PROCESS FOR THE PRODUCTION OF CHLORINE USING A CERIUM OXIDE CATALYST IN AN ADIABATIC REACTION CASCADE

Abstract

A process for the production of chlorine by thermo-catalytic gas phase oxidation of hydrogen chloride and oxygen is described, the process comprising at least (1) a cerium oxide catalyst and (2) an adiabatic reaction cascade, containing at least two adiabatic stages connected in series with intermediate cooling, wherein the molar O.sub.2/HCl-ratio is equal or above 0.75 in any part of the cerium oxide catalyst beds.

Claims

1-15. (canceled)

16. A process for the production of chlorine by thermo-catalytic gas phase oxidation of hydrogen chloride gas with oxygen in the presence of a catalyst, and separation of the chlorine from the reaction products comprising chlorine, hydrogen chloride, oxygen and water, wherein a) a cerium oxide is used as catalytically active component in the catalyst and b) the reaction gases are converted at the cerium oxide catalyst in an adiabatic reaction cascade, comprising at least two adiabatic reaction zones with catalyst beds and which are connected in series by an intermediate cooling zone for cooling the reaction products, wherein the molar ratio of O.sub.2/HCl is at least 1.5 in any part of the catalyst beds comprising cerium oxide.

17. Process according to claim 16, wherein 3 to 7 adiabatic reaction stages are provided.

18. Process according to claim 16, wherein an additional hydrogen chloride gas stream is mixed with the reaction products in the intermediate cooling zones, preferred before entering the next adiabatic reaction zone.

19. Process according to claim 16, wherein the temperature of the cerium oxide catalyst is kept in the range of 200-600 C. in any reaction zone of the adiabatic reaction cascade, in particular by keeping the inlet gas temperature of any reaction zone at a temperature of at least 200 C. and keeping the outlet temperature of the reaction gases of each reaction zone at a temperature of at least 600 C., particular preferred by controlling the temperature of each catalyst bed via controlling the entire inlet gas.

20. Process according to claim 19, wherein the outlet gas temperature of the last adiabatic reaction zone is controlled via the composition of the reaction gases entering the preceding reaction zones to be at least 450 C.

21. Process according to claim 16, wherein the outlet gas temperature of the reaction zone of the last of said at least two adiabatic zones is kept lower than the outlet gas temperature of each preceding reaction zone of the preceding adiabatic zones.

22. Process according to any of the preceding claims, wherein the absolute pressure in the adiabatic reaction cascade is kept in the range of 2 to 10 bar.

23. Process according to claim 16, wherein a catalyst is used comprising ruthenium metal and/or ruthenium compounds and cerium oxide as catalytically active component.

24. Process according to claim 16, wherein at least two different types of catalysts are present in different reaction zones, wherein a first type of catalyst comprises ruthenium metal and/or ruthenium compounds as catalytically active component and a second type of catalyst comprises cerium oxide as catalytically active component.

25. Process according to claim 24, wherein the ruthenium based catalyst is applied in a reaction zone with a gas temperature in the range of 200 to 400 C., whereas the cerium oxide catalyst is applied in a reaction zone with a gas temperature in the range of 300 to 600 C.

26. Process according to claim 24, wherein at least one adiabatic reaction zone comprises at least two reaction sub zones, a first reaction sub zone comprising a ruthenium based catalyst and a second reaction sub zone comprising a cerium oxide catalyst.

27. Process according to claim 16, wherein during operation of the process the initial activity of the cerium oxide catalyst is restored by raising the ratio of O.sub.2/HCl, and keeping the raised ratio of O.sub.2/HCl for a period of about at least half an hour and then returning to the previous ratio of O.sub.2/HCl.

28. Process according to claim 16, wherein a cerium oxide catalyst is applied which has been heated up during its preparation to a temperature of 500 C. to 1100 C.

29. Process according to claim 16, wherein a cerium oxide catalyst is used in the process which comprises no CeCl.sub.3.6H.sub.2O or CeCl.sub.3 phases, and which in particular does not exhibit significant X-ray diffraction reflections which are characteristic for CeCl.sub.3.6H.sub.2O or CeCl.sub.3 phases.

30. Process according to claim 16, wherein the cerium oxide catalyst used in the process will be subjected to an activity restoring treatment at increased molar O.sub.2/HCl-ratio or replaced by fresh catalyst if more than 3 theoretical layers of oxygen in the cerium oxide catalyst are exchanged by chlorine during use of the catalyst.

