A novel approach to the explanation the effect of microwave heating on isothermal kinetic of crosslinking polymerization of acrylic acid

The effect of microwave heating (MWH) on the isothermal kinetic of crosslinking-polymerization of acrylic acid (CPAA) was investigated. The kinetic curves of CPAA were determined in the temperature range from 303 to 328 K. By applying the model-fitting method it was revealed that the isothermal kinetics of CPAA was described by the first order chemical reaction kinetics model under the MWH and by the second order chemical reaction rate model for the conventionally heated (CH) process. The values of the reaction rate constants of CPAA are about 40 times higher for the microwave heated system than for the conventional heating. The kinetic parameters (activation energy (E _a) and pre-exponential factor (lnA)) of the CPAA are significantly lower than the corresponding values for CH process. It was found that the increase in the reaction rate of CPAA for MWH was not a consequence of overheating neither the hot spots in the reaction system. Based on model of selective energy transfer between the reacting molecules and the heating bath a novel explanation of the established effects of MWH on the kinetics of CPAA is given. A quantized nature and value of activation energy was confirmed. The decrease in the value of activation energy of CPAA under microwave heating is explained by the increased value of energy of ground vibration level of resonant oscillator in the AA molecule (v = 1417 cm^?1) caused by the absorption of non-thermal energy of MW field.     

Critical Evaluation of the Microwave Effect on Radical (Co)Polymerizations

Critical evaluations of the microwave effect on initiation, propagation, and termination during conventional radical polymerizations (RPs) of methyl methacrylate (MMA) and random copolymerization of styrene (St) with (meth)acrylates are examined by comparing microwave heating (MWH) and conventional heating (CH). Poly(methyl methacrylate) with similar , / , and conversion are obtained under precisely controlled temperature, indicating very small changes of propagation rate constant. Rate enhancement in the absence of precise temperature control is mostly due to the higher reaction temperature of the reaction mixture than the apparent value indicated on display. Rates of initiator decomposition under well‐controlled temperature are essentially the same for MWH and CH.     

A Microwave-Assisted Boudouard Reaction: A Highly Effective Reduction of the Greenhouse Gas CO2 to Useful CO Feedstock with Semi-Coke

The conversion of CO₂ into more synthetically flexible CO is an effective and potential method for CO₂ remediation, utilization and carbon emission reduction. In this paper, the reaction of carbon-carbon dioxide (the Boudouard reaction) was performed in a microwave fixed bed reactor using semi-coke (SC) as both the microwave absorber and reactant and was systematically compared with that heated in a conventional thermal field. The effects of the heating source, SC particle size, CO₂ flow rate and additives on CO₂ conversion and CO output were investigated. By microwave heating (MWH), CO₂ conversion reached more than 99% while by conventional heating (CH), the maximum conversion of CO₂ was approximately 29% at 900 °C. Meanwhile, for the reaction with 5 wt% barium carbonate added as a promoter, the reaction temperature was significantly reduced to 750 °C with an almost quantitative conversion of CO₂. Further kinetic calculations showed that the apparent activation energy of the reaction under microwave heating was 46.3 kJ/mol, which was only one-third of that observed under conventional heating. The microwave-assisted Boudouard reaction with catalytic barium carbonate is a promising method for carbon dioxide utilization.     

Microwave-assisted C-C coupling reaction using polymer-supported electron-rich oxime palladacycles in aqueous condition

Previously reported polymer-supported oxime palladacycle catalyst has shown effective catalytic activity in the Suzuki coupling reaction. In this work, the effect of microwave on reaction rate and induction period was examined by comparing them with the conventional heating. Undoubtedly, microwave heating effectively enhanced the catalytic performance in the Suzuki reaction. In-depth observation of the kinetic profiles revealed that the microwave irradiation not only reduced the overall reaction time but also significantly decreased the induction period to less than 3 min. Finally, the performance of the catalyst in water, coupling of potassium phenyltrifluoroborate and aryl bromides, and recyclability were also examined.     

