Dynes 1 DT wel


The Gibbs-Duhem Equation  [c.19]

The pressure at which standard-state fugacities are most conveniently evaluated is suggested by considerations based on the Gibbs-Duhem equation which says that at constant temperature and pressure  [c.20]

If we vary the composition of a liquid mixture over all possible composition values at constant temperature, the equilibrium pressure does not remain constant. Therefore, if integrated forms of the Gibbs-Duhem equation [Equation (16)] are used to correlate isothermal activity coefficient data, it is necessary that all activity coefficients be evaluated at the same pressure. Unfortunately, however, experimentally obtained isothermal activity coefficients are not all at the same pressure and therefore they must be corrected from the experimental total pressure P to the same (arbitrary) reference pressure designated P. This may be done by the rigorous thermodynamic relation at constant temperature and composition  [c.20]

In this case, there is no superscript on y because, by assumption, Y is independent of pressure. The disadvantage of this procedure is that the reference pressure p" is now different for each component, thereby introducing an inconsistency in the iso-baric Gibbs-Duhem equation [Equation (16)]. In many, but not all, cases, this inconsistency is of no practical importance.  [c.22]

All of the above calculations are done at the specified system temperature.  [c.308]

Polymerization reactions. There are two broad types of polymerization reactions, those which involve a termination step and those which do not. An example that involves a termination step is free-radical polymerization of an alkene molecule. The polymerization requires a free radical from an initiator compound such as a peroxide. The initiator breaks down to form a free radical (e.g., CH3 or OH), which attaches to a molecule of alkene and in so doing generates another free radical. Consider the polymerization of vinyl chloride from a free-radical initiator R. An initiation step first occurs  [c.21]

Catalytic degradation. The performance of most catalysts deteriorates with time. The rate at which the deterioration takes place is another important factor in the choice of catalyst and the choice of reactor conditions. Deterioration in performance lowers the rate of reaction, which, for a given reactor design, manifests itself as a lowering of the conversion. This often can be compensated by increasing the temperature of the reactor. However, significant increases in temperature can degrade selectivity considerably and often accelerate the mechanisms that cause catalyst degradation. Loss of catalyst performance can occur in a number of ways a. Physical loss. Physical loss is particularly important with homogeneous catalysts, which need to be separated from reaction products and recycled. Unless this can be done with high efficiency, it leads to physical loss (and subsequent environmental problems). However, physical loss as a problem is not restricted to homogeneous catalysts. It also can be a problem with heterogeneous catalysts. This is particularly the case when catalytic fluidized-bed reactors are employed. Attrition of the particles causes the catalyst particles to be broken down in size. Particles which are carried over from the fluidized bed are normally separated from  [c.48]

Kilns. Reactions involving free-flowing solid, paste, and slurry materials can be carried out in kilns. In a rotary kiln, a cylindrical shell is mounted with its axis making a small angle to horizontal and rotated slowly. The material to be reacted is fed to the elevated end of the kiln and tumbles down the kiln as a result of the rotation. The behavior of the reactor usually approximates plug flow. High-temperature reactions demand refractory lined steel shells and are usually heated by direct firing. An example of a reaction carried out in such a device is the production of hydrogen fluoride  [c.60]

Having made an initial specification for the reactor, attention is turned to separation of the reactor effluent. In addition, it might be necessary to carry out separation before the reactor to purify the feed. Whether before or after the reactor, the overall separation task normally must be broken down into a number of intermediate separation tasks. The first consideration is the choice of separator for the intermediate separation tasks. Later we shall consider how these separation tasks should be connected to the reactor. As with reactors, we shall concentrate on the choice of separator and not its detailed sizing.  [c.67]

If the mixture to be separated is homogeneous, a separation can only be performed by the addition or creation of another phase within the system. For example, if a gaseous mixture is leaving the reactor, another phase could be created by partial condensation. The vapor resulting from the partial condensation will be rich in the more volatile components and the liquid will be rich in the less volatile components, achieving a separation. Alternatively, rather than creating another phase, one can be added to the gaseous mixture, such as a solvent which would preferentially dissolve one or more of the components from the mixture. Further separation is required to separate the solvent from the process materials allowing recycle of the solvent, etc. A number of physical properties can be exploited to achieve the separation of homogeneous mixtures.If a heterogeneous or multiphase mixture leaves the reactor, then separation can be done physically by exploiting differences in density between the phases.  [c.67]

