Multicomponent adsorption modeling: isotherms for ABE model solutions using activated carbon F-400

An investigation into the adsorption mechanism of n-butanol by ZIF-8: a combined experimental and ab initio molecular dynamics approach

The zeolitic imidazolate framework, ZIF-8, has been shown by experimental methods to have a maximum saturation adsorption capacity of 0.36 g g^-1 for n-butanol from aqueous solution, equivalent to a loading of 14 butanol molecules per unit cell or 7 molecules per sodalite β-cage. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows the presence of hydrogen bonding between adsorbed butanol molecules within the cage; the presence of three different O-H stretching modes indicates the formation of butanol clusters of varying size. Ab initio molecular dynamics simulations show the formation of intermolecular hydrogen bonding between the butanol molecules, with an average hydrogen-bond coordination number of 0.9 after 15 ps simulation time. The simulations also uniquely demonstrate the presence of weaker interactions between the alcohol O-H group and the π-orbital of the imidazole ring on the internal surface of the cage during early stages of adsorption. The calculated adsorption energy per butanol molecule is -33.7 kJ mol^-1, confirming that the butanol is only weakly bound, driven primarily by the hydrogen bonding. Solid-state MAS NMR spectra suggest that the adsorbed butanol molecules possess a reasonable degree of mobility in their adsorbed state, rather than being rigidly held in specific sites. 2D ¹³C-¹H heteronuclear correlation (HETCOR) experiments show interactions between the butanol aliphatic chain and the ZIF-8 framework experimentally, suggesting that O-H interactions with the π-orbital are only short lived. The insight gained from these results will allow the design of more efficient ways of recovering and isolating n-butanol, an important biofuel, from low-concentration solutions.

Enzymatic biodegradation of highly p-xylene contaminated soil using cold-active enzymes: A soil column study

Enzymatic bioremediation is a sustainable and environment-friendly method for the clean-up of contaminated soil and water. In the present study, enzymatic bioremediation was designed using cold-active enzymes (psychrozymes) which catalyze oxidation steps of p-xylene biodegradation in highly contaminated soil (initial concentration of 13,000 mg/kg). The enzymes were obtained via co-culture of two psychrophilic Pseudomonas strains and characterized by kinetic studies and tandem LC-MS/MS. To mimic in situ application of enzyme mixture, bioremediation of p-xylene contaminated soil was carried out in soil column (140 mL) tests with the injection (3 pore volume) of different concentrations of enzyme cocktails (X, X/5, and X/10). Enzyme cocktail in X concentration contained about 10 U/mL of xylene monooxygenase (XMO) and 20 U/mL of catechol 2, 3 dioxygenases (C2,3D). X/5 and X/10 correspond to 5x and 10x dilution of enzyme cocktail respectively. The results showed that around 92-94% p-xylene removal was achieved in the treated soil column with enzyme concentration X, X/5 after second enzyme injection. While the p-xylene removal rate obtained by X/10 concentration of enzyme was less than 30% and near to untreated soil column (22.2%). The analysis of microbial diversity and biotoxicity assay (root elongation and seed germination) confirmed the advantage of using enzymes as a green and environmentally friendly approach for decontamination of pollutants with minimal or even positive effects on microbial community and also enrichment of soil after treatment.

Separation of biobutanol from ABE fermentation broth using lignin as adsorbent: A totally sustainable approach with effective utilization of lignocellulose

Adsorption is considered to be a promising butanol recovery method for solving the issue of inhibition in the ABE (acetone-butanol-ethanol) fermentation. As a byproduct in the second generation biobutanol industry, lignin was found to be a good adsorbent for the butanol enrichment. It is conducive to the full utilization of renewable lignocellulose biomass resource. Kinetic and equilibrium experiments indicated that lignin had a satisfactory adsorption rate and capacity that are comparable to those of many synthetic materials. Multicomponent adsorption experiments revealed that lignin had higher adsorption selectivity toward butanol than that of ethanol and acetone. The adsorption capacity of lignin for butanol first increased and then gradually decreased with increasing temperature. And maximum adsorption capacity reached 304.66 mg g^-1 at 313 K. The inflection point of temperature is close to the ABE fermentation temperature of 310 K. The condensed butanol by desorption was 145 g L^-1, with a satisfying regeneration performance. ¹H NMR and FT-IR spectra indicated that the aromatic units of lignin formed π-systems with A/B/E. The π-system is particularly significant for butanol due to its longer hydrocarbon chain. These results could contribute to the emerging lignin-based materials for butanol separation.

Energy-Saving and Sustainable Separation of Bioalcohols by Adsorption on Bone Char

The separation of ethanol, propanol, and butanol from aqueous solutions was studied using adsorption on bone char. Adsorption kinetics and thermodynamic parameters of this separation method were studied at different conditions of pH and temperature. Results showed that the maximum adsorption capacities of these bioalcohols were obtained at pH 6 and 20°C. An exothermic separation was identified, which can be mainly associated to hydrophobic interactions between bone char surface and bioalcohols. Binary adsorption studies were also performed using mixtures of these bioalcohols. An antagonistic adsorption was observed for all bioalcohols where the ethanol and propanol separation was significantly affected by butanol. A model based on an artificial neural network was proposed to correlate both single and binary adsorption isotherms of these bioalcohols with bone char. It was concluded that the bone char could be an interesting adsorbent for the sustainable separation and recovery of bioalcohols from fermentation broths, which are actually considered emerging liquid biofuels and relevant industrial chemicals.

