US2220696A - Treatment of hydrocarbons - Google Patents

Description

Nov. 5, 1940. K M. WATSQN 2,220,696

TREATMENT oF HYDRocARBoNs Filed Aug. 20, 193s Patented Nov. 5, 1940 UNITED STATES TREATMENT or HYDRooARBoNs Kenneth M. Watson, Chicago, vIll., assignor toV Universal Oil Products Company, Chicago, 111 a corporation of Delaware Application August 20, 1938, Serial No. 225,920

1 Claim.

This invention refers to an improved apparatus and process for the pyrolytic conversion of hydrocarbon oils whereby to produce therefrom a motor fuel of higher volatility and better antiknock rating than that normally produced vby conventional methods and means of cracking.

More particularly, the invention is concerned with an improved method and means of controlling fractionation in a cracking system whereby the average volatility of the gasoline produced is materially lowered and its antiknock value improved without materially altering its initial or end boiling points.

From experience I have found that the motor fuel produced in a selectivecracking operation (i. e., a cracking operation wherein light and heavy oils are cracked in separate coils under independently controlled conditions) is of higher average volatility and higher octane number than that produced in a single coil operation employing the same charging stock and producing a gasoline product of the same end-boiling point. 'Ihe volatility of the product is ordinarily judged by the temperature reached in an Engler distillation when the rst 50% of the sample has been distilled over. The higher the 50% boiling point the lower the average volatility and vice versa.

Also, relatively low volatility generally indicates tems operated for the production of gasoline, to

return regulated quantities of the gasoline produced to the upper portion of the fractionator, wherein separation of the desired gasoline product from the heavier components of the vaporous conversion products is accomplished, for the purpose of assisting fractionation, the recycled gasoline serving as a reuxing medium and as a means of controlling the vapor outlet temperature from the fractionator and hence the endboiling point of the gasoline product. In the process herein provided, this method of controlling the top temperature in the fractionator and thus controlling the end-boiling point of the gasoline is preferably employed, although any other well known method may be substituted, when desired, and in addition I provide for returning regulated quantities of the gasoline 60 product to an intermediate point in the fractionator. This additional step functions, in cooperation with the reaction accomplished in the cracking zone of the'system, to increase the av- V,erage volatility of the gasoline recovered and increase its Vantiknock-value by increasing the relative proportion of low-boiling fractions in the gasoline. This may be accomplished without decreasing its end-boiling point and Without inateriallydecreasing the quantity of gasoline produced In some cases it may result in an appre- 5 ciable increased yield of gasoline.

Byin'troducing a regulated portion of the recirculated gasoline to an intermediate point in the fractionator, the temperature of the vapors undergoing fractionation above this'intermediate 0 point-of introduction is decreased and consequntly more refluxing liquid is condensed from the vapors. Thus a smaller amount of gasoline y recirculated to the upper portionof the frac- -tionator will produce the same vapor'outl'et'tem- :l5y

perature from thiszone as compared with a conventional operation-'wherein all of the recycled gasoline is supplied to the upper portion of the fractionator.- Consequently, the total mount o f u gasoline recirculated to both the upper and the gd" intermediate portion of the fractionator need notbe materially'increased ascompared with conventional practice. Since the lower, vas well j as the-upper portion of the fractionator is operatedata lower temperature as compared with 25" conventional practice, due to this additional intermediate cooling, less reboilin'gv or stripping of the reflux condensate supplied to the cracking coil'isaccomplishedand the latter will contain a considerable'quantity of heavy gasoline frac- 30 tions which, upon being recycled through the cracking zone of the system, will be converted intoadditional yields of lower boiling gasoline fractions, thus'increasing both the antiknock v value and volatility of the gasoline recovered as 35 the nal product.

Due to the inclusion `of substantial quantities of heavy gasoline fractions in the combined feed supplied to the'cracking coil of the system, some- ,i what more severe cracking conditions than would 40 otherwise be utilized for the same raw oil charging stock-are preferablyemployed and this will,

` in manyv cases, serve to appreciably increasethe yield, as well as the quality of the gasolinel recovered. 45

By employing lthe features of the invention, one may produce in a `single coil cracking system, a vgasoline comparable in volatility and antiknock value to that ordinarily produced in a selective or multiple coil cracking system. Thus, 50V one of the most important advantages of the selective or multiple coil type of cracking system may be obtained ina smaller and less expensive installation. One specificl embodiment of the invention com- 55'* prises cracking reflux condensate, produced as hereinafter described, at elevated temperature and substantial superatmospheric pressure in a heating coil and communicating enlarged reaction chamber, introducing the resulting vaporous and liquid conversion products into a reduced pressure vaporizing and separating chamber wherein said liquid products are appreciably further vaporized, recovering the resulting nonvaporous residue, supplying said vaporous products and the evolved vapors from the vaporizing and separating chamber to a fractionating zone, condensing from the vapors in the fractionating zone, as said reflux condensate, components thereof which boil above the range of the desired gasoline product and a substantial quantity of fractions boiling within the range of gasoline, removing fractionated vapors of the desired endboiling point, consisting of materials boiling within the range of gasoline and normally gaseous products, from the fractionating zone, subjecting the same to condensation, separating the resulting condensed gasoline from uncondensed and undissolved gases, returning a portion of said gasoline to the upper portion of said frac- -tionating zone in quantities regulated to maintain the desired vapor outlet temperature from this Zone, returning another portion of said gasoline to an intermediate point in said fractionating zone in quantities regulated to reduce the ytemperature in the fractionator and materially increase the quantity of gasoline fractions included in the reflux condensate supplied therefrom to said heating coil.

