EP0850212A1

EP0850212A1 - Process for producing methanol and catalyst therefor

Info

Publication number: EP0850212A1
Application number: EP96907504A
Authority: EP
Inventors: Alkis Sofianos; Erich Armbruster; Olaf Frei; Josef Heveling
Original assignee: Lonza AG
Current assignee: Lonza AG
Priority date: 1995-07-21
Filing date: 1996-03-19
Publication date: 1998-07-01
Also published as: ZA966164B; JP2000512261A; WO1997003937A1; CA2225449A1; AU5110696A; US6054497A

Abstract

The description relates to a process for the synthesis of methanol on X-ray amorphous catalysts with a copper, zinc and zirconium oxide content in relative proportions of 10-70 wt.% copper, 10-50 wt.% zinc and 20-80 wt.% zirconium, and suitable catalysts and a process for their production. The process for the synthesis of methanol is distinguisched by high space-time yields.

Description

METHOD FOR PRODUCING METHANOL AND CATALYST THEREFOR

The present invention relates to a method for producing methanol by reacting a gas mixture which contains hydrogen and carbon monoxide and / or carbon dioxide over a catalyst.

It is known that methanol can be produced from H ₂ and CO and / or CO ₂ on copper-containing catalysts. It is also known for this purpose to use catalysts which, in addition to copper, also contain zinc oxide, zirconium oxide and optionally further oxides (GB-A 2 151 498, US Pat. No. 5,254,520, Y. Nitta et al., Catal. Lett. 1994, 26, 345-354). The catalysts known hitherto already provide usable space-time yields in the synthesis of methanol, but it was desirable to further increase them. In addition, the known catalysts often contain additives which make it difficult to dispose of or reprocess the spent catalyst. It was therefore an object of the present invention to provide a process for the production of methanol with a higher space-time yield by using an improved catalyst, the catalyst preferably not containing any toxic or otherwise questionable components. According to the invention the object is achieved by the method according to claim 1. It has surprisingly been found that excellent results can be achieved even with a catalyst having a simple composition of 10-70% Cu, 10-50% Zn and 20-80% Zr if the latter is essentially X-ray-amorphous. The percentages indicate the relative proportion of the metallic elements Cu, Zn and Zr, ie the sum of the three values is always 100%, regardless of whether there are any other elements. The specification of the composition in percentages by weight of the metals (and not the metal oxides) is expedient here, because changes in the oxidation stage during the course of the manufacture, activation or use of the catalyst have no effect on this. Here and in the following, catalyst is understood to mean only the catalytically active substance in all the information relating to the composition. This can, of course, be applied to a carrier or assembled in some other way. A catalyst is referred to as “essentially X-ray amphib”, the X-ray diffraction pattern of which, like that of a liquid or a glass, has no discrete diffraction lines.

The catalyst used according to the invention preferably contains 20-50% Cu, 10-40% Zn and 30-60% Zr. The catalyst is preferably prepared by coprecipitating a precursor from a solution of water-soluble copper, zinc and zirconium salts. This is washed and dried. and then calcined at 300-500 ° C. In this temperature range there is no appreciable crystallization of the amophene Catalyst precursor instead. The catalyst is expediently activated before use for the synthesis of methanol. This is achieved by heating in a hydrogen-containing atmosphere to a final temperature of 200 to 350 ° C. The catalyst is preferably first kept at a lower temperature in an inert atmosphere, for example under nitrogen or argon, and then gradually or continuously exposed to slowly increasing temperatures and hydrogen concentrations until the final temperature is reached. The chlorides or nitrates are preferably used as water-soluble copper, zinc and zirconium salts. The coprecipitation is preferably effected by adding an alkali metal hydroxide solution to the solution of the water-soluble copper, zinc and zirconium salts. The co-precipitation can take place continuously or discontinuously, whereby in any case an intensive mixing of the reactants must be ensured.

The methanol synthesis itself can be carried out under the usual temperature and pressure conditions. The temperature is advantageously 200 to 320 ° C, preferably 220 to 280 ° C. The pressure is advantageously in the range from 1 to 10 MPa, preferably from 3 to 7 MPa.

With the catalysts according to the invention, the methanol synthesis is preferably carried out at a space velocity (Gas Hourly Space Velocity, GHSV) of 3200 to 40,000 ml / (g-h) (based on normal conditions), particularly preferably at 5000 to 20,000 ml / (g-h).

