Liquid Water Phase Research Articles

Effect of plasma-activated water on the settling characteristics of ultrafine kaolinite

Coal slurry water is a complex multiphase system, and its settling characteristics are influenced not only by the solid phase coal slime but also by the liquid phase water. This paper firstly explores the effect of plasma-activated water (PAW) on the settling of ultrafine kaolinite through settling experiments, turbidity tests & dynamic observations. The findings show that PAW significantly improves the settling behavior of ultrafine kaolinite, manifested by an increased settling velocity, higher final settling height, shorter settling end time, and reduced turbidity of the supernatant. Furthermore, the potential mechanisms by which PAW enhances the settling of ultrafine kaolinite are analyzed through laser particle size detections, fractal dimension calculations, zeta potential measurements & contact angle determinations. The mechanism analysis indicates that PAW not only reduces the electrostatic repulsion of ultrafine kaolinite particles but also enhances the hydrophobicity, thereby increasing both the size and density of ultrafine kaolinite flocs, which improves the settling performance of ultrafine kaolinite. This study not only provides new insights for enhancing ultrafine kaolinite settling with PAW but also offers new approaches for the efficient settling of coal slurry water.

Construction of the technological process and design development of a multifunctional unit for processing vital soybeans with ultrasound. Feasibility of water-crude suspension

Cereals and legumes have a porous structure, being an inert carrier during mass exchange processes; they contain voids in the form of pores and stomata, on the surface of which there are foreign extractable substances in a solid state, in particular, trypsin and urease inhibitor proteins. These substances, due to their harmful effect on the final product, are subject to removal by extraction. One of the methods for inactivating anti-nutritional substances is ultrasonic treatment of soybeans.The article discusses the technology of inactivating inhibitors that worsen food and protein value of vital soybeans. The developed technology was aimed at dissolving a solid substance - soybean inhibitor protein in a liquid, carried out due to molecular diffusion, intensifying the processes of mass transfer and mass return. When creating a suspension by mixing the solid (crushed soybean grain) and liquid (water) phases, water molecules, which are a solvent, penetrate under the action of capillary forces into the pores and stomata of the treated body, begin to penetrate. On this basis, technological directions of research have been established, a sequence has been built and the physical essence of operations has been substantiated, consisting of four main ones - grinding soybean grain, creating a “water-soybean” suspension, ultrasonic (US) treatment of soybeans, drying. As a result of the conducted research, optimal technological parameters have been established for intensifying the process of inactivation of anti-nutritional substances contained in native soybeans: the degree of grinding of soybean grains is 0.5-1.0 mm; the ratio of water-soy suspension (1:1). The efficiency of the developed technological process will be factors affecting the quality of the resulting products, the duration and energy intensity of the process, resource conservation, simplicity of design and low cost of manufacture, the possibility of automation.

Molecular dynamic simulation study on effect of anionic–nonionic surfactants on decane desorption from SiO2 surface

During oil production, some amount of crude oil is adsorbed on the rock layer. Therefore, surfactants are needed to detach the residual crude oil from this layer, thereby improving the overall oil recovery rate. In this study, five kinds of anionic–nonionic surfactants were designed by changing the length of ethylene oxide (EO) chains based on the structure of saturated cardanol. 8PO8EOSO3 exhibited good oil-detachment effectiveness, and this was assessed by studying the energy of interface interaction between the solid phase (SiO2) and the liquid phase (oil phase molecules, surfactants, and water). The density distribution data further elucidated that the good interface properties of 8PO8EOSO3 affected the degree of aggregation of the oil phase molecules on the SiO2 surface. This was mainly because the appropriate length of EO chains could realize optimal diffusion coefficients at the oil–water interface. Thus, in the 8PO8EOSO3 system, the oil phase molecules exhibited greater intermolecular distance and weak interactions with SiO2 (radial distribution function). Further, the study of the solid–liquid interface properties and effect of different chain lengths of EO chains on desorption showed that the appropriate number of and EO chains was an important factor in designing the structure of the extended surfactant to ensure that the surfactant realizes a high degree of detachment of the oil phase from SiO2.

