Production of ammonia from plasma-catalytic decomposition of urea: Effects of carrier gas composition

Effects of carrier gas composition(N_2/air) on NH_3 production, energy efficiency regarding NH_3 production and byproducts formation from plasma-catalytic decomposition of urea were systematically investigated using an Al_2 O_3-packed dielectric barrier discharge(DBD) reactor at room temperature. Results show that the presence of O_2 in the carrier gas accelerates the conversion of urea but leads to less generation of NH_3. The final yield of NH_3 in the gas phase decreased from 70.5%, 78.7%, 66.6% and 67.2% to 54.1%, 51.7%, 49.6% and 53.4% for applied voltages of 17, 19, 21 and 23 kV, respectively when air was used as the carrier gas instead of N_2.From the viewpoint of energy savings, however, air carrier gas is better than N_2 due to reduced energy consumption and increased energy efficiency for decomposition of a fixed amount of urea. Carrier gas composition has little influence on the major decomposition pathways of urea under the synergetic effects of plasma and Al_2 O_3 catalyst to give NH_3 and CO_2 as the main products. Compared to a small amount of N_2 O formed with N_2 as the carrier gas, however,more byproducts including N_2O and NO_2 in the gas phase and NH_4 NO_3 in solid deposits were produced with air as the carrier gas, probably due to the unproductive consumption of NH_3, the possible intermediate HNCO and even urea by the abundant active oxygen species and nitrogen oxides generated in air-DBD plasma.     

纳米二氧化钛制备与表征

通过水热反应法合成出了两种纳米二氧化钛粉体材料,通过差热分析、X衍射分析、扫描电镜分析,粉体的平均直径小于100nm,通过光催化试验分析,纳米二氧化钛的光催化性能可以达到47%.     

Ex-ante environmental assessments of novel technologies - Improved caprolactam catalysis and hydrogen storage

Utrecht University has conducted a pilot sustainability assessment for the executive board of the chemistry program ACTS (Advanced Chemical Technologies for Sustainability) of the Netherlands’ Organization for Scientific Research (NWO). These assessments represent prospective, i.e. ’ex-ante’ studies on the production of caprolactam by an improved catalyst and on different hydrogen storage options (i.e. compressed and liquefied hydrogen, storage in metal hydrides and storage in a metal organic framework). The pilot sustainability assessments followed the principles of environmental life cycle assessment (LCA), thereby focusing on non-renewable energy use (NREU) and climate change (GWP100). It was found that caprolactam with the novel catalyst has lower impacts than petrochemical caprolactam production from benzene but higher impacts than bio-based caprolactam produced via fermentation. Regarding hydrogen storage, it was found that compressed and liquid hydrogen have the highest impacts. The impacts of the metal hydrides and the metal organic frameworks show by far the lowest environmental impacts. The main reason is that these materials can be reused up to 1500 times (refilling of tank), while for compressing and liquefaction of hydrogen energy is needed each time a tank needs to be refilled. The study demonstrates the successful application of ex-ante technology assessment.     

有机废水的电催化法降解研究现状

阐释了有机废水电催化法降解机理;综述了传统二维电极、新型三维电极电催化降解有机废水的原理及其应用现状,PbO2电极在三维电极处理有机废水中的应用现状、反应机理以及改性PbO2电极的研究进展;最后对未来发展方向进行了展望。     

硅胶催化光度法测定空气中微量NO2

为测定空气中的微量NO2,提出一种新方法,即硅胶催化光度法.显色剂为对氨基苯磺酰胺和N-(1-萘基)-乙二胺盐酸盐,将其在硅胶颗粒介质中与NO2反应,生成玫瑰红色偶氮染料.在波长540 nm下,测定其吸光度,从而计算NO2含量.将该方法与标准方法-Saltzman法进行对比.结果表明,在硅胶的催化作用下,显色反应的时间由Saltzman法的15 min降至8 min,分析测定的灵敏度也有所提高.该法操作简单方便,无干扰,用于测定空气样品中的微量NO2,结果较为满意.     

