US2168261A - Method of producing light hydrocarbons - Google Patents

Description

Aug. 1, 1939. R. M. lSHAM 2,168,261

umnon OF raonucms LIGHT nynnocmsous Filed Dec. 14, 19:52

Patented Aug. 1, 1939 UNITED STATES METHOD OF PRODUCING LIGHT HYDROCARBONS Robert M. Isham, Okmulgee, 0kla., assignor of three-fourths to William B. Pine, Okmulgee,

Okla.

Application December 14, 1932, Serial No. 647,281

2 Claims.

This invention relates to a method of producing light hydrocarbons, and more particularly to the production of gasoline.

In the extraction of gasoline from casinghead gas or from natural gas, whether by compression and liquefaction or by absorption, there is obtained along with the stable gasoline a' large amount of material which is highly volatile because of its high vapor tension. Heretofore much of this material has been wasted by evaporation into the air in the course of weathering, while where use has been made of this material it has been largely used in vapor form as a fuel, or held in liquid form under pressure and sold as liquefied petroleum gas for use in gas generators and the like. This highly volatile material is largely composed of saturated hydrocarbons or members of the paraifin series, principally propane, isobutane and butane.

While it has heretofore been proposed to subject this highly volatile material to pyrogenetic decomposition so as to produce unsaturated hydrocarbons and free hydrogen, and efforts have been made to use these unsaturated hydrocarbons, as by polymerization under the influence of high temperature and pressure in the presence of a suitable catalyst, or by combining them with one or more of the hydrocarbons of the aromatic series, as naphthalene, under suitable conditions with or without the presence of a catalyst, so far as I am aware none of these proposed procedures has proved entirely satisfactory, if in fact usable, for the commercial production of gasoline.

It has also been proposed to subject casinghead or natural gas to a relatively high temperature and pressure and then introduce it into a still in conjunction with petroleum oil to be cracked, the heated gas being used as the sole source of heat for the cracking process so as to prevent undesirable separation of carbon in the still by overheating of portions of the oil therein, but this heating of the saturated gaseous hydrocarbons of the paraflin series under a relatively high pressure is not accompanied by any efficient decomposition of the saturated hydrocarbons into unsaturated hydrocarbons.

In order to improve upon these known processes, I have heretofore proposed, in my application Serial No. 510,839, filed January 23, 1931, to utilize the highly volatile, saturated hydrocarbons obtained in any suitable way during the abstraction of gasoline from casinghead or natural gas for increasing the yield of stable gasoline produced by cracking petroleum oil. In

this prior process I discovered that if the highly volatile hydrocarbons extracted from casinghead or natural gas are subjected at substantially atmospheric pressure to any suitable cracking process, so as to obtain a maximum yield of unsaturated hydrocarbons, particularly olefins, and if these unsaturated hydrocarbons are then raised to or above a certain critical pressure and then intermingled with petroleum oil, also at or above the critical pressure, and at the cracking 1 temperature, the olefins will interact and react with the fractions obtained by the cracking process, producing an increased yield of gasoline.

While this last mentioned process provides a greatly improved method of cracking petroleum 15 oil so as to obtain an increased yield of the desired lighter hydrocarbons, and in fact yields a volume of gasoline greater than that of the petroleum oil treated, I have since discovered still another method of utilizing the highly vola- 20 tile, saturated hydrocarbons extracted from casinghead or natural gas for the production of gasoline wherein the gasoline is produced entirely from the uncondensed hydrocarbon gases without the addition to the system of any petroleum oil as required by my prior method.

It is therefore one of the objects of the present invention to provide a novel method of utilizing the highly volatile constituents derived from casinghead or natural gas for the production of a light. hydrocarbons, such as those of the naphtha class.

Another object is to provide an improved method of treating hydrocarbons wherein gasoline is produced entirely from the uncondensed, highly volatile, saturated hydrocarbon gases obtained during the abstraction of gasoline from casinghead or natural gas, and without the addition thereto of any petroleum oil.

A further object is to provide a novel method of producing gasoline by polymerization under pressure of the unsaturated hydrocarbons derived from' the highly volatile, saturated hydrocarbons obtained from casinghead and natural gas. 45

Another object is to provide a novel method of producing gasoline by polymerization under pressure of unsaturated hydrocarbons wherein the heavier oils resulting from the process are recycled so as to control the character of the 50 polymerization product.

These and other objects will appear more fully upon a consideration of the detailed description of the invention which follows. Although only one embodiment of the process and an apparatus for 55 carrying out the same has been described and diagrammatically illustrated, it is to be expressly understood that the description and drawing are for the purpose of illustration only and are not to be construed as defining the scope of the invention, reference being had for this purpose to the appended claims.

In practicing the method of the present invention, although casinghead gas and natural gas may be used directly, I prefer to extract from the casinghead or natural gas the stable gasoline and the highly volatile hydrocarbons, leaving the dry" hydrocarbon gas for use as a gas, and to then separate the highly volatile hydrocarbons from the stable gasoline. The highly volatile hydrocarbons so obtained are then subjected at substantially atmospheric pressure to any suitaable cracking process so as to obtain a maximum yield of unsaturated hydrocarbons, particularly olefins, which are obtained with hydrogen and some saturated hydrocarbon gases.