微波辐照下丙烯酰胺的原子转移自由基共聚合

在微波辐射下,以水为反应介质,2-氯丙酰胺为引发剂,氯化亚铜/2,2′-联吡啶为催化体系,自制的磺基甜菜碱两性离子功能单体3-(2-甲基丙烯酰氧乙基二甲胺基)丙磺酸盐(DMAPS)与丙烯酰胺(AM)单体进行原子转移自由基共聚合反应,得到磺基甜菜碱型两性离子聚合物P(AM-DMAPS)。 讨论了微波功率、反应时间、单体用量、引发剂用量、催化剂和配体用量等因素对聚合反应的影响,并与相应的热聚合法进行了对照。 结果表明,微波辐射功率240 W,反应时间为1250 s时,微波辐射下共聚合的表观速率常数(Kappp)为热聚合法4.5倍,此时AM与DMAPS在水介质中的最佳合成条件为:单体总浓度4 mol/L(其中功能性单体DMAPS在混合单体中所占摩尔分数为1.0%),引发剂浓度0.015 mol/L,催化剂浓度0.01 mol/L。 此时转化率为40.15%,Mn为46410。     

Microwave-Assisted Synthesis of Poly(ε-caprolactone)-block-poly(ethylene glycol) and Poly(lactide)-block-poly(ethylene glycol)

Summary: This study reported the preparation and characterization of PCL-b-mPEG (poly(ε-caprolactone)-block-poly(ethylene glycol)) and PLL-b-mPEG (poly(L-lactide)-block-poly(ethylene glycol)) diblock copolymers by microwave heating and comparison of resulted products the ones with prepared by conventional heating. Diblock copolymers were synthesized successfully by the microwave-assisted ROP in the presence of stannous octoate (SnOct₂) as catalyst under nitrogen atmosphere in different monomer ratios. Structural and functional characterization of copolymers were performed by FTIR, ¹H-NMR and DSC. Molecular weight values were determined by GPC and also calculated from ¹H-NMR. According to the results, microwave irradiation allowed to obtain polymers with very narrow size distribution in very short reaction time. Similar polymers prepared by conventional heating were also synthesized for comparison. Molecular weight and conversion of polymers were increased by irradiation time. This change was continued until a certain time point after which no more increase was observed. It was concluded that microwave irradiation is a succesful method to obtain these diblock copolymers in very short reaction time and with a similar conversion obtained by conventional method.     

甲烷选择催化还原NO研究进展

 近十年来,甲烷选择催化还原NOx已引起各国环境研究工作者的关注．综述了近年来甲烷选择催化还原NOx方面的研究进展,着重分析了用于该反应的催化剂的研究状况,探讨了目前比较公认的甲烷选择催化还原NOx的反应机理（NO2机理）,详细介绍了目前催化剂用于提高甲烷DeNOx反应活性的方法;并展望了甲烷选择催化还原NOx今后的研究方向．     

A Novel Production Route for Nylon-6: Aspects of Microwave-Enhanced Catalysis

Summary: Microwave irradiation was used for the amidation of a nitrile with an amine with a freshly prepared zirconium-based heterogeneous catalyst. Microwave irradiation selectively heats the catalyst which enhances its activity as compared to conventional heating. The difference between microwave heating and conventional heating disappears when Zr(OH)₄ is used instead of ZrO₂, indicating a microwave-induced shift in the hydrolysis equilibrium, i.e. the distribution of ZrO₂, ZrO(OH)₂ and Zr(OH)₄, of the zirconium-based catalyst. The catalyst efficiently catalyzes the amidation of valeronitrile with n-hexylamine with conventional as well as with microwave heating. Zr(OH)₄ was also used for the polymerization of 6-aminocapronitrile using conventional and microwave heating. With both heating methods a relatively low molecular weight polymer with a M_n of 4000 g/mol was obtained in a sealed vessel, due to the presence of water and ammonia. A post-polymerization step under microwave irradiation, with active removal of water and ammonia shifts M_n to 10000 g/mol. Pressure decrease to facilitate water removal resulted in products with higher molecular weights. A pressure reduction to 50 Pa and operation in an argon atmosphere at 230 °C resulted in nylon-6 with a M_n of 65000 in rather short reaction times. Lower pressures led to end-biting and evaporation of the volatile ε-caprolactam at 230 °C. As a consequence the resulting product has than a much lower molecular weight. The combination of a heterogeneous zirconium based catalyst and microwave heating is promising for process intensification for nylon-6 production.     

