Industrial processes BASF acetic acid process

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 It was soon superceded by highly selective, low-pressure rhodium/iodide-based catalysts developed by Monsanto.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. 

As mentioned in the previous section, the carbonylation of methanol to acetic acid is an important industrial process. Whereas the [Co2(CO)s]-catalyzed, iodide-promoted reaction developed by BASF requires pressures of the order of 50 MPa, the Monsanto rhodium-catalyzed synthesis, which is also iodide promoted and which was discovered by Roth and co-workers, can be operated even at normal pressure, though somewhat higher pressures are used in the production units.4,1-413 The rhodium-catalyzed process gives a methanol conversion to acetic acid of 99%, against 90% for the cobalt reaction. The mechanism of the Monsanto process has been studied by Forster.414 The anionic complex m-[RhI2(CO)2]- (95) initiates the catalytic cycle, which is shown in Scheme 26. 

In this chapter we discuss the mechanistic and other details of a few industrial carbonylation processes. These are carbonylation of methanol to acetic acid, methyl acetate to acetic anhydride, propyne to methyl methacrylate, and benzyl chloride to phenyl acetic acid. Both Monsanto and BASF manufacture acetic acid by methanol carbonylation, Reaction 4.1. The BASF process is older than the Monsanto process. The catalysts and the reaction conditions for the two processes are also different and are compared in the next section. Carbonylation of methyl acetate to acetic anhydride, according to reaction 4.2, is a successful industrial process that has been developed by Eastman Kodak. The carbonylation of propyne (methyl acetylene) in methanol to give methyl methacrylate has recently been commercialized by Shell. The Montedison carbonylation process for the manufacture of phenyl acetic acid from benzyl chloride is noteworthy for the clever combination of phase-transfer and organometallic catalyses. Hoechst has recently reported a novel carbonylation process for the drug ibuprofen. 

Mankind has produced acetic acid for many thousand years but the traditional and green fermentation methods cannot provide the large amounts of acetic acid that are required by today s society. As early as 1960 a 100% atom efficient cobalt-catalyzed industrial synthesis of acetic acid was introduced by BASF, shortly afterwards followed by the Monsanto rhodium-catalyzed low-pressure acetic acid process (Scheme 5.36) the name explains one of the advantages of the rhodium-catalyzed process over the cobalt-catalyzed one [61, 67]. These processes are rather similar and consist of two catalytic cycles. An activation of methanol as methyl iodide, which is catalytic, since the HI is recaptured by hydrolysis of acetyl iodide to the final product after its release from the transition metal catalyst, starts the process. The transition metal catalyst reacts with methyl iodide in an oxidative addition, then catalyzes the carbonylation via a migration of the methyl group, the "insertion reaction". Subsequent reductive elimination releases the acetyl iodide. While both processes are, on paper, 100%... 

The production of carboxylic acids via carbonylation catalysis is the second most important industrial homogeneous group of processes. Reppe developed most of the basic carbonylation chemistry in the 1930s and 1940s. The first commercial carbonylation process was the stoichiometric Ni(CO)4-based hydroxycarbonylation of acetylene to give acrylic acid (see Section 3.5 for details). This discovery has since evolved into a trae Ni-catalyzed process, used mainly by BASF. The introduction of rhodium catalysts in the 1970s revolutionized carboxylic acid production, particularly for acetic acid, much in the same way that Rh/PPhs catalysts changed the importance of hydroformylation catalysis. 

The synthesis of carboxylic acids by carbonylation of unsaturated hydrocarbons or alcohols was developed mainly by Reppe and his co-workers in the laboratories of BASF at Ludwigshafen. Many industrially important processes such as the synthesis of acrylic acid, propionic acid, and acetic acid were elaborated there in the period from the late 1930s to the mid-1950s [1, 2]. Reppe s introduction of metal carbonyls as catalysts for carbonylation reactions was of paramount importance and many processes, which are still industrially relevant today, were developed rapidly (eq. (1), [3]). 

Actual operating capacities of Reppe carbonylation processes are difficult to estimate since only a few data are available in the literature. However, it is known that some of the syntheses are carried out on an industrial scale, e. g. the synthesis of acrylates from acetylene, carbon monoxide and alcohols (BASF) [1004, 1005], the acetic acid synthesis from methanol and carbon monoxide and the synthesis of higher molecular weight saturated carboxylic acids from olefins, carbon monoxide and water. Propionic acid (30,000 tons/year) and to a smaller extent heptadecanoic dicarboxylic acid are manufactured via the carbonylation route at BASF. Butanol is made from propylene in Japan [1003, 1004]. 

The production of acetic acid by a fermentation process is far too slow and thus too expensive. The first industrial process for synthetic production of acetic acid was based on the liquid-phase oxidation of acetaldehyde. In the 1950s, as the petrochemical industry developed rapidly, the direct liquid phase oxidation of butane and naphtha became the preferred route to acetic acid. Significant amounts of by-products are formed, and complex purification units were needed. Today, the industrially preferred process is the conversion of methanol with CO (catalytic carbonylation). The reaction is exothermic and shows a volume decrease, and thus the equilibrium is favored by low temperatures and high pressures. There are two general technologies for methanol carbonylation, high-pressure carbonylation at 700 bar (BASF) or low-pressure carbonylation at 30 bar (Monsanto, BP). 

---