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chemical engineering
Questions and Answers of
Chemical Engineering
Develop or adapt a spreadsheet (e.g., Figure 2.B3) to determine bubble points.a. Find the bubble point temperature and the vapor mole fractions for a liquid mixture that is \(50.0 \mathrm{~mol} \%\)
The paper by McCabe and Thiele (1925) is a classic in chemical engineering. Read it. Write a one-page critique of the paper.
If we wish to separate the following systems by distillation, is CMO approximately valid?a. Methanol and waterb. Isopropanol and waterc. Acetic acid and waterd. Benzene from toluene
a. Solve Example 4-4 with a process simulator.Example 4-4A 60 mol% methanol and 40 mol% water feed is input as a two-phase mixture that flashes so that VF/F = 0.3. Feed flow rate is 350 kmol/h. The
Use a process simulator to find the optimum feed stage and total number of equilibrium stages for Problem 3.D6. Report the VLE correlation used. Record the values of \(Q_{\text {condenser }}\) and
Separation of dilute mixtures of acetic acid from water is an important separation problem, particularly in the food industry. The difficulty is not in designing a system that will do the separation.
Explain why the external mass balances cannot be solved for a ternary distillation system without an additional assumption. Why are the equations for the following not useful?a. External energy
Show approximately for the simulation illustrated in Figure 5-2 (CMO not strictly valid) that \(\mathrm{L} / \mathrm{V}\) is more constant than either \(\mathrm{L}\) or \(\mathrm{V}\). Explain why
Define the following:a. Heavy keyb. Heavy non-keyc. Sandwich componentd. Optimum feed stagee. Minimum reflux ratio
In Figure 5-4, HNK and HK concentrations cross near the column bottom, and in Figure 5-5, LK and LNK concentrations do not cross near the top of the column. Explain when concentrations of HK and HNK
Explain Figure 5-5 in terms of the distillation of binary pairs.Figure 5-5 1.0 Toluene (LK) Xi .5- Cumene (HK) Benzene (LNK) R 2 4 6 8 10 12 14 16 18 C STAGE LOCATION
A distillation column is separating methane, ethane, propane, and butane. We pick methane and propane as the keys; thus, ethane is a sandwich component.a. Show the approximate composition profiles
We are distilling a mixture that is \(10.0 \mathrm{~mol} \%\) methanol, \(20.0 \mathrm{~mol} \%\) ethanol, \(30.0 \mathrm{~mol} \% \mathrm{n}\)-propanol, and \(40.0 \mathrm{~mol} \%
In the next to last paragraph of this chapter, the following sentence occurs, "Perhaps surprisingly, separations with an HNK or LNK and a sandwich component converge reasonably well." Explain why.
It is often suggested that when the corresponding \(\mathrm{NK}\) component is present, key components should be withdrawn as side streams at the location where their concentration maximum occurs. If
Develop a key relations chart for this chapter. Probably useful to include sketches.
In Figure 5-4, a 99.0\% recovery of benzene does not give a high benzene purity. What would you change to also achieve a high benzene purity in distillate?Figure 5-4 1.0 0.75 Toluene (HK) Xi 0.50
For parts 1 to 5 , determine whether the following multicomponent distillation problems can or cannot be solved with a stage-by-stage calculation, and if a stage-by-stage calculation can be used,
A distillation column with a partial condenser (PC) and a partial reboiler (PR) is separating a feed that is \(40 \mathrm{~mol} \%\) methanol and \(60 \mathrm{~mol} \%\) water. Feed flow rate is
Plant Trouble-Shooting. A distillation column is separating \(127.6 \mathrm{~kg} / \mathrm{min}\) of a feed at \(30^{\circ} \mathrm{C}\) and \(130 \mathrm{kPa}\) that is \(37.6 \mathrm{wt} \%
A distillation column at \(1.0 \mathrm{~atm}\) with a total condenser and a total reboiler is separating ethanol from water. Reflux is returned as a saturated liquid, and boilup is returned as a
\(1000 \mathrm{kmol} /\) day of a saturated liquid feed that is \(30 \mathrm{~mol} \%\) acetone and \(70 \mathrm{~mol} \%\) ethanol is fed at the optimum feed location to a column with a partial
A continuous, steady-state distillation column with a total condenser and a partial reboiler is separating \(100 \mathrm{kmol} / \mathrm{h}\) of a \(55 \mathrm{~mol} \%\) methanol, \(45 \mathrm{~mol}
We are separating ethanol and water. All percentages are mol\%. Column pressure is at \(1.0 \mathrm{~atm}\). VLE data are in Table 2-1. Find the q values and plot the feed lines for the following
Assume \(\mathrm{C}_{\mathrm{P}, \mathrm{L}}\) is not a function of \(\mathrm{T}\) or \(\mathrm{p}\). Assume \(\mathrm{CMO}\) is valid.a. A feed mixture of ethanol and water is \(40 \mathrm{~mol}
