Ethene is hydrated industrially in the gas phase to produce ethanol:…

CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)

Problem

Ethene is hydrated industrially in the gas phase to produce ethanol:

\mathrm{C_2H_4(g)+H_2O(g)}\;\longleftrightarrow\;\mathrm{C_2H_5OH(g)}\qquad \Delta H_{1} = -45\,\text{kJ mol}^{-1}

Unfortunately, ethanol can further react with excess ethene to form diethyl ether:

2\,\mathrm{C_2H_5OH(g)}\;\longleftrightarrow\;\mathrm{(C_2H_5)_2O(g)+H_2O(g)}\qquad \Delta H_{2} = +25\,\text{kJ mol}^{-1}

At 600 K the equilibrium constants are

K_{p1}=4.8

for hydration and

K_{p2}=1.2

for ether formation. Assume a plug-flow reactor operates isothermally at 600 K and 50 atm with a feed containing 1.0 mol \% water and 99.0 mol \% ethene (no ethanol or ether initially). Ideal-gas behavior applies. (a) Write the expressions for the reaction quotients

Q_{p1}

and

Q_{p2}

using the initial partial pressures of all species in the feed. (b) Using your expressions, determine whether each reaction will proceed in the forward or reverse direction upon entering the reactor. Show your reasoning. (c) Process engineers can independently adjust the inlet water mole fraction and the total pressure. Propose specific changes to these two variables that would maximize ethanol production while minimizing ether formation, and justify each proposal with quantitative or qualitative arguments. (d) Discuss two operational constraints (such as catalyst activity, corrosion, or separation costs) that could limit the practical implementation of your recommended conditions.

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