DE949734C - Process for the catalytic conversion of methane or similar gaseous hydrocarbons or gases containing them - Google Patents

Description

Process for the catalytic conversion of methane or similar gaseous Hydrocarbons or gases containing them The invention relates to a method for the catalytic conversion of methane or homologous gaseous hydrocarbons or gases containing such by means of oxygen or air with an increased oxygen content in gases containing carbon monoxide and hydrogen, using ferrous ones Reduction catalysts.

It is known to convert methane or gases containing methane into gases which contain carbon oxide and hydrogen, to convert the methane first with air on a combustion catalyst with partial combustion of the methane converts, whereupon the resulting gas mixture comes into contact with an iron catalyst is brought, in the presence of which the not yet converted methane with the Reaction products C02 and H20 converts the first process stage.

However, it has been found that interference with this mode of operation occur when the oxygen content of the air is increased or with pure oxygen is worked, what z. B. is necessary to avoid reaction gases of low nitrogen content to create. If you get the methane gas oxygen or air with an increased oxygen content brings about reaction in the manner described, the iron catalyst becomes inactive or ineffective. This phenomenon is based, as has been found, thereon, that the iron catalyst in the reduction stage downstream of the oxidation stage through Water vapor and carbonic acid are oxidized, -which in the reaction with oxygen or air with increased oxygen content under a significantly higher partial pressure stand than during the reaction of methane gas with air with normal oxygen content. Try the reaction of water vapor and carbonic acid with the iron catalyst to prevent by lowering the reaction temperature or to a harmless one Decreasing value turned out to be negative. It was found that below too 65o ° an oxidation of the iron catalyst takes place, while at temperatures side reactions disadvantageous by 45o ° come to the fore.

According to the invention, methane or homologous gaseous hydrocarbons are now used or such .containing gases on a combustion catalyst using converted by oxygen or air with an increased oxygen content (oxidation stage), and the gas mixture obtained, still containing methane, is before the introduction in the reduction stage, in which complete conversion takes place over an iron catalyst of the methane takes place, a certain amount of the reaction gas (cracked gas) is added, namely such an amount that the partial pressure of the water vapor and, if necessary the carbon dioxide in this mixture is lowered to that value which is when the methane is reacted with air with normal oxygen content.

This lowering of the partial pressures for water vapor and carbonic acid can also be achieved in continuous operation when converting methane gas with oxygen or air with increased oxygen content, perfect operating results and practical the same long service life of the iron catalyst as with the conversion of methane gas with air with normal oxygen content.

Another advantage of the method according to the invention is that that, under certain circumstances, the methane gas before the mentioned partial combustion with oxygen can add a certain amount of water vapor, e.g. B. to the explosion limit of the To influence the methane gas-oxygen mixture without d: ate by this addition of water vapor the reaction on the iron catalyst would be disturbed.

It is known per se, cracked gas that results from a two-stage reaction originates from methane, to partially mix in again with the starting gas in order to reduce the methane concentration to keep below 50% in the initial mixture, otherwise increased penalties in the implementation occurs. However, this recirculation of cracked gas took place in such a conversion process, in which nickel catalysts are used in both stages (oxidation and reduction stage) which, compared to iron catalysts, have a much lower sensitivity have to water vapor and / or carbonic acid, but also not inconsiderable are more expensive. In the present invention, cracked gas is recycled for the purpose and to the extent that in the reduction stage to be converted Mixture there is no higher water vapor concentration than when using normal air for the oxidation stage, but without recirculation of cracked gas.

One embodiment of the invention consists in that from the cracked gas the water or water vapor formed before being returned to the reduction process be separated in a suitable manner, for example by means of an impact separator or Condensation in order to lower the partial pressure aimed at by the invention for water vapor to reach. It may be useful to extract from the reaction gas also the carbonic acid in a suitable manner, e.g. B. by washing out with water or alkali. Embodiment To hourly i_Nm3 methane according to the Equation CH4 + 1/202 = C0 + 2 H2 to convert into cracked gas are in a vertical position Reaction tube 540 cm3 of magnesite-based nickel catalyst and 216o cm3 of one Iron melt contact arranged spatially separated from one another. The whole. Catalyst volume of 2.7 liters, 100 liters of methane and 62o liters of oxygen are applied per hour, correspondingly a space velocity of 600. At the beginning of the operation, the zone of the nickel catalyst is heated to 65 ° to 700 ° in an oxygen-free atmosphere. Then the CH4-02 mixture is slowly switched over, followed by the combustion of the methane immediately sets in with a bright red heat. A controllable amount of reaction gas is then added to the gas, from which water vapor and optionally carbonic acid was deposited, added and the temperature of the iron catalyst increased to 74.o to 76o °. For the specified Working temperature is a space velocity of the recycled reaction gas 125o volume of gas per volume of catalyst and hour is sufficient to use the iron catalyst protect from oxidation. When using 216o cm3 of iron melt contact Hourly 2700 1 cracked gas circulated. The total loading of the iron catalyst is under the specified working conditions about 2ooo 1 per 1 catalyst and Hour.

From zooo 1 methane and 620 1 oxygen, 22 () o 1 fission gas is formed, with the following composition: CO 2 = 6.911 / o, CO = 28.4%, H2 = 55.2%, C H4 = 8.69 / o , N2 = o, 9 0/0. Soot formation and oxidation are not detectable.

Claims (2)

PATENT CLAIMS: 1. Process for the catalytic conversion of methane or homologous gaseous hydrocarbons or gases containing them into a gas rich in carbon oxide and hydrogen, the methane first being reacted with an oxygen-containing gas on a combustion catalyst (oxidation stage) and the reaction mixture still containing methane via a iron-containing reduction catalyst is performed for the purpose of practically complete conversion of the methane (reduction stage), characterized in that, using oxygen or air with an increased oxygen content for the oxidation stage, the reaction mixture formed in this stage is admixed with such amounts of cracked gas before introduction into the reduction stage that the partial pressure of the water vapor and, if appropriate, of the carbonic acid in this mixture can be lowered to that value which results from the reaction of the methane with air with a normal oxygen content. 2. The method according to claim i, characterized in that water vapor and optionally carbonic acid are separated from the recycled cracked gas before mixing with the reaction mixture of the oxidation zone. Considered publications: German Patent Specifications Nos. 583 205, 558 430; Walter König, "The catalytic pressure hydrogenation of coal, tars and mineral oils", Berlin 1950; P. 1 82.