US2187696A - Production of motor fuel - Google Patents

Description

Jan. 16, 1940. H, v A-rwELL PRODUCTION OF MOTOR FUEL Filed Deo. 14. 1955 2 Ai# C Q O Q e211 55.3K SR t ii m?. Q oN 2 mf wi ifi Q. Huw s. ov 15 mv .QSK eu .v

W. mm u ma o L No n 1M uw A H `l both heavier and lighter than gasoline.

Patented Jan. -16, l194() PRODUCTION OF MOTOR FUEL Harold V. Atwell, White Plains, N. Y., signor to Process Management Company, Inc., New York, N. Y., a corporation of Delaware Application December i4, 1935, seria No. 54,411

1 Claim.

My invention relates to the production of lowboiling hydrocarbon oils suitable for use as motor i'uel and having high anti-detonating properties -from relatively high-boiling hydrocarbon oils by 5' a combination of pyrolytic decomposition and polymerization steps.

In cracking oil for the manufacture' of gasoline, the products ordinarily include, in addition to gasoline, various other types of hydrocarbons,

The customary procedure is to fractionally separate these products in the order of decreasing boiling points. Thus the cracked products are nrst separated into vaporousV and residual products or ll tars, which are either converted into coke or removed from the system as fuel oil, it being ordinarily impracticable to attempt to crack these heavy materials to gasoline on account of thefact that they decompose too readily to carbon and because of the relatively poor yield of gasoline produced thereby. The separated vaporous products are then fractionated to recover relatively highboiling but non-residual distillation products which are ordinarily designated gas oils and 2li which may include products boiling over a fairly wide range, for example, from around 400 F. to 700 F. or more, depending somewhat upon the end-point of the gasoline fraction and other factors. This gas oil, being free from residual con- $0 stituents, forms a good cracking stock and may be recycled for further cracking to produce gasoline, especially since in many instances it consists in part of virgin constituents distilled from uncracked or crude oil charged into the system at a 86 point beyond the actual cracking zone. However, the lighter constituents in the gas oil range are relatively much more refractory than the heavier constituents and, consequently, when it is attempted to recycle the entire gas oil cut 40 lying between residual oil or tar on the one hand and gasoline on the other hand, the cracking conditions must of necessity constitute a compromise between conditions most desirable for the conversion of the heavier constituents of this fraction and conditions most desirable for the conversion of the lighter constituents of this fraction, and, consequently, neither group of constituents is cracked under optimum conditions. After the separation of the products having 50v higher boiling points than gasoline, the remaining vapors are separated into a condensable or gasoline fraction and a gas fraction consisting partly of hydrogen and methane, which are relatively inert materials. In addition to hydrogen Il and methane, however, there are present various paramnic and olennic gases, such as ethane, ethylene, propane, propylene, butanes and butylenes, which may be regarded as more or less intermediate between the xed gases and the true gasoline fraction. A certain amount of these nori mally gaseous materials may be included in the gasoline fraction but under present day conditions there is normally an excess of these materials. As a result of this, depending upon the conditions and particularly the pressure under 10 which condensation is eected, these intermediates may either be included in the gas drawn from the gas separator or separately recovered in the stabilization of the gasoline. In any event, these light intermediate materials, especially when free 1I` or relatively free from hydrogen and methane, may be polymerized to normally liquid low-boiling hydrocarbon oils suitable for use as motor fuel and having exceptionally high anti-detonating properties, by subjecting them to suitably elevated 2.0 temperatures and pressures, with or without catalysis.

While it has thus been suggested to effect the polymerization of the gases liberated in the ordinary course of cracking, little attention has been paid to the possibility of employing polymerization as a means of obtaining a further additional yield of gasoline of high quality from an oil cracking unit over and above that obtainable by simply polymerizing the cracked gases normally pro- 80 duced.

