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.     

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.     

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.     

Preparation of CO2 responsive wormlike micelles and the effect of hydrogen bond on the strength of the network

We first prepared two types of CO₂-responsive wormlike micelles based on N-butyldiethanolamine–sodium oleate (BDEA–NaOA) and N,N-diethyl butylamine–sodium oleate (DEBA–NaOA), respectively. And then, we compared the two different systems to investigate the effect of hydrogen bond on the properties of wormlike systems. The results of the pH and conductivity variation show that tertiary amine groups on BDEA and DEBA were ionized to quaternary ammonium salts after bubbling of CO₂ into the systems, which work with OA^? to form wormlike micelles based on electrostatic interaction. The results of rheological measurements exhibit that the viscosity and viscoelastic of the BDEA–NaOA were obviously superior to DEBA–NaOA. The dramatically difference of the two kind of wormlike micelles was due to the strong intermolecular hydrogen bond between the BDEA and NaOA. This indicates that the hydrogen bond could show great effect on the properties of the wormlike micelles. Finally, a reasonable mechanism was proposed based on the molecular structure, micelles assembly, and the intermolecular interactions.     

Nanofiltration membrane behavior in a supercritical medium

The permeability values of “TN” organomineral nanofiltration membranes to water, L, and to supercritical CO₂, G, were compared. The resulting values for G were an order of magnitude higher than for L. The difference may be directly related to the viscosity difference between the two fluids. Temperature- and pressure-related variations in G were also analyzed; for this purpose, Poiseuille's model satisfactorily accounts for experimental behavior, while Knudsen's model is unsuitable. A hysteresis effect was observed on the isotherms corresponding to variations in G versus pressure, suggesting partially irreversible CO₂ adsorption on the micropore walls, that would diminish the radius. This phenomenon could be enhanced by an increased fluid density and viscosity.     

Soybean-Oil-Based CO2-Switchable Surfactants with Multiple Heads

Oligomeric surfactants display the novel properties of low surface activity, low critical micellar concentration and enhanced viscosity, but no CO₂ switchable oligomeric surfactants have been developed so far. The introduction of CO₂ can convert tertiary amine reversibly to quaternary ammonium salt, which causes switchable surface activity. In this study, epoxidized soybean oil was selected as a raw material to synthesize a CO₂-responsive oligomeric surfactant. After addition and removal of CO₂, the conductivity analyzing proves that the oligomeric surfactant had a good response to CO₂ stimulation. The viscosity of the oligomeric surfactant solution increased obviously after sparging CO₂, but returned to its initial low viscosity in the absence of CO₂. This work is expected to open a new window for the study of bio-based CO₂-stimulated oligomeric surfactants.     

CO2-Switchable Nanoemulsion Based on N,N-dimethyl Oleoaminde-Propylamine (DOAPA) and Sodium Dodecyl Sulphate (SDS)

This research reported a CO₂-switchable nanoemulsion that was formulated by dilution of water in oil microemulsion, which was formed by mixture of N,N-dimethyl oleoaminde-propylamine (DOAPA), sodium dodecyl sulphate (SDS), n-hexane, n-butanol, and water. A reversible switch process was observed between a monophasic nanoemulsion and complete phase separation at R = 1:1 with the CO₂ and N₂ bubbling alternately. The phase separation was not found, but the reversible switch between single phase nanoemulsion was detected by zeta potential, electrical conductivity, and dynamic light scattering at R = 1:1.5 and 1.5:1.     

Quaternary ammonium salts as highly efficient and green alkylating agents for <Emphasis Type="Italic">N</Emphasis>-alkylation of azaheterocycles under microwave irradiation

An efficient, simple and green procedure for N-alkylation of azaheterocycles by quaternary ammonium salts in the presence of K₂CO₃ under microwave irradiation is described. Using this method, N-alkyl derivatives of azaheterocycles are obtained in good to excellent yields and short reaction times.     

Thermal sensitivity of poly(N-vinylpyrrolidone) solutions in water-saline media

The effect of salts on the behavior of aqueous solutions of poly(N-vinylpyrrolidone), which is known to show no thermal sensitivity in the absence of additives, has been studied. The introduction of some salts, for example, KF, KH₂PO₄, K₂CO₃, and Na₂SO₄, leads to the occurrence of phase transitions. The corresponding phase transition temperatures depend on the nature and concentration of salts. Even moderate concentrations (0.3–0.6 mol/l) of the most active salts (K₂CO₃ and Na₂SO₄) are shown to reduce the phase transition temperature to 10–20°C.     

