Experimental investigation and modelling of CO2-foam flow in heavy oil systems

In this work, the C_14-16 alpha olefin sulphonate (AOS) surfactant, octylphenol ethoxylate (TX-100), and methyl bis[Ethyl(Tallowate)]-2-hydroxyethyl ammonium methyl sulphate (VT-90) surfactant were selected as representatives of anionic, nonionic, and cationic surfactant to stabilize foam. The effects of surfactant concentration and gas/liquid injection rates on foam performance were examined by performing a series of oil-free foam flow tests by injecting CO₂ and a foaming surfactant simultaneously into sandpacks. Foam flooding was conducted as a tertiary enhanced oil recovery (EOR) method after conventional water flooding and surfactant flooding. Furthermore, a new method was proposed to determine the residual oil saturation. The foam stability in the presence and absence of heavy oil was studied by a comparative evaluation of the mobility reduction factor (F_MR) in both cases. The foam fractional flow modelling by Dholkawala and Sarma^[36] was modified based on experimental results obtained in this study. The range of the ratio of two important model parameters (C_g/C_c) at various foam qualities was determined and could be used for large-scale predictions. The results showed that during the oil-free foam displacement experiments higher foam apparent viscosities () were attained at lower gas flow rates and the maximum was attained at a total gas and liquid injection rate of 0.25 cm³/min with a gas fractional flow ratio of 0.8 for the foam in the absence of oil. The presence of oil reduced the foam mobility reduction factors (F_MR) to different degrees with F_MR-_{without oil} / F_MR-_{with oil} ranging from 4.25–13.69, indicating that the oil had a detrimental effect on the foam texture. The foam flooding successfully produced an additional 8.1–21.52 % of OOIP, which can be attributed to the combined effect of increasing the pressure gradient and oil transporting mechanisms.     

Stabilization of natural gas foams using different surfactants at high pressure and high temperature conditions

Natural gas foam can be used for mobility control and channel blocking during natural gas injection for enhanced oil recovery, in which stable foams need to be used at high reservoir temperature, high pressure and high water salinity conditions in field applications. In this study, the performance of methane (CH₄) foams stabilized by different types of surfactants was tested using a high pressure and high temperature foam meter for surfactant screening and selection, including anionic surfactant (sodium dodecyl sulfate), non-anionic surfactant (alkyl polyglycoside), zwitterionic surfactant (dodecyl dimethyl betaine) and cationic surfactant (dodecyl trimethyl ammonium chloride), and the results show that CH₄-SDS foam has much better performance than that of the other three surfactants. The influences of gas types (CH₄, N₂, and CO₂), surfactant concentration, temperature (up to 110°C), pressure (up to 12.0 MPa), and the presence of polymers as foam stabilizer on foam performance was also evaluated using SDS surfactant. The experimental results show that the stability of CH₄ foam is better than that of CO₂ foam, while N₂ foam is the most stable, and CO₂ foam has the largest foam volume, which can be attributed to the strong interactions between CO₂ molecules with H₂O. The foaming ability and foam stability increase with the increase of the SDS concentration up to 1.0 wt% (0.035 mol/L), but a further increase of the surfactant concentration has a negative effect. The high temperature can greatly reduce the stability of CH₄-SDS foam, while the foaming ability and foam stability can be significantly enhanced at high pressure. The addition of a small amount of polyacrylamide as a foam stabilizer can significantly increase the viscosity of the bulk solution and improve the foam stability, and the higher the molecular weight of the polymer, the higher viscosity of the foam liquid film, the better foam performance.     

Influence of Hydrocarbon Chain Branching on Foam Properties of Olefin Sulfonate with FoamScan

The influence of surfactant structure on foam properties of internal olefin sulfonate (IOS) and alpha olefin sulfonate (AOS) in aqueous solutions was estimated from measurements of the foamability, foam stability, and foam morphology, as obtained from conductivity and image analyses techniques. It was found that the foamability and foam stability of C_16–18 AOS are higher compared to that of C_16–18 IOS, indicating that hydrocarbon chain branching decreases the foamability and foam stability. The foamability and foam stability are enhanced with increasing surfactant concentration, which increases the adsorbed quantity of surfactant molecules at the air–water interface. The influence of hydrocarbon chain branching on foam morphology was also investigated. It was found that foam cells produced by branched chain C_16–18 IOS are larger than the foam cells generated by straight chain C_16–18 AOS.     

