Isosteric Heat Of Adsorption Values Research Articles

Investigation of performance of potential adsorbents for emissions mitigation in a diesel generator.

Globally, the release of greenhouse gases primarily carbon dioxide (CO2) emissions to our Earth's surface has climbed by about 45% to its present atmospheric concentration rate of 420 parts per million (ppm) during the industrial era. An unprecedented rise in atmospheric CO2 concentration has been claimed to lead to significant factors such as global warming potential (GWP) and climate change effects. An increase in atmospheric CO2 concentrations is a serious threat to the environment. Recent research efforts have focused on mitigating emissionsfrom anthropogenic point sources. Adsorption-based post-combustion CO2 capture using solid adsorbents is the most effective and efficient method for mitigating gas adsorption in the exhaust system. In the current study, activated carbons are obtained from three potential biomass, namely, (i) coconut shell, (ii) rice husk, and (iii) eucalyptus wood, through a - single-stageactivation method. The prepared activated carbon materials are analyzed using proximate and ultimate analyses. Further investigations are performed using different characterization techniques to ensure their adsorption efficiency. Adsorbents are packed one after the other in an in-house fabricated double adsorption chamber and coupled to the exhaust unit of a generator. Test experiments are conducted to examine adsorbents' capture efficiency in emissions mitigation. Adsorbents' adsorption parameters are evaluated in experimental investigations. At 2.5bar and 50°C, a maximum loading capacity of samples is achieved by 4.85mmol/g, 4.58mmol/g, and 5.96mmol/g for coconut shell, rice husk, and eucalyptus wood adsorbents, respectively. With a post-combustion carbon adsorption chamber, CO2 and NO are captured about40-64% and 38-58%, respectively, for all three adsorbents. The thermodynamic parameter of isosteric heat of adsorption value is below 40kJ/mol, ensuring physisorption for all adsorbents.

Activated char from the co-pyrolysis of polystyrene and olive stone mixtures for the adsorption of CO2

Yogurt plastic containers made of polystyrene (PS), olive stone, and mixtures of both have been converted into activated carbon materials transforming them firstly into char via pyrolysis and secondly with activation using either KOH or H2SO4. The pyrolysis of the olive stone gave a higher yield of material than the plastic PS. However, the activation of the PS char with KOH was more effective, reaching surface areas of 508 vs 194 m2 g−1 of the corresponding prepared with olive stone. The prepared materials were tested as CO2 adsorbent in thermobalance and fixed-be column assays. The materials activated with H2SO4 slightly enhanced the adsorption ability of the original char but were far from the performance obtained with KOH activation. The CO2 isotherms showed high synergy of CO2 uptake and selectivity when using activated chars prepared with the char from the mixture of raw materials, specially at a 1:1 mass ratio. The isosteric heat of adsorption values were those expected for a physisorption process. Further experiments in a fixed-bed column were also studied at atmospheric pressure at different inlet CO2 concentrations (10–50%). The CO2 retention increased as the partial CO2 pressure rose. Besides, a very similar performance of the material prepared with plastic and olive stones was obtained at 50%, i.e. 220 and 197 mg g−1 respectively. At low CO2 concentrations, the materials enriched with plastic displayed better performance than those prepared with olive stone. Cycles of adsorption-desorption were carried out in the column to assess the stability of the materials. The curves obtained did not display any substantial change, demonstrating the lack of adsorption retention.

