NL7904504A - PROCESS FOR PREPARING A DENITRATING CATALYST. - Google Patents

Description

- .. - '·· <4 -1- 20726 / JD / tj

Applicant: Hitachi Shipbuilding & Engineering Co. Ltd., Osaka, Japan.

Short designation: Process for preparing a denitrating catalyst.

The invention relates to a process for preparing a denitrating catalyst.

Denitrating catalysts are used in a reaction where nitrogen oxides (Ν0χ) in exhaust gases are selectively reduced catalytically with NH4.

Many methods of treating Ν0χ in exhaust-10 gases have already been proposed. Of these processes, the denitration process is most feasible in which nitrogen oxides are selectively reduced catalytically to harmless at a specific temperature with NH 2 in the presence of a catalyst. Although many catalysts have also been proposed for use in this process, it is still necessary to improve them. Applicant prepared a porous metal catalyst, shown in U.S. Pat. No. 4,040,981, by immersing a metal catalyst major component in a silica-containing bath and drying the catalyst main component to form a porous silicon oxide. covering. Applicant discovered that the catalyst has high mechanical strength and maintains sustained stable activity, and is not affected by poisoning such as KC1 poisoning. The present invention relates to improvements in this catalyst.

The present invention provides for forming silica-oxide coatings with improved porosity and thereby increased permeability to the reaction gases. Furthermore, the present invention provides deniter catalysts with improved activity and satisfactory strength.

The present invention provides a process for preparing a denitrating catalyst, characterized in that a support is formed with a porous silicon oxide coating by immersing a catalyst component of a porous metal in a silicon dioxide coating bath. and drying the resulting main component, after which an active component is applied to the support by immersing the support in a solution with the active component 7904504% -2-20726 / JD / tj and drying the resulting support.

These and other features of the present invention will become more likely with reference to the following detailed description regarding the accompanying drawings, in which: Fig. 1 is a graph showing the relationship between the pore size and the total pore volume; Fig. 2 is a graph showing the relationship between treatment time and average wear thickness; Figures 3 and 4 are graphs each showing the relationship between the reaction temperature and the deniter yield; Fig. 5 is a graph showing the relationship between the coating thickness and the deniter yield; FIG. 6 is a graph showing the relationship between the concentration of the V compound and the amount of V carried by the carrier per amount of absorbed substances; and FIG. 7 is a graph showing the relationship between the deniter yield and the amount of V carried by the support per amount of absorbed substances.

Examples of main catalyst components useful in this invention are those prepared from metallic materials having an aluminum alloy surface layer by treating the materials with an aluminum soluble solution, and those obtained by etching the surfaces of the metallic materials before forming porous rough surfaces. Examples of useful metal-containing materials are pure iron, iron-based alloys, steel, nickel, nickel-based alloys and copper-based alloys. For example, the metal-bearing materials with a kt alloy surface layer are prepared by subjecting a metal-coated material containing kZ to heat. kJL can be made of metallic materials with a kZ alloy surface layer. be dissolved by immersing such a substance in an AJt soluble solution or by spraying the solution on the substance. Examples of useful KZ soluble solutions are aqueous solutions of alkali metal hydroxides such as NaOH, alkali metal carbonates, alkaline earth metal hydroxides and mineral acids. The aluminum dissolving treatment forms a porous surface layer on the metallic substance.

7904504

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Preferably, the porous metal-containing material is subjected to an oxidation and / or SO 2 treatment. Although the treatment temperature, treatment time and oxygen concentration for the oxidation treatment are not particularly limited, it is preferable for the metal-containing substance in an atmosphere of 0.1-2.8 vol. % oxygen at room temperature up to 400 ° C

for 0.1-20 hours. The SO 2 treatment is preferably carried out in an atmosphere containing at least 100 ppm SO 2 at room temperature up to 400 ° C for 0.1-20 hours.

