Acetic acid BASF high pressure process

Chemistry of the BASF High Pressure Acetic Acid Process. The chemistry for the BASF high pressure process is shown in Eqs. (14)-(19). The reaction takes place in the gas phase at 250°C (482 F) and 680 bars (10,000 psig). 

Meanwhile, Wacker Chemie developed the palladium-copper-catalyzed oxidative hydration of ethylene to acetaldehyde. In 1965 BASF described a high-pressure process for the carbonylation of methanol to acetic acid using an iodide-promoted cobalt catalyst (/, 2), and then in 1968, Paulik and Roth of Monsanto Company announced the discovery of a low-pressure carbonylation of methanol using an iodide-promoted rhodium or iridium catalyst (J). In 1970 Monsanto started up a large plant based on the rhodium catalyst. 

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). 

The carbonylation of methanol is currently one of the major routes for acetic acid production. The basic liquid-phase process developed by BASF uses a cobalt catalyst at 250°C and a high pressure of about 70... 

Methanol process. BASF introduced high-pressure technology way back in I960 to make acetic acid out of methanol and carbon monoxide instead of ethylene. Monsanto subsequently improved the process by catalysis, using an iodide-promoted rhodium catalyst. This permits operations at much lower pressures and temperatures. The methanol and carbon monoxide, of course, come from a synthesis gas plant. 

The concept that acetic acid can be prepared by carbonylation originated in use of routine acids. Carbonylation of methanol was first practiced in a high temperature and pressure process using boron trifluoride or phosphoric acid. A carbon monoxide pressure of 10,000 psi at 300 C was needed for the reaction (10). Metal salts came to replace acids as carbonylation catalysts. Carbonylation of methanol using a metal carbonyl catalyst was first discovered by Reppe and practised later by BASF. However, the process again required high pressure, 7500-10,000 psi, and the selectivity was low (11-14). 

Originally, acetic acid was produced by fermentation this is still the major process for the production of vinegar. Modern production is by acetaldehyde oxidation, liquid phase hydrocarbon oxidation and preferentially by methanol carbonylation. The latter process is to be preferred because of the low raw material and energy costs. As early as 1913 BASF described the carbonylation of methanol at high temperature and pressure ... 

In the BASF process the 1,2-diacetate is the substrate for the hydroformylation step. It can be prepared either directly via oxidative acetoxylation of butadiene using a selenium catalyst or via PtCl4-catalyzed isomerization of the 1,4-diacetate (see above). The latter reaction affords the 1,2-diacetate in 95% yield. The hydroformylation step is carried out with a rhodium catalyst without phosphine ligands since the branched aldehyde is the desired product (phosphine ligands promote the formation of linear aldehydes). Relatively high pressures and temperatures are used and the desired branched aldehyde predominates. The product mixture is then treated with sodium acetate in acetic acid to effect selective elimination of acetic acid from the branched aldehyde, giving the desired C5 aldehyde. 

The carbonylation of methanol to acetic acid and methyl acetate, and the carbonylation of the latter to acetic anhydride, was found by W. Reppe at BASF in the 1940s, using iodide-promoted cobalt salts as catalyst precursors. This process required very high pressure (600 bar) as well as high temperatures (230°C) and gave ca. 90% selectivity for acetic acid. 

The low-pressure acetic acid process was developed by Monsanto in the late 1960s and proved successful with commercialization of a plant producing 140 X 10 metric tons per year in 1970 at the Texas City (TX, USA) site [21]. The development of this technology occurred after the commercial implementation by BASF of the cobalt-catalyzed high-pressure methanol carbonylation process [22]. Both carbonylation processes were developed to utilize carbon monoxide and methanol as alternative raw materials, derived from synthesis gas, to compete with the ethylene-based acetaldehyde oxidation and saturated hydrocarbon oxidation processes (cf. Sections 2.4.1 and 2.8.1.1). Once the Monsanto process was commercialized, the cobalt-catalyzed process became noncom-... 

Before 1970, acetic acid was manufactured by the BASF process utilizing cobalt-based catalysts, and high temperatures and pressures. Replacement of this procedure by the Monsanto process brought advantages of milder conditions and greater selectivity (Table 25.3). The Monsanto process uses a rhodium-based catalyst, and involves two interrelated... 

In the BASF carbonylation process, methanol and CO are converted in the liquid phase (solvent dimethyl ether, water) at 250 °C and 700bar. The reaction rate depends strongly on the concentration of methanol and the partial pressure of CO. The proposed mechanism for the Co-catalyzed carbonylation of methanol is presented in detail in Example 16.6.2. Acetic acid yields are typically 90% (based on methanol) and 70% (based on carbon monoxide). Selectivities are high, with the production of 100 kg of acetic acid affording 4 kg by-products (mainly CO2, CH4, ethanol, acetaldehyde, and propionic acid). 

In the BASF process, methanol and CO are converted in the liquid phase by a homogeneous Co-based catalyst. The reaction takes place in a high-pressure Hastelloy reactor. In recent decades the BASF process has been increasingly replaced by low-pressure alternatives mainly due to lower investment and operating costs. In the low-pressure Monsanto process methanol and CO react continuously in liquid phase in the presence of a Rhl2 catalyst. In 1996, BP developed a new attractive catalyst based on iridium (Cativa process) the oxidative addition of methyl iodide to iridium is 150-times faster than to rhodium. The search for acetic acid production processes with even lower raw material costs has led to attempts to produce acetic acid by ethane oxidation. In the near future ethane oxidation will most likely not compete with methanol carbonylation (even though ethane is a very cheap and attractive raw material) because of the low ethane conversions, product inhibition problems, and a large variety of by-products. 

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 ... 

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. 

The discovoy of methanol carbonylation to acetic acid, with cobalt iodide as the catalyst, goes back to 1913. In 1960 BASF operated a small Co-based methanol carbonylation plant. The Co-catalyzed process requires high pressure and temperature ( 00 bar, 230°C) and is of moderate selectivity. The selectivity with respect to CO and methanol are -70% and -90%, respectively. Acetic acid production is accompanied by unwanted side products such as acetaldehyde, ethanol, and propionic acid. 

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