US1792744A - Process for converting hydrocarbons - Google Patents

Description

Feb. 17, 1931. J. 1. `:AKowsKY 1,792,744

PROCESS FOR CONVERTING HYDROCARBONS Filed July 22, 1924 J Jckomf SHO: new

Patented Feb. 17, 1931 UNITED STATES PATENT OFFICE.

y JAY J. JAKOWSKY, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR T C & C DEVELOP- DVG COMPANY, OF KANSAS CITY, MISSOURI, A CORPORATION OF .ARIZONA PROCESS FOR CONVERTING HYDROCARBONS ApplicationV fuea .my 22,Y

This invention relates to processes for converting hydrocarbons; land it relates more particularly to the conversion or transformation of relatively heavy hydrocarbons, particularly mineral oils, into more useful products of lower boiling point by thermal decomposition or cracking, the operation being aided and supplemented by suitable application of a high tension electrical discharge of the corona type to the hydrocarbons undergoing treatment in the cracking or converting zone.

It has been proposed heretofore to subject relatively heavy mineral oil vapors to the action of a high tension silent or corona discharge for the purpose of decomposing the mineral oil into lower boiling products such as gasoline or other forms of motor fuel. It has been supposed by some that the action of the high tension electrical discharge, when suiiiciently high frequencies are employed, would set up molecular vibration of such rapidity and intensity as to bring about the desired breaking down of the larger molecules with resultant production of smaller molecules characterizing lower boilin mineral oil products of the gasoline type. thers have believed that high tension discharge resulting from the use of a current that is chiefly unidirectional would bring about something analogous to electrolytic decomposition of the heavy hydrocarbon compounds, with resultant production of lower boiling substances.

The present invention is based upon the discovery that when mineral oil vapors are passed through a suitable decomposing chamber heated to proper cracking temperatures, the efficiency of the thermal decomposition or cracking of the mineral oil vapors can be notably increased by applying to the vapors passing through the converting or cracking zone a high tension electrical discharge of the corona type in such manner as to cause precipitation of the thru-going heavy oil particles or the creation of an electical wind, particularly if this be done in such a way as to direct the heavy oil vapor particles toward the hot walls of the cracking 1924. serial No. (i2/7,536.

cracking attained at any one temper ture' depends in large measure upon the extent of the heated surfaces to which the vapors are exposed or with which they are brought into contact during their passage through the converting zone which is usually in the form of a tube. Attempts have been made to increase the area of such hot contact surfaces by employing filling material of various kinds in the cracking tube, but this method has generally failed because of stoppage of the tube by heavy carbon and coky deposits on the filling material. On the other hand, in passing through a cracking tube not containing filling material of some kind, the gases and vapors have a tendency to channel, and since the interior of the vapor space is at'a temperature lower than the heated walls of the cracking tube under the conditions assumed, much less cracking takes place in the main body of the vapors than occurs in close proximity to the hot tube walls where the vapors are practically in physical Contact with said walls.

It has now been found that if the physical condition of the vapors passing throu h an unfilled or unobstructed cracking tu e be properly controlled, this channeling or stratification of vapors within the tube can be done away with, and other useful and important effects attained, by application of a suitable high tension electrical discharge of Athe corona type. As applied in the practice of the present invention, this high tension discharge is believed to act mainly in much the same way that it is generally understood to act in precipitating processes and apparatus of the well known Cottrell type. That is to say, just as the particles of dust or liquid are driven from the central fine-wire discharge electrode of the Cottrell precipitating apparatus toward the collecting plate, so in an analogous manner may particles of mineral oil in a sufficiently saturated vapor of such oil be driven toward the heated walls of a cracking chamber, such as a tube, thereby breaking up the before-mentioned channeling of the vapors and not only ensuring cihcient contact of the heavy hydrocarbons with. said heated walls but also rendering the temperature throughout the cross-section of the tube more nearly uniform than would otherwise be possible. As a result, it becomes unnecessary to overheat the cracking tube in order to attain suitable cracking temperatures near the axis of the tube. However, in order to attain results ot practical importance by this method, it is essential to so control the operating conditions that the heavy hydrocarbon compounds which-it is desired to'decompose or crack may be in such physical condition or state that they may be etticiently susceptible to the precipitating or directing action of the high tension electrical discharge in question. It has been found that upon substances existing in true gaseous condition, as distinguished from the condition of a mist or fog or analogous vapor form, a high tension electrical discharge has little or no precipitating or directing effect, and that accordingly no ei'ective precipitation results from the application of said discharge to substances in true gaseous condition. It seems to be essential that in order for such precipitating or directing action to occur, the substance subjected to the electrical discharge must exist in the form of molecular aggregates, such as particles or droplets of appreciable size like those characterizing for example, a visible mist or fog. This means, in treating a mineral oil, for example, that under given conditions the temperature must not exceed a certain critical point at which the most volatile of those heavy hydrocarbon constituents which it is desired to convert change from molecular aggregates, tangible particles or droplets into true gaseous condition. For the purposes of this invention, therefore, the optimum condition is Where the vaporized mineral oil passing through the cracking or converting zone contains a maximum proportion ofsuch ag regates, particles or droplets in the form o mist or fog. In this condition the vaporized mineral oil may be compared to steam in the condition of saturation or wetness, superheating of the vaporized mineral oil being absent or minimized. Y

