3-氯-4-氟硝基苯的微波合成法

研究了以3,4-二氯硝基苯为原料通过卤素交换氟化合成3-氯-4-氟硝基苯的反应。结果表明，微波加热条件下反应速率是常规加热的3～12倍。收率和选择性也都有提高。金属Lewis酸A1C13和SbCl3用作本反应的催化剂可以取得良好的效果，其中SbCl3效果最好，用于400W微波加热反应10min可得到97．0％的收率。     

Microwave heating processes involving carbon materials

Carbon materials are, in general, very good absorbents of microwaves, i.e., they are easily heated by microwave radiation. This characteristic allows them to be transformed by microwave heating, giving rise to new carbons with tailored properties, to be used as microwave receptors, in order to heat other materials indirectly, or to act as a catalyst and microwave receptor in different heterogeneous reactions. In recent years, the number of processes that combine the use of carbons and microwave heating instead of other methods based on conventional heating has increased. In this paper some of the microwave-assisted processes in which carbon materials are produced, transformed or used in thermal treatments (generally, as microwave absorbers and catalysts) are reviewed and the main achievements of this technique are compared with those obtained by means of conventional (non microwave-assisted) methods in similar conditions.     

Highly active Fischer–Tropsch synthesis Co/SiO2 catalysts prepared from microwave irradiation

Studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) as well as energy-diffusive X-ray spectroscopy (EDX), a highly active Co/SiO₂ catalyst which was prepared through microwave irradiation showed more uniform and better dispersion of the Co particles within the catalyst pellets, compared to that prepared by the conventional heating method. The Fischer–Tropsch (FT) synthesis activity of the microwave-irradiated catalyst was greater than that of the conventional heating one. Not only did the catalytic activity depend on the particle distribution, but also the irradiative time. The longer irradiative time increased the catalytic activity. It was shown that the irradiative time of 14 min was an optimum. It was found that cobalt distributed uniformly inside the whole catalyst pellet prepared by the microwave irradiation. On the contrary, cobalt concentration at the outer surface, with agglomerated form, was greater than that at the center or inner part of the catalyst pellet made by the conventional heating method. Higher dispersion state of the supported cobalt, as also proved by XRD, realized at the microwave irradiated catalyst determined its improved FT activity.     

Scale Continuous Microwave Dry‐Media Reactor – Part II: Application to Waxy Esters Production

The solvent free esterification reaction between stearic acid and stearyl alcohol has been examined with a montmorillonite clay as catalyst. To aim for industrial application the system has been studied on reaction rate, product purity, catalyst behavior and water removal as function of the process conditions. To avoid an etherification side reaction and to aim for the highest reaction rate, the temperature should be strictly maintained at 170 °C. This is provided on larger scale by the application of microwave heating. Although the examined Brønsted acid clay was found to lose its catalytic activity at very low water activities, a yield of 95 % pure stearyl stearate can be obtained by simply filtering of the clay without solvent extraction or distillation. The “waxy” esterification reaction was investigated with the pilot plant continuous microwave dry‐media reactor (CMDR). The reaction time needed for 95 % yield was reduced by a factor 20–30 in comparison with industrial conventional reactors. This was due to the more homogeneous heat transfer of microwaves, which allows to reach a higher bulk temperature.     

Kinetics of microwave‐assisted polymerization of ϵ‐caprolactone

The kinetics of polymerization of ?‐caprolactone (CL) in bulk was studied by irradiating with microwave of 350 W and frequency of 2.45 GHz with different cycle‐heating periods (30–50 s). The molecular weight distributions were determined as a function of reaction time by gel permeation chromatography. Because the temperature of the system continuously varied with reaction time, a model based on continuous distribution kinetics with time/temperature‐dependent rate coefficients was proposed. To quantify the effect of microwave on polymerization, experiments were conducted under thermal heating. The polymerization was also investigated with thermal and microwave heating in the presence of zinc catalyst. The activation energies determined from temperature‐dependent rate coefficients for pure thermal heating, thermally aided catalytic polymerization, and microwave‐aided catalytic polymerization were 24.3, 13.4, and 5.7 kcal/mol, respectively. This indicates that microwaves increase the polymerization rate by lowering the activation energy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1450–1456, 2004     

微波条件下植物纤维素降解工艺条件的优化

在微波加热条件下,采用HCl/H<,2>O<,2>催化剂对植物纤维素进行降解.通过中心组合实验优化的适宜降解条件为:催化剂体积分数5.0%、反应温度100℃、反应时间2.0 h,在此条件下,纯植物纤维素的降解率为70.6%,较常规加热降解率提高了32.01%.SEM分析微渡加热和常规加热下降解产物的结构特征,发现微波作...     

