A review of advanced oxidation process towards organic pollutants and its potential application in fracturing flowback fluid.

Fracturing flowback fluid (FFF) including various kinds of organic pollutants that do harms to people and new treatments are urgently needed. Advanced oxidation processes (AOPs) are suitable methods in consideration with molecular weight, removal cost and efficiency. Here, we summarize the recent studies about AOP treatments towards organic pollutants and discuss the application prospects in treatment of FFF. Immobilization and loading methods of catalysts, evaluation method of degradation of FFF, and continuous treatment process flow are discussed in this review. In conclusion, further studies are urgently needed in aspects of catalyst loading methods, macromolecule organic evaluation methods, industrial process, and pathways of macromolecule organics' decomposition.

2D MOF derived cobalt and nitrogen-doped ultrathin oxygen-rich carbon nanosheets for efficient Fenton-like catalysis: Tuning effect of oxygen functional groups in close vicinity to Co-N sites.

Developing highly efficient catalysts for peroxymonosulfate (PMS) activation is an important issue in advanced oxidation processes (AOPs) technology. In this work, cobalt and nitrogen-doped ultrathin oxygen-rich carbon nanosheets derived from 2D metal-organic framework (MOF) were successfully fabricated. The as-prepared catalyst can effectively degrade tetracycline (TC) with a high reaction constant (0.088 min-1). Quenching test, electron paramagnetic resonance (EPR) technology, and the electrochemical test indicate that the radical pathway plays a minor role in the degradation process, the 1O2 based nonradical pathway dominates the reaction. Experimental and density functional theory (DFT) studies revealed that the Co-N sites on the carbon structure serve as the dominant active sites, and the oxygen functional groups in close vicinity to Co-N sites can dramatically influence local electronic structure and its interaction with PMS molecule, a high correlation between the reaction constant and hydroxy groups content could be due to the Co-N sites close to hydroxyl groups has a moderate PMS adsorption energy. This work provides new insight into the design of highly efficient Fenton-like catalysts.

Investigation on Pulverized Coal Control Using Calcium Sulfoaluminate Cementitious Proppants in Coalbed Methane Fracturing.

Coalbed methane is a type of high-quality clean energy. The development of coalbed methane helps protect the living environment of humans and solves the safety problems in coal mining. However, a large amount of pulverized coal is generated after coalbed methane fracturing, which reduces the production of coalbed methane. Reduction of pulverized coal generation and prevention of pulverized coal migration are important for the development of coalbed methane. This study innovatively mixed calcium sulfoaluminate particles and sand to create a new fracturing proppant. The new proppant was carried by the fracturing fluid into the formation cracks and cured to form a permeable cement stone with a certain compressive strength and permeability at formation temperature and pressure. The permeability and compressive strength of the permeable cement stone were measured at different curing temperatures. Results showed that when the compressive strength of the permeable cement stone was 5.46 MPa, the gas and water permeabilities could reach 2.06 and 0.57 D, respectively. The pore diameter distribution was measured with the semi-permeable diaphragm method. The distribution curve was bimodal, and the range of the variation in pore size was 0.6-300 µm. Blocked pulverized coal size was determined using the seepage theory of particles in porous media and verified through a pulverized coal control experiment. Pulverized coal with a diameter larger than 7.67 µm was blocked by the permeable cement stone. The efficiency of the permeable cement stone in controlling pulverized coal could reach 96%. This study proved that calcium sulfoaluminate cementitious proppants can fix pulverized coal and prevent its migration. It also provided the compressive strength of propping fractures and the high permeability needed for drainage under formation conditions.

A robust underwater superoleophobic aminated polyacrylonitrile membrane embedded with CNTs-COOH for durable oil/water and dyes/oil emulsions separation.

