Component Sorption Research Articles

Robust metal-organic frameworks for dry and wet biogas upgrading

Biofuels are considered as viable, sustainable and renewable alternatives to fossil fuels. One amongst them is biomethane which has emerged as one of the valuable contributors in facilitating the essential transition towards green energy sources. Industrially, anaerobic digestion of biomass results in the production of crude biogas that comprises mainly of methane (CH4) and other components like carbon dioxide (CO2) and water (H2O). Biogas is saturated in water vapour which must be removed to ensure the operational stability and safety of the technology systems that handles wet biogas and employs the end-product biomethane. Through a series of separation processes, the biogas is cleaned (drying) and upgraded (CO2/CH4 separation) to biomethane. The adsorptive separation technology with nanoporous materials for biogas upgrading has become progressively competitive due to their meritorious features. In particular, metal-organic frameworks (MOFs) have shown a tremendous potential in upgrading biogas under dry conditions. However, their affinity for water promotes competitive co-adsorption, and this, coupled with their relatively low hydrolytic stability affects their upgrading performance negatively. This fact requires the complete removal of moisture before the adsorptive based gas separation upgrading process can be carried out. A similar situation applies for highly hydrophilic zeolite adsorptive systems. In this work, we present two permanently porous MOFs made of aluminium metal ions (Al(III)) and tetra-carboxylate ligands with strong CO2 binding pockets comprising of two aromatic rings which are 7 Å apart. Both MOFs are robust, and adsorption isotherms revealed that they are porous to CO2 and CH4 at 303 K with isosteric heat of adsorption of −25 to −40 and −13 to −16 kJ/mol, respectively. Interestingly, these materials are found to be non-porous to water at low relative humidity as shown by water vapour isotherms. Inspired by their single component sorption behaviours, we demonstrate that their biogas upgrading performance is not affected regardless of the high water vapour content (4 vol% and 85% RH) in the feed gas of the multicomponent fixed bed breakthrough experiments. This is due to the lack of competitive co-adsorption of CO2 and H2O within the hydrophobic CO2 binding pockets. This makes both MOFs presented in this work as industrially relevant candidates for biogas upgrading application which can withstand residual moisture of dried biogas as well as the momentary breakthroughs of wet biogas.

Metal-Organic Frameworks for the Adsorptive Removal of Gaseous Aliphatic Ketones.

Recent research endeavors have established metal-organic frameworks (MOFs) as suitable platforms for the adsorptive removal of various environmental pollutants. In this regard, the sorptive performances of four MOFs (MOF-199, UiO-66, UiO-66-NH2, and Co-CUK-1) were investigated against two gaseous aliphatic ketones (methyl ethyl ketone (MEK) and methyl isobutyl ketone (MiBK)) at a low partial pressure (0.1 Pa). Activated carbon was utilized as a reference commercial sorbent. The 10% breakthrough volume (BTV10) values for MEK decreased in the following order: MOF-199 (4772 L atm g-1) > activated carbon (224 L atm g-1) > UiO-66-NH2 (106 L atm g-1) > UiO-66 (53 L atm g-1) > Co-CUK-1 (16 L atm g-1). In case of MiBK, the relative ordering in BTV10 was consistently maintained while showing noticeable increases in its magnitude: MOF-199 (7659 L atm g-1) > activated carbon (816 L atm g-1) > UiO-66-NH2 (304 L atm g-1) > UiO-66 (150 L atm g-1) > Co-CUK-1 (31 L atm g-1). The superiority of MOF-199 was confirmed toward the adsorptive removal of gaseous aliphatic ketones. For a binary mixture of ketones, the BTV10 values of MOF-199 were reduced considerably for MEK and MiBK (in comparison to single component sorption) such as 1579 and 3969 L atm g-1, respectively, reflecting competitive inhibition of the adsorption process. Theoretical simulations based on density functional theory (DFT) elucidated the involvement of highly favorable coordination between the carbonyl group present in ketone molecules and the uncoordinated Cu(II) sites in the MOF-199 structure (Lewis acidic centers). Interestingly, MOF-199 maintained appreciable performance toward the mixture of ketones up to 5 cycles to support its practical merit.

