Acetic acid, production catalyst

The arylhydrazone 29 of a 2-substituted cyclohexanone gave a mixture of indolenine 30 and tetrahydrocarbazole 30. It was reported that the relative amounts of 30 and 31 produced depended upon the catalyst employed. For example, glacial acetic acid as catalyst provided largely 30, whereas aqueous sulfuric acid gave 31 as the major product. 

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... 

A typical configuration for a methanol carbonylation plant is shown in Fig. 1. The feedstocks (MeOH and CO) are fed to the reactor vessel on a continuous basis. In the initial product separation step, the reaction mixture is passed from the reactor into a flash-tank where the pressure is reduced to induce vapourisation of most of the volatiles. The catalyst remains dissolved in the liquid phase and is recycled back to the reactor vessel. The vapour from the flash-tank is directed into a distillation train which removes methyl iodide, water and heavier by-products (e.g. propionic acid) from the acetic acid product. 

Figure 2 illustrates the effect of incremental changes in ruthenium catalyst content upon the production of acetic acid and its C1--C2 alkyl acetate esters. Acetic acid production is maximized at Ru/Co ratios of ca. 1.0 1.5 however, the data in Figure 2 do show an approximate first order dependence of lOAc (acetic acid plus acetate esters) upon initial ruthenium content—at least up to the 2/1, Ru/Co stoichiometry under the chosen conditions. Selectivity to acetic acid in the liquid product peaks at 92 wt % (carbon efficiency 95 mol %) for a catalyst combination with initially low Ru/Co ratios (e.g. 1 4). The formation of C1-C2 alkanols and their acetate esters rapidly exceeds acetic acid productivity when the Ru/Co atomic ratio is raised above 1.5, although two-carbon oxygenates continue to be the predominant fraction. Smaller quantities of glycol may also be in evidence. 

For Reaction 4 to proceed selectively it will be necessary that Reaction 5c proceeds faster than, or concertedly with. Reactions 5a, b so that no substantial build-up of EDA can take place and hence Reaction 6 will be prevented. Thus, we interpret the exceptional behaviour of Znl2, CH3I, and HI as iodide promoters in the sense that they allow a high hydrogenolysis-hydrogenation activity of the Ru function in the catalyst system. Whereas the hydrocarbonylation function of Rh (Reactions 5a, b)is promoted by a variety of iodides, it appears that the hydrogenolysis function of Ru (Reaction 5c)is very sensitive to the nature of the iodide source used, as evidenced by a low ethyl acetate/acetic acid product ratio obtained with iodides such as AII3 and Lil. 

In principle, the zeolite catalyst system would offer advantages over the existing homogeneous catalyst, particularly with respect to corrosion due to the absence of HC1 and chlorine-containing by-products. However, acetaldehyde and acetic-acid production via ethylene has recently become less economically attractive compared to methanol carboxylation chemistry. 

Avada A one-step catalytic process for making ethyl acetate from ethylene and acetic acid. The catalyst is a silicotungstic acid made by Johnson Matthey. Developed from 1997 by BP and Johnson Matthey. Commercial production started in Hull, UK, in 2001. 

As well as the water produced by esterification, quite a high concentration of water (ca. 10 M) is required to maintain high rates and prevent deactivation by precipitation of the rhodium catalyst (see Box 3). Separation of water from the acetic acid product by distillation incurs substantial costs. In addition, high water levels increase the rate of the water gas shift reaction (Section 4.1.3), catalyzed in competition with carbonylation by the rhodium/iodide system... 

Acetic acid is a key commodity building block [1], Its most important derivative, vinyl acetate monomer, is the largest and fastest growing outlet for acetic acid. It accounts for an estimated 40 % of the total global acetic acid consumption. The majority of the remaining worldwide acetic acid production is used to manufacture other acetate esters (i.e., cellulose acetates from acetic anhydride and ethyl, propyl, and butyl esters) and monoehloroacetic acid. Acetic acid is also used as a solvent in the manufacture of terephthalic acid [2] (cf. Section 2.8.1.2). Since Monsanto commercially introduced the rhodium- catalyzed carbonylation process Monsanto process ) in 1970, over 90 % of all new acetic acid capacity worldwide is produced by this process [2], Currently, more than 50 % of the annual world acetic acid capacity of 7 million metric tons is derived from the methanol carbonylation process [2]. The low-pressure reaction conditions, the high catalyst activity, and exceptional product selectivity are key factors for the success of this process in the acetic acid industry [13]. 

