LU82074A1 - CATALYTIC REDUCTION OF NITROGEN OXIDES BY AMMONIA IN THE PRESENCE OF CLINOPTILOLITE - Google Patents

Description

.......-. 4 * The invention relates to the selective catalytic reduction of nitrogen oxides (NO) by reducing gases on a new zeolite catalyst.

Selective catalytic reduction of NO by ammonia on various types of catalysts has been the subject of significant research in recent years. Attempts to find more efficient and stable catalysts for selective catalytic reduction is one of the main research topics in many industrial as well as academic laboratories.

4 Synthetic hydrogenated sodium mordenite and synthetic faujasite have been used in this reduction of nitrogen oxides by ammonia (U.S. Patents

N ° 3.895.094 and 4.052.337).

It has been found that a one of a kind adsorbent material prepared from clinoptilolite, described in the U.S. Patent. No. 4,059,543, is a very effective catalyst in the selective catalytic reduction of NO by ammonia. Not only is it more effective than synthetic mordenite but it can also be used over a wider range of operating conditions.

The present invention relates to a catalyst A.

25 comprising the hydrogen form of clinoptilolite and a method of using this catalyst for the removal of nitrogen oxides gas in exhaust gases. Virtually complete removal of the nitrogen oxides (98% or more) was achieved at temperatures between 200 and 450 ° C and at NEU to NO molar ratios of 0.6 to 2.5.

These results are obtained in the presence of a large quantity of oxygen (equal to that found in air). Volume hourly space velocities of 4,000 to 20,000 are preferred.

The invention will now be described by examples, with reference to the accompanying drawings in which:

Figure 1 is a diagram of the apparatus used in the following examples.

i 2

In Figure 1, 10 shows a tubular furnace used to heat the gas stream flowing to the tubular furnace 10 'which comprises a first section 11 containing an inert ceramic material and a section 12 5 containing the catalyst. At 13 is a three-way valve for flow from the sample port 23 to an analyzer, or from the sample port 22 to an analyzer.

At 14 is a metering valve which regulates the flow 10 from the ammonia source 20; 15 designates a metering valve for the nitrogen oxide source 21, and 16 designates a metering valve for the air source 24. Flow meters for the three gas streams are shown at 17, 18 and 19. The air and the nitrogen oxides are combined before they enter the tube furnace 10; ammonia is introduced at the inlet of the oven 10 '.

Figure 2 is a diagram showing the comparative results between the mordenite used as a catalyst and the catalyst according to the present invention, for the reduction of nitrogen oxides.

EXAMPLE 1

Natural clinoptilolite which has been crushed, crushed and sieved on a sieve with a mesh opening of 74 microns is exchanged three times with a 3N solution of ammonium nitrate, in an amount of 4 ml of solution per gram of material. solids for 3 hours under reflux conditions, then it is drained and treated with 0.5N hydrochloric acid under reflux conditions for 4 hours, using 4 ml of acid per gram of solids.

The dried powder is air dried and calcined at 300 ° C for one hour. Then this dry powder is mixed with 50% by weight of kaolin (Ajax P) and 33% by weight of water. After this mixing, the mixture is extruded into 1.6 mm pellets. The pellets are air dried overnight and calcined at 540 ° C for one hour.

These pellets are used to catalyze the reduction of nitrogen oxides using the device shown Λ 3% in Figure 1. In the experiments, the air in the plant is mixed with gaseous nitric oxide obtained from Union Carbide (containing more than 99% of nitric oxide) and preheated to around 180 ° C before the introduction of ammonia. This mixture of gases which enters the reaction system is then heated to the desired temperature using the tube furnace. Under steady-state conditions, the content of NO (NO and oxides in the oxidation state) is analyzed.

X

upper) in samples of gas entering and leaving the reaction system.

The reductions of Nov obtained with the preceding catalyst and with the Zeolon 200 H catalyst at various temperatures are given in Table I. It can be seen that, for each operating temperature, the reduction of NO with the clinoptilolite in hydrogen form is greater than that obtained with Zeolon 200 H. This comparison is illustrated in FIG. 2, in which curve A represents the curve obtained with the catalyst according to the present invention and curve B that obtained with the conventional catalyst.

20 TABLE I

% NO REDUCTION AT VARIOUS TEMPERATURES

X

Clinoptilolite in hydrogen form (Zeolon 400 H)

Temperature ° C 273 342 390 452 * Reduction,% 88 99> 99> 99 25

Mordenite in hydrogen form (Zeolon 200 H) Temperature, ° C 261 315 365 422 Reduction,% 69 81 89 92

Operating conditions 30 Spatial speed, h 1 6000 NEL / NO (by volume) 1.0

X

NO concentration, ppm (V / V) 2500

Carrier gas Air saturated with water at 7 kg / cm2

workforce and 27 ° C

It can be seen that despite the presence of almost 20% oxygen (from the air), very high transformations are obtained at NH- / NO ratios as low as 1.0.

4 .Λ * 'EXAMPLE 2

A study was made of the effect of the ratio of NH3 to NO on the efficiency of reduction using the catalyst of Example 1, and the results obtained are shown in Table II. It can be seen that a very large reduction of NO is obtained at various NH, / NO ratios.

X ô X

TABLE II

EFFECT OF THE NH- / NO REPORT ON THE% REDUCTION --3-X- NH- / NO 0.8 1.0 1.3

ό X

10 Reduction,% 95> 99> 99 OPERATING CONDITIONS Spatial speed, h 1 6000

Temperature, ° C 370

NO concentration, 15 ppm (V / V) 2500

Carrier gas Air saturated with water at 7 kg / cm ^ effective and 27QC EXAMPLE 3

A study was made of the effect of space velocity on the efficiency of reduction, using the catalyst of Example 1. The results obtained are shown in Table III. We can see that we get very high reductions over a wide range of v space velocities.

25 TABLE III

EFFECT OF SPACE SPEED ON% NO REDUCTION

--x

Spatial speed, h 4000 4500 6000 10.000. Reduction,% 99 99 99 96

30 OPERATING CONDITIONS

NO concentration, ppm (V / V) 2500

X

NH3 / N03 1.0

Temperature, ° C 370

Carrier gas Air saturated with water at 35 kg / cm ^ 7 effective and

27 ° C

Claims (3)

4 Λ Γ-. 1. A method of reducing nitrogen oxides with ammonia, where the nitrogen oxides (NO) to be reduced are found in a gas mixture containing up to 21% oxygen, in which the gas stream to be treated passes over clinoptilolite in hydrogen form, the temperature being greater than 200 ° C, the space speed being from 4,000 to 20,000 h * "and the NH- / NO ratio being between 0.4 and ό X 2.5 . 2. Method according to claim 1, wherein the clinoptilolite is essentially in hydrogen form. 3. The method of claim 1, wherein the catalyst is prepared from natural clinoptilolite by ion exchange with an ammonium nitrate solution and then treatment with an aqueous solution of a strong acid. ♦