Temperature Dependence Of Adsorption Research Articles

Flexible-Rigid Aluminum-Organic frameworks with Ultra-Fine Pore-Environment regulation for benchmark acetylene storage and purification

Rational regulation of functional groups on the pore surface of robust aluminum metal–organic framework (CAU-10-H) from amino (–NH2), hydrazino (–N2H3), to azido (–N3) continuously control their framework rigidity-flexibility together with ultra-fine pore-size change in the scale of 0.1–0.5 Å. Benefited from the rigid architecture and suitable pore environments, CAU-10-NH2 exhibits a supreme acetylene (C2H2) storage density (473 g/L) exceeding the values of liquid C2H2 (393 g/L) and all reported MOF adsorbents under ambient conditions. Different from CAU-10-H/NH2/N2H3, CAU-10-N3 exhibited temperature-dependent flexible stepwise adsorption behaviors for C2H2 with azido groups as the guest-sensitive gate, having highest storage capacity (106 cm3 cm−3) and second-high storage density (405 g/L) among these materials. Notably, compared with other C2-hydrocarbon and CO2 molecules, only C2H2 can open the azido door at 298 K, and thus effectively enhancing their separation selectivity with top-level uptake ratios for C2H2/C2H4 (2.65) and C2H2/CO2 (2.93), which are further supported by the practical fixed-bed breakthrough curves and theoretical simulations. Such a rational combination of rigidity and flexibility breaks new ground in MOF chemistry and sets a benchmark for acetylene storage and purification.

High-temperature adsorption of nitrogen dioxide for stable, efficient, and scalable doping of carbon nanotubes

This work is devoted to a novel efficient strategy for single-walled carbon nanotube doping employing heat treatment with nitrogen dioxide (NO2). Unlike numerous reports of unstable NO2 doping at room temperature, our method combines high efficiency and stability, enabled by its temperature-dependent adsorption on the nanotube surface. We reveal that doping stability increases with the treatment temperature reaching maxima at 300 °C avoiding any detrimental effect on nanotube structure and optical transmittance. As a result, we demonstrate doped carbon nanotube transparent conductive films exhibiting competitive performance (in respect to films treated with other dopants) with a less than 50% drop in conductive characteristics for over a year. Thermo-programmed desorption analysis and X-ray photoelectron spectroscopy confirm the preferential formation of long-living adsorbed nitrogen species, such as NO3-groups, as a result of high-temperature treatment. We believe the current work provides a basis for the robust and technologically efficient doping of single-walled carbon nanotubes and related structures at industrial scales, as the developed method could be easily coupled with a continuous technology of carbon nano materials production.

Temperature-dependent molecular sieving of fluorinated propane/propylene mixtures by a flexible-robust metal-organic framework.

The electronics industry necessitates highly selective adsorption separation of hexafluoropropylene (C3F6) from perfluoropropane (C3F8), which poses a challenge due to their similar physiochemical properties. In this work, we present a microporous flexible-robust metal-organic framework (Ca-tcpb) with thermoregulatory gate opening, a rare phenomenon that allows tunable sieving of C3F8/C3F6. Remarkably, the temperature-dependent adsorption behavior enhances the discrimination between the larger C3F8 and the smaller C3F6, resulting in unprecedented C3F6/C3F8 selectivity (over 10,000) compared to other well-known porous materials at an optimal temperature (298 K). Dynamic breakthrough experiments demonstrate that high-purity C3F8 (over 99.999%) could be obtained from a C3F6/C3F8 (10:90) mixture under ambient conditions. The unique attributes of this material encompass exceptional adsorption selectivity, remarkable structural stability, and outstanding separation performance, positioning it as a highly promising candidate for C3F6/C3F8 separation. Single-crystal structural analysis of C3F6-loaded Ca-tcpb and theoretical calculations elucidate the host-guest interaction via multiple intermolecular interactions.

