Micro process steps

Recently, microstructured reactors have stepped into chemical production [4] and thus microreactor process and plant design, including economic incentives, is the issue at this time. For this purpose, large-capacity microstructured apparatus is needed ( micro inside, fist- to shoebox size outside ) and plant concepts have to be proposed which include all process steps. 

As C-C bond formation is an important step in organic synthesis, particularly for pharmaceutical applications, it is useful to look for operation modes of chemical micro processing that allow one to carry out combinatorial chemistry investigations. As such, the serial introduction of multiple reactant streams by flow switching was identified [66,67]. The wide availability of precursors for acyiiminium cations has led to the expression cation pool [66, 67]. 

Whereas in a micro plant only the most important process steps and some of the recycle loops are tested, in the miniplant the complete process with all recycle loops is executed and processed continuously for several weeks. For environmental and economic reasons, solvents and unconverted reactants are recycled. Here, it is especially important to find out if small impurities below the detection limit will possibly accumulate or form deposits. To minimize the up-scaling risk for the final production plant, often a pilot plant is the next scale-up step. Now the final product is produced and often first samples are sent to customers. Every step in this scale-up procedure is followed by an evaluation step defined in a number of evaluation studies, which assist in the decision as to whether the project has to be terminated, repeated or further processed. 

Mechanical stress High web tension causes micro-cracks within the metal layer. Reduction of the barrier in thicker layers is mentioned in the literature, but is probably a result of the stress to which the metal layer is exposed in subsequent process steps (e.g. lamination). 

The above remarks throw a critical view onto the contemporary efforts to simulate entire chemical processes on the smallest possible scale. Beyond all doubt, this technology can produce the proof about the feasibility of a synthesis. In addition, all process steps carried out in a homogeneous medium and dependent on micro-mixing, will be correctly executed on the micro-scale. Furthermore, the scale-dependent process steps will also be carried out in a satifactory manner on the micro-scale, because their scale-dependence could not express itself. But from these results no statement concerning the scale-up can be made In other words Mini-plants are not suitable to gain any scale-up rules for scale-dependent steps. 

Fig. 3.2 Process steps for the fabrication of the micro-DMFC chip on a silicon wafer...

Traditional fermentation generally involves many process steps which are inefficient and uneconomical in terms of utilization of raw materials,recovery of product, and energy consumption. Continuous cross-flow membrane micro-filtration and ultrafiltration, when correctly introduced, have been shown to improve this process significantly. 

Micro-structured (membrane) reactors are quite interesting due to their (i) improved mass and heat transfer owing to the reduction of the scale length in the micro-channels (ii) removal of mass transfer limitations (concentration polarization) (iii) high degree of process intensification by integrating different process steps in a small-scale device. 

Other studies on membrane micro-reactors were carried out for integrating different process steps in one micro-device for portable hydrogen production for fuel cell applications (see a.o. Ref. [60-62]). 

In a large number of applications, the ability to accurately and repeatedly deposit nanogram quantities of a given substance is critical (4). This is largely driven by the usage of micro- and nanoscale products that require extremely accurate processing steps. Many... 

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