硝基苯还原生产苯胺安全性评价

苯胺是一种重要的有机化工原料,目前国内生产均采用硝基苯气相加氢还原工艺.本文对苯胺生产安全性进行了评价分析,存在物质危险性和生产工艺危险性.     

H4SiW12O40-catalyzed oxidation of nitrobenzene in supercritical water: kinetic and mechanistic aspects

The catalytic effect of a heteropolyacid, H₄SiW₁₂O_40, on nitrobenzene (20 and 30 μM) oxidation in supercritical water was investigated. A capillary flow-through reactor was operated at varying temperatures (T=400–500 °C; P=30.7 MPa) and H₄SiW₁₂O₄₀ concentrations (3.5–34.8 μM) in an attempt to establish global power-law rate expressions for homogenous H₄SiW₁₂O₄₀-catalyzed and uncatalyzed supercritical water oxidation. Oxidation pathways and reaction mechanisms were further examined via primary oxidation product identification and the addition of various hydroxyl radical scavengers (2-propanol, acetone, acetone-d₆, bromide and iodide) to the reaction medium. Under our experimental conditions, nitrobenzene degradation rates were significantly enhanced in the presence of H₄SiW₁₂O₄₀. The major differences in temperature dependence observed between catalyzed and uncatalyzed nitrobenzene oxidation kinetics strongly suggest that the reaction path of H₄SiW₁₂O₄₀-catalyzed supercritical water oxidation (average activation E_a=218 kJ/mol; k=0.015–0.806 s⁻¹ energy for T=440–500 °C; E_a=134 kJ/mol for the temperature range T=470–490 °C) apparently differs from that of uncatalyzed supercritical water oxidation (E_a=212 kJ/mol; k=0.37–6.6 μM s⁻¹). Similar primary oxidation products (i.e. phenol and 2-, 3-, and 4-nitrophenol) were identified for both treatment systems. H₄SiW₁₂O₄₀-catalyzed homogenous nitrobenzene oxidation kinetics was not sensitive to the presence of OH√ scavengers.     

Scale-up of a fixed bed electrochemical reactor consisting of parallel screen electrode used for p-aminophenol production

The behavior of a fixed bed consisting of amalgamated copper screens has been investigated for the electrolytic reduction of nitrobenzene to p-aminophenol under potentiostatic condition (controlled potential). The preparative electrolysis of nitrobenzene was carried out using supporting electrolytes consisting of 2 M H₂SO₄ in a solution of 50% 2-propanol/50% water (v/v). The criterion for scale-up (?_n) was determined through application of one-dimensional model. The polarization curves that describe the reduction of nitrobenzene to p-aminophenol were obtained experimentally by using a pilot scale for different nitrobenzene concentrations and flow rates of catholyte.It was found that the effectiveness factor (?_n) increases with increasing flow rate, and decreasing nitrobenzene concentration. An optimum thickness of bed equal to 0.6 cm was obtained, in which the effectiveness factor not less than 0.588, to ensure a well distribution of current and potential.     

Quantum Chemical Studies on the Formation of Ozone Adducts to Aromatic Compounds in Aqueous Solution

The rate constants of the reactions of ozone with nitrobenzene, chlorobenzene, benzene, methylbenzene, methoxybenzene, phenol, 1,3,5-trimethoxybenzene and phenolate ion in aqueous solution span ten orders of magnitude. The logarithms of the rate constants correlate with the Gibbs free energies of adduct formation (ranging from +18.5 to ?21.6 kcal mol^?1) calculated with the help of the Jaguar 7.5 program using a dielectric continuum model to account for solvent effects. The electrophilic nature of these reactions is reflected by good correlations with Mulliken charge and similar parameters of these compounds accessible to quantum chemical calculations. Data on the Gibbs free energies of Criegee ozonide formation are also provided.     

苯硝化生产硝基苯过程的安全性探讨

介绍了硝基苯生产过程中存在的主要危险因素,并分析了原因,给出了预防措施。     

Effect of increasing nitrobenzene loading rates on the performance of anaerobic migrating blanket reactor and sequential anaerobic migrating blanket reactor/completely stirred tank reactor system

A laboratory scale anaerobic migrating blanket reactor (AMBR) reactor was operated at nitrobenzene (NB) loading rates increasing from 3.33 to 66.67 g NB/m³ day and at a constant hydraulic retention time (HRT) of 6 days to observe the effects of increasing NB concentrations on chemical oxygen demand (COD), NB removal efficiencies, bicarbonate alkalinity, volatile fatty acid (VFA) accumulation and methane gas percentage. Moreover, the effect of an aerobic completely stirred tank reactor (CSTR) reactor, following the anaerobic reactor, on treatment efficiencies was also investigated. Approximately 91–94% COD removal efficiencies were observed up to a NB loading rate of 30.00 g/m³ day in the AMBR reactor. The COD removal efficiencies decreased from 91% to 85% at a NB loading rate of 66.67 g/m³ day. NB removal efficiencies were approximately 100% at all NB loading rates. The maximum total gas, methane gas productions and methane percentage were found to be 4.1, 2.6 l/day and 59%, respectively, at a NB loading rate of 30.00 g/m³ day. The optimum pH values were found to be between 7.2 and 8.4 for maximum methanogenesis. The total volatile fatty acid (TVFA) concentrations in the effluent were 110 and 70 mg/l in the first and second compartments at NB loading rates as high as 66.67 and 6.67 g/m³ day, respectively, while they were measured as zero in the effluent of the AMBR reactor. In this study, from 180 mg/l NB 66 mg/l aniline was produced in the anaerobic reactor while aniline was completely removed and transformed to 2 mg/l of cathechol in the aerobic CSTR reactor. Overall COD removal efficiencies were found to be 95% and 99% for NB loading rates of 3.33 and 66.67 g/m³ day in the sequential anaerobic AMBR/aerobic CSTR reactor system, respectively. The toxicity tests performed with Photobacterium phosphoreum (LCK 480, LUMIStox) and Daphnia magna showed that the toxicity decreased with anaerobic/aerobic sequential reactor system from the influent, anaerobic and to aerobic effluents.     

