This all stainless steel, dual-column distillation system was designed by Sabic to separate and purify up to 18 mt/hr of toluene from a complex mixture including isomers, Bisphenol-A, and water. The system consists of a feed tank, vaporizer, pre-flash vessel, upper column, lower column, two column reboilers, and two overhead condensers with vacuum jets.
Subsystem from Complete Bisphenol A (BPA) Plant, IPP Stock #600363
Toluene Recovery System Process Flow Diagram
In this design, up to 20 mt/hr of crude toluene enters the feed tank at 60°C and 1.0 bar-absolute. There is a low-pressure steam coil in the 304 stainless steel feed tank. The crude toluene is then pumped through the vaporizer rated for 2.0 MM kcal/hr where the temperature is increased to 120°C. After the crude toluene is vaporized, it enters the pre-flash vessel operated at 120°C and 1.1 bar-absolute. The bottoms from the pre-flash vessel enter the middle section of the 304 stainless steel upper toluene column. This column is 1 m (dia) x 8.3 m (tall) with (2) packed sections and operates at 111°C and 1.02 bar-absolute in the top section and 177°C and 1.04 bar-absolute in the bottom section.
The overheads from both the pre-flash vessel and the upper toluene column combine and flow to the overhead condenser which is rated for 1.6 MM kcal/hr and then to the secondary condenser which is rated for 1.4 MM kcal/hr. The bottoms from the upper toluene column circulate through a reboiler rated for 1.4 MM kcal/hr. The final product flow from the secondary condenser is up to 18 mt/hr of pure toluene.
A side-stream from the upper toluene column reboiler loop feeds the lower toluene column. This column is 0.3 m (dia) x 6.5 m (tall) operates at 166°C and 1.04 bar-absolute in the top section and 195°C and 1.08 bar-absolute in the bottom section. The overheads from the lower toluene column go back to the upper toluene column. The bottoms from the lower toluene column circulate through a reboiler rated for 0.05 MM kcal/hr with a small side-stream returning the separated BPA back to the process.
This toluene recovery system includes the following major components:
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