Application of CO2-Switchable Oleic-Acid-Based Surfactant for Reducing Viscosity of Heavy Oil

CO₂-switchable oligomeric surfactants have good viscosity-reducing properties; however, the complex synthesis of surfactants limits their application. In this study, a CO₂-switchable “pseudo”-tetrameric surfactant oleic acid (OA)/cyclic polyamine (cyclen) was prepared by simple mixing and subsequently used to reduce the viscosity of heavy oil. The surface activity of OA/cyclen was explored by a surface tensiometer and a potential for viscosity reduction was revealed. The CO₂ switchability of OA/cyclen was investigated by alternately introducing CO₂ and N₂, and OA/cyclen was confirmed to exhibit a reversible CO₂-switching performance. The emulsification and viscosity reduction analyses elucidated that a molar ratio of OA/cyclen of 4:1 formed the “pseudo”-tetrameric surfactants, and the emulsions of water and heavy oil with OA/cyclen have good stability and low viscosity and can be destabilized quickly by introducing CO₂. The findings reported in this study reveal that it is feasible to prepare CO₂-switchable pseudo-tetrameric surfactants with viscosity-reducing properties by simple mixing, thus providing a pathway for the emulsification and demulsification of heavy oil by using the CO₂-switchable “pseudo”-oligomeric surfactants.     

A Conventional Surfactant Becomes CO2‐Responsive in the Presence of Switchable Water Additives

We have developed a new benign means of reversibly breaking emulsions and latexes by using “switchable water”, an aqueous solution of switchable ionic strength. The conventional surfactant sodium dodecyl sulfate (SDS) is not normally stimuli‐responsive when CO₂ is used as the stimulus but becomes CO₂‐responsive or “switchable” in the presence of a switchable water additive. In particular, changes in the air/water surface tension and oil/water interfacial tension can be triggered by addition and removal of CO₂. A switchable water additive, N,N‐dimethylethanolamine (DMEA), was found to be an effective and efficient additive for the reversible reduction of interfacial tension and can lower the tension of the dodecane/water interface in the presence of SDS surfactant to ultra‐low values at very low additive concentrations. Switchable water was successfully used to reversibly break an emulsion containing SDS as surfactant, and dodecane as organic liquid. Also, the addition of CO₂ and switchable water can result in aggregation of polystyrene (PS) latexes; the later removal of CO₂ neutralizes the DMEA and decreases the ionic strength allowing for the aggregated PS latex to be redispersed and recovered in its original state.     

CO2/N2-switchable viscoelastic fluids based on a pseudogemini surfactant system

We prepared a CO₂/N₂-switchable pseudogemini surfactant system composed of sodium oleate (NaOA) and N, N, N’, N’-tetramethyl-1, 6-hexanediamine (TMHDA) at a mole ratio of 2:1. The two tertiary amine groups of the TMHDA can be protonated into quaternary ammonium salt when the system was bubbled with CO₂, which can ‘‘bridge’’ two NaOA molecules via electrostatic attraction to form a pseudogemini surfactant. The formed pseudogemini surfactant can further self-assemble to wormlike micelles, causing a sharp increase in viscosity. The viscoelastic property and structure transitions of the pseudogemini surfactant system were investigated before and after bubbling of CO₂. The pseudogemini surfactant system transformed from water-like to gel-like fluid with the bubbling of CO₂, followed by white precipitate. The cryo-transmission electron microscope (cryo-TEM) characterization and rheological measurements exhibited that the sol–gel transition was attributed to a spherical-wormlike micelle transition. Moreover, this transition was switchable at least in three cycles. Finally, a reasonable mechanism of aggregate behavior transition was proposed from the viewpoint of the molecular states, micelle structures, and intermolecular interactions.     

碳氢表面活性剂在超临界CO2中形成微乳液的研究进展

在超临界CO₂中形成微乳液可以克服CO₂对高分子量和亲水性物质溶解能力差的缺点。碳氢表面活性剂成本低,对环境友好,利用碳氢表面活性剂形成超临界CO₂微乳液有利于工业应用,但绝大部分碳氢表面活性剂不能形成微乳液,所以需要对碳氢表面活性剂进行选择和设计。本文介绍了微乳液的形成、表征和评价,从表面活性剂的亲CO₂性能和界面活性两方面,综述了碳氢表面活性剂的设计思想和进展。另外介绍了助表面活性剂对形成超临界CO₂微乳液的作用,并对常规碳氢表面活性剂在助表面活性剂的作用下形成超临界CO₂微乳液的体系进行了综述。最后,介绍了含碳氢表面活性剂的混合表面活性剂在形成超临界CO₂微乳液方面的研究情况。     

