Gas Flow Research Articles

Rarefied gas flow in functionalized microchannels

The interaction of rarefied gases with functionalized surfaces is of great importance in technical applications such as gas separation membranes and catalysis. To investigate the influence of functionalization and rarefaction on gas flow rate in a defined geometry, pressure-driven gas flow experiments with helium and carbon dioxide through plain and alkyl-functionalized microchannels are performed. The experiments cover Knudsen numbers from 0.01 to 200 and therefore the slip flow regime up to free molecular flow. To minimize the experimental uncertainty which is prevalent in micro flow experiments, a methodology is developed to make optimal use of the measurement data. The results are compared to an analysis-based hydraulic closure model (ACM) predicting rarefied gas flow in straight channels and to numerical solutions of the linearized S-model and BGK kinetic equations. The experimental data shows that if there is a difference between plain and functionalized channels, it is likely obscured by experimental uncertainty. This stands in contrast to previous measurements in smaller geometries and demonstrates that the surface-to-volume ratio of 0.4 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}m-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document} seems to be too small for the functionalization to have a strong influence and highlights the importance of geometric scale for surface effects. These results also shed light on the molecular reflection characteristics described by the TMAC.

One-dimensional temperature measurement of gases based on femtosecond laser-extended electrode discharge spectroscopy (FEEDS)

Temperature, and hence thermometry techniques, are critical for characterizing gaseous flows and flames. Therefore, it is always attractive to develop new thermometry techniques to satisfy different demands. Here, we propose a thermometry technique for one-dimensional gas temperature measurements based on femtosecond laser-extended electrode discharge spectroscopy (FEEDS). By FEEDS measurements in gas flows containing hydrogen, we found that the temperature of the gas flow has a strong correlation with the full width at half maximum (FWHM) of the atomic hydrogen line at 656 nm, and this correlation is monotonic in the temperature range we measured, i.e., the temperature of gas flows can be extracted by measuring this FWHM. We applied this technique to methane/air gas mixtures and realized temperature measurements in the range of 300–1806 K with an error of ∼50 K. Also, we found that the technique has the capability to achieve one-dimensional measurements; more importantly, we found that changes in the stoichiometric ratio of the gas mixture do not affect the temperature measurements. Finally, we applied this technique to a premixed methane/air jet flame.

High-rate etching of silicon oxide and nitride using narrow-gap high-pressure (3.3 kPa) hydrogen plasma

We investigated the etching behavior of silicon oxide (SiO x ) and silicon nitride (SiN x ) in narrow-gap, high-pressure (3.3 kPa) hydrogen (H2) plasma under various etching conditions. Maximum etching rates of 940 and 240 nm min−1 for SiO x and SiN x , respectively, were obtained by optimizing the H2 gas flow rate. The dependence of the etching rate on gas flow rate implied that effective elimination of etching products is important for achieving high etching rates because it prevents redeposition. The sample surfaces, especially the oxide surfaces, were roughened and contained numerous asperities after etching. Etching rates of both SiO x and SiN x decreased as the temperature was raised. This suggests that atomic H adsorption, rather than H-ion bombardment, is an important step in the etching process. X-ray photoelectron spectroscopy revealed that the etched nitride surface was enriched in silicon (Si), suggesting that the rate-limiting process in high-pressure H2 plasma etching is Si etching rather than nitrogen abstraction. The etching rate of SiO x was three times higher than that of SiN x despite the higher stability of Si–O bonds than Si–N ones. One reason for the etching difference may be the difference between the bond densities of SiO x and SiN x . This study presents a relatively non-toxic, low-cost, and eco-friendly dry etching process for Si-based dielectrics using only H2 gas in comparison with the conventional F-based plasma etching methods.

