Process for preparing a pre-reforming catalyst having resistance to deactivation by passage of steam in the absence of a reducing agent, and a pre-reforming catalyst

Abstract

The present invention relates to a process for preparing a pre-reforming catalyst having resistance to deactivation by passage of steam in the absence of a reducing agent comprising ruthenium and an alumina support. Furthermore, the Ru/alumina catalyst according to the present invention becomes much more resistant to deposition of coke with the addition of Ag.

Claims

1. A process for preparing a pre-reforming catalyst comprising: preparing a solution comprising an inorganic ruthenium (Ru) salt and silver nitrate (AgNO.sub.3); impregnating a theta-alumina support with the solution to provide an impregnated material; drying the impregnated material in air at a temperature between 30 and 200° C. for 1 to 24 hours, wherein the theta-alumina support is impregnated by a pore volume technique or by the excess solution method using an incipient wetness impregnation method; and the pre-reforming catalyst has resistance to deactivation by passage of steam in the absence of a reducing agent.

2. The process according to claim 1, wherein the inorganic Ru salt is hydrated ruthenium chloride RuCl.sub.3.Math.H.sub.2O.

3. The process according to claim 1, wherein the theta-alumina support additionally comprises between 0.1 and 10 percent by weight (wt %) of alkali metal, based upon the weight of the theta-alumina support.

4. The process according to claim 3, wherein the alkali metal is potassium.

5. The process according to claim 1, further comprising: taking a material that results from the drying of the impregnated material and reducing said material in a stream of a reducing agent, selected from hydrogen, formaldehyde and methanol, in temperature conditions between 300 and 500° C., for 1 to 5 hours to provide a reduced material; and cooling the reduced material and subjecting the reduced material to an air stream at temperatures between 20 and 60° C., for 1 to 5 hours.

6. A pre-reforming process comprising: reacting hydrocarbons with steam at temperatures between 400 and 550° C. to produce a product stream comprising hydrogen and having a methane content above 20 percent by weight (wt %), based upon the weight of the product stream, wherein the pre-reforming is carried out in the presence of a catalyst obtainable by a process according to claim 1.

7. The pre-reforming process according to claim 6, wherein the hydrocarbons are reacted with the steam at temperatures between 430 and 490° C.

8. A pre-reforming catalyst prepared by the process comprising: preparing a solution comprising an inorganic ruthenium (Ru) salt and silver nitrate (AgNO.sub.3); impregnating a theta-alumina support with the solution to provide an impregnated material; and drying the impregnated material in air at a temperature between 30 and 200° C. for 1 to 24 hours, wherein the pre-reforming catalyst comprises Ru between 0.1 and 1.0 percent by weight (wt %) and Ag between 0.1 and 0.5% w/w deposited on the theta-alumina support, based upon the weight of the pre-reforming catalyst, wherein the theta-alumina support is impregnated by a pore volume technique or by the excess solution method using incipient wetness impregnation method; and the pre-reforming catalyst has resistance to deactivation by passage of steam in the absence of a reducing agent.

9. The pre-reforming catalyst according to claim 8, wherein the Ru comprises between 0.1 and 0.5 wt %, based upon the weight of the pre-reforming catalyst.

10. The pre-reforming catalyst according to claim 8, wherein a total surface area of the pre-reforming catalyst is between 60 square meters per gram (m.sup.2/g) and 120 m.sup.2/g.

11. A pre-reforming process comprising: reacting hydrocarbons with steam at temperatures between 400 and 550° C. to produce a product stream comprising hydrogen and having a methane content above 20 percentage by weight (wt %), based upon the weight of the product stream, wherein the pre-reforming is carried out in the presence of the pre-reforming catalyst of claim 10 and in the absence of a reducing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention relates to a process for preparing a catalyst comprising ruthenium endowed with resistance to deactivation by passage of steam in the absence of a reducing agent for use in a steam pre-reforming process.

(2) Usually, in the commercial nickel-based pre-reforming catalysts, when exposed to the presence of steam and absence of a reducing agent, the nickel phase is oxidized, so that they cannot be reduced again, and they become active in the temperature conditions of the pre-reforming reaction.

(3) The support of the claimed catalyst is alumina. Alumina is a solid containing atoms of Al and O. However, depending on the crystalline structure, there may be various types of alumina, such as gamma, alpha, theta, among others. The alumina of the alpha type has a low surface area and higher temperature resistance, and is used as a support for steam reforming catalysts. The present invention uses theta-alumina, which has a larger surface area, giving a higher activity potential, and sufficient heat resistance for use in conditions of pre-reforming. The theta-alumina support may contain up to 10% of calcium aluminate, magnesium aluminate or other refractory cements for greater mechanical strength. The particles of the support may be of various shapes suitable for industrial use in the steam pre-reforming process, such as spheres, cylinders or cylinders with a central hole (Raschig rings).

