Effect of KOH on the continuous synthesis of cobalt oxide and manganese oxide nanoparticles in supercritical water

The effects of KOH on the supercritical hydrothermal synthesis of cobalt oxide and manganese oxide particles are investigated using a continuous-flow reactor. Significant changes in morphology, particle size, and oxidation state are observed by adding KOH. The spinel Co₃O₄ phase is transformed to a rocksalt CoO phase and the pyrolusite MnO₂ phase is transformed to a hausmannite Mn₃O₄ phase in the presence of 0.5 M KOH. The average particle size of the metal oxides decreased with an addition of KOH. The OH⁻ ions of KOH may act as a reducing agent as well as a supersaturation enhancing agent under supercritical water conditions.     

Electrocatalytic oxidation of methanol at Ni–Al layered double hydroxide film modified electrode in alkaline medium

Ni–Al–NO₃ layered double hydroxides (LDH) are electrodeposited on the glassy carbon (GC) electrodes and the electrocatalytic activities of the modified electrodes toward methanol oxidation are studied in detail by cyclic voltammetry and chronoamperometry. Various factors affecting the electro-oxidation of methanol are investigated for optimizing the electrocatalytic properties and making the mechanism clearly such as methanol concentration, scan rate, KOH concentration, Ni:Al ratio of Ni–Al LDH used. The results show that Ni–Al–NO₃ LDH exhibit higher electrocatalytic activity for methanol oxidation and better stability than that of Ni(OH)₂ prepared under the same condition. The LDH with Ni:Al ratio of 3:1 display a good electrocatalytic activity for methanol oxidation in 0.5 M KOH. The mechanism of methanol oxidation on Ni–Al LDHf/GC electrode is also proposed according to the experimental results, involving in both a chemical oxidation via Fleischmann's mechanism and a direct electro-oxidation on the Ni³⁺ oxide surface.     

Electrochemical and XPS investigations of cobalt in KOH solutions

The electrochemical behaviour of cobalt in KOH solutions of different concentrations was studied. The effects of applied potential, temperature and the presence of aggressive Cl^– ions were investigated. Different electrochemical methods such as open-circuit potential measurements, polarisation techniques and electrochemical impedance spectroscopy (EIS) were used. The electrochemical behaviour of cobalt in naturally aerated KOH solutions is characterized by three different regions according to the alkali concentration. Corrosion behaviour was observed at high concentrations (0.3–1.0 M); passivation at lower concentrations (0.01–0.05 M), and at intermediate concentrations (0.1–0.2 M) corrosion followed by passivation was recorded. The corrosion parameters (i _corr, E _corr, and R _corr) under various conditions were calculated. Equivalent-circuit models for the electrode–electrolyte interface under different conditions were proposed. The experimental impedance data were fitted to theoretical data according to the proposed models. The relevance of the proposed models to the corrosion–passivation phenomena occurring at the electrode–solution interface was discussed. The electrochemical experimental results and discussions were supported by surface analytical techniques.     

The electrochemistry of silver in KOH at elevated temperatures—IV. AC impedance study

The ac impedance properties of silver in 1 mol kg^?1 KOH were studied under potentiostatic conditions over the temperature range 295–478 K. Measurements were obtained over the frequency range 0.5 Hz–5 kHz, and were analyzed in terms of equivalent in terms of equivalent circuits. It was shown that provision for surface roughness is required for a satisfactory explanation of the impedance data. Values for the double layer capacity and the concentration AgO^? ions at the electrode surface could generally then be obtained. At potentials corresponding to the formation of Ag₂O, it is demonstrated that both diffusion in solution and diffusion in the oxide film are operative. At elevated temperatures, the rate of growth of Ag₂O centres is controlled partly by diffusion in the oxide and party by a reaction step at the growing interfaces of the centers. The subsequent formation of Ag₂O₂, at all temperatures in the range studied, is interpreted on the basis of an electrocrystallisation impedance.     