Description of the pictures

1 contains the X-ray diffractograms of the catalyst before / after, ie before calcination, from Example 1 (curve 1) and comparative example (2), and the diffraction lines of the crystalline comparative substance (CU _{Q 2} Zno _g ) ₅ (CO ₃ ) ₂ (OH) ₆ from the database of the "Joint Committee on Powder Diffraction Standards" (International Center for Diffraction Data, 1601 Park Lane, Swarthmore PA 19081, USA) [JCPDS 380154] (3). 2 contains the X-ray diffractograms of the catalysts from Example 1 (1) and Comparative Example (2) after the calcination and the diffraction lines of synthetic zincite (ZnO) [JCPDS 361451]. (3). The following examples illustrate the implementation of the method according to the invention:

example 1

Preparation of the catalyst from the chlorides:

To prepare a catalyst with 25% Cu, 25% Zn and 50% Zr, 625.3 g of zinc chloride and 804.8 g of copper (II) chloride dihydrate were dissolved in 1.4 l of demineralized water. The two solutions were then combined and 4.242 kg of a zirconyl chloride solution which contained 1.172 kg of ZrOCl ₂ were added. The solutions were mixed well and diluted with a further 1.8 l of water. Then, with intensive stirring (ultra-

Turrax®) within 1-2 h with 30% sodium hydroxide solution at a pH of 8.5. Then the rest of the amount of sodium hydroxide required by stoichiometry was added. The precipitate was filtered in a chamber filter at 1.8 bar and washed with deionized water until the pH of the wash water was below 8.0 and the chloride content of the filter cake was below 0.01%. The filter cake was dried at 100 ° C, treated again with water and dried again at 100 ° C. An X-ray diffractogram was taken from a sample of the dried material (FIG. 1, curve 1), which showed that the material was completely amorphous. The dried catalyst precursor was then heated in 50 K steps from 100 ° C. to 300 ° C. and held at each temperature level for 30 minutes. Finally, the temperature was raised to 350 ° C. and held at this value for 3 hours. After this calcination, the catalyst had the following properties: BET surface area: 75 m ² / g Cu surface area: 10.9 m ² / g (determined by N ₂ O chemisoφtion) Crystallite size: <2 nm (x-ray amorphous), see X-ray diffractogram Fig. 2 (1).

Example 2

Analogously to Example 1, a catalyst with the composition 40% Cu, 20% Zn, 40% Zr was produced, the corresponding nitrates being used as starting materials instead of the chlorides. The catalyst thus obtained had a BET surface area of 177 m ² / g before the calcination and was completely radiopaque. The calcined sample was also completely X-ray and had a BET surface area of 62 m ² / g Comparative example

According to GB-A 2 151 498, Example 1, a Cu / Zn / Zr catalyst with the composition 29% Cu, 23% Zn, 48% Zr, but without the addition of chromium, was produced: to a solution of 631 g of ammonium hydrogen carbonate in 30 l of water a solution of 317.4 g of copper (II) nitrate trihydrate, 294.5 g of zinc nitrate hexahydrate and 400.9 g of zirconyl nitrate dihydrate in 10 l of water was added at 60 ° C. while stirring vigorously to 60 ° C. . The mixture was stirred at 60 ° C for 1 h. The temperature was then kept at 80 ° C. for 30 minutes and finally stirred at this temperature for a further 30 minutes. After cooling, the precipitate was filtered off, washed four times with 10 l of water each time and then kneaded in a kneader for 2 hours. Then, by adding 1.25 l of water, a suspension with a solids content of 16% was prepared, which was dried in a spray dryer (air inlet temperature 220 ° C.). An X-ray diffractogram of the dried material was recorded, which had a clear structure on a continuous background, which could be assigned to the diffraction lines of (Cu, Zn) ₅ (CO ₃ ) ₂ (OH) ₆ (FIG. 1, curve 2 ). The material was therefore partially crystalline. Finally, the material was calcined at 380 ° C for 2 hours. An X-ray diffractogram was also made of the catalyst obtained in this way (FIG. 2, curve 2). This showed reflections on an unstructured surface, which could be assigned to the mineral zincite (ZnO). The calcined material was thus also partially crystalline.

