Carbonylation Celanese process

In the BHC (Boots-Hoechst Celanese) process about 3500 tons of ibuprofen per annum are produced by Pd/PPh3-catalysed carbonylation of IBPE (Figure 9) in the presence of HC1, in organic media.446 447,459 461 However, a shortcoming of this process is the cumbersome separation of the Pd/PPh3 catalyst from the... 

Boots-Hoechst-Celanese process More recently, a shorter three-step catalytic route has been developed and is illustrated in the following scheme. Here, a Pd catalyzed carbonylation reaction is employed in the final step to introduce the carboxyl group. 

Celanese process for the manufacture of ibuprofen on a 3500-ton scale has been operating since 1992. In this process isobutyl benzene is acylated and then hydrogenated over a heterogeneous catalyst to give the appropriate precursor alcohol. This alcohol is then carbonylated. The overall synthetic scheme is shown by reaction 4.14. The conventional process for ibuprofen manufacture was based on six synthetic steps and generated a large amount of salt as a solid waste. 

A striking example of this is the manufacture of ibuprofen using the Boots Hoechst-Celanese process based on homogeneous catalytic carbonylation of p-isobutylphenyl-ethanol as a key step. 

Butane. Butane LPO has been a significant source for the commercial production of acetic acid and acetic anhydride for many years. At various times, plants have operated in the former USSR, Germany, Holland, the United States, and Canada. Only the Hoechst-Celanese Chemical Group, Inc. plants in Pampa, Texas, and Edmonton, Alberta, Canada, continue to operate. The Pampa plant, with a reported aimual production of 250,000 t/yr, represents about 15% of the 1994 installed U.S. capacity (212). Methanol carbonylation is now the dominant process for acetic acid production, but butane LPO in estabhshed plants remains competitive. 

Propane, 1-propanol, and heavy ends (the last are made by aldol condensation) are minor by-products of the hydroformylation step. A number of transition-metal carbonyls (qv), eg, Co, Fe, Ni, Rh, and Ir, have been used to cataly2e the oxo reaction, but cobalt and rhodium are the only economically practical choices. In the United States, Texas Eastman, Union Carbide, and Hoechst Celanese make 1-propanol by oxo technology (11). Texas Eastman, which had used conventional cobalt oxo technology with an HCo(CO)4 catalyst, switched to a phosphine-modified Rh catalyst ia 1989 (11) (see Oxo process). In Europe, 1-propanol is made by Hoechst AG and BASE AG (12). 

One approach which enables lower water concentrations to be used for rhodium-catalysed methanol carbonylation is the addition of iodide salts, especially lithium iodide, as exemplified by the Hoechst-Celanese Acid Optimisation (AO) technology [30]. Iodide salt promoters allow carbonylation rates to be achieved at low (< 4 M) [H2O] that are comparable with those in the conventional Monsanto process (where [H20] > 10 M) while maintaining catalyst stability. In the absence of an iodide salt promoter, lowering the water concentration would result in a decrease in the proportion of Rh existing as [Rh(CO)2l2] . However, in the iodide-promoted process, a higher concentration of methyl acetate is also employed, which reacts with the other components as shown in Eqs. 3, 7 and 8 ... 

The Boots Hoechst Celanese (BHC) ibuprofen process involves palladium-catalyzed carbonylation of a benzylic alcohol (IBPE). More recently, we performed this reaction in an aqueous biphasic system using Pd/tppts as the catalyst (Figure 9.6 tppts = triphenylphosphinetrisulfonate). This process has the advantage of easy removal of the catalyst, resulting in less contamination of the product. 

The major conventional processes for the production of acetic acid include the carbonylation of methanol (originally developed by Monsanto, and now carried out by several companies, such as Celanese-ACID OPTIMIZATION, BP-CATIVA, etc.), the liquid-phase oxidation of acetaldehyde, still carried out by a few companies, and the liquid-phase oxidation of n-butane and naphtha. More recent developments include the gas-phase oxidation of ethylene, developed by Showa Denko K.K., and the liquid-phase oxidation of butenes, developed by Wacker [2a],... 

