The mechanical and thermal properties of aluminum oxide, such as γ alumina, adapted for use as a catalyst or catalyst carrier are improved through a treatment thereof with a silicon compound such as an alkyl orthosilicate in which the aluminum oxide is impregnated with the silicon compound or a solution thereof in a compatible organic solvent whose boiling point is lower than the boiling point of the silicon compound. The impregnated aluminum oxide is dried at a temperature in the range from above the boiling point of the silicon compound to 500°C and is then subjected to controlled oxidation.
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8. Stabilized alumina having a sliicon content, expressed as silicon atoms per A2 of area, of from 0.01 to 0.06 which shows, after a treatment at 1200°C over a period of 24 hours, no transformation other than from phase to phase, and which, after a treatment for 40 hours at 250°C under a steam pressure of 15 ata, keeps unchanged its starting crystalline structure and, after a treatment at 1000°C for 24 hours, shows a volume shrinkage lower than 2%.
1. The process of improving the mechanical and thermal properties of aluminum oxide adapted for use as a catalyst or catalyst carrier which comprises impregnating said aluminum oxide with a silicon compound having the general formula: ##STR2## in which X, Y, Z and W are selected from the group consisting of (--R), (--Cl), (--Br), (--SiH), (--COOR), (--SiH nCl m), --[OSi(OR)]p, OSi, (OR)3, in which R is an alkyl, cycloalkyl, aromatic, alkylaromatic or alkyl-cycloalkyl radical having from 1 to 30 carbon atoms; n, m and p are whole numbers from 1 to 3, by bringing said silicon compound or a solution thereof in a compatible organic solvent whose boiling point is lower than the boiling point of the silicon compound into contact with said aluminum oxide, drying said impregnated aluminum oxide at a temperature in the range of from the boiling point of the silicon compound to 500°C, and then subjecting said impregnated aluminum oxide to controlled oxidation.
2. Process according to
3. Process according to
4. Process according to
5. Process according to
6. Process according to
7. Process according to
9. Stabilized alumina according to
10. The process for improving the mechanical and thermal properties of aluminum oxide adapted for use as a catalyst or catalyst carrier which comprises impregnating said aluminum oxide with a silicon compound having the general formula: ##STR3## in which X, Y, Z and W are selected from the group consisting of (--R), (--OR) (--Cl), (--Br), (--SiH3), (--COOR), (--SiHn Clm), --[OSi(OR)2 ]p, OSi(OR)3, in which R is H or an alkyl, cycloalkyl, aromatic, alkylaromatic or alkyl-cycloaklyl radical having from 1 to 30 carbon atoms; n, m and p are whole numbers from 1 to 3, by bringing said silicon compound or a solution thereof in a compatible organic solvent whose boiling point is lower than the boiling poit of the silicon compound into contact with said aluminum oxide, drying said impregnated aluminum oxide at a temperature in the range of from the boiling point of the silicon compound to 500°C, and then subjecting said impregnated aluminum oxide to controlled oxidation.
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The present invention relates to a process for obtaining materials of high thermal and mechanical stability which are constituted by oxides of aluminium and more particularly, materials used as catalysts or as catalyst carriers for chemical reactions in the heterogeneous phase and also to the materials obtained thereby.
It is known that, when chemical processes are based on chemical reactions carried out by means of catalysts in the heterogeneous phase, the catalyst undergoes irreversible transformations which decrease the effectiveness thereof and necessitate the frequent replacement of the catalyst itself. Such a process would be improved by decreasing the rate of such transformations, which increases the efficacious employment period of the catalyst.
Generally the activity of a heterogeneous phase catalyst increases with increases of the catalyst surface in contact with the reagents. For this purpose use is made of catalysts having a high porosity and surface area or shperes spheres, again dried at 150°C for 20 hours and then weighed.
The friction resistance (K) was expressed as weight percentage loss of the sample.
The results obtained from the various determinations are reported in table 1.
According to the procedure of example one, a spheroidal γ-Al2 O3 was prepared containing 3% SiO2 (b).
The product was obtained by adding colloidal silica Ludox AS (Du Pont) to a mixture of ammonium-acetate, aluminum chlorohydroxide and gelling agent.
On the sample so obtained were carried out the determinations of surface area, volume shrinkage and abrasion after a thermal treatment at 1000°C and 1100°C; the results of these determinations are listed in Table 1.
A sample of the same γ-Al2 O3 used in the example 1 had Ba added thereto in the following way:
100 g of alumina were impregnated with a solution obtained by dissolving 9.8 g. of Ba(NO3)2 into 80 cc. of H2 O.
