US2069847A - Process of improving the antidetonating quality of gasoline - Google Patents

Description

A. E. PEW, JR

Feb. 9, 1937.

PROCESS OF IMPROVING THE ANTIDETONATING QUALITY OF' GASOLINE Filed May 20, 1952 Patented Feb. 9, 1937 PATENT OFFICE PROCESS 0F mROVING THE ANTIDETO- NATING QUALITY 0F GASOLINE f Arthur E. Pew, Jr., Bryn Mawr, Pa., assigner toA Sun Oil Company, Philadelphia, Pa., a corporation ol' New Jersey Application May 20, 1932, Serial No. 612,393

5 Claims.

The present invention relates to a process for improving the antidetonating qualities of a straight run gasoline and more particularly to a process for improving those qualities by heat treatment while admixed with heavier or higher boiling hydrocarbons.

In my co-pending application Ser. No. 584,581, 'led January 2, 1932, I describe a process for improving the anti-knock qualities of a lower boiling portion of straight run gasoline byheat treatment alone. In the process described in that application the anti-detonating qualities are improved by subjecting the gasoline to a temperature just above sufficient to eect such molecular rearrangement of certain hydrocarbons that have inferior or no anti-knock characteristics or that may promote or induce knocking as to produce other hydrocarbons having relatively good anti-knock characteristics, while avoiding the conversion or decomposition of all or most 1 of the hydrocarbons having good anti-knock ities.

characteristics. What occurs in the process is, it is believed, mainly an intra-molecular rearrangement as distinguished from that inter-molecular rearrangement which is characteristic of cracking. An example of what is believed mainly occurs in this process is the conversion of normal octane, which has very low anti-detonating qualities, to one of its isomers, such as trimethyl pentane, which has very high anti-detonating qual- Other hydrocarbons contained in a lower boiling portion of straight run gasoline are subject to similar intra-molecular rearrangement.

I have discovered that itis-highly advantageous to practice the described heat treating process in conjunction 'with the heat treatment of other and substantially higher boiling hydrocarbons, as hereinafter described. The improved process not only effects the described molecular rearrangement ment in anti-detonating qualities, but it improves the straight run gasoline fraction ln other respects, such as a very material reduction of gum forming constituents, making it in various respects a greatly improved motor fuel or motor fuel constituent.

The improved process is also applicable, in the case of certain crudes, to the heat treatment of the whole, instead of the lower boiling portion, of gasollne,.although in such case the higher boiling portion of the gasoline may' or may not be more or less cracked with improvement, in either case, of its anti-detonating qualities.

5g The preferred way of practicing the process is with accompanying improve- (Cl. 19a- 50) to subject the straight run gasoline, or gasoline fraction, while in admixture with a relatively high boiling hydrocarbon, preferably fuel oil. which cracks at a relatively low` temperature, to

such heat treatment as will effect, simultaneous- 5 ly with the molecular rearrangement of the gasoline, a moderate or limited cracking of the fuel oil; in other words, to heat-treat straight run gasoline while in admixture with fuel oil that is undergoing a viscosity breaking, or fuel crack- 10 ing, operation. Another possible way of practicing the process is to heat-treat such straight `run gasoline while in admixtureV with any re- .iactory higher boiling hydrocarbon such as gas oil which has been subjected to such crack- 15 ing (usually two or more separate crackings) that it has limited or no capacity for further re-cracking. In either case there is provided a reiiux material for a bubble tower distillation, after the heat treatment, to remove gum-forming sub- 20 stances.

The present process may best be described by reference to the accompanying drawing, of which- Figure 1 is a'diagrammatic view of an appa- 25 ratus wherein the preferred embodiment of my improved process may be carried out.