My invention, therefore, has for an object the provision of a method whereby the products obtained in an oil cracking operation may be converted to a higher degree than has heretofore 85 been possible to motor fuel products of exceptionally good character, without overburdening the primary oil cracking operation, together with such additional operative advantages and improvements as may hereinafter be found to obtain. 40

My invention contemplates cracking a hydrocarbon oil under the usual conditions with recycling of the heavier clean distillation products, and with the segregation of the heavy residual products or tars as well as a refractory distillate lighter than the recycle stock and which will hereinafter be designated for convenience as a light gas oil." According to my invention, this light gas oil fraction is then subjected to a very high temperature in order to drastically crack the same and eiect its conversion in large measure to gaseous products of a highly olenic character. The highly heated products are then commingled with the residual oil or tar referred to hereinabove in order to accomplish a conversion of the latter u tocoke or very heavy residuum and lighter products including a considerable amount of normally gaseous constituents. The gases obtained in this operation are then subjected to gas polymerization either with or without previous fractionation operation may be combined with those obtainedr by cracking the light gas oil and residual oil before being subjected to polymerization. In any event, the polymerization is so conducted as to obtain a low-boiling motor fuel product having high anti-detonating properties while any higherboiling polymers may be returned advantageously to the primary oil cracking operation for further conversion.

In order that my invention may be fully set forth and understood, I now describe, with reference to the drawing accompanying and forming part of this specication, a preferred form and manner in which my inventionmay be practiced and embodied. In this drawing, the single figure is a more or less diagrammatic elevational view of apparatus for effecting conversion of hydrocarbons in accordance with my invention.

Referring to the drawing, a suitable hydrocarbon oil charging stock, such as a reduced crude or a gas oil, is introduced by means of a pump I and a line 2 into an evaporator 3 receiving hot cracked products from an oil cracking furnace 4. In a preferred instance, the evaporator 3 is maintained under a pressure of about 200 lbs. per sq. in. (although higher or lower pressures may be used) and under such temperature as to retain as liquids heavy residual constituents unsuitable for further cracking to gasoline in the ordinary manner, while permitting distillable constituents to pass overhead in vapor form into a fractionating column 5, where distillate higher boiling than the desired motor fuel fraction is condensed and separated. The charging stock, especially where its consists of gas oil, may be introduced above the tray 6 if desired. A higher boiling distillate or heavy gas oil fraction is removed from the bottom of the fractionating column by means of.' a trapout tray 5 and is delivered by means of a line I and a pump 8 to the oil cracking furnace 4, where it is subjected to conversion conditions of temperature and pressure, for example, a temperature of from 950 to 1050 F., under a pressure oi' from 300 to 1,000 lbs. per sq. in. The hot products from the oil cracking furnace 4 then pass through a transfer line 9 having a pressure-reducing valve Il into the evaporatorv 3.

The oil collected inthe bottom of the evaporator 3, especially where the evaporator 3 is maintained under a pressure of, for example, about 200 lbs. per sq. in. or more, will ordinarily contain some distillable constituents and, in order to recover these, the heavy oil from the bottom of the evaporator 3 is delivered through a line I2 having a pressure-reducing valve I3 to a. tar flasher I4, which may be maintained under a reduced pressure of, for example, from atmospheric pressure to v50 lbs. per sq. in. The distillate separated'in the tar flasher I4 passes in vapor 2| is also delivered by aisance form'through a line Il to a condenser Il and separator I1, from which this distillate may be withdrawn through a line I3 having a valve Il and a pump and returned to the fraotionating column 5. The flashed residual oil or tar is removed from the ,bottom of the tar flasher through a line 2i having a valve 22..