Colloidal silicon oxides include alkali olloids containing a large amount of alkali metal and acidic colloids containing a small amount of alkali metal, the latter being the most preferred for use. Useful acidic colloides have a pH of 3-4. The concentration and temperature of the coating bath, the time by which the main catalyst component is immersed in the bath, and the number of repetitive immersion processes are suitably determined so that the resulting coating will have the desired thickness. The immersed main catalyst component is dried at a temperature of 50-150 ° C. The coating step is preferably performed with a colloidal silicon oxide containing 10-30 wt. % SiO2 as the coating bath by immersing the main catalyst component in the bath at room temperature for about 10 minutes, extracting the main component therefrom, drying the main component at about 90 ° C for 1 hour and immersing and drying to be repeated for one to 6 times to obtain a coating with a thickness of 7-20 µg. When the coating step is carried out with a coating bath containing a mixture of colloidal silicon oxide and an emulsion of a high molecular weight substance by dipping of the catalyst main component in the bath, drying the wet component to form a coating thereon, and baking the coated main component, then the resulting coating will have a largely improved porosity. Examples of useful high molecular weight substances are acrylic compounds that do not release noxious gas during baking. The concentration of the high molecular weight substance in the coating bath is suitably selected in accordance with the desired mechanical strength, component and particle size of the substance in the reaction gas 7904504 4 -4-20726 / JD / tj is sitting. Preferably 10-50 wt parts of the high molecular weight substance are used per 100 wt. parts of SiO2 in the colloid. The coated main ingredient is baked in air at a temperature of 450-700 ° C, preferably 500-650 ° C for 1-5 hours. The high molecular weight organic component is removed from the coated main ingredient during the baking phase.

When a mixture of a colloidal silicon oxide, an emulsion of a high molecular weight substance and a titanium compound is used as the coating bath, the resulting support will have improved properties, whereby a catalyst with a sustained activity is obtained. Furthermore, a coating bath comprising a mixture of a colloidal silicon oxide, an emulsion of a high molecular weight substance, a titanium compound and a tin-15 compound, when used, gives a catalyst with a high resistance to sulfuric acid. Examples of useful titanium compounds are water-soluble organic titanium compounds such as ammonium salt of Ti (0H) 2 ~ [0CH (CH3) C00HJ2 and TifCNH2O2. Examples of useful tin compounds are organic tin compounds such as di-20-butyltin laurate. Such titanium and tin compounds undergo thermal decomposition during baking, producing TiOg and SiO2, respectively. Preferably, the resulting coating contains 40-100 wt. parts of TiO 2 per 100 wt. parts SiO2, and 30-70 wt. parts of Sn02 per 100 wt. parts of SiO2.

Examples of solutions containing an active component useful for the immersion treatment of the carrier are solutions with a vanadium compound such as vanadyl sulfate, vanadyl oxalate, ammonium metavanadate or the like; solutions containing a hydrolyzable titanate such as tetraisopropyl titanate, and solutions of a sulfate or halide of copper, iron or antimony, tungstate or chromate. When the carrier is immersed in a solution, a V-compound, Ti-compound, iron compound, copper compound,

Sb connection, W connection and / or Cr connection are carried by the wearer.

35 The concentration and temperature of the solution, the immersion 7904504

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20726 / JD / tj time and similar conditions depend on the amounts of active components that can be carried by the wearer. The preferred * weight amounts to be carried by the wearer are 0.15-1.5? for V, 0.15-1.5? for Ti, 0.16-1.6? for Fe, 0.17-1.7? for Cu, 0.1-3.0? for Sb, 0.15-1.5? for W and 0.2-2.0? in front of

Cr.

The catalysts thus obtained all have a high de-nitriding activity. Especially the catalysts with a V-compound and a Ti-compound applied thereon have an even higher activity and a high resistance to sulfuric acid.

Example I

Measure the porosity of the coverings.

A colloidal silicon oxide (pH = 3.5) containing 22 wt. ? Contains SiO 2, and three kinds of emulsions a, b and c of high molecular weight acrylic substances shown in Table A were mixed together in different amounts to prepare 11 kinds of coating baths A, B, ... K.

