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Home , Ruthenium tetroxide

(19) TZZ ¥ZZ_T

(11) EP 2 823 900 A1

(12) EUROPEAN PATENT APPLICATION published in accordance with Art. 153(4) EPC

(43) Date of publication: (51) Int Cl.: 14.01.2015 Bulletin 2015/03 B09B 3/00 (2006.01) C01G 55/00 (2006.01)

(21) Application number: 13758228.4 (86) International application number: PCT/CN2013/072105 (22) Date of filing: 04.03.2013 (87) International publication number: WO 2013/131451 (12.09.2013 Gazette 2013/37)

(84) Designated Contracting States: • LAI, Bo AL AT BE BG CH CY CZ DE DK EE ES FI FR GB Wuhan GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO Hubei 430223 (CN) PL PT RO RS SE SI SK SM TR • SONG, Dechen Designated Extension States: Wuhan BA ME Hubei 430223 (CN) • LIU, Qianqian (30) Priority: 05.03.2012 CN 201210055796 Wuhan Hubei 430223 (CN) (71) Applicant: Sunshine Kaidi New Energy Group Co., • HAN, Yiming Ltd. Wuhan Wuhan, Hubei 430223 (CN) Hubei 430223 (CN)

(72) Inventors: (74) Representative: Zeuner Summerer Stütz •XU,Li Nußbaumstrasse 8 Wuhan 80336 München (DE) Hubei 430223 (CN)

(54) METHOD FOR PREPARING SOLID NITROSYL NITRATE BY USING WASTE CATALYST CONTAINING RUTHENIUM

(57) Disclosed is a method for preparing solid nitrosyl ruthenium nitrate by using a waste catalyst containing ruthenium. Steps of the method are: drying and calcining a waste catalyst containing ruthenium to acquire a black solid containing ruthenium, grinding the black solid con- taining ruthenium into powder, feeding for re- duction to form metal ruthenium, oxidizing metal ruthe- nium by using mixed gas of ozone and air to produce a ruthenium tetra gas, collecting the gas, feeding the gas in a nitric acid solution, adding solid nitrite to prepare a solution containing nitrosyl ruthenium nitrate, and finally using diethyl ether for extraction, and evapo- rating diethyl ether to acquire a nitrosyl ruthenium nitrate solid. The method can effectively reclaim noble metal ruthenium in various load-type waste catalysts contain- ing ruthenium, so as to achieve effective recycling of ru- thenium resources, and has simple operation steps and does not involve the introduction of ruthenium interme- diates, which ensures a high product yield. The acquired solid nitrosyl ruthenium nitrate is free of halogen, has high purity, and is capable of being directly applied to the preparation of catalysts. EP 2 823 900 A1

Printed by Jouve, 75001 PARIS (FR) 1 EP 2 823 900 A1 2

Description SUMMARY OF THE INVENTION

FIELD OF THE INVENTION [0006] In view of the above-described problems, it is one objective of the invention to a method for preparing [0001] The invention relates to the recycling of a plat- 5 a solid of ruthenium nitrosyl nitrate using a ruthenium- inum group metal, and more particularly to a method for containing spent catalyst. The method is simple and high- preparing a solid of ruthenium nitrosyl nitrate using a ru- ly efficient, can produce high purity of a solid of ruthenium thenium-containing spent catalyst. nitrosyl nitrate from a supported ruthenium-containing spent catalyst. The solid of ruthenium nitrosyl nitrate can BACKGROUND OF THE INVENTION 10 be used for preparation of a ruthenium-containing cata- lyst. [0002] With excellent catalytic performance, ruthe- [0007] To achieve the above objective, in accordance nium is widely used in preparation of ammonia, selective with one embodiment of the invention, there is provided hydrogenation of benzene to yield cyclohexene, hydro- a method for preparing a solid of ruthenium nitrosyl nitrate genation of dioxide to yield methanol, and so on. 15 using a ruthenium-containing spent catalyst, the method However, ruthenium is expensive and has a limited re- comprises the following steps: source, and the global annual production is only a few dozen tons, thereby greatly limiting the application of ru- 1) drying a ruthenium-containing spent catalyst, and thenium. Recycling ruthenium from a ruthenium-contain- calcining the spent catalyst at a temperature of be- ing spent catalyst for preparation of ruthenium-based cat- 20 tween 300 and 500°C for between 2 and 4 hours, alysts can significantly reduce the production cost of the and cooling to room temperature to yield a black ru- catalyst and environmental pollution caused by waste thenium-containing solid; disposal, thereby having a bright prospect.

