Demercaptanization of Light Hydrocarbon Fractions with Strong Aqueous Ammonia without Producing Sulfur Caustic Wastewate
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OCHEMISTRY AND OIL REFINING
Demercaptanization of Light Hydrocarbon Fractions with Strong Aqueous Ammonia without Producing Sulfur Caustic Wastewater B. V. Andreeva, *, A. S. Ustinova, A. V. Akopyanb, A. V. Anisimovb, E. A. Esevab, A. V. Kleimenovc, D. O. Kondrashevc, D. V. Khrapovd, and R. V. Esipenkod a
b
OOO IPOS Proekt, Moscow, 117246 Russia Faculty of Chemical, Moscow State University, Moscow, 119991 Russia c PAO Gazpromneft, St. Petersburg, 190000 Russia d AO Gazpromneft—ONPZ, Omsk, 644040 Russia *e-mail: [email protected]
Received October 8, 2018; revised January 28, 2019; accepted January 29, 2019
Abstract—A technology for the demercaptanization of light hydrocarbon fractions and liquefied petroleum gas with 25% aqueous ammonia is proposed. One advantage of this method for the demercaptanization of oil fractions over conventional processes such as Merox is the absence of a stage of oxidative catalytic recovery of spent caustic and highly toxic sulfur caustic wastewater. Spent (saturated with sulfur compounds) aqueous ammonia is recovered at the same plant for the distillation of sulfur ammonia wastewater in which aqueous ammonia is produced. Keywords: liquified hydrocarbon gases, mercaptans, sweetening, strong aqueous ammonia, sulfur ammonia wastewater, sulfur caustic wastewater, wastewater treatment, hydrogen sulfide, ammonia DOI: 10.1134/S004057952005005X
INTRODUCTION The most popular method for the demercaptanization of light hydrocarbon fractions and liquefied petroleum gas in oil refinery is currently the traditional caustic washing, which consists of the extraction of mercaptans1 from the hydrocarbon phase into the aqueous phase by mixing petroleum products with a caustic solution. Being acidic compounds (pKa = 10– 11), mercaptans in the presence of hydroxide ions pass into the aqueous phase as salts—mercaptides: (1) RSH + OH− → RS− + H2O. Using a strong aqueous caustic (typically 15% NaOH) as an extractant in the industrial process requires a stage of catalytic recovery of the spent (saturated with sulfur compounds) caustic solution for its further use. The recovery uses atmospheric oxygen, by which the mercaptans passed into the aqueous phase are oxidized to disulfides, whereas the sulfides and hydrogen sulfide that are present are oxidized to thiosulfates, elemental sulfur, and sulfates. Disulfides are 1 Mercaptans
are organic sulfur compounds with the overall formula RSH, where R is a hydrocarbon radical. In light hydrocarbon fractions and liquefied petroleum gas, which are considered in this work, R is typically CH3 or C2H5. C3H7SH occurs rarely and in much smaller amounts. Heavier mercaptans are not encountered in these fractions.
then extracted from the spent aqueous caustic with an organic solvent (e.g., gasoline). Other water-soluble sulfur-containing compounds and carbonates that formed by the interaction of caustic with air containing carbon dioxide are accumulated in the circulating working caustic solution, reducing the free caustic concentration. Such spent caustic solutions canno
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