Example 3

The catalysts described in Examples 1 and 2 and Comparative Examples 1 and 2 were tested for their suitability for methanol synthesis. The reaction was carried out in fixed bed microreactors (18 mm 0). The CO + CO ₂ conversion, the yield of methanol, the methanol selectivity and the space-time yield were determined. The analysis of the reaction products was carried out by o «- / me gas chromatography. The catalyst activity results from the conversion of CO + CO ₂ , the methanol yield, the selectivity (in each case in mol%, based on the carbon content of the synthesis gas), and the space-time yield in kg / (kg-h) (= kg per kg catalyst and hour).

The catalysts were activated in situ as follows: The reactor was slowly heated to 130 ° C. under nitrogen (0.8 MPa). Then 2% hydrogen was added to the nitrogen and the temperature was raised to 200 ° C. at 20 K / h. After 16 hours, the hydrogen content was increased to 12%, the temperature was raised to 240 ° C. and held at this level for 2 hours.

The methanol synthesis was carried out at 250 ° C and 5 MPa. A synthesis gas mixture of 32 vol.% Carbon monoxide, 5 vol.% Carbon dioxide and 63 vol.% Hydrogen was used as the starting material. The space velocity was 8000 ml / (gh). The results (conversion, yield, selectivity and space-time yield) are summarized in Table 1 below. These are the current values after a reaction time of 49 hours, i.e. after reaching a steady state.

Table 1

Examples 4-6

Analogously to Example 2, further catalysts of different compositions were produced. The model Polytron® PT45-80 was used as a stirrer for the continuous coprecipitation. The composition in% by weight and the precipitation conditions (temperature θ, pH, concentration c, stirring frequency v and metering speed ή) are summarized in Table 2 below.

Table 2

For characterization, the specific surfaces were determined according to BET and X-ray diffractograms (XRD) were made before and after the calcination. The results are summarized in Table 3 below. Table 3

O before the calcination ⁽²⁾ after the calcination

After a reaction time of 55 h under the conditions given in Example 3, the results summarized in Table 4 below were achieved in the methanol synthesis:

Table 4

Claims

Claims:

1. A process for the production of methanol from a gas mixture containing hydrogen and carbon monoxide and / or carbon dioxide in the presence of a catalyst containing copper oxide, zinc oxide and zirconium oxide, characterized in that the

Catalyst contains the elements copper, zinc and zirconium in relative proportions of 10 to 70% by weight of Cu, 10 to 50% by weight of Zn and 20 to 80% by weight of Zr and is essentially X-ray-free.

2. The method according to claim 1, characterized in that the catalyst, the elements copper, zinc and zirconium in relative proportions of 20 to 50 wt .-% Cu, 10 to 40 wt .-% Zn and 30 to 60 wt .-% Zr contains.

3. The method according to claim 1 or 2, characterized in that the catalyst by coprecipitation of a precursor from a solution of water-soluble copper, zinc and zirconium salts and optionally other additives, washing, drying, calcining the dried precursor at 300 to 500 ° C. , and activation at 200 to 350 ° C in a hydrogen-containing atmosphere.

4. The method according to claim 3, characterized in that as a solution more water-soluble

Copper, zinc and zirconium salts a solution of the chlorides and / or nitrates is used.

5. The method according to claim 3 or 4, characterized in that the coprecipitation by adding an alkali hydroxide solution to the solution of the water-soluble copper,

Zinc and zirconium salts are carried out.

6. Copper oxide, zinc oxide and zirconium-containing catalyst, in particular for methanol synthesis, characterized in that it contains the elements copper, zinc and zirconium in relative proportions of 10 to 70% by weight of Cu, 10 to 50% by weight of Zn and 20 contains up to 80% by weight of Zr and is essentially X-ray-amorphous.

7. Catalyst according to claim 6, characterized in that it contains the elements copper, zinc and zirconium in relative proportions of 20 to 50 wt .-% Cu, 10 to 40 wt .-% Zn and 30 to 60 wt .-% Zr .

8. A process for the preparation of the catalyst according to claim 6, characterized in that by co-precipitation from a solution of water-soluble copper, zinc and zirconium salts and optionally other additives, a catalyst precursor is precipitated, washed, dried, calcined at 300 to 500 ° C and activated at 200 to 350 ° C in a hydrogen-containing atmosphere.

9. The method according to claim 8, characterized in that a solution of the chlorides and / or nitrates is used as a solution of water-soluble copper, zinc and zirconium salts.

10. The method according to claim 8 or 9, characterized in that the coprecipitation is carried out by adding an alkali hydroxide solution to the solution of the water-soluble copper, zinc and zirconium salts.