US2325891A - Manufacture of antiknock gasoline - Google Patents

Description

Aug. 3, 1943. c. K. vlLAND MANUFACTURE OF ANTKNOCK GASOLINE 2 Sheets-Sheet l Filed Oct. 23, 1959 Aug. 3, 1943. c. K. VLAN@ 2,325,891

MANUFACTURE OF ANTIKNOCK \GASOLINE Filed OCT.. 25, 1939 2 Sheets-Sheet 2 TAR PH ODUCT Patented Aug. 3, 1943 UNITED STATES PATENT OFFICE MANUFACTURE OF ANTIKNOCK GASOLINE Clare Kenneth Viland, Martinez. Calif., assignor to Tide Water Associated Oil Company, San Francisco, Calif., a corporation of Delaware Application October 23, 1939, Serial No. 300,727

s claims. (Cl. 196410) desired vapor pressure, such as for example 8 to 10 pounds at 100 F. An alternate method of stabilization commonly employed is to remove from the raw pressure distillate the entire by a combination of cracking, distillation, and 5 amount of light hydrocarbons up to and includpolymerization processes. y ing the butanes and butylenes. From these re- It is the principal object of this invention to moved light hydrocarbons a fraction consisting provide a method whereby vthe antiknock properof butanes and butylenes is separated. A suffities of cracked lgasoline of desired volatility cient quantity of this butanes-butylenes fracspecications may be substantially increased. 10. tion is then blended with heavier hydrocarbons It is also an object of this invention to increase of the pressure distillate to bring the vapor presthe yield of the total gasoline fraction obtainable sure of the latter up to the desired value. by a combination of the cracking and polymer- Until recently the normally gaseous hydrocarization processes. bons resulting from the stabilization of the raw It is a further object of the invention to propressure distillate have found use only as refinery vide a method whereby a thermal polymerization fuel or low priced gaseous fuel. The excess buprocess, operating in conjunction with a cracktane-butylene has been marketed in liquid form ing process, may be operated with greater freeunder pressure as a cheap motor fuel. Recently dom from the formation of polymer tars and it has become common practice to convert a coke resulting in longer periods of continuous large portion of these normally gaseous hydrooperation without shutdowns for cleaning, recarbons into hydrocarbons of the gasoline 4boilpairs, etc. ing range by means of the so-called polymeriza- Other objects will be apparent from the followtion processes. As commonly employed, these ing description. polymerization processes consist briefly in sub- In the manufacture of gasoline motor fuel by jecting the propane, propylene, butanes and buthe so-called cracking processes, wherein high tylenes to temperatures in the range of 1000 to boiling hydrocarbons are converted into lower 1300 F. whereby an increase in the olelnic conboiling hydrocarbons by the application of high tent of the gases is obtained. The gases are then temperatures, with or without pressure, there are subjected to temperatures of about 1000 to 1150 formed large quantities of normally gaseous hyat which temperatures the olefine molecules drocarbons including hydrogen, methane; tend to unite with other olenes to form higher ethane, propane, propylene, butanes, and buboiling molecules most of which are in the gastylenes. Most of these have too high a vapor oline boiling range. However, substantial quanpressure to be included in marketable gasoline. tities of heavy oils are also formed which have a However, the butanes and butylenes have sufiitendency to form coke and thereby interrupt ciently low vapor pressure that a certain percentthe successful operation of the plant. 'I'he forage may be incorporated in the finished gasoline mation of these heavy oils also results in the without raising the vapor pressure cf the nnished degradation to 10W priced fuel Oil of constituproduct above the desired value. ents which might otherwise be manufactured As commonly practiced, in the manufacture 40 into higher priced motor fuel. Bv proper choice of gasoline by cracking processes, the products of constituents fed to the polymerization process, resulting from the cracking operation are first the formation of these heavy oils can be greatly fractionated to obtain a raw pressure distillate reduced with a resulting higher overall yield of of the desired end boiling point, a gas oil fracthe desired motor fuel. tion Which iS generally recycled t0 the Cracking 45 According to the present invention a segregaoperation, and a residual fuel oil. The raw prestion of the constituents of the normally gaseous sure distillate is then stabilized by fractional hydrocarbons is made in such a manner that the distillation to remove the propane and lower portions blended with the stabilized pressure disboilng constituents as well as suicient of the tillate to provide the desired vapor pressure are butanes and butylenes to leave a product of the those of the highest antiknock quality and at the same time the constituents charged to the polymerization operation are adapted to provide maximum yields of polymerized gasoline fractions and maximum freedom from operating troubles in the operation of the polymerization plant.