A comparative study of KOH loaded on double aluminosilicate layers, microporous and mesoporous materials as catalyst for biodiesel production via transesterification of soybean oil

Transesterification of soybean oil (TSO) with methanol to methyl esters (biodiesel) was found to proceed in the presence of KOH loaded on aluminosilicate layers (bentonite, kaolinite), microporous materials (zeolite Y, clinoptiloite), mesoporous materials (MCM-41, Al-MCM-41), some oxides (Al₂O₃, TiO₂, SiO₂), and silica gel as heterogeneous catalysts. Effect of reaction parameters such as KOH wt.%, amount of catalyst, reaction time, reaction temperature, molar ratio of methanol to oil and TSO yields up to 99% will be discussed in this presentation. Utilization of bentonite and kaolinite as cheap and eco-friendly solid supports is promising.     

Biodiesel from rapeseed oil,methanol and KOH. 3. Analysis of composition of actual reaction mixture

Detailed analysis is described of the samples taken after suitable reaction times from the actual reaction mixture during the production of biodiesel fuel using methanolysis of rapeseed oil catalyzed by KOH. Three methods for stoppage of reaction (neutralisation of catalyst, dilution by two suitable solvents) in the sample are used. The contents of mono‐, di‐ and triacylglycerols, methylesters of fatty acids (biodiesel) and potassium salts of fatty acids of rapeseed oil, glycerol (by HPLC method), basicity (by potentiometric titration) and water (by GC and Karl‐Fischer method) in the samples are determined. An example of these determinations is described.     

Liquid phase methanol and dimethyl ether synthesis from syngas

The Liquid Phase Methanol Synthesis (LPMeOH^TM) process has been investigated in our laboratories since 1982The reaction chemistry of liquid phase methanol synthesis over commercial Cu/ZnO/Al₂O₃ catalysts, established for diverse feed gas conditions including H₂-rich, CO-rich, CO₂-rich, and CO-free environments, is predominantly based on the CO₂ hydrogenation reaction and the forward water-gas shift reactionImportant aspects of the liquid phase methanol synthesis investigated in this in-depth study include global kinetic rate expressions, external mass transfer mechanisms and rates, correlation for the overall gas-to-liquid mass transfer rate coefficient, computation of the multicomponent phase equilibrium and prediction of the ultimate and isolated chemical equilibrium compositions, thermal stability analysis of the liquid phase methanol synthesis reactor, investigation of pore diffusion in the methanol catalyst, and elucidation of catalyst deactivation/regenerationThese studies were conducted in a mechanically agitated slurry reactor as well as in a liquid entrained reactorA novel liquid phase process for co-production of dimethyl ether (DME) and methanol has also been developedThe process is based on dual-catalytic synthesis in a single reactor stage, where the methanol synthesis and water gas shift reactions takes place over Cu/ZnO/Al₂O₃ catalysts and the in-situ methanol dehydration reaction takes place over -Al₂O₃ catalystCo-production of DME and methanol can increase the single-stage reactor productivity by as much as 80%. By varying the mass ratios of methanol synthesis catalyst to methanol dehydration catalyst, it is possible to co-produce DME and methanol in any fixed proportion, from 5% DME to 95% DMEAlso, dual catalysts exhibit higher activity, and more importantly these activities are sustained for a longer catalyst on-stream life by alleviating catalyst deactivation.     

Surface strengthening of building tiles by ion exchange with adding molten salt of KOH

The surface strengthening by ion exchange technology was used to improve the strength of thin building tiles. The effects of exchange time, exchange temperature, and content of KOH additive on strengthening of building tiles were investigated by analyzing the flexural strength and distribution of K⁺ in the samples. The results showed that the addition of .3 mol% KOH to the molten salt of industrial KNO₃ at 450°C for 5 h resulted in a maximum flexural strength of 86.53 MPa, which was 50.3% higher than that of the sample without ion exchange and 8.9% higher than without KOH addition. After ion exchange, the concentration of K⁺ ion in cross-section of the sample decreased with increasing distance from the sample surface, and the diffusion coefficient changed with the change of the content of KOH additive in the molten salt, increasing the diffusion coefficient of K⁺ ion from .93 × 10⁻¹⁵ to 1.8 × 10^–15 m²/s by adding .3 mol% KOH.     

Biodiesel fuel from rapeseed oil,methanol, and KOH. Analytical methods in research and production

The enumeration of the analytical methods used in the production of biodiesel from rapeseed oil and methanol catalyzed by KOH and published till 1997 is given. Some of our original methods for individual or simultaneous determination of the main components in the reaction mixture are described. All these methods can be also used to analyse the non-equilibrium complex and heterogeneous mixture.     