A stripping column with two feeds is separating acetone and ethanol at \(1 \mathrm{~atm}\). Feed \(\mathrm{F}_{1}\) is a saturated liquid and is fed into the top of column (no condenser). Flow rate
A distillation column is operating with subcooled reflux. The vapor streams have an enthalpy of \(\mathrm{H}_{1}=\mathrm{H}_{2}=17,500 \mathrm{Btu} / \mathrm{lbmol}\), while the saturated liquid
A distillation column operating at \(1.0 \mathrm{~atm}\) is separating a mixture of methanol and water. The feed is a saturated liquid. The column has a total condenser and a partial reboiler. The
A distillation column with a total condenser is separating a feed that is \(30 \mathrm{~mol} \%\) acetone from ethanol. Distillate \(\mathrm{x}_{\mathrm{D}}=0.90\), and bottoms
For Problem 4.D7 for separation of acetone from ethanol, with \(q=0.692\) determinea. The number of stages required at total reflux.b. The values of \((\mathrm{L} / \mathrm{V})_{\min }\) and
A distillation column with a partial reboiler and a partial condenser is separating two feeds containing mixtures of ethanol and water. Operation is at \(1.0 \mathrm{~atm}\) and CMO is valid. Feed A
A distillation column is separating phenol from p-cresol at \(1 \mathrm{~atm}\) pressure. Distillate is \(96 \mathrm{~mol} \%\) phenol. An external reflux ratio of \(\mathrm{L} / \mathrm{D}=4\) is
A distillation column is connected to another separation device. The fresh feed to the column is \(\mathrm{F}=1000.0 \mathrm{kmol} / \mathrm{h}\) of a saturated vapor that is \(20.0 \mathrm{~mol}
a. We have \(150 \mathrm{kmol} / \mathrm{h}\) of a saturated vapor feed at \(1.0 \mathrm{~atm}\) that is \(20 \mathrm{~mol} \%\) methanol and \(80 \mathrm{~mol} \%\) water. This feed is sent to a
A distillation column with open steam heating is separating a feed that is 80.0 \(\mathrm{mol} \%\) methanol and \(20.0 \mathrm{~mol} \%\) water in a steady-state operation. The column has 10 stages,
One of the old columns in your plant failed. You have been putting together a jury-rigged system to separate propane from n-butane. The column you have found is empty, so within reason you can put in
A distillation column with a partial condenser and a partial reboiler operating at \(1.0 \mathrm{~atm}\) is separating \(200 \mathrm{kmol} / \mathrm{h}\) of a feed that is \(60 \mathrm{~mol} \%\)
A mixture of acetone and ethanol is fed to an enriching column. The feed flow rate is \(100.0 \mathrm{~mol} / \mathrm{min}\). Feed is \(60.0 \mathrm{~mol} \%\) acetone and is a saturated vapor. A
A stripping column with an additional feed is separating two feeds containing acetone and ethanol. The column has a partial reboiler and no condenser. Feed 1 is \(70.0 \mathrm{~mol} \%\) acetone, has
A distillation column is separating acetone and ethanol. The column effectively has six equilibrium stages plus a partial reboiler. Feed is a two-phase feed that is \(40 \%\) liquid and \(75
A distillation column with a total condenser and a partial reboiler is separating ethanol and water at \(1 \mathrm{~kg} / \mathrm{cm}^{2}\) pressure. Feed is \(32 \mathrm{~mol} \%\) ethanol and is at
The following hybrid system shown for separating methanol and water is one way of coupling membrane separators with distillation. The gas permeation membrane separator is designed to produce
When water is the more volatile component, we do not need a condenser but can use direct cooling with boiling water. This situation was shown in Problem 3.D3. \(\mathrm{y}_{\mathrm{D}}=0.92,
We plan to distill \(1100 \mathrm{kmol} /\) hour of a saturated vapor stream that is \(16 \mathrm{~mol} \%\) ethanol and \(84 \mathrm{~mol} \%\) water. The column has another feed that is \(900
We are separating methanol and water. Calculate the internal reflux ratio inside the column, \(\mathrm{L}_{1} / \mathrm{V}_{2}\), for the following cases. The column is at \(101.3 \mathrm{kPa}\).
A distillation column with a total condenser uses a flash distillation system as the partial reboiler. The \(200 \mathrm{kmol} / \mathrm{h}\) of feed is \(55 \mathrm{~mol} \%\) methanol and \(45
A distillation column is separating methanol from water at a pressure of \(1 \mathrm{~atm}\). The column has a total condenser and a partial reboiler. In addition, a saturated vapor stream of pure
We are separating acetone (MVC) from ethanol in a distillation column that has a partial reboiler and a total condenser. Operation is at \(1.0 \mathrm{~atm}\). CMO can be assumed to be valid. The
A distillation column uses the optimum feed stage. A liquid side stream is withdrawn on the third stage below the total condenser at a rate of \(15.0 \mathrm{kmol} / \mathrm{h}\). Feed rate is
A distillation column is separating methanol from water. The column has a total condenser that subcools the reflux so that 1 mole of vapor is condensed in the column for each 3 moles of reflux.
