Isopropyl Alcohol Manufacture by the Strong-acid Process

Isopropyl alcohol has been called the first petrochemical (IARC, 1992). It can be prepared via three different methods: indirect hydration of propylene, direct hydration of propylene, and catalytic hydrogenation of acetone. Indirect hydration, also called the sulfuric-acid process, was the only method used to produce isopropanol worldwide until the first commercial direct-hydration process was introduced in 1951. Each method has its advantages and disadvantages. For example, direct hydration is less corrosive than indirect hydration mediated by sulfuric acid. However, the direct method requires a pure propylene feed, in contrast to the indirect process, which can use a dilute, refinery stream (Lee et al., 2003). In the indirect-hydration process, propylene is reacted with sulfuric acid to produce monoand diisopropyl sulfates, which are then hydrolysed to isopropanol. In the two-step strong-acid process, separate reactors are used for the propylene-absorption phase and the hydrolysis of the sulfate esters. The reaction occurs at high sulfuric acid concentration (> 80% wt) and low temperature (e.g. 20–30 °C). The weak-acid process is conducted in a single step at lower acid concentration (60–80% wt) and higher temperature (60–65 °C) (Logsdon & Loke, 2001).