Comparison of Wicke-Kallenbach and Graham's diffusion cells for obtaining transport characteristics of porous solids

Counter-current gas diffusion measurements on a series of porous solids covering a broad range of pore sizes (mean pore radii between 78 nm and ) were performed in the Wicke-Kallenbach and Graham's diffusion cells. Mutual agreement of diffusion fluxes from both cells was found in the whole range of tested pore radii and inert gas systems. For pore materials with mean pore radii exceeding the experimentally unavoidable tiny total pressure gradient induces additional permeation flow which precludes the use of Graham's law for evaluation of transport parameters of the porous solids. Transport parameters together with 95% confidence regions were determined for porous materials with pore radii up to and the prevailing diffusion mechanism, intimately connected with the shape of confidence regions, was estimated.     

Influence of carbon dioxide partial pressure and fluidization velocity on activated carbons prepared from scrap car tyre in a fluidized bed

The effect of carbon dioxide partial pressure and fluidization velocity on activated carbons produced by carbon dioxide activation of scrap car tyre rubber in a fluidized bed has been studied. The method consisted of carbonization at under nitrogen followed by activation at . Three types of activated carbons were produced using activated gas concentrations of 20, 60 and 100% carbon dioxide by volume, the rest nitrogen, at a constant fluidization velocity (0.0393 m/s) to investigate the influence of carbon dioxide partial pressure. Within the experimental setup and activation time of 4 h, it was observed that BET surface area and total pore volume increased with carbon dioxide partial pressure reaching and , respectively, for 100% activation with carbon dioxide. Three other types of activated carbons were produced using 100% carbon dioxide at two (0.0393 m/s), three (0.0589 m/s) and four (0.0786 m/s) times the minimum fluidization velocity (U_mf). The BET surface area and total pore volume were observed to increase with fluidization velocity (which can be viewed as an indicator of the intensity of mixing in the bed), reaching and , respectively, at four times the minimum fluidization velocity.     

Permeation behavior during the catalytic oxidation of CO in a Pt-loaded Y-type zeolite membrane

A Pt-loaded Y-type zeolite (Pt/NaY) membrane was prepared on the surface of a porous α-Al₂O₃ support tube by hydrothermal synthesis and then ion-exchanged with platinum. The thickness of the zeolite layer and the amount of Pt loaded were ca. and , respectively. The membrane was employed in the form of a cylindrical thin catalyst for the selective oxidation of CO in an H₂-rich mixture. A mixture of CO, O₂ and H₂ was fed to the outer surface of the membrane, and CO was selectively oxidized during its permeation through the thin layer. The permeation fluxes for H₂ and CO were determined at 423-. Permeation fluxes also calculated by means of a mathematical model using effective diffusion coefficients and reaction kinetics. The effective diffusion coefficients through the zeolite membrane were estimated from gas permeation test data, obtained at 423-, and the oxidation rates of CO were determined over a particulate catalyst that had the same composition as the Pt/NaY membrane. As a result, the diffusion coefficients of O₂, N₂ and CO were determined to be (0.7-1.0) at 423-, and the activation energies for the rate constants for CO oxidation were 61-. The predicted permeation fluxes of H₂ and CO using the mathematical model were in good agreement with the experimental data, when the oxidation selectivity of CO to H₂ was assumed to be 80% in the model calculation.     

Kinetics and equilibrium of dissolved oxygen adsorption on activated carbon

The macroscopic adsorption behavior of dissolved oxygen on a coconut shell-derived granular activated carbon has been studied in batch mode at 301 and 313 K for initial dissolved oxygen concentrations of 10-30 mg/l and oxygen/carbon ratios of 2-180 mg/g. BET (Brunauer, Emmett, and Teller) surface area, micropore volume, and pore size distribution were determined from N₂ isotherm data for fresh and used samples of carbon. The surface groups were characterized using Boehm titrations, potentiometric titrations, and FTIR study. The material is characterized by its high specific surface area , microporocity (micropore volume ), its basic character ( total basic groups) and its high iron content (15,480 ppm Fe). BET n-layer isotherm describes adsorption equilibrium suggesting cooperative adsorption and important adsorbate-adsorbate interactions. Kinetic data suggest a process dependent on surface coverage. At low coverage a Fickian, intraparticle diffusion rate model assuming a local equilibrium isotherm (oxygen dissociation reaction) adequately describes the process. The calculated diffusion coefficients (D) vary between and for initial oxygen concentration of 10 and 20 mg/l, respectively. Sensitivity analysis shows that the oxygen dissociation equilibrium constant determines the equilibrium concentration, whereas the diffusion coefficient controls the kinetic rate of the adsorption process having no effect at the final equilibrium concentration. A combined kinetic mass transfer model with concentration-dependent diffusion (parabolic form) has been developed and successfully applied on the dissolved oxygen adsorption system at high surface coverage. For equilibrium uptake of the estimated mean mass transfer coefficient and adsorption rate constant are and , respectively.     

