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engineering
chemical engineering
Questions and Answers of
Chemical Engineering
When is it safe to ignore subcooling of the reflux liquid and treat the reflux as a saturated liquid? In other words, how many °C subcooling can be ignored? Do a few numerical calculations for
When might you use an intermediate condenser on a column? What are the possible advantages?
Explain with a McCabe-Thiele diagram how changing feed temperature (or equivalently, q) may help an existing column achieve the desired product specifications.
Equations (4-53) and (4-54) are mass balances on particular phases. When are these equations valid?Equation (4-53) Equation (4-54) L = L' + S
Several ways of adapting existing columns to new uses were listed. Generate new methods that might allow existing systems to meet product specifications that could not be met without modification.
A distillation column separating ethanol from water is shown in the following figure. Pressure is \(1 \mathrm{~kg} / \mathrm{cm}_{2}\). Instead of having a condenser, a stream of pure, saturated
A distillation column with a total condenser and a partial reboiler is separating \(200 \mathrm{kmol} / \mathrm{h}\) of a feed that is \(40 \mathrm{~mol} \% \mathrm{n}\)-pentane and \(60
A distillation column receives a feed that is \(40 \mathrm{~mol} \% \mathrm{n}-\mathrm{pentane}\) and 60 \(\mathrm{mol} \% \mathrm{n}\)-hexane. Feed flow rate is \(2500 \mathrm{lbmol} / \mathrm{h}\),
A continuous, steady-state distillation column is fed a mixture that is 70 \(\mathrm{mol} \% \mathrm{n}\)-pentane and \(30 \mathrm{~mol} \% \mathrm{n}\)-hexane. Feed rate is \(1000 \mathrm{kmol} /
A distillation column receives a feed that is \(40 \mathrm{~mol} \% \mathrm{n}-\mathrm{pentane}\) and 60 \(\mathrm{mol} \% \mathrm{n}\)-hexane. Feed flow rate is \(2500 \mathrm{lbmol} / \mathrm{h}\),
Some azeotropic systems can be separated by operating two coupled distillation columns at different pressures. The azeotrope concentration shifts enough that pure products can be recovered from the
A distillation column is separating \(150 \mathrm{kmol} / \mathrm{h}\) of a saturated liquid mixture that is \(30 \mathrm{~mol} \%\) methanol and \(70 \mathrm{~mol} \%\) water. The column operates at
A distillation column with a partial condenser and a partial reboiler is separating methanol and water. Column pressure is \(1.0 \mathrm{~atm}\). We desire a bottoms product flow rate of \(120
A distillation column receives a feed that is \(30 \mathrm{~mol} \% \mathrm{n}-\mathrm{pentane}\) and 70 \(\mathrm{mol} \% \mathrm{n}\)-hexane. Feed flow rate is \(3600 \mathrm{lbmol} / \mathrm{h}\),
For the column shown in Problem 3.D2, derive equations for \(D, B, Q_{c}\), and L/D. D2.* A distillation column separating ethanol from water is shown in the following figure. Pressure is 1 kg/cm2.
Show that for binary distillation in a column with a single feed, a total condenser, and a partial reboiler,\(\mathrm{FR}_{\text {MVC,dist }}=\frac{\mathrm{x}_{\mathrm{MVC}, \text { dist
Show that Eqs. (3-3) and (3-4) are valid for a column with two feeds (e.g., shown in Figure 4-18) as long as we define \(\mathrm{F}_{\text {total }}=\mathrm{F}_{1}+\mathrm{F}_{2}\) and
A partial condenser takes vapor leaving the top of a distillation column and condenses a portion of it. The vapor portion of mole fraction \(\mathrm{y}_{\mathrm{D}}\) is removed as the distillate
Solve for \(\mathrm{Q}_{\mathrm{c}}\) and \(\mathrm{Q}_{\mathrm{R}}\) in Problem 3.D1 with a process simulator.a. Part a.b. Part b.Note: With Aspen Plus, use RADFRAC with an arbitrary (but large)
Solve Problem 3.D6 using a process simulator to find \(Q_{c}\) and \(Q_{R}\). Do a hand calculation to find the value of \(\mathrm{D}\). Then arbitrarily set \(\mathrm{N}=40\) and \(\mathrm{N}_{\text
A distillation column with two feeds is separating ethanol from water. The first feed is \(60 \mathrm{wt} \%\) ethanol, has a total flow rate of \(1000 \mathrm{~kg} / \mathrm{h}\), and is a mix of
A distillation column separating ethanol from water is shown in the following figure. Pressure is \(1 \mathrm{~kg} / \mathrm{cm}_{2}\). Instead of having a reboiler, 100 \(\mathrm{kg} /
Explain how a distillation column works.