[0003] Solid ruthenium nitrosyl nitrate (Ru(NO)(NO 3)3) 2) grinding the black ruthenium-containing solid ob- contains no toxic element against catalysts such as hal- 25 tained in step 1) to yield a powder, introducing the ogen, , , and is easily soluble in , powder to a fluidized bed reactor, aerating the fluid- ether, and acetone, so it is an ideal precursor for prepa- ized bed reactor with or an inert gas for be- ration of a ruthenium-containing catalyst. Thus, prepar- tween 0.5 and 2 hours, charging hydrogen, heating ing high purity of a solid of ruthenium nitrosyl nitrate from the fluidized bed reactor to a temperature of between a ruthenium-containing spent catalyst has high industrial 30 100 and 600°C for a reduction reaction, whereby ob- application value. taining a metal of ruthenium; [0004] Conventionally, there are two typical methods for preparing ruthenium nitrosyl nitrate. One is to directly 3) contacting a mixed gas of ozone and air with the dissolve Ru04 in a cooled nitric acid solution, and the metal of ruthenium obtained in step 2), allowing the other is to dissolve and reflux nitrosyl ruthenium hydrox- 35 mixed gas and the metal of ruthenium to react at a ide using nitric acid. Chinese Patent Publication No. temperature of between 600 and 650°C, whereby CN101638727A discloses a method for recycling ruthe- obtaining a gas of ruthenium tetroxide; nium from an activated carbon supported ruthenium cat- alyst, which involves the preparation of ruthenium nitrosyl 4) introducing the gas of ruthenium tetroxide ob- nitrate. In the method, ruthenium hydroxide40 or tained in step 3) into a three-stage absorption plant

RuO2·2H2O is mixed and stirred with micro-boiled nitric comprising a nitrite acid solution, to yield an acid acid in a reflux device to yield a nitric acid solution of solution comprising ruthenium nitrate;

Ru(NO)(NO3)3, which has high acidity, and is difficult for storage and transportation. 5) adding a solid of sodium nitrite to the acid solution [0005] Chinese Patent Publication 45 No.comprising ruthenium nitrate obtained in step 4), stir- CN102167405A discloses a preparation method of ru- ring, and heating a resulting solution in the state of thenium nitrosyl nitrate. Ruthenium trichloride and sodi- micro-boiling reflux, to yield a solution of ruthenium um nitrite react to yield an intermediate of ruthenium ni- nitrosyl nitrate; and trosyl chloride, which is allowed to react with nitrate to yield a ruthenium nitrosyl nitrate solution. The solution 50 6) extracting the solution of ruthenium nitrosyl nitrate is extracted with ether and the ether extraction solution obtained in step 5) with anhydrous ether, collecting is evaporated to yield a solid of ruthenium nitrosyl nitrate. and evaporating an extraction solution for removal However, the method has the following disadvantages: of ether, to yield a solid of ruthenium nitrosyl nitrate. 1. The chloride is involved, which is toxic to the catalyst; 2. The method involves the intermediate of ruthenium 55 [0008] In step 1), the ruthenium-containing spent cat- nitrosyl chloride, thereby reducing the product yield; 3.As alyst is dried in the presence of nitrogen or an inert gas raw materials, ruthenium trichloride presents in the form at a temperature of 100 and 150°C for between 1 and 2 of a crystalline hydrate, which is expensive. hours. The ruthenium-containing spent catalyst is cal-

