Selective Conversion of Glycerol to Propylene Glycol Over Fixed Bed Raney® Cu Catalysts

Net propylene glycol (1,2 propanediol) yields of up to 94% at 100% glycerol conversion have been achieved over a fixed bed Raney^® Cu catalyst in trickle bed mode, at relatively low total pressure, 14 bar (200 psig), and minimal feedstock dilution (20 wt% water). The main identified byproducts are ethylene glycol and ethanol (each <2%), with methanol and 1,3 diol both <1%. The other key operating parameters for high yields are a narrow optimum in temperature (near 205 °C), and a high H₂/liquid flow ratio, about 375/0.05 by volume. The effects of chromium promotion have also been studied for effects on side reactions and rates. Our evidence points to initial dehydrogenation as the rate-limiting step in a likely three step mechanism.     

Adsorption of CO2 on Hydrotalcite‐like Compounds in a Fixed Bed

Abstract

The reduction of carbon dioxide emission from flue gases can be achieved using post‐combustion technologies, such as adsorption employing efficient solid sorbents. In this work, the adsorption of CO₂ on hydrotalcite‐like Al‐Mg compounds partially carbonated was studied using dynamic and static methods. The breakthrough curves were obtained at different flow gas rates in the range 60 to 100 mL/min and total pressure 1.0 atm. Different mixtures of CO₂ diluted in helium were used (3–20% v/v) at temperatures in the range 29 to 350°C. The experimental equilibrium data were described according to a Langmuir‐like equation. The capacity of adsorption presented a weak dependence on the temperature due to opposite effects of increasing of entropy and increasing of MgO (non‐carbonated) content in the adsorbent at high temperatures. The linear driving force model was suitable to describe the breakthrough curves. The dispersion and mass transfer coefficients were calculated by theoretical correlations and the model described quite very well the adsorption of CO₂ on hydrotalcite‐like compounds in a fixed bed in any temperature.     

Study of the Fixed‐Bed Adsorption Behavior of Phenylalanine on Solvent Impregnated Resins,Part III

Abstract

The implementation of the SIR technique for the amino acid separation from diluted aqueous solutions in a fixed‐bed column is presented and a mathematical model for the prediction of the adosrption behavior is developed. Independently determined equilibrium and kinetic parameters are used for the calculation of the breakthrough curves. Fixed‐bed parameters, such as axial dispersion and bed porosity, are determined experimently and compared with correlations. Analysis of the Biot and Bodenstein number reveal that the mass transfer through the film liquid around the particles, as well as the axial dispersion in the column, could be neglected at the studied experimental conditions. A simplified mathematical model was found to give the best prediction to the experimental breakthrough curves over a wide range of feed concentrations and flow rates.     

Breakthrough Data Analysis of Adsorption of Toluene Vapor in a Fixed‐Bed of Granular Activated Carbon

Abstract

Toluene vapor was adsorbed in a laboratory‐scale packed‐bed adsorber using granular activated carbon (GAC) at constant pressure (101.3 kPa). The adsorber was operated batchwise with the charge of GAC in the range of 2–4 g to obtain the breakthrough curves of toluene vapor. Experiments were carried out at different adsorption temperatures (25–50°C), sparger temperatures (20–30°C), and the flow rates of nitrogen (80–150 cm³/min) to investigate the effects of these experimental variables on the breakthrough curves. The deactivation model was tested for these curves by combining the adsorption of toluene vapor and the deactivation of adsorbent particles. The observed values of the adsorption rate constant and the deactivation rate constant were evaluated through analysis of the experimental breakthrough data using a nonlinear least squares technique. The experimental breakthrough data were fitted very well to the deactivation model than the adsorption isotherm models in the literature.     

Adsorption and Thermal Desorption of Volatile Organic Compounds in a Fixed Bed – Experimental and Modeling

Adsorption and thermal desorption dynamics of acetone in fixed-bed silica gel were studied experimentally and theoretically. The effect of process factors on adsorption and desorption performances was established. Acetone adsorption from air stream was performed by the dynamic (flowing gas) method in a laboratory setup at two levels of air superficial velocity (0.7 and 1.7 cm s^?1), temperature (30 and 40°C), and adsorbent particle diameter (0.21 and 0.54 cm). The values of saturation adsorption capacity (0.147–0.270 g g^?1) increased up to 78% and 36%, respectively, with a decrease in air velocity and adsorption temperature. Acetone thermal desorption from spent silica gel was studied in a thermobalance at three levels of process temperature (60, 70, and 80°C) and two values of particle size (0.21 and 0.54 cm). Equilibrium desorption efficiency (63–81%) was up to 14% larger for finer particles and increased with the desorption temperature. Kinetic models with relevant parameters adjusted based on experimental data were adopted to predict the dynamics of acetone adsorption and thermal desorption. The models simulated well the real conditions and could be applied to scale up and operate the adsorption columns used for air remediation.     