反应条件对Ni-CaO-ZrO2催化剂上CH4-CO2重整反应及积炭的影响

用共沉淀法制备了Ni-CaO-ZrO₂催化剂,并将其用于CH₄-CO₂重整反应。考察了反应温度、空速和反应物配比对催化剂性能和积炭的影响。通过热力学计算和实验表征研究发现,反应条件对CH₄-CO₂重整反应结果和积炭有重要的影响。由于高温条件同时有利于CH₄裂解和碳物种的及时消除,升高温度可以提高催化剂的活性和稳定性。增大空速则使CH₄的转化率和消碳反应的速率均降低,导致积炭量增加。同时,反应物配比对催化剂表面的积炭量也有很大影响;稍高的CO₂/CH₄摩尔比有利于抑制CH₄-CO₂重整反应过程中的积炭。     

Use of a silicon carbide multi-well plate in conjunction with microwave heating for rapid ligand synthesis, formation of palladium complexes, and catalyst screening in a Suzuki coupling

The preparation of a library of bis-imidazolium salts and corresponding palladium complexes is reported. These complexes are screened as catalysts in the Suzuki reaction between 4-bromoanisole and phenylboronic acid. Each step is performed in parallel using a 24-position silicon carbide plate and microwave heating. The plate allows for use of standard glass vials as reaction vessels. The ease and speed of operation show the potential for microwave heating in conjunction with the silicon carbide plate as a tool for catalyst screening.     

Long‐lived intermediates in reversible addition–fragmentation chain‐transfer (RAFT) polymerization generated by γ radiation

A novel experimental procedure is presented that allowed probing of reversible addition–fragmentation chain‐transfer (RAFT) free‐radical polymerizations for long‐lived species. The new experimental sequence consisted of gamma irradiation of a mixture of initial RAFT agent (cumyl dithiobenzoate) and monomer at ambient temperature, a subsequent predetermined waiting period without initiation source also at ambient temperature, and then heating of the reaction mixture to a significantly higher temperature. After each sequence step, the monomer conversion and molecular weight distribution were determined, indicating that controlled polymer formation occurs only during the heating period. The results indicated that stable intermediates (either radical or nonradical in nature) are present in such experiments because thermal self‐initiation of the monomer can be excluded as the reason for polymer formation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1058–1063, 2002     

Creating patterned poly(dimethylsiloxane) surfaces with amoxicillin and poly(ethylene glycol)

This paper reports a simple microwave plasma patterning of poly(dimethylsiloxane) (PDMS) surfaces, which is accomplished by allowing selective surface areas to microwave plasma exposure in the presence of gaseous monomer. When maleic anhydride is used for microwave plasma reaction in the presence of physical barrier on the PDMS substrate, the resulting patterned surfaces with chemically bonded maleic anhydride and carboxylic acid groups are generated. In this particular study we attached amoxicillin via ammonolysis under weak base conditions in the presence of a catalyst as well as poly(ethyleneglycol) (PEG). A combination of internal reflection IR imaging (IRIRI) and atomic force microscopy (AFM) revealed that amoxicillin and PEG can be readily reacted on the microwave plasma patterned PDMS surfaces. Surface areas directly exposed to microwave plasmons exhibit the highest reactivity due to higher content of functional groups. These studies also show that molecular weight of PEG has also significant effect on kinetics of surface reactions.     

Scope and mechanism of the intermolecular addition of aromatic aldehydes to olefins catalyzed by Rh(I) olefin complexes

Rhodium (I) bis-olefin complexes Cp*Rh(VTMS)(2) and CpRh(VTMS)(2) (Cp* = C(5)Me(5), Cp = C(5)Me(4)CF(3), VTMS = vinyl trimethylsilane) were found to catalyze the addition of aromatic aldehydes to olefins to form ketones. Use of the more electron-deficient catalyst CpRh(VTMS)(2) results in faster reaction rates, better selectivity for linear ketone products from alpha-olefins, and broader reaction scope. NMR studies of the hydroacylation of vinyltrimethylsilane showed that the starting Rh(I) bis-olefin complexes and the corresponding Cp*/Rh(CH(2)CH(2)SiMe(3))(CO)(Ar) complexes were catalyst resting states, with an equilibrium established between them prior to turnover. Mechanistic studies suggested that CpRh(VTMS)(2) displayed a faster turnover frequency (relative to Cp*Rh(VTMS)(2)) because of an increase in the rate of reductive elimination, the turnover-limiting step, from the more electron-deficient metal center of CpRh(VTMS)(2). Reaction of Cp*/Rh(CH(2)CH(2)SiMe(3))(CO)(Ar) with PMe(3) yields acyl complexes Cp*/Rh[C(O)CH(2)CH(2)SiMe(3)](PMe(3))(Ar); measured first-order rates of reductive elimination of ketone from these Rh(III) complexes established that the Cp ligand accelerates this process relative to the Cp* ligand.     

