Method and apparatus for removal of h2s from a process gas, including thiosulfate and/or cyanide salt decomposition

A method of removing H.sub.2 S and HCN from a process gas including the steps of:

• intimately contacting the process gas with a catalytic polyvalent metal redox solution to absorb the H.sub.2 S and HCN and to form cyanide salts of cyanide complexes in the polyvalent metal redox solution, and simultaneously forming a reduced catalytic polyvalent metal redox solution;
• intimately contacting the catalytic reduced polyvalent metal redox solution with an oxidizing gas capable of oxidizing the reduced catalytic polyvalent metal redox solution sufficiently to regenerate the catalytic polyvalent metal redox solution to form an oxygenated polyvalent metal redox solution capable of again absorbing said H.sub.2 S and HCN from said process gas;
• anaerobically heating a portion of the polyvalent metal redox solution containing the cyanide salts or cyanide complexes to a temperature in the range of about 400.degree. F. to about 700.degree. F. and a pressure of at least about 1000 psig, without the addition of hydrogen, for a time sufficient, to decompose the cyanide salts or complexes;
• and
• flowing the oxygenated polyvalent metal redox solution in intimate contact with said process gas for further absorption of H.sub.2 S and HCN from said process gas.

In an apparatus for effecting mass transfer of a liquid sequentially with two different gases in a separate mass transfer zone for each gas without permitting both gases to contact the same portion of the liquid simultaneously, including a first mass transfer zone for mass transfer between a liquid reagent and the first gas into the first mass transfer zone;

• a second mass transfer zone in liquid, but not vapor, communication with the first mass transfer zone;
• means for directing the liquid reagent from the first mass transfer zone into the second mass transfer zone;
• means for directing a second gas into the second mass transfer zone for intimate contact and mass transfer therebetween the improvement comprising:
• an anaerobic hydrothermal converter disposed in the process to receive a portion of the liquid reagent, after said reagent has absorbed one or more materials from the process gas, said converted including means for heating the liquid reagent to a temperature sufficient to decompose thiosulfate salts to smaller molecules that are capable of forming elemental sulfur in the first or second mass transfer zone of the process.