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There exists a phase change for hydrate dissociation process during which is accompanied by a density difference, that also known as Stefan moving boundary problem. The conduction equations of the heat-dissociation hydrates are derived creatively for a semi-infinite slab reservoir. Based on the Rankine-Hugoniot jump conditions, the moving boundary condition of the dissociation frontier is innovatively deduced from a multidiscipline perspective. Exact solutions are derived in detail for the temperature distribution and the dissociation frontier location. Compared with models of the constant density, laws of the temperature and the frontier location are obtained for a sample hydrate reservoir considering some effect factors, such as various densities, heated-water temperatures and injection times.

Hydrate phase equilibrium conditions of CO2/CH4 + 2-methyl-2-propanol (tBA) + water system, CH4 + 1,1-dichloro-1-fluoroethane (HCFC-141b) + water system, CO2 + HCFC-141b + water system, and CO2/CH4 + HCFC-141b + water system were measured. The moles fraction of CO2 in the mixture gases were 0.33 and 0.5, respectively. The mole fraction of HCFC-141b and tBA were 0.056. The measured temperature range is from 283.0 to 294.2 K. The phase equilibrium conditions were tested by an isochoric pressure-search method. Results showed that HCFC-141b has a stronger promotion effect on CH4 hydrate formation than on CO2 hydrate. The effect of CO2 content on the phase equilibrium conditions of CO2/CH4 mixture + HCFC-141b + water is weak. tBA also acts as a promoter for CO2/CH4 mixture gas. In the presence of tBA, the phase equilibrium conditions of the system with higher CO2 content moved to higher pressure and lower temperature region compared with the system with lower CO2 content.

In this work, the thermal behaviors, kinetic parameters, high pressure properties, and product characteristics of Qi 40 heavy oil in air, nitrogen, carbon dioxide, oxygen-denuded air, and flue gas atmospheres were systematically and comparatively studied by thermogravimetric analysis, kinetic analysis, pressure-volume-temperature test, and stimulation experiments. The thermal decomposition of heavy oil occurred in three major zones. The comprehensive devolatilization indices of heavy oil in nitrogen, carbon dioxide, oxygen-denuded air, air, and flue gas atmospheres were 3.32 × 10−7, 2.94 × 10−7, 2.07 × 10−7, 2.30 × 10−7, and 2.58 × 10−7% K−3 min−2, respectively. The kinetics analysis indicated that, except for zone 2 in oxygen-denuded air, the best kinetic models of three zones were (1 − x)1/3, (1 − x)3/4, and (1 − x), respectively. Pressure-volume-temperature tests displayed that the high pressure properties of heavy oil were mainly influenced by the gas solubility effects at low temperatures, and the heating effects at high temperatures. Moreover, Fourier transform infrared spectra, crude oil group, element, and gas chromatography analysis on products from stimulation experiments of heavy oil all showed that the product characteristics might be influenced by the existence of oxygen in the non-condensable gases. The results of this study provided useful information for potential application of non-condensable gases injection on thermal enhanced oil recovery.

The formation and accumulation of clathrate hydrates in oil/gas pipelines are responsible for flow blockages. How to effectively prevent the blockage of hydrate in the pipeline? Pipeline coating, as a potential new technology, is expected to solve this problem. In the present work, a biomimetic flower like CeO2/pDA@X80 coating was first fabricated using static self-assembly method. The coating exhibited excellent super-hydrophobicity both in air and oil conditions with contact angles of 154.7°, 155.5° and sliding angles of 3°, 2°, respectively. The coating possesses good mechanical stability, which was able to maintain its super-hydrophobicity during 2 h sand abrasion test. The adhesive ability of the CeO2/pDA@X80 coating was satisfied with the requirements of Grade 2, that standing for good adhesion between the coating and substrate. In addition, the hydrate adhesive forces were measured between CeO2/pDA@X80 coating and cyclopentane hydrate by a micromechanical force method. The results suggested that the hydrate adhesion force of CeO2/pDA@X80 coating was about 98.9% below compared with X80. More importantly, the coating can still achieve ultralow hydrate adhesion after 2 h sand abrasion tests. When a liquid water droplet was hanged on the X80 surfaces, the hydrate can be firmly connected with the substrate and failed to be separated, however, the coating can effectively avoid this condition, because the water droplet can easily detach from the superhydrophobic surface. The coating method can provide an alternative choice for preventing hydrate blockages and play a supplementary role in preventing hydrate plugging.

Solidified natural gas storage (SNG) using hydrate can provide environmentally friendly, highly compact and non explosive mode of NG storage at mild storage conditions. The efficient and rapid formation of natural gas hydrate is of great significance to the industrial application of SNG. In this work, in order to improve the gas storage capacity and absorption rate of CH4 hydrate, experiments were carried by adding expanded graphite (EG) with sodium dodecyl sulfate (SDS) with a pressure range of 5.0–8.0 MPa and a temperature of 273.2 K. The results indicate that EG can not only promote the formation of hydrate by promoting the nucleation of hydrate, but also accelerated the growth of hydrate by enhancing hydration heat transfer. EG system (0.05 wt%, 0.08 wt%, and 0.10 wt%) enabled faster hydrate formation than a liquid water system, with a content of 0.08 wt% optimal for the enhancement of hydrate formation. In the combination of EG (0.08 wt%) and SDS solution, EG + 0.03 wt% SDS system can improve the kinetics of hydrate formation to the greatest extent; the maximum gas storage capacity reached 190.4 STP/g H2O, and the maximum gas storage speed reached 20.84 cm3·g−1·min−1 at 273.2 K and 6 MPa. Compared with the SDS system, the maximum methane uptake and rates of EG + 0.03 wt% SDS system increased by 11.90% ~ 26.18% and 15.09% ~ 51.67% under different pressures respectively. At relatively low pressure, the hydrate can achieve a saturation of ~90% in EG + 0.03 wt% SDS system. On the other hand, compared with other carbon materials such as graphite and carbon nanotubes, the gas storage capacity and average gas storage rate of EG system were 1.12–1.37 times and 1.67–30.17 times higher, respectively, under similar temperature and pressure conditions. Therefore, a collaborative mode of enhancing gas concentration, nucleation site and heat transfer efficiency at the gas–liquid interface of hydrate reaction with only one material (EG) was proposed to promote the formation of hydrate. Further study on the promotion mechanism of EG and amplification experiments are expected to provide an effective way for the commercial application of SNG process in future work.

