Acetic dominant manufacturing process

It is now nearly 40 years since the introduction by Monsanto of a rhodium-catalysed process for the production of acetic acid by carbonylation of methanol [1]. The so-called Monsanto process became the dominant method for manufacture of acetic acid and is one of the most successful examples of the commercial application of homogeneous catalysis. The rhodium-catalysed process was preceded by a cobalt-based system developed by BASF [2,3], which suffered from significantly lower selectivity and the necessity for much harsher conditions of temperature and pressure. Although the rhodium-catalysed system has much better activity and selectivity, the search has continued in recent years for new catalysts which improve efficiency even further. The strategies employed have involved either modifications to the rhodium-based system or the replacement of rhodium by another metal, in particular iridium. This chapter will describe some of the important recent advances in both rhodium- and iridium-catalysed methanol carbonylation. Particular emphasis will be placed on the fundamental organometallic chemistry and mechanistic understanding of these processes. 

Worldwide production of acetic acid is dominated by the BP Chemicals methanol carbonylation process originally developed by Monsanto in the 1960s. Previously, acetic acid was manufactured by air-based oxidation of acetaldehyde or light hydrocarbons. Currently about of the acetic acid... 

Today, methanol carbonylation is the favored way for manufacturing acetic acid. The route is claimed to have the lowest production costs, especially for large-scale production. In general, the production costs of commodity chemicals are dominated by the raw material costs. In fact, methanol produced from synthesis gas (mainly from natural gas) is nowadays a cheap starting material. In 2006, processes based on methanol carbonylation accounted for about 78% of the world capacity for acetic acid. 

The industrial manufacture of acetic acid by methanol carbonylation (Equation (1)) has utilized catalysts based upon all three of the group 9 metals, since the initial development by BASF of a cobalt/iodide-based system. " The BASF process required harsh conditions of temperature and pressure, and suffered from relatively low selectivity. It was soon superceded by highly selective, low-pressure rhodium/iodide-based catalysts developed by Monsanto. The Monsanto process (and related variants operated by other manufacturers) quickly became dominant and remains one of the most successful examples of the commercial application of homogeneous catalysis.Rhodium catalysts for methanol carbonylation are discussed in Chapter 7.03. 

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