The bathA did not contain an emulsion. The 11 baths were placed in 11 stainless steel dishes with an internal diameter of 5 cm and a depth of approximately 4 mm, respectively. Each bath was heated at 90 ° C for 20 hours to remove water, and the remaining solid was baked in air at 500 ° C for one hour. The coating formed on the tray was separated, and the porosity of the coating was measured by a high pressure mercury porosimeter. Table B shows the results.

25 3 _Table A_ emulsion glass transition temperature particles _ (QC) _size a -45 2000 b +25 400 30 J c -55 2000 35 7904504 i -6- 20726 / JD / tj ί *

Table B

bath composition bath (parts by weight) total pore substance with high molecular weight volume 3

SiOg emulsion a emulsion b emulsion c (cm / g) 5__ A 100 - 0.028 B 94.7 5.3 - 0.100 C 90. 10.0 - 0.119 D 81.8 18.2 - 0.231 10 E 75 25.0 - 0.319 F 82 13.2 5.0 0.220 G 82 8.2 10.0 '0.210 H 94.7 - 5.3 0.083 I 90.0 - 10.0 0.190 15 J 75.0 - 18.2 0.432 K 90 0.0 5.0 5.0 0.127

The relationship between the pore size and the total pore volume was determined for the coatings <\, f ?, y, 5 and f formed from baths A, C, E, 20 G and J. The results are shown in Figure 1 which reveals that cover

king o Formed from the emulsion bath has a slightly lower porosity but the coatings formed from the emulsion baths have a high porosity. The curve $ indicates that the use of emulsion a composed of a high molecular weight substance with a low glass transfer temperature gives pores in the coating which are mainly 30-70 A

large and almost no pores with a size of at least

O

1000 A and suitable for the transmission of the reaction gas through the coating.

As represented by curve &, the emulsion b, composed of a high molecular weight substance and a high glass transfer temperature, provides a coating formed with a relatively large number of pores not less than 100 Å and which has good gas permeability.

Example II

a) The preparation of the carriers.

Steel panels of SUS 304 (JIS), 2 mm x 33 mm x 50 mm, were immersed in a molten aluminum bath at 680 ° C for 20 minutes 7904504 6-7 20726 / JD / tj * to obtain samples panels covered with aluminum. Each panel was then heat treated in a nitrogen gas atmosphere at 800 ° C for one hour to allow aluminum to diffuse through the panel to form an aluminum alloy surface layer on the panel. The panel was then immersed in 200 ml of an aqueous solution containing 10 wt. % NaOH, at 80 ° C for 3 hours to dissolve the Al from the alloy, making the surface layer porous. Then the steel panel was washed with water, dried in air and exposed to nitrogen gas containing 3 vol. % oxygen, at 300 ° C for 10 hours to oxidize the porous surface layer. In this way, the main catalyst components of porous steel were formed.

Single catalyst major components were immersed in the coating bath A according to Example I at room temperature for 10 minutes, then taken out and dried at 90 ° C for 1 hour.

Dipping and drying was repeated 3 times to form a 7-10 µm thick porous silica coating on the main ingredients. The resulting major constituents were then baked in air at 600 ° C for 1 hour to remove the high molecular weight organic component to yield a support a. In the same manner as above, carriers c, d, g and j were prepared using the coatings C, D, G and J prepared according to Example I.

b) Measuring the strength of the carriers.

The resulting support a was placed in a stirring container filled with silicon oxide gel powdered to 60-80 mesh (250-180 µm), and the silicon oxide gel was stirred to wear out the surfaces of support a.

Variations in the weight of the support a were measured at specific time intervals to determine the average thickness of the worn support a. The same procedure as above was repeated with the supports c, d, g and j to determine the relationship between the average wear thickness and stirring time. The results are shown in Fig. 2. Typically the wear resistance, namely the mechanical strength, decreases with increasing porosity. Fig. 2 shows that the supports c, d, g and j prepared with the emulsion baths have a higher porosity than the support a obtained by using the bath without emulsion and despite that .35 have a comparable strength.