Rotationally invariant local bond order parameters for accurate determination of hydrate structures

Averaged local bond order parameters based on spherical harmonics, also known as Lechner and Dellago order parameters, are routinely used to determine crystal structures in molecular simulations. Among different options, the combination of the q ¯ 4 and q ¯ 6 parameters is one of the best choices in the literature since distinguishes between solid- and liquid-like particles and between different crystallographic phases, including cubic and hexagonal phases. Recently, Algaba et al. [J. Colloid Interface Sci. 623, 354, (2022)] have used the Lechner and Dellago order parameters to distinguish hydrate- and liquid-like water molecules in the context of determining the carbon dioxide hydrate-water interfacial free energy. According to the results, the preferred combination previously mentioned is not the best option to differentiate between hydrate- and liquid-like water molecules. In this work, we revisit and extend the use of these parameters to deal with systems in which clathrate hydrates phases coexist with liquid phases of water. We consider carbon dioxide, methane, tetrahydrofuran, nitrogen, and hydrogen hydrates that exhibit sI and sII crystallographic structures. We find that the q ¯ 3 – q ¯ 12 combination is the best option possible between a large number of possible different pairs to distinguish between hydrate- and liquid-like water molecules in all cases.

Erosion-corrosion failure of overhead air cooler in atmospheric tower

ABSTRACT During the hydrogenation process in a petrochemical plant, the air cooler serves as a crucial heat exchanger in atmospheric towers. However, the frequent corrosion and leaks of air coolers significantly impact the safety of the process. Firstly, the Aspen software is utilized to simulate the operation of an air cooler. Then, Computational Fluid Dynamics (CFD) calculations are performed to analyze the internal flow in the air cooler. Finally, four inlet optimization strategies are proposed. It is indicated that the condensation of the oil phase results in the formation of liquid-phase oil droplets that cause erosion-corrosion. The absence of liquid-phase water condensation implies that there is minimal dew point corrosion in the tube bundle. The turbulence kinetic energy near the entrance exhibits significant variation, making erosion-corrosion more likely to occur near the entrance of the cooling tube bundle. Furthermore, vortexes form near the entrances of the first and second rows, exacerbating the corrosion in the tube bundle. By optimizing the air cooler, numerical simulations showed that the shear force of the vortex on the tube wall is reduced by nearly 50%. The internal erosion and scour effect of the improved air cooler is reduced.

Early prediction of spinodal-like relaxation events in supercooled liquid water.

Several computational studies on different water models reported evidence of a phase transition in supercooled conditions between two liquid states of water differing in density: the high-density liquid (HDL) and the low-density liquid (LDL). Yet, conclusive experimental evidence of the existence of a phase transition between the two liquid water phases could not be obtained due to fast crystallization in the region where the phase transition should occur. For the same reason, the investigation of possible transition mechanisms between the two phases is committed to computational investigations. In this work, we simulate an out-of-equilibrium temperature-induced transition from the LDL to the HDL-like state in the TIP4P/2005 water model. To structurally characterize the system relaxation, we use the node total communicability (NTC) we recently proposed as an effective order parameter to discriminate the two liquid phases differing in density. We find that the relaxation process is compatible with a spinodal-like scenario. We observe the formation of HDL-like domains in the LDL phase and we characterize their fluctuating behavior and subsequent coarsening and stabilization. Furthermore, we find that the formation of stable HDL-like domains is favored in the regions where the early formation of small patches of highly connected HDL-like molecules (i.e., with very high NTC values) is observed. Besides characterizing the LDL- to HDL-like relaxation from a structural point of view, these results also show that the NTC order parameter can serve as an early-time predictor of the regions from which the transition process initiates.