After drying at 120°C for 12 hours and an air calcination at 500°C for 2 hours, a γ-Al2 O3 was obtained containing 5.2% of Ba (c). The determinations carried out on the sample so obtained are reported in Table 1.
By always employing same alumina as example 1, 100 g of Al2 O3 were immersed in 200 cc of (C2 H5 O)4 Si and kept in contact with the liquid for 4 hours; at the end the solid was separated from the excess liquid, and was transferred into a quartz pipe put in an electric oven; a nitrogen stream was sent and the whole was slowly heated up to the boiling temperature of ethylorthosilicate (160°-170°C) so as to completely distill the unreacted product. The thermal treatment was then prosecuted up to 500°C, when the nitrogen flow was stopped and air was sent; the duration of the final treatment was 2 hours. A product was obtained having a SiO2 content equal to 6.1% (d). The results of the thermal treatments and the other determinations performed on the so obtained sample are reported in table 1. In table 1 there are reported also the results of X-ray examinations carried out on the samples of examples 1, 3 and 4 at 1100°C and 1200°C
| TABLE 1 |
| __________________________________________________________________________ |
| SA m2 /g |
| ΔV % K % R X R X |
| Starting after treatment |
| after treatment |
| K % after treatment |
| after treatment |
| after treatment |
| SAMPLE |
| SA m2 /g |
| 1000°C |
| 1100°C |
| 1000°C |
| 1100°C |
| starting |
| 1000°C |
| 1100°C |
| 1100°C |
| 1200° |
| __________________________________________________________________________ |
| C. |
| a 196 80 68 9 14 3.2 6.1 9.3 THETA + ALPHA |
| ALPHA |
| b 208 88 65 6 12 1.7 6.9 6.9 n.d. n.d. |
| c 190 100 71 7 12 3.2 6.4 10.5 THETA + DELTA |
| n.d. |
| d 200 140 136 1 4 0.9 2.1 2.3 DELTA DELTA |
| __________________________________________________________________________ |
| wherein SA means the surface area, ΔV is the voiding shrinkage |
| expressed as percent, K is the friction resistance expressed as percent o |
| abraded material. |
By comparing the data of Table 1 it is possible to infer that the treatment of a γ---Al2 O3 γδAl2 O3 with Si(OC2 H5)4 causes a stabilizing effect much higher than that of other known common methods.
A spheroidal γ-alumina sample ws prepared according the rotating place pelletizing technique in the following way: γ---Al2 O3 γδAl2 O3 , reduced into a very fine powder, was put in a rotating plate; while the plate was rotating, as aqueous solution containing 0.1% of hydrated methyl cellulose (Methocel) was nebulized onto the powder itself; spheroidal nuclei formed, the sizes of which could be regulated according to the residence - time in the plate and the alumina powder present therein. When the desired sizes have been obtained, the alumina spheroids were dried for 24 hours at 120°C, then air calcined up to 500°C (e). The characteristics of these aluminas are illustrated in table 2. A sample of this alumina was immersed in an excess of (C2 H5 O)4 Si; according to the same process as example 3, a γAl2 O3 was obtained containing 6.3% of SiO2 (f). This sample too was subjected to the sinterization tests and the obtained results are reported in table 2.
100 g of the same alumina as example 5 were put in a self-heating autoclave together with 40 g of (C2 H5 O)4 Si. The autoclave was evacuated and repeatedly washed with N2 in order to remove all O2 traces, then it was charged at a 5 kg/cm2 pressure with N2. The autoclave was heated to 200°C and this temperature was kept for 4 hours, at the end it was cooled, the pressure was released and alumina was recovered, which was subjected to a following thermal treatment of 2 hours at 200°C under N2, and then to an air calcination at 500°C for 4 hours.
The γ-Al2 O3 little spheres, treated in such a way, after analysis, showed a SiO2 content equal to 10.2% (g).
The results of the sinterization tests are listed in table 2.
The alumina as example 5 was treated with CH3 Si (OC2 H5)3 in the vapour phase at room pressure in the following way; 100 g of alumina were put in a quartz pipe immersed in a heating oven; the pipe was bottom connected to a two necked flask, containing 30 cc of methyltriethoxylane, and immersed in a thermostatic bath. Alumina was heated at 400°C under a nitrogen stream; this temperature having been achieved in the alumina bed, the thermostatic bath was brought up to 120°C and N2 was sent to the flask containing CH3 Si (OC2 H5)3 until total vaporization of the silicon compound occurred.
The treatment at 400°C was prosecuted with air for 4 hours, then the whole was cooled.