Fixed‐Bed Removal of Free and Complexed Ni from Synthetic and Industrial Aqueous Solutions

Abstract

This paper evaluates the application of several biosorbents for Ni removal from aqueous solutions in the absence and in the presence of EDTA. Fixed bed experiments were performed (Ni influent concentration, 2 mg dm^?3; EDTA doses, 0, 5, and 10 mg dm^?3; pH=7) to study the process feasibility as refining after conventional physicochemical treatment. In absence of EDTA, uptake capacity followed the order peat > Posidonia oceanica > chitosan > chitin ? Scharlau AC. Maximum uptakes of 8.95 mg g^?1 and 5.10 mg g^?1 were found for peat and Posidonia oceanica, respectively. In the presence of EDTA, removal capacity decreased for all biosorbents; Ni was detected in the effluent from the beginning of the operation, indicating low ability to retain Ni EDTA‐complexes. Activated carbon presented the ability to remove complexed Ni. Peat exhibited the best performance for the treatment of an industrial spill from a metal‐finishing facility, with effluent Ni concentration lower than 0.2 mg dm^?3 for more than two weeks of treatment (3500 pore volumes of treated wastewater).     

Adsorption Characteristics of Toluene and p‐Xylene in a Reversed‐Phase C18 Column for Simulated Moving Bed Chromatography

Abstract

The adsorption equilibria and transport properties of toluene and p‐xylene on a Eurosil 100‐30‐C₁₈ column were measured from a chromatographic response in a reversed‐phase HPLC. Moment method was applied to the effluent peaks obtained from various temperatures and eluent compositions. The adsorption equilibrium constants were obtained from the first moment analysis. On the other hand, the transport properties such as the axial dispersion coefficient and effective diffusivity were obtained from the second moment analysis. The simulated results of the simulated moving bed process using the parameters obtained from the moment analysis agreed well with the experimental results. And the separation of toluene/p‐xylene mixture could be successfully separated by the simulated moving bed process.     

Acidity of Zeolite Y—Probed by Adsorption of 1-Naphthylamine and Studied by Laser-Induced Fluorescence Spectroscopy

Proton transfer reactions between zeolite Y surface and 1-naphthylamine (NA) in the ground and excited states have been studied by laser-induced picosecond spectroscopy. The acidic form of zeolite Y readily protonates NA in the ground state. At low acid strength of the zeolite the excited state of the protonated NA transfers back the proton to the zeolite surface as indicated by the fluorescence spectra. At high acid strength of the zeolite the fluorescence comes from the protonated form of NA and from an adduct X previously found in highly concentrated HClO₄ solutions. The concentrations of the protonated NA and X increase with the reduction in the unit cell size. The presence of these species is discussed in terms of the next nearest neighbor NNN theory of zeolite Y acidity and the role of the non-framework aluminum. The acidity of the zeolite is estimated, based on the fluorescence lifetimes of X, to vary from 3.7 to 17 M HClO₄ depending on the unit cell size. Low loading levels of NA in the zeolite pores are best in studying the proton transfer reaction and for the estimation of the surface acidity of zeolite Y.     

Uptake of Fluoride by Al3+ Pretreated Low‐Silica Synthetic Zeolites: Adsorption Equilibrium and Rate Studies

Abstract

The removal of fluoride from single component aqueous solution using Al³⁺‐ pretreated low‐silica synthetic zeolites (Al‐Na‐HUD, Al‐HUD, Al‐F9, and Al‐A4) was studied. The effects of adsorbent mass, initial solution pH, and initial concentration on fluoride removal in a batch system were evaluated. Equilibrium data were simulated using simple isotherms such as the Freundlich (F), Langmuir‐Freundlich (LF), Redlich‐Peterson (RP) and Dubinin‐Radushkevitch (DR) isotherms. From the DR model, initial pH effects and desorption studies, it was considered that the fluoride adsorption onto the zeolites proceeded by ion‐exchange or chemisorption mechanism. In interpreting the kinetic results, reaction kinetics (using Elovich equation) and mass transfer processes (both external mass transfer and intraparticle diffusion) were considered. Equilibrium and kinetic results of fluoride adsorption onto the adsorbents demonstrated the following order of performance: Al‐Na‐HUD>Al‐F9> Al‐HUD>Al‐A4.     

