Thermodynamic Inhibitors Research Articles

Microscopic insights into synergism effect of different hydrate inhibitors on methane hydrate formation: Experiments and molecular dynamics simulations

To reveal the synergism effect of hydrate inhibitors on the formation of methane hydrate was the key to developing new gas hydrate inhibitors and drilling and completion fluid systems. The characteristics of hydrate formation under thermodynamic inhibitors, kinetic inhibitors, and their compound systems were investigated by experiments and molecular simulations from macroscopic and microscopic points of view, respectively. The experimental results presented that a thermodynamic inhibitor was able to significantly reduce the hydrate formation temperature in combination with a kinetic inhibitor, where a compound system of 1% PVP and 5% CaCl2 was comparable to 9.76% CaCl2, or 10.84% NaCl, or 19.85% MEG for the formation of hydrate. The molecular simulation results showed that the thermodynamic inhibitors (NaCl) reduced the steric effects of the kinetic inhibitors (PVP) by limiting the motion of water molecules, which enhanced the effect of inhibitors on methane molecules and accelerated the aggregation of those to form nanobubbles. This study helps us to understand the mechanism of a synergism effect with different hydrate inhibitors on methane hydrate formation and is of applicable importance to develop new natural gas hydrate inhibitors and drilling and completion fluid systems.

Clathrate Hydrates Coexisting Thiazole: Two Roles of Structure II Hydrate Former and Structure I Thermodynamic Inhibitor

In this study, we report a novel hydrate former that acts as a structure II (sII) former and thermodynamic inhibitor. Thiazole is an aromatic five-ringed molecule with two heteroatoms. Thiazole forms an sII hydrate crystal with small CH4 and CO2 molecules. The Rietveld refinement result of sII (CH4 + thiazole) hydrate positions the thiazole off the center of 51264 cages, and S and N atoms face O atoms at the apex of two pentagonal faces and one hexagonal face of the 51264 cage, respectively. Considering the nearest N–O/S–O distances between N/S atoms of thiazole and O atoms in the 51264 cage, both N and S atoms of thiazole exhibit guest–host interactions with water frameworks, such as O–H···N/O–H···S hydrogen bonds. Meanwhile, the thiazole molecule cannot form an sII hydrate with the C2H6 molecule. It functions as a thermodynamic inhibitor of the structure I (sI) C2H6 hydrate. The guest–host interaction of thiazole would not be so strong as that of tetrahydrofuran, which can form an sII hydrate without small molecules. Therefore, because the 51264 cage is difficult to form by the combination of thiazole and C2H6 molecules, the C2H6–thiazole–water system would form the sI C2H6 hydrate.

Experimental measurement and model prediction on methane hydrate equilibrium conditions in the presence of organic carboxylic sodium salts

Gas hydrate inhibitors are employed to mitigate gas hydrate formation in pipelines. The effects of thermodynamics inhibition were evaluated by measuring the vapor - liquid aqueous solution - solid hydrate (VLH) equilibrium conditions on methane (CH4) hydrate in the presence of three organic carboxylic sodium salts (sodium formate, sodium acetate, sodium propionate) in this study. The experiments were carried out in the temperature range of 273.65 K to 281.65 K. Compared with deionized water, in the electrolyte solutions of sodium formate, sodium acetate and sodium propionate with mole fraction of 0.010 and 0.020, the VLH equilibrium pressure change (ΔP) increased by 12.93, 27.68 %; 18.78, 38.15 %; 23.51, 49.41 %, respectively. Both of the three organic carboxylic sodium salts have obvious thermodynamic inhibition effect on CH4 hydrate. The strength of hydrate inhibition is related to the carbon chain length of organic carboxylate. The dissociation enthalpy (ΔHdiss) of CH4 hydrate in three organic carboxylic sodium salts solutions remains quite uniform with deionized water, which indicates that three organic carboxylic sodium salts have not been involved in the formation of hydrate nucleus. The Chen-Guo hydrate model and N-NRTL-NRF activity model were employed to predict the VLH equilibrium conditions in electrolyte solutions. In the three organic carboxylic sodium salts solutions, the average absolute relative deviations (AARD) of the VLH equilibrium condition data between the predicted and the experimental were 0.81, 2.17, and 3.02 %, respectively. In the sodium chloride (NaCl) and potassium chloride (KCl) solutions, the AARD between the predicted and literature were 1.44, 1.69 %, respectively. The model has good universality and accuracy. Both sodium acetate and sodium propionate are food grade preservatives. Consequently, these are beneficial for the development of environmental-friendly hydrate inhibitors.

