US2176353A - Manufacture of automotive fuel - Google Patents

Description

Oct. 17, 1939. J, Q MORRELL 2,176,353

MANUFACTURE OF AUTOMOTIVE FUEL Filed July 30, 1936 Wr/206e r 55 [ondelzser Patented Oct. 17, 1939 UNITED STATES PATENT OFFICE MANUFACTURE OF AUTOMOTIVE FUEL Application July 30,

2 Claims.

This invention relates more particularly to the manufacture of hydrocarbon fuels suitable for use in'motors of the compression-ignition type.

More specifically the invention is concerned With a process for the manufacture of fuels suitable for use in Diesel and similar engines by an adaptation of a cracking process in which motor fuel suitable for use in spark ignition engines is concurrently produced.

The characteristics of fuels which are to be used in compression-ignition engines and those which are to be used in spark-ignition engines are generally opposite. As is well known, the spark ignition engines used on motorvehicles require a fuel of considerable volatility and of slow burning characteristics so that there is no cracking of the fuel during combustion or development of peak pressures which cause the phenomenon known as knocking, In fuelinjection engines of the Diesel type wherein the heat of compression is relied upon to cause ignition at a definite point in the cycle of combustion, the most reliable fuels are those which have a tendency to crack and produce reactive molecules or radicals which readily ignite in the presence of air under the compression ratios utilized in Diesel engines which are commonly of the order of from 1 to 20:1.

Up until recently, with the limited use of the Diesel engine in automotivevehiclesl little attention has been paid to increasing the yields of suitable Diesel fuel fractions from petroleum and efforts have been principally concentrated upon the manufacture of gasoline of high antiknock value by cracking and reforming operations and by the use of antiknock agents such as tetra ethyl lead. The requirements of a suitable fuel for light Diesel engines which may be used on trucks and to some extent on pleasure vehicles are generally met by straight run gas oil or fuel distillate fractions boiling within the approximate range of 40G-700 F. and it has been found that the higher the percentage of parafns or readily breakable hydrocarbons in these fractions the more suitable. they are for Diesel engine use. This property may be designated as parafflnicity, and it is commonly measured in terms of mixtures of the hydrocarbons cetane and alpha-methyl-naphthalene. Prospective fuels are tested in a standard Diesel engine lhook-up and the compression ratio found at which they ignite, and varying blends of the two chemicalv compounds mentioned are employed in comparison until one is found which ignites at the same compression ratio as the pro- 1936, Serial No. 93,372

posed fuel, which is then given a cetane number rating corresponding to the percentage of this compound in the blend.

Ordinarily the cracking reaction, which has a tendency to produce unsaturated and cyclic hy- 5 drocarbons, does not produce Diesel fuel fractions of superior characteristics. However, by limiting the reactions of cracking to the primary reactions which do not extend to the formation of material amounts of cyclic hydrocarbons, Diesel fractions of suitable characteristics can be produced in economical quantities. It has been shown that the breaking down of a heavy oil into gasoline and gas may be preceded by the formation of intermediate fractions and the present invention utilizes this fact for the production of Diesel fuels.

In one specific embodiment the present invention comprises cracking heavy petroleum fractions under conditions of time, temperature and pressure conducive to the formation of yhigh yields of intermediate Diesel fuel fractions and separately cracking residual heavier fractions from this operation to produce gasoline of good antiknock value.

The present process thus consists of a series of cooperative steps in which both Diesel fuel and gasoline are produced by cracking, and in order to illustrate the general steps of the Drocess the attached .drawing has been provided, which indicates diagrammatically in side elevation by the use of conventional figures an arrangement of apparatus in which the process may be conducted.

Referring to the drawing, charging oils are admitted by way of line I containing control Valve 2 to a charging pump 3, which discharges by way of line 4 containing control valve 5 into and through a tubular heating element 6 disposed to receive heat from a furnace 1. The preferred charging stocks are those which contain relatively low percentages of gas oil fractions and which have a paraiiinic or mixed base character. The best stock is a parafiinic residue which containsv very littlematerial boiling below 500 F. Naphthenic or asphaltic residue are not as suitable since they consist to a large extent of cyclic and poly-cyclic hydrocarbons which have high coke-forming tendencies and which tend to produce intermediate cracked distillates of a cyclic character having relatively high antiknock characteristics which are not desirable in a Diesel fuel.

According to the present invention it is proposed to limit the reactions of decomposition as 55 far as practical to those of a primary character in the first stage of the process. Thus, relatively high temperatures of the order of 950 to 1100" F. and low time factors of the order of less than 5 seconds are preferably employed in the heating and reaction Zones. The pressure factor is important in determining the capacity of equipment but is not necessarily controlling.

The heated products from heater 6 pass through line 8 containing control valve 5 to a reaction chamber I0, Which is proportioned, along with the capacity of the heating element, to give the proper time factor in connection with the feed rate employed.

