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chemical engineering
Questions and Answers of
Chemical Engineering
Derive Eq. (8-14) for the two-column, binary heterogeneous azeotrope system.Equation (8-14) Ybut strip but in w -[(strip strip-1]Xbut in w,bot.strip
Separate a mixture of pyridine \(\left(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{~N}\right)\) and water, which form a homogeneous azeotrope, by using extractive distillation using bisphenol-A
Develop plots for vapor pressure of water and n-decane. For water, two plots are useful in the range of values in Table 8-1. A plot of VP versus T is convenient for rapid estimates but is not as
We wish to separate two organics that form a homogeneous azeotrope. This will be done in a two-column azeotropic system with water as the solvent. Sketch possible system arrangements to do this.
Generation of distillation curves for systems with constant relative volatility is fairly straightforward and an excellent learning experience. Generate distillation curves in Figure 8-10 for a
Set up a two-stage countercurrent continuous steam distillation as shown in Figure 8-7B, solve Example 8-2 for a two-stage countercurrent process, and determine the energy savings compared to a
The following statement is made after Eq. (8-21): "If \(\mathrm{D}_{2}\) is large, Eq. (8\(21 \mathrm{~A}\) ) indicates that \(\mathrm{D}_{1}\) must also be large." Why does \(\mathrm{D}_{2}\) and
Derive an equation for \(\alpha_{\text {org-w in w }}\) similar to Eq. (8-8). Compare the predicted equilibrium in water with the butanol-water equilibrium data given in Problem 8.D3. Comment on the
Your company plans to produce pure acetone from a mixture of acetone, methyl ethyl ketone, and methyl isobutyl ketone in an ordinary single-feed distillation column with a total condenser and a
We are conducting a reaction/separation in a distillation column for the reversible reaction \(\mathrm{A}+\mathrm{B}=\mathrm{C}+\mathrm{D}\) where \(\mathrm{A}\) and \(\mathrm{B}\) are reactants and
Nitromethane and water are separated in a stripping column that has a partial reboiler. There is no condenser and no liquid-liquid settler. The saturated liquid feed is \(8.0 \mathrm{~mol} \%\)
VLE data for water and n-butanol at \(1.0 \mathrm{~atm}\) are given in Table 8-5. The fresh feed is \(100.0 \mathrm{kmol} / \mathrm{h}\) of saturated liquid that is \(30.0 \mathrm{~mol} \%\) water.
Why is a cooler required in Figure 8-14? How can this energy be reused in the process?Figure 8-14 A Product Feed Solvent Recycle Cooler B B Make up Solvent 2 B Product
For a binary heterogeneous azeotrope separation, feed can be introduced into the liquid-liquid separator. In this case two stripping columns are used.a. Sketch the column arrangement.b. Draw the
We will use a system similar to Figure 8-5A, except both columns have direct reflux from their condensers in addition to reflux from a decanter. Distill a feed that is \(17.0 \mathrm{~mol} \%\) water
VLE data for water and n-butanol are given in Table 8-5. We have flash distillation systems separating \(100.0 \mathrm{kmol} / \mathrm{h}\) of two different water and \(\mathrm{n}-\) butanol
Produce pure water from seawater by boiling it with n-decane vapor (see figure). This is sort of the reverse of steam distillation. Seawater is roughly \(3.5 \mathrm{wt} \%\) salt, which can be
Explain the purpose of the liquid-liquid settler in Figures 8-3A, 8-5A, and 8-17.Figure 8-3AFigure 8-5AFigure 8-17 V in Feed V L Dry Organic Organic Phase A Water Phase
The following statement appears after Eq. (8-27): "Equation (8-27) also proves that the points representing bottoms, distillate, and the feed all lie on a straight line. . ." Prove that this
The system water-acetonitrile \(\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{~N}\right)\) forms an azeotrope. This system can be separated using a two-pressure distillation system. Both columns have
The VLE data for formic acid \(\left(\mathrm{CH}_{2} \mathrm{O}_{2}\right)\)-water are presented in Table 8-6.a. Determine the value of \(\alpha\) at each data point from
In this chapter, some of the operating lines pass through the equilibrium curve and are used on the outside of the equilibrium curve. Explain how this is possible.
