GB2059404A

GB2059404A - The Simultaneous Separation of Sulfur and Nitrogen Oxides from A Gaseous Mixture

Info

Publication number: GB2059404A
Application number: GB7932997A
Authority: GB
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 1979-09-24
Filing date: 1979-09-24
Publication date: 1981-04-23
Also published as: GB2059404B

Abstract

In order to achieve the simultaneous separation of sulfur and nitrogen oxides from a gaseous mixture containing said oxides and oxygen the gaseous mixture and ammonia are contacted with a solid sulfur oxides acceptor comprising copper and/or copper oxide dispersed on a carrier material in conjunction with ruthenium and rhenium and/or the oxides thereof. The sulfur oxides acceptor acts also as catalyst for reduction of nitrogen oxides by ammonia.

Description

SPECIFICATION The Simultaneous Separation of Sulfur and Nitrogen Oxides from a Gaseous Mixture It has become well known that the oxides of sulfur and nitrogen resulting, for example, from the combusion or air oxidation of high sulfur coal or fuel oil, are among the major pollutants of our environment.

Sulfur oxides are conveniently separated from an oxygen-containing gas mixture, such as flue gas, by contacting the mixture with a solid acceptor at an elevated temperature. Typically, the solid acceptor comprises a supported copper and/or copper oxide capable of retaining the sulfur oxides as a sulfate. The process can be used to remove sulfur oxides from flue gases so that the latter may be freely discharged to the atmosphere. Since the solid acceptor requires frequency regeneration, the process generally comprises a repeating acceptance-regeneration cycle. During regeneration, the sulfate is decomposed at an elevated temperature in the presence of a reducing gas to yield a regenerated acceptor and a regeneration off-gas of increased sulfur dioxide concentration. This off-gas is useful, for example, in the manufacture of sulfuric acid and elemental sulfur.

The present invention seeks to improve this process so that nitrogen oxides can be separated substantially simultaneously with the sulfur oxides from a gaseous mixture comprising said oxides and oxygen.

According to the invention there is provided a process for the simultaneous separation of oxides of sulfur and nitrogen from a gaseous mixture comprising said oxides and oxygen, which comprises contacting said mixture and ammonia at a temperature of from 1500 to 4500C with a solid sulfur oxides acceptor comprising copper and/or copper oxide dispersed on a carrier material in conjunction with ruthenium and rhenium or the oxides thereof.

A preferred carrier material is an alumina support having a surface area of at least 50 m2/gm.

A more specific embodiment of this invention, the features of which are preferred singly and in combination, the process comprises contacting said gaseous mixture at a temperature of from 1 500 to 4500C, with ammonia employed in a from 0.5:1 to 2.5:1 mole ratio with the nitrogen oxides content of said gaseous mixture, and a solid acceptor comprising from 5 to 15 wt.% copper, copper oxide or mixture thereof dispersed on a gamma-alumina support or carrier material in combination with ruthenium and rhenium or the oxides thereof, each of the ruthenium and rhenium components comprising from 0.01 to 2 wt.% of the solid acceptor, calculated as the elemental metal, and regenerating the solid acceptor, when it has become deactivated, by heating it in contact with a reducing gas comprising hydrogen, carbon monoxide and from 50 to 90 vol.% steam.

In the art relating to the separation of sulfur oxides from a gaseous mixture comprising sulfur oxides and oxygen, solid acceptors comprising copper, copper oxide or a mixture thereof are well known. The copper component is most often dispersed on a refractory inorganic oxide carrier material.