Since the high tension electrical discharge has little or no precipitating effect upon true gases, the progress of gasoline or similar low boiling products through the cracking tube, which is heated to above their critical points, is unimpeded by the high tension electrical dischar e which acts selectively upon the particles o the heavy oil fog or mist and drives them toward the tube Walls. As a result, the gasoline and other low-boiling products pass rapidly out of the cracking tube 'and are not subjected in large measure to the cracking weave/a eect due to delayed passage through the cracking zone or 'to excessive contact with the hot tube walls, while the high-boiling hydrocarbons are held back by continually being precipitated against hot walls and resubjected to such cracking conditions. Moreover, such heavy hydrocarbons as may inisystem to which the low boiling products pass from the cracking tube and, in eect, increases the capacity-of such system. This method of separating and condensing highboiling constituents of a mixture of vapors and gases by means of a high tension electrical discharge, and then passing the residual gaseous mixture to a cooling system for recovery of a desired condensate, is believed to be broadly new not only in the petroleum art but also in other elds, such as alcohol distillation, where relatively high-boiling constituents of a mixture of distillation vapors and gases are required to be separated from a desired cut or fraction. By knocking out such heavier constituents with a high tension discharge before the distillation vapor and gas mixture is passed to the cooling and condensing system, not only is the load on the latter reduced but a sharper separation of heavy products from lighter products is made possible.

In practicing the present invention, the high tension corona or silent discharge may be produced with'various types of current, either alternating or direct, and either high or low frequency, the particular type of current employed being ordinarily immaterial. In practice, high tension direct current usually offers advantages. The oil to be converted is vaporized and passed through the cracking tube which is externally heated toa temperature sufliciently high to effect cracking on and closely adjacent the inner walls of the tube, a common range of convert-ing temperatures in vapor phase cracking being from 500 to 700o C. The corona or silent discharge is caused to pass transversely of the path of vapor, travel and in effect acts like a trap or filter through which the gasoline and other relatively low boiling products, whose critical points are below the temperature maintained in the cracking zone, pass freely, While the higher boiling products are knocked out and driven to or toward the hot walls of the tube and either under o cracking or are condensed and reilu'xed to the source of oil vapors. While the employ-ment of pressure on the vapors in the cracking zone is not essential, itis often advantageous for certain oils and to recover certain liquid erd reaction products, and may amount to 100 pounds per square inch, or more, in a typical instance. y

It has been found that in operating in accordance with the principles of the invention as herein disclosed, the gasoline or other lowboiling product obtained is substantially lower in unsaturates than is the corresponding product obtained by vapor phase cracking as ordinarily conducted. This is doubtless attributable in part to the fact that the present invention makes it possible to avoid overheating the tube walls and thus effecting unnecessarily drastic cracking in an attempt to obtain large yields of cracked products. In the most advantageous mode of practic-- ing the invention, it is desirable that the cracking tube contain an appreciable amount of heavy mineral oils in liquid form as well as in the form of vapors, in order thatI the gas and vapor mixture through which the high tension discharge is passed may be maintained in a condition of maximum saturation or wetness, the desirability of which has already been discussed.

Various forms of apparatus may be employed in carrying out the process of the invention, but in general the employment of a vertical tubular cracking chamber is found to be most satisfactory. One particularly suitable type of apparatus is illustrated more or less diagrammatically in the accompanying drawing which is a central vertical section through a furnace chamber enclosing a plurality of 'cracking tube units shown in elevation. Referring to the drawing, 10 rep,- resents generally a vertical cracking tube unit, of which any suitable number may be housed within a circular shaft furnace whose walls of irebrick or the like are indicated at 11. The cracking tubes, which may be of iron, steel, or other suitable metal, are suspended from near their upper ends by means of supporting collars 12 which rest upon a plate 13 covering the top of the furnace, said plate being in turn-carried upon a steel supporting frame 14 which stands on a suitable foundation, not shown. The construction is such that the entire Weight of the cracking tubes is carried by the framework 14 which is outside the furnace and is therefore not subjected to the effects of high heating. An expansion joint 15 pro-vides for slight relative movement between the supporting plate 12 and the furnace walls. Each cracking tube unit has an enlarged lower part 16 adapted to contain a substantial body of liquid and to function as a vaporizer. Adjacent this enlarged lower portion of the cracking tubes is provided suitable firing means such as ring burners 17 for gas or the like, one of which may be provided for each tube. Substan- Jtially in the vertical axis of each cracking tube is a fine wire discharge electrode 18, supported at its upper and lower ends, respectively, by high tension insulators 19 and 20, provision being made at 21 at the upper end of Said discharge electrode to connect the same to a high voltage supply of suitable character. The cracking tube may be grounded and constitutes the other electrode, in this instance the collecting electrode. The tube forms at its lower end a settling chamber and is provided with a clean-out and blowof pipe connection 22-23, the pipe 23 being provided with check valve 24 and shut-off valve 25. Oil may be introduced into the converting tubes either at the top or bottom, but in the installation here illustrated, each tube is supplied with oil through supply pipe 26 having a shut-off valve 263, said pipe 26 entering pipe 23 between the tube and valve 25. Valve 25 is of course closed except when the tube is being cleaned out, in which case valve 26a is closed.

