Clathrate hydrates of carbon dioxide represent a subject of considerable interest in both fundamental science and the development of promising technologies. The phase behavior of CO2 hydrate in the presence of concentrated aqueous solutions remains poorly understood. In this study, we conducted a comprehensive investigation into the impact of magnesium chloride (0-24 mass%) and methanol (0-40 mass%) on the thermodynamic stability of CO2 hydrate. New experimental data on the three-phase gas-aqueous solution-gas hydrate equilibrium in the temperature range 243-283 K and pressure range 1-4.5 MPa were obtained. A correlation is proposed for the precise representation of equilibrium pressure-temperature lines. A comparison of the anti-hydrate effect, as indicated by the parameter ∆Th, of these substances demonstrated that ionic MgCl2 exhibits a stronger thermodynamic inhibitory effect on CO2 hydrate formation than nonionic MeOH. The results of measuring the melting point of ice at 0.1 MPa for aqueous solutions of MgCl2 and MeOH confirmed the thermodynamic consistency of the hydrate equilibrium data. A detailed comparison of the anti-hydrate effect of MgCl2 and MeOH in a wide concentration range was performed on hydrates of different gases (CO2 and CH4). The phase composition of CO2 hydrate samples obtained from water and aqueous solutions of MgCl2 and MeOH was examined using powder X-ray diffraction (PXRD) at 133 K. The PXRD results indicate the formation of sI CO2 hydrate with a cell parameter of 11.86 ± 0.04 Å in all cases.

—This study explores the potential of creating hybrid porous materials to develop gas storage and transport technologies based on gas hydrates. The research provides a brief overview of materials used as containers for producing and storing gas hydrates. It analyzes the properties of cellulose-based hydrate carriers using FT-IR spectroscopy and scanning electron microscopy, and examines a methane hydrate growth in the proposed hybrid material based on cellulose and polystyrene. The mass fraction of water in the tested material was 44

This work systematically investigates the effect of methanol (MeOH) in a wide range of concentrations (0, 1, 2.5, 5, 10, 20, 30, 40, and 50 mass%) on methane hydrate nucleation and growth kinetics. Multiple measurements of gas hydrate onset temperatures and pressures for CH4–H2O and CH4–MeOH–H2O systems were performed by ramp cooling experiments (1 K/h) using sapphire rocking cell RCS6 apparatus. The dataset comprises 96 ramp experiments conducted under identical initial conditions for each solution (gas pressure of 8.1 MPa at 295 K). The reported hydrate onset temperatures and pressures range within 248–282 K and 6.2–7.5 MPa, respectively. The methane hydrate onset subcooling was calculated using literature data on the three-phase gas–aqueous solution–gas hydrate equilibrium for the studied systems. The study determined the numerical values of the shape and scale parameters of gamma distributions that describe the empirical dependences of methane hydrate formation cumulative probability as a function of hydrate onset subcooling in the aqueous methanol solutions. Gas uptake curves were analyzed to characterize the kinetics of methane hydrate growth under polythermal conditions for different methanol concentrations.

Gas hydrate deposition is a complex issue with significant implications for the oil and gas industry. The formation of solid gas hydrates in the hydrocarbon transportation pipelines leads to production disruptions and potentially even complete blockages, resulting in huge financial losses and operational difficulties. For over two decades, kinetic gas hydrate inhibitors have played a crucial role in preventing the formation of gas hydrates within the flow lines of oil and gas production. They directly influence the kinetics of hydrate formation, hindering nucleation and slowing down crystal growth. In this study, five new waterborne polyurethanes (WPUs) with varying degrees of hydrophobicity as inhibitors for cubic structure II gas hydrates were synthesized and tested using rocking cells and differential scanning calorimetry. The synthesis of WPUs involved the reaction between dialkylamines (diethyl, dipropyl, dibutyl, dibenzyl, and dioctyl) and glycidol under mild conditions. All WPUs effectively prevented gas hydrate formation, and a correlation between their efficiency and the alkyl chain length was observed. The inhibitory efficacy of WPUs increased with the extension of the alkyl chain from ethyl to butyl. WPU-DBuA, featuring butyl groups, exhibited the highest inhibition activity. It provided a subcooling temperature of 12.9 and 15.6 degrees C at 0.25 and 0.5 wt%, respectively, surpassing commercial samples, such as Luvicap EG and Luvicap 55 W. Additionally, the solutions containing 1 and 2 wt% of WPU-DBu exhibited maximum subcooling temperatures of 16.2 degrees C and 16.7 degrees C, respectively, which correspond to a 79.7 % and 85.4 % reduction in gas uptake during hydrate growth compared to pure water. However, the inhibitory power of WPUs diminished with larger alkyl (dioctyl) or aromatic groups (dibenzyl), indicating that dibutyl represents the optimal alkyl length for achieving maximum performance. Moreover, WPUs demonstrated a reduction in hydrate conversion under static conditions, signifying their efficiency when the flow is stopped. WPUs lowered the onset temperature of hydrate formation from 3 degrees C in pure water to temperatures below -12 degrees C. Thus, WPUs demonstrated a remarkable ability to prevent the formation of structure II gas hydrates, even under high subcooling conditions. Additionally, WPU-DBuA exhibits a considerable degree of biodegradability, as evidenced by its biodegradation level of 44 %, suggesting that it has the potential to break down more easily in the environment compared to Luvicap 55 W. This research contributes to a deeper understanding of the structure - property relationships of KHIs. This can facilitate the development of more effective and eco-friendly inhibitors, which helps address environmental concerns associated with using KHIs in the oil and gas industry.

