超临界CO_(2)吸附引起煤体变形及吸附应力的研究

对煤体恒温吸附氦气/超临界CO_(2)及变形进行测试试验,对煤体产生的轴向变形和径向变形实时监测,揭示有效应力作用和吸附应力作用分别引起的煤体膨胀变形量以及煤体对超临界CO_(2)的吸附应力.研究结果表明:煤体吸附不同气体表现出的轴向应变值要高于径向应变,氦气和超临界CO_(2)引起的煤体应变随注气压力的变化规律具有相似性.在温度升高过程中,煤体吸附氦气体积应变表现为先增后减的特征,而煤体吸附超临界CO_(2)体积应变逐步减小.随着温度的升高,煤体吸附超临界CO_(2)过程中煤体变形从吸附应力引起的变形占主导逐渐转变为有效应力引起的变形占主导,吸附应力体积应变与有效应力体积应变之比在逐步减小.煤体对超临界CO_(2)的吸附应力随着温度的升高而减小,温度从60℃增加到80℃,吸附应力仅降低了29%,同时超临界CO_(2)与瓦斯吸附应力的比值在60℃达到最大,该温度下超临界CO_(2)驱替瓦斯效果最优.

考虑吸附膨胀应力影响的煤层瓦斯流–固耦合渗流数学模型及数值模拟

已有研究表明,煤吸附瓦斯后要发生相应的膨胀变形,而当这种膨胀变形受到一定的限制时,将会产生膨胀应力。为此,在考虑煤吸附瓦斯产生膨胀应力的前提下,根据煤体受力平衡条件建立考虑吸附膨胀应力的煤体有效应力表达式,并根据流–固耦合渗流理论的基本思想,建立煤层瓦斯流–固耦合数学物理模型。采用有限元和有限差分相结合的方法对模型进行离散化处理,并对其进行模拟求解。和未考虑吸附膨胀应力的流–固耦合模型的模拟结果进行比较分析,研究成果表明,未考虑吸附膨胀应力的流–固耦合模型计算的压力下降较该模型要小,两种模型的模拟结果存在一定的差别,从而表明在煤层瓦斯流–固耦合数学模型中应考虑吸附膨胀应力的影响。

含吸附煤层气煤的有效应力分析

煤层中的气体(煤层气)主要呈吸附状态,固体煤和吸附气体之间的相互作用关系是目前人们关心的问题,它与煤矿瓦斯防治和煤层气开采有关。根据表面物理化学和弹性力学原理,推导了煤吸附膨胀变形、吸附膨胀应力及有效应力计算公式,理论计算结果和试验结果基本一致。分析表明,裂隙中自由气体的压力对煤层中的应力状态影响很小,在煤层内部吸附膨胀应力和吸附膨胀变形规律服从虎克定律。

吸附诱导表面应力的分子动力学模拟

应用分子动力学方法结合镶嵌原子势,模拟研究了同质吸附Cu/Cu(100)和异质吸附Al/Ni(100)纳米薄膜中的吸附诱导表面应力.结果表明吸附原子对表面应力的影响主要源于两种原子间的相互作用;吸附原子和底物表面原子的结合将导致底物表面原子之间的化学键的强度减弱和平衡键长增加,从而导致表面压应力增加;吸附原子之间的相互作用也导致表面应力的变化,吸附原子间的吸引作用导致表面拉应力,而排斥作用导致表面压应力.这两种原子间相互作用所引起的表面应力与吸附原子的密度密切相关,吸附原子与底物表面原子的结合所引起的表面应力的大小与吸附原子的密度成线性关系,而吸附原子间的相互作用所引起的表面应力与吸附原子密度间呈非单调的依赖关系.