Considering the emulsified oil and water-soluble dyes in wastewater, the exploitation of easy-manufacturing, energy-saving and high-efficiency separation materials is urgently required. In this work, integrating the positively charged polyethyleneimine (PEI) with negatively charged CNTs-COOH constructed the superhydrophilic Cassie-Baxter structure onto the electrospun polyacrylonitrile (PAN) membrane surface by ultrasonic, electrostatic interaction and thermal treatment. Based on it, the PEN@CNTs membrane achieved efficient separation for surfactant-free, tween 80-stabilized, SDS-stabilized, and CTAB-stabilized emulsions (the fluxes reached 508-3158 L m-2 h-1, the separation efficiency reached 99.42%) by the splendid water-penetration and oil-repellency, electrostatic interaction, and "aperture sieve". Moreover, because of the porosity and strong charged surface of PEN@CNTs membrane, the anionic dyes can be quickly removed by one-step filtrate method (∼403 L m-2 h-1). Meanwhile, the PEN@CNTs membrane also achieved synchronous and efficient remediation for oil/dye mixture emulsions after many cycles. More importantly, facing the complex physical and chemical environments, the combination of the stabilized PEN membrane, inactive CNTs-COOH layer, and the bond of embedding method between CNTs-COOH and PEN nanofibers made the PEN@CNTs membrane demonstrated robust stability and durable separation capability.

Water leak control for the oil-producing wells using Downhole Water Sink Technology.

Casing or tubing leaks cause unwanted water production from oil-producing wells. Many chemical and mechanic water control technologies can be used to solve this problem, including squeezing chemical shutoff fluids into the targeted zone or using plugs, cement, packers, patches to block the leakage. Although those methods are field-proven to be effective, the mechanical solutions may require well logs to detect the water entry point in the well. Chemical methods may present environment risks. In this study, an alternative method, Downhole Water Sink, is proposed to solve the problem of unwanted water production from a casing or tubing leak. The effectiveness of this method to control water production in a well with casing or tubing leaks is tested using the Hele-Shaw experimental model. The results show that this method can control unwanted water production via dynamic control of the pressure drawdown in the reservoir. From a technical standpoint, the advantage of this technology is that it eliminates the need to run logs to locate the water entry point and does not require chemical injection into the formation. From an environmental standpoint, this technology has the circular economy elements. Because the produced water in this technology contains little or no oil, it can be reused for reinjection into the reservoir for water flooding or pressure maintenance purposes. Therefore, a production-reinjection process to recycle the produced water is established to reduce the pollution caused by discharging the wastewater into the environment.

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%.

Study of a Polyamine Inhibitor Used for Shale Water-Based Drilling Fluid.

Here, we report a water-soluble shale inhibitor for inhibiting shale hydrate formation. The copolymer denoted as thermogravimetric analysis (TGA) was synthesized via triethanolamine, two maleic anhydrides, and glacial acetic acid. The infrared (IR) and gas chromatography (GC) results indicated that TGA is a low molecular weight polymer inhibitor (IR) and is the most commonly used method to identify compounds and molecular structures qualitatively. It is mainly used to study the molecular structure of organic substances and conduct qualitative and quantitative analyses of organic compounds. The main function of GC is for polymer molecular weight analysis. With the aid of shale rolling recovery experiments, particle size distribution experiments, triaxial stress experiment methods, bentonite slurry rate inhibition experiments, and thermogravimetric experiments to evaluate TGA inhibition characteristics, the inhibition effect of TGA is better than that of the traditional inorganic salt inhibitor KCl, polymer amine inhibitor UHIB, and organic cationic shale inhibitor NW-1. When the mass fraction is 0.2%, the cutting recovery rate increases from 18.3 to 94.1%. The compressive strength of the shale core after adding 1% TGA inhibitor is 177.9 MPa, which is close to the original core compressive strength of 186.5. The wet sodium montmorillonite crystal layer spacing after treatment with 0.5%, 1.5%, and 3% TGA aqueous solution is 1.38, 1.35, and 1.35 nm, respectively, and the sodium montmorillonite crystal layer spacing after diesel treatment is 1.34 nm, indicating that the inhibitory effect of TGA on sodium montmorillonite is equivalent to that of diesel and that TGA can effectively inhibit the hydration and dispersion of sodium montmorillonite. At the same time, the crystal layer spacing and the weight loss rate of sodium montmorillonite modified by TGA inhibitors did not change significantly after adsorption of deionized water, which proved that TGA inhibitors could be adsorbed in the crystal layer space of sodium montmorillonite to inhibit hydration and dispersion of sodium montmorillonite. Field test results show that TGA can significantly improve the inhibition performance of the field drilling fluid, and the effect is better than the strong conventional inhibition water-based drilling fluid system, which solves the problems of wellbore instability and considerable friction in horizontal shale sections and provides a new idea and method for efficient shale gas drilling.

