Induction Time Of Hydrate Formation Research Articles

Beyond gas supersaturation: Dissecting the secondary formation of methane hydrate

Rapid secondary formation of gas hydrate is a critical issue in gas transportation and at the same time has foreseeable potential in future gas storage. Despite the devoted research in the past decade, the intrinsic mechanism of the secondary formation of gas hydrate, is still an on-going subject of debate. Because the secondary formation of gas hydrate is commonly observed under conditions with extraordinarily high content of gas, gas supersaturation is hypothesized as one crucial mechanism. To dissect the gas supersaturation hypothesis, Molecular Dynamics simulations were conducted systematically with hydrate secondary formation in solutions with various gas concentrations covering supersaturation conditions. The effects of key parameters influencing the secondary formation of hydrate, including system temperature and local methane concentration, were explored. The results revealed for the first time a U-shape-like trend in the induction time of hydrate formation with the increase of gas concentration, pinpointing an optimal gas content with the given environmental temperature and pressure. Importantly, the findings highlighted the needed revision of the current gas supersaturation hypothesis in both methane hydrate mitigation and application. This work not only advanced the current understanding of the secondary formation of methane hydrate but also contributed to the fundamental knowledge essential for future gas storage by gas hydrates.

Study on the hydrate growth characteristics and rheology of silica-containing sand water-in-oil emulsion system

Understanding the transportability of silica-sand-containing hydrate slurries is crucial for production safety of non-consolidated natural gas hydrate reservoirs, especially when solid-state fluidization technology is utilized. Despite some research on silica sand and marine sediments’ influence on hydrate formation kinetics, rheological studies are scarce for systems with silica sands. The formation process of cyclopentane hydrates under the coexistence of hydrophilic silica particles and surfactants were observed. The effects of the concentration and particle size of silica sands as well as the water cut and surfactant concentration of emulsion on the rheological properties of hydrate slurries were investigated using a rheometer. The results indicated: (1) Hydrophilic sand aggregates were entrapped in water droplets, indirectly affecting the oil–water contact area due to the increase in water droplet volume, which was conducive to the combination of alkanes and water molecules to form a hydrate shell; silica particles provided nucleation sites at the oil–water interface to promote the adsorption and aggregation of cyclopentane molecules. (2) The synergistic effect of silica sand and surfactants significantly shortened the induction time of hydrates and increased the viscosity of the slurry. As the concentration of silica sand (1 wt%, 5 wt%, 10 wt%) increased, the induction time of hydrate formation decreased by 44.8 min. Within the concentration range below 5 wt%, the viscosity of the slurry increased as the concentration increased, with an amplitude of 13830.7 mPa·s. The induction time of hydrate formation decreased with increasing silica sand particle size (2 μm, 6.5 μm, 12 μm), but the size of silica sand particles had no significant effect on the viscosity of the slurry. (3) Hydrate slurries in all systems exhibited shear-thinning behavior. There was no obvious relationship between the yield stress of slurry under different silica sand concentrations. However, the yield stress of the slurry was inversely proportional to the size of silica sand particles. The yield stress decreased by 141.13 Pa when the size of silica sand particles increased from 2 μm to 12 μm. Overall, this study highlighted the influence of silica sand presence on flow safety assurance in solid-state fluidization technology.

Effect of anti‐Agglomerants on carbon dioxide hydrate formation in oil–water systems

AbstractThe experiments in high‐pressure pipelines simulate the formation and fluid of hydrate under deep‐sea conditions, which has practical significance for the deep‐sea landfill of carbon dioxide (CO2) and the safe running of oil and gas pipelines. In this paper, pure water, white oil, CO2, and arquad 2C‐75 were used to study the formation and flow characteristics of CO2 hydrate in the oil–water system with the help of a loop device, and the growth morphology of hydrate was observed through the view‐window on the loop. The experimental results show that in the low water cut system without anti‐agglomerates, hydrate mainly forms on the surface of water droplets and the surface of the free water layer at the bottom of the loop. In the high water cut system, hydrate forms on the pipe wall in the form of hydrate film. Increasing water cuts can shorten the induction period of hydrate formation. Anti‐agglomerates in the oil–water system can inhibit the growth of hydrate film on the pipe wall effectively. Anti‐agglomerates can shorten the induction time of hydrate formation.

