Search

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.

Natural gas hydrate is a kind of clean energy with huge reserves, and the saturation (volume percentage of hydrate in pore space of sediments) is the key parameter for determining whether the reservoir is worthy of exploitation. In this work, rapid hydrate dissociation by the combination of heat injection and NaCl inhibitor addition was studied, and an on-site evaluation method for hydrate saturation in sediment samples was proposed by using a core sampler to transfer hydrate samples under pressure. The results showed that the average gas production rate per unit volume was increased significantly to reach 7.22 L/Lr·min-1 by the injection of NaCl aqueous solution with 50.9 °C, which was attributed to the increase of the chemical potential to further accelerate the rate of hydrate dissociation in the presence of NaCl. Furthermore, for the measurement of methane hydrate samples saturation with a volume of 673 cm3 (which contained 1.4 mol hydrates with the saturation of 58%), hydrate saturation could be accurately achieved within 30 min with a relative error lower than 11.7% This work may provide new thoughts for on-site saturation evaluation and rapid dissociation of hydrate samples during natural gas hydrate exploitation.

Methane hydrate is a crystalline compound with methane molecules as guest species trapped in host water cages. In this study, we detected methane hydrate with water cages doped by (C

sH hydrate is a kind of hydrate that is consisted of only organic large molecule and water. Since each organic large molecule can bring five small cages that easily capture hydrogen molecules, sH hydrate is potential hydrogen storage material. In this paper, methylcyclohexane-hydrogen hydrate was used for hydrogen storage. Two different processes, the simultaneous formation and the induced formation, were studied by molecular dynamics simulation. The simultaneous formations of methylcyclohexane-hydrogen binary hydrate were simulated at 230 K & 110 MPa and the hydrogen storage capacity of binary hydrate was 1.08 wt%. The induced formation of methylcyclohexane-hydrogen binary hydrate was simulated at 240–260 K &20–110 MPa.The simulation results showed that hydrogen storage capacity of hydrate was mainly affected by temperature. The hydrogen storage capacity of hydrates was low (≤1.0 wt%) at 250–260 K even the pressure increased to 110 MPa. While the hydrogen storage capacity was greatly improved (≥1.6 wt%) at 240 K. At 250–260 K, hydrogen molecules only entered the cavities that were near the interface, which seems that 512 cages layers obstructed the hydrogen molecules. The results indicated that the induced hydrogen formation required milder conditions than the simultaneously hydrogen storage formation, and the hydrogen storage was higher.

Natural gas hydrate (NGH) is one of the most potential alternative energy sources in the future due to its huge reserves. Economic, efficient, and safe exploitation of hydrate reservoirs is key to ...

Research on gas hydrates is relevant to many industrial issues including flow assurance in oil and gas production and transportation, exploitation of new energy deposits in the form of natural gas ...

Effective water removal from bio-oil is very important for upgrading bio-oil quality via esterification because water strongly inhibits the conversion and simultaneously lowers the heating value. In the present study, ZSM-5 zeolite membranes are applied to make bio-oil pervaporation dehydration more efficient. An investigation of the permeation performance demonstrated that water mainly permeated through ZSM-5 membranes via intercrystalline pores, whereas intracrystalline pores in the membrane were almost completely blocked because of intensive membrane fouling. The above result showed that tuning water transport paths was significantly important when designing high-performance ZSM-5 membranes for bio-oil pervaporation. A decrease in membrane fabrication time successfully created loose membrane structures with abundant intercrystalline pores and resulted in highly selective and stable ZSM-5 membranes with significantly improved permeation flux in bio-oil dehydration. These robust ZSM-5 membranes show great potential for bio-oil refining in industrial applications.

To provide evidence for hydrate occurrence states in marine sediments, cyclopentane (CP) hydrate crystal growth at interfaces of water–CP, water–silica–CP, and water–kaolin–CP was observed through ...

Hydrate plugging is one of the major risks for oil and gas transportation in pipelines. To mitigate the adhesion between hydrate particles and pipeline walls, hexagonal boron nitride (HBN), polydim...

Natural gas hydrates attract worldwide attention for extensive reserve. Current exploitation methods of thermal stimulation, depressurization and inhibitor injection consume much energy, inducing f...