2 3 EP 2 823 900 A1 4 cined in a muffle furnace. of the invention. [0009] In step 2),a flow rate of the hydrogen is prefer- ably between 1200 and 4000 h-1, and a reduction time DETAILED DESCRIPTION OF THE EMBODIMENTS is between 1 and 12 hours, preferably, between 6 and 5 12 hours. The redox chemical equation is: RuO2 + 2H2 [0017] For further illustrating the invention, experi- = Ru + 2H2O. ments detailing a method for preparing a solid of ruthe- [0010] In step 3), a flow rate of the mixed gas of ozone nium nitrosyl nitrate using a ruthenium-containing spent and air is between 1200 and 4000 h -1, a volume percent catalyst are described below. It should be noted that the of the ozone in the mixed gas is between 1 and 20%, following examples are intended to describe and not to preferably, 15%; and an oxidation time is between 1 and 10 limit the invention. 12 hours, preferably, between 8 and 12 hours. The chem- ical equation is: Ru + 2O 2= RuO 4↑, 3Ru + 4O 3 = 3RuO 4↑. Example 1 [0011] In step 4), the nitrite acid solution has a temper- ature of between 50 and 95°C, a mass concentration of [0018] 60 g of a ruthenium-containing spent catalyst 15 between 45 and 68%, an actual addition thereof is be- (Ru/Al2O3, spherical, comprising 5 wt. % of Ru) was put tween 1.2 and 2.0 times a theoretical consumption into a crucible, and transported to a muffle furnace. The amount calculated on the basis of a ruthenium content furnace was aeratedwith nitrogen. The catalyst was dried in the ruthenium-containing spent catalyst, and the three- at 120°C for 2 hours, calcined at 450°C for 3 hours for stage absorption plant is three brown containers con- removal of organic residues in the spent catalyst, and 20 nected in series. The chemical equation is: 2RuO4+ cooled to room temperature. 58.6 g of a black solid was 16HNO3 = 2Ru(NO3)3 + 8H2O +5O2↑ + 10NO2↑. obtained. The black solid was ground into powders and [0012] In step 5), an actual addition of the solid of so- transported to a fluidized bed reactor. The fluidized bed dium nitrite is between 1.2 and 2.0 times a theoretical reactor was aerated first with nitrogen for 30 min, and consumption amount thereof calculated on the basis of then with hydrogen having a flow rate of 1200 h -1, heated a ruthenium content in the ruthenium-containing spent 25 to 300°C for reduction for 12 hours. The temperature was catalyst. The solid of sodium nitrite is slowly added to the further increased to 600°C. A mixed gas of ozone and acid solution comprising ruthenium nitrate with stirring. air comprising 15 vol. % of ozone was charged into the A heating time is between 1 and 8 hours, preferably, be- reactor, with a flow rate of 1200 h -1 for 12 hours, to yield tween 4 and 8 hours. The reaction vessel is a three- a gas of RuO 4. The gas of RuO 4 was successively intro- necked round bottom flask. The chemical equation is: 30 duced to three absorption bottles each comprising 40 g

