Methyl Tert-butyl Ether Adsorption Research Articles

Adsorption of methyl tert-butyl ether using granular activated carbon: Equilibrium and kinetic analysis

The adsorption of methyl tert-butyl ether by granular activated carbon was investigated. The experimental data were analyzed using the Freundlich isotherm and the Langmuir isotherm. Although equilibrium data were found to follow Freundlich isotherm model, it were fitted better by the Langmuir model with a maximum adsorption capacity of 204.1 mg/g. The kinetic data obtained at different concentrations were analyzed to predict the constant rate of adsorption using three common kinetic models: pseudo-first-order, pseudo-second-order equation and intraparticle diffusion equation. The pseudo-second-order model was suitable for describing the adsorption kinetics for the removal of methyl tert-butyl ether from aqueous solution onto granular activated carbon. Both the Lagergren first-order rate constant k 1 and pseudo-second-order rate constant k 2 decrease with increasing initial concentrations of methyl tert-butyl ether and the intraparticle diffusion rate constant k p shows the reverse characteristic. Analysis of sorption data using a boyd plot confirmed that external mass transfer is the main rate-limiting step at the initial stage of adsorption. Results illustrate that granular activated carbon is an effective adsorbent for methyl tert-butyl ether and also provide specific guidance into adsorption of methyl tert-butyl ether on granular activated carbon in contaminated groundwater.

Iron amendment and Fenton oxidation of MTBE-spent granular activated carbon

Fenton-driven regeneration of methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) involves an Fe amendment step to increase the Fe content and to enhance the extent of MTBE oxidation and GAC regeneration. Four forms of iron (ferric sulfate, ferric chloride, ferric nitrate, ferrous sulfate) were amended separately to GAC. Following Fe amendment, MTBE was adsorbed to the GAC followed by multiple applications of H 2O 2. Fe retention in GAC was high (83.8–99.9%) and decreased in the following order, FeSO 4·7H 2O > Fe 2(SO 4) 3·9H 2O > Fe(NO 3) 3·9H 2O > FeCl 3. A correlation was established between the post-sorption aqueous MTBE concentrations and Fe on the GAC for all forms of Fe investigated indicating that Fe amendment interfered with MTBE adsorption. However, the mass of MTBE adsorbed to the GAC was minimally affected by Fe loading. Relative to ferric iron amendments to GAC, ferrous iron amendment resulted in lower residual iron in solution, greater Fe immobilization in the GAC, and less interference with MTBE adsorption. MTBE oxidation was Fe limited and no clear trend was established between the counter-ion (SO 4 2−, Cl −, NO 3 −) of the ferric Fe amended to GAC and H 2O 2 reaction, MTBE adsorption, or MTBE oxidation, suggesting these processes are anion independent.

What is the correct form of BET isotherm for modeling liquid phase adsorption?

In this work subtleties of application of BET isotherm for liquid phase adsorption is presented. It has been shown that direct use of the classical BET equation (which was developed for gas phase adsorption) to liquid phase adsorption leads to ambiguous and erroneous results. Some cases of misuse of BET equation for liquid phase adsorption have been revisited. By close examination of the development of the classical equation, the causes of misunderstandings were elucidated and the suitable form of the BET equation for liquid phase adsorption was developed. As case studies, the classical form of the BET equation along with the correct form of the equation for liquid phase have been applied for modeling liquid phase adsorption of methyl tert-butyl ether (MTBE) on perfluorooctyl alumina, phenol on activated carbon and pentachlorophenol on carbonized bark. It has been shown that direct application of the classical BET isotherm to liquid phase adsorption results in poor and erroneous estimation of the equation parameters. For example, in aqueous phase adsorption of MTBE on perfluorooctyl alumina, the monolayer adsorption capacity of the adsorbent was calculated as 9.7 mg/g instead of 3.3 mg/g or the saturation concentration of MTBE in water was calculated as 1212 mg/L instead of 42000 mg/L.

The application of silicalite-1/fly ash cenosphere (S/FAC) zeolite composite for the adsorption of methyl tert-butyl ether (MTBE)

Silicalite-1/fly ash cenosphere (S/FAC) zeolite composite has been applied for batch adsorption of methyl tert-butyl ether (MTBE) from water systems. Here the key experimental conditions, including the ratio of initial MTBE concentration to the amount weight of S/FAC, adsorption time and temperature, have been discussed in detail. The results show that approximately 93–95% MTBE could be adsorbed with initial concentration of MTBE solution 1000 μg l −1. The column flow-through experiments also prove the high capacity of S/FAC composite for MTBE removal. The distinct advantages of S/FAC zeolite composite as adsorbent lie in (1) enhanced adsorption rate and capacity based on hierarchical micro and meso/macroporosity of S/FAC; (2) more easily operation and recycling process by assembly of nano-sized silicalite-1 zeolite on FAC support.

