Acetone is an organic compound, chemically known as propanone or dimethyl ketone, with the formula \(\text{C}_3\text{H}_6\text{O}\). It is the simplest member of the ketone family, characterized by a carbonyl group bonded to two methyl groups. This colorless, volatile, and flammable liquid dissolves both polar and nonpolar substances. Its solvency and fast-evaporating properties make it useful in numerous industrial and consumer applications.
The Dominant Production Method (The Cumene Process)
The vast majority of the world’s acetone, exceeding 90% of global production, is manufactured via the Cumene process. This method is primarily designed to produce phenol, making acetone a necessary co-product. The process begins with the alkylation of benzene with propylene. This reaction is carried out in the liquid phase over an acidic catalyst, such as a solid phosphoric acid or zeolite, at high pressure and around 250°C to yield cumene, or isopropylbenzene.
Once cumene is synthesized, it is subjected to a liquid-phase oxidation step using oxygen from air. This reaction is controlled, performed at temperatures between 80°C and 130°C in an alkaline environment, to produce cumene hydroperoxide (CHP). The alkaline conditions stabilize the CHP intermediate, preventing its premature decomposition. The oxidation reaction is halted at a specific conversion rate to minimize the formation of by-products.
The final stage is the acid-catalyzed cleavage of the cumene hydroperoxide. The CHP is treated with an acid, commonly sulfuric acid, near 60°C. This causes the unstable hydroperoxide molecule to decompose rapidly into the two products: phenol and acetone. The ratio of the products is fixed by stoichiometry, with approximately 0.6 tons of acetone produced for every 1.0 ton of phenol. The resulting mixture is then separated and purified through distillation to isolate the high-purity acetone product.
Other Commercial Synthesis Routes
While the Cumene process dominates, other methods are used when “on-purpose” acetone is desired without the co-production of phenol. Historically, a major route was the dehydrogenation of Isopropanol (IPA), which is still employed. This endothermic reaction passes isopropyl alcohol vapor over a metal catalyst, such as zinc oxide and zirconium oxide, at high temperatures between 350°C and 500°C.
The catalyst facilitates the removal of hydrogen from the IPA molecule, yielding acetone and hydrogen gas. This method offers the advantage of producing acetone directly, with hydrogen being the only co-product. The process is favored for smaller-scale operations or when high-purity acetone is required for pharmaceutical or specialty applications.
Another technique is the direct oxidation of propylene, sometimes referred to as a Wacker-type process. This route involves a palladium-based catalyst system with a copper co-catalyst. The process allows for the direct conversion of propylene into acetone, yielding high selectivity. Although less common globally than the Cumene process, these alternative routes ensure flexibility based on feedstock availability and market demand.
Primary Industrial Uses of Acetone
Acetone manufacturing is justified by its extensive use as both a direct solvent and a chemical building block. As a solvent, accounting for approximately 40% of global demand, acetone is used in protective coatings, adhesives, and lacquers. Its ability to dissolve plastics and resins makes it suitable for thinning fiberglass resins and cleaning tools. The pharmaceutical industry utilizes it as a solvent and a denaturant in alcohol products.
A significant portion of acetone is consumed as a reactant in the synthesis of polymers and specialty chemicals. One major application is the production of Methyl Methacrylate (MMA), the monomer for acrylic plastics like Plexiglas. This synthesis begins with the reaction of acetone with hydrogen cyanide to form acetone cyanohydrin, which is then processed to yield the MMA monomer.
Acetone is a precursor for Bisphenol A (BPA), a compound manufactured by condensing acetone with phenol. BPA is an intermediate material for creating polycarbonate plastics, used in safety glasses, food-grade containers, and epoxy resins. These three applications—solvent use, MMA production, and BPA synthesis—account for the majority of global acetone consumption.