Dissolution dynamics of a binary switchable hydrophilicity solvent-polymer drop into an acidic aqueous phase

Switchable hydrophilicity solvents (SHSs) are solvents defined by their ability to switch from their hydrophobic form to a hydrophilic form when brought into contact with an acidic trigger such as CO₂. As a consequence, SHSs qualify as promising alternatives to volatile organic compounds during industrial solvent extraction processes, as greener and inexpensive methods can be applied to separate and recover SHSs. Furthermore, because of their less volatile nature, SHSs are less flammable and so increase the safety of a larger scale extraction process. In this work, we study the dynamics and in-drop phase separation during the dissolution process of a drop composed of a SHS and a polymer, triggered by an acid in the surrounding aqueous environment. From 70 different experimental conditions, we found a scaling relationship between the drop dissolution time and the initial volume with an overall scaling coefficient of ∼0.53. We quantitatively assessed and found a shorter dissolution time related to a decrease in the pH of the aqueous phase or an increase in the initial polymer concentration in the drop. Examining the internal state of the drop during the dissolution revealed an in-drop phase separation behavior, resulting in a porous morphology of the final polymer particle. Our experimental results provide a microscopic view of the SHS dissolution process from droplets, and findings may help design SHS extraction processes for particle formation from emulsions.

Experimental Study on the Optimization of Multi-level Nano-Microsphere Deep Profile Control in the Process of Gas Injection in Fracture-Type Buried-Hill Reservoirs

Fracture-type buried-hill reservoirs refer to dual media which have a fast breakthrough speed and a low sweep efficiency in the process of gas injection displacement. In order to overcome this problem, in this paper, a new profile control and oil displacement technology of pre-slug deep plugging by injection of different levels of nano-microspheres and natural gas was proposed. The mercury intrusion experiments were used to compare the fractal characteristics of the pore structures of the matrix and artificial fractured cores in the buried-hill reservoir. The results show that the heterogeneous characteristics of pores and fractures are the main factors leading to excessive gas breakthrough. Three nano-microsphere systems (WJ1, WJ2, and WJ3) with good temperature resistance, salt resistance, swelling properties, and stability were prepared using the inverse emulsion method. Core plugging performance tests show that WJ3 has the best plugging effect among the three nano-microsphere systems, followed by WJ2 and WJ1. According to the scanning electron microscopy observations, it was found that the sealing mechanism of nano-microspheres includes direct sealing, bridging sealing, adhesive sealing, direct pass, deformed pass, and crushing pass. Finally, the displacement experiments with a composite fractured core showed that compared with pure natural gas injection, the breakthrough time of the combined displacement process of nano-microspheres and natural gas was greatly extended, and the final oil displacement efficiency was increased to greater than 80%.

A New Green In Situ Effervescent CO2-Table-Induced Switchable Hydrophilicity Solvent Extraction Method of Rhodamine B in Food and Soft Drink Samples

BACKGROUND

A new and simple effervescent CO2-table-induced switchable hydrophilicity solvent extraction method (CI-SHS) was used for the preconcentration of rhodamine B (RB).

OBJECTIVE

The main theme of the proposed method to disperse green solvent by in situ CO2-table system overcome on the contamination and to avoid the dispersion by using different chemicals.

METHODS

Switchable hydrophilicity solvent (N, N-Dimethyl cyclohexylamine) was dispersed in an aqueous solution by reaction of CO2-table of sodium carbonate and citric acid to enhance the contact area between two medium, which radically improved the extraction capacity of the RB from aqueous medium to switchable solvent. The phase separation was achieved by simple heating not by centrifugation that makes a change on hydrophilicity to hydrophobicity. The supernatant-enriched RB- N, N-Dimethyl cyclohexylamine phase was withdrawn and injected into the UV glass cells. The absorbance was measured at 542.

RESULTS

Limit of detection and enhancement factor were achieved to be 0.042 and 50 µg/L. Validity and accuracy of the method verified by analysis of real samples by the spiking addition method. The relative standard deviation was obtained at 3.2%. The method was applied to food and soft drink samples.

CONCLUSIONS

This method offers high sensitivity, selectivity, accuracy, and precision for the separation, preconcentration, and spectrophotometric determination of RB. Simple, fast, low-cost, and green extraction method was developed.