The SiO2 content of the so treated alumina was equal to 8.5% (h). The sinterization tests gave the results listed in table 2.
100 g of the same alumina as example 5 were impregnated with an aqueous solution of orthosilicic acid obtained in the following way:
25 cc of sodium silicate (40 Be) were kept in 70 cc of H2 O; the solution was contacted with an ion exchange resin (Amberlite IRC-50 H+) in order to completely remove Na+ ions.
After the cationic exchange, the solution was utilized for impregnating alumina. After drying at 120°C and air calcination at 500° C. for 4 hours, an alumina was obtained having a SiO2 content equal to 6.5% (i).
The results of the sinterization tests, the sample was subjected to, are listed in table 2.
Another sample of the same alumina as example 5 was impregnated with colloidal silica Ludox SM (Du Pont) in the following way:
7 g of colloidal silica at 30% were diluted in 80 cc of H2 O; 100 g of alumina were impregnated with the resulting solution. After drying at 120°C for 12 hours and calcination at 500°C in air for 4 hours, an alumina was obtained containing 1.6% of SiO2 (l).
The results of the tests carried out on this sample are listed in table 2.
A sample of the same alumina as example 5 was treated with SiCl4 in the vapour phase according to the following way: 100 g of Al2 O3 were put into a quartz pipe immersed in an electric oven; a nitrogen stream was sent and the sample was heated up to 400°C; then the pipe was connected to a saturating vessel containing SiCl4 kept at room temperature, through which an anhydrous nitrogen stream flowed, which was then sent onto the alumina sample.
After 4 hours of treatment, the nitrogen flow through the saturating vessel containing SiCl4 was stopped, and air was sent.
After 1 hour of air treatment it was cooled and alumina was recovered which, at analysis, showed a SiO2 content equal to 7.3 (m).
The so obtained sample, subjected to sinterization tests, gave the results reported in table 2.
| TABLE 2 |
| __________________________________________________________________________ |
| SA m2 /g |
| ΔV % K % |
| SA m2 /g |
| after treatment |
| after treatment |
| K % after treatment |
| SAMPLE |
| starting |
| 1000°C |
| 1100°C |
| 1000°C |
| 1100°C |
| starting |
| 1000° C. |
| 1100°C |
| __________________________________________________________________________ |
| e 269 124 50 13 26 23.2 |
| 37.2 42.5 |
| f 272 220 180 1 7 3.8 6.3 6.4 |
| g 290 238 203 1 8 0.9 0.5 1.4 |
| h 300 211 200 2 6 1.8 1.7 2.8 |
| i 300 111 95 8 14 8.4 9.0 19.7 |
| l 295 105 69 11 20 6.5 23.2 39.9 |
| m 305 209 158 4 10 3.0 5.3 15.3 |
| n 275 198 170 2 9 1.5 2.3 2.8 |
| __________________________________________________________________________ |
A drawing was performed of the same alumina prepared according to the process disclosed in example 5, which was treated with (CH3 O)2 SiCl2 in the following way: 100 g of Al2 C3 were put into a quartz pipe immersed in an electric oven; the pipe was connected to a N2 stream and was heated up to 200°C; after 2 hours the pipe was connected to a saturation vessel containing (CH3 O)2 SiCl2, kept at 60°C, and through which an anhydrous N2 stream was passed.
After 4 hours of this treatment, the vapour stream was stopped and air was sent; the temperature was raised to 500°C and the air treatment was prosecuted for 4 hours; at the end it was cooled and the material (n) was recovered, which was subjected to various tests in order to evaluate the thermal stability and mechanical characteristics thereof; the results of the performed tests are reported in table 2.
By using γ-Al2 O3 of example 1, two tablets were prepared suitable to be examined at I.R.
The first tablet was treated with ethyl orthosilicate under the same conditions and according to the procedure of example 6, the second one was treated with colloidal silica Ludox S.M. (Du Pont) according to the procedure of example 9. The so prepared two samples, after dehydration under vacuum at 450°C, were examined at I.R. and the spectrum is reported in the FIGS. 1 and 2, wherein the abscissae refer to the frequency of the infrared radiation expressed in cm1 and the ordinates refer to the percentage transmission.
In the first case (FIG. 1) there was obtained an absorption spectrum typical of silica wherein a very clear band was observed at 3745 cm-1, awarded to an Si--OH group with a disappearance of the bands at 3737 cm-1 and 3795 cm-1 and a strong attenuation of the bands at 3698 cm-1 awarded to an Al--OH band.
In the second case (FIG. 2) there was obtained an overlapping absorption spectrum, typical of a mixture of silica and alumina, this latter being the prevailing one.