Enhancing hydrate formation for cold storage by isotridecanyl polyoxyethylene ether series surfactants in quiescent conditions

The promotion technology of hydrate formation is the key to the industrial application using hydrates. To study how nonionic surfactants affect hydrate formation, four isotridecanyl polyoxyethylene ether series surfactants with hydrophilic lipophilic balance (HLB) values from 8 to 18 are selected to analyse nonionic surfactants influence on hydrate formation. All four surfactants can enhance 1,1-dichloro-1-fluoroethane (HCFC-141b) hydrate formation in quiescent conditions, and each surfactant has an ideal concentration regarding of hydrate formation induction time. E-1306 (HLB = 11.2) has the most effective on improving hydrate formation. The hydrate nucleation needs minimum time (61 min), and hydrate cooling storage capacity reaches 203.5 kJ·kg−1 with 1.0 wt% E-1306. Hydrate nucleation stability is also the best with 1.0 wt% E-1306. The hydrophobic effect and micelle effect of surfactants are the main methods for promoting hydrate formation. The effect of surfactants with large HLB values on promoting hydration is not obvious. The influence of surfactant on the stability of HCFC-141b emulsion is also an important factor affecting hydrate formation.

Enhanced the formation kinetics of CO2 hydrate using graphene oxide and L-methionine

Although carbon dioxide capture and storage based on hydrate technology has the characteristics of recyclability, high safety, and low pollution, it is hindered by the harsh conditions and the slow rate of hydrate formation. To improve the formation rate and the storage capacity of CO2 hydrate, the effects of graphene oxide (GO) and L-methionine (L-met) on CO2 hydrate formation kinetics were studied in this work. The experimental results showed that GO could effectively promote CO2 hydrate formation, and its promotion effect was related to the concentration of GO. For the single GO system, when the concentration of GO increased from 0.005 wt% to 0.025 wt%, the total gas consumption increased by 7.83%–16.59% compared with that of the pure water system. It was found that the optimal concentration of GO in the single GO system was 0.015 wt%, in which the induction time was shortened by 59.68% compared with that of the pure water system. For the compound system of GO and L-met, a synergistic promotion effect for CO2 hydrate formation was found between GO and L-met, and the optimal concentration in the compound system was 0.015 wt% GO mixed with 0.15 wt% L-met. Compared with the pure water system, the induction time and the time required for 90% hydrate formation to complete (T90) were shortened by 74.79% and 55.17%, respectively. According to the morphological observation of hydrates, it was inferred that the L-met enhanced the hydrate formation and mass transfer. Compared with the published data, the compound optimal system of GO and L-met had a higher gas storage capacity and a shorter induction time for hydrate formation. This work is helpful for advancing the commercialization of CO2 capture and storage based on hydrate technology.

Effects of wax on the formation of methane hydrate in oil-dominate systems: Experiments and molecular dynamics simulations

Hydrate formation and wax deposition in underwater multiphase pipelines have become two vital problems affecting the flow assurance safety. Experiments and molecular dynamics (MD) simulations were performed to investigate the effect of wax crystals on hydrate nucleation and growth. Our experimental results showed that wax crystals had an inhibitory effect on hydrate growth, but played a dual role in methane hydrate nucleation (promotion and inhibition). The addition of wax could decrease mass transfer coefficient of methane by increasing viscosity of oil phase, which lower methane supply from the oil bulk phase to the oil–water interface. The simulation results revealed that the wax crystals at the interface influenced the mass transfer of methane molecules instead of providing heterogeneous nucleation sites. Small wax crystal adjacent to the oil–water interface accelerated methane supersaturation dissolution and restricted gas diffusion in the aqueous phase because of adsorption to methane, which promoted hydrate nucleation and shifted the nucleation position toward the oil–water interface. While the large wax crystal could effectively block the methane mass transfer from oil phase to aqueous phase by covering the oil–water surface, which reduced the concentration of methane in the aqueous phase and prolonged the induction time of hydrate formation. These results of this work would provide a better understanding of the interaction mechanism between hydrate and wax.