Sketch the flowsheet for pressure-swing distillation of a binary system with a maximum boiling azeotrope. After you have finished, you can check your flowsheet with the simplified flowsheet
\(200.0 \mathrm{kmol} / \mathrm{h}\) of saturated vapor feed, \(80.0 \mathrm{~mol} \%\) water and \(20.0 \mathrm{~mol} \%\) n-butanol, is condensed and sent to a decanter. The water layer is the
a. Aspen Plus automatically generates residue curves for ternary mixtures. Generate residue curve at \(5.0 \mathrm{~atm}\) for a mixture of propane, \(n\)-butane, and n-pentane. Report the VLE
Why are makeup solvent additions shown in Figures 8-14 and 8-18?Figure 8-14.Figure 8-18 A Product Feed Solvent Recycle Cooler 2 B B Make up Solvent B Product
What is the lever-arm rule for streams D, M, and B in Figure 8-15?Figure 8-15 Ethanol (351.40 K) 1.0 D 0.8- 0.6 0.4- M 0.2- S FL 0.0+ B 0.0 0.2 0.4 0.6 0.8 Ethylene glycol (470.40 K) 1.0 Water
To understand how two-pressure distillation works, in Lab 7 plot \(\mathrm{y}-\mathrm{x}\) diagrams (from Aspen Plus Analysis) for MEK versus water (plot MEK mole fractions) at \(1.0 \mathrm{~atm}\)
A water and n-butanol mixture is separated in a stripping column with a partial reboiler. The feed \((\mathrm{F}=100 \mathrm{kmol} / \mathrm{h}, \mathrm{z}=0.65\) [mole fraction water], saturated
Explain why extra stages do not increase separation in steam distillation.
Do the following distillation problem after Part A or Part B in Lab 6 is finished. We are separating \(100.0 \mathrm{kmol} / \mathrm{h}\) of a feed containing propane, \(\mathrm{n}-\) butane, and
Recover \(90.0 \%\) of a gasoline component, \(\mathrm{n}\)-nonane \(\left(\mathrm{C}_{9} \mathrm{H}_{20}\right)\), in the distillate from a nonvolatile mixture of oils, grease, and solids with a
\(15,000 \mathrm{~kg} / \mathrm{h}\) of saturated liquid diisopropyl ether \(\left(\mathrm{C}_{6} \mathrm{H}_{14} \mathrm{O}\right)\) that contains \(0.4 \mathrm{wt} \%\) water is fed to the \(2
When will extra stages be helpful in steam distillation?
a. \(200.0 \mathrm{kmol} / \mathrm{h}\) of an aqueous liquid feed saturated with \(\mathrm{n}\)-butanol is fed to a kettle reboiler at \(1.0 \mathrm{~atm}\). Vapor at a flow rate
When doing distillation with reaction, the column should be designed both as a reactor and as a distillation column. How might these columns differ from normal distillation columns?
Reactions are usually not desirable in distillation columns. If there is a reaction occurring, what can be done to minimize it?
A single-stage steam distillation system is recovering n-decane from a small amount of nonvolatile organics. Pressure is \(800.0 \mathrm{~mm} \mathrm{Hg}\). The still is operated with liquid water
A single-stage, continuous steam distillation of 1-octanol at \(760.0 \mathrm{~mm} \mathrm{Hg}\) with liquid water present distills \(1.0 \mathrm{kmol} / \mathrm{h}\) of a feed of \(90.0
If a liquid mixture of \(n\)-butanol and water that is \(20.0 \mathrm{~mol} \% \mathrm{n}\)-butanol is partially vaporized, what is the vapor composition of the first bubble of vapor? Repeat for
Resolve Example \(8-1\) with \(\mathrm{y}_{\mathrm{W}, \mathrm{az}}=0.298\) and (\alpha_{\mathrm{w}-\text { benz_in_benz }}=27.88\).Data From Example 8-1A benzene stream contains 1.0 mol% water.