Thermodynamics and inhibition mechanism of imidazolium-based ionic liquids for inhibiting spontaneous combustion of iron sulfide

The process safety and sustainable development of the petrochemical industry have been seriously threatened by the spontaneous combustion of iron sulfide. In this paper, four kinds of ionic liquids were used to study the inhibition of spontaneous combustion of iron sulfides (FeS, FeS2). The thermodynamic characteristics, inhibition performance, and mechanism of ionic liquids on the spontaneous combustion of iron sulfide have been systematically studied. The results showed that the iron sulfide samples’ overall surface roughness and the proportion of fine particles in the samples increased after the ionic liquid treatment. In the process of oxidative spontaneous combustion, the extrapolation reaction onset temperatures of the samples treated with ionic liquids were enhanced, and the temperature at the samples’ maximum mass loss rate also was delayed. At the same time, the effect of ionic liquids in this process also changed the samples’ reaction mechanism functions, the apparent activation energies, and the mass loss rate. And in all of the experiments, the apparent activation energy of the samples treated with [BMIM][NO3] was enhanced the most by 16.74 kJ/mol, 14.8 kJ/mol, 26.49 kJ/mol, 14.23 kJ/mol, and 13.87 kJ/mol, respectively, while the mass loss rate of the samples treated with this ionic liquid also decreased the most. Therefore, [BMIM][NO3] had the best inhibiting effect among the four ionic liquids in this study. In addition, the results of molecular simulations showed that there is an adsorption process between the ionic liquid and the iron sulfide. In the adsorption process, the ionic liquid dominated the adsorption competition with oxygen molecules, which raises the iron sulfide’s activation energy of the oxidation reaction, thus inhibiting spontaneous combustion.

Mechanisms of synergistic inhibition of NaCl and glycine mixtures on methane hydrate formation: Experimental and molecular dynamic simulation

Composite inhibitors exhibit significant performance in inhibiting hydrate nucleation and growth and reducing hydrate production, however, their working processes and mechanisms need to be further clarified. Herein, the effects of NaCl-glycine mixture on methane hydrate formation and the underlying mechanisms were investigated through experimental and molecular dynamic simulation. The results showed that in addition to changing the phase equilibrium conditions of the hydrate, NaCl can inhibit hydrate growth owing to the salt resistance of water clathrate structures. Glycine, which is a promising new inhibitor, possesses both kinetic and thermodynamic inhibition capabilities. The ratio C of water molecules disturbed by the mixture of NaCl and glycine decreased to below 0.733, and the hydrate phase equilibrium pressure increased to above 3.919 MPa, which effectively inhibited hydrate nucleation and growth. Moreover, during the hydrate growth stage, NaCl reduced the solubility of methane and glycine promotes the formation of methane nano bubbles, associated with the accelerated diffusion and high degrees of disorder of water molecules in the composite inhibitor solution, which further hindered hydrate growth. A higher glycine dosage led to stronger synergistic inhibition. When the mixture consists of 5.0 wt% glycine and 3.5 wt% NaCl, the induction time was 10.69 times longer than that of pure water, and correspondingly, the methane consumption decreased by 51.35%, with the average methane consumption rate dropping by 75.38%.

A cage-specific hydrate equilibrium model for robust predictions of industrially-relevant mixtures.