31. Process according to claim 23, wherein the content of cerium oxide (calculated as CeO2) is 1-30% of the total amount of the calcined catalyst, and wherein during operation of the process the initial activity of the cerium oxide catalyst is restored by raising the ratio of O.sub.2/HCl to the double.

Description

[0043] The invention will now be described in further detail with reference to the figures and the following non-limiting examples.

[0044] FIG. 1 describes an adiabatic reaction cascade with total HCl-injection with HCl-feed 1, oxygen-containing feed 2 and the mixed feed gas stream 3, which is fed to a reactor I. The product gas stream 4 leaving the reactor is cooled by an intermediate heat exchanger IV using a cooling media (inlet: 14, outlet: 15). The product gas stream is not cooled below the dew point, accordingly the chemical composition of the product gas streams 4 and 5 are identical. Thereafter the product gas stream 5 is fed to reactor II to yield into a product gas stream 6, characterized by an increased HCl-conversion compared to the product gas stream 5. Again, the product gas stream 6 leaving the reactor II is cooled by an intermediate heat exchanger V by using a flow of cooling media 16, 17, yielding a product gas stream 7 of identical chemical composition. Thereafter the product gas stream 7 is fed to reactor III to yield into a product gas stream 8, characterized by an increased HCl-conversion compared to the product gas stream 7. The product gas stream 8 leaving the reactor III is finally cooled by a heat exchanger VI by using a flow of cooling media 18, 19, yielding a product mixture 9 of identical chemical composition.

[0045] FIG. 2 describes an adiabatic reaction cascade with split HCl-injection with HCl-feed 1, oxygen-containing feed 2 and the mixed feed gas stream 3, which is fed to a reactor I. The product gas stream 4 leaving the reactor is cooled by an intermediate heat exchanger IV using a cooling media. The product gas stream is not cooled below the dew point, accordingly the chemical composition of the product gas streams 4 and 5 are identical. Fresh HCl 20 is added. Thereafter the mixed gas stream is fed to reactor II to yield into a product gas stream 6, characterized by an increased HCl-conversion compared to the product gas stream 5. Again, the product gas stream 6 leaving the reactor II is cooled by an intermediate heat exchanger V by using a flow of cooling media, yielding a product gas stream 7 of identical chemical composition. Fresh HCl 21 is added. Thereafter the mixed gas stream is fed to reactor III to yield into a product gas stream 8, characterized by an increased HCl-conversion compared to the product gas stream 7. The product gas stream 8 leaving the reactor III is finally cooled by a heat exchanger VI by using a flow of cooling media, yielding a product mixture 9 of identical chemical composition.

[0046] FIG. 3 shows the result of a phase analysis with XRD according to example 10.

EXAMPLES

Example 1 (Invention): Supported Catalyst Preparation

[0047] A supported cerium oxide catalyst was prepared by: (1) Incipient wetness impregnation of an alumina carrier from Saint-Gobain Norpro (SA 6976, 1.5 mm, 254 m.sup.2/g) with an aqueous solution of commercial cerium (III)chloride heptahydrate (Aldrich, 99.9 purity), followed by (2) drying at 80 C. for 6 h and (3) calcination at 700 C. for 2 h. The final load after calcination calculated as CeO.sub.2 was 15.6 wt. % based on the total amount of catalyst.

Example 2 (Invention): Crushing of Supported Catalyst

[0048] The cerium oxide catalyst from example 1 was crushed to a sieve fraction (100-250 m particle diameter).

Example 3 (Comparative O.SUB.2./HCl-Ratio): Short-Term Supported Catalyst Testing

[0049] 1 g of the cerium oxide catalyst from example 1 as prepared was filled into a tube (8 mm inner diameter) for each experiment. The catalyst in the tube was heated up under nitrogen flow. After reaching steady conditions, a gas mixture of HCl and oxygen (see table 1) was fed to the tube at 430 C. under approximately atmospheric pressure. By trace heating of the tube the temperature was kept constant at 430 C. Several times the product stream was passed through a sodium iodide solution (20 wt. % in water) for approximately 15 min and the thereby produced iodine was titrated with a 0.1 N thiosulfate-solution. The space time yield (STY) was calculated by using the following equation:

Space time yield [g/gh]=m.sub.Cl2m.sub.catalyst.sup.1t.sub.sampling.sup.1

Wherein m.sub.Cl2 is the amount of chlorine, m.sub.catalyst is the amount of catalyst which was used and t.sub.sampling is the sampling time.