Although the features of the invention are "particularly advantageous as applied to a single coil cracking system, such as described in the preceding paragraph, of the full flashing or series-chamber type operated for the production of end-point gasoline, they may be utilized to advantage in practically any type of cracking system operated for the production of either end' point gasoline or a lower boiling or a higher boiling distillate product. The application of the features of the invention to other specific types of cracking systems will be readily apparent to those familiar with the cracking art and obvious departures from the modifications to thespeciflc embodiment of the invention above described are entirely within the scope of the broader features of the improved process herein provided.

The accompanying diagrammatic drawing illustrates one specific form of apparatus embodying the features of the invention and in which the process of the invention may be successfully conducted.

Referring to the drawing, heating coil I is disposed within a furnace 2 by means of which the required heat is supplied to the commingled oils passing through the heating coil to bring them to the desired cracking temperature, preferably at a substantial superatmospheric pressure.

The highly heated products are discharged from coil I through line 3 and valve 4 into reaction chamber 5, which is also preferably maintained at a substantial superatmospheric pressure and wherein appreciable continued cracking of said conversion products and particularly their vaporous components is accomplished. Chamber 5 is preferably insulated to conserve heat, although insulation is not indicated in the drawing.

In the'particular case here illustrated, both ,vaporous and liquid conversion products pass through substantially the entire length of the reaction chamber and are directed in commingled state from the lower portion of this zone through line 6 and valve 'I to vaporizing and separating chamber 8.

Chamber 8 is preferably maintained at a substantially reduced pressure relative to that employed in chamber 5 by regulation of valve 'I in line 6, and the reduction in pressure between these two zones is suiicient t'o effect substantial further vaporization of the liquid conversion products supplied to chamber 8, whereby they are reduced to a non-vaporous residue of the desired characteristics. Separation of vapors from non-vaporous residue is accomplished in chamber 8 and provision is made for removing residual liquid from the lower portion of the latter zone through line 9 and valve I0 to cooling and storage or elsewhere, as desired.

The vaporous products supplied to and evolved in Vchamber 8 are directed from the upper portion of this zone through line II and valve I2 to fractionation in fractionator I3. Fractionation is so controlled in fractionator I3, as will be later described, that substantially all of the com-- is made, as will be later described for including in said reux condensate a substantial quantity of fractions boiling within the range of the overhead vaporous products removed from this zone and, particularly, relatively high-boiling components of this product.

The total reux condensate formed in fractionator I3 is, in the case here illustrated, directed from the lower portion of fractionator I3 through line Ill and valve I5 to pump I6 by means of which it is supplied through line I'I and valve I8 to the cracking treatment, previously described, in heating coil I.

The charging stock for the process which may comprise any desired type of hydrocarbon oil suitable for cracking is directed from storage or elsewhere, as desired, through line I9 and valve 20 to pump 2I by means of which it may be supplied, all or in part, through line 22, valve 23 and line I1 directly to heating coil I for cracking treatment or, when desired, a regulated portion or all of the charging stock may be directed from pump 2I through line 22' and valve 23 into fractionator I3, entering this zone at one or a plurality of suitable intermediate points therein and being directly commingled in the fractionator with the relatively hot vapors undergoing fractionation therein, whereby the charging stock is preheated and assists cooling and fractionation of the vapors. In case the charging stock contains no substantial quantity of material boiling within the range of the desired light distillate product of the process, substantially all of the charging stock supplied to fractionator I3 will commingle in this zone with the reflux condensate formed therein and will be supplied therewith, in the manner previously described, to cracking treatment in heating coil I. In case the charging stock contains substantial quantities of materials boiling Within the range of the desired light distillate product, v

lili

densa-tien and cooling in condenser 26. The reaeaoige Y Fractionated vapors of the desired end-boiling point which, in vaccordance with the preferredA embodiment ofthe invention, will consist of gasoline vapors and normally gaseous products, are directed from the upper Vportion of fractionator I3 lthrough line 24 and valve 25 to `consulting distillate and uncondensed gases are directed through line 21 and valve 28 to collection and separation in receiver 29. The gases which remain uncondensed and undissolved in the distillate are released from the receiver through line 30 and valve 3l. The distillate product is removed from receiver 29 through line 32 and valve 33 to storage or to any desired treatment.