Influence of the Steric Hindrance,Ligand Hydrophobicity,and DN of solvents on Structure and Extraction of Cu(II) Complexes of 1‐Alkyl‐2‐Ethylimidazoles

Abstract

Formation of Cu(II) complexes of 1‐alkyl‐2‐ethylimidazoles (where alkyl=propyl, butyl, pentyl, hexyl, and octyl) has been studied by using the liquid‐liquid partition method, at 25°C and a fixed ionic strength of the aqueous phase (I=0.5; (HL)NO₃, KNO₃). The complexes were extracted with 2‐pentanone, 2‐butanol, isoamyl alcohol, 2‐ethyl‐1‐hexanol, dichloromethane, trichloromethane, and toluene. The length of the 1‐alkyl group and the nature of solvent have been shown to influence the extraction process. Extraction curves (log D_M vs. pH) are displaced towards lower pH's with increasing chain length of the 1‐alkyl substituent and donor number of the solvents. Stability constants of the complexes in aqueous solution were determined as well as their partition ratios between the aqueous and organic phase. The stability of the Cu(II) complexes increased with increasing 1‐alkyl chain length. The stability constants are comparable with β_n ones for the Cu(II) complexes of 1‐alkyl‐2‐methylimidazoles, but smaller than those of the Cu(II)–1‐alkylimidazole counterparts. The P_c‐partition ratios of the 1‐alkyl‐2‐ethylimidazole complexes with Cu(II) are high, and increased with increasing 1‐alkyl chain length and the donor number of the solvents. Both the strong steric effect of the ethyl substituent at position 2 and the bulkiness of the 1‐alkyl‐2‐ethylimidazole molecules as well as the strong electron‐donating properties of the solvent molecules have an effect on the change of the coordination number of Cu(II) from 6 to 4. The 4‐coordinate Cu(II) complexes (distorted tetrahedron) are more readily extractable by organic solvent than are the 6‐coordinate ones and for this reason their partition constants, P_c, are high. This finding offers the possibility of extraction of the Cu(II) ions from a mixture cations.     

Characterization of Extraction of Chromatographic Materials Containing Bis(2‐ethyl‐1‐hexyl)Phosphoric Acid, 2‐Ethyl‐1‐Hexyl (2‐Ethyl‐1‐Hexyl) Phosphonic Acid,and Bis(2,4,4‐Trimethyl‐1‐Pentyl)Phosphinic Acid

Abstract

This work describes the uptake of a wide range of metal ions, including alkaline earths, transition metals, post‐transition metals, lanthanides and actinides, from acidic nitrate and chloride media on extraction chromatographic resins prepared from three different acidic organophosphorus compounds: bis(2‐ethyl‐1‐hexyl) phosphoric acid (HDEHP), 2‐ethyl‐1‐hexyl(2‐ethyl‐1‐hexyl)phosphonic acid, (HEH[EHP]) and bis(2,4,4‐trimethyl‐1‐pentyl)phosphinic acid (H[DTMPP]). The data is plotted in a format allowing for the easy comparison of the uptake of all metal ions under a given condition. Additionally, examples of several novel separations using the three extraction chromatographic materials are discussed.     

EPR Study of CO Adsorption onto CoZSM-5 Zeolite: Evidence for Spin Crossover upon Coordination and |z2, 2A1〉 Ground State

Adsorption of CO onto dehydrated cobalt-exchanged ZSM-5 zeolite was studied by CW-EPR techniques. It is shown that the reversible formation of a low spin carbonyl ¹{Co(CO) _n }⁷ adduct upon addition of carbon monoxide at p _CO>50–60 Torr involves significant change in the spin state of Co²⁺ from S=3/2 to 1/2. The spin Hamiltonian parameters of the adduct g _x =2.222, g _y =2.184, g _z =2.011, |A _x |=3.8 mT, |A _y |=3.2 mT, |A _z |=7.9 mT were determined by a computer simulation and further discussed in terms of the possible ground state and molecular structure. It is shown that the ¹{Co(CO) _n }⁷ cage complex exhibits a C_2v symmetry with |z ²,²A₁ ground state.     

