US1948872A - Conversion of hydrocarbons into lower boiling compounds - Google Patents

Description

Patented Feb. 27, 1934 UNITED STATES PATENT OFFICE CONVERSION OF HYDROOARBONS INTO LOWER BOILING COMPOUNDS Application April 8, 1929.

4 Claims.

This invention relates to a process and apparatus for conversion of higher boiling hydrocarbons into lower boiling hydrocarbons, and is particularly applicable to the cracking of higher 5 boiling hydrocarbons in vapor phase to produce lower boiling hydrocarbons and especially lower boiling hydrocarbons suitable for fuel in internal combustion engines and having a high antiknock value.

When hydrocarbon oils are subjected while in a liquid state to temperatures between 750 F. and 850 F. cracking takes place at a rate increasing with the temperature to which the oil is heated, and the higher the temperature to which the oil is heated the greater the tendency toward the production of fixed gases and coke or carbon. Some oils, and especially oils which have once passed through a cracking operation, must be subjected to temperatures as high as 950 F. in order to produce an appreciable conversion, but in the cracking, while in liquid state, of the hydrocarbons ordinarily supplied to cracking operations the temperatures to which the oil is heated-are usually maintained between 750 and 850 F. in order to avoid excessive production of fixed gases and free carbon. Investigation of the cracking of hydrocarbons while they are in vapor phase shows that temperatures approximately 200 to 250 F. higher than the temperatures best suited to cracking the same hydrocarbons while they are in liquid phase, must be employed in order that the desired rate andextent of conversion of the hydrocarbons that are in vapor phase will take place. Thus in cracking the same hydrocarbons in vapor phase, .the vapors must be heated to temperatures as high and higher than 900 F., conversion occurring at a very low rate at 900 F. If the vapors are heated to temperatures as high as 1200 F. and higher, the conversion resembles that which occurs when the hydrocarbons while in liquid state are heated to temperatures up to and above 850 F., 'in that larger amounts of fixed gas and free carbon are produced.

It has been proposed to crack hydrocarbons in vapor phase by vaporizing the hydrocarbons and subjecting them together with steam and in the presence of a catalytic agent to desired cracking temperatures; and it is known, that it is advantageous to cool promptly and rapidly the vapors that have been subjected to cracking temperature, in order to limit the duration or the conversion; and it has been proposed to ef-,

- feet such cooling by spraying a sufllcient quantity of liquid into contact with the vapors that Serial No. 353,474

have been brought to cracking temperature, and to thereby arrest the conversion.

My invention includesseveral features which may be used separately with advantage and which cooperate to produce advantages greater 4 than the advantages of the separate features. Thus, an important feature of my invention is that the vapors that have been subjected to cracking conditions are cooled, and the duration of the conversion is terminated and limited, bymixing with cooler hydrocarbon-vapors, the vapors that have been subjected to cracking conditions. For brevity, the term vapors as used herein refers to both vapors and gases regardless of whether liquids are present and regardless of whether the vapors are superheated. An advantage in using cooler vapors for the purpose of cooling vapors that have been subjected to cracking conditions, is that, because of the higher temperatures required for the cracking of hydrocarbons that are in vapor phase, the hydrocarbon vapors used for cooling will not be cracked by the contact therewith of the hot vapors coming from the cracking operation. Moreover, if the vapors used for cooling are cracked by such contact there is less tendency toward the formation of free carbon and fixed vapors than there wouldbe from such contact with hydrocarbons that are in liquid phase, and any carbon produced'by the vapor phase cracking is in the form of powder and is readily prevented from clogging the apparatus. Another advantage is that, because of the higher temperatures required for the cracking of hydrocarbons that are in vapor phase, the cooling of the converter vapors does not have to be carried so far, the conversion being sufficiently arrested or retarded if the resulting mixture of converter vapors and vapors used for cooling is brought to temperatures that are even as high as 900 F. or slightly higher. By way of comparison, it is pointed out that when liquid hydrocarbons are contacted with converter vapors in vapor phase cracking to check the conversion, such liquid hydrocarbons are subjected to temperatures that tend to produce excessive quantities of fixed gas and free carbon from liquids, while hydrocarbon vapors used for such cooling are subjected at most to only temperatures that are desirable in vapor phase cracking and not to temperatures that are so high as to produce excessive quantities of fixed gases and free carbon from hydrocarbons that are in a vapor state. Thus, the use of liquid bydrocarbons to check the reaction occurring in vapor phase cracking subjects those liquids to conditions wholly unsuited to the cracking of liquids and which tend to produce excessive quantities of gases and free carbon, while the use of vapors to cool the converter vapors subjects such cooling vapors to only normal cracking conditions; and the carbon produced from liquid phase cracking at excessively high temperatures is excessive in quantity and very harmful to the system while carbon produced from vapors at temperatures appropriate to the cracking of vapors is small in quantity and relatively harmless in character.

