3. Propylene is reacted with oxygen to form acrylic acid by: C3H6 + 1.5 O2 C3H4O

Question

3. Propylene is reacted with oxygen to form acrylic acid by: C3H6 + 1.5 O2 C3H4O2 + H2O Propylene is fed to the reactor with 50% excess oxygen where the oxygen flow rate is 260 kmol/hr. Acrylic acid exits the reactor at 90 kmol/hr.

(a) Determine the entering flow rate of propylene in kmol/hr. (1 XP)

(b) Determine the extent of reaction (with units), then write the expression for the molar flow rate of oxygen exiting the reactor in terms of the extent of reaction (assuming no side reaction) and solve for this flow rate. (1 XP)

(c) Find the fractional conversions of oxygen and propylene assuming no side reactions are present. (1 XP)

There is a side reaction to form acetic acid by: C3H6 + 2.5 O2 C2H4O2 + CO2 + H2O and the selectivity of acrylic acid to acetic acid is 13.8.

(d) Determine the total amount of oxygen that reacts due to the two reactions. (1 XP)

(e) Determine the yield of acrylic acid. (1 XP)

Explanation / Answer

(a) Determine the entering flow rate of propylene in kmol/hr.

The ratio of propylene and oxygen as per the equation is

1 mole of propylene and 1.5 mole of oxygen since oxygen is 50% excess the actual flow rate of oxygen is 1.5 + 0.5 x 1.5 = 2.25 moles

The oxygen flow rate is given as 260 kmol/hr

So the propylene flow rate should be 260/2.25 = 115.5 kmol/hr

(b) Determine the extent of reaction (with units), then write the expression for the molar flow rate of oxygen exiting the reactor in terms of the extent of reaction (assuming no side reaction) and solve for this flow rate.

1 mole of propylene gives 1 mole of acrylic acid

SInce propylene is entering @ 115.5 kmol/hr the production of acrylic acid should be 115.5 kmol/hr

But the acrylic acid exiting is 90 kmol/hr

So extent of reaction is 90 kmol/hr

Molar flow rate of oxygen exiting is 260 - 260 kmol/2.25 x 1.5 x 0.7792 = 124.94 kmol/hr

(c) Find the fractional conversions of oxygen and propylene assuming no side reactions are present.

Fractional conversion of propylene is 90 kmol/115.5 kmol = 0.779

Fractional conversion of oxygen is 260 - 124.94/260 = 0.519

There is a side reaction to form acetic acid by: C3H6 + 2.5 O2 C2H4O2 + CO2 + H2O and the selectivity of acrylic acid to acetic acid is 13.8.

(d) Determine the total amount of oxygen that reacts due to the two reactions.

acrylic acid to acetic acid is 13.8 since 90kmol of acrylic acid is formed acetic acid is 90/13.8 = 6.52 kmol/hr

So oxygen is 6.52 x 2.5 = 16.3 + 90 x 1.5 = 135 = 151.3 kmol/hr of oxygen is consumed.

(e) Determine the yield of acrylic acid.

Yield of acrylic acid is 77.9% (from the fractional conversion calculated above)

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