Regenerating the catalytic activity of a spent catalyst

Abstract

The invention relates to a method of regenerating the catalytic activity of a spent catalyst comprising nickel on a refractory oxide support, said method comprising the steps of contacting the spent catalyst with a nitric acid solution, heat-treating the spent catalyst, calcining and reducing the catalyst.

Claims

1. A method of regenerating the catalytic activity of a spent catalyst comprising nickel, said spent catalyst being: (a) a spent steam reforming catalyst comprising a support, in which the nickel content is 5-20 wt % Ni and the support is an oxide comprising aluminium, zirconium, magnesium, calcium, lanthanum, yttrium, and/or cerium, and wherein the spent catalyst is provided in the form of tablets or pellets, or (b) a spent steam reforming catalyst in which the nickel content is 5-20 wt % Ni, said spent steam reforming catalyst being a structured catalyst comprising a macroscopic structure, wherein said macroscopic structure is formed by a metallic material and at least partly supported by a refractory oxide support; said method comprising the steps of: i) contacting the spent catalyst with a nitric acid solution, in which the nitric acid solution is at least 60 wt % HNO.sub.3, and adding one or more organic acids; ii) heat-treating the spent catalyst at a suitable temperature for reacting nickel with nitric acid, said suitable temperature being in the range 50-100 C., and subsequently drying the spent catalyst at 100-125 C.; and iii) calcining and reducing the spent catalyst, in which the calcining is conducted in air at 500-1300 C. for 1-4 hours, and the reducing is conducted in the presence of hydrogen at 400-600 C. for 2-4 hours, wherein the tablets or pellets of spent catalyst (a) are spherical, oblong, cylindrical, multilobe, ring-shaped, or any combinations thereof; wherein the macroscopic structure of spent catalyst (b) is a monolith; and wherein the shape of the spent catalyst (a) or the macroscopic structure of the spent catalyst (b) is preserved during the regenerating method.

2. The method of claim 1, wherein the one or more organic acids are selected from the group consisting of: 2-hydroxypropane-1,2,3-tricarboxylic acid, 2-hydroxypropanoic acid, ethanedioic acid, propanedioic acid, 1,4-butanedioic acid, 1,3-propanedicarboxylic acid, and 2-aminopentanedioic acid.

3. The method of claim 2, wherein the content of the one or more organic acids in nitric acid solution is 40 wt % or less.

4. The method of claim 1, wherein the nitric acid solution is free of other inorganic acids.

5. The method of claim 1, wherein the steps of contacting and heat-treating are repeated at least once prior to said drying or calcining.

6. The method of claim 1, wherein nickel is the only catalytically active element in the spent catalyst.

7. The method of claim 1, wherein the nickel in the spent catalyst is in oxidic form.

8. The method of claim 1, wherein the step of contacting with the nitric acid solution is conducted at 20-25 C.

9. The method of claim 8, wherein the spent catalyst is heat-treated at 70-80 C. for a duration of at least 10 min.

10. The method of claim 1, wherein the drying is conducted at 110 C.

11. The method of claim 1, wherein the calcining is conducted in air at 400-500 C. for 1-2 hours, and the reducing is conducted in the presence of hydrogen at 500-550 C. for 2-4 hours.

12. The method of claim 1, wherein the metallic material is an alloy comprising Fe, Cr, and Al, and the support is zirconium oxide (ZrO.sub.2).

13. The method of claim 1, wherein said method consists of the steps of: i) contacting the spent catalyst with a nitric acid solution, in which the nitric acid solution is at least 60 wt % HNO.sub.3, and adding one or more organic acids; ii) heat-treating the spent catalyst at a suitable temperature for reacting nickel with nitric acid, said suitable temperature being in the range 50-100 C., and subsequently drying the spent catalyst at 100-125 C.; and iii) calcining and reducing the spent catalyst, in which the calcining is conducted in air at 500-1300 C. for 1-4 hours, and the reducing is conducted in the presence of hydrogen at 400-600 C. for 2-4 hours.

