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Adsorbed natural gas (ANG) is a promising solution for improving the safety and storage capacity of low-pressure gas storage systems. The structural–energetic and adsorption properties of active carbon ACPK, synthesized from cheap peat raw materials, are presented. Calculations of the methane–ethane mixture adsorption on ACPK were performed using the experimental adsorption isotherms of pure components. It is shown that the accumulation of ethane can significantly increase the energy capacity of the ANG storage. Numerical molecular modeling of the methane–ethane mixture adsorption in slit-like model micropores has been carried out. The molecular effects associated with the displacement of ethane by methane molecules and the formation of a molecule layered structure are shown. The integral molecular adsorption isotherm of the mixture according to the molecular modeling adequately corresponds to the ideal adsorbed solution theory (IAST). The cyclic processes of gas charging and discharging from the ANG storage based on the ACPK are simulated in three modes: adiabatic, isothermal, and thermocontrolled. The adiabatic mode leads to a loss of 27–33% of energy capacity at 3.5 MPa compared to the isothermal mode, which has a 9.4–19.5% lower energy capacity compared to the thermocontrolled mode, with more efficient desorption of both methane and ethane. [ABSTRACT FROM AUTHOR]

Summary The hydrogen storage performance of a series of Basolite metal‐organic frameworks (MOFs) has been estimated within a pressure range up to 700 bar at temperatures from 77 to 293 K. Crystal structure and texture properties of the MOFs were determined using X‐ray diffraction and nitrogen cryoadsorption, respectively. Hydrogen excess adsorption isotherms were measured and then converted to gravimetric and volumetric total adsorption. To calculate the total volumetric capacity, the crystallographic density of materials for the theoretically maximum capacity was used. At 700 bar, the highest volumetric total adsorption was about 65 mg/cm3 shown by Z1200 and Z377. The heat of adsorption at 298 K vs pressure was evaluated by the Clausius‐Clapeyron equation. Peculiar adsorption behavior of C300 in the high‐pressure region manifested in specific forms of isotherms and baric dependence of the heat of adsorption has been revealed. The relation of this phenomenon with a possible transition from Cu2+ to Cu+ in the C300 framework under the reducing effect of hydrogen has been discussed. The upper‐pressure limit of the MOFs' effectiveness in hydrogen storage systems compared to adsorbent‐free compressed gas has been estimated and did not exceed 127 bar at 298 K and 82 bar at 77 K due to the large amount of hydrogen that remains adsorbed at release pressure 5 bar. It has been concluded that conventional testing methods based only on excess adsorption isotherm measurements give initial data on the surface interaction and do not reflect the actual amount of stored and deliverable hydrogen. Besides the excess adsorption, the density of the adsorbent and the low‐pressure capacity are the key factors defining the applicability of materials in high‐pressure storage systems. [ABSTRACT FROM AUTHOR]

Summary: Pressure swing adsorption (PSA) technology is widely applied to hydrogen purification from mixed gas. This article mainly studies the adsorption dynamics, breakthrough behavior, and temperature profiles of the typical H2/CO2 mixture by activated carbon in the adsorption bed. Based on the Comsol Multiphysics simulation platform, a one‐dimensional multicomponent adsorption, heat and mass transfer modeling is established and validated by published data of H2/CO2 adsorption breakthrough experiments. By comparing the simulated data with the experimental data, it is found that the breakthrough curves are in good agreement, but the temperature profiles are not fit perfectly. After a comprehensive literature review, we found that the heat of adsorption dramatically influences the temperature profiles. The constant heat of adsorption has limitations for modeling breakthrough experiments. A variable heat of adsorption was proposed and applied to improve the temperature profiles. The results show that the variable heat of adsorption can effectively improve the temperature profiles in the gas adsorption process, and it works well for different adsorption temperatures, pressures, and compositions. The variable heat of adsorption instead of the constant heat of adsorption can significantly increase the peak value of the temperature profiles to be more consistent with experimental results. The relative deviations between the simulated and experimental values of the temperature profiles are reduced from 11.42% to 1.47% using the variable heat of adsorption. The simplification form of the Clausius‐Clapeyron equation gives the outline and trend of the correlation between the heat of adsorption and the amount of adsorption for different adsorption temperatures, pressures, and compositions. [ABSTRACT FROM AUTHOR]

Thermodynamic characteristics of adsorption of hydrocarbon molecules with the linear, planar, and cage structures and their isostructural chlorine derivatives were determined by equilibrium gas adsorption chromatography on columns with graphitized thermal carbon black in the range of the lowest concentrations of the adsorbate in the gas phase (Henry's region). When the planar molecules of methylbenzenes and chlorobenzenes are adsorbed, the methyl groups and chlorine atoms, which are close in polarizability, make the same contribution to the heat of adsorption. However, in the adsorption of bulky molecules, the replacement of the methyl groups by chlorine atoms results in an average increase of 4 kJ mol−1 for the heats of adsorption. A possible reason for the differences in the heats of adsorption of the bulky hydrocarbons and isostructural chlorine derivatives is that induction interactions R-Cl...π(graphite) are imposed on dispersion interactions characteristic of adsorption on the graphite-like adsorbents. The induction interactions developed are due to specific features of the orientation of the R-Cl polar bonds in the bulky molecules of the adsorbates relative to the planar graphite surface at the adsorption equilibrium. [ABSTRACT FROM AUTHOR]

Adsorption is a physicochemical phenomenon important in both natural and engineering processes. In the research and practice of adsorption equilibrium, a long-standing challenge is how to reconcile the classical models proposed by Gibbs, Langmuir, Freundlich, and Temkin for interpreting experimentally obtained adsorption isotherms. Here, we show that the Langmuir, Freundlich, and Temkin isotherms can be derived from the Gibbs equation under different conditions for the change of surface energy (a.k.a. surface tension) by adsorption. When the change of surface energy is predominantly controlled by the change of chemical potential with negligible contribution from the change of internal energy and entropy, the Gibbs equation can be integrated to give the Langmuir isotherm. When changes of internal energy and entropy are no longer negligible, the integration of the Gibbs equation gives the Freundlich and Temkin equations, according to a change of surface energy either independent or linearly dependent on the adsorption capacity. These results indicate that the classical models share the common mechanism of phase equilibrium described by the Gibbsian thermodynamics, thereby providing novel insights for their application. [ABSTRACT FROM AUTHOR]