The solvent of choice, with respect to activity, selectivity, and product isolation, is acetic acid. Comparable catalyst activities are also obtained using longer-chain carboxylic acids such as propionic or valeric acid, but their co-oxi-dizing properties are expressed much more compared with acetic acid and therefore it is often not feasible to use them for commercial applications [5]. Water supresses catalyst activity drastically, thus its application is restricted to certain cases and substrates. 

A comparable study on the acid-catalyzed benzylidenation of D-ribose has appeared.18 The reaction using zinc chloride and acetic acid as catalyst was studied at 5,27, and 80°. As the difference in the energy of the syn and anti isomers of a cis-fused 2-phenyl-1,3-dioxolane ring is small, both products are often present in the products of the acid-catalyzed benzylidenation of vicinal 1,2-diols. Grindley and Szarek18 found that the main product at 5° is the thermodynamically most stable 2,3-0-benzylidene-/3-D-ribofuranose (both diastereoisomers). At 27°, the main products were found to be di-O-benzylidene-riboses (not characterized), together wih a small proportion of the 2,3-acetal. At 80°, however, the preponderant product is di-(2,3-0-benzylidene-/3-D-ribo-furanose) 1.5 T,5-dianhydride. It is evident that the temperature may play a decisive role in determining the number and type of products. 

The same diastereoselectivity was observed for reduction with sodium borohydride of enamine functions present in natural products, both in the presence and absence of acetic acid as catalyst... 

A reaction section, where operations are conducted in a reactor fed in descending stream with a mixture of p-xyiene, acetic acid and catalyst solution prepared in a separate device. The reaction medium is agitated by the introduction of air at the bottom. The corrosive action of bromine and organic acids on carbon steels makes it necessary to use special, stainless materials (Hastelloy C), both for the reactor and for certain parts of the equipment, particularly the heat recovery system. The temperature and oxygen content of the reaction medium must be carefully controlled to prevent the formation of undesirable side products. The heat of reaction is removed by vaporization of part of the reaction medium (acetic acid, p-xylene and water), and by condensation and reflux to the reactor. Residence time is about one hour, and the yield is up to 95 molar per cent... 

The reactor effluent pressure is reduced and adiabatically flashed to recover acetic acid as vapor. The liquid phase contains the homogeneous catalyst which is pumped back to the reactor. The flashed vapor enters the light ends column where low molecular weight hydrocarbons are removed and a heavy fraction including water and hydrogen iodide is condensed and recycled to the reactor flash tank. The acetic acid product is removed from the column as a liquid side draw and further purified in downstream distillation columns. 

A highly enantioselective hydrogenation of enamides (152) to afford amines (153), catalyzed by a dual chiral-achiral acid system has been developed by Antilla and Liu (Scheme 41). By employing a substoichio-metric amount of the chiral phosphoric acid (154) and acetic acid, the catalyst loading as low as 1 mol %, excellent chemical yields and enan-tioselectivities of the reduction products (153) were obtained. 

Roth and co-workers [84] at the Monsanto company developed an acetic acid production process by the reaction of methyl alcohol with carbon monoxide in the presence of rhodium carbonyl as the major catalyst. 

Between 1995 and 2000, BP Chemicals commercialized and began to operate the Cativa process for the production of acetic acid. The catalyst is cz5-[Ir(CO)2l2] in the presence of a ruthenium-based promoter (e.g. Ru(CO)4l2) or an iodide promoter (a molecular iodide, e.g. Inl3). Catalyst... 

A direct ethylene oxidation process for the acetic acid production was commercialized by Denko in 1997. This process is only competitive for small- or medium-scale plants. The raw material ethylene is more expensive than methanol and carbon monoxide, but the investment costs of these plants are much lower. Table 6.15.1 gives an overview of the catalysts, reaction conditions, yield, and byproducts for the major acetic add processes. The different processes are discussed in more detail in Sections 6.15.1-6.15.4. 

---