Hydrogen storage in clathrate hydrates is a promising approach for industry-scale utilizations. However, extreme operation conditions such as high pressure (about GPa) limit the development. In this work hydrogen hydrate phase equilibrium in addition of methane, tert-butyl alcohol (tBA), trichloromethane (CHCl3) and 1,1-dichloro-1-fluoroethane (HCFC-141 b) are reported at 6 MPa–20 MPa and 274 K–286 K, which including 21 points in total. Mechanism studies using Raman spectroscopy show that tBA and H2O form metastable hydrate cages via hydrogen bonds, then form stable sII hydrates with the help of CH4. Hydrate-based hydrogen storage capacity in 5.6 mol%HCFC-141 b-water mixture could reach 46 V/V (0.36 wt%) at 273 K and 10 MPa. Combing with chemical energy of HCFC-141 b, this work achieved high capacity of hydrogen and chemical energy storage in gas hydrate at mild conditions. This study will provide guidance on hydrate-chemical hybrid hydrogen storage technology, and leads to the next generation of hybrid hydrate-based hydrogen technology in the future.

In this work, binary gas mixtures of 92 mol % CH4/CO2 and ternary gas mixtures of 87 mol % CH4/5 mol % C2H6/CO2 were studied as simulate associated petroleum gas. It mainly consists of two parts: o...

During the development and application of natural gas, hydrate plugging the pipelines is a very important issue to solve. Currently, adding thermodynamic hydrate inhibitors (THIs) and kinetic hydrate inhibitors (KHIs) in gas-dominated pipelines is a main way to prevent hydrate plugging of flow lines. This paper mainly reviews the efforts to develop THIs and KHIs in the past 20 years, compare the role of various THIs, such as methanol, ethylene glycol and electrolyte, and give the tips in using. The direction of KHIs is toward high efficiency, low toxicity, low pollution and low cost. More than a hundred inhibitors, including polymers, natural products and ionic liquids, have been synthesized in the past decade. Some of them have better performance than the current commercial KHIs. However, there are still few problems, such as the complex synthesis process, high cost and low solubility, impeding the commercialization of these inhibitors. The review also summarized some application of KHIs in China. Research of KHIs in China began late. There are no KHIs used in gas pipelines. Only a few field tests have been carried out. In the end of this paper, the field test of self-developed KHIs by China is summarized, and the guidance is given according to the application results.

To provide an evidence of natural gas hydrate occurrence state, a series of experiments on multiple growth and dissociation of 90.0% methane/10.0% propane hydrates at 1.3 MPa and 270.15 K were carried out in two sediments for morphology observation via a visible jacketed-reactor. The gas hydrate crystals were observed to form and grow on the surface of sediments at the initial growth. During the thermal decomposition, gas and liquid products had an unceasingly impact on the sediments, then gas/liquid–solid migration occurred, and a large number of cavitation appeared. In the later growth and dissociation experiments, the gas hydrate particles were in suspension or supporting states in the interstitial pore space between the sediment particles, indicating that the gas hydrate displayed a pore-filling characteristics. Through analyzing the distribution of gas hydrates and bubbles, it was found that the amount of gas hydrates distributed in the sediments was improved with multiple growth-dissociation cycle proceedings. Gas migration enhanced the sediment movement, which led to the appearance of the increasing quantity of gas bubbles in the sediments during cycles. Salts affected the growth of the gas hydrates and the migration of sediment grains, which also restricted the accumulation of gas bubbles in the sediments. According to the Raman analysis, the results showed that sII hydrates were formed for CH4 and C3H8 gas mixtures in different sediments and solutions with hydration number of 5.84–6.53. The Salt restricted the access of gas into the hydrate cages.

A novel MnOx-deposited paper-like stainless steel fibers entrapped activated carbon catalyst (Mn-GAC/PSSF) was synthesized by papermaking technology and incipient wetness impregnation (IM) method for methyl ethyl ketone (MEK) combustion, and Mn-deposited granular activated carbon catalyst (Mn-GAC) was prepared simultaneously as a contrast. Characterization of all the samples were carried out by using X-ray diffraction patterns (XRD), N2 adsorption-desorption, scanning electron microscopy (SEM), H2-Temperature programmed reduction (TPR) and X-ray photoelectron spectra (XPS). SEM showed that the Mn oxides on the carbons were relatively well distributed as that on the stainless steel fibers. XPS indicated that the Mn coexisted as Mn3+ and Mn4+. The catalytic activity test for MEK combustion was carried out at atmospheric pressure in a continuous fixed bed stainless steel tube reactor, the results revealed that the Mn-GAC/PSSF catalysts were much more active than Mn-GAC catalyst due to the properties of excellent mass transfer and contacting efficiency offered by PSSF structure, and exhibited high selectivity for complete oxidation of intermediates. Catalyst with higher Mn loading presented higher catalyst activity, the conversion of MEK reached to 90% at 521 K over the 30%-Mn-GAC/PSSF catalysts, while it was 566 K and 530 K over the 10%-Mn-GAC/PSSF catalyst and 20%-Mn-GAC catalyst, respectively.

