Favorable Isotherm Research Articles

Performance evaluation and mechanism of Al2O3/TiO2 sorbents for fluoride remediation in groundwater

Excessive fluoride levels in drinking water are problematic in several countries, particularly those which are relatively poor. Thus, there is a need to create cost effective sorbents which can easily be applied to make the water safe to use. Therefore, this study focussed on Al2O3/TiO2 sorbents which appear to address issues with commercially available alumina such as aluminium dissolution. Adjusting the alumina/titania ratio significantly influenced not only the fluoride uptake capacity but also the uptake of a wide range of contaminants found in groundwater. The exchange kinetics were relatively fast regardless of mixed oxide composition with equilibrium obtained within 6 h. Equilibrium isotherms were unfavourable for fluoride removal where titania compositions were dominant. In contrast, favourable isotherms were noted when alumina was the dominant oxide present. Barium, calcium, strontium, boron, iron, manganese, zinc, potassium, lithium, and silica were all substantially removed by varying the alumina/silica ratio in the sorbent. This behaviour may be valuable for broader remediation of dissolved species in groundwater (not just fluoride). Based upon the tests data a 70% Al2O3 – 30% TiO2 material was recommended to be the preferred composition for comprehensive treatment of groundwater. The sorbents appeared to comprise of alumina and titania with surface areas between 129 and 255 m2/g. There was no evidence for new oxide phases nor for a relationship between surface area and performance. Mechanistically both ion exchange and surface complexation may occur when treating groundwater.

Cocos nucifera Husk Biomass as an Effective Adsorbent for Industrial Wastewater Removal: Harnessing the Power of Nature.

Rapid industrialization has polluted waterways, threatened aquatic ecosystems and endangered human health. To solve this problem, sustainable industrial practices and innovative water treatment technology must be implemented to ensure clean and safe water for future generations. This study aimed to investigate the adsorbent capacity of Cocos nucifera husk for ineffective removal of methylene blue (MB), a cationic dye abundantly found in industrial effluent. Adsorption capacity is measured using parameters such as dye elimination percentage and polymer dosage. The Langmuir and Freundlich isotherms, adsorption kinetics (pseudo-first, pseudo-second, and second order), and intraparticle diffusion were determined to better understand the adsorption process. The increased dosage of cellulose fiber results in the availability of a greater number of adsorption sites and an increased surface area. However, the dye removal efficacy decreased after reaching a specific dosage of 0.6 g/L. A concentration of 0.05 g/L was most effective in eliminating Methylene blue (MB). The value of the separation factor (0.99) suggested a favorable adsorption isotherm. The reciprocal of the heterogeneity factor (-1.469) demonstrated the concentration-independent adsorption behavior of Fiber. Freundlich and Langmuir's isotherm model showed that the pseudo-second-order kinetic model demonstrated the highest level of correlation with the experimental data about the mechanism of adsorption. The Methylene blue (MB) adsorption is not limited by the intraparticle diffusion and adsorption is influenced by surface area and concentration variation of fiber as well as solvent concentration, as evidenced by low R2 value and the fact that the intraparticle diffusion plot does not intersect with the origin. The study concludes that Cocos nucifera husk can be effectively used for the treatment of wastewater.

Fe3O4 embedded κ-carrageenan/sodium alginate hydrogels for the removal of basic dyes

Here, we introduce κ-carrageenan and sodium alginate based hydrogel (CAG-NaAlg-cl-polyAA) and hydrogel nanocomposite (CAG-NaAlg-cl-polyAA/Fe3O4) through a free radical crosslinking method using acrylic acid/ N,N′- methylenebisacrylamide as a monomer/crosslinker system. The hydrogel is stimuli-responsive and its water absorption efficiency is enhanced through the optimization of synthesis parameters. The synthesized superabsorbents have been sequentially characterized through HR-TEM, powder XRD, FTIR, SEM-EDS, and XPS analysis. The average particle size of Fe3O4 nanoparticles stabilized through the CAG-NaAlg-cl-polyAA hydrogel matrix is 10.7 ± 2.5 nm. The CAG-NaAlg-cl-polyAA hydrogel exhibited > 95 % dye removal efficiency for the removal of basic dyes (auramine O, crystal violet and malachite green), whereas the % dye removal potential of CAG-NaAlg-cl-polyAA/Fe3O4 is enhanced upto 99 % after the incorporation of Fe3O4 nanoparticles. Langmuir adsorption is the most favorable adsorption isotherm with R2 = 0.992 (auramine O, AU), 0.989 (malachite green, MG), and 0.974 (crystal violet, CV). Kinetic studies indicate that the adsorption of AU, CV, and MG follows pseudo 2nd order kinetics. Moreover, the reusability of the fabricated samples upto five consecutive cycles further explores its potential for the separation of basic textile dyes from industrial wastewater.

