Effect of nanoparticles on the nucleation and agglomeration rates of hydrate growth using THF-water clathrates

Four types of nanoparticles,amorphous carbon,ironⅢoxide,SiO2,and amino-coated SiO2,were tested to determine changes in tetrahydrofuran-water(THF-water)clathrate hydrate nucleation and agglomeration.Rates were experimentally found to determine their viability for preventing natural gas hydrates from developing during offshore drilling operations.THF-water clathrates were chosen as a model to represent gas hydrate growth at atmospheric pressure.Concentrations of each nanoparticle between 0.15%and 1.0%by weight were tested as a kinetic inhibitor to hydrate formation.Tests were repeated at various temperatures below the formation temperature of 4.4℃for THF-water clathrate hydrates.Measurements were made to identify how the concentration of THF affects the clathrate hydrates forming under static conditions between20%and 30%by mole of THF.The primary tests in this study were performed using a 20:80 THF/water ratio.Temperature increases during hydrate nucleation for THF-water were measured between-5 and 3℃.The range of ideal nanoparticle concentrations was found to be between 0.15%and 0.45%by weight for optimal static,kinetic inhibition of hydrate nucleation.At approximately 0.3%by weight,the most significant inhibition was observed under static conditions for all four types of nanoparticles tested.We found that functionalized amino-coated SiO2 nanoparticles,across all tests,significantly increased the time required for the formation of THF-water clathrate hydrates compared to the other three non-functionalized nanoparticles.The amorphous carbon and ironⅢoxide nanoparticles performed similarly across each test and were both the least effective in their inhibition of the clathrate hydrates of the four nanoparticles studied compared to a control.

Electrical Transport Properties of Type-Ⅷ Sn-Based Single-Crystalline Clathrates (Eu/Ba)8Ga16Sn30 Prepared by Ga Flux Method

Single-crystalline samples of Eu/Ba-filled Sn-based type-Ⅷ clathrate are prepared by the Ga flux method with different stoichiometric ratios. The electrical transport properties of the samples are optimized by Eu doping. Results indicate that Eu atoms tend to replace Ba atoms. With the increase of the Eu initial content, the carrier density increases and the carrier mobility decreases, which leads to an increase of the Seebeck coefficient. By contrast, the electrical conductivity decreases. Finally, the sample with Eu initial content of x = 0.75 behaves with excellent electrical properties, which shows a maximal power factor of 1.51 mW·m^-1K^-2 at 480K, and the highest ZT achieved is 0.87 near the temperature of 483K.

Synthesis and high temperature thermoelectric transport properties of Si-based type-Ⅰ clathrates

N-type Si-based type-Ⅰ clathrates with different Ga content were synthesized by combining the solid-state reaction method,melting method and spark plasma sintering （SPS） method.The effects of Ga composition on high temperature thermoelectric transport properties were investigated.The results show that at room temperature,the carrier concentration decreases, while the carrier mobility increases slightly with increasing Ga content.The Seebeck coefficient increases with increasing Ga content. Among all the samples,Ba7.93Ga17.13Si28.72exhibits higher Seebeck coefficient than the others and reaches -135μV·K^-1 at 1000 K.The sample prepared by this method exhibits very high electrical conductivity,and reaches 1.95x 10^5 S·m^-1 for Ba8.01Ga16.61Si28.93 at room temperature.The thermal conductivity of all samples is almost temperature independent in the temperature range of 300-1000 K,indicating the behaviour of a typical metal.The maximum ZT value of 0.75 is obtained at 1000 K for the compound Ba7.93Ga17.13Si28.72.