Kinetics of water sorption on SWS-1L (calcium chloride confined to mesoporous silica gel): Influence of grain size and temperature

Kinetics of water sorption on loose grains of composite sorbent CaCl₂ confined to mesoporous silica (SWS-1L) was measured at and over water uptake range 0-0.47 g/g for various particle sizes R_p (between 0.355 and 1.4 mm). The measurements were performed in a constant pressure unit based on a CAHN microbalance under isothermal external conditions.The results obtained evidence an enhancement of the sorption rate and apparent diffusion constant with the decrease in the particle size (approximately as at ). Contribution of thermal effects was found for water sorption on smaller SWS particles (0.355-0.425 mm), which decreases the sorption rate.The apparent water diffusivity was found to depend on the local slope of the SWS water sorption isotherm. The pore diffusivity of water in the temperature range 33-69 °C was calculated from experimental data that is approximately 10 times lower than the Knudsen pore diffusivity estimated for pores of silica KSK. The possible reasons of the diffusivity reduction are discussed.     

Anomalous IR optical properties of aggregates of Pd nanoparticles induced through electrochemical cyclic voltammetry

IR optical properties of Pd nanoparticles with different size and aggregation state were studied in the current paper. The dispersed Pd nanoparticles () stabilized with poly(N-vinylpyrrolidone) (PVP) were synthesized by the seeding growth method, in which the seeds were formed step by step through reducing H₂PdCl₄ with ethanol. The dispersed Pd nanoparticles of much large size () were grown from the by keeping the colloid of undisturbed for 150 days at room temperature around 20 °C. The aggregates of () were prepared through an agglomeration process induced during a potential cyclic scanning between −0.25 V and 1.25 V for 20 min at a scan rate of 50 mV s⁻¹. Scanning electron microscope (SEM) patterns confirmed such aggregation of . Fourier transform infrared (FTIR) spectroscopy together with CO adsorption as probe reaction was employed in studies of IR optical properties of the prepared Pd nanoparticles. The results demonstrated that CO adsorbed on films substrated on CaF₂ IR window or glassy carbon (GC) electrode yielded two strong IR absorption bands around 1970 cm⁻¹ and 1910 cm⁻¹, which were assigned to IR absorption of CO bonded on asymmetric and symmetric bridge sites, respectively. Similar IR bands were observed in spectra of CO adsorbed on films, except the IR bands were much weak, whereas CO adsorbed on film produced an IR absorption band near 1906 cm⁻¹, and an anomalous IR absorption band whose direction has been completely inverted around 1956 cm⁻¹. The direction inversion of the IR band of CO bonded to asymmetric bridge sites on was ascribed to the interaction between Pd nanoparticles inside the aggregates. Based on FTIR spectroscopic and cyclic voltammetric results, the aggregation mechanism of Pd nanoparticles from to has been suggested that the agglomeration of Pd nanoparticles was driven by the alteration of electric field across electrode-electrolyte interface, when the PVP stabilizer was stripped via oxidation during cyclic voltammetry.     

Removal of chlorinated volatile organic contaminants from water by pervaporation using a novel polyurethane urea-poly (methyl methacrylate) interpenetrating network membrane

Polymer membranes are potentially selective for separation of organic compounds from a mixture by pervaporation. A novel crosslinked hydroxyterminated polybutadiene based (HTPB) polyurethane urea (PUU)-poly (methyl methacrylate) (PMMA) interpenetrating network (IPN) membrane has been developed for the selective removal of chlorinated volatile organic compounds (VOCs) such as 1,1,2,2-tetrachloroethane, chloroform, carbon tetrachloride, trichloroethylene present in water in very low concentration by pervaporation. IPNs of different PMMA content and also different crosslink density were used. Since the selective permeation and diffusion of the VOCs through the membrane are dependent on their interaction with the membrane material, their sorption and diffusion behaviors through the membrane were also investigated by swelling the membrane in pure VOCs. The sorption and diffusion behaviors were explained with the help of their solubility parameter data and calculated interaction parameter data of the membrane polymers with the VOCs. From the swelling kinetics data, diffusion coefficients of the VOCs through the membrane were calculated. Diffusion coefficients increased with the increase in crosslink density and PMMA content in the membrane. In pervaporation experiment, concentrations of chlorinated organic compounds in feed were varied from 100 ppm (0.01%) to 1000 ppm (0.1%). All the three IPN membranes showed excellent separation performances of the chlorinated VOCs from water. One IPN containing 26% PMMA (PUU-PMMA-3) produced 88.7% trichloroethylene in permeate, trichloroethylene flux and a separation factor of 7842 from a 0.1% aqueous feed after a pervaporation run of 3 h at . All the three IPN membranes of different compositions have shown the separation performances, viz., flux and separation factor for all the VOCs in the order .     