AO Plus [Acid Optimisation Plus] A process for making acetic acid by carbonylating methanol. Based on the Monsanto Acetic Acid process, but an improved catalyst (rhodium with lithium iodide) permits operation at lower levels of water. Developed by Celanese in the 1980s and operated by that company in Clear Lake, TX. Residual iodide in the product is removed by the Silverguard process. 

Acetic acid is made by carbonylation of methanol. U.S. 5,001,259 (to Hoechst Celanese) describes changes to the reaction medium that improve catalyst stability and productivity. U.S. 3,769,329 (to Monsanto) describes the conventional process. Is it economically attractive to implement the changes proposed by the Hoechst patent in a new world-scale plant ... 

Since 1979, numerous reviews have appeared on the kinetics, mechanisms, and process chemistry of the metal-catalyzed methanol carbonylation reaction [11, 14-20], especially the Monsanto rhodium-catalyzed process. In this section, the traditional process chemistry as patented by Monsanto is discussed, with emphasis on some of the significant improvements that Monsanto s licensee, Celanese Chemicals (CC) has contributed to the technology. The iridium-based methanol carbonylation process recently commercialized by BP Chemicals Ltd. (BP) will be discussed also. 

Low-water operation can be accomplished with modifications to the process which include significant changes in the catalyst system [23]. The main catalytic cycle for high-water methanol carbonylation is still operative in the low-water process (see Section 2.1.2.1.1), but at low water concentration two other catalytic cycles influence the carbonylation rate. The incorporation of an inorganic or organic iodide as a catalyst co-promoter and stabilizer allows operation at optimum methyl acetate and water concentrations in the reactor. Carbonylation rates comparable with those realized previously at high water concentration (ca. 10 molar) are demonstrated at low reaction water concentrations (less than ca. 4 molar) in laboratory, pilot plant, and commercial units, with beneficial catalyst stability and product selectivity [23]. With this proprietary AO technology, the methanol carbonylation unit capacity at the Celanese Clear Lake (TX) facility has increased from 270 X 10 metric tons per year since start-up in 1978 to 1200 X 10 metric tons acetic acid per year in 2001 with very low capital investment [33]. This unit capacity includes a methanol-carbonylation acetic acid expansion of 200 X 10 metric tons per year in 2000 [33]. 

Based on the palladium-catalyzed carbonylation of l-(4-isobutylphenyl)etha-nol, which is produced via salt-free acylation of isobutylbenzene to 4-isobutyl-acetophenone and subsequent hydrogenation, the former Hoechst Celanese Corporation [33] developed an ecologically superior process to produce ibuprofen in a plant operating since 1992 on a 3500-ton scale (eq. (9) 1 bar = 0.1 MPa) [34]. 

Even though methanol carbonylation is the favored process for new acetic acid capacity today, existing paraffin oxidation plants remain quite competitive where coproducts can be marketed successfully [2, 3]. Over half the original capacity of acetic acid plants based on paraffin oxidation remains in use today. In North America, Hoechst Celanese operates two facilities using the butane oxidation process to make acetic acid. The reported 1994 capacity at Pampa, Texas, is 250000 metric tons/year, while that at monton, Alberta, is 75 000 metric tons/year [4]. There are two plants believed to be using the naphtha oxidation process to make acetic acid BP Chemicals in Hull, England, with a capacity of 210000 metric tons/year [5] and a state complex in Armenia (in the former USSR) with a capacity reported to be 35 000 metric tons/year [6]. 

A key property of catalytic processes is selectivity. Catalysis has revolutionized process chemistry by replacement of wasteful, unselective (i.e. multiple-product-forming) reactions with efficient, selective (i.e. one-product-dominating) ones. For example, selective catalytic methanol carbonylation (practiced by BP, BASF Monsanto, Eastman) has to a large extent substituted unselective non-catalytic n-butane oxidation (Celanese, and Union Carbide processes). 