If a liquid mixture of n-butanol and water that is \(20 \mathrm{~mol} \% \mathrm{n}\)-butanol is totally vaporized, what is the average vapor composition?
Water is separated from n-butanol in a system with two feeds. Feed \(1\left(\mathrm{~F}_{1}\right.\) \(=100.0 \mathrm{kmol} / \mathrm{h}, \mathrm{z}_{1}=0.84\) [mole fraction water], saturated vapor)
Extractive distillation (Figure 8-14) is used to separate ethanol from water with ethylene glycol as solvent. The A product will be ethanol and the B product water. Stages are counted with condenser
A two-pressure system (similar to Figure 8-8) separates a feed that is 15.0 \(\mathrm{mol} \%\) benzene and \(85.0 \mathrm{~mol} \%\) ethanol. The saturated liquid feed rate is \(100.0 \mathrm{kmol}
Continuous steam distillation is used to recover 1 -octanol from \(100.0 \mathrm{~kg} / \mathrm{h}\) of feed that is \(15.0 \mathrm{wt} \% 1\)-octanol, and the remainder consists of nonvolatile
When pressure-swing distillation works, it is often the method of choice for separating binary homogeneous azeotropes. Explain why.
Nitromethane and water are separated in a rectifying column system with a total condenser and a liquid-liquid settler similar to Figure 8-3A, except the column is a rectifying column. The saturated
Fill in the rows for \(\mathrm{x}_{\mathrm{L}}=0.25\) and 0.4 in Table 8-3. TABLE 8-3. Results for two-stage cross-flow steam distillation system shown in Figure 8-7A XL L kmol/h n org 1 nw1 norg2
An extractive distillation system is separating ethanol from water using ethylene glycol as solvent. The makeup solvent is pure ethylene glycol. In Figure 8-14, ethanol is A product, and water is B
We are separating nitromethane and water in a distillation system consisting of two columns, two total condensers, two partial reboilers, and a liquid-liquid separator. CMO is valid, and \(p=1.0
The azeotropic distillation shown in Figure 8-18 uses n-hexane as an entrainer to separate a feed that is \(81.0 \mathrm{wt} \%\) ethanol and \(19.0 \mathrm{wt} \%\) water into ethanol and water. The
This problem explores the azeotropic distillation column shown in Figure 8-18 with mole fraction profiles shown in Figure 8-19. The feed to the distillation column in Figure 8 - 18 is a saturated
Water containing \(1.6 \mathrm{~mol} \% \mathrm{n}\)-butanol is sent at a rate of \(75.0 \mathrm{kmol} / \mathrm{h}\) to a two-column distillation system similar to Figure 8-5A. The feed is a
\(100.0 \mathrm{kmol} / \mathrm{h}\) of a saturated vapor feed that is \(25.0 \mathrm{~mol} \%\) nitromethane (NM) and \(75.0 \mathrm{~mol} \%\) water is separated in a system with two distillation
We are separating n-butanol and water in a single distillation column with two feeds and a decanter. Feed 1 is \(36.0 \mathrm{~mol} \%\) water, the flow rate is \(\mathrm{F}_{1}=\) \(50.0
Continuous steam distillation is used to recover benzene from \(100.0 \mathrm{~kg} / \mathrm{h}\) of a mixture that is \(20.0 \mathrm{wt} \%\) benzene, and the remainder consists of nonvolatile
Derive a form of Eq. (7-13) for \(\left(\mathrm{FR}_{\mathrm{NK}, \text { bot }}\right)\) in terms of \(\left(\mathrm{FR}_{\mathrm{LK}, \text { dist }}\right)\).Equation 7-13 (NK-HK) Nmin FRNK.dist
Explore the sensitivity of Eq. (7-35) in Example 7-3 at \(X=0.455\) by determining \(\mathrm{Y}\) and \(\mathrm{N}\) as the value of the constant 0.99357 changes. Try constant values of
If the pinch point occurs at the feed point, mass balances can be used to find the minimum flows. Derive these equations. A pinch point at the feed can occur but is unusual in multicomponent
The choice of developing the Underwood equations in terms of \(\mathrm{V}_{\text {min }}\) instead of solving for \(\mathrm{L}_{\min }\) is arbitrary. Rederive the Underwood equations solving for
