Process-scale considerations mechanical design

The processes occurring in a high-speed newsprint paper machine have been discussed above. There are several additional considerations of note in the overall process picture. Paper for the most part is a commodity item (i.e., production costs are more economical per unit when large tonnages of uniform specifications are produced). Most mills have a break-even point at an 85% capacity so it is vital to operate mills at design capacity. Economies of scale are also found for pulp and paper mills at levels of about 1000 tonnes of paper per day for full chemical mills and 200—400 tonnes of paper per day for semichemical or mechanical mills. Thus, the outputs of paper mills are... 

One area that is surely set to benefit from research aimed at developing the self-assembly of mechanical systems is molecular electronics. Initially, one can look with considerable interest towards the development of chemical sensors and molecular switches of a quite novel design. Furthermore, the ability to store and manipulate information at a molecular level and on the nanometer-scale is clearly on the horizon. It will open the way for the development of molecular electronics and, ultimately perhaps, the molecular-scale computer. The objective at present is to be able to control die assembly, the form, and the function of synthetic nanometer-scale structures with the same degree of precision that is displayed by nature, so as to make it possible to achieve these ambitious goals. Only now are chemists beginning to learn how to construct molecular assemblies and supramolecular arrays such that information might ultimately be written into them, processed by them, stored in them, and eventually read back out of them. 

As we have seen in the past few chapters, there are a number of reaction mechanisms used to make polymers. Some reactor designs (semibatch and CSTRs) have been discussed as ways to form uniform or well-characterized polymers and copolymers. This chapter covers some of the important considerations with scaling up polymerizations, starting with bulk polymerization, and takes into account how transport processes (heat and mass transfer) may influence the design of polymerization reactors. 

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