Overhead vapors from the bubble tower t and comprising gasoline, fixed gases and intermediate gases or vapors, pass through a vapor line to a condenser 26 and thence to a gas separator 2 from which fixed gases may be withdrawn through a valved line 23 while the separated gasoline is withdrawn through a line 29, which may be provided with a pump 30, and delivered to a stabilizer 3i. The stabilizer 3i may be of the usual type, stabilized gasoline being withdrawn from the bottom of the stabilizer through a valved line 32 While overhead products pass through a line 33 to a condenser 34 and receiver 35. The stabilizer 3i will ordinarily be operated under several hundred pounds pressure and, under these conditions, the products recovered from the receiver 35 will ordinarily comprise liquefied gases of paraflinic and oleflnic character, largely free from hydrogen and methane and suitable for gas polymerization. 'I'hese products are withdrawn from the receiver 35 through a line 33 having a pump 31 and a portion of these products may be returned through a valved line 33 to the stabilizer 3| as reflux. Any gases ar vapors which separate in gaseous form at this point may be withdrawn from the receiver 35 through a valved line 33.

In accordance with my` invention, a portion of the gas oil condensate condensed in the fractionating column 5, and preferably comprising a lighter and more refractory fraction than that withdrawn from the trap-out tray I, is withdrawn as a side stream from a trap-out tray 4I located at an intermediate point in the fractionating column 5. This fraction then passes through a line 42 to a pump 43 and is then delivered by means of a line 44 to a second oil cracking furnace 45, where it is subjected to very drastic cracking conditions with the object of converting it largely to gases or, at any rate, to obtain a relatively high yield of gas and without any especial attempt to obtain a high gasoline yield per se. For this purpose, the light gas oil fraction may be subjected to a temperature of from 1100u to 1300" F. under a relatively low pressure ordinarily in excess of lbs. per sq. in, but preferably not exceeding 500 lbs. per sq. in., and with a sutllcient rate of flow through the furnace to prevent deposition of carbon therein. The highly heated cracked products then pass through a transfer line 45 into a reaction chamber or coking drum 41. .Tar or residual oil withdrawnV from the tar flasher I4 through the line means of a pump 48 and a line 49 to the chamber 4'I. In the preferred instance illustrated, the line 43 may communicate with the transfer line 45 between the furnace 45 and the chamber 4'I but it will be obvious to those skilled in the art that the tar or residual oil may be delivered directly to the chamber 4I if desired. In the chamber 4T the tar is sufficiently heated by the cracked products from the furnace 45 to eil'ect a cracking thereof largely to gaseous products and coke. 'I'he coke may be removed from the bottom of the chamber 41, of which a number may be provided in the usual manner in order to permit intermittent removal of coke without shutting down the entire operation. 'It is preferred to maintain a temperature of from 900 to 1100'l F. in the chamber 41 and if the heat of the cracked products from the furnace 45 proves insufllcient for this purpose the tar from the tar flasher I4 may be independently heated by any suitable means (not shown on the drawing) before being brought into contact with the .iot products from the furnace 45. The temperature of such independentheating may be as high as possible without undue deposition of carbon from this l avy and dirty stock, for example to about '750- 50 F. The vaporous products from the chamber 41 then pass through a line 5| to a fractionating column 52 where they are fractionated in the usual manner to remove products heavier than glsoline. Relatively heavy products of this character containing dirty residual constituents car-"led out of the chamber 41 are withdrawn from the bottom of the fractionating column 52 through a line 58 having a valve 54 and a pump 55 and may be returned through a line 56 to the chamber 41, the line 55 either communicating with the transfer line 48 as shown or leading directly to the chamber 41. Clean condensate or gas oil may be withdrawn as a side stream from a trap-out tray located as shown in the fractionating column 52 and recycled by means of a line 8| having a valve 52 and a pump 63 to the inlet of the oil-cracking furnace 45 through a line 83'.