Adsorption of n-butane onto ACS microporous carbon adsorbent with a wide pore-size distribution was studied at a pressure as high as 0.25 MPa and the temperatures of 303, 313, 323, and 333 K. The specific volume of micropores of the adsorbent was 2.00 cm3/g. ACS adsorbent had a bimodal pore-size distribution, with the effective pore sizes of 1.42 and 3.8 nm. At a temperature of 303 K and pressure of 0.231 MPa, the maximum value of n-butane adsorption reached 18.62 mmol/g. The BET specific surface was SBET = 2560 m2/g. The initial differential molar heat of adsorption of n-butane onto ACS adsorbent was found to be 29.1 kJ/mol. The differential molar heats of adsorption of n-butane onto ACS adsorbent weakly depended on temperature and passed through a maximum of ~30 kJ/mol at the adsorption value of ~12 mmol/g. A further increase in the value of n-butane adsorption up to 16 mmol/g led to a drop in the heat of adsorption to ~25 kJ/mol. The isotherms of n-butane adsorption were described using the two-term equation of the theory of volume filling of micropores (TVFM). It was found that the bimodal equation of the TVFM well described the n-butane adsorption using the structure and energy parameters of the adsorbent determined from the data on adsorption of benzene and nitrogen vapors throughout the entire ranges of temperatures and pressures. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZIF-8 is synthesized and functionalized with Triethylenetetramine (TETA). • Study on CO 2 capture performance using pure ZIF-8 and amine-modified ZIF-8. • CO2 adsorption capacity increases and reaches optimum for increase in amine loading. • Experimental CO2 adsorption data are correlated using adsorption isotherm models. • Isosteric heats of adsorption are calculated in the temperature range of 25–60 °C. Zeolitic imidazolate framework-8 (ZIF-8), a metal–organic framework (MOF) is well known for its large surface area, and superior thermal and chemical stability with respect to other adsorbents. The adsorbents are synthesized and analyzed using HR-XRD, FTIR, BET, TGA, FESEM, EDX, and CHNS techniques. Pure ZIF-8 demonstrates comparatively low CO 2 capture capacity. The present study aims to improve the CO 2 adsorption capacity of ZIF-8 by functionalization with 10 to 40 % triethylenetetramine (TETA) using the wet impregnation process. The iSorpHP2 pressure sorption apparatus is employed to evaluate the carbon dioxide uptake capacity in the range of varying pressure (0 to 30 bar) and temperature conditions (25 to 80 °C) of ZIF-8 and TETA-grafted ZIF-8 adsorbents. The impact of temperature, pressure, and amine loading as independent variables on the experimental CO 2 adsorption capacity as the response function was assessed and optimized using the response surface methodology (RSM) based on the Box-Behnken design (BBD). An excellent match was found between the experimental data and the model prediction. The isoteric heat of adsorption of ZIF-8 and TETA-incorporated ZIF-8 adsorbents is measured in the temperature range of 25 to 60 °C through the utilization of the Van't Hoff depicted in the iSorbHP2-Win software for acquiring knowledge on the level of heterogeneity and the distribution of surface energy of materials. The Sips model has demonstrated superior performance in its ability to correlate experimental data as compared to the Toth, Langmuir, and Freundlich models. Among the amine-impregnated ZIF-8 adsorbents, ZIF-8–30 % TETA adsorbs 3.89 mmol CO 2 /g of solid adsorbent at 25 °C and 1 bar pressure which is 4.52 times greater than that of ZIF-8. [ABSTRACT FROM AUTHOR]

The surface chemistry of silica-alumina gels is largely determined by number and type of silanol groups present. However, until now the influence of different silanol groups on adsorption processes is largely unknown. The aim of this study is to develop a method for an energetic characterization of silica-alumina gels by combining data measured by nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA) and adsorption calorimetry. The silica-alumina gels used for the studies are systematically modified by pretreating at temperatures between 200 °C and 1000 °C. To quantify number and distribution of silanol groups, complementary data from 29Si-NMR and 1H NMR and thermogravimetric measurements is combined. Adsorption measurements with the adsorptives cyclopentane (nonpolar) and pyrrolidine (polar molecule capable of hydrogen bonding) provide further information. Based on the adsorption isotherms and load-dependent heats of adsorption, it is shown that number and distribution of silanol groups have little effect on the adsorption of cyclopentane. In contrast, different energy levels are found for the heat of adsorption of pyrrolidine at ∼106 kJ mol−1, ∼95 kJ mol−1, ∼87 kJ mol−1, and ∼80 kJ mol−1 depending on pretreatment temperature. Based on the combination of all data, a model is proposed to assign the identified energy levels of adsorption to different silanol groups. [Display omitted] • Structural characteristics and surface chemistry influence energetical properties. • Adsorption calorimetry is performed to measure the heat of adsorption. • Combination of 1H NMR and 29Si-NMR measurements with thermogravimetry. • Model for adsorption mechanisms of pyrrolidine at silanol groups is proposed. [ABSTRACT FROM AUTHOR]

The adsorption of CO in the temperature range of 300–713 K on the PtSn particles of a reduced (H2, 713 K) 1.2%Pt-2.7%Sn/Al2O3 catalyst is studied by FTIR spectroscopy to reveal the geometric and electronic effects of Sn on the Pt sites. By comparison with a 1.2% Pt/Al2O3 it is shown that Sn (a) suppresses the Pt sites forming bridged CO species due to a geometric effect and (b) displaces the IR band of a linear CO species on Pt sites at 300 K from 2066 cm−1 to 2044 cm−1 due to an electronic effect. According to the AEIR method, the change in the IR band on the PtSn particles with the increase in Ta in isobaric condition (PCO = 1 kPa) provides the heats of adsorption of the linear CO species (named L1PtSn) at high (58 kJ/mol) and low (130 kJ/mol) coverages. By comparison with the values of the linear CO species on Pt particles (named LPt): 220 and 106 kJ/mol at low and high coverages, respectively, these values reveal the strong impact of the electronic effect of Sn on the heats of adsorption of CO. For Ta > 463 K there is a reconstruction of the PtSn particles due to the segregation of Sn as SnOx species associated with an enrichment of the surface in Pt. On the reconstructed PtSn particles, a new IR band is observed at 2057 cm−1 after adsorption of CO at 300 K ascribed to a new L2PtSn CO species. Its heats of adsorption are significantly higher than those of the L1PtSn species: 165 and 65 kJ/mol at low and high coverages. Moreover, successive reconstruction/H2 reduction at 713 K cycles leads to a sintering of the PtSn particles associated to the progressive increase in the heats of the L2PtSn CO species until a value at low coverage: 210 kJ/mol similar to that of the LPt species whereas at high coverage a significant difference exists between the two species (70 and 115 kJ/mol for L2PtSn and LPt, respectively). These data show that the impacts of Sn on the heat of adsorption of the linear CO species on the Pt sites are dependent on (a) the Pt/Sn surface ratio which changes with reconstruction and the particle size and (b) the coverage of the Pt sites. The comparison of the heats of adsorption of the L CO species on the fresh, reconstructed and aged PtSn particles with experimental and theoretical literature data reveals that they are consistent with some of them. [ABSTRACT FROM AUTHOR]

The microscopic mechanism of the competitive adsorption of CH 4 , CO 2 and N 2 in coal is the theoretical basis for enhancing coal seam gas recovery by injecting CO 2 (CO 2 -ECBM). Based on this principle, this work used Grand Canonical Monte Carlo and Molecular Dynamics to investigate the microscopic adsorption mechanism of single, binary, and ternary component gases in Wiser bituminous coal molecules. The adsorption mechanism was explored by changing gas composition and concentration. The comparison of adsorption separation coefficients suggested that CO 2 had the highest adsorption capacity, whereas N 2 had the lowest capacity. When the CO 2 concentration in the gas mixture was high, the adsorption amount was large and the adsorption separation coefficient was small. This finding indicated that high concentrations of CO 2 had negative effects on competitive adsorption. Energy changes were also evaluated. The potential energy between CO 2 and the framework was the strongest among the two other gases. The inhibition of CH 4 adsorption intensified with decreasing molar fraction of CO 2. This phenomenon was explained from the perspective of heat of adsorption. As the molar fraction of CO 2 in the adsorption system decreased, the heat of the isotherm adsorption increased. Meanwhile, the adsorption system became unstable and the capacity of CH 4 adsorption on the framework weakened. Results provide a theoretical basis for the use of CO 2 -ECBM. [Display omitted] • Molecular simulation was carried out to study the microscopic adsorption mechanism of single- and multi-gases in bituminous coal. • The greater the content of strongly adsorbed gas, the weaker the gas adsorption selectivity. • Van der Waals and electrostatic energy are the main potential energy affecting gas adsorption in coal molecules. • The energy distribution of different types and contents of gas in the adsorption system is analyzed. • Clarified the linear relationship between the heat of adsorption and the amount of adsorption. [ABSTRACT FROM AUTHOR]

