Page 136 - Chemical and process design handbook

Speight_Part II_B 11/7/01 3:11 PM Page 2.77

BENZENE 2.77

Extractor Stripper Extract recovery Separator Separator Raffinate

Feedstock

Extract
Raffinate
wash water

FIGURE 2 Benzene manufacture by sulfolane extraction.

Hydrogen recycle
Fuel gas

Benzene

Reactor Separator Separator Xylenes
Toluene

Makeup
hydrogen

Recycle toluene and C9 aromatics
FIGURE 3 Benzene manufacture by toluene hydrodealkylation.

(4 to 6 MPa). The reaction is exothermic and temperature control (by injec-
tion of quench hydrogen) is necessary at several places along the reaction
sequence. Conversions per pass typically reach 90 percent and selectivity to
benzene is often greater than 95 percent. The catalytic process occurs at
lower temperatures and offers higher selectivity but requires frequent
regeneration of the catalyst. Products leaving the reactor pass through a sep-
arator where unreacted hydrogen is removed and recycled to the feed.
Further fractionation separates methane from the benzene product.