Acetic anhydride from coal

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. 

Eastman Goal Chemicals. In 1983 Eastman Chemical Co. became the first chemical producer in the United States to return to coal as a raw material for large-scale manufacture of industrial chemicals (35). In that year, Eastman started manufacturing acetic anhydride from coal. Acetic anhydride is a key intermediate for production of coatings, ceUulosic plastics, and cellulose acetate fibers. Acetic anhydride from other sources also is used in the manufacture of pharmaceuticals, starches and sweeteners, and flavors and fragrances. 

Chem.Br., 1983, 19, 896 here it is reported that Tennessee Eastman is commissioning a plant for the production of acetic anhydride from coal which uses a Texaco entrained-bed gasifier to produce syngas. 

In 1980, the Tennessee Eastman unit of Eastman Kodak announced that it would begin construction of a facility to make acetic anhydride from coal, which was readily available at reasonable cost.17 18 This decision reflected a changing of the raw materials base of much of the chemical industry due to such factors as the rising cost of natural gas and petroleum and the large coal reserves of the United States. 

Figure 4. Block flow diagram for production of acetic anhydride from coal.

Victor. H. Agreda, Acetic Anhydride from Coal, Chemtech (April 1988). Roger A. Sheldon, Chemicals from Synthesis Gas, D. Reidel, Dordrecht, (1983). 

Higher crude oil prices had revived studies in the use of coal as a chemical feedstock. But while the Fischer-Tropsch synthesis was still used in South Africa by Sasol, the only other industrial gasification unit was the one Eastman Kodak brought on stream in Kingsport, Tennessee, in 1983, to produce coalbased acetic anhydride. The coal came from the Appalachian mountains and was cheap enough relative to oil prices at the time to warrant such an installation, and the plant is now to be expanded. 

In the 1970s, the oil crisis generated a need for alternative raw materials. Coal and especially natural gas were reconsidered as carbon sources. Synthesis gas, now produced from natural gas, became an alternative feedstock for the production of oxygenated hydrocarbons. For instance, a new process employing organorhodium compounds was developed to produce acetic anhydride from synthesis gas via carbonylation of methyl acetate. 

Synthesis gas is obtained either from methane reforming or from coal gasification (see Coal conversion processes). Telescoping the methanol carbonylation into an esterification scheme furnishes methyl acetate directly. Thermal decomposition of methyl acetate yields carbon and acetic anhydride,... 

The first anhydride plant in actual operation using methyl acetate carbonylation was at Kingsport, Tennessee (41). A general description has been given (42) indicating that about 900 tons of coal are processed daily in Texaco gasifiers. Carbon monoxide is used to make 227,000 t/yr of anhydride from 177,000 t/yr of methyl acetate 166,000 t/yr of methanol is generated. Infrared spectroscopy has been used to foUow the apparent reaction mechanism (43). 

The Eastman acetic anhydride [108-24-7] process provides an extension of carbonylation chemistry to carboxyUc acid esters. The process is based on technology developed independendy in the 1970s by Eastman and Halcon SD. The Eastman acetic anhydride process involves carbonylation of methyl acetate [79-20-9] produced from coal-derived methanol and acetic acid [64-19-7]. 

The Eastman Chemicals from Coal faciUty is a series of nine complex interrelated plants. These plants include air separation, slurry preparation, gasification, acid gas removal, sulfur recovery, CO /H2 separation, methanol, methyl acetate, and acetic anhydride. A block flow diagram of the process is shown in Eigure 3. The faciUty covers an area of 2.2 x 10 (55 acres) at Eastman s main plant site in Kingsport, Teimessee. The air separation plant is... 

The cmde product from the gasifier contains CO2 and H2S, which must be removed before the gas can be used to produce chemicals. The Rectisol process is used to remove these contaminants from the gas. This is accompHshed by scmbbing the product with cold methanol which dissolves the CO2 and H2S and lets the H2 and CO pass through the scmbber. The H2S is sent to a Claus sulfur plant where over 99.7% of the sulfur in the coal feed is recovered in the form of elemental sulfur. A portion of the clean H2 and CO are separated in a cryogenic distillation process. The main product from the cryogenic distillation is a purified CO stream for use in the acetic anhydride process. The remaining CO and hydrogen are used in the methanol plant. 

Production of Eastman s entire acetic anhydride requirement from coal allows a reduction of 190,000 m /yr (1.2 million barrels/yr) in the amount of petroleum used for production of Eastman chemicals. Now virtually all of Eastman s acetyl products are made in part from coal-based feedstocks. Before the technology was introduced, these chemicals had been made from petroleum-based acetaldehyde. Reduced dependence on petroleum, much of which must be obtained from foreign sources, is important to maintain a strong domestic chemical industry. 