Binary Component Sorption of Cadmium, and Copper Ions onto Yangtze River Sediments with Different Particle Sizes

Sorption is a crucial process that influences immobilization and migration of heavy metals in an aqueous environment. Sediments represent one of the ultimate sinks for heavy metals discharged into water body. Moreover, the particle size of sediments plays an extremely important role in the immobilization of heavy metals. In this study, the sorption and desorption of cadmium (Cd) and copper (Cu) onto sediments with different particle sizes were investigated to predict the rate and capacity of sorption, to understand their environmental behaviors in an aqueous environment. Batch sorption and kinetic experiments were conducted to obtain the retained amount and rate of Cd and Cu in a binary system. Experimental data were simulated using sorption models to ascertain the sorption capacity and the kinetic rate. Results of European Communities Bureau of Reference (BCR) sequential extraction showed the highest concentration of Cd (0.344 mg kg−1), and its distribution varied with sediment particle size and site. Furthermore, most of Cu (approximately 57% to 84%) existed as a residual fraction. The sorption of Cu onto six sediments followed a pseudo-first order reaction, whereas that of Cd followed a pseudo-second order reaction. Additionally, the competitive Langmuir model fitted the batch sorption experimental data extremely well. The highest sorption capacities of Cd and Cu reach 0.641 mmol kg−1 and 62.3 mmol kg−1, respectively, on the smallest submerged sediment particles. The amounts of Cu and Cd desorbed (mmol kg−1) increased linearly with the initial concentration increasing. Thus, sediment texture is an important factor that influences the sorption of heavy metal onto sediments.

The Simulation of Binary Component Sorption Kinetics from the Data of Single Component Sorption

This research is mainly focused on the wastewater treatment using biosorption techniques. The biosorption kinetics of binary sorption of heavy metals by green macro alga Caulerpa lentillifera were studied where such alga was used in the shrimp farm as the nitrogen controller but it grow rapidly so the farmer get rid of its excess amount as waste. The studies of sorption capacity and sorption kinetics of Lead (Pb2+) and Copper (Cu2+) ions in single and binary components were conducted using batch experiments. The new binary sorption kinetic model was developed to predict the experimental results and the calculated outputs from the model were consistent with experimental data.

Changes in gas storage and transport properties of coal as a result of enhanced microbial methane generation

This study was aimed at identifying the changes in coal storage and transport properties affecting gas production from coal-gas reservoirs, when treated with microbial consortia to generate/enhance production of methane. The work expanded on the technology of bio-conversion, first proposed in order to imitate the natural/microbial process of biogenic gasification leading to recharging coalbed methane reservoirs or, setting up natural gas reservoirs in non-producing coalbeds or, to coal waste, typically in the form of fines/ultra-fines. The pressure parameter was considered critical since, with continued production of methane, the produced gas would first diffuse into the coal matrix and get adsorbed with increasing pressure. During production, the pressure would decrease and the process would be reversed, gas diffusing out of the coal matrix and arriving at the cleat system.The experimental work tested the variation in the sorption and diffusion properties of treated coal, post continued bio-conversion since these are the first two physical phenomena in CBM production. During the first phase, single component sorption–diffusion experiments were carried out using methane and CO2 on virgin coals retrieved from the Illinois basin. Coals were then treated with nutrient amended microbial consortia for different periods. Gas production was monitored over thirty and sixty day periods of treatment after which, sorption–diffusion experiments were repeated on treated coals, thus establishing a trend over the sixty-day period. The sorption data was characterized using the Langmuir model. The variation trend in the value of diffusion coefficient, D, was also established as a function of pore pressure.The results indicated an increase in the sorption capacity of coal as a result of continued bioconversion. This was attributed to increased pore surface area due to microbial actions resulting in changes in the pore size or, creation of new pores. It was further shown that the rate of diffusion increased, especially for methane, which exhibited rates higher than that for CO2. These findings clearly support improved gas storage capacity with continued bio-conversion as well as significantly enhanced diffusion rates. As a continuation of this effort, change in permeability, the second gas transport phenomenon in coal-gas production, is currently being evaluated.

