PRACS

Like alcohol dehydrations El reactions of alkyl halides can be accompanied by carbocation rearrangements Eliminations by the E2 mechanism on the other hand nor mally proceed without rearrangement Consequently if one wishes to prepare an alkene from an alkyl halide conditions favorable to E2 elimination should be chosen In prac tice this simply means carrying out the reaction m the presence of a strong base... 

Recognizing that cyclohexene may be prepared by dehydration of cyclohexanol a prac tical synthesis of cyclohexane from cyclohexanol becomes apparent... 

The reference state at To and To is arbitrarily selected, and the values assigned to Hq and are also arbitrary In prac tice, only changes in H and S are of interest, and the reference-state values ultimately cancel in their calculation. 

Simplified forms of Eq. (6-8) apply to special cases frequently found in prac tice. For a control volume fixed in space with one inlet of area Ai through which an incompressible fluid enters the control volume at an average velocity Vi, and one outlet of area Ao through which fluid leaves at an average velocity V9, as shown in Fig. 6-4, the continuity equation becomes... 

The effect of the disturbance on the controlled variable These models can be based on steady-state or dynamic analysis. The performance of the feedforward controller depends on the accuracy of both models. If the models are exac t, then feedforward control offers the potential of perfect control (i.e., holding the controlled variable precisely at the set point at all times because of the abihty to predict the appropriate control ac tion). However, since most mathematical models are only approximate and since not all disturbances are measurable, it is standara prac tice to utilize feedforward control in conjunction with feedback control. Table 8-5 lists the relative advantages and disadvantages of feedforward and feedback control. By combining the two control methods, the strengths of both schemes can be utilized. 

Programmer consoles. These are programming terminals. Developing system software on the host machines is a common prac-... 

At first acquaintance, the language of accountancy appears illogical to most engineers. Although accountants normally express themselves in tabular rm, the basis of all their prac tice can be simply expressed by... 

In prac tice, the existence of a tight cost-control system tends to spread a cost consciousness among the personnel involved in the project. Such an awareness, even in construction-equipment maintenance and job housekeeping, can lead to efficient cost control throughout. 

Steam pressure. The main boosters can operate on steam pressures from as low as 0,15 bar up to 7 bar gauge. The quantity of steam required increases rapidly as the steam pressure drops (Fig, 11-106), The best steam rates are obtained with about 7 bar. Above this pressure the change in quantity of steam required is prac tically negligible. Ejectors must be designed for the highest available steam pressure, to take advantage of the lower steam consumption for various steam-inlet pressures. 

Fluidized-bed filters. Fluidized beds of granules have received considerable study on theoretical and experimental levels but have not been applied on a prac tical commercial scale. 

The illustrative construction lines of Fig. 18-81 have been made with the assumption of constant underflow. In the more reahstic case of variable underflow, the points C, C, D, D would lie along line GL. Like the prac tical tie hnes, GL is a representation of experimental data. 

Any difference in physical properties of the individual solids can be used as the basis for separation. Differences in density size, shape, color, and electrical and magnetic properties are used in successful commercial separation processes. An important factor in determining the techniques that can be prac tically applied is the particle-size range of the mixture. A convenient guide to the application of different solid-solid separation techniques in relation to the particle-size range is presented in Fig. 19-1, which is a modification of an original illustration by Roberts et al. 

None of the energy Taws apply well in prac tice, and they have failed to yield a starting point for further development of understanding of miUing. They are mainly of historical interest. Most of the early papers... 

Osmotic Pinch Ejfect Feed is pumped into the membrane train, and as it flows through the membrane array, sensible pressure is lost due to fric tion effects. Simultaneously, as water permeates, leaving salts behind, osmotic pressure increases. There is no known practical alternative to having the lowest pressure and the highest salt concentration occur simultaneously at the exit of the train, the point where AP — AH is minimized. This point is known as the osmotic pinch, and it is the point backward from which hydrauhe design takes place. A corollary factor is that the permeate produced at the pinch is of the lowest quality anywhere in the array. Commonly, this permeate is below the required quahty, so the usual prac tice is to design around average-permeate quality, not incremental quahty. A I MPa overpressure at the pinch is preferred, but the minimum brine pressure tolerable is 1.1 times H. 

Distribution of Catalyst in Pores Because of the prac tical reqmrements of manufacturing, commercial impregnated catalysts usually have a higher concentration of ac tive ingredient near the outside than near the tip of the pores. This may not be harmful, because it seems that effectiveness sometimes is better with some kind of nonuni-form distribution of a given mass of catalyst. Such effects may be present in cases where the rate exhibits a maximum as a function of... 

Semibatch hydrogenation of edible oils has a long history and a well-estabhshed body of prac tice by manufacturers and catalyst suppliers. Problems of new oils, new specifications, new catalyst poisons,... 

Mounting electrodes in a bioreactor is costly, and there is an additional contamination risk for sensitive cell cultures. Some other sensors of prac ticai importance are those for dissolved oxygen and for dissolved carbon dioxide. The analysis of gas exiting from a bioreactor with an infrared unit that detects carbon dioxide or a paramagnetic unit that detects oxygen (after carbon dioxide removal) has been replaced by mass spec trophotometry. Gas chromatographic procedures coupled with a mass spectrophotometer will detect 1 the volatile components. 

Types of Solid Wastes The term solid wastes is aU-inchisive and encompasses all sources, types of classifications, compositions, and properties. As a basis for subsequent discussions, it will be helpful to define the various types of solid wastes that are generated. It is important to note that the definitions of solid-waste terms and the classifications vary greatly in prac tice and in literature. Consequently, the use of published data requires considerable care, judgment, and common sense. The following definitions are intended to serve as a guide. 

In a canyon site, filling starts at the head end of the canyon (see Fig. 25-70) and ends at the mouth. The prac tice prevents the accumulation of water behind the landfill. Wastes usu ly are deposited on the canyon floor and from there are pushed up against the canyon face at a slope of about 2 to 1. In this way, a high degree of compaction can be achieved. 

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