I have discovered that if, after this olefin hearing gas is preferably cooled, it is compressed to or above what may be called a critical pressure, such as 600 pounds or more per square inch, and then mixed with hot oil from a later stage of the process, said oil also being at or above the critical pressure, and the mixture of gas and oil is heated to the polymerization temperature of the unsaturated hydrocarbons present in the gas, preferably to about 775 F., the oil is largely vaporized and dilutes the gaseous hydrocarbons during polymerization so as to prevent excessive polymerization to hydrocarbons heavier than gasoline. The heavier polymers of the oil thus displace the equilibrium point of polymerization so that the polymerization product consists of gasoline hydrocarbons rather than hydrocarbons of heavier classes.

From the polymerization element such as a coil the mixture of gas, oil and oil vapors may pass to a separator where any liquid oil is removed, the gas and oil vapors then passing through a pressure reducing valve, whereby the pressure is reduced to about 100 pounds per square inch, into a dephlegmation tower in which fractionation occurs. The spent gas and gasoline vapors may then be collected and separated in any desirable manner, while the heavy hydrocarbons which have been produced during polymerization are collected in the bottom of the dephlegmation tower in the form of oil and continuously pumped therefrom back to the inlet to the polymerizing coil where it again mingles with the compressed unsaturated hydrocarbons. The unvaporized oil collected in the separator is also recirculated, first through a tar still in which the more volatile portions are separated, and then through a condenser from whence said portions are pumped back to the polymerizing chamber through a heater exposed to the hot vapors within the dephlegmation tower.

Any suitable apparatus may be employed for carrying out the method just described, and any suitable temperatures and pressures may be used dependent upon the particular conditions to be observed and results to be obtained. As one embodiment of the invention, however, the following procedure may be taken as exemplary, reference being had for purposes of illustration to the accompanying diagrammatic drawing: the uncondensed, highly volatile, saturated hydrocarbon gases from the distillation unit of a plant for extracting gasoline 'from casinghead or natural gas enter the system through a pipe I and are first passed through heater tubes 2 in a suitable furnace 3 wherein they attain a temperature of from 1300 to 1350 F. at substantially atmospheric pressure and are cracked so as to yield a substantial percentage of unsaturated hydrocarbons. It has been found that during this cracking step the volume of the incoming gases is increased from 60% to 100%, and a cracked gas is produced which contains approximately 30% unsaturated hydrocarbons. The cracked gas then passes through the cooling coil 4 of a suitable cooler 5 wherein its temperature is reduced to substantially that of the atmosphere.

The cooled, unsaturated hydrocarbon gas is then compressed, as by a suitable pump 6, to what is a critical pressure for the ensuing reaction, for example a pressure of 600 pounds per square inch or more, and conducted from the pump through a pipe I to a T connection 8 leading into the coil 9 of apolymerization heating chamber In. The pressure to be employed may greatly exceed the pressure of 600 pounds per square inch stated above, the reaction taking place more rapidly as the pressure is increased. Good results are obtained, for example, with 1000 pounds pressure. Economic considerations, however, make it desirable to keep the pressure low in order to reduce costs. the compressed, unsaturated hydrocarbons are mixed with hot oil which is supplied thereto, also under a corresponding pressure, through a pipe II from the dephlegmation tower and tar still later to be described. The mixture of unsaturated hydrocarbon gases and oil is then heated in its passage through coil 9 of polymerizing chamber H] to the polymerization temperature of the unsaturated hydrocarbons, this temperature preferably being in the neighborhood of 775 F.

,During its passage through polymerizing coil 9, a large proportion of the oil is vaporized and the vapors of these heavier polymers serve to dilute the unsaturated gaseous hydrocarbons during polymerization and to prevent excessive polymerization to hydrocarbons heavier than gasoline. They also serve to assist in regulating the temperature within the polymerizing coil by absorbing a portion of the heat given off by the strongly exothermic polymerization reaction. The introduction of the oil prior to polymerization thus displaces the equilibrium point of polymerization and results in gasoline hydrocarbons as the polymerization product.

From polymerization coil 9, the mixture of gas, oil and oil vapors passes through a pipe l2 to a suitable separator 13 wherein any liquid oil may be separated out. of the separator l3 through pipe l4, and, after passing through a pressure reducing valve l5 of any suitable construction, wherein the pressure may be reduced to approximately 100 pounds per square inch, are supplied to a dephlegmation tower I6 wherein fractionation occurs. After fractionation the spent gas and vapors of finished gasoline hydrocarbons leave the top of dephlegmation tower l6 through a pipe I! and are supplied thereby to a suitable condenser I8 wherein the gasoline is condensed. At the same time, any heavier hydrocarbons which have been produced by the polymerization step descend to the bottom of dephlegmation tower 16 in the form of oil, said oil being removed therefrom through a suitable pipe I9 by a hot oil pump which raises its pressure to substantially the same critical pressure as that produced by gas pump 6 and returns the oil through pipes 2| and H to T 8 where it again AtTB.

