US2029752A - Treatment of petroleum - Google Patents

Description

Feb. 4, 1936. J. B. BARNES TREATMENT OF PETROLEUM Filed Dec. 3, 1931 mQQZmDm INVENTOR JOHN B. BARNES ATTORN Patented Feb. 4, 1936 PATENT OFFICE TREATMENT OF PETROLEUM John B. Barnes, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, 111., a corporation of South Dakota Application December 3, 1931, Serial No. 578,765

Claims.

This invention relates to the simultaneous topping and cracking of petroleum to increase the yield and to improve the quality of the low boiling motor fuel fractions obtainable therefrom. As a novel feature of the invention, the petroleum is topped preferably from the heat of the cracking process itself, the reduced crude or the like subjected to the suitable cracking conditions of temperature and pressure and the so-called straight run gasoline obtained from the topping action is cracked so as to increase its antiknock quality without interfering with the main cracking reaction.

To this end, the crude petroleum is preferably first preheated in indirect contact with the cracked products and thence further topped by coming in direct contact with a selected portion of the cracked products, the straight run gasoline subjected to a controlled heat to increase its antiknock quality preferably in the so-called reaction zone while the reduced crude is subjected to the main cracking reaction.

As is well known, the chemical nature of crude petroleums from different areas varies widely. The extreme types of parafiinic crudes are characteristic of Pennsylvania and the Muskegon field of Michigan, while crudes of certain fields of California and Texas represent the asphaltic or naphthenic type', containing large percentages of cyclic hydrocarbons. Between these types are all gradations and compositions known as the mixed base crudes. While the paraflinic or crude oils of high hydrogen-carbon ratio commonly yield large quantities of fractions of motor fuel boiling range, these naturally contained gasolines are found to possess detonating characteristics when used as fuel in internal combustion engines of a high compression ratio. The asphaltic crudes, on the other hand, while not usually yielding as high percentages of gasoline fractions by straight distillation, at least yield gasoline which has better combustion characteristics and does not detonate.

Gasolines produced by cracking the heavier portions of different types of crude oils compare in a general way as regards their antiknock characteristics with the straight run gasolines produced from the same crudes. However, by the use of intensive cracking conditions on the heavier portions of paraffim'c crudes it is possible to produce gasolines with anti-detonating characteristics substantially equivalent to those produced from asphaltic or naphthenic crudes under less severe conditions of operation,

In the development of methods of refining crude oils to produce maximum yields of motor fuel it has been common practice up to a comparatively recent date to toptthe crudes to remove the natural gasoline and then to further crack the residuum to produce additional yields of low boiling fractions, which were blended in whole or in part with the natural or straight run product to produce marketable fuels of varying quality. A still more recent development has been the subjection of natural gasolines of poor antiknock value to a recracking or re-forming operation to increase the percentage of aromatics and unsaturates and. thereby obtain a higher overall yield of premium gasoline. This idea has led to the combination of recracking or re-forming operations with the topping and cracking operations, and it is with improvements in such combination treatments that the present invention is concerned.

In one specific embodiment the invention comprises distilling a portion or all of the gasoline from a crude oil by heat obtained from indirect contact with flashed vapors from the cracked residuum and that obtained by direct contact with a portion of the cracked vapors, heating the topped crude mixed with intermediate refluxes at elevated temperatures and pressures, passing the heated products to an enlarged reaction zone, adding the vapors of the natural gasoline to the reaction zone, passing a portion of the cracked vapors from the reaction zone to a primary fractionator in direct contact with incoming crude oil, passing nonvaporized liquids and the remainder of the cracked vapors from the reaction zone to a flashing chamber under reduced pressure, withdrawing flashed residuum from the system, passing the flashed vapors in indirect heat exchange relation to the incoming crude, fractionating the flashed vapors to produce vapors of desired boiling point range, which are cooled, condensed and collected, and intermediate insufficiently converted refiuxes which are returned to the heating zone for further treatment.

The details and features of the invention will be made clear from a description of one type of operation by reference to the attached drawing, which shows diagrammatically by-useof conventional figures in side elevation a particular arrangement of elements in which it may be carried out.

Referring to the drawing, crude oil of any type may be taken by a pump 3 through a supply line I containing a control valve 2 and discharged through a line 4 controlled by a valve 5 to indirect heat exchanger 6, in which the incoming crude is partially heated by heat exchange with flashed vapors which are produced in a manner to be more fully described later. The heated crude may then pass through a line I having a control valve 8 interposed therein and partly from the heat added to a portion of cracked products introduced from a line 22 containing a valve 23', as Will be presently described.

It is a characteristic feature of the invention that the degree of stripping for removal of light fractions from the crude oil in fractionator 9 may be controlled by varying the amount of hot cracked products introduced at this point, so that in some cases the crude is completely deprived of its natural gasoline; in other cases of only a portion thereof. Non-vaporized liquid accumulating as a residuum in fractionator 9 and including such portions of the cracked products as have been liquefied pass through line l containing a control valve II to a feed pump l2, which is of a type and capacity sufiicient to discharge the entering liquids through a line 23 containing a control valve I4 at sufiicient pressure to force them through a heating element |5 disposed to receive heat from a suitable furnace 16. Intermediate refluxes amenable to further heat treatment for the production of increased yields of gasoline are preferably introduced into line l3 from line 55, as Will be described in detail later.

