Patent EA-002241-B1 (EA)
Title: High efficiency process for recovering sulfur from h2s-bearing gas
Inventor: LYNN SCOTT
IPC: C01B17/05
Filed: 1998-09-03
Abstract: 1. A process for recovering sulfur from H2S-bearing gas, said process comprising: (a) feeding said H2S-containing stream to a continuous-flow reactor and contacting said H2S-containing stream in said reactor with an SO2-containing stream and an organic liquid solvent under the following conditions: (i) said organic liquid solvent contains a homogeneous catalyst that promotes the liquid-phase reaction 2 H2S + SO2 -> 3 S + 2 H2O , (I) (ii) the temperature in said reactor is maintained above the melting point and below the boiling point of said solvent, and (iii) said H2S-containing and SO2-containing streams are fed at relative feed rates such that H2is fed in excess relative to SO2 in accordance with reaction (I), to convert substantially all of said SO2 to liquid elemental sulfur and to produce a reactor discharge containing said liquid elemental sulfur and unreacted H2S; (b) combusting said unreacted H<2>S with an O2-containing gas in accordance with the reaction 3 H2S + 3 O2 -> 2 SO2 + 2 H2O (II) to convert said unreacted H2S to SO2, and to produce a combustion gas containing SO2 and H2O; and (c) passing said combustion gas through an SO2 absorber to recover substantially all SO2 from said combustion gas, thereby leaving a tail gas substantially free of H2S and SO2, and recycling all of said SO2 thus recovered to said continuous-flow reactor as the entire SO2 feed thereto. 2. A process in accordance with claim 1 in which said temperature in (a)(ii) is maintained between 119 degree C and 155 degree C. 3. A process in accordance with claim 1 in which said temperature in (a)(ii) is maintained between 125 degree C and 145 degree C. 4. A process in accordance with claim 1 in which said H2S-containing stream is a gas stream, said SO2-containing stream is liquid-phase SO2 dissolved in said solvent, and said catalyst is also dissolved in said solvent. 5. A process in accordance with claim 1 in which both said H2S-containing stream and said SO2-containing stream are gas streams, and both are absorbed in said reactor by said solvent, said solvent containing said catalyst dissolved therein. 6. A process in accordance with claim 5 in which said reactor is a column-type gas-liquid contactor, and in which said gas streams flow cocurrently with said solvent and with said liquid elemental sulfur. 7. A process in accordance with claim 5 in which said reactor is a column-type gas-liquid contactor, and in which said gas streams flow countercurrently with said solvent and with said liquid elemental sulfur. 8. A process in accordance with claim 5 further comprising: (d) passing said reactor discharge through a separator to separate a liquid sulfur phase, an organic liquid phase, and a gas phase into separate streams; (e) extracting H2S from said organic liquid phase in a steam stripper, leaving a liquid stripper bottom stream of substantially H2S-free organic solvent, water, and sulfur; (f) flashing said liquid stripper bottom stream in a vacuum crystallizer to evaporate a substantial amount of said water from said liquid stripper bottom stream and to precipitate sulfur therefrom, thereby forming a slurry of crystalline sulfur; (g) permitting crystalline sulfur to settle in said slurry to form a concentrated slurry and a clarified solvent; and (h) feeding said clarified solvent to said SO2 absorber and said concentrated slurry to said separator of step (d). 9. A process in accordance with claim 1 further comprising feeding an additional H2S-containing gas stream to step (b) that has not passed through said continuous-flow reactor of step (a) in combination with said unreacted H2S from said reactor discharge, the H2S in said additional H2S-containing gas stream amounting to about 10% to about 30% of the total H2S fed to said process, the total H2S fed to said process being approximately 50% excess relative to said SO2 fed to said continuous-flow reactor in accordance with reaction (I). 10. A process in accordance with claim 1 further comprising contacting said liquid elemental sulfur formed in step (a) with liquid-phase SO2 to remove dissolved H2S from said liquid elemental sulfur. 11. A process in accordance with claim 7 further comprising introducing said SO2-containing stream into said column-type gas-liquid contactor at a location below the location of introduction of said H2S-containing stream, both for upward flow countercurrent to downward flowing liquids therein, to remove dissolved H2S from liquid elemental sulfur prior to withdrawing said liquid elemental sulfur from said contactor. 12. A process in accordance with claim 1 in which said solvent selected from the group consisting of ethers of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, and tetrapropylene glycol. 13. A process in accordance with claim 1 in which said solvent is a member selected from the group consisting of monomethyl, dimethyl, monoethyl, and diethyl ethers of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, and tetrapropylene glycol. 14. A process in accordance with claim 1 in which said solvent is a member selected from the group consisting of monomethyl and dimethyl ethers of diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol. 15. A process in accordance with claim 1 in which said homogeneous catalyst is a member selected from the group consisting of pyridine and isoquinoline, optionally substituted at one or more sites other than carbon atoms adjacent to the ring nitrogen with a polar group that is a member selected from the group consisting of hydroxyl, hydroxyalkyl, acetamido, acetamidoalkyl, acetyl, acetylalkyl, acetyloxy, acetyloxyalkyl, alkoxy, alkoxyalkyl, amino, alkylamino, and aminoalkyl. 16. A process in accordance with claim 1 in which said homogeneous catalyst is a member selected from the group consisting of pyridine and isoquinoline, substituted at a site other than a carbon atom adjacent to the ring nitrogen with a member selected from the group consisting of hydroxyl, hydroxymethyl, acetamido, acetamidomethyl, acetyl, acetylmethyl, acetyloxy, and acetyloxymethyl. 17. A process in accordance with claim 1 in which said homogeneous catalyst is pyridine substituted at a site other than a carbon atom adjacent to the ring nitrogen with a member selected from the group consisting of hydroxymethyl, acetamido, acetamidomethyl, acetyl, acetylmethyl, acetyloxy, and acetyloxymethyl. 18. A process in accordance with claim 1 in which said homogeneous catalyst is 3-(hydroxymethyl)pyridine.