Refractory inorganic oxides suitable for use include naturally occurring materials, for example clays and silicates such as fuller's earth, attapulgus clay, feldspar, hailoysite, montmorillonite, kaolin, and diatomaceous earth (frequently referred to as siliceous earth, diatomaceous silicate or kieselguhr) which naturally occurring material may or may not be activated prior to use by one or more treatments including drying, calcining, steaming and/or acid treatment. Synthetically prepared refractory inorganic oxides such as alumina, silica, zirconia, boria, thoria, magnesia, titania or chromia, or composites thereof, particularly alumina in combination with one or more other refractory inorganic oxides, for example alumina-silica, alumina-zirconia or alumina-chromia, are also suitable.Alumina is a preferred refractory inorganic oxide, and the alumina may be any of the various hydrous aluminum oxides or alumina gels, for example alpha-alumina monohydrate (boehmite), alpha-alumina trihydrate (gibbsite) and beta-alumina trihydrate (bayerite). Activated aluminas, such as have been thermally treated to eliminate substantially all of the water and/or hydroxyl groups commonly associated therewith, are particularly useful. Preferably, the alumina is an activated alumina with a surface area of from 50 to 500 m2/gm, especially gamma-alumina and eta-alumina resulting from the thermal treatment of boehmite alumina and bayerite alumina, respectively, generally at a temperature of from 4000 to 1 0000C. The refractory inorganic oxide may be employed in any suitable shape or form including spheres, pills, extrudates, granules, briquettes, rings, etc.The copper content of the solid acceptor, present as copper and/or copper oxide but calculated as the elemental metal, is generally in the range of from 1 to 25 wt.% depending at least in part on the available surface area of the selected carrier material. The copper component, calculated as the elemental metal, preferably comprises from 5 to 1 5 wt.% of the solid acceptor.

Pursuant to the present invention, the copper component is dispersed on the selected carrier material in combination with ruthenium and rhenium or the oxides thereof. The ruthenium component employed in combination with the rhenium component effects an unexpected improvement in the nitrogen oxides conversion activity of the solid acceptor. The improvement resulting from the inclusion of the ruthenium-rhenium combination as a component of the solid acceptor is unexpected in view of the lack of improvement in nitrogen oxides conversion resulting from the inclusion of platinum or palladium in combination with rhenium.The ruthenium component in combination with the rhenium component also further improves the capacity of the solid acceptor for sulfur oxides while effecting substantially complete suppression of sulfur oxides break-through during the acceptance phase of the operation before said capacity is achieved. And a still further improvement is in the regeneration characteristics of the solid acceptor, regeneration being able to be effected at a faster rate and to a greater extent. Each of the ruthenium and rhenium components suitably constitutes from 0.01 to 2 wt.% of the solid acceptor, calculated as the elemental metal.

The solid acceptor herein contemplated may be prepared in any conventional or otherwise convenient manner. It is a preferred practice to impregnate the desired metal component on a preformed support or carrier material from an aqueous solution of a precursor compound of said metal component, the impregnated carrier material being subsequently dried and calcined to form the desired metal component dispersed on the carrier material. Preferred precursor compounds include the soluble halides, oxides and nitrates decomposable to the desired metal component upon calcination. The metal components are preferably and advantageously impregnated on the selected carrier material from a common impregnating solution thereof.

The solid acceptor used in this invention is suitably employed in a fixed bed type of operation utilizing two or more reactors alternating between the acceptance and regeneration phases of the operation to provide a continuous process. The sulfur oxides acceptance phase is usually effected at a temperature of from 1500 to 4500C as provided by hot flue gases, a temperature of from 3500 to 4500C being preferred. The regeneration phase is carried out at an elevated temperature in the presence of reducng gas-usually a hydrogen and/or carbon monoxide-containing gas mixture diluted with nitrogen, steam or other suitable diluents.The acceptor is preferably and advantageously regenerated in contact with a reducing gas comprising carbon monoxide and hydrogen in a mole ratio of from 0.5:1 to 1.5:1. Regeneration is further advantageously effected in the presence of steam with a regeneration gas preferably comprising from 50 to 90 vol.% steam to further inhibit the formation of copper sulfide.

Regeneration temperatures may vary over a relatively wide range, but preferably are in the range of from 3500 to 45000.

The following Examples are presented in illustration of the improvement resulting from the practice of this invention.

Example 1 (Comparative) In preparation of a solid acceptor representative of the prior art, 1/16" spheroidal gammaalumina particles were employed as a carrier material. The spheroidal particles, precalcined in air for 2 hours at about 10000C, had an average bulk density of about 0.55 gms/cc, an average pore volume of about 0.31 cc per gm, an average pore diameter of about 129 Angstroms, and a surface area of about 96 m2/gms. 300 gms. of the spheroidal alumina particles were immersed in an impregnating solution of 60.78 gms of copper nitrate trihydrate dissolved in 400 ml of water. The alumina spheres were tumbled in the solution at ambient temperature conditions for about 1/2 hour utilizing a steamjacketed rotary dryer. Steam was thereafter applied to the dryer jacket and the solution evaporated to dryness in contact with the tumbling spheres.The impregnated spheres were then calcined in air for 2 hours at about 53500 to yield a solid acceptor containing 5 wt.% copper. This solid acceptor is hereinafter referred to as Acceptor Example II In this example, representing one preferred embodiment of this invention, 1/1 6a spheroidal gamma-alumina particles, substantially as described in Example I, were utilized as a carrier material.