HIGHLIGHTS

High enrichment factor and lower detection limits were observed in this microextraction method. Present method is sensitive, selective, very accurate, and precise.

Molecular dynamics simulation of CO2-switchable surfactant regulated reversible emulsification/demulsification processes of a dodecane-saline system

CO2-Switchable surfactants are of great potential in a wide range of industrial applications related to their ability to stabilize and destabilize emulsions upon command. Molecular dynamics simulations have been performed to reveal the fundamental mechanism of the reversible emulsification/demulsification processes of a dodecane-saline system by a CO2-switchable surfactant that switches between active (i.e., N'-dodecyl-N,N-dimethylacetamidinium (DMAAH+)) and inactive (i.e., N'-dodecyl-N,N-dimethylacetamidine (DMAA)) forms. The density profiles indicate that DMAAH+ could increase the oil-water interfacial thickness to a greater extent compared to DMAA. DMAAH+ could sharply reduce the interfacial tension of the dodecane-saline system, while DMAA only exhibits a limited decrease, which is in accordance with the experimental observation that DMAAH+/DMAA can reversibly emulsify/demulsify alkane-water systems. Our simulations showed that both the number and lifetime of hydrogen bonds (HBs) between DMAA and water are almost equal to those between DMAAH+ and water. In DMAA, the N atom connecting with the alkyl tail acted as a HB acceptor, while the N atom attached by a proton in DMAAH+ acted as a HB donor. Furthermore, the HBs between DMAAH+ and HCO3- at the interfaces are relatively limited. Hence, it is deduced that the HBs are insufficient to achieve the CO2-switchability of DMAA/DMAAH+. The Lennard Jones and coulombic potentials between DMAA/DMAAH+ and other species show that the coulombic potentials between DMAAH+ and water or anions (i.e., Cl- and HCO3-) sharply decrease with the increase of DMAAH+ and are much lower than those in models with DMAA. The enhanced coulombic interactions between DMAAH+ and anions lead to a remarkable reduction in interfacial tension and the emulsification of the alkane-saline system. Therefore, coulombic interactions are of crucial importance to the reversible emulsification/demulsification processes regulated by CO2-switchable surfactants, namely DMAAH+/DMAA.

Nitrogen-containing switchable solvents for separation of hydrocarbons and their derivatives

Solvent extraction is commonly used to separate mixtures of hydrocarbons and their derivatives, and solvent choice is strongly influenced by the affinity to the target component, cost and safety. Nitrogen-containing switchable solvents can switch from water-immiscible form to water-miscible bicarbonate salts when CO₂ is injected and back to water-immiscible form when N₂ is injected. Switchable solvents, as a type of recyclable green solvent, can be used not only to separate such mixtures but also to reduce process costs. Herein, four switchable solvents, namely, dipropylamine, di-sec-butylamine, N,N-dimethylcyclohexylamine (CyNMe₂), and N,N,N′,N′-tetraethyl-1,3-propanediamine (TEPDA), were employed to separate benzene/cyclohexane, ethyl acetate/acetonitrile, and ethyl acetate/n-heptane mixtures, and the corresponding partition and selectivity coefficients were determined. In all cases, separation selectivity increased in the order of dipropylamine < di-sec-butylamine < CyNMe₂ < TEPDA, i.e., TEPDA was best suited for the separation of hydrocarbons and their derivatives. In addition, cycling experiments revealed that the TEPDA can be re-used at least 15 times and was well suited for industrial applications. In the end, the mechanism of the separation was put forward.

Solvent extraction is commonly used to separate mixtures of hydrocarbons and their derivatives, and solvent choice is strongly influenced by the affinity to the target component, cost and safety.

Switchable-Hydrophilicity Triethylamine: Formation and Synergistic Effects of Asphaltenes in Stabilizing Emulsions Droplets

In this study, SHT (switchable-hydrophilicity triethylamine, [Et₃NH]·[HCO₃]) has been synthesized and instrumentally characterized by Fourier transform⁻infrared spectroscopy (FTIR) and ¹³C nuclear magnetic resonance (NMR). The operational synthesis conditions of SHT were optimized and determined at 25 °C, Et₃N/H₂O volume ratio of 1:2 and CO₂ injection rate at 300 mL/min. When it was used to extract heavy oil from unconventional oil ore, it was found that it could break maltenes-in-water emulsions. When asphaltenes were present in the oil phase, it was observed that SHT could cooperate with asphaltenes. These results indicated that SHT works with asphaltenes, leading to synergistic effects in stabilizing oil⁻water (o/w) emulsions.

