Iodine acetate monoxide

However, since 1970 the preferred method of acetic acid manufacture is carbonylation of methanol (Monsanto process), involving reaction of methanol and carbon monoxide (both derived from methane) with rhodium and iodine as catalysts at 175°C and 1 atm. The yield of acetic acid is 99% based on methanol and 90% based on carbon monoxide. 

The mechanism for the reaction is believed to be as shown in Eq. 15.170 (start with CH3OH, lower right, and end with CHjCOOH, lower left).180 The reaction can be initiated with any rhodium salt, e.g., RhCl3, and a source of iodine, the two combining with CO to produce the active catalyst, IRItfCO y. The methyl iodide arises from the reaction of methanol and hydrogen iodide. Note that the catalytic loop involves oxidative addition, insertion, and reductive elimination, with a net production of acetic acid from the insertion of carbon monoxide into methanol. The rhodium shuttles between the +1 and +3 oxidation states. The cataylst is so efficient that the reaction will proceed at atmospheric pressure, although in practice the system is... 

The concept of co-carbonylation of methanol/methyl acetate mixtures was first introduced by BASF in the early 1950s, but the reaction chemistry was not fully developed to commercial realization [75]. Not until the mid-1980s, after the development of carbonylation processes to produce acetic acid and acetic anhydride, were co-carbonylation processes patented using homogeneous rhodium/iodine catalyst systems (Table 2) [2, 56]. The basic process concept is to manufacture acetic acid and acetic anhydride from methanol and carbon monoxide as the only raw materials and to generate methyl acetate within the process. Similiarly, the suitability of dimethyl ether as a raw material for the generation of the anhydride equivalent in addition to or as a substitute for methyl acetate was revealed by Hoechst [76]. To produce a small fraction of acetic acid besides acetic anhydride as the main product, the carbonylation of methyl acetate could be conducted with small amounts of water or methanol. This variant, first demonstrated by Hoechst [56], is practiced by Eastman Kodak [2]. 

The reaction now preferred on economic grounds for acetic acid prodnction is the combination of methanol with carbon monoxide (both derived from natnral gas) over a catalyst that contains rhodium and iodine. The overall reaction is... 

The Monsanto process to acetic acid uses a rhodium-iodine-containing catalyst to convert a mixture of methanol and carbon monoxide under mild conditions and ambient pressure to very high (994-% based on methanol) yields of the product (Eq. 19.18) [16]. Several stages of distillation are required to recover the acetic acid (b.p. 118°C) in purities of 99.8% or... 

Chemistry of Acetic Acid by Carbonylation. Two processes have been commercialized for the carbonylation of methanol to acetic acid. BASF understood the possibility of a methanol and carbon monoxide process for acetic acid, using a cobalt- and iodine-based catalyst, since the early 1920s. But development was held back by the lack of suitable construction materials for the severe operating conditions and corrosive environment necessary. The operating temperature is 250°C (482 F) and the required pressure is 680 bars (10,000 psig). In the late 1950s, development of molyb-... 

The Monsanto process and the hi er pressure BASF processes have been reviewed [3,1012]. In the Monsanto process (Fig. 1) [9], methanol and carbon monoxide are fed to a continuous reactor system. The corrosive nature of iodine in an acid medium requires the use of a highly corrosion-resistant metal reactor (made of such material as Hastelloy C). The acetic acid produced is piuified by conventional distillation. The purified acetic acid is sent to a drying column. The dried acetic acid is removed as the bottom product and sent to the product column to reduce the small concentration of propanoic acid. The typical composition of the acetic acid from this process is [9] as follows ... 

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