Intensification of nitrous acid oxidation

An alternative solution to the reduction of a discharge of residual nitric oxide and nitrogen dioxide into atmosphere has been proposed. Instead of using methane or ammonia for SCR or gas absorption into alkali solutions, which are the most popular treatment methods of tail gases, now the use of powerful oxidant—ozone capable of transforming nitrous acid and nitric oxides into nitrogen of the highest oxidation level—could be employed for this purpose. As the intensive oxidation and ozonation of nitrous acid is the heterogeneous gas-liquid process, the solubility of oxygen and ozone in HNO₂/HNO₃ aqueous solution was necessary to be determined. Variations of reaction rates depending on temperature, ozone dose and nitrous and nitric acid concentrations were studied experimentally. The kinetic model of the reactions, 2HNO₂+O₂→2HNO₃ and HNO₂+O₃→O₂+HNO₃, were proposed and the kinetic parameters (rate constants and activation energies) were estimated on the basis of experimental data in semi-batch laboratory gas-liquid contactor with the liquid phase drawn from an absorption column in the nitric acid plant. The determined kinetic parameters were then used in designing and modeling of the oxidation of nitrous acid using ozone-oxygen mixture in a continuous bubble column. The model consists of mass transfer kinetic equations and material balance equations for the gas and liquid phases. The co-current flow of gas and liquid phases and the complex kinetics of chemical reaction in the liquid phase were taken into account. The variation of the following process conditions, flow rate, compositions of the gas and liquid phases, temperature, and pressure in the bubble column of different diameters and heights, were studied in numerical solutions of the proposed model.     

An oxygen transfer model for high purity graphite oxidation

An intrinsic mathematical model is developed for the investigation of the gas–solid reaction kinetics of high-purity graphite and oxygen. This model is based upon the oxygen transfer mechanism and uses physically meaningful parameters that are directly comparable to the experimental and theoretical literature of the carbon–oxygen reaction system. The model was used to extract reaction parameters for NBG-18 polycrystalline graphite for oxygen/nitrogen mixtures with a total pressure of 100 kPa. Experimental temperatures ranged from 500 to 850 °C for oxygen partial pressures of 1, 5, 10, 20, and 40 kPa. The optimized model parameters are in good agreement with previously reported literature values.     

The oxygen activated by the active vanadium species for the selective oxidation of benzene to phenol

The activation of oxygen is a key step for the selective oxidation of benzene to phenol and the reason is discussed. The active oxygen species is produced from molecular oxygen in a so-called “reductive activation” process. The vanadium oxide supported on alumina was pre-reduced by hydrogen or ascorbic acid to lower valence vanadium species acting as reduction source and the activity is investigated in the reaction. It is found that the V⁴⁺ valence vanadium (VO²⁺) is effective for the reaction from the characterization of catalysts by XPS.     

Liquid-phase oxidation of benzene to phenol by molecular oxygen over transition metal substituted polyoxometalate compounds

Transition metal substituted polyoxometalate (TMSP) compounds were used as catalysts for the liquid-phase oxidation of benzene to phenol by molecular oxygen with ascorbic acid as a reducing agent in an acetone/sulfolane/water mixed solvent. [(C₄H₉)₄N]₅[PW₁₁CuO₃₉(H₂O)] is the best catalyst tested in this study. It showed 9.2% benzene conversion (TON = 25.8) and 91.8% selectivity to phenol for the oxidation of benzene at 323 K for 12 h. The effect of the substituted transition metal in the TMSP compounds on the benzene conversion is in the order: Cu > V > Fe ≫ Mn > Ti > Cr > Co > Ni > Zn. The effect of the central atom in the TMSP compounds on the benzene conversion is in the order: P ≈ Si > Ge > B. [SiW₁₁O₃₉]⁸⁻ is a good polyoxometalate ligand for transition metal ions as [PW₁₁O₃₉]⁷⁻ for the oxidation of benzene. The selectivity to phenol was dramatically improved by adding the sulfolane solvent, but the benzene conversion decreased when a large amount of sulfolane was used in the mixed solvent. Ascorbic acid is indispensable for forming phenol from benzene oxidation by O₂ over TMSP compounds. Higher O₂ pressure in the catalytic system ensured more oxygen molecules solving in the solvent, and promoted the benzene conversion.     