Dysbiosis not observed in Canadian horses with free fecal liquid (FFL) using 16S rRNA sequencing

Free Fecal Liquid (FFL), also termed Fecal Water Syndrome (FWS), is an ailment in horses characterized by variable solid and liquid (water) phases at defecation. The liquid phase can be excreted before, during, or after the solid defecation phase. While the underlying causes of FFL are unknown, hindgut dysbiosis is suggested to be associated with FFL. Three European studies investigated dysbiosis in horses with FFL using 16S rRNA sequencing and reported results that conflicted between each other. In the present study, we also used 16S rRNA sequencing to study the fecal microbial composition in 14 Canadian horses with FFL, and 11 healthy stable mate controls. We found no significant difference in fecal microbial composition between FFL and healthy horses, which further supports that dysbiosis is not associated with FFL.

Contaminant Removal in Soil and Wash Water Residue from Ex-Mining Area in Jambi using Soil Washing Remediation

Soil washing is one of the effective methods to remove contaminants in polluted soil by moving them from the solid phase (soil) to the liquid phase (water). This study examines the effect of soil washing on the concentration of Total Petroleum Hydrocarbon (TPH) in petroleum-polluted soil at the Ex-Mining Area in Jambi and the removal of oil and grease in soil washing residue using a fixed bed column. The soil washing method uses a leaching column with various concentrations of Tween 80 surfactant solution of 0.5% (v/v) and 1% (v/v). In addition, leaching was repeated 0, 1, and 2 times. Coffee husk biochar was used as a medium in a fixed bed column to remove oil and grease from soil-washing residue with thickness variations of 10 cm, 20 cm, and 30 cm. The results showed that the soil was loamy sand with an initial TPH content of 3092.75 mg/kg. The soil-washing process reduced the TPH concentration with a removal efficiency of 72.45-90.40%. The highest TPH removal occurred in one leaching repetition at a 0.5% surfactant concentration. The optimum oil and fat removal from the use of a fixed bed column is at 30 cm thickness which is 94.35%.

Transferable Water Potentials Using Equivariant Neural Networks.

Machine learning interatomic potentials (MLIPs) have emerged as a technique that promises quantum theory accuracy for reduced cost. It has been proposed [J. Chem. Phys. 2023, 158, 084111] that MLIPs trained on solely liquid water data cannot accurately transfer to the vapor-liquid equilibrium while recovering the many-body decomposition (MBD) analysis of gas-phase water clusters. This suggests that MLIPs do not directly learn the physically correct interactions of water molecules, limiting transferability. In this work, we show that MLIPs using equivariant architecture and trained on 3200 liquid water structures reproduces liquid-phase water properties (e.g., density within 0.003 g/cm3 between 230 and 365 K), vapor-liquid equilibrium properties up to 550 K, the MBD analysis of gas-phase water cluster up to six-body interactions, and the relative energy and the vibrational density of states of ice phases. We show that potentials developed using equivariant MLIPs allow transferability for arbitrary phases of water that remain stable in nanosecond long simulations.

Liquid-Vapor Coexistence and Spontaneous Evaporation at Atmospheric Pressure of Common Rigid Three-Point Water Models in Molecular Simulations.

Molecular dynamics (MD) simulations are widely used to investigate molecular systems at atomic resolution including biomolecular structures, drug-receptor interactions, and novel materials. Frequently, MD simulations are performed in an aqueous solution with explicit models of water molecules. Commonly, such models are parameterized to reproduce the liquid phase of water under ambient conditions. However, often, simulations at significantly higher temperatures are also of interest. Hence, it is important to investigate the equilibrium of the liquid and vapor phases of molecular models of water at elevated temperatures. Here, we evaluate the behavior of 11 common rigid three-point water models over a wide range of temperatures. From liquid-vapor coexistence simulations, we estimated the critical points and studied the spontaneous evaporation of these water models. Moreover, we investigated the influence of the system size, choice of the pressure-coupling algorithm, and rate of heating on the process and compared them with the experimental data. We found that modern rigid three-point water models reproduce the critical point surprisingly well. Furthermore, we discovered that the critical temperature correlates with the quadrupole moment of the respective water model. This indicates that the spatial arrangement of the partial charges is important for reproducing the liquid-vapor phase transition. Our findings may guide the selection of water models for simulations conducted at high temperatures.

