Takes

The solvent components usually have a low mutual solubility and are present in reasonably large mole fractions in the system. If solvents are not so designated, we take as the "solvent components" those two components, present in significant mole fraction in the system, that have the lowest binary solubilities. ... 

In describing reactor performance, selectivity is usually a more meaningful parameter than reactor yield. Reactor yield is based on the reactant fed to the reactor rather than on that which is consumed. Clearly, part of the reactant fed might be material that has been recycled rather than fresh feed. Because of this, reactor yield takes no account of the ability to separate and recycle unconverted raw materials. Reactor yield is only a meaningful parameter when it is not possible for one reason or another to recycle unconverted raw material to the reactor inlet. By constrast, the yield of the overall process is an extremely important parameter when describing the performance of the overall plant, as will be discussed later. 

The choice of reactor temperature, pressure, arid hence phase must, in the first instance, take account of the desired equilibrium and selectivity effects. If there is still freedom to choose between gas and liquid phase, operation in the liquid phase is preferred. 

Catalytic gas-phase reactions play an important role in many bulk chemical processes, such as in the production of methanol, ammonia, sulfuric acid, and nitric acid. In most processes, the effective area of the catalyst is critically important. Since these reactions take place at surfaces through processes of adsorption and desorption, any alteration of surface area naturally causes a change in the rate of reaction. Industrial catalysts are usually supported on porous materials, since this results in a much larger active area per unit of reactor volume. 

Further consideration of the reaction system reveals that the ammonia feed takes part only in the primary reaction and in neither of the secondary reactions. Consider the rate equation for the primary reaction ... 

Separation of the different phases of a heterogeneous mixture should be carried out before homogeneous separation, taking advantage of what already exists. Phase separation tends to be easier and... 

Tunnel dryers are shown in Fig. 3.15a. Wet material on trays or a conveyor belt is passed through a tunnel, and drying takes place by hot air. The airflow can be countercurrent, cocurrent, or a mixture of both. This method is usually used when the product is not free flowing. 

Although the flowsheet shown in Fig. 4.7a is very attractive, it is not practical. This would require careful control of the stoichiometric ratio of decane to chlorine, taking into account both the requirements of the primary and byproduct reactions. Even if it was possible to balance out the... 

This is an exothermic, reversible, homogeneous reaction taking place in a single liquid phase. The liquid butadiene feed contains 0.5 percent normal butane as an impurity. The sulfur dioxide is essentially pure. The mole ratio of sulfur dioxide to butadiene must be kept above 1 to prevent unwanted polymerization reactions. A value of 1.2 is assumed. The temperature in the process must be kept above 65°C to prevent crystallization of the butadiene sulfone but below lOO C to prevent its decomposition. The product must contain less than 0.5 wt% butadiene and less thM 0.3 wt% sulfur dioxide. 

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. 

If there is a three-component mixture and simple columns are employed, then the decision is between two sequences, as illustrated in Fig. 5.1. The sequence shown in Fig. 5.1a is called the direct sequence, in which the lightest component is taken overhead in each column. The indirect sequence, shown in Fig. 5.16, takes the heaviest component as the bottom product in each column. There may be... 

Take two different sequences for the separation of a four-component mixture" (Fig. 5.7). Summing the feed flow rates of the key components to each column in the sequence, the total flow rate is the same in both cases ... 

Details of how this design was developed in Fig. 6.9 are included in Chap. 16. For now, simply take note that the targets set by the composite curves are achievable in design, providing that the pinch is recognized, there is no transfer of heat ac ss it, and no inappropriate use of utilities occurs. However, insight into the pinch is needed to analyze some of the important decisions still to be made before network design is addressed. 

The fuel consumption is now calculated by taking the flue gas from theoretical flame temperature to ambient temperature ... 

Now let us take a closer look at the two most commonly used heat engines (steam and gas turbines) to see whether they achieve this efficiency in practice. To make a quantitative assessment of any combined heat and power scheme, the grand composite curve should be used and the heat engine exhaust treated like any other utility. 

Taking the heat capacity of water to be 4.3 kJ kg K , heat duty on boiler feedwater preheating is... 

Most refrigeration systems are essentially the same as the heat pump cycle shown in Fig. 6.37. Heat is absorbed at low temperature, servicing the process, and rejected at higher temperature either directly to ambient (cooling water or air cooling) or to heat recovery in the process. Heat transfer takes place essentially over latent heat profiles. Such cycles can be much more complex if more than one refrigeration level is involved. 

Let us take each of these components in turn and explore whether they can be accounted for from the material and energy balance without having to perform heat exchanger network design. 

Take note that Ft can therefore be regarded as depending only on the inlet and outlet temperatures of the streams in a 1-2 exchanger. Three basic situations can be encountered when using 1-2 exchangers (Fig. 7.8) ... 

Here we shall restrict consideration to safety and health considerations that can be built in while the design is developing rather than the detailed hazard and operability studies that take place in the later stages of design. The three major hazards in process plants are fire, explosion, and toxic release. ... 

Let us take each of these in turn and consider how reactor waste can... 

This problem is solved in the reactor shown in Fig. 10.6. Ethylene and chlorine are introduced into circulating liquid dichloroethane. They dissolve and react to form more dichloroethane. No boiling takes place in the zone where the reactants are introduced or in the zone of reaction. As shown in Fig. 10.6, the reactor has a U-leg in which dichloroethane circulates as a result of gas lift and thermosyphon effects. Ethylene and chlorine are introduced at the bottom of the up-leg, which is under sufficient hydrostatic head to prevent boiling. 

Knowing where waste is going is the key to reducing it. When reducing waste from process operations, a steady-state mass balance is not usually comprehensive enough. A balance that takes into account start-up, shutdown, and product changeovers is required. 

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