Published August 2003
Hydroquinone is used in photographic chemicals, rubber & food antioxidants, polymerization inhibitors, and water treatment chemicals. Hydroquinone is predominantly produced by the oxidation of p-Diisopropylbenzene (p-DIPB), in a process similar to that for cumene oxidation to phenol. By-products by this method are predominantly resorcinol. An alternate route is the hydroxylation of phenol, by homogeneous or heterogeneous catalysis. In this PEP review, we consider EniChem s process for heterogeneously-catalyzed hydroxylation of phenols, using a titanium-silicate catalyst. Experimentation with cosolvents (water, dioxanes, benzophenones, furans, glycol ethers) in hydroxylation has given more flexibility over the catechol:hydroquinone production ratio. One of the bases for this process was an unusually broad patent, US 4,410,501, assigned to Snamprogetti S.p.A., which granted a wide set of claims over crystalline structures containing silicon and titanium oxides. EniChem operates a 10,000 ton/year plant in Ravenna, Italy using this process. In our analysis, this process has a substantial cost advantage over the homogeneously-catalyzed hydroxylation of phenol process, and over hydroquinone production by oxidation of p-DIPB. The Snamprogetti invention has reached the end of its patent life, so it is possible that other producers may be able to use aspects of EniChem s technology. However, despite the cost advantage of the EniChem process, we would not expect processes using Ti-Si catalyst to rapidly displace the current capacity for hydroquinone. This is because of the limited market for the byproduct catechol, the small market growth projected for hydroquinone, and the fact that a large portion of hydroquinone production uses by-product p-DIPB from cumene production for phenol (which would dramatically lower costs).