Urea is an environmentally benign substance considered a promising gas hydrate inhibitor in flow assurance. Nevertheless, its effect on gas hydrate formation kinetics remains poorly understood. This study investigates the impact of urea and hybrid urea/polymer KHI samples on the nucleation and growth kinetics of sII natural gas hydrates. Hydrate formation was observed at a lower onset temperature with increasing urea and polymer concentration. The nucleation of sII hydrate in aqueous urea solutions occurred at a higher subcooling (7.50 ± 0.58 K at 30 mass%) than in pure water (5.17 ± 0.69 K). These findings indicate that urea acts as a nucleation inhibitor of sII hydrates, although its capacity is not as potent as that of polymer KHI.The analysis of the hydrate nucleation probability distributions revealed that the sII hydrate nucleation rate exhibited a significant decline, approximately one order of magnitude, at subcooling of 5.3–6 K for 20 mass% urea compared to water. A similar behavior was noticed in an aqueous solution of polymer KHI. Urea has succeeded in providing a total benefit of up to 10 K in hydrate onset temperature due to a shift in the hydrate stability zone and nucleation retardation.Consequently, urea is a green dual-acting anti-hydrate chemical that inhibits the formation of sII hydrates by thermodynamic and kinetic mechanisms. Besides, adding 10 mass% urea increases the cloud point temperature of vinyl lactam polymer Luvicap 55W by 14 K. Urea is an additive that considerably augments the stability of the polymer in aqueous solutions at elevated temperatures. These findings make urea an effective and environmentally friendly top-up inhibitor that significantly enhances the anti-hydrate properties of polymer KHI.

In order to systematically study the synergistic effect of gas hydrate inhibition with mixtures of methanol (MeOH) and magnesium chloride (MgCl2), the impact of these compounds on the thermodynamic stability of methane hydrate in the systems of CH4–MeOH–H2O, CH4–MgCl2–H2O, and CH4–MeOH–MgCl2–H2O was experimentally investigated. The pressure and temperature conditions of the three-phase vapor–aqueous solution–gas hydrate equilibrium were determined for these systems. The resulting dataset has 164 equilibrium points within the range of 234–289 K and 3–13 MPa. All equilibrium points were measured as the endpoint of methane hydrate dissociation during the heating stage. The phase boundaries of methane hydrate were identified for 8 systems with MeOH (up to 60 mass%), 5 MgCl2 solutions (up to 26.7 mass%), and 14 mixtures of both inhibitors. Most equilibrium points were measured using a ramp heating technique (0.1 K/h) under isochoric conditions when the fluids were stirred at 600 rpm. It was found that even a 0.5 K/h heating rate for the CH4–MgCl2–H2O system at low salt concentrations, along with all mixed aqueous solutions with methanol, gives results that do not differ from 0.1 K/h, considering the measurement uncertainties. Most measurements for the CH4–MgCl2–H2O system at high salt content were acquired using a step heating technique. The coefficients of the empirical equations approximating the equilibrium points for each inhibitor concentration were defined. The change in the slope parameter of the empirical equation was analyzed as a function of inhibitor content. Correlations that accurately describe the thermodynamic inhibition effect of methane hydrate with methanol and magnesium chloride on a mass% and mol% scale were obtained. The freezing temperatures of single and mixed aqueous solutions of methanol and magnesium chloride were determined experimentally to confirm the thermodynamic consistency of the methane hydrate equilibrium data.

