DE1137718B - Process for the endothermic catalytic cracking of hydrocarbons - Google Patents

Description

Process for the endothermic catalytic cracking of hydrocarbons In gas synthesis, it is known to use gaseous hydrocarbons for conversion to mix in carbon dioxide and hydrogen with free oxygen and without preheating to be introduced into the catalyst. The undesirable side reactions, e.g. B. Penance or kickbacks, are caused by the immediate initiation of the non-preheated Mixture in the catalyst zone and through a certain arrangement of the catalyst avoided in the reactor. By the arrangement shown, it is possible, for. B., in the split of methane with air to generate a cracked gas, which has a nitrogen content of 45 to 47%. The heat necessary to maintain the reaction is caused by total internal combustion of part of the feed gas with air.

If a gas with a higher proportion of carbon oxide or hydrogen is desired and the nitrogen content is to be reduced, the proportion of combustion must be reduced. The proportion of combustion can be reduced if another type of heat supply, namely from outside, takes place. A simple way is to preheat the reactants. With extensive preheating (e.g. at 400 or 500 ° C) internal combustion is no longer necessary to maintain the reaction. B. C H4 -! - 2.38 air = CO -I- 2 H2 -f- 1.88 N2 -I- 8.97 kcal (1) 1 mole air = 0.79 mole N2 + 0.21 mole 02 is already sufficient to cover the heat losses. If the preheating is even higher (500 to 600 ° C.), a second reaction with a negative heat tone must even be used to maintain the thermal equilibrium at the usual reaction temperatures (700 to 800 ° C.). In technology mostly used is the endothermic reaction of the hydrocarbon with water vapor to carbon oxide and hydrogen, z. B.

C H4 -I- H20 (g) = CO -I- 3 H2 - 48.87 kcal (2) With the help of preheating it is possible to reduce the nitrogen content in the generated cracked gas to 37 to 39%.

Should a further increase in the hydrogen and decrease in the nitrogen content occur in the cracked gas, this can be done in two ways: 1. By replacement or partial replacement of the air by pure oxygen or 2. by the use of Compounds with bound oxygen as oxidizing agents, e.g. B. water vapor or Carbonic acid.

The presence of pure oxygen or oxygen-enriched air is not always given in technical systems, since the construction and operation of oxygen generation systems are associated with increased costs, so that to reduce the nitrogen content in the cracked gas and thus increase the hydrogen content, the free oxygen through compounds with bound oxygen , is often replaced by steam, rarely by carbon dioxide. The following equations show the possibilities used in technology with their heat effects: CH4 + 2.38 air = CO + 2H2 -; - 1.88 N2 -I- 8.97 kcal (1) C H4 -i- O = CO + 2 H2 -I- 8.97 kcal (3) C H4 -I- H2 O (g) = CO + 3 H2 - 48.87 kcal (2) C H4 -I- C 02 = 2 CO + 2 H2 - 59, 3 kcal (4) These reactions can also be used in combination with one another. It can be seen from this that the reactions with bound oxygen are very heat consuming, so that additional heat must be supplied to the reactor in order to maintain these processes. The heat can be supplied in two different ways: 1. When the reaction is carried out continuously with the lack of heat supplied from outside, e.g. B. Tube processes from Dr. C. Otto, Schiller-Bamag and Hercules Powder (described in the magazine "Erdöl und Kohlen" 1956, issue 12, pp. 847 and 848).

z. If the reaction is carried out alternately, after each heat-consuming Split period followed by a heating period, according to the procedures of ONIA-GEGI, Pintsch-Bamag, Gerhold-Didier and CCR-Philadelphia (described in the magazine "Erdöl und Kohlen", 1956, No. 12, pp. 845 and 846).

In the processes listed under 2, the necessary heat is in a heating period by burning a gas-air mixture into a combustion chamber introduced and the heating gases at high temperature to the reactor or the catalytic Reaction zone fed.

Technical systems for carrying out these processes according to 1 and 2 are required an increased expenditure on equipment such as combustion chamber, waste heat boiler, heat exchanger and saturators to recover the sensible heat from the heating and fission gases.

The present invention is concerned with a method in which the soot-free splitting of gaseous hydrocarbons with a simple apparatus structure with bound oxygen alone or in a mixture with free oxygen with high Efficiency is achieved, with the heat supply for the heat-consuming reactions is covered by internal combustion in the catalyst bed.