A new method to determine the microbial kinetic parameters in biological air filters

This paper presents a new method to determine kinetic parameters of the biodegradation of various pollutants in a biofilter. Toluene, a readily biodegradable volatile organic compound, and methane, a hydrocarbon and a greenhouse gas, have been chosen as the target pollutants. The new protocol utilized biomass immobilized on bed pellets; these directly sampled from a continuous steady-state biofilter. The comparison of this method with the conventional experimental protocol utilizing micro-organisms suspended in a liquid medium was made using the pollutant toluene. Indeed, with both methods, the kinetic parameters have been evaluated by following the microbial growth in batch, thermostated reactors, using determined amounts of pollutant substrate. This experiment has confirmed the pertinence of the new procedure. The interesting features of the new method are that: (1) it is easy to operate (no preliminary treatment of the bed samples) and (2) it provides reproducible parameters that represent the real biofilter case more adequately than liquid cultures. In addition, modeling of the experimental specific growth rates in the case of toluene has shown that the values obtained with the use of solid extracts can be correlated by a Haldane's formulation, where , , and . The maximum specific growth rate was reached for an initial concentration of toluene near . The determination of the experimental specific growth rates of micro-organisms in the methane biofilter has also been performed. This study allowed highlighting two methane concentrations’ ranges: from 1000 to 14 500 ppmv and from 14 500 to 27 000 ppmv. For the first range, the Monod model proves to be suitable with the kinetic parameters: and . For the second range, neither the Monod nor the Haldane's formulation could directly be used. However, a mathematical adjustment of the Monod model allows to find kinetic parameters and . The biomass yields for the tested methane concentrations have also been determined and showed two different tendencies, depending on the same two ranges. For the first range of methane concentrations, the biomass yield was quite constant with an average value around while for the second range, it could be approached by a polynomial second-order regression. The maximum value of the biomass yield obtained on the second range was at a methane initial concentration of 20 000 ppmv.     

Measurement of intraparticle diffusion in reversed phase liquid chromatography

The intraparticle diffusion coefficient was measured using a method based on the fitting of a set of experimental chromatographic profiles to the lumped pore diffusion model. For this purpose, both the analytical solution of the model in the Laplace domain and a numerical method were used. There was an excellent agreement between the results given by the two methods. These results are compared to those obtained by moment analysis of the same set of chromatographic profiles and by the determination of the intraparticle diffusion coefficient from the second central moment of these bands. Nearly identical results were obtained with these two independent methods. The values of the intraparticle diffusion coefficient, D_e, for rubrene in pure methanol was found to be by the modeling method and by the moment analysis method. These values increase with increasing water concentration, to 1.10×10⁻⁶ and , respectively, in a methanol/water solution and to 1.63×10⁻⁶ and , respectively, in a solution.These results confirm the validity and the consistency of the lumped pore model and the moment analysis theory. They show that both approaches describe correctly the mass transfer kinetics in the particles of packing material during the chromatographic process. Systematic determinations of the intraparticle diffusion coefficient can now be undertaken and the influence of various experimental parameters on this important property of packing materials can be investigated.     

Anodic behaviour of zinc in methanol solutions of lithium perchlorate

Anodic dissolution of poly- and single-crystals of zinc was performed in methanol solution of lithium perchlorate by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The mechanism of anodic dissolution of zinc in organic solvents occurs in two oxidation steps. It is the first step that surface anodic product is created. Stability of the surface product is much better in anhydrous organic environments than in aqueous media; because the product is stable, a barrier layer composed of is formed at low anodic overvoltage. The formation of the layer is much stronger on the low index than on the high-index plane (0 0 0 1), where the adsorption of anodic product is more difficult.     

Observation and modelling of capillary flow occlusion resulting from the capture of superparamagnetic nanoparticles in a magnetic field

The magnetic field mediated capture of 10 nm diameter superparamagnetic nanoparticles, in the form of agglomerates of mean diameter 330 and 580 nm, from microcapillary flows has been observed and modelled. The steady state thickness of the captured layer in microcapillaries of diameter 400- could be predicted for both the 330 and the 580 nm diameter agglomerates at flow rates of between 0.1 and . The model provides insight into blockage formation at a constant flow rate as a precursor to the prediction of thrombotic embolism in magnetic directed therapies. Capillary constriction was particularly acute for the 580 nm agglomerates in large microcapillaries with flow rates of . From this model, agglomerates of diameter 330 nm or less offer the potential for minimal microcapillary occlusion in a range of flow rates.     

