AU2921892A

AU2921892A - Alkanol decomposition catalyst

Info

Publication number: AU2921892A
Application number: AU29218/92A
Authority: AU
Inventors: Gordon Percival
Original assignee: Broken Hill Pty Co Ltd
Current assignee: Broken Hill Pty Co Ltd
Priority date: 1991-11-15
Filing date: 1992-11-13
Publication date: 1993-06-15
Anticipated expiration: 2012-11-13
Also published as: AU658241B2

Description

CATALYST AND PROCESS

The present invention relates to a catalyst and a process for decomposing an alkanol.

Methanol can be catalytically decomposed to form carbon monoxide and hydrogen, mixtures of which are known as synthesis gas. The catalytic decomposition of methanol can be represented as follows:

CH₃OH -> CO + 2H₂

However the catalytic decomposition of methanol can result in the production of a number of by-products. The formation of these by-products can be represented by the following equations:

CO + 3H₂ → CH. + H₂O

CO + H₂O → CO₂ + H₂

2CH₃OH → CH₃OCH₃ + H₂O

Methanol has become a widely traded commodity for use primarily in the production of formaldehyde. However it has also found application as a fuel or fuel additive in the transport industry as well as a source of synthesis gas. Synthesis gas derived from methanol has been used in the past as a means of peak shaving in the gas distribution industry. Methanol has also been proposed as a substitute for other fuels used in firing gas turbines. Methanol can be readily manufactured through a series of thermal and catalytic steps from low cost coal, natural gas or biomass. It can also be easily transported and stored. One disadvantage of using methanol as a fuel is that it has a lower heat of combustion than gasoline or natural gas and therefore a larger volume of methanol is required for equivalent energy production. Similarly methanol has a lower heat of combustion than its decomposition products carbon monoxide and hydrogen. Hence the catalytic decomposition of methanol to carbon monoxide and hydrogen could provide a more efficient means of using methanol as a fuel especially in motor vehicles. Table 1 contains enthalpies of reaction for several methanol decomposition reactions and for the combustion reactions of methanol, synthesis gas, dimethyl ether and methane. The data contained in Table 1 demonstrate that the energy output of methanol can be improved by catalytically decomposing the methanol into synthesis gas, combusting the synthesis gas, using the energy of combustion to do useful work and recovering waste heat for use in the catalytic decomposition of the methanol.

TABLE 1: REACTION ENTHALPIES FOR DECOMPOSITION

AND COMBUSTION REACTIONS

Enthalpy ΔH_r (kcal)

400°K 800°K

Decomposition Reactions

2CH₃OH→ 2CO 4H, 45 .26 49 .58

2CH₃OH → CH₃OCH₃ + H₂O -5.34 -4 .63

2CH₃OH → 2CH₂O + 2H₂ 41. 68 43 .74

Combustion Reactions

2CH₃OH + 3O₂ → 2CO₂ + 4H₂O -322 .40 -321.46

2CO + 4H₂ + 3O₂ → 2CO₂ + 4H₂O -367 . 66 -371. 04

CH₃OCH₃ + 3O₂ → 2CO₂ 3H₂O -317 . 06 -316 . 83

2CH₄ + 4O₂ → 2CO₂ + 4H₂O -364 .96 -341 .40 The decomposition of methanol into carbon monoxide and hydrogen over metal catalysts or metal supported catalysts has been demonstrated in the past. Normally Group VIII metals and/or metals from Groups I to VII of the Periodic Table of Elements alone or supported on carbon or oxide supports have been disclosed as catalysts.

Many patents and publications describe the decomposition of, and catalysts that decompose, methanol to carbon monoxide and hydrogen. However, the present invention compared with other compositions shows a catalyst of higher activity or methanol decomposition capacity and a higher selectivity to carbon monoxide and hydrogen without making by-products such as methane, carbon dioxide, dimethyl ether and water except in negligible quantities. The catalyst described herein is stable, easily controlled in the reactor system, easily regenerated and easily and inexpensively prepared. It is an object of the invention to provide a catalyst and a process for decomposing alkanols.

Accordingly in a first aspect the present invention provides a catalyst for decomposing an alkanol which catalyst comprises active metals supported on a suitable carrier wherein the active metals are copper and nickel.