The gas and oil vapors pass out mixes with the compressed cracked gas and reenters the polymerizing coil 9.

From condenser i8 the spent gas and gasoline flow to a suitable separator 22 wherein they separate by gravity. The spent gas, which now contains only a fraction of 1% of unsaturated hydrocarbons, is drawn oil through pipe 23 and pressure reducing valve 24 and supplied therefrom to the fuel supply. A portion of the gasoline which is removed from separator 22 is pumped back to dephlegmation tower l6 through a pipe 25 by pump 26, the quantity pumped back being regulated so as to produce a gasoline of the desired end point. The balance of the gasoline is then drawn off through pipe 21 to storage.

Any unvaporized oil which separates out in separator I3 is drawn ofi therefrom through a pipe 28, and, after passing through a suitable pressure reducing valve 29 wherein its pressure is reduced substantially to atmospheric, is supplied to a tar still 30 of any suitable construction. In the tar still the more volatile portions of the oil are vaporized, andfrom thence they pass into a condenser 3| wherein they are again reduced to liquid form and accumulate as liquid distillate in a suitable receiver 32. The undistilled tar which drains down to the bottom of tar still 30 is run off through a pipe 33 and valve 34 to storage. Liquid distillate from receiver 32 is supplied therefrom through a pipe 35 to a suitable pump 36 wherein its pressure is raised to substantially the same pressure as that produced by pumps 6 and 20, and by which it is supplied, passing through a heating coil 31 en route which may be exposed to the hot vapors within the dephlegmation tower It, to a T 38 where it joins the hot oil from the bottom 01' dephlegmation tower I6 and passes on to T 8 and reenters the polymerizing coil 9.

The operation of the system thus described can be regulated by raising or lowering the tempera ture within polymerizing coil 9, to decrease or increase the production of oils heavier than gasoline, so that the amount of heavy oil pumped back is constant, and only gasoline, tar and spent or dry gas leave the system. Thus an increase in temperature within polymerizing coil 9 will cause a partial depolymerization of the recycled oil, converting it partially to gasoline and decreasing the amount of heavy products returned from dephlegmation tower I6. I have found, however, that at a temperature of approximately 775 F. the amount of polymers returning from tower l6 remains substantially constant, and there is no accumulation of heavy oils in the system.

In practicing the method thus described, I have been able to produce approximately eight gallons of gasoline, or naphtha, per 1,000 cubic feet of uncondensed, saturated hydrocarbon gas treated. The gasoline, or naphtha, produced is usually from 52 to 57 Baum gravity and is of very high octane number. By blending the product of my method with a sufllcient quantity of high gravity natural gasoline produced from casinghead or natural gas, to give a product of suitable volatility, a finished motor fuel of extremely fine quality and high octane number may be produced.

.In starting the operation oi. the system thus described, it may either be operated without addition of oil so as to produce its own charge of oil for cycling, or a small quantity of recycled gas oil from an oil cracking unit may be placed in the system to give a suitable initial quantity of oil for cycling through the system.

It will thus be seen that by the present invention there is provided a novel method for utilizing the highly volatile, saturated hydrocarbon constituents of the abstraction product from casinghead or natural gas so as to produce gasoline without the addition to the system of any other material, such as petroleum oil. The gasoline is produced by polymerization of the unsaturated hydrocarbon gases which are cracked from the highly volatile, saturated starting gas, and the heavier oils resulting from the process may be recycled through the polymerizing coll so as to control the character of the polymerization product and to result in gasoline hydrocarbons of high quality. With this process, the resulting products of gasoline, spent gas and tar are obtained entirely from the highly volatile, saturated hydrocarbon gases which form the sole starting material, and it is not necessary to add to the system any petroleum oil or other similar material.

While the method has been described with considerable particularity as applied to the production of gasoline by polymerization of unsaturated hydrocarbons, it will be appreciated by those skilled in the art that the invention is of wider application, and is not limited to the particular application described nor to the embodiment illustrated in the drawing. Reference is therefore to be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. In a method of producing light hydrocarbons,

the step of compressing an unsaturated hydrocarbon gas to a pressure of at least 600 lbs. per square inch, mixing said gas with oil obtained at a subsequent point in the process, heating said mixture to the polymerization temperature of the unsaturated hydrocarbons while under said pressure, separating the mixture resulting from polymerization into a liquid fraction and a vaporous and gaseous fraction, distilling the liquid fraction to separate the oils from the tars, and returning the separated oils as the oil mixed with said compressed gas.

2. In a method of producing light hydrocarbons, the steps of compressing an unsaturated hydrocarbon gas to a pressure or at least 600 lbs. per square inch, mixing said gas with oil obtained at a subsequent point in the process, heating said mixture to the polymerization temperature of the unsaturated hydrocarbons while under said pressure, separating the mixture resulting from polymerization into a liquid fraction and a vaporous and gaseous fraction, fractlonating said vaporous and gaseous fraction to obtain as separate fractions gas, gasoline and products heavier than gasoline, distilling the liquid fraction to separate the oils from the tars, and returning both said separated oils and said heavier than gasoline fraction as the oil mixed with said compressed gas.

' ROBERT M. ISHAM.

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