Methanol oxidation over model cobalt catalysts: Influence of the cobalt oxidation state on the reactivity

X-ray photoelectron and absorption spectroscopies (XPS and XAS) combined with on-line mass spectrometry were applied under working catalytic conditions to investigate methanol oxidation on cobalt. Two cobalt oxidation states (Co₃O₄ and CoO) were prepared and investigated as regards their influence on the catalytic activity and selectivity. In addition adsorbed species were monitored in the transition of the catalyst from a non-active state, to an active one. It is shown that the surface oxidation state of cobalt is readily adapted to the oxygen chemical potential in the CH₃OH/O₂ reaction mixture. In particular, even in oxygen-rich mixtures the Co₃O₄ surface is partially reduced, with the extent of surface reduction following the methanol concentration. The reaction selectivity depends on the cobalt oxidation state, with the more reduced samples favouring the partial oxidation of methanol to formaldehyde. In the absence of oxygen, methanol effectively reduces cobalt to the metallic state, also promoting H₂ and CO production. Direct evidence of methoxy and formate species adsorbed on the surface upon reaction was found by analysing the O 1s and C 1s photoelectron spectra. However, the surface coverage of those species was not proportional to the catalytic activity, indicating that they might also act as reaction inhibitors.     

Liquid-phase synthesis of methanol using industrial copper-zinc catalyst

The industrial copper-zinc catalyst MEGAMAX®-phase synthesis of methanol was tested under the conditions of a liquid-phase process while varying the pressure (0.5–7.0 MPa) and the gas mixture flow rate (40–400 mL_N/min). The catalyst was shown to have high activity and selectivity in the synthesis of methanol. The best result (730 g(methanol)/kg(cat) h^?1 and selectivity 99.2%) was obtained under reaction conditions of 2.0 MPa, 240°C, H₂: CO: CO₂: N₂ = 70.5: 17.9: 6.5: 5.1, and reaction time 3 h. The concentration of methane by-product increased at gas mixture pressures over 3.0 MPa, lowering the selectivity of the process with respect to methanol. Trace amounts of ethane and water were found in addition to methane. Dimethyl ether, a typical by-product of methanol synthesis, was missing from the vapor-gas mixture over the range of pressures. The results from this study indicate that the MEGAMAX® can be used in the liquid-phase synthesis of methanol.     

Methanol synthesis on a Cu(100) catalyst

The synthesis of methanol on a Cu(100) single crystal surface was studied between 500–550 K and at pressures between 44–102 kPa using a gas mixture of CO₂/CO/H₂ = 1/2/12. The specific reaction rates found for methanol synthesis were approximately an order of magnitude lower than those rates previously reported for silica supported, Cu-based catalysts. Furthermore the rates observed for the Cu(100) catalyst are estimated to be several orders of magnitude smaller than those rates found for ZnO supported Cu catalysts at comparable reaction conditions. The very low concentration of ionic copper species on the surface is thought to be responsible for the low activity of the Cu(100) catalyst.     

Some aspects of removal of copper and cobalt from mixed ion dilute solutions

Some aspects of the electrodeposition of copper and cobalt from aqueous sulphate solutions containing low concentrations of their ions were studied with a view to heavy metal removal via an electrochemical process. Both metals were deposited on a vitreous carbon rotating disc electrode. Deposits formed under different conditions were studied employing linear sweep voltammetry, scanning electron microscopy and EDAX surface analysis. Constant potential electrolysis was used to simulate recovery in a laboratory batch reactor. Copper can be deposited without cobalt interference at potentials as cathodic as –1.0 V despite high Co concentrations. At more negative potentials, both metals are deposited simultaneously, although the copper proportion in the binary mixture is greater than that corresponding to the solution concentration ratio. Voltammetry studies effected under conditions in which codeposition occurs show only minor changes in copper behaviour. On the other hand, cobalt behaviour exhibits significant modifications. Even though formation of an intermetallic compound is possible, ASVL and microscopy tests indicate cobalt deposition in different crystalline forms as the more probable cause. In turn, cobalt deposition depends on the polarization conditions of the electrode and on the cobalt and copper concentrations.     