Application of CO2-Triggered Switchable Surfactants to Form Emulsion with Xinjiang Heavy Oil

Owing to the high acid number of Xinjiang heavy oil and incomplete demulsification after pipelining, this article discusses the application of CO₂-triggered switchable surfactants to the emulsified transport of several Xinjiang heavy oils in the pipeline. Results show that CO₂-triggered switchable surfactants promote the formation and stabilization of oil-in-water (O/W) emulsion in the absence of CO₂ as a base. The property parameters of heavy oils fundamentally influence the indigenous emulsifying agents. The emulsion is stable when the heavy oil has a high acid number and low asphaltene content, which is also affected by some physical factors.     

CO2 responsive wormlike micelles based on sodium oleate,potassium chloride and N,N-dimethylethanolamine

The anionic surfactant sodium oleate (NaOA) can self-assemble in aqueous solution in the presence of counter-ion inorganic salts to form wormlike micelles (WLMs), which exhibited viscoelastic behavior. In this paper, KCl was used to induce the formation of wormlike micelles with sodium oleate. In this process, we found that the addition of N, N-dimethylethanolamine (DMEA) can destroy the structure of WLMs leading significant decrease of viscosity. However, after introducing CO₂ into the ternary solution (KCl-NaOA-DMEA), the WLMs can be regenerated due to the electrostatic interaction between the protonated DMEA and the anionic surfactants. The addition of sodium hydroxide (NaOH) causes the electrostatic interaction between OA^- and DMEAH⁺ be destroyed, which results in the wormlike micelles becoming spherical micelles of lower viscosity. The transition of WLMs with high viscosity and low viscosity spherical micelles can be repeated several times by using CO₂ and NaOH.     

Tunable Viscoelastic Properties of Sodium Polyacrylate Solution via CO2-Responsive Switchable Water

Upon stimulus by CO₂, CO₂-switchable viscoelastic fluids experience a deliberate transition between non-viscous and highly viscous solution states. Despite attracting considerable recent attention, most such fluids have not been applied at a large- scale due to their high costs and/or complex synthesis processes. Here, we report the development of CO₂-switchable viscoelastic fluids using commercially available sodium polyacrylate (NaPAA) and N,N-dimethyl ethanol amine (DMEA)-based switchable water. Upon bubbling CO₂, into the solutions under study, DMEA molecules are protonated to generate quaternary ammonium salts, resulting in pronounced decreases in solutions viscosity and elasticity due to the influence of increased ionic strength on NaPAA molecular conformations. Upon removal of CO₂ via introduction of N₂, quaternary salts are deprotonated to tertiary amines, allowing recovery of fluid viscosity and elasticity to near the initial state. This work provides a simple approach to fabricating CO₂-switchable viscoelastic fluids, widening the potential use of CO₂ in stimuli-responsive applications.     

The CO2 stimulus-responsive spherical-worm-like micelles transition based on anionic surfactant sodium oleate and N,N, N′, N′, N″-pentamethyldipropylenetriamine

Here, we report a CO₂ stimulus-responsive system with anionic surfactant sodium oleate (NaOA) and N, N, N′, N′, N″-Pentamethyldipropylenetriamine (PMDPTA). The microstructure transition from spherical micelles to worm-like micelles was confirmed by rheology measurements, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (Cyro-TEM). There were three types of CO_2?responsive groups in PMDPTA. However, because of PMDPTA ionization degrees, just one responsive group of PMDPTA could be ionized by CO₂ to work with OA^?, resulting in structure transformation from spherical micelles to worm-like micelles. Besides, this system could be switchable between low-viscosity fluid and high viscoelastic by CO₂/N₂.     

Synthesis and properties of double-chain single-head acetamidinium bicarbonate switchable surfactants

A series of switchable surfactants with double hydrophobic chains and a single hydrophilic head N,N’-dialkylacetamidinium bicarbonate with an alkyl length between diC8 and diC12 were synthesized by using new approaches. The structures of acetamidinium bicarbonate were characterized by ^1?H NMR and ESI-MS spectroscopy. The surface activity in aqueous solution of N,N’-dialkylacetamidinium bicarbonate and N’-alkyl-N,N-dimethylacetamidinium were compared by surface tension methods. Some surface activity parameters were studied, such as cmc, γ_cmc, pC₂₀, cmc/C₂₀, Γ_max, and A_min. The results indicated that double-chain surfactant was superior to single-chain surfactant and showed more excellent surface activity. The switchability was confirmed by monitoring the conductivity of a solution of amidine in ethanol and their effect in emulsion stability was also investigated.     

