微波辐射下CaSO4生成反应过程中的热点特性

在微波辐射化学反应过程中，常常会因为存在热点而导致爆炸或反应物烧毁等现象发生。本文以微波辐射下的硫酸钙生成反应为例，利用有限元方法求解Maxwell方程组、流体力学方程以及热传导方程，研究了微波辐射反应过程中热点的变化情况，并用实验验证了计算结果的正确性。研究结果表明：在加热过程中，随反应的进行，热点的位置是在不断变化的，且热点常出现在物质分相界面附近。     

微波辅助合成聚酯树脂动力学研究

研究了微波辅助合成聚酯树脂的酯化反应动力学,通过对比常规反应动力学的动力学参数,分析了微波在聚酯合成中的作用原理。研究发现微波作用仅在酯化阶段作用明显,反应速率有较大提升,而在缩聚酸解过程中并未有影响。因此本研究分别在微波辐射以及传统加热2种方式下,考察了聚酯树脂酯化阶段反应动力学,并获得了2种方式下的反应动力学参数,计算处理得到微波作用下的反应活化能分别为2#:Ea2=227.5 k J/mol,5#:Ea5=42.5 k J/mol;常规加热下反应的活化能为Ea0=2 032.4 k J/mol。结果表明,微波辐射影响了该阶段的反应动力学,提升了反应速率,有微波非热效应存在,但反应平衡常数并未因此产生变化。     

微波有机合成及在混凝土减水剂制备中的应用研究进展

微波辐射作为反应活化的新型能源,已成为有机化学中普遍应用的先进技术。本文从过热、热点和选择性加热以及高极化场下的非热效应4方面阐述微波有机合成机理,结合国内外应用案例进行理论验证。重点从反应动力学角度分析了微波辐射对提高混凝土减水剂品质上的作用效果,总结了近几年微波辅助合成减水剂的研究进展,旨在推动微波技术在水泥混凝土外加剂领域中的实际应用。最后,提出微波辐射通过在电磁场作用下极性分子的快速振动实现,其热效应对体系起深层加热作用,非热效应改变反应动力学,但对作用的反应体系具有"选择性",应着重分析。微波辅助合成减水剂具有显著优势,可增大反应速率常数且存在非热效应,应加深研究及进一步推广。     

微波作用下的乙酸乙酯合成反应动力学

为揭示微波辐射效应对非均相酯化反应动力学的影响,研究了微波加热催化合成乙酸乙酯的酯化反应动力学,并与常规动力学作了对比.在自制微波功率连续可调、红外测温已校正的反应装置中,重复测定了反应温度为60,65,70和75℃时的正、逆反应速率常数,得到了Arrhenius方程参数.微波加热下的反应活化能为51.719 kJ/mol,指前因子为582.9:常规水浴加热下的反应活化能为48.581 kJ/mol,指前因子为169.2.研究结果表明,在研究的反应温度范围内,微波改变了反应动力学,加快了反应速率,存在微波非热效应,但并不改变反应平衡常数.     

水相微波诱导催化剂的调控策略及其污染物降解机理研究进展

微波诱导降解能够实现分子水平上的快速加热,并在微波吸收剂表面产生“热点”效应,在废水处理领域得到广泛应用。了解微波辐射诱导有机废水处理方法的一般研究现状,有助于进一步改进与微波辐射相关的废水处理技术。鉴此,总结了微波诱导催化材料在有机废水处理中的研究现状,对不同种类催化剂的作用机理及其与微波的协同效应进行综述,详细阐述了近年来微波诱导催化氧化反应的发展方向与调控策略。最后,总结了微波诱导催化材料以及微波应用于废水处理可能面临的挑战和未来的研究方向。     

微波辐射快速合成乙二醇硬脂酸酯

在微波辐射条件下,以对甲苯磺酸(PTSA)为催化剂,乙二醇和硬脂酸快速合成了乙二醇硬脂酸酯。讨论了微波功率、辐射时间、催化剂用量和醇酸量比对反应转化率的影响,得出最佳反应条件为:硬脂酸17 1g、乙二醇4 1g、PTSA0 23g、微波功率600W、反应时间5min,转化率为97%。该条件下的反应速率是常规加热条件下的36倍。实验中,采用煤油温度计测量了反应过程中的温度变化。     

微波辐射技术对制备催化剂和邻二甲苯在V2O5／SiO2系催化剂上发生氧化反应

当温度为Ｃａ５６３Ｋ时，通过微波辐射作用可使邻二甲苯和空气在Ｖ２Ｏ３／ＳｉＯ２系催化剂上发生氧化反应生成的邻苯二甲酸酐（ＰＡＮ）达到６７ｍｏｌ％这一高痃值。经过研究发现，如果采用微波辐射波制备催化剂，可使Ｖ２Ｏ５分更均匀地分散在ＳｉＯ２上。在微波辐射催化过程中，总反应的床最适温度下降到了５６３Ｋ，正文中还讨论了研究了微波电磁场对催化剂剂产生的影响作用。     

