Showing papers in "Adsorption-journal of The International Adsorption Society in 2012"
TL;DR: In this article, the authors present breakthrough experiments in a fixed bed adsorber packed with commercial activated carbon involving feed mixtures of carbon dioxide and hydrogen of different compositions, and they describe the adsorption process with a detailed one-dimensional model consisting of mass and heat balances and several constitutive equations.
Abstract: We present breakthrough experiments in a fixed bed adsorber packed with commercial activated carbon involving feed mixtures of carbon dioxide and hydrogen of different compositions. The experiments are carried out at four different temperatures (25 °C, 45 °C, 65 °C and 100 °C) and seven different pressures (1 bar, 5 bar, 10 bar, 15 bar, 20 bar, 25 bar and 35 bar). The interpretation of the experimental data is done by describing the adsorption process with a detailed one-dimensional model consisting of mass and heat balances and several constitutive equations, such as an adsorption isotherm and an equation of state. The dynamic model parameters, i.e. mass and heat transfer, are fitted to one single experiment (reference experiment) and the model is then further validated by predicting the remaining experiments. Furthermore, the choice of the isotherm model is discussed. The assessment of the model accuracy is carried out by comparing simulation results and experimental data, and by discussing key features and critical aspects of the model. This study is valuable per se and a necessary step toward the design, development and optimization of a pressure swing adsorption process for the separation of CO2 and H2 for example in the context of a pre-combustion CO2 capture process, such as the integrated gasification combined cycle technology.
125 citations
TL;DR: In this article, a new field of application for pressure swing adsorption (PSA) processes is the capture of CO2 to mitigate climate change, especially the separation of CO 2 and H2 in a pre-combustion context.
Abstract: A new developing field of application for pressure swing adsorption (PSA) processes is the capture of CO2 to mitigate climate change, especially the separation of CO2 and H2 in a pre-combustion context. In this process scheme the conditions of the feed to the separation step, namely a pressure of 3.5 to 4.5 MPa and a CO2 fraction of around 40% are favorable for an adsorption based separation process and make PSA a promising technology. Among the commercial adsorbent materials, activated carbon is most suitable for this application. To evaluate the potential, to benchmark new materials, and for process development a sound basis of the activated carbon thermodynamic data is required, namely equilibrium adsorption isotherms of the relevant pure components and mixtures, Henry’s constants and isosteric heats.
91 citations
TL;DR: In this paper, a conceptual adsorption process for the recovery and purification of biobutanol is proposed, where different porous materials are tested on their ability to perform the adsorptive separations relevant to the process.
Abstract: A conceptual adsorption process for the recovery and purification of biobutanol is proposed. Different porous materials are tested on their ability to perform the adsorptive separations relevant to the process. The metal-organic framework ZIF-8, silicalite zeolite and active carbon were compared with respect to their adsorption capacity of 1-butanol dissolved in water, as obtained in static and dynamic conditions by respectively batch and breakthrough measurements at room temperature. Batch experimentation showed that other compounds present in a real ABE fermentation have no significant effect on the adsorption of 1-butanol on ZIF-8. The breakthrough separation of 1-butanol from an aqueous ABE mixture was performed with a ZIF-8 packed column. The desorption of 1-butanol from a saturated ZIF-8 packed column by a stepwise increase of the temperature to 423 K in combination with a purge of a nitrogen gas (60 ml/min) shows that 1-butanol desorbs at low temperature from ZIF-8. Adsorption isotherms of ethanol, 1-butanol and water in liquid phase on the zeolite SAPO-34 were determined by batch adsorption at 298 K. Also the separation of an ethanol/1-butanol mixture and the removal of ethanol from 1-butanol could be achieved with a SAPO-34 packed column. From this experimental work, two materials—ZIF-8 and SAPO-34—thus emerged as suitable adsorbents for the recovery and purification of biobutanol by adsorption.
68 citations
TL;DR: In this article, self-diffusion measurements with methane and carbon dioxide adsorbed in the Zeolitic Imidazolate Framework-8 (ZIF-8) were performed by 1H and 13C pulsed field gradient nuclear magnetic resonance (PFG NMR).
Abstract: Self-diffusion measurements with methane and carbon dioxide adsorbed in the Zeolitic Imidazolate Framework-8 (ZIF-8) were performed by 1H and 13C pulsed field gradient nuclear magnetic resonance (PFG NMR). The experiments were conducted at 298 K and variable pressures of 7 to 15 bar in the gas phase above the ZIF-8 bed. Via known adsorption isotherms these pressures were converted to loadings of the adsorbed molecules. The self-diffusion coefficients of carbon dioxide measured by PFG NMR are found to be independent of loading. They are in good agreement with results from molecular dynamic (MD) simulations and resume the trend previously found by IR microscopy at lower loadings. Methane diffuses in ZIF-8 only slightly slower than carbon dioxide. Its experimentally obtained self-diffusion coefficients are about a factor of two smaller than the corresponding values determined by MD simulations using flexible frameworks.
61 citations
TL;DR: In this paper, two different functionalisation methods were applied for the generation of amino functionalised aerogels: co-condensation during the sol-gel process and post-treatment of the gel.