In a second aspect the present invention provides a process for decomposing an alkanol which process comprises heating an alkanol to an elevated temperature and contacting the heated alkanol with a catalyst comprising active metals supported on a suitable carrier wherein the active metals are copper and nickel. In a third aspect the present invention provides a method of improving the energy efficiency of methanol when used as a fuel which method comprises heating methanol to an elevated temperature using waste heat, contacting the heated methanol with a catalyst to form decomposition products, combusting the decomposition products with oxygen in the internal combustion engine to form combustion products, using these combustion products to perform useful work and recovering waste heat for heating the methanol wherein the catalyst comprises active metals supported on a suitable carrier, the active metals being copper and nickel. The catalyst of the present invention also improves cold start capability due to its high activity thus reducing the auxiliary energy required to heat the methanol prior to starting.

The catalyst and process of the present invention are particularly suited to the decomposition of methanol. However other alcohols such as ethanol and propanol may be decomposed to form a hydrocarbon and hydrogen.

The copper content of the catalyst may lie in the range from 5 to 95 wt% of the catalyst and the nickel content from 2 to 80 wt%. However preferably the copper content lies in the range from 10 to 80 wt% and the nickel content in the range from 2 to 60 wt%.

The carrier may comprise silica, magnesia or silica/magnesia. The selection of the carrier material has an impact on the activity and selectivity of the catalyst. Preferably the catalyst is a basic (non-acidic) catalyst. Preferably the catalyst comprises from 10 to 90 wt% of silica and from 0.1 to 60 wt% of magnesia. In particular the preferred catalysts have silica comprising 20 to 80 wt% of the catalyst and magnesia comprising 0.1 to 40% by weight of the catalysts. The catalyst of the invention may be prepared by depositing copper and nickel compounds onto the carrier by kneading and/or precipitation and/or impregnating. Precipitation or impregnation may be of organic and/or inorganic compounds from aqueous and/or non-aqueous solutions. The carrier material itself may also be prepared by kneading, precipitation and/or impregnation of inorganic and/or organic compounds (for example the silica may be derived from tetramethoxysilane) from aqueous and/or non-aqueous solutions.

The catalyst may contain a promoter or promoters such as an element or elements from Groups I to VIII of the Periodic Table of Elements. Such a promoter may be added by mixing, precipitation and/or impregnation from an aqueous and/or non-aqueous solution. The promoter may comprise from 0.01 to 10 wt% of the catalyst. If alkali metal hydroxide, carbonates or hydrogen carbonates are used during the preparation of the catalyst to precipitate the active metals, the catalyst may contain minor amounts of the alkali metal within the catalyst. These minor amounts may comprise from 0.001 to 10 wt% of the catalyst and may act as a promoter.

The catalyst may be combined, dispersed or otherwise intimately mixed with an inorganic oxide matrix or matrices in proportions that result in a product containing 10 wt% to 100 wt% of the catalyst. Matrices which impart desirable properties to the catalyst such as increased strength, attrition resistance and/or thermal stability are preferred. Oxides of aluminium, zirconium, titanium, chromium are examples of such inorganic oxides.

Normally it is desirable to calcine the catalyst in air or dilute air before use. However a reduction period in a hydrogen or a dilute hydrogen atmosphere may activate the catalyst.

The decomposition process can be performed in a fixed or fluidised bed of catalyst. The process conditions preferred are temperatures up to 1000°C, more preferably 200 to 700°C, a pressure in the range from 0.1 to 50 atmospheres, a methanol mass hourly space velocity (MHSV) in the range from 0.1 to 100 hr^-1, more preferably 0.1 to 50 hr^-1 and any other gas or liquid comprising 0 to 95 volume percent of the feed stream.

The following examples illustrate (i) methods for producing the catalysts of the invention (ii) the process of the invention (iii) the performance of the catalysts of the invention and (iv) the performance of comparative catalysts.

Examples 1 to 6 illustrate methods for producing catalysts of the invention and examples 7 to 16 illustrate the preparation of comparative catalysts.

Example 1

73.2g of magnesium carbonate (MgCO₃) were dissolved in a minimum amount of dilute nitric acid (20 wt%). To this was added 40.3g of nickel nitrate (Ni(NO₃)₂ 6H₂O) and 119.2g of copper nitrate (Cu(NO₃)₂ 2.5H₂O) dissolved in a minimum amount of water. 110g of Ludox™ (40% SiO₂) were added and the solution well stirred at 40°C. Ammonium hydrogen carbonate (NH₄HCO₃) was then added until a pH of 7 was attained. The mixture was heated to 90°C and maintained at that temperature as precipitation occurred.

The precipitate was separated, washed twice with 500 ml of water, was dried overnight at 100°C and was calcined at 550°C. The calcined material was crushed to -500 μm and then pelleted.

Examples 2, 3 and 4

The preparation of these examples of the catalyst is similar to Example 1 except the amount of copper nitrate was 90g, 67.1g and 29.8g respectively.