The thermal dissociation process that occurs in a natural gas hydrate is a Stefan phase-change problem with moving boundaries. Based on the integral form of a heat conduction model, for a continuous single-phase hydrate control volume, the energy conservation condition for interfacial coupling during the Stefan phase-change was built for the control volume of thermal dissociation of a natural gas hydrate with a sharp moving boundary. A Neumann solution of the Stefan phase-change model was obtained for the thermal dissociation in a semi-infinite natural gas hydrate reservoir, using Boltzmann similar variables. A unique solution for the Stefan model was found using a monotonic of the transcendental equation. An example analysis was used to verify, the monotonicity of the transcendental equation, and uniqueness of the solution of the Stefan model. The MATLAB program was used to study, the laws of temperature distribution, and dissociation frontal brim during the thermal dissociation process in a hydrate reservoir. Sensitivity fitting studies showed that, the solution of transcendental equation and interface position gradually increased, whereas, the depth penetrated and time penetrated gradually decreases with increasing temperature.

China’s second offshore natural gas hydrate production reveals the urgency and potential demand for ship-based gas storage and transportation technology. Three possible gas storage processes including hydrate-based natural gas (HNG), pressurized liquefied natural gas (PLNG), and compressed natural gas (CNG) processes were simulated and optimized from aspects of specific energy consumption (SPC), exergy efficiency, equipment weight, and capital expenditure (CAPEX) respectively. The SPC of HNG, PLNG, and CNG was 0.22, 0.48, and 0.24 kW h kg−1 respectively. While the CAPEX of HNG, PLNG, and CNG for gas storage production was 363.3, 405.0, and 384.8 103 US Dollars respectively. And HNG showed a payback period of 1 year in the evaluation of natural gas value chain. The comparison results indicate that HNG has low SPC, CAPEX, equipment weight, and short payback period but high exergy efficiency among the three processes, which provides a promising offshore ship-based gas storage process to offshore small-scale natural gas production.

Clathrate hydrates is an ideal host for natural gas, by entrapping CH4 molecules in cage-like structures composed of hydrogen-bonded water molecules, natural gas can be stored in solid form with high density. However, the suppression of hydrate dissociation under moderate thermodynamic conditions is still challenging. In this study, to increase the preservation stability of CH4 hydrate at atmospheric pressure, a new surface-treatment method was proposed by coating CH4 hydrate with CP-CH4 hydrate. CH4 hydrate pellets formed from ice powder or 0.03 wt% Sodium dodecyl sulfate (SDS) solution were mechanically pressurized with CP to form hydrate pellets. The presence of CP-CH4 hydrate layer on the sample surface was confirmed by Raman spectroscopy, and the hydrate pellet was successfully preserved under superheated conditions, i.e., 0.1 MPa − 0.3 MPa, 279 K − 284 K with a storage volume density up to ~146 VCH4 (STP)/Vwater, and the accumulated CH4 loss was less than 0.3 mol% for hydrate pellet formed from ice powder, and 3 mol% for hydrate pellets formed from SDS solution for at least 8 h.

Kinetic hydrate inhibitors (KHIs) combined with thermodynamic inhibitors (THIs) such as monoethylene glycol (MEG) have been good additives for the prevention of hydrate blockages in oil and gas industry operations. The regeneration and recycling of MEG are conventional process steps used to reduce costs. However, the recovery of THIs in the presence of KHIs or the recovery of the KHIs alone has rarely been investigated. In this paper, a series of experiments was designed to study the recovery of both a KHI based poly (N-vinylcaprolactam) and MEG. The results showed that the MEG recovery rate was closely related to the recovery temperature, but was not influenced by the KHI. The MEG recovery rate from solutions consisting of MEG and the KHI was as high as 94.52%, and the KHI was recovered along with the MEG. The polymer structure of the KHI was rarely changed when the recovery temperature was close to its polymerization temperature. The presence of the KHI had a negative impact on the thermodynamic inhibition efficiency of the MEG. The KHI performance of the recovered solution obtained at the KHI polymerization temperature could reach the level of the fresh combination inhibitor, but the recovered solutions obtained at temperatures far above the KHI polymerization temperature demonstrated worse inhibitory performance. The kinetic performance could be restored by adding 5.0 wt% fresh MEG. MEG enabled a subcooling temperature decrease into the range in which KHI which could play its role effectively, leading to the improved kinetic performance of the recovered solution.

It is a safe and environmentally-friendly method to exploit natural gas hydrates (“hydrate”) by using flue gas (mainly including CO 2 and N 2 ) from electric power plants. So far, however, its energy consumption and energy efficiency has not been investigated thoroughly. In this paper, the process to exploit hydrates from flue gas was established. Firstly, flue gas is injected into hydrate reservoirs after it is pressurized. The hydrates in reservoirs partially experience thermal decomposition while the rest is replaced with flue gas, so CH 4 CO 2 N 2 mixture is formed. Secondly, the concentrated CH 4 CO 2 mixture is got after N 2 is separated and removed by using membrane component. And thirdly, the CH 4 CO 2 mixture is delivered to the original electric power plant. This process was simulated by using the software Aspen Plus to analyze the production/injection ratio in the process of flue gas replacement under different injection pressures, the methane replacement ratio, and the energy consumption and energy efficiency in the whole process. It is indicated that the energy in the process of hydrate exploitation from flue gas is mainly consumed at the pressurized injection stage, and the injection pressure increase correspondingly results in the increase of energy consumption at pressurization and membrane separation stages, and to some extent improves the recovery ratio of pressure energy. Besides, when the injection pressure is 5–16 MPa, the production/injection ratio in the process of flue gas replacement is 0.03–0.26, the methane replacement ratio is 19.9–56.2%, the unit energy consumption in the whole process is 2.15–1.05 (kW·h)/kg CH4 , and the energy return on investment ( EROI ) is 7.2–14.7. It is concluded that the energy efficiency of hydrate exploitation from flue gas can be effectively improved by increasing the injection pressure in the range of 5–10 MPa.