Adsorption of methyl tert-butyl ether (MTBE) from aqueous solution by porous polymeric adsorbents

MTBE has emerged as an important water pollutant because of its high mobility, persistence, and toxicity. In this study, a postcrosslinked polymeric adsorbent was prepared by postcrosslinking of a commercial chloromethylated polymer, and a nonpolar porous polymer with comparable surface area and micropore volume to the postcrosslinked polymer was prepared by suspended polymerization. The postcrosslinked polymer, nonpolar porous polymer and chloromethylated polymer were characterized by N 2 adsorption, FTIR and XPS analysis. Results showed that postcrosslinking reaction led to the generation of a microporous postcrosslinked polymer with BET surface area 782 m 2 g −1, average pore width 3.0 nm and micropore volume 0.33 cm 3 g −1. FTIR and XPS analysis indicated the formation of surface oxygen-containing groups on the postcrosslinked polymer. The three polymers were used as adsorbents to remove aqueous methyl tert-butyl ether (MTBE). Adsorption of MTBE over the postcrosslinked polymeric adsorbent was found to follow the linear adsorption isotherm, whereas MTBE adsorption onto the nonpolar porous polymer and chloromethylated polymer followed Langmuir adsorption model. Comparison of adsorption capacities of the postcrosslinked polymer, chloromethylated polymer and nonpolar porous polymer revealed that the adsorption of MTBE from aqueous solution is dependent on both pore structure and surface chemistry of polymeric adsorbents, and the high adsorption efficiency of the postcrosslinked polymer towards MTBE is attributed to its high surface area, large micropore volume and moderate hydrophility. The process of MTBE adsorption onto the adsorbents can be well described by pseudo-second-order kinetics, and the rate of adsorption decreased at higher MTBE initial concentration.

Adsorption of Methyl tert‐butyl Ether on Perfluorooctyl Alumina Adsorbents – High Concentration Range

AbstractThe performance of two types of perfluorooctyl alumina (PFOAL) adsorbents prepared using γ‐alumina (PFOALA) and alumina‐active‐basic® (PFOALB) is reported. The equilibrium adsorption behavior of the adsorbents was studied for adsorption of methyl tert‐butyl ether (MTBE) in a wide range (5–1000 mg/L) of aqueous phase MTBE concentrations. The monolayer adsorption capacities were 3.3 and 3.5 mg MTBE/g adsorbent, and the maximum adsorption capacities were 7.1 and 6.3 mg MTBE/g adsorbent for PFOALA and PFOALB, respectively. The application of Freundlich, Langmuir, BET and BDDT (the general form of BET) isotherms were compared for the modeling of aqueous adsorption of MTBE on the surface of PFOAL adsorbents. It was shown that adsorption of MTBE on the surface of PFOAL is a type IV van der Waals adsorption, which is best modeled by the general form of the BET (BDDT) multilayer adsorption isotherm.

Iron Optimization for Fenton-Driven Oxidation of MTBE-Spent Granular Activated Carbon

Fenton-driven chemical oxidation of methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) was accomplished through the addition of iron (Fe) and hydrogen peroxide (H2O2) (15.9 g/L; pH 3). The Fe concentration in GAC was incrementally varied (1020-25 660 mg/kg) by the addition of increasing concentrations of Fe solution (FeSO4-7H2O). MTBE degradation in Fe-amended GAC increased by an order of magnitude over Fe-unamended GAC and H2O2 reaction was predominantly (99%) attributed to GAC-bound Fe within the porous structure of the GAC. Imaging and microanalysis of GAC particles indicated limited penetration of Fe into GAC. The optimal Fe concentration was 6710 mg/kg (1020 mg/kg background; 5690 mg/kg amended Fe) and resulted in the greatest MTBE removal and maximum Fe loading oxidation efficiency (MTBE oxidized (microg)/ Fe loaded to GAC (mg/Kg)). At lower Fe concentrations, the H2O2 reaction was Fe limited. At higher Fe concentrations, the H2O2 reaction was not entirely Fe limited, and reductions in GAC surface area, GAC pore volume, MTBE adsorption, and Fe loading oxidation efficiency were measured. Results are consistent with nonuniform distribution of Fe, pore blockage in H2O2 transport, unavailable Fe, and limitations in H2O2 diffusive transport, and emphasize the importance of optimal Fe loading.

