Benzene Production from Toluene & Heavy Aromatics

The process under analysis comprises two major sections: (1) Transalkylation; and (2) Fractionation.

Transalkylation. Fresh toluene and heavy aromatics feeds, toluene and heavy aromatics recovered downstream, fresh hydrogen and hydrogen-rich recycle gas are combined and preheated by heat-exchange with effluent from reactor. Subsequently, the feed stream is fed to a fired heater, where it is vaporized and raised to the reaction temperature. The feed stream is sent down-flow over a fixed bed of zeolitic catalyst, where the transalkylation / disproportionation reactions take place. The reactions yield a mixture composed primarily of benzene, toluene and mixed xylenes. The effluent from the reactor is cooled in such a way that substantially all of the hydrocarbons boiling above methane are condensed.

Fractionation. The liquid stream containing Benzene and other transalkylation / disproportionation reaction products, as well as entrained hydrogen, is routed to a gas-liquid separator, in which the hydrogen is removed. The gaseous stream is compressed and mixed to fresh hydrogen. The liquid effluent is fed to a column in which remaining gas and low-boiling hydrocarbons are stripped off from the stream. The aromatics concentrate is then submitted to a clay treatment, in such a way that impurities (e.g. trace olefins) are removed by polymerization and absorption. The treated stream is passed through a series of four distillation columns, where benzene, toluene, concentrated xylenes and C9 and C10 Aromatics are recovered. Toluene and C9 Aromatics are recycled.