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Example III

a) Preparation of catalysts.

Steel Raschig rings, 21 mm in diameter and 20 mm in height, were used as the main component for the catalyst. Six pieces of the main catalyst component were prepared by forming a porous layer on the rings in the same manner as in Example II.

The mixture of the colloidal silica and the emulsion a used in Example 1, ammonium salt of Ti- (OH) 2 [oCH (CH2) COOH] 2 and a mixture of dibutyltin laurate and emulsion a were mixed together in different proportions to preparing four types of cover baths L, Μ, N and 0 which are tabulated in Table C. Of the six previously prepared pieces of the main catalyst component, one was placed in each bath L and M, and two in each of the baths N and 0. The pieces were then subjected to a repeated immersion drying treatment and a baking step under 15 ° C. same conditions as in Example II for forming the porous coating on the pieces to obtain a substrate. The five carriers, except those obtained with bath 0, were used to carry TiO 2 and / or To apply TiC> 2, the carrier was immersed in liquid tetraisopropyl titanate at room temperature for 10 minutes, and then removed put in saturated water vapor at room temperature for 12 hours to hydrolyze the titanate after which it was dried at 100 ° C. For applying V ^ ,. the support was immersed in a solution of 1 mole NH 2 O 2 in 1 liter 15 vol. % aqueous solution of monoethanolamine at room temperature for 10 minutes and then baked in air at 300 ° C for 1 hour. To apply both TiO2 and VgOtj, the support was treated such that TiO2 was applied first. In this way, five catalysts 1, m, n-1, n-2 and o-1 are shown which are shown in Table C. The support that does not carry any of these compounds is also represented as catalyst o-2.

30 "TABLE C- 35 7904504 a -9- 20726 / JD / tj

Table C

bath composition bath supported active (parts by weight) component (parts by weight) catalyst. SiCL T10 * SnO * emulsion ** TiO. VO 2 2 2 2 2b 5 a L 100 - - 2.3 5.5 1 M 82 - 18 2.3 5.5 m N 57 25 - 18 - 5.5 n-1 10 N 57 25 - 18 2.3 5.5 n-2 0 57 11 14 18 - 5.5 o-1 0 57 11 14 18 - 0-2 (for comparison) 15 * Calculated as the metal oxide ratio of the ratio of corresponding organic metal compound used for the preparation of the bath.

** Ratio of the high molecular weight substance involved.

B) Activity test.

The catalysts were tested for activity by a flow type quartz reactor tube. The catalyst 1 was placed in the reaction tube, and a test exhaust gas of the composition shown in Table D was passed through the reaction tube at a speed of 15 m / hr per geometric unit area of the catalyst.

Table D

gas component ratio (vol.%) NO 0.02 S02 0.02 30 NH3 0.02 02 5.0 h2o 10.0 CO2 10.0 N2 remainder 35 7904504 X 'η -10- 20726 / JD / tj

The deniter yield was calculated from the difference between the NO concentration at the inlet of the reactor tube and at the outlet. The same procedure was repeated for different reaction temperatures to determine the deniter yields at the temperatures. Corresponding 5 deniter yields were determined using catalysts m, n-1, n-2, o-1 and o-2. Fig. 3 showing the results reveals that the catalysts with all included have high activity. High activity is especially available with the catalysts composed of a support prepared using the emulsion coating bath and where V 0 is supported on the support.

d. O

The catalysts obtained in this example were exposed to air containing 4000 ppm sulfuric acid vapor at 400 ° C for 2 hours and then tested for deniter yield in the same manner as above. The results are shown in Fig. 4. The comparison of Fig. 3 with Fig. 4 teaches that the catalysts 1, m, n-1, n-2 and o-2 slightly decrease the activity at temperatures not higher than 350 ° C in which the catalyst O-1 retains high activity and high sulfuric acid resistance with incorporated SnO 2 in the coating.

Example IV

A) Preparation of the catalysts.