There are some chemicals that can be made economically from coal or coal-derived substances. Methanol and CO are used to make acetic anhydride and acetic acid. Methanol itself can be made from synthesis gas over a copper-2inc catalyst (see Feedstocks, coal chemicals). 

The high cost of coal handling and preparation and treatment of effluents, compounded by continuing low prices for cmde oil and natural gas, has precluded significant exploitation of coal as a feedstock for methanol. A small amount of methanol is made from coal in South Africa for local strategic reasons. Tennessee Eastman operates a 195,000-t/yr methanol plant in Tennessee based on the Texaco coal gasification process to make the methyl acetate intermediate for acetic anhydride production (15). 

The most successful example of generating chemicals directly from coal is the Tennessee Eastman integrated process for producing acetic anhydride. The commercial plant gasifies approximately 900 tons of coal per day and performs four chemical steps to yield annually 500 million pounds of acetic anhydride, 390 million pounds of methyl acetate, and 365 million pounds of methanol. In addition, 150 million pounds per year of acetic acid may be produced from acetic anhydride. 

The overall reaction represents an all syn-gas route to acetic acid and acetic anhydride. At present, in Europe, syn-gas is being produced from natural gas, but eventually it will represent a route from coal, the future feedstock for syngas. 

The direct carbonylation of methanol yielding acetic acid, the Monsanto process, represents the best route for acetic acid. Carbonylation of methyl acetate, obtained from methanol and acetic acid, gives acetic anhydride, a technology commercialized by Tennessee Eastman (22). It is noteworthy that this process is based on coal derived synthesis gas to give as the final product cellulose acetate. A combination of Monsanto and Tennessee Eastman technology opens the door for the combined synthesis of acetic acid and acetic anhydride. 

Methanol is an ideal starting material for the synthesis of many chemicals. It is the most important feedstock for the large-scale commercial production of acetic acid and formaldehyde. Additionally, a variety of other chemicals such as methyl esters, methyl halides and methyl ethers can be produced from it. Tenessee-Eastman s recent pioneering commercialization of a coal-based process for acetic anhydride production illustrates the growing importance of methanol as chemical feedstock. 

In the future, there is no doubt that alcohols will play a major role not only as fuel components (70,71) but also as feed stocks for the syntheses of more complicated organic compounds (72). A great amount of research effort is presently directed to the economic conversion of CO and to methanol (73), and on homologation of methanol to higher alcohols (74). Conversion of synthesis gas from coal to acetic anhydride (75) through the intermediacy of methyl acetate (from methanol) will soon be a commercial reality. 

In recent years several commercial plants have been constructed for conversion of coal to synthesis gas for chemical manufacturing. These include the Eastman Chemical s acetic anhydride plant, the Ube (Japan) ammonia plant, the SAR (Germany) oxo chemicals plant, and several coal to ammonia plants in China (e.g., Weihe, Huainan, and Lunan). The Ube plant and the SAR plant have since converted to lower-cost opportunity fuels (petroleum coke and residues). The Eastman plant is still operating exclusively on coal. Feedstock changes at the other plants illustrate the vulnerability of coal conversion processes to a changing economic climate. The fact that the Eastman process remains competitive under changing conditions is due to a set of special circumstances that favor a coal-based process. The success of the Eastman chemicals from coal complex demonstrates that synthesis gas from coal is a viable feedstock for some industrial chemicals under certain conditions. 

Thermodynamically, the carbonylation of methyl acetate (AG298 -10 kJ/mol) is considerably less favourable than that of methanol (AG298 -74 kJ/mol). This means that the reaction does not reach completion but attains an equilibrium which is dependent on the temperature and the CO pressure. Two variants are currently practised commercially that developed by Tennessee Eastman, based on a Halcon process, and a BP process in which acetic acid and the anhydride are co-produced in proportions which can be varied according to demand. Syngas for the Eastman process is made from coal which is mined close to the plant in Tennessee and the acetic anhydride produced is used to make cellulose acetate for film production. The BP process uses syngas generated from North Sea gas which is piped directly to the BP plant in EIull. [Acetic anhydride manufacture M. J. Eloward, M. D. Jones, M. S. Roberts, S. A. Taylor, Catalysis Today, 1993, 18, 325]. 

Eastman Chemical Company, together with Halcon, developed a commercial acetic anhydride process to an industrial scale [41b, 47]. This process starts with coal to make a hydrogen-rich synthesis gas, which is purified (Figure 4). A portion of the syn gas is separated to produce methanol from 2 1 H2/CO. Part of the methanol is used to scrub H2S from the coal-gasification step. The remainder of the methanol is combined with acetic acid to make methyl acetate. The methyl acetate is carbonylated to give acetic anhydride. The acetic anhydride is used to produce cellulose acetate in another process, and the resulting acetic acid is recycled to the esterification section. The acetic anhydride step of the pro-... 

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