Raschig–Hooker process
The Raschig–Hooker process is a chemical process for the production of phenol. The main steps in this process are the production of chlorobenzene from benzene, hydrochloric acid and oxygen, and the subsequent hydrolysis of chlorobenzene to phenol. The first step uses either a copper or iron chloride catalyst and exposes the materials to air at 400℃. In the second step, the resulting chlorobenzene is introduced to steam at 450℃ over a silicon catalyst that hydrolyses the chlorobenzene, giving phenol and hydrogen chloride that can then be recycled back to the first step. Due to  the two step nature, the Raschig–Hooker process can be used to produce either chlorobenzene or phenol. This process is basically used in Germany. The exact nature and composition of the catalyst is a secret. The ability to recycle the hydrogen chloride made the Raschig–Hooker process preferable to the Dow and Bayer process. The reaction, however, takes place at very high temperatures in a very acidic environment with hydrogen chloride vapor and therefore the industrial setting must use highly corrosion resistant equipment for the reaction. While the Raschig–Hooker process does recycle the hydrogen chloride it produces, its use  of catalysts that need to be replaced. The harsh chemical environment, use of catalysts, and large energy consumption has made it a target for green chemistry alternatives. The Raschig–Hooker process suffers from selectivity issues in both steps. In the first step, the reaction is only run to 10% to 15% conversion to prevent the second addition of a chlorine atom to the desired chlorobenzene. Despite this, the overall selectivity of the reaction is 70% to 85%. The second step shares the low conversion rate and high selectivity of the first step. The small amount conversion per reaction offsets the  monetary benefit of recycling the hydrogen chloride due to the large initial cost of the reaction. Therefore, the Raschig–Hooker process needed to be run at high concentrations in large reactors to be industrially economical.