Abstract: Effective adsorption of CO2 at low partial pressures is required for many technical processes, such as gas purification or CO2 removal in closed loop environmental control systems. Since the concentration of CO2 in such applications is rather low, a high adsorption capacity is a required property for the adsorbent. Silica aerogels possessing an open pore structure, a high porosity and a high surface area, have a great potential for utilisation as CO2 adsorbents. Nonetheless in order to reach high adsorption capacities, silica aerogels should be functionalised, for instance by amino functionalisation. In this work, two different functionalisation methods were applied for the generation of amino functionalised aerogels: co-condensation during the sol-gel process and post-treatment of the gel. The co-condensation functionalisation allows the introduction of up to 1.44 wt.% nitrogen into the aerogel structure with minor reductions in surface area, leading however only to minor increases in the adsorption capacity at low partial pressures. The post functionalisation of the gel causes a greater loss in surface area, but the CO2 adsorption capacity increases, due to the introduction of higher amounts of amino groups into the aerogel structure (up to 5.2 wt.% nitrogen). Respectively, 0.523 mmol CO2/g aerogel could be adsorbed at 250 Pa. This value is comparable with the adsorption capacity at this pressure of a standard commercially available adsorbent, Zeolite 13X.
60 citations
TL;DR: In this article, a 3-bed 5-step VPSA process was designed to capture CO2 from flue gases, which included feed pressurization, adsorption, rinse, blowdown and countercurrent purge.
Abstract: With the development of novel adsorbent material and adsorption process, adsorption technology has become a potential tool for the CO2 removal from flue gases. The reduction of carbon dioxide emissions from flue gases with two successive vacuum pressure swing adsorption (VPSA) units, using 13XAPG as the adsorbent, was investigated both theoretically and experimentally. A 3-bed 5-step VPSA process was designed to capture CO2 from flue gases, which included feed pressurization, adsorption, rinse, blowdown and counter-current purge. It was found that was difficult to achieve both high CO2 purity and high CO2 recovery by one VPSA unit when capturing CO2 from flue gases at atmospheric pressure. After the verification of one-column VPSA experiment for further concentrating CO2 stream from one VPSA unit to above 95 % purity, two successive VPSA units were designed, composed of 3-bed 5-step cycle for the first unit and 2-bed 6-step cycle for the second unit, and the effects of operating parameters on the separation behaviors were investigated by simulation. With the proposed VPSA process, a CO2 purity of 96.54 % was obtained with recovery of 93.35 %. The total specific power consumption of the two successive VPSA units was $528.39\mbox{~kJ/kg}_{\mathrm{CO}_{2}}$
, while the unit productivity was $0.031\mbox{~kg}_{\mathrm{CO}_{2}}\mbox{/kg\,h}$
.
53 citations
TL;DR: In this paper, three different adsorbent materials, which are promising for pre-combustion CO2 capture by a PSA (Pressure Swing Adsorption) process, are synthesized, pelletized and characterized.
Abstract: Three different adsorbent materials, which are promising for pre-combustion CO2 capture by a PSA (Pressure Swing Adsorption) process, are synthesized, pelletized and characterized. These materials are USO-2-Ni metal organic framework (MOF), mesoporous silica MCM-41 and a mixed material consisting of UiO-67 MOF bound with MCM-41. On these materials, equilibrium adsorption isotherms of CO2 and H2 are measured at different temperatures (25–140 °C) in a wide pressure range (up to 15 MPa). From the experimental data the parameters of different isotherm equations (Langmuir, Sips and Quadratic) are determined, together with the isosteric heats of adsorption. Binary adsorption of CO2/H2 mixtures on USO-2-Ni MOF is additionally measured and compared to predicted values using IAST (Ideal Adsorbed Solution Theory) showing a good agreement. The potential of the materials for the application of interest is evaluated by looking at their cyclic working capacity and compared to those of a commercial activated carbon. From this evaluation especially the USO-2-Ni MOF adsorbent looks promising compared to the commercial activated carbon. For the other two materials a smaller improvement, which is limited to lower temperatures, is expected.
43 citations
TL;DR: In this article, the storage capacities of high surface area microporous adsorbents at 298 K and at pressures up to 50 MPa were investigated for automotive applications, and the peak excess adsorption of these materials ranged from 0.8-1.8 W% to 0.9 W% with varying microstructures.
Abstract: High surface area microporous adsorbents are often proposed as potential hydrogen storage materials, although typically at 77 K and less than 5 MPa. In this study, we focus on conditions more suitable for automotive applications by investigating the storage capacities of microporous materials at 298 K and at pressures up to 50 MPa. In an effort to derive trends within and across material classes, we examined a wide range of materials with varying microstructures including the activated carbons AX-21, KUA-5, and MSC-30; a zeolite templated carbon; a hypercrosslinked polymer; and the Metal Organic Frameworks MOF-177, IRMOF-20, MIL-53, ZIF-8, and Cu3(btc)2. The peak excess adsorption of these materials ranged from 0.8–1.8 wt.%, although many did not reach their maximum capacity even at high pressures. However, the total volumetric storage gains over compressed hydrogen gas were quite low and, in many cases, negative. In addressing ambient temperature adsorption at significantly higher pressures than previously reported, our data confirms and extends the range of validity of several existing DFT calculations. Furthermore, our data suggest that, for both activated carbons and MOFs, factors other than specific surface area govern ambient temperature adsorption capacity. Contrary to some reports, the high fractions of sub-nanometer pores in some of the investigated MOFs did not appear to enhance the excess adsorption even at high pressures. For on-board applications with ambient temperature storage, significant enhancements to the attractive force at the materials’ surface are required, beyond merely increasing specific surface area, or for MOFs, tuning of pore sizes.
