Acetic acid plants methanol process

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. 

Even though methanol carbonylation is the favored process for new acetic acid capacity today, existing paraffin oxidation plants remain quite competitive where coproducts can be marketed successfully [2, 3]. Over half the original capacity of acetic acid plants based on paraffin oxidation remains in use today. In North America, Hoechst Celanese operates two facilities using the butane oxidation process to make acetic acid. The reported 1994 capacity at Pampa, Texas, is 250000 metric tons/year, while that at monton, Alberta, is 75 000 metric tons/year [4]. There are two plants believed to be using the naphtha oxidation process to make acetic acid BP Chemicals in Hull, England, with a capacity of 210000 metric tons/year [5] and a state complex in Armenia (in the former USSR) with a capacity reported to be 35 000 metric tons/year [6]. 

In 1970, the discovery of these new organo-soluble catalysts based on Rh, Pd, or Pt was generally considered unfeasible for industrial processes because of the prohibitive price of the metals involved. However, the hgh activity and productivity of these catalysts made possible production levels of 100000 ty 1 with only a few dozen kilograms of precious metals needed as inventory by each single plant. Thus, the amount of precious metal involved represents only a minor part of the investment and the manufacturing costs, i.e., the price of the metal was not an important factor in the production unit cost, provided that its usage occurred without any loss. In 1972 this hypothesis was confirmed by Monsanto and its commercialization of the important process to generate acetic acid by methanol carbonylation [16]. 

An example that demonstrates the advantages of reactive distillation is the synthesis of methyl acetate by esterification of acetic acid with methanol. A chemical plant consisting of two reactors and nine distillation columns can be replaced by just one reactive distillation column. Fig. 3.2-8 shows the conventional process for... 

Since coal contains more carbon than required for methanol production, the selection of a suitable gasification process might ensure that methanol could be produced in an ideal combination with high-CX) gases - a route which would be attractive above all for the production of acetic acid from methanol and CO, as shown by the above-mentioned plant in the USA. 

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. ... 

Despite the high tonnages of petrochemicals, the chemical industry as a whole consumes rather less than 10% of available petroleum and natural gas hydrocarbons as feedstocks, with possibly a further 4-5% as fuel. For comparison, the current consumption of gasoline alone in Western Europe exceeds 120 Mt per annum, while the U.S. figure is over 300 Mt per annum. Hence, prices of individual hydrocarbon feedstocks are largely determined by other forces the most economic feedstock/route combination has frequently changed with time, and may differ in different parts of the world. Furthermore, while a specific route may be preferred for new plants, older plants for which the capital is largely written off may well remain economically viable. Finally, special situations may prompt individual solutions. For example, Rhone-Poulenc in France derive the carbon monoxide for a very modern acetic acid plant, based on Monsanto s methanol carbonylation process, from the partial... 

The process studied in this section is the heterogeneously catalyzed esterification of acetic acid and methanol to methyl acetate and water in the 100mm pilot plant depicted in Figure 11. Within the column there are three sections of structured packings, two catalytic ones at the bottom and a separating section at the top of the column. Each section has a length of Im. The plant is operated in semi-batch mode, i. e. the reboiler is filled with methanol and after the column is filled with methanol the feed is opened until the concentration of methanol is too... 

Interesting news was released by Monsanto [1011, 1012] who reported that they are going to build a large acetic acid plant at Texas City for startup in 1970. Acetic acid will be manufactured by low pressure carbonylation of methanol using a rhodium catalyst together with a halogen promotor [1009, 1010, 1013] instead of cobalt catalyst, which is used in the BASF process. 

In 1968 a new methanol carbonylation process using rhodium promoted with iodide as catalyst was introduced by a modest letter (35). This catalyst possessed remarkable activity and selectivity for conversion to acetic acid. Nearly quantitative yields based on methanol were obtained at atmospheric pressure and a plant was built and operated in 1970 at Texas City, Tex. The effect on the world market has been exceptional (36). 

The chemical complex includes the methanol plant, methyl acetate plant, and acetic anhydride plant. The methanol plant uses the Lurgi process for hydrogenation of CO over a copper-based catalyst. The plant is capable of producing 165,000 t/yr of methanol. The methyl acetate plant converts this methanol, purchased methanol, and recovered acetic acid from other Eastman processes into approximately 440,000 t/yr of methyl acetate. 

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. 