Two-dimensional oxalamide based isostructural MOFs for CO2 capture

Metal-organic frameworks (MOFs), members of porous crystalline materials, have been investigated for CO2 capture and separation from various exhaust gas mixtures. An essential element to build new MOFs with improved CO2 capture and separation abilities is to understand the influence of functional groups on the surface of pores on gas adsorption properties. Oxalamide groups have two amide moieties that feature a strong affinity to CO2. In this study, three new isostructural Co(II), Zn(II), and Cd(II)-MOFs have been synthesized by using 3,3'-(oxalylbis(azanediyl))dibenzoic acid (3-OADAH2) ligand which has a CO2-philic oxalamide group. To the best of our knowledge 3,3'-(oxalylbis(azanediyl))dibenzoic acid (3-OADAH2) was used as a linker for the first time. X-ray diffraction analysis shows that the MOFs possess two-dimensional (2D) structures and the layers interact with each other through hydrogen bonds. Co-, Zn-, and Cd-3-OADA exhibit an excellent CO2 adsorption capacity of 8.87 ​wt% (45.15 ​cm3/g), 8.40 ​wt% (42.76 ​cm3/g), and 7.93 ​wt% (40.37 ​cm3/g) at 273 ​K and 3.98 ​wt% (20.27 ​cm3/g), 4.74 ​wt% (24.15 ​cm3/g), 3.68 ​wt% (18.72 ​cm3/g) at 298 ​K under 1 ​bar with isosteric heat of adsorption values (Qst) of about 34, 25, and 33 ​kJ/mol, respectively. This work opens a new opportunity for the development of functionalized 2D-MOFs with high CO2 capture capacity.

Remarkable isosteric heat of hydrogen adsorption on Cu(I)-exchanged SSZ-39

Hydrogen storage capacity on Cu(I)-exchanged SSZ-39 (AEI), -SSZ-13 (CHA) and Ultra stable-Y (US–Y, FAU) at temperatures between 279 K and 304 K are investigated. The gravimetric hydrogen storage capacity values reaching 83 μmol H2 g−1 (at 279 K and 1 bar) are found to be comparable with the highest adsorption capacity values reported on metal-organic frameworks. The volumetric hydrogen storage capacity values; on the other hand, are found to be more than three times of those reported on metal-organic frameworks (0.57 g/L on Cu(I)-SSZ-39 at 1 bar and 296 K vs. ca. 0.18 g/L on Co2(m-dobdc) at 1 bar and 298 K (Kapelewski MT, Runčevski T, Tarver JD, Jiang HZH, Hurst KE, Parilla PA et al. Record High Hydrogen Storage Capacity in the Metal-Organic Framework Ni2(m-dobdc) at Near-Ambient Temperatures. Chem Mater 2018; 30:8179–89)). The isosteric heat of adsorption values are calculated to be between 80 kJ mol−1 and 49 kJ mol−1 on Cu(I)-SSZ-39 and between 22 kJ mol−1 and 15 kJ mol−1 on Cu(I)-US-Y indicating H2 adsorption mainly at Cu(I) cations located at the eight-membered rings on Cu(I)-SSZ-39 and at six-membered rings on Cu(I)-US-Y. Hydrogen adsorption experiments performed at 77 K showed higher adsorption capacity values for Cu(I)-SSZ-39 at 1 bar, but Cu(I)-US-Y showed potential for hydrogen storage at higher pressure values.

Adsorption of CO2 on KOH activated carbon adsorbents: Effect of different mass ratios

Nitrogen and oxygen enriched carbons were prepared by the cost-effective synthesis route of carbonization of polyacrylonitrile (PAN) and subsequent KOH activation for CO2 capture. The effect of four impregnation mass ratios (KOH: PAN = 1–4) and activation temperatures (600–900 °C) on the synthesized carbon adsorbent properties was explored by different analyses. The X-ray photoelectron spectroscopy (XPS) revealed the existence of basic nitrogen and oxygen functionalities on the adsorbent's surface which increases the adsorption rate for CO2 by providing its basic sites. By increasing mass ratio (KOH:PAN) from 1:1 to 3:1, the surface area increased from 1152.4 to 1884.2 m2 g−1 and the dynamic CO2 adsorption capacity also increased from 2.1 to 2.5 mmol g−1 respectively, at 30 °C (approximately ten times the adsorption capacity of untreated PAN, 0.22 mmol g−1). Physisorption and exothermic nature of the process were confirmed by the decrease in the adsorption capacity of the adsorbents with the increase in adsorption temperature. Moreover, good cyclic stability and regenerability over 5 adsorption-desorption cycles were obtained for the adsorbents. The fractional order kinetic and Temkin isotherm models fitted best with the adsorption data. A heterogeneous interaction between CO2 and the surface of adsorbents was suggested by the isosteric heat of adsorption values. Combined with the simple method for the preparation of activated carbon adsorbents, efficient CO2 adsorption and excellent regeneration make it appropriate adsorbents for post-combustion CO2 capture.