Sn-based type-VIII single-crystal clathrates with a large figure of merit

Single-crystal samples of type-VIII BasGa16-xCuxSn30 （x = 0, 0.03, 0.06, 0.15） clathrates were prepared using the Sn-flux method. At room temperature the carrier density, n, is 3.5-5 × 10^19 cm^-3 for all the samples, the carrier mobility, μH, increases to more than twice that of BasGa16Sn30 for all the Cu doping samples, and consequently the electrical conductivity is enhanced distinctly from 1.90×10^4 S/m to 4.40 ×10^4 S/m, with the Cu composition increasing from x = 0 to x = 0.15. The Seebeck coefficient,α, decreases slightly with the increases in Cu composition. The values are about 0.72 W/mK at 300 K and are almost invariant with temperature up to 500 K for the samples with x = 0 and x = 0.03. The lattice thermal conductivity, μL, decreases from 0.59 W/InK for x = 0 to 0.50 W/mK for x = 0.03 at 300 K. The figure of merit for x = 0.03 reaches 1.35 at 540 K.

Theoretical Studies on the Thermo- electric Properties of Tin-based Clathrates:Cs_8M_4Sn_(42)(M=Zn,Cd,Hg) and Cs_8Sn_(44)□_2

The site occupancies and thermoelectric properties of tin-based clathrates Cs8M4Sn44□2 （M = Zn, Cd, Hg） and CssSn44□2 were studied by the first principle calculations. We had provided an efficient way to probe the relationship between the crystalline structure and power factor. Detailed analyses indicated the p states of Sn at 16i and 24k sites together with the p states of M substitute contributed significantly to the maximum power factor, yet Cs atoms nearly did not. The dangling bonds of vacancies in Cs8Snn44□2 are also discussed. The power factors of p- and n-type CssMaSn42 and Cs8Sn44□2 at optimal temperature and carder concentration are predicted. Our results suggest that Cs8ZnaSn44□2 is a promising candidate at the 5.25 ×10^19 cm-3 hole carrier concentration as a high temperature thermoelectric material that is competitive to the state-of-art Ge-based clathrate thermoelectric materials.

Thermoelectric properties of In-substituted Ge-based clathrates prepared by HPHT

Bulk materials Ba_(8)Ga_(16)In_(x)Ge_(30-x)(x=0.5,1.0,1.5)were prepared by High-Pressure and High-Temperature(HPHT)method and the crystal structure has been confirmed by X-ray diffraction and cell refinement.The actual In composition was much lower than the starting composition,and lattice constants increased with the increase of substitution.As the temperature increased,the Seebeck coefficient and electrical resistivity increased first and then decreased,while the thermal conductivity was the opposite,which leads to significant enhancement on thermoelectric properties of the clathrates.The substitution of indium elements decreased the seebeck coefficient and electrical resistivity,and also changed the microstructure of the compounds.A minimum thermal conductivity of 0.84Wm^(-1)1K^(-1)was obtained,and a good ZT value of 0.52 was achieved.The grain boundaries and lattice defects generated by high pressure can effectively scatter phonons of different frequencies,which reduce the lattice thermal conductivity.

Synthesis and Characterization of β-Cyclodextrin Modified Biochar Environmental Remediation Materials

In this paper, biochar (BC) was used as raw material, activated by deionizing aqueous solution, NaCl solution, CA solution and HCl solution respectively. Epichlorohydrin (EPI) was used as crosslinking agent, and β-cyclodextrin (β-CD) was used to modify biochar (BC). The prepared modified biochar materials were labeled with β-CDBC, β-CDBC-Na, β-CDBC-CA and β-CDBC-H, respectively. The infrared spectrum, X-ray diffractometer, scanning electron microscope and specific surface area of the four modified materials were tested. The results showed that the C-O stretching vibration peak at 1020 cm−1 of the modified materials was slightly offset compared with that of biochar. The characteristic absorption peaks of XRD pattern decrease obviously at 2θ = 26.7˚ and 29.5˚. It can be obviously observed on the electron microscope image that the surface is loaded or formed clathrates, and BET data and graphs also show that the specific surface area of the modified biochar is larger. Therefore, β-cyclodextrin successfully modified biochar and formed clathrates on the surface of biochar or was loaded in the pore structure of biochar, especially β-CDBC-CA achieved better modification effect. Because biochar and β-cyclodextrin raw materials are cheap, easy to prepare and green, and less prone to secondary pollution, it has a good advantage in environmental governance.