低温条件下微波对钾长石溶出性能影响的微观机理分析

目前利用钾长石提钾的工艺研究多为过程复杂且能量损耗较大,本文提出了一种利用微波辐射协助水热反应提钾的新方法。采用微波辐射预处理钾长石粉末,加热迅速,再通过低温条件下的水热反应体系溶出钾离子,对此过程中微波辐射时间,微波辐射功率因素对钾溶出率的影响进行研究,并通过SEM、XRD等表征手段对反应后滤渣进行微观分析。优化工艺条件可以得出,在微波辐射功率600W、微波辐射时间15min、水热反应时间180min、水热反应温度180℃时效果最佳。研究结果表明:最优条件下,钾的溶出率达92%;微波辐射使钾长石预处理后表面发生变化,生成K_0.85Na_0.15AlSiO₄等产物,提高了钾长石的溶出性能;反应生成水羟方钠石[Na₈Al₆Si₆O₂₄(OH)₂(H₂O)₂];有效节约了反应时间和反应过程中的能量损耗。     

微波促进的磷钼酸对酯化反应的催化性能

以自制的磷钼酸为催化剂,研究了微波辐射条件下磷钼酸对酯化反应的催化性能。探讨了催化剂用量、微波辐射功率、微波辐射时间对反应的影响。在优化反应条件下,即磷钼酸0.05g、微波功率640W、辐射时间40min时,酯的收率达到94.5%。     

响应面法优化4-丙烯酸羟丁酯的微波合成

研究了响应面法优化4-丙烯酸羟丁酯(4-HBA)的微波合成工艺过程研究。在合成工艺中利用微波辐射法,以1,4-丁二醇(BDO)和丙烯酸(AA)为主要原料合成4-HBA。以4-HBA的酯化率为考察指标,探讨了反应温度、微波辐射时间、微波功率、催化剂用量及醇酸摩尔比等单因素对酯化反应的影响。基于单因素实验,固定反应温度110℃、微波功率700 W,采用Box-Behnken响应面法对微波合成工艺过程中的微波辐射时间、催化剂用量及醇酸摩尔比3个参数进行优化,得出最优的合成工艺条件为:n(BDO)∶n(AA)=2.9∶1,催化剂用量为3.52%(对反应物总质量),反应时间为26 min,在此最佳实验条件下进行重复实验3次,得到4-HBA的酯化率为70.04%。     

Control of microwave-generated hot spots. Part IV. Control of hot spots on a heterogeneous microwave-absorber catalyst surface by a hybrid internal/external heating method

A problem with microwave-absorbing heterogeneous catalysts (MAHCs) in non-polar solvents is resolved with a novel approach that also uses an external heating bath in combination with microwave heating. In non-polar solvents, the microwave radiation dielectrically and selectively heats only the catalyst resulting in the frequent occurrence of hot spots under these conditions. However, such hot spots can be controlled through a combined (hybrid) internal/external heating methodology (MAHS). Moreover, high temperatures can be maintained with significant energy saving. The potential benefit of MAHS has been examined by carrying out the synthesis of 4-methylbiphenyl using the Suzuki–Miyaura coupling reaction in toluene solvent in the presence of palladium catalytic particles supported on activated carbon particulates (Pd/AC). The hybrid internal/external heating method saved 65% of microwave energy and increased the chemical yield of 4-methylbiphenyl nearly twofold in comparison with a conventional microwave heating method.     

Effects of Microwave Dielectric Heating on Heterogeneous Catalysis

The effect of microwave dielectric heating on both endothermic and exothermic reactions was investigated. Apparent equilibrium shifts for both reactions were observed which were attributed to the formation of spatial hot spots in the catalyst bed. The possible location of remarkable temperature gradients was examined experimentally and theoretically.     

Carbon Dioxide Reforming of Methane with Pt Catalysts Using Microwave Dielectric Heating

Microwave heating was applied to the catalytic reforming reaction of methane with carbon dioxide over platinum catalysts. It was found that CO₂ and CH₄ conversions and the product selectivity (H₂/CO) were generally higher under microwave conditions than that obtained with conventional heating at the same measured temperature. The effect of microwave heating was attributed to the formation of hot spots with higher temperature than that measured in the bulk catalyst bed.     