Effect of delay time of working face pressure change on airflow direction in gob: A simulation study

AbstractFor shallow buried mines, the cracks generated due to the mining activities will connect the surface ground and the working face through the gob, which may result in the gas exchange between the surface and underground. In this study, we proposed the gob gas flow model and verified its applicability based on the measured data on site in our previous research and discussed the effect of delay time of pressure variation between working face and surface ground on the airflow direction according to the simulation. The results suggest that the delay time of pressure variation is the main factor affecting the pressure difference between surface and working face and airflow direction. Due to the characteristics of the surface pressure changes, the effect of delay time on airflow in gob is small in a short time, but this effect gradually increases with time. According to the airflow law in a cycle of pressure variation, the airflow direction in the gob is predictable when the delay time reaches a certain value, which can be interpreted clearly on the surface pressure variation diagram. This research may provide references for the measures taken against mine disasters caused by different airflow directions. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Recent Progress on Porous Carbons for Carbon Capture.

High emission of carbon dioxide (CO2) has caused CO2 levels to reach more than 400 ppm in air and led to a serious climate problem. In addition, in confined spaces such as submarines and aircraft, the CO2 concentration increase in the air caused by human respiration also affects human health. In order to protect the environment and human health, the search for high-performance adsorbents for carbon capture from high and low concentration gas is particularly important. Porous carbon materials, possessing the advantages of low cost and renewability, have set off a boom in the research of porous adsorbents, which have the opportunity to be utilized on a large scale for industrial carbon capture in the future. In this review, we summarize the recent research progress of porous carbons for carbon capture from flue gas and directly from air in the last five years, including activated carbon (AC), heteroatom-modified porous carbon, carbon molecular sieves (CMS), and other porous carbon materials, with a focus on the effects of temperature, water content, and gas flow rate of industrial flue gas on the performance of porous carbon adsorbents. We summarize the preparation strategies of various porous carbons and seek environmental friendly porous carbon materials preparation strategies under the premise of improving the CO2 adsorption capacity and selectivity of porous carbon adsorbents. Based on the effects of real industrial flue gas on adsorbents, we provide new ideas and evaluation methods for the development and preparation of porous carbon materials.

Investigation on foam properties of Gemini quaternary ammonium salt containing hydroxyl hydrophilic headgroup

Four Gemini quaternary ammonium salts, tetramethylene-1,4- bis [N, N-bis(hydroxypropyl)-hexa/decyloxypropylammonium] bromide (GC6/10-P) and tetramethylene-1,4-bis [N, N-bis(hydroxyethyl)-hexa/decyloxypropylammonium] bromide (GC6/10-E) were synthesized by two-step reactions. This study analyzes the foam properties, including foamability, foam stability, and foam size distribution, of GC6/10-P and GC6/10-E using the Foamscan method. The influence of surfactant concentration and gas flow rate on the properties of Gemini quaternary ammonium salt foam was also studied. Additionally, the relationship between surfactant structure and foam morphology in aqueous solutions was discussed. The results show that all four types of Gemini quaternary ammonium salt surfactants are low-foaming surfactants. The foam capacity (FC) sequence is as follows: GC10-E > GC10-P > GC6-E > GC6-P. The foamability and foam stability are enhanced with increasing surfactant concentration, which increases the adsorbed quantity of surfactant molecules at the air-water interface. The foam produced by GC6-P/E systems is the most unstable; the foam behaviors show faster Ostwald ripening and drainage process in aqueous system. It seems that 150–200 mL/min is an ideal air intake speed. The presence of hydroxyl in the molecular structure enhances the formation of hydrogen bonding between surfactants and water molecules, leading to greater molecular compactness. The results indicate that the foaming behavior of hydroxyl Gemini quaternary ammonium salts can be correlated with concentration and alkyl chains. Foamscan are proposed to research the foaming and foam stability behavior and provide a useful guide for evaluating the foamability of cationic surfactants-based systems, especially in the development of environmentally friendly foam systems suitable for low-foaming products.