39 citations
TL;DR: A recently developed carbon material, electrospun Activated Carbon nanoFiber (ACnF), exhibits strong potential for use as an adsorbent for toxic industrial chemicals (TICs) as discussed by the authors.
Abstract: A recently developed carbon material, electrospun Activated Carbon nanoFiber (ACnF), exhibits strong potential for use as an adsorbent for toxic industrial chemicals (TICs). As-prepared ACnF contains as much as 9.6 wt% nitrogen, creating a basic surface that enhances acid-gas adsorption. ACnF shows 4–20 times greater HCN adsorption capacities and 2–5 times greater SO2 adsorption capacities in dry nitrogen, compared to commercially available activated carbon fiber cloth (ACFC) and Calgon BPL™ granular activated carbon, which are considered here as reference adsorbents. ACnF has 50 % of the micropore volume (0.30 cm3/g) of these reference adsorbents, which limits its adsorption capacity at high concentrations for volatile organic compounds (>500 ppmv). However, at low concentrations (<500 ppmv), ACnF has a similar capacity to ACFC and about three times the VOC adsorption capacity of Calgon BPL™. ACnF’s small fiber diameters (0.2–1.5 μm) allow for higher mass transfer coefficients, resulting in adsorption kinetics nearly twice as fast as ACFC and eight times as fast as Calgon BPL™. ACnF drawbacks include hydrophilicity and reduced structural strength. The rapid adsorption kinetics and high capacity for acidic TICs warrant further investigation of ACnF as an adsorbent in respiratory protection and indoor air quality applications.
38 citations
TL;DR: In this paper, a novel ordered mesoporous carbon containing basic nitrogen functional groups was synthesized by ammonia-tailoring at a temperature of 1173 K and was applied for reactive dye adsorption.
Abstract: A novel ordered mesoporous carbon containing basic nitrogen functional groups was synthesized by ammonia-tailoring at a temperature of 1173 K and was applied for reactive dye adsorption. The basic nitrogen-containing functional groups incorporated into the carbon surface could enhance the dispersive interactions between the carbon and dye molecules due to the electron-donating effect as well as the electrostatic interactions between the carbon surface and the anions of the dyes. It was found that this novel functionalized ordered mesoporous carbon could increase the adsorption capacity of reactive red 2 at 298 K by around 40 % and 100 % as compared with the unmodified carbon and a commercial activated carbon, respectively. The Freundlich isotherm showed better correlation with the experimental adsorption data of ammonia-tailored samples than the Langmuir isotherm due to the increased surface heterogeneity induced by the nitrogen-containing functional groups. Adsorption of reactive red 2 was an endothermic process as the adsorption capacity increased with increasing temperature. Low desorption efficiency revealed that the adsorption of reactive red 2 on the modified CMK-3 was extremely favorable, tending to be weakly reversible.
36 citations
TL;DR: In this article, three types of agricultural waste, citrus maxima peel (CM), passion fruit shell (PF), and sugarcane bagasse (SB), were used to produce biosorbents for removing the heavy metal ions of copper(II), cadmium (II), nickel (II) and lead(II) from a pH 5.0 solution.
Abstract: Three types of agricultural waste, citrus maxima peel (CM), passion fruit shell (PF) and sugarcane bagasse (SB), were used to produce biosorbents for removing the heavy metal ions of copper(II), cadmium(II), nickel(II) and lead(II) from a pH 5.0 solution. The properties of biosorbents were characterized using scanning electron microscopy (SEM), zeta potential analyzer, Fourier transform infrared (FTIR) spectroscopy, elemental analyzer and tests of cation exchange capacity (CEC). The result indicated that the selected biosorbents possess rich carboxyl (COOH) and hydroxyl (OH) groups to produce a complexation with the heavy metals. Moreover, the negative surface charge of the biosorbent might adsorb the metal ions through the ion exchange. All of the adsorption isotherms indicated that L-type characters represented complexation and ion exchanges that were the adsorption mechanisms of biosorbents toward heavy metals. Biosorbents with higher oxygen content might generate high adsorption capacities. The adsorption capacities of CM and PF, estimated from the fitting to the Langmuir isotherm, are similar to those reported by others regarding biosorbents.
TL;DR: Tetraethylenepentamine (TEPA)-modified mesocellular silica foams (MSFs) were fabricated via physical impregnation (MSF-T-x) and chemical grafting (MS F-CT-y) methods as discussed by the authors.