The adsorption of propane on an ACW supermicroporous adsorbent with a wide pore size distribution at pressures up to 1 MPa and temperatures of 303, 313, 323, and 333 K was studied. The maximum value of propane adsorption at a temperature of 303 K and a pressure of 1 MPa is equal to 21.6 mmol/g. The dependences of the differential molar isosteric heat of adsorption of propane on the value of adsorption are calculated. In the initial region of micropore filling of up to ~6 mmol/g, the heat of propane adsorption on the microporous adsorbent is practically constant (~27 kJ/mol). Then, as the micropores are filled, the heat of adsorption drops to 25 and 23 kJ/mol at temperatures of 303 and 333 K, respectively. Thereafter, a sharper drop in heat occurs to 20 kJ/mol at 20 mmol/g. As a result of calculations, the temperature dependence of heat on propane adsorption is obtained in the form of a fan of curves. The experimental data are compared with the results of calculations of propane adsorption based on Dubinin's theory of volumetric filling of micropores using the structural and energy characteristics of the adsorbent. [ABSTRACT FROM AUTHOR]

Porous carbon and La2O3/porous carbon materials are synthesized for the study of CO2 adsorption and separation by the volumetric method. The synthesized adsorbents are characterized by X-ray diffraction, N2 adsorption–desorption isotherms, Raman spectra and scanning electron microscopy with energy-dispersive X-ray analysis. Characterization results confirm the existence of porosity in the synthesized carbon materials and uniform distribution of lanthanum(III) oxide on porous carbon. The CO2 adsorption capacity for porous carbon and La2O3/porous carbon is 21 and 33 cm3 g−1, respectively, at 298 K and 1 bar. High adsorption of CO2 is obtained for La2O3/porous carbon because of the electrostatic interaction between La2O3 and CO2. Moreover, the N2 adsorption capacity is 2.8 cm3 g−1 for porous carbon and 2.2 cm3 g−1 for La2O3/porous carbon at 298 K and 1 bar. The change in N2 adsorption is due to the decrease in surface area. For La2O3/porous carbon, the selectivity of CO2/N2 is 33.5 and the heat of CO2 adsorption is 36.5 kJ mol−1 at low adsorption of CO2. It also shows constant CO2 adsorption capacity in each adsorption cycle. [ABSTRACT FROM AUTHOR]

• Polymer-porous solids interactions depends significantly on surface chemistry. • Heat of small molecule adsorption correlates strongly with polymer-solid interaction. • Enthalpic interactions are vital in determining polymer-solid surface interaction. • Defect state of inorganic solids has a major influence on polymer-surface interaction. • Our findings potentially aid in the design of new catalysts for polymer upcycling. Understanding the interactions between molten polymers and inorganic porous solids is critical for the heterogeneous catalytic conversion of waste polymers into useful chemicals and the fabrication of nanocomposites and nanostructured polymers. Developing experimental and theoretical approaches to quantify and understand polymer-surface interactions would be extremely useful for the design of new catalysts and composites. Here, we demonstrate that the interfacial energy between molten polystyrene (PS) or polyethylene (PE) and various inorganic surfaces prepared via atomic layer deposition (ALD) such as SiO 2 , TiO 2 , WO 3 , and CaCO 3 are correlated with the adsorption of small molecules that bear structural similarity to the repeat unit of the two polymers. The interfacial energy inferred from the dynamics of polymer infiltration into ALD-modified porous solids is compared with the heats of adsorption of small molecules on mesoporous silica (SBA-15) modified with ALD. Both our experimental and computational results suggest a strong correlation between the polymer-solid interfacial energy and the adsorption strengths of their respective small molecules on the same surface. These results highlight that even though there are no specific modes of interaction between the polymers and the inorganic surfaces, their interaction energies vary significantly and are dominated by differences in the enthalpic interactions between each repeat unit and the solid surface. Besides providing a novel method for measuring the polymer-solid interaction, this work bridges the gap between the behavior of macromolecules on solid surfaces and the adsorption properties of small gas molecules. This understanding will have important implications for designing new catalysts for polymer upcycling and composite membranes for gas and potentially polymer separation. [ABSTRACT FROM AUTHOR]

Thermodynamic characteristics of the adsorption of benzene and its derivatives on the surface of a porous graphite-like Hypercarb adsorbent from binary polar eluents have been experimentally determined under the conditions of equilibrium HPLC at various temperatures. The retention on Hypercarb columns is generally maintained by non-specific intermolecular interactions with the flat graphite-like surface and depends on the size of their molecular area. The contributions of various functional groups to the heat and entropy of adsorption were determined. The influence of solvation effects on the values of adsorption parameters was demonstrated. The replacement of methanol in the mobile phase composition with acetonitrile leads to an increased influence of the solvatation effects, while for the water-acetonitrile eluent, there were no any observed correlations of parameters of the adsorption on Hypercarb from a water-methanol medium with the data acquired on gas phase adsorption on graphite. The entropy values of adsorbates in their solvated state have been for the first time determined for eluents of the different polarities and compared with the entropy values for the state of pure liquid, which allowed us to clarify the nature of solvatation of the considered compounds in the polar eluent. Using the adsorption of compounds at issue as an example, the effect of enthalpy-entropy compensation was investigated, and the values of compensation temperatures were estimated. [ABSTRACT FROM AUTHOR]

A microporous carbon adsorbent MPU-007 with a wide pore size distribution (specific micropore volume W0 calculated within the framework of the theory of micropore volume filling is 1.44 cm3 g−1; first-mode micropore diameter X01 is 1.5 nm; second-mode micropore diameter X02 is 3.5 nm; specific surface area SBET is 2520 m2 g−1) was prepared by chemical activation of a mixture of corn dextrin, ethylene glycol, and phenol formaldehyde resin. Adsorption of ethane on this adsorbent was studied at pressures up to 4 MPa at T = 303, 313, 323, and 333 K. The maximum ethane adsorption value attained in the experiments was 25 mmol g−1 or 75 wt%. The adsorption isosteres plotted in the ln P–1/T coordinates using the data obtained can be well approximated by linear functions at constant adsorption values. The dependences of the differential molar isosteric heats of adsorption of ethane on MPU-007 on the amount adsorbed in the temperature range of 303–333 K were calculated. The heat of adsorption of ethane equal to 23 kJ mol−1 remained constant throughout the initial range of micropore fillings up to ∼7 mmol g−1 and then gradually decreased to 8 kJ mol−1 at an uptake of 24 mmol g−1 at 333 K. Such a pattern of the dependence of the heat of adsorption can be due to a wide pore size distribution and to the formation of associates in the adsorbate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Semi-adiabatic breakthrough experiments were conducted on a small laboratory-scale using an insulating column manufactured of polyurethane (PUR) foam. • Breakthrough simulations under different thermal conditions were conducted. • The differences between isothermal, near-isothermal, near-adiabatic and adiabatic breakthrough were investigated and described. • The degree of adiabaticity achieved with the PUR column was quantified through the outlet excess heat value during breakthrough and thermal characterization of the column. Often lab-scale adsorptive breakthrough experiments are conducted in an isothermal manner, whereas industrial-scale adsorption processes are near-adiabatic. In this work, a polyurethane (PUR) insulating column was manufactured to mimic large-scale non-isothermal behavior via laboratory-scale breakthrough tests. Breakthrough tests with a CO 2 /N 2 gas mixture on zeolite 13X (∼5 g) were performed. A bed temperature increase of 62 °C and long cooling times were observed. When compared to a regular steel column, showing a temperature rise of only 12 °C, the column efficiency was approximately 20% lower due to adiabatic effects. The heat evacuated from the adsorbent bed via the column exhaust was used as a measure for the degree of adiabaticity. Up to 46% of the theoretical heat of adsorption could be detected at the PUR column exhaust compared to 4% at the steel column exhaust. The important difference between isothermal, non-isothermal and adiabatic limit behavior was demonstrated through breakthrough experiments and simulations. [ABSTRACT FROM AUTHOR]