TABLE-US-00001 TABLE 1 Strong deactivation of a supported cerium oxide catalyst at a O.sub.2/HCl-ratio < 0.75 HCl O.sub.2 N.sub.2 O.sub.2/HCl STY STY STY STY STY STY STY L/h L/h L/h ratio 1 h 2 h 3 h 4 h 6 h 8 h 24 h 6 4 0 0.67 0.19 0.14 0.13 0.13 0.11 0.09 0.08

Evaluation:

[0050] The supported cerium oxide catalyst from example 1 gets rapidly deactivated at an O.sub.2/HCl-ratio below 0.75. Although the HCl partial pressure is high (compared to example 4), the equilibrated STY is very low.

Example 4 (Inventive O.SUB.2./HCl-Ratio): Short-Term Supported Catalyst Testing

[0051] 1 g of the cerium oxide catalyst from example 1 was used for each experiment. The arrangement and the execution of the experiments were equal as in example 3, except that the gas flows were varied. Results are listed in table 2.

TABLE-US-00002 TABLE 2 Smooth equilibration of a supported cerium oxide catalyst at an O.sub.2/HCl-ratio > 0.75 HCl O.sub.2 N.sub.2 O2/HCl STY STY STY STY STY STY STY STY L/h L/h L/h ratio 1 h 2 h 3 h 4 h 6 h 7 h 23 h 71 h 1 4 5 4 0.43 0.40 0.39 0.38 0.37 0.34 2 4 4 2 0.66 0.59 0.58 0.60 0.60 0.58 2.29 4 3.71 1.75 0.61 0.60 0.61 0.61 0.63 0.62 0.58 1.5 2 6.5 1.33 0.38 0.40 0.38 0.37 0.38 0.38 0.37 2 2 6 1 0.39 0.35 0.33 0.31 0.3 0.27

Evaluation:

[0052] Although the HCl partial pressure is 2.6-6 times lower (compared to example 3), the equilibrated activity under a sufficient O.sub.2/HCl-ratio equal or above 0.75 is 3-6,5-times higher than under an insufficient O.sub.2/HCl-ratio below 0.75. The initial deactivation during equilibration is also much less pronounced at a sufficient O.sub.2/HCl-ratio equal or above 0.75.

Example 5 (Comparison): Short-Term Supported, Crushed Catalyst Testing

[0053] 1 g of the sieve fraction (100-250 m) from example 2 was diluted by 4 g of spheri glass and filled into a tube for each experiment. The catalyst in the tube was heated up under nitrogen flow. After reaching steady conditions, a gas mixture of HCl and oxygen as indicated in table 3 were fed to the tube at 400 C. under approximately atmospheric pressure. By trace heating of the tube the temperature was kept constant at 400 C. over the time on stream. Several times the product stream was passed through a sodium iodide solution (20 wt. % in water) and the thereby produced iodine was titrated with a 0.1 N thiosulfate-solution. The HCl-conversion was calculated by using the following equation:

HCl-conversion [%]=2n.sub.Cl2n.sub.HCl.sup.1100%

Wherein n.sub.Cl2 is the titrated molar amount of chlorine and n.sub.HCl is the fed molar amount of HCl in the same time period.

TABLE-US-00003 TABLE 3 Rapid deactivation of supported cerium oxide catalysts at O.sub.2/HCl-ratio < 0.75 O.sub.2/HCl 5 10 15 20 30 40 HCl.sup.3 O.sub.2.sup.3 N.sub.2.sup.3 ratio min min min min min min 1.32 0.88 1.32 0.67 6.3.sup.1 5.8.sup.1 5.7.sup.1 5.2.sup.1 4.8.sup.1 1.76 0.88 0.88 0.5 5.1.sup.1 4.7.sup.1 4.3.sup.1 3.9.sup.1 3.1.sup.1 .sup.1HCl-conversion at x min. .sup.3in mmol/min

Evaluation:

[0054] At an O.sub.2/HCl-ratio below 0.75 the HCl-conversion is at a very low level, with underlying strong deactivation trend.

Example 6 (Inventive O.SUB.2./HCl-Ratio): Short Term Support Crushed Catalyst Testing

[0055] 1 g of a sieve fraction (100-250 m) from example 2 was used. The arrangement and the execution of the experiments were equal as in example 4, except that the gas flows were varied (table 4).