Understanding the thermophysical properties and phase behaviour of gas hydrates is essential for industrial applications ranging from energy transport and storage, CO2 capture and sequestration, to gas production from hydrates found on the seabed. Current tools for predicting hydrate equilibrium boundaries typically use van der Waals-Platteeuw-type models which are over-parameterised containing terms with limited physical basis. Here we present a new model for hydrate equilibrium calculations with 40% fewer parameters than existing tools but with equivalent accuracy, including for multicomponent gas mixtures and/or systems with thermodynamic inhibitors. By eliminating multi-layered shells from the model's conceptual basis and focusing on Kihara potential parameters for guest-water interactions specific to each hydrate cavity type, this new model provides insight into the physical chemistry governing hydrate thermodynamics. The model retains the improved description of the empty lattice developed recently by Hielscher et al. but couples the hydrate model with a Cubic-Plus-Association Equation of State (CPA-EOS) to describe fluid mixtures with many more components including inhibitors such as methanol and mono-ethylene glycol used by industry. An extensive database of over 4000 data points was used to train and evaluate the new model and compare its performance against existing tools. The absolute average deviation in temperature (AADT) achieved with the new model is 0.92 K for multicomponent gas mixtures, compared with 1.00 K for the widely-known model of Ballard and Sloan, and 0.86 K for the CPA-hydrates model implemented in the MultiFlash 7.0 software package. With fewer, more physically justified parameters, this new cage-specific model provides a robust basis for improved hydrate equilibrium predictions particularly for industrially-important, multi-component mixtures containing thermodynamic inhibitors.

Влияние метанола на кинетику нуклеации и роста гидрата метана

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.

Investigation of small inhibitor effects on methane hydrate formation in a carbon nanotube using molecular dynamics simulation.

In this work, we simulated water molecules in fixed and rigid (15,0) CNTs and the confined water molecules formed a hexagonal ice nanotube in the CNT. After the addition of methane molecules in the nanotube, the hexagonal structure of confined water molecules disappeared and were replaced by almost all the guest methane molecules. The replaced molecules formed a row of water molecules in the middle of the hollow space of the CNT. We also added five small inhibitors with different concentrations (0.8 mol% and 3.8 mol%) to methane clathrates in CNT: benzene, 1-ethyl-3-methylimidazolium chloride ionic liquid ([emim+][Cl-] IL), methanol, NaCl, and tetrahydrofuran (THF). We investigated the thermodynamic and kinetic inhibition behaviors of the different inhibitors on the methane clathrate formation in the CNT using the radial distribution function (RDF), hydrogen bonding (HB), and angle distribution function (ADF). Our results showed that the [emim+][Cl-] IL is the best inhibitor from both aspects. It was also shown that the effect of THF and benzene is better than that of NaCl and methanol. Furthermore, our results showed that the THF inhibitors tended to aggregate in the CNT, but the benzene and IL molecules were distributed along the CNT and can affect the inhibitor behavior of THF in the CNT. We have also examined the effect of CNT chirality using the armchair (9,9) CNT, the effect of CNT size using the (17,0) CNT, and the effect of CNT flexibility using the (15,0) CNT by the DREIDING force field. Our results showed that the IL has stronger thermodynamic and kinetic inhibition effects in the armchair (9,9) and the flexible (15,0) CNT than the other systems, respectively.

New insights into methane hydrate inhibition with blends of vinyl lactam polymer and methanol, monoethylene glycol, or diethylene glycol as hybrid inhibitors

Gas hydrate inhibition is a relevant topic of flow assurance. Thermodynamic hydrate inhibitors (THIs) and kinetic hydrate inhibitors (KHIs) are applied to prevent gas hydrates formation in oil and gas production facilities. We have carried out extensive experimental studies to further develop the hybrid inhibition strategy involving KHI/THI formulations. We determined methane hydrate equilibrium conditions for an aqueous solution of methanol, MEG, and DEG (≤50mass%). Subsequently, we studied the kinetics of methane hydrate nucleation and growth for an aqueous solution of commercial vinyl lactam KHI and its blends with alcohols. KHI loses its ability to inhibit hydrate nucleation at ≥ 20 mass%methanol. Adding MeOH to KHI solution also accelerated the growth of methane hydrate. The addition of glycols to KHI increases the hydrate onset subcooling. KHI/MEG blends are optimal for hybrid inhibition as they demonstrate the enhanced delay of gas uptake and reduced rate of methane hydrate growth.

