硝基苯间接电还原制备对氨基苯酚

以发泡铜为阴极材料,ZnSO4为反应媒质,硫酸溶液为导电介质,对硝基苯阴极间接电还原制备对氨基苯酚进行了研究,并考察了温度、酸度、媒质浓度、电解电压等实验条件对反应产率的影响。结果表明,硝基苯阴极间接电还原制备对氨基苯酚的最佳条件为:温度65℃,20%硫酸溶液,电解电压2.0 V,通电量为85%理论通电量,硝基苯浓度2.0 mol/L,媒质浓度0.1 mol/L,最高产率能达到94.4%,具有工业化应用前景。     

对氨基苯酚的绿色电化学合成及其工业化

研究了在阴极转动分隔式电解槽中硝基苯电化学还原制备对氨基苯酚（PAP）时阴极转速、反应温度等工艺参数对电解性能的影响,并考察了不同阳极材料的稳定性.实验结果表明,增大阴极转速和升高反应温度有利于反应的进行;自制的Pb-Sb-Sn-Ag-Cu五元合金作为阳极材料具有比Ti/Ir阳极更长的工作寿命.当以铅合金为阳极材料、体系温度为90℃、阴极转速为900 r•min^-1、电解电流为3000 A时,硝基苯的平均转化率为99%,PAP平均收率为69.9%,电解直流电单耗为7.24 kW•h•(kg PAP)^-1,产品纯度大于98%,熔点为186.1～187.3 ℃.     

Pt-Cr-SO42-/ZrO2的制备及其催化硝基苯加氢制备对氨基苯酚的研究

采用等体积浸渍法,以 ZrO₂为载体制备了 Pt-Cr-SO₄^2-/ZrO₂催化剂。考察了硫酸浸渍浓度、焙烧温度及助剂对 Pt-Cr-SO₄^2-/ZrO₂催化硝基苯加氢制备对氨基苯酚的影响。对催化剂进行了 BET、XRD、TG 和 IR 表征,试验结果表明 ：(w)Pt 为 3%、硫酸浸渍浓度 0.5 mol/L、焙烧温度 600 ℃、Cr 为助剂是 Pt-Cr-SO₄^2-/ZrO₂制备的最优条件。在反应温度 150 ℃、压力 0.5 MPa、催化剂用量 0.08 g 和反应时间 8 h 的工艺条件下加氢效果最好,硝基苯的转化率为 85.81%,对氨基苯酚的选择性为 60.93%。     

硝基苯电解还原制备对氨基苯酚

用旋转圆柱电极反应器和固定床反应器电解还原硝基苯制备对氨基苯酚(PAP)。在温度约85℃、槽电压约2.0伏、硫酸浓度约为20％的条件下,对氨基苯酚的摩尔收率为80％,电流效率大于75％。电解液经萃取及重结晶,得到纯度大于99％的PAP白色晶体,熔点为189℃。文章还讨论了该工艺工业化的若干问题。     

硝基苯在发泡铜阴极上电还原为对氨基苯酚研究

研究了以发泡铜为阴极材料 ,硝基苯电解还原制备对氨基苯酚。考察了反应物浓度、介质酸度、电解温度、电解电流、电极尺寸等因素对对氨基苯酚产率的影响。在 80℃ ,硫酸介质体积分数为 2 0 % ,硝基苯在体积分数为 2 0 %正丁醇水溶液中的浓度 1 .8mol L ,通氮气 75mL min ,电解电流 4A条件下 ,电解 2h ,对氨基苯酚的产率达到 93%以上 ,电流效率高于 92 %。     

