HYDRATION OF ISOBUTYLENE (Ter-Butyl Alcohol [(CH₃)₃COH])

The acid-catalyzed hydration of isobutylene produces ter-butyl alcohol. The reaction occurs in the liquid phase in the presence of 50–65% H₂SO₄ at mild temperatures (10–30°C). The yield is approximately 95%:

ter-Butyl alcohol (TBA) is used as a chemical intermediate because a tertiary butyl carbocation forms easily. It is also used as a solvent in pharmaceutical formulations, a paint remover, and a high-octane gasoline additive. The alcohol is a major by-product from the synthesis of propylene oxide using tertiary butyl hydroperoxide. Surplus ter-butyl alcohol could be used to synthesize highly pure isobutylene for MTBE production by a dehydration step. The reaction conditions, the catalyst used in a pilot-scale unit, and the yield are reviewed by Abraham and Prescott.  It was concluded that MTBE conversion increases from 8 wt% to 88 wt% as the temperature increases from 400°F to 600°F at about 40 LHSV (liquid hourly space velocity). At a lower space velocity

(≈20 LHSV), conversion increased from 12 wt% to 99 wt% for the same temperature range. Figure 1.1 shows the effect of temperature and LHSV on the conversion:

Figure 1.1. Effect of temperature and liquid hourly space velocity on conversion.

Figure 1.2 is a simplified flow diagram of a TBA dehydration pilot unit.

Figure 1.2. A simplified flow diagram of a tertiary butyl alcohol pilot plant.

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