Porous Polymer Structures with Tunable Mechanical Properties Using a Water Emulsion Ink.

Recently, the manufacturing of porous polydimethylsiloxane (PDMS) with engineered porosity has gained considerable interest due to its tunable material properties and diverse applications. An innovative approach to control the porosity of PDMS is to use transient liquid phase water to improve its mechanical properties, which has been explored in this work. Adjusting the ratios of deionized water to the PDMS precursor during blending and subsequent curing processes allows for controlled porosity, yielding water emulsion foam with tailored properties. The PDMS-to-water weight ratios were engineered ranging from 100:0 to 10:90, with the 65:35 specimen exhibiting the best mechanical properties with a Young's Modulus of 1.17 MPa, energy absorption of 0.33 MPa, and compressive strength of 3.50 MPa. This led to a porous sample exhibiting a 31.46% increase in the modulus of elasticity over a bulk PDMS sample. Dowsil SE 1700 was then added, improving the storage capabilities of the precursor. The optimal storage temperature was probed, with -60 °C resulting in great pore stability throughout a three-week duration. The possibility of using these water emulsion foams for paste extrusion additive manufacturing (AM) was also analyzed by implementing a rheological modifier, fumed silica. Fumed silica's impact on viscosity was examined, revealing that 9 wt% of silica demonstrates optimal rheological behaviors for AM, bearing a viscosity of 10,290 Pa·s while demonstrating shear-thinning and thixotropic behavior. This study suggests that water can be used as pore-formers for PDMS in conjunction with AM to produce engineered materials and structures for aerospace, medical, and defense industries as sensors, microfluidic devices, and lightweight structures.

Определение диэлектрических свойств воды в тонком слое

A technique is proposed for determining the dielectric properties of water in a nanoscale layer at frequencies corresponding to orientation polarization. The method is based on the registration of the change in the velocity of elastic surface waves resulting from the interaction with a thin layer of a liquid. It was assumed that the dispersion of the dielectric permittivity of water in the thin layer is described by the Debye's equations of dielectric relaxation. In order to demonstrate the capabilities of the proposed method, the values of the real part of the dielectric permittivity of adsorbed water at various frequencies f (43.2; 64.8; 108; 129.6, 194.4, 302.4, 388.8 MHz) were experimentally determined at a fixed thickness of the adsorption layer h (2.2; 2.8; 3.7; 13 nm). The determination of the value of the imaginary part of the dielectric permittivity as well as the calculation of the time of dielectric relaxation, static, and high-frequency dielectric permittivities was enabled by the use of the experimental values and Debye's equations. A comparison was made between the dielectric properties of adsorbed water and those of water in the bulk liquid phase. The high-frequency dielectric permittivity of adsorbed water was found to be lower than that of water in the bulk liquid phase, while the static dielectric permittivity was significantly higher. The dielectric relaxation time of adsorbed water is dependent on the thickness of the adsorption layer and is significantly longer than that of water in the bulk liquid phase.

Impact of Low-Temperature Water Exposure and Removal on Zeolite HY.

Aqueous-phase postsynthetic modifications of the industrially important Y-type zeolite are commonly used to change overall acid site concentrations, introduce stabilizing rare-earth cations, impart bifunctional character through metal cation exchange, and tailor the distribution of Brønsted and Lewis acid sites. Zeolite Y is known to undergo framework degradation in the presence of both vapor- and liquid-phase water at temperatures exceeding 100 °C, and rare-earth exchanged and stabilized HY catalysts are commonly used for fluidized catalytic cracking due to their increased hydrothermal resilience. Here, using detailed spectroscopy, crystallography, and flow-reactor experiments, we reveal unexpected decreases in Brønsted acid site (BAS) density for zeolite HY following exposure even to room-temperature liquid water. These data indicate that aqueous-phase ion-exchange procedures commonly used to modify zeolite Y are impacted by the liquid water and its removal, even when fractional heating rates and inert conditions much less severe than standard practice are used for catalyst dehydration. X-ray diffraction, thermogravimetric, and spectroscopic analyses reveal that the majority of framework degradation occurs during the removal of a strongly bound water fraction in HY, which does not form when NH4Y is immersed in liquid water and which leads to reduced acidity in HY even when dehydration conditions much milder than those typically practiced are employed. Na+-exchanged HY prepared via room-temperature aqueous dissolution demonstrates that Brønsted acid sites are lost in excess of the theoretical maximum that is possible from sodium titration. The structural impact of low-temperature aqueous-phase ion-exchange methods complicates the interpretation of subsequent data and likely explains the wide variation in reported acid site concentrations and catalytic activity of HY zeolites with high-Al content.