Ultra-Stable Silica Nanoparticles as Nano-Plugging Additive for Shale Exploitation in Harsh Environments.

Owing to the harsh downhole environments, poor dispersion of silica at high salinity and high temperature can severely restrict its application as the nano-plugging agent in shale gas exploitation. The objective of this study is to improve salt tolerance and thermal stability of silica. Herein, silica was successfully functionalized with an anionic polymer (p SPMA) by SI-ATRP (surface-initiated atom transfer radical polymerization), named SiO2-g-SPMA. The grafted pSPMA brushes on silica provided sufficient electrostatic repulsion and steric repulsion for stabilizing silica in a harsh environment. The modified silica (SiO2-g-SPMA) had excellent colloidal stability at salinities up to 5.43 M NaCl (saturated brine) and standard API brine (8 wt% NaCl + 2 wt% CaCl2) for 30 days at room temperature. Simultaneously, the SiO2-g-SPMA was stable at 170 °C for 24 h as well as stable in weakly alkali environment. Furthermore, the plugging performance of SiO2-g-SPMA in water-based drilling fluids for low permeate reservoir reached to 78.25% when adding a small amount of 0.5 wt% SiO2-g-SPMA, which effectively hindered the water invasion into formation and protected the reservoir.

Hierarchically Stabilized PAN/ß-FeOOH Nanofibrous Membrane for Efficient Water Purification with Excellent Antifouling Performance and Robust Solvent Resistance.

Filtration membranes, with good antifouling performance and robust solvent resistance (e.g., organic solvents or highly acidic/alkaline/saline solvents), that can effectively purify complex polluted water systems are especially demanded in practice but present a challenge to be conquered. Herein, a simple method has been demonstrated to address the obstacles, applying the stabilized polyacrylonitrile (SPAN) nanofiber/ß-FeOOH nanorod composite membrane as a model. In this work, simply stabilizing PAN nanofibers in air can achieve robust solvent resistance against organic solvents and strong inorganic acidic/alkaline/saline solutions. Hydrophilic ß-FeOOH nanorods were anchored onto SPAN nanofibers of our electrospun membrane and achieve superhydrophilicity (0°)/underwater superoleophobicity (>155°) for various oils. More importantly, the SPAN/ß-FeOOH nanofibrous membrane exhibits robust mechanical strength (274 MPa of Young's modulus), excellent chemical stability, fast separation flux (2532-10146 L m-2 h-1), and satisfying removal ratio (>98.2%) against insoluble oils and soluble cationic dyes. In addition, good photocatalytic activity against organic pollutants provides our membranes with excellent flux restorability and a long-term use capacity. These outstanding performances endow our membrane with a great potential application in purifying polluted aquatic systems in worldly harsh conditions.

Biodiesel fuel production from waste cooking oil by the inclusion complex of heteropoly acid with bridged bis-cyclodextrin.

The inclusion complex of Cs2.5H0.5PW12O40 with bridged bis-cyclodextrin (CsPW/B) is prepared as a highly efficient catalyst for the direct production of biodiesel via the transesterification of waste cooking oil. CsPW/B is characterized by X-ray diffraction, and the biodiesel is analyzed by Gas Chromatography-Mass Spectrometer. The conversion rate of waste cooking oil is up to 94.2% under the optimum experimental conditions that are methanol/oil molar ratio of 9:1, catalyst dosage of 3 wt%, temperature of 65 °C and reaction time of 180 min. The physical properties of biodiesel sample satisfy the requirement of ASTM D6751 standards. The novel CsPW/B catalyst used for the transesterification can lead to 96.9% fatty acid methyl esters and 86.5% of the biodiesel product can serve as the ideal substitute for diesel fuel, indicating its excellent potential application in biodiesel production.

ß-Cyclodextrin modified anionic and cationic acrylamide polymers for enhancing oil recovery.

Both of acrylamide and allyl-ß-cyclodextrin are utilized to react with acrylic acid and dimethyl diallyl ammonium chloride respectively to synthesize the novel anionic acrylamide polymer and cationic acrylamide polymer by redox free-radical copolymerization. The structures of copolymers are characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. Subsequently, the copolymers are evaluated on several aspects such as optimum polymerization conditions, intrinsic viscosity, interfacial tension and stability experiments. It is found that the anionic and cationic acrylamide polymers containing cyclodextrin moieties show better performances on interfacial tension, salt resistance, temperature tolerance, viscosification property and shear resistance than that of polyacrylamide. By the comprehensive comparison and analysis, the anionic polymer is more conductive to decrease the interfacial tension for the tertiary oil recovery process, while the cationic polymer is more suitable for enhancing oil recovery in high-temperature and high-mineralization oilfield.

