Selecting a Process

The previews sections present many process types and variations, and a question naturally arises as to how one can chouse the most economical process embodiment for a penicutar separation. The purpose of this section is to present a method by which a reasonable answer can be given to this question. Economics of the processes are chiefly a function of capilal (investment-related) costs and energy costs, and to a lesser extant labor and other costs, Siuce capital and energy costs can vary from site to site, hard-and-fast criteria cannot be given, but the following procedure will seldom mislead. 

In Table 12.6-1, nine statements are given that can be used to characterize [he seperaiion desired. The numbers of the statements that are true are then used in the matrix given in Table 12.6-2. Encountering a No1 for any true statement under a given process eliminates that process from consideration a process having all Yeses woold deserve stroag consideration. Entries other than Yes or No provide a way of ranking processes if more than ona process seems to be a possibility, Below are several examples to illustrate the use of [he tables. 

Nine statentents are given below. To find the adsorption process must likely to be the best for a particular separation, firs determine which of these statements are tnie for that separation. Then refer to Table 12.6-2 and read across. If a No is encountered under a certain process, then that process can effectively be eliminated ns an economic possibility. A certain process that has a1i Yeses ahonid be investigated. 

Feed is a liquid that can be folly vaporized at less than about 200 0. 

Feed is a liquid that cannot be fully vaporized at 200 C. 

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Select a process chemistry or synthesis route that is inherently safer. 

Select a process chemistry or synthesis route that is inherently safer (e.g., nontoxic, nonflammable materials, less severe operating condition)... 

To select a process, determine flow rate, temperature, pressure, concentration of the acid gases in the inlet gas, and allowed concentration of acid gases in the outlet stream. With this information, calculate the partial pressure of the acid gas components. 

Clearly, the designer should always select a process that is inherently safe whenever it is practical, and economic, to do so. However, most chemical manufacturing processes are, to a greater or lesser extent, inherently unsafe, and dangerous situations can develop if the process conditions deviate from the design values. 

Before selecting a process analytical technology to implement, it is helpful to understand the capabilities and limitations of the technology. Good introductions to NIR spectroscopy and instrumentation can be found in Chapter 5, and to chemometric methods in Chapter 12. NIR pharmaceutical applications are covered in Chapters 13 and 14. Additional information on NIR techniques and applications can be found in Williams, ... 

In summary, effective surface treatments can be obtained in a variety of ways and in selecting a process for a particular purpose account should be taken, inter alia, of the sizes, configuration and numbers of components to be handled,... 

Select a process parameter (Flow, Pressure, etc.) and specify the design intention relating to this parameter. 

When there are multiple recycles present, it is sometimes more effective to solve the model in a simultaneous (equation-oriented) mode rather than in a sequential modular mode. If the simulation problem allows simultaneous solution of the equation set, this can be attempted. If the process is known to contain many recycles, then the designer should anticipate convergence problems and should select a process simulation program that can be run in a simultaneous mode. 

Any process that is suitable for the final enrichment can be employed for upgrading also. The criteria for selecting a process are reliability, simplicity, and conservation of costly feed. Distillation and electrolysis fulfill these requirements. ... 

The butene conversion level is highly dependent on its initial concentration. For instance, today commercial Dimersol-X technology achieves 80% conversion of butenes with up to 85% octene selectivity. A process flow diagram is depicted in Figure 1. The reaction takes place at low temperature (40-60 °C) in three or four consecutive well-mixed reactors. The pressure of 1.5 MPa is sufficient to maintain all reactants and products in the liquid state. Mixing and heat removal are ensured by an external recirculation loop over a heat exchanger system. The two components of the catalytic system are injected separately into this reaction loop under precise flow control. The residence time is between 5 and 10 h. 

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