Example 5

73.2g of magnesium carbonate (MgCO₃) were dissolved in a minimum amount of dilute nitric acid (20 wt%). To this was added 40.3g of nickel nitrate (Ni(NO₃)₂) 6H₂O) and 119.2g of copper nitrate (Cu(NO₃)₂ 3H₂O) dissolved in a minimum amount of water. 110g of Ludox™ (4.0% SiO₂) were added and the solution well stirred at 40°C. Ammonium hydrogen carbonate (NH₄HCO₃) was then added until a pH of 7 was attained. The mixture was evaporated down with stirring until a firm paste was obtained and this was then dried at 110°C and calcined at 550°C.

Example 6

102.2g of MgCO₃ were dissolved in a minimum amount of dilute nitric acid (20 wt%). To this was added 40.3g of Ni(NO₃)₂ 6H₂O and 69.7g of Cu(NO₃)₂ 3H₂O dissolved in 400g of H₂O. 77.3g of Ludox™ (40% SiO₂) were added and the solution stirred at 40°C. Ammonium hydrogen carbonate was then added until a pH of 7 was attained. The mixture was aged for 30 minutes and then the temperature was increased to 80°C. This was maintained with continuous stirring until a thick paste remained. The paste was dried at 110°C and finally calcined at 550°C for 5 hours.

Catalyst Trials

The catalysts according to the invention were used in a number of experiments for the decomposition or dissociation of methanol to hydrogen and carbon monoxide. The experiments were carried out in reactors containing a fixed catalyst bed of particles 300-600 micron size. The conditions used to carry out these experiments and the results of these experiments are given below in Table 2. It is noted that methanol conversion near 100% can be achieved at high mass hourly space velocities in a small diameter reactor and that the selectivity to hydrogen and carbon monoxide is high. (The stoichiometric ratio of hydrogen to carbon monoxide of 2:1 is nearly achieved). Very small amounts of by-product, water, methane, carbon dioxide and dimethyl ether) are made over the catalysts prepared according to the invention.

The following examples describe the preparation procedure of those catalysts which lie outside the invention. Example 7

An aluminium phosphate support was prepared by dissolving 615 g of aluminium nitrate in 4 litres of hot water and adding slowly 190 g of 85% phosphoric acid, followed by 51 g of urea. The solution was heated to 90°C and with vigorous stirring concentrated ammonia solution was added until a pH of 8.3 was obtained. The resultant precipitate was stirred for 3 hours, then collected by filtration, dried at 150°C overnight, calcined at 400°C for 2 hours and ground to <1.2 mm.

77.3 g of Ni(NO₃)₂6H₂O were dissolved in 250 ml of methanol and combined with 140 g of the aluminium phosphate support. The slurry was mixed until firm, then dried at 120°C overnight, calcined at 500°C for 2 hours, ground to <1.2 mm and finally pelleted (3mm diameter pellets). Example 8

63.9 g of CeO₂ and La₂O₃, "Misch Metal" oxide (sized to <500 ) were added to a solution consisting of 20.2 g of Ni(NO₃)₂.6H₂O dissolved in 120 g of methanol. The mixture was stirred until a paste, dried at 110°C, calcined at 500°C for 4 hours, ground to <1.2 mm and finally pelleted (3 mm pellets). Example 9

52.3 g of silica support (Aldrich Silica Gel grade 63, size to -250 +150 μm and calcined at 500°C for 5 hours) were impregnated with a 7.8 g solution of 8.3% H₂PtCl₆.6H₂O in methanol. The material was dried at 110°C, calcined at 450°C and then reduced in a 10% H₂ in N₂ stream at 400°C for 2 hours. It was further impregnated with a solution of 24.4 g of Ni(NO₃)₂.6H₂O and 6.35 g of Ce(NO₃)₃.6H₂O in methanol and then dried and reduced as previously.

Example 10

On 31.8 g of activated charcoal (BDH, LR, particle size 0.85-1.77 mm, SA 856 m²/g)7.92 g of Ni(NO₃)₂.6H₂O and 6.08 g of Cu(NO₃)₂.3H₂O were impregnated from a methanol solution. The material was dried at 110°C and calcined at 300°C for 1 hour.

Example 11

37.5 g of Ludox AS40™ (ammonia stablised colloidal silica, DuPont) was mixed with 250 g of methanol and combined with 49.59 g of Ni(NO₃)₂.6H₂O dissolved in a minimum amount of methanol. The slurry was stirred until a paste then dried at 110°C and calcined overnight at 550°C. Finally the catalyst powder was pressed, crushed and sized to -500 μm + 250 μm.