This research discovered that carboxylated cellulose nanofibrils (CNF) with cations of various structures can significantly reduce the number of nucleation sites for methane hydrate formation when compared to distilled water. The electrokinetic potential of CNF in water slightly affects the concentration of hydrate crystallization centers, but it does alter the work of their formation. The energy barrier increases as the absolute value of the electrokinetic potential of nanoparticles decreases. The study of the effect of various CNF salts on the kinetics of methane hydrate formation expands our understanding of the inhibition mechanism of hydrate formation. It’s assumed that a significant negative charge prevents the adsorption of like-charged hydrate nucleation centers on CNF. A decrease in the absolute value of zeta potential of CNF due to a change in cation facilitates this process. As a result, nuclei sorbed on colloidal CNF particles are stabilized on the surface, complicating their coalescence and crystal growth. The design of cellulose-based nanoparticles with varying zeta potential will allow the development of a colloid theory for controlling the formation of gas hydrates.

The experimental data on liquid–liquid equilibrium (LLE) at ambient pressure and 273–333 K are considered and analyzed for ternary systems H2O–MeOH–hydrophobe with С3–С9 normal and branched alkanes, С5–С7 alkenes and dienes, С6–С11 cyclic hydrocarbons, and C3–C19 esters. The distribution of methanol in the ternary systems H2O–MeOH–hydrocarbon and H2O–MeOH–long-chain fatty acid methyl ester (FAME) is determined by the high polarity of alcohol: methanol is concentrated in the water-rich liquid phase and the critical points are located near the methanol–hydrophobe edge for the type I diagrams. For more hydrophilic C3–C7 esters, the equilibrium concentrations of MeOH in both liquid phases become similar, and the critical composition is reached at higher water content. The addition of salt does not induce liquid–liquid separation in water–methanol mixtures, but it affects the separation in the pseudo-ternary aqueous salt solution–methanol–hydrophobe systems.

Methanol (MeOH) is a common thermodynamic inhibitor of gas hydrates. However, its impact on the kinetics of methane hydrate formation has not been systematically investigated. We have thoroughly examined the effect of MeOH in a wide concentration range on the nucleation and growth kinetics of methane hydrate. The onset temperature To and subcooling Delta To of methane hydrate were determined under ramp cooling of 1 K/h. The mean To is not affected by methanol in the 0-2.5 mass% range but decreases within 2.5-50 mass%. At the same time, it was revealed that Delta To for 1-40 mass% MeOH is significantly smaller than that of water, making methanol a hydrate nucleation promoter within the concentration range. The relationship between Delta To and the methanol concentration shows a minimum of 0.53 +/- 0.36 K (at 20 mass%). Adding 1-30 mass% of methanol reduces the stochasticity of the methane hydrate nucleation events. The hydrate nucleation rate increases by an order of magnitude at 1.5 K subcooling when 5 % of MeOH is added to water. Besides, methanol enhances the methane hydrate growth at 1-40 mass%, with the maximum rate occurring at 10 mass% MeOH. Despite the excellent promoting properties of methanol, extrapolation suggests that MeOH may inhibit both nucleation and growth of methane hydrate in more concentrated solutions (>= 50 mass%). Methanol has a dual nature as a thermodynamic inhibitor and a kinetic promoter of methane hydrate formation. The kinetic promotion function of methanol is observed within a specific range (1-40 mass%), but in more concentrated systems, it seems to be reversed.

Despite the mechanical and physical properties of polyurethane foams (PUF), their application is still hindered by high inflammability. The elaboration of effective, low-cost, and environmentally friendly fire retardants remains a pressing issue that must be addressed. This work aims to show the feasibility of the successful application of natural nanomaterials, such as halloysite nanotubes and nanocellulose, as promising additives to the commercial halogen-free, fire-retardant triphenyl phosphate (TPP) to enhance the flame retardance of open-cell polyurethane foams. The nanocomposite foams were synthesized by in situ polymerization. Investigation of the mechanical properties of the nanocomposite PUF revealed that the nanoscale additives led to a notable decrease in the foam’s compressibility. The obtained results of the flammability tests clearly indicate that there is a prominent synergetic effect between the fire-retardant and the natural nanoscale additives. The nanocomposite foams containing a mixture of TPP (10 and 20 parts per hundred polyol by weight) and either 10 wt.% of nanocellulose or 20 wt.% of halloysite demonstrated the lowest burning rate without dripping and were rated as HB materials according to UL 94 classification.