TABLE-US-00004 TABLE 4 Smooth deactivation of supported cerium oxide catalysts at O.sub.2/HCl-ratio > 0.75 O.sub.2/HCl 5 10 15 20 30 40 HCl.sup.3 O.sub.2.sup.3 N.sub.2.sup.3 ratio min min min min min min 1.10 0.88 1.54 0.8 9.5.sup.1 9.5.sup.1 9.3 9.1.sup.1 8.7.sup.1 8.5.sup.1 0.88 0.88 1.76 1 12.1 11.9 11.8 11.6 0.66 0.88 1.98 1.33 15.7 15.6 15.3 0.44 0.88 2.20 2 24.5 23.8 22.2 22.2 0.22 0.88 2.42 4 48.8 50.1 46.9 45.1 .sup.1HCl-conversion at x min, .sup.3in mmol/min

Evaluation:

[0056] The higher the O.sub.2/HCl-ratio is, the higher the HCl-conversion is. At an O.sub.2/HCl-ratio equal or above 0.75 the deactivation is only minor.

Example 7 (Inventive O.SUB.2./HCl-Ratio): Medium-Term Supported Catalyst Testing

[0057] 1 g of the cerium oxide catalyst from example 1 as prepared was filled into a tube (8 mm inner diameter). The catalyst in the tube was heated up under nitrogen flow. After reaching steady conditions, 1 L/h HCl, 4 L/h O.sub.2 and 5 L/h N.sub.2 were fed to the tube at 430 C. under approximately atmospheric pressure. By trace heating of the tube the temperature was kept constant at 430 C. Several times the product stream was passed through a sodium iodide solution (20 wt. % in water) for approximately 15 min and the thereby produced iodine was titrated with 0.1 N thiosulfate-solution (table 5). The space time yield was calculated by using the following equation:

Space time yield [g/gh]=m.sub.Cl2m.sub.catalyst.sup.1t.sub.sampling.sup.1

Wherein m.sub.Cl2 is the amount of chlorine, m.sub.catalyst is the amount of catalyst which was used and t.sub.sampling is the sampling time.

TABLE-US-00005 TABLE 5 Stable activity of a supported cerium oxide catalyst after equilibration Time on stream [h] 16 23 88 161 185 255 308 448 STY [g/gh] 0.35 0.35 0.34 0.36 0.35 0.35 0.37 0.36

Evaluation:

[0058] The activity of the supported cerium oxide catalyst from example 1 after equilibration (compare example 4) is very stable at an O.sub.2/HCl-ratio equal or above 0.75.

Example 8 (Inventive O.SUB.2./HCl-Ratio): Long-Term Supported Catalyst Testing

[0059] 80 g of the cerium oxide catalyst from example 1 as prepared were filled into a tube (14 mm inner diameter, 1.5 m length, including an inner tube with moveable thermocouple). The catalyst inside the tube was heated up under a preheated nitrogen flow. After reaching steady conditions, 0.3 mol/h HCl and 0.75 mol/h oxygen (O.sub.2/HCl-ratio of 2.5) under approximately atmospheric pressure were fed to the tube. By pre-heating of the gas mixture and trace heating of the tube the temperature profile was kept approximately constant over 5005 h time on stream (table 6). Several times the product stream was passed through a sodium iodide solution (20 wt. % in water) for approximately 15 min and the thereby produced iodine was titrated with a 0.1 N thiosulfate-solution (table 7). The HCl-conversion was calculated by using the following equation:

HCl-conversion [%]=2n.sub.Cl2n.sub.HCl.sup.1100%

Wherein n.sub.Cl2 is the titrated molar amount of chlorine and n.sub.HCl is the fed molar amount of HCl in the same time period.

[0060] The process condensate (saturated hydrochloric acid at room temperature) was sampled three times:

[0061] after 671 h, 1127 h and 3253 h time on stream. According to ICP-OES analysis the alumina content in the condensate was always below 2 wt. ppm (671 h, 1127 h) and even below 0.5 wt. ppm after 3253 h. The cerium content in the condensate was always similar or below 0.3 wt. ppm!

TABLE-US-00006 TABLE 6 Temperature profile (+/2 K for each taken point) position inlet +2 cm +4 cm +6 cm +8 cm +10 cm +12 cm +14 cm T [ C.] 397 400 403 404 405 404 403 402 position +16 cm +18 cm +20 cm +22 cm +24 cm +26 cm +28 cm +30 cm T [ C.] 401 400 401 402 407 412 418 425 position +32 cm +34 cm +36 cm +38 cm +40 cm +42 cm +44 cm +46 cm T [ C.] 432 437 441 443 445 446 447 447 position +48 cm +50 cm +52 cm +54 cm +56 cm +58 cm +60 cm +62 cm T [ C.] 448 449 449 449 449 450 450 450 position +64 cm +66 cm +68 cm +70 cm +72 cm +74 cm +76 cm +78 cm T [ C.] 450 450 449 449 448 449 450 453 position +80 cm +82 cm +84 cm +86 cm +88 cm +90 cm +92 cm +94 cm T [ C.] 455 457 458 458 459 459 458 456 position +96 cm +98 cm outlet T [ C.] 454 450 445