Accurate knowledge of hydrate phase equilibria is of fundament in terms of the hydrate-based gas separation process (HBGS) for post-combustion CO2 capture. In this work, we experimentally investigated the phase equilibria of flue gas during hydrate-based CO2 capture. Additionally, new experimental data for dissociation pressure of flue gases with different CO2 concentration were reported. Subsequently, a more accurate thermodynamic model combining Cubic-Plus-Association Equation of State (CPA-EoS) and Chen-Guo model was employed to predict the dissociation pressure of flue gases. To better perform the hydrate equilibria, a temperature dependent binary interaction parameter kij and new parameters for Chen-Guo model were developed. The results showed that the general tender of the new experimental data was in line with previous results. In addition, an improved accuracy was noticed for the mixtures with an Average Absolution Deviation (AAD) approximately to 4.07%, through comparing the predicted results with the experimental data. Especially, in terms of the gases with a CO2 concentration less than 85.32%, the improvement was significant. Lastly, this work also utilized the thermodynamic model and the Clausius-Clapeyron equation to predict the dissociation enthalpies of CO2 hydrate. The results showed that the prediction results were located in the margin of experimental data, which demonstrated the thermodynamic model proposed in our work was capable of describing the gas hydrate behavior with high accuracy.

The kinetics of tetra-n-butylammonium bromide (TBAB) hydrate formation orientated within the space of a small dimensional tube is investigated through microscopic experiments in the temperature range of −5.5 to −9.7 °C. Based on the experimental data, a kinetic model in a small dimensional space is proposed to describe the formation process. Hydrate crystals are observed uniformly growing in the small dimensional space. The experimental results show that the nucleation time of TBAB hydrate increases from 9 to 25 min and the linear growth rate decreases from 16.36 to 9.66 μm/s with the increasing temperature. Crystal morphologies show that the tube wall has less effect on the inner crystal growth when the temperature is lower. Furthermore, the number of nucleation sites increases under even lower temperatures. The varying degree of brightness of the crystals indicates that there is a variation of facets of hydrate crystals formed at different temperatures. Hydrate crystals under lower temperatures exhibit more growth points, and the linear growth rate of crystals in a tube is larger than that in the bulk because of heat-transfer effects. A negative activation energy during hydrate formation in this study is obtained according to the kinetic equation to be −58.27 kJ/mol.

Molecular dynamics simulation was employed to examine the growth and dissociation process of methane hydrate in the presence of static/oscillation electric fields at T = 260 K and P = 100 bars. The intensity of electric field was in range of 1.0–2.0 v/nm, and the frequency of applied e/m field was in range of 2.45 GHz–1.0 THz. Electric field would be a factor controlling the hydrate growth and dissociation because the migration of water molecules may be affected. Total energy of simulation system, final system configurations, hydrate-like methane numbers, radial distribution functions, H-bond numbers with simulation time, and dipole moment were analyzed. There is intensity threshold for e-field to exert an effect on methane hydrate. Static electric fields above the intensity threshold (1.5 v/nm) could push hydrate dissociation by inducing the arrangement of water molecules along the field. Cosine oscillation electric fields could promote both methane hydrate growth and dissociation, and there are different critical field magnitudes for different frequency e-fields to play positive roles in methane hydrate growth or dissociation. In order to promote methane hydrate dissociation, higher the e-field magnitude will need as the e-field frequency is higher.