Regulated quantities ofthe distillate product collected in receiver 29 are directed therefrom vthrough line 34 and valve 35 to pump 36 by means of which they are fed through line 31 and directed, in part, through valve 38 in this line to the upper portion of fractionator I 3 and, in part, through line 39 and valve 40 to an intermediate point in fractionator I3. Although not illustrated in the drawing, regulated quantities of the recirculated distillate may, when desired, be introduced into fractionator I3 at more than one intermediate point therein. The quantity of distillate recycled to the upper portion of fractionator I3 is regulated to control the temperature of the fractionated vapors leaving this zone through line 24 and thus control the end-boiling point of the distillate product. The additional quantity of distillate supplied to the intermediate section of the fractionator I3 is regulated to control fractionation and decrease re- 40 boiling or stripping of the reflux condensate in the lower portion of the fractionator whereby a substantial quantity of relatively light materials corresponding to the heavy components of the distillate product are included in said reilux con- 45 densate and subjected therewith to cracking treatment in coil I.

The preferred range of operating conditions which may be employed to accomplish the desired results, in an apparatus such as illustrated 50 and above described, may be approximately as follows: As previously mentioned, the cracking conditions employed are preferably somewhat more severe than those which would normally be employed for the same charging stock in a 55 cracking system of the same general type but incorporating the features of the invention. The severity of the cracking conditions may be increased by employing a higher temperature or higher pressure in the cracking zone or by providing for more prolonged cracking time in the heating coil and/or reaction chamber or by any desired combination of increased time, temperature and pressure. As an example, when the charging stock is a relatively heavy oil such as topped crude or the like, the temperature employed at the outlet of coil I may be some 10 to 20 degrees higher than that which would ordinarily be employed for the same cracking stock in a similar type of cracking system wherein distillate is not recycled to an intermediate point in the fractionator. Depending upon the type of charging stock employed, this temperature may range, for example, from 850 to 1050 F., or more, and the superatmospheric pressure preferably employed at the outlet of the heating coil may range, forfexampla'from 150 to-1000 pounds, ormore, per squarel inch. .The reaction chamber may employ a superatmospheric pressure.

substantially the-same orsomewhat lower than that prevailing at theoutlet of the heating coil and a substantially reducedpressure ranging, for example,j fromv 100 pounds, or thereabouts, per` square inch downto substantially atmosphericpressure may be employed in the succeeding; vaporizingand separating chamber. The

pressure employed in. thev latter zone may be.

substantially equalized or reduced in the fractionating, condensing and collecting portions of the system.

As an example of one specific operation of the process herein provided as it may be conducted in an apparatus such as illustrated and above described: The charging stock is a Mid-Continent topped crude of about 25 A. P. I. gravity which is supplied, together with the reflux condensate from fractionator I3, to heating coil I and therein heated to an outlet temperature of approximately 930 F. at 4a superatmospheric pressure of about 375 pounds per square inch. The resulting heated products are supplied to reaction chamber which is maintained at substantially the same pressure and the total resulting vaporous and liquid products are supplied from the reaction chamber to vaporizing and separating chamber 8 which is operated at a superatmospheric pressure of approximately 50 pounds per square inch. Substantially the same pressure is employed in fractionator I3 and in the succeeding condenser and receiver. The process is operated for the production of 400 F. end-point gasoline and approximately 120% by volume of the gasoline recovered as a final product is recycled to the fractionator. Approx-l imately 50% of the recycled gasoline is supplied to the upper portion of fractionator I3 and the remainder is supplied to an intermediate point in this zone.

The yield of 400 F. end-point gasoline produced in the above described operation is substantially the same as that produced from the same charging stock in the same cracking system when none of the gasoline product is recycled to an intermediate point in the fractionator, the other operating conditions being the same except that the temperature employed at the outlet of the heating coil in the conventional operation is approximately 920 F. and the pressure employed at this point in the system and in the succeeding reaction chamber is approximately 350 pounds per square inch. However, the gasoline produced in the operation rst described, has an octane number some two points higher than that produced in the conventional operation .and its 50% boiling point is approximately 20 degrees lower.

I claim as my invention:

In a cracking process wherein a hydrocarbon oil charging stock heavier than gasoline is cracked to produce substantial yields of gasoline and heavier fractions, the resulting vaporous conversion products separated from non-vaporous residual conversion products, the vapors fractionated to condense therefrom as reflux condensate substantially all of the components boiling above the range of gasoline and the fractionated vapors condensed to form an overhead dlstillate product, the improvement which comprises. returning a portion of said overhead distillate to the upper portion of the fractionat:

ing zone in quantities regulated to so control the temperature of the overhead vaporous stream cracking of said charging oil and heavier fractions of the reflux condensate to produce additional yields of gasoline, the process being further characterized in that the fty per cent boiling point of the nal gasoline product is materially lower than that which Would result from the same operation Without returning any portion of said overhead distillate to said intermediate point in the fractionating zone,

KENNETH M. VATSON.

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