Influence Of Pore Structure Research Articles

Bio-methanol conversion into light olefins catalyzed by zeolites: Influence of pore structure and acid Properties

Currently, most of the global methanol is derived from reforming syngas obtained from natural gas. However, thermochemical processes like gasification and pyrolysis, which use biomass as a feedstock for syngas production, are increasingly promising for producing methanol from renewable sources. The conversion of methanol into light olefins, catalyzed by zeolites with different acid and structural characteristics, such as HZSM-5, HFER, SAPO-34, and HMCM-22, was studied. The physicochemical characterization of the samples was carried out using XRF, XRD, nitrogen physisorption, SEM, IR spectrometry with pyridine adsorption, and temperature programmed desorption of NH3 (TPD NH3). The catalyst performances were compared under the same initial conditions with an isoconversion of 75 ± 5%. The acid and structural characteristics exerted a strong influence on the catalytic performance in terms of activity, stability, and selectivity for the reaction products.

Insights into the pore structure effect on the mass transfer of fuel cell catalyst layer via combining machine learning and multiphysics simulation

Analysis of the catalytic layer (CL) pore structure and three-phase (electron phase, proton phase, and reactant phase) mass transfer in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) is critical for improving concentration polarization and optimizing performance. However, there is a lack of studies on the pore structure’s impact on the catalytic layer three-phase mass transfer. In this work, the influence of pore structure on catalytic layer three-phase mass transfer and multiphysics distribution was investigated by combining machine learning and multiphysics simulation. Among many key factors investigated by machine learning that impact the performance of catalytic layer, porosity emerges as the primary influencing factor. Porosity accounts for 32.7 % of the electric potential drop, with macro/micro porosity contributing 27.6 % and 5.1 %, and 32.8 % of the current density, with macro/micro porosity contributing 15.6 % and 17.2 %. Furthermore, the macropore structure has a much greater influence on the performance of the catalytic layer compared to the micropore structure. Moreover, the simulation results demonstrated that porosity has a great influence on three-phase mass transfer, the oxygen molarity increases with increasing porosity. The electric potential difference increases exponentially as porosity increases. The relationship between current density and porosity is a volcanic relationship, which can be expressed as a quadratic polynomial function. The mesoscopic pore-scale model (PSM) with an εeff of 0.502 (εmic of 0.2 and εmac of 0.378) exhibits the highest mean current density at 619.526 mA/cm2@0.5 V, attributed to a more uniform and efficient three-phase transfer path. The accuracy of the mesoscopic pore-scale model and the polynomial equation is further confirmed through corresponding experiments. The experiment results show that the current density decreased as the εeff increased from 0.682 to 0.702, which aligns with the theoretical predictions of the PSM model and polynomial equation. These studies are valuable for comprehending the internal three-phase mass transfer behavior and optimizing the catalytic layer pore structure to enhance HT-PEMFC performance.

Fire retardancy of epoxy composites: A comparative investigation on the influence of porous structure and transition metal of metal-organic framework

Metal-organic frameworks (MOFs) are crystalline porous materials constructed by metal nodes and organic linkers. A series of key features such as high surface area, catalytic performance provide a platform for preparing MOF-based fire retardants (FRs). However, understanding the role of the porous structure and catalytic metal species remains a key issue towards the fire retardant mechanism of MOFs. This work systematically studied the difference between the performance of a zirconium based MOF(UiO-66), its derived porous zirconium oxide (U-ZrO2), and commercial ZrO2 (C-ZrO2), in imparting fire retardancy, suppressing smoke and charring property towards epoxy. With the presence of 3 wt% porous U-ZrO2, EP/3U-ZrO2 sample showed better performance in suppressing heat (10 % reduction) and toxic carbon monoxide (14 % reduction) than that of EP/3C-ZrO2 due to the “tortuous path” effect and formation of a compact char. Moreover, a greater number of exposed catalytic sites on MOF compared with thermally treated metal oxide significantly reduced total smoke production (TSP) of the EP/MOF sample by 38 %. Catalytic carbonization attributed to the great number of metal sites on MOF is crucial in providing compact char residue, thereby suppressing smoke for EP. In perspective, this work opens a window for understanding the fire retardant mechanism of MOF-based FR towards polymers.