变压吸附塔结构及应力分析探讨

变压吸附塔长期承受交变载荷,主要失效模式为疲劳失效。本文介绍变压吸附塔的结构及其应力分析,针对椭圆形封头及球形封头开孔处应力分布,提出变压吸附塔封头结构形式的优化。

煤层气开采过程中渗透率模型比较研究

为了得到煤层气开采过程中渗透率的准确预测模型,分析了不同泊松比和孔隙压力下的储层孔隙率变化规律,通过理论分析对4种经典渗透率模型进行了比较研究。研究结果表明:P&M模型和C&B模型对泊松比敏感度较小,改进P&M模型和S&D模型对泊松比敏感度较大;改进P&M模型能有效反映渗透率变化趋势,在p<1.4 MPa和p>4.1 MPa时k/k0数值拟合度较高;P&M模型和S&D模型不能准确描述p<1.4 MPa时k/k0变化情况,而在p>1.4MPa时k/k0数值拟合度较高;煤层渗透率随孔隙压力增大表现为"U"型趋势,包含低孔隙压力骤减区、中孔隙压力稳定区和高孔隙压力稳步升高区3个阶段,改进P&M和S&D模型更能表现煤层气渗透率随孔隙压力变化趋势。

Adsorption and desorption behaviors of ssDNA molecules on mica surface by surface forces apparatus

An approach for studying the adsorption and desorption behaviors of single-stranded DNA（ ssDNA） molecules on the mica surface by the surface forces apparatus（ SFA） is reported,which can be used to characterize the precise thickness,configuration and mechanical properties of ssDNA layers on the mica surface at a certain buffer solution. The formation of ss DNA layers is first studied by tuning the ssDNA concentrations, and the experimental results indicate that the ss DNA concentration of 100 ng / μL is ideal for forming a ssDNA monolayer structure on the mica surface, and the hardwall value measured to be 1.04 nm under this circumstance is regarded as the thickness of the ssDNA monolayer confined on mica. The desorption behavior of ssDNA molecules from the mica surface is further studied by observing and comparing different shapes of the force-distance curves under certain conditions. It is found that the desorption of ss DNA molecules from the mica surface occurs as the monovalent salts are added into the gap buffer. It is inferred that the competition effect between monovalent and divalent salts can induce the release of ssDNA from substrate.The results also reveal that 10 mmol / L monovalent salts（ Na~＋）is sufficient for the desorption of ssDNA from mica. This work provides an applicable method to study the binding mechanism of ss DNA molecules on inorganic substrates.

Temperature Effect on Boron Adsorption-Desorption Kinetics in Soils

The effect of temperature on the properties of boron adsorption-desorption in brown-red soil, yellowbrown soil and calcareous alluvial soil of Hubei Province was investigated with the mobile displacement technique. The experimental data of B adsorption-desorption amounts and reaction t line at 25 and 40℃ were fitted by the zero-order, first-order and parabolic diffusion kinetic equations. The adsorption process was in conformity with the parabolic diffusion law at both the temperatures, and the values of rate constant of the parabolic diffusion equation in B adsorption were 0.138, 0.124 and 0.105 mg kg-1 min-1/2 at 25℃, and 0.147, 0.146 and 0.135 mg kg-1 min-1/2 at 40℃ for the brown-red soil, yellow-brown soil, and calcareous alluvial soil, respectively. The relationship between amount of B desorption and reaction time could be well described by the first-order kinetic equation, and the corresponding values of rate constant were 0.0422, 0.0563 and 0.0384 min-1 at 25℃, and 0.0408, 0.042 3 and 0.0401 min-1 at 40℃ for the brown-red soil, the yellow-brown soil and the calcareous alluvial soil, respectively. Therefore, the desorption process of B might be related to the amount of B adsorbed in soil. The higher the temperature, the lower the amount of B adsorption for the same soil in the same reaction time. The values of the apparent activation energy of B adsorption in the three soils calculated with the rate constants of parabolic diffusion equation were 3.27, 8.44 and 12.99 kJ mol-1, respectively, based on the experimental data of B adsorption amounts and reaction time at 25 and 40℃.

Application of Modified Attapulgite Clay as the Adsorbent in Gasoline Desulfurization

Attapulgite clay is a kind of special silicate mineral with high adsorption capacity thanks to its loose structure and porous surface. In this paper, the attapulgite clay was treated effectively with acid under microwave thermal activation and ultrasonic vibration, respectively, and characterized by XRD, N2 adsorption, FT-IR and SEM. The desulfurization performance of the modified attapulgite clay was then evaluated by using simulated gasoline as the feed. The test results showed that the thiophene removal rate increased with an increasing dosage of hydrochloric acid during microwave modification of attapulgite clay. When the concentration of hydrochloric acid reached 15%, the increase of desulfurization rate became slower, and the desulfurization rate was about 69%.