For binary systems, Eq. (7-28) simplifies to a linear equation for both saturated liquid and saturated vapor feeds. Prove this statement.Equation (7-28) AV feed Vmin - Vmin = i-ref (FZ;) = i=1 i-ref-
If NKs do not distribute, you solve the Underwood Eq. (7-28) for \(\varphi\), which satisfies \(\alpha_{\mathrm{LK}-\text { ref }}>\varphi>\alpha_{\mathrm{HK}-\text { ref. }}\). However, if a
A column flash distillation (Figure 4-24) with three stages is processing a feed with \(10.0 \mathrm{~mol} \%\) methane, \(12.0 \mathrm{~mol} \%\) n-butane, \(33.0 \mathrm{~mol} \% \mathrm{n}\)
The Fenske equation:a. Is valid only for binary systems.b. Was derived for minimum reflux.c. Requires CMO.d. Requires constant \(\mathrm{K}\) values.e. All of the above.f. None of the above.
If you want to use an average relative volatility, how do you calculate it for the Underwood equation?
Develop your key relations chart for this chapter.
In multicomponent distillation the Fenske equation can be used to:a. Estimate the fractional recoveries of the NKs at total reflux.b. Calculate the number of equilibrium contacts at minimum reflux.c.
With the ready availability of process simulators, why do chemical engineers still use the Fenske-Underwood-Gilliland (FUG) method?
Suppose you are doing a ternary distillation where component B, the \(\mathrm{LK}\), has a \(98.3 \%\) recovery in the distillate, and component C, the \(\mathrm{HK}\), has a \(99.8 \%\) recovery in
In Davis's fit for the Gilliland correlation, what are the values of \(\mathrm{N}\) and \(\mathrm{L} / \mathrm{D}\) when \(\mathrm{X} \rightarrow 0\) and \(\mathrm{Y} \rightarrow 1\) ? What are the
An engineer claims that fit A of the Gilliland correlation is better than fit B because when they compared the predictions of both fits to detailed simulator results for a separation of interest, fit
Use a process simulator to completely solve Example 6-1. Do not assume CMO. Compare temperature and mole fractions on each stage to the values obtained in Example 6-1 after one trial.Example 6-1A
An ordinary, single-feed distillation column is separating propane, nbutane, isobutane, 2-methyl-butane, and n-hexane. There are 37 trays in the column, and feed location in column is tray 18 below
An ordinary, single-feed distillation column is separating n-butane, npentane, benzene, and toluene. There are 17 trays in column, and feed location in column is tray 9 below condenser (input feed as
The feed mole fractions are methanol \(=0.2\), ethanol \(=0.5\), and \(1-\) propanol \(=0.3\). The feed is at \(75^{\circ} \mathrm{C}\), the flow rate is \(1000.0 \mathrm{kmol} / \mathrm{h}\), and
An ordinary, single-feed distillation column is separating methanol, ethanol, 1-propanol, and n-butanol. There are 27 trays in column, and feed location in column is tray 13 below condenser (input as
At the end of Example 5-2, we noted that process simulators provide an easy method to do bubble- and dew-point calculations. One approach is to draw a flash distillation system with Flash 2 or a
Suppose a liquid sidestream of composition \(\mathrm{x}_{\mathrm{i}, \mathrm{s}}=\mathrm{x}_{\mathrm{i}, \mathrm{j}}\) and flow rate \(\mathrm{S}_{\mathrm{j}}\) is removed from stage \(\mathrm{j}\)
Derive the mass balance expression for the matrix approach if there is a partial condenser instead of a total condenser. Replace Eqs. (6-7) to \((6-9)\).Equation (6-7) to (6-9) Lx + DXD-Vy = F Bl1+
Derive the energy balance expression for the matrix approach if there is a partial condenser instead of a total condenser. Replace Eqs. (6-23), \((6-24)\), and \((6-29 a)\).Equation (6-23) , (6-24),
Suppose there is a total reboiler instead of a partial reboiler. Eqs. (6-10) to (6-12) will be changed and the neat logic of the tridiagonal matrix does not work as well.Equation (6-10) to (6-12)a.