Sorption of vapour mixtures of methanol and dimethyl carbonate in PTMSP: Cooperative and competitive sorption in one system

Equilibrium sorption of vapour mixtures of methanol and dimethyl carbonate in poly[(trimethylsilyl)propyne], PTMSP, is reported. The experiments were conducted at 40°C and at atmospheric pressure using an apparatus that combined the sorption gravimetry in a carrier gas and the analysis of the desorbate by Fourier transform infrared spectroscopy (FT-IR). An unusual combination of competitive and cooperative sorption effects of dimethyl carbonate on methanol was observed. The cooperative sorption occurred at small methanol vapour activities, at which the sorption of pure methanol vapour is anomalously, and advantageously, small. The sorption isotherms of pure vapours and vapour mixtures were plausibly parameterized using Guggenheim, Anderson, De Boer (GAB) model and its semi-empirical extension for vapour mixtures, respectively. While the ideal separation factor of sorption, observable from the pure component sorption data, ranged 2–248, the real separation factor was significantly lowered by the co-sorption effects to 1–20. Overall, the highest real separation factors were observed for the higher dilutions of the binary feed mixtures with the inert gas and, advantageously, for methanol rich feed mixtures (i.e. in the vicinity of the composition of the azeotropic mixture).

Competitive Sorption of Methane/Ethane Mixtures on Shale: Measurements and Modeling

As the primary mechanism of gas storage in shale, sorption phenomena of CH4 and other hydrocarbons in the micropores and mesopores are critical to estimates of gas-in-place and of the long-term productivity from a given shale play. Since C2H6 is another important component of shale gas, besides CH4, knowledge of CH4–C2H6 binary mixture sorption on shale is of fundamental significance and plays a central role in understanding the physical mechanisms that control fluid storage, transport, and subsequent shale-gas production. In this work, measurements of pure component sorption isotherms for CH4 and C2H6 for pressures up to 114 and 35 bar, respectively, have been performed using a thermogravimetric method in the temperature range (40–60 °C), typical of storage formation conditions. Sorption experiments of binary (CH4–C2H6) gas mixtures containing up to 10% (mole fraction) of C2H6, typical of shale-gas compositions, for pressures up to 125 bar under the aforementioned temperature conditions have also been co...

Sorption, desorption and diffusion processes in membrane permeation

A majority of the anomalous permeation in the literature can be resolved if the solubility coefficient of the diffusion-solubility model is expanded into its component sorption and desorption processes.Examples of these anomalies are (a) the permeability coefficient decreases with decreasing membrane thickness, (b) the membrane׳s selectivity changes with membrane thickness, (c) the surface concentrations are time dependent, and (d) the steady-state solubility and surface concentration are less than the equilibrium values. In the three parameter model, the sorption (K1) and desorption (K2) processes are included as part of the boundary conditions of the model. The permeability coefficient (K) becomes DS/(1+2/B) where B, the thickness scaling parameter, is K2L/D. L is the membrane thickness, D is the diffusion coefficient and S is the solubility coefficient. At equilibrium, S becomes Seq. For large B, K approaches DS and the DS model is adequate. For some thin and ultrathin membranes where B is small, K approaches K1L/2 and the normalized membrane flux (K/L) becomes independent of the thickness. In these cases, permeation looks more like a sorption and desorption process. These features are well described by the DK1K2 model but are anomalous for the DS model. For small B, the selectivity is determined by the relative values of K1 which is the principal selection parameter for sorption processes. A simple method is reintroduced (first used over a half-century ago) to determine the three parameters from experimental permeability data. Experimental data are analyzed for liquid-membrane, vapor-membrane, gas-membrane and pervaporation systems. Values of D, K1 and K2 are given for these systems.

Sorption and pervaporation of methanol/water mixtures with poly(3-hydroxybutyrate) membranes