Effect of Triblock Copolymer on Carbon-Based Boron Nitride Whiskers for Efficient CO2 Adsorption.

Herein, we investigated novel carbon-containing P123 copolymer-activated boron nitride whiskers (P123-CBNW) fabricated via a structure directing approach followed by a single-step heat treatment under N2. The resulting materials were found to be highly micro- and mesoporous. The influence of the activating agent (P123 copolymer) on the CO2 adsorption efficiency was determined. The prepared samples possessed high specific surface areas (594–1732 m2/g) and micropore volumes (0.258–0.672 cm3/g). The maximum CO2 uptakes of the prepared adsorbents were in the range 136–308 mg/g (3.09–7.01 mmol/g) at 273 K and 1 bar and 97–114 mg/g (2.22–4.62 mmol/g) in the following order: CBNW < P123-CBNW3 < P123-CBNW2 < P123-CBNW1 < P123-CBNW0.5. The isosteric heat of adsorption values (∆Qst) were found to be 33.7–43.7 kJ/mol, demonstrating the physisorption nature of the CO2 adsorption. Extensive analysis revealed that the presence of carbon, the high specific surface area, the high microporosity, and the chemical structural defects within the adsorbents are responsible for raising the CO2 adsorption ability and the selectivity over N2 gas. The fabricated adsorbents show excellent regeneration ability after several repeated adsorption cycles, making the prepared adsorbents promising candidates for gas storage applications.

A Mn(II)-porphyrin based metal-organic framework (MOF) for visible-light-assisted cycloaddition of carbon dioxide with epoxides

Abstract The construction of a microporous 3D supramolecular Mn(II)-porphyrin metal-organic framework, [{Mn(TCPP)0.5(H2O)2}.2H2O]n (MOF1) (where, TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) exhibiting unprecedented visible-light-assisted cycloaddition of CO2 with epoxides to generate cyclic carbonates at mild conditions of room temperature (RT) and 1 bar CO2 has been reported. Single crystal structure determination reveals that MOF1 has an interesting microporous 2D network structure with 1D channels of dimension, 6.32 × 11.88 A2 along the crystallographic c-axis. The 2D networks are further interacting through O-H⋯O hydrogen bonding interaction between carboxylate oxygen and hydrogen of water molecules coordinated to Mn(II) center forming a 3D supramolecular framework. Gas adsorption studies revealed selective adsorption property of MOF1 for CO2 (selectivity constants for CO2/H2 = 39, CO2/N2 = 19, CO2/Ar = 21) with the isosteric heat of adsorption value of 32.9 kJ/mol. Further, MOF1 acts as an efficient recyclable heterogeneous catalyst for cycloaddition of CO2 with epoxides to generate cyclic carbonates with high selectivity and yield at mild conditions of RT and 1 bar of CO2. More interestingly, the rate of catalytic conversion of CO2 was enhanced with irradiation of visible light owing to good visible light absorption property of the porphyrin linker. The enhanced catalytic activity of MOF1 under the irradiation of visible-light has been attributed to the in situ generation of thermal energy by photo-thermal effect. Therefore, herein, for the first time, visible-light-assisted efficient cycloaddition of CO2 with epoxides catalyzed by a Mn(II)-porphyrin MOF has been reported.

Rational Design of a 3D MnII -Metal-Organic Framework Based on a Nonmetallated Porphyrin Linker for Selective Capture of CO2 and One-Pot Synthesis of Styrene Carbonates.