Вплив детонаційної хвилі на перерозширений надзвуковий потік газу в со-плі

This paper proposes to use the detonation process to solve the problem of controlling highly maneuverable flying vehicles. The goal of the work is to study a new way of the thrust vector control of a rocket engine using the effect of a detonation shock wave on the gas flow in the nozzle. It is known that the method of thrust vector control by gas injection into the supersonic nozzle area of a rocket engine features one of the lowest losses of specific momentum and a high response speed and produces a significant lateral force. However, for the current level of rocket technology, there is a need to improve these characteristics. Detonation is considered as a method to intensify processes that affect the main gas flow and produce a lateral force. Its features make it possible to develop a system for pulse trajectory correction. In order to study the features of such a system, experimental studies of the detonation wave effect on a supersonic nozzle flow were conducted. A nozzle model and a gas generator for initiating a detonation wave interacting with the main supersonic air flow were developed and made. In the course of experiments, the effect of separation of the main flow from the nozzle wall by the detonation wave during the nozzle operation in the overexpansion mode was revealed. The duration of this effect was much longer than that of the detonation product effect on the main air flow in the nozzle, thus allowing it to be used in the development of a new thrust vector control method. To better understand the experimental results, a numerical simulation of the detonation wave propagation in a supersonic flow was carried out for the test conditions. The simulation was carried out in a non-stationary 2D formulation using the Solid Works software package. The goal of the simulation was to estimate the flow structure and the value of the relative lateral force produced by the change of this structure during detonation product injection into the supersonic nozzle area. The time evolution of the pressure field was obtained. The relative lateral force produced by detonation product injection into the supersonic air flow in the nozzle was determined. The presented features and method of jet engine thrust vector control may be used in unmanned systems operating in a wide range of speeds.

Numerical simulation and optimization of the multi-stage air/gas supply system in a coke oven battery with 7.1 m coking chambers

ABSTRACT 3-D numerical simulations based on diffusion combustion technology were employed to optimize the multi-stage air/gas supply system in a coke oven battery with 7.1 m coking chambers. In the heating flues, the Eddy-Dissipation Concept (EDC) model and the ideal gas model were utilized to numerically investigate diffusion combustion. What is more, the radiation between the flue gas and the silicon brick was calculated using the Discrete Ordinates (DO) model. After validating the reliability of the model with field-measured data, insights into the temperature field and gas flow in the heating flue, and heat flux distribution over the heating wall were obtained. To characterize the vertical heating uniformity, an index of the standard deviation of the heat flux over the vertical heating walls was proposed. By optimizing the multi-stage air/gas supply design of heating flues, the vertical heating uniformity was improved by 60% according to the index values. The approach developed in this work can be a useful tool for the design of large-capacity coke oven batteries at different scales.

Effect of Gas Composition on Temperature and CO2 Conversion in a Gliding Arc Plasmatron reactor: Insights for Post-Plasma Catalysis from Experiments and Computation.

Plasma-based CO2 conversion has attracted increasing interest. However, to understand the impact of plasma operation on post-plasma processes, we studied the effect of adding N2, N2/CH4 and N2/CH4/H2O to a CO2 gliding arc plasmatron (GAP) to obtain valuable insights into their impact on exhaust stream composition and temperature, which will serve as feed gas and heat for post-plasma catalysis (PPC). Adding N2 improves the CO2 conversion from 4 % to 13 %, and CH4 addition further promotes it to 44 %, and even to 61 % at lower gas flow rate (6 L/min), allowing a higher yield of CO and hydrogen for PPC. The addition of H2O, however, reduces the CO2 conversion from 55 % to 22 %, but it also lowers the energy cost, from 5.8 to 3 kJ/L. Regarding the temperature at 4.9 cm post-plasma, N2 addition increases the temperature, while the CO2/CH4 ratio has no significant effect on temperature. We also calculated the temperature distribution with computational fluid dynamics simulations. The obtained temperature profiles (both experimental and calculated) show a decreasing trend with distance to the exhaust and provide insights in where to position a PPC bed.