It is known in the literature that metals, as they are on the Catalysts used for hydrocarbon splitting are applied, such as. B. copper or nickel, during the oxidation to metal oxide heat is released. So will z. B. British Patent 768,626 and U.S. Patent 2,759 805 this released heat is used in combination with hot flue gases to achieve a favorable temperature distribution during the heating-up period. Similar Lines of thought are described in U.S. Patents 2,671,719 and 2,220,849. Other methods, such as B. described in French patent specification 1056 321, take advantage of this effect either by using them during the heating process Pass hot flue gases with excess oxygen through the catalyst or after the Carry out a brief oxidation with air and possibly at the same time Burn off any deposits on the catalyst, such as soot or sulfur.

However, in all of these above-mentioned methods, special in reactions that consume a lot of heat, such as the water vapor splitting of hydrocarbons represents, the main part of the heat brought in by hot flue gases. This requires as already mentioned, great expense in terms of equipment.

The present invention differs from those previously known Process in that the entire heat input directly and only in the catalyst bed is carried out without supplying hot flue gases and only by sole Oxidation and subsequent reduction (combustion sequence) on the catalyst. To the exclusive heat input through internal combustion in the catalyst bed and the optimal conditions for a technical high-performance process with the simplest To achieve a device arrangement, the reduction of the metal oxide is according to the invention carried out under certain conditions and at the same time by changing the Direction of flow of the individual reactants after oxidizing, Reduction and splitting through regenerative heat exchange with the least amount of equipment Effort the greatest possible efficiency achieved.

Before the actual catalytic partial oxidation to carbon dioxide and hydrogen, which is only used in the presence of a reduced active catalyst, while, according to the invention, the catalyst as a result of the preceding oxidation is in the oxidized state, a reduction is carried out in which the catalyst or the metal oxide (e.g. Ni0) is reduced and activated at the same time the gases used for reduction are subjected to total oxidation. This reduction Experience has shown that it can only work with hydrocarbons under certain conditions itself or with other oxidizable gases such as carbon oxide and hydrogen.

Hydrocarbons alone are eliminated because, on the one hand, the reaction rate the reduction is sluggish and on the other hand soot formation and decomposition of the catalyst enter.

The admixture of gases with bound oxygen such as water vapor or carbonic acid to the hydrocarbons, according to equation (2) and / or (4) is possible, but undesirable, since the reaction takes place slowly and endothermically does not meet the practical requirements. The addition of carbon dioxide and Hydrogen in a certain ratio to the hydrocarbons is also feasible, but this reduction process produces soot. For the same reason technical gases such as coal gas or town gas, the hydrocarbons, are saturated or unsaturated, contained, not desirable for the reduction process. Gases that are practically free of hydrocarbons, such as generator gas, synthesis gas, which consist mainly of carbon oxide and hydrogen, can be used for the reduction process can be used. The same can be done in the same system in the following Fission process generated fission gas can be used for reduction, if it is largely is free of hydrocarbons. However, this mode of operation means for the system a reduction in performance, since cracked gas generated for the heating process or for the reduction is lost.

The use has proven to be the most advantageous and economical of the feed gas, i.e. the hydrocarbon-containing gas, for the reduction process proven. After thorough tests, this can be done without soot formation and without signs of disintegration for the catalytic converter only if the hydrocarbon gas (feed gas) at least as much oxygen (air) is added as for partial oxidation [e.g. B. for CH4 according to equation (1) for C 0 and H2] is required. Will a hydrocarbon-oxygen or hydrocarbon-air mixture via a Reduction catalyst, e.g. B. nickel on a carrier, and is the nickel in oxide form, then in the layer of the catalyst closest to the gas inlet as a result of the exothermic, very rapid combustion reaction in the shortest possible time Time the nickel oxide is reduced and activated, so that at this point the catalytic Conversion of the hydrocarbons takes place according to equations (3) and (1).

