Removal of residual sulfur compounds from a caustic stream

• US 7,875,185 B2
• Filed: 09/10/2007
• Issued: 01/25/2011
• Est. Priority Date: 09/10/2007
• Status: Expired due to Fees

• Current Assignee: Merichem Technologies LLC
• Original Assignee: Merichem Company
• Inventors: Zhang, Tiejun
• Primary Examiner(s): Savage; Matthew O
• Application Number:
  US11/900,105
• Publication Number:
  US 20090065434A1
• Time in Patent Office: 1,233 Days
• Field of Search: 210/665, 210/668, 210/763, 210/671, 210/693, 210/694, 208/235
• US Class Current: 210/668
• CPC Class Codes: B01D 15/00 Separating processes involving the treatment of liquids with solid sorbents using liquid sorbents B01D11/00; ion exchange processes or materials, sorbent materials in general B01J, e.g. sorbents for chromatography B01J20/281; for investigating or analysing materials G01N30/00; Apparatus therefor
• CPC Class Codes: B01J 20/20 comprising free carbon; comprising carbon obtained by carbonising processes
• CPC Class Codes: B01J 20/223 containing metals, e.g. organo-metallic compounds, coordination complexes
• CPC Class Codes: B01J 20/28057 Surface area, e.g. B.E.T specific surface area
• CPC Class Codes: B01J 20/28069 Pore volume, e.g. total pore volume, mesopore volume, micropore volume
• CPC Class Codes: B01J 20/3204 Inorganic carriers, supports or substrates
• CPC Class Codes: B01J 20/3236 containing metal, other than zeolites, e.g. oxides, hydroxides, sulphides or salts
• CPC Class Codes: B01J 20/3265 with an organic functional group containing a metal, e.g. a metal affinity ligand
• CPC Class Codes: B01J 20/3416 of sorbents or filter aids comprising free carbon, e.g. activated carbon
• CPC Class Codes: B01J 20/3475 in the liquid phase
• CPC Class Codes: C10G 19/08 Recovery of used refining agents
• CPC Class Codes: C10G 2300/202 Heteroatoms content, i.e. S, N, O, P

Abstract

A process for the removal of residual sulfur compounds from a liquid caustic stream is disclosed. One embodiment of my invention adsorbs disulfides from a caustic stream using an activated carbon adsorbent while another combines both oxidation and adsorption in single step to remove residual sulfur compounds from a rich caustic stream using metal phthalocyanine supported on a solid adsorbent. This process is especially useful as a polishing step in a caustic regeneration process flow scheme.

Claims

1. A process for removing residual sulfur compounds from a caustic feed stream, comprising, in combination,

a) obtaining a caustic feed stream from a lower layer of a gravity separator, wherein caustic entering the gravity separator has been previously oxidized in an oxidization process, and wherein residual sulfur compounds in the caustic feed stream comprise less than 500 weight ppm measured as elemental sulfur;

b) introducing the caustic feed stream of step a) into a polishing unit;

c) introducing an oxidant into the polishing unit;

d) admixing and contacting the caustic feed stream and oxidant within the polishing unit in the presence of a catalyst bed comprising a metal phthalocyanine catalyst supported on a catalyst support;

e) converting mercaptans that are present as part of the sulfur compounds in the caustic feed stream to disulfides;

f) adsorbing on the catalyst support the disulfides formed in step e) and disulfides introduced into the polishing unit as part of the sulfur compounds in the caustic feed stream; and

g) removing from the polishing unit a polished caustic stream product comprising less than 20 weight ppm of sulfur compounds measured as elemental sulfur.

2. The process of claim 1 where the sulfur compounds in the caustic feed stream comprise less than 100 weight ppm measured as elemental sulfur.

3. The process of claim 1 where the sulfur compounds in the caustic feed stream comprise mercaptans and disulfides.

4. The process of claim 3 where the mercaptans comprise less than 50 weight ppm measured as elemental sulfur in the caustic feed stream.

5. The process of claim 1 where the caustic feed stream and oxidant is contacted within the polishing unit with a fixed bed of activated carbon impregnated with metal phthalocyanine.

6. The process of claim 5 where the metal is selected from the group comprising cobalt, iron and mixtures thereof.

7. The process of claim 5 where the activated carbon has a pore volume of 0.5-1.5 cc/g BJH N₂ and/or surface area of 500-2,000 m²/g BET.

8. The process of claim 5 where the activated carbon is wood based.

9. The process of claim 1 where the oxidant is air or at least one oxygen-containing gas.

10. The process of claim 1 where at least a portion of the catalyst support adsorbent is subjected to a regeneration process.

11. The process of claim 1 where the sulfur compounds in the polished caustic stream product comprise less than 5 weight ppm measured as elemental sulfur.