Overhead vapors comprising gasoline and lighter products pass from the top of the fractionating column 52 through a line 64 to a condenser and thence to a separator 56 from which any gasoline may be withdrawn through a valved line 61. Due to the relatively low pressure at which condensation is effected in this type of operation the intermediate gases lying between methane on the one hand and gasoline 0n the other hand are ordinarily separated in gaseous form at this point and may be withdrawn from the separator 68 together with hydrogen and methane and delivered through a valved line 10 having a pump 1I to a suitable 'gas fractionating unit 12 Where they are separated into two fractions, one comprising largely hydrogen and methane and the other comprising largely ethane, ethylene, propane, propylene, butanes and butylenes. 'I'he details of the gas fractionating unit 12 have not been illustrated, as units for this purpose are well known in the art and since my invention is not concerned with the manner of fractionation.

The hydrogen and methane fraction is withdrawn from the gas fractionating unit through a valved line 13 While the fractionated paraiilnic and olefinic gases pass through lines 14 and 15 to a pump or compressor 16 and thence through a line 11 to a gas polymerizing furnace 18. In passing through the furnace 18, the gases are subjected to a suitable elevated temperature and pressure and for a suillcient time to effect the desired degree of polymerization to low-boiling normally liquid products. Where catalysts are not employed, or where the effect of such catalysts as may be present is secondary, the temperature and pressure employed at this point are preferably from 750 to 1050 F. and 500 to 3,000 lbs. per sq. in., although higher temperatures and lower pressures may be employed where products of a more highly aromatic character are desired. Where highly eifective catalysts are employed, the temperatures and pressures may be considerably lower; thus, for example, when using phosphoric acid type catalysts and other catalysts of about the same degree of effectiveness. temperamay be withdrawn through a valved line 82.

while liquid products pass through a line 8l having a pressure-reducing valve 84 into a fractionating column 85 of conventional construction.

In the fractionating column 85, the fractionation is so carried out as to pass overhead all gasoline-like materials and lower-boiling products while condensing and separating polymers .having boiling points too highto warrant their inclusion in the motor-fuel product. These highboiling polymers are withdrawn from the bottom of the fractionating column 85 through a line 88 having a valve 81 and may be delivered by means of a pump 88 and line 89 to the inlet of the oil cracking furnace 4 for further conversion. A1-

ternatively, this material may be diverted from 25 the system for any desired purpose.

The overhead products from the fractionating column 85 pass through. a vapor line 9| to a condenser 92 and thence to a separator 93 from which polymerized gasoline is withdrawn through a valved line 84, while overhead products comprising largely constituents lying between methane on the one hand and gasoline on the other hand are removed through a valved line 36 and are returned through the line 15 to the pump or compressor 18 and thence into the furnace 18. Where catalysts are employed, such recycling may sometimes be dispensed with.

Where the original charging stock consists` of a distillate, such as gas oil, the oil in the evaporator 3 may contain a considerable amount of 0 refractory products of cracking but more suitable for cracking to gas than to gasoline. Where this is true, such constituents may be segregated from the heavier residual constituents and delivered to the furnace 45. For example, in the instance shown in which bottoms from the evaporator 3 are flashed in the tar flasher I4, the flashed distillate recovered at I1 or any desired portion thereof may be delivered to the furnace 45 through a line |00 having a pump |0| and a valve |02, for cracking in the manner set forth hereinabove with reference to the light gas oil withdrawn from the trap-out tray 4I.

Those products of the initial oil cracking operation which are lighter than gasoline and suitable for polymerization can be delivered to the gas polymerizing furnace 18. In the preferred instance illustrated, the excess material recovered from the separator 35 over and above that required for refluxing to the stabilizer 3| is delivered from the pump 31 through a line 91 having a valve 98 and communicating with the line 15 whereby these products are delivered to the pump or compressor 16 and thence to the gas polymerizing furnace 18.