TABLE-US-00007 TABLE 7 Long-term stable activity of a supported cerium oxide catalyst Time on stream [h] 551 1055 1535 2039 2509 3085 3661 4141 5005 HCl-con- 41.0 39.2 38.5 38.4 38.8 37.9 37.4 38.3 36.9 version [%]

Evaluation:

[0062] At an O.sub.2/HCl-ratio of 2.5 only a very minor deactivation is observable over 5005 h time on stream! Based on condensate analysis the estimated percentage loss of cerium and alumina is below 0.1% over 5005 h time on stream. Consequently the loss of catalyst constituents is negligible, which is a further proof for catalyst stability.

Example 9 (Comparative and Inventive O.SUB.2./HCl-Ratio): Short-Term Unsupported Catalyst Testing

[0063] Cerium oxide powder (Aldrich, nanopowder) was calcined at 900 C. for 5 h. For each experiment 0.5 g of the calcined sample (particle size=0.4-0.6 mm) was filled into a tube (8 mm inner diameter). The catalyst powder inside the tube was heated up under nitrogen flow. After reaching steady conditions, HCl, O.sub.2 and N.sub.2 were fed under approximately atmospheric pressure to the tube. By trace heating of the tube the catalyst temperature was kept constant at 430 C. The O.sub.2/HCl ratio was varied between 0.5 and 7, keeping the partial pressure of HCl constant, and between 0.25 and 2, keeping the oxygen partial pressure constant. After 1 h time on stream in each O.sub.2/HCl ratio the outlet gas was passed through a sodium iodide solution (2 wt. % in water) for approximately 5 min and the thereby produced iodine was titrated with 0.1 M sodium thiosulfate solution. The HCl-conversion was calculated by using the following equation:

HCl-conversion [%]=2n.sub.Cl2n.sub.HCl.sup.1100%

Wherein n.sub.Cl2 is the titrated molar amount of chlorine and n.sub.HCl is the fed molar amount of HCl in the same time period.

TABLE-US-00008 TABLE 8 Dependency of (nearly equilibrated) HCl-conversion on O.sub.2/HCl-ratio Experiment a b c d e f g h i j k HCl [%] 10 10 10 10 10 10 40 30 20 10 5 O.sub.2 [%] 5 10 20 30 40 70 10 10 10 10 10 N.sub.2 [%] 85 80 70 60 50 20 50 60 70 80 85 O.sub.2/HCl 0.5 1 2 3 4 7 0.25 0.33 0.5 1 2 HCl-conversion [%] 8.8 12.1 16.6 18.7 21.6 26.3 1.0 2.3 7.1 14.5 22.9

Evaluation:

[0064] An increase of the O.sub.2/HCl ratio appears beneficial to achieve higher conversion levels in the low O.sub.2/HCl-ratio range. In particular, an increase of the O.sub.2/HCl-ratio from 0.25 to 0.5 (g-h-i) improves the HCl-conversion by a factor of 7, while an increase of the O.sub.2/HCl-ratio from 1 to 7 improves the HCl-conversion only by a factor of 2. Consequently, at O.sub.2/HCl ratios below 0.75 the process economics can be dramatically optimized by increasing the O.sub.2/HCl-ratio, whereas at O.sub.Z/HCl-ratios equal or above 0.75 one has to balance surplus oxygen costs (running) against catalyst costs (one time). Consequently, experiments b-f and j-k are recognized as according to the invention, whereas experiments a and g-i are considered as comparative examples.

[0065] Note that the equilibration of an unsupported cerium oxide powder catalyst is assumed to be much faster than the equilibration of a supported, pelletized catalyst. The observed HCl-conversion is accordingly treated as nearly equilibrated. Longer equilibration times would have resulted in substantially identical HCl-conversion levels for O.sub.2/HCl-ratios equal or above 0.75, but in even lower activity levels for O.sub.2/HCl-ratios below 0.75, shown to lead to deactivation. This point is further detailed in Example 12.