Briefly, the invention may be described by reference to Figure 1 which is a schematic flow diagram of the process'. Hydrocarbon oil to be cracked for the production of motor fuel is charged through line I into a cracking still,

which is represented by cracking coil 2, wherein the oil is subjected to such temperature conditions, with or without the aid of pressure or catalysts, as to convert a substantial portion of the oil into lower boiling hydrocarbons. Such temperature may vary between 800 F. and 1300" F., depending upon the reaction time and type of charging stock as is well known in the art. The products of the cracking operation enter fractionating zone 3 which may consist of one or more fractionating towers, a series of stills, or any other suitable fractionating equipment. In the fractionating zone the products are fractionated into a plurality of fractions represented as leaving the zone through lines l, 5, 5, 1, 8, 9. I0, and Il, in their respective order of volatility. 'I'he lightest fraction is composed oi' hydrogen, methane, and such other light fractions which are unsuited for either blending into gasoline or for polymerization. Ordinarily this fraction will include substantially all hydrocarbons which are more volatile than propylene. This fraction leaves the fractionating zone through line 4 and is used as fuel gas or otherwise disposed of. The next lighter fraction leaves the fractionating zone through line 5 and consists essentially-of propylene and propane which is well adapted as charging stock for the cracking furnace of a polymerization plant. The third fraction consists substantially of isobutane which leaves the fractionating zone through line 5. According to the in- Vention this fraction is used as an important blending agent in the finished gasoline. It is therefore passed to storage in the gasoline storage tank 20. The next heavier fraction consisting substantially of butylenes leaves the fractionating zone through line 1. According to the invention this fraction is preferably used for charge to the polymerization plant in a special way resulting in increased yields of polymer gasoline. The fourth fraction, consisting substantially of normal butane, leaves the fractionating zone through line 8, and is added to the finished gasoline in gasoline storage tank 20. The fraction leaving through line 9 is the main cody of cracked gasoline and comprises the remaining components of the cracked products which are desired in the finished gasoline. This fraction is likewise passed to the gasoline storage tank. A gas oil or recycle fraction is withdrawn through line I0 and is introduced with fresh charge entering the cracker through line I, or, if desired. this fraction maybe wholly or in part disposed of in any suitable manner. The residuum from the cracking is discharged from the process through line I I.

' of the butanes-butylene fraction (i. e. isobutane) It may be seen that the gasoline made by the process described above is composed of raw pressure distillate of the desired end boiling point which has been stabilized by the removal of propane and lighter hydrocarbons together with the or by eliminating a proportional part of all the butanes butylene fraction. This is clearly brought out in the following Table l showing the octane ratings of the constituents of this fraction:

TABLE 1 Vapor pressure Octane number Hydrocarbon F. pounds per A. S. 'l. M.- square inch D357-37'l Iso-butane 73 09 Butylenes L 63 Si N butane 52 i nl When it is realized that the octane number of the total cracked gasoline is about '70, it is clear from Table l that a greater gain in octane number for a given increase in vapor pressure is realized by the addition of either isobutane or normal butane to the cracked gasoline than by the addition of butylene.

The propane-propylene fraction in line 5 together with the butylene fraction in line 'l may be passed to a polymerization plant, which may be of any type including the use of catalysts if desirable. When using the thermal polymerization process, to which the invention is preferably directed, it has been found that the yield of polymer gasoline obtained by subjecting butylenes to pyrolysis, or cracking, and polymerizing the products is far in excess of the yield obtainable from the same quantity of isobutane or butane under the same operating conditions. Thus, in eliminating the butylenes as blending stock for the cracked gasoline there is obtained a material which, while less suitable as a blending stock, is more desirable for use in the polymerization process. 'I'his is more clearly brought out in the following Table 2, which shows results obtained in a conventional thermal polymerization process when subjecting mixtures of these hydrocarbons to pyrolysis and polymerization:

