toluene

benzene; xylene

To selectively convert toluene to high-purity benzene and a unique xylene product with a para-xylene content of up to 95 %, which significantly exceeds equilibrium concentration, using the Mobil Selective Toluene Disproportionation (MSTDP) process.

Description: Dry toluene feed and hydrogen-rich recycle gas are pumped through feed effluent heat exchangers and the charge heater into the MSTDP reactor (1). The vapor then flows down through the fixed bed of MSTDP catalyst. Toluene disproportionation occurs in vapor phase in the MSTDP reactor at elevated temperature to produce benzene and the para-rich xylene product. The reactor effluent is cooled by heat exchange with the liquid feed and the resulting liquid and vapor phase are separated (2). Hydrogen-rich vapor phase is recycled back to the reactor charge together with make-up hydrogen. Separator liquid is first stripped of dissolved gaseous products in the stabilizer (3) and then fractionated on the light aromatics tower to separate the benzene and xylene products from unconverted toluene and a small quantity of heavy aromatic material. Unconverted toluene is recycled to extinction.

Yields, wt% from MSTDP reactor:

	Feed	Product
C5 & lighter Benzene Toluene Ethylenezene p-Xylene m-Xylene o-Xylene C9 + Aromatics	100.0	1.8 13.9 70.0 0.6 11.4 1.4 0.3 0.6
	----- 100.0	----- 100.0
Toluene conversion, wt% p-Xylene in xylene fraction, %		30.0 87.0

Operating conditions: Temperature, pressure and space velocity are moderate and the hydrogen to toluene mole ratio is low.
   The key to the MSTDP process is the synergistic combination of a proprietary Mobil catalyst and a novel pretreatment procedure that selectivates the catalyst at the beginning of each cycle. The catalyst is a shape selective zeolite catalyst that contains unique pore structure. While the catalyst is fully regenerable, operating cycles of six to 12 months are achieved before the catalyst needs to be regenerated.