Influence of pore structure on catalytic performance of Cs-Zr/SiO2 catalyst for methyl methacrylate synthesis from methyl propionate and formaldehyde

Methyl methacrylate (MMA) synthesis via aldol condensation of methyl propionate with formaldehyde over Cs-based supported catalysts is intensively investigated, while the effect of their pore structures on catalytic performance still lacks in-depth understanding. Herein, series of Cs-Zr/SiO2 catalysts with different pore structures were prepared for this aldol condensation. The physicochemical characteristics of as-prepared Cs-Zr/SiO2 catalysts were characterized using physical N2 adsorption–desorption isotherms and CO2-/NH3-TPD. In addition, the impact of pore structure on mass transfer, adsorption, and desorption of reactants and products was studied through in situ DRIFTS. The results show that the acid and base site densities elevated with the increasing pore volume. The mass transfer of reactants and products could be promoted with increasing pore size, while their adsorption energies exhibited a volcanic trend. As a result, the Cs-Zr/SiO2 catalysts having average pore diameter of 12-18 nm and acid-base balance was considered as the optimal candidate for MMA production.

Removal of PFOA from water by activated carbon adsorption: Influence of pore structure

Activated carbon (AC) adsorption is a practical process for the removal of perfluorooctanoic acid (PFOA) in aquatic environments, but the relationship between its pore structure and adsorption performance is not well understood. In this study, the KOH-activated carbons (KACs) with different tailored pore structures were prepared, and presented a 2.61-fold higher adsorption capacity and a 2.21-fold higher adsorption rate than the raw AC. An in situ characterization method and a modified adsorption model were introduced to investigate the impact of pore size, which demonstrated that the ultra-micropores (<1.2 nm) and small mesopores (2.0–3.0 nm) contributed significantly to the adsorption of PFOA, with the highest mean contribution factor (k) of 0.45 and the second highest of 0.39, respectively. Molecular dynamics simulations revealed that PFOA molecules tend to attach to the pore walls at various pore sizes. The adsorption of PFOA in the ultra-micropores was dominated by enhanced interactions due to the overlapping potentials of the bilateral pore walls (maximum of −567.32 Kcal·mol−1) and hydrophobic interactions. PFOA micelles or hemi-micelles could be formed in the small mesopores, allowing them to function as both the molecule transportation channels and strong adsorption sites. This study would guide the development of activated carbon tailored for the selective adsorption of PFOA from water.

Influence of pore structures on friction and wear properties of iron-based oil-containing composites under dry and self-lubricated sliding conditions

This study successfully prepares iron-based oil-containing materials with connected porous structures using TiH2 and nylon 66 short fibers as pore-forming agents. The dehydrogenation of TiH2 can produce large pore cavities and the nylon 66 short fiber with a highly regular shape has a unique advantage in pore channel production. Compared to the iron-based specimen without the pore-forming agent, the oil content of the iron-based specimen with the two pore-forming agents increases by 33.86 %. The tribologica23ee3l properties of the iron-based oil-containing materials under dry and self-lubricated sliding conditions are evaluated using the MM-200 ring-block sliding tribometer and the HDM-20 end-face friction and wear tester, respectively. Special emphasis is given to the effect of pore structures on wear patterns. The results showed that the material's surface is subjected to significant shear failure under dry sliding conditions, leading to the closure of pores due to plastic deformation during the initial sliding. The connected pore structure is a non-dense region, allowing shear damage to occur in the deeper subsurface of the matrix and increasing the material's wear rate. Under self-lubricated conditions, the connected pore structure facilitates the rapid release of lubricating oil, improves the initial lubrication state, and delays pore closure. As compared with dry friction, the wear rate can be reduced by two orders of magnitude under self-lubricating conditions. At a sliding speed of 0.46 m/s, an appropriate load (about 900 N) can enhance the material's ability to continuously and rapidly supply oil.