Adsorption equilibria and kinetics of CO2, CH4, CO, N2, and H2 on KOH-treated activated carbon pellets up to 1000 kPa

• Adsorption behaviors of CO 2 , CH 4 , CO, N 2 , and H 2 on KOH-treated ACs were studied. • KOH-treated ACs showed improved adsorption capacities, but reduced adsorption rates. • Affinity for CO increased on KACi, in the presence of intercalated K chemicals. • KACi showed higher capacity and selectivity than CAC and KACa based on volume. • Adsorption rate of KACi was faster for CO 2 , CH 4 , and N 2 and slower for CO than KACa. Activated carbon (AC) is critical for bulk separation to produce high-purity H 2 . Coal-based AC pellets (CAC) were modified through KOH activation (KACa) or impregnation (KACi) via bulk preparation. The adsorptive behaviors of CO 2 , CH 4 , CO, N 2 , and H 2 , which are components of various H 2 mixtures, were investigated at 293.15–323.15 K and up to 1000 kPa. The experimental data and model parameters are tabulated for applications by related researchers. The experimental isotherms fitted well to the Sips and dual-site Langmuir models. The improved textural properties of KACa resulted in higher adsorption capacity based on the adsorbent mass. However, based on volume-based evaluation, KACi showed higher adsorption capacities for CO 2 , CO, and CH 4 at low pressures, with capacities almost equivalent to those of KACa at high pressures, despite the deterioration of textural properties due to K impregnation. Furthermore, more favorable isotherms on KACi resulted in higher selectivities toward various H 2 mixtures. From the non-isothermal kinetic model, CO 2 and CH 4 showed a lower adsorption rates than CO and N 2 due to higher heats of adsorption. Compared to those of KACa, the adsorption rates of KACi were faster for CO 2 , CH 4 , and N 2 and slower for CO, but within the same order of magnitude. KACa was found to be more affected by pre-adsorbed molecules than KACi. KACa and KACi exhibited enhanced performances with excellent cyclic stabilities and batch preparation consistencies. Considering its selectivity and adsorption rate, KACi can be used for improving the efficiencies of adsorptive processes for H 2 production.

Synergistic adsorption and photocatalytic properties of AC/TiO2/CeO2 composite for phenol and ammonia–nitrogen compound degradations from petroleum refinery wastewater

This study focuses on the utilization of AC/TiO2/CeO2 composite on the removals of phenol and ammonia–nitrogen (NH3-N) compounds from petroleum refinery wastewater (PRW) through a combination of adsorption and photocatalytic process. The composite was prepared by hydrothermal method with the composite formulation of 53.43%-wt of AC, 21.96 %-wt of TiO2, and 24.61 %-wt of CeO2. Characterization results revealed that the surface micromorphology, elemental, and oxide contents on synthesized composite significantly changed with the addition of TiO2 and CeO2. Optical UV–vis analysis showed that the estimated bandgap energy of the synthesized composite was 2.60 eV, which is lower than pristine TiO2 or CeO2, indicating that the photocatalysis is easier to perform that reflecting the successful combination of TiO2 and CeO2 as the photocatalyst in the composite. The Langmuir isotherm and pseudo-second order kinetic showed to be the most favorable isotherm and kinetic model for the adsorption process. The photocatalytic activity and kinetic evaluations showed that the photocatalytic process remarkably improved the removal performance and was followed the pseudo-first order kinetic. Moreover, the rate constants of photocatalysis were higher than the adsorption process, indicating that the rate of photocatalysis on the pollutant degradations is faster than the adsorption process. The final pollutant removals by using AC/TiO2/CeO2 composite were 50.91% for phenol removal and 65.83% for NH3-N removal. Three consecutive cycles test showed that the AC/TiO2/CeO2 composite has excellent durability and can nicely maintain the phenol and NH3-N removals from PRW.