Without looking at the text, define the following:a. Isothermal distillationb. The four flow regimes in a staged distillation columnc. Reflux and reflux ratiod. Boilup and boilup ratioe. Rectifying
Explain the reasons a constant pressure distillation column is preferable toa. An isothermal distillation system.b. A cascade of flash separators at constant temperature.c. A cascade of flash
In a countercurrent distillation column at constant pressure, where is the temperature highest? Where is it lowest?
Develop your own key relations chart for this chapter. In one page or less, draw sketches, write equations, and include all key words useful for solving problems.
For a binary separation, is \(\mathrm{K}_{\mathrm{MVC}} \mathrm{V} / \mathrm{L}\) usually less than, equal to, or greater than 1.0? For a binary separation, is \(\mathrm{K}_{\mathrm{LVC}} \mathrm{V}
Specifications for a distillation column similar to Figure 3-8 cannot include all three flow rates F, D, and B. Why not? H. y. Vin -+-1 Qc F2 hp(TF) 1 V2L1 Vj+4 f Lo xo Vkk kk-1 VN+1 N B(Xehe D. XD D
Is column pressure approximately constant \({ }^{*}\) for the following problems:a. Column operating at nominal pressure \(\mathrm{p}=1.0 \mathrm{~atm}\) with 10 traysb. Column operating at nominal
In an abstract sense, is boilup a type of reflux?
Why is the assumption of constant column pressure often reasonable for columns at atmospheric pressure and above, but often not reasonable for vacuum columns?
A common misconception of new graduates is that reflux is usually a saturated liquid. In practice, if the reflux needs to be pumped, the reflux is always subcooled. Explain why. (Note: We will see in
In the paragraph immediately before Example 3-1, the following sentence occurs: " \(\mathrm{Q}_{\mathrm{c}}\) is proportional to \((1+\mathrm{L} / \mathrm{D}) \mathrm{F}\), and
There are ways in which columns can be specified other than those listed in Tables 3-1 to 3-3.a. Develop alternative specifications for design problems.b. Develop alternative specifications for
We flash distill a mixture that is \(5.0 \mathrm{~mol} \%\) methane, \(12.3 \mathrm{~mol} \%\) ethane, 11.5 \(\mathrm{mol} \%\) n-butane, \(22.2 \mathrm{~mol} \%\) n-pentane, \(25.4 \mathrm{~mol}
We flash distill a mixture that is \(24.1 \mathrm{~mol} \%\) ethane, \(39.7 \mathrm{~mol} \% \mathrm{n}\)-hexane, and \(36.2 \mathrm{~mol} \% \mathrm{n}\)-heptane. If \(\mathrm{p}_{\text {drum
We flash distill a mixture that is \(28.1 \mathrm{~mol} \%\) n-butane, \(42.8 \mathrm{~mol} \% \mathrm{n}\)-pentane, and \(29.1 \mathrm{~mol} \% \mathrm{n}\)-heptane. \(\mathrm{T}_{\text {drum
Develop a spreadsheet to solve problem 2.D13, parts b and c. Use Eq. (2-28). (Note: The easiest approach to solving this problem is to develop a spreadsheet similar to Figures 2-B2 and run the
To explore what happens if a nonvolatile component is in the feed to a flash distillation, modify Figure 2-B2 to add \(37.5 \mathrm{kmol} / \mathrm{h}\) of a nonvolatile component to the feed.a. Keep
Benzene-toluene equilibrium is often approximated as \(\alpha_{\mathrm{BT}}=2.34\). Generate the \(\mathrm{y}-\mathrm{x}\) diagram for this relative volatility. Compare your results with data in the
Ethylene glycol and water are flash distilled in a cascade of three drums connected as shown in the figure. All drums operate at 228 mm Hg. Feed is 40 mol% water. One-third of the feed is vaporized
Pure water at a flow rate of \(1500 \mathrm{~kg} /\) minute at \(\mathrm{p}=5000 \mathrm{kPa}\) and \(\mathrm{T}=500 \mathrm{~K}\) is sent to an adiabatic flash system operating at \(\mathrm{p}=100
Use the Peng-Robinson VLE correlation in Aspen Plus to solve Problem 2.D13, part \(\mathrm{b}\), except feed is a saturated liquid at 10.0 bar. Pressure is dropped to 6.0 bar in the flash drum.