Adsorption of MTBE on nano zeolite composites of selective supports

The selected zeolite composites silicalite-1/fly ash cenosphere (S/FAC) and silicalite-1/diatomite (S/D) are successfully applied for effective removal of methyl tert-butyl ether (MTBE) from water system through batch adsorption process. Adsorption isotherms of zeolite composites demonstrated that the Langmuir model provided a good fit throughout the concentration rang (from 100 μg l −1 to 100 mg l −1). S/FAC had a higher maximum adsorption capacity ( q max = 92 551 μg g −1) than S/D ( q max = 48 465 μg g −1), due to the higher amount of silicalite-1 coated on its outer surface (21%) than that on S/D (12%). Other factors that associated with the practical application of zeolite composites were also discussed. Synthesis conditions of S/FAC are relatively mild and energy-saving, while S/D is more economical when considering the cost of the expensive organic template during the preparation process.

Adsorption of MTBE from contaminated water by carbonaceous resins and mordenite zeolite

Equilibrium and kinetic adsorption of methyl tert-butyl ether (MTBE) onto two carbonaceous resins and one zeolite was elucidated in this study. The Freundlich isotherm is adequate for describing the adsorption equilibrium of MTBE onto all the tested adsorbents in deionized water and natural waters. The resins of Ambersorb 563 and 572 have the highest adsorption capacity and almost twice the capacity of mordenite in deionized water. A different extent of NOM competition with MTBE was found for the carbonaceous resins in natural waters. For mordenite, no competitive adsorption was observed in natural water. The ideal adsorbed solution theory combined with equivalent background compound (IAST-EBC) model successfully described and predicted the adsorption of MTBE onto the carbonaceous resins in natural waters. The pore diffusion and micropore diffusion model fit the experimental data fairly well and successfully predicted the transport of MTBE within the adsorbent under different operating conditions. The small tortuosity factor between 1.2 and 2.3 of the resins for the diffusion of MTBE was observed, indicating a superior transport property for the carbonaceous resins in natural waters. The intracrystalline diffusivity of MTBE in natural water was much slower than that in deionized water, only 1/10 in STL and 1/3 in FS natural water, since the aperture entrances of mordenite was appreciably hindered by NOM.

Competitive and Hindering Effects of Natural Organic Matter on the Adsorption of MTBE onto Activated Carbons and Zeolites

Equilibrium and kinetic adsorption of methyl tert-butyl ether (MTBE) onto three coal-based activated carbons, one coconut-based activated carbon, and two zeolites are elucidated in this study. Natural organic matter (NOM) and MTBE competed for the adsorption of activated carbons to different extents. The ideal adsorbed solution theory (IAST) combined with the equivalent background compound (EBC) model can adequately describe the NOM competition and predict the isotherms of MTBE onto the activated carbons. No competitive adsorption was observed for one of the zeolites, mordenite, due to the molecular effect. Besides, the aperture size, and the SiO2/Al2O3 ratio of the zeolite may also play an important role in the adsorption of MTBE from the aqueous phase. The surface diffusion model accurately simulated the transport of MTBE within the adsorbents employed in different water matrices. For all the activated carbons tested, the surface diffusivity of MTBE in natural water was nearly equal to that in deionized water, indicating that no apparently hindering effect occurs. A much slower adsorption kinetic of mordenite in natural water was observed since the opening apertures on mordenite may be appreciably hindered and blocked by NOM.

Simultaneous decontamination of hexavalent chromium and methyl tert-butyl ether by UV/TiO 2 process

Hexavalent chromium and methyl tert-butyl ether (MTBE) are two important environmental pollutants. Simultaneous decontamination of Cr(VI) and MTBE was studied by UV/TiO 2 process. The influences of pH and the concentrations of pollutants on the kinetics of the photocatalytic reactions were evaluated. Dark adsorption tests showed that the acidic pH favored the adsorption of Cr(VI) while neutral pH favored the adsorption of MTBE. Under UV irradiation, Cr(VI) reduction was observed in Cr(VI)/TiO 2 system, and MTBE oxidation was observed in MTBE/TiO 2 system. The system containing Cr(VI) and MTBE by UV/TiO 2 process demonstrated the synergistic effect between oxidation of MTBE and reduction of Cr(VI). The results demonstrated that two pollutants Cr(VI) and MTBE could be eliminated simultaneously by UV/TiO 2 process. tert-Butyl formate, tert-butyl alcohol and acetone were identified as primary degradation products of MTBE by gas chromatography–mass spectrometry in the degradation of MTBE by UV/TiO 2 process.