Effects of Inorganic Salts and Polymers on the Foam Performance of 1-Tetradecyl-3-methylimidazolium Bromide Aqueous Solution

The foaming performance of 1-tetradecyl-3-methylimidazolium bromide (C₁₄mimBr) aqueous solution, in the presence of polymers (PEG or PVA) or inorganic salts (NaBr, MgCl₂, NaNO₃, Na₂SO₄ or Na₃PO₄), was investigated at 25.0?°C by using the self-made apparatus and the conductivity method. The experimental results show that the foaming ability and foam stability of the ternary aqueous systems of C₁₄mimBr coexisting with PEG or PVA are stronger than those of the C₁₄mimBr solutions in the absence of a polymer, and both the efficiency of foaming ability and foam stability of the surfactant solutions are evidently enhanced with an increase in polymer concentration. However, the addition of inorganic salts can decrease the foaming ability and foam stability of C₁₄mimBr solution. Especially, the inorganic salts, with high valence state of the anion (SO₄ ^2? and PO₄ ^3?), are good antifoam agents which can remove and inhibit foam quickly. For the aqueous solution of the surfactant, the effect of temperature on foaming properties was also examined. The results show that both the foaming ability and stability of the foams of the surfactant solutions decrease with an increase in the temperature within the range from 25.0 to 45.0?°C.     

Pressure drop in cocurrent upflows

Experimental results were obtained for a water-air cocurrent upflow in a tube (d = 28 mm, l = 2.85 m) in the disperse film regime (q = 0.88–8.18 cm²/s) within a range of gas velocities of 10–36.3 m/s. The functions w ₀ = f(q) and φ₀ = f(q) were shown to have a kink at q = 0.88 cm²/s, which indicates the transition from the film regime to the disperse film regime. An algorithm was proposed for calculating the pressure drop in the disperse film regime with allowance for the extremal character of the function ΔP = f(w).     

Continuous Foam Fractionation of Phosphate by a Cationic Surfactant

Abstract

Continuous foam fractionation experiments in one equilibrium stage were performed using ethylhexadecyldimethylammonium bromide and potassium dihydrogen phosphate. The pH of the solution was maintained at 5.4 at which only H₂PO₄- was present. The effects of surfactant and phosphate concentrations and liquid and gas flow rates on the percent stripping of phosphate and the distribution factor of phosphate were studied. Equilibria between surface and bulk liquid phases were found to be adequate to explain the inverse relationship between the distribution factor of phosphate and the phosphate and surfactant concentrations.

For optimum separation of phosphate, defined as percent stripping, [100(c_f — cw)/cf], low liquid and high gas flow rates must be used with dilute solutions of both surfactant and phosphate. Further, multiple equilibrium stages should be employed.     

Gemini Surfactants Foam Formation Ability and Foam Stability Depends on Spacer Length

A series of cationic gemini surfactants containing different spacer length were synthesized and analyzed structurally. It was shown that the surface tension (σ) and critical micelle concentration (CMC), which had a maximum for the n-C₄H₈ spacer depended on the spacer length. The foaming ability and foam stability are high for the gemini surfactants with short spacers (C₂H₄ to n-C₄H₈), while longer spacers lead to a distinct decrease of these foam parameters. Foaming properties are discussed in terms of configuration and conformation of a surfactant molecule and in relation to micellization state kinetic.     

