The Engineering of Chemical Reactions

Lanny D. Schmidt

Chapter 11 polymerizarion reactions & reactors - all with Video Answers

Educators

Chapter Questions

Problem 1

a) Why do the ionic end groups in ideal addition polymerization inhibit termination?
(b) Why does catalytic polymerization have fewer termination processes than free-radical polymerization?
(c) How does one intentionally introduce crosslinking in linear polymers?

Ian Kaigh

Numerade Educator

Problem 2

Set up and solve the algebraic equations for the concentrations of all species in ideal addition polymerization in a CSTR.

Check back soon!

Problem 3

Set up the algebraic equations to be solved to find all species concentrations in free-radical polymerization in a CSTR, analogous to those in a PFTR developed in the text.

Check back soon!

Problem 4

Set up and solve the mass-balance equations for condensation polymerization in the CSTR assuming all $k \mathrm{ks}$ equal.

Check back soon!

09:53

Problem 5

Sketch the steps in production of PET from ethane and dimethyl cyclohexanes.

Ian Kaigh

Numerade Educator

04:24

Problem 6

The polymers and plastics industries are basically concerned with replacing natural flexible and hard one-dimensional and two-dimensional materials.
(a) What were the major soft and rigid containers for liquids before synthetic materials?
(b) What is leather and how is it prepared?
(c) What is glass and how is it prepared?
(d) What is clay and how is it prepared?
(e) What is concrete and how is it prepared?
(f) What are the major natural fibers?
(g) What are the advantages and disadvantages of synthetic polymers as replacements for each of these natural polymers? Note that you probably prefer to wear natural fiber clothing but that cotton tents and silk stockings have totally been replaced by Nylon.

Ibrahim Abdullahi

Numerade Educator

Problem 7

Suppose we have found a catalyst to polymerize caprolactam, which operates with the monomer in aqueous solution. Starting with 1 molar caprolactam in a batch reactor experiment, we obtain $10 \%$ polymerization in 20 min .
(a) What time is required to obtain $90 \%$ polymerization in a CSTR starting with 4 molar caprolactam?
(b) How large must the reactor be to obtain $1 \mathrm{~kg} / \mathrm{h}$ of pure Nylon 6 ?
(c) The polymerization reaction is exothermic by $25 \mathrm{kcal} / \mathrm{mole}$ of monomer reacted. What must be the rate of cooling?

Check back soon!

01:15

Problem 8

Polystyrene is made by heating pure liquid styrene with a suitable catalyst.
(a) If $1 \%$ of the styrene has polymerized in a 100 liter CSTR with a residence time of 2 min , how much will polymerize in a 100 liter PFTR at this residence time?
(b) The heat of this reaction is $-21 \mathrm{kcal} / \mathrm{mole}$. What are the cooling rates of these reactors?

Andreas Papavassiliou

Numerade Educator

04:25

Problem 9

Write out the complete reactions for polyurethane production starting with toluene, natural gas, air, water, and salt, as sketched in Figure 11-8. Use 1,4-butane diol for the glycol starting from butane. Why is this process preferable for reaction injection molding of automobile parts compared to Nylon or PET?

Kevin Chimex

Numerade Educator

Problem 10

Write out the complete reactions for production of PMMA and phenol-formaldehyde, as sketched in Figure 1 1-1 1 . What are the advantages and disadvantages of an integrated chemical plant compared to separate plants to prepare individual chemicals and polymers?

Check back soon!

Problem 11

(a) For the polymerization reaction $A_1 \rightarrow A_2 \rightarrow A 3 \rightarrow A_4 \rightarrow \ldots$ plot $A_j$ versus $k \tau$ in PFTR for $\mathrm{j}<25$.
(b) Plot (by hand is OK$) C_j(\tau)$ versus $k \tau$ for $k \tau=2,5,10,15,20$.
(c) Plot $j C_j$ (t) versus $k \tau$. Why is this a more useful description of the polymer distribution?
(d) Repeat these calculation for a CSTR.
(e) Compare the distribution for PFTR and CSTR for given $k \tau$. Why do they have different distributions?

Check back soon!