The inhibitory performance of glycine and its synergistic potentiality for poly N-vinylcaprolactam (PVCap) was studied by evaluating subcooling temperature, induction time and crystal growth inhibition respectively. Glycine could not inhibit CH 4 hydrate formation alone but it could enhance the inhibitory performance of PVCap. The subcooling temperature of PVCap increased by 4.1 °C and the induction time also increased by 16-fold after blending the glycine with PVCap. Simultaneously, the performance of PVCap inhibiting hydrate crystal growth became more powerful in the presence of glycine. The rapid growth region of PVCap was totally avoided even at 13.5 °C subcooling with the help of glycine, leading crystal growth rate decreasing by 80%. The biggest difference between glycine and common synergists was that 1.0% mass fraction glycine could equivalently replace PVCap in the same amount, leading 40.8% lower cost and 23.4% higher biodegradability. Furthermore, the relationship between outstanding synergistic effect of glycine and its hydrophilic structure was studied.

The replacement method by CO 2 is regarded as a new approach to natural gas hydrate (NGH) exploitation method, by which methane production and carbon dioxide sequestration might be obtained simultaneously. In this study, CO 2 was used to recover CH 4 from hydrate reservoirs at different temperatures and pressures. During the CO 2 CH 4 recovery process, the pressure was selected from 2.1 to 3.4 MPa, and the temperature ranged from 274.2 to 281.2 K. Calculating the fugacity differences between the gas phase and the hydrate phase for CO 2 and CH 4 at different conditions, it has found rising pressure was positive for hydrates formation process that was helpful for the improvement of CH 4 recovery rate. Rising temperature promoted the trend of CH 4 hydrate decomposition for the whole process of CO 2 CH 4 replacement. The highest recovery rate was 46.6 % at 3.4 MPa 281.2 K for CO 2 CH 4 replacement reaction in this work.

In this paper, the three-phase coexistence points are generated for multicomponent gas hydrate in methanol (MeOH) solution for (0.05, 0.10, 0.15, and 0.35) mass fraction and ethylene glycol (EG) solution for (0.05, 0.10, 0.15, 0.35, 0.40 and 0.55) mass fraction. The phase equilibrium curves of different system were obtained by an isochoric pressure-search method on high pressure apparatus. The phase equilibrium regions of multicomponent gas hydrate were measured using the same composition of natural gas distributed in the South China Sea. And the different concentration solutions were prepared based formation water. The experimental data were measured in a wide range temperature from 267.74 to 298.53 K and a wide range pressure from 4.22 MPa to 34.72 MPa. The results showed that the hydrate phase equilibrium curves shifted to the inhibition region in accordance with the increased inhibitor concentration. In addition, the equilibrium temperature would decrease about 2.7 K when the concentration of MeOH increased 0.05 mass fraction. Besides, the suppression temperature was 1.25 K with the 0.05 mass fraction increase of EG concentration in the range of 0.05 mass fraction to 0.15 mass fraction. While in high EG concentration region, the suppression temperature was 3.3 K with the same increase of EG concentration (0.05 mass fraction).

Pretreatment is a vital process for efficient saccharification and utilization of lignocellulose. In this study, crude glycerol derived from biodiesel production was used for pretreatment to facilitate selective saccharification via fast pyrolysis. Due to the efficient removal of alkali and alkaline earth metals (>95.0%) and lignin (79.4%) by crude glycerol pretreatment, the yield of levoglucosan was evaluated to 25.2% as compared to those from pure glycerol pretreated (14.4%) and untreated sugarcane bagasse (8.4%). Meanwhile, the production of inhibitors (e.g. acetic acid, phenol) to biocatalysts was also obviously inhibited from crude glycerol pretreated biomass. Consequently, this work provided a cost-effective and eco-friendly pretreatment mode, which could not only make full utilization of crude glycerol, but also improve the fermentability of lignocellulosic pyrolysate.

“Zeolite-ice” is cavities structure constructed by water molecules that held together by hydrogen-bonds, formed by propane remove from propane hydrate, which structure is similar to zeolite. Hydrogen stored in “Zeolite-ice” is a novel method, which was investigated through experiments and molecular simulations in this paper. Hydrogen storage capacity and the hydrate structures were characterized by Raman spectra. To provide insight into experiments, a series MD simulation had been performed under 250 K–270 K and 30–70 MPa. The results showed that pressure and temperature could influence hydrogen storage performance of propane hydrate. At 270 K, the amount of hydrogen molecules that entered hydrate phase increased with increasing pressure, while hydrogen storage capacity merely fluctuated around 1.0 wt%-1.5 wt% at 260 K and 250 K. Besides, under 60 and 70 MPa, diffusion coefficient of hydrogen molecules at 260 K became relatively low, which led to higher hydrogen capacity than that at 250 K. F4 order parameter analysis and free-energy surface proved that the temperature impacted the stability of cavities of hydrate. This stability caused different motion of hydrogen molecules that doubly occupying large cages. It was feasible to use propane hydrate as a hydrogen storage material and control the pressure and temperature to develop its potential of hydrogen storage.

The dehydration of bio-oil is of great importance for improving its heating value for application as a renewable transportation fuel, and a T-type zeolite membrane was proposed for bio-oil dehydration via pervaporation in the present study. The permeation results show that water could be highly selectively removed via pervaporation from bio-oil, but the membrane was easily fouled in bio-oil due to a complex composition, which led to a rapid decrease in the permeation flux. The flux of the fouled T-type zeolite membrane in bio-oil was effectively regenerated after calcination at 220 °C, and the T-type zeolite membrane showed excellent reusability and chemical stability in the bio-oil system. Insights into the transport behaviors demonstrate that water permeated through the membrane mainly via intercrystalline pores, while most intracrystalline pores were blocked during pervaporation due to the strong adsorption of organic components in the pores, which suggests that tailoring both the amount and size of intercrystalline pores in the membrane is of great significance to effectively enhance the bio-oil dehydration performance.

