微波等离子体光谱技术的发展(二)

微波等离子体光源是一类重要的有较强激发能力的原子发射光谱光源,主要包括微波感生等离子体光源,电容耦合微波等离子体光源及微波等离子体炬光源。本文是微波等离子体光谱技术发展的第二部分,主要介绍了电容耦合微波等离子体光源及微波等离子体炬光源的结构原理和性能。并对它们的技术特点和进展进行评述。     

用于气相色谱的微波等离子体原子发射光谱检测器的发展

分别介绍和评价了用于气相色谱的微波诱导等离子体、电容耦合微波等离子体和微波等离子体炬等3种微波等离子体原子发射光谱检测器的发展、应用以及局限性。对用于气相色谱的微波等离子体原子发射光谱检测器的发展作了展望。     

离子液体-非极性溶剂微波提取法在人参化学成分研究中的应用

以离子液体作为微波吸收介质建立了离子液体-非极性溶剂微波提取法,对人参中的化学成分进行了提取,并将该法与固体微波吸收介质-非极性溶剂微波提取法、极性溶剂微波提取法以及混合溶剂微波提取法进行了对比.结果表明,极性溶剂提取的主要化学成分为极性化合物,而固体微波吸收介质-非极性溶剂微波提取法与离子液体-非极性溶剂微波提取法相比,提取所得的化学成分并无明显差别,说明离子液体是一种较好的微波吸收介质和能量传递材料.所建立的方法具有提取时间短、操作简单及绿色环保等优点,且对后期分析无明显影响,是快速提取化学成分的理想方法.     

Microwave synthesis of zeolite membranes: A review

Significant progress has been achieved in the last years on microwave synthesis of zeolite membranes. In many cases, microwave synthesis has proven to remarkably reduce the synthesis time. In addition, microwave synthesis could also result in different membrane morphology, orientation, composition, and thus the different permeation characteristics as compared with those synthesized by conventional heating. This review attempts to summarize the obtained progress in microwave synthesis of zeolite membranes. Some topics are discussed, including: (1) case study of microwave synthesis of zeolite membranes, e.g. LTA, MFI, AFI, and other types of zeolite membranes; (2) differences between conventional and microwave synthesis; (3) formation mechanism and the so called “specific microwave effect” in the case of microwave synthesis of zeolite membranes; (4) scaling-up of zeolite membrane production by employing microwave heating. The latter three topics are mainly focused on LTA type zeolite membranes. Concluding remarks and future perspective are also suggested in the end.     

微波技术在催化剂制备中的应用

微波作为一种独特的加热手段在化学领域已得到广泛应用。本文综述了微波技术在催化剂的合成、活性组分的负载等方面的研究应用,重点探讨了在分子筛催化剂的合成中微波技术所表现出的优越性,对微波合成催化剂的作用机理及影响因素作了评述,并展望了微波技术在催化领域的发展前景。     

Microwave-assisted asymmetric organocatalysis. A probe for nonthermal microwave effects and the concept of simultaneous cooling

A series of five known asymmetric organocatalytic reactions was re-evaluated at elevated temperatures applying both microwave dielectric heating and conventional thermal heating in order to probe the existence of specific or nonthermal microwave effects. All transformations were conducted in a dedicated reactor setup that allowed accurate internal reaction temperature measurements using fiber-optic probes. In addition, the concept of simultaneous external cooling while irradiating with microwave power was also applied in all of the studied cases. This method allows a higher level of microwave power to be administered to the reaction mixture and, therefore, enhances any potential microwave effects while continuously removing heat. For all of the five studied (S)-proline-catalyzed asymmetric Mannich- and aldol-type reactions, the observed rate enhancements were a consequence of the increased temperatures attained by microwave dielectric heating and were not related to the presence of the microwave field. In all cases, in contrast to previous literature reports, the results obtained either with microwave irradiation or with microwave irradiation with simultaneous cooling could be reproduced by conventional heating at the same reaction temperature and time in an oil bath. No evidence for specific or nonthermal microwave effects was obtained.     

