Quiz #3 preview

Quiz #3 Preview CHEN 2683 Fall 2014

Overview • The problems are set up so that you are to attempt to solve the problem first, then look at the solution.

Liquid methanol (CH3OH, MW = 32.04) is to be burned in a furnace with pure oxygen. The methanol has a specific gravity of 0.792. The flow rate of methanol to the furnace is 2 liters/minute. What should the molar flow rate of oxygen be in order to have 25% excess oxygen fed to the furnace?

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CH 3OH  32 O2  CO2  2 H 2O

nCH 3OH , in  nO2 , in

2 L 792 g 1 mole  49.44 moles min min L 32.04 g

 49.44 moles 1.5 moles O2 needed   min mole CH 3OH fed 

  1.25  92.7 moles min  

The following reversible reaction takes place in the gas phase, along with its associated equilibrium equation: đ?‘Śđ??ľ đ??´â†”đ??ľ đ??ž= đ?‘Śđ??´

where đ?‘Śđ??´ and đ?‘Śđ??ľ are the mole fractions of components A and B, respectively.

Component A is fed to the reactor at a rate of 10 moles/minute. Also in the feed is an inert component, I, which is fed at 5 moles/minute. There is no component B in the feed. a. Write the equations for the molar flow rates of each component leaving the reactor in terms of the reaction extent, đ?œ‰. b. Write the equations for the mole fraction of each component leaving the reactor in terms of the feed rate of each into the reactor and the reaction extent. c. Calculate the reaction extent and the molar flow rates of each component leaving the reactor when the value of the equilibrium constant, K, is equal to 2.

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①

n A,out  10

moles min

n B ,out 

   

②

nI,out  5 moles min nTotal ,out  15 ③

y B ,out

moles min



15 K 2 y A,out 15 10   20  2  

  6.67

10   y A,out  15  y B ,out  15 5 y I ,out  15

④

n A,out  10  6.67  3.33 moles min n B ,out  6.67 moles min n I ,out  5

moles min

15 liters per minute of an aqueous solution of sodium hydroxide (NaOH) is fed to a chemical reactor. The solution has a specific gravity of 1.2 and the mass fraction of the sodium hydroxide in this stream is 0.10. The molecular weight of sodium hydroxide is 40 g/g-mole.

The NaOH solution is mixed with 30 liters/minute of an aqueous solution of sulfuric acid (H2SO4). The acid solution has a specific gravity of 1.1 and the mass fraction of the sulfuric acid in this stream is 0.10. The molecular weight of sulfuric acid is 98 g/g-mole. The neutralization reaction which occurs is: 2đ?‘ đ?‘Žđ?‘‚đ??ť + đ??ť2 đ?‘†đ?‘‚4 → đ?‘ đ?‘Ž2 đ?‘†đ?‘‚4 + 2đ??ť2 đ?‘‚ a. Determine the molar flow rates (g-moles/minute) of the sodium hydroxide and sulfuric acid fed to the reactor. b. Based on your results above, for the reactant which is not the limiting reagent, determine its percent excess. c. Determine the reaction extent if all of the limiting reagent is reacted.

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n NaOH , in 

15 L 1200 g 0.1 g NaOH 1 mole  45 moles min min L g solution 40 g

n H 2 SO4 , in 

30 L 1100 g 0.1 g H 2 SO4 1 mole  33.7 moles min min L g solution 98 g

①

Limiting reagent is NaOH

②

n NaOH , in  ③

15 L 1200 g 0.1 g NaOH 1 mole  45 moles min min L g solution 40 g

n H 2 SO4 , needed 

45 moles NaOH 1 mole H 2 SO4  22.5 moles min min 2 mole NaOH

 33.7  22.5  % XS    100%  49.8% 22.5  

n NaOH , out  0  45  2 ④

  22.5

moles min

A  B  2C The feed rate of A to the reactor is 10 moles/minute. The feed rate of B to the reactor is 15 moles/minute. C is fed at 5 moles/minute.

1. Write the equations for the molar flow rate of each component using the reaction extent. Also include the flow rate of the total number of moles leaving the reactor as a function of reaction extent.

2. The mole fraction of C leaving the reactor 0.50. What is the reaction extent?

3. What are the mole fractions of A and B leaving the reactor?

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①

n A,out  10   n  15   B ,out

nC ,out  5  2 nTotal ,out  30

moles min

5  2 yC  0.50  30 moles    5 min

②

10  5 yA   0.167 30 15  5 yB   0.333 30

1) Propane (C3H8, with a molecular weight of 44 kg/kg-mole), is to be combusted in a furnace. In this reaction, propane reacts with oxygen (O2, 32 kg/kg-mole) to form carbon dioxide (CO2, 44 kg/kg-mole) and water (H2O, 18 kg/kg-mole). Air (0.21 mole fraction O2, balance N2) will be used as a source of oxygen. N2 has a molecular weight of 28 kg/kg-mole. The molecular weight of air is 28.8 kg/kg-mole. a. Write the balanced reaction for the combustion of propane with oxygen. b. If the flow rate of propane is 440 kg/minute, what mass flow rate of air should be provided so that the oxygen is fed in stoichiometric proportion (0% excess) to the propane? Report this flow rate in kg/minute. c. The air is fed at 25% excess. What is the molar flow rate of air (report in kg-moles/minute)? d. If the fractional conversion of propane is 0.93 and air is fed at the rate determined in Part c above, what is the composition of the gas leaving the furnace. Report the composition in mole fractions. Include all species present.

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①

n propane 

②

m air 

③

C3 H 8  5O2  3CO2  4 H 2O 440 kg mole  10 kmoles min min 44 kg

10 kmoles propane 5 kmoles O2 1 kmole air 28.8 kg air kg  6857 min min kmole propane 0.21 kmoles O2 kmole air

 10 kmoles propane 5 kmoles O2 1 kmole air nair   min kmole propane 0.21 kmoles O2 

 1.25  297.6 kmoles  min 

10 kmole  0.93  9.3 kmoles   min min  10    0.7 kmoles

n propane reacted 

④

n propane, out

min

  16 kmoles noxygen, out  297.6 kmoles  0 .

21  5  min min nnitrogen, out  297.6 kmoles  0.79  235.1 kmoles min min ntotal , out  0.7  16  234.4  251.8 kmoles min y propane 

0.7 16 234.4  0.0028; yoxygen   0.064; ynitrogen   0.93 251.8 251.8 251.8

A reaction takes place where 1 mole of A forms 1 mole of B. The reactor is depicted below. An inert compound, C, is also fed with A into the reactor. The reactor outlet stream passes through a separator where some C and all of A are removed and recycled back to the inlet of the reactor. The outlet of the entire process (the product stream) contains only B and C. Exactly half of C entering the separator leaves with component B in the product; the other half is recycled with component A. The composition of the fresh feed is 90 mole% A, and 10 mole% C. The fresh feed rate is 100 moles/minute. The recycle stream contains 50 mole% C and 50 mole% A.

What are the flow rates (moles/minute) of components B and C in the product stream leaving the separator?

What are the flow rates (moles/minute) of components A and C in the recycle stream?

What is the fractional conversion of A in the reactor?

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①

moles   90 moles ; n  n A,out  0  90  ;   90 moles ; n    10 B ,out C ,out min min min

②

③

moles  nC ,recyle  10 moles ; n  10 A, recyle min min

n A,reactor feed  90  10  100 moles min 90 fA   0.9 100