钢丝对废橡胶微波裂解过程的影响分析

研究钢丝对废橡胶微波裂解过程的影响并进行有限元仿真和试验探究。仿真结果表明,含钢丝的废橡胶在钢丝附近场强明显增强,热点增多且分布均匀。裂解试验结果表明,废橡胶中存在适量钢丝会促进废橡胶的裂解,使裂解升温更快,出油比例更高。由此认为,废轮胎整胎微波裂解更有利于提高裂解效率、促进节能环保和改善裂解产物品质。     

干燥方式对红枣动力学及挥发性成分的影响

采用热风干燥、真空冷冻干燥和微波真空干燥对红枣进行干燥处理，结合顶空固相微萃取-气相色谱-质谱（headspace solid-phase microextraction-gas chromatography-mass spectrometry，HS-SPME-GC-MS）和电子鼻对枣片挥发性成分进行了分析，并对比了3种干燥方式对红枣色泽、动力学和挥发性成分的影响。结果表明，热风干燥和微波真空干燥对枣片色泽影响较大，真空冷冻干燥能够更好的保持原始色泽；对动力学方程进行拟合，发现Page 模型为预测红枣3种干燥方式干燥特性最适合的数学模型；干燥对枣片挥发性成分种类及相对含量差异显著，其中干燥前后相同的挥发性成分有19种。挥发性物质主要有酸类、酯类、醇类、醛类、酮类、烃类、杂环类和其他化合物，干燥过后枣片中酸类和烷烃类挥发性成分相对含量显著增加，醛类和杂环类物质显著降低。电子鼻结果表明干燥后枣片香气特征与新鲜红枣有较大的区别，热风干燥和微波真空干燥香味特征较为接近，微波真空干燥枣片的焦甜香特征更为明显。相较于热风干燥和真空冷冻干燥，微波真空干燥效率较高、能耗较低、周期较短，更适于制备干燥枣片。     

Analysis of catalytic reaction systems under microwaves to save energy

Effects of microwaves on catalytic reaction systems are analyzed theoretically in this work. Use of microwaves is encouraged to save energy. The effects of microwave heating are analyzed theoretically by assuming that the catalyst pellet is homogeneous. The temperature and concentration profiles within the catalyst pellet were obtained by numerical simulations for the cases of microwave heating and conventional heating. In the modeling the catalyst pellet is regarded as a continuum. When a chemical reaction was conducted in a heterogeneous medium with microwave heating, the reaction rate and the yield were found to be increased compared to conventional heating under the same reaction conditions. This is due to hot spots generated by selective heating of the catalyst pellet, resulting in an increased reaction rate.     

中低热固相反应研究进展

中低热固相反应作为一种新型的绿色合成方法,其独特的优势已逐渐成为化学研究的热点,为此对中低热固相反应研究现状进行了综述,列举了几种典型的中低热固相反应方法--研磨法、球磨法、微波法以及超音速气流低热固相反应法,并重点阐述了研磨法、球磨法、微波法和超音速气流低热固相反应法在化学反应中的应用.提出了当前中低热固相反应方法的缺陷,对今后中低热固相反应研究进行了展望.     

AN INVESTIGATION OF THE HEATING OF WOOD IN AN INDUSTRIAL MICROWAVE APPLICATOR: THEORY AND PRACTICE

In this work a comprehensive set of experimental results are used as an excellent means to understand the coupling that exists between the material and die electromagnetic fields in a specific industrial microwave applicator. The analysis of the infrared images allows an accurate map of the power and temperature distributions within the wood sample to be determined. This map, together with the simulation results of a previously developed computational electromagnetic model, can provide a detailed understanding of the design features of the microwave applicator. In particular, it is possible to locate the occurrence of localised hot spots and to examine the uniformity of the heat distribution throughout the sample. The simulation results provide the evolution of the electromagnetic fields inside the entire applicator and the sample. The coupling of theory and practice is the best way to proceed in optimising the design and for proposing new applicator geometry that can heat the material more effectively.     

AN INVESTIGATION OF THE HEATING OF WOOD IN AN INDUSTRIAL MICROWAVE APPLICATOR: THEORY AND PRACTICE

ABSTRACT

In this work a comprehensive set of experimental results are used as an excellent means to understand the coupling that exists between the material and die electromagnetic fields in a specific industrial microwave applicator. The analysis of the infrared images allows an accurate map of the power and temperature distributions within the wood sample to be determined. This map, together with the simulation results of a previously developed computational electromagnetic model, can provide a detailed understanding of the design features of the microwave applicator. In particular, it is possible to locate the occurrence of localised hot spots and to examine the uniformity of the heat distribution throughout the sample. The simulation results provide the evolution of the electromagnetic fields inside the entire applicator and the sample. The coupling of theory and practice is the best way to proceed in optimising the design and for proposing new applicator geometry that can heat the material more effectively.