Theoretical study of adsorption of methyl tert‐butyl ether on the substituted tetrahedral surface of dickite

AbstractThe adsorption of methyl tert‐butyl ether (MTBE) on the substituted tetrahedral surface of dickite has been studied using the n‐layered integrated molecular orbital and molecular mechanics (ONIOM) approach and Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (B3LYP)/6‐31G(d):PM3 approximation. Two Si atoms of the tetrahedral side were substituted by Al atoms in three different mutual arrangements (1,2‐, 1,3‐, and 1,4‐substitution). The negative charge of the layer originating from the substitution was compensated by the exchangeable Mg2+ cation. Initially the Mg2+ cation was placed above the center of the six‐member ring with the tetrahedral structure of the mineral fragment. The Mg2+ cation plays a crucial role in the adsorption of MTBE on the substituted surface of dickite. Methyl tert‐butyl ether is adsorbed due to the formation of a chemical bond between the oxygen atom of MTBE and the Mg2+ cation and due to the formation of multiple weak C‐H…O hydrogen bonds between the C–H groups of MTBE and the surface oxygen atoms. The adsorption results in changes in the structural parameters of MTBE that are the most significant in the case of the 1,3‐substituted system. The interaction energies of MTBE adsorbed on the substituted surface of dickite corrected by basis set superposition error were predicted. The values of adsorption energies range from −42.8 kcal/mol (1,2‐substitution) to −45.9 kcal/mol (1,3‐substitution) to −47.2 kcal/mol (1,4‐substitution). © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Adsorption of MTBE Vapors onto Activated Carbon

This work reports some experimental data on the adsorption of methyl tert-butyl ether (MTBE) and of 1-methylbutane vapors onto commercial activated carbon. 1-Methylbutane is assumed to simulate hydrocarbons present in vapor emissions from gasoline car tanks. Equilibrium adsorption data for MTBE + air and 1-methylbutane + air systems have been obtained from breakthrough curves and have been correlated by means of the Langmuir isotherm. Furthermore, the pseudoternary system MTBE + 1-methylbutane + air has been studied and the experimental competitive equilibrium data have been successfully compared with those obtained by ideal adsorbed solution theory. Experiments give information also on the kinetics of the adsorption operation. Modeling breakthrough curves allow the value of an overall mass transfer coefficient to be evaluated.

Removal of Methyl tert-Butyl Ether from Contaminated Water by Macroreticular Resin

Removal of methyl tert-butyl ether (MTBE), a widely used gasoline additive, by adsorption was investigated. Commercially available macroreticular resin was employed in the adsorption process. Batch experiments were conducted to determine the equilibrium MTBE adsorption capacity which, in turn, was utilized to identify the adsorption isotherms. Column tests were made to examine the performances of continuous adsorption operations under conditions of different inlet MTBE concentrations, feed flow rates, and temperatures. A theoretical model based on the general logistic function was adopted and tested for describing the MTBE breakthrough behaviors of the adsorption resin column. The identified breakthrough model significantly facilitates practical design of the MTBE adsorption system. Regeneration of exhausted adsorption resin was also preliminarily investigated to determine its effectiveness for repeated use. The resin adsorption process was found to be efficient in the removal MTBE from contaminated water relative to GAC.

Catalytic conversion of MTBE to biodegradable chemicals in contaminated water

The behavior of different acid zeolites in the hydrolysis at room temperature of methyl tert-butyl ether (MTBE) was studied with reference to the possibility of its conversion to more biodegradable products in underground water contaminated by MTBE. The effect of the structure of the zeolite and SiO2/Al2O3 ratio was analyzed. The results indicate that acid H-MFI and H-BEA zeolites are effective in both adsorption and hydrolysis of MTBE and may be applied for both in situ underground water remediation and as protection barrier for wells or leaking tanks. However, other zeolites (mordenite and faujasite) result completely inactive. Furthermore, contrary to what was expected, the increase of the Si/Al ratio promotes the reactivity which is determined by the resistance to diffusion of MTBE in the pores of zeolites and the resistance of back-diffusion of the reaction products.

Influence of water on the gas-phase decomposition of methyl tert.-Butyl ether catalysed by a macroporous ion-exchange resin

Sulphonic ion-exchange resins are very hygroscopic and readily adsorb water. As a result, the catalytic activity of this type of ion-exchange resin decreases substantially when water contaminates the reaction medium. The influence of water on the gas-phase decomposition of methyl tert.-butyl ether (MTBE) at 50.5°C catalysed by the macroporous ion-exchange resin Amberlyst 15 was studied. The results show that the addition of small amounts of water causes a very strong decrease in decomposition rate of MTBE. A set of Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models are proposed. The statistical discrimination between them permits the selection of two models whose only difference lies in the adsorption model of MTBE: on two active centres with or without dissociation. The values of the parameters of these models (overall kinetic constant, kK IK M; MTBE adsorption constant, K E; and water adsorption constant, K W) obtained from the fit of data coincide, within the limits of experimental error, with those obtained from the fit of each of the curves r E vs. P E corresponding to different amounts of water in the feed. It is concluded that water reduces the rate of the MTBE decomposition reaction by occupying active centres in a competitive way with the ether. Finally, the values for K W in the literature agree fairly well with those determined in this work.