DE1745946A1 - Process for the thermal cracking of hydrocarbons - Google Patents

Description

1745946 Patent attorney Dipl.-Phys. Gerhard üedl 8 Munich 22 Steinsdorfstr. 21-22 Tel. 29 84

B 3584

MONSANTO COMPANY, 800 North Lindbergh Boulevard, 66 St. Louis, Missouri / USA

Process for the thermal curing of hydrocarbons

The invention relates to thermal cracking processes for hydrocarbons and in particular a process for the thermal cracking of normally liquid hydrocarbons, whereby decoking of the cracking furnace is aimed at in the process.

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It is known that olefins, diolefins and aromatic hydrocarbons are derived largely from the thermal cracking processes of hydrocarbons. The special processes used to crack these hydrocarbons to olefins, diolefins and other products are known to the person skilled in the art. They are currently generally in the presence of Steam is carried out in tubular ovens, such as those in U.S. patents 2,608,527, 2,340,814, 2,917,564 and 3,182,638. The ratio of length to diameter of this tubular ovens is generally greater than 100: 1 for all of these processes Difficulties arise from the formation of coke in the tubular furnaces, leading to costly shutdowns of the cracking furnaces for the purpose the purification of coke forces. Although coking also occurs in batches of light hydrocarbons, e.g. B. at Ethane, that wins Problem of particular concern with the cracking of heavier, liquid batches, e.g. naphtha and crude oils, with a shutdown of the furnaces for decoking often after a throughput time of 100 hours is required.

According to the present invention, there is now a method for cracking normally liquid hydrocarbons are proposed, significantly increasing the time periods at which the Cracking in the stream can be operated continuously. Here should

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the crack oven can be decoked while it is working and flowing through it will.

According to a preferred embodiment of the present invention is used in the thermal cracking of normally liquid hydrocarbons in a tubular cracking furnace, in which a coking of the When the furnace would occur, the following improvement was suggested:

One normally liquid hydrocarbon charge and one normally gaseous hydrocarbon off charge are alternately im Cracked pass, with an initial period of time during each cycle in which the normally liquid hydrocarbon charge is cracked, and a second period of time is provided during which the normally gaseous hydrocarbon off-charge is cracked, the Ratio between the first period of time and the second period of time is at least 10 * 1.

The method according to the present invention is based on the thermal Cracking virtually any normally liquid hydrocarbon feed applicable. Generally, there are the normally liquid batches which are subjected to thermal cracking are made up of mixtures of several and sometimes of thousands

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different connections. Accordingly, these batches have not a single boiling point. Rather, the boiling point ranges from an initial boiling point to an end boiling point. They are usually there liquid hydrocarbons to which the process according to the present invention is most applicable, generally those which have final boiling points above 93.3 ° C (200 ° F). Among the normally liquid hydrocarbon batches as they are used in the process are useful according to the present invention include naphtha, natural crude oils, heating oils, gas oils, kerosol, gasoline, petroleum condensates, reduced crude oils, residual oils, naphtha residues, coal tar fractions, Shale oils and the like. Preferably the process according to the present invention is applied to batches of petroleum derivatives which have normal boiling ranges essentially between about 37.8 ° C (100 ° F) to about 816 ° C (1,500 ° F). Than usually liquid hydrocarbon batches, petroleum condensates are particularly preferred. The preferred petroleum condensates can are characterized by boiling point ranges essentially between 37.8 C (100 F) to 427 ° C (800 ° F) as set forth by A.S.T.M. Experiment no. D-86 are intended. It is not intended to be the present To restrict the invention to the cracking of a batch which consists exclusively of normally liquid hydrocarbons, since coking inhibitors and compounds to modify the cracking

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pattern or the like can be present. In a large number of processes, smaller amounts of normally gaseous hydrocarbons, such as butane, are also present, which can be circulated to the cracking ovens with the normal liquid hydrocarbon feed. The present invention is also intended to encompass such methods ,

Those useful in the method according to the invention, normally Gaseous hydrocarbons can be saturated or unsaturated. Examples of such normally gaseous hydrocarbons are Ethane, propane, butane, propylene and isobutylene as well as mixtures of normally gaseous hydrocarbons, e.g. B. propane and ethane or refining gas, which contains 1-4 carbon atoms. Preferred the saturated hydrocarbons, especially ethane. According to a preferred embodiment of the method, as normally gaseous hydrocarbons are those used in the reactor effluent from cracking the normally liquid hydrocarbon feed and which are fed back into the furnace in the cycle.