C2 selectivity enhancement in oxidative coupling of methane over microwave-irradiated catalysts

The oxidative coupling of methane over Li/MgO and BaBiO_{3 - x} catalysts irradiated by microwaves and classically heated is reported. Enhanced selectivities in C₂⁺ products are observed at lower temperatures under microwave conditions, especially with the Li/MgO catalyst.

The complex permittivity measurements of BaBiO_{3 - x} show that the regeneration of the active oxygen species on the surface is lower under microwave irradiation than classical heating. X-ray diffraction analyses of the catalyst before and after catalytic reaction, when it is classically heated and when it is heated by microwave irradiation, corroborate these results. Therefore, the CH₃⁻ carbanions are less oxidated at the catalyst surface under microwave irradiation.

On the other hand, the quenching of the output gas probably decreases the oxidation of CH°₃ radicals in the gas phase when the Li/MgO catalyst is irradiated by microwaves. The quenching of the output gas is a unique consequence of microwave irradiation which heats the catalyst without heating the wall of the reactor.     

微波辐射合成柠檬酸三乙酯

采用微波辐射法在强酸性阳离子交换树脂催化下,由柠檬酸和乙醇合成得到了柠檬酸三乙酯。主要考察了微波加热时间、催化剂用量等对产率的影响。结果表明,收率达90．6％的合成工艺条件为：微波功率为225W,加热时间约40min,催化剂用量约2％。常规法合成柠檬酸三乙酯需要在醇溶液中长时间加热制备,与常规方法相比,该法反应速度提高约12倍。     

Particle size effect in microwave-enhanced catalysis

Heat transfer analysis is used to determine the potential for selective heating of metallic catalyst particles attached to a support through the use of microwaves. Important parameters are identified and estimated. Using these estimates, it is concluded that selective heating is possible with microwave fields of high frequency heating catalyst beds cooled by gases at low pressures. Selective heating is found to have a strong dependence on catalyst particle size, with optimum sizes in the 40-80 nm range. There is also strong dependence on microwave frequency. Areas of greatest uncertainty are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental and theoretical study of microwave enhanced catalytic hydrodesulfurization of thiophene in a continuous-flow reactor

Hydrodesulfurization (HDS) of thiophene, as a gasoline model oil, over an industrial Ni-Mo/Al₂O₃ catalyst was investigated in a continuous system under microwave irradiation. The HDS efficiency was much higher (5%–14%) under microwave irradiation than conventional heating. It was proved that the reaction was enhanced by both microwave thermal and non-thermal effects. Microwave selective heating caused hot spots inside the catalyst, thus improved the reaction rate. From the analysis of the non-thermal effect, the molecular collisions were significantly increased under microwave irradiation. However, instead of being reduced, the apparent activation energy increased. This may be due to the microwave treatment hindering the adsorption though upright S-bind (η¹) and enhancing the parallel adsorption (η⁵), both adsorptions were considered to favor to the direct desulfurization route and the hydrogenation route respectively. Therefore, the HDS process was considered to proceed along the hydrogenation route under microwave irradiation.     

Kinetics of the Transesterification of Castor Oil with Maleic Anhydride Using Conventional and Microwave Heating

The transesterification of castor oil with maleic anhydride was studied using conventional and microwave heating. Reactions were followed by measuring the acid value and the reaction products were characterized by FTIR and ¹H NMR. A kinetic model that fit the experimental data was derived. The transesterification was non-catalytic and first-order with respect to each reactant. Non-thermal effects of microwaves were not observed. Activation energy, enthalpy of activation, entropy of activation and free energy of activation were similar regardless of the heating method. Rate constants and the pre-exponential factor were lower with the use of microwave heating, which could be a consequence of the decrease in the dielectric constant of the reaction liquid as the reaction progresses.     

