Consider the isomerization of n-butane to iso-butane as a first order gas phase reaction with ideal gas behavior. A rate constant of 0.0015 min was found at 27 C. The activation energy is 25 kcal mol. The reaction is to be carried out in parallel tubes that are 3 m long with and inside diameter of 2.5 cm. The reaction is to be carried out at 125 C and 10 bar. How many tubes are required for a production of 500 kg h of iso-butane if the conversion n-butane is 90%?