Description

EXAMPLES

(1) Sulfur Capacity.

(2) 1 g of catalyst crushed down to 2.8-4 mm sieve fraction is placed in the reactor. A gas mixture with composition 14 ppm H.sub.2S in 200 Nl/h H.sub.2, 2 g/h H.sub.2O, is led over the catalyst at 550 C. for 2 to 4 days. After sulfidation the catalyst is analysed for sulfur.

(3) Methane Steam Reforming Activity.

(4) 10 to 50 mg of catalyst crushed down to 125-300 m sieve fraction is placed in the reactor. A gas mixture with composition 0.8 Nl/h H.sub.2, 2 Nl/h CH.sub.4 and 6.45 g/h of water is passed through the catalyst. The conversion of CH.sub.4 is measured by GC at 500 and 450 C. The activity is given as moles of CH.sub.4 converted/h/g of catalyst.

(5) Method for Regenerating Catalytic Activity.

(6) Six (6) pellets of spent catalyst (spent catalyst is used catalyst from industry), or lab-aged catalyst, was immersed in 150 g's of 65 wt % HNO.sub.3 at room temperature, i.e. 20-25 C. After one minute, the pore volume is filled with the nitric acid, and the pellets are withdrawn from the liquid and placed in a heating cupboard at 75 C. After a couple of minutes, the refresh reaction starts with evolution of NO.sub.2:
Ni+4HNO.sub.3=Ni(NO.sub.3).sub.2+2NO.sub.2+2H.sub.2O

(7) The reaction is completed in 15 minutes, whereby the pellets are dried at 110 C., calcined, reduced and ready for testing. The results are presented in Table 1 in a spent catalyst having MgAl.sub.2O.sub.4 as the support (carrier) and a spent catalyst having an alumina support with hibonite as one of the calcium aluminate phases. The table shows that the large sintered nickel particles are dissolved and re-dispersed during calcination and reduction, thus regaining some of the sulfur capacity and the activity.

(8) Even better values of activity and sulfur adsorption capacity (S-capture) are obtained when an organic acid is used as promotor. The organic acid promotor effect on the nickel particle size is also unexpected, since despite resulting in a larger nickel size, the S-capture significantly increases. This may also reflect the fact, that the use of XRPD (X-Ray Powder Diffraction) for determining particle size gives an average particle size, covering both small re-dispersed nickel particles and big nickel particles.

(9) TABLE-US-00001 TABLE 1 Organic Ni Activity Catalyst Ni S-capture H-BET acid pro- size** (mol/g/h) at support (wt %) (ppm) (m.sup.2/g) motor* () 500 C./450 C. MgAl.sub.2O.sub.4 fresh 15.3 2610 18.9 none 135 2.4/0.68 MgAl.sub.2O.sub.4 Spent 14.3 230 7.68 none 637 0.15/0.04 MgAl.sub.2O.sub.4 Refresh 980 none 244 1.1/0.3 (15 min) MgAl.sub.2O.sub.4 Refresh 1010 11.4 1 365 1.24/0.35 (15 min) MgAl.sub.2O.sub.4 Refresh 1240 11.2 2 229 1.39/0.41 (15 min) MgAl.sub.2O.sub.4 Refresh 1340 13 3 247 1.45/0.41 (15 min) Hibonite fresh 13.8 1390 7.48 none 163 1.3/0.34 Hibonite spent 13.9 250 2.99 none 605 0.16/0.04 Hibonite Refresh 720 none 274 0.36/0.10 (15 min) Hibonite Refresh 1170 8.25 1 272 0.70/0.21 (15 min) *1: 2-hydroxypropane-1,2,3-tricarboxylic acid; 2: ethanedioic acid; 3: 1,4-butanedioic acid. **Ni particle size is determined from XRPD

(10) Moreover, by repeating the steps of contacting and heat-treating at least once prior to said calcining or drying steps, with the use of an organic acid, it is also possible in a quick and efficient manner to regain up to 100% of the original activity of the catalysts.