Interfacial tension between water and high pressure CO2 in the presence of hydrocarbon surfactants

Interfacial tension of water–CO₂ interface was measured by pendant drop method in the presence of a surfactant of various concentrations. The surfactants used were three surfynols which are non-ionic blanched hydrocarbon with different length of the alkyl side chain. Prior to the interfacial tension measurements, the solubility of the surfynols in CO₂ were determined from cloud point method. The measured interfacial tensions indicated that an addition of small amount surfactant did reduce the interfacial tension. The interfacial activities of surfactants were evaluated from the slope of the interfacial tension reduction curve against the surfactant concentration and rationalized in terms of the molecular natures such as hydrophobic alkyl chain length.     

Selective and Efficient CO2 Electroreduction to Formate on Copper Electrodes Modified by Cationic Gemini Surfactants

Electroreduction of CO₂ into valuable chemicals and fuels is a promising strategy to mitigate energy and environmental problems. However, it usually suffers from unsatisfactory selectivity for a single product and inadequate electrochemical stability. Herein, we report the first work to use cationic Gemini surfactants as modifiers to boost CO₂ electroreduction to formate. The selectivity, activity and stability of the catalysts can be all significantly enhanced by Gemini surfactant modification. The Faradaic efficiency (FE) of formate could reach up to 96 %, and the energy efficiency (EE) could achieve 71 % over the Gemini surfactants modified Cu electrode. In addition, the Gemini surfactants modified commercial Bi₂O₃ nanosheets also showed an excellent catalytic performance, and the FE of formate reached 91 % with a current density of 510 mA cm⁻² using the flow cell. Detailed studies demonstrated that the double quaternary ammonium cations and alkyl chains of the Gemini surfactants played a crucial role in boosting electroreduction CO₂, which can not only stabilize the key intermediate HCOO* but also provide an easy access for CO₂. These observations could shine light on the rational design of organic modifiers for promoted CO₂ electroreduction.     

Switchable Spherical-Wormlike Micelle Transition in Sodium Oleate/N-(3-(Dimethylamino)propyl)-Octanamide Aqueous System Induced by Carbon Dioxide Stimuli and pH Regulation

The structure transitions of the aggregates in the sodium oleate (NaOA)/N-(3-(dimethylamino)propyl)-octanamide (DPOA) aqueous system was investigated upon CO₂ stimuli. During the process of bubbling of CO₂, three appearance states of sol, gel, and emulsion with little white precipitate were observed continuously. The cryo-transmission electron microscope characterization and rheological measurements exhibited that the sol–gel transition was attributed to a spherical-wormlike micelle transition. Moreover, this transition was switchable at least three cycles in the pH range of 10.91–9.56 by CO₂ stimuli and pH regulation (adding NaOH), which could be explained by the protonation of DPOA and deprotonation of DPOA · H⁺. Bubbling of CO₂ resulted in protonation of DPOA, which not only inserted into the OA^– as a co-surfactant but also screened the electrostatic repulsion among OA^–, corporately leading to the spherical-wormlike micelle transition. Adding NaOH caused the deprotonation of DPOA · H⁺ and hence reversed this transition. This surfactant system with switchable micelle transition not only displays tremendous application potential in various fields but also is of key importance in cyclic utilization of surfactant.     

Thermosensitive amphiphilic polyphosphazenes and their interaction with ionic surfactants

Temperature-responding physical hydrogels are promising materials as injectable drug delivery carriers which could hold useful bioactive materials inside the polymer networks for further controlled releases. Aimed at desired qualities at body temperature, those gel characteristics need to be adjusted carefully. In this point of view, surfactant is one of the useful molecules to be used by simple formulations without harmful chemical reactions. In this study, thermothickening of amphiphilic nonionic polyphosphazene solution is modified by anionic and cationic surfactants with different alkyl chains and counter-ions. Specified in the thermothickening system, a maximum viscosity (η_max) and a temperature at that point (T_max) are changed independently reflecting unique intermolecular interactions. At low concentration (1–9 mM) of the added surfactant, the η_max is maximized at 3 mM surfactant regardless of the surfactant type while the T_max is increased continuously along with the surfactant concentration. From a kinetic point of view, this 3 mM surfactant at the maximized η_max reflects a polymer-dominating interaction and highly favorable polymer–surfactant interaction with a low selectivity in the surfactant type. However, the magnitude of the maximum viscosity (η_max) is dependent on the surfactant tail, which reflects the lifetime and the strength of the hydrophobic domains of the polymer network affected by the surfactants. Meanwhile, the magnitude of the T_max depended on the surfactant head group, which means the interfacial tension of the polymer solutions changed by the surfactants. At high concentration (10 and 30 mM) of the cationic surfactants added to the polymer solutions with two different viscosities, the cationic surfactants are supposed to interact either with the hydrophobic parts of the aggregated polymer with high viscosity or on the backbone of the less- or non-aggregated polymer with low viscosity.Ionic surfactants change the thermothickening of the amphiphilic nonionic polyphosphazene solution in a unique tail- or head-dependent way. Moreover, the concentration of the added surfactants and the association pattern of the pure polymer solutions are also crucial for the thermothickening phase behaviors. Temperature-responsive polyphosphazenes in this work exhibit unique and controllable interactions with ionic surfactants.     