Foaming and defoaming properties of CO2-switchable surfactants

The present study is about the foaming and defoaming properties of the CO₂-switchable surfactant N,N-dimethyltetradecylamine (C₁₄DMA) and its advantages compared with the non-switchable counterpart tetradecyltrimethylammonium bromide (C₁₄TAB). In the absence of CO₂, C₁₄DMA is a water insoluble organic molecule without any surface activity thus being unable to stabilize foams. In the presence of CO₂, the head group becomes protonated which transforms the water insoluble molecule into a cationic surfactant. Comparing the surface properties and foamability of C₁₄DMA and C₁₄TAB one finds a very similar behavior. However, the foam stabilities differ depending on the gas. Foaming the two-surfactant solutions with CO₂ leads to very unstable foams in both cases. However, foaming the two surfactant solutions with N₂ reveals the switchability of C₁₄DMA: while the volume of foams stabilized with C₁₄TAB hardly changes over 1600 s, the volume of foams stabilized with C₁₄DMA decreases significantly in the same period of time. This difference is due to the fact that the surface activity, that is, the amphiphilic nature, of C₁₄DMA is continuously switching off since CO₂ is displaced by N₂ thus deprotonating and deactivating the surfactant.     

Lauryl alcohol and amine oxide as foam stabilizers in the presence of hardness and oily soil

The effects of two potential foam boosters, n-dodecanol (or lauryl alcohol: LA) and tetradecyldimethylamine oxide (C₁₄DMAO), were investigated for two situations in which foam made from a 0.01 wt% solution of a common alkylethoxy sulfate surfactant was highly unstable in the presence of oil drops consisting of an n-hexadecane/oleic acid mixture. In one case in which dissolved CaCl₂ was present at alkaline pH, insoluble calcium oleate particles formed in situ and facilitated foam breakage. In the other, a much higher concentration of calcium was present at neutral pH, and drops of a microemulsion phase formed but no calcium oleate. In both cases, 0.005 wt% LA reduced the entry coefficient, E, of the oil to the air-water surface sufficiently to prevent drop entry and stabilized the foam. In contrast, 0.005 wt% C₁₄DMAO caused smaller reductions in E and was ineffective as a foam booster. LA was more effective because it was able to form a more compact monolayer with the surfactant than C₁₄DMAO at the air-water surface, which led to lower surface tensions and hence lower values of E.     

Synthesis of few-layered Ti3C2Tx/ WO3 nanorods foam composite material for NO2 gas sensing at low temperature

The few-layered Ti₃C₂T_x/WO₃ nanorods foam composite material was synthesized by electrostatic self-assembly and bidirectional freeze-drying technologies. The phase structure and microstructure of synthesized samples was characterized by XRD, FESEM, TEM and their gas sensing properties estimated via a self-designed equipment with four test channels. The results demonstrate WO₃ nanorods were successfully anchored on the surface and between layers of few-layered Ti₃C₂T_x MXene by electrostatic self-assembly strategy and the composite material simultaneously has a low-density foam morphology by means of bidirectional freeze-drying processes. There exists a typical heterostructure at the interfaces owing to the inseparable contact between the few-layered Ti₃C₂T_x MXene and WO₃ nanorods. Compared with the original WO₃ nanorods, the few-layered Ti₃C₂T_x/WO₃ nanorods foam composite material displays excellent gas sensing properties for NO₂ detection at low temperature, in particular the optimal value of gas sensing response (R_g/R_a) reaches to 89.46 toward 20 ppm NO₂ at 200 °C. The gas sensing mechanism was also discussed. The increase of gas sensitivity is attributed to a fact that during the reaction process of gas sensing, the excellent conductivity of the few-layered Ti₃C₂T_x MXene provided faster transport channels of free carriers, and the heterojunctions formed by few-layered Ti₃C₂T_x MXene and WO₃ nanorods enhanced the carriers separation efficiency. Meanwhile, the low-density layered structure of few-layered Ti₃C₂T_x/WO₃ nanorods foam composite material provides convenient diffusion paths for gas molecules to the surface of WO₃ nanorods.     

