Macro scale operations

Distillation under reduced pressure. The student should first read details of this operation on a macro-scale (p. 28). For micro-scale work the apparatus shown in Fig. 40 is very convenient. A small pear-... 

Reaction and Transport Interactions. The importance of the various design and operating variables largely depends on relative rates of reaction and transport of reactants to the reaction sites. If transport rates to and from reaction sites are substantially greater than the specific reaction rate at meso-scale reactant concentrations, the overall reaction rate is uncoupled from the transport rates and increasing reactor size has no effect on the apparent reaction rate, the macro-scale reaction rate. When these rates are comparable, they are coupled, that is they affect each other. In these situations, increasing reactor size alters mass- and heat-transport rates and changes the apparent reaction rate. Conversions are underestimated in small reactors and selectivity is affected. Selectivity does not exhibit such consistent impacts and any effects of size on selectivity must be deterrnined experimentally. 

The falling film micro reactor (Figure 5.1) transfers this well-known macro-scale concept to yield films of a few tens of micrometers thickness [1-3]. For this reason, the streams are guided through micro channels. To obtain a reasonable throughput, many micro channels are operated in parallel. 

Additionally, the influence of the life time of the micro-structured devices as well as the expenditure of the peripheral equipment was estimated in order to obtain insight into the ecological hot-spots of the system. A conventional macro-scaled semi-continuously operated batch process was chosen as a reference process. The comparison of both technological systems was performed by means of the two-step synthesis of m-anisaldehyde serving as model reaction. 

The synthesis of m-anisaldehyde [3] is a very exothermic lithium-organic reaction (Scheme 7.1). In a macro-scaled batch reactor, this synthesis can only be carried out under extensive safety precautions and with high energetic effort for operating the cooling system. 

Conventional combustion calorimeters operate on a macro scale, that is, they require samples of 0.5-1.0 g per experiment. Unfortunately, many interesting compounds are available only in much smaller amounts. In the case of oxygen combustion calorimetry, however, several combustion microcalori-meters that only demand 2-50 mg samples have been developed in recent years. The achievements and trends in this area through 1999 have been reviewed [7-10], and interested readers are directed to these publications. Since then, a few new apparatus have been reported [11-17], Nevertheless, it should be pointed out that the general principles and techniques used to study compounds at the micro scale are not greatly different from those used in macro combustion calorimetry. 

R 18] [A 3] As in every macro-scale chemical plant, all process I/O operations are visualized in the graphical user interface (Figure 4.62) The process data can be recorded as a function of time and also exported in ASCII code (Figure 4.63). 

These examples underline the fact that macro-scale process simulation tools such as Aspen Plus will have to be supplemented by micro-type unit operations as introduced by the FAMOS initiative which consider the location of a fluidic cell in the device and does not assume a perfect mixing, piston flow or uniform heat transfer coefficient [13]. 

The adaptive spectrometer described in this paper produces either non-imaging, onedimensional or two-dimensional multispectral radiance datasets ( datacube in the case of two-dimensional spectral mapping) for gas or aerosol discrimination and classification. The spectral, temporal and spatial resolution of the data collected by the instrament are adjustable in real time, making it possible to keep the tradeoff between sensor parameters at optimum at all times. The instrument contains no macro-scale moving parts making it an excellent candidate for the development of a robust, compact, lightweight and low-power-consumption device suitable for field operation. 

This problem is due to the fact that stirring experiments are generally carried out in small laboratory devices (D < 1 m), in which the micro-scale turbulence is predominant. They therefore often do not supply reliable information on scale-up for that mixing operation in which macro-scale turbulence is essential. The latter is... 

The volume of a reaction mixture may sometimes be increased by use of additional solvent, so that certain operations such as filtration can be carried out on a macro scale. 

Interaction of the dynamic properties of a catalyst, a micro-scale physic-chemical system, and the dynamic properties of the macro-scale reactor creates an opportunity to improve the performance of catalytic processes using forced unsteady-state operation. Forced dynamic operation makes it possible to generate spatio-temporal patterns of temperature, composition and catalyst states that caimot be attained under steady-state operation. 

Wet reactions macro apparatus and analytical operations on a macro scale... 

Due to their small characteristic dimensions, microreactors have fundamental advantages in comparison with conventional macro-scale systems. As a consequence, microreactors are suitable for performing and/or studying reactions under relatively safe conditions, which is important in the case of potentially dangerous processes, such as highly exothermic reactions, reactions in which flammable, explosive or toxic chemicals are involved or reactions that require harsh conditions in terms of temperature or pressure. In fact, microreactors open the way to new operating regimes and applications [1,2],... 

The language that makes hoth the macro scale and the micro scale accessible to us is mathematics. Although we need not do the mathematical operations ourselves, we do need to appreciate some of the things that quantum mechanics has to say to us. Chapter 1 also focuses strongly on Lewis structures— pictorial representations of atoms and ions. The abihty to write good Lewis structures easily and to determine the locations of charges in molecules with ease is an essential skill. This skill is part of the language of chemistry and will be as important in Chapter 23 as it is in Chapter 1. 

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