A simulation study on selection of optimized process for azeotropic separation of methanol and benzene: Internal heat integration and economic analysis

This work provides an insight into the separation of azeotropic mixtures by using two different techniques: pressure swing distillation and extractive distillation. Both methods are used to separate an azeotropic mixture of methanol and benzene. This mixture exhibits a minimum boiling azeotrope at temperature 57.97 °C and pressure 1 bar with mole fractions of 0.61 and 0.39 for methanol and benzene, respectively. However, the azeotropic point in methanol and benzene mixture is pressure sensitive, which can be shifted by changing pressure with a process called pressure swing distillation. Extractive distillation with suitable solvent is another method to separate such kind of mixture. Both methods are rigorously simulated and optimized for minimum heat duties. Internal heat integration is applied too for increasing energy efficiency. New optimization techniques are carried out with process simulator Aspen HYSYS V8.4 and results reveal the best method for separation of methanol and benzene azeotropic mixture.     

Synthesis and catalytic behaviors of cobalt nanocrystals with special morphologies

Cobalt nanocrystals with highly ordered snowflake-like, cauliflower-like, ball-like morphologies, and some less ordered shapes were prepared through the reduction of Co(NO₃)₂ by hydrazine hydrate in the solution of methanol, ethanol, ethylene glycol, and 1,2-propanediol. Based on the characterization results of X-ray powder diffraction and scanning electron microscope, crystal and morphologic structures of cobalt particles were correlated with the reaction conditions of temperature, Co(NO₃)₂ concentration, and the alcohols used. By changing temperature and/or Co(NO₃)₂ concentration, pure hexagonal close-packed (hcp) cobalt or a mixture of hcp and face-centered cubic (fcc) cobalt was obtained. The catalytic performance of as-prepared cobalt nanocrystals for the thermal decomposition of ammonium perchlorate (AP) was evaluated by differential scanning calorimetry. The decomposition temperature of AP was significantly decreased, and the apparent decomposition heat was over doubled when 2 wt.% cobalt was added into AP. Among the samples tested, snowflake-like cobalt showed the best performance in the aspect of decreasing the decomposition temperature of AP while the ball-like cobalt exhibited the highest apparent decomposition heat.     

Describing the sorption characteristics of a ternary system of benzene (1) and alcohol (2) in a nonporous polymer membrane (3) by the Flory–Huggins model

The Flory–Huggins equation was used to describe results of total and preferential sorption measurements for the binary liquid mixture of benzene (1) and alcohol (2) in one of two nonporous polymer membranes (3), low‐density polyethylene (LDPE) and Nafion membrane. The concentration dependence of binary and ternary interaction parameters was determined. The interaction parameters for the benzene – methanol binary mixture were obtained from binary vapor‐liquid equilibrium data in the literature to decrease the number of adjusted parameters. The results show that use of a ternary interaction parameter is necessary. Data treatment was performed assuming either no crystallinity or an average crystallinity typical for the studied membranes. Subsequently, the limiting activity coefficients of solutes in LDPE were calculated from the values of the interaction parameters and their values compared to values of the limiting activity coefficients of benzene and methanol in hypothetical liquid alkane with the same density as LDPE obtained by the UNIFAC method. POLYM. ENG. SCI., 55:1187–1195, 2015. © 2014 Society of Plastics Engineers     

The separation and recovery of copper(Ⅱ), nickel(Ⅱ), cobalt(Ⅱ), zinc(Ⅱ),and cadmium(Ⅱ) in a sulfate-based solution using a mixture of Versatic 10 acid and Mextral 984H