Another feature of my invention is that the vapors prepared for the purpose of being subjected to cracking conditions and the vapors prepared for cooling the converter vapors may be derived from the same source. An advantage of this feature is that regardless of the rate at which liquid hydrocarbons are supplied to the system and vaporized, the rate at which vapors are passed through the converter can be varied within wide limits to vary the duration of the period during which the vapors are subjected to cracking conditions, and the remaining vapors may be by-passed around the converter and brought into contact with the converter vapors to cool them. This provides for a wide range of control of the conversion operation regardless of Another feature of my invention that may be used separately or in cooperation with the last mentioned feature is that hydrocarbon vapors, which are commonly termed fixed gases resulting from the cracking operation, may be employed as the vapors mixed with the converter vapors to cool them. When compression and cooling are employed to effect extensive condensation of the low boiling products of the cracking operation, such fixed vapors will be available at low temperature. Thus, when the fixed vapors are employed in the cooling operation, the proportion of charging-stock vapors used for cooling may be reduced, even to zero, and bring to a maximum the rate of flow of vapors through-the converter, and the system will still supply suificient vapors for cooling purposes. On the other hand, large quantities of charging-stock vapors may be used for cooling 1 purposes with corresponding decrease in the rate the resulting mixture to a temperature at which conversion is suiiiciently retarded, is contacted with fresh charging-stock coming into the system. An advantage of this feature resides in the heat economy and another advantage is that the lower boiling constituents of the fresh charging-stock are vaporized; and as will appear a feature of my invention is that the vapors of lower boiling constituents, that are so produced, are mixed with the vapors of the desirable constituents produced by the cracking operation.

Another feature of my invention is that the products of the cracking operation, including the vapors mixed therewith for the cooling thereof, are fractionated; and the undesirably high-boiling constituents thereof are mixed with the fresh charging-stock, or the residue thereof, to provide a body of higher-boiling liquid hydrocarbons from which vapors are produced for introduction into the converter and for cooling of the converter vapors. In the practice of my in- Lo gers vention this liquid is heated by waste heat from the heat supplied to the converter, for the purpose of producing the desired vapors. If such heat does not vaporize a sufficient proportion of such liquid, a relatively small quantity of steam may be introduced to vaporize further quantities of such liquid; and such steam will pass with the vapors through the converter or to the operation in which the converter vapors are cooled. But, it is to be understood that my invention is not limited to the presence of steam in the vapors entering the converter or in the vapors used for cooling. Moreover, my invention is not limited to the use of a catalyst in the converter although some operators may desire the presence of a catalyst therein.

In the practice of my invention the fresh charging-stock may be passed in heat exchange relation with the vapors coming from the fractionating operation above referred to, and may be passed in heat exchange relation with any liquid residue of the vaporizing operation in which vapors are produced for introduction to the converter and for cooling; an advantage of my invention being that that vaporizing operation may be carried so far that the residue consists only of very high boiling substances, the apparent limit ofthe vaporizing operation being that the residue will preferably remain liquid at the temperature employed. In the practice of my invention the fact that only enough cooling vapors need be employed to bring the mixture to a temperature in the neighborhood of 900 F. and the fact that the resulting mixture of vapors is thereafter contacted with fresh charging-stock, results in substantial heat economies.