In this contribution, poly(3-hydroxybutyrate) (PHB) membranes were evaluated in sorption and pervaporation experiments for methanol/water separation. Single component sorption tests showed that PHB membranes have higher affinity toward methanol than water: at 40°C the sorption degree was 18.4 and 1.1%, respectively. This was in agreement with contact angle measurements, performed with both liquids, and Hansen solubility parameter. PHB sorption degree in the whole methanol/water composition range and three temperature levels were determined, showing an anomalous behavior (sigmoid like curves). A simple technique, named by us “Desorption by Dissolution”, was developed to determine sorbed mixture composition. It basically consists on dissolving the polymer after sorption equilibrium in the mixture has been reached, to completely extract the mixture. Then, chromatographic analysis is used to determine solution composition. It does not require adapting equipment or using vacuum devices neither cold traps. When both components were present, methanol grams sorbed in the membrane were always lower than the mixture in which they were immersed, while water sorption was enhanced due to methanol presence. Very low standard deviation values were registered (<0.84) confirming the technique reliability. Single component fluxes and mass flux ratio in pervaporation increased with temperature: methanol flux was 3.5×10−5kgm−2s−1 at 25°C, whereas at 50°C exceeded 7×10−5kgm−2s−1; water flux increased from 1.8×10−5kgm−2s−1 at 30°C to 2.2×10−5kgm−2s−1 at 50°C. Since permeances decreased, the increase in fluxes with temperature can be attributed to the increase in vapor pressure driving forces. Mixture pervaporation results showed similar behavior, highlighting the fact that separation factor increased with temperature as well: 3.5 at 30°C and 3.8 at 50°C. Selectivities were higher than 12 for 10wt% water/methanol+water mixtures. Results were discussed in terms of polymer crystallinity, solubility parameters, component size, activation energies and cluster formation.

The first example of commensurate adsorption of atomic gas in a MOF and effective separation of xenon from other noble gases

In industry, cryogenic rectification for separating xenon from other noble gases such as krypton and argon is an energy and capital intensive process. Here we show that a microporous metal–organic framework, namely Co3(HCOO)6 is capable of effective capture and separation of xenon from other noble gases. Henry's constant, isosteric heat of adsorption (Qst), and IAST selectivity are calculated based on single component sorption isotherms. Having the highest Qst reported to date, Co3(HCOO)6 demonstrates high adsorption capacity for xenon and its IAST selectivity for Xe–Kr is the largest among all MOFs investigated to date. To mimic real world conditions, breakthrough experiments are conducted on Xe–Kr binary mixtures at room temperature and 1 atmosphere. The results are consistent with the calculated data. These findings show that Co3(HCOO)6 is a promising candidate for xenon capture and purification. Our gas adsorption measurements and molecular simulation study also reveal that the adsorption of xenon represents the first example of commensurate adsorption of atomic gases near ambient conditions.

Polyaromatic hydrocarbons (PAHs) sorption behavior unaffected by the presence of multi-walled carbon nanotubes (MWNTs) in a natural soil system

The batch equilibrium approach was used to examine the influence of multi-walled carbon nanotubes (MWNTs) on the sorption behaviors of polyaromatic hydrocarbons (PAHs) in soil. To the knowledge of the authors, this is the first study of PAH sorption to MWNTs in real natural soil systems. The sorption behavior of three PAHs (naphthalene, fluorene, and phenanthrene) in the presence of commercially available MWNTs in two natural soils (a sandy loam and a silt loam) and Ottawa sand was evaluated. Adsorption of PAHs by MWNTs in this study was three orders of magnitude higher than that of natural soils. Sorption coefficients of PAHs (Kd and Koc) were unchanged in the presence of 2 mg g(-1) MWNTs in soil (p > 0.05). A micro-mechanics approach, termed 'the rule of mixtures' was used for predicting PAH sorption behaviors in mixtures based on sorption coefficients derived from single sorbents. The equation, KT = KMα + KN(1 - α) (K, sorption coefficients, Kd or Koc), predicted sorption coefficients in a mixture based on mixture component sorption coefficients and mass fractions. Data presented in this study could be used to fill data gaps related to the environmental fate of carbon nanotubes in soil.

Prediction of sorption in polymers using quantum chemical calculations: Application to polymer membranes

The knowledge of sorption of vapors and liquids in polymer membranes is important for the derivation of structure–property relationships between the polymer structure and membrane performance, which facilitates preparation of better membranes. Experimental methods for the determination of sorption are tedious and expensive. Conventional predictive methods are often inadequate. In this work, a combination of the Cosmo-SAC model based on quantum chemical calculations and the Flory–Rehner equation is used to predict the sorption in polymer membranes. A single adjustable parameter is used for each polymer. It is shown that the model can adequately predict sorption in several membrane polymers including block copolymers for both single component and two component sorption. In addition, two component sorption data can be predicted from single component sorption data. Further, the measurement of the sorption of a pure liquid in a polymer by simple swelling experiments is sufficient for obtaining initial estimates of single component sorption over the entire activity range as well as the two component sorption from liquid mixtures over the entire activity range. Hence, the use of complex equipment and tedious multicomponent sorption experiments can be minimized or avoided. This significantly simplifies the experiments required for measurement of sorption in polymer membranes.