微波波谱技术和应用*

微波波谱法具有研究分子系统的结构、构象平衡、分子间相互作用、分子内部运动等物理化学动力学过程的能力。本文综述了微波波谱技术的进展。对微波吸收波谱仪、脉冲喷嘴傅立叶变换微波波谱仪、线性脉冲傅立叶变换微波波谱仪等技术进展进行了论述,详细介绍了脉冲喷嘴阀技术、外部场调制、微波二次共振、线性脉冲、快速扫描等技术,分析了微波谱仪在分析测试领域的发展。对微波谱仪的未来发展做了展望。     

微波诱导甲烷在活性炭/碳化硅上直接转化制C2烃

 在高功率脉冲微波辐照下甲烷可在常压条件下在活性炭/碳化硅和活性炭碳化硅等 三种催化剂上直接转化为C2烃。研究结果表明,当使用合适的微波作用条件时,微波加热与微波 等离子协同作用可使甲烷在多孔碳化硅担载的活性炭催化剂上以很高的转化率和选择性直接转化为乙炔,除单独的微波加热诱导作用和微波等离子催化作用外,转移反应机制可能是微波加热与微波等离子交互作用的具体表现形式,对促进甲烷向乙炔直接转化起了重要作用。     

控温下微波反应装置用于壳聚糖羧甲基化反应

微波加热近年来被广泛应用在化学合成中。本文报道了通过外接恒温槽的恒温循环水的方法，实现了微波反应系统的恒温控制。将该装置应用于壳聚糖的羧甲基化反应，采用水溶剂代替传统加热方法的异丙醇溶剂，制备出取代度达0．85的羧甲基壳聚糖。     

柳树河油页岩微波干燥及其对热解特性的影响

在对家用微波炉改造基础上搭建了微波干燥实验台,研究了柳树河油页岩微波干燥特性及对热解特性的影响。结果表明,微波干燥所需的时间为传统干燥所需时间的20%;微波干燥速率要明显大于传统干燥速率;Page模型适用于描写柳树河油页岩微波干燥过程。微波干燥的油页岩同热风干燥后及原样油页岩的热解活化能随转化率的变化曲线基本一致,整体呈先上升后下降的趋势,在转化率为0.7时达到最大值;热解活化能在80~200 kJ/mol变动;微波干燥油页岩热解反应有机质分解段的活化能增加。     

微波对烯丙基芳醚的Claisen重排反应影响研究

5种烯丙基芳醚衍生物在无溶剂、无催化剂的条件下进行Claisen重排反应,采用了微波加热和常规加热方式,比较了同等温度下微波加热和常规加热反应速率的差异.结果表明微波加热可以显著提高烯丙基苯醚Claisen重排反应的速率.反应温度为190℃时,微波加热下反应速率可提高5～10倍.微波加热是一种无催化剂、高产率的Claisen重排反应的方法.     

微波辐射对TiO2制备及其光催化氧化乙醛性能的影响

采用微波辐射与常规加热法由TiO₂溶胶制备出TiO₂催化剂，采用高频低功率微波-光催化装置考察了微波对两种催化剂上CH₃CHO光催化氧化转化率和产物分布的影响。结果表明，微波干燥制备的TiO₂晶体比普通加热制备的TiO₂晶体对乙醛有更高的光催化活性和更强的氧化能力，且它们对乙醛光催化氧化的途径不同，前者的初始中间体为甲醛和甲酸，后者的初始中间体却为乙酸。还发现，微波辐射对两种样品上乙醛的光催化转化率有不同的影响，对微波辐射法所制样品的影响比对常规加热法所制样品的影响显著。微波辐射通过场效应可加速光催化初始中间体的转化，但它不改变光催化反应的途径，反应途径取决于光催化剂的特性。     

微波-炭还原法处理一氧化氮的研究

报道了一种不需要催化剂而直接采用微波-炭还原技术处理-氧化氮(NO)的新方法.讨论了气体流量、反应温度、微波功率和施加微波时间对活性炭与一氧化氮发生还原反应的影响.比较了连续施加微波和间歇式施加微波方式下一氧化氮与活性炭发生化学反应转化为无公害的氮气(N₂)和二氧化碳(CO₂)的效率.研究结果表明,微波功率和反应器的类型及升温速率对一氧化氮与活性炭反应效率的影响较大.在连续施加微波时,一氧化氮与活性炭反应率可达98％以上.此外,还对一氧化氮与活性炭反应后的产物进行了表征.     

微波辐射对乙酸乙酯皂化反应的影响

采用电导率法研究了微波辐射对乙酸乙酯皂化反应动力学常数的影响.结果表明,反应物经微波辐射后化学反应的动力学常数增大,且与辐射时间长短呈正相关.分析了微波辐射使动力学常数增大的原因.     