Even though choices of separators must be made at this stage in the design, it must be borne in mind that the assessment of separation processes ideally should be done in the context of the total system. As is discussed later, separators which use an input of heat to carry out the separation often can be run at effectively zero energy cost if they are appropriately heat integrated with the rest of the process. This includes the three most common types of separators, i.e., distillation columns, evaporators, and dryers. Although they are energy intensive, they also can be energy efficient in terms of the overall process if they are properly heat integrated (see Chaps. 14 and 15).  [c.76]

The most common alternative to distillation for the separation of low-molecular-weight materials is absorption. In absorption, a gas mixture is contacted with a liquid solvent which preferentially dissolves one or more components of the gas. Absorption processes often require an extraneous material to be introduced into the process to act as liquid solvent. If it is possible to use the materials already in the process, this should be done in preference to introducing an extraneous material for reasons already discussed. Liquid flow rate, temperature, and pressure are important variables to be set.  [c.83]

Temperature. Decreasing temperature increases the solubility of the solute. In an absorber, the transfer of solute from gas to liquid brings about a heating effect. This usually will lead to temperature increasing down the column. If the component being separated is dilute, the heat of absorption will be small, and the temperature rise down the column also will be small. Otherwise, the temperature rise down the column will be large, which is undesirable, since solubility decreases with increasing temperature. To counteract the temperature rise in absorbers, the liquid is sometimes cooled at intermediate points as it passes down the column. The cooling is usually to temperatures which can be achieved with cooling water, except in special circumstances where refrigeration is used.  [c.84]

Having dissolved the solute in the liquid, it is often necessary to then separate the solute from the liquid in a stripping operation so as to recycle to the absorber. Now the stripping factor for component i, KiV/L, should be large to concentrate it in the vapor phase and thus be stripped out of the liquid phase. For a stripping column, the stripping factor should be in the range. 2[c.84]

All that can be done is to make a reasonable initial assessment of the number of stages. Having made a decision for the number of stages, the heat flow through the system is temporarily fixed so that the design can proceed. Generally, the maximum temperature in evaporators is set by product decomposition and fouling. Therefore, the highest-pressure stage is operated at a pressure low enough to be below this maximum temperature. The pressure of the lowest-pressure stage is normally chosen to allow heat rejection to cooling water or air cooling. If decomposition and fouling are not a problem, then the stage pressures should be chosen such that the highest-pressure stage is below steam temperature and the lowest-pressure stage above cooling water or air cooling temperature.  [c.87]

For a heterogeneous or multiphase mixture, separation usually can be achieved by phase separation. Such phase separation should be carried out before any homogeneous separation. Phase separation tends to be easier and should be done first.  [c.92]

The liquid stream can be separated readily into pure components by distillation, the benzene taken ofif as product, the diphenyl as an unwanted byproduct, and the toluene recycled. It is possible to recycle the diphenyl to improve selectivity, but we will assume that is not done here.  [c.111]

This process could be continued and possible sequences identified for further consideration. Some possible sequences would he eliminated, narrowing down the number suggested by Table 5.1.  [c.134]

Consider the sequence of simple columns shown in Fig. 5.12. In the direct sequence shown in Fig. 5.12, the composition of component B in the first column increases below the feed as the more volatile component A decreases. However, moving further down the column, the composition of component B decreases again as the composition of the less volatile component C increases. Thus the composition of component B reaches a peak only to be remixed.  [c.149]

First, determine the shifted temperature intervals T from actual supply and target temperatures. Hot streams are shifted down in temperature by and cold streams up by AT J2, as detailed  [c.175]

Now cascade any surplus heat down the temperature scale from interval to interval. This is possible because any excess heat available from the hot streams in an interval is hot enough to supply a deficit in the cold streams in the next interval down. Figure 6.18 shows the cascade for the problem. First, assume that no heat is supplied to the first interval from a hot utility (Fig. 6.18a). The first interval has a surplus of 1.5 MW, which is cascaded to the next interval. This second interval has a deficit of 6 MW, which reduces the heat cascaded from this interval to -4.5 MW. In the third interval the process has a surplus of 1 MW, which leaves -3.5 MW to be cascaded to the next interval, and so on.  [c.178]