Adsorption kinetics of CH4 and CO2 on shale: Implication for CO2 sequestration

The adsorption kinetic behavior of CH4 and CO2 in shale is critical for design and practice the CO2 sequestration with enhanced shale gas recovery. In this study, adsorption isotherms and kinetics curves of CH4 and CO2 in two shale samples were measured by the volumetric method at the temperature of 308.15 K, 323.15 K, 338.15 K and 353.15 K with the pressures up to 12 MPa. The pseudo-first-order (PFO) model, pseudo-second-order (PSO) model and Bangham model were used to describe the adsorption kinetics data. Furthermore, the influence of pressure and temperature on the adsorption kinetic behavior of CH4 and CO2 was clarified. The results show that the adsorption kinetic curves can be classified into three stages: rapid adsorption, slow adsorption and adsorption equilibrium stage. The fitting accuracy of the three kinetic models is in the order of Bangham > PSO > PFO. Moreover, the adsorption kinetics of CH4 and CO2 are highly dependent on pressure and temperature. The adsorption rate constant (kb) of CH4 and CO2 increases first and then decreases with increasing pressure. At the pressure below the supercritical pressure of CO2, the kb of CO2 shows a decreasing trend with the increase of temperature, which is the same as that of CH4. However, after exceeding the supercritical pressure of CO2, the variations in kb of CO2 with temperature presents an opposite trend as it increased with increasing temperature. Therefore, the pressure and temperature dependent adsorption kinetic behaviors requires consideration for optimizing engineering parameters in application of CO2 enhanced shale gas recovery and sequestration.

Effective Removal of Hexavalent Chromium from Aqueous Solutions Using Quaternary Ammonium-Functionalized Magnetic Graphene Oxide Composites

Novel quaternary ammonium/magnetic graphene oxide composites (M-PAS-GO) that efficiently remove Cr(VI) ions were fabricated through the introduction of the (3-aminopropyl) triethoxysilane and Fe3O4 nanoparticles on the surface of GO, and then modified with n-butyl bromide. The fabricated M-PAS-GO was comprehensively characterized by SEM, TEM, EDX, XRD, Raman spectroscopy and FTIR, and the results manifest that the quaternary ammonium group was introduced onto the surface of GO. Under the reaction conditions of pH 3.20, temperature of 25 °C and M-PAS-GO dosage of 0.01 g/50 mL, 90% of 10 mg/L Cr(VI) ions were removed from the solution within 20 min. The kinetics study indicates that the adsorption process followed the pseudo-second-order model and was surface reaction-controlled. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggest that the adsorption process was an exothermic and spontaneous process. The maximum adsorption capacities of Cr(VI) ions on M-PAS-GO composites calculated by the Langmuir model were 46.48 mg/g. Moreover, the reusability and stability of M-PAS-GO demonstrates its economic sustainability. This study suggests that M-PAS-GO is a potential candidate adsorbent for the separation of Cr(VI) from wastewater.

Surface modification of natural clay with H2O2 for high adsorption of acid Red 114: Experimental and modelling studies

The water contamination problem caused by dyes and the understanding of their adsorption mechanism in aqueous media is still significant nowadays. This study investigates the adsorption performance of natural montmorillonite clay treated with H2O2 (MMT-H2O2) and employed as an adsorbent to remove Acid Red 114 (AR-114) from aqueous solutions. MMT-H2O2 and the natural clay without treatment (MMT) were analysed using different analytical techniques such as XRF, XRD, FESEM, EDS, FTIR, TGA/DTG, N2-adsorption/desorption curves, CHNS/O analysis, hydrophobicity Index (HI). It also provides a theoretical analysis of the adsorption phenomenon utilising Statistical Physics methods to understand the adsorption mechanism between AR-114 and MMT-H2O2 adsorbent associated with batch adsorption conditions and adsorption equilibrium. The treated clay with H2O2 showed a higher oxygen content and a better adsorption capacity than the untreated one. The maximum adsorption capacity (Qmax) values obtained with the best-fitted model (Liu) ranged from 421.9 and 1178.5 mg g−1. This high adsorption capacity for AR-114 dye can be explained by considering the remarkable characteristics of the MMTH2O2 material, such as high oxygen content, variety of surface functional groups, porous interlayer structure, and hydrophilicity. The computational adsorption results suggest that the AR-114 molecules adsorbed onto the surface site of the MMTH2O2 adsorbent in a perpendicular orientation. This indicates that the n2 values increased as the operating temperature was raised, demonstrating the endothermic accumulation of dye molecules on the treated clay mineral surface. Moreover, the temperature-dependent adsorption energies (E1 and E2) levels were less than 40 kJ mol−1, highlighting the primary physical interactions between AR-114 and MMTH2O2 clay mineral by electrostatic attraction and hydrogen bonding.