Catalytic wet oxidation of phenol with homogeneous iron salts

The catalytic wet oxidation of phenol has been investigated in a 1 L semi‐batch reactor in the presence of both ferrous and ferric salts. Oxidation reactions follow first‐order kinetics with respect to phenol and half‐order kinetics with respect to dissolved oxygen. The activation energy for the reaction was 44.5 and 48.3 kJ mol^?1 for runs employing Fe³⁺ and Fe²⁺, respectively. Rate constants and induction periods were also similar for both catalysts. This result could be explained by analysing the evolution of iron during the oxidation process. For pH > 2, Fe²⁺ was rapidly oxidized under reaction conditions to Fe³⁺, resulting in a unique catalytic redox system Fe²⁺/Fe³⁺. It was also shown that if pH < 2 the dissolved oxygen was unable to oxidize ferrous ion, resulting in a much slower oxidation rate of phenol. The absence of a redox pair resulted in a complete lack of catalytic activity of the dissolved iron salt. Copyright © 2005 Society of Chemical Industry     

Synthesis of crosslinked polyacrylonitrile via atom transfer radical polymerization with activators regenerated by electron transfer and use of the resin in mercury removal after modification

Crosslinked polyacrylonitrile (PAN) was synthesized with divinylbenzene as the crosslinker with an iron(III)‐mediated atom transfer radical polymerization method with activators regenerated by electron transfer. The polymerization exhibited first‐order kinetics with respect to the polymerization time. Hydroxylamine hydrochloride (NH₂OH·HCl) was used to modify the cyano groups of the crosslinked PAN to obtain amidoxime (AO) groups. The AO‐crosslinked PAN was used to remove Hg(II). The optimum pH, adsorption kinetics, and adsorption isotherms were investigated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of pH on the wet oxidation of phenol with copper catalyst

This work reports the influence of pH on the catalytic wet oxidation (CWO) of phenol performed with a commercial copper-based catalyst. The results obtained show that pH is a critical parameter able to modify the chemical stability of the catalyst, the significance of the oxidation reaction in the liquid phase, the reaction mechanism and, consequently, the oxidation route of phenol. Experiments have been carried out to study the mentioned aspects. Stirred basket and fixed bed reactors (FBRs) have been employed, at 140 °C and at 16 bar of oxygen pressure. Three initial pH values have been used: 6 (the pH of the phenol solution), 3.5 (adjusted by H₂SO₄) and 8 (by addition of Na₂CO₃). Furthermore, some phenol oxidation runs without solid catalyst but with different concentrations of copper in solution have been accomplish at pHo=3.5. At acid pH, important leaching of copper from the catalyst to the solution was achieved, finding this negligible at pH 8. It was found that the major contribution to the phenol conversion reached at acid pH by using the solid catalyst was due to the catalytic activity of the leached copper. Both oxidation mechanisms at acid and basic conditions have been elucidated to explain the differences in the type and distribution of the intermediates obtained. The catalytic phenol oxidation route found at pH=8 comprises intermediates less toxic than phenol while at acid pH the cyclic intermediates formed as first oxidation intermediates are far more toxic than phenol.     

On the involvement of radical oxygen species O− in catalytic oxidation of benzene to phenol by nitrous oxide

Catalytic oxidation of benzene to phenol by nitrous oxide over Fe-MFI zeolites was studied in relation to the active oxygen species taking part in the oxidation. A linear dependence of the reaction rate on the concentration of independently identified active sites generating O⁻ radicals (α sites) was obtained within a broad range of values. The dependence is interpreted as convincing evidence of the O⁻ involvement in the catalytic (not only stoichiometric) oxidation of benzene to phenol. This conclusion is of particular importance in connection with a long discussion in the literature on a possible role of O⁻ radicals in selective oxidation catalysis over V and Mo oxides. Reliable evidence of the catalytic role of O⁻ obtained with zeolites may renew general interest in the once-suggested but not recognized role of radical oxygen in oxidation over widely used metal oxide catalysts.     

Catalytic oxidation of phenol in aqueous solutions

The objective of this work is to investigate catalyst systems for the oxidation of phenol in water in a batch autoclave. The main experimental variables are the type and the composition of the catalyst, the catalyst loading, temperature, oxygen partial pressure, initial phenol concentration and the stirrer speed. Commercial catalysts were used. Experimental work was conducted in two different laboratories. In one laboratory, the catalysts tested were 35% CuO+65% ZnO; 5–15% CuO+85–95% Al₂O₃; 26% CuO+74% Cu Chromite. In the other laboratory, the catalysts tested included 35% CuO+65% ZnO; 5–10% Ba₂CO₃+<5% C+30–40% CuO+60–70% ZnO; and 8–15% Al₂O₃+1–5% C+35–45% CuO+40–50% ZnO. With some of these catalysts depending on the operating conditions, complete phenol conversion could be obtained within 90 min. Under certain experimental conditions, the reaction underwent an induction period after which there was a transition to a much higher activity regime. The induction period may be due to an autocatalytic reaction system or to a very slow rate of formation of hydroquinone and catechol which then readily oxidize to o- and p-benzoquinone. An increase in the temperature and the oxygen partial pressure decreased the induction period, which increased as the catalyst to phenol ratio increased. 26% CuO+74% Cu Chromite and 8–15% Al₂O₃+1–5% C+35–45% CuO+40–50% ZnO were found to be the most active catalysts.     