Phenol Removal from Aqueous Solution by Adsorption Technique Using Coconut Shell Activated Carbon

Adsorption is one of the simplest techniques with low economic requirements. Coconut shell is an abundant agriculture waste which is inexpensive and easy to be obtained in Malaysia. This agriculture waste was transformed to activated carbon via 600°C of carbonization and zinc chloride activation. The ability of coconut shell-based activated carbon to remove phenolic compounds from aqueous solutions was evaluated. From the experiment, the equilibrium time for the adsorption of phenol onto coconut shell-based activated carbon is 120 minutes. The effect of the operating parameters, such as contact time, initial concentration, agitation speed, adsorbent dosage, and pH of the phenolic solution were studied. Adsorption kinetics models (pseudo-first-order, pseudo-second-order, and Elovich equation) and isotherm models (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich) were used to fit the experimental data.Pseudo-second-order was found to be the best fitted kinetics model to describe the adsorption of phenol on coconut shell-based activated carbon. While the equilibrium experiment data was well expressed by the Temkin isotherm model, The maximum adsorption capacity is determined as 19.02 mg/g, which is comparatively lower than the previous research. Meanwhile, 92% of removal efficiency was achieved by a dosage of 10g/L. Meanwhile, the adsorption of phenol by activated carbon was more favorable under acidic conditions. The favourable isotherm behavior was indicated by the dimensionless separation factor. The functional group and compound class of activated carbon before and after the experiment were determined through the analysis of Fourier-transform infrared (FTIR) spectroscopy.

Adsorbtion of Nitrogen Compounds from Hydrocarbon Liquids by Using Fixed Packed Bed Activated Carbon

The Extraction behavior of nitrogen compounds (quionoline, indole, and pyridine) from a liquid hydrocarbon (nonane, C9) was studied by using batch and fixed bed activated carbon experiments. The adsorption isotherm curves and the extraction percentage were determined in batch experiments in the conditions of initial concentration 20,40,60,80,and 100 ppm of either of quionoline, indole, and pyridine, fuel/(AC) ratio of 20 wt/wt, room temperature 30 ± 1°C , and stirring time of 2h.
 In the fixed bed experiments the breakthrough curves were determined as a function of the following variables:
 
 Bed height of activated carbon 3, 5, and10 cm.
 Initial concentration of nitrogen compounds 50, 75, and100 ppm.
 Flow rate of the feed (15, 25, and35) ml/min.
 Particle Diameter of activated carbon 1.5, 1.2, and1 mm.
 
 The adsorption capacity increases with increasing equilibrium concentration of the nitrogen compounds in the liquid phase, which is a very favorable isotherm irreversible adsorption. Also the activated carbon has very high affinity for the nitrogen compounds in the order indole < quinoline < pyridine and the conversion values were (50, 46, and42) % respectively. In fixed bed experiments the time to breakthrough point decreases with:
 
 Decreasing in bed height.
 The increase in flow rate.
 The increase in initial concentration of nitrogen compounds.
 There is no effect of varying the particle diameter of the activated carbon because the experimental values of the activated carbon lies in the region of the large particle size and macrospore volume and there is no gradient in the particle size.

Highly efficient removal of diazinon pesticide from aqueous solutions by using coconut shell-modified biochar