The thermal cracking of both the normally liquid carbon

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Hydrocarbons as well as the normally gaseous hydrocarbons is generally carried out in the presence of an inert diluent, preferably in the presence of steam. The inert diluent is added in order to reduce the partial pressure of the charge in the reaction zone and thus to increase the degree of conversion _ enable which without excessive formation of undesirable products can be reached. The addition of steam also serves to keep the linear velocity of the batch at a maximum for that desired Keeping conversion, reducing the possibility of excess carbon formation. The amount of inert Diluent is generally between about 0.05 to 4.0 parts by weight per part by weight of the hydrocarbon charge introduced into the cracking furnace. Preferably about 0.2 to about 2.0 kg inert diluent added per kg feed when a normally gaseous hydrocarbon feed is used, and preferably about 0.05 to about 1.5 kg of diluent per kg of feed when a normally liquid hydrocarbon feed is used.

Thermal cracking of both the normally liquid hydrocarbon as well as the normally gaseous hydrocarbon can be carried out under various conditions in terms of time, temperature and pressure, namely in

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Dependence on such factors as the particular construction of the Furnace or the products desired in the effluent stream. in the

en.
generally the temperature will be in the range of 454 C (850 F) to

982 ° C (1. £ ÖG ° F) and the pressures in the range of about atmospheric pressure

2 2 2

to 70.3 kg / cm, preferably from 0.7 kg / cm to 11.2 kg / cm. Temperatures of 732 ° C to 899 ° C (1,350 ° F to 1,650 F) are preferred for the normally gaseous hydrocarbon feeds, while temperatures from 593 ° C to 843 ° C (1,100 ° F to 1,550 ° F) are preferred for the normally liquid batches. The dwell time in the crack zone is generally not more than about 2.0 seconds, if a significant formation of undesired by-products is to be prevented. It can be shorter than 0.01 see.

example

Two endurance tests were carried out with a petroleum condensate, which has an initial boiling point of about 46.7 C (116 F) and an ending boiling point of about 330 ° C (625 ° F) - determined by A.S.T.M. Trial D-86 - possessed. The petroleum condensate was cracked in a tubular furnace at a temperature of about 816 ° C (1,500 ° F). During the cracking of the petroleum condensate, a steam to hydrocarbon weight ratio was created of about 0.25. The first

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Run was made according to the present invention with an ethane charge carried out, which was cracked periodically. Another run was made without using the method according to the invention carried out. During the ethane cracking periods, a temperature of about 843 ° C (1,550 ° F) and steam became ethane weight ratio of about 0.4 applied. The results of the two runs are illustrated in the drawing, from which the inlet pressure of the cracking furnace (sometimes referred to as back pressure) as a function of time. According to the present invention The run carried out is indicated by dash-dotted lines, while the run carried out without the application of the present invention is indicated with is shown by a solid line. The furnace inlet pressure is on a good measure of the degree of coking of the furnace tubes. It increases as the coking of the furnace pipes increases. In the used

P th special furnace, a shutdown for decoking was required for

borrowed after a back pressure of about 8.44 kg / cm at the operating conditions specified in the example was reached.

As can best be seen from the drawing, it could be used without application of the method according to the invention carried out pass - as indicated by a solid line - only Work in a continuous stream for 200 hours before such a strong one

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Coke formation occurs that the furnace will be shut down for decoking had to. However, if ethane and petroleum condensate are alternately cracked in accordance with the present invention, then the furnace can be about 590% Hours, i.e. about 25 days, can be operated continuously. This run consisted of approximately 4 1/2 cycles according to the procedure of the invention, wherein the first cracking cycle consists of about 100 hours of cracking of petroleum condensate and 4 hours of ethane cracking, the second cycle from about 104 hours of cracking petroleum condensate and 3 1/2 hours of ethane cracking, the third cycle of about 139 hours of cracking petroleum condensate and 4 hours of ethane cracking and the fourth cycle of about 111 Hours of cracking petroleum condensate and 3 hours of ethane cracking consisted. After the fourth cycle, petroleum condensate was cracked for about 120 hours; then the routine maintenance run was interrupted, although - as indicated by the back pressure - the furnace would not have required shutdown for decoking. From this example it can be seen that according to the method of the invention, considerably longer Operating times can be achieved without interruption than would be the case if the periodic ethane cracking was not used would have been.