TABLE 2 Yields ,from pyrolysis and thermal polymerization While the propane-propylene fraction may be mixed with the butylene fraction and the mixture charged to the pyrolytic coil of the polymerization process, or if desired, directly to the polymerization zone, the invention comprehends a novel utilization of the two fractions whereby optimum operating conditions may be obtained from the polymerization process. This feature is shown in Figure l. The propane-propylene fraction in line 5 is conducted into a cracking or pyrolytic coil I2 maintained at a temperature sufficient to substantially increase the olefinic content of the fraction. Temperatures of the order of 1000 F. to 1300 F. are satisfactory for this purpose. However, since the fraction consists mainly of propane and propylene, higherl temperatures may be used than in the case where butanes and butylenes are present.

For this purpose a temperature range between 1125 and 1300 F. is preferred to obtain optimum oleflnie content of the vapors and gases discharged from pyrolytic coil. The

gases issue from pyrolytic coil I2 through line I3. At this point the butylenes in lineHI may be introduced. 'The effect of introducing the butylenes at this point is to cool the vapors and gases issuing from coil I2 to a temperature suitable for polymerization and simultaneously to heat the butylenes to the polymerization temperature which may be from 1050 to 1150 F., a temperature of about 1100 F. being preferred. The mixture of vapors and gases in line I3, being at the desired temperature, is passed to polymerization zone I4 which may be in any desired form such as a coil or a chamber The vapors and gases remain in zone I4 sufficiently long to produce a substantial quantity of hydrocarbons boiling within the gasoline range or socalled Polymer gasoline. They then pass from zone I4, through line I5 into fractionating zone I6 wherein they are fractionated to produce a polymer gasoline which passes from the zone through line I9 to tank 20. The over polymerized or heavy oily fractions, undesired for gasoline. are removed through line I8, and the lighter fractions through line I'I. The lighter fractions may be recycled through the process or otherwise disposed of as desired.

It is obvious to those versed in fractional distillation that absolute separation of iso-butane, butylenes, and normal butane into pure hydrocarbons is not generally commercially obtained, and that the fractions in lines 6, 1, and 8 will not generally be pure isobutane, pure butylenes, and pure normal butane respectively. Absolute fractionation is not essential to the successful operation of the process. The invention comprehends fractionation where the amount of the desired hydrocarbon recovered in each fraction is at least 75% of the amount of that hydrocarbon present in the charge to the fractionating zone.

It is also obvious that, if desired, the operation of fractionating zone 3 may be so conducted that the products obtained in streams 8 and 9 may be obtained in a single stream. Thus, the normal butane and the heavier components of the cracked gasoline may be fractionated in a single stream Without departing from the spirit of the invention.

It will be apparent that at times the vapor pressure desired in the nished gasoline may be somewhat below that obtainable when blending the entire amounts of the isobutane and normal butane fractions. Under such conditions less amounts of these fractions should be used. The invention, however, contemplates that at least 75% of the total isobutane and normal butane present in the products of cracking shall be included in the finished gasoline.

The advantages of the entire system may be summarized as follows:

(al The finished gasoline is brought up to the -desired vapor .pressure by blending constituents v` which arel of highest octane rating and which are least suitable for polymerization.

(d) Higher temperatures may be used in the pyrolytic or decomposition stage of the'polymerization process resulting in vhigher yields of olenic'l vapors` and gases vfrom the propane charge, because the butylenes are not cracked therein.

(e) The temperature of the vapors and gases from the pyrolytic stage of the polymerization process is reduced to the desired amount for polymerization without the loss of heat.

(j) Butylene, used as a quench material for the pyrolized propane fractions is not subjected to undesirable pyrolysis, but is charged directly to the polymerization zone and thus assists materially in obtaining maximum gasoline yields.

(y) Yields from polymerization utilizing optimum temperatures in the pyrolytic and reaction zones as more fully described below in the preferred form of the invention may be as much as of the normal yields indicated in Table 2.

(h) Conversion per pass through the equipment may be increased by as much as 20% compared to optimum conditions under conventional operation when employing the preferred form of the invention, thereby increasing capacity of the plant or reducing the size of equipment required for a given amount of product.