This study evaluates the adsorption of diazinon from aqueous solutions onto coconut shell-modified biochar using a batch system. The amount of dosage and initial pH are the main parameters being studied to obtain maximum adsorption capacity of the probe molecules. The carbonized coconut shell biochar (BC1), activated coconut shell biochar (BC2), chemically modified phosphoric acid (BC3) and sodium hydroxide coconut shell biochar (BC4) were prepared and tested as variables in the adsorption experiment. The characteristic of biochar via SEM, EDX and BET analysis revealed the large porous of surface morphology and slight changes in the composition with high surface area (405.97 – 508.07 m2/g) by following the sequence of BC3 > BC2 > BC4. Diazinon removal percentage as high as 98.96% was achieved at pH 7 with BC3 as adsorbent dosing at 5.0 g/L. The high coefficient of determination, R2 with a small value of ERRSQ and χ2 error analysis present the BC1 (0.9971) and BC2 (0.9999) are best fitted with Freundlich isotherm indicates multilayer sorption onto heterogeneous surface whereby the Langmuir isotherm model is the best fitting is described of monolayer adsorption process onto the homogenous surface of BC3 and BC4. The results indicated the maximum adsorption capacity (qm) was achieved by BC3 with 10.33 mg/g, followed by BC2 (9.65 mg/g) in accordance to the Langmuir isotherm while Freundlich isotherm showed the highest adsorption capacity (kF) with 1.73 mg/g (L/mg)1/n followed by BC4 with 0.63 mg/g (L/mg)1/n at favorable adsorption isotherm (1 ≤ n ≤ 10). Thus, the results obtained depicted that BC2 and BC3 are highly efficient adsorbents and both exhibit great potential in removing diazinon from aqueous solutions.

Structure and functional properties of Capto™ Core 700 core-shell particles

Capto™ Core 700 is a core-shell chromatographic support with an adsorbing core contained within an inert shell layer designed to purify larger biomolecules and bioparticles in a flow-through mode. The present study aims to characterize the structure and functional properties of this resin using bovine serum albumin (BSA, Mr~65 kDa) and thyroglobulin (Tg, Mr~660 kDa) as model impurity proteins. The functionalized adsorbing core and the inert shell have the same fibrous structure typical of agarose-based beads. The resin average bead size is 90.7 μm with a range of 50–130 μm, the shell thickness is 4.18 µm with a range of 3–6 µm and a standard deviation of 0.55 µm, and the pore radius, obtained by inverse size exclusion chromatography, is 50.4 ± 1.3 nm. Both proteins present highly favorable binding isotherms with maximum binding capacities of 55 and 105 mg/mL of total bead volume for BSA and Tg, respectively. The addition of 500 mM NaCl reduces the binding capacity by less than 50%, showing the ability of the resin to operate at high salt conditions. For both proteins, the effective pore diffusivity in the core is smaller than in the shell due to additional hindrance by bound protein in the core area. Effective pore diffusivities values in the core are 1.6 × 10−7 and 0.16 × 10−7 cm2/s for BSA and Tg, respectively. The DBC10% at 2 min residence time are 24 and 2 mg/mL for BSA and Tg, respectively. This study provides qualitative and quantitative information about Capto™ Core 700 resin. This information could be used to predict and optimize the purification of large biomolecules and bioparticle in route to the establishment of more effective downstream processes.

Equilibrium theory analysis of thermal regeneration of a humid adsorption column: Selection of optimal hot purge gas temperature

A Thermal Swing Adsorption (TSA) process has been widely commercialised for its application to air drying. In designing an air-drying TSA, zeolite 13X is chosen as a desiccant when required to produce a very low dew point dry air due to its highly nonlinear, favourable isotherm. It is essential to make use of an external hot purge gas in producing such an extremely low dew point dry air, as the column has to be regenerated thoroughly for the next adsorption step. In case of the externally heated TSA, usage of a hot purge gas gives rise to huge energy consumption. Also the cycle time has to be made as short as possible to enhance the bed productivity. To optimise this energy-intensive process, it is crucial to find an optimal hot purge gas temperature at which the column can be regenerated as quickly as possible with less energy consumed. In this study, Equilibrium Theory approach was taken to analyse the thermal regeneration breakthrough of a zeolite 13X column saturated with a water vapour in which the equilibrium isotherm is estimated by Toth or Aranovich-Donohue isotherms. As a result of Equilibrium Theory analysis, it was found that the trailing front of a thermal regeneration breakthrough would exhibit a transition of the shape from simple to shock wave with increasing purge gas temperature. The purge gas temperature has to be chosen so that after thermal regeneration the targeted water vapour concentration remaining in the column lies within the concentration range occupied by the shock wave. A useful correlation that relates the targeted dew point of the remaining water vapour with the purge gas temperature was proposed. The presence of the optimal hot purge gas temperature estimated by Equilibrium Theory was validated by both full numerical simulation and ideal work consumption.