We studied the separation and recovery of copper(Ⅱ), nickel(Ⅱ), cobalt(Ⅱ), zinc(Ⅱ), and cadmium(Ⅱ) from magnesium and calcium, using synergistic solvent extraction(SSX) in a typical hydrometallurgical waste solution. A mixture of Versatic 10 acid and Mextral 984 H, diluted with Mextral DT100, was used to obtain fundamental data on p H and distribution isotherms, as well as the kinetics of extraction and stripping. We also investigated the main effects and interactions of common solvent extraction factors: the extraction p H at equilibrium, the temperature, and the extractant concentration. The synergistic effect for extracting metals was confirmed. The results showed that the addition of Mextral 984 H enhanced the separation factors of copper, nickel, cobalt,zinc, and cadmium over magnesium and calcium. Compared with Versatic 10 acid alone, for a mixture of0.5 mol·L~(-1) Versatic 10 acid/0.5 mol·L~(-1)Mextral 984 H, Δp H50 values of copper, nickel, cobalt, zinc, and cadmium were found to be N 2.0, 3.30, 2.85, 0.95, and 1.32 p H units, respectively. The Δp H_(50)(Zn–Mg)and Δp H_(50)(Zn–Ca)values were 3.27 and 2.25, respectively, indicating easy separation and recovery of copper, nickel, zinc, cobalt,and cadmium. The extraction and stripping of copper, cobalt, zinc, and cadmium were fast, with 90% of the metal transferred in 2 min. We next studied whether the metals could be stripped from the extracted liquid selectively in sequence, by using sulfuric acid at different concentrations. The influence of the molecular structure of the oxime and carboxylic acid components upon the synergistic effects was identified by numerical analysis.Excellent separation of copper, nickel, cobalt, and zinc over magnesium and calcium was achieved with this synergistic solvent extraction system.     

Quenching mechanism and kinetics of ascorbyl palmitate for the reduction of the gamma irradiation-induced oxidation of oils

The effects of 0, 250, 500, and 1000 ppm (wt/vol) ascorbyl palmitate (AP) on the gamma irradiation-induced oxidation of soybean oil, cottonseed oil, corn oil, tallow, lard, or linoleic acid either in a solvent mixture (benzene/methanol, 4:1 vol/vol) or in methanol, was studied immediately after gamma irradiation with a dose of 1–5 kGy. Steady-state kinetic approximation was used to determine a quenching mechanism and quenching rate constant of AP on the gamma irradiation-induced oxidation of purified soybean oil in a solvent mixture (benzene/methanol, 4:1 vol/vol). Irradiation greatly increased oxidation of all oils, as was expected. AP was extremely effective at minimizing oxidation in all oils, and its effectiveness was concentration dependent. AP showed significantly greater antioxidative activity than α-tocopherol for the reduction of oxidation in all oils (P<0.05). The steady-state kinetic studies indicated that AP quenched oxygen only to minimize the oxidation of oils. The calculated total quenching rate of AP was 7.51×10⁷ M⁻¹s⁻¹. The present results clearly show the effective oxygen quenching ability of AP for the reduction of gamma irradiation-induced oxidation of oils.     

Characterization of some poly(methyl methacrylate) prepared by emulsion polymerization in presence of egyptian delta titano magnetite ore (EDTMO)

The emulsion polymerization of methyl methacrylate was studied in water using potassium persulphate as initiator and dedocyl–benzene sodium sulphonate as emulsifying agent at 85°C. The effect of Egyptian delta titano magnetite ore (EDTMO) upon the activation energy and on the mean average molecular weights of the obtained polymers was studied. It was found that the viscosity average molecular weights increase with decrease of reaction temperature and initiator concentration but increase with increase of monomer concentration in the reaction medium. Some of the polymer samples prepared in absence and in presence of some (EDTMO) were separated on tlc plates according to molecular weight in binary mixture, benzene:methanol (1:1.4 by volume) at 30°C. The tlc techniques were performed to give an idea about the molecular weight distribution of the polymer samples obtained.     

Flammability studies of benzene and methanol with various vapor mixing ratios at 150°C

Both benzene and methanol are important raw materials in petrochemical industries worldwide. However, with increased demand in the past few years, the fire and explosion hazards from both benzene and methanol under abnormal conditions have increased rapidly with the demand. This study investigated the flammability characteristics of a binary solution for the mixture of benzene and methanol at various vapor-mixing ratios (100/0, 75/25, 50/50, 25/75, 0/100 vol%) under 150°C, 760 and 1,520 mmHg by using a 20 Liter Spherical Explosion Vessel. Such work leads to specific safety-related property parameters, including upper explosion limit (UEL), lower explosion limit (LEL), minimum oxygen concentration (MOC), maximum explosion pressure (P _max ), maximum rate of explosion pressure rise (dP/dt) _max , and gas or vapor explosion constant (K _g ). Along with the results which show that the UEL, P_max, and K_g all increased with the pressure and oxygen concentration, a triangular flammability diagram was also established. This all serves to elucidate the potential hazards when vapors of different flammable chemicals are mixed. This paper was presented at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November 3 and 4, 2004.     