Further features and advantages of my invention will occur, in the light of this description, to those skilled in the art and will appear from the following description of the apparatus illustrated in the drawing wherein there is shown diagrammatically apparatus embodying my invention and whereby my process may be prac-, ticed.

Referring to the drawing, charging-stock, which may consist of hydrocarbons of limited boiling range or of crude petroleum oil, is passed by pump 12 through heat exchanger '7, and then by pipe 2'7 through heat exchanger 8, and then by pipe 28 into an intermediate level of the upper portion A of column 1. Partition 29 in column 1 divides said upper portion A from a lower portion B. The portions A and B constitute, in

effect, separate columns and will be so referred to although they are shown in a single column for convenience.

A heating chamber 4 of any suitable construction is heated in any suitable manner as by means of burner 40. Liquid is withdrawn through pipe 30 from the lower portion of column A and passed through oil heating coil or pipe still 2 in the upper part of heating chamber 4, the liquid being thus heated by waste heat, and the heated oil is condifiited by pipe'Bl into the upper part of column B wherein vaporization occurs. If a sufiicient proportion of the oil coming from the bottom of column A is not vaporized by such heating, steam may be introduced by pipe 32 into the lower portion of column B which is preferably provided with bubble trays 33 of known construction. Unvaporized liquids pass from the. bottom of column B through pipe 34 and through heat exchanger 8 and are passed by pipe 15 to 35 to a separator 6 or other suitable device in which they are substantially freed of all liquid hydrocarbons. Substantially dry vapors pass from separator 6 into converter 3 which may be of any suitable construction but is-preferably a single pipe made up of sections connected in series and is placed in proper relation to the burner 40 in order that the vapors passing therethrough may be brought to proper conversion temperature,

preferably above 1000 F. and even up to 1400 F.

The converter vapors pass to a cooling chamber 20 that may be of any construction and may consist merely of a pipe into which other vapors may be injected. Hydrocarbon vapors for cooling the converter vapors may be brought into mixture therewith in any manner and from any source. In accordance with the preferred form of my invention vapors from separator 6 and at temperatures between 600 F and 800 F. are conducted by pipe 36 to cooling chamber 20, the flow of vapors through pipe 36 being controlled by valve 5. From cooling chamber 20 the converter vapors mixed with the cooling vapors, which may be vapors of higher-boiling hydrocarbons supplied through pipe 36, are conducted by pipe 37 into tower A above the level of liquid therein and preferably below the several bubble trays 38 in tower A. The rising vapors contact first with the downwardly flowing fresh charging-stock supplied through pipe 28 and act to vaporize higher-boiling constituents thereof and then the vapors rise and are cooled as they rise, and pass through pipe 39 to heat exchanger 7 from which they pass to condenser 17 and then to separator 16 from which liquids pass by pipe 42 to tank 10 in which there is collected the desired product of the operation. Vapors pass from separator 16 through pipe 43 to compressor 18 and the compressed vapors pass through cooler 44 which discharges into tank 19 from the bottom of which condensed liquid may be withdrawn and from the top of which vapors are conducted through pipe 45 to cooling chamber 20 or through relief valve 21 to gas holder 22.

Pump '13 draws cool liquid from tank 10 and passes it through pipe 46, as a reflux, into the top of column A for the purpose of maintaining the top of that columnat a temperature, for example 300 F., at which hydrocarbons having a desired end point will pass in vapor form through pipe 39 from the top of column A.