三维铜网阴极上电解制备2,6-二氯-4-氨基苯酚

以氯苯/硫酸水溶液为电解液,在三维铜网阴极上电解2,6-二氯-4-硝基苯酚制备2,6-二氯-4-氨基苯酚。在铜微电极上用循环伏安法对其电化学行为进行研究,表明2,6-二氯-4-硝基苯酚的电还原反应是一个受扩散控制的不可逆反应。对电极材料、助溶剂的体积分数、电流密度、温度和硫酸浓度进行了单因素考察,得到最佳实验条件为:以铜网为阴极、助溶剂氯苯的体积分数为10%、电流密度为800 A/m2、温度为40℃、支持电解质硫酸浓度为2 mol/L。在该条件下,2,6-二氯-4-氨基苯酚的产率为94.8%。阴极电解液连续循环使用8次后,产率仍维持在95%左右。表明阴极电解液没有活性损失,可以被重复利用。     

硝基苯催化加氢合成对氨基苯酚工艺研究

采用Pt/C作为催化剂对硝基苯选择加氢合成对氨基苯酚进行了研究,考察了温度、酸度、反应时间、压力、催化剂等因素对反应的影响,确定了反应的优化条件。在反应温度75℃、压力2.45kPa、硫酸浓度13%、反应时间4h的条件下,用2%Pt/C催化加氢还原硝基苯可获得较高质量的产物对氨基苯酚。     

专利选登

硝基苯电解还原制备对氨基苯酚的方法公开号 CN 1342785A 公开日 2002.4.3申请人华东理工大学 一种硝基苯电解还原制备对氨基苯酚的方法。本发明通过向阴极电解液中投加抗氧剂和根据电解过程中对氨基苯酚的浓度变化及时调整电流密度和阴极电解液的流速,从而提高电解过程的对氨基苯酚选择性和电流效率,从而提高了对氨基苯酚的收率,并不需要回收溶剂,降低了生产成本,且易于工业化实施。     

2-氯-5-三氯甲基吡啶电化学氢化脱氯合成2-氯-5-甲基吡啶

2-氯-5-三氯甲基吡啶（TCMP）选择性氢化脱氯制备2-氯-5-氯甲基吡啶（CCMP）或2-氯-5-甲基吡啶（CMP）在农药“吡虫啉”合成中具有重要应用价值。首先在弱酸性的甲醇/乙酸/水混合溶剂中研究了TCMP电化学脱氯合成CCMP或CMP的可行性;其次,研究了阴极材料和电解液组成对TCMP选择性脱氯反应的影响;最后,采用膜厚度极距的板框式电解槽分别研究了阴、阳极支持电解质对电解槽压和电流密度与底物浓度对脱氯反应效率的影响。实验结果表明,在弱酸性的甲醇/乙酸/水混合溶剂中,TCMP能在银网阴极上高选择性的氢化脱氯成CMP;CMP收率从高到低的阴极依次为：银> 铜> 锌> 铅> 钛> 石墨> 镍。阴阳极支持电解质从四丁基高氯酸铵分别换成乙酸锂和硫酸,电解槽压大幅度下降。降低电流密度和提高底物浓度有利于TCMP电化学氢化脱氯效率。在优化条件下（阴极液：含10%乙酸+5%水+0.2 mol·L^-1乙酸锂的甲醇溶液;阴极：银网;电流密度：333 A·m^-2;温度：30℃）,0.2 mol·L^-1 TCMP 能高效地转化为CMP（收率：91%）,电流效率可达54%,电解槽压大约为3.0 V。     

对氨基苯酚的工艺研究

研究硝基苯催化加氢制备对氨基苯酚的工艺条件,对影响因素进行了探讨。结果表明,最佳制备工艺条件为:硝基苯20 mL,硫酸浓度15%,氢气压力为20 cm水柱,温度85℃,十二烷基三甲基溴化铵用量为0.1 g,搅拌速率1 500 r/m in,2.5%Pt/C催化剂0.5 g,反应时间为5 h。在此条件下,硝基苯转化率最高达39.8%,对氨基苯酚选择性最高达99%,产品质量达到日本JISK4144—1986标准要求。     

硝基苯电解合成对氨基苯酚的工业化试验

采用1000L阴极转动分隔式电解槽,研究了硝基苯电解合成对氨基苯酚(PAP)的工业化放大过程。研究表明,转动阴极电解槽的工作特性与阴极转速、电流强度、温度、隔膜材料等因素有关。当电解电流为3000A时,硝基苯的平均转化率为91.0%,PAP平均收率为67.6%,直流电单耗为7.34 kWh(kg PAP)-1。电解合成的PAP纯度在97%以上,熔点为187.2~188.4C。     

