam stabilization mechanisms of all foaming agents were investigated by the dilational surface tension. Our results indicated that the CTAB-grafted FAU nanoparticles were able to stabilize the liquid films of CO2 foam at low surfactant concentrations via surfactant coverage on the surface of nanoparticles, which optimized the viscoelastic and surface tension properties of CO2 foam. In fact, below the CMC of CTAB (∼335 ppm), the initial foam volume and half-life remained constant after the addition of the FAU nanoparticles, whereas the foam properties were highly enhanced above the CMC (350–3000 ppm). Our foam stabilization results showed that the optimum stable CO2 foam was generated by CTAB-grafted FAU nanoparticles at a concentration of 1000 ppm (∼500 ppm grafted CTAB), which had a half-life of 773 s, in contrast to the other systems that had a half-life of less than 350 s at 500 ppm CTAB concentration. The surface tension results showed that grafting 50 and 100 ppm CTAB on FAU nanoparticles resulted in 60.20 and 51.52 mN/m initial dynamic surface tension measurements, whereas the virgin CTAB solutions at the same surfactant concentrations had initial dynamic surface tensions of 69.78 and 60.44 mN/m, respectively. On the other hand, at a surfactant concentration of 50 ppm (100 ppm CTAB-FAU nanoparticles), the viscoelastic modulus was almost identical to the viscoelastic modulus measurement at the CMC of CTAB. Interestingly, the CTAB-grafted FAU nanoparticles, compared with the other systems, had almost 1.5–4 times higher liquid holdup and formed smaller and homogeneous bubble sizes during the first 360 s. Hence, the CTAB-grafted FAU nanoparticles could retard the foam destabilization mechanisms, including foam bubble coalescence and ripening effects, due to their ability to maximize the viscoelastic modulus and reduce the surface tension at these low surfactant concentrations. Our findings can provide an economical solution for implementing conventional CO2 foams in enhanced oil recovery (EOR) applications while hindering the agglomeration of nanoparticles.

Stabilization of Carbon Dioxide Foam by a Low Concentration of Cetyltrimethylammonium Bromide-Grafted Nano-Faujasite Zeolite. Part 2: Modeling

“…By comparison of the coalescence rates of all foam stability experiments, the exponent n was the minimum for the cases of the dispersion of 250 and 500 ppm of FAU nanoparticles and CTAB at a concentration of 750 ppm, which was 0.23 for both systems. Hence, this supports our surface tension and dilational viscoelastic modulus results that the addition of FAU nanoparticles enhances the stabilization of CO 2 /liquid films by maximizing the adsorption of the surfactant on the CO 2 /liquid films at concentrations near the CMC from part 1 of the study . Although increasing the surfactant concentration above the CMC and the addition of nanoparticles significantly decreased the ripening function A of the CO 2 foams shown in Figure b compared to foams generated at surfactant concentrations below the CMC, the coarsening rates were significantly high, as indicated from the n exponents ( n > 0.27) of A .…”

“…and stable CO 2 foam bubbles. Furthermore, these results matched the surface tension and dilational viscoelastic modulus results presented in part 1 of the study . Although the bubble size distribution of the grafted system presented in Figure a became broader as a result of bubble coalescence and coarsening destabilization mechanisms at a drainage time in the range of 0–180 s, the foam generated using the physically mixed system of CTAB and FAU nanoparticles at concentrations of 100 and 500 ppm (Figure b), respectively, collapsed after 110 s. Panels c and d of Figure show the obtained bubble size distribution generated using two foam systems of CTAB concentrations above the CMC.…”

“…Afterward, the average diameters of the bubbles were calculated from both approaches. Further information about this method is included in the Supporting Information of part 1 of the study …”

“…As will be shown in the Results and Discussion section, the log-normal distribution can be used for fitting the diameters of the experimentally discrete bubbles for all foams generated using various foaming agent systems. Figure summarizes the experimental method used for CO 2 foam generation and the fitting of foam bubble sizes into continuous probability distributions that was covered in part 1 of the study …”

“…Part 1 of the current study aimed to examine the impact of faujasite (FAU)-based zeolite nanoparticles grafted with CTAB cationic surfactant on the foamability and stability of CO 2 foam, at concentrations both below and above the critical micelle concentration (CMC). The results of part 1 indicated that CTAB-grafted FAU nanoparticles could stabilize the liquid films of CO 2 foam at low surfactant concentrations (<CMC) through monolayer surfactant adsorption on the surface of nanoparticles, which helped to optimize the viscoelastic and surface tension properties of CO 2 foam.…”