Figure 2 illustrates apparatus suitable for car.- rying out a preferred form of the invention, it being understood that in both figures valves are to be inserted at any and all parts of the system for maintaining a desired or necessary pressure, or oW. Gas and cracked gasoline from an oil cracking process enters gas separator 22 through line 2|. Gas is removed from the separator 22 through line 23 andenters absorber 24 where it is stripped of substantially 4all propylene and heavier hydrocarbons and the stripped or xerl gas consisting essentially of ethane and lighter hydrocarbons is withdrawn from the system by line 25. Absorption' oil enters the absorber by line 23 through heat exchanger 2'I and cooler 28 and rich oil leaves the absorber by line 29 after .absorbing substantially all propylene and heavier hydrocarbons. The absorption oil is pumped through line 29, through heat exchanger 21 into still 30, where the propylene and heavier constituents contained in the cracked gas are distilled overhead into line 3| and injected into stabilizing column 32, into which is also charged the unstable gasoline from separator 22 by means f of line 33. Stabilizer 32 is operated at such pressure and temperature conditions that the overhead distillate in line 34 consists essentially of propylene, propane, and iso-butane hydrocarbons which are passed into tower 35 for *further fr'actionation removing overhead a propylene-propane fraction through line 36 which is liquefied in cooler 3'I and passed into tank 38. Any uncondensed vapors are vented from tank 38 through line 39 and reprocessed in absorber 24. Liqueed propylene-propane in tank 38 is charged by means of pump 40 into pyrolysis or cracking furnace 4I. Obviously a preheater may be used in conjunction with the pyrolysis or cracking furnace if desired. The bottom product from the stabilizing column 32 which product contains substantially all the butylenes and heavier hydrocarbons is charged through line 42 into fractionating column 43. Column 43 is operated at such pressure and temperature conditions that the gasoline is stripped of substantially all butylenes and the stripped gasoline, consisting of substantially al1 normal butane and heavier hydrocarbons, leaves the column through cooler 44 and line 45 and is passed into gasoline product receiving tank 4 6. The overhead product from tower 43, consisting of a butylene fraction, is removed by lne 4l and condensed in cooler 48 and passed into tank 49. Any uncondensed vapors are vented from tank 49 through line 50 and reprocessed in absorber 24. The liquefied butylene fraction is pumped by means of pump 5| into the stream of pyrolized fractions in line 52 from furnace 4|. The butylene fraction entering line 52 may or may not be heated in heater 53 before comingling with the pyrolized fraction, depending upon quantity and temperature of the butylene fraction, but in any case enters line 52 at temperatures substantially below cracking or polymerizing temperatures. The temperature of vthe pyrolized fractions leaving furnace 4| is so adjusted that the final temperature at the inlet to reaction zone 54 after admixture of the butylene fraction in line 52 is at the desired polymerization temperature without the further addition of heat.

Generally it has been found desirable from the standpoint of obtaining optimum polymer gasoline yields in a conventional thermal polymerization plant to adjust the temperature of pyrolized vapors and gases leaving the pyrolysis furnace between the limits of 1125 to 1200 F. or such temperatures depending upon the time conditions in the cracking or pyrolysis zone so that the total volumetric furnace throughput including unconverted recycle fractions when compared with the net fresh liquefied gas charge obtainedrfrom the oil cracking process through line 2| is in the ratio of between about 5 to 1 and 9 to 1. The maintaining of such furnace recycle ratios is an important factor in preventing excessive formation of incondensible gas, coke, and tars to the detriment of gasoline yields and length of runs obtainable before the plant must be shut down and cleaned out.

Under conditions of the preferred form of the invention it is now possible to increase the conversion per pass in the cracking or pyrolysis zone preceding the polymerization step by increasing conversion temperatures by 5 to 25 F. when quenching with the butylenes fraction before subjecting the combined stream to polymerization conditions so that the throughput ratio in the polymerization zone expressed as liquid volume of total charge including recycle fractions divided by the liquid volume of the fresh feed derived from the oil cracking process may be reduced to between 4 to 1 and` 7 to 1 thereby increasing throughput considerably while also obtaining greater gasoline yields. In other words, due to the novel process herein not only is there less stock available for recycling due to greater conversion into valuable gasoline fractions but there is less recycle stock used which materially increases the capacity of the polymerization zone for increased yields.