Kinetic Equations of Potassium Desorption and the Ap－plication of Equation Constants

Elovich, parabolic diffusion, power function and exponential equations were used to describe K desorptionkinetics of 12 soils in a constant electric field of electro-ultrafiltration (EUF). Results showed that the Elovich,parabolic diffusion and power function equations could describe K desorption kinetics well owing to their highcorrelatfon coefficients and low standard errors; but the exponential equation was not suitable to be usedin this study due to its relatively low correlation coefficients and relatively high standard errors. This workestablished successfully the relationships between the constants (slope or intercept) of kinetic equations andthe barley responses to K fertilizer in the multiple-site field experiments and K-supplying status of soils, theconstants of Elovich, parabolic diffusion and power function equations were very significantly or significantlycorrelated to the soil available K, relative yield of barley and K uptake of barley in NP plot. It was suggestedthat the kinetic equation constants could be used to estimate K-supplying power of soils.

Study on law of raw coal seepage during loading process at different gas pressures

In order to reveal the law of raw coal seepage at different gas pressures, the gravity constant load seepage experimental system was developed and used. The law of raw coal seepage at different gas pressures with He, N2 and CO2 was investigated. The results show that, in a given state of stress during the experiment, with the increase of gas pressure, the permeability of raw coal sample prone to outburst exhibits a significantly decrease, and then exhibits an increasing trend when reaching the extreme point. The law of Klingberg coefficient related to the stress state and the gas adsorption properties was also obtained. Under the same experimental conditions, the Klingberg coefficient of He is greater than that of N2; and the Klingberg coefficient of CO2 has minimum value; so the stronger the gas adsorption is, the smaller the Klingberg coefficient of gas goes. Klinkenberg coefficient decreases with the increase of effective stress. Under the same conditions, the permeability of He is greater than that of N2; the permeability of CO2 has minimum value; so the stronger the gas adsorption is, the lower the permeability of the coal sample goes. The results have important significance in revealing the mechanism of gas seenage. Dredicting coal mine gas disaster, and gas drainage and safety nroduction.

Topological Transition in Monolayer Blue Phosphorene with Transition-Metal Adatom under Strain

We carried out first-principles calculations to investigate the electronic properties of the monolayer blue phosphorene(BlueP)decorated by the group-IVB transition-metal adatoms(Cr,Mo and W),and found that the Cr-decorated BlueP is a magnetic half metal,while the Mo-and W-decorated BlueP are semiconductors with band gaps smaller than 0.2 eV.Compressive biaxial strains make the band gaps close and reopen,and band inversions occur during this process,which induces topological transitions in the Mo-decorated BlueP(with strain of-5.75%)and W-decorated BlueP(with strain of-4.25%)from normal insulators to topological insulators(TIs).The TI gap is 94 meV for the Mo-decorated BlueP and218 me V for the W-decorated BlueP.Such large TI gaps demonstrate the possibility to engineer topological phases in the monolayer BlueP with transition-metal adatoms at high temperature.

Oil spill sorption using raw and acetylated sugarcane bagasse

In the recent decades oil spills in the aquatic environments are one of the major sources of environmental pollutions, which are steadily growing with the increase in oil consumption. Adsorption is a rapid and cost effective process to minimize the environmental impacts of oil spills and cleanup these pollutants. In this work, the crude oil sorption capacity was examined with raw sugarcane bagasse and acetylated sugarcane bagasse. Results show that the acetylated bagasse was significantly more oleophilic than the raw bagasse and acetylation reaction can increase bagasse oil sorption ability by about 90%. The maximum sorption capacities of acetylated bagasse were obtained about 11.3 g and 9.1 g in dry system(crude oil sorption) and oil layer sorption, respectively. The physicochemical characteristics of the sorbents such as composition, water solubility, moisture content and density were measured according to ASTM standard methods. Also Fourier transform infrared spectroscopy(FTIR) of raw and acetylated bagasse was performed to investigate the effect of acetylation on sugarcane bagasse structure.

