DE967973C - Process for carrying out endothermic chemical reactions - Google Patents

Description

ISSUED JANUARY 2, 1958

A 21846 IFa / 12g

In the case of endothermic chemical reactions, the heat required to carry out the reaction can either be supplied through the walls of the reaction space or directly by means of a suitable heat transfer medium. Such heat carriers can be solid, liquid or gaseous. However, if you want to carry out reactions that take place at high temperatures, as is particularly true for cracking reactions in which a high yield of gaseous hydrocarbons, such as acetylene, ethylene or propylene, etc., is desired, the supply of heat through the walls of the prepares Reaction space through great technical difficulties in two respects. On the one hand, the temperature of the heating medium cannot be increased as much as would be desirable in the interest of good heat transfer to achieve the highest possible temperature difference (AT) between the outer and inner walls of the reactor, since the thermal resistance of the wall material does not allow this; secondly, a certain period of time is required in order to heat the material to be thermally treated to the desired high reaction temperature. The time required for this heating also means that temperature ranges are passed through for a relatively long time in which undesired reactions can occur. Are for such rea-

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functions, ζ. B. Cracking reactions, extremely short reaction times are a prerequisite, so this condition can usually not be met with indirect heating. Various "methods have therefore been proposed which are intended to circumvent these difficulties. One attempt was made to generate the heat in the reaction material itself by burning a part of the input material with a certain amount of air or oxygen and generating it in this way Heat converts the rest of the input material (autothermal cracking or Siachsse process of methane splitting). This process is ideal from a thermal point of view; however, there are also disadvantages that cannot be overlooked. Firstly, a certain part of the input material is used as a mere heating material, Which means a significant economic disadvantage for valuable raw materials, but secondly, the desired product is _{more or less diluted by the combustion products CO, CO 2} , N ₂ , so that its pure preparation is difficult and usually causes considerable costs the warmth by means of highly heated, solid, inert and kata If a lytic heat transfer medium is used, the desired end product is not diluted, but the technical difficulties resulting from the heating and transport of the highly heated solid heat transfer material are increased. The result is usually extremely complex, repair-prone apparatuses of considerable size. If, however, a gaseous heat transfer medium is used, it is desirable that it meet two conditions: on the one hand, it must be easy to separate from the reaction product, on the other hand, it should have as high a specific heat as possible in order to achieve a maximum with a minimum of heat transfer volume To be able to bring thermal energy into the reaction chamber. The following requirements arise: i. The feed material is to be preheated as high as is possible and essentially only the heat required to carry out the endothermic reaction is to be introduced with the heat carrier gas in order to reduce the amount of heat carrier gas as much as possible. However, the separate heating of the heat carrier gas and the charge again requires additional equipment.

2. In the interest of maintaining short response times must be ensured by a suitable design of the reaction space that a The fastest and most complete possible mixing of charge and heat transfer gas is guaranteed. 3. To protect the wall material, its temperature must be kept as low as possible.

It has now been found that these three conditions, firstly the necessary preheating of the feed, secondly the ideal and spontaneous mixing of the components and thirdly, keeping high temperatures away from the walls of the reaction chamber, can be met at the same time in the simplest way by using one reaction chamber , which is designed in the manner according to the invention, as shown in Fig. 1, for example, that is, represents a cyclone. The liquid, vapor or gaseous charge enters at A in the form of a screw tangent and forms a flow that glides on the wall. This flow moves forward to the top of the cyclone with constantly increasing angular velocity, where it reverses and swirls again in the core of the cyclone at C. If one now leads z. B. at B a flow of the gaseous or vaporous heat carrier gas in the vicinity of the reversal point of the cyclone flow or at the same, one achieves an almost ideal mixing between the heat carrier gas and the input material, on the other hand the gas flow flowing from B to C heats, in which the desired reaction takes place, that cold entering charge largely cools itself down in the vicinity of the exit point C to such an extent that undesired further reactions no longer occur and the equilibrium is frozen. This achieves very significant advantages over all previously known types of reactor: r. The reaction time can be varied in an almost unlimited manner without the reaction space having to be enlarged or reduced by a) increasing or decreasing the total throughput rate while maintaining the quantitative ratio of heat transfer gas to feed and while maintaining the temperature of the heat transfer gas; b) reduces the temperature of the heat transfer gas and increases its amount, while the amount of the input material is kept constant; this not only shortens the reaction time, but at the same time also lowers the partial pressure under which the feed material reacts, so that the reaction can be steered more in a desired direction if the reaction temperature is maintained; c) conversely, the temperature of the heat carrier gas can be increased and its amount reduced, while the amount of the input material is kept constant; this in turn extends the reaction time while maintaining the reaction temperature, while at the same time increasing the partial pressure.

2. The reaction temperature can be varied by a) maintaining the temperature of the heat transfer gas increases or decreases its amount in relation to the input material, b) while maintaining the quantitative ratio of heat carrier gas to charge, the temperature of the Heat transfer gas decreased or increased.

In this way it becomes possible to direct the reaction in any desired direction. So can one z. B. crack a heavy hydrocarbon in the same apparatus and get a) at high Temperatures, short reaction times and low partial pressure, high yields of gaseous Hydrocarbons such as acetylene, ethylene, propylene and butylene; b) at lower temperatures, longer response times and higher

Partial printing of less gaseous and more liquid products, including highly aromatic products Gasoline with good octane ratings.