Abstract: Tetraethylenepentamine (TEPA)-modified mesocellular silica foams (MSFs) were fabricated via physical impregnation (MSF-T-x) and chemical grafting (MSF-CT-y) methods. The CO2 adsorption on these TEPA-modified MSFs was measured by using microbalances at 348 K and their adsorption capacities were observed to be 26.4–193.6 mg CO2/g-sorbent under ambient pressure using dry 15 % CO2. It was found that the CO2 adsorption capacities of MSF-CT-y were smaller than those of MSF-T-x sorbents which may be attributed to their higher density of amine groups. On the contrary, MSF-CT-y exhibited enhanced stability during repeated adsorption-desorption cycles compared to MSF-T-x sorbents. This notable enhancement in the durability of CO2 adsorption-desorption process was probably attributed to the decreased leaching of TEPA which is chemically bonded to the surface of MSF.
TL;DR: In this paper, two series of zeolite X/activated carbon composites with different ratios of zerosolite and activated carbon were prepared through a combination process of CO2 activation of the mixtures of elutrilithe and pitch and subsequent hydrothermal crystallization in alkaline solution.
Abstract: Two series of zeolite X/activated carbon composites with different ratios of zeolite and activated carbon were prepared through a combination process of CO2 activation of the mixtures of elutrilithe and pitch and subsequent hydrothermal crystallization in alkaline solution. An additional surface modification was achieved in diluted NH4Cl solution. CO2 and N2 uptakes on the composites before and after modification were determined for pressures up to 101 kPa at 273 and 298 K, respectively. Langmuir-Freundlich and Toth adsorption models were used to describe the adsorption isotherms of CO2 and the corresponding heats of adsorption were estimated with the Clausius-Clapeyron equation. Both before and after modification, all composites exhibited a remarkable preferential adsorption of CO2 compared to N2, with the modified composites showing a higher adsorption selectivity to CO2 over N2 than the unmodified composites. With an increasing ratio of zeolite in the composites, adsorption capacity and adsorption heat of CO2 on the composites increased simultaneously. Lower adsorption heat was observed both before and after modification especially at the low-loading region and when there was less energetic heterogeneity on the surface of the modified composites. The results may be attributed to the elimination of strong basic sites on the modified composites, which is favorable for desorption of CO2 on the adsorbents and application in pressure swing adsorption processes.
TL;DR: MIL-101 is a chromium-based metal organic framework known to adsorb a large amount of gases such as H2, CO2 and CH4 as mentioned in this paper, which was synthesized through solvothermal route and the H2 adsorption capacity was measured using a standard gravimetric method.
Abstract: MIL-101 is a chromium-based metal organic framework known to adsorb large amount of gases such as H2, CO2 and CH4. The framework was synthesized through solvothermal route and the H2 adsorption capacity was measured using a standard gravimetric method. X-ray absorption spectroscopy was performed to understand the fine structure, neighbors, coordination number and bond distance. The BET specific surface area of MIL-101nf (treated with NH4F) was 2,868 m2/g with a type I hysteresis loop measured from N2 adsorption isotherm. The hydrogen storage capacity was 0.16 wt% measured at 32 bar and room temperature for MIL-101nf. This capacity was increased up to 0.45 wt% by doping metal-supported carbon catalyst (Pd/AC and Pt/AC) through a carbon bridge with MIL-101. XANES spectra indicated that the valency of MIL-101 MOFs was Cr(III). EXAFS data also revealed that MIL-101 has a first shell of Cr-O bonding with the bond distance of 1.97 A and the coordination number of 5.4.
TL;DR: In this paper, the adsorption of butane, toluene and nitric oxide on NaMordenite exchanged with different amounts of silver was studied and the effects of water adsorptions were also addressed.
Abstract: In this work, we studied the adsorption of butane, toluene and nitric oxide on NaMordenite exchanged with different amounts of silver. The reactions that occurred when the adsorbed hydrocarbons interacted with NO and the effect of water adsorption were also addressed. Different silver species were formed after ion exchange and they were detected by TPR analysis. Highly dispersed Ag2O particles were reduced at temperatures lower than 300 °C whereas Ag+ exchanged ions showed two TPR peaks, which can be ascribed to species exchanged at different mordenite sites. The TPD experiments after adsorption of NO at 25 °C showed that the only desorbed species was NO2 which was formed by the total reduction of Ag2O particles. When the adsorbed butane was exposed to NO (1000 ppm), isocyanate species were formed on Ag+ ionic sites as well as Ag+–(NOx)–CO species. Toluene adsorption was stronger than butane since adsorbed toluene molecules were held even at 400 °C. The characteristic bands of the aromatic ring C=C bond was observed as well as that of methyl groups interacting with Ag+ and Na+ ions. However, the appearance of carboxylic groups at temperatures above 300 °C in inert flow indicated the partial oxidation of toluene due to Ag2O species present in the samples. After contacting adsorbed toluene with NO, different FTIR bands correspond to organic nitro-compounds, isocyanate, cyanide and isocyanide species adsorbed on Ag+ ions, were detected. The presence of water inhibited the formation of NO2 species and the hydrocarbon adsorption on Na+ sites but did not affect the toluene-Ag+ interaction.
