Method for producing silicic acid with variable thickening

Abstract

A process for production of silica having variable thickening wherein a) a product stream I containing at least a vaporous, hydrolysable and/or oxidizable silicon compound, b) a product stream II containing oxygen and c) a product stream III containing at least a combustible gas
are made to react, where d) a feed port in a pipepiece A, the pipepiece A containing one or more static mixing elements, is used to import product stream I into product stream II, or vice versa and thereby create product stream IV, then e) a feed port in a pipepiece B, the pipepiece B containing one or more static mixing elements, is used to import product stream III in product stream IV and thereby create product stream V, f) product stream V leaving pipepiece B is imported into a reaction chamber, ignited therein and reacted in a flame, and g) the resultant solid material is separated off.

Claims

1. A process for production of silica having variable thickening, the process comprising reacting: a) a product stream I comprising at least one silicon compound selected from the group consisting of a vaporous silicon compound, a hydrolysable silicon compound, and an oxidizable silicon compound, b) a product stream II comprising oxygen, and c) a product stream III comprising a combustible gas, wherein the process comprises: importing product stream I into product stream II, or importing product stream II into product stream I, through a feed port in a first pipe piece A to create product stream IV, wherein the first pipe piece A comprises at least one static mixing element; importing product stream III into product stream IV, through a feed port in a second pipe piece B to create product stream V, wherein the second pipe piece B comprises at least one static mixing element; importing product stream V leaving the second pipe piece B into a reaction chamber, igniting the reaction chamber, and reacting the product stream V in a flame; and separating solids resulting from igniting the reaction chamber and reacting the product stream V in the flame, wherein V.sub.B is a velocity with which the product stream III comprising a combustible gas is imported into the product stream IV, wherein V.sub.B is at least 50 Nm/s.

2. The process according to claim 1, wherein the at least one static mixing element of the first pipe piece A and of the second pipe piece B is designed as a flange mixer.

3. The process according to claim 2, wherein the flange mixer has a single punctiform feed port.

4. The process according to claim 1, wherein V.sub.B is a velocity with which the product stream III comprising a combustible gas is imported into the product stream IV, and V.sub.A is a velocity of the product stream IV at a point of importing the product stream III comprising a combustible gas, wherein V.sub.B/V.sub.A is at least 4.

5. The process according to claim 1, wherein V.sub.A is a velocity of the product stream IV at a point of importing the product stream III comprising a combustible gas, wherein V.sub.A is at least 15 Nm/s.

6. The process according to claim 1, wherein L.sub.A/D.sub.A is =2 to 20, where L.sub.A=length of pipepiece A, and D.sub.A=internal diameter of the first pipe piece A.

7. The process according to claim 1, wherein L.sub.B/D.sub.B is =2 to 20, where L.sub.B=length of pipepiece B, and D.sub.B=internal diameter of the second pipe piece.

8. The process according to claim 1, wherein an amount of oxygen is at least sufficient to convert the at least one silicon compound and the combustible gas.

9. The process according to claim 1, wherein the at least one silicon compound is selected from the group consisting of SiCl.sub.4, CH.sub.3SiCl.sub.3, (CH.sub.3).sub.2SiCl.sub.2, (CH.sub.3).sub.3SiCl, (CH.sub.3).sub.4Si, HSiCl.sub.3, (CH.sub.3).sub.2HSiCl, CH.sub.3CH.sub.2CH.sub.2SiCl.sub.3, Si(OC.sub.2H.sub.5).sub.4, Si(OCH.sub.3).sub.4, and mixtures thereof.

10. The process according to claim 1, further comprising introducing a product stream VI comprising oxygen and/or steam into the reaction chamber.

11. The process according to claim 1, further comprising cooling a reaction mixture leaving the reaction chamber to form a cooled reaction mixture and treating the cooled reaction mixture with steal before separating the solids.

Description

EXAMPLES

(1) CompaX mixers from Sulzer are used as pipepieces A and B comprising static mixing elements.