Synergistic Effect of Water-Soluble Hydroxylated Multi-Wall Carbon Nanotubes and Graphene Nanoribbons Coupled with Tetra Butyl Ammonium Bromide on Kinetics of Carbon Dioxide Hydrate Formation

In this work, the thermodynamics and kinetics of hydrate formation in 9.01 wt% tetra butyl ammonium bromide (TBAB) mixed with water-soluble hydroxylated multi-wall carbon nanotube (MWCNTol) systems were characterized by measuring hydrate formation conditions, induction time, and final gas consumption. The results showed that MWCNTols had little effect on the phase equilibrium of CO2 hydrate formation. Nanoparticles (graphene nanoribbons (GNs) and MWCNTols) could significantly shorten the induction time. When the concentration was ≤0.06 wt%, MWCNTols had a better effect on the induction time than the GN system, and the maximum reduction in induction time reached 44.22%. The large surface area of MWCNTols could provide sites for heterogeneous nucleation, thus shortening the induction time of hydrate formation. Furthermore, adding different concentrations of nanoparticles to the 9.01 wt% TBAB solution effectively increased the final gas consumption, and the maximum increase was 10.44% of the 9.01 wt% TBAB + 0.08 wt% GN system. Meanwhile, the suitable initial pressure and experimental temperature could also promote the hydrate formation and increase the motivation in hydrate formation. The 9.01 wt% TBAB + 0.02 wt% MWCNTol system had the best effect at 3.5 MPa and 277.15 K. The induction time was reduced by 66.67% and the final gas consumption was increased by 284.11% compared to those of the same system but at a different initial pressure and experimental temperature. This work helps to promote the industrial application of hydrate technology in CO2 capture and storage.

Development and evaluation of aloe vera dry extract quantum dots as novel hydrate inhibitor for the control of flow assurance problems in the oilfields

Application of quantum dots in the oil and gas field operations is an emerging area, especially in tracer application and as hydrate inhibitors. This study involves development and evaluation of a novel low-dosage hydrate inhibitor aloe vera dry extract quantum dots, prepared by hydrothermal method, to prevent the formation of clathrate hydrates. Experimental studies were performed for THF model hydrate system in crude oil-water emulsion to evaluate the effect of wax content on hydrate formation. Quantum dots were tested for varying concentrations from 0.1 wt% to 1.0 wt% and the best result was obtained at 1.0 wt% in the experimental solutions. The quantum dots have shown the ability of anti-agglomerants, which allowed the tiny hydrate particles formed to remain dispersed in the experimental solution for a longer duration of time and also increased the induction time with increasing concentration of quantum dots. The study also revealed that presence of wax delayed the induction time of hydrate formation, but once hydrate formation occurred, the wax particles acted as nucleation sites for the agglomeration of more hydrate particles.

Probing the Effects of Ultrasound-Generated Nanobubbles on Hydrate Nucleation: Implications for the Memory Effect

Understanding the microscopic hydrate phase transition process is of crucial importance to the application of hydrate-based techniques. This process is nevertheless significantly limited by the insufficient enrichment of hydrophobic gas molecules in the solution. Here, in this work, ultrasonic technology was applied to generate stable and large amount of nanobubbles in pure water to promote hydrate formation kinetics. The particle size distribution of the nanobubbles was following the log-normal distribution, with a concentration of ∼109 mL–1 and a diameter concentrated in 100–120 nm. The concentration of the nanobubbles increased with the ultrasonic duration and power. Notably, the concentrations of nanobubbles produced by hydrate decomposition were slightly higher with the bubble size concentrated around 200 nm. The effect of nanobubbles on the induction time of hydrate formation was further analyzed by forming from the nanobubble solution with different concentrations and particle size distributions. Hydrate formation induction time was reduced by up to 61.13%. We further analyzed the mechanism of the nanobubble dominant hydrate memory effect. The results proved ultrasound as an approach to enhance the solubility of gases in water and thus promote hydrate formation kinetics, providing evidence for the dominant role of nanobubbles in the memory effect.

Designing Robust Superhydrophobic Materials for Inhibiting Nucleation of Clathrate Hydrates by Imitating Glass Sponges.

Superhydrophobic surfaces are suggested to deal with hydrate blockage because they can greatly reduce adhesion with the formed hydrates. However, they may promote the formation of fresh hydrate nuclei by inducing an orderly arrangement of water molecules, further aggravating hydrate blockage and meanwhile suffering from their fragile surfaces. Here, inspired by glass sponges, we report a robust anti-hydrate-nucleation superhydrophobic three-dimensional (3D) porous skeleton, perfectly resolving the conflict between inhibiting hydrate nucleation and superhydrophobicity. The high specific area of the 3D porous skeleton ensures an increase in terminal hydroxyl (inhibitory groups) content without damaging the superhydrophobicity, achieving the inhibition to fresh hydrates and antiadhesion to formed hydrates. Molecular dynamics simulation results indicate that terminal hydroxyls on a superhydrophobic surface can inhibit the formation of hydrate cages by disordering the arrangement of water molecules. And experimental data prove that the induction time of hydrate formation was prolonged by 84.4% and the hydrate adhesive force was reduced by 98.7%. Furthermore, this porous skeleton still maintains excellent inhibition and antiadhesion properties even after erosion for 4 h at 1500 rpm. Therefore, this research paves the way toward developing novel materials applied in the oil and gas industry, carbon capture and storage, etc.