Temperature-dependent ethylene dissociative adsorption on ruthenium

The dissociative adsorption of ethylene onto Ru(111) at different temperatures was computed systematically at the first time. At 105 K, ethylene dissociative adsorption has the co-adsorbed CH2C*+2H* and CH3C*+H* as the first and second stable surface intermediates. At over 330 K, CH3C*+H* is converted back into CH2C* accompanied by H2 desorption and the subsequent dissociation of CH2C* into HCC*, HC*+C* and 2C*. The computed Arrhenius activation barriers of the dissociation of CH2CH2 (0.18 vs. 0.22 ± 0.04 eV) and CH3C (0.54 vs. 0.52 ± 0.04 eV) agree perfectly with the available experimental values, and CH3C* represents the most stable surface species. Under CO co-adsorption, the most stable surface species are the co-adsorbed CH3C*+H*+3CO*. It is found that CO co-adsorption promotes H2 desorption and stabilizes CH3C* by blocking the surface sites for dissociation and raises the dissociation barrier compared to the clean surface (0.78 vs 0.54 eV). Brønsted–Evans–Polanyi relationship between the activation Gibbs free energy barrier and reaction Gibbs free energy is found for CH2C*+2H*+nCO* = CH3C*+H*+nCO* and CH2C*+2H*+nCO* = HCC*+3H*+nCO* (n = 0–3). Ethylene adsorption has di-σ and π adsorption configurations in very close energy, and H2 has adsorption energy of about 0.90 eV.

Effect of anionic surfactants on the heavy metal ions removal by adsorption onto ion exchangers - batch and column studies

Adsorption of heavy metals by various sorbents has been widely studied by many scientists due to the processes of industrialization as well as the great concentration of these toxic and dangerous pollutants in the environment the elimination of which is significant important. The ion exchangers Lewatit MonoPlus SR7, Lewatit MonoPlus TP220, Purolite A830 and Lewatit AF5 were used as adsorbents to remove heavy metal ions (M(II)) such as zinc (Zn(II)), nickel (Ni(II)) and copper (Cu(II)) (especially Cu(II)) in the presence of anionic surfactants to examine the adsorption efficiency in such systems. The main objective of this paper were the kinetic, equilibrium, thermodynamic and column studies in the HCl–M(II)–anionic surfactant (AS) such as SDS (Sodium Dodecyl Sulfate), ABS (Dodecylbenzene Sulfonic Acid) or ABSNa50 (Sodium Dodecylbenzene Sulfonate) systems. The largest adsorption capacities were obtained in the HCl–M(II)–AS systems for Lewatit MonoPlus TP220 (Cu(II): 9.9–10 mg/g; Zn(II): 8.5–8.9 mg/g and Ni(II): 7.3–9.2 mg/g) compared to the other ion exchangers. Therefore, after the first selection, Lewatit MonoPlus TP220 and the systems containing Cu(II) were further examined. The isotherms models were applied in the experimental data analysis and show that the Langmuir (determination coefficient, R2 > 0.993) and Temkin (R2 = 0.948–0.965) isotherm models exhibit the best fitting. The results of the temperature-dependent adsorption of Cu(II) in the presence of SDS on Lewatit MonoPlus TP220 suggested that the adsorption was spontaneous, thermodynamically favourable, and exothermic in nature (the enthalpy, ∆H° = −7.19 kJ/mol (↓CMC) and −7.03 kJ/mol (↑CMC). The largest working ion exchange capacities of the anion exchange resin were obtained for the ABS surfactant (Cw = 30 g/L (↓CMC) and 12 g/L (↑CMC)). As follows from the current investigations Lewatit MonoPlus TP220 has a great potential for the removal of Cu(II) in the presence of ABS and SDS. For comparison, Cu(II) ions removal by the micellar enhanced ultrafiltration process was also presented and exhibits 54–73.88 % Cu(II) removal efficiency in the presence of SDS and ABS.