3. The wall of the reaction space is created by the relatively cold flow sliding on the wall of the input material is cooled. The consequence is that the reactor is not specially selected expensive, highly thermally resistant material must be built and that - also the external Insulation of the reaction space due to the lower temperature difference to the outside less difficulties and the heat losses are lower.

4. The charge is required so far without any heat transfer through walls evaporates and the gas or steam is heated approximately up to the temperature at which the reaction begins target.

5. Does the input material contain components or such are formed during the intended reaction:

temperature cannot be evaporated (e.g. carbon from the cracking of heavy oils or petroleum residues), these substances can easily be removed from point B at the tip of the cyclone. In this case, the heat transfer gas must be introduced through a special central tube protruding into the reaction chamber at B. A special feature of the invention is that the type of cyclic flow separates the charge and the heat transfer gas without any partition until spontaneous mixing occurs at the turning point and the reaction begins. In order to preheat it, only the part of the radiation of the heat that would otherwise have to be lost is given to the input material.

The apex angle of the cyclone cone depends on the type of reaction desired, in particular on the desired duration of the reaction and the fact whether solid or liquid products are to be discharged. It can be between o ° (cylindrical shape, as shown in Fig. 2) and may vary from about 90 ^0, and is preferably 30 ^0. The heat yields to be achieved in apparatuses of the form according to the invention are extraordinarily high and reach almost 100%. The quenching required in many reactions, for example for the purpose of freezing the equilibrium, is already carried out by the feedstock itself and is thus directly beneficial to the heat balance of the overall reaction The heat given off to this cooling medium can then only be recovered very imperfectly and with renewed expenditure on apparatus, it is practically lost.

If the use of a catalyst appears necessary to achieve special effects, this can either be arranged in the form of a network or on a porous support near the mixing point on the reaction zone BC . It can also be particularly advantageous to swirl in powdered catalysts with the flow of the heat carrier gas or through a special 6§ feed line at D , to leave them in contact with the feed during the reaction time and to separate them in a downstream separator, e.g. B. cyclone to discharge again.

example

In a reaction chamber designed according to Fig. 1 or 2, 300 kg of a light petrol from the boiling range ο to 105 ^{0 are} injected per hour at A. The radiation evaporates as soon as it emerges from the nozzle. The hydrocarbon vapor heats up on its path along the wall 400 to about ⁰ on and occurs at B in the stream of 400 kg / h to 1200 ⁰ superheated steam. On the way from B to C , the steam gives off its heat to the hydrocarbon, which converts it into paraffins, olefins and hydrogen which are gaseous at normal temperature. The emerging mixture is cooled in the usual way and the steam is condensed. 8g In terms of weight, the gaseous component consists of

47% acetylene + ethylene
24% propylene + butylene
12% methane

4% ethane + propane + butane 10% hydrocarbons C ₅ and higher 3% hydrogen

100%,

it is separated in a manner known per se and the valuable olefins are obtained therefrom.

It is already known that there is a helical flow in a reaction vessel can be maintained if you tangentially at one or more points in the charge Introduces reaction space. These procedures are generally used to ensure a good and intense Ensure thorough mixing of the reactants without the use of stirring.

This generally results in a uniform temperature level (mixed temperature) in the entire reaction space. Subject of the present However, it is the invention by suitable guidance of the partial flows (cyclonic flow) Allow the reaction to proceed independently of the wall in the free central space of the cyclone-shaped reactor. As a result, there are possibly harmful catalytic influences on the wall material and also Wall reactions are switched off, and on the other hand the wall of the reaction space itself becomes relatively cold held so that reactions that take place at high temperatures are carried out in materials that cannot cope with such temperatures per se.

Claims (1)

PATENT CLAIMS: i. Process for carrying out endothermic chemical reactions, in particular cracking reactions, characterized in that the liquid, vapor or gaseous material to be converted is tangential to a cyclone-like material The reactor is fed and a suitable heat carrier gas is introduced into the reactor in a counter-current flow near the reversal point of the cyclone flow.
2. The method according to claim i, characterized in that superheated steam is used as the heat carrier gas. 3. The method according to claim 1 and 2, characterized in that a heat transfer gas is used Mixture of gaseous combustion products is used. 4. The method according to claim 1 to 3, characterized in that non-evaporable or fixed proportions of the input material at the top of the j 5 reactor are discharged. 5. The method according to claim 1 to 4, characterized in that a raw material is used as the feedstock Petroleum is used, the non-evaporable parts of which are discharged from the reactor will. 6. The method according to claim 1 to 5, characterized characterized in that the liquid feedstock with the implementation of a circulation cracking Using recycled gases atomized and introduced tangentially into the reaction chamber will. 7. The method according to claim 1 to 6, characterized in that catalysts in the Reaction zone fixed or whirled in with the heat carrier gas in the form of dust and discharged again in a downstream separator. Considered publications:
Belgian Patent No. 506697;
German Patent Nos. 879091, 578710; U.S. Patent Nos. 2,582,246, 2582710; German patent application ρ 48265 I a / 241 (published March 5, 1953). 1 sheet of drawings