Enhanced solvent recovery process boosts PTA production, saves energy

Two producers of purified terephthalic acid (PTA) have licensed a new enhanced solvent-recovery process. The process uses a proprietary solvent that boosts the capacity of the acetic acid recovery system while reducing energy usage. Because acid recovery is usually the limiting step in PTA production, increasing it can boost PTA capacity 5-10%. The solvent recovery enhancement (SRE) technology is licensed by Glitsch Technology Corp. (GTC), Houston. The GT-SRE process can be applied in

Dec. 16, 1996

3 min read

Because acid recovery is usually the limiting step in PTA production, increasing it can boost PTA capacity 5-10%.

The solvent recovery enhancement (SRE) technology is licensed by Glitsch Technology Corp. (GTC), Houston. The GT-SRE process can be applied in grassroots or existing plants.

Mexico's Temex Corp. is installing GT-SRE in its 500,000 metric tons/year (mty) PTA plant in Cosoleacaque, Veracruz. The unit will debottleneck Temex's acetic acid recovery section as part of its revamp project to increase plant capacity to 600,000 mty. Start-up is scheduled for mid-1997.

Sam Nam Petrochemical Co. Ltd. also licensed GT-SRE for its 600,000 mty plant at Yocheon, South Korea. With the addition of a new production train, PTA capacity at Yocheon will increase to 1.0 million mty. Sam Nam expects to start up the new train late next year.

GTC says the SRE process can increase output from existing PTA plants by 5-10% without investing in additional production or waste water treatment capacity. The process reduces dehydrator reboiler duty, waste water treatment loads, and volatile organic compounds (VOC) emissions in vent streams.

The process

The GT-SRE process replaces the water used in high and low-pressure absorbers with a phosphine oxide-based solvent (Fig. 1 [39697 bytes]). The solvent is most selective to acetic acid, but is also selective to methyl acetate and, to a lesser extent, paraxylene. This selectivity increases recovery of these components from vent streams.

Using the proprietary solvent in the high and low-pressure absorbers and adding a liquid-liquid extraction column result in milder operating conditions in the acetic acid dehydrator. This change in operations increases PTA capacity.

The concentration of acid in the dehydrator is 10-15%, compared to 0.5% in conventional solvent-recovery units used in PTA production. Acid is recovered selectively from the dehydrator overhead by liquid-liquid extraction in an agitated unit. The same solvent used in the absorber is used in this agitated extractor.

Methyl acetate and paraxylene are stripped from the solvent system and recycled back to PTA production.

Table 1 [7677 bytes] shows typical feed and product analyses for the GT-SRE process, as compared to conventional PTA production processes. For a 250,000 mty plant, the addition of SRE will increase PTA capacity by 10,000-25,000 mty and reduce the energy used for solvent recovery by 25 MMBTU/hr.