The temperature of the commingled pyrolized propane-propylene fractions at the inlet to zone 54 may be from 1l25 to 1200 F., depending upon the charging stock and the type of polymers desired, and a temperature of about 1050 to 1150 F. within the reaction or polymerization zone is preferred. The liquid polymers and gaseous fractions leaving zone 54 are treated by wellknown methods for separation of liquid polymers and for recovery and recycling to furnace 4|, or reaction zone 54, the normally gaseous liquefiable hydrocarbons which were unconverted in the process.

This may be further exemplified by passing such reaction products from zone 54 through line into fractionating tower 56 which is operated at such temperatures and pressures that a substantial portion of the butanes and lighter hydrocarbons are removed overhead in line 5l and passed back into absorber 24 for separation and rejection of xed gases formed in the process. The bottom product from tower 56 containing the polymer gasoline, tar and the remainder of the C4 and lighter hydrocarbons is cooled in cooler 58 and a portion returned by means of line 59 back into line 55 as a quenching medium to stop the reaction obtained in zone 54.\ The remainder is passed through line 60 into to\wer 6| where all C4 and lighter hydrocarbons are removed overhead through line 62 and cooler 63 and receivedr into tank 64. The uncondensed vapors from tank 64 are vented by line 65 back into absorber 24 for reprocessing and the condensate removed by line 66, if consisting largely of propylene and propane, may be injected by pump 61 through line 68 back to pyrolysis furnace 4| or, if operating conditions are such that the condensate in line 66 contains substantial amounts of butanes and butylenes, the condensate is passed through line B9 back into line 2| and separator 22 for reprocessing in the gas fractionating system. The bottom product from tower 6| comprising the stable polymer gasoline and polymer tars is passed through line l0 into fractionating tower 1| where polymer gasoline is removed overhead through cooler `|2 and line 13 into gasoline product tank 46. Polymer tars leaving tower are cooled in cooler '|4 and passed through line 15 into tar product receiving tank '|6.

Returning to tower 35 in which was processed the propylene-propane-isobutane fraction previously mentioned, the bottom product comprising substantially all the isobutane is cooled in cooler 'l'| and passed by means of line 'I8 into gasoline product ytank 16 which then contains the (a) normal butane and all heavier gasoline products from the cracking operation first mentioned together with any normal butane produced by thermal polymerization of propylene, propane or butylenes; (b) the polymer gasoline product obtained by thermal polymerization of propylene, propane, and butylenes; and (c) the isobutane fraction contained in the original cracked gas and gasoline together with any isobutane produced by thermal polymerization of propylene, propane, or butylenes.

The advantages to be gained by the invention from the combined operation of a cracking and polymerization plant to produce a finished gasoline of suitable vapor pressure, such as 9# Reid vapor pressure, is clearly shown by the example given in Table 3, wherein the total yield and octane number of stabilized gasoline obtainable from a typical unstabilized cracked gasoline when operating under optimum conditions in conventional methods is compared to the total yields and octane number obtainable from the pre ferred form of the invention as outlined above in the description of Figure 2. It will be noted that, for every 1000 barrels of cracked products available for the production of finished cracked and polymer gasoline, operation under the invention results in an increased yield of 22 barrels of finished gasoline having an enhanced octane rating of 0,5 octane number over that obtainable under good practice with conventional operation. This increased yield and octane number obtainable according to the invention is equivalent to the addition of 22 barrels of 92.7 octane gasoline to the gasoline produced under conventional operation.

Due to the variations in composition of ycracked distillates and accuracy of renery fractionation TABLE 3 With conventional stabilizing Improved operation of sta- C H t plant charging all C; and bihz ing and thermal polyons l ein s 50% of C; fraction to thermerlzatlon plants for promesa tn mal olymerization plant duing 9# gasoline as de. a' to ma e 9# gasoline scribed crekedlgas an 888 me' Barrels Barrels Total Barrels Barrels Total barrels polymer cracked barrels polymer cracked barrels gasoline gasoline gasoline gasoline gasoline gasoline P o lene 28 14 14 17 17 I, Pognem- 86 26 26 3l 31 Isobutane-. 16 3 8 l1 16 16 Butylenes.. 52 16 26 42 37 37 N. butano 46 9 23 32 46 46 Iso-pentane and heavier. 772 772 772 772 772 Total 1,000 68 829 897 85 834 919 Va or ressure 100 F pounds.. 9 9 OctjauepNo. (A. S. T. M. method D-357-37T) 71.8 72. 3 Increased yield per 1,000 barrels cracked products, producing same 22 vapor pressure gasoline Increased octane number of total gasoline of same vapor pressure 0.5 Equivalent blending octane number of the 22 barrels increased production if mixed with conventional production 7 In the example shown in Table 3 the operating conditions of the various units were chosen so as to give optimum yields with minimum production of tar and coke. Such conditions are shown in Table 4.