Figure 2 is a diagrammatic view of an apparatus wherein a modiiication of my improved process may be practiced.l

In the procedure practiced in the apparatus illustrated in Figure l, the crude oil, .by means of a pump i, is forced through the heating coil B in the furnace A, wherein it is heated to any temperature that will eiect limited or no substantial cracking, as, for instance, a temperature of 600 F. after which, through line 3, it is passed to bubble tower E and therein partially ashed to vapor. The unvaporized residue, or

fuel oil, is drawn off from the bottom of the tower through line 4 to tank 5, while the vapors pass upwardly through the tower and are fractionally condensed into one or more side streams; for example, heavy gas oil 8, light gas oil 1, and heavy naphtha 8. After the side stream or side streams have been condensed from the vapors, the uncondensed vapors, comprising a gasoline fraction, pass out through the overhead vapor line 9 to condenser and cooler I0, wherein they are condensed and cooled. The liquid gasoline is then passed to separator Il, where any gas, which may be present in small amounts, is separated from the gasoline. From the separator Il the buik of the gasoline is transferred by' une l2 to" tank I3, while e einen portion is returned, by it from the tower E is varied according to the type of crude being run and the anti-knock qualities ofthe gasoline forming part thereof. It is generally true that the lower boiling constituents of the gasoline hydrocarbons have better antiknock qualities than' the higher boiling constituents. If a full cut of gasoline M10-437 F. end

, point) has an octane number so (relatively) high that, if subjected to the within described reforming operation, its octane number will be suiilcientiy high to enable it to be blended with gasoline formed by cracking side streams 6, I and 8, and thereby form a marketable fuel of the desired high octane number, the tower E is so regulated as to allow a full gasoline cut to pass off as vapor through the overhead line I. More frequently, however, a full straight run gasoline has so low an octane number that the reforming operation will not raise it suiliciently high to enable it to be blended with gasoline produced by cracking the side streams. In such case the tower is so regulated as to carry overhead vapors comprising only a lower boiling portion of gasoline, as, for example, a light gasoline having .an end point of 220 F. to 330" F. In exceptional cases, a very light fraction of the straight run gasoline may have a sufficiently high octane number to justify its use, in blending, without heat treatment, in which case there may be separated, within or outside the tower E, a very light straight run gasoline a straight run gasoline fraction comprising the remainder of the gasoline or an intermediate fraction thereof, and side streams comprising heavier fractions of the crude. For the reasons stated, the desirable end point of the separated overhead gasoline thus varies with the character of the crude oil and the desired octane number of the commercial gasoline produced, and no definite overhead fraction can be prescribed, although, desirably, in most cases, it will comprise or include, if not wholly consist of, a lower boiling fraction*l of straight run gasoline.

It is known to crack the fuel oil residue from crude oil, and in an application flied by me January' 19, 1932, Serial No. 587,480, I describe the partial cracking of such fuel oil to gas oil, which in turn is subjected to cracking for the production of gasoline. If such residual fuel oil, as is usual, has an initial boiling point approximately 600- 700" F. and contains all of the crude oil fractions boiling above that point, it is not suitable for cracking direct to gasoline, as such procedure would necessitate so high a degree of cracking as to cause the formation of coke in prohibitive quantities. Due to this fact, the residue is subjected to a light cracking operation which pro'- duces a minimum quantity of gasoline, say about 5% of the charge, a larger quantity of gas oil, say about 42% of the charge, and the balance fuel oil, which represents about- 52% of the charge, the remaining 1% being gas and loss. 'The gas oil so obtained is an excellent cracking stock for producing gasoline. 'Ihe fuel oil so obtained may be subjected to another similar operation which yields gasoline, gas oil and fuel oil bottoms which represent respectively approximately 5%, 32%, and 62% of the stock charged. 'Ihe temperaaccesa turesto which these fueloilbottomsaresub-v jected in the cracking or reducing operation vary -in accordance with their initial boiling points and the crudes from which they are derived. The

cracking temperature for the fuel oil usually may varyzo from 820 to 890 F., preferably 'from 830 to I have discovered that if the hereinbefore described separated straight run. gasoline fraction is mixed with fuel oil, either the uncracked fuel oil escaping through line 4, or the fuel oil which has been subjected to a cracking operation as above described. and if said mixture is subjected to the best treatment required to eifectively crack the fuel oil without substantially, cracking the straight run gasoline. I effect not only a reformation, or molecular rearrangement, of the straight run gasoline fraction, but also, during fractionation, largely remove its gum forming constituents besides producing a mixture of a larger proportion of substantially uncracked but reformed gasoline with a smaller proportion of cracked gasoline, the mixture having a higher octane number than reformed straight run gasoline.