Dynamics of mixed surfactants in aqueous solutions.

The dynamics of mixed surfactants in aqueous solution has been studied at a molecular level by nuclear magnetic resonance (NMR) spectroscopy. The line widths and line shapes of the resonance peaks of two types of binary mixed surfactant systems, ionic/nonionic mixed solutions (12-2-12/TX-100, 14-2-14/TX-100, 14-2-14/Brij-35, and SDS/TX-100) and ionic/ionic mixed solutions (12-2-12/TTAB and 14-2-14/TTAB), in the (1)H NMR spectra offered semiquantitative results about the influence of mixing on the surfactant exchange dynamics between monomers in aqueous solution and those in the micelles. The results showed that the exchange rates of the mixed surfactants were enhanced by each other for the three cationic/nonionic mixed solutions, while the exchange rates were lowered by each other for the two cationic/cationic mixed solutions. As for SDS/TX-100 mixed systems, the addition of SDS made the exchange rate of TX-100 in solution faster, while TX-100 made the exchange rate of SDS slower. These results provide some information about surfactant interaction in mixed solutions.

Dynamics study of the atmospheric reaction involving vibrationally excited O(3) with OH.

We investigate the title atmospheric reaction of highly excited O(3) with vibrationally cold OH. Particular attention will be paid to initial vibrational energies of O(3) between 9 and 21 kcal mol(-1). The calculations employ the quasiclassical trajectory method and the realistic double many-body expansion potential energy surface for HO(4)((2)A). Many aspects of the title process are presented. It is found that it may not be possible to ignore this process when studying the stratospheric ozone budget.

Mechanism of the mixed surfactant micelle formation.

This article provides a full description of the mixed micelle formation process at a molecular level. The mechanism of mixed micelle formation in binary surfactant aqueous solution systems, ionic/nonionic mixed systems (12-2-12/TX-100, 14-2-14/TX-100, and SDS/TX-100), and ionic/ionic mixed systems (12-2-12/TTAB, 14-2-14/TTAB, and SDS/CTAB), in heavy water solutions was studied by (1)H NMR spectroscopy. The critical micellization concentrations of each individual component in the mixed surfactant solutions were gained by analyzing changes in chemical shift and intensities of resonance peaks. The chemical shift changes indicated that in the 12-2-12/TX-100 and SDS/TX-100 systems, micelles of TX-100 formed first, and then 12-2-12 or SDS molecules were fused in the micelles, respectively, which has been proved by 2D NOESY experiments. In contrast, 14-2-14 was the first component to form the micelles in the 14-2-14/TX-100 system. Although 12-2-12 and 14-2-14 are analogs and differ only in the length of the hydrophobic chain by two methylene groups, they showed different behaviors in the micellization processes in the mixture with TX-100. The observation suggests that in the binary surfactant system under current study, the component with lower cmc in the mixed solution aggregates first; then, the other one fuses, resulting in the mixed micelles as the total concentration increases. The same results were obtained for the ionic/ionic solutions, 12-2-12/TTAB, 14-2-14/TTAB, and SDS/CTAB. The above results suggest that the two mixed surfactants do not aggregate synchronously. It obviously demonstrates that the so-called "cmc of the mixed surfactant solution" needs reconsideration.

NMR study of the dynamics of cationic gemini surfactant 14-2-14 in mixed solutions with conventional surfactants.

Three kinds of conventional surfactants, namely, two nonionic surfactants [polyethylene glycol (23) lauryl ether (Brij-35) and Triton X-100 (TX-100)], one cationic surfactant [n-tetradecyltrimethyl ammonium bromide (TTAB)], and an anionic surfactant [sodium n-dodecyl sulfate (SDS)}, were mixed into the quaternary ammonium gemini surfactant [C(14)H(29)N(+)(CH(3))(2)](2)(CH(2))(2).2Br(-) (14-2-14) in aqueous solution. The exchange rate constants between 14-2-14 molecules in the mixed micelles and those in the bulk solution were detected using two nuclear magnetic resonance (NMR) methods: one-dimensional (1D) line shape analysis and two-dimensional (2D) exchange spectroscopy (EXSY). The results obtained from these two methods were consistent. Both showed that mixing a nonionic conventional surfactant, either Brij-35 or TX-100, enhanced the exchange process between the 14-2-14 molecules in the mixed micelles and those in the bulk solution. In contrast, the anionic surfactant SDS and the cationic surfactant TTAB slowed the process slightly.

