微波辅助萃取过程中有效成分扩散的动力学特征

为研究微波条件下萃取过程的动力学规律,从有效成分与微波场之间的相互作用出发,分析了有效成分在微波场中所获得的非热效应能,并在微波条件下建立有效成分扩散速率公式的基础上,分析讨论了微波辅助萃取中有效成分扩散的动力学特征。理论分析结果表明,对不同条件的萃取实验,有不同的萃取动力学特征,主要表现为在萃取时间内是否出现时间拐点。当存在时间拐点时,微波条件下动力学关系曲线为先上凹再上凸的特征形式;当不存在时间拐点时,动力学关系曲线为一致上凸的特征形式;先上凹再上凸的动力学特征形式是微波条件下特有的,是不同于传统萃取方法的动力学特征。通过对实验结果拟合表明:从理论上得到的扩散动力学特征与实验结果一致,验证了微波条件下扩散动力学特征有两种可能的理论分析.     

中药材挥发油提取过程的传质动力学模型

利用Fick第二扩散定律和膜模型理论,分别建立了内扩散控制和气膜扩散控制的传质速率模型,并以苍术挥发油的提取实验以及文献数据对模型进行检验。实验结果表明,苍术颗粒半径较大时,挥发油提取过程由内扩散控制,服从一级动力学方程;颗粒半径小于0.090 mm时,出油速率由气膜扩散控制,出油量和时间呈正比。利用所建立的动力学模型对其他5种中药材的数据进行拟合,得到了与文献数据较为吻合的计算结果,表明该模型是可靠的,能反映实际提取情况,具有一定适用性。     

微波作用下酸解磷矿动力学模型研究

在微波和加热作用下进行硫酸分解磷矿实验,建立了不同条件下的反应动力学模型,并研究了两种条件下反应过程的差异.实验结果表明.微波和加热作用下的化学反应活化能分别为20.82kJ/mol和13.56kJ/mol.微波作用使反应活化能和频率因子提高.当反应温度高于40℃,微波化学反应速率超过加热化学反应速率.反应温度低于70℃,微波能够提高传质、扩散速率.     

花生四烯酸发酵动态代谢通量分析模型

分析了高山被孢霉发酵生产花生四烯酸的动力学特征,建立了氮源与葡萄糖双底物限制动力学模型,并结合代谢流分析理论提出了花生四烯酸发酵动态代谢通量分析模型,通过非线性最小二乘法优化拟合获得参数.进一步实验表明这个模型具有较高的精确度,能很好地模拟发酵过程,并能很容易地获得不同发酵时间的代谢流分布.     

超声波场强化解吸速率的机理及场协同分析

从分子动力学原理出发,提出了外场作用下的解吸动力学模型,分析讨论了超声场强化解吸速率的机理及超声场与吸附相分子振动之间的协同作用.根据超声条件下吸附相分子的受迫振动和非吸附相分子的波动,分别讨论了吸附相分子及非吸附相分子在超声波场中获得的能量并进行了数量级分析和比较.结果表明,在超声波场中吸附相分子比非吸附相分子获得更多的能量,一般要大10个数量级以上,这正是超声波场强化解吸速率的本质所在.进一步理论分析表明,对一定频率的超声波,能流越大解吸速率越大,这是与实验相符的;同时,在超声波能流一定的情况下,可使超声波频率达到吸附相分子的固有频率而使解吸速率强化,这是超声波场与吸附相分子振动之间协同的结果.     

煤质活性炭对苯酚吸附动力学研究

通过静态吸附实验研究了煤质活性炭对苯酚的吸附特性,并用两种动力学模型对实验数据进行了拟合。结果表明,准二级动力学模型能精确描述苯酚在煤质活性炭上的吸附动力学行为;颗粒内扩散模型拟合表明内扩散过程为该吸附过程的主要控制步骤,但不是唯一控制步骤,吸附同时还受外扩散过程影响。     

分段法研究焦油析出动力学过程的探讨

COREX炉内加入的块煤会热解并析出焦油,焦油析出包含了热解缩聚反应及分子扩散的不同过程。考虑到在实验室高温条件下煤焦油的析出特点,提出块煤中焦油析出是一个集非等温与等温、化学反应与分子扩散于一体的过程。基于焦油析出初期、中期和后期的理化特点,分别建立了非等温的收缩核模型、一级热解反应模型和反Jander方程描述的分子扩散模型。由此三个模型得到的拟合结果与试验数据均呈现出良好的线性相关性,给出了不同控制过程的时间转换点,验证了模型的合理性。由拟合结果,分别计算了上述控制过程的热解速率常数krea、焦油分子扩散系数D、活化能Ea等动力学参数,为深入研究煤焦油析出过程的机理提供了必要的基础。分段法有很大的普适性,可以应用在其他过程的动力学研究中。     