Mixed Micellization Study of Alkyltrimethylammonium and Alkyltriphenylphosphonium Bromides in Aqueous Solution

Mixed micellization study of cationic surfactants viz. alkyltrimethylammonium bromides (C_nTAB) and alkyltriphenylphosphonium bromides (C_nTPPB) with similar hydrophobic groups (C₁₂-, C₁₄-, and C₁₆-) was performed using tensiometry and UV–visible light spectrophotometry techniques. Critical micelle concentration (CMC) values of the single and binary surfactant mixtures were obtained from a plot of surface tension versus the logarithm of surfactant concentration (C _s). The degree of synergy and various mixed micelle parameters like interaction parameter (β), activity coefficients (f ^m ) and interfacial parameters like surface pressure (π _CMC), packing parameter (P), surface excess concentration (Г _max), surface tension at the CMC (γ _CMC), and minimum area per molecule (A _min) were evaluated using the regular solution theory (RST). Thermodynamic parameters were calculated using several proposed models which suggest the mixed micellar system to be more thermodynamically stable than their respective individual components. In addition, a dye solubilization study was performed using a spectrophotometric method to validate the CMC data obtained from tensiometric method. Conductometric measurements were also carried out for the mixture of C₁₂TAB + C₁₂TPPB only as it showed a more negative β, indicating a higher degree of synergism.     

Improvement of methane activation using n-hexane as co-reactant over Zn/HZSM-11 zeolite

Significance of effective conversion of methane (C₁) to more valuable compounds such as aromatics is studied using n-hexane (C₆) as co-reactant. AH yield was as high as 30 mol% C using the following reaction conditions: temperature, 500 °C; contact time w/f=30 g h mol⁻¹ and a C₁ molar fraction, X_C1:=(C₁/C₁ + C₆)=0.60, was achieved. The effect of the contact time, molar fraction, and time on stream was analyzed in order to obtain more information about different species evolution. The C₁ conversion reached at 50 mol% C using Zn/HZSM-11 with 2.13 mol Zn per cell unit.     

Determination of mass transfer coefficients for packing materials used in biofilters and biotrickling filters for air pollution control—2: Development of mass transfer coefficients correlations

Correlations that allow determination of gas film mass transfer coefficients (k_Ga_t, k_Ga_w) and liquid film mass transfer coefficients (k_La_w) for packing materials used in biofilters and biotrickling filters for air pollution control are presented. Lava rock, polyurethane foam cubes (PUF), Pall rings, porous ceramic beads, porous ceramic Raschig rings, and various compost-woodchips mixtures were used as packing materials. The functionality of gas and liquid velocity on mass transfer coefficients (k_Ga_t,k_Ga_w,k_La_w) obtained experimentally (see Part 1 of this paper) was correlated using modified Onda-type equations. The correlation equations helped to better understand the sensitivity of gas and liquid velocities on mass transfer, and the effects of packing wetting. Each packing had a different functionality with gas and liquid velocity and different wetting property, hence different correlation equations were needed for the different packing materials. Most of the fitted data fell within ±20% of the experimental values.     

Evaluation of the physical and mechanical properties of high drug load formulations: Wet granulation vs. novel foam granulation

The purpose of this study was to evaluate the influences of intrinsic drug mechanical properties and different granulation binder delivery processes on the physical and mechanical properties of high drug load granulations after wet granulation. Formulations (80% w/w) of acetaminophen (APAP), metformin and aspirin, which are brittle, viscoelastic, and ductile, respectively; were granulated by high-shear wet granulation. Two modes of binder delivery for wet granulation, either conventional or binder foam, were investigated. Particle size, surface area and pore size of the granulations were characterized. Compacts were prepared at a solid fraction of 0.9 under tri-axial decompression and Hiestand indices (worst-case bonding index (BI_w) and brittle fracture index (BFI)) of the compacts were determined. APAP formulations exhibited the smallest geometric mean particle sizes (d_g) and showed only slight differences in d_g values between the two granulation processes. Binder delivery mode affected mechanical properties of the granulated model drugs differently. Foam granulation appeared to enhance the granule plasticity for APAP while aspirin showed a mixed deformation mechanism based on both its high BI_w and high BFI values. The higher BI_w value for aspirin after foam granulation may be attributed to improved binder distribution among particles during granulation. On the other hand, conventional wet granulation improved the plasticity of metformin as measured by the higher BI_w and lower BFI values. Therefore, conventional wet granulation process conferred advantages in manufacturability and product quality for metformin; as compared to foam granulation which did not enhance plasticity for metformin. Based on this study, a wet granulation process can be selected based on knowledge of the intrinsic drug mechanical properties.     

