Facts

Equation (7-8). However, for liquid-liquid equilibria, the equilibrium ratios are strong functions of both phase compositions. The system is thus far more difficult to solve than the superficially similar system of equations for the isothermal vapor-liquid flash. In fact, some of the arguments leading to the selection of the Rachford-Rice form for Equation (7-17) do not apply strictly in the case of two liquid phases. Nevertheless, this form does avoid spurious roots at a = 0 or 1 and has been shown, by extensive experience, to be marltedly superior to alternatives. 

We might think that we can find all the structural options by inspection, at least all of the significant ones. The fact that even long-established processes are still being improved bears evidence to just how difficult this is. 

In fact, cooling of the reactor effluent by direct heat transfer can be used for a variety of reasons ... 

In fact, it is often possible with stirred-tank reactors to come close to the idealized well-stirred model in practice, providing the fluid phase is not too viscous. Such reactors should be avoided for some types of parallel reaction systems (see Fig. 2.2) and for all systems in which byproduct formation is via series reactions. 

Given the choice of a batch rather than continuous process, does this need a different approach to the synthesis of the reaction and separation and recycle system In fact, a different approach is not needed. We start by assuming the process to be continuous and then, if choosing to use batch operation, replace continuous steps by batch steps. It is simpler to start with continuous process operation... 

The reactor now becomes batch, requiring the reaction to be completed before the separation can take place. Figure 4.14 shows the time-event chart for a repeated batch cycle. Note in Fig. 4.14 that there is a small overlap between the process steps. This is to allow for the fact that emptying of one step and filling of the following step occur at the same time. 

A simple method to achieve this is based on the fact that for any value of R there is a maximum asymptotic value for P, say, P axi which is given as Ft tends to - c and is given by ... 

Also, if there are two separators, the order of separation can change. The tradeoffs for these two alternative flowsheets will be different. The choice between different separation sequences can be made using the methods described in Chap. 5. However, we should be on guard to the fact that as the reactor conversion changes, the most appropriate sequence also can change. In other words, different separation system structures become appropriate for different reactor conversions. 

We should be on guard for the fact that as the reactor conversion changes, the most appropriate separation sequence also can change. In other words, different separation system structures become appropriate for different reactor conversions. 

In fact, the true fire load will be greater than the energy release calculated in Example 9.1. In practice, such a release of superheated liquid generates large amounts of fine spray in addition to the vapor. This can double the energy release based purely on vaporization. 

Fixing the rate of heat transfer in a batch reactor is often not the best way to control the reaction. The heating or cooling characteristics can be varied with time to suit the characteristics of the reaction. Because of the complexity of hatch operation and the fact that operation is usually small scale, it is rare for any attempt to be made... 

Let us now consider a few examples for the use of this simple representation. A grand composite curve is shown in Fig. 14.2. The distillation column reboiler and condenser duties are shown separately and are matched against it. Neither of the distillation columns in Fig. 14.2 fits. The column in Fig. 14.2a is clearly across the pinch. The distillation column in Fig. 14.26 does not fit, despite the fact that both reboiler and condenser temperatures are above the pinch. Strictly speaking, it is not appropriately placed, and yet some energy can be saved. By contrast, the distillation shown in Fig. 14.3a fits. The reboiler duty can be supplied by the hot utility. The condenser duty must be integrated with the rest of the process. Another example is shown in Fig. 14.36. This distillation also fits. The reboiler duty must be supplied by integration with the process. Part of the condenser duty must be integrated, but the remainder of the condenser duty can be rejected to the cold utility. 

It is in fact the tick-off heuristic that steered the design toward the minimum number of units. The target for the minimum number of units was given by Eq. (7.2) ... 

There can be an element of maintenance costs that is fixed and an element which is variable. Fixed maintenance costs cover routine maintenance such as regular maintenance on safety valves which must be carried out irrespective of the rate of production. There also can be an element of maintenance costs which is variable. This arises from the fact that certain items of equipment can need more maintenance as the production rate increases. Also, royalties which cover the cost of purchasing another company s process technology may have different bases. Royalties may be a variable cost, since they can sometimes be paid in proportion to the rate of production. Alternatively, the royalty might be a single-sum payment at the beginning of the project. In this case, the single-sum payment will become part of the project s capital investment. As such, it will be included in the annual capital repayment, and this becomes part of the fixed cost. 

Note that in liquid phase chromatography there are no detectors that are both sensitive and universal, that is, which respond linearly to solute concentration regardless of its chemical nature. In fact, the refractometer detects all solutes but it is not very sensitive its response depends evidently on the difference in refractive indices between solvent and solute whereas absorption and UV fluorescence methods respond only to aromatics, an advantage in numerous applications. Unfortunately, their coefficient of response (in ultraviolet, absorptivity is the term used) is highly variable among individual components. 

The determination of the elemental composition of a petroleum cut is of prime importance because it provides a quick means of finding out the quality of a given cut or determining the efficiency of a refining process. In fact, the quality of a cut generally increases with the H/C ratio and in all cases, with a decrease in hetero-element (nitrogen, sulfur, and metals) content. 

Separation of families by merely increasing the resolution evidently can not be used when the two chemical families have the same molecular formula. This is particularly true for naphthenes and olefins of the formula, C H2 , which also happen to have very similar fragmentation patterns. Resolution of these two molecular types is one of the problems not yet solved by mass spectrometry, despite the efforts of numerous laboratories motivated by the refiner s major interest in being able to make the distinction. Olefins are in fact abundantly present in the products from conversion processes. 

Natural gas analysis has considerable economic importance. In fact, commercial contracts increasingly specify not just volume but the calorific or heating value as well. Today the calorific value of a natural gas calculated from its composition obtained by chromatography is recognized as valid. There is therefore a large research effort devoted to increasing the precision of this analysis. 

Liquid chromatography is preceded by a precipitation of the asphaltenes, then the maltenes are subjected to chromatography. Although the separation between saturated hydrocarbons and aromatics presents very few problems, this is not the case with the separation between aromatics and resins. In fact, resins themselves are very aromatic and are distinguished more by their high heteroatom content (this justifies the terms, polar compounds or N, S, 0 compounds , also used to designate resins). 

Represented by its abbreviation, MAV, the Maleic Anhydride Value Is based on the fact that olefinic conjugated double bonds can be added to maleic anhydride by the reaction below m]... 

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