Investigation of melt pool dynamics and solidification microstructures of laser melted Ti-6Al-4V powder using X-ray synchrotron imaging

Titanium alloy (Ti-6Al-4V) is widely used in additive manufacturing (AM) industry. However, as laser powder-bed fusion (PBF-L) additive manufacturing (AM) advances towards reliable production of titanium parts, a thorough understanding of the process-structure-properties (PSP) relationships remain to be fully understood. A study of the laser melting was paired with high-speed X-ray synchrotron imaging at the 32-ID beamline of the Advanced Photon Source at Argonne National Laboratory. Simultaneous melting and imaging was carried out on a Ti-6Al-4V powder layer held in a custom device designed to mimic single-track scans of the PBF-L process at different laser power levels, powder size distributions, and cover gas environments (Ar and He) on top of AM Ti-6Al-4V base metal. It was found that the thickness of the powder layer significantly affected the melt behavior: too much powder led to the formation of molten droplets that wetted the surface of the titanium, yet did not contribute to a uniform melting profile. Residual gas pores in the atomized powder were also observed to contribute to the pores observed in the melt pool, with the porosity of the powder (defined as volume of pores divided by total material volume) constant with powder size distribution (i.e., larger particles contained more entrapped gas, which increased final part porosity). When varying Ar or He through the same gas flow meter settings and nozzle, the difference in flow rates likely contributed more to the resultant porosity of the solidified material than did the thermal conductivity of the gasses, with He being the greater contributor to porosity. The microstructure of the heat affected zone contained α′, α, and an increased β phase fraction relative to the base material. The crystallographic texture of the melt pool region adopted that of the base metal.

Remote inductively coupled plasmas in Ar/N2 mixtures and implications for plasma enhanced ALD

Plasma enhanced atomic layer deposition (PEALD) is a cyclic atomic layer deposition (ALD) process that incorporates plasma-generated species into one of the cycle substeps. The addition of plasma is advantageous as it generally provides unique reactants and a substantially reduced growth temperature compared to thermal approaches. However, the inclusion of plasma, coupled with the increasing variety of plasma sources used in PEALD, can make these systems challenging to understand and control. This work focuses on the use of plasma diagnostics to examine the plasma characteristics of a remote inductively coupled plasma (ICP) source, a type of plasma source that is commonly used for PEALD. Ultraviolet to near-infrared spectroscopy and spatially resolved Langmuir probe measurements are employed to characterize a remote ICP system using nitrogen-based gas chemistries typical for III-nitride growth processes. Spectroscopy is used to characterize the relative concentrations of important reactive and energetic neutral species generated in the remote ICP as a function of gas flow rate, Ar/N2 flow fraction, and gas pressure. In addition, the plasma potential and plasma density for the same process parameters are examined using an RF compensated Langmuir probe downstream from the ICP source. The results are also discussed in terms of their impact on materials growth.

Presence of hazardous chemical elements in low-cost children's toys: A risk to their development in early childhood

ObjectivesThe objectives of the current study was to study the presence of hazardous chemical elements (Ba138, Cd111, Cr52, Pb208, As75, Co59, Cu63, Mn55, Ni60, Se82, Sr88, Zn66 and Hg202) in low-cost children's toys, and the effect of color types on chemical element concentrations. MethodsChildren's toy samples were analyzed using microwave digestion and inductively coupled plasma/mass spectrometry (ICP/MS) method. Samples were prepared into small pieces, and 500 mg of homogenized sample was used for digestion by means of digesting regents HNO3 (65 %, 5 mL) and H2O2 (35 %, 1 mL). During the digestion process, the pressure was held constant at 90 bar and the temperature, hold time, and power were varied 150–170-40° C, 10–30-5 min, 70–90-0 %, respectively. The main operating conditions of ICP/MS were: spray chamber temperature (−20 °C), RF Power (1450 W), nebulizer gas flow (0.9 L/min), auxiliary gas flow (0.8 L/min) and plasma gas flow (14.85 L/min). Samples and blanks were analyzed for 30 s and system was operated in standard mode. ResultsThe excellent method performance was achieved in terms of limit of detection (LOD, 0.001–14.89 µg/L); limit of quantification (LOQ, 0.003–45.12 µg/L); correlation coefficient (R2, 0.975–0.999) with relative standard deviation values (RSD, 0.70–4.98 %). Chemical elements were found in all the toys (0.01–742.72 ng/g) except sample S2 where only Hg202 was found (0.01 ng/g). Outcomes revealed that the Hg202 was present at a very low level (0.01 ng/g) while Zn66 was present at very high level (742.72 ng/g). Furthermore, the toys contamination was also found to be color-specific, with significant amount of chemical elements was found in black type car sample (S5, 946.98 ng/g) whereas other color type samples constitute lower amounts (0.001–210.53 ng/g). Low-cost toys designed for children's use are found to contain chemical elements that should be addressed in the course of action. As a result of exposure to high amounts of chemical elements in toys, children have a high chance of developing cancer.