A 3D MnII -porphyrin metal-organic framework (MOF), [{Mn2 (TCPP)⋅2H2 O}⋅DMF]n (MOF1) (TCPP=5,10,15,20-tetrakis(4-benzoate)porphyrin), was constructed; it exhibits an interesting 3D framework structure with two types of 1D channels of dimensions of 3.94×8.37 Å2 and 4.66×4.93 Å2 running along the crystallographic a axis. Owing to the presence of a nonmetallated porphyrin cavity, MOF1 exhibits selective storage of CO2 with an isosteric heat of adsorption value of 32.1 kJ mol-1 , which is further supported by theoretical calculations with the calculated binding energy (BE) of 29.78 kJ mol-1 . Interestingly, the nonmetallated nature of the porphyrin ligand was exploited for implantation of coordinatively unsaturated FeIII ions to generate a FeIII @MOF1 framework, which acts as an efficient recyclable catalyst for the oxidation of styrenes to the corresponding epoxides in the presence of PhIO as an oxidant at room temperature. Moreover, the one-pot synthesis of styrene carbonates from styrenes and CO2 was also achieved using FeIII @MOF1 as a catalyst. The rational design of a porous MnII -porphyrin MOF for the selective capture of CO2 and the one-pot synthesis of styrene carbonates at mild conditions is reported.

SO2 gas adsorption on carbon nanomaterials: a comparative study.

Owing to their high stability against corrosive gases, carbon-based adsorbents are preferentially used for the adsorptive removal of SO2. In the present study, SO2 adsorption on different carbon nanomaterials namely carbon nanohorns (CNHs), multiwalled carbon nanotubes (MWNTs), single-walled carbon nanotubes (SWNTs) and vertically aligned carbon nanotubes (VACNTs) are investigated and compared against the adsorption characteristics of activated carbon and graphene oxide (GO). A comprehensive overview of the adsorption behavior of this family of carbon adsorbents is given for the first time. The relative influence of surface area and functional groups on the SO2 adsorption characteristics is discussed. The isosteric heat of adsorption values are calculated to quantify the nature of the interaction between the SO2 molecule and the adsorbent. Most importantly, while chemisorption is found to dominate the adsorption behavior in activated carbon, SO2 adsorption on carbon nanomaterials occurs by a physisorption mechanism.

Development of chemically activated N-enriched carbon adsorbents from urea-formaldehyde resin for CO2 adsorption: Kinetics, isotherm, and thermodynamics

Nitrogen enriched carbon adsorbents with high surface areas were successfully prepared by carbonizing the low-cost urea formaldehyde resin, followed by KOH activation. Different characterization techniques were used to determine the structure and surface functional groups. Maximum surface area and total pore volume of 4547 m2 g−1 and 4.50 cm3 g−1 were found by controlling activation conditions. The optimized sample denoted as UFA-3-973 possesses a remarkable surface area, which is found to be one of the best surface areas achieved so far. Nitrogen content of this sample was found to be 22.32%. Dynamic CO2 uptake capacity of the carbon adsorbents were determined thermogravimetrically at different CO2 concentrations (6–100%) and adsorption temperatures (303–373 K) which have a much more relevance for the flue gas application. Highest adsorption capacity of 2.43 mmol g−1 for this sample was obtained at 303 K under pure CO2 flow. Complete regenerability of the adsorbent over four adsorption-desorption cycles was obtained. Fractional order kinetic model provided best description of adsorption over all adsorption temperatures and CO2 concentrations. Heterogeneity of the adsorbent surface was confirmed from the Langmuir and Freundlich isotherms fits and isosteric heat of adsorption values. Exothermic, spontaneous and feasible nature of adsorption process was confirmed from thermodynamic parameter values. The combination of high surface area and large pore volume makes the adsorbent a new promising carbon material for CO2 capture from power plant flue gas and for other relevant applications.

