An Experimental Study on the Conductivity Changes in Coal during Methane Adsorption-Desorption and their Influencing Factors

During the processes of methane adsorption and desorption,the internal structure of coal changes,accordingly leading to changes in electrical conductivity.In this paper,using low rank coal seams of the Yan'an Formation in the Dafbsi field as the research subject,the relationship between coal resistivity,methane adsorption quantity,and equilibrium pressure is analyzed through proximate analysis,mercury injection tests,low temperature liquid nitrogen adsorption tests,and coal resistivity measurements during methane adsorption and desorption.The results show that during the process of pressure rise and methane adsorption,the conductivity of coal increases,resulting from heat release from methane adsorption,coal matrix swelling and adsorbed water molecules replaced by methane,but the resistivity reduction gradually decreases.The relationship between coal resistivity and methane adsorption quantity and equilibrium pressure can be described by a quadratic function.During the processes of depressurization and desorption,the resistivity of coal rebounds slightly,due to decalescence of methane desorption,coal matrix shrinkage and water-gas displacement,and the relationship coincides with a linear function.Methane adsorption leads to irreversible changes in coal internal structure and enhances the coal conductivity,and resistivity can not be restored to the initial level even after methane desorption.The resistivity and reduction rate of durain are higher than those of vitrain,with relatively greater homogeneous pore throat structure and fewer charged particles in the double electric layer.In addition,moisture can enhance the conductivity of coal and makes it change more complexly during methane adsorption and desorption.

Study on sulfur migration in activated carbon adsorption-desorption cycle: Effect of alkali/alkaline earth metals

Activated carbon(AC)has been widely used in the removal of SO_(2) from flue gas owing to its well-developed pore structure and abundant functional groups.Herein,the effect of alkali/alkaline earth metals on sulfur migration was investigated based on the dynamic adsorption and temperature programmed desorption experiment.The adsorption and desorption properties of six types of AC(three commercial and three laboratory-made)were carried out on a fixed-bed experimental device,and the physical and chemical properties of samples were determined by X-ray fluorescence,X-ray diffraction,scanning electron microscopy/energy dispersive X-ray,and X-ray photoelectron spectroscopy analysis.The experimental results showed that the adsorbed SO_(2) cannot be completely desorbed by increasing the regeneration temperature(350-850℃),while the SO_(2) fixed in the AC combines with the Ca-based minerals in the ash to form a stable sulfate.For different samples,higher ash content,higher CaO content in the ash and a more developed pore structure lead to a higher SO_(2) fixation rate.Moreover,the multiple adsorption-desorption cycles experiment showed that the effect of SO_(2) fixation is mainly reflected in the first cycle,after which the adsorption and desorption amount are approximately the same.This study elucidates the effect of alkali/alkaline earth metals on the adsorption-desorption cycle of AC,which provides a deeper understanding of sulfur migration in the AC flue gas desulfurization process.

Accumulation and exploration enlightenment of shallow normal-pressure shale gas in southeastern Sichuan Basin, SW China

Based on the drilling, logging, experimental and testing data of Well PD1, a shallow normal-pressure shale gas well in the Laochangping anticline in southeastern Sichuan Basin, the shallow shale gas reservoirs of the Ordovician Wufeng Formation to Silurian Longmaxi Formation (Wufeng-Longmaxi) were investigated in terms of geological characteristics, occurrence mechanism, and adsorption-desorption characteristics, to reveal the enrichment laws and high-yield mechanism of shallow normal-pressure shale gas in complex structure areas. First, the shallow shale gas reservoirs are similar to the medium-deep shale gas reservoirs in static indicators such as high-quality shale thickness, geochemistry, physical properties and mineral composition, but the former is geologically characterized by low formation pressure coefficient, low gas content, high proportion of adsorbed gas, low in-situ stress, and big difference between principal stresses. Second, shallow shales in the complex structure areas have the gas occurrence characteristics including low total gas content (1.1-4.8 m3/t), high adsorbed gas content (2.5-2.8 m3/t), low sensitive desorption pressure (1.7-2.5 MPa), and good self-sealing. Third, the adsorbed gas enrichment of shales is mainly controlled by organic matter abundance, formation temperature and formation pressure: the higher the organic matter abundance and formation pressure, the lower the formation temperature and the higher the adsorption capacity, which is more beneficial for the adsorbed gas occurrence. Fourth, the shallow normal-pressure shale gas corresponds to low sensitive desorption pressure. The adsorbed gas can be rapidly desorbed and recovered when the flowing pressure is reduced below the sensitive desorption pressure. Fifth, the exploration breakthrough of Well PD1 demonstrates that the shallow complex structure areas with adsorbed gas in dominance can form large-scale shale reservoirs, and confirms the good exploration potential of shallow normal-pressure shale gas in the margin of the Sichuan Basin.