Manipulation of Thermoresponsive Polymers Using Biomolecules

Thermoresponsive polymers (TRPs) have attracted considerable interest in the scientific community because of their potential applications in sensors, gels, drug delivery devices, biotechnology, and pharmacology. Certain biomolecules alter the phase transition behavior of TRPs by acting as external biological stimuli. Herein, we describe recently reported results and trends for TRP/biomolecule mixed systems in which biological stimuli modulate temperature-dependent polymer transitions and reviewed studies related to protein–polymer assembly formation, interactions, and temperature-dependent protein adsorption. Modifying polymer properties in response to biomolecules, which are inherently present in the human body, designs polymeric biomaterials with envisaged applications. We hope this review sheds light on scientific problems concerning biomolecule–polymer mixed systems and helps in designing next-generation “smart” polymers.

Time-Resolved MIR Reflection–Absorption Spectroscopy of N2O, CO, and CH4 Adsorption on Graphene

The time- and temperature-dependent adsorption of N2O, CO, and CH4 on CVD-grown graphene has been investigated by MIR reflection–absorption spectroscopy to gain information about the adsorption kinetics, notably the rate constants k and activation energies Ea of the adsorption step. The gas adsorption is followed by determining the change of the reflected beam intensity with time by taking difference spectra, i.e., subtracting the baseline signal (reflectivity of graphene at the respective gas excitation line) from the measurement with added gas. The experiments yield adsorption activation energies Ea of −19.6 ± 1.1 (N2O), −12.1 ± 0.2 (CO), and −9.5 ± 1.7 kJ/mol (CH4). The obtained Ea values are in excellent agreement with the literature results from theory, thereby confirming these studies. The Ea values indicate physisorption, i.e., no strong bonding of the gas molecules to graphene. The analyzed adsorption rate constants k are reported for the first time and are on the order of 1011 to 1012 molecules·s–1·cm–2 with N2O showing the highest value and CH4 the lowest value. The adsorption rate constants follow the series N2O > CO > CH4, in line with the charge transfer abilities of the molecules. This work can be easily extended to kinetic studies of other gases hazardous to the environment and adsorption studies with other 2D materials using versatile MIR reflection–absorption spectroscopy.

Temperature-Programmed Separation of Hexane Isomers by a Porous Calcium Chloranilate Metal-Organic Framework.

The full separation of alkane isomers as a function of different degrees of branching remains a daunting challenge due to its stringent requirement with respect to pore dimensions of the adsorbents. In this work, we report a novel microporous coordination network built on calcium (II) and chloranilate. The compound has a flexible framework and exhibits temperature-dependent adsorption behavior toward hexane isomers. At 30 °C, it accommodates substantial amounts of linear and monobranched hexanes but fully excludes their dibranched isomer, and at elevated temperatures such as 150 °C, it acts as a splitter for linear and branched alkanes. Its capability of efficient discrimination of hexane isomers as a function of branching is verified by experimental breakthrough measurements. Ab initio calculations have uncovered the underlying selective size-exclusion separation mechanism.

A novel passive polymer-sorbent thermal battery for low-temperature energy applications: A numerical feasibility study

Sorption thermal energy storage (STES) systems offer great potential for meeting the growing energy needs and increasing the use of renewable energy resources. However, the complexity and large-scale of current STES technologies lead to relatively low-efficiency systems, severely limiting their widespread implementation. To address this challenge, this study presents a novel and compact smart-polymer sorbent (SPS) thermal battery with passive material-enabled mechanisms for controlled low-temperature thermal energy storage applications. A numerical model is established to investigate the coupled heat and mass transport processes underlying the working behavior of the SPS battery. It is also used to reveal the interdependence of the two processes and the limiting factors for the battery's thermal performance. The heating performance of several SPS battery designs was studied as an example, focusing on their application for cold environment thermal protection. Moreover, the influence of various design parameters was examined, including sorbent selection, void fraction, relative humidity, gate thickness, and gate-to-sorbent area, along with their implications to the coupled mass-heat transport processes. The results revealed that diffusion-based mass transport is the limiting process affecting the SPS battery thermal performance. The numerical simulation results also indicated that the sorbent selection should consider their low recharge temperature (40 °C–100 °C) and less pronounced temperature-dependent adsorption behavior to maximize the heating performance of the SPS battery. In addition, the SPS battery heating efficiency could be enhanced by increasing the sorbent void fraction to 0.35, relative humidity (RH) to 40 %, and gate-to-sorbent area to 60 % while decreasing the gate thickness to 0.1 μm effectively, which facilitate the diffusion-controlled mass transport process. Lastly, a single layer SPS battery is beneficial for thermal regulation at low temperatures; however, using distributed battery designs had a significant thermal performance enhancement benefit of 90 % compared to the single layer design. Hence, our study reveals the complex coupling effects of the heat and mass transport processes within the proposed SPS battery and provides insights and guidance (e.g., materials selections and SPS design) for engineering emergent small-scale passive STES applications.

