Acetic acid, production

The various routes to acetic acid warrant a brief review, to illustrate the chemical industry s response to change and provide an introductory guide to future options. 

The earliest route to acetic acid was the bacterial souring of wine, which eventually became the basis of vinegar manufacture. Wood distillation yielded stronger solutions of acetic acid (15 to over 90%). Surprisingly, some 10 000 tonnes per annum of acetic acid were still produced by this means in the U.S.A. in the mid-1960s. 

However, the major routes to acetic acid, developed during and after the 

First World War, were based on the oxidation of acetaldehyde derived from either acetylene or fermentation ethanol. The latter could well return to favour in countries such as Brazil (section 12.7.1.). After the Second World War, fermentation ethanol gave way to synthetic ethanol, via the direct hydration of ethylene. (Synthetic ethanol made by the sulphuric acid process had already made some inroads in the U.S.A.). From 1960 onwards, the Wacker oxidation of ethylene added a further option for acetaldehyde manufacture. 

When we turn to energetic aspects, acetylene hydration and ethylene oxidation have already been discussed in section 12.3.3.1. The appropriate energy input for fermentation ethanol is somewhat difficult to establish (see section 12.7.1.), but for the hydration of ethylene and subsequent oxidation of synthetic ethanol (in modern plants) we have  

---

Figure 3 shows the production of acetaldehyde in the years 1969 through 1987 as well as an estimate of 1989—1995 production. The year 1969 was a peak year for acetaldehyde with a reported production of 748,000 t. Acetaldehyde production is linked with the demand for acetic acid, acetic anhydride, cellulose acetate, vinyl acetate resins, acetate esters, pentaerythritol, synthetic pyridine derivatives, terephthaHc acid, and peracetic acid. In 1976 acetic acid production represented 60% of the acetaldehyde demand. That demand has diminished as a result of the rising cost of ethylene as feedstock and methanol carbonylation as the preferred route to acetic acid (qv). 

Acetic acid has a place in organic processes comparable to sulfuric acid in the mineral chemical industries and its movements mirror the industry. Growth of synthetic acetic acid production in the United States was gready affected by the dislocations in fuel resources of the 1970s. The growth rate for 1988 was 1.5%. 

About half of the wodd production comes from methanol carbonylation and about one-third from acetaldehyde oxidation. Another tenth of the wodd capacity can be attributed to butane—naphtha Hquid-phase oxidation. Appreciable quantities of acetic acid are recovered from reactions involving peracetic acid. Precise statistics on acetic acid production are compHcated by recycling of acid from cellulose acetate and poly(vinyl alcohol) production. Acetic acid that is by-product from peracetic acid [79-21-0] is normally designated as virgin acid, yet acid from hydrolysis of cellulose acetate or poly(vinyl acetate) is designated recycle acid. Indeterrninate quantities of acetic acid are coproduced with acetic anhydride from coal-based carbon monoxide and unknown amounts are bartered or exchanged between corporations as a device to lessen transport costs. 

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. 

Jamieson and McNeill [142] studied the degradation of poIy(vinyI acetate) and poly(vinyI chloride) and compared it with the degradation of PVC/PVAc blend. For the unmixed situation, hydrogen chloride evolution from PVC started at a lower temperature and a faster rate than acetic acid from PVAc. For the blend, acetic acid production began concurrently with dehydrochlorination. But the dehydrochlorination rate maximum occurred earlier than in the previous case indicating that both polymers were destabilized. This is a direct proof of the intermolecular nature of the destabilizing effect of acetate groups on chlorine atoms in PVC. The effects observed by Jamieson and McNeill were explained in terms of acid catalysis. Hydrochloric acid produced in the PVC phase diffused into the PVAc phase to catalyze the loss of acetic acid and vice-versa. 

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... 

Activating groups at the 5-position led to high yields when bromination took place in chloroform or acetic acid. Products obtained were the 4-bromo derivatives of 5-amino- (90%), 5-hydroxy- (95%), and 5-methoxy-benzisothiazole (40%). Use of the bromine-sulfuric acid-silver sulfate system raised the yield of the last-named product to 87% [80JCR(S)197], 7-Amino-4-chloro-l,2-benzisothiazole was brominated in the 6-position [71JCS(C)3994],... 