Adsorption Reaction Dynamics of Systems Lysozyme and Nanodiamond/Nanosilica at pH=7-13

Adsorption reactions between surfaces of nanodiamond and nanosilica with diameter of 100 nm prepared as suspension solutions of 0.25μg/μL and lysozyme molecule with different concentrations of 7 mmol/L PPBS at pH=7, 9, 11, and 13 have been investigated by fluores- cence spectroscopy. Adsorption reaction constants and coverages of lysozyme with different concentrations of 0-1000 nmol/L under the influences of different pH values have been ob- tained. Helicities and conformations of the adsorbed lysozyme molecules, free spaces of every adsorbed lysozyme molecule on the surfaces of nanopartieles at different concentrations and pH values have been deduced and discussed. The highest adsorption capabilities for both sys- tems and conformational efficiency of the adsorbed lysozyme molecule at pH=13 have been obtained. Lysozyme molecules can be prepared, adsorbed and carried with optimal activity and helicity, with 2 and 10 mg/m2 on unit nanosurface, 130 and 150 mg/g with respect to the weight of nanoparticle, within the linear regions of the coverages at around 150-250 nmol/L and four pH values for nanodiamond and nanosilica, respectively. They can be prepared in the tightest packed form, with 20 and 55 mg/m2, 810-1680 and 580-1100 mg/g at threshold concentrations and four pH values for nanodiamond and nanosilica, respectively.

Experimental study on gas permeability by adsorption under 3D-stress

Using self-developed gas-seepage experimental installation,under the sameeffective stress conditions,coal permeability experiments on different adsorption characteristicsof gases,different temperatures and different gas adsorption contents were performed,and the influence law of adsorption on coal permeability was studied.At the sametime,experimental analogy showed clearly that gas drawing plucks the permeability variationlaw.The results show that adsorption has a major impact on coal permeability.Thegreater the adsorption,the more the gas adsorption capacity and the coal permeabilitybecomes smaller.Permeability becomes smaller along with confining of pressure andtemperature,and this is in accord with local practice results.

Kinetic Modeling of Isothermal or Non-isothermal Adsorption in a Pellet：Application to Adsorption Heat Pumps

Understanding the interaction between a fluid and a solid phase is of fundamental importance to the design of an adsorption process.Because the heat effects associated with adsorption are comparatively large,the as-sumption of isothermal behavior is a valid approximation only when uptake rates are relatively slow.In this article,we propose to determine when it is needed to choose the isothermal or non-isothermal assumption according to two physical parametersα（ratio convection/capacity） andβ（quantity of energy/capacity） .The proposed problem is solved by a mathematical method in the Laplace domain.Whenα→∞（infinitely high heat transfer coefficient） or β→0（infinitely large heat capacity） ,the limiting case is isothermal.When the diffusion is rapid（α10） the kinetics of sorption is controlled entirely by heat transfer.If the adsorption process is to be used as a heat pump,it shall be represented by an isotherm model withαandβas high as possible.

幂率型裂隙分布煤层渗流场与变形应力场耦合模型及数值模拟

煤体的微观结构对其产气量有着显著的影响,然而,现阶段的煤层气开采模型都未将此因素考虑在内。为了定量分析煤层微观结构对宏观渗流过程的影响,基于幂律分形渗透模型,构建一种能够同时考虑煤层微观结构与多物理场因素相互作用的裂隙-孔隙渗流模型。模型将多物理场效应(包括气体吸附-解吸效应、气体渗流诱导储层形变效应、煤层基质形变、裂隙-基质相互作用等)定义为储层有效应力的函数,进而作用于储层孔隙率与微观结构。分析煤体的主要结构参数对宏观渗透率的影响,包括:(1)裂隙长度幂律指数α;(2)裂隙长度最值比r;(3)最大裂隙长度l,并分析煤层形变及渗透率的时空演化趋势。模拟结果表明:煤体结构参数对煤体渗透率有着显著的影响。当孔隙率等其他煤体参数保持不变时,储层宏观渗透率与裂隙长度最值比r、最大裂隙长度l成正比,与裂隙长度幂律指数α成反比;此外,与裂隙长度幂律指数、裂隙长度最值比相比,煤层最大裂隙长度对煤层渗透率有着更为显著的影响。

