A Novel Production of γ-Butyrolactone Catalyzed by Ruthenium Complexes

γ-Butyrolactone (hereafter abbreviated GBL) is produced by the two-stage hydrogenation of maleic anhydride (MAH) in the liquid phase: the hydrogenation of MAH to succinic anhydride (SAH) in the first stage and the subsequent hydrogenation of SAH to GBL in the second stage. The latter hydrogenation has been studied using a homogenous catalyst. A novel ruthenium catalyst system consisting of Ru(acac)3, P(octyl)3, and p-toluenesulfonic acid (p-TsOH) was developed for hydrogenating the SAH, which exhibited excellent catalytic performance, exceeding 95% selectivity for GBL and higher activity than that reported in the literature. It was found that p-TsOH plays an important role not only in enhancing the reaction rate, but also in improving selectivity. p-TsOH induces a structual change in the Ru complexes, leading to the cationic change which shows higher catalyst activity. It also prevents the undesired side reaction catalyzed by free P(octyl)3 thus resulting in high selectivity for GBL. A process to produce GBL was investigated. Some novel features of this process include the external preparation method of the Ru complex, the coupling reaction, and the separation to remove H2O, a product of hydrogenation of SAH, to increase the reaction rate. A catalyst recovery system was also developed to recover over 90% of the catalyst.