Ru(NO3)3+2NaNO2 + 2HNO3 = Ru(NO)(NO3)3 + of 68 wt. % a nitrite acid solution having a temperature 2NaNO3+ NO2↑ + H2O. of about 75°C, to yield an acid solution comprising ruthe- [0013] In step 6), the extraction with anhydrous ether nium nitrate (Ru(NO3)3). is carried out for several times for improving the yield of [0019] The acid solution comprising ruthenium nitrate the solid of ruthenium nitrosyl nitrate. 35 was added to a three-necked round bottom flask, fol- [0014] In a class of this embodiment, the ruthenium- lowed by 6 g (which is 1.5 times a theoretical consumption containing spent catalyst is a supported catalyst, and a amount calculated on the basis of a ruthenium content supporter thereof is alumina, silica, zirconia, titania, ze- in the ruthenium-containing spent catalyst) of NaNO2 olite, or a combination thereof. The shape of the support- powder, stirred, and heated for reflux for 8 hours to yield er is spherical, cylindrical, clover-type, four-leaf, ring40 a dark red black solution. The dark red black solution was type, or honeycomb type. extracted thrice using 130 mL of anhydrous ether, and [0015] Advantages of the present disclosure are sum- an extraction solution was collected and evaporated for marized as follows. 1. The method has low recycling removal of ether, to yield 8.84 g of a brown yellow solid, costs, and the resulting solid product is convenient for which, based on KBr Pellets-infrared analysis, had a storage and transportation. 2. The solid of ruthenium ni- 45 characteristic peak at 1924 cm -1, identical to the charac- trosyl nitrate contains no halogen, and thus the toxicity teristic structural parameters of Ru(NO)(NO 3)3. The yield is prevented. 3. The method has a simple process and of Ru(NO)(NO3)3 was 96.2%, and metallic impurities involves no intermediate of ruthenium, which is condu- were less than 30 ppm. cive to improving the product yield. In short, the method has low costs, simple process, high product yield, and 50 Example 2 the resulting product has high purity, and is suitable for large-scale production. [0020] 50 g of a ruthenium-containing spent catalyst

(Ru/SiO2, cylindrical, comprising 3 wt. % of Ru) was put BRIEF DESCRIPTION OF THE DRAWINGS into a crucible, and transported to a muffle furnace. The 55 furnace was aeratedwith nitrogen. The catalyst was dried [0016] FIG. 1 is a flow chart of a method for preparing at 120°C for 2 hours, calcined at 450°C for 3 hours, and a solid of ruthenium nitrosyl nitrate using a ruthenium- cooled to room temperature. 48.9 g of a black solid was containing spent catalyst according to one embodiment obtained. The black solid was ground into powders and

3 5 EP 2 823 900 A1 6 transported to a fluidized bed reactor. The fluidized bed orated for removal of ether, to yield 1.44 g of a brown reactor was aerated first with nitrogen for 30 min, and yellow solid, which, based on KBr Pellets-infrared anal- then with hydrogen having a flow rate of 2500 h -1, heated ysis, had a characteristic peak at 1924 cm -1, identical to to 350°C for reduction for 10 hours. The temperature was the characteristic structural parameters of 5 further increased to 620°C. A mixed gas of ozone and Ru(NO)(NO3)3. The yield of Ru(NO)(NO3)3 was 97.3%, air comprising 15 vol. % of ozone was charged into the and metallic impurities were less than 30 ppm. reactor, with a flow rate of 2500 h -1 for 10 hours, to yield a gas of RuO 4. The gas of RuO 4 was successively intro- Example 4 duced to three absorption bottles each comprising 24 g of 60 wt. % a nitrite acid solution having a temperature 10 [0024] 60 g of a ruthenium-containing spent catalyst of about 75°C, to yield an acid solution comprising ruthe- (Ru/TiO2, four-leaf type, comprising 5 wt. % of Ru) was nium nitrate (Ru(NO3)3). put into a crucible, and transported to a muffle furnace. [0021] The acid solution comprising ruthenium nitrate The furnace was aerated with nitrogen. The catalyst was was added to a three-necked round bottom flask, fol- dried at 120°C for 2 hours, calcined at 450°C for 3 hours lowed by 3.6 g (which is 1.8 times a theoretical consump- 15 for removal of organic residues in the spent catalyst, and tion amount calculated on the basis of a ruthenium con- cooled to room temperature. 58.1 g of a black solid was tentin the ruthenium-containing spentcatalyst) of NaNO 2 obtained. The black solid was ground intro powders and powder, stirred, and heated for reflux for 4 hours to yield transported to a fluidized bed reactor. The fluidized bed a dark red black solution. The dark red black solution was reactor was aerated first with nitrogen for 30 min, and extracted thrice using 80 mL of anhydrous ether, and an 20 then with hydrogen having a flow rate of 2000 h -1, heated extraction solution was collected and evaporated for re- to 350°C for reduction for 8 hours. The temperature was moval of ether, to yield 4.41 g of a brown yellow solid, further increased to 620°C. A mixed gas of ozone and which, based on KBr Pellets-infrared analysis, had a air comprising 10 vol. % of ozone was charged into the characteristic peak at 1924 cm -1, identical to the charac- reactor, with a flow rate of 1500 h-1 for 5 hours, to yield 25 teristic structural parameters of Ru(NO)(NO 3)3. The yield a gas of RuO 4. The gas of RuO 4 was successively intro- of Ru(NO)(NO3)3 was 95.8%, and metallic impurities duced to three absorption bottles each comprising 27 g were less than 30 ppm. of 68 wt. % a nitrite acid solution having a temperature of about 75°C, to yield an acid solution comprising ruthe-

