Methanol carbonylation technology

In 1996 BP announced the commercialization of their version of a low-water methanol carbonylation technology named Cativa based upon a promoted iridium catalyst. The Cativa process replaced the high-water Monsanto process which had been used by BP. 

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. 

The worldwide production of acetic acid is more than 10 million tons per year of which about 80% is based on methanol carbonylation technology. Methanol can be carbonylated to give acetic acid by using metal complexes of cobalt or rhodium or iridium as catalysts. All the three processes require the presence of some water and methyl iodide in the... 

In 1996, BP Chemicals introduced Ir-based methanol carbonylation technology called Cativa . The Ir-based process operates under conditions similar to that of the Monsanto process. However, it has a better tolerance to lower CO partial pressures and to low water content. This is advantageous because separation of a large amount of water from acetic acid by distillation adds to the cost of its manufacturing. In the Ir-based process, apromoter has to be used for increasing catalytic activity. It can be operated with water content as low as 5%. 

MEK is also produced as a by-product in the Hquid-phase oxidation of / -butane to acetic acid (31—33). This route was once the most favored route to acetic acid, however, since the early 1980s the acetic acid technology of choice has become methanol carbonylation, and MEK growth by this path is doubtflil. 

MMA from Propyne. Advances in catalytic carbonylation technology by Shell researchers have led to the development of a single-step process for producing MMA from propyne [74-99-7] (methyl acetylene), carbon monoxide, and methanol (76—82). 

Methanol Carbonylation without Mel. While resolving the selectivity issue in ethylene carbonylation was exciting, the observations indicating that the reaction was likely proceeding via a nncleophihc reaction between Rh and the ionic liqnid and did not require EtI provided an even more exciting opportnnity. If a nncleophihc mechanism is operahve, it is likely that we conld extend the technology to the much more commercially important carbonylahon of methanol. 

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 ... 

Abstract The principle of catalytic SILP materials involves surface modification of a porous solid material by an ionic liquid coating. Ionic liquids are salts with melting points below 100 °C, generally characterized by extremely low volatilities. In the examples described in this paper, the ionic liquid coating contains a homogeneously dissolved Rh-complex and constitutes a uniform, thin film, which itself displays the catalytic reactivity in the system. Continuous fixed-bed reactor technology has been applied successfully to demonstrate the feasibility of catalytic SILP materials for propene hydroformylation and methanol carbonylation. 

In SILP carbonylation we have introduced a new methanol carbonylation SILP Monsanto catalyst, which is different from present catalytic alcohol carbonylation technologies, by using an ionic liquid as reaction medium and by offering an efficient use of the dispersed ionic liquid-based rhodium-iodide complex catalyst phase. In perspective the introduced fixed-bed SILP carbonylation process design requires a smaller reactor size than existing technology in order to obtain the same productivity, which makes the SILP carbonylation concept potentially interesting for technical applications. 

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. 

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-... 

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]. 

In the 1990s, BP re-examined the iridium-catalyzed methanol carbonylation chemistry first discovered by Paulik and Roth and later defined in more detail by Forster [20]. The thrust of this research was to identify an improved methanol carbonylation process using Ir as an alternative to Rh. This re-examination by BP led to the development of a low-water iridium-catalyzed process called Cativa [20]. Several advantages were identified in this process over the Rh-catalyzed high-water Monsanto technology. In particular, the Ir catalyst provides high carbonylation rates at low water concentrations with excellent catalyst stability (less prone to precipitation). The catalyst system does not require high levels of iodide salts to stabilize the catalyst. Fewer by-products are formed, such as propionic acid and acetaldehyde condensation products which can lead to low levels of unsaturated aldehydes and heavy alkyl iodides. Also, CO efficiency is improved. 

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. 

A remarkable step change to existing technology has been 1996 the introduction of the Cativa technology by BP Chemicals (now BP Amoco). This process incorporated the first commercial use of iridimn (promoted by iodine, Ru-salt etc.), rather than rhodimn, as a catalyst for methanol carbonylation. The main improvements of the process are much higher reactivity (45 mol L h, Rh 10-15 mol L h ) coupled with low by-product formation and lower energy requirements for the purification of the product acid. 

This process still operates today, but is only viable due to the added value of the by-products and can not compete with modem methanol carbonylation for acetic acid production. There is continued interested even today in the oxidation of hydrocarbons, especially ethane, but these technologies are not competitive with modem methanol carbonylation for the generation of acetic acid. 

These two derivatives of the earlier Monsanto technology are the predominant acetic acid processes today and are equally competitive in the market place. Since the advent of the Monsanto Acetic Acid process almost all new acetic acid plants are based on methanol carbonylation and acetaldehyde oxidation has been nearly phased out as a source of acetic acid. The advances in Rh and Ir based methanol carbonylation have recently been reviewed. ... 

Subsequent developments of Eastman carbonylation technology are yet to be commercialized production routes to acetaldehyde, propionic acid, propionic anhydride, methacrylates, and acrylates (29). It is also relevant to note that dimethyl ether, readily available from methanol by dehydration, has recently achieved some prominence as a suitable raw material in carbonylation technology, via the intermediacy of methyl acetate and acetic anhydride in the case of acetic anhydride manufacture. It also offers the advantage of processing under totally anhydrous conditions. 

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