DE919288C - Process for the production of iron catalysts which are suitable for the catalytic hydrogenation of carbons, which is carried out in particular under high gas loads - Google Patents

Description

In the case of the catalytic hydrogenation of carbohydrates carried out with iron catalysts, in addition to high Turnover to strive for a work-up of the synthesis gas as appropriate to the species as possible, d. H. Carbon dioxide and Hydrogen must be used up in the ratio offered. In addition, one is possible aim for high contact loads and the lowest possible methane formation. One can use carrier or use unsupported iron catalysts. Diatomaceous earth is preferably used as the carrier substance, in special cases, however, activated aluminum oxide, fuller's earth and the like are also used for this purpose Substances suitable.

Supported iron catalysts have a fairly good work-up ratio at synthesis pressures above 5 to 10 kg / qcm, which, for example, when processing water gas with conversions of up to 60 ° / ₀ (CO- _{1-H 2} ) can be approximately appropriate. The dilution of the catalyst metal caused by the support material, however, requires a fairly high synthesis temperature at this level of conversion. With the commonly designated as a normal load of gas hourly space ioo parts of gas per liter of contact synthesis temperatures must be observed of approximately 250 ^0th However, if the gas load is increased to a multiple of the normal load, the synthesis temperature must be increased to such an extent that the synthesis operation becomes uneconomical because of increased methane formation and carbon deposition.

With strapless iron catalysts, the synthesis is at approximately 30 to 40 ⁰ lower temperatures as are required for carrier-containing catalysts run. In a straight pass, the exposure can be increased to 10 to 2 times the above-mentioned normal exposure and a (CO + H ₂ ) conversion of up to 70% can still be achieved. However, it is disadvantageous that unsupported iron catalysts cause a considerable conversion of the gas constituents. As a result, the remaining residual gas is so rich in hydrogen that an increase in the conversion up to 90% (CO + H ₂ ) and more cannot be achieved either directly or using downstream synthesis steps.

In the production of iron catalysts, numerous individual measures for improving the synthesis properties are known, alone and in combination. The catalyst metals have already been precipitated from hot meta-nitrate solutions with hot soda solution while maintaining a certain hydrogen ion concentration. It is also known that the synthetic properties of iron catalysts can be influenced to a large extent by impregnation with alkali compounds, preferably with potassium compounds. Potash water glass has already been used for impregnation. When an iron catalyst per 100 parts of its iron content is soaked, for example, having from 8 to 10 parts K ₂ O and 40 to 50 parts of SiO _2, can then be 220-240 ⁰ with normal load and gas recirculation conversions of 60 to 70% (CO + H ₂ ) reach. However, with increased exposure, for example ten times the normal exposure, too much methane is formed and, in addition, undesirable carbon deposits can occur. Iron catalysts have also already been impregnated in such a way that 1 to 1.5 parts of K ₂ O and 3 to 5 parts of SiO ₂ are used per 100 parts of iron. Although these catalysts could be operated with increased gas loading, they had an unsatisfactory work-up ratio and high methane formation.

To improve the synthesis properties, one also has the reduction of the iron catalyst in Changed many ways and worked with both high and low reduction temperatures. Here sometimes high and sometimes low velocities of the reducing gases were used. The composition of the reducing gases has also been largely changed by both pure hydrogen and carbon-hydrogen mixtures and in special cases pure carbon monoxide were used.

With all the previously known combinations of these manufacturing measures, it was not previously possible to To win iron catalysts, the high gas load, high conversion, appropriate work-up the synthesis gases and low methane formation combine with one another in a satisfactory manner.

It has been found that a novel combination of the individual measures known per se can be used Can win iron catalysts, for example, water gas in only work up to over 90% in a two-stage process.

For the production according to the invention of iron catalysts which are suitable for the catalytic hydrogenation of carbohydrates, which is carried out in particular under high gas loads and which contain no or only small amounts of carriers and the usual amount of copper or other activating metals, the hot solution of the metal nitrates used is hotter with such amounts Soda solution precipitated with intensive stirring so that after the precipitation the pH is 6.8 to 7.2. The precipitated mass is _{then washed out to an alkali content calculated as K 2} O of no more than 0.5 parts K ₂ O per 100 parts iron content, initially mixed with a small amount of water for the purpose of comminution and then converted into a suspension with the addition of further amounts of water, this suspension mixed with such amounts of a potassium water glass solution that for every 100 parts of iron there are 20 to 25 parts of SiO ₂ , and then treated with nitric acid in such a way that the catalyst mass remaining after filtration has a K ₂ O-SiO ₂ ratio of about 1: 4 to 1: 5. This mass is then dried and immediately shaped without recirculation of dusty constituents and the shaped catalyst using high gas velocities of ι to 2 m / sec. at 200 to 350 °, preferably at 250 to 300 °, reduced in such a way that 30 to 50% of the total iron content is in the form of free iron in the finished catalyst.