Next, calculate the shifted interval temperatures. Hot streams are shifted down by 2.5°C, and cold streams are shifted up by 2.5°C (Table 6.5).  [c.179]

Heat exchanger cost data usually can be manipulated such that the fixed costs, represented by the coefficient a in Eq. (7.20), do not vary with exchanger specification. If this is done, then Eq. (7.6), as derived in App. F, can be modified to  [c.229]

A detonation generates greater pressures and is more destructive than a deflagration. Whereas the peak pressure caused by the deflagration of a hydrocarbon-air mixture in a closed vessel at atmospheric pressure is on the order of 8 bar, a detonation may give a peak pressure on the order of 20 bar. A deflagration may turn into a detonation, particularly if traveling down a long pipe.  [c.258]

Product removal during reaction. Separation of the product before completion of the reaction can force a higher conversion, as discussed in Chap. 2. Figure 2.4 showed how this is done in sulfuric acid processes. Sometimes the product (or one of the products) can be removed continuously from the reactor as the reaction progresses, e.g., by allowing it to vaporize from a liquid phase reactor.  [c.277]

Reducing waste from multiple reactions producing waste byproducts. In addition to the losses described above for single reactions, multiple reaction systems lead to further waste through the formation of waste byproducts in secondary reactions. Let us briefly review from Chap. 2 what can be done to minimize byproduct formation.  [c.278]

Recycle waste streams directly. Sometimes waste can be reduced by recycling waste streams directly. If this can be done, it is clearly the simplest way to reduce waste and should be considered first. Most often, the waste streams that can be recycled directly are aqueous streams which, although contaminated, can substitute part of the freshwater feed to the process.  [c.280]

In early designs, the reaction heat typically was removed by cooling water. Crude dichloroethane was withdrawn from the reactor as a liquid, acid-washed to remove ferric chloride, then neutralized with dilute caustic, and purified by distillation. The material used for separation of the ferric chloride can be recycled up to a point, but a purge must be done. This creates waste streams contaminated with chlorinated hydrocarbons which must be treated prior to disposal.  [c.285]

Let us now suggest what can be done, particularly in design, to overcome such waste.  [c.289]

It is strictly for convenience that certain conventions have been adopted in the choice of a standard-state fugacity. These conventions, in turn, result from two important considerations (a) the necessity for an unambiguous thermodynamic treatment of noncondensable components in liquid solutions, and (b) the relation between activity coefficients given by the Gibbs-Duhem equation. The first of these considerations leads to a normalization for activity coefficients for nonoondensable components which is different from that used for condensable components, and the second leads to the definition and use of adjusted or pressure-independent activity coefficients. These considerations and their consequences are discussed in the following paragraphs.  [c.17]

Equation (16) is a differential equation and applies equally to activity coefficients normalized by the symmetric or unsymme-tric convention. It is only in the integrated form of the Gibbs-Duhem equation that the type of normalization enters as a boundary condition.  [c.20]

More general forms of the Gibbs-Duhem equation have been derived to allow for variations in temperature or pressure (or both) but these are not useful for our purposes since they are not easily integrated. Equation (16) is satisfied by various simple algebraic forms relating an y to x well-ltnown examples are the Margules and van Laar equations but many others exist. The particular relation used in this work, the UNIQUAC equation, while significantly different from the equations of Margules and van Laar, is also a solution to the Gibbs-Duhem differential equation.  [c.20]

In a chemical process, the transformation of raw materials into desired products usually cannot be achieved in a single step. Instead, the overall transformation is broken down into a number of steps that provide intermediate transformations. These are carried out through reaction, separation, mixing, heating, cooling, pressure change, particle size reduction and enlargement, etc. Once individual steps have been selected, they must be interconnected to carry out the overall transformation (Fig. 1.1a). Thus the synthesis of a chemical process involves two broad activities. First, individual transformation steps are selected. Second, these individual transformations are interconnected to form a complete structure that achieves the required overall transformation. A flowsheet is the diagrammatic representation of the process steps with their interconnections.  [c.1]