As merely illustrative operating conditions, to which my invention is not limited, the vapors'in the converter may attain a temperature between 1000 F. and 1400 F. and the vapors mixed therewith for the cooling thereof may bring the resulting mixture passing through pipe 37 to temperatures between 700 F. and 900 F. The cracking operation may be carried on at different pressures dependent upon the character of the oil to be cracked and with certain types of oil the pressure of the cracking operation may be substantially atmospheric. The mixture of oil passing from column A to pipe 30, and consisting of fresh charging-stock and condensed higher-boiling constituents of the converter vapors which are recycled and condensed cooling vapors, may have a temperature in the neighborhood of 600 F. and the oil entering chamber B may have a temperature between 700 F and 850 F. The vapors entering the converter may be between 650 F. and 800 F. Liquids passing through pipe 30 to the vaporizing operation include the fresh charging-stock, or the residue thereof, and higherboiling hydrocarbons condensed from the converter vapor and from the vapors used to cool the converter vapors. I

- From the foregoing it will be apparent that in the apparatus described the converter vapors are cooled for the retarding or arresting of the conversion, by having mixed therewith cooler hydrocarbon vapors and as a result undesirable cracking of the cooling medium will not occur. And, adjustment of the valve 5 will determine the amount of vapors by-passed around the converter and therefore determine the rate of flow through the converter in order that conversion to a proper degree will be effected by the heat available, this regulation being in addition to the regulation afforded through control of the burner 40. Any insufiiciency in the quantity of vapors passing through valve 5, for the cooling of the converter vapors to the temperature at which conversion is arrested, may be compensated for by controlling the flow of fixed vapors through pipe 45 by regulation of valve 50.

In the practice of my invention, particularly as a result of the controlling of the conversion reaction as to duration and intensity and the cooling of the converter vapors by means of other vapors, there is produced a maximum amount of gasoline having a high anti-knock value and a minimum amount of fixed gas, fuel oil and free carbon, and the resulting fuel oil is relatively free of such carbon, and the use of steam and catalysts in the converter may be dispensed with.

I claim:

1. In a process in which hydrocarbons in the vapor phase are pyrolytically converted at temperatures between 1000 F. and 1400 F. to form hydrocarbons having lower boiling points, that method of arresting the pyrolytic reaction of conversion to prevent an excessive formation of undesirable hydrocarbons which includes the steps of heating a hydrocarbon oil to vaporizing temperature without substantial pyrolytic decomposition, flashing the heated oil into vapors in a vaporizing zone, and directly admixing the vapors with the hydrocarbons formed in the pyrolytic conversion zone of the vapor phase conversion process in sufficient quantity to bring the temperature of the resultant mixture to between 700 and 900 F.

2. A process for the pyrolytic conversion of hydrocarbons including the steps of heating a hydrocarbon oil to vaporizing temperatures without substantial pyrolytic decomposition, flashing the oil so heated'into' vapors in a vaporizing zone, converting a portion of said vapors to lower boiling hydrocarbons at temperatures between 1000 F. and 1400 F., admixing the remainder of said vapors directly with the hydrocarbons formed in the conversion step to bringthe temperature of the resultant mixture between 700 and 900 F. whereby the pyrolytic reaction is arrested to prevent an excessive formation of gaseous hydrocarbons.

3. A process for the pyrolytic conversion of hydrocarbons including the steps of heating a hydrocarbon oil to vaporizing temperatures without substantial pyrolytic decomposition, flashing the oil so heated into vapors in a vaporizing zone,

converting a portion of said vapors to lower boiling hydrocarbons at temperatures between 1000f F. and 1400 F., admixing the remainder of said vapors directly with the hydrocarbons formed in the conversion step to bring the temperature of the resultant mixture between 100 and 900 F. whereby the pyrolytic reaction is arrested toprewithout substantial cracking, separating the vapors from unvaporized oil, dividing the vapors into separate streams, heating one of said streams to cracking temperature, then substantialiy immediately mixing the vapors of the other of said streams therewith in suflicient quantity to thereby reduce the temperature of the vapors to between 700" and 900 F.

MALCOLM H. TUTTLE.

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