Mild preparation of structured solid amine adsorbent pellets with the assistance of alginate for efficient and stable CO2 adsorption

The industrialization of solid amine adsorbents requires the molding of the adsorbents, and the blockage or collapse of the pore structure caused by the molding process will inevitably affect the CO2 adsorption performance. Herein, the structured solid amine adsorbent pellets (SA-T/M) were fabricated based on the crosslinking of alginate and Ca2+ under mild conditions. The pelletized SA-T/M well preserved the pore structure of the original support, with only a 26.8 % diminution in specific surface area, which profited to a more uniform loading and dispersion of amine. Benefitting from the influence of pore structure on amine dispersion, SA-T/M achieved a pretty CO2 adsorption capacity of 2.49 mmol g−1. The hydroxyl group of alginates can form hydrogen bonds with the amines, which greatly improved the amine stability of the adsorbent and enabled SA-T/M to exhibit excellent cyclic stability. After 30 adsorption-desorption cycles, the adsorption capacity of SA-T/M merely decreased by 15.6 %. Considering the adsorption capacity and stability of structured adsorbents, the molding strategy with the assistance of alginate provides a potential path for the industrial application of solid amine adsorbent molding technique.

Effect of biochar structure on the selective adsorption of heavy components in bio‐oil

AbstractIn this study, biochars with different structures were prepared through HNO3 oxidation and secondary pyrolysis to study the relationship between the structure of biochar and its selectivity for the adsorption of light and heavy aromatics in bio‐oil. The results showed that the adsorption rates of biochar with different structures ranged from 2.90 to 4.00 g bio‐oil per g biochar. The influence of pore structure was dominant, followed by the influence of O‐containing functional groups and the degree of graphitization. The higher the adsorption capacity of biochar for bio‐oil, the smaller the concentrations of the light aromatic model compounds in the absorbed bio‐oil (ABO). Among the five light aromatics, biochar has the best adsorption selectivity for dihydroxybiphenyl and the worst for eugenol and propyl phenol. This is attributed to the diphenyl ring structure of dihydroxybiphenyl, which makes it more susceptible to adsorption, and other light model compounds only have one benzene ring. In summary, biochar demonstrates better adsorption selectivity for heavy aromatics than light aromatics. The more developed the pore structure is, the more enriched O‐containing functional groups are, and the higher the graphitization degree of biochar is, the better the selective adsorption of aromatic compounds in bio‐oil.

Experimental study on the influence of pore structure on spontaneous imbibition in marine black shale

Experimental study on the influence of pore structure on spontaneous imbibition in marine black shale

Numerical research on liquid water removal mechanism and the influence of pore structure on water removal rate based on real pore GDL structure during shutdown purge of fuel cell

This paper establishes a two-phase flow model of the real pore structure to explore the liquid water removal process during the shutdown purge. The Monte Carlo algorithm is used to randomly throw circles in the rectangular region to simulate the two-dimensional interface of the real GDL pore structures. The real pore structure with different porosity is established by change the number of random circles to explore the influence of porosity on the liquid water removal process. A solid mechanical model is established to explore the variation of GDL under the effect of assembly force. The equivalent model of the compressed real pore GDL is established to explore the effect of the assembly force on the removal of liquid water during the shutdown purge stage. The results show that the liquid water under the ribs is difficult to remove during the removal of liquid water, affecting the speed of liquid water removal. The reduction of GDL porosity is conducive to the diffusion of air and the displacement of liquid water, thus improving the removal speed of liquid water. The assembly force can reduce the porosity below the rib, and effectively promote the removal speed of liquid water below the rib.

