Chemical microwave process

Microwave-Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes... 

In contrast, design of chemical microwave processes, especially scale-up of operating conditions, involves knowledge and control of several nonlinear feedback... 

Individual flavor components are subjected to losses through distillation, flavor binding by starches and proteins, and chemical degradation during the microwave process. Specific data on flavor loss by distillation as affected by the various media and chemical modification of flavor precursors is presented in this paper. Data on flavor binding during microwave processing is addressed in a subsequent paper. 

Chemical reactions occur during microwave processing of food systems, however, their contribution to flavor appears to be minimal. The volatile aldehydes quickly flash off during subsequent heating. The desirable baked, toasted, and roasted flavors typical of Maillard Browning do not develop in microwave heated food products. 

Table VI summarizes the effect of heating medium on the loss of acids after 3 minutes of microwave heating. Loss of volatile acids varied widely dependent on the microwave medium. Acetic and caproic acids had losses ranging from 20-80% and 0-73%, respectively, depending on medium composition. The dielectric property, specific heat, or other physical/chemical properties of individual flavor compounds can provide valuable insight into the potential behavior of these compounds during the microwave process. The dielectric property of the total food system and the affinity of the flavor compound for the microwave medium, however, were primarily responsible for the behavior of these flavor compounds during microwave heating.

Behera et al. (2004) concluded that the optimum conditions for the conventional roasting method were 125°C for 10 min and, in the microwave processing method, the best conditions were 730 W for 10min. The yields and physico-chemical properties of the volatile oils were similar in both cases. Changes were observed in the optical rotation values, which indicated differences in the chemical compositions. GC and GC-MS analysis of optimized condition samples showed that microwave-heated samples could better retain the characteristic flavour compounds of cumin (i.e. total aldehydes) than conventionally roasted samples (Table 11.5). Earlier GC reports showed cuminaldehyde as the only major aldehyde present in Indian cumin oil, but this study revealed the... 

Indeed, flow processes are already combined with functionalized solid phases, with ionic liquids, supercritical fluids such as carbon dioxide, and microwave irradiation. Nevertheless, numerous examples of above mentioned processes with standard and more and less innovative laboratory equipment take advantage of this new approach. Whatever chemists and chemical engineers require - synthesis of few milligrams of compounds in drug chemistry, synthesis of building blocks on a multigram scale for parallel synthesis, or even the kilogram production of fine chemicals - flow processes are a helpful tool and a crucial link between differently scaled reactions. 

Microwave processing of zeolites and their application in the catalysis of synthetic organic reactions has recently been excellently reviewed by Cundy [25] and other authors [26], The microwave synthesis of zeolites and mesoporous materials was surveyed, with emphasis on those aspects which differ from conventional thermal methods. The observed rate enhancement of microwave-mediated organic synthesis achieved by use of these catalysts was caused by a variety of thermal effects, including very high rates of temperature increase, bulk superheating, and differential heating. Examples of microwave activation of chemical reactions catalyzed by zeolites will be presented in Section 13.3. 

Physical methods such as ultrasonication [57, 58], microwave [59, 60] and gamma radiation have also been reported. Steam explosion is reported to be an excellent alternative to the conventional methods such as CMP (chemical mechanical pulps) and chemical thermomechanical processes. The principle of steam explosion technique are that the steam xmder pressure with increased temperature penetrates through the space between the fibers, thus the middle lamella and the fiber adherent substance become soft and water soluble [61,62]. Marchessault [63] described the steam explosion... 

In addition to the two reviews that are mentioned at the beginning of this section, a number of other relatively recent reviews of the processes and methods that have been developed and evaluated for the devulcanisation of waste rubber are available. For example, Majumdar published an overview in 2009 in the Chemical Weekly journal [4], which covered the challenges that face workers in this field and covered the main types of systems that have been developed (i.e., chemical, microwave, ultrasonic and so on). This article also covered the production and use of rubber crumb from waste rubber. In another article [5], Majumdar reviews the three main sources of reclaimed rubber that are available in the marketplace (rubber crumb, rubber powder and chemically digested reclaimed sheet) and describes their properties and uses. 

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