Kinetic Properties of CO2 Hydrate Formation in the Wax-Containing System at Different Concentrations

Precipitation of wax crystals and hydrate formation during deep-sea multiphase pipeline transportation would limit pipeline transportation flow and even trigger accidents. It is necessary to study the hydrate formation behavior in the wax-containing system. This paper utilized a mixture of number 60 Kunlun paraffin wax and number 2 industrial white oil to simulate the wax-containing system, and the CO2 hydrate was formed in the wax-containing system. The morphology of CO2 hydrate formation was captured by the microscope and the charge-coupled device imaging system. In this study, the influences of the wax crystal concentrations on the induction time and cumulative gas consumption of hydrate formation were investigated, and the effects of wax crystal precipitation on the CO2 hydrate nucleation mechanism were discussed. The experimental results indicated that, for the wax crystal concentrations of 1.50 and 2.50 wt %, the induction time of CO2 hydrate formation in the wax-containing system was reduced by 29.23 and 69.23% compared to that in the pure water system, respectively. However, for the wax crystal concentration of 0.50 wt %, the induction time of CO2 hydrate formation in the wax-containing system was increased by 130.77% compared to that in the pure water system. The reason for this was that the precipitation of wax crystals at high concentrations increased the chance of heterogeneous nucleation and the probability of heterogeneous nucleation increased with the increase of wax crystal concentrations. However, for the wax crystals at low concentrations, it not only lowered the chance of cross nucleation but also increased the mass transfer resistance for gas diffusion, thereby resulting in the increase of the induction time of hydrate formation. It was also found that, with the increase of the wax crystal concentrations, the cumulative gas consumption during hydrate formation decreased gradually. When the wax crystal concentration increased to 2.50 wt %, the cumulative gas consumption was reduced by 32.96% compared to that of the pure water system. The experimental results obtained in this study were helpful for understanding the kinetic characteristics of hydrate formation in the wax-containing system, which is meaningful for the pipeline flow assurance, safety, and economic security of pipeline transportation as well as the development of carbon capture and storage.

Effect of residual guest concentration in aqueous solution on hydrate reformation kinetics

Since the occurrence of gas hydrate mainly takes place at water–gas interface where having higher gas concentration, the gas concentration in the aqueous solution plays an important role in affecting the hydrate nucleation. Meanwhile, the aqueous solutions with dissolved gas are commonly found in oil / natural gas reservoirs, production wells and multiphase transportation pipelines, since these systems are always pressurized. This work investigated the reformation characteristics of gas hydrate in the aqueous solution with residual guest concentration, which was achieved by setting the dissociation (hold) pressure above the atmospheric pressure. The experimental results demonstrate that the induction time of hydrate reformation would significantly decrease with the increase of hold pressure, while barely change with duration time and reformation time. As the hold pressure can accelerate hydrate nucleation, an equivalent driving force model was established. This model exhibits more accurate and universal to represent the actual driving force of hydrate formation compared with using the subcooling. Based on the relationship between the induction time and the equivalent driving force, another model was established to predict the induction time of hydrate formation. When the difference of gas concentration in aqueous solution was eliminated by keeping the same hold pressure, the induction times of fresh water are higher than those of the decomposed water under all the higher driving forces. In addition, even though the hold pressures were always kept the same, a heat treatment in the hold pressure stage would cause the increase of the induction time of the subsequent hydrate reformation. All these findings prove the existence of some residual water structures in the solution after hydrate decomposition, resulting in the memory effect.

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.