The aim of this study is to unravel the influence of single, double and triple bonds in hydrocarbons on the mechanisms of adsorption on zeolites. Therefore, the adsorption of the C2 hydrocarbons ethane, ethene and ethyne on different adsorbents is studied by adsorption calorimetry. As adsorbents pure sodium LTA (NaA) and FAU (NaX) zeolites and calcium exchanged CaNaA and CaNaX zeolites are used. Based on experimental loadings and heat of adsorption, the influence of the number and distribution of cations on different cation positions are discussed in detail. With increasing degree of exchange the increasing number of Ca2+-cations introduce energetically more valuable adsorption sites into the zeolites. On the other hand, the decreasing total number of cations has a negative effect on saturation loading. The impact of these opposing effects and the different occupation of cation positions on the interactions and mechanisms occurring are discussed. The loading increases from ethane to ethene to ethyne and shows higher values on FAU compared to LTA. In terms of interactions, due to the single bond, in ethane only dispersion and induction interactions are formed. In ethene and ethyne due to the double and triple bonds, respectively, additional quadrupole cation and π-interactions occur. In this study, for the first time the formation of a π-complex with Ca2+-cations at position I in LTA and at positions II, III, and III’ in FAU is demonstrated. For ethyne, additional π-complex formation with Na+-cations on the identical positions is also detected, which was previously unknown in literature. [ABSTRACT FROM AUTHOR]

Highlights • Energy consumption of desiccant coated heat exchanger systems are analyzed. • Effects of climatic conditions and sensible heat ratios are discussed. • R410A and R32 are promising refrigerants. • Desiccants with adsorption heat of 2300–3000 kJ/kg satisfies most conditions. • Desiccants with adsorption heat more than 4000 kJ/kg need a careful decision. Abstract DCHE (Desiccant coated heat exchanger) based heat pump systems can handle sensible and latent loads simultaneously and separately within one single component via flowing refrigerant and coated desiccant. Their characteristics have a crucial impact on the performance of the whole system. To ensure energy efficiency of DCHE based systems, the restriction between refrigerant and desiccant is discussed based on energy consumption analysis. Results show that energy consumption of the DCHE based heat pump is intimately related with its coefficient of performance and adsorption heat of coated desiccant. R410A and R32 are found to be promising refrigerants for DCHE systems. Maximum allowable values of adsorption heat under different ambient air conditions and sensible heat ratios are obtained. Desiccant materials with adsorption heat of 2300–3000 kJ/kg such as various silica gels, all-silica zeolites and salt supported composites are within maximum allowable values of adsorption heat for most conditions. When applying the majority of zeolite type desiccants that possess adsorption heat more than 4000 kJ/kg, great attention should be paid to the determination of supply-air temperature difference. This paper provides the underlying insights needed to guide a fast and proper selection of refrigerants and desiccants for DCHE based systems. [ABSTRACT FROM AUTHOR]

In this paper, we report a simulation study of the effect of the herringbone orientational phase transition on the isosteric heat of adsorption and the heat capacity of the nitrogen adsorption monolayer on graphite surface. We use the previously proposed regression equations of state for phases with the short- and long-ranged orientational ordering (Ustinov et al. in J Phys Chem C 122:2897–2908, 2018). The proposed approach allows one to give an exhaustive thermodynamic description of the isobaric phase transition without direct estimation of the chemical potential, using only the pVT data obtained in a canonical Monte Carlo simulation. The herringbone orientational phase transition is indicated by a peak in the temperature dependence of the heat capacity. Its height and shape is close to those observed experimentally. In addition, the heat spike is observed on the isosteric heat curves near the transition region. It decreases with increasing temperature and completely disappears at a temperature close to the melting point in the gas-crystal system. A combined analysis of the heat capacity and isosteric heat of adsorption demonstrates that the nitrogen monolayer on graphite surface has similar features inherent in a three-dimensional system and, therefore, the translational and rotational degrees of freedom normal to the surface are involved in the mechanism of the long-to-short-ranged orientational transition. [ABSTRACT FROM AUTHOR]

Highlights • An alternative and efficient open absorption cycle is proposed. • The new cycle aims at recovering latent and sensible heat from moist gas. • The new cycle works on a wide temperature and humidity ranges of moist gas. • Membrane absorber is combined with the new cycle to enhance latent heat recovery. • The performances of the absorber and the new cycle are evaluated numerically. Abstract Compared to conventional closed absorption cycles, the open absorption cycle has a greater potential in latent heat recovery from exhausted moist gas since it recovers latent heat by mass transfer instead of heat transfer. Existing open absorption cycles including single-effect and multi-stage cycles have limitations on the waste heat utilization. This paper suggests a novel variable-stage open absorption heat pump cycle which can work on a wide range of temperature and humidity of exhaust gas. A membrane contactor is also suggested to replace traditional direct-contact absorbers to integrate with the new cycle. The membrane contactor has a higher mass and heat transfer efficiency and a greater potential to avoid solution carryover. Thermodynamic model of the new cycle combined with the membrane absorber model is developed. Parametric analysis is carried out to evaluate the performance of the new cycle. Simulation results show that, under the analyzed conditions, the equivalent stage number of the new cycle varies from 4 to 1 while coefficient of performance increases approximately from 1.2 to 2 with the increase of generation temperature and air humidity ratio. It indicates that the new cycle can cover the working temperature or humidity ranges of at least four conventional absorption cycles, including single-stage, 1.5-stage, double-stage, triple-stage absorption cycles. The new cycle works on a much wider temperature and humidity ranges than conventional multi-stage cycles because the pressures of the low-pressure generator and absorber will adjust themselves to adapt to the variations of generation temperature and air humidity ratio. The self-adaption of the pressures of the low-pressure generator and absorber is realized by the control of the solution mass flow rate. During the evaluated working ranges, coefficient of performance of the new cycle increases by 5.9–28.2% compared to conventional multi-stage absorption cycles. Influences of the operating conditions on the absorption rate of the membrane absorber is also conducted and discussed. [ABSTRACT FROM AUTHOR]