硝基苯加氢制备对氨基苯酚的工艺要素研究

在稀硫酸介质中,Pt/C催化,硝基苯加氢还原、转位得到目标化合物对氨基苯酚。工艺要素研究表明:硝基苯20mL,氢气压力为1kPa的水封压力,温度85～90℃,十六烷基三甲基溴化铵用量为0.1g,2%Pt/C催化剂0.5g,反应时间为5h时,所得产品质量达到并优于日本JISK4144 1986标准要求。     

Analysis of molar flux and current density in the electrodialytic separation of sulfuric acid from spent liquor using an anion exchange membrane

Separation of sulfuric acid from a dilute solution involved a plate and frame type electrodialysis unit using a commercial anion exchange membrane. Experiments were conducted in batch with catholyte concentrations ranging from 1 to 5 wt%. Effect of applied current density, initial catholyte concentration and initial concentration difference of catholyte and anolyte on the molar flux was studied extensively. The maximum molar flux was estimated to be 10.52×10^-8 mol cm^-2s^-1 at 4.45 wt% catholyte concentration and applied current density of 30 mA cm^-2. Current efficiencies were observed to be 75 to 85% at lower current density, which rose to more than 100% at 20 and 30mA cm^-2, at equal initial concentration of catholyte and anolyte. Diffusive flux and flux due to membrane potential contributed very less compared to total flux in presence of applied electric current. An equation was developed to predict the practical molar fluxes, which fitted satisfactorily with minor standard deviation. Pristine and used membrane specimens were characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).     

Hydroxylamine production by electroreduction of nitric oxide in a trickle bed cell

Hydroxylamine was produced in a trickle bed cell by passing nitric oxide gas and sulphuric acid catholyte co-currently downward through a cathode bed of tungsten carbide particles. The dependence of hydroxylamine concentration and current efficiency on cathode activity and particle size, flow rate and composition of gas and catholyte, bed height, and reactor temperature and pressure are reported. Hydroxylamine concentrations of up to 0.18 mol/L were produced at 62% current efficiency in a single pass through a 0.375 m high cell operated at atmospheric pressure and a current density of 213 A/m². The hydroxylamine concentration increased with cell pressure, gas flow rate and decreases in catholyte flow and could be raised to 0.4 mol/L by recycling the catholyte. The process appears to be controlled by mass transfer at current densities over 400 A/m² and by electrochemical reaction below about 300 A/m².     

Electroreduction of nitrobenzene to p-aminophenol using voltammetric and semipilot scale preparative electrolysis techniques

This paper describes an investigation of the reduction of nitrobenzene to p-aminophenol by the use of CV, RDE and preparative electrolysis with Cu and Cu(Hg) electrodes. The preparative electrolyses of nitrobenzene were carried out at controlled current and controlled potential conditions using copper and amalgamated copper using a new semipilot (laboratory) scale system in the absence of an organic cosolvent. The effects of redox reagents and the concentration of nitrobenzene in catholyte added to the medium were also examined. The best results were obtained with 2.3% BiCl₃ at nitrobenzene concentration of 0.144 g cm^–3 catholyte. The most suitable electrode material was found to be amalgamated copper and the reduction of nitrobenzene to p-aminophenol was found to follow an ECE mechanism.     

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.     

硫酸铬电解氧化反应的研究

为了制备间接电氧化合成菲醌的氧化剂Cr2O72-,对硫酸铬电解氧化反应进行了实验研究,考察了电流密度、电解时间、反应温度及硫酸含量对电解效率的影响。通过实验得出:在隔膜电解槽中,采用Pb作阴极,Pb-PbO2作阳极,Cr3 电氧化的最佳条件是反应时间4 h,电解液中硫酸浓度30%,电流密度67 mA/cm2,所得Cr2O72-收率为95%左右。