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.     

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.     

Preparation and drug release property of CO2 stimulus-sensitive poly(N, N-dimethylaminoethyl methacrylate)-b-polystyrene nanoparticles

The CO₂ stimulus-sensitive nanoparticles based on poly(N, N-dimethylaminoethyl methacrylate)-b-poly styrene (PDMAEMA-b-PS) were prepared via surfactant-free miniemulsion reversible addition–fragmentation chain transfer (RAFT) polymerization. The as-prepared nanoparticles exhibited core–shell structure with about 120 nm in diameter. Their dispersion/aggregation in water can be adjusted by alternatively bubbling of CO₂ and N₂. Drug release from these nanoparticles can be accelerated (or delayed) by bubbling (or removing) of CO₂.     

Phthalocyanines and Related Compounds: XL. Synthesis of β-Diethylaminoethyl-substituted Octa-4,5-carboxyphthalocyanine Tetraimides and Their Quaternary Salts

Cobalt, zinc, hydroxoaluminum, and iron complexes of N,N′,N″,N?-tetrakis(β-diethylaminoethyl) phthalocyanine-2,3 : 9,10 : 16,17 : 23,24-tetrakis(dicarboxamide) were synthesized and were converted into the corresponding water-soluble quaternary salts by treatment with methyl iodide, methyl p-toluenesulfonate, diethyl and dimethyl sulfates, and trimethyl phosphate. The electronic absorption spectra of the quaternary salts indicated their considerable aggregation in aqueous solution; the degree of aggregation decreases in going to solutions in ethanol and disappears in DMSO.     

Synthesis of quaternary allylammonium salts via ring opening of 1-benzyl-2-(bromomethyl)aziridines

Treatment of 1-benzyl-2-(bromomethyl)aziridine, and some aryl substituted analogues, with an excess of iodomethane resulted in N-allyl-N-benzyl-N,N-dimethylammonium salts, in good yields. These quaternary allylammonium salts are of importance in different fields, from organic synthesis and polymeric chemistry to agricultural use.     

Synthesis, structure and electrochemical properties of N-substituted diiron azadithiolates as active site models of Fe-only hydrogenases

As biomimetic models for the active site of Fe-only hydrogenases,six new N-substituted diiron azadithiolates (ADT) were prepared.Treatment of CH₂Cl₂ solutions of primary amines RNH₂ with paraformaldehyde followed by an excess of SOCl₂ gave N,N-bis(chloromethyl)amines RN(CH₂Cl)₂ (1,R = CH₂CO₂Et;2,C₆H₄C(O)Me-p;3,C₆H₄CO₂Me-p;4,C₆H₄SCN-p) in 30-90% yields.Further treatment of the chloromethylated amines 1-4 with (μ-LiS)₂Fe₂(CO)₆ in THF resulted in formation of the corresponding N-substituted ADT-type models [(μ-SCH₂)₂NR]Fe₂(CO)₆ (5,R = CH₂CO₂Et;6,C₆H₄C(O)Me-p;7,C₆H₄CO₂Me-p;8,C₆H₄SCN-p) in 24-75% yields.Also prepared were the N-substituted models [(μ-SCH₂)₂NC(O)CH₂C₁₀H₇-α]Fe₂(CO)₆ (9) and 1,4-[Fe₂(CO)₆(μ- SCH₂)₂NC(O)]₂C₆H₄ (10) by reaction of CH₂Cl₂ solutions of [(μ-SCH₂)₂NH]Fe₂(CO)₆ with α-C₁₀H₇CH₂COCl and 1,4-C₆H₄(COCl)₂ in 81% and 28% yields, respectively. All the new compounds 1-10 were characterized by elemental analysis and spectroscopy, as well as for 5-7 and 9 by X-ray crystallography. The crystallographic studies indicated that the functionality of 5 attached to the bridged N atom lies in an equatorial position, whereas those of functionalities of 6, 7, and 9 are located in an axial position. This is presumably due to different electronic and steric effects between the N-substituted aliphatic and aromatic functionalities. More interestingly, model 7 has been found to be a catalyst for proton reduction in the presence of either strong acid CF₃CO₂H or weak acid HOAc under electrochemical conditions. In addition, two mechanisms ECCE and EECC are preliminarily suggested for such two electrocatalytic H₂ production processes, respectively.     