Two feeds containing methanol and water are sent to the same flash drum. Feed 1 is \(20 \mathrm{~mol} \%\) methanol, \(F_{1}=150 \mathrm{kmol} / \mathrm{h}\), and \((V / F)_{1}=0.4\). Feed 2 is \(30
Use a process simulator to solve Problem 2.D16. Do "what if?" simulations to see what happens to V/F and product compositions as temperature and/or pressure vary.Problem 2.D16. A feed that is 50.0
One \(\mathrm{kmol} / \mathrm{s}\) of a feed containing \(20 \mathrm{~mol} \%\) furfural, \(75 \mathrm{~mol} \%\) water, and \(5 \mathrm{~mol} \%\) ethanol at \(105^{\circ} \mathrm{C}\) and 3.0 bar
Use a process simulator to solve the following flash distillation problem. Feed is \(2 \mathrm{~mol} \%\) methane, \(30 \mathrm{~mol} \%\) n-butane, \(47 \mathrm{~mol} \% \mathrm{n}\)-pentane, and
A vertical flash drum will be used to separate \(1000 \mathrm{kmol} / \mathrm{h}\) of a feed that is 10.0 \(\mathrm{mol} \%\) isopropanol and \(90.0 \mathrm{~mol} \%\) water. Feed is at 9.0 bar and
A flash drum is to flash \(10,000 \mathrm{lbmol} / \mathrm{h}\) of a feed that is \(65 \mathrm{~mol} \% \mathrm{n}\)-hexane and \(35 \mathrm{~mol} \% \mathrm{n}-o c t a n e\) at \(1.0 \mathrm{~atm}\)
A flash drum at \(1.0 \mathrm{~atm}\) is separating a feed consisting of methanol and water. If the feed rate is \(2000 \mathrm{~kg} / \mathrm{h}\) and the feed is \(45 \mathrm{wt} \%\) methanol,
We are separating a mixture of methanol and water in a flash drum at 1 atm pressure. Equilibrium data are listed in Table 2-8.a. Feed is 60.0 mol% methanol, and 40.0% of the feed is vaporized. What
Two flash distillation chambers are hooked together as shown in the diagram. Both are at 1 atm pressure. The feed to the first drum is a binary mixture of methanol and water that is 55.0 mol%
Data for the equilibrium of water and n-butanol at 1.0 atmosphere are given in Table 8-5. Plot yw vs. xw. A feed of 100.0 kmol/h that is 20.0 mol% water is fed to flash chamber A, which is the first
A mixture of methanol and water is sent to a flash distillation drum operating at 1.0 atm. Feed rate is 10.0 kmol/h. The feed before the valve in Figure 2-1 is at 102.0C and a pressure of 5.0 bar.
We have a feed that is a binary mixture of methanol and water (55.0 mol% methanol) that is sent to a system of two flash drums hooked together. The vapor from the first drum is cooled, which
Antoine constants for 1-octanol and 1-propanol are listed in Table 2- 3.a. At 1.50 atm and 100.0C, what is vapor pressure of 1-octanol in mm Hg?b. Assuming Raoult's law is valid, what is the K value
Your plant feeds 100.0 kmol/h of a mixture that is 46.0 mol% ethanol and 54.0 mol% water to a flash drum. Your boss thinks that results will be better with two flash drums (same configuration as in
A flash drum at 700.0 kPa is separating binary mixtures of ethane and n-butane.a. The following equilibrium results were generated using correct units in Eq. (2-28) and then converting temperature to
We wish to flash distill an ethanol-water mixture that is \(30.0 \mathrm{wt} \%\) ethanol and has a feed flow of \(1000 \mathrm{~kg} / \mathrm{h}\). Feed is at \(200.0^{\circ} \mathrm{C}\). The flash
We have a mixture that is \(35.0 \mathrm{~mol} \% \mathrm{n}\)-butane with unknown amounts of propane and n-hexane. We are able to operate a flash drum at \(400.0 \mathrm{kPa}\) and \(70.0^{\circ}
An equilibrium mixture of ethylene and propylene is at \(2500 \mathrm{kPa}\) and \(25.0^{\circ} \mathrm{C}\). Find the vapor and liquid mole fractions of ethylene. Use DePriester charts or Eq.