In this paper, hydrate phase equilibrium data for the CH4/CO2 + water system, CH4 + tetrabutylammonium bromide (TBAB) + water system, CO2 + TBAB + water system, and CH4/CO2 + TBAB + water system were measured at temperature ranged from 273.6 to 294.2 K and pressure ranged from 0.54 to 14.57 MPa with the 1.76 and 14.00 mass fraction of TBAB solutions. The mixture gas hydrate formation equilibrium temperature and pressure were tested by an isochoric pressure-search method. The mixture gas were composed of 67.00 mol % CH4 and 33.00 mol % CO2. The experiment results show that at low TBAB concentration (1.76 wt %), TBAB solution have promote effect under low pressure (lower than 3 MPa), and have nonsignificant promote effect at high pressure. The phase equilibrium conditions for CH4/CO2 mixture gas hydrates with TBAB mainly were determined by the concentration of TBAB solution and did not rely on the concentration of CH4/CO2 mixture gas.

In this study, CO2 capture from (67.00 mol %) CH4/CO2 mixed gas with tetra-n-butylammonium bromide (TBAB) solution at 281.3 K through a pressure recovery of hydrate separation method were studied. During the experiment, pressure was recovered by TBAB solution injected into the cell to improve the separation efficiencies of CO2, and the effects of the concentration of TBAB solution and the operating conditions was investigated. The results showed that the CH4 concentration in the gas phase could achieve 93.52 mol % with a pressure recovery method at 1.14 MPa and 0.293 mol % TBAB. Under the pressure of 1.14 MPa and 0.1 mol % TBAB, the maximum CO2 separation factor was 52.87 and the CH4 separation and recovery factor was 2.050. The results demonstrated that the pressure recovery method can significant enhance the separation efficiency of hydrate separation. It is an effective method to cut down energy consumption of hydrate-based gas separation.

In this study, one flow field was considered for the hydrate bulk, and one-dimensional mass transfer mathematical models, which were included three phases, were built for the heated-water dissociation interface of a natural gas hydrate in porous media, with the aid of the Darcy seepage principle. Numerical solutions for these models were presented, by using the numerical difference method and the linearization method, in conjunction with an iterative scheme. An example model application was presented to carry on researching the sensitive parameters into the hydrate reservoir; and the variation laws were fitted for permeability, saturation and pressure during the dissociation process in the hydrate reservoir. The hydrate permeability was reduced to the hydrate zone value of 12.5 × 10 −9 m 2 with increasing distance; however, with increasing time, the hydrate permeability increased to that of porous media (55 × 10 −9 m 2 ). The hydrate saturation increased to the initial value of 45% with increasing distance, but gradually decreased over time. The water saturation decreased to that of irreducible water (17%) with increasing distance, but increased over time. The hydrate pressure increased with increasing distance, but was slightly lower than the initial value of 3.0 MPa for the boundary effect. The hydrate pressure decreased with increasing time, with a reduction from 24.14% to 21.82%.

Gel-supported surfactant dry solution (GDS) was prepared by mixing gelling agent, sodium dodecyl sulfate (SDS) solution, hydrophobic silica nanoparticles and air in a high speed blender. GDS has the merits of surfactant dry solution (DS) and gel-supported dry water (GDW). The stack of micron-sized GDS droplets provides abundant gas transport channels and large surface area for gas–liquid contacting. Each droplet is a micro system with active surface and gelling structure. Methane storage in clathrate hydrates using GDS was investigated in a stainless steel vessel without stirring under the condition of 5.0 MPa and 273.15 K. The results demonstrated that the dispersed GDS droplets could significantly enhance formation kinetics, storage capacity and storage repeatability of methane hydrate. In addition, GDS exhibited faster storage rate (4.5221 m 3 m −3 min −1 ) and higher storage capacity (152.23 m 3 m −3 ) than GDW. Compared with SDS-DS, GDS has similar storage rate and better storage repeatability (by experiment of 9 cycles), but its storage repeatability slightly became poor and capacity decay occurred due to the agglomeration of droplets after these cycles of hydration/dissociation.

Molecular dynamics simulation was used to examine the growth of methane hydrate in the presence of natural product pectin at different concentrations, including the mass fractions 2.46% and 3.62%. Snapshots of the system configurations with time, radial distribution functions of the carbon atoms, and the total energy of the system were employed to characterize the effect of pectin on methane hydrate growth. Results indicated that pectin is a good inhibitor of methane hydrate. The higher the concentration of pectin is, the better the effect of inhibition is. The double-bonded oxygen atoms of pectin combine with hydrogen atoms of water, and the hydrogen atoms of hydroxyl in pectin combine with oxygen atoms of water through hydrogen bonds, which disturbed the further growth of the methane hydrate. The role of the pectin’s active groups in hydrogen bonds with water both as proton donor and as electron acceptor makes pectin have a better inhibitory effect on the growth of methane hydrate.

In this paper, the gas-hydrate-bearing cores were analyzed for giving a good insight into the exact reserves of natural gas hydrate. The cores were collected from the China National Offshore Oil Corporation (CNOOC) drilling expeditions in 2015 at the LW3-1 area, closed to China's first trial production of natural gas hydrate in 2017. The gas composition of natural gas hydrate and their origin were mainly investigated. The results showed that the gas is mainly methane, up to 98.30%–99.20%. It also contains a small amount of carbon dioxide and other hydrocarbons, which are 0.58%–1.31% CO2, and trace of C2 ~ C4 (less than 0.5%). Gas is generated by mixed-genetic actions dominated by microbial origin. C1 is generated by microbial actions, while C2 is generated by thermogenic actions. Meanwhile, the surface morphology, composition, and distribution of grain size of the host sediments were also studied. The results showed that, the percentage of silty sand is up to 83.57%, where the content of coarse silts is up to 25.12%. There are a preponderance of microfossils and pore structures in the host sediments which consists of silica (SiO2), calcite (CaCO3) and illite, providing a space for the accumulation of gas hydrates. The chloride ion concentration in pore water is 349.09–364.41 mmol/L, which suggested that the hydrate saturation is in a range of 42.81%–45.58% with a good exploitation potential.