A microporous carbon adsorbent labeled as LCN was prepared by thermochemical synthesis from lignocellulose, and methane adsorption on it was studied within the temperature range from 303 to 333 K and at pressures up to 40 MPa. The total pore volume was determined to be 0.68 cm3/g. The maximum values of methane adsorption of ~14.5 mmol/g (23.2 wt %) were obtained at the temperature of 303 K and the pressure of 40 MPa. The calculated differential molar isosteric heat of methane adsorption is, on average, ~12–13 kJ/mol. Methane adsorption on LCN was calculated with the use of the Dubinin–Radushkevich and Dubinin–Astakhov equations, as well as the linearity of adsorption isosteres. It was shown that the Dubinin–Radushkevich and fundamental regularities of the theory of volume filling of micropores provide the best description of experimental data using only the standard structural and energy characteristics of the adsorbent. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Oxygen release from PdO due to the reverse spillover from the CeO 2 -PdO interface. • Evidence for reduction of surface ceria at low temperatures in the presence of Pd. • Adsorption calorimetry evidence for surface re-oxidation with water. Abstract The enhanced rates of reduction and re-oxidation of ceria in the presence of Pd, was investigated on both bulk ceria as well as ceria deposited over γ-Al 2 O 3. Pd addition and surface area enhancement by γ-Al 2 O 3 decreased the reduction temperature of CeO 2 as monitored by temperature programmed reduction (TPR) in H 2. Temperature programmed oxidation (TPO) and temperature programmed thermal decomposition (TPtD) measurements revealed similar results of more favorable temperatures of oxidation and thermal decomposition. Pd assisted oxygen removal from CeO 2 through a reverse spillover process as monitored by the temperature programmed thermal decomposition experiments was evident from the decomposition temperature of PdO to Pd. The adsorption microcalorimetry measurements at 323 K revealed that hydrogen adsorption initiated over Pd extends to CeO 2 by migration (or spillover). Oxygen adsorption, however, was restricted to Pd surface at 323 K. Also at the same temperature, initial H 2 O adsorption was accompanied by very high heats at low coverages indicating surface oxidation. At higher pressures, H 2 O adsorption extended to coverages representative of the monolayer over γ-Al 2 O 3 , the heats of adsorption measured at these high coverages corresponded to water condensation. [ABSTRACT FROM AUTHOR]

Abstract An extended two-site exchange model is presented, which is used to evaluate pulsed field gradient (PFG) nuclear magnetic resonance (NMR) measurements of water in the nanoporous metal-organic framework MIL-100(Al). Here the water molecules exchange between the inter- and the intracrystalline space during the observation time, but are also restricted in their movement by the crystal surface. The evaluation of temperature and loading dependent PFG NMR data yields information about the intracrystalline diffusion process, the radius of the restricting geometry and the time constants of the exchange process. The intracrystalline mean residence time is found to decrease with increasing temperature, which allows an estimate of the heat of adsorption under the equilibrium conditions of the NMR measurements. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Assessment of the heat of adsorption as a function of loading and temperature. • Incommensurate packing of CCl 4 on a graphene surface. • The role of octopole on adsorption is negligible. • Correct choice of the potential model for CCl 4 is important. Abstract We have carried out molecular simulations of carbon tetrachloride adsorption on graphite, in order to investigate the role of the octopole in potential models for the CCl 4 /graphite system, and the temperature dependence of the first-order gas-liquid transition in the first adsorbate layer. Two classes of potential model for carbon tetrachloride were considered: the first has 5 LJ sites and the second includes five partial charges to model the leading octopole. Both models are adequate to represent the vapour-liquid equilibrium, suggesting that the octopole makes an insignificant contribution to the properties of the bulk phase. Both models show that adsorbed CCl 4 molecules are delocalized on a graphite surface because of the strong intermolecular interactions. It is found that the LJ sites on the chlorine atoms, not the octopole, play the most important role in matching the experimental isotherm and isosteric heat data with simulation. The heat is constant, across the first-order transition of the first adsorbate layer. The simulation results show that both the magnitude of the density jump, and the isosteric heat across the first-order transition, decrease as the temperature increases. This is in qualitative agreement with the 1972 experimental data of Avgul and Kiselev, but these experimental data exhibit an unusually strong decrease in the isosteric heat, and the coexistence region between the two phases displays an unusual asymmetrical shape. Detailed analysis of our simulation results, together with the calculated isosteric heat from the experimental isotherms of Machin and Ross, show that there may be errors associated with the heat data of Avgul and Kiselev at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract Adsorption chiller technology has received much attention in the last few decades due to its advantages in utilizing low grade thermal energy and eco-friendly refrigerant. However, it has not been wide commercialized due to its low coefficient of performance (COP) and low specific cooling power (SCP) compared to conventional refrigeration technologies. This paper reviews different strategies to improve the COP and SCP of adsorption chillers. Heat recovery, mass recovery, multi-stage, multi-bed, improved adsorption structures and optimized operating conditions are discussed in this review. This study revealed that: (i) for operating conditions of low evaporative temperature, low generation temperature or high condensing temperature, a mass recovery technique is strongly recommended; (ii) in the case of intermittent cold production systems, use of constant temperature adsorption cooling cycle strategy is preferred; (iii) an appropriate cycle time and switching time are important to achieve the optimal system performance since the adsorption chiller performance is strongly dependent on the operating conditions; (iv) by employing a novel composite adsorbent material, along with improvements in heat exchanger design, advanced adsorption cycles can be a promising technology to improve adsorption chiller performance. This review highlights the need for further research to reduce chiller manufacture costs, increase power-to-mass ratio and improve understanding of dynamic long term chiller performance when driven by solar or waste thermal energy. Highlights • Review different strategies to improve the COP and SCP of adsorption chillers. • Review effect of operating and structure parameters on adsorption chiller COP and SCP. • Highlight main advantages and limitations of techniques for performance improvement. • Evaluate characteristics and potential applications of the adsorption system. • Provide guidelines for the adsorption system design, optimization and applications. [ABSTRACT FROM AUTHOR]

The trinuclear copper(I) pyrazolate complex [Cu3] rearranges to the dinuclear analogue [Cu2⋅(C2H4)2] when exposed to ethylene gas. Remarkably, the [Cu3]↔[Cu2⋅(C2H4)2] rearrangement occurs reversibly in the solid state. Furthermore, this transformation emulates solution chemistry. The bond‐making and breaking processes associated with the rearrangement in the solid‐state result in an observed heat of adsorption (−13±1 kJ mol−1 per Cu–C2H4 interaction) significantly lower than other Cu–C2H4 interactions (≥−24 kJ mol−1). The low overall heat of adsorption, "step" isotherms, high ethylene capacity (2.76 mmol g−1; 7.6 wt % at 293 K), and high ethylene/ethane selectivity (136:1 at 293 K) make [Cu3] an interesting basis for the rational design of materials for low‐energy ethylene/ethane separations. [ABSTRACT FROM AUTHOR]