Seepage law and permeability calculation of coal gas based on Klinkenberg effect

Focused on the Klinkenberg effect on gas seepage, the independently developed triaxial experimental system of gas seepage was applied to conduct research on the seepage characteristics of coal seam gas. By means of experimental data analysis and theoretical derivation, a calculation method of coal seam gas permeability was proposed, which synthesized the respective influences of gas dynamic viscosity, compressibility factor and Klinkenberg effect. The study results show that the Klinkenberg effect has a significant influence on the coal seam gas seepage, the permeability estimated with the method considering the Klinkenberg effect is correct, and this permeability can fully reflect the true seepage state of the gas. For the gas around the standard conditions, the influences of dynamic viscosity and compressibility factor on the permeability may be ignored. For the gas deviating far away from the standard conditions, the influences of dynamic viscosity and compressibility factor on the permeability must be considered. The research results have certain guiding significance in forming a correct understanding of the Klinkenberg effect and selecting a more accurate calculation method for the permeability of coal containing gas.

Influence of Clay Minerals on Some Soil Fertility Attributes: A Review

Clay minerals constitute an important component of the soil system and knowledge of their role in soil fertility is imperative for sustainable soil management and productivity. The aim of this work is to overview the influence of clay minerals on some major soil fertility attributes. The rationale for carrying out this work is that most soil fertility studies rarely incorporate soil mineralogy. Clay minerals, through their physical and chemical properties, affect soil fertility by controlling nutrient supplies and availability, through the sequestration and stabilization of soil organic matter, by controlling soil physical properties through microaggregate formation, by influencing soil acidity and controlling soil microbial population and activity. The main processes involved in these relationships are dissolution-precipitation and adsorption-desorption processes, alongside mechanisms involving the formation of short-range-ordered phases. Although the determination of soil mineralogical properties is very costly and time-consuming, information about a soil’s mineralogy is imperative for a holistic understanding and proper management of soil fertility. Therefore, the development of rapid, low-cost, reliable and efficient techniques of soil mineralogical analysis, directly applicable to soil fertility investigations, constitutes a major challenge. Also, future research should investigate the relationships between clay minerals and soil nitrogen vis-à-vis sequestration and stabilization. Lastly, clay minerals should be considered in studies dealing with soil quality assessment, especially in the choice of soil quality indicators.

Adsorption and desorption behavior under coal–water–gas coupling conditions of high- and low-rank coal samples

High-and low-rank coalbed methane(CBM)are both important fields of CBM development in China,but their formation and production mechanisms differ considerably.The adsorption/desorption behavior of high-and low-rank coals under the coupling of coal–water–gas was investigated using two series of samples.Coal samples from Zhangjiamao(ZJM)coal mine,Ordos basin,and Sihe(SH)coal mine,Qinshui basin,were tested by isothermal adsorption–desorption experiment,natural imbibition experiment,nuclear magnetic resonance,mercury injection porosimetry,contact angle test,and permeability test.Isothermal adsorption and desorption experiments under dry,equilibrium water,and saturated water,were performed to explore the differences between the adsorption and desorption characteristics.The results show that the wettability and permeability of the ZJM low-rank coal sample was considerably higher than that of the SH high-rank coal sample.The imbibition process of the ZJM sample exhibited a high imbibition rate and high total-imbibition volume,whereas the SH sample exhibited a slow imbibition rate and low total-imbibition volume.The ZJM sample had a complex pore structure and diverse pore-size distribution with a lower mercury withdrawal efficiency at 59.60%,whereas the SH sample had a relatively uniform pore-size distribution with a higher mercury withdrawal efficiency at 97.62%.The response of adsorption and desorption of the ZJM sample to water was more significant than that of the SH sample.The desorption hysteresis of the ZJM sample was stronger than that of the SH sample and was more prominently affected by water,which was consistent with its strong wettability and complex pore-throat configuration.A comprehensive adsorption and desorption mode was constructed for high-and low-rank coal samples under coal–water–gas coupling condition.The research results are important to enrich the geological theory of high-and low-rank CBM and to guide efficient CBM recovery.

Zirconia prepared from UIO-66 as a support of Ru catalyst for ammonia synthesis

The development of effective Ru catalyst for ammonia synthesis is of important practical value and scientific significance because of the wide application of ammonia as a fertilizer and its promising applications in the renewable energy.Generally,ZrO_(2) was regarded as an inferior support for Ru catalyst used in ammonia synthesis.Here we prepare ZrO_(2) with monoclinic phase and carbon species from ZrCl_(4) following the preparation route of UiO-66 as well as ammonia treatment.Owing to the presence of a larger amount of hydrogen adsorption as well as the easier desorption of hydrogen species,the ill effect of hydrogen species on the nitrogen adsorption-desorption and ammonia synthesis can be effectively alleviated.The resulting ZrO_(2)-supported Ru catalyst showed 4 times higher ammonia synthesis activity than the conventional Ru/ZrO_(2) obtained from zirconium nitrate.