With the generated cracked gas, which mainly consists of carbon oxide and Hydrogen and a low residual methane content, this is in the catalyst bed Nickel oxide present above the already reduced layer with a high reaction rate and reduced with the development of heat in rapid succession for the subsequent cleavage process and activated. The subsequent catalytic cleavage process according to the equation C H4 + H2 O (g) = C O + 3H2 - 48.87 kcal (2) is heat consuming on the reduced and activated catalyst. After the temperature in the catalyst bed has dropped, caused by the heat-consuming reaction (2), the catalyst bed becomes initially oxidized with pure air and then with a hydrocarbon-oxygen or hydrocarbon-air mixture reduced by those for the heat consuming To add heat required to the cleavage process. The cycle for catalytic fission of hydrocarbon grease with steam or carbonic acid or a mixture of these runs with a more or less high addition of free oxygen or air, in accordance with the concept of the invention, in three phases. First phase: oxidation of the Metal on the catalyst, e.g. B. Nickel on a carrier, to nickel oxide. Second phase: Reduction and activation of the oxidized catalyst with a hydrocarbon-oxygen mixture, which oxygen in free form and in proportion at least to partial oxidation to carbon oxide and hydrogen, but no more than close to the upper ignition limit of the Contains mixture.

Third phase: normal splitting process on the reduced and activated Catalyst.

The reactions proceed according to the three phases, e.g. B. with methane, in the following order: First phase: oxidation according to equation 3 Ni + 7.14 Air = 3 Ni 0 + 5.64 N2 + 175.2 kcaI (5) Second phase: reduction and activation of the catalyst First, the lowest layer of the oxidized catalyst reduced according to the equation CH., + 2.38 air + 3 NiO = 3 Ni + C 02 + 2 H2 O (g) + 1.88 N2 + 17.06 kcal (6) Immediately afterwards on that in the entrance layers reduced catalyst the process of splitting the hydrocarbon-oxygen mixture one, its cleavage products on the still oxidized catalyst above burn according to the equations C H4 + 2.38 air = CO + 2 H2 + 1.88 N2 + 8.97 kcal (1) CO + NiO = Ni T C 02 + 9.21 kcal (7) 2H2 + 2 Ni O = 2 Ni + 2 H2O (g) - 1.12 kcal (8) In total, reactions (1), (7) and (8) correspond to the reaction (6).

Reactions (5) and (6) result in the complete combustion of the methane (fuel gas) in the process according to the equation C H4 -; - 9.52 air = CO. + 2 H2 O (g) + 7.52N2 + 192.26 kcal (9) to carbon dioxide and water vapor with the positive heat of reaction that corresponds to the combustion. Third phase: Fission process The subsequent heat-consuming fission process takes place without taking into account the heat losses, the sensible heat of the exhausting gases as well as the conduction and radiation losses according to the equation 3.95 C H4 + 3.95 H20 (g) = 3.95 CO + 11, 85 Hz - 192.26 kcal B. at CH "(upper flammability limit of CH4 in air at 15 percent by volume, corresponding to a natural gas-air ratio of 1: 5.7). Here, less nickel oxide is required for complete combustion, so that the process can also be carried out with catalysts that have a lower nickel content, can be performed.

The oxidation of nickel proposed according to the idea of the invention on the catalyst can be achieved in various ways, e.g. B. such that over and under the cracking catalyst proper, catalysts of various compositions and various activity. The practical implementation of this Arrangement can be as follows. The catalyst layer arranged in the middle of the reactor is divided into three zones. In the lowest or uppermost zone, depending on Operating mode, whether the air flows from above or from below through the reactor, the actual oxidation carried out. This zone can be used both with pronounced oxidation catalysts, such as iron, copper, etc., or with reduction catalysts, such as z. B. finely divided nickel on a carrier, with reduction catalysts also therefore, since these after the oxidation up to their complete reduction and activation the Also direct the fission reaction in the direction of complete combustion. In the middle zone which is constantly in a reduced state existing actual fission catalyst.

An embodiment for carrying out the 3-phase method is shown the schematic drawing.

The reactor 4, which is followed by a gas cooler 5, contains in in the middle the reaction zone 6, which consists of a highly active reduction catalyst layer consists. The preheating zones are then located on both sides of the reaction zone 6 7, which are filled with weakly active reduction catalyst. The two preheating zones 8 can be filled with granular, inactive material. To start up the reactor 4 are feed gas and air by means of a side-mounted burner in a Combustion chamber 9 is burned and the catalyst bed is heated with the hot flue gases. The heating takes place in an oxidizing atmosphere until the cleavage occurs necessary temperature in the catalyst has been reached.

The start-up of the cleavage process in three phases is as follows Carried out: Through the pipelines, 1 the water vapor, 2 the Air and through 3 the hydrocarbon-containing feed gas for process control to the reactor 4 forwarded. The control spools 10 to 22 shown in the diagram, which are automatic remote controlled are closed.