Example 12

31 g of MgCO₃ were dissolved in a minimum amount of dilute HNO₃ and added to 38.02 g of Cu(NO₃)₂.3H₂O dissolved in a minimum amount of methanol. The slurry was stirred until a paste then dried at 110°C and calcined at 550°C. Finally the catalyst powder was pressed, crushed and sized to

-500 μm + 250 μm. Example 13

Example 12 was repeated except the Cu(NO₃)₂.3H₂O was replaced with 49.59 g of Ni(NO₃)₂.6H₂O.

Example 14

Example 11 was repeated except the Ni(NO₃)₂.6H₂O was replaced with 38.02 g of Cu(NO₃)₂.3H₂O.

Example 15

15.5 g of MgCO₃ were dissolved in a minimum amount of dilute HNO₃ and added to 18.75 g of Ludox AS40™ mixed with 125 g of methanol. To this solution was added 49.59 g of Ni(NO₃).6H₂O dissolved in a minimum amount of methanol. The slurry was stirred until a paste then dried at 110°C and calcined overnight at 550°C. Finally the catalyst powder was pressed, crushed and sized to -500 μm + 250 μm.

Example 16

Example 15 was repeated except the Ni(NO₃)₂.6H₂O was replaced with 38.02 g of Cu(NO₃)₂.3H₂O.

Catalysts made according to examples 7 to 16 as well as commercially available catalysts were tested for their capacity to decompose methanol to provide H₂ and CO. The results are reported in Table 3.

Comparing the results in Table 3 with those in Table 2 it can be seen that for the commercial catalyst and catalysts of examples 7 to 16, that either the methanol conversion was inadequate at the specific mass hourly space velocity tested or that the selectivity to hydrogen and carbon monoxide was poor with by-products such as either methane, carbon dioxide, dimethyl ether, water or formaldehyde being made in substantial quantities.

Claims

1. An alkanol decomposition catalyst comprising active metals supported on a suitable carrier wherein the active metals are copper and nickel.

2. An alkanol decomposition catalyst according to Claim 1 wherein copper comprises from 5 to 95 weight per cent of the active metals and nickel comprises from 2 to 80 weight per cent of the active metals.

3. An alkanol decomposition catalyst according to Claim 1 wherein copper comprises from 10 to 80 weight per cent of the active metals and nickel comprises from 2 to 60 weight per cent of the active metals.

4. An alkanol decomposition catalyst according to Claim 1 wherein the carrier is selected from the group consisting of silica, magnesia and silica/magnesia.

5. An alkanol decomposition catalyst according to Claim 1 wherein the carrier is a mixture of silica and magnesia.

6. An alkanol decomposition catalyst according to Claim 5 wherein the silica comprises from 10 to 90 weight per cent of the catalyst and the magnesia comprises from 0.1 to 60 weight per cent of the catalyst.

7. An alkanol decomposition catalyst according to Claim 1 wherein the catalyst contains a promoter, the promoter being an element selected from Groups I to VIII of the Periodic Table.

8. An alkanol decomposition catalyst according to Claim 7 wherein the promoter comprises from .01 to 10 weight per cent of the catalyst.

9. An alkanol decomposition catalyst according to Claim 8 wherein the promoter is an alkali metal.

10. An alkanol decomposition catalyst according to Claim 1 wherein the catalyst is intimately mixed with an inorganic oxide matrix so that the catalyst comprises from 10 to 100 weight per cent of the mixture.

11. A process for decomposing an alkanol which process comprises heating an alkanol to an elevated temperature and contacting the heated alkanol with an alkanol decomposition catalyst according to any one of claims 1 to 10.

12. A process according to Claim 11 wherein the process is performed in a fixed or fluidised bed of catalyst and the temperature lies in a range up to 1000°C.

13. A process according to Claim 12 wherein the temperature lies in a range from 200 to 700°C.

14. A process according to Claim 12 wherein the process is performed at a pressure in the range from 0.1 to 50 atmosphere.

15. A process according to Claim 12 wherein the alkanol is introduced into the fixed or fluidised bed at a mass hourly space velocity in a range from 0.1 to 100 hr^-1.

16. A process according to Claim 12 wherein the alkanol is introduced into the fixed or fluidised bed at a mass hourly space velocity in the range from 0.1 to

50 hr^-1.

17. A method of improving the energy efficiency of methanol when used as a fuel in an internal combustion engine which method comprises heating methanol to an elevated temperature, combusting the heated methanol with a catalyst to form decomposition products, combusting the decomposition products with oxygen in the internal combustion engine to do useful work and recovering waste heat for heating the methanol wherein the catalyst is a alkanol decomposition catalyst according to any one of claims 1 to 10.