Modeling of thermal processes when melting ice on power lines

An analysis of the problem of ice formation on power line wires was carried out, and a review of work in the field of melting ice on various lines was carried out. Existing achievements and problems are noted. One of the reasons for the low equipment of lines with automated melting systems is the need to transfer the line from the operating state to the melting mode. One way to solve the problem is to combine these modes by loading the line with additional current without increasing the power transmitted to consumers. A set of issues on modeling thermal processes in the ice shell of power line wires during ice melting is considered. Limiting the power of heat generation in wires leads to the need to build a sufficiently accurate mathematical model to guarantee melting at different values of wind speed and temperature. A study of wire heating processes was carried out using models of stationary and non-stationary thermal conductivity. An algorithm is proposed for solving the thermal problem when a heated wire penetrates an ice shell, based on simulating the movement of the interface between the solid and liquid phases of water. The features of modeling the melting and crystallization process using a numerical method are described. When ice transitions to a molten state, melting reflects a change in density and the formation of an air gap, accompanied by a significant decrease in heat flows to the lower region of the ice shell. The results of numerical modeling of the process of melting an ice shell with a wire at different values of the convective heat transfer coefficient are presented. When analyzing the modeling results, conditions were identified for the occurrence of unacceptable overheating of a wire freed from ice. Various options for constructing a control system for the smelting process have been proposed to prevent overheating of the wire.

Pressure dependence of adsorption isotherm parameters and transport dynamics of a nonionic surfactant, LS-36, at the carbon dioxide (CO[formula omitted]) gas–liquid water interface

Surfactants are important to a wide variety of elevated pressure processes; however, little is understood about the effect of pressure on surfactant interfacial thermodynamics or transport. While some experimental studies exist, concrete conclusions are difficult to infer due to experimental artifacts, e.g., non-equilibrium conditions. We recently showed that few experiments are capable of achieving bulk fluid saturation, which is essential to careful measurements of surfactant thermodynamics and transport dynamics. In other words, the accurate study of surfactant adsorption equilibrium and transport parameters first and foremost requires bulk fluids that are otherwise in equilibrium. This work uses our recently developed high pressure microtensiometer (HPMT), which ensures bulk phase saturation, to measure thermodynamic isotherms for tri(ethylene glycol)-hexa(propylene glycol)-monododecyl ether (LS-36) surfactant (concentrations between 10−7 and 10−3mol/L and pressures between 1 and 57bar) at the CO2 gas–liquid water surface. All measurements were conducted at 22.5 °C. Note that in this study, the surfactant was dissolved in the liquid water phase and is unable to partition into the gaseous CO2 phase. Isotherms at different pressures were determined from surface tension data, analyzed, and compared to determine trends in thermodynamic parameters. Dynamic surface tension measurements were performed to assess transport dynamics in terms of the well-studied diffusion timescale. We find that surface tension depends non-linearly on pressure and surfactant concentration, such that surfactants are less effective at lowering surface tension as pressure increases. Furthermore, surfactant adsorption is a non-monotonic function of pressure and goes through a maximum at intermediate pressures. This result suggests that surfactant adsorption is strongly dependent on the free energy of the CO2-water surface. Overall, this work shows that the thermodynamics of surfactants at equilibrium surfaces under pressure are non-trivial and need additional investigation to quantify the driving forces for surfactant adsorption and to develop models for high pressure processes.