Based on the requirement of the new technology to achieve comprehensive utilization of sodium and magnesium resources by using the mother solution from the preparation of potassium salt as raw material, the phase equilibrium data of the quaternary system NH4Cl-MgCl2-NaCl-H2O as well as its ternary subsystems MgCl2-NH4Cl-H2O and NaCl-NH4Cl-H2O were investigated by an isothermal equilibrium method under atmospheric pressure at 348.15 K, and the dry-salt phase diagram and water-phase diagram were drawn. Two invariant points and four crystallization fields including two single salts NH4Cl and NaCl, one hydrate salt MgCl2·6H2O, and one double salt MgCl2·NH4Cl·6H2O were determined in this quaternary system. Combining our results with available experimental data in the literature, an optimized process to produce ammonium carnallite and NaCl was proposed. Using the Pitzer electrolyte solution model, the experimental results were regressed and calculated. The calculated values agree well with the experimental values.

To perform the continuous simulation of CO2/H2 separation by hydrate-based gas separation (HBGS) process, a new multi-phase isothermal flash calculation method, which is more simple, accurate, and easier to converge, has been proposed. In this method an “infinitesimal elements” theory is developed to avoid the non-convergence caused by the improper initial value. Following, the relationship among the main thermodynamic parameters of the system is discussed under equilibrium stage. Then with the flash calculation, the simulation and optimization of the HBGS for 40% CO2 + 60% H2 at 277 K are performed. The results show to obtain a mixture with CO2 more than 90%, three stages of separation are needed. The split fractions are 28.74%, 13.99% and 48.19% in sequence. The separation factors are 29.88, 13.65 and 41.57, respectively. Then the three-stage and two-stage hybrid hydrate-membrane separation processes are proposed. It declares that HBGS may be more suitable for enrichment of CO2 from CO2/H2.

Clathrate hydrate particle cohesion dominates agglomeration of hydrate particles in gas/oil pipelines, and the existence of a capillary bridge between hydrate particles was assumed to be the reason of hydrate particle cohesion. This assumption implied the cohesive force between hydrate particles were radius-dependent but without any experimental validations. The cohesive force between cyclopentane (CP) hydrate particles in liquid CP phase and the cohesive force between CH4/C2H6 gas hydrate particles in the gas phase were measured respectively by using micromechanical force apparatus, and the effects of particle size and annealing time on hydrate particle cohesion in different phases were investigated. The cohesive force between hydrate particles was found independent of particle size in liquid CP phase but was linearly correlated with the effective radius of the hydrate particle pair in the gas phase. Long annealing time decreased cohesive force measured in liquid CP phase but had no significant effect on the cohesion of hydrate particle in the gas phase. A possible mechanism was therefore proposed to interpret hydrate particle cohesion in different phases: The cohesion of hydrate particles in liquid hydrocarbon was dominated by the sintering of asperities, but hydrate particle cohesion in gaseous hydrocarbons was still caused by the existence of capillary bridge.

Based on the requirement of the new technology for producing ammonium carnallite and NaCl via the solution left after the preparation of potassium salt as raw materials, the solubilities of the quaternary system NaCl-MgCl2-NH4Cl-H2O and ternary subsystem NaCl-MgCl2-H2O at 333.15 K were measured using the isothermal dissolution method, and the corresponding phase diagrams were plotted. The phase diagram of the ternary system consists of three fields of crystallization, which correspond to NaCl, MgCl2·6H2O and their co-existing fields respectively. There are four fields of crystallization in the quaternary system, which correspond to MgCl2·6H2O, NH4Cl, NaCl and the double salt MgCl2·NH4Cl·6H2O respectively. By analyzing and calculating the phase diagrams, a technological route was proposed, which indicated that the Na-Mg resources were fully utilized. The extended Pitzer model was applied to the phase equilibrium calculation and the results showed that the calculated data were consistent with experimental values well.

This study experimentally investigated the effects of operation conditions for the CO2 capture from biogas by clathrate hydrate formation. The experiments were tested at 3.0 MPa and 278 K in the present of 5.0 wt % tetra-n-butylammonium bromide (TBAB). In addition, the dissociation enthalpies of CH4/CO2 hydrates in TBAB solution was calculated for energy consumption. The hydrate process simulation with Aspen Plus was carried out at the same experimental conditions to simulate the actual hydrate-based CO2 capture (HBCC), and the energy consumption of this process was analyzed. Experimental results show that the CH4 fraction in the residual gas phase increased with the decrease of gas liquid volume ratio (Rv). Rv decreased from 35.93 to 3.61 while the concentration of CH4 in residual gas increased from 80.5 mol % to 92.76 mol %. The CH4 concentration in residual gas phase was enriched from 67.00 mol% to 97.00 mol% by two stages of HBCC. Process simulation results showed that the energy cost was 1.17 kWh/kg CH4. According to the handing capacity of the feed gas, the energy cost was 0.390 kWh/kg biogas, which was lower than that by chemical absorption method. After adjusting the process parameters and increasing exhaust gas energy recovery, the energy consumption was reduced to 0.357 kWh/kg biogas. The energy consumption could be decreased to 0.204–0.223 kWh/kg biogas by using static hydration enhancement technology.