Fungal biocatalyst activated by an electric field: Improved mass transfer and non-specificity for hydrocarbon degradation in an airlift bioreactor

The combination of biological and electrochemical techniques enhances the bioremediation efficiency of treating oil-contaminated water. In this study a non-growing fungal whole cell biocatalyst (BC; Aspergillus brasiliensis attached to perlite) pretreated with an electric field (EF), was used to degrade a hydrocarbon blend (hexadecane-phenanthrene-pyrene; 100:1:1w/w) in an airlift bioreactor (ALB). During hydrocarbon degradation, all mass transfer resistances (internal and external) and sorption capacity were experimentally quantified. Internal mass transfer resistances were evaluated through BC effectiveness factor analysis as a function of the Thiele modulus (using first order reaction kinetics, assuming a spherical BC, five particle diameters). External (interfacial) mass transfer resistances were evaluated by k_La determination. EF pretreatment during BC production promoted surface changes in BC and production of an emulsifier protein in the ALB. The BC surface modifications enhanced the affinity for hydrocarbons, improving hydrocarbon uptake by direct contact. The resulting emulsion was associated with decreased internal and external mass transfer resistances. EF pretreatment effects can be summarized as: a combined uptake mechanism (direct contact dominant followed by emulsified form dominant) diminishing mass transfer limitations, resulting in a non-specific hydrocarbon degradation in blend. The pretreated BC is a good applicant for oil-contaminated water remediation.

Comparative Study of the Effect of Defects on Selective Adsorption of Butanol from Butanol/Water Binary Vapor Mixtures in Silicalite-1 Films

A promising route for sustainable 1-butanol (butanol) production is ABE (acetone, butanol, ethanol) fermentation. However, recovery of the products is challenging because of the low concentrations obtained in the aqueous solution, thus hampering large-scale production of biobutanol. Membrane and adsorbent-based technologies using hydrophobic zeolites are interesting alternatives to traditional separation techniques (e.g., distillation) for energy-efficient separation of butanol from aqueous mixtures. To maximize the butanol over water selectivity of the material, it is important to reduce the number of hydrophilic adsorption sites. This can, for instance, be achieved by reducing the density of lattice defect sites where polar silanol groups are found. The density of silanol defects can be reduced by preparing the zeolite at neutral pH instead of using traditional synthesis solutions with high pH. In this work, binary adsorption of butanol and water in two silicalite-1 films was studied using in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy under equal experimental conditions. One of the films was prepared in fluoride medium, whereas the other one was prepared at high pH using traditional synthesis conditions. The amounts of water and butanol adsorbed from binary vapor mixtures of varying composition were determined at 35 and 50 °C, and the corresponding adsorption selectivities were also obtained. Both samples showed very high selectivities (100-23 000) toward butanol under the conditions studied. The sample having low density of defects, in general, showed ca. a factor 10 times higher butanol selectivity than the sample having a higher density of defects at the same experimental conditions. This difference was due to a much lower adsorption of water in the sample with low density of internal defects. Analysis of molecular simulation trajectories provides insights on the local selectivities in the zeolite channel network and at the film surface.

Adsorption of Butanol and Water Vapors in Silicalite-1 Films with a Low Defect Density

Pure silica zeolites are potentially hydrophobic and have therefore been considered to be interesting candidates for separating alcohols, e.g., 1-butanol, from water. Zeolites are traditionally synthesized at high pH, leading to the formation of intracrystalline defects in the form of silanol defects in the framework. These silanol groups introduce polar adsorption sites into the framework, potentially reducing the adsorption selectivity toward alcohols in alcohol/water mixtures. In contrast, zeolites prepared at neutral pH using the fluoride route contain significantly fewer defects. Such crystals should show a much higher butanol/water selectivity than crystals prepared in traditional hydroxide (OH^-) media. Moreover, silanol groups are present at the external surface of the zeolite crystals; therefore, minimizing the external surface of the studied adsorbent is important. In this work, we determine adsorption isotherms of 1-butanol and water in silicalite-1 films prepared in a fluoride (F^-) medium using in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. This film was composed of well intergrown, plate-shaped b-oriented crystals, resulting in a low external area. Single-component adsorption isotherms of 1-butanol and water were determined in the temperature range of 35-80 °C. The 1-butanol isotherms were typical for an adsorbate showing a high affinity for a microporous material and a large increase in the amount adsorbed at low partial pressures of 1-butanol. The Langmuir-Freundlich model was successfully fitted to the 1-butanol isotherms, and the heat of adsorption was determined. Water showed a very low affinity for the adsorbent, and the amounts adsorbed were very similar to previous reports for large silicalite-1 crystals prepared in a fluoride medium. The sample also adsorbed much less water than did a reference silicalite-1(OH^-) film containing a high density of internal defects.The results show that silicalite-1 films prepared in a F^- medium with a low density of defects and external area are very promising for the selective recovery of 1-butanol from aqueous solutions.