PROMOTION EFFECT OF Mo IN AMORPHOUS Ni-P CATALYSTS FOR THE LIQUID-PHASE CATALYTIC HYDROGENATION OF NITROBENZENE TO ANILINE

Amorphous Ni-P catalysts were prepared by a chemical reduction method, and the promotional effects of Mo on the hydrogenation of nitrobenzene to aniline on Ni-P catalyst were investigated. However, the two crystallization temperatures of the 1% Ni-Mo-P catalyst were 644 K and 723 K, which were 15 K and 43 K higher, respectively, than those of the Ni-P catalyst itself; these results indicate that the presence of Mo increased the thermal stability of the Ni-P catalysts. SEM results showed that the particle size of the active component of Ni-P in the 1.0% Ni-Mo-P catalyst was smaller than that in the amorphous Ni-P catalyst. The N₂ adsorption isotherms for the amorphous Ni-Mo-P catalysts were the III-type, and the N₂ isothermal adsorption-desorption curves exhibited H₃-type hysteresis loops. H₂-TPR results showed that the addition of Mo had no effect on the reduction of NiO in the catalyst but negatively affected the reduction of Ni-P-O. H₂-TPD results showed that the hydrogen adsorption capacity of the amorphous Ni-P catalysts can be enhanced through the addition of Mo, and the optimal amount of Mo was determined to be 1.0%. The XPS results indicated the presence of a small amount of free metallic Mo in the amorphous Ni-Mo-P catalysts in addition to the Mo in MoO₃. The use of 1% amorphous Ni-Mo-P catalyst at 383 K and under 1.0 MPa of hydrogen for 3.0 h resulted in a nitrobenzene conversion rate and aniline selectivity of 64.5% and 98.8%, respectively.     

极谱测定苯胺中微量硝基苯的方法研究

通过正交实验和验证实验确定极谱测定苯胺中微量硝基苯的最佳条件,同时对悬汞电极、静态滴汞电极、滴汞电极等3种电极模式以及微分脉冲极谱和经典直流极谱2种极谱类型进行了实验比较,得出相应的结论。     

Catalytic ozonation for the degradation of nitrobenzene in aqueous solution by ceramic honeycomb-supported manganese

Catalytic ozonation of nitrobenzene in aqueous solution has been carried out in a semi-continuous laboratory reactor where ceramic honeycomb and Mn–ceramic honeycomb have been used as the catalysts. The presences of the two catalysts significantly improve the degradation efficiency of nitrobenzene, the utilization efficiency of ozone and the production of oxidative intermediate species compared to the results from non-catalytic ozonation, and the improvement of them is even more pronounced in the presence of Mn–ceramic honeycomb. Adsorptions of nitrobenzene on the two catalytic surfaces have no remarkable influence on the degradation efficiency. Addition of tert-butanol causes the obvious decrease of degradation efficiency, suggesting that degradation of nitrobenzene follows the mechanism of hydroxyl radical (OH) oxidation. Some of the main operating variables like amount of catalyst and reaction temperature exert a positive influence on the degradation efficiency of nitrobenzene. Initial pH also presents a positive effect in the ozonation alone system while the optimum working initial pH is found to be around 8.83 and 10.67 to the processes of ozonation/ceramic honeycomb and ozonation/Mn–ceramic honeycomb, respectively. The surface characteristics measurement of the two catalysts indicates that the loading of Mn increases the specific surface area, the pH at the point of zero charge (pH_PZC) and the density of surface hydroxyl groups, and results in the appearance of new crystalline phase of MnO₂. The results of mechanism research confirm that the loading of Mn promotes the initiation of OH.     

冰冻条件下水中硝基苯的变化

为了解松花江水中硝基苯在自然冰冻情况下的归趋,进行了硝基苯水样的冰冻实验.同时对松花江达连河断面主河道上冰层中硝基苯含量进行了分层检测.冰冻实验结果表明,在水样全部结冰情况下,冰中硝基苯浓度(以融化后水中硝基苯浓度计,下同)与原水样中硝基苯浓度比值与冰冻速度没有明显关系,该比值一般在0.47～0.80间;在水样不完全结冰情况下,结冰速度对硝基苯在冰相与水相中的分配比具有显著影响,快速结冰时分配比为0.21,而慢速结冰时仅为0.050.冰冻过程中水中硝基苯逐渐被浓缩,部分硝基苯挥发到大气中.污染带流经达连河断面时所结冰的各个层位中硝基苯浓度均远远低于国家《地表水环境质量标准》(GB 3838-2002)限值.