An Experimental Study on the Seepage Characteristics of Rough Fractures in Coal under Stress Loading

Fracture and stress environments significantly affect the flow of coalbed methane. Under stress, fracture deformation and damage occur, which change the original fracture characteristics and lead to changes in gas flow characteristics. The change in gas pressure gradient makes the fluid flow obviously nonlinear. Using linear flow theory to describe the fracture flow leads to a large error in predicting coalbed methane productivity. In this study, seepage tests on fractured coal are carried out under different stresses and gas pressure gradients, the nonlinear flow and changes in related parameters are analyzed, and the applicability of the nonlinear flow equation is evaluated. The resulting seepage of the gas flow in the fracture under stress is obviously nonlinear, which gradually increases with increasing effective stress and gas pressure gradient. When the Forchheimer equation is used to characterize the nonlinear seepage in fractures, the coefficients increase with increasing effective stress. The permeability, nonlinear factor, and critical Reynolds number decrease with increasing effective stress. When the Izbash equation is used for this case, the linear coefficient ranges from 1015 to 1016, and the nonlinear coefficient ranges from 1.064 to 1.795. The coefficients are related to the effective stress through a power function. Both the Forchheimer and Izbash equations can characterize the flow in rough fractures in coal during stress loading. However, the Forchheimer equation better reveals the mechanism of flow transformation from linear to nonlinear in fractures.

3D-CFD Modeling of Hollow-Fiber Membrane Contactor for CO2 Absorption Using MEA Solution.

Membrane technology is considered an innovative and promising approach due to its flexibility and low energy consumption. In this work, a comprehensive 3D-CFD model of the Hollow-Fiber Membrane Contactor (HFMC) system for CO2 capture into aqueous MEA solution, considering a counter-current fluid flow, was developed and validated with experimental data. Two different flow arrangements were considered for the gas mixture and liquid solution inside the HFMC module. The simulation results showed that the CO2 absorption efficiency was considerably higher when the gas mixture was channeled through the membranes and the liquid phase flowed externally between the membranes, across a wide range of gas and liquid flow rates. Sensitivity studies were performed in order to determine the optimal CO2 capture process parameters under different operating conditions (flow rates/flow velocities and concentrations) and HFMC geometrical characteristics (e.g., porosity, diameter, and thickness of membranes). It was found that increasing the membrane radius, while maintaining a constant thickness, positively influenced the efficiency of CO2 absorption due to the higher mass transfer area and residence time. Conversely, higher membrane thickness resulted in higher mass transfer resistance. The optimal membrane thickness was also investigated for various inner fiber diameters, resulting in a thickness of 0.2 mm as optimal for a fiber inner radius of 0.225 mm. Additionally, a significant improvement in CO2 capture efficiency was observed when increasing membrane porosity to values below 0.2, at which point the increase dampened considerably. The best HFMC configuration involved a combination of low porosity, moderate thickness, and large fiber inner diameter, with gas flow occurring within the fiber membranes.