Thermodynamic limits of atmospheric water harvesting with temperature-dependent adsorption

Adsorption-based atmospheric water harvesting (AWH) has vast potential for addressing global water shortage. Despite innovations in adsorbent materials, fundamental understanding of the physical processes involved in the AWH cycle and how material properties impact the theoretical limits of AWH is lacking. Here, we develop a generalized thermodynamic framework to elucidate the interplay between adsorbent properties and operating conditions for optimal AWH performance. Our analysis considers the temperature dependence of adsorption, which is critical but has largely been overlooked in past work. Using metal-organic framework (MOF) as an example, we show that the peak energy efficiencies of single-stage and dual-stage AWH devices, after considering temperature-dependent adsorption, increased by 30% and 100%, respectively, compared with previous studies. Moreover, in contrast to common understanding, we show that the adsorption enthalpy of MOFs can also be optimized to further improve the peak energy efficiency by 40%. This work bridges an important knowledge gap between adsorbent materials development and device design, providing insight toward high-performance adsorption-based AWH technologies.

Rational design of thermally stable polymorphic layered cathode materials for next generation lithium rechargeable batteries

Classical layered transition metal oxides have remained the preferred cathode materials for commercial lithium-ion batteries. Variation in the transition metal composition and local ordering can greatly affect the structure stability. In classical layered cathodes, high concentrations of electrochemically inert Mn elements usually act as a pillar to stabilize the structure. When excess amount of Li and Mn are present in the layered structure, the capacity of the Li-rich layered oxide (molar ratio of lithium over transition metal is larger than one by design) can exceed that expected from transition metal redox. However, the over lithiation in the classical layered structure results in safety issues, which remains challenging for the commercialization of Li-rich layered oxides. To characterize the safety performance of a series of Li-rich layered cathodes, we utilize differential scanning calorimeter and thermal gravimetric analysis; this is coupled with local structural changes using in situ temperature dependent synchrotron X-ray diffraction and X-ray adsorption spectroscopy. These methods demonstrate that the gradual decrease of the Mn–M (M = Ni, Co, Mn and Li) coordination number directly reduces structural stability and accelerates oxygen release. For safety characterization tests in practice, we evaluate the thermal runaway process through accelerating rate calorimeter in 1.0 Ah pouch cells to confirm this trend. Using the insights obtained in this work, we design a polymorphic composition to improve the thermal stability of Li-rich layered cathode material, which outperforms Ni-rich layered oxides in terms of both electrochemical and safety performances.

Temperature-dependent electrowetting behavior on Teflon AF1600

In the growing application field of electrowetting (EW), reliable control of the wetting behavior by an applied voltage is required over a wide temperature range. Despite the rising interest of EW, only few data are reported in the literature on the EW behavior as a function of temperature. In this paper, we investigate the quasi-static EW response on one of the most widely used hydrophobic materials, Teflon AF1600, in a temperature range from 25 to 70,^{circ }mathrm{C}. The contact angle versus voltage is analyzed to illustrate the EW behavior. The results are in good agreement with the friction-adsorption model, which explains the contact angle (CA) hysteresis by a temperature-independent friction-like force and a temperature-dependent contribution of liquid adsorption onto a dielectric surface. The EW-CAs show a small asymmetry with respect to the polarity of the applied voltage, which might be due to the temporary and reversible charge trapping on the dielectric layer. The results underline that the different effects of the temperature-independent friction force and the temperature-dependent adsorption need to be taken into account to predict and control the CA in any EW-based application scenario.Graphical abstract