Aggregation behavior of silicone surfactants in ethylammonium nitrate ionic liquid

The aggregation behavior of two silicone surfactants (monomeric and Gemini) was studied by surface tension measurements in a room temperature ionic liquid, ethylammonium nitrate (EAN), at various temperatures. A series of parameters, including critical micelle concentration (CMC), surface tension at the CMC (γ _CMC), adsorption efficiency (pC ₂₀), and effectiveness of surface tension reduction (Π _CMC), were obtained. By comparing the silicone surfactants with traditional surfactants, we deduced that the surface activity of the silicone surfactants in EAN was superior to the activity of other surfactants. In addition, from the CMC values and their temperature dependence, we estimated the thermodynamic parameters of the micelle formation, $ \Delta G_m^0 $ , $ \Delta H_m^0 $ , and $ \Delta S_m^0 $ . It was revealed that the micellization of the silicone surfactants is entropy driven at low temperature and enthalpy driven at high temperature. Isothermal titration calorimetry measurements were also carried out to study the micellization of Gemini silicone surfactant. ¹H NMR was performed to study the silicone surfactant micelle formation mechanism in EAN.     

Foaming Properties of CO2-Triggered Surfactants for Switchable Foam Control

Switchable surfactants, particularly those triggered by CO₂ used for switchable foam control, are relatively less documented. In this article, the foaming performance of 2-alkyl-1-hydroxyethylimidazolinium bicarbonate cationic surfactants (HEAIBs) was investigated for the first time. The foaming properties of these surfactants demonstrate that HEAIBs can generate foam with moderate stability, on demand, can be rapidly yet reversibly dissipated upon exposure to air. The results illustrated such a facile trigger, and the foam on/off transition would have huge potential to form a new class of stimuli-response foaming agents.      

A CO2-Switchable Polymer Surfactant Copolymerized with DMAEMA and AM as a Heavy Oil Emulsifier

A CO₂-switchable polymer surfactant was synthesized with acrylamide (AM) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The changes in conductivity, particle size, and ζ-potential were adopted to illustrate its switchability. The CMC of the surfactant was determined by the break point of the curve of surface tension versus concentration. An oil emulsion with 8 g/L surfactant almost reached the highest stability. The thermodynamic stability of the emulsion decreased sharply upon increase of the temperature. Adding an inorganic salt was hard to affect the emulsion stability because the surfactant is non-ionic. The emulsion could maintain its stability even if the concentration of NaCl was as high as 10 g/L. The emulsion could easily be broken by bubbling CO₂. Its dehydration rate was 155 times faster than that without the presence of CO₂, and the amount of residual oil in water was only 32.22 ppm, which displayed brilliant performance of de-emulsification.     

SYNTHESIS,CHARACTERIZATION, AND SURFACE ACTIVITY OF SURFACTANTS DERIVED FROM NONYLPHENOL,ETHYLENE OXIDE AND CARBON DIOXIDE

The synthesis of the nonylphenol poly(ethylene carbonate) surfactants derived from nonylphenol (NP), carbon dioxide and ethylene oxide (EO) were carried out with high yields in the presence of alkali metal salts (K₂CO₃, Na₂CO₃, K₂SnO₃ and zinc glutamate) as base catalysts. The synthesis reactions were carried out in a stainless-steel reactor in the temperature range of 150-200°C under an initial pressure of 800 psi, with an initial molar ratio of CO2/EO = 0·21, catalyst concentration of 1 × 10³ M for a 24 h-period. The surfactants were characterized by FT-IR and by H-NMR. The percentages of carbon dioxide incorporation were between 7 and 16% indicating that the activation of CO₂ is a rather difficult process under the catalytic conditions used L175-200 °C and 800 psi of final pressure)

It was found that the most probable mechanism for the synthesis of the surfactants occurs in two steps. The first reaction involves the role of the base as a catalyst for the formation of the cyclic ethylene carbonate from CO₂ and ethylene oxide. The next step is the reaction of the nonylphenol in the presence of cyclic ethylene carbonate and ethylene oxide to generate the surface active compounds. This mechanism indicates that for each mol of carbon dioxide incorporated, one mol of EO has to be added.