Porous structure and adsorptive properties of pineapple peel based activated carbons prepared via microwave assisted KOH and K2CO3 activation

The present research explores the feasibility of microwave irradiation for preparation of high surface area activated carbon from pineapple peel (PPAC), an agricultural effluent emitted from the food can processing industries via KOH and K₂CO₃ activation. The activation process was performed at the microwave power of 600 W and irradiation time of 6 min. The equilibrium behavior of PPAC was investigated by performing batch adsorption experiments using methylene blue as adsorbate. Nonlinear adsorption isotherm models, Langmuir, Freundlich and Temkin were used to simulate the equilibrium data. KOH activated sample demonstrated a better development of pore structure, with the BET surface area, total pore volume and average pore size of 1006 m²/g, 0.59 m³/g and 23.44 Å, respectively, while the monolayer adsorption capacity of methylene blue was determined to be 462.10 mg/g. The findings support the potential use of microwave assisted KOH and K₂CO₃ activation as a promising activation technique.     

Bubble behaviour during oxygen and hydrogen evolution at transparent electrodes in KOH solution

For oxygen and hydrogen evolving transparent nickel electrodes in KOH solutions, parameters characterizing the behaviour of bubbles which are adhered to the electrode surface during gas evolution, have been determined in dependence on current density, i, velocity of solution flow, v, pressure, p, temperature, T, and concentration of KOH. Based on experimental data a new basic bubble parameter, J, has been introduced, which accounts for the bubble behaviour. It has been found that J = a₁i^h₁ and J/(J₀?J) = a₂v^h₂ where J₀ = J at v = 0 ms^?1 and a₁,a₂h₁ and h₂ are empirical constants; some of these depend on nature of gas evolved. Moreover, the parameter J is almost proportional to the KOH concentration, increases in a decreasing rate with increasing pressure and increases linearly with the reciprocal of the absolute temperature.     

Feasibility of recycling KOH in chemical activation of oil‐sands petroleum coke

Although potassium hydroxide (KOH) is known to be effective in generating highly porous activated carbons, the mechanism of KOH activation has not been well elucidated. To develop porosity in carbon, a high KOH/carbon mass ratio must be maintained. Consequently, KOH, as the activating agent, represents a major part of the cost of the activation process. Focusing on the mechanism, particularly the activation products, the present work attempted to establish the technical feasibility of recycling KOH. Experiments revealed that the major products of KOH activation at 600–900°C are metallic K, K₂CO₃, CO and H₂, which is supported by thermodynamic analysis. The overall reaction may be written as 6KOH + 4C = K₂CO₃ + 4K + 3H₂ + 3CO. At temperatures over 900°C, K₂CO₃ becomes unstable and participates in activation reactions with carbon; a more suitable overall reaction would be KOH + C = CO + K + 0.5H₂. As potassium ion is reduced to metallic K which is readily converted into KOH and hydrogen gas upon reacting with water, KOH recycling is feasible. The reuse of KOH in chemical activation could substantially reduce the cost of activation process. © 2011 Canadian Society for Chemical Engineering     

Effect of KOH concentration in the gel polymer electrolyte for direct borohydride fuel cell

The performance of a direct borohydride fuel cell (DBFC) based on a polyacrylamide (PAAm) gel polymer electrolyte system is investigated at different electrolyte concentrations. The DBFC, constructed using 2M sodium borohydride (NaBH₄) as the fuel and potassium hydroxide (KOH) solution gelled with PAAm as the electrolytes yield the highest electrical conductivity of 2.73 × 10^?1 S cm^?1 at 6M KOH. The optimized composition, PAAm + 2M NaBH₄ + 6M KOH, and the selected composition, PAAm + 2M NaBH₄ + 3M KOH are then used in preparing the cells. Open‐circuit voltages for fuel cells is about 0.85–0.92 V, and the discharge characteristic produce discharge capacities of about 257.12–273.12 mAh cm^?2 for cells with PAAm‐6M KOH. Current‐voltage and current density‐power density plots and internal resistance for both cells are almost the same. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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.     