The spheroidal particles, precalcined in air at about 1 0000C for 2 hours, had an average bulk density of about 0.55 gms/cc, an average pore volume of about 0.27 cc per gm, an average pore diameter of about 120 Angstroms, and a surface area of about 90 m2/gm. 65 gms of the spheroidal particles were immersed in an impregnating solution contained in a steamdacketed rotary dryer and prepared by dissolving 13.21 gms of copper nitrate trihydrate, 0.112 gms of ruthenium tetrachloride pentahydrate, and 0.088 gms of rhenium heptoxide in 87 ml of water. The spheres were tumbled in the solution at ambient temperature conditions for about 1/2 hour. Steam was thereafter applied to the dryer jacket and the solution evaporated to dryness in contact with the tumbling spheres.The impregnated spheres were then calcined in air for about 1 hour at 53500 to yield a solid acceptor containing about 5 wt.% copper and about 0.05 wt.% ruthenium and 0.05 wt% rhenium. The solid acceptor of this example is hereinafter referred to as Acceptor II.

Example Ill (Comparative) This example is presented to demonstrate the poor nitrogen oxides conversion resulting when platinum is substituted for the ruthenium component of the solid acceptor of this invention, both platinum and ruthenium being members of the platinum group metals of Group VIII of the periodic table. In this example, 1/1 6n alumina spheres, substantially as described in the previous examples, were immersed in an impregnating solution contained in a steamjacketed rotary dryer. In this instance, the impregnating solution was prepared by dissolving about 13.2 gms of copper nitrate trihydrate, 10.52 milliliters of chloroplatinic acid solution (3.08 milligrams of platinum per milliliter), and 2.24 milliliters of perrhenic acid solution (10 milligrams of rhenium per milliliter) in 100 milliliters of water.

The spheres were tumbled in the solution for about 1/2 hour at ambient temperature conditions after which steam was applied to the dryer jacket and the solution evaporated to dryness in contact with the tumbling spheres. The impregnated spheres were calcined in air at about 53500 for one hour to yield a solid acceptor containing 5 wt.% copper, 0.05 wt.% platinum and 0.05 wt.% rhenium. The solid acceptor of this example is hereinafter referred to as Acceptor Ill.

Example IV (Comparative) This example is presented to further demostrate the poor nitrogen oxides conversion resulting when palladium is substituted for the ruthenium component of the solid acceptor of this invention, both palladium and ruthenium being members of the platinum group metals of Group VIII of the periodic table. In this example, 1/1 6" alumina spheres, substantially as described in the previous examples, were immersed in an impregnating solution contained in a steam-jacketed rotary dryer. In this instance, the impregnating solution was prepared by dissolving about 13.2 gms of copper nitrate trihydrate, 10.8 milliliters of chloropalladic acid solution (3 milligrams of palladium per milliliter) and 2.24 milliliters of perrhenic acid solution (10 milligrams of rhenium per milliliter) and 100 milliliters of water.

The spheres were tumbled in the solution for about 1/2 hour at ambient temperature conditions after which steam was applied to the dryer jacket and the solution evaporated to dryness in contact with the tumbling spheres. The impregnated spheres were calcined in air at about 53500 for one hour to yield a solid acceptor containing 5 wt.% copper, .05 wt.% palladium and .05 wt.% rhenium. The solid acceptor of this example is hereinafter referred to as Acceptor IV.

Example V A comparative evaluation of the described solid acceptors -IV was effected. 50 cc of the acceptor was in each case disposed as a fixed bed in a vertical tubular reactor with a 7/8" inside diameter. The acceptors were first evaluated with respect to a gaseous mixture comprising about 0.2 vol.% sulfur dioxide, 0.075 vol.% nitrogen oxides, 3 vol.% oxygen, 1 5 vol.% steam, 0.075 vol.% ammonia and about 81.6 vol.% nitrogen. The acceptors were then further evaluated with respect to a gaseous mixture differing from the first only in the ammonia content-the ammonia comprising 0.1125 vol.% of the mixture in the latter case.The acceptor of Example I evaluated with respect to the first mentioned gaseous mixture is hereinafter referred to as Acceptor la, and the acceptor of Example I evaluated with respect to the last mentioned gaseous mixture is hereinafter referred to as Acceptor Ib.