Predicting adsorbed gas capacity of deep shales under high temperature and pressure: Experiments and modeling

Temperature and pressure conditions of deep shale are beyond experiment range, and the amount of adsorbed gas is difficult to determine. To predict the adsorbed gas content of deep shales under formation conditions, isothermal adsorption experiments and model building were conducted on shale samples from Longmaxi Formation in China. A temperature-dependent adsorption model based on the Langmuir equation is proposed, which can be well-fitted by observed isotherms with a high correlation coefficient. Based on the fitted parameters at 303.15 K, the isothermal adsorption curves at 333.15 K, 363.15 K, and 393.15 K are predicted, showing a good agreement with experimental curves available. Compared with previous prediction methods, the biggest advantage of the proposed method is that it can be carried out only based on one-time isothermal adsorption experiment. Based on the predictions, the downward trend of the excess adsorption curves will slow down under high temperature and pressure conditions, and when the pressure reaches a certain level (> 80 MPa), the temperature has little effect on the excess adsorption capacity. While for absolute adsorption, the gas adsorption reaches saturation much slowly at high temperature, it can also reach saturation under formation pressure. Under the burial depth of marine shale, temperature plays a major role in controlling the adsorbed gas, resulting in the decrease of adsorbed gas content in deep shale, and its ratio will further decrease as the depth increases. Cited as: Zhou, S., Wang, H., Li, B., Li, S., Sepehrnoori, K., Cai, J. Predicting adsorbed gas capacity of deep shales under high temperature and pressure: Experiments and modeling. Advances in Geo-Energy Research, 2022, 6(6): 482-491. https://doi.org/10.46690/ager.2022.06.05

Kinetic, isotherm and thermodynamic adsorption studies of organophosphorus compound (phosmet) on reduced graphene oxide

Organophosphorus compounds are those compounds which are widely used as pesticide or insecticide. But, these compounds have serious harmful effects if these compounds may enter in food chain via biomagnifications process. Therefore, different research groups have been working on modalities for removal of these toxic compounds from the environment. The current study investigates the potential of adsorption capacity of synthesized reduced graphene oxide for phosmet, which is a toxic organophosphorus compound. Reduced graphene oxide (rGO) was synthesized in high yield (88 %) using L-ascorbic acid as a reducing agent and further, it was characterized using UV–Vis, FT-IR, powder-XRD, Raman, FE-SEM, BET, and TGA techniques. The surface area of synthesized rGO was determined to be 334 m2/g using the BET technique. The adsorption study showed the uptake capacity of rGO for phosmet was found to be dependent on rGO dose, pH effect, contact time, and temperature effect. The highest adsorption capacity (2680 mg/g) and removal efficiency (96 %) were obtained at pH 6.8. The kinetic data were best described by pseudo-second-order model, suggesting that the adsorption of phosmet on rGO surface is chemisorptions type. The equilibrium adsorption studies were best fitted with Langmuir isotherm model; thus, confirming the homogeneous adsorption of phosmet on rGO surface. The temperature-dependent adsorption of phosmet on rGO investigation suggested that adsorption was enthalpy driven (ΔH0 = −150 kJ mol−1) and spontaneous (ΔG0 = −10.6 kJ mol−1) in nature. The adsorbent reusability was examined, and it was found that after 5 cycles, there was a little loss (19 %) in the adsorption efficacy of rGO for phosmet with no significant change in surface morphology. The current investigation reveals the synthesized adsorbent has a great potential for the removal of phosmet.