Interfacial Adhesion Forces of Hydrate Particles in the Presence of Hydrate Inhibitors

Hydrate inhibitors are traditionally utilized to prevent hydrate plugging. In this study, the adhesion forces of cyclopentane (CP) hydrates with thermodynamic inhibitors (ethanol, urea, and NaCl) and anti-agglomerant inhibitors [sorbitan monooleate (Span 80) and lecithin] were measured to understand the effects of hydrate inhibitors on the adhesion forces of hydrates. It was found that the thermodynamic inhibitors increased the early hydrate interparticle adhesion force due to the enhanced liquid bridge force. However, the liquid bridge acted as a lubricant layer to prevent the irreversible agglomeration of hydrate after long-term contact. The hydrate adhesion forces decreased by 90.5-93.0% and 76.6-92.7% with an increase in the concentration of Span 80 and lecithin, respectively, from 0.1 to 1 wt %. Both rough morphology and low interfacial tension contributed to the adhesion force decrease of hydrate after the addition of anti-agglomerant inhibitors. The results may be helpful for understanding the mechanism of influence and quantifying the impact of hydrate inhibitors on hydrate interparticle adhesion force.

Machine learning models for fast selection of amino acids as green thermodynamic inhibitors for natural gas hydrate

Natural amino acids are non-toxic thermodynamic hydrate inhibitors without negative environmental impact, but it is difficult to accurately select the appropriate amino acid as a quick response to the operational conditions changes in the natural gas pipeline. The objective of this study was to develop mathematical models to predict the hydrate formation temperature (HFT) in presence of amino acids, capture the relationship between amino acid structure properties and their hydrate inhibition strength, and determine the optimal type and concentration to use. The HFT prediction was evaluated using multiple linear regression (MLR) and three machine learning methods including random forest (RF), M5 Rule (M5R) and support vector machine (SVM). After parameter optimization using the trial-and-error method, the coefficient of determination (R2) of the four models were 0.9328, 0.9793, 0.9795 and 0.9980, respectively. The SVM prediction of HFT outperformed other models as the root mean square error (RMSE) was 83%, 76% and 69% lower than that of the MLR, RF and M5R, respectively. Results also demonstrated that the relative importance of the amino acid concentration to the hydrate phase equilibrium was 5-fold higher than that of the intrinsic properties of the amino acid molecular. The SVM model proposed in this study served an easy-to-use tool for reliable prediction of HFT by just providing a new set of input data. This made it possible to accurately determine the minimum concentration of amino acids to be used during the gas pipeline transportation.

Towards Gas Hydrate-Free Pipelines: A Comprehensive Review of Gas Hydrate Inhibition Techniques

Gas hydrate blockage is a major issue that the production and transportation processes in the oil/gas industry faces. The formation of gas hydrates in pipelines results in significant financial losses and serious safety risks. To tackle the flow assurance issues caused by gas hydrate formation in the pipelines, some physical methods and chemical inhibitors are applied by the oil/gas industry. The physical techniques involve subjecting the gas hydrates to thermal heating and depressurization. The alternative method, on the other hand, relies on injecting chemical inhibitors into the pipelines, which affects gas hydrate formation. Chemical inhibitors are classified into high dosage hydrate inhibitors (thermodynamic hydrate inhibitors (THI)) and low dosage hydrate inhibitors (kinetic hydrate inhibitors (KHI) and anti-agglomerates (AAs)). Each chemical inhibitor affects the gas hydrate from a different perspective. The use of physical techniques (thermal heating and depressurization) to inhibit hydrate formation is studied briefly in this review paper. Furthermore, the application of various THIs (alcohols and electrolytes), KHIs (polymeric compounds), and dual function hydrate inhibitors (amino acids, ionic liquids, and nanoparticles) are discussed thoroughly in this study. This review paper aims to provide a complete and comprehensive outlook on the fundamental principles of gas hydrates, and the recent mitigation techniques used by the oil/gas industry to tackle the gas hydrate formation issue. It hopes to provide the chemical engineering platform with ultimate and effective techniques for gas hydrate inhibition.