Microcracking of strawberry fruit cuticles: mechanism and factors

Microscopic cracks in the cuticle (microcracks) are the first symptom of the strawberry fruit disorder ‘water soaking’ in which the fruit surface appears watery, translucent, and pale. Water soaking severely impacts fruit quality. The objective was to investigate the factors and mechanisms of cuticular microcracking in strawberry. Fluorescence microscopy revealed numerous microcracks in the achene depressions, on the rims between depressions and at the bases of trichomes. Microcracks in the achene depressions and on the rims were either parallel or transversely oriented relative to a radius drawn from the rim to the point of attachment of the achene. In the achene depression, the frequency of microcracks with parallel orientation decreased from the calyx end of the fruit, towards the fruit tip, while the frequency of those with transverse orientation remained constant. Most microcracks occurred above the periclinal cell walls of the epidermal cells. The long axes of the epidermal cells were primarily parallel-oriented. Microcracking increased during fruit development. Cuticle mass per fruit remained constant as fruit surface area increased but cuticle thickness decreased. When fruit developed under high relative humidity (RH) conditions, the cuticle had more microcracks than under low RH conditions. Exposing the fruit surface to increasing RHs, increased microcracking, especially above 75% RH. Liquid-phase water on the fruit surface was markedly more effective in inducing microcracking than high vapor-phase water (high RH). The results demonstrate that a combination of surface area growth strain and water exposure is causal in inducing microcracking of the strawberry cuticle.

Water-assisted densification and broadband dielectric response of cold-sintered CaCu3Ti4O12-SnF2 composites

Miniaturization of electronic devices is one of the great challenges faced by the scientific and engineering community; hence extensive research has focused on novel materials, devices and technologies to implement the same. Calcium copper titanate (CCTO), a unique electro-ceramic material with a complex perovskite structure and reasonably high temperature-stable relative permittivity, is a potential candidate for the miniaturization of capacitors. In the present work, cold sintering is used to synthesize xCCTO–(1 – x)SnF2 (x = 0.5–0.8 vol fraction) composites at ultra-low temperature (<150 °C) in 30 min at a pressure of 500 MPa, which has not been reported earlier. The effect of the liquid phase (water) on the densification and microstructure of these composites is also investigated. X-ray diffraction (XRD) analysis confirms the co-existence of CCTO and SnF2 phases in the composites. As the volume fraction of SnF2 increases in the presence of the liquid phase, an evolution of microstructure showing the enhancement in densification is observed. A high relative density (>90%) is obtained for SnF2-based, cold-sintered systems, which can be due to the melting of SnF2, thus forming a liquid phase during cold sintering that enhances the dissolution-precipitation mechanism. Microstructural studies reveal that a certain amount of SnF2 and water enhances the densification in the composite through dissolution–precipitation followed by melting of SnF2. The relative permittivity (εr), dielectric loss (tan δ) and micro-hardness of the xCCTO-(1 – x) SnF2 composite increase from 21.6 to 25.3, from 0.026 to 0.039 and from 3.6 to 5.1 GPa, respectively, with increasing SnF2 content. Further, a comparison of sintering temperature, relative permittivity, dielectric loss and micro-hardness of this system reveals that the 0.8CCTO–0.2SnF2 composite cold-sintered at 150 °C achieves moderate relative permittivity (25.3 at 950 MHz), low dielectric loss (0.039 at 950 MHz) and good micro-hardness (3.6 GPa).

Representative Elementary Volume Estimation and Neural Network-Based Prediction of Change Rates of Dense Non-Aqueous Phase Liquid Saturation and Dense Non-Aqueous Phase Liquid–Water Interfacial Area in Porous Media

