On a Levenspiel plot, what is plotted on the vertical axis?

On a Levenspiel plot, what is plotted on the vertical axis?

• A. FA0/(-rA)
• B. X
• C. rA
• D. FA

Answer: (A)

The quantity on the vertical axis in a Levenspiel plot is the ratio F_A0 divided by the rate of disappearance of A, -r_A. This comes directly from the design equation for a PFR: dV = F_A0 dX / (-r_A). Rearranging gives dV/dX = F_A0/(-r_A), so plotting F_A0/(-r_A) versus conversion X shows how much volume is needed per unit increase in conversion. The area under the curve up to a given X represents the reactor volume (for a given inlet molar flow F_A0) required to reach that conversion. The horizontal axis is conversion X, while the other quantities listed (r_A as a rate, or F_A as inlet flow) aren’t the quantity used to represent incremental volume in this plot.

The quantity on the vertical axis in a Levenspiel plot is the ratio F_A0 divided by the rate of disappearance of A, -r_A. This comes directly from the design equation for a PFR: dV = F_A0 dX / (-r_A). Rearranging gives dV/dX = F_A0/(-r_A), so plotting F_A0/(-r_A) versus conversion X shows how much volume is needed per unit increase in conversion. The area under the curve up to a given X represents the reactor volume (for a given inlet molar flow F_A0) required to reach that conversion. The horizontal axis is conversion X, while the other quantities listed (r_A as a rate, or F_A as inlet flow) aren’t the quantity used to represent incremental volume in this plot.