Batch TML Reactor

After about 170 min, most of the aniline has been consumed (plot at the bottom of the left column in Fig. 4.41). The hydrogen concentration increases (which increases reactor pressure and reduces the hydrogen feed) and the reaction rate slows (which reduces the heat generation). The reactor temperature drops, cutting the cooling water. The batch is stopped when the conversion of aniline reaches 99.9% at 214 min. 

Large quantities of tetramethyl lead (TML) were used back in the 1960s as an antiknock additive in high-octane gasoline before they were banned because of air pollution problems. TML was produced in a batch reactor that had the interesting feature of requiring the removal of a byproduct during the batch. The main reaction involves a solid sodium-lead alloy and liquid methyl chloride  

The solid is in the form of flakes that have significant variability in particle size. The reaction is highly exothermic. It uses a catalyst of aluminum chloride and is conducted at about 383 K and 25.8 atm, but both temperature and pressure vary during the batch cycle. Since TML is an explosive, some toluene is added with the reactor charge to serve as a moderator. 

The third valve is on a vent stream from the condenser. This vent is needed because there is a second undesirable reaction that produces ethane  

The ethane is much lighter than the methyl chloride, so it accumulates in the condenser and acts essentially like an inert substance that blankets the condenser. The effect of the inert substance can be considered to reduce either (1) the bubblepoint temperature, thus reducing the differential temperature driving force and reducing heat transfer, or (2) the effective heat transfer area. Either effect is a reduction in heat transfer. So if the ethane is not vented off during the batch, the pressure cannot be controlled even with the chilled water valve wide open. 

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