First phase: reduction from top to bottom The control spools 22, 17, 12 and 11 are opened one after the other. The reduction participant mix, consisting of of hydrocarbons and oxygen, is passed through the mixer 26 into the preheating zone 8, is preheated there to around 400 ° C and then enters the next second preheating zone 7, consisting of material with a weak catalytic effect. In the second preheating zone 7 is in the presence of the weakly active catalyst with further Preheating prevents thermal cracking with soot formation. That almost on the reaction temperature heated reduction mixture meets in the highly active catalyst layer on nickel oxide, on which the total combustion begins. At the same time the nickel oxide becomes reduced in the entry layer and activated for the subsequent cleavage process. After activating the entry layer, the reduction mixture turns into carbon dioxide and Hydrogen and partial combustion to form carbonic acid and water vapor, depending on the oxygen content in the mixture, split. The carbon monoxide and hydrogen burn in the following Layers in the presence of the nickel oxide still present to form carbonic acid and water vapor. The hot combustion gases give off their heat first in reverse order weakly active material, zone 7, then again in the regeneration zone 8 and enter the open air through the control slide 22 via the exhaust pipe 23. After completion of the reduction period, the duration of which, like that of the rest of the period, of the Strength of the heat-consuming reaction depends on the order the control slides 11, 12, 17 and 22 are closed.

Second phase: gap period from bottom to top There are the control spools 19 and 18 and then the control slides 15, 13 and 10 open. In the mixer 24 the reactants are mixed and fed to the reactor 4 from below. Preheating takes place in zones 8 and 7. In the subsequent reaction zone 6 they become in the presence of the reduced activated catalyst of the cleavage subject. The fission products enter the zones after they have given off their sensible heat 7 and 8 in the upper part of the reactor via the slide 19 into the cooler 5 are here cooled from 100 to 120 ° C to normal temperature and after possible carburation fed through the line 25 for further use. The temperature in the reaction zone 6 is, depending on the desired equilibrium composition, 700 to 1200 ° C. After the end of the gap period, the control spools 10, 13 and 15 are closed and the steam slide is used to purge the remaining fission gas in the reactor 16 open for about 5 to 15 seconds. After closing the slide 16, the both control slides 18 and 19 also closed. Third phase: oxidation of top to bottom After the cleavage period, the catalyst is oxidized. For this purpose, the control slides 22, 17 and 14 are opened. Air flows into the from above Reactor and effects after preheating in zones 8 and 7 with strong heat development the oxidation of the catalyst in the reaction zone 6. The remaining nitrogen the air gives off its heat again in the lower zones 7 and 8 and is through the control slide 22 is discharged via the exhaust line 23. After the end of the oxidation period As at the beginning, the catalyst is reduced again, only this time in the opposite direction Direction, namely with entry of the reduction mixture from below into the reactor 4 and discharge of the combustion gases via the open control slide 20 to the outside.

Claims (4)

l ATENT CLAIMS: 1. Process for the endothermic catalytic cleavage of hydrocarbons with bound oxygen alone or in a mixture with free oxygen in a shaft furnace filled with catalyst in carbon oxide and hydrogen in a cycle that heats up the reaction space with simultaneous oxidation of the Kat.alysatormetalls, the subsequent reduction of the metal oxide formed with oxidizable gases and the catalytic cleavage, characterized in that the heating of the reaction space during operation exclusively by the known oxidation of the catalyst metal with air and by the reduction of the metal oxide formed with a gaseous hydrocarbon-air or oxygen mixture takes place, the oxygen content in the reduction mixture being at least sufficient for partial oxidation of the hydrocarbon gas to carbon oxide and hydrogen, but adjusted at most to near the upper ignition limit of the mixture and that the reactants are not preheated outside the shaft furnace, and that the direction in which the reactants flow through the shaft furnace is reversed after each oxidizing, reducing and cracking. 2. Procedure according to claim 1, characterized in that in the upper and lower part of the Shaft furnace weakly active catalyst is used. 3. The method according to claims 1 and 2, characterized in that above and below in the shaft furnace zones with granular, inactive material are arranged. 4. Process according to claims 1 to 3, characterized in that oxidation catalysts such. B. iron or copper on carrier material, can be arranged above and below the actual fission catalyst. References considered: British Patent No. 768,626; French Patent No. 1056 321; "Petroleum and Coal", 9th year (1956), p. 848; »Chemical Engineering Technology«, 21st year (1949). P.3.