Nanoporosity development in the thermal-shock KOH activation of brown coal

Thermal-shock KOH activation of brown coal (800 °C, KOH/coal ratio 1 g/g) was shown to produce nanoporous activated carbon with more developed surface area than thermally-programmed heating (S_BET up to 1700 vs 1000 m²/g). Increasing the KOH/coal ratio (up to 1 g/g) in the activated mixture increases the total pore volume (0.14–1.0 cm³/g), the micropore volume (0.03–0.71 cm³/g), and also the volume of subnanometer pores (0.01–0.40 cm³/g). Thermal shock produces nanoporosity at lower KOH/coal ratios (0.5-1.0 g/g) than respective low-rate heating KOH activation.     

Oxidation of methanol on nickel—zinc catalysts

The activity of nickel—zinc and smooth nickel electrodes for methanol oxidation is investigated in KOH 1 M + CH₃OH 1 M at 60°C. Nickel—zinc alloys of different composition are easily obtained from electrodeposition. After their attack in KOH 1 M, the electrodes contain about 50% of zinc and they have the βNiZn alloy structure. The I(V) curves are compared. On smooth nickel the oxidation of methanol is strongly inhibited by the superficial oxides whereas on nickel—zinc electrodes superficial oxides are easier to reduce. The effect of adsorbed hydrogen and of mixed oxides is discussed.     

Isobaric vapor-liquid equilibrium for methanol+benzene+1-octyl-3-methylimidazolium tetrafluoroborate

Isobaric vapor-liquid equilibrium (VLE) data for {methanol (1)+benzene (2)+1-octyl-3-methylimidazolium tetrafluoroborate (3)} where 3 is an ionic liquid ([OMIM]⁺[BF₄]^?) at atmospheric pressure (101.32 kPa) were measured with a modified Othmer still. The results showed that the ionic liquid studied can transfer the azeotropic point and eliminate the azeotropic phenomena when its concentration is up to x₃=0.30. This means that [OMIM]⁺[BF₄]^? can be used as a promising entrainer in the application of extractive distillation. The measured ternary data were correlated using the NRTL model.     

KOH/bentonite catalysts for transesterification of palm oil to biodiesel

A potential application of KOH/bentonite as a catalyst for biodiesel production was studied. A series of KOH/bentonite catalysts was prepared by impregnation of bentonite from Pacitan with potassium hydroxide. The ratios between KOH and bentonite were 1:20, 1:10, 1:5, 1:4, 1:3, and 1:2. The characterization of KOH/bentonite and natural bentonite was conducted by nitrogen adsorption and XRD analysis. The effects of various reaction variables on the yield of biodiesel were investigated. The highest yield of biodiesel over KOH/bentonite catalyst was 90.70 ± 2.47%. It was obtained at KOH/bentonite 1:4, reaction time of 3 h, 3% catalyst, methanol to oil ratio of 6, and the reaction temperature at 60 °C.     

Water density effects on methanol oxidation in supercritical water at high pressure up to 100 MPa

Reaction kinetics of methanol oxidation in supercritical water at high pressure condition (420 °C; 34-100 MPa; ρ = 300-660 kg/m³) was investigated. Pseudo-first order rate constant for methanol decomposition increased with increasing water density. Effects of supercritical water on the reaction kinetics were investigated using a detailed chemical kinetics model. Incorporating the effect of diffusion in a reduced model revealed that overall kinetics for SCWO of methanol is not diffusion-limited. Roles of water as a reactant were also investigated. The dependence of sensitivity coefficient for methanol concentration and rate of production of OH radical on water density indicated that a reaction, HO₂ + H₂O = OH + H₂O₂, enhanced the OH radical production and thereby facilitated the decomposition of methanol. It is presumed that concentration of key radicals could be controlled by varying pressure intensively.     

Pore structures of multi-walled carbon nanotubes activated by air, CO2 and KOH

Multi-walled carbon nanotubes (MWNTs) synthesized by the catalytic decomposition of benzene were activated by KOH, CO₂ or air. The adsorption isotherms of the activated MWNTs were analyzed and their pore size distributions were obtained. The results showed that the specific surface areas of the MWNTs activated by KOH, CO₂ and air were increased to 785 m²/g, 429 m²/g and 270 m²/g, respectively. The MWNTs activated by KOH were rich in micropores and mesopores, especially high mesopores having volumes up to 1.04 cm³/g. The CO₂-activated MWNTs also had many micropores while the air-activated MWNTs had a much smaller micropore volume. The morphologies of the activated MWNTs were examined by transmission electron microscopy and high resolution transmission electron microscopy, and the activation mechanisms were discussed.