Find the diameter and length of a horizontal flash drum for Problem 2.D1c if a hold-up time of 1.0 hours is specified.Problem 2.D1cc. If the feed is \(30.0 \mathrm{~mol} \%\) methanol and we desire a
We flash distill a mixture of methane and n-butane at \(\mathrm{p}_{\text {drum }}=6.0\) bar.a. Use the DePriester charts or Eq. (2-28). For several temperatures from \(\mathrm{T}=\) \(-60^{\circ}
A ternary mixture of methanol, n-propanol, and n-butanol is flash distilled at a pressure of \(0.74 \mathrm{~atm}\). The feed is \(36 \mathrm{~mol} \%\) methanol, \(42 \mathrm{~mol} \%
We have a flash drum separating \(50.0 \mathrm{kmol} / \mathrm{h}\) of a mixture of ethane, isobutane, = and n-butane. The ratio of isobutane to n-butane is held constant at 0.80 (that is, Zic4/ZnC4
A feed that is \(50.0 \mathrm{~mol} \%\) methane, \(10.0 \mathrm{~mol} \% \mathrm{n}\)-butane, \(15.0 \mathrm{~mol} \% \mathrm{n}\)-pentane, and \(25.0 \mathrm{~mol} \% \mathrm{n}\)-hexane is flash
Two feeds containing ethanol and water at \(1.0 \mathrm{~atm}\) are fed simultaneously to the same flash drum. Feed 1 is \(10.0 \mathrm{~mol} \%\) ethanol, \(\mathrm{F}_{1}=150.0 \mathrm{kmol} /
\(10 \mathrm{kmol} / \mathrm{h}\) of a feed that is \(10.0 \mathrm{~mol} \%\) propane, \(30.0 \mathrm{~mol} \% \mathrm{n}\)-butane, and 60.0 \(\mathrm{mol} \% \mathrm{n}\)-hexane is flash distilled
A flash drum operating at \(300 \mathrm{kPa}\) is separating \(1000.0 \mathrm{kmol} / \mathrm{h}\) of a mixture that is \(40.0 \mathrm{~mol} \%\) isobutane, \(25.0 \% \mathrm{n}\)-pentane, and \(35.0
\(200 \mathrm{kmol} / \mathrm{h}\) of a feed that is \(10.0 \mathrm{~mol} \%\) ethanol and \(90.0 \mathrm{~mol} \%\) water is separated in a pair of flash drums. The vapor from drum 1 is partially
We wish to flash distill a feed that is \(55.0 \mathrm{~mol} \%\) ethane and \(45.0 \mathrm{~mol} \% \mathrm{n}-\) pentane. \(\mathrm{p}_{\text {drum }}=700 \mathrm{kPa}\) and \(\mathrm{T}_{\text
\(50 \mathrm{kmol} / \mathrm{h}\) of a vapor feed that is \(70 \mathrm{~mol} \%\) methanol and \(30 \mathrm{~mol} \%\) water is partially condensed in a heat exchanger and then fed to a flash drum
You specified a 5.5 -foot diameter, 22.0 -foot long drum with a mesh demister for Example 2-4. This drum was built. Later, your boss informed you that a minor [the boss' word] mistake had been made
We plan to separate a mixture of propane and n-hexane at 300 kPa.a. Using the data in the DePriester charts, plot ypropane VS. Xp Xpropane for this mixture at 300 kPa. Xpropane and T vs.b. If the
Two feeds containing ethanol and water at \(1.0 \mathrm{~atm}\) are fed simultaneously to the same flash drum. Feed 1 is \(20.0 \mathrm{~mol} \%\) ethanol, \(\mathrm{F}_{1}=150.0 \mathrm{kmol} /
Use Eq. (2-11) to create a table comparing the y values for methanol for methanol-water VLE at \(1.0 \mathrm{~atm}\) versus y values from Table 2-8 (in problem 2.D1) for all the \(x\) values in Table
Antoine constants for vapor pressure for \(\mathrm{n}\)-pentane and \(\mathrm{n}\)-hexane are listed in Table 2-3.a. Predict the vapor pressure at \(0.0^{\circ} \mathrm{C}\) for pure
Repeat Example 2-4, but with \(\mathrm{F}=3000 \mathrm{lbmol} / \mathrm{h}\), and use a horizontal flash drum with holding time \(=55 \mathrm{~min}\) and surge time \(=85 \mathrm{~min}\). Calculate
Design a horizontal flash drum to separate \(15,000 \mathrm{~kg} / \mathrm{h}\) of a feed with the following mass fractions: methane 0.21 , propane 0.39 , n-butane 0.24 , i-butane 0.11 , and
