Xylenes and benzene

A process to convert toluene or toluene and C9 aromatics to xylenes and benzene by disproportionation and transalkylation.

Description: Toluene and C9 aromatics or only toluene are fed to a catalytic reactor where transalkylation and/or disproportionation take place to produce high yields of C8 aromatics and benzene. The catalyst used in this process is an inexpensive non-noble metal that is kept at a high level of activity by continuous regeneration. Hydrogen is not required so that the investment and operating cost associated with a hydrogen recycle operation are not incurred.
   Referring to the flow diagram, the fresh feed aromatics plus recycle are heat exchanged with the reactor effluent and then raised to reaction temperature by a fired heater. The vaporized feed enters the reactor and is mixed with downward flowing catalyst. In the lower portion of the reactor, product vapor is separated from the catalyst, leaves the reactor, passes through the reactor feed exchanger, and is cooled and stabilized. The stabilized product is pumped to the fractionation system to separate benzene, toluene, xylenes and, if necessary, C9 aromatics.
   The catalyst, which has accumulated a small amount of coke, passed to the regenerator (kiln) where the coke is removed by burning with air. Steam is generated in the process from excess heat in the stack gas. No special materials of construction are employed throughout the system.

Yields: Over 95% of theoretical molar yields are obtained. Depending on the mixture of toluene and C9 aromatics charged to the process, C8 aromatics yields (predominantly xylenes) range from 55 to 84 weight percent of fresh feed while benzene ranges from 40 to 10 weight percent. Minor yields of gas, heavier aromatics, and coke (non-recoverable) make up the balance.

Utilities (per metric ton of fresh feed):

Fuel (heat absorbed)     
Power
Steam (net)
Boiler feed water
Cooling water

0.50-0.85 MMkcal
20-35 kWh
100-200 kg
0.2-0.4 m ³
3.5-7.0 m ³