To eti'ect the described combined fuel oil crack- 4ing and gasoline reformation, the gasoline from porized in tower F. The unvaporized residue in tower F is withdrawn through line 20 and may be subjected to another fuel cracking or reducing.

operation in admixture with gasoline from tank Il. The vapors in the tower F are fractioned to produce a gas oil or like side stream 2i and an overhead gasoline vapor stream containing the vapors of the reformed gasoline and that formed by cracking the fuel oil from tank i. These vapors are condensed and cooled in condenser 23 and the condensate passed to a separator 24, wherein anysmall amount of gas present is separated from the gasoline. A small portion of the gasoline entering separator 24 is withdrawn by pump 21 through line 28 and returned to tower F for reiluxing purposes. 'I'he remainder of the gasoline is withdrawn through line 2i and conv eyed to storage until needed for blending vwith gasoline obtained by cracking.

The desirable percentage of straight run gasoline to be mixed with the fuel oil for reforming varies with the amount of each produced from the crude. The desirable percentage will also depend upon whether it is admixed with the fuel oil only in its rst reducing operation or whether it is admixed therewith in both reducing operations. If, for example, the gasoline to be treated represents an initial to 410 F. or 437 F. cut, the percentage in either case will be larger than if an initial 300 F. or 330 F. cut be taken. I have found however, in the latter case, that a mixture consisting of 30% gasoline and 70% fuel oil gives very good results. For instance, 30% of a light Oklahoma gasoline of 330 F. end point having an octane numberof 62 was admixed with 70% of fuel oil also from an Oklahoma crude oil and the mixture was subjected to a temperature of 840 F. After fractionation'it was `found that the treated gasolines had an octane number of 67. It was also found that the copper dish gum test disclosed 3'mg. of gum for the treated gasoline, whereas the original gasoline had shown 11 mg. on being subjected to the same test. This conclusively shows that treatment in accordance with the present invention not only provides an efficient method for reforming gasoline to improve the anti-knock value thereof without the provision of special apparatus, but also decreases the gum forming constituents, which would not occur if the gasoline was merely subjected to a heating operation without fractionation.

A modified and less preferred process embodying the broad invention may also be carried out in the apparatus disclosed in Figure 2. In practicing this modification straight run gasoline is withdrawn from tank 3| and a highly refractory gas oil or other refractory hydrocarbon oil, (for example, a gas oil which hasv been subjected to several cracking operations) is withdrawn from tank 32 through lines 33 and 34 respectively. These streams (33 and 34) are mixed and the mixture is conveyed to pump 36 by line and is thence forced through line 31, heating coil H in furnace G and line 38 to towerI. On entering the tower I the mixture is substantially all vaporized. 'I'he vapors pass up through the tower and are so cool'ed by reux liquid as to condense the gas oil, which is drawn oif through line 40. The gasoline vapors pass out through overhead line 4I to condenser 42, wherein they are cooled and condensed and then passed to separator 43, where any contained gas is given 0E. A small portion of the treated gasoline is then withdrawn and returned, by pump 45, through line 44 to tower I for refiuxing. The balance of the treated gasoline is withdrawn through line 46 to storage.

The amount of gas oil admixed with the gasoline in the operation last described may vary considerably, ranging from 5% to 25% of gas oil or other refractory hydrocarbon oil, but is usually just enoughV to provide for refluxing the towerI, it being preferable to employ a refractory oil which has a difference of 100 to 200 F. between its initial boiling point and the end point of the gasoline toinsure better fractionation. I have found that a mixture of 90% gasoline and 10% gas oil is a suitable one. The following example will serve to show how the last described method may be carried out. 10% of a highly refractory gas oil and 90% of a light Oklahoma gasoline (3309 F. end point) having an octane number of 58 were heated to a temperature of 890. After fractionation it was found that the treated gasoline had an octane number of 65. Further, the copper dish gum test on the treated gasoline disclosed 5mg., or a drop of 3 mg. from the copper dish gum test on the original'untreated gasoline. In the example just given the end point of the gasoline was raised slightly, showing that a very small amount of cracking occurred.