Competitive adsorption of phenol and 3-chlorophenol on purified MWCNTs

A commercial multiwall carbon nanotube and its carboxylated derivate (CNTC and COOHC, respectively) was used after purification to study the competitive adsorption of phenol (P) and m-chlorophenol (CP) from 0.1M aqueous NaCl solutions without external pH control. The adsorption takes place practically exclusively on the external surface of the nanotubes. The uptake of P is suppressed in comparison to its single solute behaviour on both nanotubes, independently of the initial pollutant concentration. The uptake of CP however is more sensitive to the concentration and the surface chemistry of the nanotube. The measured co-adsorption isotherms were compared to the isotherms calculated from the competitive Langmuir model (CLM). Preferential adsorption of CP was observed in about 95% of the relative concentration range. The total adsorption may exceed the corresponding single component sorption capacity.

Adsorption of Copper (II) and Lead (II) Ions onto Cottonseed Protein-PAA Hydrogel Composite

The adsorption behaviors of copper and lead ions in aqueous solution by cottonseed protein-poly (acrylic acid) copolymer (CP-PAA) hydrogel composite have been studied in single component sorption systems. The influence of cottonseed protein content in the copolymer composition on the adsorption capacity of the hydrogel is studied and the sorption of copper (II) and lead (II) ions is investigated in aqueous solution with different initial metal ion concentration and pH value, respectively. The results indicate that the hydrogel composite is a suitable sorbent for the two metal ions. The experimental data of the adsorption equilibrium from Cu(II) and Pb(II) solution correlated well with the Langmuir isotherm equation. The adsorption kinetics of the two metal ions has been analyzed and the pseudo–second-order equation provides good fits to experimental data of both metals. By treatment with aqueous HCl solution, the hydrogel can be regenerated and reused again to adsorb heavy metal ions. The characterization of the hydrogel after adsorption of metal ions by XRD, SEM and EDS reveals that the accumulation of metal ions occurs on the surface of the hydrogel composite.

Zinc-1,4-benzenedicarboxylate-bipyridine frameworks – linker functionalization impacts network topology during solvothermal synthesis

Substitution of 1,4-benzenedicarboxylate (bdc) with additional alkoxy chains is the key to construct a family of metal–organic frameworks (MOFs) of the type [Zn2(fu-bdc)2(bipy)]n (fu-bdc = functionalized bdc; bipy = 4,4′-bipyridine) exhibiting a honeycomb-like topology instead of the default pillared square-grid topology. Both the substitution pattern of the phenyl ring of the fu-bdc linker and the chain length of the alkoxy substituents have a major impact on the structure of the derived frameworks. Substitution at positions 2 and 3 leads to the trivial pillared square-grid framework, and substitution at positions 2 and 5 or 2 and 6 yields MOFs with the honeycomb-like topology. Also, simple methoxy substituents lead to the construction of a pillared square-grid topology, whereas longer substituents like ethoxy, n-propoxy, and n-butoxy generate honeycomb-like framework structures. These honeycomb MOFs feature one-dimensional channels, which are tuneable in diameter and functionality by the choice of substituent attached to the bdc-type linker. Pure component sorption isotherms indicate that the honeycomb-like frameworks selectively adsorb CO2 over N2 and CH4.

Predictive Model for the Solubility of Fluid Mixtures in Glassy Polymers

The estimation of the solubility of fluid mixtures in polymeric phases is an essential prerequisite for membrane separations and in the design of several devices, such as chemical sensors: the presence of swelling and strongly interacting components in the fluid mixture can often cause rather large deviations from the pure component sorption behavior. For rubbery polymers, the usual equilibrium tools such as the multicomponent versions of the equation of state (EoS) models can be adopted, while for the case of glassy polymers, which are not at equilibrium, such an approach cannot be followed. The general model called nonequilibrium thermodynamics of glassy polymers (NET-GP) has proved to be a successful tool for predicting the solubility of pure gases, vapors and liquids in glassy polymers, and it is here applied to the prediction of multicomponent fluid solubility. In particular, three gas–gas–polymer systems, which show significant deviations from the ideal behavior, are examined at room temperature and...

