The Celanese Process

The high concentration of LiOAc in the medium was proposed to induce the formation of a [Rhl2(CO)2(OAc)] pentacoordinated dianionic species, which would activate the methyl iodide more rapidly than would the [Rhl2(CO)2] species [19]. The net result of the Hoechst Celanese process is a better selectivity with regards to CO, since the WGS reaction is reduced by one order of magnitude [17]. 

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On the other hand, the catalytic oxidation of a n-butane, using either cobalt or manganese acetate, produces acetic acid at 75-80% yield. Byproducts of commercial value are obtained in variable amounts. In the Celanese process, the oxidation reaction is performed at a temperature range of 150-225°C and a pressure of approximately 55 atmospheres. ... 

The main promoters of this technology are Celanese, whose fust plant at Pampa, Texas (230,000 t/ycar) dates from 1952, and Huls, whose Marl plant (40,000 t/year) is now shut down. The Celanese process involves oxidation in the presence of cobalt or manganese salts, and in the Huls process conversion takes place without catalyst. Other process licensors include Distillers. Umon Carbide, etc. 

In 1960, quickly after the introduction of the Celanese process, Wacker-Chemie commercialized a liquid phase vinyl acetate process which represented and extension of its earlier acetaldehyde process wherein acetic acid was simply substituted for water. (See equation [19]. This chemical transformation is also referred to as oxidative acetoxylation.) As shown in Figure 2, wherein R=Ac, the liquid phase oxidative acetoxylation of ethylene utilized the same catalytic cycle as the Wacker-Chemie acetaldehyde process. 

Ketene Process. The ketene process based on acetic acid or acetone as the raw material was developed by B. F. Goodrich (81) and Celanese (82). It is no longer used commercially because the intermediate P-propiolactone is suspected to be a carcinogen (83). In addition, it cannot compete with the improved propylene oxidation process (see Ketenes, ketene dimers, and related substances). 

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. 

Propanol has been manufactured by hydroformylation of ethylene (qv) (see Oxo process) followed by hydrogenation of propionaldehyde or propanal and as a by-product of vapor-phase oxidation of propane (see Hydrocarbon oxidation). Celanese operated the only commercial vapor-phase oxidation faciUty at Bishop, Texas. Since this faciUty was shut down ia 1973 (5,6), hydroformylation or 0x0 technology has been the principal process for commercial manufacture of 1-propanol ia the United States and Europe. Sasol ia South Africa makes 1-propanol by Fischer-Tropsch chemistry (7). Some attempts have been made to hydrate propylene ia an anti-Markovnikoff fashion to produce 1-propanol (8—10). However, these attempts have not been commercially successful. 

Economic Aspects. U.S. capacity for production of merchant sodium dithionite (soHds basis) was estimated at 93,000 metric tons in 1994. There are three North American producers of sodium dithionite. Hoechst Celanese is the largest producer (68,000 tons capacity) with two formate production locations and one zinc process location. Olin (25,000 t capacity) produces solution product only at two locations using both the amalgam and electrochemical processes. In 1994, Vulcan started a small solution plant in Wisconsin using the Olin electrochemical process. In addition, it is estimated that 13,000 t/yr is produced at U.S. pulp mills using the Borol process from sulfur dioxide and sodium borohydride. Growth is estimated at 2—3%/yr. The... 

Formaldehyde is also produced by the oxidation of light petroleum gases, a process which also yields methanol and acetaldehyde. This process is currently used in the Celanese Corporation plant for the production of Celcon. 

Separators made by the dry process are available from Hoechst Celanese Corporation and Ube. The Celgard microporous... 

Eventually, the spent catalyst solution has to leave the oxo loop for work-up. The Ruhrchemie works of Celanese AG in Oberhausen (Germany) operate several rhodium-based oxo processes besides the well-known Ruhrchemie/Rhone-Poulenc process (RCF1/RP, the described low pressure oxo process with TPPTS-modified Rh catalyst), there are the Ruhrchemie process with an unmodified Rh catalyst at high pressure (comparable to the late ICI process [76] this variant is for the benefit of a high iso/n ratio... 

In many applications acetic acid is used as the anhydride and the synthesis of the latter is therefore equally important. In the 1970 s Halcon (now Eastman) and Hoechst (now Celanese) developed a process for the conversion of methyl acetate and carbon monoxide to acetic anhydride. The process has been on stream since 1983 and with an annual production of several 100,000 tons, together with some 10-20% acetic acid. The reaction is carried out under similar conditions as the Monsanto process, and also uses methyl iodide as the "activator" for the methyl group. 