Influence of pore structures on deformation behavior and mechanical properties of porous tantalum scaffolds fabricated by electron beam powder bed fusion

Porous tantalum scaffolds with the dodecahedron, G7, and cubic structures were fabricated by electron beam powder bed fusion (EB-PBF). The influence of pore structures on the deformation behavior and mechanical properties of porous tantalum scaffolds was investigated by compressive testing, tensile testing, three-point bending testing, and finite element analysis (FEA). In the compressive test, the deformation of G7 and cubic scaffolds was dominated by buckling. The dodecahedron scaffold was deformed mainly by bending, leading to its lower compressive strength. On the other hand, the dodecahedron scaffold had superior tensile and bending properties. The uniform maximum stress distributions of the dodecahedron scaffold in the tensile and bending tests contributed to the homogeneous structural deformation, which delayed the fracture of struts; whereas, the maximum stresses of G7 and cubic scaffolds were concentrated in the transverse struts, resulting in the fracture of transverse struts in the early deformation stage. Therefore, pore structures should be properly selected for EB-PBF manufactured porous tantalum scaffolds based on the requirements for mechanical properties.

Influence of pore structure on steam disinfection heat and mass transfer in Yunnan red loam

The obstacles to the continuous cropping of Chinese herbs in Yunnan have become increasingly prominent. Many soil-borne diseases can infect the roots of crops, affect the growth of crops, and eventually lead to quality and yield reduction. Soil steam disinfection can still be used as one of the first methods to solve the problem of continuous cropping obstacles of Chinese herbs such as Panax notoginseng. However, the steam will condense into a large amount of liquid water when it is cold, which will cause soil pore blockage and seriously affect the steam diffusion efficiency. Therefore, it is necessary to study the influence mechanism of the pore structure of Yunnan red loam on heat and mass transfer of steam disinfection. The experimental research was conducted on steam disinfection's heat and mass transfer patterns under different soil pore structure conditions. Image processing technology was used to collect accurate soil profiles and to establish real soil pore structure analysis. Then, fluid simulation technology was used to simulate the heat and mass transfer process and trend of steam distribution within the soil profile under different soil pore structures. The results showed that the steam heat flow of <2 mm, 2–4 mm and 4–6 mm treatments were uniformly diffused in the form of matrix flow in a 1/4 ellipse, and the effective disinfection range was 18 cm horizontal distance and 20 cm vertical distance, in which the highest temperature could reach more than 90 °C. The steam heat flow of the 6–8 mm and >8 mm treatment groups diffused irregularly in large pore steam flow. Therefore, some devices for breaking soil and rotary tillage need to finely rotate the soil in the future. The end effector's disinfection pipe spacing can refer to the effective disinfection range.

Study on Corrosion Behavior of Porous Pure Copper Based on Electrochemistry and Scanning Kelvin Probe

Porous metals are widely used in filtration and separation, flame retardant explosion-proof, biomedical application, etc. Compared with its corresponding dense metal, the presence of porous structures also leads to different corrosive performances in porous metal. Some studies have utilized the weight loss method, electrochemical impedance to evaluate porous metal corrosion behavior; however, the influence of pore structure on metal corrosion is still ambiguous, and present methods used for analyses of porous metal corrosion are statistical averages of the corrosion behavior of the entire porous material, which cannot accurately reflect the corrosion behavior inside the pores. Herein, we prepare the porous copper samples with 0, 24, 72, and 96 pores using a mechanical process, and employ scanning Kelvin probe combined with electrochemical polarization and impedance spectroscopy to test the corrosion performance of the porous copper in static and dynamic NaCl solutions. The relevant results indicate that in the static solution, the corrosion resistance of the samples gradually increases with the rise in the number of pores. By contrast, in the dynamic solution, the 24-pore sample is more susceptible to corrosion than the sample without the pore.

Implementation and validation of effective thermal conductivity model of coal‐rock mass with rough capillary pore structure under CT three‐dimensional reconstruction

AbstractOn the strength of the capillary physical equivalent model and heat transfer law of series‐parallel combined structural unit, the calculation model of effective thermal conductivity of coal‐rock mass is obtained. The model considers the effect of roughness, porosity factor and other factors on effective thermal conductivity. CT digital core technology is applied to reconstruct the 3D model of coal‐rock mass, and one‐way heat transfer numerical simulation is carried out according to the model. It indicates that the internal temperature of coal‐rock mass is non‐uniformly distributed under the influence of pore structure, and the isothermal surface of pore region bulges towards the boundary of heat flux. Comparing the calculated and simulated values under the same conditions, the average error percentage of the theoretical calculation model is 6.95%, and the model has outstanding prediction performance in porous media with medium porosity and regular pore distribution, which provides a reference for predicting the effective thermal conductivity of coal‐rock mass.