Prediction of organic and inorganic gas hydrates equilibrium conditions in the presence and absence of thermodynamic inhibitors

The formation of gas hydrates in surface production equipment is common and poses a significant loss to the oil and gas industry sectors. It arises primarily in the pipeline located beneath sea level, and this causes equipment blockages, increasing the operational cost. Most drilling processes incorporate thermodynamic inhibitors such as methanol, ethylene glycol, and triethylene glycol to address these issues. One method to study this relationship is by developing an empirical correlation to predict the hydrate equilibrium condition. In the current work, new empirical correlations for organic and inorganic gas hydrates in pure water and thermodynamic inhibitors are developed. It was observed that the overall mean deviation between the experimental data and the predicted correlations for organic and inorganic gas hydrates in pure water was 5.61% and 3.27%, respectively. Similarly, the overall mean deviation for CO2 in MeOH, EG, and TEG was 5.77%, 8.90%, and 2.09%, respectively. In the case of CH4 and C2H6 in TEG, the overall mean deviation was 2.03% and 2.16%, respectively. The developed correlations are in good agreement with the experimental data in the literature. The present work may be helpful in predicting the various gas hydrate equilibrium conditions, especially in natural gas production.

Dual inhibition effect of reline deep eutectic solvent on methane hydrate nucleation and formation

The search for environmentally friendly hydrate inhibitors is indispensable for flow assurance to prevent hydrate formation in gas or oil pipeline. Deep eutectic solvents (DESs) are classified as a new form of green solvents due to their non-toxic and biodegradable properties. In this work, the dissociation conditions of methane hydrates influenced by reline DES, urea, and choline chloride (ChCl) were experimentally determined. Reline is derived from urea and ChCl in a 2-to-1 M ratio. The isochoric method was applied to evaluate the hydrate-liquid water–vapor-three-phase-coexisting phase boundary for ChCl (3.09 and 5.89 wt%), urea (2.58 and 5.11 wt%), and reline (5.58 and 10.43 wt%) aqueous solutions in the temperature ranging from 272.7 to 287.7 K and the pressure ranging from 2.96 to 12.78 MPa. All these three additives consistently demonstrated an inhibitory effect on methane hydrate formation. At 3.07 MPa, the dissociation temperature of methane hydrate in the presence of reline (10.43 wt%) is lower than that of the pure water system by 2.2 K. For the kinetic studies, a high-pressure micro-differential scanning calorimeter was employed for the measurement of the induction time of hydrate formation. Compared to pure water, all the studied samples demonstrated the potential to prolong the induction time of hydrate nucleation. The reline could strongly hinder the nucleation of hydrate crystals for more than 48 h. The reline DES is identified to act as both kinetic and thermodynamic inhibitors, exhibiting a dual inhibition effect on nucleation and formation of methane hydrates.

New insights into the kinetic effects of CH3OH on methane hydrate nucleation

Methanol (CH3OH) has been recognized as an effective thermodynamic inhibitor for hydrate blockage. Recently, complimentary to its thermo effect, CH3OH is reported to exhibit complex kinetic roles on hydrate nucleation. Herein, by using the molecular dynamic (MD) simulation and based on newly proposed hydrate nucleation mechanism (ref. 32), the kinetic roles of CH3OH are investigated from perspective of compressions among CH4 hydration layers during hydrate nucleation. Specifically, hydrate nucleation is increasingly mitigated as concentrations of CH3OH increase from 1 wt% to 50 wt%. Such inhibition effects are dominantly contributed by H-bonds between –OH of CH3OH and waters, which promote integrations of CH3OH into CH4 hydration layer and result in following changes: i) inhibiting formation of key water structures that are necessary for hydrate nucleation; ii) hindering the compression probability among CH4 hydration layers. Based on these findings, hydrate inhibition efficiency of CH3OH is suggested to be regulated by changing its H-bond formation ability with waters, and the ideal models in MD simulation validate it. Overall, this study can help to better understand the kinetic roles of CH3OH on hydrate nucleation and provide guidance for the design of effective kinetic hydrate inhibitors.

