Processes for selectively reducing the concentration of hydrogen cyanide in syngas
View Patent ↗This invention pertains to processes for selectively oxidizing hydrogen cyanide contained in syngas using permanganate anion as an oxidant contained in an aqueous solution that is contacted with the syngas under certain conditions of temperature, pressure and duration of contact.
1. A process for selectively reducing the concentration of hydrogen cyanide with respect to carbon monoxide in a gas feed, said gas feed containing carbon monoxide and hydrogen cyanide, comprising:
a. continuously passing said gas feed into contact with an aqueous solution of permanganate anion under conditions sufficient for the permanganate anion to oxidize the hydrogen cyanide and generate manganese dioxide, the duration of said contacting being at least sufficient to provide a treated gas having a concentration of the hydrogen cyanide that is less than that in the gas feed;
b. continuously removing said treated gas from contact with the aqueous solution;
c. intermittently or continuously replenishing permanganate anion to said aqueous solution; and
d. intermittently or continuously removing manganese dioxide from said aqueous solution.
2. The process of claim 1 wherein the treated gas contains less than about 0.5 parts per million by volume of hydrogen cyanide.
3. The process of claim 2 wherein the treated gas contains less than about 0.1 parts per million by volume of hydrogen cyanide.
4. The process of claim 2 wherein the gas feed contains between about 1 and 50 parts per million by volume of hydrogen cyanide.
5. The process of claim 1 wherein the aqueous solution contains less than about 1000 parts per million by mass of permanganate anion.
6. The process of claim 1 wherein the average duration of contact between the gas feed and aqueous solution is less than about 30 seconds.
7. The process of claim 1 wherein the average duration of contact between the gas feed and aqueous solution is less than about 10 seconds.
8. The process of claim 1 wherein in step a less than about 100 parts per million by mass of permanganate anion in the aqueous solution are converted to manganese dioxide per second.
9. The process of claim 1 wherein in step a less than about 75 parts per million by mass of permanganate anion in the aqueous solution are converted to manganese dioxide per second.
10. The process of claim 1 wherein the contact between the gas feed and aqueous solution is conducted in an absorption vessel, and aqueous solution is continuously added and withdrawn from said absorption vessel.
11. The process of claim 10 wherein the contact between the gas feed and aqueous solution is countercurrent.
12. The process of claim 11 wherein the absorption vessel contains structured packing.
13. The process of claim 12 wherein the pressure of the treated gas is within 50 kPa below the pressure of the gas feed passed to the absorption vessel.
14. The process of claim 11 wherein at least a portion of the aqueous solution withdrawn from said absorption vessel is subjected to solids removal unit operation to remove manganese dioxide and is recycled to the absorption vessel.
15. The process of claim 14 wherein the solids removal unit operation comprises a centrifuge.
16. The process of claim 1 wherein the gas feed comprises at least one other impurity selected from the group of acetylene, nitric oxide and hydrogen sulfide, and at least a portion of said at least one other impurity is oxidized by permanganate anion during the contact of step (a).
17. The process of claim 1 wherein the oxidation of hydrogen cyanide in step a is mass transfer limited.
18. The process of claim 1 wherein the gas feed comprises 10 to 60 mole percent carbon monoxide.
19. The process of claim 1 wherein the duration of said contacting is at least sufficient to provide the treated gas having a concentration of the hydrogen cyanide that is about 30 percent less than that in the gas feed.
20. The process of claim 1 wherein:
said gas feed contains at least about 5 volume percent carbon monoxide and between about 1 and 500 parts per million by volume hydrogen cyanide;
said aqueous solution contains between about 50 and 2000 parts per million by mass of permanganate anion:
said contacting is at a temperature of between about 4° C. and 50° C.; and
said gas feed is at a pressure less than about 2000 kPa absolute.