基于DSP的PPT试验样机点火安全控制系统设计

脉冲等离子体推力器PPT(Pulsed Plasma Thruster)点火安全控制系统是PPT设计中的关键.为方便灵活地控制点火脉冲和工作频率,同时保证安全点火,采用直接有脉宽调制信号PWM(Pulse width Modulalion)输出口的数字信号处理器DSP(Digital Signal Processing)控制PPT的点火,完成了DSP辅助电路、和上位机通讯的串口电路、与PPT高压触发模块(脉冲功率装置)的接口电路以及PPT点火时序控制软件的设计.PPT工作时,点火安全控制系统接收由上位机卫星喷气姿态控制算法产生的点火时刻和点火次数命令,执行点火命令.试验表明,PPT点火安全控制系统能够控制PPT试验样机,使其准确按照时序在频率0～1.67Hz(波形分辨率最高为6.67ns)下可靠点火.     

Characteristics of gas-liquid pulsed discharge plasma reactor and dye decoloration efficiency

The pulsed high-voltage discharge is a new advanced oxidation technology for water treatment. Methyl Orange (MO) dye wastewater was chosen as the target object. Some investigations were conducted on MO decoloration including the discharge characteristics of the multi-needle reactor, parameter optimization, and the degradation mechanism. The following results were obtained. The color group of the azo dye MO was effectively decomposed by water surface plasma. The decoloration rate was promoted with the increase of treatment time, peak voltage, and pulse frequency. When the initial conductivity was 1700 μS/cm, the decoloration rate was the highest. The optimum distance between the needle electrodes and the water surface was 1 mm, the distance between the grounding electrode and the water surface was 28 mm, and the number of needle electrodes and spacing between needles were 24 and 7.5 mm, respectively. The decoloration rate of MO was affected by the gas in the reactor and varied in the order oxygen > air> argon > nitrogen, and the energy yield obtained in this investigation was 0.45 g/kWh.     

液相放电-电极催化对罗丹明B的脱色研究

放电系统中加入TiO2催化剂能更有效地利用等离子体中各种高能量而产生氧化性高的.OH。文章以Ti为阳极,在直流电压下产生弧光放电,研究了其作用于罗丹明B模拟的印染废水的脱色效率,得到最佳放电电压、电极没水深度、电解质Na2SO4浓度、初始pH、罗丹明B初始浓度值,脱色率>95%。通过与W、Al电极比较,发现Ti电极上形成的氧化膜能增强放电强度,且有催化作用,不同电压下脱色反应速率系数提高23.7%~149%。结果表明,Ti阳极上形成了液相放电-电极催化自然集成的体系,在废水处理中是有发展前景的技术。     

低温等离子体烟气脱硫脱硝技术的研究进展

低温等离子体烟气处理技术具有工艺简单、可同时去除多种污染物、占地面积小等优点,是目前烟气处理技术的研究热点之一。主要介绍了研究规模最大的3种低温等离子体烟气处理技术（电子束、脉冲等离子体、直流电晕等离子体）的发展历程和现状,分析了其优点及存在的问题,并简要讨论了其发展方向。     

Characteristics of emissive spectrum and the removal of nitric oxide in N2/O2/NO plasma with argon additive

Although the approach using non-thermal plasma (NTP) for deNOx has been studied for over 15 years, how to achieve higher removal e ciency with lower cost is still a barrier for its industrial application. In order to investigate the impact of the argon additive on electron density, energy and nitric oxide reduction process in plasma, the spectrum of the dielectric barrier discharge at atmospheric pressure in a coaxial reactor was measured using the monochromater with high resolution. The comparative experiments for NO reduction were carried out simultaneously in N2/O2/NO plasma stream with and without argon, respectively. The nitrogen molecular spectrum which is attributed to the energy level transition (C3 u ! B3 g) was compared in the wavelength range 300–480 nm and the electron density and temperature were determined based on the relative intensities and Stark broadening width of spectral lines. The spectrum results indicated that the argon additive could enhance the intensity of emissive spectrum of plasma, thus the electron concentration as well as the energy was increased, and finally prompted the ionization rate to produce active N, O and O3. The results of NO reduction showed that NO conversion e ciency increased in the range of 10%–30% with 5% addition of argon in stream comparing with the condition without argon additive. This study will play a positive role in the industrial application of dielectric barrier discharge deNOx reactor.