(22b) Extractive Catalyst Recovery in an Ionic Liquid Process for 2,5-Dihydrofuran

2,5-Dihydrofuran (2,5-DHF) is an intermediate with utility in the production of commodity, specialty and fine chemicals. The homogeneous, Lewis acid / iodide anion-catalyzed rearrangement of 3,4-epoxy-1-butene (1) to 2,5-DHF has been known since 1976 [US 3,932,468]. Typically, these rearrangement processes use a metal halide Lewis acid with an inorganic or quaternary onium iodide catalyst system in a high-boiling solvent (e.g., ZnI2 / KI / NMP).

For years, commercial processes utilizing this chemistry were unattractive due to the high cost of (1) and side reactions in the rearrangement step. Among these side reactions is the polymerization of (1) to a polyether oligomer. In continuous operation, the non-volatile oligomer accumulates causing dilution of the catalysts and filling of the reaction vessel. Recovery of the expensive catalysts and solvent from the reaction mixture is difficult to perform and is a serious problem for scale up. Following the discovery of an inexpensive, continuous, vapor-phase oxidation of 1,3-butadiene to produce (1) in 1986 [US 4,897,498] the production of 2,5-DHF from (1) was once again of industrial interest. A continuous, liquid phase process was developed utilizing a trialkyltin iodide Lewis acid / tetraalkylphosphonium iodide co-catalyst system which gave high selectivity for 2,5-DHF [US 5,238,889 and 5,315,019]. This talk will focus on separation of the catalyst from the oligomer via liquid extraction. This process was scaled-up to a semiworks facility using three continuous, stirred-tank reactors and a continuous, countercurrent, liquid-liquid extractor that provided an efficient separation of the catalyst from the oligomer.