Diamines as switchable-hydrophilicity solvents with improved phase behaviour

Removing solvents by distillation is not a sustainable process because it requires the use of volatile solvents and a high energy input. An alternative is to use a switchable-hydrophilicity solvent (SHS), which can be removed from products and recycled without any distillation step. SHSs are solvents that reversibly switch between hydrophilic and hydrophobic forms with the addition and removal of a trigger such as CO₂. Monoamine SHSs can be separated from dissolved products by extraction into carbonated water, but the solvent removal is limited by the distribution coefficient of the SHS between the carbonated water phase and the product phase. In this article, the use of diamines as SHSs with improved distribution coefficients is explored. Several diamine SHSs are identified and their properties compared to those of monoamine SHSs. Comparisons include the pK_aH (the pK_a of the conjugate acid of a base) and log K_ow (log of the octanol–water partition coefficient) requirements for amines to act as SHSs, distribution coefficients, removal from hydrophobic liquids, switching speeds, and risks to the environment and human health and safety.

Diamine switchable-hydrophilicity solvents can be removed from products, by carbonated water, with much greater efficiency than past switchable solvents.

Simple and Effective Catalyst Separation by New CO2 -Induced Switchable Organocatalysts

CO₂ -induced switchable tertiary amine-based organocatalysts were investigated for an efficient catalyst and product separation by its different partitioning between an organic and carbonated water phase. In this case study, the switching ability of eight tertiary amine-based catalysts between the organic and water phase by addition or removal of CO₂ was investigated. Here, the catalyst switched both nearly completely (99.9 %) into the aqueous phase by addition of CO₂ and effectively back into the organic phase (99.3 %) by expelling CO₂ . With this technique, the organocatalyst was successfully recovered and reused twelve times without significant loss of activity (up to 90 % enantiomeric excess) for the asymmetric nitroaldol (Henry) reaction. After the first catalyst switch, evaporation of the solvent affords the product in 98 % purity without any further purification steps.

A microfluidic study of liquid-liquid extraction mediated by carbon dioxide

Liquid-liquid extraction is an important separation and purification method; however, it faces a challenge in reducing the energy consumption and the environmental impact of solvent (extractant) recovery. The reversible chemical reactions of switchable solvents (nitrogenous bases) with carbon dioxide (CO2) can be implemented in reactive liquid-liquid extraction to significantly reduce the cost and energy requirements of solvent recovery. The development of new effective switchable solvents reacting with CO2 and the optimization of extraction conditions rely on the ability to evaluate and screen the performance of switchable solvents in extraction processes. We report a microfluidic strategy for time- and labour-efficient studies of CO2-mediated solvent extraction. The platform utilizes a liquid segment containing an aqueous extractant droplet and a droplet of a solution of a switchable solvent in a non-polar liquid, with gaseous CO2 supplied to the segment from both sides. Following the reaction of the switchable solvent with CO2, the solvent becomes hydrophilic and transfers from the non-polar solvent to the aqueous droplet. By monitoring the time-dependent variation in droplet volumes, we determined the efficiency and extraction time for the CO2-mediated extraction of different nitrogenous bases in a broad experimental parameter space. The platform enables a significant reduction in the amount of switchable solvents used in these studies, provides accurate temporal characterization of the liquid-liquid extraction process, and offers the capability of high-throughput screening of switchable solvents.

A guide to the selection of switchable functional groups for CO2-switchable compounds

CO₂-responsive species in water interconvert between neutral and bicarbonate forms, but only if the species has appropriate basicity.

Extending the range of switchable-hydrophilicity solvents

Adjusting CO₂ pressure and water volume increases the range of switchable hydrophilicity solvents.

Concentration dependent speciation and mass transport properties of switchable polarity solvents

Tertiary amine switchable polarity solvents (SPS) were produced at various concentrations for three different amines and physical properties measured. The data allowed the identification of various molecular solution states and material trends.