Problem 12

Polyurethanes are used for most plastic parts in automobiles such as bumpers and nonmetal body panels. They are made from toluene diisocyanate and ethylene glycol. We are designing a chemical plant that makes TDIC and need to evaluate the safety of the units. Phosgene is made by reacting CO and $\mathrm{Cl}_2$ in a 20 atm reactor with a residence time of 10 sec . Toluene is nitrated by reacting with concentrated nitric acid solution at $140^{\circ} \mathrm{C}$ with a 1 min residence time, and the aqueous and organic phases are separated. The organic phase is distilled to separate dinitrotoluene. The dinitrotoluene liquid is hydrogenated with $\mathrm{H}_2$ at 5 atm at $120^{\circ} \mathrm{C}$ with a liquid residence time of 20 sec . The product is reacted with phosgene in a vapor-phase reaction at $150^{\circ} \mathrm{C}$, and the TDIC is distilled. The TDIC is finally reacted with ethylene glycol in a reaction injection molding process to form the bumper.
(a) This process consists of 5 reactors. Write down the reactions that occur in each.
(b) Sketch the flow sheet of the 5 reactors and 3 separation units with feeds of $\mathrm{CO}, \mathrm{Cl}_2$, toluene, Ha , and ethylene glycol.
(c) The process is to produce 10 tons $/ \mathrm{h}$. Assume that each reactor produces $100 \%$ conversion and that the nitration process produces equal amounts of the three nitrates. What are the sizes of each of these reactors? Approximately how much chemical do they contain?
(d) These 8 units are all connected by valves that will close quickly to isolate all units in the event of an upset of any kind. Describe the potential safety hazards of each unit and the possible things that might go wrong. Include runaway reaction and dangers from venting including chemical toxicity, fire, and explosion. Write $\sim 1 / 4$ page of text on each.
(e) Order the units in terms of decreasing bazard. Which units do you request not to be assigned to?

Check back soon!

06:15

Problem 13

In Fisher Tropsch synthesis of higher hydrocarbons from natural gas, it is desired to produce products in the boiling range for diesel and gasoline rather than lighter alkanes. If the products follow the Schultz Flory distribution, what weight fractions are in the undesired $\mathrm{C}_1-\mathrm{C}_4$ range if $\alpha=0.9,0.95$, and 0.99 ?

Chareen Guzman

Numerade Educator

Problem 14

In Fisher Tropsch synthesis from CO and $\mathrm{H}_2$, different catalysts produce different types of product molecules. Referring to the figure of propagation in the FT process, sketch the termination steps that will lead to (a) alkanes, (b) a-olefins, and (c) alcohols.

Check back soon!

09:33

Problem 15

In contrast to the Fisher Tropsch synthesis of higher alkanes from CO and $\mathrm{H}_2$, Ni catalysts produce primarily methane, and $\mathrm{Cu} / \mathrm{ZnO}$ catalysts produce mainly methanol. Sketch the mechanistic steps that favor these products rather than polymerization?

Ian Kaigh

Numerade Educator

01:01

Problem 16

(a) "Permanent press" clothing is made from a blend of nylon or polyester with wool or cotton. Explain why blending synthetic and natural polymers can accomplish this property compared to the pure synthetic fabrics.
(b) Wool and cotton shrink when washed. Why do synthetic polymers not shrink?

Narayan Hari

Numerade Educator

05:12

Problem 17

Polyethylene terephthalate is unsuitable for carpets because it crystallizes slowly and the fibers therefore break with time and wear. However, if EG is replaced by 1,3-propanediol, the fibers do not erystallize and wear resistance is greatly improved. The 1,2 -diol has properties similar to EG. There are several routes to prepare this diol with reasonable selectivity from propane.
(a) Acrolein can be hydrated and reduced, but this produces a mixture of 1,2-and 1,3-diols. Sketch these reactions.
(b) A biological route uses an enzyme to convert glucose to glycerol, and another enzyme "eats" the middle OH to form the nearly pure 1,3-diol. The rate of this process is low. Sketch these reactions.
(c) In a new commercial process 1,3-propanediol is made by reacting ethylene oxide with CO , followed by hydration and reduction. Sketch the flowsheet of the reactions to prepare 1,3 -propanediol starting from propane, air, water, and methane.