The study concerned the thermal oxidative degradation kinetics of agricultural residues, peanut shell (PS) and sunflower shell (SS). The thermal behaviors were evaluated via thermogravimetric analysis and the kinetic parameters were determined by using distributed activation energy model (DAEM) and global kinetic model (GKM). Results showed that thermal oxidative decomposition of two samples processed in three zones; the ignition, burnout, and comprehensive combustibility between two agricultural residues were of great difference; and the combustion performance could be improved by boosting heating rate. The activation energy ranges calculated by the DAEM for the thermal oxidative degradation of PS and SS were 88.94–145.30 kJ mol−1 and 94.86–169.18 kJ mol−1, respectively. The activation energy obtained by the GKM for the oxidative decomposition of hemicellulose and cellulose was obviously lower than that for the lignin oxidation at identical heating rate. To some degree, the determined kinetic parameters could acceptably simulate experimental data.

Hydrate plugs are one of the highest risks for gas and oil transportation in pipelines, especially in deep sea environments. In a newly built-up loop, pilot-scale experiments were carried out to study typical hydrate plug phenomena and to explore the specific reasons behind these. A tetrahydrofuran (THF) hydrate slurry was formed and investigated in this loop fluid at two liquid loadings (50 vol% and 100 vol%) with/without a typical anti-agglomerant, KL-1. Morphology and temperature variations revealed that THF hydrate slurry evolution had four stages: (a) flowable fluid; (b) particle formation; (c) agglomeration; and (d) plug. The effect of liquid loading (LL) and an anti-agglomerant (AA) on morphology and temperature in three cases were studied. The morphologies in each stage were compared for the three cases. Hydrate conversion was calculated according to the liquid and solid volume proportion in these morphologies. From these morphologies, heterogeneous hydrate deposition was found to be more likely to happen in 50 vol% than in the 100 vol% LL system. The hydrate plug was also found to be induced by hydrate deposition rather than the bed at the bottom of the pipeline. By dispersing hydrate particle agglomeration, AA compressed hydrate deposition and the plug.

This paper presents mathematical models for radial, quasi-steady state heat transfer in a semi-infinite hydrate reservoir with a moving boundary that is related to the dissociation of natural gas hydrates. The exact solutions of the temperature in the dissociation zone and hydrate zone, using the Paterson exponential integral function, are obtained, and the dissociation frontal brim location of the hydrates is determined by combining the Deaton method with the Clausius–Claperyron equation. A sample calculation shows that the reservoir temperature falls sharply to the dissociation temperature and then drops gradually with increasing distance to the reservoir temperature. With respect to time, the temperature increases slowly to the dissociation temperature, after which, the dissociation temperature falls sharply to the temperature close to that of the injected hot-water. By increasing the temperature of injected hot-water, more hydrates participate in dissociation; with an increase in time, the radius quickly increases, but the radius of hydrate dissociation increases slowly.

Within the oil and gas industry, low-dosage hydrate inhibitors (LDHIs) are a proven technology to control hydrates. Besides hydrate inhibitors, wax inhibitors (WIs) are frequently injected to prevent wax buildup in the crude oil pipeline. However, little attention has been focused on the effect of wax inhibitors on the performance of LDHIs. In this study, performance tests of 3 LDHIs in the presence of wax inhibitors were carried out for a 67% CH4/33% CO2 gas hydrate formation. Using the isothermal cooling method at pressures of 9 MPa and temperatures of 4 °C (subcooling is 9 °C), the results showed that the induction time of CH4-CO2 gas hydrate formation with LDHI/WI was shorter than the system with only LDHI. During the growth period, when the concentration of the WIs was 1 mass%, the growth time of the system with LDHI/WI was prolonged. Taking the induction time and the growth time into consideration, it was found that WIs had a more negative impact on the kinetic hydrate inhibitor performance at low dosage. The effect of WIs at high concentration could be negligible.

Gas hydrates now are expected to be one of the most important future unconventional energy resources. In this paper, researches on gas hydrate exploitation in laboratory and field were reviewed and discussed from the aspects of energy efficiency. Different exploiting methods and different types of hydrate reservoir were selected to study their effects on energy efficiencies. Both laboratory studies and field tests have shown that the improved technologies can help to increase efficiency for gas hydrate exploitation. And it also showed the trend that gas hydrate exploitation started to change from permafrost to marine. Energy efficiency ratio (EER) and energy return on energy invested (EROI) were introduced as an indicator of efficiency for natural gas hydrate exploitation. An energy-efficient hydrate production process, called “Hydrate Chain Energy System (HCES)”, including treatment of flue gas, replacement of CH4 with CO2, separation of CO2 from CH4, and storage and transportation of CH4 in hydrate form, was proposed for future natural gas hydrate exploitation. In the meanwhile, some problems, such as mechanism of CO2 replacement, mechanism of CO2 separation, CH4 storage and transportation are also needed to be solved for increasing the energy efficiency of gas hydrate exploitation.

The separation of CO2 by clathrate hydrate formation was considered to be a promising and economically feasible technology compared with the traditional techniques. In this work, we investigated the effect of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4) on the separation of CO2 from a 33 mol % CO2/67.0 mol % CH4 gas mixture based on hydrate formation in 0.05 mass fraction tetra-n-butylammonium bromide (TBAB) aqueous solution. The influence of both the [BMIm]BF4 concentration and the operating conditions on the gas separation by hydrate formation was studied. The results showed that the content of methane in the residual gas increased and the time required to reach balance was significantly shortened when the two additives were used in combination. The highest CH4 concentration in the residual gas phase was 84.0%, obtained in TBAB solution with 1200 ppm [BMIm]BF4 at 278 K and 3 MPa by one-stage hydrate separation. The maximum CO2 separation factor of 10.3 was obtained in TBAB solution with 120...

The thermal conversion characteristics, kinetics, and thermodynamics of agricultural residues, rape straw (RS) and wheat bran (WB), were investigated under non-isothermal conditions. TGA experiments showed that the pyrolysis characteristics of RS were quite different from those of WB. As reflected by the comprehensive devolatilization index, when the heating rate increased from 10 to 30Kmin-1, the pyrolysis performance of RS and WB were improved 5.27 and 5.96 times, respectively. The kinetic triplets of the main pyrolysis process of agricultural residues were calculated by the Starink method and the integral master-plots method. Kinetic analysis results indicated that the most potential kinetic models for the pyrolysis of RS and WB were D2 and F2.7, respectively. The thermodynamic parameters (ΔH, ΔG, and ΔS) were determined by the activated complex theory. The positive ΔH, positive ΔG, and negative ΔS at characteristic temperatures validated that the pyrolysis of agricultural residues was endothermic and non-spontaneous.

