Catalytic process for removing toxic gases from gas streams

Claim 2

A multi-stage process for reducing the content of hydrogen sulfide, sulfur dioxide, carbonyl sulfide and disulfide in a gas stream which comprises (a) passing said gas stream through a first reaction stage at a temperature between about 150° and about 350° C., said stage containing a pretreated catalyst of the formula xLn.sub.2 O.sub.3.yT.sub.2 O.sub.3 in which Ln is yttrium or a rare earth element and T is selected from the group consisting of cobalt, iron and nickel and each of x and y independently is a number from 0 to 3, said catalyst being substantially non-crystalline and having a surface area of from about 10 m 2 /g to about 40 m 2 /g and having been prepared at a temperature no higher than 700° C, to obtain elemental sulfur and a first product stream having reduced content of sulfur containing gases, (b) passing the first product stream through one or more intermediate catalytic reaction stages in which the Claus reaction occurs, to obtain further elemental sulfur and a second product stream having further reduced content of sulfur containing gases, and (c) passing the second product stream through a final reaction stage at a temperature between about 150° and 300° C., said final stage containing a catalyst usable in the first reaction stage, in the presence of air to obtain elemental sulfur and still further reduced content of the sulfur containing gases, which gases can be recyled to an earlier stage.

Claim 3

A process according to claim 1 in which Ln is lanthanum.

Claim 4

A process according to claim 2 in which the gas stream, the first product stream or second product stream is passed through a special reaction stage at a temperature between about 350° C. and about 700° C. in the absence of water vapor, said stage containing a catalyst of the empirical formula La.sub.2 O.sub.2 S to obtain a product stream having reduced content of carbonyl sulfide, and said product stream is passed to the next reaction stage.

Claim 5

A process according to claim 2 in which T is cobalt.

Claim 6

A process according to claim 4 in which each of x and y ranges from 1 to 3, including non-integers.

Claim 7

A process according to claim 2 in which the temperature in the intermediate reaction stage is below about 130° C.

Claim 8

A process according to claim 2 in which the temperature in the final reaction stage is about 200° C.

Claim 9

A process according to claim 1 in which the gas stream contains more than about 7% of hydrogen sulfide and it is processed, prior to the first reaction stage, through a preliminary reaction stage at a temperature of between about 150° C. and about 750° C., said stage containing a catalyst usable in the first reaction stage, to obtain elemental sulfur and a preliminary product stream, and then passing said preliminary product stream to the first reaction stage.

Claim 10

A process according to claim 8 in which the temperature in the preliminary reaction stage is about 700° C.

Claim 11

A process according to claim 2 in which the gas stream, the first product stream or second product stream is passed through a special reaction stage at a temperature between about 150° C. and about 350° C. in the presence of water vapor said stage containing a catalyst of the empirical formula La.sub.2 O.sub.2 S to obtain a product stream having reduced content of carbonyl sulfide, and said product stream is passed to the next reaction stage.

Claim 12

A process according to claim 3 in which the temperature in the special reaction stage is between 400° C. and 700° C.

Claim 13

A multi-stage process for reducing the content of hydrogen sulfide, sulfur dioxide, carbonyl sulfide and carbon disulfide in a gas stream, which comprises (a) passing said gas stream through a first reaction stage in which (i) at least a portion of the hydrogen sulfide reacts with at least a portion of the sulfur dioxide to form elemental sulfur and water, (ii) carbonyl sulfide reacts with sulfur dioxide to form elemental sulfur and carbon dioxide, (iii) carbonyl sulfide reacts with water to form hydrogen sulfide and carbon dioxide, (iv) carbon disulfide reacts with sulfur dioxide to form elemental sulfur and carbon dioxide and (v) carbonyl sulfide reacts with water to form hydrogen sulfide and carbon dioxide, at a temperature of between about 150° and 350° C. in the presence of a pretreated catalyst of the formula xLn.sub.2 O.sub.3.yT.sub.2 O.sub.3 in which Ln is yttrium or a rare earth element, T is a transition element selected from the group consisting of cobalt, iron and nickel, and each of x and y independently is a number from 0 to 3, said catalyst being substantially non-crystalline and having a surface area of from about 10 m 2 /g to about 40 m 2 /g and having been prepared at a temperature no higher than 700° C., the elemental sulfur formed and obtaining a first product stream comprising gases selected from the group consisting of hydrogen sulfide and sulfur dioxide and a possible minor amount of carbonyl sulfide, (b) passing the product stream of said first stage through one or more intermediate reaction stages in which the hydrogen sulfide and sulfur dioxide catalytically react in the Claus reaction to form elemental sulfur and water, removing the elemental sulfur and obtaining a second product stream which may contain carbonyl sulfide and hydrogen sulfide, (c) passing the product stream of the intermediate stage through a final reaction stage in which hydrogen sulfide and carbonyl sulfide are each reacted with oxygen to form elemental sulfur, sulfur dioxide and/or carbon dioxide at a temperature between about 150° and 300° C., in presence of a catalyst usable in the first stage, removing any elemental sulfur formed and recycling any sulfur dioxide formed to the first or second stage.