Molecular simulation investigation of pore structure impact on the wettability and flotation efficiency of coal gasification fine slag

Coal gasification slag is a kind of solid waste that exhibits suboptimal resource utilization and contributes to environmental pollution. Flotation is a common method of sorting coal gasification fine slag. However, the adverse influence of the well-developed pores structure of residual carbon on wettability and flotation efficiency is not adequately addressed in the literature. In this research, the adsorption characteristics of water molecules in the residual carbon model with different pore structures were investigated by Grand Canonical Monte Carlo simulation. We employed molecular dynamics simulations and mathematical models to investigate the mechanism of pore water movement. Additionally, the influence of pore structure on the flotation effect of coal gasification fine slag was explored for molecular dynamics simulations and flotation experiments. The results indicated that water molecules were adsorbed and aggregated in the residual carbon pores in the form of clusters. The cluster size decreased as the porosity decreased. Moreover, the same pore model showed an equivalent adsorption of water molecules. The binding effect of residual carbon on water molecules was stronger for smaller pore sizes. However, the simulation and experimental findings demonstrated that the more developed the pore structure of coal gasification fine slag, the lower its flotation efficiency. Finally, various methods of strengthening the flotation of coal gasification fine slag are theoretically verified. The findings of this research elucidate the underlying microscopic mechanism responsible for the adsorption of water molecules by residual carbon pores. Moreover, we explicate the principle of weakening the pore wetting effect and lay a theoretical foundation for developing advanced flotation techniques for coal gasification fine slag. It provides some theoretical guidance and technical support for realizing high-value utilization of coal gasification slag with specific environmental and resource benefits.

Facile preparation of nitrogen-doped microporous carbon from potassium citrate/urea for effective CH4 separation and uptake

N-doped microporous carbons have attracted much attention for micromolecule gas separation and accumulation owning to their superior adsorption potential and surface polarizability. However, to prepare N-doped microporous carbon usually acquire excess corrosive KOH as activator, which limits its application in industry. Here, we propose a non-corrosion method for the manufacture of narrow N-doped microporous carbons using potassium citrate acts as activating agent, and urea acts as both a nitrogen doping agent and coactivator without any solvent. The BET surface area, micropore volume, pore size distribution and N content can be easily adjusted by changing the potassium citrate/urea ratio and activating temperature. The influence of porous structure and N content on CH4 uptake and separation was investigated, and ultra-micropore volume (<1nm) plays a dominate role in CH4 selectivity adsorption. ACK2N1 had the largest CH4 adsorption capacity of 3.00 mmol/g and CH4/N2 selectivity of 7.11 at 273.15 K and 100 KPa due to its largest ultra-micropore volume and N content. The adsorption breakthrough, regeneration experiments and adsorption thermodynamics showed that the prepared well-developed N-doped microporous carbons have very good potential for CH4 separation and enrichment from low coal bed methane. Furthermore, the pore formation mechanism of the well microporous carbon materials is proposed.

Experimental Study on the Influence of Pore Structure and Group Evolution on Spontaneous Combustion Characteristics of Coal Samples of Different Sizes During Immersion.