TL;DR: A 2D microporous electron-rich porous aromatic framework JUC-Z2 with high physicochemical stability and large surface area was studied in detail for their low-pressure N2, Ar, H2, CO2, CH4 sorption.
Abstract: A 2D microporous electron-rich porous aromatic framework JUC-Z2 with high physicochemical stability and large surface area was studied in detail for their low-pressure N2, Ar, H2, CO2, CH4 sorption. Its hydrogen, methane, and carbon dioxide storage capacities are 181 cm3 g−1 (77 K/760 mmHg), 25 cm3 g−1 (273 K/760 mmHg), and 71 cm3 g−1 (273 K/760 mmHg), respectively. Gas molecule recognition at 273 K was performed and results show only greenhouse gases such as carbon dioxide and methane could be adsorbed onto JUC-Z2.
TL;DR: In this paper, the adsorption and diffusion properties of n-octane in meso-structured HZSM-5 zeolites were studied by high precision intelligent gravimetric analysis (IGA) and ZLC technology between 293 K and 393 K.
Abstract: Adsorption and diffusion properties of n-octane in meso-structured HZSM-5 zeolites were studied by high precision intelligent gravimetric analysis (IGA) and ZLC technology between 293 K and 393 K. As expected, great increase in adsorption capacity and diffusion efficient of n-octane in the mesostructured HZSM-5 zeolites was observed compared with conventional HZSM-5. At the same time, the adsorption activation energy of n-octane in the mesostructured HZSM-5 zeolites was significantly decreased. The adsorption heats with low n-octane loading showed a clear decline with increase of mesoporosity in the zeolite samples. These results clearly indicate that introduction of mesopores into the zeolites offered a short diffusion path and high diffusion rate for reactants and products, which resulted in a high yield of fuel oil and an enhanced resistance against the catalyst deactivation in the reaction of methanol to gasoline.
TL;DR: In this paper, a dynamic column breakthrough (DCB) was used to study the separation of CH4+N2 gas mixtures using two zeolites, H+-mordenite and 13X, at temperatures of (229.2 and 301.9) K and pressures of 792.9 K. The results showed that the 13X zeolite had the greater adsorption capacity for both CH4 and N2.
Abstract: A dynamic column breakthrough (DCB) apparatus was used to study the separation of CH4+N2 gas mixtures using two zeolites, H+-mordenite and 13X, at temperatures of (229.2 and 301.9) K and pressures to 792.9 kPa. The apparatus is not limited to the study of dilute adsorbates within inert carrier gases because the instrumentation allows the effluent flow rate to be measured accurately: a method for correcting apparent effluent mass flow readings for large changes in effluent composition is described. The mathematical framework used to determine equilibrium adsorption capacities from the dynamic adsorption experiments is presented and includes a method for estimating quantitatively the uncertainties of the measured capacities. Dynamic adsorption experiments were conducted with pure CH4, pure N2 and equimolar CH4+N2 mixtures, and the results were compared with similar static adsorption experiments reported in the literature. The 13X zeolite had the greater adsorption capacity for both CH4 and N2. At 792 kPa the equilibrium capacities of the 13X zeolite increased from 2.13±0.14 mmol g−1 for CH4 and 1.36±0.10 mmol g−1 for N2 at 301.9 K to 3.97±0.19 mmol g−1 for CH4 and 3.33±0.12 mmol g−1 for N2 at 229.2 K. Both zeolites preferentially adsorbed CH4; however, the mordenite had a greater equilibrium selectivity of 3.5±0.4 at 301.9 K. Equilibrium selectivities inferred from pure fluid capacities using the Ideal Adsorbed Solution theory were limited by the accuracy of the literature pure fluid Toth models. Equilibrium capacities with quantitative uncertainties derived directly from DCB measurements without reference to a dynamic model should help increase the accuracy of mass transfer parameters extracted by the regression of such models to time dependent data.
TL;DR: In this article, the purge gas quantity required for a specific desorption duty (fraction of total N2 removed from a column) is minimum when the process is carried out under ideal, hypothetical conditions (isothermal, isobaric, and governed by local thermodynamic equilibrium).