Derive the mass balance equations and the \(\mathrm{A}, \mathrm{B}\), and \(\mathrm{C}\) terms for Eq. (6-13) for a rectifying column with a total condenser.Equation (6-13) B C 0 A2 B2 C 0 0 0. 0 0
Derive the mass balance equations and the A, B, and C terms for Eq. (6-13) for a stripping column with a partial reboiler.Equation (6-13) B C 0 A2 B2 C 0 0 0. 0 0 A3 B3 B3 C3 0 0 0 0 000 00 0 653
For the first trial of Example 6-1, determine the component matrix for n-pentane and then use the Thomas algorithm to find the n-pentane liquid flow rates leaving each stage. Compare your n-pentane
A distillation column operating at \(5.0 \mathrm{~atm}\) has a total condenser and a partial reboiler. The saturated liquid feed flow rate is \(1000.0 \mathrm{kmol} / \mathrm{h}\). Feed is \(8.0
Do the matrix for \(n\)-butane for Problem 6.D2.Problem 6.D2A distillation column operating at \(5.0 \mathrm{~atm}\) has a total condenser and a partial reboiler. The saturated liquid feed flow rate
A distillation column is separating \(100.0 \mathrm{kmol} / \mathrm{h}\) of a saturated liquid feed that is \(30.0 \mathrm{~mol} \%\) methanol, \(25.0 \mathrm{~mol} \%\) ethanol, \(35.0 \mathrm{~mol}
Repeat Problem 6.D4 except do the matrix and solution for the first trial for ethanol.Problem 6.D4A distillation column is separating \(100.0 \mathrm{kmol} / \mathrm{h}\) of a saturated liquid feed
In the matrix approach, we assumed \(\mathrm{K}=\mathrm{K}(\mathrm{T}\), p). How would the flowchart in Figure 6-1 change if \(\mathrm{K}=\mathrm{K}\left(\mathrm{T}, \mathrm{p},
The method described in this chapter is a simulation method because the number of stages and the feed and withdrawal locations must all be specified. How do you determine the optimum feed stage?
Develop your key relations chart for this chapter.
In a sequential convergence multicomponent simulation program for distillation, the loops are nested. The outermost loop is mole fractions, next is flow rates, and the innermost loop is
You run a simulator twice with exactly the same input, but the output of the two runs is slightly different. For example, a water mole fraction is reported as \(0.98014 \mathrm{E}-02\) and as
Because a new liquid flow rate is calculated in Eq. (6-17) as \(\sum_{\mathrm{i}=1}^{\mathrm{C}} \ell_{\mathrm{i}, \mathrm{j}}\), why do we not set \(\mathrm{L}_{\mathrm{j}, \text { new }}\) equal to
The enthalpies in Eqs. (6-30a) and (6-30b) assume ideal mixtures. How do the equations change if the mixtures are not ideal? Will the deviation from ideal mixture behavior be larger for liquid
What is the most important or basic assumption made by all the matrix approaches in this chapter? What do we do if this assumption is not valid?
Assume relative volatilities are constant.a. Show that mole fractions for a bubble-point calculation are given by\[\begin{equation*}\mathrm{y}_{\mathrm{i}, \mathrm{j}}=\left(\mathrm{x}_{\mathrm{i},
Prove that for ideal systems (constant relative volatility) with no interaction between an added nonvolatile solute and the volatile components, there is no effect of adding the nonvolatile solute on
Prove that for ideal systems (constant relative volatility) with no interaction between an added noncondensable, nonsoluble gas and the condensable components, there is no effect of adding the
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