In employing the described apparatus for carrying out the process of the invention, gas oil or the like, most desirably preheated in a preheater (not shown), is fed into each tube unit through pipe 26 until it stands substantially at the lever indicated at 27 in the drawing, or about half fills the lower enlarged portion 16 of each cracking tube. The upper half of this enlarged portion, which may in fact be considered the main cracking and reaction chamber, thus provides a vapor space of substantial volume. The furnace being fired to the proper cracking temperature by means of the ring burners 17, the oil is vaporized in the lower part 16 and passes upwardly through each cracking tube, being subjected meanwhile to the action of the corona discharge maintained between the discharge electrode 18 and the cracking tube walls. The more volatile products leave the cracking tube through outlet pipe 28, which is provided with an adjustably weighted pressurecontrolling valve 29 and a check valve 30. The vapors are led by pipe 28 to al coollng system (not shown) which may comprise a dephlegmator (optionally functioning as a preheater for oil fed to the tube) and one or more condensers of any usual or suitable type. The furnace chamberis of course provided with a suitable stack or chimney 31 for waste fire gases.

The proper tem erature to be maintained in the cracking tu es depends upon various factors including the particular character of oil being treated, the rate of feed, operating pressure on the vapors, etc.; but in any case, as before stated, the temperature should be somewhat below the critical point at which there ceases to be a distinctly perceptible mist or fog in the lower part of the cracking tube. To enable conditions inside the cracking tube to be observed, peep-holes, properly alined in opposite sides of the tube and protected by suitable heat-resistant glass may be provided,

together with a protected opening in the furnace wall through which a strong beam of light produced by a suitable arrangement of electric arc and condensing lens may be projected through the space within the cracking tube. ln the arrangement here shown, a housing 32, centrally located within the furnace and suitably protected from the heat, contains a high power source of light; and

vobservation tubes 33, each alined with peeptubes 33. In the upper part of the converter tubes 18, this mist or fog is found to have nearly or quite disappeared owing to the precipitating or filtering action of the high tension discharge.

What is claimed is:

1. The.- process of converting relatively heavy oils into lower boiling products which comprises vaporizing a relatively heavy oil under conditions such that a substantial part of the resultant vapors is in non-gaseous and substantially saturated condition, and subjecting said vapors, while in operative proximity to a surface heated to a converting temperature substantially above that of vaporization to the precipitating action of ahightension silent electrical discharge tending to drive such non-gaseous part of said vapors toward said heated surface, and conducting the uncondensed products away for recovery of a desired lower boiling product therefrom..

2. The process of converting oil which comprises passing vaporized oil through a converting zone having walls heated to a conf verting temperature substantially above that of vaporization and subjecting such vaporized oil, as 1t passes through said zone to a high tension electrical discharge of the corona type, a substantial part of said vaporized oil existing in the form of visible fog or mist in the converting zone under the conditions of operation, and obtainin .a useful fuel condensate from the volatile products leaving said converting zone.

3. The process oisonverting oil for production o a relatively volatile li uid motor fuel which comprises passing a su stantially `saturatedvaporous mixture of mineral oil hydrocarbons through a walled zone maintalned at a convertin temperature which is above the critical gaslying point of the motor fuel 'to be produced but below the critical gasifying points of materially higher-boiling weavers products, subjecting said vaporous mixture as it passes through mid zone to the precipitating action of a hi h tension silent electrical discharge, where y ungasified hydrocarbon aggregates are driven toward the walls of i@ said zone said walls being maintained at a converting temperature substantially above that at which said vaporous mixture was evolved, and condensing a motor fuel from the volatile mixture leaving said Zone..

4. rlhe process of converting oil into lower f l boiling products, which comprises heating a liquid body of mineral oil to produce vapors therefrom comprising both gaseous and nongaseous constituents said non-gaseous constituents being in substantially saturated vaporous condition, passing the resultant vapors, while still substantially in the presence of said liquid body of oil, through a zone having walls maintained at a convertingpmperature substantially above that at wich said vapors were evolved, and simultaneously passing a high tension silent electrical discharge through said vapors and thereby driving non-gaseous constituents thereof into effective proximity with said walls to effect conversion of said constituents, while lpermitting gaseous constituents to pass through said zone substantially without interruption, and recovering a relatively low boiling condensate from the volatile products leaving the converting zone.

In testimony whereof I hereunto aiiix my signature. JAY J. JAKOWSKY.

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