Example 10 (Scientific Prove): Catalyst Characterization by XRD

[0066] X-Ray diffraction phase analysis (PAN analytical X'Pert PRO-MPD diffractometer, 10-70 29 range, angular step size of 0.017 and a counting time of 0.26 s per step; FIG. 3, patterns a-f) was applied to characterize cerium oxide samples (Aldrich, nanopowder) treated in different conditions, namely, calcined at 900 C. (a) and exposed at 430 C. for 3 h respectively to a reaction mixture with O.sub.2/HCl-ratios of 0 (e), or 0.25 (d), or 0.75 (c) or 2 (b) or calcined at 500 C. and treated at 430 C. and 3 h in a feed with O.sub.2/HCl-ratio of 0 (f). CeO.sub.2 (JCPDS 73-6328) is evidenced as exclusive or dominant phase in the XRD patterns. Reflections of CeCl.sub.3.6H.sub.2O (JCPDS 01-0149) appear in the 29 ranges marked by the gray boxes for some of the diffractograms.

Evaluation:

[0067] After treatment of the cerium oxide sample calcined at 900 C. in a feed with an O.sub.2/HCl-ratio of 2 the XRD pattern (b) only shows the characteristic reflexions of CeO.sub.2. After treatment of cerium oxide calcined at 900 C. in a feed with O.sub.2/HCl-ratios of 0 or 0.25 reflexions specific to CeCl.sub.3.6H.sub.2O are as well evidenced in appreciable intensity. After treatment of cerium oxide calcined at 900 C. in a feed with an O.sub.2/HCl-ratio of 0.75 the diffractogram only shows the characteristic reflexions of CeO.sub.2. Diffraction lines specific to CeCl.sub.3.6H.sub.2O, if present, are not distinguishable from the noise. The XRD pattern of the cerium oxide sample calcined at 500 C. and treated in a feed with O.sub.2/HCl ratio of 0 evidences the presence of CeCl.sub.3.6H.sub.2O and in higher amount with respect to the cerium oxide sample calcined at 900 C. and similarly treated. Consequently, we believe that the deactivation of the cerium oxide catalyst, observed at O.sub.2/HCl-ratios below 0.75, is caused by the formation of the CeCl.sub.3.6H.sub.2O phase, which is much less active in HCl-oxidation than CeO.sub.2 (see also Example 11). Furthermore, calcination of cerium oxide at higher temperatures (900 C.) seems to result in a catalyst better resistant to chlorination.

Example 11 (Scientific Prove): Catalyst Characterization by BET/XPS

[0068] Cerium oxide powder (Aldrich, nanopowder) was calcined at 500 C. and 900 C. for 5 h (table 9) and from 300 C. to 1100 C. for 5 h respectively (table 10). The calcined catalyst samples were further treated in O.sub.2/HCl=2 at 430 C. for 3 h (label O.sub.2/HCl=2 in table 9, table 10) or in O.sub.2/HCl=0 at 430 C. for 3 h (label O.sub.2/HCl=0 in table 9). The fresh samples (table 10) and the treated samples (table 9) were analyzed by nitrogen adsorption to measure their surface area (Quantachrome QuadrasorbSI gas adsorption analyzer, BET-method) and X-ray photoelectron spectroscopy to assess the degree of surface chlorination (Phoibos 150, SPECS, non-monochromatized Al K (1486.6 eV) excitation, hemispherical analyzer).

TABLE-US-00009 TABLE 9 Surface area and chlorination of the catalyst evaluated by XPS BET Cl/Ce- theoretical pretreatment m.sup.2/g stoichiometry layers 1173 K, O.sub.2/HCl = 2 25 0.14 1.0.sup.1 1173 K, O.sub.2/HCl = 0 25 0.29 2.4.sup.1 773 K, O.sub.2/HCl = 2 27 0.19 1.5.sup.1 773 K, O.sub.2/HCl = 0 27 0.55 5.7.sup.1 .sup.1Calculated by model IMFP with inelastic mean free path of 22 Angstrm (by TPP-2M)

TABLE-US-00010 TABLE 10 Dependency of HCl-conversion on calcination temperature Calcination temperature 573 K 773 K 1023 K 1173 K 1273 K 1373 K Surface area [m.sup.2/g] 117 106 53 30 12 1 HCl-conversion 29 25 25 27 14 2

Evaluation:

[0069] For the unsupported cerium oxide powder sample pre-calcined at 500 C. and treated with an O.sub.2/HCl-ratio of 2, only 1-2 theoretical layer of oxygen are exchanged by chlorine (some of the detected chlorine could also be related to adsorbed chlorine on the catalyst surface), whereas after a treatment with an O.sub.2/HCl-ratio of 0, 5-6 theoretical layer of oxygen are exchanged by chlorine. The cerium oxide samples pre-calcined at 900 C. exhibit a similar but very less pronounced effect (1 theoretical layer versus 2-3 theoretical layers). The results are in line with the bulk chlorination detected by