Microwave effect on kinetics of paper cups pyrolysis

Not only are microwaves notorious in food heating, but they exhibit interesting properties in different domains including chemical engineering. Their ability to concentrate heat transfer inside dielectric materials enhances process efficiency and permits high heating rates. Nonetheless, their effect on reactions is still controversial. While some researchers believe in non-thermal effects due to the efficient conversion of microwave energy to enhance reactions without heat dissipation, others assert that microwave frequencies are not high enough to excite molecular bonds. In this study, paper cups pyrolysis is achieved in electrical and microwave TGA using two heating modes. The effect of microwaves on the kinetics of paper cups pyrolysis is shown to depend on the heating regime: at a moderate heating rate, microwave pyrolysis started at a lower temperature, while the pyrolysis in the electrical and microwave TGA have similar kinetic parameters at high heating conditions. This difference is linked with reaction mechanisms. At moderate heating conditions, cellulose decomposes first to an intermediate compound then to final products. The intermediate has a short reaction time and interacts with the microwave. Hence, hot spots at the molecular scale are generated in a short amount of time below the detectable limits of existing temperature measurements media. At a high heating rate, the decomposition of cellulose is direct and no effect is observed.     

Pilot Scale Continuous Microwave Dry‐Media Reactor – Part 1: Design and Modeling

This work presents a new pilot plant continuous microwave dry‐media reactor (CMDR) for industrial chemical applications. The CMDR consists of a 6 kW conveyor microwave oven with a subsequent hot air holding section. This microwave reactor has been designed for dry media or solvent‐free reactions and can treat through‐put in the range of 10–100 kg/h. The microwave heating behavior on the small scale is analyzed and the results are used to estimate the electromagnetic field requirements on the large scale. The temperature and the electric field distribution in the reactor are modeled and experimentally validated. In the second part of this study, a “waxy” esterification reaction was investigated with the CMDR. The reaction time needed for 95% yield was reduced by a factor of 20–30 compared to conventional industrial reactors. This was due to the more homogeneous heat transfer of microwaves, which allows a higher bulk temperature to be reached.     

微波辅助合成金丝桃素四磺酸衍生物

利用微波辅助合成的方法,对金丝桃素四磺酸衍生物合成路线中的大黄素蒽酮缩合反应分别从微波加热温度、辐射时间和催化剂3个因素进行了优化,确定了最佳反应条件:温度150℃,反应时间1 h,不使用催化剂;该步反应的产率可达82.2%,整个合成路线经放大后的总产率为65.3%。与常规加热方法相比,微波辅助合成法提高了反应效率和产率,减少了副反应的发生,使合成工艺更加低碳环保。     

Rhodium‐Catalyzed Enantioselective Hydrogenation of (E)‐Enol Acetate Acids

The novel rhodium complex [Rh(S)‐Phanephos(cod)]‐catalyzed hydrogenation of disubstituted (E)‐enol acetate carboxylic acids is reported. The catalytic cycle works under 30 bar of hydrogen under conventional heating giving different 3‐acetoxy‐2,3‐disubstituted carboxylic acids with ee ≥90%. Hydrogenation occurred also under microwave dielectric heating without eroding the enantioselectivity but improving the overall efficiency of the process. With microwaves, hydrogen pressure and reaction time required for complete hydrogenation dropped to 5 bar and 30 min, respectively. The best performance of this catalyst under microwave irradiation was TON 100, TOF 196 h⁻¹ with ee 99% on a 6‐g scale.     

Methane aromatization using Mo-based catalysts prepared by microwave heating

Mo/HZSM-5 and Cu–Mo/HZSM-5 catalysts for the non-oxidative aromatization of methane have been prepared by microwave heating method. The effects of Mo loading, the molar ratio of Cu/Mo and preparation method on the catalytic performance of catalysts were studied. The results were compared with those for the methane aromatization over catalysts prepared by conventional heating. Both two kinds of catalysts have the maximum methane conversion when the Mo loading is 6%. The catalysts prepared by microwave heating exhibited higher selectivity to benzene than that prepared by conventional heating. The addition of metal Cu to Mo/HZSM-5 catalyst prepared by microwave heating enhanced the lifetime of catalyst, and gave rise to a little increase in methane conversion. The molar ratio of Cu/Mo influenced the methane conversion, and the maximum value was attained when Cu/Mo = 0.05, whereas no significant influence on the benzene selectivity was observed with the increase molar ratio of Cu/Mo. N₂ adsorption results showed that the catalysts prepared by microwave heating have the larger surface area and the similar pore volume compared with the catalysts prepared by conventional heating. This fact revealed that the more Mo species located on the outer surface of catalysts prepared by microwave heating is the main reason why they have better catalytic performance. XRD analysis indicated that the Mo species are highly dispersed on HZSM-5 zeolite. The addition of Cu influenced the dispersion. The actual active phase Mo₂C can be identified on the catalyst surface after reaction. TEM analysis revealed the carbonaceous deposition to have the form of carbon nanotube after reaction, with a uniform size range of 10–20 nm. TG analysis indicated that carbonaceous deposition on the catalysts prepared by microwave heating is lower than that by conventional heating, and the metal Cu further prompts the stability of catalyst. Most of the carbonaceous deposition on catalysts prepared by microwave heating is formed at low temperature and it is easy to burn-off. Coke accumulation at high temperature is the main reason of catalyst deactivation. The carbonaceous deposition formed on the catalysts for non-oxidative aromatization of methane is different from those formed on the catalysts for partial oxidation of methane.     