含酚废水的氧化法处理

含酚废水是一种危害极大的工业废水，经济而有效地处理含酚废水极为重要。氧化法是一类极具发展前途的含酚废水处理技术。本文综述了氧化法处理含酚废水的研究进展。     

Kinetics of phenol mineralization by Fenton-like oxidation

The kinetics of hydrogen peroxide decomposition and the mineralization rate of phenol in homogeneous aqueous solution (pH < 3) via Fenton-like reaction were studied. Results were correlated with the generation of hydroxyl radicals as well as with iron speciation. Batch experiments were carried out in de-ionized water in a completely mixed batch reactor under a wide range of experimental conditions (3500 ≤ [H₂O₂] ≤ 8250 mg/L; 100 mg/L ≤ [Fe] ≤ 2350 mg/L; 2.5 ≤ [H₂O₂]/[Fe] ≤ 83; 0 mg/L ≤ [TOC] ≤ 1000 mg/L). Results demonstrated that the rate of hydrogen peroxide decomposition, phenol mineralization and ferrous ions formation depended on both the initial concentration of the phenol and on the weight ratio between hydrogen peroxide and iron. A linear correlation was found between the mineralization rate of phenol and the decomposition rate of hydrogen peroxide indicated that 10 g of hydrogen peroxide was required to mineralize 1 g of phenol.     

Intensification of heat transfer in the heating ducts of coke batteries

On the basis of a model of the gas flow in the heating duct, artificial turbulization is proposed as a means of intensifying the heat transfer in coke batteries. When using a brick lining of special form, the heat transfer in the heating duct is intensified as a result of the destruction of the laminar wall layer, with slight increase in the hydraulic drag. That improves the energy efficiency of the system.     

The use of electrogenerated hypobromite for the phase transfer catalysed oxidation of benzyl alcohols

A simple procedure for the oxidation of benzyl alcohols to aldehydes is described. The oxidizing agent is hypobromite generated by the anodic oxidation of aqueous bromide and the reactions are carried outin situ in an undivided cell in an amyl acetate/water emulsion containing 2% tetrabutylammonium bisulphate.     

气液反应体系相界面传质强化研究

气液反应界面传质的强化是当今高效和节能反应器研究的重要课题,弄清反应器内的气液传质机理是对气液反应器进行数学描述的关键。反应过程的能效和物效与体系中的传质系数k_G,k_L,k_S以及相界面面积a等参数直接相关,这些参数受气泡尺寸、分布、表观气速和气含率等因素的制约。就确定的体系和反应条件而言,这些因素会因反应器的结构尤其是搅拌和混合方式的变化而异。文章从理论上分析了影响气液界面传质的各因素,建立了较为详细的理论模型。理论计算结果表明:气泡大小是影响气液界面传质和最终反应速率的重要流体力学参数,微米级气泡对反应过程的强化作用明显。能量耗散率是决定体系气泡大小的深层原因,强化气液反应器设计时应重点考虑。     

Capillary reactor for cyclohexane oxidation with oxygen

Cyclohexane oxidation is the first step in the currently used technology for production of Nylon-6 and Nylon-6,6 which employs a two-stage process. In the first stage 80% selectivity to two main products, cyclohexanol and cyclohexanone (KA oil) is obtained at 4–8% cyclohexane conversion in staged bubble columns or stirred tanks. There have been reports that increased oxygen concentration in the gas phase or pure oxygen is beneficial to cyclohexane oxidation and this was confirmed in our previous study (Jevtic et al., 2009). To fully utilize this advantage here, we present a novel, safer capillary reactor for cyclohexane oxidation with pure oxygen. The discrepancy between the experimental and modeling results was attributed to lower than expected mass transfer achieved in the capillary. With a better design for gas–liquid mixing and contacting this type of a reactor could potentially become attractive for gas–liquid reactions of similar nature.     

苯酚催化氧化制苯二酚

采用正交试验的方法,研究了在无机盐催化剂作用下苯酚双氧水直接氧化制取邻、对苯二酚的合成技术。通过极差分析和方差分析,找出了影响苯二酚选择性、苯酚转化率和邻/对比的主次因素及影响程度,从而得出较佳的反应条件:苯酚质量分数0 1,苯酚/双氧水的摩尔配比2,反应温度40℃,反应时间20min,pH2。在此操作条件下,苯二酚总选择性78%左右,邻/对比为1.45左右,为进一步的深入研究提供了依据。