中草药的不同提取方法与强化传质机理研究

介绍了以中草药甘草、槐花、灵芝为基质物料、蒸馏水作提取剂，分别用索氏、回流与微波方法进行的提取目标成分为甘草酸、芦丁、灵芝多糖的动力学特性对比实验，并结合目标成分从基质向溶剂扩散的阻力分析探讨了中草药有效成分提取的强化传质机理。     

超声场对栀子甙提取过程的强化

测定了在栀子果实中栀子甙在水溶液中浸取的固液平衡关系,不同强度超声场作用下栀子甙相平衡关系,研究比较了机械搅拌法和超声场介人下栀子甙的浸取率和浸取速率。实验结果表明：超声场可以改变浸取相平衡,超声场强度越大,固体中栀子甙吸附容量越小：超声场作用下使浸取率达到最高、浸取速率达到最大。超声场可有效强化液膜传质、粒内扩散,提高浸取率、加快浸取速率,能达到机械搅拌无法达到强化传质的效果。     

AB-8大孔树脂对柴胡总黄酮的吸附行为研究

采用静态吸附法研究了AB-8树脂对柴胡总黄酮的吸附动力学及热力学特性。动力学研究表明,准二级动力学模型能较好地描述整个吸附过程;颗粒内扩散模型拟合的曲线呈现多重线性,说明不同阶段的吸附速率受到树脂孔径分布的影响。热力学研究表明,在实验温度下,AB-8树脂对柴胡总黄酮的吸附过程符合Langmuir等温模型,吸附的吉布斯自由能变ΔG<0,焓变ΔH和熵变ΔS分别为10.51 kJ/mol和44.15 J/(mol.K),说明该吸附能是自发进行的吸热过程。     

Theoretical Study of Microwave Enhanced Thermal Decontamination of Oil Contaminated Waste

This paper demonstrates that microwave enhanced thermal decontamination of oil contaminated waste is a potentially important and highly efficiency approach to achieving the required environmental discharge limit. Numerical simulation of microwave thermal decontamination of oil contaminated wastes within an applicator known to support high electric field strengths was used to assess the influence of electric field and power loss density distributions on oil removal from the waste materials. It was found during this study that the water content plays the most important role in oil removal. As the microwave receptors within the material matrix, water molecules absorbed the bulk of the applied microwave energy. This energy was subsequently transferred to the oil in the form of heat, and was shown to cause thermal desorption. The boiling point of oil can also be reduced when it is mixed with water, since free water is beneficial to uniform heating, whilst bound water has a significant effect on the latter stages of oil removal. The experimental and simulation results suggest that the lowest residual oil levels were achieved when the sample material had a high dielectric loss factor and was placed in the position of maximum electric field strength. The cost of using a microwave technique for the remediation of oily waste can be up to 20 times lower than conventional heating.     

Simulation of Microwave Sintering of Ceramic Bodies with Complex Geometry

Microwave sintering, an emerging technology in which the energy is applied directly to the material, enabling rapid sintering, shows potential for the synthesis of advanced ceramic materials with superior properties. The process is complex, combining the propagation and absorption of electromagnetic waves in the ceramic material, heat transport within the geometric body, and densification. The densification changes both macroscopic shape and microstructural morphology. A dynamic balance between the rate of electromagnetic energy absorbed within the bulk of the sample and the rate of energy loss from its surface generally results in temperature gradients. These temperature gradients may be especially important during the microwave sintering of bodies with a complex geometry, because neither the diffusion distance nor the electromagnetic penetration depth scale with sample dimensions. The gradients generated in a ZnO green body of a complex geometry were studied theoretically using various microwave-sintering approaches, and it was found that (1) dual-frequency (2.45 and 30 GHz) microwave processing leads to a decrease in the duration of the temperature gradients, and (2) an increase in the heating rate from 5°C/min to 1400°C/min at 2.45 GHz decreases the total required microwave energy by a factor of 55, while at the same time the internal temperature gradients are maintained over a substantially shorter time.     

基于加热均匀性的微波干燥研究进展

微波干燥通过电磁场辐射物体而在其内部产生热量,促进物体内部水分向外部迁移,是一种先进的干燥技术。但是,微波干燥存在加热不均匀的问题。本文针对该问题,分析了导致微波加热/干燥不均匀的影响因素,综述了通过提高微波干燥室内电磁场分布均匀性及改变被处理物料位置,以改进微波加热均匀性的可行措施,最后指出进一步实现微波均匀干燥的研究发展趋势。     

电磁场作用下的强化传质研究进展

总结了电场、磁场和电磁场作用下强化传质的一些实验与理论工作,分析了3种强化传质方式在传质对象和传质机理方面的一些不同.进行比较后显示,电磁场强化传质的应用更加广泛,其强化传质机理可解释为:电磁场与物质的相互作用改变了物质的活性,降低了传质过程的活化能,从而使扩散得到增强.最后介绍了微波非热效应的一些实验与理论研究进展.研究表明,一些化学反应、陶瓷烧结和萃取等过程的传质得到强化确实是由于微波非热效应的作用.     