Effects of sodium hydroxide and calcium hydroxide on the phase equilibria of methane hydrates

Alkalis such as sodium hydroxide (NaOH) and calcium hydroxide [Ca(OH)2] find lots of applications in oil and gas industry where formation of methane hydrates (and resulting flow hindrance) is a common occurrence. While many hydrate inhibitors have been identified to maintain flow assurance, effects of these alkalis on the phase stability of methane hydrate have not yet been explored in detail. In this study, the phase behaviour of methane hydrate has been investigated in the presence of aqueous solutions of NaOH and Ca(OH)2 with varying concentrations of 0.005, 0.01, 0.02, and 0.04 mass fractions in a high pressure stirred tank reactor. The phase equilibrium of methane hydrate in aqueous alkali solutions has been generated in the pressure and temperature ranges of 4.27–7.90 MPa and 276.60–283.22 K, respectively. Both the alkalis have found to exhibit inhibition of methane hydrate formation, and the inhibition effect becomes more pronounced at higher concentrations of the alkalis, with NaOH performing as a better inhibitor than Ca(OH)2. A plausible mechanism for the same has also been discussed. The heat of dissociation has been calculated to show that the presence of the alkalis does not influence the structure (sI) of methane hydrate. In addition, a simple model based on the van der Waals-Platteeuw (vdW-P) thermodynamic model consisting of single parameter has been used to predict the phase equilibrium of methane hydrate in the presence of aqueous alkali solutions. The absolute average relative deviations (AARD%) in pressure for the model were measured for the 40 experimental data points generated in this work. The predictions are well within 4 % of the experimental values, which suggests that the model can adequately predict the methane hydrate phase stability in the presence of alkalis. These alkalis are used in various operations during exploration and production of oil and gas. This study therefore will assist in designing an effective and economic thermodynamic inhibitor for methane hydrate based on alkalis for the oil and gas industry.

Synthesis and evaluation of poly (N-vinyl caprolactam)–co-tert-butyl acrylate as kinetic hydrate inhibitor

• A new KHI PVCap- co -TBA was synthesized and evaluated in different hydrate forming systems. • The relationship between the dosage of KHI and the inhibition performance was analyzed. • PPG was proposed as a good synergist for PVCap- co -TBA with concentration of 1.0 wt%. Low dosage kinetic hydrate inhibitors (KHIs) are a kind of alternative chemical additives to high dosage thermodynamic inhibitors for preventing gas hydrate formation in oil & gas production wells and transportation pipelines. In this paper, a new KHI, poly ( N -vinyl caprolactam)– co - tert -butyl acrylate (PVCap- co -TBA), was successfully synthesized with N -vinyl caprolactam (NVCap) and tert -butyl acrylate. The kinetic inhibition performances of PVCap- co -TBA on the formations of both structure I methane hydrate and structure II natural gas hydrate were investigated by measuring the onset times of hydrate formation under different conditions and compared with commercial KHIs such as PVP, PVCap and inhibex 501. The results indicated that PVCap- co -TBA outperformed these widely applied inhibitors for both structure I and structure II hydrates. At the same dosage of KHI, the maximum tolerable degree of subcooling under which the onset time of hydrate formation exceeded 24 hours for structure I hydrate was much lower than that for structure II hydrate. The inhibition strength increased with the increasing dosage of PVCap- co -TBA; The maximum tolerable degree of subcooling for the natural gas hydrate is more than 10 K when the dosage was higher than 0.5% (mass) while it achieved 12 K when that dosage rose to 0.75% (mass). Additionally, we found polypropylene glycol could be used as synergist at the dosage of 1.0 % (mass) or so, under which the kinetic inhibition performance of PVCap- co -TBA could be improved significantly. All evaluation results demonstrated that PVCap- co -TBA was a very promising KHI and a competitive alternative to the existing commercial KHIs.