[0070] XRD analysis (Example 10), confirming the postulated relationship between deactivation and CeCl.sub.3.6H.sub.2O phase formation. Calcination of cerium oxide at temperatures in the range of 300-1100 C. produces materials with different initial surface areas (decreasing with increasing calcination temperature, table 10). Contrarily, the surface area values of the samples calcined at 500 C. drops significantly after treatment either in O.sub.2/HCl=2 or 0 while that of the sample calcined at 900 C. and equally treated is changed to minor extent (table 9). Thus, calcination at higher temperature is beneficial to obtain a stabilized catalyst and is the feasible origin of the higher resistance towards chlorination shown by XRD (Example 10) and XPS.

Example 12 (Invention): Catalyst Regeneration

[0071] Cerium oxide powder (Aldrich, nanopowder) was calcined at 900 C. for 5 h. For each experiment 0.5 g of the calcined powder was filled into a tube (8 mm inner diameter). The catalyst powder inside the tube was heated up under nitrogen flow. After reaching steady conditions, experiments were carried out at 430 C. combining a deactivation step, in which the catalyst was exposed to a not inventive feed composition O.sub.2/HCl=0 (3 h) or 0.25 (5 h), and a regeneration step (inventive), in which excess of oxygen was fed (O.sub.2/HCl=2 or 7) for 2 h in order to study the reoxidation of the catalyst.

TABLE-US-00011 TABLE 11 Deactivation followed by regeneration experiments over unsupported CeO.sub.2 Experiment 1 Deactivation Regeneration HCl [%] O.sub.2 [%] N.sub.2 [%] O.sub.2/HCl HCl [%] O.sub.2 [%] N.sub.2 [%] O.sub.2/HCl Conditions.sup.a 10 2.5 87.5 0.25 10 20 70 2 Time-on- 0.25 1 2 3 4 5 5.25 5.5 6 7 stream [h] HCl-conver- 5.9 5 4.6 4.1 3.8 3.7 13.4 15.0 15.9 16.4 sion [%] Experiment 2 Deactivation Regeneration HCl [%] O.sub.2 [%] N.sub.2 [%] O.sub.2/HCl HCl [%] O.sub.2 [%] N.sub.2 [%] O.sub.2/HCl Conditions 10 2.5 87.5 0.25 10 70 20 7 Time-on- 0.25 1 2 3 4 5 5.25 5.5 6 7 stream [h] HCl-conver- 5.4 5 4.8 4.4 4.3 4 28.1 28.2 27.8 26.8 sion [%] Experimen 3 Deactivation Regeneration HCl [%] O.sub.2 [%] N.sub.2 [%] O.sub.2/HCl HCl [%] O.sub.2 [%] N.sub.2 [%] O.sub.2/HCl Conditions 10 0 90 0 10 70 20 7 Time-on- 0.17 0.5 1 2 3 3.17 3.5 4 5 stream [h] HCl-conver- 1.2 0.9 0.7 0.2 0 9.5 29.7 30.3 29.1 sion [%]

Evaluation:

[0072] A progressive decrease in activity is observed with O.sub.2/HCl=0.25 (table 11, experiment 1). Upon increasing the O.sub.2 content in the feed (O.sub.2/HCl=2), the activity is slowly restored. However, the activity level expected for the O.sub.2/HCl=2 feed composition (HCl conversion=22%, Example 9) is not completely reached within 2 h. Regeneration with O.sub.2/HCl=7 is on the other hand extremely fast (table 11, experiment 2). This evidence supports chlorination of the catalyst (Example 10) in the deactivation phase and fast chlorine displacement by excess oxygen.

[0073] When performing the deactivation phase in O.sub.2/HCl=0 (table 11, experiment 3) the catalyst activity is logically completely lost in 3 h. In Example 10 it is shown that cerium oxides indeed chlorinated to larger extent in the presence of the sole HCl. Still, regeneration in O.sub.2/HCl=7 fully restores the original activity in 1 h.

Example 13 (Invention): Design Example of an Adiabatic Cascade with a Cerium Oxide Catalyst

[0074] As feed streams 1.37 kmol/h HCl, 0.69 kmol/h O.sub.2, 0.03 kmol/h Cl.sub.2, 0.08 kmol/h H.sub.2O and 0.38 kmol/h N.sub.2 are provided at approximately 5 bar (gauge). The HCl feed split, the inlet and outlet temperatures of the adiabatic stages and other relevant parameter are provided in table 1. The minimal O.sub.2/HCl-ratio is 0.84 for the inlet of the 4.sup.th adiabatic stage. Note that the minimal O.sub.2/HCl-ratio is always at the inlet of a catalyst bed due to the reaction stoichiometry (4 moles of HCl converted per mol of oxygen).