Investigating hydrate formation and flow properties in water-oil flow systems in the presence of wax

The coexistence of wax and hydrates will pose intractable challenges to the safety of offshore oil and gas production and transportation, especially for deep sea or ultra-deep sea reservoirs. Understanding the effect of wax crystals on hydrate formation, flow properties, and plugging risks of flow systems is imperative to the flow assurance industry. Experiments using systems composed of natural gas, water-in-oil emulsion with different wax contents, and AA (anti-agglomerant) were conducted in a high-pressure flow loop. For wax-containing systems, wax precipitates out during the induction period of hydrate formation. The induction time of hydrate formation decreased with the increasing wax content under the experimental conditions in this work. It was also found that the induction time for both wax-free and wax-containing systems increased with the increasing flow rate. The hydrate growth rate and the cumulative gas consumption were significantly reduced due to the existence of wax. Although the hydrate volume fraction of wax-containing systems was much smaller than that of wax-free systems, a stable slurry flow state could not be reached for wax-containing systems, the pressure drop of which gradually increased with the decreasing flow rates. The coexistence of wax and hydrates results in the deterioration of transportability and higher plugging risks. Based on the Darcy–Weisbach hydraulic formula, a dimensionless parameter was defined to characterize the plugging risk of flow systems with the coexistence of wax and hydrates. Additionally, regions with different levels of plugging risks could be evaluated and divided.

Microscopic molecular insights into methane hydrate growth on the surfaces of clay minerals: Experiments and molecular dynamics simulations

Clay is widely present in hydrate reservoirs and drilling and completion fluids. A quantitative understanding of hydrate growth characteristics on clay solid phase surfaces is vital for predicting hydrate formation and preventing secondary hydrate generation in solid-phase-containing drilling fluid systems. The experiments and nonequilibrium molecular dynamics simulations are performed to investigate the characteristics of methane hydrate growth on the surfaces of kaolinite and montmorillonite. The experiments and dynamics simulated results demonstrate that a large number of bound waters is absorbed on the clay surface. However, the bound water does not participate in hydrate formation. The mechanisms by which clay minerals influence the formation of hydrates are different. Kaolinite reduces the induction time of hydrate formation, but the massive amount of bound water on the kaolinite surface reduces the total amount of free water molecules, which hinders the formation of hydrates, and the inhibition effect on hydrates is more significant than that with montmorillonite. Significantly, the hydrolysis of interlayer cations on the montmorillonite surface inhibits the formation of hydrates. This study will help us to understand the mechanism for gas hydrates formation on reservoir clay minerals, and to predict the amount of hydrate reservoir reserves, which will further aid hydrate resource drilling and exploration.

The study on the relationship between the molecular structures of chitosan derivatives and their hydrate inhibition performance

Methane hydrate blockage has been a major problem to be solved urgently in the industry of petroleum and natural gas. In this work, seven chitosan derivatives with various hydrophilic/hydrophobic properties were synthesized based on the biodegradable chitosan/carboxymethyl chitosan to study the relationship between the chitosan derivatives’ molecular structures and their hydrate inhibition performance. Our experimental results indicated that the inhibitory effects of chitosan derivatives on methane hydrates were significantly better than that of carboxymethyl chitosan derivatives with similar physicochemical properties or the same functional groups at the same concentration. Moreover, the length and properties of the branched chain of the chitosan derivatives played a vital role in hydrate inhibition, and the long branched chains with hydrophobic functional groups was propitious to enhance the hydrate inhibitory performance of additives. By introducing gas-induced agitation, which created a channel for methane gas to enter the aqueous solution, the hydrate inhibition mechanism of chitosan derivatives was further revealed. The experimental phenomena indicated that the chitosan derivatives with superior hydrate inhibition effects enhanced the interfacial resistance of gas molecules migrating to the liquid phase, thus significantly reducing the gas dissolution velocities and prolonging the induction time of hydrate formation. This study verified the vital role of chitosan derivatives in inhibiting crystallized methane hydrate and provided inspiration for the further research and development of efficient and environmentally friendly kinetic inhibitors.

Effect of liquid alkane on carbon dioxide hydrate formation

Hydrophobic surface affects gas hydrate formation. It is an effective method to promote hydrate formation by adding hydrophobic materials into hydrate formation system. However, it is little known about the interaction between hydrate formation and macroalkane. n-Dodecane and n-tetradecane are selected as additives to investigate their effect on CO2 hydrate formation in this work. The addition of liquid alkanes effectively improves hydrate nucleation, shortens the induction time of CO2 hydrate formation, and improves the hydrate growth rate. In addition, the total CO2 uptake at the end of the experiments was increased in the presence of liquid alkanes. Compared with the addition of n-dodecane, n-tetradecane has a weaker effect on CO2 hydrate formation. Increasing the stirring rate can effectively reduce the induction time of hydrate formation and improve hydrate growth rate, but has little effect on gas storage capacity in hydrates. The experimental results also show that the increase of experimental pressure or the decrease of temperature is conducive to hydrate formation.

