Recent advances in processes and catalysts for the production of acetic acid
Introduction
Acetic acid is an important commodity chemical used in a broad range of applications. As shown in Fig. 1, acetic acid is used primarily as a raw material for vinyl acetate monomer (VAM) and acetic anhydride synthesis, and as a solvent for purified terephthalic acid (PTA) production. The demand for acetic acid has increased, especially in southeast Asia, where several new PTA plants have been built. With the increased demand and installed capacity for PTA in southeast Asia, the region has become a major producer of polyester (PET) fiber, film, and resin. Although the economic crisis in Asia momentarily suppressed the demand for acetic acid to less than expected levels, in the medium and long terms there is potentially a great demand for acetic acid in this market.
The total world capacity of acetic acid has reached approximately 7.8 million t in 1998 with BP-Amoco and Celanese accounting for more than 50% of the world’s capacity [1]. BP-Amoco and Celanese have installed capacities of 1.5 million t (19%), and 2.0 million t (26%), respectively.
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Processing routes to acetic acid
Originally, acetic acid was produced by aerobic fermentation of ethanol, which is still the major process for the production of vinegar. The first major commercial process for the synthetic production of acetic acid was based on the oxidation of acetaldehyde. In an early process for the conversion of acetylene to acetaldehyde introduced in 1916 in Germany and used in China until recently, an organo-mercury compound was used as the catalyst. The toxicity of the mercury catalyst resulted in
Rhodium catalyzed methanol carbonylation
The methanol carbonylation process, “Monsanto process”, is operated under mild conditions (180–220 °C, 30–40 atm) and exhibits high selectivity to acetic acid based on methanol (99%) and carbon monoxide (85%) [7]. While the reaction, as shown below, can be carried out in a variety of rhodium (I) or rhodium (III) complexes [6], [18], under reaction conditions they are almost invariably converted to the active catalyst [RhI2(CO)2]−1. As shown in Fig. 3, methyl iodide is provided by the reaction of
Methyl formate isomerization
It has been proposed that acetic acid can be produced by isomerization of methyl formate in the presence of a homogeneous rhodium catalyst together with other metal additives [52], [53]. Heterogeneous rhodium catalysts supported on poly-vinyl pyridine resin have also been proposed for this application [54]. This catalyst has the same chemical morphology as a methanol carbonylation catalyst. Methyl formate is produced by dehydrogenation of methanol [55] or by methanol carbonylation under high
Synthesis gas route to acetic acid
A nearby synthesis gas plant to produce CO is normally required to provide feed to an acetic acid plant.
On the contrary, an efficient integrated synthesis gas and methanol synthesis plant and acetic acid plant are available by combination of current technology at the natural gas source. This integrated process could achieve a significant capital cost reduction relative to the conventional flow scheme.
Applying this concept, Haldor Topsoe proposed an integrated process that includes the synthesis
Vapor phase oxidation of ethylene
The two-step oxidation process for the production of acetic acid, starting from ethylene through acetaldehyde, was first commercialized in 1960:This route involves the liquid phase oxidation of acetaldehyde using air and typically a manganese acetate catalyst operating at 50–60 °C. The reaction is based on a free radical mechanism. Although this process features high yield (approximately 90%) and a relatively low capital investment cost, it suffers from high
Ethane oxidation
In the 1980s, an acetic acid route from ethane was introduced. Two reaction mechanisms based on:different catalyst systems were proposed: (1) partial oxidation of the methyl group, and (2) ethane oxidation to ethylene followed by ethylene hydration to ethanol, or ethylene to acetaldehyde.
A patent refers to the production of acetic acid by reacting ethane, ethylene, or mixtures of ethane and ethylene with oxygen over a catalyst containing molybdenum, vanadium,
Conclusions
Acetic acid represents a commodity chemical growing at 3.5–4.5% per year from a significant and large base capacity. Significant developments in both process and catalyst technology have supported the growth in this market since the 1950s when the first commercial synthetic process was introduced. Methanol carbonylation has emerged as the dominant route to this product and currently over 60% of the world acetic acid is produced using this route. However, significant catalyst innovation has
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