Using the iron catalysts thus obtained, one can with one over the normal Gas load to 10 to 20 times the load with only two-stage operation water gas for example work up to over 90%. Of the two synthesis stages, one is in a straight line Passage and the other operated with gas circulation, with a gas reflux ratio of 1: 1 to 1: 3 applies.

Potassium salts of non-volatile acids are used to impregnate the catalysts important because with alkali hydroxide, carbonate, acetate or similar salts, the properties according to the invention of the new catalytic converter cannot be reached. During the filtration of the precipitated catalyst mass A pH value of 6.8 to 7.2 is important because it is at higher or lower pH values the precipitated mass is difficult to filter and wash out. To touch the pressed Filter cake must comply with the specified amounts of water during the division and suspension formation otherwise the desired impregnation cannot be achieved with sufficient certainty leaves.

During the shaping of the catalyst, dust-like fractions, such as those for example, are recycled is used in the production of cobalt catalysts is not possible because the catalyst according to the invention has a reduced activity and does not have sufficient grain strength.

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Only if the contact is deformed immediately after filtration will a stable grain result optimal synthesis properties.

In the reduction of the iron catalyst according to the invention powerful and active ones can only be obtained by using high gas velocities Catalysts. When using low gas velocities, as they have been customary up to now, result iron catalysts of insufficient ίο activity.

example

There were 100 liters of a hot solution containing 40 g Fe as Fe (NO ₃ ) ₃ and 2 g Cu as Cu (NO ₃ ) ₂ per liter with 1050 l of a hot solution containing 100 g Na ₂ CO _{3 per liter} contained, brought together with vigorous stirring. The mixture was stirred until the split off carbonic acid had completely escaped, with the mixture being heated continuously to the boil

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When the precipitation was complete, the ρπ value was 7.0. The precipitated metal compounds were separated from the solution in a filter press and immediately afterwards washed out with hot condensate water for 30 minutes at an excess pressure of 3 kg / cm 2 in order to remove the alkali present as far as possible. When maintaining a pH of 7.0, the alkali content of the filter cake could be reduced without difficulty to such an extent that it was 0.4 parts of K ₂ O per 100 parts of iron _{(calculated as K 2 O).} If, in deviation from this, the precipitation was carried out in the alkaline range, the remaining alkali content could hardly be reduced to below 1.5 to 2 parts of K ₂ O per 100 parts of iron in spite of the significantly longer washing time.

The washed-out filter cake was first made into a paste with a little water in a mixer in order to break up the moist mass as much as possible. For this purpose, 100 kg of the moist filter cake were combined with 30 l of water. The divided catalyst mass was then mixed with a further 350 l of water until a uniform suspension of approximately syrupy consistency was obtained. Immediately thereafter, 17 kg of potassium waterglass containing 8.1% K ₂ O and 20.5% SiO ₂ were added.

_{The suspension impregnated with potassium silicate was mixed with 2.11 nitric acid (48% HNO 3} ) per 100 kg of the moist filter cake for the purpose of neutralization, the acid being added in a thin stream with vigorous stirring. After neutralization, the suspension was separated from the solution in a filter press. The separated filter cake contained 100 parts of iron (Fe), 4.6 parts of K ₂ O and 23 parts of SiO ₂ .

The filter cake was shaped into roller-shaped pieces 2 to 4 mm in diameter and 3 to 6 mm in length without recycling of dust-like fractions, resulting in extremely hard and resistant catalyst grains. These were ^{reduced at 280 °} with a hydrogen-nitrogen mixture for 60 minutes, a gas velocity of 1.5 m (measured linear and cold) per second being used. The finished catalyst contained the reduced iron present in the form of free iron 42 ° / _0th

Claims (1)

PATENT CLAIM: Process for the production of iron catalysts which are suitable for the catalytic carbohydrate hydrogenation carried out, in particular, under high gas loads and which contain no or only small amounts of carriers and, to the usual extent, copper or other activating metals, characterized in that the hot solution of the metal nitrates used is mixed with such amounts of hot soda solution falls with vigorous stirring that after the precipitation the pH is 6.8 to 7.2, the precipitated mass except for an _{alkali content calculated as K 2} O of at most 0.5 parts of K ₂ O per 100 parts Washes out the iron content, first mixed with a small amount of water for the purpose of comminution and then converted into a suspension with the addition of further amounts of water, this suspension is mixed with such amounts of a potassium silicate solution that for every 100 parts of iron content there are 20 to 25 parts of SiO ₂ , and then with such amounts Nitric acid treated that after the Filtrati on the remaining catalyst _{mass has a K 2} O-SiO ₈ ratio of about 1: 4 to 1: 5, whereupon this mass is dried and immediately shaped without recirculation of dusty components and the deformed catalyst using high gas velocities of 1 to 2 m / Sec. , preferably, is reduced at 200 to 350 ° at 250 to 300 ⁰ such that in the finished catalyst 30 to _50/0 ° are present the total iron content in the form of free iron. © 9558 10.54