Process for regenerating a catalyst comprising ruthenium oxide for the oxidation of hydrogen chloride

Abstract

The invention relates to a process for regenerating a hydrogen chloride oxidation catalyst comprising ruthenium oxide on a support material, which comprises the steps a) reduction of the catalyst in a gas stream comprising hydrogen chloride and optionally an inert gas at a temperature of from 100 to 800 C., b) recalcination of the catalyst in an oxygen-comprising gas stream at a temperature of from 150 to 800 C.

Claims

1. A process for the catalytic oxidation of hydrogen chloride, comprising i) introducing a stream comprising hydrogen chloride and an oxygen-comprising stream into an oxidation reactor comprising a hydrogen chloride oxidation catalyst comprising ruthenium oxide on a support material and oxidation of hydrogen chloride to chlorine over the catalyst until the catalyst has a reduced activity ii) regenerating the catalyst comprising a) reducing the catalyst in a gas stream consisting of hydrogen chloride and optionally an inert gas at a temperature of from 380 to 430 C., wherein the hourly gas throughput is from 0.1 to 1 kg of gas per kg of catalyst, b) recalcinating the catalyst in an oxygen-comprising gas stream at a temperature of from 330 to 450 C., wherein the hourly gas throughput is from 0.1 to 1 kg of gas per kg of catalyst, iii) continuing oxidizing hydrogen chloride to chlorine according to step i) over the regenerated catalyst obtained in ii); and wherein i)-iii) are carried out in the same reactor.

2. The process according to claim 1, wherein the gas stream comprising hydrogen chloride comprises from 10 to 100% by volume of hydrogen chloride.

3. The process according to claim 2, wherein the gas stream comprising hydrogen chloride comprises nitrogen as inert gas.

4. The process according to claim 1, wherein the oxygen-comprising gas stream comprises from 1 to 100% by volume of oxygen.

5. The process according to claim 1, wherein the catalyst comprises ruthenium oxide on a support material selected from the group consisting of oxides of aluminum, silicon and titanium.

6. The process according to claim 5, wherein the support material is alpha-aluminum oxide.

7. The process according to claim 1, wherein the process is carried out in a fluidized-bed reactor.

8. A process for regenerating a hydrogen chloride oxidation catalyst comprising ruthenium oxide on a support material of alpha-alumina, said process comprises a) reducing the catalyst in a gas stream consisting of hydrogen chloride and optionally an inert gas at a temperature of from 380 to 430 C., wherein the hourly gas throughput is from 0.1 to 1 kg of gas per kg of catalyst, b) recalcinating the catalyst in a gas stream composed of oxygen and optionally an inert gas at a temperature of from 330 to 450 C., wherein the hourly gas throughput is from 0.1 to 1 kg of gas per kg of catalyst, wherein a) and b) are carried out in direct succession.

Description

EXAMPLES

Example 1

(1) 585 g of a used catalyst (RuO.sub.2 on -Al.sub.2O.sub.3) are operated at 400 C. using 195 standard l.Math.h.sup.1 of HCl and 97.5 standard l.Math.h.sup.1 of O.sub.2 in a fluidized-bed reactor having a diameter of 44 mm, a height of 990 mm and a bed height of from 300 to 350 mm. The catalyst is in the form of a powder having an average diameter of 50 microns (d.sub.50). A hydrogen chloride conversion of 61% is obtained. The oxygen is then switched off for 24 hours at 400 C. and 292.5 standard l.Math.h.sup.1 of HCl is instead passed over the catalyst. After 24 hours, operation is changed back to the original conditions and an HCl conversion of only 4% is obtained. Changing the gases over to 60 standard l.Math.h.sup.1 of O.sub.2 and 240 standard l.Math.h.sup.1 of N.sub.2 and recalcination for a period of 30 minutes at 400 C. reactivates the catalyst. After this treatment, the catalyst displays a conversion of HCl of 83% using 195 standard l.Math.h.sup.1 of HCl and 97.5 standard l.Math.h.sup.1 of O.sub.2 at 400 C.

Example 2

(2) 21 kg of a used catalyst (RuO.sub.2 on -Al.sub.2O.sub.3) are operated at 400 C. using 10.5 kg.Math.h.sup.1 of HCl, 4.6 kg.Math.h.sup.1 of O.sub.2 and 0.9 kg.Math.h.sup.1 of N.sub.2 in a fluidized-bed reactor having a diameter of 108 mm, a height of from 4 to 4.5 m and a bed height of from 2.5 to 3 m. The catalyst is in the form of a powder having an average diameter of 50 microns (d.sub.50). A HCl conversion of 77% is obtained. The oxygen is then switched off for 20 hours at 400 C. and 10.0 kg.Math.h.sup.1 of HCl is instead passed over the catalyst. After 20 hours, the catalyst is recalcined at 400 C. for 30 minutes under 2.0 kg.Math.h.sup.1 of O.sub.2 and 8.0 kg.Math.h.sup.1 of N.sub.2 and thus reactivated. After this treatment, the catalyst displays a conversion of HCl of 84% using 10.5 kg.Math.h.sup.1 of HCl, 4.6 kg.Math.h.sup.1 of O.sub.2 and 0.9 kg.Math.h.sup.1 of N.sub.2 at 400 C.

Example 3

(3) 1% by Weight of RuO.sub.2 on -Al.sub.2O.sub.3

(4) 100 g of -Al.sub.2O.sub.3 (powder, d=50 m) are impregnated with 36 ml of an aqueous ruthenium chloride solution (2.1% based on ruthenium) in a rotating glass flask. The moist solid is dried at 120 C. for 16 hours. The resulting dry solid is calcined in air at 380 C. for 2 hours.