Experimental studies of flame stability and emission characteristics of simple LPG jet diffusion flame

In the present study, experiments were carried out to measure the lift-off height, H_L; flame length, L_f and blow-off velocity for a simple LPG (liquefied petroleum gas) jet diffusion flames. It is observed that lift-off height is proportional to the fuel exit velocity, U_f. A semi-empirical correlation between lift-off height and global strain rate, U_f/D_f is proposed. Two regimes identified either as buoyancy or momentum dominated were characterized by Froude number, Fr. For momentum dominated jet diffusion flames, L_f/D_f remains almost constant and therefore is independent of the Froude number. The NO_x emissions, expressed in terms of emission index, EINO_x is found to decrease with U_f. This decreasing trend is consistent with the concept that increasing jet velocity reduces the residence time as reported in the literature. The present data is also compared with the available data of propane gas and found to be in good agreement well particularly in trend wise. Besides these data, EINO_x scaling law is also reported in the present study.     

New method for the determination of surfactant solubility and partitioning between CO2 and brine

A novel method is presented for measuring solubility in supercritical CO₂ (scCO₂), which can be used in conjunction with traditional cloud point measurements to obtain information directly on the soluble portion of a given sample and, ultimately, a much more informative data set. In this method, surfactant from a known amount of CO₂ solution was transferred into an aqueous solution and the surfactant concentration of the aqueous solution was measured directly by HPLC (high-performance liquid chromatography). In this work, the partitioning of a series of 2-ethylhexanol (2-EH) alkoxylate surfactants among an aqueous phase (water or brine) and scCO₂ as a function of electrolyte concentration, temperature, and pressure was also investigated. Surfactant partition coefficient was determined based on the reduction of HPLC measured surfactant concentration in the aqueous phase due to surfactant partitioning into CO₂. An understanding of surfactant partitioning between brine and scCO₂ is particularly important in the design of CO₂ foam processes, particularly for surfactant stabilized foam in subsurface systems, where it can affect surfactant transport and foam propagation. In general, the solubility in scCO₂ increased with pressure and decreased with temperature. The partitioning of the surfactants between CO₂ and water phases was almost proportional to pressure, and decreased as temperature increased, where the latter held more sensitivity. The partition coefficient was very sensitive to surfactant formula. For the 2-EH-PO5-EO_x series, the partition coefficient between scCO₂ and the aqueous phase increased with decreasing EO content.     

Characterization of foam flow in horizontal pipes by using two-flow-regime concept

Foam has been widely used in numerous scientific and engineering applications. Although foam has relatively low fluid density because of high gas content, it can exhibit a viscosity value enormously higher – often several orders of magnitude higher – than that of bulk gas or liquid phase. Since foam typically exists as a complex fluid system with internal gas bubbles and external liquid phase, understanding and characterizing its flow behavior is very challenging.The objective of this study is to investigate the characteristics of foam rheology in horizontal pipes in a wide range of experimental conditions—two different pipe materials (stainless steel and nylon pipes with about 0.5 in in outer diameter and 12 ft in length), three surfactant formulations (Cedepal FA-406, Stepanform-1050, and Aquet-944), and three surfactant concentrations (0.1, 0.5, and 5 wt%). The experimental data can be collected in terms of (i) pressure measurements at several positions along the pipes and (ii) visual analysis of bubble size and bubble-size distribution during the shear flow. The concept of “two foam-flow regimes” consisting of high-quality regime and low-quality regime is at the heart of interpreting the experimental outcome.The experimental results showed that there were two distinct high-quality and low-quality foam flow regimes which could be identified by both pressure responses and direct visual observations. The results further showed that the high-quality regime was characterized by unstable and oscillating pressure responses represented by the repetition of fine-textured foam and free gas (i.e., slug flow), while the low-quality regime was characterized by stable pressure responses represented by either the flow of fine-textured foams (i.e., plug flow) or the flow of upper-layer foams and lower-layer liquid (i.e., segregated flow). These two regimes, separated by a locus of f_g^? in the contour plot, were shown to have different sensitivities to the change in gas and liquid velocities: (1) foam rheology in the high-quality regime was dependent upon both gas and liquid velocities because the lengths of fine-textured-foam and free-gas sections were altered to adjust to the new flow conditions, and (2) foam rheology in the low-quality regime was primarily dependent upon gas velocity because of the development of fine-textured foams with increase in shear rates, and was relatively independent of liquid velocity because of lubricating effect and drainage effect.The implication of these experimental findings is discussed for applications such as foam-assisted underbalanced drilling processes and foam fracturing treatments in the petroleum industry.     