Abstract: Efficient desorption of selectively adsorbed N2 from air in a packed column of LiX zeolite by rapidly purging the adsorbent with an O2 enriched gas is an important element of a rapid cyclic pressure swing adsorption (RPSA) process used in the design of many medical oxygen concentrators (MOC). The amount of O2 purge gas used in the desorption process is a sensitive variable in determining the overall separation performance of a MOC unit. Various resistances like (a) adsorption kinetics, (b) column pressure drop, (c) non-isothermal column operation, (d) gas phase mass and thermal axial dispersions, and (e) gas-solid heat transfer kinetics determine the amount of purge gas required for efficient desorption of N2. The impacts of these variables on the purge efficiency were numerically simulated using a detailed mathematical model of non-isothermal, non-isobaric, and non-equilibrium desorption process in an adiabatic column. The purge gas quantity required for a specific desorption duty (fraction of total N2 removed from a column) is minimum when the process is carried out under ideal, hypothetical conditions (isothermal, isobaric, and governed by local thermodynamic equilibrium). All above-listed non-idealities (a–e) can increase the purge gas quantity, thereby, lowering the efficiency of the desorption process compared to the ideal case. Items (a–c) are primarily responsible for inefficient desorption by purge, while gas phase mass and thermal axial dispersions do not affect the purge efficiency under the conditions of operation used in this study. Smaller adsorbent particles can be used to reduce the negative effects of adsorption kinetics, especially for a fast desorption process, but increased column pressure drop adds to purge inefficiency. A particle size range of ∼300–500 μm is found to require a minimum purge gas amount for a given desorption duty. The purge gas requirement can be further reduced by employing a pancake column design (length to diameter ratio, L/D<0.2) which lowers the column pressure drop, but hydrodynamic inefficiencies (gas mal-distribution, particle agglomeration) may be introduced. Lower L/D also leads to a smaller fraction of the column volume that is free of N2 at the purge inlet end, which is required for maintaining product gas purity. The simulated gas and solid temperature profiles inside the column at the end of the rapid desorption process show that a finite gas-solid heat transfer coefficient affects these profiles only in the purge gas entrance region of the column. The profiles in the balance of the column are nearly invariant to the values of that coefficient. Consequently, the gas-solid heat transfer resistance has a minimum influence on the overall integrated N2 desorption efficiency by O2 purge for the present application.
TL;DR: In this paper, an experimental and computational protocol based on the characterization of the extra-column volume in terms of step-response experiments performed under various flow rates and pressures of 1 bar, 5 bar and 10 bar is presented.
Abstract: This study aims at highlighting the importance of an accurate characterization of the extra-column volume (ECV) and presents an experimental and computational protocol based on the characterization of the extra-column volume in terms of step-response experiments performed under various flow rates and pressures of 1 bar, 5 bar and 10 bar. The experiments are interpreted by describing the extra-column volume with a compartment model that reflects the geometry of the physical setup and that involves a stagnant zone to account for the non-ideal flow behavior through the piping system. The use of a mathematical model combining the description of the adsorption column and of the ECV can successfully predict experimental CO2–H2 breakthrough profiles performed at different pressures on an activated carbon adsorbent. This work shows how the presence of non-negligible extra-column effects can be accounted for, for the determination of adsorption transport parameters.
TL;DR: In this paper, the effect of physical activation with CO2 of carbon xerogels, synthesized by pyrolysis of a resorcinol-formaldehyde aqueous gel, on the adsorption capacities of Methylene Blue (MB) was studied.
Abstract: The effect of physical activation with CO2 of carbon xerogels, synthesized by pyrolysis of a resorcinol-formaldehyde aqueous gel, on the adsorption capacities of Methylene Blue (MB) was studied. The activation with CO2 lead to carbon materials with micropore volumes ranging from $0.28\ \mathrm{to}\ 0.98~\mathrm{cm}^{3}\,\mathrm{g}_{\mathrm{C}}^{-1}$
. MB-adsorption isotherm studies showed that the increase of micropore volume and corresponding surface area led to: (i) a significant improvement in the capacity of MB-adsorption at monolayer coverage, from $212\ \mathrm{to}\ 714~\mathrm{mg}\,\mathrm{g}_{\mathrm{C}}^{-1}$
, and (ii) an increase of the binding energy related to Langmuir isotherm constant up to 45 times greater than those of commercial microporous activated carbons used as reference (NORIT R2030, CALGON BPL and CALGON NC35). It is proposed that the increase of the binding energy results from chemical cleaning of the O-groups onto carbon surface as a consequence of CO2-activation, increasing the π–π interaction between MB and graphene layers of the carbon xerogels. Finally, a series of batch kinetics were performed to investigate the effect of CO2-activation conditions on the mechanism of MB-adsorption. Experimental data were fitted using pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. From pseudo-second-order kinetic model, one observes an increase in the initial rate of MB-adsorption from 0.019 to 0.0565 min−1, by increasing the specific surface area from $630\ \mathrm{to}\ 2180~\mathrm{m}^{2}\,\mathrm{g}_{\mathrm{C}}^{-1}$
via CO2-activation. Depending on the activation degree of the carbons, two different mechanisms control the MB-adsorption rate: (i) at low activation degree, the intraparticle diffusion is the rate-limiting phenomenon, whereas (ii) at high activation degree, the reactions occurring at the solid/liquid interface are the rate-limiting steps.
TL;DR: In this article, it was found that the change in amount of hydrogen sorbed hydrogen is closely related to the moisture of coal and that the most considerable amounts of hydrogen are sorbed by coal characterized by strong surface hydrophobicity and high content of aliphatic hydrocarbons.
Abstract: Performed tests showed that at 298 K hard coals sorb relatively small amounts of hydrogen. Those amounts depend on carbon and oxygen content in tested coals. The most considerable amounts of hydrogen are sorbed by coals characterized by strong surface hydrophobicity and high content of aliphatic hydrocarbons. The hydrophilic nature of coal surface does not lead to higher sorption of hydrogen. It was found that the change in amount of sorbed hydrogen is closely related to the moisture. For high moisture coal a significant decrease in hydrogen sorption is observed. Also tests on hydrogen desorption on hard coals were carried out using method of lowering hydrogen pressure above the sorbent. Obtained results showed that tested coals desorb various amounts of hydrogen. Process of sorption is reversible only for some coals, while for the others the desorption isotherm partially lies beneath the sorption isotherm, which indicates that in addition to hydrogen some other chemical substances are emitted from coal.