Germanium isotope effect induced guest rattling and cage distortion in clathrates

Intermetallic clathrates are materials characterized by a large cage structure where guest atoms can move anharmonically,providing these materials exotic thermoelectric properties.Unfortunately,the dynamical and atomic nature of the rattling phonons,and their interactions with the electronic structure,are not fully understood.Here,we report that a germanium isotope effect can trigger an inherent guest rattling and cage distortion in clathrate Ba8Ga16Ge30(BGG).Raman-scattering spectroscopy and advanced electron microscopy demonstrate that the atomic germanium isotope effect induces an offcentre rattling at the 6d sites as well as a tetrakaidecahedron deformation which is anisotropic for ntype BGG but isotropic for p-type BGG.The present findings indicate that the large n-type germanium isotope effect arises from the strong electron-phonon coupling,which opens up a novel avenue for manipulating dynamical motions of phonons via atomic isotope engineering.

Formation of the structure-Ⅱgas hydrate from low-concentration propane mixed with methane

It has been recognized that a small amount of propane mixed with methane can change greatly in not only the thermodynamics but also the structural properties of gas hydrate.However,its mechanism is still not well understood yet.In this research,structure-Ⅱ(sⅡ)hydrate is synthesized using a methanepropane gas mixture with an initial mole ratio of 99:1,and it is found that large(5~(12)6~4)cages are cooccupied by multiple gases based on the rigid structure analysis of neutron diffraction data.The first principles calculation and molecular dynamics simulation are conducted to uncover the molecular mechanism for sⅡmethane-propane hydrate formation,revealing that the presence of propane inhibits the formation of structure-Ⅰ(sⅠ)hydrate but promotes sⅡhydrate formation.The results help to understand the accumulation mechanism of natural gas hydrate and benefit to optimize the condition for gas storage and transportation in hydrate form.

Polyphenols Extracted from Enteromorpha clathrata Induce Apoptosis in Hepa1-6 Cell by Activating the Mitochondrial Apoptosis Signaling Pathways

Green alga Enteromorpha clathrata(E.clathrata)contains a variety of bioactive compounds,including polysaccharides,polyphenols and fat-soluble pigments etc.,among which polyphenols exhibit a wide range of medicinal properties.E.clathrata polyphenols(ECPs)have shown various biological activities such as antioxidant,anti-inflammatory and antidiabetic effects;however,the potential of ECPs as an anti-cancer reagent remains unclear.The aim of this study was to investigate the anti-tumor activity and underlying mechanisms of ECPs on hepatocellular carcinoma.The cytotoxicity of Hepa1-6 cells was determined by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)and lactate dehydrogenase(LDH)assay.Flow cytometry and fluorescence microscope analysis of cell apoptosis after annexin V-fluorescein isothiocyanate(FITC)/propidium iodide(PI)staining.2',7'-dichlorodihydrofluorescein diacetate(DCFH-DA)assay was used for intracellular reactive oxygen species(ROS)detection.caspase-9 activity was determined using cspase-9 colorimetric assay.Mitochondrial transmembrane potential(Δψm)was measured using JC-1.Western blot and quantitative real-time PCR(qPCR)were used to assess the expressions of the apoptosis regulators Bax,Bcl-2,cytochrome c and caspase-3.It was found that ECPs showed a dose-dependent cytotoxicity against Hepa1-6 cells by inducing apoptosis.The apoptosis in ECPs-treated Hepa1-6 cells was accompanied by the loss of mitochondrial membrane potential,elevated ROS generation,increased release of mitochondrial cytochrome c,and up-regulation of caspase-9 and caspase-3.The expressions of Bax(pro-apoptotic molecule)and Bcl-2(apoptosis suppressor)were up-regulated and down-regulated,respectively,at both mRNA and protein levels.These molecular alterations revealed that ECPs caused apoptosis of cells through the mitochondrial pathway,suggesting that ECPs are potential candidates to be developed for liver cancer treatment.