Claim 14

A multi-stage process for reducing the content of hydrogen sulfide, sulfur dioxide, carbonyl sulfide and carbon disulfide in a gas stream, which comprises (a) passing said gas stream through a first reaction stage in which (i) at least a portion of the hydrogen sulfide reacts with at least a portion of the sulfur dioxide to form elemental sulfur and water, (ii) carbonyl sulfide reacts with sulfur dioxide to form elemental sulfur and carbon dioxide, (iii) carbonyl sulfide reacts with water to form hydrogen sulfide and carbon dioxide, (iv) carbon disulfide reacts with sulfur dioxide to form elemental sulfur and carbon dioxide and (v) carbonyl sulfide reacts with water to form hydrogen sulfide and carbon dioxide, at a temperature of between about 150° and 350° C. in the presence of a pretreated catalyst of the formula xLn.sub.2 O.sub.3.yT.sub.2 O.sub.3 in which Ln is yttrium or a rare earth element, T is a transition element selected from the group consisting of cobalt, iron and nickel, and each of x and y independently is a number from 0 to 3, said catalyst being substantially non-crystalline and having a surface area of from about 10 m 2 /g to about 40 m 2 /g and having been prepared at a temperature no higher than 700° C., the elemental sulfur formed and obtaining a first product stream comprising gases selected from the group consisting of hydrogen sulfide and sulfur dioxide and a possible minor amount of carbonyl sulfide, (b) passing the product stream of said first stage through one or more intermediate reaction stages in which the hydrogen sulfide and sulfur dioxide catalytically react in the Claus reaction to form elemental sulfur and water, removing the elemental sulfur and obtaining a second product stream which may contain carbonyl sulfide and hydrogen sulfide, (c) passing the product stream of the intermediate stage through a final reaction stage in which hydrogen sulfide and carbonyl sulfide are each reacted with oxygen to form elemental sulfur, sulfur dioxide and/or carbon dioxide at a temperature between about 150° and 300° C., in presence of a catalyst usable in the first stage, removing any elemental sulfur formed and recycling any sulfur dioxide formed to the first or second stage.

Claim 15

A process according to claim 12 in which Ln is lanthanum.

Claim 16

A process according to claim 13 in which T is cobalt.

Claim 17

A process according to claim 14 in which each of x and y is a number from 1 to 3, including non-integers.

Claim 18

A process according to claim 15 in which, in the first stage, the amount of carbonyl sulfide is reduced to less than 100 ppm and the amount of carbon disulfide is reduced to less than 10 ppm.

Claim 19

A process according to claim 13 in which the temperature in the intermediate reaction stage is below about 130° C.

Claim 20

A process according to claim 13 in which the temperature in the final reaction stage is about 200° C.

Claim 21

A process according to claim 12 in which the gas stream contains more than about 7% of hydrogen sulfide and it is passed, prior to the first reaction stage, through a preliminary reaction stage at a temperature of between about 150° C. and about 750° C., said stage containing a catalyst usable in the first reaction stage and in which a portion of the hydrogen sulfide reacts with sulfur dioxide to form elemental sulfur and water, the elemental sulfur is removed, and a preliminary product stream containing a reduced amount of hydrogen sulfide is passed to the first reaction stage.

Claim 22

A process according to claim 19 in which the temperature in the preliminary reaction stage is about 700° C.

Claim 23

A process according to claim 19 in which the preliminary product stream contains less than 7% of hydrogen sulfide.

Claim 24

A process according to claim 13 in which the gas stream, the product stream of the first stage or a product stream of an intermediate stage is passed through a special reaction stage in which carbonyl sulfide reacts with sulfur dioxide to form carbon dioxide and elemental sulfur, at a temperature between about 150° C. and about 350° C. in the presence of water vapor and a catalyst of the empirical formula La.sub.2 O.sub.2 S, removing the elemental sulfur formed and the product stream is passed to the next reaction stage.

Claim 25

A process according to claim 24 in which the temperature in the special reaction stage is between 400° and 700°.

Claim 26

A process according to claim 13 in which the gas stream, the product stream of the first stage or a product stream of an intermediate stage is passed through a special reaction stage in which carbonyl sulfide reacts with sulfur dioxide to form carbon dioxide and elemental sulfur, at a temperature between about 350° C. and about 700° C. in the absence of water vapor and in the presence of a catalyst of the empirical formula La.sub.2 O.sub.2 S removing the elemental sulfur formed, and the product stream is passed to the next reaction stage.