TL;DR: In this paper, the effect of specific surface area, pore size and pore volume on the separation coefficient was observed and a linear correlation between the separation coefficients and the small pore (0.7-1.3 nm) volume reduced to unit surface area was shown.
Abstract: The separation between CH4 and N2 bears importance in coalbed methane enrichment, and activated carbon is a major adsorbent for industrial PSA (pressure swing adsorption) separation. However, the adsorption of both gases shows supercritical features, and the physicochemical properties are also similar, which results in similar adsorption behavior and renders the separation difficult. To maximize the separation coefficient, the effect of carbon pore structure on the separation was studied and a series of carbons was prepared at different extent of activation. The effect of specific surface area, pore size and pore volume on the separation coefficient was observed and a linear correlation between the separation coefficient and the small pore (0.7–1.3 nm) volume reduced to unit surface area was shown.
TL;DR: In this paper, magnetic mesoporous carbon microspheres were synthesized by impregnating iron oxide precursors in the mesopore carbon followed by the in situ conversion of the precurors into magnetite nanoparticles.
Abstract: Carbon materials such as activated carbons have been used in the field of water and wastewater treatments. However, the lack of mesopore and, particularly, the difficulty in recovering the spent carbon limited their applications. In this work, magnetic mesoporous carbon microspheres were synthesized by impregnating iron oxide precursors in the mesoporous carbon followed by the in situ conversion of the precursors into magnetite nanoparticles. The as-synthesized carbon microspheres with a high surface area of 742 m2/g and large mesopores of ∼4.4 nm exhibited an excellent adsorption capacity for aqueous organic pollutants. The superparamagnetic microspheres with a saturation magnetization of 7.15 emu/g can be easily separated from the treated solution by external magnetic field.
TL;DR: In this article, amorphous precipitated Zeosil 1165 MP silica was silylated with low grafting degrees of organosilicons bearing different alkoxy and hydrocarbon tails, like monomethoxy(dimethyl)octadecylsilane (DMODMS), monometrichoxytrimethylsilane (TMMS), trimethoxymercaptopropyl silane (MPTS), and 3-octanoylthio-1-propyltriethoxysilane(NXT®).
Abstract: Amorphous precipitated Zeosil 1165 MP silica was silylated with low grafting degrees of organosilicons bearing different alkoxy and hydrocarbon tails, like monomethoxy(dimethyl)octadecylsilane (DMODMS), monomethoxytrimethylsilane (TMMS), trimethoxymercaptopropylsilane (MPTS), and 3-octanoylthio-1-propyltriethoxysilane (NXT®). Thermogravimetry and Elemental Analysis were used to determine the degree of silane grafting and the final number of free silanol OH groups/nm2 on the modified Zeosil surface. Free energy, enthalpy and entropy of adsorption of hydrocarbon probes were determined by Inverse Gas Chromatography at infinite dilution and dispersive component, $\gamma_{s}^{d}$
, and specific interaction parameter, I
sp
, of the surface tension of the silica surface were calculated. Silylation changes the hydrophilic character of Zeosil silica to the hydrophobic one, on increasing the grafting degree and, mainly, the length of hydrocarbon tail of the silane molecule (DMODMS and NXT®). The long hydrocarbon tails practically shield the silica particle surface and the adsorbed probes preferentially interact with them. In the case of TMMS-Zeosil the adsorbed probes practically interact with the silica surface, with loss of entropy well above that of the bare silica, while being equal the values of the enthalpy of adsorption. All the other modified silicas show loss of entropy lower than that of bare silica. Steric hindrance, played by the presence of methyl groups of TMMS, is suggested to reduce the freedom of translational and rotational movements of the adsorbed probe.
TL;DR: In this article, a bifunctional activated carbon with the ability of both photocatalysis and adsorption was fabricated via the sol-gel route combined with hydrothermal treatment and N2 reactivation method.
Abstract: Bifunctional activated carbons (AC) with the abilities of both photocatalysis and adsorption were fabricated via the sol–gel route combined with hydrothermal treatment and N2 reactivation method. TiO2 was located mainly at the entrance of the surface macropores of AC. Under UV light irradiation, efficient removal of phenol was realized by combination of adsorption and photocatalytic degradation for the obtained bifunctional materials. In insufficient light or dark, phenol removal occurred mainly through adsorption. The prepared bifunctional carbon with a mass ratio of 50 TiO2 per AC ratio exhibited high efficiency for phenol removal. The total phenol removal capacity of 50TiO2/AC was almost 5 times of that of pure AC and 6 times of that pure TiO2 after 10 cycles. The prepared bifunctional carbons possess the advantages of high pollutant removal capability and good recyclability, making them promising for the efficient treatment of lightly polluted aqueous solutions.
TL;DR: In this paper, the pore size distribution of the silica gel and the quantity of pre-sorbed water impact the formation of the CO2 hydrates, and the sorption equilibria of carbon dioxide on three types of Silica Gel (SG) with different pore sizes distributions in the presence of water were studied experimentally using a volumetric method at 275 K with pressures from 0 to 3.7 MPa.