Effects of the NaCl Concentration and Montmorillonite Content on Formation Kinetics of Methane Hydrate

Most resources of natural gas hydrate (NGH) exist in marine sediments where salts and sea mud are involved. It is of great importance to investigate the effects of salts and sea mud on NGH formation kinetics. In this study, the mixture of silica sand and montmorillonite was used to mimic sea mud. The effects of the NaCl concentration of pore water and montmorillonite content on methane hydrate formation were studied. A low NaCl concentration of 0.2 mol/L and a low montmorillonite content range of 10–25 wt% is beneficial to reduce the induction time of hydrate formation. The high NaCl concentration and high content of montmorillonite will significantly increase the induction time. The average induction time for the experiments with the NaCl concentrations of 0, 0.2, 0.6, and 1.2 mol/L is 20.99, 8.11, 15.74, and 30.88 h, respectively. In the pure silica sand, the NaCl concentration of 0.2 mol/L can improve the final water conversion. In the experiments with pure water, the water conversion increases with the increase of the montmorillonite content due to the improvement of the dispersion of montmorillonite to water. The water conversion of the experiments in pure water with the montmorillonite contents of 0, 10, 25 and 40 wt% is 12.14% (±1.06%), 24.68% (±1.49%), 29.59% (±2.30%), and 32.57% (±1.64%), respectively. In the case of both montmorillonite and NaCl existing, there is a complicated change in the water conversion. In general, the increase of the NaCl concentration enhances the inhibition of hydrate formation and reduces the final water conversion, which is the key factor affecting the final water conversion. The average water conversion of the experiments under the NaCl concentrations of 0, 0.2, 0.6 and 1.2 mol/L is 24.74, 15.14, 8.85, and 5.74%, respectively.

Theoretical Study of the Influence of Seeding on the Dynamics of Propane Hydrate Nuclei Formation in Pure and Sea Water

The effect of the addition of a propane hydrate seed on the dynamics of nucleation in propane solutions based on pure or seawater is considered within the framework of the molecular dynamics method. The time dependencies of the number of long-lived hydrogen bonds and the number of 512 and 51264 cavities formed were calculated. It was shown that presence of the seed leads to the immediate increase in the number of “stable” hydrogen bonds and the growth of hydrate nuclei, which can significantly reduce the induction time of hydrate formation in industrial use and, consequently, enhance the efficiency of the hydrate method of seawater desalination.

Kinetics of methane + hydrogen sulfide clathrate hydrate formation in the presence/absence of poly N-vinyl pyrrolidone (PVP) and L-tyrosine: Experimental study and modeling of the induction time

Gas hydrates, or clathrate hydrates, formation can dramatically damage the transmission lines and operational equipment of the natural gas dominated system, which in turn to ruptured pipeline or destruction equipment. To prevent these problems, hydrate inhibitor injection is one of the most practical approaches. Subsequently, in several experimental studies, the induction time appraisement is employed as an expression for the inhibition accomplishment of kinetic hydrate inhibitor (KHI). Therefore, predicting/estimating the gas hydrate induction time is a crucial and essential subject in this field. To tackle this substantial issue, in the current investigation, the kinetics of methane + hydrogen sulfide hydrate formation (induction time) was investigated. The effects of using two types of KHI including Poly N-vinyl pyrrolidone (PVP) and L-Tyrosine with different concentrations (less than 2 wt%) on the induction time of the aforesaid system were revealed. The experiments were performed in a 100 cm3 stirred autoclave at temperatures ranging from 274.15 to 280.15 K over the primary pressure of 10 MPa. The experimental results indicate that KHIs at low concentrations (less than 2 wt%) approximately have no observational effects on thermodynamic equilibrium conditions but have a significant impact on increasing the induction time and abating the gas consumption during crystalline solid formation. This study also aimed at utilizing the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) based model of induction time for hydrate phase appearance of the binary gaseous comprising of 0.995 mole fraction (MF) CH4 + 0.005 mole fraction (MF) H2S at different subcooling in the presence and absence of PVP and L-Tyrosine applying the Freundlich adsorption isotherm. Model results show a satisfactory agreement with experimental data. The model can be used for reliable calculation of hydrate formation induction time for the methane + hydrogen sulfide + water system in the presence/absence of the aforementioned KHIs.