New Oil and Gas Plays in the Cis-Urals

Abstract ––The search for oil and gas in folded zones and in the foredeep of the cis-Uralian region for many decades was reduced to testing of easy-to-find closures and reefs located at shallow depths. Many important discoveries were made as a result, but the overall performance of the work remained relatively low. On the one hand, this was due to the poor subsurface imaging of the data for reliable preparation of structures in regions of complex structure. On the other hand, the peculiarities of the development of oil and gas systems in these regions were ignored during the assessment of prospecting sites. In comparison with traditional production hubs centers in the platform regions of the Volga–Ural and Timan–Pechora basins, this distinguishing feature was caused by a thicker sedimentary cover, the variability of its composition and structure, and multiple phases of structural development. Many failures were due to the formation of traps after the passage of the primary migration flow of oil and gas, low capacity of reservoirs, and their fracturing by faults. As shown by interpretation of new geodata using modern knowledge about the oil and gas potential of regions of similar structure, the cis-Uralian region contains poorly studied oil and gas accumulation zones that can contain large deposits. These include blind thrust regions, subsalt traps in development zones of dislocated diapirs, and also stratigraphic and combined traps associated with unconformities and facies changes. The utmost attention is paid to new prospecting objects in the Timan–Pechora basin in which the thickness of the Paleozoic cover has increased. The preparation of new promising objects in these zones has become possible due to new knowledge and better geophysical data.

The high-temperature gas soft measurement method based on the temperature attenuation patterns of flowing argon gas inside a cavity

The device for generating the airflow temperature signal is employed in aircraft ground simulation. This process involves heating the argon gas by the arc discharge to generate high-temperature gas, which subsequently flows into the cavity and mixes with cold gas to produce the temperature signal. However, the temperature of argon gas at the entrance of the cavity is excessively high, and sensor installation is challenging, making direct measurement difficult. This paper introduces a high-temperature gas soft measurement method based on the temperature attenuation patterns of flowing argon gas inside the cavity, and establishes a mathematical model for the flow and temperature distribution of argon gas within the cavity. The method calculates the target temperature at the entrance of the cavity by measuring the lower-temperature argon gas at the outlet of the cavity. Furthermore, a simulation and experimental platform were set up to validate the proposed method. The experimental results indicate that there is a 7.9% deviation between the soft measurement values and the directly measured values of argon gas temperature in the middle of the cavity. At the outlet of the cavity, the maximum deviation between the directly measured argon gas temperature and the simulation calculation results based on the soft measurement values at the entrance temperature is 5.2%. The paper rigorously validates the accuracy of the soft measurement method from various perspectives. Notably, this method offers the advantage of remote indirect measurement, and indirectly expanding the upper limit of the temperature sensor.

Pore-scale study of the dynamic evolution of multi-phase seepage parameters during hydrate dissociation in clayey silt hydrate-bearing sediments

Unlike conventional oil and gas sources, natural gas hydrate (NGH) is stored in solid form within the pores of loose submarine sediments. Production by any method poses a complex problem involving phase transition and multi-phase flow of gas and water. The evolution of hydrate dissociation from the solid phase to gas and liquid phases in a hydrate reservoir is a dynamic process incorporating pore structure and multi-phase seepage. The solid–gas-liquid phase dissociation of NGH affects reservoir seepage properties by altering the micropore structure of the hydrate-bearing sediments. This study, based on the lattice Boltzmann method of modeling fluids flow, clearly demonstrates the micropore-scale changes in pressure and heat transfer that take place during hydrate dissociation. Pore-scale heterogeneity is found to influence the complex development of hydrates in a porous clayey silt medium during dissociation. The effect of hydrate, gas and water saturation on the evolution of relative permeability is identified, and the relationship between relative permeability and hydrate saturation during hydrate dissociation is quantified. These findings provide theoretical support for the implementation of marine natural gas hydrate production testing and future commercial production in China.