Similarly, the acceptors of Examples ll, III and IV are hereinafter referred to as Acceptors Ila and llb, villa and Illb, and IVa and IVb.

The gaseous mixture was in each case preheated to 40000 and charged upflow through the acceptor bed at a gaseous hourly space velocity (GHSV) of about 11,000. The reactor effluent was analyzed and discharged to the atmosphere through a wet test meter. After one hour, the solid acceptor was regenerated. Regeneration was by preheating a reducing gas to 40000 and charging the reducing gas upwardly through the acceptor bed for 15 minutes at a gaseous hourly space velocity of 1000. Each of the acceptors was regenerated utilizing hydrogen admixed with carbon monoxide in a 1:1 mole ratio, the reducing gas being employed in a 1:4 mole ratio with steam. Again, the reactor effluent was analyzed and discharged to the atmosphere through a wet test meter. The solid acceptors were evaluated over about 8 acceptance-regeneration cycles.The average acceptance efficiency per acceptance cycle was determined, the acceptance efficiency being the actual capacity of the acceptor for sulfur oxides as a percentage of the sulfur oxides charged to the acceptor bed. The average regeneration efficiency per generation cycle was likewise determined after about 8 cycles, the regeneration efficiency being the percent of available copper reduced to the elemental metal during the regeneration cycle. The sulfur oxides acceptance efficiency, nitrogen oxides conversion efficiency, and the regeneration efficiencies are tabulated below.

Efficiency Acceptor NOx Conversion SO2 Acceptance Regeneration la 53 76 83 lb 77 76 83 Ia 58 86 97 lIb 91 86 97 Illa 2 93 96 Illb 1.8 93 96 IVa 2.9 87.8 97 lVb It is apparent that the acceptors Ila and lIb proposed according to the invention combine a nitrogen oxide conversion and sulfur oxide acceptance efficiency as good as or better than acceptors lacking all additives with a regeneration efficiency as good as acceptors containing platinum or palladium as additive, which acceptors give very poor nitrogen oxide conversion efficiency.

Claims

1. A process for the simultaneous separation of oxides of sulfur and nitrogen from a gaseous mixture containing said oxides and oxygen, which comprises contacting said mixture and ammonia at an elevated temperature with a solid sulfur oxides acceptor comprising copper and/or copper oxide dispersed on a carrier material in conjunction with ruthenium and rhenium in elemental or oxidic form.

2. A process as claimed in claim 1 wherein the ruthenium and rhenium components each individually constitute from 0.01 to 2 wt% of the solid acceptor, calculated as the elemental metal.

3. A process as claimed in claim 1 or 2 wherein copper and/or copper oxide constitutes from 5 to 1 5 wt.% of the solid acceptor.

4. A process as claimed in any of claims 1 to 3 wherein the carrier material for the solid acceptor is an alumina with a surface area of at least 50 m2/gm.

5. A process as claimed in any of claims 1 to 4 wherein the carrier material is gamma-alumina.

6. A process as claimed in any of claims 1 to 4 wherein the carrier material is eta-alumina.

7. A process as claimed in any of claims 1 to 6 wherein the ammonia is employed in a mole ratio with the nitrogen oxide content of the gaseous mixture of from 0.1:1 to 2.5:1.

8. A process as claimed in any of claims 1 to 7 wherein, when the activity of the solid acceptor lessens it is regenerated by heating in contact with a reducing gas comprising hydrogen, carbon monoxide and from 50 to 90 vol.% steam.

9. A process as claimed in claim 1 wherein a solid sulfur oxides acceptor produced by a process substantially as described in the foregoing Example II is used.

10. A process as claimed in claim 1 carried out substantially as hereinbefore described or exemplified.

11. A solid sulfur oxides acceptor comprising copper and/or a copper oxide, ruthenium and/or ruthenium oxide and rhenium and/or rhenium oxide disposed on a refractory inorganic oxide carrier material.

12. An acceptor as claimed in claim 11 comprising from 5 to 15 wt.% copper, from 0.01 to 2 wt.% ruthenium and from 0.01 to 2 wt.% rhenium, calculated as elemental metal.