We first measured the hydrate equilibrium of two real gases from the South China Sea in the pressure range of 1.85 MPa to 9.32 MPa. Then, three kinetic hydrate inhibitors (poly(N-vinyl) pyrrolidone, Inhibex501, and synthesized KHI-HY4) were tested from 275.15 K to 283.15 K and the pressure range from 2 MPa to10 MPa in the case of two real gases under 11.6 K to 14.0 K subcooling. The results show that the maximum subcooling temperature of three hydrate inhibitors increased with the increase of the pressure for the real gases, and hydrate formation induction time increased more than 1.5 times with the inhibitor concentration decreasing for HY4 or Inhibex501 for the real gases at a certain subcooling range. It was believed that each inhibitor has its optimal subcooling for usage in real gas. When the subcooling reached the optimal value, remarkable inhibitory performance could be displayed.

Class 3 hydrate reservoirs exploiting using horizontal well by depressurization and thermal co-stimulation was simulated using the HydarteResSim code. Results showed that more than 20% of hydrates in the reservoirs had been dissociated within 450 days at the well temperature of 42 °C and well pressure of 0.1P 0 , 0.2P 0 (P 0 is the initial pressure of the reservoirs, simplifying 42 °C & 0.1P 0 , 42 °C & 0.2P 0 ). While the production behavior of 42 °C & 0.5P 0 , 42 °C & 0.8P 0 were not so exciting. In order to understand the production character of the well in long term, the cross section of 1 m length reservoirs was simulated. Simulation results showed that 4.5 × 10 5 m 3 gas would be collected within 4500 days and 1.1 × 10 6 kg water could be produced within 1500 days in the well at 42 °C & 0.1P 0 . 3.5 × 10 5 m 3 gas would be collected within 8500 days and 1.1 × 10 6 kg water could be produced within 1500 days in the well at 42 °C & 0.2P 0 . The heat flow was 1620 W at the beginning and then decreased rapidly in the two cases. For reservoirs of 1495.2 m in length, about 6.7 × 10 8 m 3 and 5.3 × 10 8 m 3 gas would be collected in the well corresponding to conditions of 42 °C & 0.1P 0 , and 42 °C & 0.2P 0 .

In this study, mechanical force applied to squeeze poly(sodium acrylate-co-2-hydroxyethyl methacrylate) hydrogels that contained seawater in order to obtain fresh water. By incorporating ionic monomer sodium acrylate (SA) into hydrogels, the salt rejection was significantly enhanced from 27.62% to 64.57% (feed concentration 35.00g/L NaCl solution). As SA's concentration continuously increased, salt rejection declined due to the change in hydrogel's matrix structure. Therefore, water recovery raised as the current swelling degree increased. We also measured pore size distribution by applying mercury intrusion porosimetry on each hydrogel sample in the interest of finding out whether the sample SA5/HEMA15 owned multi pore structure, since the result could be good for the desalination performance. After 4 times reused, the hydrogel remained good desalination performance. Although compared to reverse osmosis (RO) and multistage flash distillation (MSF)multiple effect distillation (MED) the salt rejection of this hydrogel (roughly 64%) seemed low, the hydrogels can be used for forward osmosis and reverse osmosis, as pretreatment of seawater to reduce the energy consumption for the downstream.

In this paper, hydrate phase equilibrium data for the CO2/CH4 + water system, CO2/CH4 + tetrabutylammonium bromide (TBAB) + water system, CO2/CH4 + tetrabutylammonium chloride (TBAC) + water system, and CO2/CH4 + tetrabutylammonium fluoride (TBAF) + water system were measured at temperatures from 280.2 K to 291.3 K and pressures from 0.61 MPa to 9.45 MPa with the 2.93·10–3 mole fraction of tetrabutylammonium halide. The equilibrium hydrate formation conditions were measured by an isochoric pressure-search method. The mole fractions of the mixture gas used in this work were 0.33 CO2 and 0.67 CH4. The experimental data for the CH4 + water system were contrasted with the published equilibrium data in the literature. Both have a good consistency, which demonstrates that the experimental method and the apparatus used in this paper are feasible and reliable. The experiment results show that the hydrate stable region was enlarged by adding TBAB, TBAC, or TBAF. Among the three additives, TBAF is the best and the ...

The permeation of hydrogen through palladium membranes can be described by Sieverts' law. In a membrane separator, hydrogen flow rates and partial pressures may vary along the flow directions on both sides of the separator. Sieverts' law itself cannot be directly used for the design of membrane separators. Seven flow scenarios are considered in which the flow pattern, flow direction and the existence of a sweep gas in a membrane separator are considered. Maximum potential hydrogen production rates are obtained. The relationship between the hydrogen production rate and the membrane permeation capacity is derived. A procedure is recommended for the design of membrane separators, and a typical design case is presented. Concepts of economical permeation capacity and hydrogen production rate are proposed and defined.

Morphology and growth of hydrate crystals with cyclic structure inhibitors at a hydrate–liquid interface were directly observed through a microscopic manipulating apparatus. Tetrahydrofuran (THF) hydrate was employed as an objective. The effects of four kind of cyclic structure inhibitors, polyvinylpyrrolidone (PVP), poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine) (PVPP), poly(2-vinyl pyridine-co-N-vinylcaprolactam) (PVPC) and poly(N-vinylcaprolactam) (PVCap), were investigated. Morphological patterns between each hydrate crystal growth from hydrate–liquid interface into droplet were found differ significantly. Lamellar structure growth of hydrate crystal was observed without inhibitor, while with PVP was featheriness-like, PVPP was like long dendritic crystal, PVPC was Mimosa pudica leaf-like and PVCap was like weeds. The growth rate of hydrate crystal without inhibitor was 0.00498 mm 3 /s, while with PVPP, PVPC and PVCap, were 0.00339 mm 3 /s, 0.00350 mm 3 /s, 0.00386 mm 3 /s and 0.00426 mm 3 /s, respectively. Cyclic structure inhibitors can decrease the growth rate, degree of reduction in growth rate of hydrate crystals decrease with the increase of cylinder number.