Choosing to use a continuous rather than a batch reactor, plug-flow behavior can be approached using a series of continuous well-mixed reactors. This again sdlows concentrated sulfuric acid to be added as the reaction progresses, in a similar way as suggested for some parallel systems in Fig. 2.2. Breaking the reactor down into a series of well-mixed reactors also allows good temperature control, s we shall discuss later.  [c.52]

When separating a three-component mixture using simple columns, there are only two possible sequences (see Fig. 5.1). Consider the first characteristic of simple columns. A single feed is split into two products. As a first alternative to two simple columns, the possibilities shown in Fig. 5.10 can be considered. Here, three products are taken from one column. The designs are in fact both feasible and cost-effective when compared with simple arrangements on a standalone basis (i.e., reboilers and condensers operating on utilities) for certain ranges of conditions. If the feed is dominated by the middle product (typically more than 50 percent of the feed) and the heaviest product is present in small quantities (typically less than 5 percent), then the arrangement shown in Fig. 5.10a can be an attractive option. The heavy product must find its way down the column past the sidestream. Unless the heavy product has a small flow and the middle product a high flow, a reasonably pure middle product cannot be achieved. In these circumstances, the sidestream is usually taken as a vapor product to obtain a reasonably pure sidestream.  [c.147]

Although composite curves can he used to set energy targets, they are inconvenient because they are based on a graphic construction. A method of calculating energy targets directly without the need for graphic construction can be developed. The process is first divided into temperature intervals in the same way as was done for construction of the composite curves. Figure 6.14a shows that it is not possible to recover all the heat in each temperature interval, since temperature driving forces are not feasible throughout the interval. This problem can be overcome if, purely for the purposes of construction, the hot composite is pretended to be T iJ2 colder than it is in practice and the cold composite is pretended to be ATmin/2 hotter than it is in practice (see Fig. 6.146). The shifted composite curves now touch at the pinch. Carrying out a heat balance between the shifted composite curves within a shifted temperature interval shows that heat transfer is feasible throughout each shifted temperature interval, since hot streams in practice are actually ATmin/2 hotter and cold streams T iJ2 colder. Within each shifted interval the hot streams are in reality hotter than the cold streams by just  [c.174]

In general, the final network design should be achieved in the minimum number of units to keep down the capital cost (although this is not the only consideration to keep down the capital cost). To minimize the number of imits in Eq. (7.1), L should be zero and C should be a maximum. Assuming L to be zero in the final design is a reasonable assumption. However, what should be assumed about C Consider the network in Fig. 7.16, which has two components. For there to be two components, the heat duties for streams A and B must exactly balance the duties for streams E and F. Also, the heat duties for streams C and D must exactly balance the duties for streams G and H. Such balemces are likely to be unusual and not easy to predict. The safest assumption for C thus appears to be that there will be one component only, i.e., C = 1. This leads to an important special case when the network has a single component and is loop-free. In this case,  [c.215]

Equation (7.21) uses a single cost function in conjunction with the targets for the number of units (or shells) and network area. Differences in cost can be accounted for either by introducing new cost functions or by adjusting the heat exchange area to reflect the cost differences. This can be done by weighting the stream heat transfer coefficients in the calculation of network area with a factor [c.229]


See pages that mention the term Dynes 1 DT wel : [c.21]    [c.21]    [c.21]    [c.174]    [c.178]    [c.68]    [c.69]    [c.108]    [c.121]    [c.259]    [c.276]    [c.283]    [c.294]   
Sourse beds of petroleum (1942) -- [ c.194 , c.195 , c.196 , c.197 , c.198 , c.199 , c.200 , c.201 , c.202 , c.203 , c.204 , c.205 , c.206 , c.207 , c.208 , c.209 , c.210 , c.211 , c.212 , c.213 , c.214 , c.215 , c.216 , c.217 , c.218 , c.219 , c.220 , c.221 , c.222 , c.223 , c.224 , c.225 , c.226 , c.227 , c.228 , c.229 , c.230 , c.231 , c.232 , c.233 , c.234 , c.235 , c.236 , c.237 , c.237 , c.238 , c.239 , c.240 , c.241 , c.242 ]