Adsorption Characteristics of Benzaldehyde,Sulphanilic acid,and p‐Phenolsulfonate from Water,Acid, or Base Solutions onto Activated Carbon Cloth

Abstract

Adsorption of benzaldehyde (BA), sulphanilic acid (SA), and sodium salt of p‐phenolsulfonic acid (p‐PhS) from water, acid, or base solutions onto activated carbon cloth (ACC) was studied by in‐situ UV‐spectrophotometric method. Kinetics of adsorption was followed over 90 min and the data were fitted to first order rate law. The order of rate of adsorption was found to be BA>SA≈p‐PhS in water, BA>p‐PhS>SA in 1 M H₂SO₄ and BA>SA >> p‐PhS in 0.1 M NaOH. Competitive adsorptions of BA and SA from an equimolar mixture in 1 M H₂SO₄ and of BA and p‐PhS from an equimolar mixture in H₂O were studied for exploring the possibilities of separation of binary mixtures. It was found that p‐PhS was not adsorbed at all from 0.1 M NaOH solution. Adsorption isotherms of BA, SA, and p‐PhS at 30°C were derived and the data were fitted to the Langmuir and Freundlich models. The Freundlich model was found to represent the experimental data better than the Langmuir model.     

Retention,Thermodynamics and Adsorption Profile of Th(IV) Ions onto 1‐(2‐Pyridylazo)‐2‐Naphthol (PAN) Loaded Polyurethane Foam from Acetate Media and its Separation from Rare Earths

Abstract

The sorption behavior of 2.7×10^?5 M solution of Th(IV) ions on 1‐(2‐pyridylazo)‐2‐naphthol (PAN) loaded polyurethane foam (PUF) has been investigated. The quantitative sorption was occurred from pH 6 to 9 from acetate buffer solutions. The sorption conditions were optimized with respect to pH, shaking time, and weight of sorbent. The sorption data followed the Freundlich, Langmuir, and Dubinin‐Radushkevich (D‐R) isotherms very successfully at low metal ions concentration. The Freundlich isotherm constant (1/n) is estimated to be 0.22±0.01, and reflects the surface heterogeneity of the sorbent. The Langmuir isotherm gives the maximum monolayer coverage is to be 8.61×10^?6 mol g^?1. The sorption free energy of the D‐R isotherm was 17.85±0.33 kJ mol^?1, suggesting chemisorption involving chemical bonding was responsible for the adsorption process. The numerical values of thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) indicate that sorption is endothermic, entropy driven, and spontaneous in nature. The adsorption free energy (ΔG_ads) and effective free energy (ΔG_eff) are also evaluated and discussed. The effect of different anions on the sorption of Th(IV) ions onto PAN loaded PUF was studied. The possible sorption mechanism on the basis of experimental finding was discussed. A new separation procedure of Th(IV) from synthetic rare earth mixture using batch, column chromatography, and squeezing techniques were reported.     

Removal of Copper and Lead from Aqueous Solution by Adsorption onto Cross-Linked Chitosan/Montmorillonite Nanocomposites in the Presence of Hydroxyl–Aluminum Oligomeric Cations: Equilibrium,Kinetic, and Thermodynamic Studies

Adsorption removal of Cu (II) and Pb (II) on cross-linked chitosan/Al₁₃-pillared montmorillonite (CCPM) was examined in solutions. The chitosan dosage was drastically reduced in the new nanocomposite, which is made from the treated clay (Al₁₃-pillared montmorillonite). Several important parameters that influenced the adsorption of Cu (II) and Pb (II) ions, such as cross-linked chitosan-to-clay ratio, pH, temperature, initial concentration, dosage, and contact time effect, were systematically investigated. Result showed that in the nanocomposite with cross-linked chitosan-to-clay ratio of 0.45:1, the maximum removal efficiencies of Cu (II) [pH 6.5, dosage 10 g/L, initial Cu (II) concentration 100 mg/L, contact time 2 h, 298 K] and Pb (II) [pH 6.0, dosage 5 g/L, initial Pb (II) concentration 100 mg/L, contact time 2 h, 298 K] were 96.0% and 99.5%, respectively. Kinetic and isotherm studies have indicated that the adsorption process of Cu (II) or Pb (II) nanocomposites was better fitted by the pseudo-second-order equation and the Freundlich equation, with chemical adsorptions as the rate-limiting step. The metal–ion affinity to the functional groups of CCPM followed the order Pb (II) > Cu (II). The thermodynamic parameters ΔH and ΔS values showed that the sorption process of Cu (II) or Pb (II) was spontaneous (ΔG < 0), was endothermic (ΔH < 0), and had decreased entropy (ΔS < 0). HNO₃ (0.1 M) could be a good desorbent in the recovery of metal ions after adsorption and regeneration of the adsorbent.     