Carbon isotope fractionation during shale gas transport: Mechanism, characterization and significance

The gas in-place(GIP)content and the ratio of adsorbed/free gas are two key parameters for the assessment of shale gas resources and have thus received extensive attention.A variety of methods have been proposed to solve these issues,however none have gained widespread acceptance.Carbon isotope fractionation during the methane transport process provides abundant information,serving as an effective method for differentiating the gas transport processes of adsorbed gas and free gas and ultimately evaluating the two key parameters.In this study,four stages of methane carbon isotope fractionation were documented during a laboratory experiment that simulated gas transport through shale.The four stages reflect different transport processes:the free gas seepage stage(Ⅰ),transition stage(Ⅱ),adsorbed gas desorption stage(Ⅲ)and concentration diffusion stage(Ⅳ).Combined with the results of decoupling experiments,the isotope fractionation characteristics donated by the single effect(seepage,adsorption-desorption and diffusion)were clearly revealed.We further propose a technique integrating the Amoco curve fit(ACF)method and carbon isotope fractionation(CIF)to determine the dynamic change in adsorbed and free gas ratios during gas production.We find that the gases produced in stage Ⅰ are primarily composed of free gas and that carbon isotope ratios of methane(δ13C1)are stable and equal to the ratios of source gas(13C 10).In stage Ⅱ,the contribution of free gas decreases,while the proportion of adsorbed gas increases,and the δ13C1 gradually becomes lighter.With the depletion of free gas,the adsorbed gas contribution in stage Ⅲ reaches 100%,and the δ13C1 becomes heavier.Finally,in stage Ⅳ,the desorbed gas remaining in the pore spaces diffuses out under the concentration difference,and the δ13C1 becomes lighter again and finally stabilizes.In addition,a kinetic model for the quantitative description of isotope fractionation during desorption and diffusion was established.

Exploring on the optimal preparation conditions of activated carbon produced from solid waste produced from sugar industry and Chinese medicine factory

The waste biomass produced from sugar industry and Chinese medicine factory such as bagasse,reed root residue,pueraria residue and liquorice residue were selected as the raw material for the preparation of activated carbon with zinc chloride as activator.With the same activation time,the influence of temperature and impregnation ratio on the preparation of activated carbon was investigated and the reasonable preparation conditions of activated carbon were monitored and analyzed.The obtained activated carbon samples were characterized by scanning electron microscopy,Brunauer-Emmett-Teller,methylene blue adsorption,thermogravimetric analysis and nitrogen adsorption-desorption.Analysis from the experimental data,bagasse,reed root residue,pueraria residue are suitable for preparing activated carbon.For bagasse,the optimum preparation condition was 700℃ and the impregnation ratio was 1:1,the adsorption capacity of methylene blue reached 246.83 mg/g at the moment.For reed root residue,the optimum preparation condition was 600℃ and the impregnation ratio was 1:2,the adsorption capacity of methylene blue reached 268.07 mg/g at the moment.For Pueraria residue,the optimum preparation condition was 700℃ and the impregnation ratio was 1:2.The adsorption capacity of methylene blue reached 297.33 mg/g at the moment.

DFT calculation on p-xylene sensing mechanism of (C_(4)H_(9)NH_(3))_(2)PbI_(4) single crystal based on physisorption

P-xylene(p-C_(8)H_(10))is extremely harmful and dangerous to human health due to high toxicity and strong carcinogenicity.Exploring sensitive material to effectively detect p-xylene is of importance.In this paper,perovskite single crystal(C_(4)H_(9)NH_(3))_(2)PbI_(4) has been successfully synthesized via solution method.The obtained product was analyzed by single crystal X-ray diffraction.With the space group Pbca,orthorhombic(C_(4)H_(9)NH_(3))_(2)PbI_(4) layered perovskite structure consists of an extended two-dimensional network of corner-sharing PbI_(6) octahedron.Single layer perovskite sheets of distorted PbI_(6) octahedron alternated with protonated n-butylammonium cation bilayers,which offers many advantages and provides the possibility of forming a gas sensor device based on the change of resistances.Density functional theory(DFT)simulations regarding the adsorption energy revealed that this organicinorganic hybrid perovskite compound has excellent selectivity toward p-xylene compared with other gases including C_(2)H_(5)OH,C_(6)H_(6),CH_(2)Cl_(2),HCHO,CH_(3)COCH_(3) and C_(7)H_(8).The calculation of electron density,density of states and electron density difference showed the sensing mechanism of p-C_(8)H_(10) is mainly derived from physical adsorption-desorption in view of electron transfer.

Probing Intermittent Motion of Polymer Chains in Weakly Attractive Nanocomposites

In this study,we investigate the motion of polymer segments in polymer/nanoparticle composites by varying nanoparticle(NP)volume fractions.By studying the probability distribution of segment displacement,segment trajectory,and the square displacement of segment,we find the intermittent motion of segments,accompanied with the coexistence of slow and fast segments in polymer nanocomposites(PNCs).The displacement distribution of segments exhibits an exponential tail,rather than a Gaussian form.The intermittent dynamics of chain segments is comprised of a long-range jump motion and a short-range localized motion,which is mediated by the weakly attractive interaction between NP and chain segment and the strong confinement induced by NPs.Meanwhile,the intermittent motion of chain segments can be described by the adsorption-desorption transition at low particle loading and confinement effect at high particle loading.These findings may provide important information for understanding the anomalous motion of polymer chains in the presence of NPs.