The equilibrium conditions of sII methane/propane hydrates have been experimentally determined for the C3H8/CH4-H2O-urea system. The equilibrium dissociation temperatures and pressures of sII hydrates span a wide P,T-range (266.7–293.9 K; 0.87–9.49 MPa) and were measured by varying the feed mass fraction of urea in solution from 0 to 50 mass%. The experimental points at feed urea concentration ≤ 40 mass% correspond to the V-Lw-H equilibrium (gas-aqueous urea solution-gas hydrate). A four-phase V-Lw-H-Su equilibrium (with an additional phase of solid urea) was observed because the solubility limit of urea in water was reached for all points at a feed mass fraction of 50 mass% and for one point at 40 mass% (266.93 K). Gas hydrate equilibria were measured using a high-pressure rig GHA350 under isochoric conditions with rapid fluid stirring and slow ramp heating of 0.1 K/h. Each measured point represents complete dissociation of the sII hydrate. The phase equilibrium data was compared with the literature reported for the C3H8/CH4-H2O and CH4-H2O-urea systems. A comprehensive analysis of the thermodynamic inhibition effect of urea to sII C3H8/CH4 hydrates on pressure and concentration of the inhibitor was carried out. The phase composition of the samples was analyzed by powder X-ray diffractometry at 173 K.

This work revealed that most water-soluble compounds have a dual nature (thermodynamic promotion or hydrate inhibition) depending on thermobaric conditions. Indeed, by lowering the melting point of ice, water-soluble organic compounds expandthe region of water-containing liquid phase existence below 0°C. This work considered typical thermodynamic hydrate inhibitors as alcohols (methanol, ethanol, and isopropanol). It turned out that even methanol does not exhibit inhibitory properties below the ice crystallization line, and it does not affect the equilibrium conditions of methane hydrate formation. In this case, the observed four-phase hydrate-ice-solution-gas equilibrium either corresponds to the hydrate-ice-gas line for the water-methane system (in the case of methanol) or lies at higher temperatures (in the case of ethanol and isopropanol). This allowed us to assume that practicallyany water-soluble organic compounds will either exhibit the properties of thermodynamic hydrate promoters in a specific temperature range below 0°C or will not affect the hydrate-ice-gas equilibrium. In addition, the presence of the ice and an aqueous liquid mixture in the system accelerates the hydrate growth (compared to the hydrate growth from the bulk phase of ice). It should alsobe noted that, unlike conventional thermodynamic promoters, methanol does not alter the methane hydrate's structure and gas capacity, which is more favorable. The data obtained can contribute to developing hydrate-based technologies for gas storage and separation of gas mixtures.

Polymeric models of the core prepared with a Raise3D Pro2 3D printer were employed for methane hydrate formation. Polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), carbon fiber reinforced polyamide-6 (UltraX), thermoplastic polyurethane (PolyFlex), and polycarbonate (ePC) were used for printing. Each plastic core was rescanned using X-ray tomography to identify the effective porosity volumes. It was revealed that the polymer type matters in enhancing methane hydrate formation. All polymer cores except PolyFlex promoted the hydrate growth (up to complete water-to-hydrate conversion with PLA core). At the same time, changing the filling degree of the porous volume with water from partial to complete decreased the efficiency of hydrate growth by two times. Nevertheless, the polymer type variation allowed three main features: (1) managing the hydrate growth direction via water or gas preferential transfer through the effective porosity; (2) the blowing of hydrate crystals into the volume of water; and (3) the growth of hydrate arrays from the steel walls of the cell towards the polymer core due to defects in the hydrate crust, providing an additional contact between water and gas. These features are probably controlled by the hydrophobicity of the pore surface. The proper filament selection allows the hydrate formation mode to be set for specific process requirements.

Precise data on the non-variant equilibrium of the four phases (vapor–aqueous solution–ice–gas hydrate) in P–T coordinates are highly desired for developing accurate thermodynamic models and can be used as reference points (similar to the triple point of water). Using the two-component hydrate-forming system CO2–H2O, we have proposed and validated a new express procedure for determining the temperature and pressure of the lower quadruple point Q1. The essence of the method is the direct measurement of these parameters after the successive formation of the gas hydrate and ice phases in the initial two-phase gas–water solution system under intense agitation of the fluids. After relaxation, the system occurs in the same equilibrium state (T = 271.60 K, P = 1.044 MPa), regardless of the initial parameters and the order of crystallization of the CO2 hydrate and ice phases. Considering the combined standard uncertainties (±0.023 K, ±0.021 MPa), the determined P and T values agree with the results of other authors obtained by a more sophisticated indirect method. Validating the developed approach for systems with other hydrate-forming gases is of great interest.