Preventing the Formation of Methane Hydrates in Natural Gas Transmission Pipelines–A Comprehensive Review

Hydrates are usually formed during the transportation and treatment of natural gas, resulting in hydrate plugging of pipelines. Hydrates are crystal like structure being formed from the mixture of gas and water. They occur at low temperature and highpressure conditions. These hydrate plugs cost the oil and gas industry significant amounts in revenue cuts and is a major problem for the industry. There are many preventive measures that can be implemented such as inhibitors to avoid the formation of hydrates. This paper aims to highlight the different measures and analyse their effectiveness for hydrate-plug prevention. One such method for the reduction of hydrate formation is the removal of existing hydrates by using different types of inhibitors. The most common method of hydrate prevention in deep-water developments is injection of thermodynamic inhibitors, which include methanol, glycols, and others. If hydrate prevention methods are unsuitable and hydrates are liable to form, the process of dehydration can be used wherein the water gets removed from the gas stream. Electrical heating is also used as a way to dehydrate the pipe. This paper compares a variety of inhibitors and various hydrate preventive methods and discusses their influence in the mitigation of hydrate formation in gas pipelines.

Engineering 3d-2p-4f Gradient Orbital Coupling to Enhance Electrocatalytic Oxygen Reduction.

The development of highly efficient and economical materials for the oxygen reduction reaction (ORR) plays a key role in practical energy conversion technologies. However, the intrinsic scaling relations exert thermodynamic inhibition on realizing highly active ORR electrocatalysts. Herein, a novel and feasible gradient orbital coupling strategy for tuning the ORR performance through the construction of Co 3d-O 2p-Eu 4f unit sites on the Eu2 O3 -Co model is proposed. Through the gradient orbital coupling, the pristine ionic property between Eu and O atoms is assigned with increased covalency, which optimizes the eg occupancy of Co sites, and weakens the OO bond, thus ultimately breaking the scaling relation between *OOH and *OH at Co-O-Eu unit sites. The optimized model catalyst displays onset and half-wave potential of 1.007 and 0.887V versus reversible hydrogen electrode, respectively, which are higher than those of commercial Pt/C and most Co-based catalysts ever reported. In addition, the catalyst is found to possess superior selectivity and durability. It also reveals better cell performance than commercial noble-metal catalysts in Zn-air batteries in terms of high power/energy densities and long cycle life. This study provides a new perspective for electronic modulation strategy by the construction of gradient 3d-2p-4f orbital coupling.

Experimental investigation and modelling of synergistic thermodynamic inhibition of Diethylene Glycol and glycine mixture on CO2 gas hydrates

In this experimental and modelling study, Diethylene glycol (DEG) and Glycine (Gly) mixtures are introduced to hinder carbon dioxide hydrate formation by pushing the phase boundaries on the lower temperature side. The mixture of DEG and Gly with the ratio of 1:1 is experimented at 15, 10, and 5 wt% concentrations and the pressure vary from 2.5 to 4.0 MPa. The T-cycle method is employed to assess the effect of the studied blends on the CO2 hydrate by evaluating the hydrate dissociation temperature. Varied compositions of pure DEG and Gly as well as their mixtures are used to compute the synergistic effect. The studied system's thermodynamic hydrate inhibition (THI) influence is a concentration-driven phenomenon. Higher concentration can shift the hydrate liquid vapor equilibrium (HLVE) curve to lower temperatures and high-pressure regions. The outcomes depict that mixture of DEG and Gly at 15 wt%. Shows comparatively better results than the mixtures at 5 and 10 wt%, respectively. The obtained 10 wt% mixture results have also been compared with the conventional hydrate inhibitors and other THIs systems and provide a significant hydrate average suppression (ΔT) of 2.4 K. Furthermore, the freezing point-based Dickens and Quint Hunt model was also applied to predict the HLVE data of CO2 hydrates and satisfactory agreement found with maximum mean absolute error (MAE) of 0.498 K. A better inhibitory performance was seen when diethylene glycol and glycine were combined, demonstrating the potential of amino acids as synergistic inhibitors in the exploitation of hydrates, transportation of oil and gas, and flow assurance.