Coal bed methane (CBM) has a huge potential to be purified to relieve the shortage of natural gas meanwhile to weaken the greenhouse effect. This paper proposed an optimal design strategy for CBM to obtain an integrated process configuration consisting of three each single separation units, membrane, pressure swing absorption, and cryogenics. A superstructure model was established including all possible network configurations which were solved by MINLP. The design strategy optimized the separation unit configuration and operating conditions to satisfy the target of minimum total annual process cost. An example was presented for the separation of CH 4 /N 2 mixtures in coal bed methane (CBM) treatment. The key operation parameters were also studied and they showed the influence to process configurations.

CO2 capture by hydrate formation is a novel gas separation technology, by which CO2 is selectively engaged in the cages of hydrate and is separated with other gases, based on the differences of phase equilibrium for CO2 and other gases. However, rigorous temperature and pressure, high energy cost and industrialized hydration separator dragged the development of the hydrate based CO2 capture. In this paper, the key problems in CO2 capture from the different sources such as shifted synthesis gas, flue gas and sour natural gas or biogas were analyzed. For shifted synthesis gas and flue gas, its high energy consumption is the barrier, and for the sour natural gas or biogas (CO2/CH4 system), the bottleneck is how to enhance the selectivity of CO2 hydration. For these gases, scale-up is the main difficulty. Also, this paper explored the possibility of separating different gases by selective hydrate formation and reviewed the progress of CO2 separation from shifted synthesis gas, flue gas and sour natural gas or biogas.

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.

Shenzhen is a typical city of southern China. The current situation of natural gas utilization in Shenzhen is introduced. The experience of world energy consumption, especially the development trends of natural gas is reviewed. According to the characteristics of the economic development trends and the energy utilization planning in Shenzhen, the development prospect of natural gas utilization in Shenzhen is comprehensively analyzed. After the analysis, it is pointed out that natural gas will be a vital new source of energy utilization in Shenzhen. In the meanwhile, the problems and solution of interchangeability, price and alternate energy source in the natural gas development trend in Shenzhen are discussed. The results of the current study can be used as guidelines for the natural gas utilization and CO 2 emission reduction in other cities of southern China. Copyright , Oxford University Press.

Substantial oxygen enrichment is observed in the natural air hydrates formed in Arctic and Antarctic ice sheets. Inspired by this phenomenon, a novel air separation method, utilizing hydrate crystallization, is proposed in our work. The three-phase equilibrium pressure for the air + water system is greater than 15 MPa as the temperature is upon ice point, which makes the air separation impractical by hydrate formation under mild temperature conditions. So, some additives were selected to reduce the phase equilibrium pressure of air hydrates at a fixed temperature. In this work, hydrate dissociation conditions for the air + tetrahydrofuran (THF) + water system (x = 0.0300 and 0.0500), the air + cyclopentane (CP) + water system (x = 0.0300 and 0.0556), and the air + tetra-n-butyl ammonium bromide (TBAB) + water system (w = 0.20 and 0.30) were measured in the temperature ranges of (279.7 to 290.5) K, (284.0 to 296.2) K, and (283.4 to 288.0) K, respectively. The comparison result shows that, in the pressure r...

In oil and gas field, the application of kinetic hydrate inhibitors (KHIs) independently has remained problematic in high subcooling and high water-cut situation. One feasible method to resolve this problem is the combined use of KHIs and some synergists, which would enhance KHIs' inhibitory effect on both hydrate nucleation and hydrate crystal growth. In this study, a novel kind of KHI copolymer poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine)s (HGs) is used in conjunction with TBAB to show its high performance on hydrate inhibition. The performance of HGs with different monomer ratios in structure II tetrahydrofuran (THF) hydrate is investigated using kinetic hydrate inhibitor evaluation apparatus by step-cooling method and isothermal cooling method. With the combined gas hydrate inhibitor at the concentration of 1.0 wt%, the induction time of 19 wt% THF solution could be prolonged to 8.5 h at a high subcooling of 6 °C. Finally, the mechanism of HGs inhibiting the formation of gas hydrate is proposed.

In oil and gas exploration and transportation, low dosage hydrate inhibitors (LDHIs) are more favorably utilized to inhibit the formation of hydrates than thermodynamic inhibitors (THs) as a trend. However, there are no industrial products of LDHIs available domestically, and the corresponding application experience is in urgent need. In this paper, a combined hydrate inhibitor (HY-1) was synthesized after a series of reaction condition optimization, and its performance on THF hydrate inhibition was investigated using kinetic hydrate inhibitor evaluation apparatus with 6 cells bathing in air. The results show that when the reaction temperature is 60°C, the reaction time is 6 h, and the monomer: solvent ratio is 1:2, the product has the best kinetic hydrate inhibitor performance on THF hydrate. On these bases, the scale-up production of this combined hydrate inhibitor was carried out. Although the scale-up product (HY-10) performs less effectively on the THF hydrate inhibition than HY-1, it functions better than a commercial product (Inhibex501) during in-house tests. HY-10 was successfully applied to the gas production process. Field trials in northern Shaanxi PetroChina Changqing Oilfield Company (PCOC) show that 2 wt% of HY-10 is effective on natural gas hydrate inhibition. It is found through economic analysis that the use of HY-10 has obvious economical advantage over methanol and Inhibex501.

In this work, hydrate phase equilibrium data for oxygen + tetrahydrofuran (THF) + water, nitrogen + THF + water, and air + THF + water systems were measured in the temperature range of (281.84 to 3...