Industrial methanol carbonylation

The enthalpy of reaction, AH, is the other important thermodynamic parameter to consider. On its own, whether a reaction is exothermic or endothermic will not determine if a reaction is industrially feasible or not. Both exothermic and endothermic processes are known in industry, methanol carbonylation to acetic acid (Equation 3 AH —123 kJ/mol at 200°C), being an example of the former and the steam reforming of methane to synthesis gas, (Equation 4 AH + 227 kJ/mol at 800°C), being an example of the latter. 

The subject has been reviewed (37,38). Water may be added to the feed to suppress methyl acetate formation, but is probably not when operating on an industrial scale. Water increase methanol conversion, but it is involved in the unavoidable loss of carbon monoxide. A typical methanol carbonylation flow sheet is given in Figure 2. 

Acetic Acid. Methanol carbonylation has become the process of choice for production of this staple of the organic chemical industry, which is used in the manufacture of acetate fibers, acetic anhydride [108-24-7] and terephthaUc acid, and for fermentation (see Acetic acid and derivatives). 

Metha.no Ca.rbonyla.tion, An important industrial process cataly2ed by rhodium complexes in solution is methanol carbonylation to give acetic acid. 

Methanol carbonylation is one of only a few industrially important catalytic reactions for which the quantitative reaction kinetics is known (21). 

The ionic attachment strategy for catalytic methanol carbonylation has recently seen a resurgence of interest from both industry [49-53] and academic groups [54-57]. Most significantly, in 1998 Chiyoda and UOP announced their Acetica process, which uses a polyvinylpyridine resin tolerant of elevated temperatures and pressures [8,58]. The process attains increased... 

Carbonylation of methanol to form acetic acid has been performed industrially using carbonyl complexes of cobalt ( ) or rhodium (2 ) and iodide promoter in the liquid phase. Recently, it has been claimed that nickel carbonyl or other nickel compounds are effective catalysts for the reaction at pressure as low as 30 atm (2/4), For the rhodium catalyst, the conditions are fairly mild (175 C and 28 atm) and the product selectivity is excellent (99% based on methanol). However, the process has the disadvantages that the proven reserves of rhodium are quite limited in both location and quantity and that the reaction medium is highly corrosive. It is highly desirable, therefore, to develop a vapor phase process, which is free from the corrosion problem, utilizing a base metal catalyst. The authors have already reported that nickel on activated carbon exhibits excellent catalytic activity for the carbonylation of... 

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. 

Chiyoda and UOP jointly developed an improved methanol carbonyl-ation process on the basis of this supported rhodium complex catalyst the process is called the Acetica process. This process for the production of acetic acid has found several industrial applications in Asia. The process description emphasizes the use of a three-phase reactor, a bubble column, or gas-lift reactor. The reactor column contains a liquid, a solid catalyst, and a bubbling gas stream containing CO efficient dissolution of the gas in the liquid is ensured by the design, which minimizes gas-liquid mass transfer resistance. 

This development began to reduce steadily the capacities of acetaldehyde which previously had been made by oxidation of ethylene (Wacker-Hoechst process cf. Section 2.4.1) and converted to acetic acid (cf. Section 2.4.4). Moreover, the Monsanto process, the second-generation process for methanol carbonylation is now being followed by the third generation of highly efficient carbonylation processes, enabling acetic anhydride as well as acetic acid to be produced (cf Scheme 2 Tennessee-Eastman [36] and BP [37] processes). The most advanced process (Hoechst [40]) has so far not been implemented industrially because of neglects... 

Acetic acid is a key commodity building block [1], Its most important derivative, vinyl acetate monomer, is the largest and fastest growing outlet for acetic acid. It accounts for an estimated 40 % of the total global acetic acid consumption. The majority of the remaining worldwide acetic acid production is used to manufacture other acetate esters (i.e., cellulose acetates from acetic anhydride and ethyl, propyl, and butyl esters) and monoehloroacetic acid. Acetic acid is also used as a solvent in the manufacture of terephthalic acid [2] (cf. Section 2.8.1.2). Since Monsanto commercially introduced the rhodium- catalyzed carbonylation process Monsanto process ) in 1970, over 90 % of all new acetic acid capacity worldwide is produced by this process [2], Currently, more than 50 % of the annual world acetic acid capacity of 7 million metric tons is derived from the methanol carbonylation process [2]. The low-pressure reaction conditions, the high catalyst activity, and exceptional product selectivity are key factors for the success of this process in the acetic acid industry [13]. 