Hydrogen diffusion in C′_(1) phase clathrate hydrate

Recently,a new phase C'_(1) H_(2) hydrate was experimentally identified.In this work,the diffusive behaviors of H_(2) in C'_(1)phase clathrate hydrate are explored using classic molecular dynamics(MD)simulations.It reveals that the cage occupancy by H_(2) molecule negligibly influences the C'_(1) phase clathrate structure but greatly dictates the diffusion coefficient of H_(2)molecule.Due to the small cage size and small windows connecting the neighboring cages in C'_(1) phase clathrate,nonoccupancy of the neighboring cages is demanded to enable the diffusion of H_(2) molecule that is primarily dominated by hopping mechanism.Moreover,the analysis of diffusive free energy landscape reveals lower energy barrier of H_(2) molecule in C'_(1) phase clathrate hydrate than that of other gases in conventional clathrate hydrates,and that H_(2) molecule travels through the windows between neighboring cages with preferential molecular orientation.This study provides critical physical insights into the diffusion behaviors of H_(2) in the C'_(1) phase clathrate hydrate,and implies that the C'_(1) clathrate hydrate is a promising solid structure for the next-generation H_(2) storage.

热电材料的最新进展

简要介绍热电效应及利用热电效应实现温差发电和通电制冷的原理. 评估了热电材料的性能因子Z , 热电材料的研究发展过程及近几年的最新研究动向, 给出评价理想热电材料的必要条件及改善性能因子Z的可能途径, 并指出热电材料在绿色能源工程及制冷技术上的广阔应用前景.

可视化技术在分析新型蓄冷材料——笼型化合物(Clathrate)溶解过程中的应用(二)

运用折射率匹配 (Refractive IndexMatching)技术 ,使混浊液内部自然对流的可视化图像速度测量成为可能。但由于来自微粒子的散乱光的影响 ,所得到的速度场出现了少量的误对应现象。为了解决这个问题 ,开发了新的可视化实验组合技术———折射率匹配与激光诱导荧光法 (LIF :Laser InducedFluorescence)组合 ,利用不同种类的粒子发光波长不同的特性 ,有效地去除了微粒子的散乱光 ,获得了清晰的示踪粒子的图像。笔者将简要介绍激光诱导荧光法的工作原理及其实验结果。

可视化技术在分析新型蓄冷材料——笼型化合物(Clathrate)溶解过程中的应用(一)

混浊液内部的流动 ,由于微粒子之间的相互作用以及因浊度高不易进行内部观察 ,所以无论是分析还是可视化实验都相当困难 ,存在着许多未弄清的问题。通过采用折射率匹配 (Refractive IndexMatching)技术 ,使透明的微粒子与透明的溶媒的折射率近乎相同 ,做成一种透明的“混浊液” ,从而使混入其中的示踪粒子的运动轨迹能被摄像机捕捉到 ,并以微粒子的沉降和温度的干涉所引起的流动现象为焦点 ,利用图像速度测量法来处理分析所拍摄到的可视化图像 ,成功地获得了定量的混浊液内部的速度场 ,为进一步揭示混浊液内部自然对流的流动机理提供了实验依据。

Hydrate capture CO_2 from shifted synthesis gas, flue gas and sour natural gas or biogas

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.

Intensification of methane and hydrogen storage inclathrate hydrate and future prospect

Gas hydrate is a new technology for energy gas（methane/hydrogen）storage due to its large capacity of gas storage and safe.But industrial application of hydrate storage process was hindered by someproblems.For methane,the main problems are low formation rateand storage capacity,which can be solved by strengthening mass andheat transfer,such as adding additives,stirring,bubbling,etc.Onekind of additives can change the equilibrium curve to reduce the formation pressure of methane hydrate,and the other kind of additivesis surfactant,which can form micelle with water and increase the interface of water-gas.Dry water has the similar effects on the methanehydrate as surfactant.Additionally,stirring,bubbling,and sprayingcan increase formation rate and storage capacity due to mass transferstrengthened.Inserting internal or external heat exchange also canimprove formation rate because of good heat transfer.For hydrogen,the main difficulties are very high pressure for hydrate formed.Tetrahydrofuran（THF）,tetrabutylammonium bromide（TBAB） andtetrabutylammonium fluoride（TBAF） have been proved to be able todecrease the hydrogen hydrate formation pressure significantly.

