DE2009374A1 - - Google Patents

Description

High-temperature catalysts based on iron oxide and process for their production

The invention relates to catalysts and in particular to catalysts for the so-called high temperature water gas reaction as well as their production.

The response can be given by the following equation weruen: _

CO + H ₂ O

-> GO ₂ + H ₂

This reaction is often activated with Ghrorii Iron oxide i.e. a mixture of iron and chromium oxides in ± ulverform used.

-Z-

009939/1896

-2- 1A-37,547

If the metal oxide mixture in the catalyst is to have the required chemical activity, it must be produced in a special porous form which has a large specific surface area. This shape cannot be obtained by mechanically crushing the solid material. A suitable method of obtaining the required surface area consists in precipitating the hydroxides from a mixture of the water-soluble salts of these metals by means of basic reagents such as alkali or alkaline earth metal hydroxides / the aqueous ammonia. Substantial amounts of undesirable contaminating anions are entrained in the precipitation of these hydroxides and it is not possible to adequately wash and remove them. Especially because of the extraordinarily strong absorption potential of iron hydroxide against various anions such as chloride, sulfate, phosphate and arsenate. Therefore, iron oxide catalysts obtained by precipitation ¹ of Fe (OH) ₂ or Fe (OH) contain 1500-5000 ppm of such undesirable anions, especially sulfur compounds, even after extremely thorough washing. Since iron sulfate and chloride are cheap, these water-soluble salts are preferably used as starting materials for the production of Fe — Cr oxide conversion catalysts.

However, these chlorides and sulfates are catalyst poisons and reduce both the activity and the quake of the catalysts. In addition, when using the catalyst, chloride and sulfate are converted into volatile compounds such as HCl and HpS. Except that the catalyst itself is poisoned, such a catalyst containing sulfate / chloride gives off HPS or HCl to the resulting gas and can thereby poison any other catalyst that is used in subsequent processes.

^ m * \ mm

009839/1896

-3-. 1A-37 547

This is e.g. the! Pall in the so-called feather-temperature shift catalysts (shift catalysts), which are increasingly used in second converters, the with the VYassergas he generators are connected, in which such High temperature catalysts can be used.

To avoid such contamination is. it is necessary that emerging from a sulfur- or chlorine-containing catalyst Remove gas and eliminate it until the resulting water gas is sufficiently pure J which is evident-J affects the effectiveness of the procedure.

■ ■ * - ' i

It is therefore an object of the present invention to develop improved high-temperature catalysts that have efelgehalt a significantly lower SChv / ah iron oxide _r or-hyaroxidniederschläge with a negligibly small sulfur content, gunstigerweise of less than ppm produce 50, wherein possible, a reagent used that can be recovered, thereby enabling a continuous process.

According to the present invention, it is possible to do such to manufacture improved high-temperature catalysts-n that Iron oxides with a sulfur content of less than 50 ppm, and preferably contain less than 20 ppm. -

It has been shown that lead oxide has been very successful can be used as an activator for the iron oxide catalyst can. However, if sulphate impurities are present at the same time are how they are normally used in the manufacture of PegO ^ occur, the activation effect of disappears PbO, which is evident with a fresh catalyst, after a certain time, so that the addition of PbO no longer brings any significant advantage. However, with PbO you can do a Achieve lasting effects when using an iron oxide catalyst

009839/1896

-4- 1A-37 547

which is very pure and does not contain more than 20 to 50 ppm sulfur.

According to the invention it is possible to produce high temperature catalysts, the iron oxide obtained by precipitation with a sulfur content of less than 50 ppm Favorably less than 20 ppm. and activated with PbO. ·

According to the present invention are 'catalysts on Iron oxide base produced by precipitating a coarsely crystalline salt of an organic acid from solutions of soluble iron salts, this crystalline precipitate washes in order to remove soluble impurities and then treats it with an alkaline solution, whereby flaky iron oxide or hydroxide with a high specific Surface is created and the organic acid reagent can be recovered.

Catalysts made from mixed oxides can of course be produced according to the invention, starting from mixed solutions which, in addition to the soluble iron salts, also contain other soluble salts. In the first step according to the invention, the water-soluble iron salts are converted into slightly soluble, coarsely crystalline iron salts, which can easily be completely freed from impurities, since the coarsely crystalline precipitate, in contrast to the iron oxides or hydroxides, does not tend to absorb anions and to hold on.