Piecewise loading bed for reversible adsorption of VOCs on silica gels

Abstract The vacuum swing adsorption (VSA) with silica gel (SG) is proved to be a promising method for the recovery of volatile organic compounds (VOCs). The adsorption mechanisms of o-xylene on silica gels with different pore size have been revealed through the mathematic modeling of adsorption isotherms. The analysis of adsorption kinetics indicates that SG with micropore shows a steep concentration front and a long breakthrough time due to the strong adsorption force field, negligible transfer resistance and compressive effect of favorable isotherm. However, the reversible capillary condensation and mass transfer resistance cause a dispersed front and a short breakthrough time for mesoporous SG. The fast desorption rate makes mesoporous SG more energy-efficient compared with SG with micropore. Accordingly, to further improve the front slope and utilization of mesoporous SG in the adsorption process, a small amount of SG with micropore was loaded in the end of the fixed bed. The breakthrough time of the piecewise loading bed increased by 55.8% at the same loading volume with single mesoporous SG. The energy consumption was observed to exhibit an obviously decrease from 1.819 kWh/m3 to 1.295 kWh/m3, which proved that the piecewise loading method could recover VOCs in a more energy-saving way.

H2S adsorption on NaY zeolite

Abstract In this work, high-pressure H2S adsorption data in equilibrium and fixed bed conditions using NaY zeolite as adsorbent were determined. Adsorption and desorption isotherms for different temperatures and H2S partial pressures up to 1.2 bar were obtained experimentally and modelled with Toth and Dubinin-Astakhov equations in order to give information about adsorbate/adsorbent and adsorbate/adsorbate interactions. H2S adsorption in a fixed bed column was achieved for different inlet volumetric flow rates and breakthrough curve data were evaluated considering adsorbed amount, length of mass transfer zone, contributions of internal and external mass transfer resistances and were modelled with Linear Driving Force (LDF) model to estimate adsorbent particle's effective mass transfer coefficient. Equilibrium results indicate maximum uptake capacities are above 6.0 mol kg−1 for highest partial pressures. Isotherms' modeling suggests the predominance of physisorption of H2S in NaY zeolite. However, a hysteresis effect was observed for desorption curves and attributed to H2S chemisorption on zeolite surface, as pointed out by strongly favorable isotherms obtained. Fixed bed adsorption data showed breakthrough curves were nonsymmetrical, which indicated the presence of internal resistance mainly, probably due to the microporosity of adsorbent particle. In accordance, mass transfer zones did not vary significantly with inlet flow rate. Effective intraparticle mass transfer coefficients obtained with LDF model increases as flow rate increases, due to a higher availability of H2S molecules at adsorbent surface, which increases the driven force necessary for mass transfer in the intraparticle region.

Evaluation of hybrid neutralization/biosorption process for zinc ions removal from automotive battery effluent by dolomite and fish scales

ABSTRACTThis work focused in the evaluation of Oreochromis niloticus fish scales (FS) as biosorbent material in the removal of Zn from a synthetic effluent based on automotive battery industry effluent and, further, a hybrid neutralization/biosorption process, aiming at a high-quality treated effluent, by a cooperative use of dolomite and FS. For this, a physicochemical and morphological characterization (i.e. SEM–EDX, FTIR, XRD, and TXRF) was performed, which helped to clarify a great heterogeneity of active sites (phosphate, carbonate, amide, and hydroxyl) on the biosorbent; also the inorganic constituents (apatites) leaching from the FS was identified. Biosorption results pointed out to a pH-dependent process due to changes in the functional group’s anionic character (i.e. electrostatic interactions), where an initial pH = 3 favored the Zn uptake. Kinetic and equilibrium studies confirmed the heterogeneous surface and cooperative sorption, wherein experimental data were described by Generalized Elovich kinetic model and the favorable isotherm profile by Langmuir–Freundlich isotherm ( = 15.38 mg g–1 and ). Speciation diagram of Zn species along with the leached species demonstrated that, for the studied pH range, the biosorption was the most likely phenomena rather than precipitation. Finally, the hybrid neutralization/biosorption process showed great potential since both the Zn concentration levels and the pH reached the legislation standards (CZn = 4 mg L–1; pH = 5). Hence, based on the characterization and biosorption results, a comprehensive evaluation of the involved mechanisms in such complex system helped to verify the prospective of FS biosorbent for the Zn treatment from solution, in both individual and hybrid processes.