Abstract: The sorption equilibria of carbon dioxide on three types of silica gel (SG) with different pore size distributions in the presence of water were studied experimentally using a volumetric method at 275 K with pressures from 0 to 3.7 MPa. Both the pore size distribution of the silica gel and the quantity of pre-sorbed water impact the formation of the CO2 hydrates. For wet silicon gel A(SG-A) with water loading ratio of 0.75, the highest CO2 sorption was about 2.5 mmol of CO2 per gram of dry sorbent at 275 K. Similarly, the highest sorption was about 2.7 mmol for wet SG-B with Rw=0.81. However, CO2 hydrate did not form on the wet surface of SG-C due to its large pore sizes.
TL;DR: In this paper, a combination of ab initio quantum mechanical calculations and canonical Monte Carlo (CMC) simulations are employed to investigate possible usage of single-walled silicon nanotubes (SWSiNTs) as a novel media for hydrogen and methane adsorption as well as their separation from each other.
Abstract: A combination of ab initio quantum mechanical (QM) calculations and canonical Monte Carlo (CMC) simulations are employed to investigate possible usage of single-walled silicon nanotubes (SWSiNTs) as a novel media for hydrogen and methane adsorption as well as their separation from each other. By fitting the force field, a Morse potential model is selected as an efficient potential to describe the binding energies between both hydrogen-SiNTs and methane-SiNTs obtained from ab initio calculations. Then CMC simulations are performed to evaluate the adsorption and separation behaviors of H2 and CH4 on the three different sizes of SiNTs including (5, 5), (7, 7), and (9, 9) SiNTs at ambient temperatures and pressures from 1 up to 10 MPa. As a comparison, the adsorption and separation of H2 and CH4 on the (8, 8) CNTs which are isodiameter with (5, 5) SiNTs are also simulated. Results are indicative of remarkable enhancement of H2 and CH4 adsorption capacity on the SiNTs compared to the CNTs, which arise from stronger van der Waals (VDW) attractions. In the case of methane adsorption on SiNTs, the stored volumetric energy exceeds the goal of the US Freedom CAR Partnership by 2010, which can not be achieved by methane compression at such low pressures. Moreover, simulation results indicate that SiNTs preferentially adsorb methane relative to hydrogen in their equimolar mixture, which results in efficient separation of these gases from each other at 293 K.
TL;DR: In this article, a study was conducted on batch and column competitive adsorption of fluroxypyr (FLX) and tannic acid (TA) from distilled (DW) and tap water (TW) on activated carbon cloth (ACC) and granular activated carbon (GAC).
Abstract: A study was conducted on batch and column competitive adsorption of fluroxypyr (FLX) and tannic acid (TA) from distilled (DW) and tap water (TW) on activated carbon cloth (ACC) and granular activated carbon (GAC). Thermal desorption of the adsorbates from the spent ACC was also studied. FLX adsorption was higher from TW than from DW at low FLX equilibrium concentrations, and the inverse was observed at high FLX concentrations. The presence of TA diminished the amount of FLX adsorbed from both solvents due to partial blocking of the microporosity, but the same trends as before were observed at low and high FLX concentrations. Carbon consumption, obtained from the breakthrough curves, was lower as a function of superficial contact time with ACC than with GAC. The presence of TA increased carbon consumption, which was related to the microporosity of the adsorbents. Thermal desorption profiles of the spent ACC showed two peaks and one peak after adsorption from DW and TW, respectively. Desorption peaks shifted to higher temperatures with an increase in the heating rate, allowing the apparent activation energies and pre-exponential factors of the desorption processes to be determined.
TL;DR: In this article, the influence of organic additives on the crystallization process and adsorption performances of zeolite were investigated, and the results showed that all the organic additives but SCMC diminish the rate of crystal growth.
Abstract: The crystallization of zeolite A was monitored by measuring the adsorption capacities of synthetic products. The influences of organic additives on the crystallization process and adsorption performances of zeolite were investigated. SDS (sodium dodecyl sulphonate), TWEEN (Tween-80), and PEG (poly(ethylene glycol)) shorten the induction period by reducing the interfacial energy while SCMC (sodium carboxymethylcellulose) can prolong the induction period by increasing the interfacial energy. TEA (triethanolamine) can also suppress the nucleation through reducing the effective supply of aluminum. All the organic additives but SCMC diminish the rate of crystal growth. CTAB (cetyltrimethylammonium bromide) causes the destruction of crystal structure and reduce the concentration of OH− ions. As a result, the rate of crystal growth is significantly reduced. Meanwhile, PAM (poly(acrylamide)), SDS, TWEEN, HMTA (hexamethylenetetramine), and PEG increase the viscosities of synthesis systems, thus, diminish the growth rate. PAM restrains the transformation of zeolite A crystal into hydroxysodalite one, therefore, tremendously improves the stability of crystals of zeolite A. In addition, PAM can promote the rates of n-hexane adsorption on zeolite 5A because of the impact of PAM on the crystal-size distributions of zeolite 5A.