It will likewise be obvious that the gases from the separators 21, 35 and 8|, which are withdrawn therefrom through the lines 28, 38 and 82, respectively, may likewise be delivered to the gas polymerizing furnace 18. Preferably, however, these gases and particularly those withdrawn from the separators 21 and 8|, if returned at all, are not entirely returned due to their content of hydrogen and methane but are preferably first delivered to the gas fractionating through the unit 'l2 to the lines 14, 1l and 11 in the .manner described hereinabove. y

It will be obvious in any event that my inven-y tion is not limited to the details of the specific fractionating methods employed in connection with any ofthe three conversion units, the light products of each of these units being fractionated in any suitable manner to separateagasoline fraction, a hydrogen and methane fraction and an intermediate fraction consisting primarily of polymerizable gases rree from hydrogen and methane, the gasoline fractions being Withdrawn for use, the hydrogen and methane fraction being discarded from the system and the intermediate fractions being delivered or recycled as the case may be to the gas polymerizing furnace it.

It will likewise be obvious to those skilled in the art that the ydetails oi' the oil cracking operation may be considerably varied in accordance with the requirements of the original charging stock and the particular type oi process employed and that in some cases the tar or residual oil withdrawn from the primary evaporator 3 may be delivered directly to contact with the hot products v from the cracking furnace 65 without first being passed to the tar flasher I4. However, the tar flasher il is useful in -eilecting the segregation of materials which may be vadvantageously recycled in the cracking operation and residual materials which may more advantageously be delivered to the more drastic cracking operation conducted primarily for the purpose of making polymerizable gas.

It will be clear from the above that my invention makes it possible to carry out an oil conversion operation in an advantageous manner since those products which are suitable for cracking to gasoline in the usual manner are segregated as such and cracked for the production of gasoline under optimum conditions, while products less suitable for cracking on account of their residual or refractory character, as the case may be, are segregated as formed from the oil cracking operation and are advantageously converted into gaseous products capable of being polymerized to produce a motor fuel of exceptionally high character. As a matter of fact, the gasoline produced in each of the three conversion operations is of exceptionally good character and any two or all three of these gasoline products may be blended in any desired proportions to produce a' blended motor fuel product of exceptionally lood quality.

Itwillfurtherbeob'vioustothcse-skilledinthe art that while I have described my invention hereinabove with reference to various preferred l details of operation, my invention is not limited to such illustrative details but may variously be practiced and embodied within the scope of the claim hereinafter made.

I claim:

A process of manufacturing low boiling hydrocarbon oil suitable for use as motor fuel which comprises subjecting a relatively heavy hydrocarbon oil to an elevated temperature to crack the heavy oil to higher and lower boiling products, separating heavy residual oil unsuitable for recycling frein the cracked products, fractionating the remaining cracked products to recover a heavy gas oil suitable for recycling, a distillate fraction comprising a light refractory gas oil, a cracked. gasoline fraction, a ilxed gas fraction consisting largely of hydrogen and methane, and a fraction intermediate the gasoline fraction and the ilxed gas traction, recycling the last mentioned heavy gas oil to the iirst cracking step, separately subjecting the distillate fraction to a temperature of about 1100 F. to 1300 F. to crack the distillate fraction to produce primarily olenic gas without regard to producing an optimum yield of motor fuel, commingling the high temperature highly cracked products from the last mentioned high temperature cracking step with the first mentioned heavy residual oil to crack the heavy residual oil largely to coke and gaseous products, fractionating the gaseous products to 35 separate all material higher boiling than gasoline to heavy and light fractions, a gasoline fraction and gases containing olefins, returning the light fraction to the high temperature cracking step and commingling the heavy fraction with the high temperature highly cracked products from the high temperature cracking step, combining the last mentioned gases containing olefins with the fraction intermediate the gasoline fraction and the xed gas fraction and subjecting the mixture of gases to an elevated temperature to effect the polymerization of the constituents thereof to normally liquid low boiling oil, recovering a gasoline-like fraction and a heavier fraction from the products of polymerization and returning at least a part of the heavier fraction to the first cracking step for further conversion.

HAROLD V. ATWELL.

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