(4) The pre-reforming catalyst with high resistance to deactivation by passage of steam in the absence of a reducing agent and by deposition of coke of the present invention comprises Ru between 0.1 and 1.0 wt % deposited on a support of the theta-alumina type. Preferably, the Ru content varies between 0.1 and 0.5 wt %.

(5) Furthermore, the total surface area of the catalyst is from 60 m.sup.2/g to 500 m.sup.2/g. Preferably, the total surface area varies from 60 m.sup.2/g to 120 m.sup.2/g.

(6) Moreover, the catalyst may be impregnated with silver, so as to increase the resistance to the deposition of carbon. In this case, an Ag content between 0.1 and 1 wt %, preferably between 0.1 and 0.5 wt %, is added to the Ru/alumina catalyst.

(7) The claimed catalyst may be exposed to passage of steam in the absence of a reducing agent for a minimum period of 24 h at temperatures between 400 and 550° C. without loss of pre-reforming activity.

(8) The process for preparing the pre-reforming catalyst of the present invention involves the following steps:

(9) preparation of an aqueous solution of an inorganic Ru salt;

(10) impregnation of a theta-alumina support in the granulometric range from 100 to 200 mesh (equivalent to 0.075 mm to 0.150 mm), preferably from 100 to 150 mesh (equivalent to 0.105 mm to 0.150 mm);

(11) drying the impregnated material containing Ru in air at a temperature varying between 30 and 200° C., preferably between 50° C. and 150° C. for 1 to 24 hours.

(12) The inorganic Ru salt is preferably water-soluble, such as hydrated ruthenium chloride [RuCl.sub.3.Math.xH.sub.2O]; aqueous solution of ruthenium nitrosyl nitrate [Ru(NO)(NO.sub.3).sub.3]. It is also possible to use ruthenium salts that are soluble in organic solvents, such as ruthenium (III) acetylacetonate [Ru(C.sub.5H.sub.7O.sub.2).sub.3].

(13) Furthermore, impregnation of the support may be effected by the pore volume technique (wet point) or by the excess solution method.

(14) If the catalyst is impregnated with Ag to increase the resistance to deposition of carbon, the aqueous solution used in catalyst preparation additionally comprises a solution containing Ag, preferably AgNO.sub.3.

(15) The catalyst prepared on the basis of the present process is active, stable and ready for use, and does not have to undergo calcination in air, otherwise it would lose its properties of reduction and of activity at temperatures typical of the pre-reforming reactor, which are between 400° C. and 550° C. Absence of the calcination step brings clear benefits of reduction of the cost of production.

(16) The catalyst thus prepared may also be reduced beforehand in a stream of a reducing agent, selected from hydrogen, formaldehyde and methanol in temperature conditions between 300 and 500° C., for 1 to 5 h, and then cooled and subjected to an air stream at temperatures between 20 and 60° C., for 1 to 5 h, to avoid the material having a pyrophoric character during handling.

(17) Preferably, the catalyst of the present invention is prepared from the inorganic oxide support, preferably by the method of incipient wetness impregnation. In this method, the support is brought into contact with a volume of solution, preferably aqueous, of the nickel, lanthanum and cerium salts, sufficient to fill the pores of the support completely. Preferably, the solvent of the impregnation solution is water, alcohols, such as methanol or ethanol, or combinations thereof.

(18) Alternatively, the support may have a content between 0.1 and 10 wt %, preferably between 1 and 5 wt % of alkali metals. The alkali metal, preferably potassium, may be introduced into the support beforehand or during the steps of impregnation with the solution of nickel salt.

(19) Examples illustrating various embodiments of the present invention, but without limiting its content, are presented below.

COMPARATIVE EXAMPLE

(20) This example illustrates the preparation of a commercial catalyst as known in the prior art.

(21) The commercial pre-reforming catalyst has an Ni content between 40 and 60% (w/w) and is supplied in the pre-reduced state.

EXAMPLES

(22) The following examples 1 to 5 illustrate the preparation of steam pre-reforming catalysts by the process of the present invention.

Example 1

(23) This example illustrates the preparation of a pre-reforming catalyst according to the present invention. Forty grams of a theta-alumina (Axens SPH 508F), ground beforehand in the granulometric range from 100 to 150 mesh, were impregnated by the pore volume technique with 28 ml of an aqueous solution containing 0.9 g of RuCl.sub.3.Math.xH.sub.2O. The material was dried at a temperature between 90 and 120° C. for 12 h, giving a pre-reforming catalyst of the Ru/theta-alumina type containing 1 wt % of Ru and with a specific surface area determined by the N.sub.2 adsorption method of 62 m.sup.2/g.

Example 2

(24) This example illustrates the preparation of a pre-reforming catalyst according to the present invention. Thirty grams of a theta-alumina (Axens SPH 508F), ground beforehand in the granulometric range from 100 to 150 mesh, were impregnated by the pore volume technique with 21 ml of an aqueous solution containing 0.68 g of RuCl.sub.3.Math.xH.sub.2O and 0.15 g of AgNO.sub.3. The material was dried at a temperature between 90 and 120° C. for 12 h, giving a pre-reforming catalyst of the AgRu/theta-alumina type containing 1 wt % of Ru and 0.30 wt % of Ag and having a specific surface area determined by the N.sub.2 adsorption method of 58 m.sup.2/g.