Example 3 nium nitrate (Ru(NO3)3). 30 [0025] The acid solution comprising ruthenium nitrate [0022] 120 g of a ruthenium-containing spent catalyst was added to a three-necked round bottom flask, fol- (Ru/ZrO2, clover-type, comprising 4 wt. ‰ of Ru) was put lowed by 3.56 g (which is 0.9 times a theoretical con- into a crucible, and transported to a muffle furnace. The sumption amount calculated on the basis of a ruthenium furnace was aerated with nitrogen. The catalyst was dried content in the ruthenium-containing spent catalyst) of 35 at 120°C for 2 hours, calcined at 450°C for 3 hours, and NaNO2 powder, stirred, and heated for reflux for 6 hours cooled to room temperature. 118.2 g of a black solid was to yield a dark red black solution. The dark red black obtained. The black solid was ground into powders and solution was extracted thrice using 100 mL of anhydrous transported to a fluidized bed reactor. The fluidized bed ether, and an extraction solution was collected and evap- reactor was aerated first with nitrogen for 30 min, and orated for removal of ether, to yield 8.21 g of a brown then with hydrogen having a flow rate of 4000 h -1, heated 40 yellow solid, which, based on KBr Pellets-infrared anal- to 350°C for reduction for 6 hours. The temperature was ysis, had a characteristic peak at 1924 cm -1, identical to further increased to 650°C. A mixed gas of ozone and the characteristic structural parameters of air comprising 15 vol. % of ozone was charged into the Ru(NO)(NO3)3. The yield of Ru(NO)(NO3)3 was 90.3%, reactor, with a flow rate of 4000 h-1 for 8 hours, to yield and metallic impurities were less than 30 ppm. 45 a gas of RuO 4. The gas of RuO 4 was successively intro- duced to three absorption bottles each comprising 13 g Example 5 of 45 wt. % a nitrite acid solution having a temperature of about 75°C, to yield an acid solution comprising ruthe- [0026] 60 g of a ruthenium-containing spent catalyst nium nitrate (Ru(NO3)3). (Ru/Al2O3-ZSM-5, ring type, comprising 1 wt. % of Ru) [0023] The acid solution comprising ruthenium nitrate 50 was put into a crucible, and transported to a muffle fur- was added to a three-necked round bottom flask, fol- nace. The furnace was aerated with nitrogen. The cata- lowed by 1.29 g (which is 2.0 times a theoretical con- lyst was dried at 120°C for 2 hours, calcined at 450°C for sumption amount calculated on the basis of a ruthenium 3 hours for removal of organic residues in the spent cat- content in the ruthenium-containing spent catalyst) of alyst, and cooled to room temperature. 59.0 g of a black 55 NaNO2 powder, stirred, and heated for reflux for 6 hours solid was obtained. The black solid was ground into pow- to yield a dark red black solution. The dark red black ders and transported to a fluidized bed reactor. The flu- solution was extracted thrice using 60 mL of anhydrous idized bed reactor was aerated first with nitrogen for 30 ether, and an extraction solution was collected and evap- min, and then with hydrogen having a flow rate of 2000

