Industrial Cativa process

For approximately 30 years, the most successful industrial process for the carbonylation of methanol relied on an iodide-promoted rhodium catalyst. This technology, originally developed by Monsanto and acquired by BP Chemicals in 1986, is responsible for the majority of the acetic acid synthesized industrially. Since then, the most important development in industrial carbonylation chemistry is the Cativa process, announced by BP Chemicals in 1996. ... 

Scorpionate or pyrazole V(V) 1-4, 6, 10, and 15, and Re(in) 11, 12, 16, 17, 24-26 complexes have been used as catalysts for the carboxylation of gaseous alkanes via single-pot conversions [5a,fj. These syntheses of carboxylic acids are much simpler than those used in industry. For instance, in the case of the conversion of methane into acetic acid, the current industrial routes commonly involve three distinct stages and use more expensive catalysts and harder experimental conditions (e.g., the Mosanto and BP-Amoco Cativa processes of carbonylation of methanol, at the third stage, are based on Rh and Ir catalysts, respectively) [8b]. 

The conversion of MeOH to MeCOjH (eq. 25.15) is carried out on a huge industrial scale, and 60% of the world s acetyls are manufactured using the Monsanto and Cativa processes. Currently, 7 Mt per year of acetic acid are consumed worldwide, with the formation of vinyl acetate (25.15) being the most important commercial end use. Vinyl acetate is the precursor to polyvinylacetate (PVA, 25.16). 

The first step in the Cativa process is the reaction between Mel and c -[Ir(CO)2l2]. However, the catalyst may also react with HI and this step initiates a water gas shift reaction that competes with the main catalytic cycle, (a) What chemical is manufactured in the Cativa process Why is this product of industrial importance (b) Why is HI present in the system (c) Give an equation for the water gas shift reaction, and state conditions typically used in industry, (d) Figure 25.22 shows the competitive catalytic cycle described above. Suggest identities for species A, B, C and D. What type of reaction is the conversion of czj -[Ir(CO)2l2] to A What changes in iridium oxidation state occur on going around the catalytic cycle, and what is the electron count in each iridium complex ... 

Jones, J.H. (2000) The Cativa process for the manufacture of acetic acid iridium catalyst improves productivity in an established industrial process. Platinum Met. Rev., 44, 94-105. 

Although rhodium and iridium are high-priced precious metals, their complexes are indispensable for homogeneous catalysis. Prominent examples for their use on the industrial scale are, among others, asymmetric hydrogenation, hydroformyla-tion, and the Monsanto acetic acid or the Cativa process [1]. 

Industrial-scale production in the Cativa process (181-195°C, 22-32 bars) involves a primary reactor where methanol, catalyst, and the promoter are reacted with CO. The reactants are mixed by the jet mixing effect provided by the cooling loop in the primary reactor. The reactant mixture is passed into the second reactor to improve the formation of acetic acid, after which the catalyst is separated and recycled. The by-products in the Cativa process are propionic acid and acetaldehyde, which are separated from acetic acid by distillation. By oxidizing the latter, the yield can be improved. 

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