\(150 \mathrm{~mol} / \mathrm{h}\) of a saturated liquid that is \(25 \mathrm{~mol} \%\) ethanol and \(75 \mathrm{~mol} \%\) water is fed to a distillation column with a total condenser and a partial
A distillation column with a total condenser (TC) and a partial reboiler (PR) is separating a feed that is \(45.0 \mathrm{~mol} \%\) methanol and \(55.0 \mathrm{~mol} \%\) water. Feed flow rate is
A continuous column flash system (Figure 4-24) is separating \(100 \mathrm{kmol} / \mathrm{h}\) of a saturated liquid feed that is \(45 \mathrm{~mol} \%\) methanol and \(55 \mathrm{~mol} \%\) water
A continuous column flash system (Figure 4-24) is separating \(100 \mathrm{kmol} / \mathrm{h}\) of a saturated liquid feed that is \(45 \mathrm{~mol} \%\) methanol and \(55 \mathrm{~mol} \%\) water
Derive Eq. (4-35) for the feed line in terms of \(q\) by doing a mass balance around the feed stage using the balance envelope shown in Figure 4-9, and then substituting the result into Eq.
Derive Eq. (4-34) for the feed line by starting with either Eq. (4-30) or Eq. (4-35).Equation (4-34)Equation (4-30)Equation (4-35) 1-f 1 y=- f X+-Z x+ f
Derive Eqs. (4-51) and (4-52) for side streams.Equation (4-51)Equation (4-52) L' DXD+SLXS y=- x+. V'
For a binary distillation column with two feeds,a. Show that the intersection of the top and bottom operating lines occurs at the feed line for fictitious feed \(F_{T}\) where \(F_{T}=F_{1}+F_{2},
Derive the operating equations for the two middle operating sections when an intermediate reboiler is used (see Figures 4-22A and 4-22B). Show that the operating line with slope of
Show that the total amount of cooling needed is the same for a column with one total condenser \(\left(Q_{c}\right)\) as for a column with a total condenser and an intermediate total condenser
For the stripping column shown in Figures 4-23A and 4-23C, show formally that the intersection of the bottom operating line and the feed line is at \(y_{D}\). In other words, solve for the
Derive Eqs. (4-56a) and (4-56b).Equation 4-56a and 4-56b (H) 1 saturated liquid feed min z(-1)' (), 1 min x*(-1)" , saturated vapor feed
For Example 4-3 prove that:Example 4-3A distillation column with a total condenser and a partial reboiler is separating an ethanol-water mixture. Feed is 20 mol% ethanol, feed rate is 1000 kmol/h,
Derive the operating equation for the middle section of Figure 4-17. Show that the equations are equivalent whether the mass balance envelope is drawn around the top of the column or the bottom of
Sketch the McCabe-Thiele diagram if the Murphree liquid efficiency is constant and \(\mathrm{E}_{\mathrm{ML}}=0.75\)
For a simple, single-feed distillation column, derive an equation for calculation of \((\overline{\mathrm{V}} / \mathrm{B})_{\min }\) from \((\overline{\mathrm{L}} / \overline{\mathrm{V}})_{\max }\)
\(100 \mathrm{kmol} / \mathrm{h}\) of a \(60 \mathrm{~mol} \%\) methanol and \(40 \mathrm{~mol} \%\) water feed at \(40^{\circ} \mathrm{C}\) is distilled in a column that does not have a reboiler but
The system shown in Figure 3-9 is the stripping section of a distillation column with open steam heating. There is no condenser and no reboiler. This type of system is called a "beer still" in
A mixture of water and ammonia is distilled in an ordinary distillation system (Figure 3-8) at a pressure of \(6 \mathrm{~kg} / \mathrm{cm}^{2}\). The feed is \(30 \mathrm{wt} \%\) ammonia at
In the figure shown below, what streams are represented by point A? By point B? How would you determine the temperature of stage 2? How about the temperature in the reboiler? If feed composition is
For the McCabe-Thiele diagram below, answer the following questions:a. (1) What is the actual feed tray?(2) What is the mole fraction MVC in the feed?(3) What is the vapor composition on the feed
For which of the following binary pairs is constant mass overflow a reasonable assumption for distillation calculations: n-butane and n-pentane, n-butane and n-hexane, n-butane and n-heptane,
Drawing the McCabe-Thiele graph as yMVC vs. xMVC is traditional but not necessary. Repeat Example 4-3, but plot yw vs. xw for the McCabe-Thiele diagram. Note the differences in the diagram. Do you
A5. For distillation when CMO is valid, show the flow profiles schematically (plot Lj and Vj vs. stage location) for:Subcooled liquid feedTwo-phase feedSuperheated vapor feed
A distillation column is operating under a vacuum. The column has 18 stages with the feed at stage 9, a partial reboiler, and a partial condenser. The pressure drop is 5.0 mm Hg in the condenser, 4.0
Develop a key relations chart for binary McCabe-Thiele distillation. That is, on one sheet of paper summarize everything you need to know about binary distillation. You will probably want to include
What happens if we try to step off stages from the top down and EMV is given? Determine how to do this calculation.
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.
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