Analysis of H_2S Tolerance of Pd-Cu Alloy Hydrogen Separation Membranes

The presence of a limited amount of H2S in H2-rich feed adversely affects the Pd-Cu membrane permeation performance due to the sulphidization of the membrane surface. A theoretical model was proposed to predict the S-tolerant performance of the Pd-Cu membranes in presence of H2S under the industrial water-gas-shift(WGS) reaction conditions. The ideas of surface coverage and competitive adsorption thermodynamics of H2S and H2 on Pd-Cu surface were introduced in the model. The surface sulphidization of the Pd-Cu membranes mainly depended on the pressure ratio of H2S to H2, temperature and S-adsorbed surface coverage, i.e., the occurrence of sulphidization on the surface was not directly related with the bulk compositions and structures [body centered cubic and face centered cubic(bcc or fcc)] of Pd-Cu alloy membranes because of the surface segregation phenomena. The resulting equilibrium equations for the H2S adsorption/sulphidization reactions were solved to calculate the pressure ratio of H2S to H2 over a wide range of temperatures. A validation of the model was performed through a comparison between lots of literature data and the model calculations over a rather broad range of operating conditions. An extremely good agreement was obtained in the different cases, and thus, the model can serve to guide the development of S-resistant Pd alloy membrane materials for hydrogen separation.

Vertically ordered silica mesochannels as preconcentration materials for the electrochemical detection of methylene blue

Silica mesochannels(SMCs) vertically and regularly oriented to the surface of indium tin oxide(ITO) electrodes were prepared and utilized for preconcentration and detection of methylene blue(MB) in aqueous solution. The positively charged MB can be adsorbed to the SMCs by following the pseudo-first-order kinetic model. The negative value of ?G=?34.73 k J/mol derived from the Langmuir adsorption isotherm indicated the thermodynamic feasibility of the adsorption and the spontaneous nature of the process. Moreover, the adsorbed MB can undergo an electrochemical reaction on the ITO electrode at a suitable potential and the resulting electrical current can be utilized to quantify the MB in aqueous solution. A good analytical performance for MB with a linear range from 10 nmol/L to 1.0 ?mol/L and a detection limit at the nmol/L level was obtained. We believe that such a platform consisting of SMCs perpendicularly tethered to the underlying electrode surface simultaneously allows enrichment and electrochemical detection and can be extended for the detection of various charged dyes, as well as many other charged species.

Effect of recycled powder on the yield stress of cement paste with varied superplasticizers

The influence of superplasticizer on the yield stress of cement pastes with recycled powder(RP)was examined in the study.Four superplasticizers were used to obtain the similar fluidity by adjusting the dosage.The results show that the 10%RP decreases the yield stress of paste compared to the reference paste at the same fluidity,but 20%and 30%RP increases the yield stress,ranging from 11 to 599%.The superplasticizer with adsorptive group of phosphate-type minimizes the yield stress of paste than that of polycarboxylate-type,but it made a significant increment in yield stress as the incorporating of RP increased.Besides,the polycarboxylate superplasticizer with the higher molecular weight of side chain and charge density led to lower yield stress.Based on the Yodel model,the yield stress of paste with RP was analyzed by the polymer adsorption and particle packing density of particles to reveal the influence of RP with different superplasticizers on the colloidal interaction and contact network among the particles.The packing density of particles with recycled powder was a little higher than the reference paste,but the higher fraction of fine particles made a stronger PSD effect,which improved the particle contact interaction.On the other hand,due to the higher polymer adsorption of recycled powder than cement,especially for superplasticizer with phosphate group,the average surface coverage was increased,which extended the separation distance,so that colloidal interaction among particles was weaken.