Monsanto trial

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The Monsanto process is a process for the industrial preparation of acetic acid . The process takes place at a pressure of 30 to 60 bar and a temperature of 150 to 200 ° C with a selectivity of over 99%.

history

It was developed by BASF in 1960 and improved by Monsanto in 1966 by introducing a different catalyst system. In this process, methanol is catalytically converted to acetic acid with carbon monoxide . The sum equation is:

mechanism

Catalytic cycle of the Monsanto process

The catalytically active species is the anionic complex cis- [Rh (CO) 2 I 2 ] - (1) . The catalytic cycle consists of six steps, two of which do not involve rhodium : the conversion of the methanol into methyl iodide and the hydrolysis of the acetyl iodide into acetic acid. The first step is the oxidative addition of the methyl iodide to the rhodium complex to form the complex [(CH 3 ) Rh (CO) 2 I 3 ] - (2) . This complex rearranges rapidly into the acetyl complex [(CH 3 CO) Rh (CO) I 3 ] - (3) with insertion of the carbonyl into the metal-methyl bond .

Another carbon monoxide molecule is attached to this five-coordinate complex. This complex decomposes with reductive elimination of the acetyl iodide CH 3 COI, which decomposes with hydrolysis in acetic acid and hydrogen iodide (HI) to form the starting compound. The reaction is first order with respect to the catalyst and the methyl iodide. Therefore, it is believed that the rate limiting step is the oxidative addition of the methyl iodide to the catalyst.

variants

Cativa process

The Monsanto process has now been supplemented by the Cativa process , which uses an iridium catalyst with a similar reaction mechanism and which was developed by BP. In the Cativa process , the iridium complex [Ir (CO) 2 I 2 ] - the catalytically active species. On the one hand, iridium is a cheaper catalyst metal, the process also requires less water in the reaction solution and thus saves drying stages in later process steps. Development of the process began in the 1990s, and in November 1995 the first commercial plant went into operation in Texas City , USA.

Tennessee Eastman Acetic Anhydride Process

Another way of producing acetic acid is the Tennessee-Eastman process, with the formation of acetic anhydride . Acetic anhydride is formed by the carbonylation of methyl acetate in a process that is based on the Monsanto process:

Tennessee Eastman Acetic Anhydride Process 2.png

Rhodium iodide and lithium salts are used as catalysts . In contrast to the above methods, this method is carried out with the exclusion of water because of the sensitivity of the anhydride. The methyl acetate is split into methyl iodide and lithium acetate by lithium iodide. The acetyl iodide formed in the catalytic cycle forms the product acetic anhydride with the lithium acetate.

Individual evidence

  1. Greener Industry: Ethanoic Acid - Production Method: The Monsanto Process , (English)
  2. ^ Jones JH: The Cativa Process for the Manufacture of Acetic Acid . In: Platinum Metals Review . 44, No. 3, 2002, pp. 94-105.
  3. ^ A b Sunley GJ, Watson DJ: High productivity methanol carbonylation catalysis using iridium - The Cativa process for the manufacture of acetic acid . In: Catalysis Today . 58, No. 4, 2000, pp. 293-307. doi : 10.1016 / S0920-5861 (00) 00263-7 .
  4. Zoeller, JR; Agreda, VH; Cook, SL; Lafferty, NL; Polichnowski, SW; Pond, DM Eastman Chemical Company Acetic Anhydride Process In: Catalysis Today 1992 , 13 , pp. 73-91. doi : 10.1016 / 0920-5861 (92) 80188-S

Web links

Commons : Monsanto process  - collection of images, videos and audio files
Commons : Cativa process  - collection of images, videos and audio files