TABLE 4 Conventional Preferred Charge operation operation Total fresh liquefiable gas charge to process barrels 1000 1000 Total furnace throughput do. 5500 4750 Total iiaction addel cgtolpolylnieriation zone containin 5 u y enes g tamis.. o 25o 4o Total throughput ratio 5. 5:1 5:1

Convem Preferred Yield tional o eration operation p Polymer gasoline .barrels. 415 455 Polymer tars do 35 30 Residue gases MCF-. 1400 1240 O eratin conditions Ctoiloliln- Prefmed p g operation operation Temperature pyrolysis furnace out F 1130 1150 55 Temperature reaction zone out- ".F" 1085 1025 Temperature butylenes to reaction zone F 650 Pressure furnace out pounds.- 500 500 Pressure reaction zone out do. 450 450 when the typicai Cracked distinate shown in Table 3 is stabilized according to the present invention, with the elimination of the butylenes and the retention of the iso-butane and normal butane, a stabilized cracked gasoline results which has the following composition:

Per cent by volume the composition of cracked gasoline stabilized according to the invention will normally fall within the following limits:

Per cent by volume While the invention is primarily directed to the manufacture of gasoline Within specification limits customarily employedin carbureted automotive engines and such is, the preferred embodiment, the invention is not restricted to such and the term ,gasoline used in the appended claims should be construed to include any normally liquid mixture suitable for use as a fuel for internal combustion engines of the carbureted type. The terms propane-propylene fraction, isobutane fraction," butylenes fraction, and normal butane fraction are used to indicate fractions predominating in the respective hydrocarbons named and containing at least of the respective hydrocarbons available in the stock subjected to fractionation.

Itis thus seen that the herein described operations comprise two methods of producing a lfinished gasoline `of overlapping boiling ranges either of which `provide a motor fuel of increased octane number and the products of which, when blended as in -a continuous renery operation, not only provide a finished gasoline of increased octane number, but alsoa'greatly increased yield ofsuchgasoline having a required vapor pressure.

I claim as my invention:

1. A process of producing gasoline which comprises: removing from a mixture of normal butane, butylene. iso-butane, propane and propylene, the major portion of its normal and isobutane content and the major portion of its butylene content, leaving a mixture of hydrocarbons consisting mainly of propane and proof olenic content, adding a fraction consisting mainly of butylene to the mixture after passage through said zone, subjecting the combined stream to conditions effecting combination of molecules therein, then fractionating the mixture to recoverka product of gasoline boiling range.

2. A process of producing gasoline which comprises: removing from a mixture 'of normal butane, butyiene, iso-butane, propane and propylene, the major portion of its normal and isobutane content and the major portion oi its butylene content, leaving a mixture consisting mainly of propane and propylene, flowing same through a cracking zone while at a temperature between about 1125 F. and 1300 F. for suflicient time to increase the percentage of olenes therein, re-mixing the fraction consisting mainly of butylene with the cracked product after passage through the cracking zone, passing the mixture through a thermal zone at a temperature of about1050 F. to 1130 F. suiiicient to effect combination of molecules therein,then fractionating the mixture and recovering a product of gasoline boiling range.

3. A process of producing gasoline which comprises: removing from a mixture of normal butane, butylene, iso-butane, propane and propylene, the major portion of its normal and isobutane content and the major portion of its butylene content, leaving a mixture consisting mainly of propane and propylene, flowing same through a cracking zone While at a temperature between about 1125 F.- and 1300 F. for sufiicient time to increase the percentage of olenes therein, re-mixing the fraction consisting mainly of butylene with the cracked product after passage of the latter through the cracking zone, passing the mixture through a thermal zone at a temperature suiiicient to eiect combination of molecules therein but below the cracking temperature of butylene, and fractionating the mixture to recover a product' of gasoline boiling range.

CLARE KENNETH VILAND.

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