What happens to unreacted gases in the ethene hydration process described for ethanol production?

• A. They are recycled
• B. They are vented to atmosphere
• C. They are converted to water
• D. They are stored as liquids

Answer: (A)

In the industrial hydration of ethene to make ethanol, not all ethene reacts in the reactor. Some ethene remains unreacted as a gas after the reaction has reached its practical limit under the operating conditions. To use this ethene efficiently and minimize waste, the unreacted gas is captured and recycled back into the reactor feed along with fresh ethene and steam. This recycling boosts overall yield and reduces the need to supply more ethene from outside, making the process more economical and efficient.

Venting the unreacted gas would waste a valuable reactant and raise costs and emissions. Converting unreacted ethene to water isn’t how this reaction proceeds, since the goal is to form ethanol from ethene and water, not to transform the ethene into water. Storing the unreacted gas as liquids isn’t appropriate for these process conditions, where the components are gases or vapors; it would require substantial energy to liquefy and store, and isn’t how the process operates.