Provided are a layer-separation method of a spent caustic solution, and a recycling method of an additive, and more particularly, a layer-separation method of a spent caustic solution including: injecting an additive and an acidic compound to the spent caustic solution occurring from a refinery process to break down a red oil emulsion and to perform layer-separation into an upper layer fraction and a lower layer fraction, wherein the additive is an aliphatic hydrocarbon compound having a water solubility of 0.1 to 10 g/L at 20 C.

A light naphtha feedstock containing olefins is introduced with hydrogen sulfide into a mercaptanization zone for conversion of the olefins into a mercaptan stream that is substantially free of olefins, after which the mercaptans are sent with an alkali caustic solution into a mercaptan oxidation treatment unit (MEROX) to produce a spent caustic stream and sweet light naphtha product stream that is substantially free of olefins and of mercaptans. Disulfide oils are produced from the wet air oxidation of the spent caustic, and the disulfide oils can be further processed to provide high purity olefin building blocks.

An integrated mercaptan extraction and/or sweetening and thermal oxidation and flue gas treatment process for a wide variety of sulfur, naphthenic, phenolic/cresylic contaminated waste streams is described. It provides comprehensive treatment for the safe disposal of sulfidic, naphthenic, phenolic/cresylic spent caustic streams, disulfide streams, spent air streams, spent mixed amine and caustic streams (also known as COS solvent streams) from sulfur treating processes. It allows the use of regenerated spent caustic in the sulfur oxide removal section of the thermal oxidation system reducing the need for fresh NaOH. It may also contain an integrated make-up water system. The integration allows the use of the liquefied petroleum gas or other hydrocarbon feeds to the respective extraction or sweetening process to offset external fuel gas requirements for the thermal oxidation system and for the push/pull system of the spent caustic surge drum and optional hydrocarbon surge drum.

The present invention relates to the field of the extraction of sulphur-containing compounds such as the mercaptans, COS or H.sub.2S from a hydrocarbon-containing cut. This selective extraction is carried out by bringing the hydrocarbon-containing cut in liquid phase into contact with an alkaline solution, for example soda. The process according to the invention is an improved process for the regeneration of the alkaline solution, making it possible to reduce the quantity of alkaline solution required in the regeneration section.

The present invention relates to the field of the extraction of sulphur-containing compounds such as the mercaptans, COS or H.sub.2S from a hydrocarbon-containing cut. This selective extraction is carried out by bringing the hydrocarbon-containing cut in liquid phase into contact with an alkaline solution, for example soda. The process according to the invention is an improved process for the regeneration of the alkaline solution, making it possible to reduce the quantity of alkaline solution required in the regeneration section.

The present invention relates to the field of extraction of sulphur-containing compounds such as mercaptans, COS, H.sub.2S or CS.sub.2 from a hydrocarbon cut. This selective extraction is carried out by bringing the hydrocarbon cut in the liquid phase into contact with an alkaline solution, for example caustic soda. The process in accordance with the invention is an improved process for the regeneration of alkaline solution which can be used to reduce the quantity of alkaline solution necessary in the regeneration section.

The present invention relates to the field of extraction of sulphur-containing compounds such as mercaptans, COS, H.sub.2S or CS.sub.2 from a hydrocarbon cut. This selective extraction is carried out by bringing the hydrocarbon cut in the liquid phase into contact with an alkaline solution, for example caustic soda. The process in accordance with the invention is an improved process for the regeneration of alkaline solution which can be used to reduce the quantity of alkaline solution necessary in the regeneration section.

A regeneration method for a liquefied gas thiol-removing alkaline solution comprising the following steps: performing an oxygenation reaction with respect to a liquefied gas thiol-removing alkaline solution and, at the same time, utilizing a high air-liquid condition to extract a disulfide and a polysulfide into a gas phase, thus completing the separation of the disulfide and the polysulfide from the alkaline solution, and implementing the regeneration of the liquefied gas thiol-removing alkaline solution.

An integrated mercaptan extraction and/or sweetening and thermal oxidation and flue gas treatment process for a wide variety of sulfur, naphthenic, phenolic/cresylic contaminated waste streams is described. It provides comprehensive treatment for the safe disposal of sulfidic, naphthenic, phenolic/cresylic spent caustic streams, disulfide streams, spent air streams, spent mixed amine and caustic streams (also known as COS solvent streams) from sulfur treating processes. It allows the use of regenerated spent caustic in the sulfur oxide removal section of the thermal oxidation system reducing the need for fresh NaOH. It may also contain an integrated make-up water system. The integration allows the use of the liquefied petroleum gas or other hydrocarbon feeds to the respective extraction or sweetening process to offset external fuel gas requirements for the thermal oxidation system and for the push/pull system of the spent caustic surge drum and optional hydrocarbon surge drum.

A process and apparatus for sweetening a hydrocarbon stream. The apparatus includes two vessels. In a first extraction vessel, caustic removes mercaptans from the hydrocarbon stream. In a second oxidation vessel, the mercaptans in the rich caustic are converted in disulfides. The lean caustic and disulfides are passed back to the first extraction vessel in which the disulfides are separated into the sweetened hydrocarbon phase. The second vessel may receive a wash oil, such as the sweetened hydrocarbon phase, to remove disulfides from a vented gas stream.