Change in Pressure

Add an entrainer to the distillation. A mass separation agent, known as an entrainer, can be added to the distillation. The separation becomes possible because the entrainer interacts more strongly with one of the azeotrope-forming components than the other. This can in turn alter in a favorable way the relative volatility between the key components. 

Use a membrane. If a semipermeable membrane is placed between the vapor and liquid phases, it can alter the vapor-liquid equilibrium and allow the separation to be achieved. This technique is known as pervaporation and was discussed in Chapter 10. 

If the azeotrope is not sensitive to changes in pressure, then an entrainer can be added to the distillation to alter in a favorable way the relative volatility of the key components. Before the separation of an azeotropic mixture using an entrainer is considered, the representation of azeotropic distillation in ternary diagrams needs to be introduced. 

Substituting mg from Equation 12.1 into Equation 12.3 gives  

In Chapter 9, a relationship was developed for total reflux conditions at any Stage n  

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Figure 3.8a shows the temperature-composition diagram for a minimum-boiling azeotrope that is sensitive to changes in pressure. This azeotrope can be separated using two columns operating at different pressures, as shown in Fig. 3.86. Feed with mole fraction of A Ufa)) of, say, 0.3 is fed to the high-pressure column. The bottom product from this high-pressure column is relatively pure B, whereas the overhead is an azeotrope with jcda = 0-8, jcdb = 0.2. This azeotrope is fed to the low-pressure column, which produces relatively pure A in the bottom and in the overhead an azeotrope with jcda = 0.6, jcdb = 0.4. This azeotrope is added to the feed of the high-pressure column.

Whether heat integration is restricted to the separation system or allowed with the rest of the process, integration always benefits from colder reboiler streams and hotter condenser streams. This point is dealt with in more general terms in Chap. 12. In addition, when column pressures are allowed to vary, columns with smaller temperature differences are easier to integrate, since smaller changes in pressure are required to achieve suitable integration. This second point is explained in more detail in Chap. 14. 

Certain curves, T = f(% distilled), level off at high temperatures due to the change in pressure and to the utilization of charts for converting temperatures under reduced pressure to equivalent temperatures under atmospheric pressure. 

The main component of sandstone reservoirs ( siliciclastic reservoirs ) is quartz (Si02). Chemically it is a fairly stable mineral which is not easily altered by changes in pressure, temperature or acidity of pore fluids. Sandstone reservoirs form after the sand grains have been transported over large distances and have deposited in particular environments of deposition. 

D is basically a succession of 2D or 3D surveys repeated at intervals of time during which it is expected that some production effect has occurred, of sufficient magnitude to effect the acoustic impedance contrast seen by the propagating waves. For example, this oould be changes in the water or gas saturation, or changes in pressure. 

Pressure depletion in the reservoir can normally be assumed to be isothermal, such that the isothermal compressibility is defined as the fractional change in volume per unit change in pressure, or... 

The other main physical property of gas which distinguishes it from oil is its compressibility the fractional change in volume (V) per unit of change in pressure (P) at constant temperature (T). Recall that... 

The typical compressibility of gas is 500 10 psi, compared to oil at 10 10 psr, and water at 3 10 psi When a volume of gas is produced (8V) from a gas-in-place volume (V), the fractional change in pressure (8P) is therefore small. Because of the high compressibility of gas it is therefore uncommon to attempt to support the reservoir pressure by injection of water, and the reservoir is simply depleted or blown down . 

If the total surface area is small (say, a few hundred square centimeters), the amount adsorbed becomes so little that measurements are difficult by normal procedures. Thus the change in pressure-volume product on admitting gas to the adsorbent becomes so small that precision is impaired. 

Applied to a two-phase system, this says that the change in pressure with temperature is equal to the change in entropy at constant temperature as the total volume of the system (a + P) is increased, which can only take place if some a is converted to P ... 

A sudden change in pressure can aiso be used to shift a chemicai equiiibrium, tire change being given by tire tiiemrodynamic reiation... 

Joule-Thompson Coefficient for Real Gases. This expresses the change in temperature with respect to change in pressure at constant enthalpy ... 

A typical loop injector showing the sampling position with pressurized solvent flowing through one loop onto the column and the sample solution placed in the other loop at atmospheric pressure. Rotation of the loop carrier through 180° puts the sample into the liquid flow at high pressure with only momentary change in pressure in the system. 

Fig. 4. Typical nylon-6,6 autoclave polymerisation cycle showing the changes in pressure (—) and temperature (---). To convert MPa to psi, multiply by...

Most thermometry using the KTTS direcdy requites a thermodynamic instmment for interpolation. The vapor pressure of an ideal gas is a thermodynamic function, and a common device for reali2ing the KTTS is the helium gas thermometer. The transfer function of this thermometer may be chosen as the change in pressure with change in temperature at constant volume, or the change in volume with change in temperature at constant pressure. It is easier to measure pressure accurately than volume thus, constant volume gas thermometry is the usual choice (see Pressure measurement). 

The second step is the evaluation of the change in fugacity of the liquid with a change in pressure to a value above or below For this isothermal change of state from saturated liquid at to liquid at pressure P, Eq. (4-105) is integrated to give... 

An example of a pneumatic PI controller is shown in Fig. 8-64 7. This controller has two stages of pneumatic amphfication and a Bourdon tube input element that measures process pressure. The Bourdon tube element is a flattened tube that has been formed into a cui ve so that changes in pressure inside the tube cause vertical motions to occur at the ungrounded end. This motion is transferred to the left end of the beam, as shown. 

A flowing fluid is acted upon by many forces that result in changes in pressure, temperature, stress, and strain. A fluid is said to be isotropic when the relations between the components of stress and those of the rate of strain are the same in all directions. The fluid is said to be Newtonian when this relationship is linear. These pressures and temperatures must be fully understood so that the entire flow picture can be described. 

The effect of compressibility is important in high mach number machines. Mach number is the ratio of velocity to the acoustic speed of a gas at a given temperature M = Vja. Acoustic speed is defined as the ratio change in pressure of the gas with respect to its density if the entropy is held constant ... 

Change in pressure drop aeross heat exehangers... 

A gas is defined as the state of matter distinguished from solid and liq uid states by very low density and viscosity, relatively great expansion and contraction with changes in pressure and temperature, and the ability to diffuse readily, distributing itself uniformly throughout any container... 

The compressibilities of solvents vary significantly from one solvent to another. The compressibility of cyclohexane is about 0.67% per thousand p.s.i. change in pressure [11] and, thus, for a column operated at 6,000 p.s.i. (mean pressure 3,000 p.s.i.), there will be an error in retention volume measurement of about 2%. In a similar manner, n-heptane has a compressibility of about 1.0% per 1,000 p.s.i. change in pressure [11] and, under similar circumstances, would give an error of about 3% in retention volume measurement. Fortunately, as already discussed in Part 1 of this book, there are other retention parameters that can be used for solute... 

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