The trinuclear copper(I) pyrazolate complex [Cu3] rearranges to the dinuclear analogue [Cu2⋅(C2H4)2] when exposed to ethylene gas. Remarkably, the [Cu3]↔[Cu2⋅(C2H4)2] rearrangement occurs reversibly in the solid state. Furthermore, this transformation emulates solution chemistry. The bond‐making and breaking processes associated with the rearrangement in the solid‐state result in an observed heat of adsorption (−13±1 kJ mol−1 per Cu–C2H4 interaction) significantly lower than other Cu–C2H4 interactions (≥−24 kJ mol−1). The low overall heat of adsorption, "step" isotherms, high ethylene capacity (2.76 mmol g−1; 7.6 wt % at 293 K), and high ethylene/ethane selectivity (136:1 at 293 K) make [Cu3] an interesting basis for the rational design of materials for low‐energy ethylene/ethane separations. Three's a crowd: A polyfluorinated, trinuclear copper complex absorbs ethylene and undergoes a major structural rearrangement leading to a dinuclear copper–ethylene complex. Upon removal of ethylene it reverts back to the trinuclear species. This process occurs both in solution and in the solid state. [ABSTRACT FROM AUTHOR]

Highlights • One-step polymerization and activation method is used for designing nitrogen-enriched carbons. • MCKC-3 possesses high surface area (2060 m2/g), ultramicropores (<0.7 nm) and high nitrogen content (2.3 wt%). • Excellent CO 2 uptake performance of 354 mg/g (8.03 mmol/g) at 273 K and 1 bar was observed. Abstract Microporous carbon materials are envisaged as efficient contenders for mitigating CO 2 levels by virtue of their favorable surface chemistry, high specific surface area, tunable pore structures, moderate heat of adsorption, and facile regeneration. This study presents a solvent-free one-step polymerization and activation method for designing a series of nitrogen-enriched carbons to delineate the role played by nitrogen moieties and ultra-micropores on CO 2 capture. Two activating agents were used at high temperature to fabricate microporous carbons with tunable pore structure and variable nitrogen content. The optimized material, MCKC-3, possesses high surface area (2060 m2/g) comprising of ultramicropores (<0.7 nm) and high nitrogen content (2.3 wt%). This material exhibit an outstanding CO 2 uptake performance of 354 mg/g (8.03 mmol/g) at 273 K and 1 bar, comparable to the highest adsorption reported so far for carbon-based materials. In conclusion presence of both the ultra-micropores and nitrogen functionalities contribute a major role in CO 2 adsorption, the former being predominant. [ABSTRACT FROM AUTHOR]

The performance of metal-organic frameworks in gas chromatographic separation investigations has been widely study in recent years. However, to use chromatographic methods to determine materials properties of metal-organic frameworks instead of using them just for analyte separations is a field still largely unexplored. The presented study has been conducted to quantify the systematic changes in the interaction of a series of related unbranched aliphatic analytes (C2-C10) with HKUST-1 as the stationary phase not only to obtain information about the MOF analyte interaction strength but also to gain materials parameters characterizing the MOF system, like its response to non-specific interactions. Thermodynamic as well as by kinetic parameters governing the adsorption process were determined using various chromatographic evaluation techniques. The method of inverse chromatography was used to derive the generic susceptibility of HKUST-1 to aliphatic methylene groups and to determine interfacial energy contributions of the intrinsic surface of the porous material. [ABSTRACT FROM AUTHOR]

A hybrid composite containing NiDOBDC [Ni-MOF-74 or Ni 2 (dobdc)] and graphene oxide (GO) was successfully synthesized using a facile method for enhanced CO 2 and H 2 storage. Additional porous spaces were created when the nanocomposite material with a three-dimensional (3-D) architecture was constructed with two-dimensional (2-D) graphene oxide sheets and microporous NiDOBDC nanoparticles. The analysis of gas storage performance reveals that the generation of new porosity resulted in enhanced CO 2 and H 2 adsorption. In particular, the NiDOBDC/GO composite with 10 wt% GO loading exhibited the highest CO 2 and H 2 storage values, up to 10.5 mmol/g (298 K, 20 bar) and 1.39 mmol/g (298 K, 20 bar), respectively, values that are significantly higher than those of the Ni-DOBDC metal–organic framework. Besides, enhanced CO 2 /N 2 selectivity was also observed for NiDOBDC/GO composite due to the additional storage sites for CO 2 . The strategy demonstrated in this work can also be applied to other microporous materials to enhance their gas adsorption properties. [ABSTRACT FROM AUTHOR]

Micro/nanoscale Mg-MOF-74 materials with different morphologies and sizes have been fabricated in the presence of polyvinylpyrrolidone (PVP) by adjusting the amount of aqueous ammonia and reaction temperature. The obtained samples were characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and it was found that the Mg-MOF-74 particles show morphology and size dependent adsorption properties. The selectivity factors of the Mg-MOF-74 particles at 273 K were calculated based on the experimental single-component isotherms by ideal adsorbed solution theory (IAST). The results indicate that the Mg-MOF-74 particles have intrinsic high selectivity for adsorption of CO 2 over CH 4 and N 2 . [ABSTRACT FROM AUTHOR]

In natural gas processing, adsorptive units remove higher hydrocarbons from the crude gas, for example to avoid freezing in consecutive cryogenic units. This article describes a detailed investigation on the adsorption of C 6 hydrocarbons (benzene, cyclohexane, n-hexane) at low concentrations up to 5000 ppm mol in a N 2 carrier gas on two industrial produced silica alumina gels. Adsorption isotherms were derived from cumulative breakthrough experiments in a fixed-bed adsorber between 25 °C and 75 °C and 1.3 bar (abs.). The isosteric heat of adsorption was determined from the temperature-dependent isotherms. Furthermore an adsorption potential model was developed to describe the temperature dependency of equilibrium capacity and heat of adsorption. The paper discusses the experimental data with respect to molecular structure of the adsorptives as well as surface chemistry and pore structure of the adsorbents. In comparison to the other adsorptives, the aromatic benzene exhibits the highest loadings and the highest heat of adsorption. In addition it shows the strongest load- and temperature-dependency of the heat of adsorption. [ABSTRACT FROM AUTHOR]

Measures heats of adsorption of metals on single-crystalline surfaces using a calorimetric approach. Use of a pyroelectric polymer ribbon for heat input detection; Sticking probability; Differential heat of adsorption.

Reports on the measurement of heat data for the adsorption of oxygen on the three low-index planes of nickel at 300 Kelvins along with corresponding sticking probabilities, using single-crystal adsorption calorimetry. Sticking probabilities in the chemisorption region; Sticking probabilities in the thin oxide film regime; Adsorption heat data.

Reports on the coverage dependencies of the differential heats of adsorption for carbon monoxide (CO) and nitrogen oxide (NO) on Pd{100}, at room temperature, using single crystal adsorption calorimetry (SCAC). CO adsorption; NO adsorption; Comparison with other systems; Magnitude of pairwise repulsive interactions between CO molecules; Kinetics for CO and NO.