4 7 EP 2 823 900 A1 8 h-1, heated to 350°C for reduction for 8 hours. The tem- ysis, had a characteristic peak at 1924 cm -1, identical to perature was further increased to 620°C. A mixed gas of the characteristic structural parameters of ozone and air comprising 15 vol. % of ozone was charged Ru(NO)(NO3)3. The yield of Ru(NO)(NO3)3 was 97.2%, into the reactor, with a flow rate of 3000 h -1 for 8 hours, and metallic impurities were less than 30 ppm. 5 to yield a gas of RuO 4. The gas of RuO 4 was successively introduced to three absorption bottles each comprising Result analysis: 16 g of 45 wt. % a nitrite acid solution having a temper- ature of about 75°C, to yield an acid solution comprising [0030] As shown in the measurement results in Exam- ruthenium nitrate (Ru(NO3)3). ples 1-6, the product yields of the method for preparing [0027] The acid solution comprising ruthenium nitrate 10 the solid of ruthenium nitrosyl nitrate using a ruthenium- was added to a three-necked round bottom flask, fol- containing spent catalyst all exceed 90%, and under pref- lowed by 1.2 g (which is 1.5 times a theoretical consump- erablereaction conditions, theproduct yield reaches 95% tion amount calculated on the basis of a ruthenium con- and more. The method effectively utilizes waste resourc- tentin the ruthenium-containing spentcatalyst) of NaNO 2 es of ruthenium, and has low costs, simple process, and powder, stirred, and heated for reflux for 6 hours to yield 15 high product yield. The resulting product has high purity, a dark red black solution. The dark red black solution was and is suitable for large-scale production. extracted thrice using 50 mL of anhydrous ether, and an extraction solution was collected and evaporated for re- moval of ether, to yield 1.78 g of a brown yellow solid, Claims which, based on KBr Pellets-infrared analysis, had a20 characteristic peak at 1924 cm -1, identical to the charac- 1. A method for preparing a solid of ruthenium nitrosyl teristic structural parameters of Ru(NO)(NO 3)3. The yield nitrate using a ruthenium-containing spent catalyst, of Ru(NO)(NO3)3 was 96.6%, and metallic impurities the method comprising the following steps: were less than 30 ppm. 25 1) drying a ruthenium-containing spent catalyst, Example 6 and calcining the spent catalyst at a temperature of between 300 and 500°C for between 2 and 4 [0028] 160 g of a ruthenium-containing spent catalyst hours, and cooling to room temperature, where-

(Ru/Al2O3-SiO2, honeycomb type, comprising 2 wt. ‰ of by yielding a black ruthenium-containing solid; Ru) was put into a crucible, and transported to a muffle 30 2) grinding the black ruthenium-containing solid furnace. The furnace was aerated with nitrogen. The cat- obtained in step 1) to yield a powder, introducing alyst was dried at 120°C for 2 hours, calcined at 450°C the powder to a fluidized bed reactor, aerating for 3 hours for removal of organic residues in the spent the fluidized bed reactor with nitrogen or an inert catalyst, and cooled to room temperature. 156.4 g of a gas for between 0.5 and 2 hours, charging hy- black solid was obtained. The black solid was ground 35 drogen, heating the fluidized bed reactor to a into powders and transported to a fluidized bed reactor. temperature of between 100 and 600°C for a The fluidized bed reactor was aerated first with nitrogen reduction reaction, whereby yielding a metal of for 30 min, and then with hydrogen having a flow rate of ruthenium; 2000 h-1, heated to 350°C for reduction for 8 hours. The 3) contacting a mixed gas of ozone and air with temperature was further increased to 620°C. A mixed 40 the metal of ruthenium obtained in step 2), al- gas of ozone and air comprising 15 vol. % of ozone was lowing the mixed gas and the metal of ruthenium charged into the reactor, with a flow rate of 2500 h-1 for to react at a temperature of between 600 and