100 g of the same alumina as example 5 were put in a self-heating autoclave. The autoclave was evacuated and repeatedly washed with nitrogen in order to remove all oxygen traces: then, from time to time, the following amounts of silicon compounds were introduced:
| ______________________________________ |
| Example |
| ______________________________________ |
| 13 g 30 |
| of diethylchlorosilane |
| (C2 H5)2 SiCl2 |
| 14 g 17 |
| of tetramethylsilane |
| (CH3)4 Si |
| 15 g 17 |
| of acetoxisilane |
| H3 Si(OOCCH3) |
| 16 g 18 |
| of methoxidisilane |
| CH3 OSiH2 (SiH3) |
| 17 g 22 |
| of triethylsilane |
| (C2 H3)3 SiH |
| 18 g 45 |
| of polymethylsiloxane |
| (CH3)3 SiO(CH3)2 SiOSi(CH3) |
| 3 |
| ______________________________________ |
The pressure was brought to 5 Kg/cm2 by nitrogen.
The autoclave was heated up to 200°C over 8 hours; at the end it was cooled, the pressure was released and alumina was recovered, which was heated in a quartz pipe under a nitrogen stream for 4 hours at 200° C., and then air calcined at 500°C for 4 hours.
the characteristics of these modified aluminas are emphasized in table 4, where are collected the results of the measurements carried out after the thermal ageing treatment at 1100°C for 24 hours.
For the sake of comparison, we report also the sample as such prepared according to example 1 (a).
100 g of the same alumina used in example 1 were immersed into 200 cc of (C2 H5 O)4 Si and kept in contact with the liquid for 1 hour; at the end the solid was separated from the excess liquid in excess δand was transferred into a quartz pipe immersed in an electric oven; a nitrogen stream was sent and the whole was heated to the boiling temperature of ethylorthosilicate, so as to completely distill the unreacted product.
After the end of the ethylorthosilicate distillation, the nitrogen flow was stopped, air was sent and the heating was prosecuted by gradually increasing the temperature; when this reached 350°C, determined on alumina, a combustion reaction was started on the organic groups bound to the alumina surface and on the condensation products thereof, therefor the temperature rapidly rose to 900°-1000°C
The violent combustion occurring negatively affects the physical and mechanical characteristics of the final product, as it is possible to infer from the data of table 4.
| TABLE 4 |
| ______________________________________ |
| EX- Starting Sample After treatment |
| at 1100°C |
| AMPLES SA m2 /g |
| K % SA m2 /g |
| k % ΔV% |
| ______________________________________ |
| 13 193 1.9 110 4.5 7 |
| 14 190 2.3 112 5.2 5 |
| 15 205 1.4 108 3.6 5 |
| 16 203 3.1 131 4.3 5 |
| 17 198 2.8 119 4.8 6 |
| 18 195 2.3 121 4.7 6 |
| 19 192 1.8 102 7.8 10 |
| a 196 3.2 68 9.3 14 |
| ______________________________________ |
By using two samples of γ-alumina, the former prepared according to example 1 and the latter according to example 4, hydrothermal treatments were carried out, at growing times, at 250°C, 300°C and 350°C
15 g of the two samples were introduced into two test tubes, which were put into 0.5 l autoclave to which 10 cc of water were added.
The autoclave temperature was brought to the stated temperature (250°C, 300°C, 350°C) and the pressure was reguated at a steam pressure of 15 atmospheres by means of a manometer suitably connected to the autoclave, made possible by releasing the excess pressure through a suitable valve.
The surface area of the samples, so treated over periods of from 4 to 64 hours is reported in the diagram of FIG. 3, wherein the abscissae refer to the treatment duration and the ordinates relate to the surface area (m2 /g). It is to be noted that the stabilized alumina (curve 1) does not undergo any modification, whereas alumina as such (curves 2, 3, 4) undergoes progressive decreases of the surface area which means, as confirmed by X-ray analyses, a change, higher and more higher, of γ-alumina into aluminum monohydrates.
The curve 1 refers to the three temperature values, whereas the curve 2 refers to 350°C, the curve 3 to 300°C and the curve 4 to 250°C
Fattore, Vittorio, Notari, Bruno, Buonomo, Franco
| Patent | Priority | Assignee | Title |
| 5507940, | Aug 30 1991 | Shell Oil Company | Hydrodenitrification catalyst and process |
| Patent | Priority | Assignee | Title |
| 2852473, | |||
| 3416888, | |||
| 3535232, |
| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Mar 12 1979 | Snamprogetti, S.p.A. | (assignment on the face of the patent) | / |
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