• Zeolitic tuff core shows thermal pulse from vapor transport is much faster than wetting front. • Data from heat of wetting spontaneous imbibition test used to estimate tortuosity to water vapor diffusion. • Analytical solution for heat conduction used to estimate thermal conductivity and source strength. An analytical expression is derived for the thermal response observed during spontaneous imbibition of water into a dry core of zeolitic tuff. Sample tortuosity, thermal conductivity, and thermal source strength are estimated from fitting an analytical solution to temperature observations during a single laboratory test. The closed-form analytical solution is derived using Green's functions for heat conduction in the limit of "slow" water movement; that is, when advection of thermal energy with the wetting front is negligible. The solution has four free fitting parameters and is efficient for parameter estimation. Laboratory imbibition data used to constrain the model include a time series of the mass of water imbibed, visual location of the wetting front through time, and temperature time series at six locations. The thermal front reached the end of the core hours before the visible wetting front. Thus, the predominant form of heating during imbibition in this zeolitic tuff is due to vapor adsorption in dry zeolitic rock ahead of the wetting front. The separation of the wetting front and thermal front in this zeolitic tuff is significant, compared to wetting front behavior of most materials reported in the literature. This work is the first interpretation of a thermal imbibition response to estimate transport (tortuosity) and thermal properties (including thermal conductivity) from a single laboratory test. [ABSTRACT FROM AUTHOR]

Understanding atomic-level mechanisms of methane adsorption in nanoporous materials is of great importance to increase their methane storage capacity targeting energy sources with low carbon emission. In this work, we considered layered covalent organic frameworks (COFs) with low density and revealed the effect of slipping and chemical functionalization on their methane adsorption and separation properties. We performed grand canonical Monte Carlo simulations studies of methane (CH4) adsorption and carbon-dioxide:methane (CO2:CH4) separation in various slipped structures of TpPa1, TpBD, PI-COFs, and functionalized TpPa1 and TpBD COFs as well. We observed that the slipping improves the total CH4 uptake by 1.1-1.5 times, while functionalization does not have a significant effect on CH4 uptake. We also observed improvement in CO2:CH4 selectivity due to slipping, whereas functionalization results in decrease in the selectivity. In all considered COFs, we found the highest CH4 delivery capacity of 141 cm³ (STP) cm-3 at 65 bar and selectivity of ~25 at 1 bar in 60-AB slipped structure of TpBD COF. We analyzed the molecular details of CH4 adsorption using binding energy, heat of adsorption, pore characteristics, and expectation energy landscape. Our results show that COFs with increasing profile of heat of adsorption with pressure have the higher CH4 delivery capacity. In these COFs, we found proximity (~4-6 Å) of CH4 binding sites, resulting in higher CH4-CH4 interactions and hence the increasing profile of CH4 heat of adsorption. [ABSTRACT FROM AUTHOR]

Adsorption (chemical) heat transformation (AHT) is a new energy conservation and environmentally friendly technology that allows efficient use of heat sources with low temperature potential. Recently, a new cycle, called “Heat from Cold” (or HeCol) has been proposed to upgrade the temperature potential of the ambient heat. In the HeCol cycle, a natural reservoir of water with a temperature above 0°C is used as a heat source, and ambient air at T = (-20)-(-50)°C as a heat sink. The cycle is designed to produce heat at a temperature of 30-50°C, which can be used for heating of dwellings. The aim of this work is to select the adsorbent for the HeCol cycle and to test the laboratory prototype with the selected adsorbent. The work consists of three parts: (a) formulation of requirements to adsorbent, specialized for the HeCol cycles under various conditions; (b) analysis of data on adsorption equilibrium of commercial activated carbons and selection among them the materials suitable for the new cycle; and c) study of the laboratory prototype HeCol with the chosen adsorbent to analyze the feasibility of the new cycle. The main findings of this study are (i) the experimental demonstration of the HeCol cycle feasibility and (ii) the achievement of the specific heat generation power 8 kW/kg, which is of practical interest. [ABSTRACT FROM AUTHOR]

This study was to investigate the impact of the characteristics of adsorbents on the performance of the desiccant wheel. Since the physical parameters of different wheels are not identical, the measured results would not truly reflect the sole influence of the adsorbents. As such, the performances of the desiccant wheels using RD silica gel (SG), AQSOA-Z02 and CECA-3A were compared through computer modeling. The variation of the absorbent condition through the entire cyclic humidification/dehumidification process was evaluated in order to review the role of adsorption isotherms. With the ambient humidity ratio of 16.04 g/kg, the desiccant wheel using SG, AQSOA-Z02 and CECA-3A would decrease the humidity ratio of the process air by 33.0%, 22.6% and 18.7% respectively at the regeneration temperature of 50 °C; while further by 65.2%, 64.5% and 51.1% respectively at 90 °C. Although AQSOA-Z02 was presented to have higher dehumidification capability from the adsorption isotherms, it was found that the desiccant wheel using SG would generally have better performances due to its lower heat of adsorption. CECA-3A was evaluated to have the lowest dehumidification capability because of narrow moisture uptake range. As a result, it is essential to appraise the adsorbent performance in a holistic approach. [ABSTRACT FROM AUTHOR]

Adsorption methods for determining the properties of stainless steel surface are presented. The relation between the actual and geometric surface is determined. The dependence of adsorption heat on the coverage logarithm is derived from experimental adsorption isotherms for water at 298 K. On the basis of this dependence, differential and integral distribution functions of adsorption sites by adsorption heat is calculated. It is shown that in the case of water adsorption on the surface of stainless steel at 298 K, adsorption heat for 90% of adsorption sites ranges from 4.4 × 10 7 to 7.9 × 10 7 J/kmol. [ABSTRACT FROM AUTHOR]

The strength of the acid sites in isostructural hierarchical porous zeolites increases in the order BSiO < GaSiO < AlSiO, and the concentration in the structural types increases in the order MTW < BEA < MOR. Zeolite materials with BEA and MOR topology, which consist of nanocrystals with ultrathin-layer morphology, are characterized by a marked decrease of the adsorption potential compared with isostructural materials with nanorods or nanosphere morphology due to a 1.5-fold decrease in the isosteric heats of adsorption of triethylamine. [ABSTRACT FROM AUTHOR]

In this paper, composite silica gel and potassium formate as typical organic weak acid salts is proposed to use in desiccant coated heat exchanger (DCHE). An experimental study on dynamic adsorption performance of desiccant coated metal sheet samples is conducted to obtain results with different proportions of silica gel and potassium format. A DCHE testing platform is then used to compare thermodynamic performance between single silica gel coated heat exchanger (SCHE) and composite potassium formate and silica gel coated heat exchanger (PSCHE). It is found that impregnating potassium formate into porous silica gel is an effective method to improve adsorption capacity, and 75% saturated potassium formate solution is recommended to constitute composite desiccant under experimental conditions. Compared with SG coated sheet, on average the maximum adsorption mass of SG&0.75PF coated sheet increases 2–3 times. Besides, PSCHE can obtain about 20% higher moisture removal capacity compared with SCHE under experimental condition, meaning the utilization of composite silica gel and potassium formate desiccant can effectively improve dehumidification capacity. PSCHE also can obtain 50% higher total cooling capacity compared with SCHE. [ABSTRACT FROM AUTHOR]

Water vapor ad/desorption isotherms were measured for a Marcellus shale at 303.15 K, 313.15 K and 328.15 K and a relative vapor pressure up to 0.95 to investigate the adsorption behavior of water on shale. Dent’s multilayer model was applied to fit three measured adsorption isotherms simultaneously using a global fitting approach. This model can also be used to estimate the primary and secondary adsorption sites for water on shale. The difference between the adsorption and desorption isotherms under different temperatures showed a similar hysteresis loop with a temperature-dependency feature. Based on the successful application of the Dent’s multilayer model, the isosteric heat of adsorption are calculated analytically, unlike the routinely used Clausius–Clapeyron approximation. By this method, the temperature dependence, as well as the uptake dependence of the isosteric heat, can be readily investigated. Using the ideal gas law will result in an overestimation of the isosteric heat of adsorption at high vapor pressure conditions. This work therefore not only discloses the temperature-dependency feature of the hysteresis behavior, but justifies the method for modeling water vapor adsorption isotherms and obtains the corresponding isosteric heat of adsorption laying the foundation for future investigation of the interaction between water and shale to optimize shale gas development. [ABSTRACT FROM AUTHOR]