The total products from the reaction chamber may be discharged through line H containing control valve l2 into a reduced pressure evaporator I3, which functions to separate vapors containing Diesel fuel fractions and lighter fractions unavoidably produced from the heavier residual material. The vapor mixture passes through line I4 containing control valve l5 into a fractionator 16, which in turn serves to separate lighter overhead fractions and a Diesel fuel reflux. The overhead vapors pass through line l1 containing control valve i3 and the condensable portions thereof are liquefied during passage through a condenser 19 and passed together With uncon- .densed gases through line 20 containing control valve 2l to a distillate receiver 23 having the conventional gas release line 24 containing control valve 25 and a liquid draw line 26 containing control valve 21. The liquid produced at this point Will generally be a good cracked gasoline which can be blended with the corresponding product from the second stage of the process as desired. The Diesel fuel fractions are removed from the bottom of fractionator IB by way of line 28 containing control valve 29 and pass through a cooler 68 and thence through line 69 containing control valve to a receiver 30, which also is provided with a gas release line 3l containing control valve 32 and a liquid line 33 containing control `valve 34. The hot residual products accumulating in evaporator i3 are taken by Way of line 35 containing control valve 35 to a pump' 31 and discharged through line 38 containing control valve 39 into a heating element 40 arranged in a furnace setting 4l. The conditions of cracking in this secondary system are preferably more severe than those employed in the primary system, particularly in regard to increased pressure and time factor, the former only being limited by the tendency of the residue to deposit coke in the heater tubes and introduced hazards on account of local overheating. Temperatures of the order of from 850 to 950 F. are preferably employed at this point, and pressures as high as 500 pounds per square inch or higher may be used. Time factors are of the order of l0 to 40seconds depending upon the character of the stock introduced and the temperature employed. Y

The products from heater 40 pass through line 42 containing control valve 43 into a reaction chamber 44, which is of a suitable capacity to permit the use of the preferred time factors and which may be insulated to conserve heat necessary for the completion of the cracking reactions.

The total products from chamber 44 are transferred by Way of line 45 containing control valve 46 to a reduced pressure evaporator 41, Which is ordinarily operated at pressures from approximately -50 to 100 pounds per square inch and from which residues unsuitable for further conversion are Withdrawn through line 48 containing control valve 49 for use as fuel.

Vapors from evaporator 41 pass through line 50 containing control valve 5| to a second stage fractionator 52, which functions to separate the vapors into those comprising gasoline and fixed gases and heavier intermediate reuxes suitable for further conversion. The overhead passes through line 53 containing control valve 5d and through a condenser 55, in Which the gasoline vapors are liquefied to pass with uncondensed gases through run-down line 55 containing control valve 51 to a receiver 58 having a gas release line 59 containing control valve 60 and a gasoline .draw line '6| containing control valve 62.

'I'he intermediate insufficiently converted refluxes pass through line 63 containing control valve 64 to a recycle pump 65, which discharges through line 66 containing control valve 61, back to line 38 and thence to the second stage heating element 40 along with the primary residues from the first stage. A portion or all of the reflux may be withdrawn through line 55' controlled by valve 61 and passed through cooler 68, line 69 controlled by valve 10 into receiver 35 to augment the main supply o-f Diesel'fuel oil product.

'Ihe following example is introduced to illustrate the type of results obtainable in practice by a process of the present character. It is characteristic but is not introduced With the intent of limiting the scope of the invention correspondingly.

The charging stock to the process Was a Mid- Continent topped crude Which contained about 10% by volume of material boiling from 60G-700 F., the remainder boiling above '700 F. This stock was given a light cracking at a temperature of 910 F. and a pressure of 200 lbs. per sq. in., the oil being exposed to these conditions for a time of approximately 3 to 4 secs. As a result of this operation the following yields were obtained.

Per cent by Weight Fixed gas 3 437 F. end point gasoline 10 Intermediate distillate stock 20 Residuum 67 The intermediate fraction in the above tabulation had a cetane number of approximately 45.

The residuum from the primary cracking step was then further cracked using a temperature of 935 F. and a pressure of 300 lbs. per sq. in., and a time of approximately 30 secs. in the heating and cracking zones. The following tabulation indicates the yields of products by volume based on the primary residuum charged.

Per cent 405 F. end point gasoline 50 Cracked residuum 40 Gas 10 The blend of gasoline from the primary and secondary cracking steps had an octane number of 68-70 by the motor method, and the cracked residuum was 10W in suspended carbonaceous material so that it could be marketed directly as a Bunker fuel.

The nature of the present invention and its commercial value can be seen from the preceding specication and single example though neither section is intended to be unduly limiting upon its generally broad scope.

I claim as my invention:

1. A process for producing Diesel engine fuel and fuel for spark ignition engines from parainic and mixed base residues heavier than gas oil, which comprises, subjecting such residue to a temperature of from about 950 to 1100 F. for a cracking time of the order of less than five seconds, separating resultant vapors from unvaporized oil, fractionally condensing the vapors to form a condensate of hydrocarbons heavier than gasoline and removing this condensate from the process, subjecting said unvaporized oil to a temperature of from about 850 to 950 F. for a time period ranging from about 10 to 40 seconds to convert a substantial portion thereof into gasoline, fractionating the vapors formed by the lastnamed cracking treatment to condense fractions thereof heavier than gasoline, and finally condensing and collecting the fractionated vapors.

2. A process for producing Diesel engine fuel and fuel for spark ignition engines from parainic and mixed base residues heavier than gas oil, which comprises subjecting such residue to a tempertature of from about 950 to 1100 F. for a cracking time of the order of less than 5 seconds', separating resultant vapors from unvaporized oil, rfractionally condensing the vapors to form a condensate of hydrocarbons heavier than gasoline and removing this condensate from the process, subjecting said unvaporized oil to a temperature of from about 850 to 950 F. for a time period ranging from about 10 to 40 seconds to convert a substantial portion thereof into gasoline, fractionating the vapors formed by the lastnamed cracking treatment to condense fractions thereof heavier than gasoline, combining at least a portion of the resultant reflux condensate with the first-named condensate and'recovering the resultant blend as the Diesel fuel product of the process, and finally condensing and collecting the fractionated vapors.

J ACQUE C. MORRELL.

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