8 hours, to yield a gas of RuO4. The gas of RuO4 was 650°C, whereby yielding a gas of ruthenium successively introduced to three absorption bottles each tetroxide; comprising 8.6 g of 45 wt. % a nitrite acid solution having 45 4) introducing the gas of ruthenium tetroxide ob- a temperature of about 75°C, to yield an acid solution tained in step 3) into a three-stage absorption comprising ruthenium nitrate (Ru(NO3)3). plant comprising a nitrite acid solution, whereby [0029] The acid solution comprising ruthenium nitrate yielding an acid solution comprising ruthenium was added to a three-necked round bottom flask, fol- nitrate; lowed by 0.64 g (which is 1.5 times a theoretical con- 50 5) adding a solid of sodium nitrite to the acid sumption amount calculated on the basis of a ruthenium solution comprising ruthenium nitrate obtained content in the ruthenium-containing spent catalyst) of in step 4), stirring, and heating a resulting solu-

NaNO2 powder, stirred, and heated for reflux for 8 hours tion in the state of micro-boiling reflux, whereby to yield a dark red black solution. The dark red black yielding a solution of ruthenium nitrosyl nitrate; solution was extracted thrice using 130 mL of anhydrous 55 and ether, and an extraction solution was collected and evap- 6) extracting the solution of ruthenium nitrosyl orated for removal of ether, to yield 0.95 g of a brown nitrate obtained in step 5) with anhydrous ether, yellow solid, which, based on KBr Pellets-infrared anal- collecting andevaporating an extraction solution

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for removal of ether, whereby yielding a solid of ruthenium nitrosyl nitrate.

2. The method of claim 1, characterized in that in step 1), the ruthenium-containing spent catalyst is dried 5 in the presence of nitrogen or an inert gas at a tem- perature of 100 and 150 °C for between 1 and 2 hours.

3. The method of claim 1, characterized in that in step 10 2), a flow rate of the hydrogen is between 1200 and 4000 h-1, and a reduction time is between 1 and 12 hours.

4. The method of claim 3, characterized in that in step 15 2), the reduction time is between 6 and 12 hours.

5. The method of claim 1, characterized in that in step 3), a flow rate of the mixed gas of ozone and air is between 1200 and 4000 h -1, a volume percent of the 20 ozone in the mixed gas is between 1 and 20%, and an oxidation time is between 1 and 12 hours.

6. The method of claim 5, characterized in that in step 3), the volume percent of the ozone in the mixed gas 25 is 15%, and the oxidation time is between 8 and 12 hours.

7. The method of claim 1, characterized in that in step 4), the nitrite acid solution has a temperature of be- 30 tween 50 and 95°C, a mass concentration of be- tween 45 and 68%, an actual addition thereof is be- tween 1.2 and 2.0 times a theoretical consumption amount calculated on the basis of a ruthenium con- tent in the ruthenium-containing spent catalyst, and 35 the nitrite acid solution is loaded in three brown con- tainers connected in series.

8. The method of claim 1, characterized in that in step 5), an actual addition of the solid of sodium nitrite is 40 between 1.2 and 2.0 times a theoretical consumption amount thereof calculated on the basis of a ruthe- nium content in the ruthenium-containing spent cat- alyst, and a heating time is between 1 and 8 hours. 45 9. The method of claim 8, characterized in that in step 5), the heating time is between 4 and 8 hours.

10. The method of any one of claims 1-9, characterized in that the ruthenium-containing spent catalyst is a 50 supported catalyst, and a supporter thereof is alumi- na, silica, zirconia, titania, zeolite, or a combination thereof.

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• CN 101638727 A [0004] • CN 102167405 A [0005]

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