This plant is designed to extract and purify isobutylene from a mixed-C4 stream (Raffinate I stream) in oil refineries or from isobutylene-rich stream in butadiene plants. The plant uses Cold Acid Extraction process which is suitable to feedstock stream containing 17 – 48% of raw isobutylene. Depending on the concentration of isobutylene in feedstock, the plant can produce approximately 50,000 – 120,000 tons/years of purified isobutylene.
The cold acid extraction technology solves the problem caused by the similar boiling points of feedstock stream components. The mixed isobutylene, butene and butanes are brought in contact with dilute (49.5%) sulfuric acid. The acid selectively converts the isobutene into Tertiary Butyl Alcohol (TBA) which is soluble in the acid. The mixture of TBA and acid, called extract, is purified and then heated and reconverted to recover isobutylene in a pure form. In general, the plant is divided into five process sections: (1) Reaction, (2) Extract Purification, (3) Regeneration, (4) Isobutylene Purification, (5) TBA Recovery.
In the reaction section, there are three chains A, B and C, each consisting of a reactor, emulsion pump, cooler and settler. The feed is introduced into the "A" reactor emulsion pump and travels through A,B,C chains becoming leaner in Isobutene. The lean sulfuric acid is introduced at "C" reactor emulsion pump and travels through C, B, A chains becoming richer in TBA before going to Purifying step from the bottom of "A" stage settler. The Spent (Raffinate II) leaves the top of "C" settler and is sent to the Spent C4 wash tower. In the Purifying substep, recovered TBA is injected into the extract and is heated by low pressure steam on temperature control and passes through a vessel which is maintained in a vacuum. In the Regenerating substep, purified extract is heated.
Normally every three years the plant had a turnaround, which temporarily shut down the plant for less than three weeks.
All the equipment is in excellent condition. A large quantity of pipes, exchangers, and process equipment is made of alloy 20, zirconium and other alloys. Complete documents set include detailed process description, PFDs, P&IDs, equipment data sheets, maintenance and inspection files.