Study on heat transport analysis and improvement method in a single CaCO3 pellet for thermochemical energy storage

CaCO3/CaO thermochemical energy storage (TCES) pellets have significant advantages in bulk energy storage density, transport, and utilization. However, severe heat transport limitations within the milli-sized CaCO3 significantly affect the TCES efficiency and economy. Currently, investigations on the effect of initial porosity, bulk gas flow velocity, and reaction rate on heat transport and methods of enhancing the heat transport inside the pellet are lacking. In this paper, we developed a mathematical model coupling calcination reaction, mass transfer, and heat transfer to reveal the effects of pellet parameters and operating conditions on heat transport and reaction conversion rate within a CaCO3 pellet. The results show that the size of the CaCO3 pellet, bulk gas temperature, and reaction rate generate the most pronounced impacts on heat transport in a single CaCO3 particle during the TCES process. Furthermore, the heat transport inside the CaCO3 pellet can be improved by appropriately increasing the bulk gas flow velocity. Finally, this paper first numerically investigates the addition of SiC as a thermal conductivity enhancer to improve the heat transport performance inside a CaCO3 pellet. This study can guide the design of high-performance CaCO3 composite pellets and inform the selection of operating conditions for subsequent reactor applications.

Effect of hydrofluoric acid on Guizhou anthracite structure modification and response to enhanced hydrolysis and permeability of coal

ABSTRACT To investigate the structural modification of Guizhou anthracite through the application of hydrofluoric acid and its corresponding response in terms of enhanced gas desorption and permeability, we utilized Guizhou anthracite from a mining area as the focal point of our study. We conducted a series of experiments encompassing X-ray diffraction (XRD), initial gas release velocity measurements, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR). Our investigation identified hydrofluoric acid as the primary acid solution, with an optimal concentration of 6% and a soaking duration of 12 hours. Furthermore, our theoretical analysis unveiled the physicochemical structural evolution of Guizhou anthracite under the influence of hydrofluoric acid and its subsequent response to enhanced gas desorption and permeability within the coal. Regarding chemical structure, hydrofluoric acid effectively dissolves inorganic minerals in anthracite and reduces the condensation of its regular basic structural units. Peak fitting of functional groups on the surfaces of the experimental coal samples revealed that hydrofluoric acid induces side chain reactions in the molecular structure of anthracite, promoting the gradual ordering of the aromatic structure. Simultaneously decreasing the content of cyclically closely bonded and self-associated hydroxyl hydrogen bonds. These alterations in irregular basic structural units can diminish coal’s adsorption capacity for gas, thereby enhancing gas desorption. Regarding the physical structure, treatment with hydrofluoric acid leads to the dissolution of minerals within specific pores and fissures of the coal samples, generating numerous dissolution pores. These pores and fissures expand and interconnect. The surface morphology quantified by fractal dimension has decreased by about 25.8%, indicating that pore and fracture structures often become relatively simple, which is conducive to gas flow and desorption in coal. Furthermore, the effective porosity and total porosity of the coal samples increase, as does the total movable fluid porosity. This enhances pore connectivity within the coal seam. Calculations reveal that after acidification, the permeability of the experimental coal samples increases by approximately 1.37 times, confirming the permeability-enhancing effect of hydrofluoric acid on anthracite.

Harnessing microwave energy to transform Nephelium lappaceum L. peel into activated carbon for chloramphenicol eradication in aqueous solutions

Emerging contaminants (EC) like chloramphenicol in wastewater are highly related to human, livestock, and aquaculture therapeutic activities. High levels of chloramphenicol in water may cause toxic effects on an aquatic environment, humans, and animals. The removal of chloramphenicol in wastewater was the main objective of this study. This study explores the use of microwave irradiation in the production of Rambutan peel-based activated carbon (RPAC) at a heating power of 700 W for 15 min under carbon dioxide, CO2 gas flow. RPAC had a BET surface area of 583.44 m2/g, mesopores surface area of 469.87 m2/g, total pore volume of 0.27 cm3/g, and average pore diameter of 2.31 nm. The equilibrium study shows that the concentration of Cp adsorbed by RPAC increased as the initial concentration increased from 4.93 mg/g to 25.10 mg/g. Isotherm adsorption determined that Langmuir was the preferred model since it has the lowest RSME and highest R2 of 3.34 and 0.9994, respectively. It was observed from kinetic studies that the adsorption system relies on the pseudo-second order. According to thermodynamic studies, the enthalpy change, △H° and Gibbs free energy, △G° obtained indicating that the adsorption process occurs in an exothermic and spontaneous state.