Experimental characterization of guest molecular occupancy in clathrate hydrate cages: A review

Study on the microscopic structure of clathrate hydrate has made significant progress in the past decades.This review aims to summarize the state of the art of the experimental characterization of guest molecular occupancy in clathrate hydrate cages,which is an important area of the microscopic structures.The characterizing method and features of different guest molecular,such as hydrocarbon,carbon dioxide,hydrogen and inhibitor/promoter,in different hydrate cages have been extensively reviewed.A comprehensive use of advanced technologies such as X-ray diffraction,Raman spectroscopy and nuclear magnetic resonance may provide better understanding on the compositions and microscopic mechanisms of clathrate hydrate.

THERMAL CONDUCTIVITY OF THF CLATHRATE HYDRATE FROM 243 K TO 263 K

Using transient plane source technique, we measured THF hydrate thermal conductivity from 243 K to 263 K. The sample THF solution is over saturated in order to avoid the effect of ice. And also to avoid the effect of crystal anisotropy, the THF hydrate was crushed to measure. In the test temperature value increases with the temperature increasing.

Insights into kinetic inhibition effects of MEG,PVP,and L-tyrosine aqueous solutions on natural gas hydrate formation

It is necessary to understand all the prerequisites, which result in gas hydrate formation for safe design and control of a variety of processes in petroleum industry. Thermodynamic hydrate inhibitors (THIs) are normally used to preclude gas hydrate formation by shifting hydrate stability region to lower temperatures and higher pressures. Sometimes, it is difficult to avoid hydrate formation and hydrates will form anyway. In this situation, kinetic hydrate inhibitors (KHIs) can be used to postpone formation of gas hydrates by retarding hydrate nucleation and growth rate. In this study, two kinetic parameters including natural gas hydrate formation induction time and the rate of gas consumption were experimentally investigated in the presence of monoethylene glycol (MEG), L-tyrosine, and polyvinylpyrrolidone (PVP) at various concentrations in aqueous solutions. Since hydrate formation is a stochastic phenomenon, the repeatability of each kinetic parameter was evaluated several times and the average values for the hydrate formation induction times and the rates of gas consumption are reported. The results indicate that from the view point of hydrate formation induction time, 2 wt% PVP and 20 wt% MEG aqueous solutions have the highest values and are the best choices. It is also interpreted from the results that from the view point of the rate of gas consumption, 20 wt% MEG aqueous solution yields the lowest value and is the best choice. Finally, it is concluded that the combination of PVP and MEG in an aqueous solution has a simultaneous synergistic impact on natural gas hydrate formation induction time and the rate of gas consumption. Furthermore, a semi-empirical model based on chemical kinetic theory is applied to evaluate the hydrate formation induction time data. A good agreement between the experimental and calculated hydrate formation induction time data is observed.

Accelerated methane storage in clathrate hydrates using surfactantstabilized suspension with graphite nanoparticles

In this study,enhanced kinetics of methane hydrate formation in the sodium dodecyl sulfate(SDS)solution with different concentrations of suspended graphite nanoparticles(GNPs)were investigated at 6.1-9.0 MPa and 274.15 K.The GNPs with rough surfaces and excellent thermal conductivity not only provided a considerable number of microsites for hydrate nucleation but also facilitated the fast hydrate heat transfer in the suspension system.At a relatively low pressure of 6.1 MPa,the suspension with 0.4 wt%of GNPs exhibited the minimum induction time of 22 min and maximum methane uptake of 126.1 cm3·cm-3.However,the methane storage performances of the suspensions with higher and lower concentrations of GNPs were not satisfactory.At the applied pressure,the temperature increase arising from the hydrate heat in the suspension system with the optimized concentration(0.4 wt%)of GNPs was more significant than that in the traditional SDS solution.Furthermore,compared with those of the system without GNPs,enhanced hydration rate and storage capacity were achieved in the suspensions with GNPs,and the storage capacities were increased by 3.9%-17.0%.The promotion effect of GNPs on gas hydrate formation at low pressure is much more obvious than that at high pressure.