Acetic acid process

Conversion of acetaldehyde is typically more than 90% and the selectivity to acetic acid is higher than 95%. Stainless steel must be used in constmcting the plant. This is an estabHshed process and most of the engineering is weU-understood. The problems that exist are related to more extensively automating control of the system, notably at start-up and shutdown, although even these matters have been largely solved. This route is the most rehable of acetic acid processes. 

The Acetic Acid Process. Prior to the energy crisis of the 1970s, acetic anhydride was manufactured by thermal decomposition of acetic acid at pressures of 15—20 kPa (2.2—2.9 psi) (22), beginning with the first step ... 

Acetic Acid and Anhydride. Synthesis of acetic acid by carbonylation of methanol is another important homogeneous catalytic reaction. The Monsanto acetic acid process developed in the late 1960s is the best known variant of the process. 

Ca.ta.lysis, The readily accessible +1 and +3 oxidation states of rhodium make it a useful catalyst. There are several reviews of the catalytic properties of rhodium available (130—132). Rhodium-catalyzed methanol carbonylation (Monsanto process) accounted for 81% of worldwide acetic acid by 1988 (133). The Monsanto acetic acid process is carried out at 175°0 and 1.5 MPa (200 psi). Rhodium is introduced as RhCl3 but is likely reduced in a water... 

Hoechst Celanese officials said it was too early to decide whether to rebuild the butane reactor, install a newer methanol-to-acetic acid process, or start up a standby acetic acid facility at Hay City, TX, to replace the idled 350-million-lb per year acetic acid plant. 

Process names which combine the name of a company with the name of a chemical, e.g. the Monsanto Acetic Acid process, have mostly been excluded because they are self-explanatory and can be found in the encyclopaedias. 

As a case study an acetic acid process has been given. Acetic acid is produced by a liquid-phase methanol carbonylation. Acetic acid is formed by the reaction between methanol and carbon monoxide which is catalysed by rhodium iodocarbonyl catalyst. The process diagram is shown in Figure 7. 

Figure 7. Flowsheet of the acetic acid process 1) reactor, 2) separator, 3) scrubber, 4) light ends separator, 5) drying column, 6) product recovery, 7) product finishing.

For the safety comparison analysis the ISBL of acetic acid process was divided into two steps reaction section (reactor, separator, scrubber) and distillation train. Both steps were handled separately during the analysis. The analysis of the data and the results are presented in the Table 26 for reaction section and in the Table 27 for the distillation train. 

The Safe Process Structure Subindex for the acetic acid process is discussed in more detail in Chapter 13.2. 

Table 26. Safety analysis for the reaction section of the acetic acid process.

For the evaluation of the safe process structure of the acetic acid process (Ch. 12, Fig. 7) CBR database searches were done on two levels (Heikkila et al., 1998). First level was the acetic acid process as a whole. On the second level the reactor system was studied in more detail. 

First the acetic acid process was studied as a whole to find out if the alternative processes have differences in the safety on the conceptual (i.e. process) level. The search (Table 28) found cases for carbonylation and oxidation processes (Table 29). It can be seen that there has been explosions and fires on both types of plants. The explosion in the carbonylation plant was due to static electricity in... 

Table 28. Input data of the search for the acetic acid process.

Monoterpenoid ketones, 24 536-541 Monoterpenoids, 24 468, 470, 472, 484-541 Monothiocarboxylic acids, 23 739 Monotropic phase transitions, 15 101 Monounsaturated fatty acids, 10 830 Monounsaturated olefins, hydrogenation of, 26 879-880 Monovinylacetylene, 1 230 Monsanto acetic acid process, 19 646 Monsanto adiponitrile process, 17 236 Monsanto aluminum chloride-based Alkylation process, 23 333 Monsanto Prism separator, 16 21 Monsanto process (Lummus-UOP Classic process), 16 74 23 339, 341 Monsanto-Washington University collaboration, 24 390, 400-401 Montanic acid... 

Reactions 7 and 8 involve oxidation of rhodium(I) to rhodium(III). Reaction 8 can also be written as an oxidative addition of I2 (formed thermally from 2 HI) to the Rh(I) complex. Rhodium(III) iodide (for convenience written as an anionic carbonyl complex) may precipitate from the reaction medium. It has to be converted to rhodium(I) again. This is done in the acetic acid process by water and carbon monoxide. 

This protonation may, besides the desired CO insertion, also form inactive trivalent rhodium iodides. In the Monsanto acetic acid process the addition of the reducing agent H2 is not required for two reasons ... 

In the Monsanto acetic acid process (not in the Hoechst version) there is a lot of water present through the equilibrium between CH3OH and HI... 

Monsanto, 34 208 acetic acid process, 34 85 proposed mechanism for, 34 89 Monte Carlo simulations... 

In this connection the reduction of acetic acid to ethanol by Humphreys Glasgow, Davy McKee and BASF must be quoted as an attractive route to ethanol. This route combines the high selectivity of the Monsanto acetic acid process with a hydrogenation step. 