Effect of Ce,Sb and Sn on mechanism and activation energy for crystallisation of X‐ray irradiated photosensitive glass

Abstract

Abstract

This work aims to determine the effect of Ce, Sb, Sn and Ag on the mechanism and activation energy of crystallisation for an X‐ray irradiated photosensitive lithium silicate glass composition and to compare it with the one that contained only Ag. According to the obtained results, while the addition of Ce, Sb and Sn changed the crystallisation mechanism of lithium silicate crystal from two‐ to three‐dimensional growths, these additions did not affect the activation energy of crystallisation for lithium metasilicate. Differential thermal analysis was used for studying the mechanism and activation energy for crystallisation of these glasses through the Matusita and the modified Kissinger methods; SEM and XRD were used to investigate the lithium silicate and silver crystallisation in the glasses.     

Propane Ammoxidation over Mo–V–Te–Nb–O M1 Phase Investigated by DFT: Elementary Steps of Ammonia Adsorption,Activation and NH Insertion into π-Allyl Intermediate

The selective ammoxidation of propane into acrylonitrile catalyzed by the bulk Mo–V–Te–Nb–O system has received significant attention because it is more environmentally benign than the current process of propene ammoxidation and relies on more abundant propane feedstock. The reaction mechanism is proposed to consist of a series of elementary steps including propane oxidative dehydrogenation, ammonia and O₂ activation, and NH_x insertion into C₃ intermediates. In this study density functional theory calculations have been performed to investigate the energetics of ammonia adsorption and activation in the proposed active center in the ab plane of the M1 phase. The formation of NH _x (x = 0, 1, 2, 3) species is found to be highly favored on reduced, oxo-depleted metal sites. The reduced Mo site is determined to be the most favorable site for ammonia activation by comparing the reaction energy profiles for the sequential dehydrogenation of ammonia on the various metal sites. The activation barrier for the initial H abstraction from ammonia was found to depend strongly on the surface sites that stabilize H and NH₂, and is as low as 0.28 eV when NH₂ is stabilized by the reduced Mo site and H is abstracted by the telluryl oxo group. The subsequent step of surface NH insertion into a π-allyl gas intermediate was also found to have a low activation energy barrier of 0.03 eV on the reduced Mo site.     

Adsorption of Off‐Gases from Steam Methane Reforming (H2, CO2, CH4, CO and N2) on Activated Carbon

Abstract

Hydrogen is the energy carrier of the future and could be employed in stationary sources for energy production. Commercial sources of hydrogen are actually operating employing the steam reforming of hydrocarbons, normally methane. Separation of hydrogen from other gases is performed by Pressure Swing Adsorption (PSA) units where recovery of high‐purity hydrogen does not exceed 80%.

In this work we report adsorption equilibrium and kinetics of five pure gases present in off‐gases from steam reforming of methane for hydrogen production (H₂, CO₂, CH₄, CO and N₂). Adsorption equilibrium data were collected in activated carbon at 303, 323, and 343 K between 0‐22 bar and was fitted to a Virial isotherm model. Carbon dioxide is the most adsorbed gas followed by methane, carbon monoxide, nitrogen, and hydrogen. This adsorbent is suitable for selective removal of CO₂ and CH₄. Diffusion of all the gases studied was controlled by micropore resistances. Binary (H₂‐CO₂) and ternary (H₂‐CO₂‐CH₄) breakthrough curves are also reported to describe the behavior of the mixtures in a fixed‐bed column. With the data reported it is possible to completely design a PSA unit for hydrogen purification from steam reforming natural gas in a wide range of pressures.