Example 1

(2) Product stream I consists of 8 kg/h of vaporous silicon tetrachloride, has a velocity v.sub.I of 1.9 Nm/s and is mixed via the punctiform feed port, 3 mm in diameter, of a CompaX mixer A with L.sub.A/D.sub.A=5 into a product stream II, which consists of 11.9 Nm.sup.3/h air and has a velocity v.sub.II of 467.6 Nm/s. The velocity v.sub.A of resultant product stream IV is 23.4 Nm/s. A CompaX mixer B, which has the dimensions L.sub.B/D.sub.B=5 and whose punctiform feed port has a diameter of 1 mm, is used to import a product stream III in the form of 3.9 Nm.sup.3/h hydrogen into said product stream IV. The speed v.sub.B at which product stream III leaves the punctiform feed port is 1379.3 Nm/s. The way the feedstocks are added is shown in FIG. 2A. Resultant product stream V is imported into a reaction chamber via a nozzle 15 mm in internal diameter, resulting in a velocity v.sub.RC of 26.5 Nm/s, and ignited therein. Additionally imported into the reaction chamber is product stream VI consisting of 18 Nm.sup.3/h air. Resultant product stream VII, now comprising silica particles, hydrochloric acid, steam and air, is initially cooled down to a temperature of 120 to 150° C. The silica is subsequently filtered off and steam treated at a temperature of 400 to 500° C.

(3) The silica has a BET surface area of 186 m.sup.2/g and a thickening effect of 3550 mPas at 22° C.

(4) Examples 2 to 8 are carried out in a similar manner, the operational settings are reported in the table. It is evident that the different diameters of the feed port of Compax mixer B and the associated velocities v.sub.B produce for the same dimensions L.sub.A, D.sub.A, L.sub.B and D.sub.B and substantially the same v.sub.A, silicas having substantially the same BET surface area, 186 to 218 m.sup.2/g, and significantly differing thickening, 3575 to 4250 mPas.

(5) Example 9 is a repeat of Example 1 except that product stream II is introduced into product stream I via the punctiform feed port of CompaX mixer A. L.sub.A/D.sub.A is further=3. The way the feedstocks are added is shown in FIG. 2B. Operational parameters and product properties are reported in the table.

(6) Examples 10 and 11 have the same operational parameters as Example 9 except that the length of pipepiece A comprising static mixing elements was varied. L.sub.A/D.sub.A is 3 in Example 9, 6 in Example 10 and 15 in Example 11. While there is substantially the same BET surface area for the silicas obtained, thickening varies distinctly, from 3085 to 3495 mPas.

(7) A mixture of methyltrichlorosilane and silicon tetrachloride is used in Example 12. For substantially the same BET surface area as in Examples 1 to 11, the silica obtained has very low thickening.

(8) TABLE-US-00001 TABLE Operational parameters and product properties Example 1 2 3 4 5 6 7 8 9 10 11 12 Product stream I SiCl.sub.4 kg/h 8 8 8 8 8 8 8 8 8 8 8 6.sup.a) v.sub.I Nm/s 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.6 Product stream II.sup.b) Air Nm.sup.3/h 11.9 12.3 12.1 12 11.9 11.95 12.05 12.05 13.2 13.2 13.2 12.9 v.sub.II Nm/s 467.6 483.4 475.5 471.6 467.6 469.6 473.5 473.5 518.7 518.7 518.7 506.9 v.sub.A Nm/s 23.4 24.1 23.7 23.6 23.4 23.5 23.6 23.6 25.7 25.7 25.7 24.9 Product stream III H.sub.2 Nm.sup.3/h 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9 1.5 Ø hole Mm 1.0 1.2 1.4 1.6 1.9 2.2 2.6 3.6 3 3 3 3 v.sub.B Nm/s 1379.3 957.9 703.7 538.8 382.1 285.0 204.0 106.4 153.3 153.3 153.3 516.4 v.sub.B/v.sub.A 59.0 39.7 29.6 22.9 16.3 12.1 8.6 4.5 6.0 6.0 6.0 20.8 Product stream V.sup.c) lambda.sup.d) 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.4 1.4 1.4 1.3 v.sub.RC.sup.e) Nm/s 26.5 27.1 26.8 26.7 26.5 26.6 26.7 26.7 28.5 28.5 28.5 — Product stream VI Air Nm.sup.3/h 18.0 18.0 18.0 18.0 18.0 18.0 18.0 18.0 19.0 19.0 19.0 18 Silica BET m.sup.2/g 186 214 218 199 200 204 206 208 207 204 203 205 Thickening mPas 3550 4250 3955 3625 3600 3575 3770 4070 3340 3085 3495 2580 .sup.a)75:25 parts by weight CH.sub.3SiCl.sub.3/SiCl.sub.4; .sup.b)diameter of hole for feed port of product stream II into product stream I: 3 mm; .sup.c)Diameter of feed port of product stream V in reaction chamber: 15 mm; .sup.d)gamma equals 1.9 in all examples; .sup.e)velocity of feed into reaction chamber