With continuing refinements to the rhodium-catalyzed, liquid-phase, methanol carbonylation technology (see Section 2.1.2.1.5), this industrial process will remain the most competitive route to acetic acid, well into the 21 st century. 

With the permission of the author [3], we borrow here data (Table 1) which indicates the production capacity of the major industrial processes using oxygen for functionalizing hydrocarbons. The production of acetic acid should be added to the list, although 60% of its 6.1 million t/year total world capacity (to reach 67% in the next future) is due to the Monsanto process (methanol carbonylation) [4]. Only the rest (2.4 million t/year) is produced by oxidation of butane or other alkanes or acetaldehyde or, for a small proportion, hy the Showa Denko process (oxidation of ethylene). 

The original mechanistic investigations of iridium/iodide-catalyzed methanol carbonylation were conducted by Forster [6,7,19,115,132-135]. Some other studies were also reported in the late 1970s [136-138]. Since the 1990s, interest in the fundamental aspects of the reaction mechanism has been rekindled by the industrial significance of iridium-complex catalysts. 

The synthesis of acetaldehyde, essentially intended for conversion to acetic acid, was the main outlet for ethanol until a few years ago. The industrial development of methanol carbonylation to acetic arid has relegated this application to the background. Ethanol is chiefly used today as a solvent and for the preparation of esters (ethyl acetate, ethyl chloride). It is also employed in cosmetics and pharmaceuticals. 

In 1970, the discovery of these new organo-soluble catalysts based on Rh, Pd, or Pt was generally considered unfeasible for industrial processes because of the prohibitive price of the metals involved. However, the hgh activity and productivity of these catalysts made possible production levels of 100000 ty 1 with only a few dozen kilograms of precious metals needed as inventory by each single plant. Thus, the amount of precious metal involved represents only a minor part of the investment and the manufacturing costs, i.e., the price of the metal was not an important factor in the production unit cost, provided that its usage occurred without any loss. In 1972 this hypothesis was confirmed by Monsanto and its commercialization of the important process to generate acetic acid by methanol carbonylation [16]. 

This reaction mechanism is supported by model studies. Paricularly advantageous are the mild reaction conditions (30-40 bar, 150-200°C) and the high selectivity with respect to methanol (99 %) and CO (> 90 %) compared to the older cobalt process. Methanol carbonylation is one of the few industrially important catalytic reactions whose kinetics are known in full [7]. 

Despite the high tonnages of petrochemicals, the chemical industry as a whole consumes rather less than 10% of available petroleum and natural gas hydrocarbons as feedstocks, with possibly a further 4-5% as fuel. For comparison, the current consumption of gasoline alone in Western Europe exceeds 120 Mt per annum, while the U.S. figure is over 300 Mt per annum. Hence, prices of individual hydrocarbon feedstocks are largely determined by other forces the most economic feedstock/route combination has frequently changed with time, and may differ in different parts of the world. Furthermore, while a specific route may be preferred for new plants, older plants for which the capital is largely written off may well remain economically viable. Finally, special situations may prompt individual solutions. For example, Rhone-Poulenc in France derive the carbon monoxide for a very modern acetic acid plant, based on Monsanto s methanol carbonylation process, from the partial... 

The application of SIL catalysis for continuous methanol carbonylation was reported [33]. The authors developed a siHca-SIL rhodium iodide Monsanto-type catalyst system, [BMIM][Rh(C0)2l2]-[BMIM]I-Si02, which used less catalyst material and allowed a simple process design. Compared to conventional and IL-based carbonylation systems, the advantage of this process was without recirculation and pressure change of tlie catalytic system. Moreover, the SIL catalyst exhibited excellent activity and selectivity toward acetyl products in fixed-bed, continuous gas-phase methanol carbonylation at industrially relevant reaction conditions. 

---