The combined feed passing through heating element |5 is preferably brought to a certain optimum temperature for inducing conversion reactions to a point consistent with best overall results. Since the actual temperature employed at this point will vary with a large number of factors such as the nature of the crude oil processed, the amount of topping to which it has been subjected, and the extent of conversion desired,

it is impossible to state even approximately what temperature should be used at this point. However, it is safe to state that for commercial work temperatures below 850 F. will seldom be used, and on the other hand that 1100 F. will be the approximate upper limit, temperatures in excess of this point tending to induce carbon troubles in the tubes of the heating element and reduce the tensile strength of the metals to a dangerously low point. Pressures will necessarily be varied to control the degree of vaporization and consequently the time factor, and may vary from slight super-atmospheric to several hundred pounds per square inch, the higher super-atmospheric values being preferred on account of the usual presence of low boiling fractions, which need more extensive conversion to produce the qualities desired in the finished product.

The heated products may be passed through a transfer line H containing a control valve l8 and 'enter a line l9 having a control valve 29 and leading to an enlarged chamber 2 5. At this point another novel feature of the invention appears in the introduction of the gasoline va pors produced from the primary fractionator.

'These vapors, which are evolved through line 22 and control valve 23, are preferably picked up I by a vapor pump 24 of relatively large capacity and pumped under sufficiently increased pressure through a line 25 containing a control valve 25 to join with the transfer line liquids in line 9 and be subjected to re-forming conditions in reaction zone 2|.

It will be appreciated by those familiar with the art of cracking hydrocarbon oils that the mean temperature which must be maintained in reaction zone 2| will be dependent upon the relative proportions of straight run gasoline vapors and the products coming from the heating zone, as wellas upon the physical and chemical characteristics of both. When the proportion of straight run vapor introduced at this point is high the temperature will need to be raised to a considerable degree, perhaps in the neighborhood of 950 to 975 F., for best results. It will also be evident that some temperature rise will be obtained from the adiabatic compression of the straight run vapors by pump 24, which assists in the conversion reactions. The capacity of reac tion chamber 2| is preferably sufi'icient to permit the total conversion reactions to continue to an economical point, the majority of the products from the reaction chamber, both liquid and vaporous, being removed from the bottom of the chamber to avail themselves of the full capacity thereof and transferred preferably with substantial reduction of pressure through a line 29 containing a control valve 39 to a flash chamber 3|. Reaction chamber 2| may be provided With upper and lower removable manheads 21 and 28 to insure easy entry for inspection and cleaning purposes.

To control the primary fractionation of the crude petroleum in fractionator 9, a portion of the vaporous products from the conversion reactions in chamber 2| are diverted through line 22 containing a control valve 23 to fractionator 9. Obviously, such portions of the cracked vapors thus introduced as are volatile under the temperatures and pressures obtaining in fractionator 9 will be recycled to the reaction chamber along with the straight run gasoline vapors and be consequently subjected to an increased time of reaction.

In flash chamber 3| conditions of pressure are preferably maintained to permit the volatilization of all portions of the entering products which are desirable as finished motor fuel or Which are suitable for return to the heating zone for further treatment. Residual liquids may be removed through a line 5? containing a control valve 58 and utilized as fuel for the process or for other heating, or for any other purpose to which they are suited, such as for example the manufacture of asphalt. Flash chamber 3| is again provided with manheads 32 and 33 to to permit entry for cleaning and inspection.

Vapors from flash chamber 3| pass through vapor line 34 containing control valve 35 and yield a portion of their contained heat to the incoming crude oil, as previously indicated. After this heat exchange the cooled and partly condensed vapors may pass through line 3 containing valve 35 and enter a final fractionator 36. In thisfractionator conditions are maintained to produce an overhead gasoline of desired boiling range characteristics, these fractions passing through vapor line 31 containing control valve 38 and their liquefiable portions condensed by condenser 39, the liquids and cooled gases then passing through run-down line 49 containing control valve 4| to receiver 42. This receiver may have the usual gas release line 43 containing control valve 49, valve 44 being used to regulate the back pressure upon the preceding portions of the equipment, and the receiver may have also a gasoline run-down line 45 with a regulating valve 46.

To assist in controlling the boiling point range of the gasoline vapors from fractionator 36 a recirculating pump 49 may take suction upon liquids in receiver 42 through a line 41 containing a control valve 43 and deliver the same to the top of the fractionator through a line 50 containing a control valve 5|.

Liquid refluxes accumulating in the bottom of fractionator .36 will commonly yield further lowboiling gasoline fractions upon subjection to the conditins of temperature and pressure obtaining in the heating zone, and may be returned to this zone through a line 52 being controlled by valve 53, leading to a reflux pump 54 which discharges such liquids to line I3 through line 55 containing control valve 56.