Toward SERS based localized thermometry of Polymer-Supported silver and gold nanostructures

In order to accurately account for the contribution of different plasmon mediated phenomena when developing materials for applications in photothermal therapy, photovoltaics, or photocatalysis reliable, precise, and localized temperature measurements are required. In this work we applied two surface-enhanced Raman scattering (SERS) spectroscopy based methods to measure the local temperature increase due to the thermoplasmonic effect in gold and silver nanoparticles on thin polystyrene films. The first method relies on the temperature dependence of the anti-Stokes to Stokes Raman bands intensity ratio for a label Rhodamine 6G deposited on the nanostructures. We found that the method enables good measurements in the 20–60 °C temperature range but becomes less reliable at higher temperatures when the system undergoes transformations and the plasmonic response of the nanoparticles changes with heating. The second method makes use of the temperature dependent adsorption geometry of phenyl isocyanide (PIC) and a corresponding shift of ν(C≡N) vibration. The method demonstrates greater temperature sensitivity of gold nanoparticles than silver. The difference in sensing capability is related to the difference in molecular adsorption geometry of PIC on Au compared to Ag. We conclude that for universal thermometry of the nanoparticle/ thin film composite a combination of the two methods provides more precise localized temperature measurements.

Quantification of Temperature-Dependent Sorption Isotherms in Shale Gas Reservoirs: Experiment and Theory

Summary A critical component of natural gas in organic-rich shales is adsorbed gas within organic matter. Quantification of adsorbed gas is essential for reliable estimates of gas-in-place in shale reservoirs. However, conventional high-pressure adsorption measurements for coal using the volumetric method are prone to error when applied to characterize sorption isotherm in shale gas systems due to limited adsorption capacity and finer pores of shale matrix. Innovative laboratory apparatus and measurement procedures have been developed to accurately determine the relatively small amount of adsorbed gas in a Marcellus shale sample. The custom-built volumetric apparatus is a differential unit composed of two identical single-sided units (one blank and one adsorption side) connected with a differential pressure transducer. The scale of the differential pressure transducer is ±50 psi, a hundred-fold smaller than the absolute pressure transducer measuring to 5,000 psi, leading to a significant increase in the accuracy of adsorption measurement. Methane adsorption isotherms on Marcellus shale are measured at 303, 313, 323, and 333 K with pressure up to 3,000 psi. In addition, a fugacity-based Dubinin-Astakhov (D-A) isotherm is implemented to correct for the nonideality and to predict the temperature dependence of supercritical gas sorption. The Marcellus shale studied generally displays linear correlations between adsorption capacity and pressure over the range of temperature and pressure investigated, indicating the presence of a solute gas component. It is noted that the condensed-phase gas storage exists as the adsorbed gas on the shale surface and dissolved gas in kerogen, where the solute gas amount is proportional to the partial pressure of that gas above the solution. One of the major findings of this work is the experimental observation of the contribution of dissolved gas to total gas storage. With adsorption potential being modeled by a temperature-dependence expression, the D-A isotherm can successfully describe supercritical gas sorption for shale at multiple temperatures. Adsorption capacity significantly decreases with temperature attributed to the isosteric heat of adsorption. Lastly, the broad applicability of the proposed fugacity-based D-A model is also tested for adsorption data provided in the literature for Woodford, Barnett, and Devonian shale. Overall, the fugacity-based D-A isotherm provides precise representations of the temperature-dependent gas adsorption on shales investigated in this work. The application of the proposed adsorption model allows predicting adsorption data at multiple temperatures based on the adsorption data collected at a single temperature. This study lays the foundation for an accurate evaluation of gas storage in shale.

Highly efficient removal of hexavalent chromium using hexagonal disc shaped barium hydrogen phosphate

Novel hexagonal disc-shaped barium hydrogen phosphate was synthesized and analyzed by X-ray diffraction, X-ray photoelectron spectroscope, scanning electron microscope, transmission electron microscopy, thermogravimetric analysis, Brunauer–Emmett–Teller, and FTIR. The effects of adsorbent dose, adsorption time, initial concentration, initial pH, temperature, and sodium chloride on hexavalent chromium, Cr (VI), adsorption by BaHPO4 were studied. Effective Cr (VI) adsorption capacity was observed in the pH range of 4–5. The temperature-dependent adsorption data showed sorption is endothermic and spontaneous in nature. The adsorption occurs via electrostatic interaction and is described by second order kinetic, and the adsorption isotherm was best fitted with the Langmuir model. The equilibrium adsorption capacity and maximum adsorption capacity were found to be 128.7 mg/g and 146.8 mg/g, respectively at room temperature and pH 6. Adsorbent is stable, recyclable, environmentally friendly, and can be produced on a large scale at a low cost. This can be utilized for the treatment of Cr (VI) contaminated water.