Unit operations, micro-structured

Oroskar a. R., VandenBussche, K., Abdo, S. F., Intensification in micro-structured unit operations performance comparison between mega and microscale, in Matlosz, M., Ehreeld, W, Baselt, J. 

Process Intensification through Micro-structured Unit Operations I 49... 

These filled tubes or capillaries hence are mini fixed beds with internal micro flow regions. Such approach is a link between real micro structured units and conventional equipment. The type of processing may be analogous to conventional processing, e.g. fixed-bed or trickle-bed operation. 

In a conventional design, each unit operation is modeled using terms and values which do not depend on the location inside the device. On the one hand, convection and diffusion in a micro structured device strongly influence the functioning of the device, and on the other hand the convection and diffusion conditions are affected by the shape of the device. To obtain an optimized fluidic micro device, some constraints on the shape of the device are necessary. These are constraints, e.g., on the average residence time, the residence time distribution and the temperature distribution [13]. 

The designer of a plant needs information about the availability of devices and unit operations. A market study executed by the Institut fur Mikrotechnik Mainz and YOLE Developpment [51] helps to make a first survey of commercially available devices. It also estimates future needs and objectives of the chemical industry and delivers a comparison between offered and required components (Figure 4.6). The providers of micro structured devices can deliver most of the components required by the chemical industry. On the other hand, there is a lack of separation devices but this is not fully transparent in Figure 4.6. Extraction devices are under represented and the important rectification units were not asked for by the interviewers, possibly because they hardly exist. 

Micro structured devices are often specialized products designed for a single purpose. Costs for individually developed and manufactured devices are certainly higher than those for products from the shelf. The non-existent compatibility of devices from different suppliers represents another restraint, especially because many suppliers offer only a limited number of devices and thus cannot provide the complete range of unit operations. 

Nowadays, the most common small-scale application of hydrogen is the use in residential or mobile fuel cell systems. Special requirements of this application are compact design, integrated CO-removal, high energetic efficiency, quick start-up and fast transient behavior. The proposed solutions comprise unit-operation-based concepts as well as multifunctional, micro-structured reactors. 

The separation and purification of gas mixtures by adsorption is an important unit operation in the chemical and petrochemical industries. The demand of products with high purity has increased and, therefore, attention has focused on separation processes. The two main types of adsorbents used for this purpose are zeolites and CMS. In both cases, their micro-porous structure allows the separation of molecules on a shape and size basis. These CMS have some advantages over molecular sieve zeolites, including shape, selectivity for planar molecules, higher hydrophobicity, higher resistance to both alkaline and acid media and... 

Until now, all in the literature proposed LAPS devices are complete autarkic measurement systems. Further applications can be found by the integration of LAPS devices into existing analytic fields. This requires the development of inexpensive integrated electronic units to operate the LAPS and to provide a standardised communication with higher process levels. The LAPS devices need to be easy in use to allow the operation in commercial environments. Due to the simple structure of the LAPS, the integration into micro-electro-mechanical systems (MEMS), lab-on-chip and micro-total analysis systems (p-TAS) might be of special interest in the near future. 

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