Ethyl alcohol is a product of fermentation of sugars and cellulose but the alcohol is manufactured mostly by the hydration of ethylene.
An indirect process for the manufacture of ethyl alcohol involves the dissolution of ethylene in sulfuric acid to form ethyl sulfate, which is hydrolyzed to form ethyl alcohol (Fig. 1). There is always some by-product diethyl ether that can be either sold or recirculated.
3CH2=CH2 + 2H2SO4 ? C2H5HSO4 + (C2H5)2SO4
C2H5HSO4 + (C2H5)2SO4 + H2O ? 3C2H5OH + 2H2SO4
C2H5OH + C2 H5HSO4 ? C2H5OC2H5
The conversion yield of ethylene to ethyl alcohol is 90 percent with a 5 to 10 percent yield of diethyl ether (C2H5OC 2H5).
A direct hydration method using phosphoric acid as a catalyst at 300o C is also available (Fig. 2):
CH2=CH2 + H2O ? C2H5OH
and produces ethyl alcohol in yields in excess of 92 percent. The conversion per pass is 4 to 25 percent, depending on the activity of the catalyst used.
In this process, ethylene and water are combined with a recycle stream in the ratio ethylene/water 1/0.6 (mole ratio), a furnace heats the mixture to 300o C, and the gases react over the catalyst of phosphoric acid absorbed on diatomaceous earth. Unreacted reagents are separated and recirculated. By-product acetaldehyde (CH3CHO) is hydrogenated over a catalyst to form more ethyl alcohol.
Iso-propyl alcohol is a widely used and easily made alcohol. It is used in making acetone, cosmetics, chemical derivatives, and as a process solvent. There are four processes that are available for the manufacture of iso-propyl alcohol:
1. A sulfuric acid process similar to the one described for ethanol hydration
2. A gas-phase hydration using a fixed-bed-supported phosphoric acid catalyst
3. A mixed-phase reaction using a cation exchange resin catalyst
4. A liquid-phase hydration in the presence of a dissolved tungsten catalyst
The last three processes (2, 3, and 4) are all essentially direct hydration processes.
CH3CH=CH2 + H2 O ? CH3CHOHCH3
Per-pass conversions vary from a low of 5 to a high of 70 percent for the gas-phase reaction.
Secondary butanol (CH3CH2CHOHCH3) is manufactured by processes similar to those described for ethylene and propylene.
Hydrolysis usually refers to the replacement of a sulfonic group (–SO3H) or a chloro group (–Cl) with an hydroxyl group (–OH) and is usually accomplished by fusion with alkali. Hydrolysis uses a far wider range of reagents and operating conditions than most chemical conversion processes. Polysubstituted molecules may be hydrolyzed with less drastic conditions. Enzymes, acids, or sometimes water can also bring about hydrolysis alone.
ArSO3Na + 2NaOH ? ArONa + Na2SO3 + H2O
ArCl + 2NaOH ? ArONa + NaCl + H2O
Acidification will give the hydroxyl compound (ArOH). Most hydrolysis reactions are modestly exothermic.
The more efficient route via cumene has superceded the fusion of benzene sulfonic acid with caustic soda for the manufacture of phenol, and the hydrolysis of chlorobenzene to phenol requires far more drastic conditions and is no longer competitive. Ethylene chlorohydrin can be hydrolyzed to glycol with aqueous sodium carbonate.
ClCH2CH2OH ? HOCH2CH2OH
Cast-iron or steel open fusion pots heated to the high temperatures required (200 to 325oC) with oil, electricity, or directly with gas, are standard equipment.