While, in the foregoing examples, specic temperatures have been given, it is not to be assumed that these temperatures will hold for any gasoline from any crude. A mere change in the temperatureto which the gasoline is heated should not', therefore, be-regarded as a departure from the scope of the present invention. In fact,

the temperature at which the most notable reformation will occur may vary widely, say from 820 F. to 900 F., depending, of course, on the type of crude from which the gasoline is derived and the boiling range of the cut. It is well known that the higher boiling hydrocarbons crack more easily than the lower boiling hydrocarbons; so it follows, generally, that a very light cut of gasoline can be heated to a higher temperature. without cracking, than can a heavy, or initial to 437 F. cut. Before proceeding to heat treat any gasoline by either of the above described methods, it isy best -to treat f'several samples of the-gasoline to be reformed in small bombs, applying a different degree of heat to each sample to ascertain the most eilicient temperature for heat treating the gasoline without'substantially cracking the same. It is unnecessary to describe how such tests should be made, asl suchbombs and laboratory distilling apparatus for separating the products are a part of the equipment of any well organized refinery and the use of such apparatus is known to thosev skilledin the art.

One advantage. lof the present process is that it permits, in many cases, of heat treatment at a temperature below the critical temperature of the mixture. Straight run gasoline has a low critical temperature and the temperature required to reform it,-although much lower than the temperature required to substantiallycrack it, is substantially above its critical temperature. Fueloil, on the contrary, has a high critical temperature and the temperature required to eiliciently crack it is below its critical temperature. The critical temperature ofthe mixture is of course below the critical temperature of fuel oil and above the critical temperature of straight run gasoline and may be slightly above the temperature at which the heat treatment processes herein described may be practiced, especially lif fuel oil be the hydrocarbon with which the gasoline is mixed.

What I claim and desire to protect by Letters Patent is:

l. 'I'he process of treating gasoline or a lighter fraction thereof to increase its anti-detonating qualities and facilitate subsequent removal of gum forming constituents, which comprises admixing said gasoline in liquid phase with a liquid hydrocarbon oil having an initial boiling point substantially above the end point of the gasolineconstituent so as to provide a liquid mixture containing substantially no hydrocarbons boiling within said end point and said initial boiling point, then subjecting the mixture to heat suilicient to raise the anti-detonating qualities of the gasoline constituent but less than that required to substantially crack the gasoline constituent, and then fractioning the mixture to separate the desired low boiling constituent.

2. The process of treating gasoline or a lighter boiling oil and raise the anti-detonating qualities of the gasoline constituent but not suiiicient to raise the mixture to the criticaltemperature or to substantially -crack the gasoline constituent, and then fractioning the mixture to separate a mixture of the substantially uncracked -gasoline constituent anda relatively small percentage of the low boiling fraction'of the synthetic product obtained by cracking the high boiling hydrocarbon oil.

3. The process of reforming a straight run gasoline or lighter fraction thereof comprising admixing it in liquid phase with a highly refractory liquidA hydrocarbon oil having an initial boiling point substantially above the end point oi' the gasoline constituent so as to provide a liquid mixture containing substantially no hydrocarbons boiling within said end point and said initial boiling point, then subjecting the mixture to a t perature, sulcient to increase the antidetonating qualities of the gasoline constituent without substantially cracking either the gasoline or said refractory hydrocarbon', and then fractioning the mixture to obtain the reformed gasoline.

4. The process of reforming -a straight run gasoline or lighter fraction thereof which comprises admixmg it in liquid phase with a substantially non-refractory fuel oil having an initial boiling point substantially above the end point of the gasoline constituent so as to provide a liquid mixture containing substantially n hydrocarbons boiling within said end pointl and said initial boiling point, then subjecting the mixture to a temperature suiilcient to increase the anti-detonating qualities of the gasoline without substantially cracking it, and then fracsubsequent removal ot gum iorming constituents.

which. comprises mixing saidflowboiling constituent with a hydrocarbon oil having an initial boiling point substantially above the end point of the low boiling constituent so as to provide i a liquid mixture containing substantially no hydrocarbons boiling within said end point and said initial boiling point, the mixing being effected while each constituent is at a temperature substantially below that to which the mixture is subjected in the next speciiled step, and suboconstituent. without substantially cracking it. and

then fractioning the mixture to separate the desired low boiling constituent. e

AR'I'HU'Ry E. PEW. JR.

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