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Technology Profile: Acetic Acid Production from Methanol

By Intratec Solutions |

This column is based on “Acetic Acid Production from Methanol – Cost Analysis,” a report published by Intratec. It can be found at: www.intratec.us/analysis/acetic-acid-production-cost.

Acetic acid (also known as ethanoic acid) is a carboxylic acid found as dilute solutions in plant and animal systems. Industrially, the chemical is widely used in organic processes, primarily in the production of vinyl acetate monomer and acetic anhydride.

The process

The following paragraphs describe a process for producing acetic acid from methanol and carbon monoxide, based on rhodium-catalyzed carbonylation. Figure 1 presents a simplified flow diagram of the process.

    Figure 1. The diagram shows a typical rhodium-catalyzed carbonylation process for acetic acid production

Figure 1. The diagram shows a typical rhodium-catalyzed carbonylation process for acetic acid production

Catalyst preparation. Initially, recycled rhodium catalyst is treated to recover the rhodium. The treated catalyst is mixed with fresh catalyst, a promoter (methyl iodide) and a stabilizer (iodide salt). The mixture is then dissolved in hot acetic acid under pressurized carbon monoxide.

Carbonylation. The reactor is fed with the catalyst solution, methanol and carbon monoxide, along with recycle streams. The reaction occurs in the liquid phase, where dissolved carbon monoxide combines with methanol to yield acetic acid. Gases vented from the reactor are cooled to recover unreacted methanol, methyl iodide and methyl acetate. Uncondensable species are sent to the methanol scrubber, to prevent the loss of low-boiling components, such as methyl iodide.

Liquid product is drawn off from the reactor at a rate sufficient to maintain a constant level, and is fed to a flash vessel, where the catalyst solution is withdrawn as a base stream and recycled to the catalyst preparation. The product overhead of the flash vessel — an acetic acid stream containing methyl iodide, methyl acetate and water — is purified in distillation columns.

Purification. In the crude acetic acid column, a gaseous stream from the overhead, containing water, methyl iodide, methyl acetate and some acetic acid, is condensed and recycled to the carbonylation stage. A crude acetic acid liquid stream, withdrawn as a side draw, is routed to the drying column. The bottom product, containing dissolved catalyst, is recycled to the flash.

In the drying column, water, methyl iodide and methyl acetate are removed from the crude acetic acid as an overhead distillate, which is further recycled to the carbonylation unit. The column bottom stream, containing acetic acid, is fed to a finishing column, where heavy ends are removed.

The acetic acid stream is finally passed through ion-exchange resin beds to remove iodide contaminants. Heavy-ends from the finishing column are sent to the acetic acid stripper, where residual acetic acid is recovered as overhead product and recycled to the finishing column, while the bottom product is discarded as waste acid.

 

Production pathways

Currently, the most important production routes for acetic acid are based on methanol carbonylation and oxidation of acetaldehyde or light hydrocarbons. Figure 2 presents different pathways for acetic acid production.

Figure 2. Methanol carbonylation is one of several possible pathways for the production of acetic acid

Figure 2. Methanol carbonylation is one of several possible pathways for the production of acetic acid

 

Economic performance

The total operating cost (raw materials, utilities, fixed costs and depreciation costs) estimated to produce acetic acid is about $560/ton of acetic acid. The analysis is based on data from the second quarter of 2013 using a plant with capacity to produce 650,000 metric ton per year of acetic acid.

Edited by Scott Jenkins

Editor’s note: The content for this column is supplied by Intratec Solutions LLC (Houston; www.intratec.us) and edited by Chemical Engineering. The analyses and models presented are prepared on the basis of publicly available and non-confidential information. The content represents the opinions of Intratec only. More information about the methodology for preparing analysis can be found, along with terms of use, at www.intratec.us/che.

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