Uniformity Issue in Microwave Drying

Microwave drying is an advanced drying technique in which heat is generated inside the material due to transformation of high-frequency electromagnetic energy so the liquid moisture is intensively evaporated and transported toward the material surface. However, an inherent problem in microwave drying is nonuniform heat generation, which leads to uneven drying. In this article, the factors causing nonuniform microwave heating were identified, and feasible approaches to solving the nonuniformity problem were analyzed in terms of improving the uniformity of the electromagnetic field distribution and random or organized dislocation of the processed material in virtually nonuniform microwave field. The R&D trends in microwave drying toward reducing uneven heating were pointed out and discussed.     

吸波材料辅助的液体物料微波冷冻干燥多物理场耦合模型

为了研究吸波材料辅助微波加热对传统冷冻干燥过程的强化作用,建立了多孔介质温度、浓度和电磁场耦合的多相传递模型;以烧结的碳化硅(SiC)为吸波材料、以甘露醇水溶液为待干料液进行了微波冷冻干燥实验,并测定了甘露醇固体的介电特性。模拟和实验结果均表明,吸波材料对初始非饱和多孔物料微波冷冻干燥具有显著的强化作用。初始非饱和样品微波冷冻干燥时间比传统冷冻干燥缩短了18%,比常规饱和样品传统冷冻干燥缩短了30%。模拟结果与实验数据吻合良好。这表明提出的新型干燥方法确实能够实现过程传热传质的同时强化。通过考察样品内部温度、饱和度和电场强度的实时分布,分析了微波冷冻干燥过程的传热传质和电磁波传播与耗散机理。在微波冷冻干燥过程中,初始非饱和样品累计吸收的辐射能和微波能的总和与传统冷冻干燥相当。这说明,该干燥方法只是提高了能量效率,从而大幅缩短了冷冻干燥时间。     

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。     

柳树河油页岩微波干燥特性及干燥模型

干燥预处理对油页岩的利用具有重要的意义,微波干燥是一种快速、高效和节能的干燥方式。在家用微波炉改造基础上搭建了微波干燥实验台,研究了不同微波功率对柳树河油页岩微波干燥特性的影响。并采用单项扩散模型等13个薄膜干燥模型等对微波干燥分别进行动力学分析,结果表明：微波干燥所需的时间远小于传统干燥所需的时间;微波干燥速率要远大于传统干燥干燥速率;油页岩微波干燥过程适用于双项扩散的半经验模型,油页岩微波干燥机理为湿分（液体或蒸气）双项扩散控制过程;300、400和550 W三个功率干燥时能耗相差不大。为了以较少的能耗达到相同的干燥效果,对于柳树河油页岩,以功率550 W干燥为佳。     

Three-stage hybrid osmotic–intermittent microwave–convective drying of apple at low temperature and short time

ABSTRACT

In recent years, intermittent microwave coupled with hot air-drying has been used increasingly, thanks to considerable improvements observed in drying properties. The aim of this study was to investigate the effect of process of drying apple pretreated osmotically with sucrose solution at five concentrations of 0 (control), 10, 30, 50, and 70% (w/w), using intermittent microwave at four power levels of 0 (control), 360, 600, and 900?W, four pulse ratios of 1, 2, 3, and 4, and convective hot air (40°C) on drying kinetics, effective moisture diffusion coefficient, shrinkage, bulk density, rehydration ratio, and energy consumption. Results showed that the three-stage hybrid osmotic–intermittent microwave–convective drying of apple at low temperature yielded higher drying rates (with 41.5% decrease in drying time) and improved quality of final product. The effective moisture diffusion coefficient increased with an increase in power, pulse ratio, and the concentration of osmotic solution. Furthermore, shrinkage, bulk density, and energy consumption of the samples decreased with an increase in power, pulse ratio, and the concentration of osmotic solution. In summary, the use of intermittent microwave coupled with forced convection of hot air (at low temperature) in drying of apple pretreated by sucrose osmotic solution led to products with improved properties in terms of both quality and quantity.     

微波辅助萃取过程中的分子扩散系数

建立了微波萃取虎杖中白藜芦醇过程中的分子扩散势垒模型;结合粘度理论建立了分子扩散系数与活化能之间的关系;利用活化能的概念和微波吸收功率密度表达式得到微波作用下的扩散系数表达式。从表达式可以看出,微波作用下的扩散系数与目标萃取物质的密度、微波频率及萃取温度有关,与未加微波的情况比较扩散系数明显增大。在微波辅助萃取有效成分过程中,若萃取温度较高,应选择频率较高的微波进行萃取,以最大限度提高扩散系数;对可能发生热失控现象的物质进行提取时,萃取温度应选择在临界温度附近,此时扩散系数较大。