Process intensification and miniaturization

Process Intensification and Miniaturization Centre, School of Chemical Engineering and Advanced Materials and Institute for Nanoscale Science and Technology, University of Newcastle, Newcastle Upon Tyne, U.K. 

Mohamed O. Abdalla / Department of Chemistry, Tuskegee University, Tuskegee, Alabama, U.S.A. Abdullah M. Aitani / King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia G. Akay / Process Intensification and Miniaturization Centre, School of Chemical Engineering and Advanced Materials and Institute for Nanoscale Science and Technology,... 

Akay, G., Process Intensification and Miniaturization, Principles and Applications in Biological, Chemical and Environmental Technologies, Elsevier, New York, 2004. 

Wegeng, R. S., Drost, M. K., Brenchley, D. L., Process intensification through miniaturization of chemical and thermal systems in the 21. century, in Ehreeld, W. (Ed.), Microreaction Technology 3rd International Conference on Microreaction Technology, Proc. of IMRET 3, pp. 2-13, Springer-Verlag, Berlin (2000). 

The combination of process intensification and process miniaturization is an important element of sustainable technology and a platform for advancement in multidisciplinary science and engineering. There are now several examples of intensified processes being utilized in industry, as apparent from patent activity. Some of these intensified processes are confined to a single unit operation, while others integrate several intensified unit operations in the more efficient production of existing/improved/novel products. 

Miniaturization in biocatalysis and fermentation is another necessary step. This will allow continuous processes with the benefits that could derive in terms of process intensification and reduction of waste. Miniature (less than 10 mL) stirred reactors and microtiter plates (MTP) have been introduced mainly with the idea of allowing high-throughput screening to speed up bioprocess development, even though they are available now also for production uses [172-174]. Notably, problems emerge with these miniature bioreactors (MBRs), such as evaporation and surface tension, which determine the performances, but which are masked in larger bioreactors. 

Finally, it is worth mentioning that a successful integration of catalytic reaction steps with product separation and catalyst recovery operations will also be dependent on innovative chemical reaction engineering. This will require the widespread application of sustainable engineering principles [48].In this context process intensification , which involves the design of novel reactors of increased volumetric productivity and selectivity with the aim of integrating different unit operations to reactor design, and miniaturization will play pivotal roles [49, 50]. 

However, the integration of PIM also creates synergy in the development of intensified processes, novel product forms, and size dependent phenomena, which in turn provides novel intensified processes. Process intensification-miniaturization is seen as an important element of sustainable development because it can deliver 1) at least a 10-fold decrease in process equipment volume 2) elimination of parasitic steps and unwanted by-products, thus eliminating some downstream processing operations 3) inherent safety because of reduced reactor volume 4) novel product forms 5) energy, capital, and operating cost reduction, and an environment friendly process 6) plant mobility, responsiveness, and security and 7) a platform for other technologies. 

Fig. 1 Relationship between PI fields, physical PI, process miniaturization, selectivity, process viability, and phenomenon-based intensification. (View this art in color at www.dekker.com.)...

There is growing interest in Process Intensification, where studies to obtain a basic understanding of unit operations - often via miniaturization approaches - is important to reducing capital and operating costs. This approach has resulted in the application of micro-instrumentation to the areas of process development and process optimization. 

Transport phenomena are crudal in the scale-up of conventional, large-scale chemical reactors because many processes are heat and/or mass transfer controlled. Since transport coeflEcients are typically inversely proportional to the characteristic dimension of the system, miniaturization of chemical systems leads to a substantial increase in transport rates. This increase in turn enhances the overall rate of processes that are transport limited, leading to considerable process intensification, i.e. the same throughput can be achieved with a much smaller device and thus with much lower capital. Alternatively, much higher throughput can be achieved using a system of the same size as a conventional one, but made up of many small components (scaling out). 

Over the last 15 years, substantial research on small-scale structured devices for chemical applications has been undertaken and a host of academic studies have established a solid scientific basis for the fabrication of individual (generally unconnected) units. A number of reference books are now available [8, 9] as a substantial contribution to the already well-established general area of process intensification [10]. This research has demonstrated that miniaturized components can be exploited to act on the specific length scales (several tens to hundreds of micrometers) that are particularly relevant to chemical processing boundary layers, transport processes, reaction and mixing zones. 

For all of these reasons, the structured multi-scale chemical devices envisioned here offer the perspective of significant innovation through the use of microfabrication in the chemical process industries. To illustrate these possibilities, the following sections demonstrate how multi-scale structuring can provide a new degree of freedom for process intensification/miniaturization and contribute to the satisfaction of criteria for sustainability. In conclusion, a critical comparison of scale-up, numbering-up and multi-scale design is proposed. 

Reaction and Process System Analysis, Miniaturization and Intensification Strategies... 

The concepts of process miniaturization and process intensification have developed considerably in chemical engineering since the 1990s, in relation to the principle of sustainable development. These concepts often appear as potential solutions not only to meet the societal demand concerning a smaller, cheaper and safer chemical industry, but also to satisfy an ever more dynamic market in search of portable, distributed and responsive process solutions. 

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