阶跃升温分解法对非负载型镍催化甲烷分解活性的影响

 以乙醇为洗涤溶剂采用沉淀法制备了非负载型 Ni 催化剂, 考察了预处理过程对催化剂上 CH4 分解活性的影响. X 射线衍射及 CH4 程序升温表面反应结果表明, 降低还原温度可减小 Ni 粒子尺寸, 从而提高催化剂活性. 同时, 采用 CH4 多温度逐步分解 (多点阶跃升温分解) 法可形成较稳定的 Ni 粒子, 有效提高催化剂的活性及稳定性, 500 oC 下 CH4 初始转化率可达 8.40%, 反应 120 min 时升至 11.20%; 而在 350 和 500 oC 两点阶跃升温分解的 CH4 最高转化率只有 1.61%.     

Systematic and in situ energy dispersive X-ray diffraction investigations on the formation of lanthanide phosphonatobutanesulfonates: Ln(O(3)P-C(4)H(8)-SO(3))(H(2)O) (Ln = La-Gd)

Using the flexible linker H(2)O(3)P-C(4)H(8)-SO(3)H (H(3)L) and rare earth ions Ln(3+) (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) we were able to synthesize the new isostructural inorganic organic hybrid compounds Ln(O(3)P-C(4)H(8)-SO(3))(H(2)O). High-throughput experiments were employed to study the influence of the molar ratios Ln:H(3)L and pH on the product formation. The crystal structure of the compounds Sm(O(3)P-C(4)H(8)-SO(3))(H(2)O) (1) and Pr(O(3)P-C(4)H(8)-SO(3))(H(2)O) (2) were determined by single crystal diffraction. The structures are built up from chains of edge-sharing LnO(8)-polyhedra that are connected by the phosphonate and sulfonate groups into layers. These layers are linked by the -(CH(2))(4)- group to form a three-dimensional framework. The synthesis of compound 1 was scaled up in a conventional oven as well as in a microwave reactor system. A modification of a microwave reactor system allowed its integration into the beamline F3 at HASYLAB, DESY, Hamburg. The crystallization was investigated in situ by means of energy dispersive X-ray diffraction using conventional as well as microwave heating methods applying temperatures varying from 110 to 150 °C. The formation of Sm(O(3)P-C(4)H(8)-SO(3))(H(2)O) takes place in two steps. In the first step a crystalline intermediate was observed, which transforms completely into compound 1. The method by Sharp and Hancock was used to determine the rate constants, reaction exponents, and the Arrhenius activation energy for both reaction steps. Comparing both heating methods, microwave heating leads to fully crystallized reaction product after shorter reaction times, but neither the temperature nor the heating method has significant influence on the induction time.     

交联聚苯乙烯树脂固载甲酰基的微波辅助还原

在微波照射的相转移催化(MI-PTC)条件下,3种甲酰基功能化的交联聚苯乙烯树脂——对甲酰基苯氧基甲基树脂、对甲酰基-2-甲氧基苯氧基甲基树脂和对甲酰基-3-甲氧基苯氧基甲基树脂固载的甲酰基被NaBH4还原,得到相应的3种苄羟基功能化的树脂——Wang树脂、Sasrin树脂和新型的对苄羟基-3-甲氧基苯氧基甲基树脂.考察了溶剂、相转移催化剂等因素对反应的影响,优化的反应介质为THF/H2O混合溶剂,相转移催化剂为苄基三羟乙基氯化铵(BTHAC).然而,在传统加热和微波辐射条件下,最有效混合溶剂的配比有所不同.在水浴加热条件下,最有效的反应溶剂为12 mL THF+3 mL H2O;而在微波加热的条件下,最有效的反应溶剂却是3 mL THF+12 mL H2O.在优化的溶剂、催化剂条件下,微波功率为60 W时,高分子固载的甲酰基30 min之内几乎被定量地还原成羟基.与传统加热方式比较,MI-PTC还原聚苯乙烯固载甲酰基可以大大缩短反应时间,提高反应效率,是一种进行高分子化合物官能团转化的良好方法.     