In a preferred embodiment of the method the organic acid reagent is applied in the form of an ammonium or alkali salt of the acid, whereby the removal the anions of the originally used rock salt

-5-BAD OBlOLNAt

009839/1896 ^BW ——

-5- U-37 547

is made easier.

For the process according to the invention, oxalic acid is very suitable and it is normally used in the form of its ammonium, sodium or potassium salt. If sodium oxalate and iron (II) sulfate are used, the process according to the invention can be used to obtain an iron oxide with a high specific surface area which has a sulfur content of only 10 ppm. First, the iron (II) oxalate is precipitated from a solution of iron (II) sulfate with sodium oxalate. The supernatant solution containing sodium sulfate is poured off and the coarse crystalline precipitate of · | Iron oxalate washed _y ' very thoroughly to remove traces of sulphate. When the iron oxalate is hydrolyzed with sodium hydroxide, a suitable precipitate of iron oxide or hydroxide and the sodium oxalate is formed. will be recovered.

It turns out that the properties of iron oxalate for the processes according to the invention are particularly suitable. It is sparingly soluble, easily crystallizes in regular crystals, The surface does not tend to be absorbed and thereby facilitates the removal of sulfate and chloride ions from the precipitate and hycirolizes easily without decomposing the acid, which makes the economy more economical of the procedure is increased.

after the iron (II) oxalate has precipitated, it is not necessary to to isolate the slightly soluble precipitate from the liquid phase.

After the sulfate and / or chloride from the iron oxalate suspension have been completely removed, the hydrolysis step can be carried out as follows: An amount of NaOH, KOH. Or NILOH is added to the pure suspension which is equivalent to the length of the iron oxalate then kept at a temperature between 50 and 100 ° 0 until hydrolysis occurs, and a flaky and ultra-pure Pe (OH) ₀ -lower r ■ '- · ■ _ .i, -

009839/1896

-6- 1A-37 547

shock arises, which can be separated by filtering off the alkaline Na, K or NHr oxalate solution. After washing out, the resulting Pe (OH) ₂ suspension is brought together with water-soluble compounds, especially nitrates ^, which give the oxides such as Cr ₂ O and PbO that are desired to activate the iron oxide. The water-soluble oxalates released during hydrolysis are collected and reused for precipitation.

The invention is explained in more detail by the following examples, in which parts are always to be understood as parts by weight are.

Example A 1

100 parts of PeSO .. 7H ₂ O were dissolved in 264 parts of pure cold water. 48 parts of sodium oxalate (Na ₂ G ₂ O.) were then added with stirring. There was no need to heat. After one hour, a precipitate of iron oxalate FeC ₂ O ^ had formed. 2H ₂ O formed. The sulfate concentration was determined by repeated decanting and washing on a. Filter down until a qualitative sulfate analysis was negative. The purified iron oxalate was slurried in 300 parts of pure water, and 29 parts of NaOH or 41 parts of KOH were added. The mixture was heated to 95 ° C. for 1 h and then the Fe (OH) _{2 formed was} filtered off and washed. The filtrate was collected to recover the oxalate. After washing, the pure Fe (OH) _{2 was} slurried in water. To this was added eye give 2 parts chromic acid, and the mixture '1/2 h at 10O ⁰ C heated. The precipitate was filtered off and dried.

The finished catalyst was burned at 400 ° C. for 2 hours. Yield 28.4 parts (thermal yield 30.2 parts).

-7-

009839/1898

-7- 1A-37 547

Example B 1

The procedure was as in Example A 1, with the exception that 71 parts of PeCl ₂ . 4H ₂ O as starting material. were used. , The yield was 29.0 parts (theoretical yield 30.2)

Example C 1 . .

Be procedure was as in Example A 1 except that the addition of the chromic acid, and after 1/2 hour heating at 100 ⁰ C wurdennach 6 parts of lead nitrate supplied go, yield 33.0 parts j (theoretical yield 34.2 parts).