TABLE-US-00012 TABLE 12 Design parameters of a 5-stage adiabatic reaction cascade with a cerium oxide catalyst HCl HCl HCl acc. con- HCl O.sub.2 min T T split split inlet version outlet O.sub.2 inlet consumed O.sub.2/HCl- stage inlet outlet % kmol/h kmol/h % kmol/h kmol/h kmol/h ratio 1 320 480 30 0.41 0.41 20 0.13 0.688 0.070 1.67 2 349 480 24 0.33 0.46 40 0.19 0.618 0.069 1.34 3 385 480 23 0.32 0.50 58 0.27 0.549 0.058 1.10 4 390 480 23 0.32 0.58 76 0.33 0.490 0.063 0.84 5 360 400 0 0 0.33 84 0.21 0.427 0.029 1.30

Example 14 (Invention): Design Example of an Adiabatic Cascade with a Combination of a Cerium Oxide Catalyst and a Ruthenium Based Catalyst

[0075] Feed streams are equal as in example 13, feed streams are provided at approximately 5 bar (gauge). The HCl feed split, the inlet and outlet temperatures of the adiabatic stages and other relevant parameter are provided in table 13. There are two reaction sub zones in the 1.sup.st adiabatic stage (1a/b) and 2.sup.nd adiabatic stage (2a/b). The first reaction sub zone contains a ruthenium-based catalyst (a), the second reaction sub zone contains a cerium oxide catalyst (b). In the 3.sup.rd adiabatic stage only a ruthenium-based catalyst is applied. The minimal O.sub.2/HCl-ratio for the cerium oxide catalyst is 0.75 for the inlet of the (cerium oxide catalyst containing) 2.sup.nd reaction zone (2b). Note that the minimal O.sub.2/HCl-ratio is always at the inlet of a catalyst bed due to the reaction stoichiometry (4 moles of HCl converted per mol of oxygen).

TABLE-US-00013 TABLE 13 Design parameters of a 3-stage adiabatic reaction cascade with a combination of a ruthenium based catalyst and a cerium oxide catalyst HCl HCl HCl acc. con- HCl O.sub.2 min T T split split inlet version outlet O.sub.2 inlet consumed O.sub.2/HCl- stage inlet outlet % kmol/h kmol/h % kmol/h kmol/h kmol/h ratio 1a 241 365 50 0.68 0.68 18 0.44 0.688 0.060 1b 365 480 0 0 0.44 35 0.21 0.627 0.058 1.41 2a 288 365 50 0.68 0.90 50 0.69 0.569 0.052 2b 365 480 0 0 0.69 73 0.37 0.517 0.078 0.75 3 303 365 0 0 0.37 85 0.21 0.438 0.042

Example 15 (Invention): Supported Catalyst Testing at 4 Bar (Gauge)

[0076] 25 g of the cerium oxide catalyst from example 1 as prepared were filled into a tube (21 mm inner diameter, 330 mm length, including an inner tube with moveable thermocouple). The catalyst inside the tube was heated up under a preheated nitrogen flow. After reaching steady conditions, varying gas feeds under approximately 4 bar (gauge) were fed to the tube (table 14). Two times (after 60 min and 120 min) the product stream was passed through a sodium iodide solution (20 wt. % in water) and the thereby produced iodine was titrated with a 0.1 N thiosulfate-solution (table 7). The HCl-conversion was calculated by using the following equation:

Space time yield [g/gh]=m.sub.Cl2m.sub.catalyst.sup.1t.sub.sampling.sup.1

Wherein m.sub.Cl2 is the amount of chlorine, m.sub.catalyst is the amount of catalyst which was used and t.sub.sampling is the sampling time. In table 14 the average value of the two titrations is given.

TABLE-US-00014 TABLE 14 STY of cerium oxide catalyst at elevated pressure and an O.sub.2/HCl-ratio > 0.75 HCl O.sub.2 N.sub.2 T O.sub.2/HCl STY [L/h] [L/h] [L/h] [ C.] ratio [g/gh] 40 100 360 276 2.5 0.78 40 100 360 400 2.5 1.21

Evaluation:

[0077] At an O.sub.2/HCl-ratio of 2.5 the cerium oxide catalyst exhibits a sufficient activity at 276 C. and at 400 C.