Sorption enhanced reaction for high purity products in reversible reactions

Reversible reactions (A + B = C + D) can be performed to near completion using an admixture of catalyst and sorbent that will selectively adsorb one of the reaction products. For an initially clean sorbent and a favorable adsorption isotherm and a long reactor, the adsorbed product, C, will propagate as a sharp, shock‐like front. While the adsorbed product will not move faster than this front, the second, nonadsorbed product, D, will, in principle, leave the reactor, uncontaminated. However, a parametric analysis of the two examples presented in this work, the water gas shift and the cracking of hydrogen sulfide, reveals an unexpectedly complex behavior. While assuming adsorption equilibrium the effect of the equilibrium constant, the reaction kinetics and adsorption isotherm on the reactant and product concentration profiles are simulated. It is found that desired behavior is favored by large equilibrium constants, rapid kinetics, and strong nonlinear adsorption. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5452–5461, 2017

Biosorption of nickel(II) and copper(II) ions in batch and fixed-bed columns by free and immobilized marine algae Sargassum sp.

In this study, the brown algae harvested in the State of Pernambuco - Brazil, Sargassum species, and the commercial sodium alginate were used as free and immobilized biosorbents for the removal of nickel and copper ions in batch and continuous experiments from aqueous solutions. The alginate beads and immobilized biosorbent were produced from the ionic polymerization using the drip method in calcium chloride solution. Equilibrium data show that the calcium alginate matrix increased the maximum biosorption capacity in immobilization, and both biosorbent materials presented greater affinity and uptake capacity for copper ions than for nickel ions. The experimental results were better fitted to the Langmuir model than to the Freundlich model, obtaining favorable type isotherms. Continuous systems showed a different equilibrium condition, once the experiments carried out in fixed-bed columns presented higher biosorption capacity than those performed in batch experiments, also suggesting that the bed packed with immobilized biosorbent was not affected by the low porosity. The immobilized biosorbent also had easy packing.

Effect of dispersed hydrophilic silicon dioxide nanoparticles on batch adsorption of benzoic acid from aqueous solution using modified natural vermiculite: An equilibrium study

The equilibrium adsorption of benzoic acid from an aqueous medium on a natural vermiculite-based adsorbent was studied in the presence and absence of hydrophilic silicon dioxide nanoparticles in batchwise mode. The adsorbent was prepared through grinding natural vermiculite in a laboratory vibratory disk mill and the surfactant modification of ground vermiculite by cetyltrimethylammonium bromide, subsequently. The equilibrium isotherm in the presence and absence of nanoparticles was experimentally obtained and the equilibrium data were fitted to the Langmuir, Freundlich, Dubinin–Radushkevich and Temkin models. The results indicated that the dispersion of silicon dioxide nanoparticles at optimum concentration in the liquid phase remarkably increases the removal efficiency. Furthermore, it yields a more favorable equilibrium isotherm and changes the compatibility of equilibrium data from the Langmuir and Temkin equations to just the Langmuir equation. A quadratic polynomial model predicting the equilibrium adsorbent capacity in the presence of nanoparticles as a function of the adsorbate and initial nanoparticle concentrations was successfully developed using the response surface methodology based on the rotatable central composite design. A desirability function was used in order to optimize the values of all variables, independent and dependent ones, simultaneously.

Critical analysis of adsorption data statistically

Experimental data can be presented, computed, and critically analysed in a different way using statistics. A variety of statistical tests are used to make decisions about the significance and validity of the experimental data. In the present study, adsorption was carried out to remove zinc ions from contaminated aqueous solution using mango leaf powder. The experimental data was analysed statistically by hypothesis testing applying t test, paired t test and Chi-square test to (a) test the optimum value of the process pH, (b) verify the success of experiment and (c) study the effect of adsorbent dose in zinc ion removal from aqueous solutions. Comparison of calculated and tabulated values of t and χ2 showed the results in favour of the data collected from the experiment and this has been shown on probability charts. K value for Langmuir isotherm was 0.8582 and m value for Freundlich adsorption isotherm obtained was 0.725, both are <1, indicating favourable isotherms. Karl Pearson’s correlation coefficient values for Langmuir and Freundlich adsorption isotherms were obtained as 0.99 and 0.95 respectively, which show higher degree of correlation between the variables. This validates the data obtained for adsorption of zinc ions from the contaminated aqueous solution with the help of mango leaf powder.