Surfactant properties of purified polyglycerol monolaurates

A series of purified polyglycerol monolaurates (PGML), such as di-, tri-, tetra-, and pentaglycerol monolaurates, were synthesized, and their surfactant properties in aqueous solutions were examined. The surfactant properties of PGML were compared with those of n-dodecyl polyoxyethylene monoethers (C₁₂EO_n) to examine the function of the hydrophilic part of these compounds. The critical micelle concentration (CMC) values and the surface tension at CMC of PGML and C₁₂EO_n increased linearly with an increase in the number of glycerol and oxyethylene units, respectively; the slope of the increase was greater for PGML than C₁₂EO_n. The minimum surface area per molecule of PGML was smaller than that of C₁₂EO_n at the air/aqueous solution interface. The initial foam heights of the surfactants at the CMC increased with an increase in the number of glycerol or oxyethylene units, and the foam heights of PGML were consistently higher and more stable than those of C₁₂EO_n. Detergency depended on a reduction in interfacial tension. Triglycerol monolaurate showed the lowest interfacial tension and the highest detergency among all the surfactants tested. Overall, the PGML showed better performance in all the surfactant properties tested than C₁₂EO_n. It is noteworthy that the surfactant properties of PGML having few glycerol units (di- to tetraglycerol monolaurates) are on par with those of C₁₂EO_n having many oxyethylene units (hexa- and octaoxyethylene). These results suggest that PGML having a secondary hydroxyl group on every glycerol unit of the hydrophilic part could be more hydrophilic than C₁₂EO_n; this characteristic feature guaranteed the superior surfactant properties of PGML.     

A novel strategy for realising environmentally friendly pigment foam dyeing using polyoxyethylene ether surfactant C14EO5 as a foam controller

Development of an environmentally friendly pigment dyeing process with excellent colour depth and levelness is an effective strategy for solving pollution problems in traditional dyeing. A functional polyoxyethylene ether nonionic surfactant, tetradecyl alcohol polyoxyethylene ether with an EO chain length of 5 (C₁₄EO₅), was used as a foam controller, namely a foaming agent and foam stabiliser, in the pigment foam dyeing process. The foamability and the foam stability of C₁₄EO₅ were tunable by adjusting its concentration. The foaming ratio and the foam half-life of C₁₄EO₅ were 5.22 and 32.21 min, respectively, at a concentration of 8 wt%. The addition of pigment dispersion (ranging from 1 to 6 wt%) slightly affected the foaming ratio and the foam half-life owing to the interplay of increased viscosity and pigment particle destabilisation. After the influences of binder on foam properties of C₁₄EO₅ were investigated, the concentration of binder and the stirring time for foaming were determined as 15 wt% and 7 min respectively. Owing to the stable foaming ratio and foam half-life of the pigment foam dyeing dispersion, the colour depth of dyed cotton fabric was tailored solely by changing the dosage of pigment dispersion. Furthermore, the dyed cotton fabric showed not only a high K/S value but also perfect colour levelness and fastness. These results demonstrate that the pigment foam dyeing process with a foam controller, C₁₄EO₅, reduces chemical and water consumptions, as well as improving the colour depth and levelness. This represents a significant step forward as regards environmentally friendly pigment dyeing.