【作者】 赵剑利；

【导师】 王祥生； 郭洪臣；

【作者基本信息】 大连理工大学 ， 工业催化， 2009， 博士

【摘要】 过氧化氢（H₂O₂），作为一种绿色氧化剂，已广泛地应用在造纸、水处理及精细化学品合成领域。目前蒽醌法H₂O₂生产技术在全球市场处于主导地位，但由于工艺过程复杂及设备投资大等问题，该技术只有在大规模集中生产时才会带来较好的经济效益。所以对于大多数分散用户而言，使用H₂O₂就必须承担其安全存储及带水运输过程引入的附加成本。而近年来，以H₂O₂为氧源的钛硅沸石催化丙烯环氧化技术，作为传统环氧丙烷生产工艺的理想替代技术，在工业化过程中也受制于商品H₂O₂的高昂成本。因此，小规模、低投资、方便灵活的H₂O₂生产新工艺越来越受研究者们重视。目前此领域最活跃的研究集中在贵金属催化氢氧液相直接合成过程，但由于该体系固有的多相间传质及产物分解等问题，致使其在近百年的漫长发展后，仍难以满足市场的需要。氢氧等离子体直接合成H₂O₂技术，以其工艺简单、产物纯度及浓度高等特点，已成为极具潜力的H₂O₂合成新方法之一。然而，同大多数等离子体化学技术一样，该合成过程中较低的能量效率严重限制了它的工业应用。因此，为推动该技术的工业化进程，须选择适宜的放大合成路线及设计稳定高效的放大反应器。另外，作为一种方便灵活的现场H₂O₂合成方法，该过程可与丙烯液相环氧化集成生产环氧丙烷，以减少H₂O₂存储及运输过程的成本。为解决以上问题，本论文在前期工作的基础上，开展了氢氧等离子体合成H₂O₂的实验室放大研究及其与丙烯液相环氧化工艺的集成研究，探讨了放大合成H₂O₂过程中的反应特性及能效变化规律，并对所用的反应器进行了优化。此外，分析了H₂O₂合成过程中决定能量效率的主要因素，并对电源与反应器负载间的阻抗匹配问题做了探索研究。研究中得到的主要结果如下：1．利用并联连接的多个介质阻挡放电管构成的反应器，在常温常压下研究了氢氧等离子体放大合成H₂O₂过程的反应特性及能量效率。发现放电管数量的变化对氢氧等离子体的放电模式没有明显影响，H₂O₂选择性维持在64％左右，不随管数及注入功率改变。注入功率为4．9～5．0 W、原料气停留时间为18 s、放电频率为14 kHz时，放大过程中H₂O₂产能由7．1 mmol／h增至20．1 mmol／h，反应器能效由50 gH₂O₂／kWh增至136 gH₂O₂／kWh。合成过程的总能效受制于极低的电源能量注入效率，后者的提升需通过优化电源与反应器负载间的阻抗匹配来实现。2．放电管电极间距、高压电极材质、放电区长度及放电频率对H₂O₂合成过程中的反应特性及能量效率有重要影响。采用窄极间距的金属高压电极放电管既有利于反应器能效的提高，也有利于氧转化率及H₂O₂产率的提高。适当增加放电区长度及放电频率也可提高合成过程中的氧转化率、H₂O₂产率及反应器能效。使用电极间距为1．0 mm、放电区长度为30 cm的金属高压电极放电管，原料气总流速及氧浓度分别为420 ml/min和4．8vol％、电源放电频率为16 kHz、注入功率为2．9 W时，单管反应可得到高达151gH₂O₂／kWh的反应器能效。将其应用于三管放大合成，原料气总流速为630 ml／min、电源放电频率为14 kHz时，最高可得到165 gH₂O₂／kWh的反应器能效和8．7 gH₂O₂/kWh的总能效。3．放电系统中，电源变压器漏感L与反应器负载等效电容C形成的LC电路中存在谐振问题，电源工作于谐振频率f_R时其与反应器负载间的阻抗匹配最优。电源工作频率f_W与f_R间的偏离越大，电路的阻抗匹配程度越差，电源的能量注入效率越低。为提高反应器能效，需采用窄极间距的金属高压电极反应器，且应在较高频率下放电。在此基础上设计电源时，应在一定范围内减小变压器漏感L，使f_R增大，同时调整f_W，使放电系统在较高频率范围内实现阻抗匹配。由此可同时得到较高的反应器能效和电源能量注入效率，使合成H₂O₂过程的总能效得到大幅提升。4．等离子体法H₂O₂直接合成过程可以安全、简洁地为选择氧化反应提供高纯度的H₂O₂氧化剂溶液。利用该法现场制备的氧化剂溶液，成功实现了氢氧等离子体合成H₂O₂技术与丙烯液相环氧化反应的集成。在常温常压下，放电反应器的注入功率为3．5W、原料气停留时间为18 s、甲醇溶剂的补入速率为13．2 ml／h时，可得到流量为12 ml／h、浓度为0．70 mol／L的H₂O₂氧化剂溶液。固定床反应器进料中丙烯／H₂O₂摩尔比为4．2、反应温度为50℃、压力为3．0 MPa、进料总空速为3．7 h^-1时，在18 h的运转过程中，此集成装置运行平稳，H₂O₂转化率和有效利用率分别保持在92～94％及72～77％，环氧丙烷选择性与产率稳定于94～95％及63～68％。更多还原