The tppts process has been commercialised by Ruhrchemie (now Celanese), after the initial work conducted by workers at Rhone-Poulenc, for the production of butanal from propene. Since 1995 Hoechst (now Celanese) also operates a hydroformylation plant for 1-butene. The partly isomerised, unconverted butenes are not recycled but sent to a reactor containing a cobalt catalyst. The two-phase process is not suited for higher alkenes because of the... 

Hoechst-Ruhrchemie (now Celanese) reported that no detectable losses of rhodium occur. We assume that propene is stripped from the aldehyde product and finally distillation of the aldehyde is conducted to separate the branched (8%) and linear product (92%). Note that the amounts of water lost in the aldehyde phase have to be replaced. Note also that by-products arising from aldol condensation, if any, are separated from the catalyst together with the product. These heavy ends end up in the bottom of the product distillation, which is advantageous, as the bottom can be sent to an incinerator. In processes such as the Shell process (Figure 7.6), the heavy end is a mixture of... 

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. 

Butane from natural gas is cheap and abundant in the United States, where it is used as an important feedstock for the synthesis of acetic acid. Since acetic acid is the most stable oxidation product from butane, the transformation is carried out at high butane conversions. In the industrial processes (Celanese, Hills), butane is oxidized by air in an acetic acid solution containing a cobalt catalyst (stearate, naphthenate) at 180-190 °C and 50-70 atm.361,557 The AcOH yield is about 40-45% for ca. 30% butane conversion. By-products include C02 and formic, propionic and succinic acids, which are vaporized. The other by-products are recycled for acetic acid synthesis. Light naphthas can be used instead of butane as acetic adic feedstock, and are oxidized under similar conditions in Europe where natural gas is less abundant (Distillers and BP processes). Acetic acid can also be obtained with much higher selectivity (95-97%) from the oxidation of acetaldehyde by air at 60 °C and atmospheric pressure in an acetic acid solution and in the presence of cobalt acetate.361,558... 

Because ibuprofen has been a successful drug on the market for almost 30 years with no patent protection since 1985, there is a widespread competition for commercial production of this product throughout the world. As a result, several practical and economical industrial processes for the manufacture of racemic ibuprofen (14) have been developed and are in operation on commercial scales.38 Most of these processes start with isobutylbenzene (15) and go through an isobutylstyrene3 4 or an acetophenone intermediate.42 The most efficient route is believed to be the Boots-Hoechst-Celanese process, which involves 3 steps from isobutylbenzene, all catalytic, and is 100% atom-efficient (Scheme 6.1).43 44... 

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. 

Three commercial homogeneous catalytic processes for the hydroformyla-tion reaction deserve a comparative study. Two of these involve the use of cobalt complexes as catalysts. In the old process a cobalt salt was used. In the modihed current version, a cobalt salt plus a tertiary phosphine are used as the catalyst precursors. The third process uses a rhodium salt with a tertiary phosphine as the catalyst precursor. Ruhrchemie/Rhone-Poulenc, Mitsubishi-Kasei, Union Carbide, and Celanese use the rhodium-based hydroformylation process. The phosphine-modihed cobalt-based system was developed by Shell specih-cally for linear alcohol synthesis (see Section 7.4.1). The old unmodihed cobalt process is of interest mainly for comparison. Some of the process parameters are compared in Table 5.1. 

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. 

The industrial process for the vapor-phase manufacture of vinyl acetate monomer is quite common (Daniels, 1989) and utilizes widely available raw materials. Vinyl acetate is used chiefly as a monomer to make polyvinyl acetate and other copolymers. Hoechst-Celanese, Union Carbide, and Quantum Chemical are reported U.S. manufacturers. DuPont also currently operates a vinyl acetate process at its plant in LaPorte, Texas. To protect any proprietary DuPont information, all of the physical property and kinetic data, process flowsheet information, and modeling formulation in the published paper come from sources... 

In the 1990s the Hoechst Celanese Corporation (together with the Boots company they formed the BHC process to prepare and market ibuprofen, 1.16) developed a new three-stage process (Scheme 1.9), with an atom economy of 77.4%. 

A recent study indicates that if the Wacker process proves to be substantially cheaper than the acetylene route, no more vinyl acetate plants will be built in the United States, based on the latter process (38). Table XV gives estimated production costs for manufacturing vinyl acetate. Several companies are building or have already built plants to manufacture vinyl acetate from ethylene. These include Distillers Co., Ltd., British Celanese, Imperial Chemical Industries, and Celanese Corp., to name only a few. 

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 ... 

Back in 1974, Celanese (later Hoechst Celanese) started the production of bu-tanals by a process [192] which closely resembles the LPO one subsequently (1976) established by UCC. It is an open question which of the two companies was the really first to introduce low-pressure hydroformylation, as UCC claims to have run an ethylene hydroformylation unit at Ponce before the start-up of the propene unit at the same site [222]. There are only minor differences if any, between the Celanese and the UCC process [192]. 

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]. 

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