Studies on electrochemical oxidation of azithromycin and Hemomycin at gold electrode in neutral electrolyte

The aim of the present study was to examine the oxidative properties and an assay of azithromycin and Hemomycin^® at a gold electrode in neutral electrolyte using cyclic linear sweep voltammetry. The maximum value of the current of the oxidation peak of pure azithromycin and azithromycin from Hemomycin^® at 0.6 V versus SCE in 0.05 M NaHCO₃ and in a mixture methanol −0.05 M NaHCO₃ (1:1) at a scan rate of 50 mV s⁻¹ is a linear function of the concentration in the range of 0.235-0.588 mg/cm³. HPLC analysis of the bulk of electrolyte confirmed the data obtained by analysis of the values of the current peak concerning the concentration of antibiotic in the investigated concentration range. The role of methanol, when present, is discussed. In the case of azithromycin, the presence of methanol leads to higher current peak values. However, in the case of Hemomycin^®, methanol should be avoided because of its inhibiting influence on the qualitative and quantitative determination of azithromycin and on the azithromycin/lactose separation.     

Influence of noble metals on the performance of Co/SiO2 catalyst for 1-hexene hydroformylation

Effect of small amount of Pt, Pd and Ru promoters on the characteristics and performance of Co/SiO₂ catalyst, which was prepared from the mixture of cobalt nitrate and cobalt acetate, was investigated in the hydroformylation of 1-hexene. It was found that the addition of small amount of a noble metal to the supported cobalt catalyst led into great improvement of catalyst activity for hydroformylation of 1-hexene. The 1-hexene conversion as high as 89.7% and oxygenate products selectivity of 88.9% were obtained after reaction of 2 h over Pd promoted Co/SiO₂ catalyst. The increasing of reduction degree, the minimizing of cobalt particle size and the enhancement of carbonyl and linear CO adsorption were responsible for the improved performance of the catalyst.     

Catalysis over bimetallic zeolites: Influence of copper on the catalytic behaviour of nickel in sodium and hydrogen Y zeolites

The catalytic activity of a range of bimetallic nickel/copper zeolite catalysts prepared from NaY and NH₄Y as starting materials has been investigated; the reactions chosen were alkylation of toluene with methanol and the hydrogenation of benzene. The samples prepared from NH₄Y did not reduce benzene although they contained metallic nickel; this is attributed to nickel migration and agglomeration. All the catalysts were active in alkylation and there is evidence that a Cu:Ni ratio of 3:2 favours the formation of intrazeolitic clusters and confers increased acidity on the catalysts.     

Separation of benzene/cyclohexane by pervaporation through chelate poly(vinyl alcohol)/poly(allyl amine) blend membrane

Summary Chelate poly(vinyl alcohol)/poly(allyl amine) blend membrane was prepared and used for the separation of benzene/cyclohexane mixture by pervaporation processes. The coordination of benzene in the feed with cobalt in the membrane plays a major role in the separation of the mixture. Chelate poly(vinyl alcohol)/poly(allyl amine) blend membrane showed a preferential sorption toward benzene and was found to be more effective for permeating benzene in the benzene/cyclohexane mixture than an original Schiff base poly(vinyl alcohol)/poly(allyl amine) membrane.     

The Extraction of Divalent Manganese,Cobalt, Copper,Zinc, and Cadmium from Hydrochloric Acid Solutions by Tri-n-octylamine

Abstract

The distribution of divalent manganese, cobalt, copper, zinc, and cadmium between hydrochloric acid solutions and solutions of tri-n-octylamine (TOA, R₃N) in benzene has been investigated under different conditions. It is found that the extraction of these divalent metals by TOA proceeds as MCl₂(aq) + 2R₃NHCl(org) ? (R₃NH)₂MCl₄(org). The electronic, electron spin resonance, and infrared spectral results indicate that all the complexes formed in the organic phases are in a tetrahedral arrangement. Further, the stability constants of the aqueous chloro complexes of divalent manganese, cobalt, copper, and zinc are determined on the basis of the equilibrium equation.     

