Automatic pH control in a process for removal of hydrogen sulfide from a gas

Claim 1

A continuous process for removing hydrogen sulfide from a sour gaseous stream comprising: (A) contacting said sour gaseous stream in a contact zone with a first aqueous alkaline solution at a temperature below the melting point of sulfur, said solution comprising at least one polyvalent metal chelate in a higher valence state in an effective amount suitable for oxidizing substantially all the hydrogen sulfide removed from said gaseous stream to produce a sweet gaseous stream, a second aqueous alkaline solution comprising sulfur, and at least one polyvalent metal chelate in a lower valence state; (B) separating in a separation zone said sulfur from said second aqueous alkaline solution; (C) passing said second aqueous alkaline solution as an electrolyte from said separation zone to a cathode compartment of an electrochemical cell, said cell comprising an anode in an anode compartment and a cathode in said cathode compartment, said compartments separated by a cell membrane and said anode and cathode connected through an external electrical circuit; (D) producing said first aqueous alkaline solution by passing said second aqueous alkaline solution from said cathode compartment to said anode compartment and oxidizing at said anode said polyvalent metal chelate to a higher valence state while producing hydrogen at said cathode and hydroxide ions in said electrolyte; and (E) recycling said first aqueous alkaline solution from said electrochemical cell to said contact zone; whereby the pH of said first aqueous alkaline solution is maintained in said contact zone at about 7 to about 9.