The anhyd salt decomp when heated at moderate temp. It is sol in w ale. Can be prepd by neutralizing the pyroligneous liquors from hardwood distn with Ca carbonate followed by evapn, drying and purifica-t ior., Until about 1932 it was the only important source for prepn of acetone and acetic acid but the development of the Weiz-mann fermentation process (yielding acetone and synthetic acetic acid), as well as direct acetic acid processes have relegated the salt to a place of minor industrial importance... 

Fig Reaction steps involved in the catalytic Monsanto acetic acid process. 

Organometallic compounds are used widely as homogeneous catalysts in the chemical industry. For example, if the alkene insertion reaction continues with further alkene inserting into the M C bond, it can form the basis for catalytic alkene polymerisation. Other catalytic cycles may include oxidative addition and reductive elimination steps. Figure above shows the steps involved in the Monsanto acetic acid process, which performs the conversion... 

Transition-metal-catalyzed carbonylation reactions are useful one-carbon homologation techniques in organic synthesis, involving industrially important processes, for example, Fisher-Tropsch reaction, Monsanto acetic acid process, and hydroformylation (oxo reaction) [25]. 

Flash distillation of the product where very high vacuums are applied at moderate temperatures so the solvents and products vaporize, which are collected and condensed in a condenser, leaving the catalyst behind in the vessel. In the Monsanto acetic acid process, the catalyst rhodium iodide is left behind in the reboiler once the products are flashed off (see Section 4.9). 

In the late 1960s, workers at Monsanto began studies into the carbonyla-tion of methanol to acetic acid. The process they developed (9-11), now known worldwide as the Monsanto acetic acid process, is based on an iodide-promoted rhodium catalyst system. Because of the high efficiency and selectivity of the reaction (typical commercial operating conditions are 150-200°C and 30-100 atm, giving selectivities >99% based on CH3OH),... 

Mankind has produced acetic acid for many thousand years but the traditional and green fermentation methods cannot provide the large amounts of acetic acid that are required by today s society. As early as 1960 a 100% atom efficient cobalt-catalyzed industrial synthesis of acetic acid was introduced by BASF, shortly afterwards followed by the Monsanto rhodium-catalyzed low-pressure acetic acid process (Scheme 5.36) the name explains one of the advantages of the rhodium-catalyzed process over the cobalt-catalyzed one [61, 67]. These processes are rather similar and consist of two catalytic cycles. An activation of methanol as methyl iodide, which is catalytic, since the HI is recaptured by hydrolysis of acetyl iodide to the final product after its release from the transition metal catalyst, starts the process. The transition metal catalyst reacts with methyl iodide in an oxidative addition, then catalyzes the carbonylation via a migration of the methyl group, the "insertion reaction". Subsequent reductive elimination releases the acetyl iodide. While both processes are, on paper, 100%... 

Reference "Acetic Acid Process Catalyzed by lonically Immobilized Rhodium Complex to Solid Resin Support," Journal of Chemical Engineering of Japan, Vol. 37, 4, pp. 536-545 (2004)... 

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. 

Cativa A process for making acetic acid by reacting methanol with carbon monoxide (carbonylation). The catalyst contains iridium acetate with promoters. Developed joindy by BP Chemicals, Hull, UK, and the University of Sheffield. First announced in 1996 and installed between 1995 and 1999 in four plants that had been using the former Monsanto acetic acid process. The first plant designed for the process was built by BP Petronas in Malaysia in 2000. A joint venture of BP with Sinopec used the process in a plant expansion in Chongqing, China, in 2005, and planned to build another plant in Nanjing, for completion in 2007. 

Process names that combine the name of a company with the name of a chemical (e.g., the Monsanto Acetic Acid process) have mostly been excluded because they are self-explanatory and can be found in the encyclopedias. Some companies (e.g., Lurgi, Texaco) are best known for one process, even though they may have developed many others in general, only their most famous one is included here under the company name. Their other processes are included if they have special names. Process names that combine the names of two collaborating companies (e.g., Mobil/Badger) have mostly been included. Company names are usually given in the styles in use at the times of their respective inventions, as given in patent applications. 

The appeal of an acetic acid process, based on ethane oxidation, lies mostly in the absence of the need for the energy demanding step for syngas production. On the other hand, it has to compete not only with the well established methanol carbonylation (Section 4.2), but also with the current utilization of ethane in steam crackers for ethylene manufacture. In fact, ethane feedstock becomes attractive for acetic acid production if it is locally abundant and can be supplied at minimal cost, e.g., in a petrochemical complex close to a large gas field. The construction of a semi-commercial plant of 30 kt/a in the Persian Gulf region has been announced. 

The WGSR is normally practised as a heterogeneously metal-catalyzed reaction Fe is the most commonly used catalyst. However other metals are also active, for example the homogeneous Rh/H catalyst in the Monsanto acetic acid process (Section 4.2.4) concurrently catalyzes the WGSR via a Rh(I)/ Rh(III) cycle (Equations 8 and 9),... 

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