Zubair Abdulla

Numerade Educator

03:14

Problem 18

1,4-butanediol is simple to prepare, but its melting point is too high to form polyester fibers, However, this diol is widely used in fibers formed from the polyurethane for clothing fibers such as Lycra and Spandex.
(a) Sketch the polymerization reaction.
(b) Sketch the reaction steps to prepare this diol from butane.
(c) Sketch the flowsheet of the reaction steps that could be used to prepare this polymer starting from butane, toluene, nitric acid, air, and water.

Nicholas Sacco

Numerade Educator

Problem 19

1,4-butanediol can also be prepared by reacting acetylene with formaldehyde, and acetylene can be prepared by partial oxidation of methane. Sketch the reactions by which 1,4-butanediol can be prepared using only methane, air, water, and hydrogen.

Check back soon!

05:16

Problem 20

Polycarbonate is a very hard and light plastic used for protection devices such as football helmets. It is made by reacting bisphenol A with phosgene in the reactions shown in Figure 1111 .
(a) Sketch the flowsheet of a polycarbonate process starting with propane, cyclohexane and methane.
(b) Why might it be economical to produce PMMA along with polycarbonate? Sketch this integrated plant.

Nicholas Sacco

Numerade Educator

Problem 21

Consider addition polymerization in a PFTR,

$$
\begin{aligned}
A+M & \rightarrow A M \\
A M+M & \rightarrow A M_2 \\
A M_j+M & \rightarrow A M_{j+1}, \quad r_{\mathrm{p}}=k_{\mathrm{p}}[M]\left[A M_j\right] \\
& \vdots
\end{aligned}
$$

with $[M]_0$ constant at 1.0 moles/liter, $[A], 0.01$ moles/liter, and $k_{\mathrm{p}}$ identical for all j .
(a) Plot $\left[A M_j\right]$ and $j\left[A M_j\right]$ versus $k_p \tau$ for $j<30$.
(b) From these results plot the molar and weight distributions versus $j$ at $k_{\mathrm{p}} \tau=1,2,5,10$, and 20 .

Check back soon!

Problem 22

Consider addition polymerization in a CSTR,

$$
\begin{aligned}
A+M & \rightarrow A M \\
A M+M & \rightarrow A M_2 \\
A M_j+M & \rightarrow A M_{j+1}, \quad r_p=k_p[M]\left[A M_j\right]
\end{aligned}
$$

with $[M]_{\mathrm{o}}$ constant at 1.0 moles $/$ liter, $\left./ A\right],=0.01$ moles/liter, and $k_{\mathrm{p}}$ identical for all j .
(a) Plot $\left[A M_j\right]$ and $j\left[A M_j\right]$ versus $k_{\mathrm{p}} \tau$ for $j<30$.
(b) From these results plot the molar and weight distributions versus j at $k_p \tau=1,2,5,10$, and 20.

Check back soon!

Problem 23

Consider addition polymerization,

$$
\begin{aligned}
A+M & \rightarrow A M \\
A M+M & \rightarrow A M_2 \\
& \vdots \\
A M_j+M & \rightarrow A M_{j+1}, \quad r_{\mathrm{p}}=k_{\mathrm{p}}[M]\left[A M_j\right]
\end{aligned}
$$

with $[M]_0$ constant at 1.0 moles/liter, $[A]_0=0.01$ moles/liter, and $k_{\mathrm{p}}$ identical for all j . Add a termination reaction

$$
A M_j \rightarrow P_j, \quad r_{\mathrm{t}}=k_{\mathrm{t}}\left[A M_j\right]
$$

where $P_j$ is a dead or unreactive polymer. Plot $\left(\left[A M_j\right]+\left[P_j\right]\right)$ and $j\left(\left[A M_j\right]+\left[P_j\right]\right)$ versus $k_{\mathrm{r}}$ for $\mathrm{j}<25$ for $k_{\mathrm{t}} / k_{\mathrm{p}}=0,0.1,0.2,0.5$, and 1 .
(d) From these results plot the molar and weight distributions of $\left[A M_j\right]+\left[P_j\right]$ for $k_p \tau=2,5$, 10 , and 20 .

Check back soon!

05:07

Problem 24

Consider the reversible condensation polymerization reaction of a hydroxyacid A to form a polyester polymer,

$$
A_j+A_{j^{\prime}} \rightleftarrows A_{j+j^{\prime}}+\mathrm{H}_2 \mathrm{O}
$$

(a) If the equilibrium constant for this reaction is 100 , what is the average polymer size at equilibrium if all species remain in a single-phase solution?
(b) In these processes water is usually removed from the solution to obtain a higher degree of polymerization. If the initial monomer concentration is 5 moles/liter, what $\mathrm{H}_2 \mathrm{O}$ concentrations will give average polymer lengths that are 2, 10, and 100 times that calculated in part (a)?