Investigation of the change rate for contaminant parameters is important to characterize dense non-aqueous phase liquid (DNAPL) transport and distribution in groundwater systems. In this study, four experiments of perchloroethylene (PCE) migration are conducted in two-dimensional (2D) sandboxes to characterize change rates of PCE saturation (So) and PCE–water interfacial area (AOW) under different conditions of salinity, surface active agent, and heterogeneity. Associated representative elementary volume (REV) of the change rate of So (So rate) and change rate of AOW (AOW rate) is derived over the long-term transport process through light transmission techniques. REV of So rate (SR-REV) and REV of AOW rate (AR-REV) are estimated based on the relative gradient error (εgi). Regression analysis is applied to investigate the regularity, and a model based on a back-propagation (BP) neural network is built to simulate and predict the frequencies of SR-REV and AR-REV. Experimental results indicated the salinity, surface active agent, and heterogeneity are important factors that affect the So rate, AOW rate, SR-REV, and AR-REV of the PCE plume in porous media. The first moment of the PCE plume along the vertical direction is decreased under conditions of high salinity, surface active agent, and heterogeneity, while these factors have different effects on the second moment of the PCE plume. Compared with the salinity and surface active agent, heterogeneity has the greatest effect on the GTP, the distributions of the So rate and AOW rate along the depth, and dM, dI. For SR-REV, the standard deviation is increased by the salinity, surface active agent, and heterogeneity. Simultaneously, the salinity and heterogeneity lead to lower values of the mean value of SR-REV, while the surface active agent increases the mean value of SR-REV. However, the mean and standard deviation of AR-REV have no apparent difference under different experimental conditions. These findings reveal the complexity of PCE transport and scale effect in the groundwater system, which have important significance in improving our understanding of DNAPL transport regularity and promoting associated prediction.

Conversion of waste into wealth in chemical recycling of polymers: Hydrolytic depolymerization of polyethylene terephthalate into terephthalic acid and ethylene glycol using phase transfer catalysis

Hydrolytic depolymerization of polyethylene terephthalate (PET) waste was studied using high pressure autoclave reactor at 240 °C (molten state) and autogenous pressure using excess of water in the presence of a phase transfer catalyst polyethylene glycol (PEG 400) and the product profile was traced at various time intervals. In comparison with zinc acetate (used before), PEG 400 was the best catalyst. Concentration profiles were developed for PET, oligomer and terephthalic acid (TPA) using HPLC. Effect of initial molar ratio of 22–110 mol of water/mol PET on depolymerization was studied by using both HPLC and end group analysis. Initial molar ratio of 55–110 mol of water/mol PET was found to give 99 percent conversion in 30 min at 240 °C. A complete conversion of ester linkages to acid group and the desired product TPA was studied. On the basis of ester linkage, 100% conversion was observed in 10–12 min reaction time. At 30 min additional time, it was found to give 95% yield of TPA. Molar concentration of PEG 400 of 2.0 × 10−5 mol/cm3 was sufficient to give the maximum conversion in breaking of ester linkages. The yield and purity of TPA was found to be 90 and 99.1%, respectively. A new mechanism of solid (polymer)-liquid (melt)-liquid (water) phase transfer catalysis (PTC) for hydrolysis was proposed and validated. A pseudo-first order rate equation was fitted for depolymerization with a rate constant of 1.4 min−1 at 240 °C and apparent activation energy of 34.4 kJ/mol. The rate of hydrolysis is very fast and complete depolymerization takes place within 30 min. This is an excellent example of circular economy and cleaner production from waste plastic.

Improving the Accuracy of Experimental Hydrate Equilibrium Point Determination: A Mini-Review

Reliable gas hydrate equilibrium data is necessary to assess the severity of hydrate problems in the oil and gas industry and successfully implement the benefit of hydrate technologies in different areas such as hydrate-based CO2 capture and storage. Furthermore, the hydrate equilibrium point prediction models rely on tuning experimental data. In this mini-review, various techniques for hydrate dissociation point (DP) measurement either in the presence or absence of liquid water phase are discussed to improve the accuracy of the measurement. While both Visual and non-visual techniques can be used to measure hydrate DP, the non-visual isochore procedure is the most common technique. The stepwise heating procedure for hydrate dissociation to measure the DP is recommended due to its ability to improve accuracy and save time. However, it is essential to exercise caution during the data interpretation to avoid measuring inaccurate DP. In particular, considering the dissociation of various hydrate structures is crucial to enhance the accuracy of DP determination when employing non-visual techniques.