A flash drum is separating \(n\)-butane and \(n\)-pentane with \(T_{\text {drum }}=20.0^{\circ} \mathrm{C}\) and \(p_{\text {drum }}\) \(=101.3 \mathrm{kPa}\). The feed is \(50.0 \mathrm{wt} \%
A feed of \(100.0 \mathrm{kmol} / \mathrm{h}\) that is \(60.0 \mathrm{~mol} \%\) methanol, and \(40.0 \mathrm{~mol} \%\) water is sent to a system of three flash drums operating at 1.0 atmosphere.
In Figure 2-9, the feed plots as a two-phase mixture, whereas it is a liquid before introduction to the flash chamber. Explain why. Why can’t the feed location be plotted directly from known values
Can weight units be used in the flash calculations instead of molar units?
Flash distillation is usually operated adiabatically. Where does the energy to vaporize part of the feed come from?
In the flash distillation of salt water, the salt is totally nonvolatile (this is the equilibrium statement). Show a McCabe-Thiele diagram for feed water containing 3.5 wt % salt. Be sure to plot
Develop your own key relations chart for this chapter. That is, on one page summarize everything you would want to know to solve problems in flash distillation. Include sketches, equations, and key
In a flash drum separating a multicomponent mixture, raising the pressure willa. increase the drum diameter and increase the relative volatilities.b. increase the drum diameter and cause no change to
a. What would Figure 2-2 look like if we plotted y2 vs. X2 (i.e., plot less volatile component mole fractions)?b. What would Figure 2-3 look like if we plotted T vs. X2 or y2 (less volatile
a. At 100.0°C and a pressure of 200.0 kPa, what is the K value of n-hexane?b. As the pressure increases, does the K value (a) increase, (b) decrease, or (c) stay constant?c. Within a homologous
Use the DePriester chart:What is the K value of propane at 240.0 kPa and 25.0°C?What is the normal boiling point of n-pentane?What is the boiling point of n-pentane at p = 600.0 kPa?
Use the vapor-liquid equilibrium data at 1.0 atm. for methanol-water (Table 2-8 in Problem 2.D1) for the following:If the methanol vapor mole fraction is 0.600, what is the methanol liquid mole
An open glass of an alcoholic beverage that is 15.0 mol% ethanol and 85.0 mol% water has been sitting on the table for a long time and is at 1.0 atm pressure and 25.0°C. The temperature and mole
Why is there a difference between degrees of freedom for equilibrium and degrees of freedom for complete design? Example: binary flash. Gibbs phase rule, F = C − P + 2 =2; entire design F = 6.
Part E of Example 2-3 determines the differences between Aspen Plus and Example 2-3 results. Explain how the % difference in V is about 4.5 times as the % difference in L yet the numerical
Figure 2-4 is at a pressure of 1.0 kg/cm2 (actually kgf/cm2), which was formerly a fairly common pressure unit. What is the pressure in bar and in atm? 100 400 O 05 100
Think of all the ways a binary flash distillation problem can be specified. For example, we have usually specified F, z, Tdrum, Pdrum in addition to T and p. If T and p are constant, what other
An existing flash drum is available. The vertical drum has a demister and is 4 ft in diameter and 12 ft tall. The feed is 30 mol% methanol and 70.0 mol% water. A vapor product that is 58 mol%
Determine the effect of pressure on the temperature, separation, and diameter of a flash drum.
Analytically solve the Rachford-Rice equation for V/F for a binary system.
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