Ameer Said

Numerade Educator

01:15

Problem 25

Consider the condensation polymerization of a bifunctional monomer $A$ in a CSTR with all rate coefficients $k$ equal.
(a) Write out the mass-balance equations for $\left[A_j\right]$.
(b) Find an expression for $\left[A_j\right](\tau)$ for the $j$ th species in terms of $[A l]$..
(e) Plot $\left[A_j\right]$ and $j\left[A_j\right]$ versus $k \tau$ for $j<25$.
(d) In a PFTR $\left[A_j\right]$ is given by the expression

$$
\left[A_j\right](\tau)=[A]_0\left(\frac{1}{1+k \tau\left[A_1\right]_0}\right)^2\left(\frac{k r\left[A_1\right]_0}{1+k r\left[A_3\right]}\right)^{j-1}
$$

Plot this $\left[A_j\right](\tau)$ and $j\left[A_j\right](\tau)$ versus $k \tau$ for $j<25$.
(c) Plot molar and weight distributions for CSTR and PFTR for $k \tau\left[A_1\right]_0=0.5,1,2$, and 4.

Andreas Papavassiliou

Numerade Educator

Problem 26

Consider the reversible condensation polymerization reaction of an amino acid $A$ to form a polyamide polymer $\boldsymbol{A}_j$ and water,

$$
A_j+A_{j^{\prime}} \rightleftarrows A_{j+j^{\prime}}+\mathrm{H}_2 \mathrm{O}
$$
(a) If the equilibrium constant for this reaction is 100 , what is the average polymer size at equilibrium if all species remain in a single-phase solution?
(b) To obtain a larger molecular weight of the polymer, the polymerization is sometimes carried out in a two-stage reactor with $\mathrm{H}_2 \mathrm{O}$ from the first stage separated before the second stage. If the first reactor forms only the dimer and the dimer without water is fed to the second reactor, what is the equilibrium polymer chain length obtainable? What chain length can one obtain if the first stage forms the trimer? Why is separation of water simpler with a dimer or trimer than if polymerization is continued to higher chain lengths?

Check back soon!

02:36

Problem 27

Suppose we want to produce a polymer with a very narrow molecular weight distribution. Which choices are preferred?
(a) CSTR or PFTR?
(b) Ideal addition or condensation?
(c) Polyester from tetrahydrofuran or 1,4-butanediol?

Nicholas Sacco

Numerade Educator

02:24

Problem 28

Engineers have learned how to prepare genetically engineered DNA molecules (a long-chain polymer) with exactly specified nucleic acid sequences by adding adenine, thymine, cytosine, or guanine (A, T, C, or G) in a DNA synthesizer. These operate by reacting one of these monomer molecules at a time in a sequence of highly automated batch reactors. Sketch the mechanism by which only a single monomer molecule is added in one reactor without mistakes and the "reactor" that accomplishes this process.

Jessica Wooten

Numerade Educator

00:42

Problem 29

Your body makes specific proteins by reacting single amino acids within cells. What is the process that makes a single protein molecule (a long-chain polymer) without mistakes?

Natalie Johns

Numerade Educator

Problem 30

In the Unipol process of olefine polymerization $0.1 \mu \mathrm{m}$ particles of Ziegler Natta catalyst are introduced into a fluidized bed containing ethylene at $250^{\circ} \mathrm{C}$. Polymer grows on the surface of this catalyst, and the catalyst expands to remain on the surface of the growing solid particle. When the particle diameter reaches $20 \mu \mathrm{m}$, the polymer particles are removed from the reactor by gravity. Calculate the time to form a $20 \mu \mathrm{m}$ polymer particle assuming that the reaction is mass transfer limited with a Sherwood number of 2.0 . Assume that the pressure of $\mathrm{C}_2 \mathrm{H}_4$ is 2 atm and $D_{\mathrm{C}_2 \mathrm{H}_4}=0.1 \mathrm{~cm}^2 / \mathrm{sec}$.

Check back soon!