Vibrational relaxation of highly vibrationally excited O3 in collisions with OH.

We report a theoretical study of highly excited O3 in collisions with vibrationally cold OH. Special emphasis is placed on initial vibrational energies of O3 between 9 and 21 kcal mol(-1). All calculations have employed the quasiclassical trajectory method and the realistic double many-body expansion potential energy surface for HO 4((2)A). Many aspects of the title relaxation process are presented. The results indicate that it may not be ignorable in studying the stratospheric ozone budget.

NMR investigation of the exchange kinetics of quaternary ammonium dimeric surfactants C14-s-C14.2Br.

The exchange kinetics of cationic gemini surfactants of the alkanediyl-alpha-omega-bis(tetradecyldimethylammonium bromide) type, with alkanediyl being 1,2-ethylene, 1,3-propylene, and 1,4-butylene, were investigated by 1H NMR, 2D COSY, and 2D EXSY experiments. In contrast to the conventional surfactants, a second set of well-resolved resonance peaks appeared in the 1H NMR spectra of these surfactants when their concentrations reached their critical concentrations. These two sets of resonance peaks originate from their monomers and micelles, which are proved by the correlation in the 2D COSY experiments and the cross polarization in the 2D NOESY spectra. Therefore, exchanges between monomers in the bulk solution and in the micelles or other aggregates of this series of surfactants occur slowly on the NMR time scale. The exchange rate constants were obtained by both NMR line shape analysis and 2D EXSY experiments, which are very consistent with each other. The exchange rate constants for the gemini surfactants were found to be orders of magnitude less than those for the conventional single surfactants, and for geminis 14-s-14, the shorter the spacer, the slower the exchange dynamic. It still has been found that the fast exchange between monomers in the bulk solution and in the micelles for gemini surfactant 12-2-12 at 25 degrees C occurs slowly at 5 degrees C on the NMR time scale.

1H NMR study on pre-micellization of quaternary ammonium gemini surfactants.

Two quaternary ammonium Gemini surfactant series, 12-s-12, ([C(12)H(25)N+ (CH(3))(2)](2)(CH(2))(s).(2)Br(-)) and 14-s-14 ([C(14)H(29)N(+)(CH(3))(2)](2)(CH(2))(s).(2)Br(-)), where s = 2, 3, and 4, have been studied by the use of (1)H NMR in aqueous solution at concentrations below their critical micelle concentrations (CMC) at 25 degrees C. The appearance of a second set of peaks for the 14-s-14 series and the changes in chemical shifts, line widths, and line shapes of the 12-s-12 series with increasing concentration below the CMC are interpreted as evidence for the formation of premicelle aggregates (oligomers) that appear at approximately one-half their CMC values. Self-diffusion coefficients (D) and transverse relaxation times (T(2)) have also been detected and support the results obtained by (1)H NMR.

Dynamics study of the OH + O3 atmospheric reaction with both reactants vibrationally excited.

The dynamics of the title five-atom atmospheric reaction is studied by the quasiclassical trajectory method for vibrational states of OH over the range 2 < or = v < or = 9 and initial vibrational energies of O3 between 9 and 21 kcal mol-1 using a previously reported double many-body expansion potential energy surface for HO4(2A). The results show that the reaction is controlled by both capture- and barrier-type mechanisms, with the rate constants depending strongly on the reactants' internal energy content. Also suggested from the magnitude of the calculated rate coefficients is that the title processes may not be ignorable when studying the stratospheric ozone budget.

The ultralow interfacial tensions between crude oils and gemini surfactant solutions.

In this paper, the interfacial tension between crude oil and solution of cationic gemini surfactant has been studied. It is found that the interfacial tension between crude oil and water is closely related to the nature of a gemini surfactant and oil; meanwhile, in the case without additives, some gemini surfactants or mixtures of some gemini surfactants can reduce the interfacial tension between crude oil and water to an ultralow value.