As a direct example of the results obtainable by the operation of the process of the invention on Pennsylvania crude oil, in comparison with results obtainable by the ordinary methods of topping and cracking, the following case may be cited.

The crude processed may be a 40.4 A. P. I. gravity crude from Venango County containing 21 percent of fractions boiling up to 300 F. and 40 percent of fractions boiling up to 425 F. In operating with this stock a temperature of 945 F. may be used at the exit of the heating element and the pressure at this point and through the reaction chamber may be 300 lbs. per square inch. The primary or topping fractionator may be operated so that only the fractions of straight run gasoline boiling up to 300 F. are volatilized and added to the transfer line ahead of the reaction chamber, these vapors attaining a temperature of approximately 900 F. as a result of their compression to the plant pressure of 300 lbs. per square inch. The mean temperature in the reaction chamber may be approximately 925 F.

Under these conditions there may be produced a total yield from crude of 77 percent of 400 endpoint gasoline having an octane number of 60 to 65 percent, whereas by separately topping the crude to remove 40 percent of straight run 400 endpoint gasoline, separately reforming this gasoline, and separately cracking the straight run residuum, there may be produced an overall yield of '79 percent of gasoline but with an octane number of only 45 to 50 percent, which is considerably below that of saleable gasoline in some localities and far below the quality demanded .in premium gasolines.

It will thus be evident that the combined top-- ping, cracking and re-forming process of the present invention produces a higher antiknock gasoline than ordinary topping and cracking processes as at present known in the art. The specification and example given have made clear the nature of the invention and indicated its commercial possibilities but the scope of the invention is not to be limited by the specific details of the disclosure nor the numerical values given in the example since the operation may be modified from that described and other beneficial results obtained when operating upon other types of charging stocks.

I claim as my invention:

1. A process for treating crude petroleum oil containing natural gasoline which comprises heating the crude oil sufliciently to vaporize the natural gasoline and separating the resultant gasoline-containing vapor from fractions of the crude heavier than gasoline, passing said fractions in a restricted stream through a heating zone and heating the same therein to cracking temperature under pressure, discharging the thus heated fractions into an enlarged reaction zone maintained under cracking conditions of temperature and pressure, introducing said gasolinecontaining vapor into said reaction zone and subjecting the same to the cracking conditions prevailing therein, separating the reaction products into vapors and residue, and dephlegmating and condensing the vapors.

2. In a process for cracking hydrocarbon oils, the method which comprises passing crude oil containing natural gasoline in heat exchange relation with vapors formed in the process and heating the same sunicientl'y to vaporize the gasoline, separating from the crude oil a gasoline fraction and an oil of higher boiling point than gasoline, passing said higher boiling oil in a restricted stream through a heating zone and heating the same therein to cracking temperature under pressure, discharging the thus heated oil into an enlarged reaction zone maintained under cracking conditions of temperature and pressure, introducing said gasoline fraction into said reaction zone and subjecting the same to the cracking conditions prevailing therein, separating the reaction products into vapors and residue, and dephlegmating and condensing the vapors.

3. A combined topping and'cracking operation which comprises passing heavy hydrocarbon oil through a heating zone and heating the same therein to cracking temperature under pressure, discharging the heated oil into an enlarged reaction zone maintained under cracking conditions of temperature and pressure, removing unvaporized oil from the reaction zone and flash distilling the same by pressure reduction, passing crude oil containing natural gasoline in heat exchange relation with resultant flashed vapors, separately removing vapors from the reaction zone and introducing the crude oil into direct contact therewith thereby vaporizing the natural gasoline, separating the natural gasoline vapors from the unvaporized portion of the crude and introducing the same to said reaction zone and subjecting them to the cracking conditions prevailing therein, and supplying the unvaporized portion of the crude to the heating zone as said heavy oil.

4. A combined topping and cracking operation which comprises passing heavy hydrocarbon oil through a heating zoneqand heating the same therein to cracking temperature under pressure, discharging the heated oil into an enlarged reaction zone maintained under cracking conditions of temperature and pressure, removing vapors and unvaporized oil from the reaction zone, passing crude oil containing natural gasoline in heat exchange relation with the vapors and vaporizing the gasoline therefrom, introducing the resultant gasoline vapors into said reaction zone and subjecting the same to the cracking conditions prevailing therein, and supplying the unvaporized portion of the crude oil to the heating zone as said heavy oil.

5. A process for producing motor fuel which comprises topping crude oil and separating therefrom a light fraction containing gasoline hydrocarbons and a heavier fraction, heating the heavier fraction to cracking temperature under pressure while flowing in a restricted stream through a heating zone, discharging the thus heated fraction into a reaction zone maintained under cracking conditions of temperature and pressure, introducing said light fraction into the reaction zone and subjecting the same to the cracking conditions prevailing therein, separating the reaction products into vapors and residue, and dephlegmating and condensing the vapors.

JOHN B. BARNES.

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