The investigated cw-stilbene derivatives, 4-methoxy, 4,4 -dimethyl, unsubstituted, and 4,4 -bis(trifluoromethyl)stilbenes, had k2 values spanning 6-7 powers of ten both in methanol and in acetic acid. Products 2, 4, 5 and 6 were formed. Table 8 reports the results of the cis-trans isomerization test in acetic acid (ref. 29). No acid catalyzed or free radical process was found to be responsible for these isomerizations. 

Acetic Acid/Products/% Acetaldehyde/Products / % C02/Products/%... 

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. 

Kinetic studies of the acetylation of several arylethers were carried out over HBEA zeolites. The main conclusion is that the rate and stability of the reactions are determined by the competition between reactant(s) and product(s) molecules for adsorption within the zeolite micropores. This competition shows that the autoinhibition of arene acetylation, that is, the inhibition by the acetylated products, and also by the very polar acetic acid product is generally observed. This effect is much more pronounced with hydrophobic substrates such as methyl and fluoro aromatics than with hydrophilic substrates because of the larger difference in polarities between substrate and product molecules. 

A novel anaerobic thermophilic fermentation process for acetic acid production from milk permeate... 

Conversion rates as high as 99% are not encountered very often in the petrochemical industry. That coupled with relatively mild operating conditions, made this route, the economic favorite since it was introduced. About 75% of the world s acetic acid production comes from the methanol route. 

In 1970, the first rhodium-based acetic acid production unit went on stream in Texas City, with an annual capacity of 150 000 tons. Since that time, the Monsanto process has formed the basis for most new capacities such that, in 1991, it was responsible for about 55% of the total acetic acid capacity worldwide. In 1986, B.P. Chemicals acquired the exclusive licensing rights to the Monsanto process, and 10 years later announced its own carbonylation iridium/ruthenium/iodide system [7, 8] (Cativa ). Details of this process, from the viewpoint of its reactivity and mechanism, are provided later in this chapter. A comparison will also be made between the iridium- and rhodium-based processes. Notably, as the iridium system is more stable than its rhodium counterpart, a lower water content can be adopted which, in turn, leads to higher reaction rates, a reduced formation of byproducts, and a better yield on CO. 

Methyl ethyl ketone is made mostly by the dehydrogenation of 5ec-butyl alcohol. A small amount is isolated as a by-product in acetic acid production by the oxidation of n-butane. 

As we shall also see, there are also many uses of CO. Examples are acetic acid production, which is made by reacting methanol with CO... 

Acetic Acid Production via Low-Pressure, Nickel-Catalyzed Methanol Carbonylation... 

A significant enhancement in both acetic acid productivity and selectivity is normally realized in the presence of controlled quantities of iodide. 

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. 

Work on technological issues was more important and even dominating over that on basic aspects from the beginning of the 19th century brewing (Roberts et al., 1995), wine, bread and acetic acid production. These topics made up important parts of the chemical technology of the time (Poppe, 1842 Knapp, 1847 Wagner, 1857 Payen, 1874). Knapp considered scientific and practical, industrial interest as equally important. 

The manufacture of cellulose acetate involves the acetylation of cellulose from cotton linters or wood pulp by acetic anhydride and acetic acid. Production started about 30 years ago, and early products that were developed include safety photographic films, airplane dopes, and acetate fabrics. It is now also produced in the form of sheeting, rods, and tubes and is widely used as a molding compound. 

Table I. Effect of Metal Ions on Efficiency of Acetic Acid Production by Acetaldehyde Oxidation...

Acid formation Species of Brettanomyces, Hansenula, Pic Ilia, Saccharomyces As a contaminant in wines. Brettanomyces spp. Forms a higher concentration of volatile acids (also isobutyiic and isovaleric acids) than S. cerevisiae. Pichia species and other yeasts are responsible for acetic acid production in brines of domestic green olives not lactobacilli, as assumed for years (Vaughn et al., 1976). 

Backus, J., Fabiilli, M., Sanchez, D., and Wong, E. 2003. Acetic acid production via carbonylation of methanol Technical and economical feasibility study, Vol. I, Fugacitech, Inc., Ann Arbor, Michigan, April, 4 (online publication, http //www-personal.engin.umich.edu/ mfabiill/Report% 20rev06.doc). 

---