Silica nanoparticles obtained by microwave assisted sol–gel process: multivariate analysis of the size and conversion dependence

Silica nanoparticles were synthesized by the sol–gel method in alcoholic solution under microwave irradiation in the presence of an ammonium catalyst. The effect of the reaction time, the reaction temperature, water and ammonium concentrations on particle size and conversion (measured by light scattering and FTIR respectively) were analyzed using multivariate analysis. The results showed that water and ammonium concentrations are the main factors that control the particle size and the conversion. Both properties increase with water and ammonium concentration. Moreover, comparing with the results obtained using traditional heating, the microwave heating gave rise to higher reaction rate and narrower dispersion of the particle size.     

Influence of drying processes on oxidative stability of ethyl corn biodiesel by differential scanning calorimetry

The influence of drying processes in the biodiesel oxidation was investigated by means of the oxidative induction time obtained from differential scanning calorimetry data. For this purpose, corn biodiesel was dried by different methods including: chemical (anhydrous sodium sulfate) and thermal (induction heating, heating under vacuum and with microwave irradiation). The drying efficiency was evaluated by monitoring IR absorption in the 3,500–3,200 cm⁻¹ range and by the AOCS Bc 2-49 method. In general, the oxidative induction times increased inversely to the heating degree, except that of microwave irradiation, which was selective to water evaporation and caused low impact over the unsaturation of biodiesel. The DSC technique was shown to be a powerful tool to evaluate with high level of differentiation the influence of the drying process on the oxidative stability of biodiesel.     

Mechanism and Kinetics of the Induction Period in Nitroxide Mediated Thermal Autopolymerizations. Application to the Spontaneous Copolymerization of Styrene and Maleic Anhydride

Recently we reported an experimental and theoretical (simulation) investigation on the mechanism of the induction period and the initial polymerization stages in the nitroxide mediated autopolymerization of styrene. In this paper we extend some of the results presented there and perform preliminary induction period experiments for the study of the mechanism and kinetics of the spontaneous copolymerization of styrene (S) and maleic anhydride (MA) in the presence of TEMPO and 4-OH-TEMPO. With even small amounts of MA (2% wt) the induction period is dramatically reduced by a factor of about 20 in comparison with the nitroxide-mediated styrene autopolymerization at 120 °C. Our results suggest that the initiation mechanism involves a first step of reaction between S and MA. We speculate that this reaction is a Diels-Alder cycloaddition followed by hydrogen abstraction through a monomer or TEMPO assisted homolysis to form a radical pair (monomer case) or a single radical (TEMPO case), which either initiates polymerization or is trapped by TEMPO depending on the conditions. Hall and Padias have studied similar electron donor-acceptor co-monomer pairs and favor the formation of a tetramethylene diradical as the initiating species for spontaneous copolymerization. In any case, the rate-limiting step would be the initial reaction of S and MA. These induction experiments allow us to obtain an initial estimate of the order of magnitude for the kinetic constant of the rate-limiting step, as 10⁻⁶ Lmol⁻¹s⁻¹.     

甲醇直接气相羰基化反应动力学

甲醇直接气相羰基化研究 ,是在无任何促进剂下 ,ＣＯ与甲醇直接进行羰基化反应 ,这与目前公认的甲醇必须有碘化物作用下构成催化循环的间接羰化不同 ,在催化理论上有可能提出新的羰基化机理。彭峰等在甲醇直接气相羰基化方面 ,对具有高活性与选择性的非铑非卤素Ｍｏ Ｃ催化剂体系进行了系列研究 ,并取得了较好的实验结果[1～ 5] 。有碘甲烷参与的甲醇羰基化液相或者气相反应 ,大多数文献认为控制步骤是碘化物中Ｃ -Ｉ键的解离及ＣＯ的插入 ,羰基化反应是由一系列平行和连串反应组成的[6～ 8] 。催化剂类型不同得到的动力学参数也不相同 ,难…