Wool graft copolymers initiated by azobisisobutyronitrile

Grafting of methyl methacrylate onto wool fibers using azobisisobutyronitrile as initiator has been investigated under a variety of conditions. Increasing the monomer concentration caused a significant increase in the graft yields. The same holds good for initiator concentration and reaction time, but to a lower degree. The grafting reaction was favorably influenced considerably by the nature of solvent used; it follows the order methanol > dimethylformamide > benzene. For practical significance, a mixture of water:methanol:DMF (75:24:1) was found to be the most effective medium for grafting. Presence of lithium chloride in the polymerization system favors grafting during the later stages of reaction, whereas presence of ceric sulfate was effective for higher grafting in the initial stages of reaction. Reduction of wool prior to grafting enhanced its ability to grafting; the latter increases in proportion to the thiol content. The opposite holds true for acetylation. Alkali solubility measurements reveal that an interaction between wool and methyl methacrylate in presence of AIBN took place.     

Formation of poly(methyl methacrylate) with novel solubility characters in the photopolymerization with bis(cyclopentadienyl)titanium dichloride in a water–methanol mixture

Methyl methacrylate (MMA) was observed to be easily polymerized in the photopolymerization with bis(cyclopentadienyl)titanium dichloride (Cp₂TiCl₂) in a water–methanol mixture under irradiation of a 15-W fluorescent room lamp. The polymerization proceeded heterogeneously. The rate (R_p) of heterogeneous photopolymerization in a 1 : 1 (v/v) water–methanol mixture at 40°C was apparently given by R_p=k[Cp₂TiCl₂]^0.2 [MMA]^2.4. The resulting poly(MMA) was found to contain a tetrahydrofuran (THF)-insoluble part. The separated THF-insoluble part differed significantly from the usual radical poly(MMA) in solubility characters. It is of great interest that the THF-insoluble poly(MMA) was soluble in benzene and toluene, but insoluble in polar solvents, such as ethyl acetate, acetone, methyl ethyl ketone, dimethylformamide, and dimethylsulfoxide. The copolymerization results of MMA and acrylonitrile revealed that the present photopolymerization initiated with Cp₂TiCl₂ proceeds via a radical mechanism. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 525–531, 1998     

Separation of copper from cobalt in sulphate solutions by using CaCO3

Lime neutralization is widely used to precipitate heavy metals including copper and cobalt from wastewater. Limestone (calcium carbonate: CaCO₃) is too stable to be used directly for this purpose. Grinding of CaCO₃ in the solutions of copper and cobalt sulphate was conducted to raise its reactivity. During the mechanochemical activation, CaCO₃ reacted with copper sulphate but not significantly with cobalt sulphate and this phenomenon allowed an easy separation of copper from cobalt. The residual of Cu(II) ions in solution could be controlled at less than 0.1%, meanwhile more than 90% of the Co(II) ions remained in aqueous solution.     

Electrooxidation of methanol and 2-propanol mixtures at platinum single crystal electrodes

In the present work the electrooxidation of methanol, 2-propanol and different mixtures of both alcohols has been studied on the three platinum basal planes in three different electrolytes (H₂SO₄, HClO₄ and NaOH). The results indicate that, like in the case of both individual alcohols, the electrooxidation of the mixture is a structure sensitive reaction and that Pt(1 1 1) leads to higher current densities for some mixture compositions as compared to what could be expected from the contribution of the individual compounds. The effect of the methanol concentration in the mixture points out that 2-propanol is the main reacting fuel at the Pt(1 1 1) surface. Interestingly, the addition of methanol clearly has a positive effect on 2-propanol oxidation. For a specific mixture composition, while results from cyclic voltammetry indicate a modest twofold increase in current density, chronoamperometric results after 10 min experiment show a nearly 200 times higher current density. IR experiments have been performed to gain information about the enhancement mechanism. Nevertheless, we have found that both methanol and 2-propanol seem to follow the same mechanism as they follow in the absence of the other alcohol, and therefore the enhancement could be probably related to a competitive adsorption for the active surface sites.