A number of pieces of the same catalyst main constituent as used in Example I were immersed in the same coating bath 0 as used in Example I and then dried, each a different number of times. The pieces were then baked and treated in the same manner as in Example 1 to support V0 and prepare many catalysts with different coating thicknesses, b) Relationship between the coating thickness and deniter yield.

The catalysts were tested for the deniter yield at 300 ° C under the same conditions as in Example 1 to determine the relationship between the coating thickness and the deniter yield. Curve t in Fig. 5 represents the results.

In the same manner as above, the relationship between coating thickness and deniter yield was determined from cordierite Raschig rings and alumina Raschig rings of the same shape as in Example 1. Curves u and v in Figure 5 represent the results.

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Fig. 5 shows that the deniter yield increases with increasing coating thickness but little or no improvement is achieved with the coating thickness of 20 µU or greater. The comparison of curve t with curves u, v reveals that the main catalyst component is porous; sample 5 in itself has a significant denitration activity.

Example V

a) Preparation of the catalysts.

Ten pieces of the main catalyst component were prepared in the same manner as in Example II except that a steel material 10 SS 41 (JIS) was used. The pieces were covered under the same conditions as in Example II using the coating bath L prepared in Example I to obtain ten carriers.

Of these carriers, one was immersed in 200 v & h 2N oxalic acid solution of NH 4 VO 2 (1.0 mol / liter) at room temperature for 30 minutes, then removed from the solution and then dried at 100 ° C for one hour before obtaining a catalyst with incorporated V.

Another support was immersed in an n-butyl alcohol solution of tetra-n-butyl titanate (1.5 mol / liter) under the same conditions as above and dried under the same conditions to prepare a catalyst with Ti incorporated therein.

The remaining eight carriers were treated in the same manner as above by using the titanate solution at different concentrations as shown in Table E with the carriers going to carry Ti. Subsequently, the resulting carriers were treated in a similar manner using the same metavanadate solution as above at different concentrations shown in Table E for the carriers to carry V. Thus, eight catalysts were prepared with both Ti and V included.

b) Activity test.

The catalysts were tested for the deniter yield at 350 ° C

in the same manner as in Example III. The catalysts were treated with sulfuric acid vapor in the same manner as in Example III and then tested for the deniter yield. Table E also gives results.

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Table E shows that the catalysts with both incorporated Ti compound and V compound have higher activity than those containing only one of them and are more resistant to sulfuric acid. Example VI

A) Preparation of the catalysts.

Seven pieces of the same catalyst main ingredients as used in Example II with a porous surface layer and the coating bath 0 prepared in Example III were used to obtain seven carriers in the same manner as in Example II. The supports were immersed in the metal salt-containing solutions AG, respectively, shown in Table F at room temperature for 10 minutes, then dried at 100 ° C for one hour and further baked at 300 ° C for one hour to obtain a catalyst with incorporated Fe, catalysts with incorporated Cu, catalyst with incorporated Sb, catalyst with incorporated Sb and Fe, catalyst with incorporated W and Fe and catalyst with incorporated Cr.

b) Activity test.

The catalysts were tested for the deniter yield at 300 ° C and 350 ° C in the same manner as in Example III except that the gas was passed through the catalyst at a rate of 24 m / hr per unit geometric area. Table F shows the results.

Table F

solution metal salt concentration deniter yield (%)

_ (mol / liter) 300 ° C-350 ° C

A FeSOjj 0.5 42 65 25 B CuSOjj 0.5 45 65 C CuC 0.5 59 71 D SbBr ^ 0.25 65 83

FeBr2 0.25 E SbBr ^ 0.5 40 60 3 ° F «V» 3 o, 25 54 79

FeSOjj 0.25 G (NH4) 2 Cr207 0.25 68 87

Fe2SO4 0.25 As shown in Table F, the catalysts have increased activity at high temperatures.

7904504 4 -14- 20726 / JD / tj

Example VII

a) Preparation of catalysts.