微波法制备生物柴油研究进展

基于微波的选择性、瞬时性及体积性加热的特点,可以有效提高反应分子的平均能量、分子的碰撞频率,加快反应速率,采用微波辅助催化酯交换反应制备生物柴油近几年得到了国内外学者的广泛关注。将微波能应用于生物柴油制备过程具有显著的优势,与传统加热方式相比,采用微波辐射加热,反应时间明显缩短,产物组成也有所变化。因此主要从酸碱催化剂催化酯交换反应和酯化反应的角度,综述了国内外对微波辅助生物柴油制备的研究进展,并对微波优势及未来发展趋势进行了展望。     

Comparative Kinetic Study and Microwaves Non-Thermal Effects on the Formation of Poly(amic acid) 4,4'-(Hexafluoroisopropylidene)diphthalic Anhydride (6FDA) and 4,4'-(Hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline (BAPHF). Reaction Activated by Microwave, Ultrasound and Conventional Heating

Green chemistry is the design of chemical processes that reduce or eliminate negative environmental impacts. The use and production of chemicals involve the reduction of waste products, non-toxic components, and improved efficiency. Green chemistry applies innovative scientific solutions in the use of new reagents, catalysts and non-classical modes of activation such as ultrasounds or microwaves. Kinetic behavior and non-thermal effect of poly(amic acid) synthesized from (6FDA) dianhydride and (BAPHF) diamine in a low microwave absorbing p-dioxane solvent at low temperature of 30, 50, 70 °C were studied, under conventional heating (CH), microwave (MW) and ultrasound irradiation (US). Results show that the polycondensation rate decreases (MW > US > CH) and that the increased rates observed with US and MW are due to decreased activation energies of the Arrhenius equation. Rate constant for a chemical process activated by conventional heating declines proportionally as the induction time increases, however, this behavior is not observed under microwave and ultrasound activation. We can say that in addition to the thermal microwave effect, a non-thermal microwave effect is present in the system.     

微波诱导PTSA催化酯化合成没食子酸正丁酯

采用微波辐射技术,以对甲苯磺酸（ＰＴＳＡ）作催化剂,没食子酸和正丁醇直接酯化合成没食子酸正丁酯。最佳反应条件为：没食子酸１９．３ｍｍｏｌ,催化剂０．５ｇ,二者的摩尔比是１∶０１３５,正丁醇２０ｍｌ,微波功率５２５Ｗ,辐射时间２０ｍｉｎ,酯化产率为８７９％。该条件下的反应速度是酶促反应速度的５４倍。     

微波离子交换法制备Cu-ZSM-11及微波辐照MeOx/Cu-ZSM-11催化分解NO

用微波辐照离子交换法制备了Cu-ZSM-11,制备的Cu-ZSM-11和金属氧化物（MeO_x）机械混合制备了微波催化剂MeO_x/Cu-ZSM-11。考察了MeO_x在微波辐照下的升温行为,筛选出吸波性能好的MeO_x（MnO₂ >CuO >Ni₂O₃）为吸波组分。分别考察了微波辐照下金属氧化物、Cu-ZSM-11和MeO_x/Cu-ZSM-11直接分解NO性能,并与常规加热条件下比较。结果表明：微波辐照显著提高了NO的转化率,微波催化剂Ni₂O₃/Cu-ZSM-11在350℃时,NO转化率达到99.27%,N₂选择性达到99.9%;相同条件下,微波辐照MeO_x/Cu-ZSM-11直接分解NO转化率高于对应金属氧化物或Cu-ZSM-11分解NO的转化率,表明微波具有催化作用。微波辐照下氧气浓度对Ni₂O₃/Cu-ZSM-11直接分解NO性能几乎无影响,微波辐照消除了氧气阻抑作用,表现出微波选择效应。水汽存在对转化率有较小影响。反应进口气体不需要预热,进出口气体温度基本不变。