Formation of gas hydrate cause a lot of problems for gas industry in the generation, transmission and processing which caused blockage in the equipment. One of the most common treatments is injection of electrolytes as chemical inhibitors. In this paper, hydrate formation conditions of methane gas in both water and NaCl, CaCl2, MgCl2 electrolyte solutions were measured and a new thermodynamic calculation method based on the original PR model and Chen-Guo model was proposed by introducing a water activity calculation equation. The comparison demonstrates that the inhibiting effect of MgCl2, NaCl, CaCl2 on the hydrate formation decrease respectively. The experimental results showed that the hydrate formation conditions are related to the electrolyte molecular mass and electrolyte concentration to a large extent, the deviation will increase as the temperature or the electrolyte concentration increases, so three parameters t1, t2, t3 (0.034, 0.15, 0.01) which are related to temperature, concentration and molecular weight of electrolyte are introduced in the new calculation method. The absolute average deviation of 41 sets of data is 7.98 and 1.96 respectively before and after the correction parameters were introduced, the accuracy has more than quadrupled.

To simulate the process of hydrate-based gas separation for post-combustion CO2 capture in non-equilibrium situation, the operational pressure of hydration reaction should be specified firstly, which was depending on the dissociation pressure and the driving force. As the main effect factor of dissociation pressure, the mole fraction of water L/(L+V) in the feed should be predicted in priori. And then the driving force could be sequentially determined based on the systematic analyses. In this work, a new computational method to predict L/(L+V) was proposed. Then based on the thermodynamic model, proposed in our previous work, CPA-SRK + Chen-Guo model, and the three-phase isothermal flash calculation method, we simulated the non-equilibrium stage hydrate-based gas separation technology (for the flue gas containing 17% CO2 and 83% N2 at the condition of 277K) with stage-by-stage calculation. For each stage, the optimized operational pressure of each stage was specified in advance, and then the rate as well as the composition of the main flows were subsequently calculated with flash calculation. Based on the obtained results, it was suggested that four stages of hydration reactions were necessary to obtain a 90% CO2 purity. Furthermore, the performances concerning on split fractions and separation factors were also assessed.

Achieving rapid and high gas storage is the primary goal of solidified natural gas storage (SNG) using hydrate. In this study, the formation and decomposition process of hydrate were visualized on the fluorinated graphite (FG) layer for the first time by sapphire visible vessel. The results show that, the addition of FG alone can promote the formation of hydrate. After adding fluorinated graphite into SDS system, the gas storage capacity can be further increased to 165.2 cm3 STP/g H2O, and the average gas storage rate can be further increased to 20.84 cm3·g−1·min−1, which were 154.7% and 507.7% of SDS system, respectively. Meanwhile, the decomposition speed was faster than SDS system. After optimizing the experimental conditions, it was found that FG-1 with superhydrophobicity could stably exist in the gas-liquid interface and cover it when the dosage reached 1wt% (13.95mg·cm−2), and the combination with 300ppm SDS could greatly promote the growth of hydrate. In addition, the excellent stability of FG made the performance of FG + SDS system remain at about 90% after 10 cycles. The unique growth phenomenon of hydrate in fluorinated graphite system was interesting. By building a hydrate formation platform, FG made water pumped from below to the gas phase and hydrate grow upward continuously. In comparison with other reported carbon nanoparticles, FG system maintained similar gas storage and had excellent gas storage speed, which was 1.35∼40.67 times faster under similar conditions. Therefore, the reusable FG+SDS system with high gas storage capacity and fast growth rate without induction time and mechanical agitation was a promising alternative to hydrate-based SNG technology.

Pectin as a novel natural kinetic hydrate inhibitor, expected to be eco-friendly and sufficiently biodegradable, was studied in this paper. The novel crystal growth inhibition (CGI) and standard induction time methods were used to evaluate its effect as hydrate inhibitor. It could successfully inhibit methane hydrate formation at subcooling temperature up to 12.5 °C and dramatically slowed the hydrate crystal growth. The dosage of pectin decreased by 66% and effective time extended 10 times than typical kinetic inhibitor. Besides, its maximum growth rate was no more than 2.0%/h, which was far less than 5.5%/h of growth rate for PVCap at the same dosage. The most prominent feature was that it totally inhibited methane hydrate crystal rapid growth when hydrate crystalline occurred. Moreover, in terms of typical natural inhibitors, the inhibition activity of pectin increased 10.0-fold in induction time and 2.5-fold in subcooling temperature. The extraordinary inhibition activity is closely related to its hydrogen bonding interaction with water molecules and the hydrophilic structure. Finally, the biodegradability and economical efficiency of pectin were also taken into consideration. The results showed the biodegradability improved 75.0% and the cost reduced by more than 73.3% compared to typical commercial kinetic inhibitors.