DE924448C - Process for the hydrogenation of carbohydrates under the pressure conditions of normal pressure synthesis on iron precipitation catalysts containing alkali silicate - Google Patents

Description

Process for the hydrogenation of carbohydrates under the pressure conditions of Normal pressure synthesis on alkalisilicate-containing eggs & precipitating catalysts at the hydrogenation of carbohydrates carried out under normal or increased pressure by a few atmospheres, the so-called normal pressure synthesis, the use of iron contacts is known, that, apart from iron, almost always small amounts of copper, and often also suitable ones Contain activators, for example calcium or zinc. Such iron contacts always have a more or less high alkali content, for example in form of soda, sodium hydroxide, potassium hydroxide or potassium carbonate.

The amount of alkali present, which is commonly referred to as K2 0 calculate is of fundamental importance. When using small amounts of alkali, for example from 0.5 to 10 / o K2 0, based on the total iron content (Fe), the proportion of high molecular weight hydrocarbons in the products is proportionate small amount. Methane formation, on the other hand, is quite high. If the amount of alkali is set to 5 until Io O / o K2 0 increases, then there are considerably higher yields of high molecular weight Hydrocarbons, while methane formation is less. Prove these contacts during the synthesis very quickly with paraffin, causing a rapid drop in their Activity leads to frequent contact extractions to be carried out at short intervals requires.

In the case of the catalytic hydrogenation of carbohydrates, special ones are sometimes used Value for a low content of high molecular weight hydrocarbons.

It has been found that one can achieve this goal under the printing conditions normal pressure synthesis under Use of iron precipitation contacts can be achieved if one uses catalysts after impregnation with Water glass with nitric acid up to an alkali oxide-Si 02 ratio of less as 1: 3 up to 1: 6, preferably 1: 5, calculated as K2 0, were washed off.

The iron precipitation contacts according to the invention show under severe synthesis conditions z. B. when working with the highest possible conversion by using appropriate reaction temperatures, only a small amount of paraffin formation, but surprisingly there is also methane formation relatively low. Even under mild working conditions there are none particularly high amounts of paraffin The formation of methane continues in these cases return.

To achieve the highest possible yield of low-boiling Hydrocarbons with a molecular size between C5 and Cr2, for example, it is advantageous to use the iron contacts according to the invention at relatively low temperature with hydrogen and when using high gas velocities to reduce. The reduction temperatures are preferably between 220 and 2500 too Select. The gas velocities should be 1.0 to 1.5 m / sec. be. A change this reduction condition yields iron contacts that are either lower Have activity or cause increased methane formation.

If the reduction is effected by water gas instead of hydrogen, then the undesired formation of high molecular weight hydrocarbons takes place in the present case again to.

The iron contacts according to the invention are best completely without or only with a low content of the usual carriers, e.g. B. Kieselguhr, prepared.

Example One consisting of 100 parts of iron and 5 parts of copper Contact was made in a manner known per se from the corresponding nitrate solutions Soda solution hot like. Immediately after the precipitation, the mother solution was filtered off and the alkali still present in the filter cake with condensate water except for one Residual content of approximately 0.80 / 0 K2 0 washed out. After that it was still damp Contact cake impregnated with a water glass solution that approximates to I part K2 0 Contained 3 parts of SiO2. After this impregnation, the moist contact mass calculated on the total iron present, contains 25% SiO2.

The excess alkali was neutralized with dilute Washed out nitric acid and subsequent filtration. This resulted in a K2 O-Si O2 ratio of 1: 5.

The contact mass was then dried for 24 hours at 110 ° then sieved to a grain size between 1 and 3 mm. The subsequent Reduction was carried out by hydrogen of 2250 with a reduction time of 60 minutes with a gas flow rate of 1.2 m / sec. The one made in this way Contact had a reduction value of 30% free iron.

This contact was carried out in a synthesis furnace in such a way as to convert Water gas uses that every part of the volume is in contact with 100 parts of water every hour at 2200 and 2 atmospheres pressure was applied. A conversion (C O + H2) achieve from 72 to 740/0, which corresponds to a 95 to 980% carbon oxide work-up is equivalent to.

The methane formation was about 7 to 80/0 of the total conversion. That Consumption ratio (CO / H2) was about 1: 0.7. The yield per NmS Ideal gas was 142 g of synthesis products without methane.

In comparison, an iron contact that reached instead of a Silicate impregnation according to the invention a corresponding impregnation with K OH had obtained a yield of 138 g per Nm3 ideal gas. As a result of the high amount however, the conversion of free alkali fell within 3 days to 47%, whereupon extraction was required to restore full contact activity.

If the contact has been impregnated according to the invention in such a way that it with approximately the same K2 0-Si 02 ratio only contained IO / o alkali (calculated as K2 0), then, with approximately the same conversion, methane formation of about 240 per cent resulted. The yield was based on 130 g of synthesis products per Nm3 of ideal gas. These However, the yield was only initially obtained because the methane formation was already after relatively short operating time tautf about 15 to 20% increase, with the Yield further decreased to 120 g per Nm3 of ideal gas.

When the contact has been impregnated in such a way that a K2 O-Si 02 ratio of 1: 3 was present, then the synthesis yielded larger amounts of high molecular weight Hydrocarbons. In addition, in this case it was after a relatively short time an extraction of the contact covered with paraffin is necessary.

If the contacts according to the invention were reduced with water gas instead of hydrogen, then there was also an increased paraffin yield.

The contact also showed a shorter lifespan than that of the Reduction with hydrogen.

If the specified amount of SiO2 was increased, contacts resulted, which showed a significantly reduced activity under the same operating conditions, so that the conversion fell to about 60 to 63 ° / o.

Claims (2)

PATENT CLAIMS: 1. Process for carbohydrate hydrogenation among the Pressure conditions of normal pressure synthesis on iron precipitation catalysts containing potassium silicate, characterized in that the catalysts after impregnation with water glass with nitric acid at an alkali oxide-SiO2 ratio of less than 1: 3 until at 1: 6, preferably 1: 5, calculated as K2 0, washed out became. 2. The method according to claim I, characterized in that the catalysts at high gas velocities, preferably at a linear gas velocity from 1.0 to 1.5 m / sec., and at relatively low temperatures, preferably at 220 to 2500, have been reduced with hydrogen. Attached publications: German patent specifications No. 742 376, 745 444; French Patent Nos. 51 974 (add. to 871 536), 862 870; Italian U.S. Patent No. 373 833 (Chem. Zentralblatt 1940, II, 2986); Smith-D'ans, Introduction to General and inorganic. Chemie, 1942, p. 254; Angewandte Chemie, I948, (B), p. 225 off.