Example 3

(25) This example illustrates the method of accelerated deactivation to which the pre-reforming catalysts were subjected by passage of steam (steaming) in the absence of a reducing agent.

(26) Two grams of the materials described in the Comparative Example and in Examples 1 and 2 were loaded in a steel reactor in a catalyst testing unit. The catalyst was heated in a stream of 600 ml/min of H.sub.2 and at a rate of 10°/min from room temperature to 450°, which was maintained for 2 h. Then the H.sub.2 was replaced with N.sub.2 and the unit was purged for 1 h, and then steam was supplied. These conditions of steaming at 450° C. were maintained for periods of time between 2 and 40 h at a pressure of 20 atm.

Example 4

(27) This example illustrates the excellent resistance of the catalysts according to the present invention to deactivation by passage of steam in the absence of a reducing agent.

(28) The initial steam reforming activity was determined in AutoChem II commercial equipment (Micromeritics). The tests were carried out using 500 mg of ground catalyst in the range between 100 and 150 mesh. The experiments were carried out at atmospheric pressure and at temperatures of 450° C., 500° C. and 550° C. by the passage of 50 ml of a stream containing 50% v/v of methane, 5% of H.sub.2 and 45% of argon saturated with steam at 90° C. The effluent gases from the reactor were analysed by gas chromatography and the activity was measured by the degree of conversion of the methane.

(29) Table 1 presents results for catalytic activity, expressed as conversion of methane, of the materials described in the Comparative Example and in Examples 1 and 2 before and after undergoing the process of accelerated deactivation due to the absence of reducing agents (steaming), as described in Example 3.

(30) TABLE-US-00001 TABLE 1 Results for catalytic activity of the catalysts prepared by the Comparative Example and Examples 1 and 2. Methane conversion at Catalyst Deactivation time (h) 450° C. (% v/v) Comparative Example 0 15.4 24 0 Example 1 0 21.3 24 24.2 Example 2 0 11.3 24 11.2

(31) The results show that the catalysts according to the present invention are not deactivated by steaming in the absence of an agent, even after 24 hours of exposure. In its turn, the commercial catalyst was completely deactivated in the same conditions.

Example 5

(32) This example illustrates the excellent resistance of the catalysts according to the present invention to deactivation by deposition of coke.

(33) The catalysts underwent comparative tests in equipment for thermogravimetric analysis (TGA Mettler Toledo) TGA/SDTA851E. The tests were carried out using 25 mg of ground catalyst in a range below 170 mesh. Initially, a pre-treatment step was performed by passage of 40 ml/min of a mixture containing 10% (v/v) of hydrogen in argon saturated with steam at 15° C. together with 40 ml/min of nitrogen (shielding gas) with programming of temperature varying from 100° C. to 650° C. at a rate of 10° C./min, maintained for 1 h. Next, the temperature was reduced to 350° C. and the measurements of the rates of coke formation were performed, by replacing the stream of H.sub.2/argon with a synthetic stream consisting of 21.9% hydrogen, 13.2% of CO, 15.9% of CO.sub.2, 43.62% of CH.sub.4, 1.77% of nitrogen and 0.20% of ethylene saturated with steam at 15° C. with temperature programming from 350° C. to 700° C. at a rate of 5° C./min. The results for carbon deposition are presented in Table 2 as the weight increase due to deposition of coke at the end of the experiment.

(34) TABLE-US-00002 TABLE 2 Content of coke deposited on the catalyst prepared according to the Comparative Example and Examples 1 and 2. Content of coke deposited by weight Catalyst (% w/w) Comparative Example 200 Example 1 0.2 Example 2 0

(35) It can be seen from Table 2 that the weight of the catalyst of the prior art increased by 200% due to the coke deposited. In contrast, the Ru/theta-alumina catalyst has a slight increase in weight due to coke, and the RuAg/theta-alumina catalyst does not have coke deposits.

(36) Numerous variations falling within the scope of protection of the present application are permitted. This reinforces the fact that the present invention is not limited to the particular configurations/embodiments described above.

(37) It can therefore be concluded, surprisingly, that the catalyst of the present invention with Ru contents below 1% w/w displays high resistance to loss of activity when exposed to periods of steaming and absence of reducing agent in conditions of temperature and pressure used in the pre-reforming step, allowing the industrial unit to be maintained in the heated and pressurized condition and minimizing the risks associated with sudden changes of temperature and pressure in the unit.

(38) Furthermore, the Ru/alumina catalyst according to the present invention is even more resistant to deposition of coke with addition of a preferred content of Ag between 0.1 and 0.5% w/w than the commercial catalyst taken as a reference, which makes the pre-reforming process more robust and less subject to operational problems.