微波提取对挥发油化学成分的影响

采用无溶剂微波辅助提取与微波水蒸气蒸馏法提取薄荷叶和花椒挥发油,气相色谱-质谱(GC-MS)分析挥发油化学成分,与传统的水蒸气蒸馏对比,考察了微波对挥发油化学成分的影响.结果表明,微波促使薄荷叶挥发油中的薄荷醇氧化,转变为长叶薄荷酮和少量的薄荷呋喃酮.花椒挥发油中的按油素等化合物受质子的催化,在长时间温度较高的提取条件...     

Investigating the existence of nonthermal/specific microwave effects using silicon carbide heating elements as power modulators

The use of passive heating elements made out of chemically inert sintered silicon carbide (SiC) allows microwave transparent or poorly absorbing reaction mixtures to be heated under microwave conditions. The cylindrical heating inserts efficiently absorb microwave energy and subsequently transfer the generated thermal energy via conduction phenomena to the reaction mixture. In the case of low to medium microwave absorbing reaction mixtures, the addition of SiC heating elements results in significant reductions (30-70%) in the required microwave power as compared to experiments performed without heating element at the same temperature. The method has been used to probe the influence of microwave power (electromagnetic field strength) on chemical reactions. Six diverse types of chemical transformations were performed in the presence or absence of a SiC heating element at the same reaction temperature but at different microwave power levels. In all six cases, the measured conversions/yields were similar regardless of whether a heating element was used or not. The applied microwave power had no influence on the reaction rate, and only the attained temperature governed the outcome of a specific chemical process under microwave conditions.     

Microwave synthesis of nanoporous materials.

Studies in the last decade suggest that microwave energy may have a unique ability to influence chemical processes. These include chemical and materials syntheses as well as separations. Specifically, recent studies have documented a significantly reduced time for fabricating zeolites, mixed oxide and mesoporous molecular sieves by employing microwave energy. In many cases, microwave syntheses have proven to synthesize new nanoporous structures. By reducing the times by over an order of magnitude, continuous production would be possible to replace batch synthesis. This lowering of the cost would make more nanoporous materials readily available for many chemical, environmental, and biological applications. Further, microwave syntheses have often proven to create more uniform (defect-free) products than from conventional hydrothermal synthesis. However, the mechanism and engineering for the enhanced rates of syntheses are unknown. We review the many studies that have demonstrated the enhanced syntheses of nanoporous oxides and analyze the proposals to explain differences in microwave reactions. Finally, the microwave reactor engineering is discussed, as it explains the discrepancies between many microwave studies.     

Microwave drying of granules containing a moisture-sensitive drug: a promising alternative to fluid bed and hot air oven drying

The impact of microwave drying and binders (copolyvidone and povidone) on the degradation of acetylsalicylic acid (ASA) and physical properties of granules were compared with conventional drying methods. Moist granules containing ASA were prepared using a high shear granulator and dried with hot air oven, fluid bed or microwave (static or dynamic bed) dryers. Percent ASA degradation, size and size distribution, friability and flow properties of the granules were determined. Granules dried with the dynamic bed microwave dryer showed the least amount of ASA degradation, followed by fluid bed dryer, static bed microwave oven and hot air oven. The use of microwave drying with a static granular bed adversely affected ASA degradation and drying capability. Dynamic bed microwave dryer had the highest drying capability followed by fluid bed, static bed microwave dryer and conventional hot air oven. The intensity of microwave did not affect ASA degradation, size distribution, friability and flow properties of the granules. Mixing/agitating of granules during drying affected the granular physical properties studied. Copolyvidone resulted in lower amount of granular residual moisture content and ASA degradation on storage than povidone, especially for static bed microwave drying. In conclusion, microwave drying technology has been shown to be a promising alternative for drying granules containing a moisture-sensitive drug.     

有机溶剂和二元体系溶液在9590兆赫的微波吸收分析应用

在９５９０兆赫和室温下，研究了一些有机溶剂和二元体系溶液的微波吸收。首次使用诱导效应指数来表达同系化合物的分子结构与其微波吸收之间的关系。研究了一些缔合和非缔合二元体系溶液的微波吸收，并提出了一个计算二元非缔合体系微波吸收的经验公式。此外，建立了利用微波测定白酒中乙醇含量的方法。     

微波化学温度模拟研究进展

在微波化学研究中,通过数学模拟分析微波作用在化学体系的温度分布及变化,有助于控制微波加热过程,了解微波与物质之间的相互作用机理.本文针对微波化学数值模拟的特点,系统介绍了各种方法及模拟过程,对数值模拟分析中的关键问题进行了讨论,综述了近年来数值模拟温度分布在微波化学中的应用,提出了目前的研究难点,并展望了发展趋势.