Acetic acid [64-19-7], CH3COOH, is a corrosive organic acid having a sharp odor, burning taste, and pernicious blistering properties. It is found in ocean water, oilﬁeld brines, rain, and at trace concentrations in many plant and animal liquids. It is central to all biological energy pathways. Fermentation of fruit and vegetable juices yields 2–12% acetic acid solutions, usually called vinegar (qv). Any sugar-containing sap or juice can be transformed by bacterial or fungal processes to dilute acetic acid. Theophrastos (272–287 BC) studied the utilization of acetic acid to make white lead and verdigris [52503-64-7]. Acetic acid was also well known to alchemists of the Renaissance. Andreas Libavius (AD 1540–1600) distinguished the properties of vinegar from those of icelike (glacial) acetic acid obtained by dry distillation of copper acetate or similar heavy metal acetates. Numerous attempts to prepare glacial acetic acid by distillation of vinegar proved to be in vain, however. Lavoisier believed he could distinguish acetic acid from acetous acid, the hypothetical acid of vinegar, which he thought was converted into acetic acid by oxidation. Following Lavoisier’s demise, Adet proved the essential identity of acetic acid and acetous acid, the latter being the monohydrate, and in 1847, Kolbe ﬁnally prepared acetic acid from the elements. Worldwide demand for acetic acid in 1999 was 2.8 Â 106 t (6.17 Â 109 lb). Estimated demand for 2003 is 3.1 Â 106 t (6.84 Â 109 lb) (1). Uses include the manufacture of vinyl acetate [108-05-4] and acetic anhydride [108-24-7]. Vinyl acetate is used to make latex emulsion resins for paints, adhesives, paper coatings, and textile ﬁnishing agents. Acetic anhydride is used in making cellulose acetate ﬁbers, cigarette ﬁlter tow, and cellulosic plastics.
2. Physical Properties
Acetic acid, fp 16.6358C (2), bp 117.878C at 101.3 kPa (3), is a clear, colorless liquid. Water is the chief impurity in acetic acid although other materials such as acetaldehyde, acetic anhydride, formic acid, biacetyl, methyl acetate, ethyl acetoacetate, iron, and mercury are also sometimes found. Water signiﬁcantly lowers the freezing point of glacial acetic acid as do acetic anhydride and methyl acetate (4). The presence of acetaldehyde [75-07-0] or formic acid [64-18-6] is commonly revealed by permanganate tests; biacetyl [431-03-8] and iron are indicated by color. Ethyl acetoacetate [141-97-9]may cause slight color in acetic acid and is often mistaken for formic acid because it reduces mercuric chloride to calomel. Traces of mercury provoke catastrophic corrosion of aluminum metal, often employed in shipping the acid. The vapor density of acetic acid suggests a molecular weight much higher than the formula weight, 60.06. Indeed, the acid normally exists as a dimer (5), both in the vapor phase (6) and in solution (6). This vapor density anomaly has important consequences in engineering computations, particularly in distillations.
Kirk-Othmer Encyclopedia of Chemical Technology. Copyright John Wiley & Sons, Inc. All rights reserved.
Table 1. Acetic Acid–Water Freezing Points Acetic acid, wt % 100 99.95 99.70 99.60 99.2 98.8 98.4 98.0 97.6 97.2 96.8 96.4 96.0 Freezing point, 8C 16.635 16.50 16.06 15.84 15.12 14.49 13.86 13.25 12.66 12.09 11.48 10.83 10.17
Acetic acid containing 90% and the selectivity to acetic acid is higher than 95%. Stainless steel must be used in constructing the plant. This established process and most of the engineering is well understood. The problems that exist are related to more extensively automating control of the system, notably at start-up and shutdown, although even these matters have been largely solved. This route is the most reliable of acetic acid processes. 4.2. Methanol Carbonylation. Several processes were patented in the 1920s for adding carbon monoxide to methanol to produce...