Example I) 1 ,

The procedure was as in Example Ci, but only 2 1/2 parts of lead nitrate were added. Yield 31.2 parts (theoretical yield 32.2).

The following chemical compositions were found for the individual examples found.

1: 94.2fo Fe ₂ O ₃ , 4.8 $ Cr ₃ O ₃ '

1: 94.2 $ Pe ₂ O ₅ , 4.8 # Cr ₂ O ₃

C 1: 84, yjo Pe ₂ O ₅ , 4.056 Cr ₂ O ₃ , 11.7 ^ PbO D 1 ί 89.5 $ Pe ₂ O ₃ , 4.3 ° / ° Cr ₂ O ₃ , 6.2fo PbO

For comparison, a number of catalysts were prepared which had identical compositions to those prepared in accordance with Examples A 1, B 1, C 1 and D T, but the stage of PeC ₂ O. in their preparation. 2H ₂ O precipitation was omitted. In other words, these comparative examples were produced by direct precipitation of Pe (OH) ₂ from an iron sulfate or iron chloride solution. These precipitations were

009839/1896

-8- 1A-37 547

Washed out in the same way as described above until the wash water no longer contained sulfate. Activation with PbO and Cr ₂ O was carried out in the same way.

These examples are referred to as A 2, B 2, C 2 and D 2, Table 1 shows the chlorine and sulfur content in all catalysts.

Table 1 example

A. 1 B. 1 C. 1 D. 1

Cl content
(*) S content
(*) 0.0037 0.002 0.0043 0.002 0.0051 0.002 010042 U, 002

Comparison example

A 2

B 2

C 2

D 2

0.0073 0.213 0.0916 0.004 0.0081 0.167 0.0070 υ, 234

The chemical activity of the samples was calculated by determining the conversion of a dry gas with the composition 6OJi H ₂ , 2Ο76 N ₂ , 10Ji CO and 10 7S CO ₂ . The steam / dry gas ratio was 1: 1. The reaction temperature was 400 ° C. and the pressure was 1 atmosphere. The measured conversion was used to calculate Ueschwingikeitskonstanten

009839/1896

-9- '1A-37 547 according to the equation r = ^ Ρ _ΠΛ -Ρ _ηη ) calculated in the

\ j U Vy Up ·· ''

COp _{1 is} the CO partial pressure in the equilibrium state.

These rate constants are given in Table 2. . '

T a b e 1 1 e 2 after 300 Ta
gene Measured 4.1 example at first Rate constant 4.0 A 1 . 7.6 after 50 days 5.3 B 1. 7.3 6.7 C 1 13.0 6.5 D 1 14.1 8.9 • 3.5. Comparison
example 9.2 3.0 A 2 6.0 3.2 B 2 8.7 5.1 3.1 C 2 9.0 4.7 D 2 10.7 5.2 *. 5.0

From Table 1 it is clear that the process according to the invention is very effective in reducing the sulfur content and is far superior to the known precipitation processes.

■ Table 2 shows that when the sulfur content is decreased the catalyst can be activated even further by adding PbO, while sulfur-containing catalysts can only be activated briefly by PbO.

-Patent claims-

009839/1896 _ ₁₀ -

Claims (6)

Claims 1. A high-temperature catalysts on oxide basis, characterized labeled in ze ichne t that she / contain less than 50 ppm and preferably less than 20 ppm schy efel. g e k e η η 2. Catalysts according to claim 1, characterized in that they also have PtO as an activator contain. : 3. A method for the production of catalysts according to claim 1 or 2, characterized in that I net, that a coarsely crystalline salt of an organic acid is precipitated from solutions of soluble iron salts coarse crystalline precipitate washes to remove soluble impurities, and then washed with an alkaline Solution treated, whereby flaky iron oxide or hydroxide with a high specific surface area is formed, and that organic acid reagent can be recovered. 4. The method according to claim 3, characterized in that that one starts from mixed solutions which, in addition to the soluble iron salts, also contain other soluble ones Contain salts. g e - 5. The method according to claim 3 or 4i thereby indicates that nan as an organic acid reagent is an ammonium or alkali salt of an organic Acid used. 6. The method according to claim 3 to 5, characterized in that the organic acid Oxalic acid used. 6245 009839/1896