Four pieces of the same catalyst main constituent as formed in Example II with a porous surface layer and the four kinds of baths ΐ-4 shown in Table G and prepared in the same manner as in Example II were used to obtain four supports in the same manner as in example II. Table G also shows the compositions of the coatings formed on the pieces.

Table G

10 bath composition bath composition cover (wt%) _ (aew. I) -

SiO, ΤΙ0 ,, * SnO * emul- Si05 Ti09 SnO? _ _l_l _l _L_ - 1 57 11 14 18 69.5 13.4 17.1 15 2 57 15 10 18 69.5 18.3 12.2 3 57 7 18 18 69.5 8.5 22.0 4 57 20 18 74.0 26.9 ^ * Same as in Table C.

** Same as in table C.

Aqueous solutions of NH 4 VO 4 at different concentrations of 50-1000 mg / liter calculated as V were prepared, and the carriers were treated to carry V by using the solutions in the same manner as in Example VI to determining the relationship between the V-compound concentration of the solution and the amount of V carried by the carrier per unit amount of absorbed substances in the coating. The amount of V carried is expressed by:

3Q

_ Weight V carried by the wearer_

Cover weight x (TiO ^ content + \ SnOg content)

The results are shown in Figure 6, which shows that the V compound is strongly absorbed on the coating, with an increased amount carried by the carrier with the increase in V concentration.

35 b) Activity test.

The catalysts were tested for the deniter yield at 300 ° C

7904504

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20726 / JD / tj in the same manner as in Example III to determine the relationship between the deniter yield and the amount of V carried by the wearer per amount of adsorbed substances in the coating. The results are given in Figure VII which reveals that the deniter yield increases. Accelerates with the increase in the amount of V carried per amount of adsorbed substances and reaches its highest level when the latter is between 0.01-0.02 which corresponds to 0.15-1.5¾ in weight terms of V.

-C0NCLUSIONS- 10 7904504

Claims (15)

1. Process for preparing a denitrating catalyst, characterized in that a support is formed with a porous silicon oxide coating by immersing a catalyst component of a porous metal in a silicon dioxide coating bath and drying the main component obtained · after which an active component is applied to the carrier, by immersing the carrier in a solution with the active component and drying the resulting carrier. Process according to claim 1, characterized in that the porous catalyst main component is formed by treating a metal-containing substance having an aluminum alloy surface layer with an aluminum-soluble aluminum dissolution solution. The method according to claim 1, characterized in that the coating bath is an acidic colloidal silicon oxide. Method according to claim 1, characterized in that the coating bath is a mixture of colloidal silicon oxide and contains an emulsion of a high molecular weight substance, and the main ingredient is baked after it has been immersed in the bath and dried. The method according to claim 4, characterized in that the high molecular weight substance is retained in an amount of 10-50 wt. parts per 100 wt. parts SiO ^. 6. Process according to claim 4, characterized in that the coating bath is colloidal silicon oxide containing a titanium compound. A method according to claim 6, characterized in that the content of the titanium compound calculated as TiO 4 40-100 wt. parts per 100 wt. parts is SiO ^. 7 '' A> -16- 20726 / JD / tj 8. A method according to claim 5, characterized in that the coating bath is a colloidal silicon oxide containing a tin compound. 9. Process according to claim 8, characterized in that the content of the tin compound calculated as SnO ^ 30-70 wt. parts per 100 wt. parts is SiO2. 10. A method according to claims 1-4, characterized in that the active component is a vanadium compound. 7904504 -17- 20726 / JD / tj Method according to claim 10, characterized in that the vanadium compound is carried by the carrier in an amount of 0.15-1.5 wt. % calculated as V. 12. Process according to claims 1-9, characterized in that the active component is a mixture of a vanadium compound and a titanium compound. A method according to claims 1-9, characterized in that an active component is a compound selected from the group consisting of sulfates and halides of iron, copper and antimony, tungstates and chromates. Method according to claims 1-9, characterized in that the coating has a thickness of 7-20 µm. A porous coating deniter catalyst is prepared according to the process of claims 1-14. 7904504