Synthesis, characterization and thermodynamic properties of poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone)

Poly(3-mesityl-2-hydroxypropyl methacrylate-co-N-vinyl-2-pyrrolidone) P(MHPMA-co-VP) was synthesized in 1, 4-dioxane solution using benzoyl peroxide (BPO) as initiator at 60 °C. The copolymer was characterized by ¹H ¹³C NMR, FT-IR, DSC, TGA, size exclusion chromatography analysis (SEC) and elemental analysis techniques. According to SEC, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of PMHPMA-co-VP were found to be 58,000, 481,000 g/mol and 8.26, respectively. According to TGA, carbonaceous residue value of PMHPMA-co-VP was found to be 6% at 500 °C. Also, some thermodynamic properties of PMHPMA-co-VP such as the adsorption enthalpy, ΔH_a, molar evaporation enthalpy, ΔH_v, the sorption enthalpy, , sorption free energy, , sorption entropy, , the partial molar free energy, , the partial molar heat of mixing, , at infinite dilution was determined for the interactions of PMHPMA-co-VP with selected alcohols and alkanes by inverse gas chromatography (IGC) method in the temperature range of 323-463 K. According to the specific retention volumes, , the weight fraction activity coefficients of solute probes at infinite dilution, , and Flory-Huggins interaction parameters, between PMHPMA-co-VP-solvents were determined in 413-453 K. According to and , selected alcohols and alkanes were found to be non-solvent for PMHPMA-co-VP at 413-453 K. The glass transition temperature, T_g, of the PMHPMA-co-VP found to be 370 and 363 K, respectively, by IGC and DSC techniques, respectively.     

High strength wastewater treatment in a jet loop membrane bioreactor: kinetics and performance evaluation

Treatment of wastewater containing high organic matter was investigated by means of a jet loop bioreactor combined with a membrane process. Volume of jet loop bioreactor and area of membrane filtration unit were 23 l and 155 cm² respectively. It was found that jet loop reactor had high mass transfer coefficient (K_La) varying from 58.8 to 486 h^-1 depending on the water flow rate (i.e. power input) and air flow rate. Oxygen transfer efficiency and oxygenation capacity of the reactor varied from 12 to 22.5% and from 0.2 to 1.8 , respectively. The efficiency of jet loop membrane bioreactor was found to be approximately 97% for a volumetric organic load of 2- over a period of 10 weeks. The reactor was not disturbed from the organic loads up to , but the treatment efficiency decreased to about 60% at higher organic loads. This decrease was due to insufficient oxygen transfer rate. The relationship between the effluent substrate concentration and the specific oxygen uptake rate (SOUR) values was determined. Applied food/microorganism (F/M) ratio was varied between 2.5 and . Critical sludge age of the system () was evaluated to be 7.2 h. Sludge with unsatisfactory settling characteristics formed at high F/M values under turbulent conditions. Therefore, membrane process was used for solid-liquid separation and effluent solid concentration was approximately zero. Specific cake resistances (α) changed with F/M ratio. It was found that permeate fluxes were significantly effected with F/M ratio much more than mixed liquor suspended solids (MLSS). Average flux was for pore sized cellulose acetate membrane. It was concluded that the jet loop membrane bioreactor has distinctive advantages such as the ability to treat high strength wastewater, low area requirements and easy operation.     

Pervaporation of dilute alcoholic mixtures using PDMS membrane

Pervaporation (PV) of methanol/water and ethanol/water mixtures through PDMS membrane was investigated using a PV cell (in laboratory scale). PDMS membrane is a well-known hydrophobic membrane for removing organics from aqueous mixtures. Experimental results were obtained at different initial alcohol (methanol and ethanol) concentrations (0.3-3 wt%) and temperatures (30-). Recirculation flow rate was kept constant at a value of 15.6 l/h. Average permeation flux (j), separation factor (α) and activation energy of permeation (E_P) were calculated. Separation factor of PDMS membrane for methanol was greater than that for ethanol. Total flux for methanol/water and ethanol/water mixtures was observed to vary from 0.37 to 0.56 and 0.52 to 0.90 at , respectively, as alcohol concentration changed from 0.3 to 3 wt%. Separation of alcohols depends on both their selective sorption in polymeric membrane and their diffusivity. The most important observation was that separation factor of methanol/water mixtures is greater than that of ethanol/water mixtures and it is because of different molecular size of alcohols. Different behavior of alcohol/water mixtures can also be explained in the entire concentration range studied using relative values of solubility parameters of the alcohols. It can be due to the fact that activation energy of alcohol permeation increases as solubility parameter difference between alcohol and membrane increases.