The study of the decomposition process of gas hydrates at atmospheric pressure and temperatures below 0°C revealed that methanol could affect this process in different ways, depending on its saturation with environmental components. Indeed, dueto the absorption of methane from the hydrate by methanol, the onset of its decomposition is observed at lower temperatures.Nevertheless, decomposition proceeds more slowly than with pure methane hydrate. When the methanol surrounding the methane hydrate is saturated with other medium components, the hydrate dissociation occurs at the equilibrium temperature (when intersecting the hydrate-ice-gas curve in a system without additives) regardless of the alcohol concentration. A similar situation is observed with hydrate obtained from a methane-propane gas mixture; however, under experimental conditions, ice beginsto melt at a lower temperature compared to the dissociation point of methane-propane hydrate (in the case of methane hydrate, the situation is reversed: the hydrate is less stable). High concentrations of methanol (above 40 mass%) lead to a significant decrease in the temperature of hydrate decomposition. The data obtained show that methanol in low dosages (about 10 mass%) can be usedfor gas storage and transportation since, under certain conditions, it does not shift the equilibrium curve of hydrate formation and slows down the process of methane hydrate decomposition.

Three-phase equilibrium conditions of vapor-aqueous solution-gas hydrate coexistence for the systems of CH4- H2O-organic thermodynamic inhibitor (THI) were experi-mentally determined. Hydrate equilibrium measurements for systems with methanol (MeOH), monoethylene glycol (MEG), and diethylene glycol (DEG) were conducted. Five concentra-tions of each inhibitor (maximum content 50 mass%) were studied in the pressure range of 4.9-8.4 MPa. The equilib-rium temperature and pressure in the point of complete dissociation of methane hydrate during constant-rate heating combined with vigorous mixing of fluids (600 rpm) in a high-pressure vessel were determined. We compared our experimental points with reliable literature data. The coeffi-cients of empirical equations are derived, which accurately describe hydrate equilibrium conditions for the studied systems. The effect of THI concentration and pressure on

In this work, we compared the shape of a binodal curve in the ternary systems “water – methanol – chloroform”, “water – methanol – dichloromethane”, “water – tert-butanol – toluene”, and “water – 2-butoxyethanol – toluene” in the vicinity of the liquid-liquid critical point (LLCP). We have shown that different approaches to characterize the binodal shape are not equivalent for real ternary systems. The preferred approach involves the calculation of distances based on the tangent to the LLCP and the perpendicular lines to the points on the binodal. The variability in the apparent degree of the binodal curve is revealed, contrary to the known literature.

To determine the ability of dimethyl sulfoxide (DMSO) to inhibit methane hydrate formation by the thermodynamic mechanism, we measured the pressures and temperatures of monovariant equilibrium of three phases: gaseous methane, aqueous DMSO solution, and methane hydrate. A total of 54 equilibrium points were obtained. Hydrate equilibrium conditions have been measured for eight different concentrations of dimethyl sulfoxide ranging from 0 to 55 mass%, at temperatures of 242–289 K and pressures of 3–13 MPa. Measurements were performed in an isochoric autoclave (volume of 600 cm3, inside diameter of 8.5 cm) at a heating rate of 0.1 K/h and intense fluid agitation (600 rpm) with four-blade impeller (diameter of 6.1 cm, blade height of 2 cm). The specified stirring speed for aqueous DMSO solutions at 273–293 K is equivalent to a range of Reynolds numbers of 5.3‧103–3.7‧104. The endpoint of methane hydrate dissociation at defined temperature and pressure values was taken as the equilibrium point. The anti-hydrate activity of DMSO was analyzed on a mass% and mol% scale. Precise correlations between the thermodynamic inhibition effect of dimethyl sulfoxide ΔTh and the influencing factors (DMSO concentration and pressure) were derived. Powder X-ray diffractometry was employed to examine the phase composition of the samples at 153 K. Measurement of ice freezing points in aqueous solutions of dimethyl sulfoxide (up to 50 mass%) at ambient pressure allowed us to clarify the location of the liquidus line in the DMSO-H2O system and to check the hydrate equilibrium data for thermodynamic consistency.

In the present work, we experimentally investigated the nucleation and growth kinetics of methane hydrate in the presence of aqueous methanol solutions at alcohol concentrations of 0, 1, 2.5, 5, 10, and 20 mass %. It was found that the addition of methanol statistically significantly reduces the supercooling of the methane hydrate onset ΔTo even at low concentrations. The value of ΔTo decreases bya factor of 5 when transitioning from water to 20 mass% methanol. We have observed that as the alcohol content increases, there isa correlation with an increase in the amount of hydrate at the end of the cooling stage. Adding methanol to water also increases the rate of methane hydrate growth. Thus, our experimental data indicate the role of methanol as a kinetic promoter of methane hydrate nucleation and growth, and the dual nature of methanol which is also a thermodynamic hydrate inhibitor.