Adsorption cycles have a distinct advantage over other systems in the ability to use low grade heat, especially waste heat of near ambient temperature. A Tri-bed twin-evaporator adsorption chiller constitute an innovative design in cooling production which allows more efficient conversion and management of low grade sources of thermal energy due to more effective way of utilization adsorptive abilities of the beds during a single work. Although it is the most effective way in chilled water production the complexity of the Tri-bed twin-evaporator adsorption chiller operation is still not sufficiently recognized and the improvement in cooling capacity (CC) of the cooler is still a challenging task. The paper introduces artificial intelligence approach for the optimization study of a Tri-bed twin-evaporator adsorption chiller using low-temperature heat from cogeneration. Genetic algorithms (GA) and artificial neural networks (ANN) are used to develop the model which allows estimating the behaviour of the adsorption heat pump. Cooling capacity (CC) as one of the main energy efficiency factor in cooling production is examined during the study for different operating sceneries. The presented non-iterative approach gives quick and accurate results as an answer to the input data sets. The CC of the chiller, evaluated using the developed model, is in good agreement with the experimental data. Maximum relative error between measured and calculated data is lower than ±10%. The developed model permits to study the influence of operating parameters on the cooling capacity of the chiller. For the considered range of input parameters the highest cooling capacity which can be obtained by the heat pump is equal 93.3 kW. The method constitutes an alternative, easy-to-apply and useful, complementary technique, comparing to the other techniques of data handling, including the complex of numerical and analytical methods as well as high costs of empirical experiments. The model can be applied for optimizations purposes and can constitute a sub model or a separate module in engineering calculations, capable to predict the CC of the Tri-bed twin-evaporator adsorption cooler, integrated into multigenerative systems. [ABSTRACT FROM AUTHOR]

The oxidation of Mg seriously limits its long-life applications as a hydrogen storage material. Considering the catalytic effects and unique redox instincts of rare earth oxides, MgH 2 with CeO 2 on the surface has been prepared by high energy ball milling MgH 2 with CeO 2 (20 wt%) in Ar and air atmosphere, respectively. It is expected to improve the oxidation resistance of Mg and elucidate the underlying mechanism by detailed microstructure observation and de-/hydrogenation kinetics analysis. CeO 2 with particle size in the range of ~ 20–100 nm are uniformly distributed on the surface of MgH 2 matrix after milling. For pure MgH 2 milled in air, both hydrogen capacity and de-/absorption kinetics deteriorate evidently comparing with those of pure MgH 2 milled in Ar. However, both MgH 2 + CeO 2 milled in Ar and air can rapidly absorb and desorb hydrogen. MgH 2 + CeO 2 milled in air can absorb ~ 4 wt% hydrogen within 4 min at 300 °C. For pure MgH 2 milled in Ar after air exposure, a long incubation period is necessary before fast dehydrogenation, while fast desorption is still observed for air-exposed MgH 2 + CeO 2 . It is believed that the uniformly distributed cerium oxides, which serve as catalysts promoting recombination of hydrogen and nucleation of new phase, can effectively prevent forming a dense and continuous MgO layer on the MgH 2 surface during air exposure due to the unique instincts of CeO 2 . The obtains in this work can be expected to provide guidelines to ameliorate the oxygen-free conditions of Mg-based hydrogen storage alloys by selecting proper catalyst and reasonable processing. [ABSTRACT FROM AUTHOR]

The surface heterogeneity of the multiwalled carbon nanotubes is investigated on the basis of adsorption isotherms from dilute aqueous phenol solutions at various temperatures. The Dubinin-Astakhov isotherm connected with the non-symmetrical distribution function of adsorption energies has been applied to describe adsorption equilibrium. Theoretical isosteric heats of adsorption connected with the Dubinin-Astakhov isotherm have been estimated as well. It is known that the decrease of the isosteric heat of adsorption with adsorbate loading is characteristic for the energetically heterogeneous surfaces. Theoretical description of kinetics is based on the Statistical Rate Theory of Interfacial Transport. The Statistical Rate Theory approach links the rate of transport between two phases with the difference in the chemical potentials of the molecules in these phases. Theoretical studies were verified successfully using the literature experimental adsorption data. [ABSTRACT FROM AUTHOR]

Adsorption characteristics of nitrogen onto granular activated carbon for the wide range of temperature (303-323 K) and pressure (0.2027-2.0265 MPa) have been reported for a single bed pressure swing adsorption refrigeration system. The experimental data were fitted to Langmuir, Dubinin-Astakhov and Dubinin-Radushkevich (D-R) isotherms. The Langmuir and D-R isotherm models were found appropriate in correlating experimental adsorption data with an average relative error of ±2.0541% and ±0.6659% respectively. The isosteric heat of adsorption data were estimated as a function of surface coverage of nitrogen and temperature using D-R isotherm. The heat of adsorption was observed to decrease from 12.65 to 6.98 kJ.mol with an increase in surface concentration at 303 K and it followed the same pattern for other temperatures. It was found that an increase in temperature enhances the magnitude of the heat of adsorption. [ABSTRACT FROM AUTHOR]

Differential molar isosteric and integral heats of methane adsorption on a range of microporous carbon adsorbents of different origin have been calculated. The values of densities of integral heats Ω of methane adsorption on the sorbents under study Ω have been determined as the ratio between integral heat of adsorption and micropore volume. The dependence of density of integral heat of adsorption on standard characteristic energy of adsorption E has been estimated. It has been shown that the value of density Ω increases as E increases. The results of calculation of specific amount of accumulated methane V depending on energy and structural parameters of adsorbents have been presented. [ABSTRACT FROM AUTHOR]

The adsorption of CHCl, CHCl, CCl, and HO vapors on the surface of multi-walled carbon nanotubes and alumina in the temperature range of 10-25 °C was studied. Dependences of the isosteric heat of adsorption on the surface coverage were plotted. The initial heat of adsorption of dichloromethane, chloroform, and CCl on AlO was found to be equal to 71, 28, and 31 kJ mol, respectively. In most cases, adsorption on the oxide adsorbent was characterized by a higher heat of adsorption compared to that found on the carbon material, which is apparently related to chemical interaction of sorbed molecules with the OH groups of the alumina surface. [ABSTRACT FROM AUTHOR]

Periodic boundary condition models are used to investigate the interaction of small hydrocarbons (C 2 -C 4 ) with MOF-74-Mg/Zn. In contrast to other studies where molecular cluster approaches are used, the complete chemical environment of the framework is included. This allows correcting the binding energies for basis-set superposition error, molecular lateral interaction, zero-point energy, and thermal contributions. As such, the presented results are directly comparable to experimental calorimetric values. This work discusses, for the first time, the origin of the fictitious agreement between binding energies obtained with molecular clusters and experimental heats of adsorption, identifying its origin as due to compensation of errors. [ABSTRACT FROM AUTHOR]