Key ratio

Experimental mea.surement of relative volatility. Rank candidate solvents by the increase in relative volatility caused by the addition of the solvent. One technique is to experimentally measure the relative volatility of a fixed-composition key component-solvent mixture (often a 1/1 ratio of each key, with a 1/1 to 3/1 solvent/key ratio) for various solvents. [Carlson et al., Jnd. Eng. Chem., 46, 350 (1954)]. The Oth-... 

Key ratio is the mole fraction ratio of the light key to the heavy key,... 

As reflux ratio iB reduced, the key ratio profile develops an inflection point. As minimum reflux is approached, the profile develops a maximum below the feed point and a minimum above the feed point. Between the maximum and the minimum, there is a region in which the key ratio actually decreases as one moves up the column. This be-... 

The key ratio in the feed stage liquid should be as close as possible to the key ratio in the liquid portion of the feed flashed to tower pressure). 

The feed point should give the most equal slopes on both sides of the feed stage in a key ratio plot (Fig. 2,20). Too high a feed causes excessive retrograde distillation below the feed, and too low a feed causes excessive retrograde distillation above it. In order to reach the optimum feed point, the feed stage should be moved from the sharp maximum (or minimum) toward the flat one (Fig. 2.20). 

Light nonkeys raise the optimum key ratio at the feed stage, while heavy nonkeys lower it. Rules 1 and 2 therefore become less reliable when there are a lot more light than heavy nonkeys or vice versa, or when the amount of nonkeys exceeds the amount of keys,... 

Nonkeys whose volatility is either close to the keys or far removed from the keys tend to shift the optimum key ratio (or light key concentration) at the feed stage to a lesser degree than nonkeys whose volatility is moderately removed from the keys,... 

Figure 2,20 Effect of feed stage on key ratio plot. Depropanizer example, feed composition same as Example 2.4. 20 theoretical stages, R/Rmin - 1.40.

Key ratio plots are primarily for identifying mislocated feed stages in multicomponent distillation. For this purpose, they are superior to x-y diagrams. Key ratio plots are easy to construct all it takes is calculating the key ratio in the liquid for a few stages in the feed region... 

Since the mid-nineties, more and more chemical companies have come to realize the importance of shareholder value, and it is crucial for this development to continue. In such a capital-intensive industry, the lack of focus on value creation (and the use of ROS as the key ratio) will typically lead to relatively low returns on invested capital. Ultimately this creates a situation in which even successfuF players do not generate value and, in some cases, actually destroy it the typical spread (i.e., the difference between return on invested capital and capital costs) for chemical companies lies between -3 percent and -f5 percent, with only a few exceptions. 

Identify mislocated feed. For binary distillation the feed point should be where the q-line intersects the equilibrium curve. For multicomponent distillation this may or may not be the case. So for multicomponent distillation feed location, key ratio plots and d/b plots are preferred and discussed next. 

Temperature profile Pressure profile Flow profiles Mass transfer rates Stripping factors Key ratio profiles Relative volatilities McCabe-Thiele diagram Ponchon Savarit... 

If templating is important, key ratios will define the cation distribution, Na Si02, K Si02, R4N Si02, and so forth, ratios which can range (individually) from zero to more than two. In Table III, examples are selected from the literature to illustrate cation effects in crystallization experiments. The Na-series examples show a shift in product from Y to mazzite-related structures (ZSM-4, Omega) on addition of only small amounts of TMA ion. When potassium replaces sodium, the L structure results but limited addition of TMA produces yet another structural type, the offretite-type zeolites. 

Pinching (either due to a mislocated feed, proximity to minimum reflux, or a tangent pinch) is commonly implicated by the above insensitivity. A McCabe-Thiele diagram and a key ratio plot can help identify the cause application of these techniques for this purpose is described elsewhere (193). Any scale-up of such efficiency data must be conservatively performed. 

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