At $650$ C phosphine vapor decomposes as follows:

$4P{H}_3-P_{4(g)}+6H_2,-r_{\text{p}\text{h}\text{o}\text{s}}=10h{r}^{-1}{C}_{\text{p}\text{h}\text{o}\text{s}}$

What size of plug flow reactor in liter operating at $649C$ and $11\mathrm{.}4$atm is needed for $75\%$ conversion of $33mo\frac{l}{h}$ of phosphine in a $\frac{2}{3}$ phosphine$-\frac{1}{3}$ inert feed?

Round your answer to $0$ decimal places.