Adsorption of CO2 on KOH activated, N-enriched carbon derived from urea formaldehyde resin: kinetics, isotherm and thermodynamic studies

High surface area nitrogen enriched carbon adsorbents were prepared from a low cost and widely available urea-formaldehyde resin using a standard chemical activation with KOH and characterized using different characterization techniques for their porous structure and surface functional groups. Maximum surface area and total pore volume of 4547 m2 g−1 and 4.50 cm3 g−1 were found by controlling the activation conditions. Nitrogen content of this sample was found to be 5.62%. Adsorption of CO2 uptake for the prepared carbon adsorbents was studied using a dynamic fixed bed adsorption system at different adsorption temperatures (30–100 °C) and at different CO2 concentrations (5–12.5%), relevant from the flue gas point application. Maximum CO2 uptake of 1.40 mmol g−1 for UFA-3-700 at 30 °C under 12.5% CO2 flow was obtained. Complete regenerability of the adsorbents over multiple adsorption-desorption cycles was obtained. Fractional order kinetic model provided best description over all adsorption temperatures and CO2 concentrations. Heterogeneity of the adsorbent surface was confirmed from Temkin adsorption isotherm model fit and isosteric heat of adsorption values. Negative value of ΔG° and ΔH° confirms spontaneous, feasible nature and exothermic nature of adsorption process. Overall, very high surface area of carbon adsorbent makes this adsorbent a new promising carbon material for CO2 capture from power plant flue gas and for other relevant applications.

Adsorption Equilibria of C1–C4 from Natural Gas on Graphene Sheets

As a new kind of adsorbent, graphene sheets (GS) possess large surface areas and excellent adsorption properties. To investigate the adsorption equilibria of C1–C4 from natural gas on GS and fit the isotherms by the Langmuir–Freundlich equation. GS were synthesized with a specific surface area of 805 m2/g and a specific pore volume of 1.03 cm3/g. The adsorption isotherms were measured using a volumetric method at five different temperatures between 263.15 and 303.15 K and at pressures of 0–6 MPa for CH4, 0–1.6 MPa for C2H6, 0–0.3 MPa for C3H8, and 0–0.05 MPa for C4H10. It was shown that, for all four hydrocarbons, the amount of adsorption decreased gradually as the temperature increased. The isotherms were described well by the Langmuir–Freundlich equation. The isosteric heat of adsorption values decreased in the order C4H10 > C3H8 > C2H6 > CH4 which was consistent with those of the extreme heats of adsorption. This suggests that the adsorption capacities of C1–C4 on GS decreased in the order C4H10 > C3H8...

Adsorption Characteristics of Nitric Oxide and Sulfur Dioxide on Coal Activated Carbon

The aim of this paper is to study the adsorption characteristics of nitric oxide (NO) and sulfur dioxide (SO2) on raw coal activated carbon over temperature ranged 298～343K using a static volumetric adsorption apparatus. The adsorption equilibrium data for NO and SO2 were fitted to Freundlich, Dubinin-Radushkevich (D-R) and Sips adsorption isotherm model. Isosteric heat of adsorption was determined by the Clausius-Clapeyron equation. It was found that Sips adsorption isotherm model is more suitable for description of NO adsorption process at 298K, 313K and 328K and SO2 adsorption process at 313K, 328K and 343K, however, D-R adsorption isotherm model is more suitable for description of the NO adsorption process at 343K and SO2 adsorption process at 298K. The isosteric heat of adsorption values of SO2 increase slightly as the adsorbed amounts increasing from 0.8 to 1.6mg/g, but the isosteric heat of adsorption values of NO show a converse trend. Meanwhile, NO and SO2 adsorbed on coal activated carbon at the four temperatures may be a dominant of physical adsorption.

Adsorption of N2, O2, and Ar in Potassium Chabazite

Chabazite with Si/Al of 2.4 ratio was synthesized and exchanged with cations viz. K+, Li+ and Ca2 +. N2, O2 and Ar adsorption isotherms were measured in the pressure range 0–1000 torr and temperatures viz. 0, 30 and 50 ∘C. K-CHA showed better O2/Ar selectivity than Ca-CHA although adsorption capacity was larger for Ca-CHA. Zero loading isosteric heat of adsorption values for K-CHA, were considerably lower than Ca-CHA which reflect diminished charge density of the K cation. The high O2/Ar selectivity is possibly due to partial pore blockage as a result of the large potassium cation located near the 8-member ring leading to the 20-hedron cage. The O2/Ar selectivity may be exploited to produce high purity oxygen (> 99%) from a two stage PSA system employing K-CHA in the second stage.