Analysis of equilibrium and kinetic parameters of water adsorption heating systems for different porous metal/metalloid oxide adsorbents

The performances of well-known porous metal/metalloid oxide adsorbents (zeolite 13X, zeolite 4A and silica gel) and less explored Engelhard titanosilicate ETS-10 for water adsorption heating systems (AHSs) were compared with the aid of computational modelling and simulations. The developed model contemplated adsorption equilibrium, one-dimensional heat and mass transfer in the bed, external heat transfer limitations, and intraparticle mass transport. The pair zeolite 13X/water seemed most promising for the AHS partly due to a higher amount of heat generated per cycle, and favourable water-adsorption isotherm features. Based on sensitivity studies, for zeolite particle diameters in the range 0.2–0.6 mm, the coefficient of performance was 1.48 and the specific heating power was in the range 1141–1254 W kgs−1. Aiming at inferior computational and numerical efforts, the impact of considering some simplified postulations (e.g. constant thermal conductivity of the adsorbent; constant isosteric heat of adsorption; constant linear driving force coefficient), while ensuring comparable predictions of the performances of the AHSs, was successfully investigated.

Ni2+-ion-exchanged dealuminated clinoptilolite: A superior adsorbent for deep desulfurization

A superior adsorbent for the deep desulfurization of liquid fuels has been developed. Clinoptilolite zeolite exhibits a very favorable adsorption isotherm for thiophene, benzothiophene, dibenzothiophene and iso-propyl mercaptan (iso-octane as solvent) upon dealumination with oxalic acid and further ion-exchange with Ni2+. This is while the raw zeolite and the Ni2+-ion-exchanged raw zeolite adsorb benzothiophene and dibenzothiophene molecules scarcely. The effect of oxalic acid molarity and time of reaction on the chemical composition, crystallinity and adsorption capacity of benzothiophene and dibenzothiophene has been investigated in the first step (screening tests). The treated samples have been characterized by X-ray diffraction, X-ray fluorescence, Fourier transform Infra-red, N2 adsorption, transmission electron microscopy and thermal gravimetry analysis. The sample exhibiting optimal adsorption characteristics was used for obtaining the adsorption isotherms for the 4 type of sulfur compounds at 20°C. The optimum sample shows an adsorption saturation capacity of 2.7mgSg−1 for large molecules like dibenzothiophene (molecular diameter>8Å), i.e. ca. 2 times that of the not-dealuminated Ni2+-ion-exchanged or raw zeolite. The enhancement achieved for the adsorptive characteristics has been discussed. The optimum sample shows an exceptional regenerability for benzothiophene and dibenzothiophene.

Hierarchical zeolites as adsorbents for mesosulfuron-methyl removal in aqueous phase

Bulky organic pollutants such as pesticides and pharmaceutical residues are found in wastewater and are difficult to remove by microporous adsorbents because of their large size. Hierarchical zeolites as potential adsorbents for removal of heavy organic pollutants from aqueous phase are investigated. Hierarchical HMOR and HZSM-5 samples were obtained by post-synthesis desilication by alkaline treatment followed or not by acid leaching of the microporous parent zeolites. The obtained materials have been fully characterized by X-ray diffraction, N2 physisorption, elemental analysis, pyridine adsorption followed by FTIR. Alkaline treatments lead to a framework desilication creating mesopores with the preservation of the Brønsted acidity. Material adsorption behaviors are studied in pesticide, mesosulfuron-methyl (MM), removal from aqueous phase. For all the materials, adsorption kinetics are well described by a pseudo-second order model indicating that MM molecules are chemisorbed via acido-basic interaction of the neutral form. Sorption isotherms are S-shape isotherms for the parent samples and evolve to more favorable concave isotherms for highly mesoporous samples. Thus hierarchical zeolites exhibit higher sorption rate and capacities than microporous ones. Soft acid leaching treatments carried out after alkaline one help to clean the zeolite porosity from silica debris and to enhance significantly zeolite adsorption efficiency.