Single and binary component sorption of the fission products Sr 2+, Cs + and Co 2+ from aqueous solutions onto sulphate reducing bacteria

This study investigates the removal of the fission products Sr 2+, Cs + and Co 2+ in single and binary metal solutions by a sulphate reducing bacteria (SRB) biomass. The effect of initial concentration and pH on the sorption kinetics of each metal was evaluated in single metal solutions. Binary component equilibrium sorption studies were performed to investigate the competitive binding behaviour of each metal in the presence of a secondary metal ion. Results obtained from single metal equilibrium sorption studies indicated that SRB have a higher binding capacity for Sr 2+ ( q max = 416.7 mg g −1), followed by Cs + ( q max = 238.1 mg g −1), and lastly Co 2+ ( q max = 204.1 mg g −1). Among the binary systems investigated, Co 2+ uptake was the most sensitive, resulting in a 76% reduction of the sorption capacity ( q max) in the presence of Cs +. These findings are significant for future development of effective biological processes for radioactive waste management under realistic conditions.

Pervaporative separation of azeotropic methanol/toluene mixtures in polyurethane–poly(dimethylsiloxane) (PU–PDMS) blend membranes: Correlation with sorption and diffusion behaviors in a binary solution system

A separation of toluene/methanol binary mixtures was pervaporated using toluene-selective polyurethane (PU)–poly(dimethylsiloxane) (PDMS) blend membranes. The separation efficiency and toluene flux from the azeotropic mixtures reached a maximum in the blend containing 20% PU content. The toluene sorption behavior from the binary mixtures into the blend was predictable using the Flory–Huggins equation with the interaction parameters ( χ iM ) determined from the single solvent sorption measurements. However, the methanol solubility from the solutions was lower than predicted, indicating the less permeable component sorption was suppressed. This competitive sorption is actually beneficial in the pervaporation process since it enlarges the sorption selectivity. The diffusivity of permeants, on the other hand, demonstrated a diffusion-coupling phenomenon from the binary solutions in the blend. The diffusion coefficient of the less permeable (methanol) component was increased by the facilitation of a toluene-swollen polymer matrix. The methanol molecules diffused at a rate higher than toluene, although the pure solvent diffusivities were comparable with each other. Despite the fact that the high sorption selectivity was slightly offset by the synergistic diffusion effect, the PV performance was dominated by the sorption characteristics. The PU–PDMS (20/80) blend exhibited excellent toluene flux with reasonable separation efficiency in toluene-lean and azeotropic compositions. This research demonstrates that polymer blends is a simple way to modulate membrane's transport properties and can achieve higher performance than the pristine polymer materials.

Binary component sorption of Cu(II) and Pb(II) with activated carbon from Eucalyptus camaldulensis Dehn bark

The objective of this work is to illustrate the potential in the use of activated carbon in the binary component sorption of copper and lead ions. Eucalyptus bark was used as a precursor for the activated carbon which was prepared through the phosphoric acid activation process. This activated carbon was then used for the sorption of copper and lead ions. The quantity of the metal ions in the solution was measured with the Flame & Graphite Furnace Atomic Adsorption Spectrophotometer. The results indicated that the optimal pH for sorption was 5. The maximum sorption capacities for Cu(II) and Pb(II) were 0.45 and 0.53 mmol g −1. Carboxylic, amine and amide groups were found to involve in the sorptions of Cu(II) and Pb(II). A major mechanism for the uptake of both heavy metals was proven not to be ion exchange but adsorption. In binary component sorptions, activated carbon still could sorb Pb(II) in a greater amount than Cu(II). However, the presence of the secondary metal ions suppressed the sorption of the primary metal ions. There seemed to have a linear inverse dependency between the sorption capacity and the concentration of the secondary metal ion.

Evaluation of Textile Dye Sorption on GAC Produced from Almond Shells Based on Optimized Isotherm Models

ABSTRACT Single component sorption of three basic dyes used by the textile industry (rhodamine b, malachite green oxalate, and methylene blue) from aqueous systems was evaluated for granular activa...