(150c) Acetic Acid and Methanol Recovery Unit

The goal of this unit is to utilize a stream from the saponification section of a Polyvinyl Alcohol plant situated on the Gulf Coast of the United States. In addition to methanol to be recovered, the feed stream contains large quantities of methyl acetate. Therefore, methyl acetate is hydrolyzed to produce additional methanol and acetic acid for sale. The total amount of methanol is purified to 99.9 weight percent and acetic acid purified to 99 weight percent to meet prescribed specifications. Biodegradable sodium acetate also enters in the feed stream and is removed through a purge stream to be dumped. A second impurity, acetaldehyde, is removed from the plant and incinerated to eliminate the carcinogenic hazard. The optimized steady-state design includes five distillation columns and one reactor and three recycle streams. Unconverted methyl acetate is returned to the front-end with only trace amounts exiting the unit unconverted. An azeotrope between methyl acetate and methanol is broken using extractive distillation techniques, resulting in a second recycle stream for the water solvent. The final recycle arises from the excess water fed to the reactor to increase methyl acetate conversion. At full capacity, the plant recovers 177 million pounds of methanol per year and produces 101 million pounds of acetic acid for sale. Further, a plant wide control scheme is implemented to operate the plant. The control structure is designed to withstand composition disturbances of +/- 10%, a 10 % increase in feed rate, and a 33% decrease in feed rate. An economic analysis shows that the plant will begin to make a profit and consistently make a profit of at least $50 million for the following 10 years with a return on investment of 233%.