Example 4

(5) 2% by Weight of RuO.sub.2 on -Al.sub.2O.sub.3

(6) 100 g of -Al.sub.2O.sub.3 (powder, d=50 m) are impregnated with 36 ml of an aqueous ruthenium chloride solution (4.2% based on ruthenium) in a rotating glass flask. The moist solid is dried at 120 C. for 16 hours. The resulting dry solid is calcined in air at 380 C. for 2 hours.

Example 5

(7) 5% by Weight of RuO.sub.2 on -Al.sub.2O.sub.3

(8) 100 g of -Al.sub.2O.sub.3 (powder, d=50 m) are impregnated with 36 ml of an aqueous ruthenium chloride solution (10.5% based on ruthenium) in a rotating glass flask. The moist solid is dried at 120 C. for 16 hours. The resulting dry solid is calcined in air at 380 C. for 2 hours.

Example 6

(9) 2% by weight of RuO.sub.2 on -Al.sub.2O.sub.3:

(10) 100 g of -Al.sub.2O.sub.3 (powder, d=50 m) are impregnated with 80 ml of an aqueous ruthenium chloride solution (1.9% based on ruthenium) in a rotating glass flask. The moist solid is dried at 120 C. for 16 hours. The resulting dry solid is calcined in air at 380 C. for 2 hours.

Example 7

(11) 2% by Weight of RuO.sub.2 on TiO.sub.2 (Rutile):

(12) 100 g of TiO.sub.2 (rutile, powder, d=33 m) are impregnated with 73 ml of an aqueous ruthenium chloride solution (2.1% based on ruthenium) in a rotating glass flask. The moist solid is dried at 120 C. for 16 hours. The resulting dry solid is calcined in air at 380 C. for 2 hours.

Example 8

(13) 2% by Weight of RuO.sub.2 on SiO.sub.2:

(14) 100 g of SiO.sub.2 (powder, d=60 m) are impregnated with 90 ml of an aqueous ruthenium chloride solution (1.7% based on ruthenium) in a rotating glass flask. The moist solid is dried at 120 C. for 16 hours. The resulting dry solid is calcined in air at 380 C. for 2 hours.

Examples 9 to 15

(15) Testing of the Fresh Catalysts:

(16) 2 g in each case of the catalysts from examples 3-8 are mixed with 118 g of the corresponding support material as inert material and 9.0 standard l/h of HCl and 4.5 standard l/h of O.sub.2 are passed through them from the bottom via a glass frit at 360 C. in a fluidized-bed reactor (d=29 mm; height of the fluidized bed: 20-25 cm).

(17) The HCL conversion is determined by passing the resulting gas stream into a potassium iodide solution and subsequently titrating the iodine formed with a sodium thiosulfate solution. The HCl conversion achieved using the catalyst from example 1 comprising 1% by weight of RuO.sub.2 on -Al.sub.2O.sub.3 is 19.0% and is assigned an activity of 1.0 for comparative purposes. If a catalyst contains more than the 1.0% by weight of RuO.sub.2 of the comparative catalyst, the activity is normalized to an RuO.sub.2 content of 1.0% by weight.

(18) Artificial Aging and Testing:

(19) 20 g of the fresh catalysts are artificially aged at 450 C. in air for 12 hours in a muffle furnace. The aged catalysts obtained in this way are examined to determine the activity in the same way as described above.

(20) Regeneration in a Fixed Bed:

(21) 6.5 ml of the aged catalysts are treated with 3 standard l/h of HCl at 400 C. in a fixed bed (l=25 cm; d=6 mm) for 24 hours and subsequently calcined at 360 C. under an air atmosphere for 1 hour. The regenerated catalyst obtained in this way is examined to determine the activity in the manner described above.

(22) The results are summarized in table 1:

(23) TABLE-US-00001 TABLE 1 Activity of the RuO.sub.2 Activity of the Activity of the regenerated [% by fresh catalyst aged catalyst catalyst weight] Support [] [] [] 1 -Al.sub.2O.sub.3 1.00 0.46 0.72 2 -Al.sub.2O.sub.3 1.95 0.24 1.13 5 -Al.sub.2O.sub.3 1.79 0.30 0.64 2 -Al.sub.2O.sub.3 0.90 0.30 0.55 2 Microrutile 0.68 0.25 0.52 2 SiO.sub.2 0.73 0.27 0.42

(24) As can be seen from the table, regeneration gives good results both at different RuO.sub.2 loadings and with different supports.

Example 16

(25) Regeneration using a Mixture of 50% of N.sub.2 and 50% of HCl

(26) 585 g of a fresh catalyst (2% of RuO.sub.2 on -Al.sub.2O.sub.3) are operated at 380 C. using 195.0 standard l.Math.h.sup.1 of HCl and 97.5 standard l.Math.h.sup.1 of O.sub.2. A conversion of the HCl of 74% is obtained. The gas flow is subsequently changed over to 150 standard l/h of N.sub.2 and 20 standard l/h of O.sub.2 and the catalyst is aged at 430 C. for 68 hours. In this state, the catalyst brings about an HCl conversion of 64% at 380 C. using 195.0 standard l.Math.h.sup.1 of HCl and 97.5 standard l.Math.h.sup.1 of O.sub.2. The catalyst is then operated at 400 C. under 300 standard l.Math.h.sup.1 of a mixture of 50% of N.sub.2 and 50% of HCl for 12 hours. After 12 hours, the temperature is adjusted to 400 C. and the catalyst is calcined under 300 standard l/h of air for 30 minutes. After this treatment, the catalyst displays an HCl conversion of 78% at 380 C. using 195.0 standard l.Math.h.sup.1 of HCl and 97.5 standard l.Math.h.sup.1 of O.sub.2. Regeneration of the aged catalyst thus also gives good results when using mixtures of HCl and inerts.