Selection of a separation process

This section is normally included at the end of a textbook on separations however, it is included here to give the reader some food for thought in deciding how they might use the material in the subsequent chapters. For additional perspectives on this topic, consult references [2-11]. The following should be taken as a heuristic or guide. 

1 Assess the feasibility. What are the property differences that you plan to exploit for the separation(s) Which processes use this property difference as their primary separating mechanism What operating conditions are associated with the feed stream (flowrate, T, P, pH, reactive components, etc.) Are these conditions extreme relative to normal operating conditions for a given separation process  

2 Determine the target separation criteria. What purity and recovery are needed for the various components in the feed stream For a feasible separation process, what is the separation factor based on the property difference chosen For an equilibrium-based process, this would be the separation factor for one stage. 

There are various molecular properties which are important in determining the value of the separation factor for various separation processes. 

3 Do the easiest separation first. This may seem obvious, but often the starting place is non-obvious when one is faced with a complex feed mixture to separate. What are some examples of easy  

It is safe to say that the ultimate criterion is economics. However, die economic criterion is subject to a number of intangible constraints. These constraints m include corporate attitude toward market strategy and timing, reliability, risks associated with innovation, and capital allocation. In this regard, separation processes are no different than any other type of process. To illustrate the influence of the intangible constraints, we might consider two extreme cases. 

The product is of high unit value with a shoit market life expectancy. 

The product is a high-volume chemical with many producers in a highly competitive market. 

In Case 1 the procedure would probably be to choose the first successful separation method found. The ultimate overall economics of this situation ate determined by getting inu the market ahead of the competition and selling as much of the product as possible while the market lasts. However, if the market turns out to have a sustained life, it would be foolish in the extreme to continue to follow this philosophy on second- and third-generation plants. As time passes and competiiots move in, products ultimately take on the nature of Case 2. 

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The selection of a separation process depends on many factors, not the least of which is the type of gas to be purified. Table 7 gives some... 

When using meked lists as a besis for separation prooess selection, avoid separation factors close to one and draw on experience to weigh theoretical potential with practical expectations. A more detailed discussion of the selection of a separation process Is given in Chepter 22,... 

The first step in the selection of a separation process is to define the problem. Usually, this entails establishing product purity and recoveiy specifications. Product purity specifications are established ultimately... 

The selectivity of a separation process is usually expressed in terms of the selectivity parameter ... 

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