In a cracking cycle of the present invention, the ratio is the length of a period during which one normally

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liquid hydrocarbon charge is cracked at a period during which a normally gaseous hydrocarbon feed is cracked, generally greater than 10: 1. It can be greater than 400: 1. In general, the ratio will be between about 20: and 300: 1, with the range of 50: 1 to 250: 1 being preferred will. The actual number of hours over which the cracking periods of each genus extend depends largely on the particular one used, normally liquid hydrocarbon charge, which is cracked because one batch forms coke more easily than the other. For example, when cracking a petroleum condensate, as used in the example given, advantageous if the cycles are about 80 to 160 hours periods of a supply of petroleum condensate, followed by a 1/2 to 5 hour period of intake of the normally include gaseous hydrocarbon. The periods for ™ cracking the normally liquid hydrocarbons and / or the

normally gaseous hydrocarbons can also cycle to vary cycle. In general, the normally liquid hydrocarbon is cracked until a certain inlet pressure is reached is followed by the supply of a normally gaseous hydrocarbon is switched. The period length required for cracking the normally liquid hydrocarbon can be achieved by easily determined by those skilled in the art, this being dependent on the particular

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Furnace design, the charge fed, the feed speed, the reaction conditions and the like. It is found, however, that when a special oven is operated without alternating cracking with a normally gaseous hydrocarbon after seven or eight days the coke formation is so strong that it is switched off Decoking is required. In this case the periods during which the normally liquid hydrocarbon according to of the present invention can be cracked for less than seven or eight days.

In carrying out the method according to the present invention the drop in back pressure or inlet pressure due to decoking sometimes occurs during the period at which it normally occurs gaseous hydrocarbon is cracked, and sometimes after being fed back to the normally liquid hydrocarbon was switched back. The point in time at which the inlet pressure decreases again and thus indicates decoking can be from Vary cycle to cycle. The reasons why decoking occurs while the reactor is in operation have not yet been fully clarified and accordingly, the invention is not limited to any particular theory. What is certain, however, is that longer operating times without interruption are possible because the decoking takes place without the furnace

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Must be shut down for a day or more to the usual Carry out decoking process. Working in a continuous cycle is advantageous on the one hand in that a higher Production is achieved, and on the other hand also in the respect that no mechanical errors occur due to the fact that because of Due to the extreme temperature changes affecting the furnace pipes, a metal fatigue break can occur if the furnace is used for the Decoking is switched off.

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Claims (12)

Claims l.j Process for the thermal cracking of normally liquid Hydrocarbons in a tubular furnace, substantial coke formation occurring in the furnace, characterized in that im alternating cycle of the normally liquid hydrocarbon containing feed and a normally gaseous hydrocarbon feed is cracked, each cycle consisting of a first period of time during which the normally liquid hydrocarbon feed and a second period of time during which the normally gaseous hydrocarbon feed is cracked is, wherein the time ratio between the first time span and the second time span is at least 10: 1. 2. The method according to claim 1, characterized in that the ratio the times for cracking the normally liquid hydrocarbon to cracking the normally gaseous hydrocarbon is between about 20: 1 to 300: 1. 3. The method according to claim 1, characterized in that the normally gaseous hydrocarbon consists essentially of ethane. ",. 209833/0110 C / sd « 4. The method according to claim 2, characterized in that the cracking the normally liquid hydrocarbon feed and the normally gaseous hydrocarbon feed at a temperature of about 454 C to about 982 C and at a pressure * of about atmospheric pressure up to about 70.3 kg / cm is carried out. ™ 5. The method according to claim 4, characterized in that the cracking the normally liquid hydrocarbon charge in the presence of a inert diluent in an amount of 0.05 to 4.0 kg of inert diluent per kg of hydrocarbons charged to the furnace lies. 6. The method according to claim 5, characterized in that the inert Steam diluent is used. 7. The method according to claim 6, characterized in that the normally liquid hydrocarbon charge consists of naphtha. 8. The method according to claim 6, characterized in that the normally gaseous hydrocarbon is ethane and that the ethane is cracked in the presence of 0.05 to 4.0 kg of steam per kg of ethane. B 3584 209833/0110 / S 9. The method according to claim 8, characterized in that the ethane is separated from the furnace effluent, which is obtained from the cracking of normally liquid hydrocarbons. 10. The method according to claim 8, characterized in that the normally is liquid hydrocarbon petroleum condensate, which is essentially in the range of 37.8 ° C to 427 ° C - determined by A.S.T.M. Experiment D-86 - boiling. 11. The method according to claim 9, characterized in that the time periods for cracking the normally liquid hydrocarbons takes about 80 to 160 hours, and the times during which which normally gaseous hydrocarbons are cracked, extend over about 0.5 to 5.0 hours. 12. The method according to claim 1, characterized in that cyclically a batch consisting of petroleum condensate and ethane is cracked, whereby each cycle of a first period of about 80 to 160 hours during which the petroleum condensate charge is cracked and of one second period of about 0.5 to 5.0 hours, during which Ethane is cracked, with the petroleum condensate charge in the presence of about 0.05 to 1.5 kg of steam per kg of the petroleum condensate charge and at 209833/0110 a temperature in the range of 593 ° C to 843 ° C is cracked while the ethane in the presence of about 0.2 to 2.0 kg of steam per kg of ethane and cracking at temperatures of about 732 ° C to 899 ° C. B 3584 209833/0110