【Abstract】 Hydrogen peroxide （H₂O₂）, as a green oxidant, is widely used in pulp bleaching, wastewater treatment and chemical synthesis. Now almost all H₂O₂ is exclusively produced by anthraquinone oxidation process, which is economically viable only on a large scale due to the complex operations and huge investment. But to most of the customers, only relatively small amounts of H₂O₂ are required at any one time, so the transportation and storage of H₂O₂ accounts for a big part of the H₂O₂ cost. Moreover, in the last decade, propene epoxidation process with H₂O₂ catalyzed by TS-1 has been intensively studied as one of the most promising alternatives to traditional technologies, but its commercialization is strongly hindered by the relatively high cost of H₂O₂. Therefore, many studies focus on the development of a green, economical, and smaller-scale technology for H₂O₂ manufacturing. One promising route to generate H₂O₂ is the direct synthesis from hydrogen and oxygen in the presence of Pd/Au supported catalyst. However, this process suffers from the decomposition of H₂O₂ which is catalyzed by the same noble metal catalysts for H₂O₂ synthesis and mass transfer problem in such a three-phase system. So this technology has not been able to meet the requirements of the market yet even though the related studies last for nearly one hundred years.The direct synthesis of H₂O₂ via non-equilibrium plasma, which is characterized by simple operation process, high concentration and ultra high purity of the product, provides a promising alternative route for H₂O₂ production. However, as a general problem of plasma chemistry technology, the relatively low energy efficiency severely limits its commercialization. In view of industrial application, it is necessary to develop a suitable scale-up route and design highly efficient scale-up reactor. Moreover, the direct synthesis of H₂O₂ by plasma technology can supply on-site oxidant to propene epoxidation process, thus the storage and transportation costs of H₂O₂ can be reduced effectively.To solve the above problems, based on our previous works, the laboratory studies on scale-up synthesis of H₂O₂ via plasma technology and integration process of H₂O₂ synthesis with propene epoxidation have been carried out. The reaction characteristics and energy efficiency in the scale-up process were discussed, and the main factors which dominated the energy efficiency were determined. Also some strategies were proposed to optimize the impendence match between the power supply and reactor load. The main results were obtained in this dissertation as follows:1. The scale-up synthesis of H₂O₂ from H₂/O₂ via a dielectric barrier discharge at ambient conditions was studied by using a reactor consisting of multiple parallel discharge tubes. Varying the number of tubes had no significant effect on discharge mode and reaction mechanism. H₂O₂ selectivity kept at around 64 %, and no decay occurred during the scale-up process. With the input power of 4.9-5.0 W, residence time of 18 s, discharge frequency of 14 kHz, the H₂O₂ productivity increased from 7.1 mmol/h to 20.1 mmol/h during the scale-up process, and the reactor energy efficiency was improved from 50 gH₂O₂/kWh to 136 gH₂O₂/kWh. The total energy efficiency was limited by the extremely low energy transfer efficiency of power supply, and might be enhanced by optimizing the impedance match between the power supply and reactor load.2. The discharge gap of reactor, material of high-voltage electrode, length of discharge zone and discharge frequency have significant effects on reaction characteristics and energy efficiency. The reactor energy efficiency, O₂ conversion and H₂O₂ yield were enhanced by using the reactor with narrow discharge gap and metal high-voltage electrode. The increase of discharge zone length and discharge frequency at a certain extent also favored the improvement of O₂ conversion, H₂O₂ selectivity and reactor energy efficiency. By using the metal high-voltage electrode reactor which had the discharge gap of 1.0 mm and discharge zone length of 30 cm, with the reactant flow rate of 420 ml/min, O₂ content of 4.8 vol %, discharge frequency of 16 kHz and input power of 2.9 W, the energy efficiency as high as 151 gH₂O₂/kWh was obtained. For the application of said reactor in scale-up setup with three parallel tubes, with the total flow rate of material gas of 630 ml/min and discharge frequency of 14 kHz, the reactor energy efficiency of 165 gH₂O₂/kWh and total energy efficiency of 8.7 gH₂O₂/kWh have been achieved.3. In this discharge circuit, resonance was formed by the transformer leak inductance （L） of power supply and equivalent capacitance （C） of reactor. When the power supply worked at resonance frequency （fR）, the optimal impedance match between power supply and reactor load could be obtained. On the other hand, using the reactor with metal high-voltage electrode and increasing discharge frequency could enhance the reactor energy efficiency remarkably. So considering the above factors, L value should be reduced at a certain extent to obtain a relatively high fR for developing a suitable power supply, and then set the working frequency of the power supply at fR, ultimately the optimal impedance match can be obtained at a high frequency. In such an optimized discharge system, the reactor energy efficiency can be effectively improved together with the energy transfer efficiency, consequently the total energy efficiency for H₂O₂ synthesis will be enhanced significantly. 4. The direct synthesis of H₂O₂ via plasma method can safely and simply provide selective oxidation reactions with high-purity H₂O₂ oxidant. The integration of on-site H₂O₂ synthesized by plasma route and liquid-phase propene epoxidation catalyzed by TS-1 catalyst was successfully actualized. At ambient conditions, with the input power of 3.5 W, residence time of 18 s, methanol compensating rate of 13.2 ml/h, the H₂O₂ oxidant solution with the flow rate of 12 ml/h and concentration of 0.70 mol/L was prepared. Set the molar ratio of propene/H₂O₂ in feedstock at 4.2, reaction temperature at 50℃, system pressure at 3.0 MPa, WHSV at 3.7 h^-1, this setup worked smoothly during a period of 18 h. H₂O₂ selectivity and utilization efficiency varied in the range of 92-94 % and 72-77 % respectively, as well as propene oxide selectivity and yield maintained in the range of 94-95 % and 63-68 % respectively.更多还原