To study the influence of water immersion on the evolution of the groups and spontaneous combustion characteristics of coal samples with different sizes, raw coal from the Fengshuigou Coal Mine operated by Pingzhuang Coal Company in Inner Mongolia was studied. The infrared structural parameters, combustion characteristic parameters, and oxidation reaction kinetics parameters of D1-D5 water immersion coal samples were tested, and the mechanism of spontaneous combustion during the oxidation of submerged crushed coal was investigated. The results were as follows. The water immersion process promoted the re-development of coal pore structure, and the micropore volume and average pore diameter were 1.87-2.58 and 1.02-1.13 times those of raw coal, respectively. The smaller the coal sample sizes, the more significant the change. At the same time, the water immersion process increased the contact point between the active group and oxygen in the coal, and the C=O, C-O, and -CH3/-CH2- groups in coal were further promoted to react with oxygen to generate -OH functional groups and improve the reactivity of coal. The characteristic temperature of water immersion coal was affected by the temperature rise rate, coal sample size, coal voidage, and other factors. Compared with the raw coal, the average activation energy of the water immersion coal with different sizes decreased by 12.4-19.7%, and the apparent activation energy of the coal sample with a size of 60-120 mesh was the lowest on the whole. In addition, the apparent activation energy in the low-temperature oxidation stage was significantly different.

Research on pore structures of fine-grained carbonate reservoirs and their influence on waterflood development

Abstract Carbonate reservoir has complex pore structures. At present, the influence of pore structure on water flooding mechanism of carbonate reservoirs is insufficient. In this article, a systematic workflow was designed in combination with scanning electron microscope, particle size, physical properties, and water flooding experiments to study the effect of pore structure on water flooding mechanism of fine-grained carbonate rocks. Due to the small particle size and strong heterogeneity, the acid fracturing operations, rather than hydraulic fracturing alone, are necessary to achieve increased production and reservoir reconstruction of carbonate reservoirs. Through this study, the mathematical model of reservoir physical parameters (permeability and porosity) was proposed, and the accuracy of the model was verified by comparing the simulated oil recovery with the experimental results. According to the comparison results, the experimental results are consistent with the simulation results, and their oil recovery efficiency is 33.62 and 31.87%, respectively. Finally, the effect of injection rate on oil production was discussed. It is shown that with the increase in injection rate, the output of displaced oil increases significantly. The cumulative oil production increases from 62.5 to 256.31 mL when the injection rate increases from 100 to 400 mL/min. The findings of this study can help for better understanding of the influencing factors and mechanisms of the development efficiency of carbonate reservoirs.

Influence of pore structure on thermal stress distribution inside coal particles during primary fragmentation

Thermal stress is an important reason of coal particle primary fragmentation, during which the role of pore structure is ambiguous. Thermal stress induced fragmentation experiments were conducted with low volatile coal/char particles, and the results show that the fragmentation severity enhances with increasing porosity. Various porous thermal stress models were developed with finite element method, and the influences of the pore shape, size, position and porosity on the thermal stress were discussed. The maximum thermal stress inside particle increases with pore curvature, the pore position affects the thermal stress more significantly at the particle center and surface. The expectation of the maximum tensile thermal stress linearly increases with porosity, making the particles with higher porosity easier to fragment, contrary to the conclusion deduced from the devolatilization theory. The obtained results are valuable for the analysis of different thermal processes concerning the thermal stresses of the solid feedstocks.

Influence of pore structure on corrosion resistance of high performance concrete containing metakaolin

Even though concrete is considered to be durable, the environment to which the concrete is exposed plays an important role in its durability. The durability of concrete is challenged due to its porous nature, which is especially important in harsh exposure conditions such as marine environment. The reinforced concrete elements of marine structures such as bridges, wharves, docks, etc. are subjected to various types of exposures such as wetting and drying action [WDA], fully submerged condition, and in contact with chlorides. To refine the pore structure of concrete and to improve the durability characteristics of such structures, it is essential to use high performance concrete [HPC]. In this study, metakaolin [MK] is used as partial replacement of cement to produce HPC. The use of metakaolin is found to be very effective in reducing the porosity of concrete. As the porosity of concrete decreases, the corrosion rate can be reduced considerably. The durability characteristics of metakaolin-incorporated HPC is studied for 365 days to investigate the changes in its pore structure in long term. The iCOR® NDT method is used to find the corrosion performance and concrete resistivity of high performance metakaolin concrete under a simulated wetting and drying action [WDA] of seawater over several periods. The deterioration effect caused by the simulated WDA of seawater is also studied by considering the bond strength of specimens subjected to normal and corrosive exposure conditions.