Synthesis of Some Selectively N-Protected (1S,2S)-p-Nitrophenylserinol–Based Diamino-1,3-dioxanes and Tripodands

The unconventional methodology for the non-epimerizable cycloacetalization of optically active (1S,2S)-2-amino-1-(4-nitrophenyl)propane-1,3-diol (p-nitrophenylserinol) (condensed H₂SO₄ 96% as solvent and catalyst, i.e., sulfuric transacetalization) producing (2R,4S,5S) diamino-1,3-dioxanes was enlarged by the use of N-protected forms of 2,2-dimethoxyethylamine (DMEA, aminoacetaldehyde dimethylacetal). Conversely, N-protected derivatives of p-nitrophenylserinol were successfully cyclocondensed with DMEA in the same sulfuric conditions. N-Functionalization of DMEA upon treatment with trimesic acid trichloride and cyanuric chloride yielded the corresponding triple amide and melamine, respectively. Their adapted sulfuric transacetalization in triplicate in reaction with arylserinols (aryl: phenyl, p-nitrophenyl) afforded a new series of optically active tripodands.     

Quaternary ammonium salt-catalyzed carboxylative cyclization of propargylic amines with CO2

By employing quaternary ammonium salts as catalysts, the carboxylative cyclization of the propargylic amines with CO₂ proceeded to afford the corresponding 2-oxazolidinones. In particular, tetra-n-butylammonium fluoride was the most effective catalyst for the reaction, providing a 2-oxazolidinone derivative in a maximum chemical yield of 99%. From a screening of the structure of a catalyst, it was found that both a quaternary ammonium cation and a basicity of the counter anion were essential to catalyze the carboxylative cyclization of the propargylic amines with CO₂.     

A simple access to metallic or onium bistrifluoromethanesulfonimide salts

Numerous salts of the (CF₃SO₂)₂N⁻ anion, called TFSI, were prepared according to an original one-pot procedure. First, N-benzyl trifluoromethanesulfonimide (N-benzyl triflimide) was treated with ethanol to form an oxonium intermediate, which was then neutralized by various bases to provide metallic or trialkylammonium triflimides salts. Alternatively, N-benzyl triflimide was directly treated with trialkyl sulfonium, quaternary ammonium or phosphonium halides to deliver the corresponding triflimide derivatives. N-Benzyl triflimide can be also reacted with di- or tri-alkylamines and phosphines to get benzyl onium salts. Analogous reactions can be carried out with N-allyl triflimide. Therefore, the TFSI anion can be very easily and expediently associated with a wide range of metallic or organic cations. Such salts can find applications as electrolytes for batteries and fuel cells, ionic liquids or Lewis acids.     

Formation of different products during photo-catalytic reaction on TiO<Subscript>2</Subscript> suspension in water with and without 2-propanol under diverse ambient conditions

Studies on photo-catalytic reduction of CO₂ using TiO₂ photo-catalyst (0.1%, w/v) as a suspension in water was carried out at 350 nm light. CO₂ from both commercially available source, as well as generated in situ through 2-propanol oxidation, was used for this study. The photolytic products such as hydrogen (H₂), carbon monoxide (CO) andmethane (CH₄) generated were monitored in TiO₂ suspended aqueous solution with and without a hole scavenger, viz., 2-propanol. Similar photolytic experiments were also carried out with varying ambient such as air, O₂, N₂ and N₂O. The yields of CO and CH₄ in all these systems under the present experimental conditions were found to be increasing with light exposure time. H₂ yield in N₂-purged systems containing 2-propanol was found to be more as compared to the without 2-propanol system. The rate of H₂ production in N₂-purged aqueous solutions containing 0.1% TiO₂ suspension were evaluated to be 0.226 and 5.8 μl/h, without and with 0.5 M 2-propanol, respectively. This confirmed that 2-propanol was an efficient hole scavenger and it scavenged photo-generated holes (h⁺), allowing its counter ion, viz., e⁻, to react with water molecule/H⁺ to yield more H₂. The formation of both CO and CH₄ in the photolysis of CO₂-purged aqueous solutions containing suspended TiO₂ in absence of 2-propanol reveal that the generation of CH₄ is taking place mainly through CO intermediate. In presence of air/O₂, the yield of H₂ in the system without 2-propanol was observed to be negligible as compared to the system containing 2-propanol in which low yield of H₂ was obtained with a formation rate of approx. 0.5 μl/h.     

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.