One approach that enables the use of lower water concentrations for rhodium-complex-catalyzed methanol carbonylation is the addition of iodide salts, as exemplified by the Celanese Acid Optimization (AO Plus) technology [11,33]. A lithium iodide promoter allows carbonylation rates to be achieved that are comparable with those in the conventional Monsanto process—but at significantly lower water concentrations. The AO technology has been implemented to increase productivity at the Celanese facility in Clear Lake, Texas, and in a new 500 kt/a plant in Singapore. 

Carbonylation of methanol catalyzed by soluble Group IX transition metal complexes remains the dominant method for the commercial production of acetic acid. The Monsanto process stands as one of the major success stories of homogeneous catalysis, and for three decades it was the preferred technology because of the excellent activity and selectivity of the catalyst. It has been demonstrated by workers at Celanese, however, that addition of iodide salts can significantly benefit the process by improving the catalytic reaction rate and catalyst stability at low water concentrations. Many attempts have been made to enhance the activity of... 

The formation of C-C bonds is of key importance in organic synthesis. An important catalytic process for generating C-C bonds is provided by carbonylation. Most carbonylation reactions have a good atom economy, because most reagent atoms are transferred to the product. Therefore, there are some applications of carbonylation processes in fine chemistry, too. For example, the analgesic ibuprofen is produced by Hoechst-Celanese by carbonylation of a substituted alcohol with 100% atom efficiency according to Eq. (8-20) [7] ... 

In 1996, British Petroleum announced an alternative methanol carbonylation based on an Ir-Ru-Mel catalyst. Like the Celanese Rh-Li catalyst, it was a low water process, but used about half the methyl iodide. The use of Ir as a catalyst was not new and had been disclosed by Monsanto contemporaneously with its disclosure of the Rh catalyst. However, it had very complex kinetics and was more difficult to operate. British Petroleum achieved this event by discovering a way to overcome a major shortcoming in the Ir process disclosed by Monsanto. 

We will begin with the carbonylation of Mel which in situ is generated from MeOH for acetic acid production because of its industrial importance. Acetic acid is an important chemical commodity with a wide range of appUcations in organic chemistry. In organic synthesis, acetic acid is mainly used as a raw material for vinyl acetate monomers and acetic anhydride synthesis, as well as a solvent for producing terephthalic acid from xylene via the oxidation process. In 1998 the world s capacity of acetic acid production was approximately 7.8 milUon tons, of which more than 50 % were produced by BP-Amoco and Celanese. 

The first commercialized homogeneous methanol carbonylation route to acetic acid was established at BASF in 1955, using a homogeneous Ni catalyst. In 1960 BASF developed an improved process it used an iodide-promoted CO catalyst and operated at an elevated temperature (230 °C) and pressure (600 bar) [2]. In 1970, Monsanto commercialized an improved homogeneous methanol carbonylation process using a methyl-iodide-promoted Rh catalyst [3-5]. This process operated at much milder conditions (180-220 °C, 30-40 bar) than the BASF process and performed much better [6]. Celanese and Daicel further improved the Monsanto... 

Following the intense work on the carbonylation reaction during the 1920s by BASF and British Celanese [1], Reppe and his research group discovered that cobalt diiodide operating at 680 bar and 250 °C catalyzes this reaction [2, 3]. But it was necessary to solve harsh corrosion problems, until 1950, when highly resistant molybdenum/nickel alloys (whose trademark is Hastelloy ) were discovered and commercialized [1]. The process developed by BASF in 1960 was not selective as the yield in acetic acid was 90% based on methanol and 70% based on CO [4] due to the large amounts of CO2 coproduced by the water-gas shift (WGS) reaction (Eq. 20.2). 

On the other hand, the rhodium catalytic system with Lil stabilizer/promoter, allows operation at around 5% w/w, and the process has been developed by Celanese [15, 30]. Here, the signiflcant amount of methyl acetate reduces the concentration of HI, which is well known to lead to the formation of the [Rhl4(CO)2]" species. This complex is inactive during carbonylation but responsible for the WGS reaction (Eq. 20.2). The role of Lil is not only to stabilize the Li[Rhl2(CO)2] catalytic species but also to allow the two reactions in Equations 20.7 and 20.8. 

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