The CMC values of the surfactants decrease (from 200 to 100 mM) with the increase in the molar ratio CO₂/EO (from 0·08 to 0·3) which can be attributted to a decrease in the hydrophilic character of the surfactant heads due to the addition of carbonate groups(-O-C(=0)-0-) to the ethoxylated chains (between I to 3 moles).     

表面活性剂对水热制备钨酸铋形貌及光催化性能的影响

通过简单水热制备了大小均一,直径约为2.5 μm的球状Bi2WO6粉体.系统研究表面活性剂SDS和PVP对水热制备Bi2WO6光催化剂的影响.利用XRD,EDS,SEM,TEM和DRS等分析技术对催化剂的组成、形貌、比表面积和带隙宽度等进行了表征.实验结果表明,表面活性剂对催化剂的形貌和催化活性有较大影响.在水热制备过...     

Effect of Organic Solvents on the Electrodeposition of Copper from Acidified CuSO4

Using Guerbet tetradecyl alcohol C₁₄GA (synthesized by Guerbet reaction using 1-heptanol as raw material) as intermediate, sodium Guerbet tetradecyl polyoxyethylene ether sulfates [C₁₄GA(EO)_nS, n = 1, 2, 4] were obtained through following steps: synthesizing Guerbet tetradecyl polyoxyethylene ether alcohols [C₁₄GA(EO)_nH, n = 1, 2, 4] by Williamson reaction, then esterifying with chlorosulfonic acid so as to form Guerbet tetradecyl polyoxyethylene ether alcohol sulfates [C₁₄GA(EO)_nSO₃H, n = 1, 2, 4], and finally neutralizing with sodium hydroxide; while sodium Guerbet tetradecyl sulfate(C₁₄GAS) was synthesized only through esterifying and neutralizing reactions. The structures of these anionic surfactants were determined by infrared, nuclear magnetic resonance, and element analysis. The surface activity of these surfactants was studied by means of surface tension. The results have shown that these surfactants possess higher surface activity than the common surfactant C₁₂H₂₅OSO₃Na. Branched-tail structure coming from Guerbet alcohol makes the anionic surfactant (C₁₄GAS) have higher critical micelle concentration (CMC) and better effectiveness in lowering the interface tension between air and water than their linear counterpart (C₁₄H₂₉OSO₃Na). Introducing oxyethyene group into the place between head group and tail group of the surfactant molecule with branched tail can lower the CMC, γ_cmc, and Krafft point. And the effectiveness for reducing the CMC, γ_cmc, Γ_max, and Krafft point of surfactant increased with the increase of oxyethylene group number (n = 1, 2, 4). The relationship between the molecular structure and surface activity of surfactant is discussed.     

Self-Assembled Structures of Diglycerol Monolaurate- and Monomyristate in Olive Oil

We have investigated the phase behavior and self-assembled structures of diglycerol monolaurate-and monomyristate (abbreviated as C₁₂G₂ and C₁₄G₂, respectivley) in olive oil over a wide range of temperatures and compositions. At lower temperatures, both the surfactants appear in solid state (α-solid), which does not swell with olive oil. The α-solid transforms into lamellar liquid crystal (L_α) phase upon heating and the solid melting temperature is practically constant at all surfactant/oil compositions, but the C₁₂G₂ melts earlier than the C₁₄G₂. There appear the dispersions of L_α phase and α-solid in the dilute regions of the C₁₂G₂/olive oil and the C₁₄G₂/olive oil systems, respectively, at 25°C. The L_α phase can solubilize some amount of olive oil, but as the oil concentration increases the excess oil separates out from the L_α phase, and there appears L_α dispersion in the dilute surfactant concentration region. The L_α phase eventually transforms into isotropic solutions (reverse micelles) with further heating. The structures (shape and size) of the reverse micelles have been characterized by small-angle x-ray scattering technique. It has found that the C₁₂G₂ and C₁₄G₂ surfactants form reverse rod-like micelles in olive oil above the L_α melting temperature and the micellar size increases with surfactant concentration, but decreases with temperatures.