Eastman Chemical Company has operated a coal-to-methanol plant in Kingsport, Tennessee, since 1983. Two Texaco gasifiers (one is a backup) process 34 Mg/h (37 US ton/h) of coal to synthesis gas. The synthesis gas is converted to methanol by use of ICl methanol technology. Methanol is an intermediate for producing methyl acetate and acetic acid. The plant produces about 225 Gg/a (250,000 US ton/a) of acetic anhydride. As part of the DOE Clean Coal Technology Program, Air Products and Cnemicals, Inc., and Eastman Chemic Company are constructing a 9.8-Mg/h (260-US ton/d) slurry-phase reactor for the conversion of synthesis gas to methanol and dimethyl... 

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 final step in the process involves reacting purified carbon monoxide from the gas separation plant with methyl acetate to form acetic anhydride, using a proprietary catalyst system and process. Part of the acetic anhydride is reacted with methanol to produce acetic acid and methyl acetate, and the latter is recirculated to the carbonylation step. 

Meanwhile, Wacker Chemie developed the palladium-copper-catalyzed oxidative hydration of ethylene to acetaldehyde. In 1965 BASF described a high-pressure process for the carbonylation of methanol to acetic acid using an iodide-promoted cobalt catalyst (/, 2), and then in 1968, Paulik and Roth of Monsanto Company announced the discovery of a low-pressure carbonylation of methanol using an iodide-promoted rhodium or iridium catalyst (J). In 1970 Monsanto started up a large plant based on the rhodium catalyst. 

Methanol process. BASF introduced high-pressure technology way back in I960 to make acetic acid out of methanol and carbon monoxide instead of ethylene. Monsanto subsequently improved the process by catalysis, using an iodide-promoted rhodium catalyst. This permits operations at much lower pressures and temperatures. The methanol and carbon monoxide, of course, come from a synthesis gas plant. 

Today acetic acid is produced mainly from methanol and carbon monoxide. This process, along with the Tennessee Eastman acetic anhydride plant using syn gas, are the current standards in the industry when considering new expansion regardless of the price of ethylene. The vinyl acetate process described here may achieve this stature if its commercial development is permitted to occur. 

Direct Oxidation. Direct oxidation of petroleum hydrocarbons has been practiced on a small scale since 1926 methanol, formaldehyde, and acetaldehyde are produced. A much larger project (29) began operating in 1945. The main product of the latter operation is acetic acid, used for the manufacture of cellulose acetate rayon. The oxidation process consists of mixing air with a butane-propane mixture and passing the compressed mixture over a catalyst in a tubular reaction furnace. The product mixture includes acetaldehyde, formaldehyde, acetone, propyl and butyl alcohols, methyl ethyl ketone, and propylene oxide and glycols. The acetaldehyde is oxidized to acetic acid in a separate plant. Thus the products of this operation are the same as those (or their derivatives) produced by olefin hydration and other aliphatic syntheses. 

Reserpine is isolated from its plant producers by using a nonaqueous solvent process, using, for example, boiling methanol extraction of the African root Rauwolfia vomitoria. Naturally, these extractions are carried out under countercurrent methods. The methanol extract is concentrated and acidified with 15% acetic acid and then treated with petroleum naphtha to remove impurities. Extraction is made using ethylene dichloride. The solvent is neutralized with dilute sodium carbonate, evaporated to drive off the ethylene dichloride, and further evaporated to crystallize the crude reserpine crystals that are then crystallized. 

As seen from the above, conventional uses of methanol cover a wide range of products which in turn find application in a very broad cross-section of industrial and consumer goods. New end uses have continued to develop and spur the growth of methanol production. One such development is the Monsanto low pressure process that carbonylates methanol to acetic acid (6). Essentially all new acetic acid capacity now being installed is based on Monsanto technology. By 1981, eleven plants converting methanol to acetic acid are scheduled to be on stream. At capacity they will consume over 300 million gallons of methanol. 

Acetica A process for making acetic acid by the heterogeneous carbonylation of methanol in a bubble column reactor. The catalyst is a rhodium carbonyl iodide, anchored by ion-pairing to a polyvinyl pyridine resin. Developed by Chiyoda Corporation and UOP and first described in 1998. Licensed to Guizhou Crystal Organic Chemical Group, China, in 2002 one plant was under construction in 2005. 

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. 

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. 

Commercial methanol carbonylation processes have employed each of the group 9 metals, cobalt, rhodium and iridium as catalysts. In each case acid and an iodide co-catalyst are required to activate the methanol by converting it into iodomethane (CH3OH + HI CH3I + H2O) catalytic carbonylation of iodomethane into acetyl iodide is followed by hydrolysis to acetic acid. A problem common to all these processes arises because the mixture of HI and acetic acid is highly corrosive this necessitates special techniques for plant construction involving the use of expensive steels. We discuss each catalyst system in turn below. 

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