A process for oxidizing mercaptan compounds in a rich caustic stream and separating disulfide oil from the rich caustic to generate a sulfur free lean caustic solution, comprising, in combination, a) feeding solvent, an oxygen containing fluid, and a stream of rich caustic containing mercaptan compounds to a single tower having a top section containing an oxidizer and a bottom section containing at least two contactors (170, 180) comprising fibers in series below the oxidizer, where the rich caustic is obtained from a separation process that separated hydrocarbons from the rich caustic and the mercaptan compounds in the rich caustic were extracted from the hydrocarbons; b) contacting the stream from step a) with a catalyst in the oxidizer to oxidize the mercaptan compounds to disulfide oil at a conversion level of 90% or greater in the presence of oxygen and forming an admixture comprising DSO, solvent, and caustic; c) directing the admixture formed in step b) from the oxidizer as a single stream to a first separation section within the single tower where the admixture contacts a bundle of vertical hanging fibers; d) separating the DSO and solvent from the caustic within the first separation section by allowing the admixture to flow through the bundle of fibers to form two distinct liquid layers, a first lower layer comprising a caustic phase and an first upper layer comprising a DSO/solvent phase, in a first collection zone; e) continuously removing a portion of the DSO/solvent phase from the first separation section; f) continuously removing a portion of the caustic phase and mixing with fresh solvent to form a second separation feed that is fed to a second separation section within the single tower where it contacts a second bundle of vertical hanging fibers; g) separating any remaining DSO and solvent from the caustic within the second separation section by allowing the second separation feed to flow through the bundle of fibers in the second separation section to form two distinct liquid layers, a second lower layer comprising a caustic phase and an second upper layer comprising a DSO/solvent phase, in a second collection zone; h) continuously removing a portion of the DSO/solvent phase from the second separation section and recycling it as the solvent of step a); and i) continuously removing a lean caustic stream from the second lower layer. a) feeding solvent, an oxygen containing fluid, and a stream of rich caustic containing mercaptan compounds to a single tower having a top section containing an oxidizer and a bottom section containing at least two contactors (170, 180) comprising fibers in series below the oxidizer, where the rich caustic is obtained from a separation process that separated hydrocarbons from the rich caustic and the mercaptan compounds in the rich caustic were extracted from the hydrocarbons; b) contacting the stream from step a) with a catalyst in the oxidizer to oxidize the mercaptan compounds to disulfide oil at a conversion level of 90% or greater in the presence of oxygen and forming an admixture comprising DSO, solvent, and caustic; c) directing the admixture formed in step b) from the oxidizer as a single stream to a first separation section within the single tower where the admixture contacts a bundle of vertical hanging fibers; d) separating the DSO and solvent from the caustic within the first separation section by allowing the admixture to flow through the bundle of fibers to form two distinct liquid layers, a first lower layer comprising a caustic phase and an first upper layer comprising a DSO/solvent phase, in a first collection zone; e) continuously removing a portion of the DSO/solvent phase from the first separation section; f) continuously removing a portion of the caustic phase and mixing with fresh solvent to form a second separation feed that is fed to a second separation section within the single tower where it contacts a second bundle of vertical hanging fibers; g) separating any remaining DSO and solvent from the caustic within the second separation section by allowing the second separation feed to flow through the bundle of fibers in the second separation section to form two distinct liquid layers, a second lower layer comprising a caustic phase and an second upper layer comprising a DSO/solvent phase, in a second collection zone; h) continuously removing a portion of the DSO/solvent phase from the second separation section and recycling it as the solvent of step a); and i) continuously removing a lean caustic stream from the second lower layer.