US2014350A - Making a motor fuel - Google Patents

Description

Sept. 10, 1935. E, E, AYRES 2,014,350

MAKING A MOTOR FUEL Filed April 15, 1951 Eugeneg yre s,

Patented Sept. 10, 1935 UNITED STATES PATENT OFFICE MAKING A MOTOR FUEL poration of Texas Application April 15, 1931, Serial No. 530,374

Claims.

This invention relates to making a motor fuel; and it comprises a method of making motor fuel in better yield and of better quality by cracking or pyrolysis wherein oil is submitted to a high 5 cracking temperature, between 800 and 1050 F. in an atmosphere of hydrogen, the hydrogen being present in substantial amount and the heating to the cracking temperature and the cooling down of the mixture of hydrogen and cracked products being quickly effected through the temperature range at which substantial hydrogenation would occur; all as more fully hereinafter set forth and as claimed.

The present invention relates more particular- 1y to a method of decomposing hydrocarbons by heat under conditions favorable to the control of yields and of qualities of products obtained. One of the objects of the invention is the production of relatively stable motor fuel of high antiknocking quality. A further object of the invention is the conversion of a larger proportion of hydrocarbon charge into motor fuel in a single passage through a heating element than can usually be secured by previously known methods of pyrolysis. A further object of the invention is to avoid the formation of substantial amounts of coke while operating at relatively high temperatures. A further object of the invention is to secure an improved volumetric yield of liquid products. A further object of the invention is the production of a relatively small proportion of fixed gas. A further object of the invention is to secure a residue boiling above the motor fuel boiling range but having a lower boiling range than is commonly obtained by other methods of pyrolysis.

The objects stated are attained and certain new advantages gained by the process of the present invention wherein heavy oils are cracked in an atmosphere of hydrogen but at a temperature precluding determinable hydrogenation. The hydrogen restrains cracking with a production of gases rich in hydrogen but is not itself added to the oil. In the atmosphere of hydrogen conveyance of heat from the walls to the vapor is much facilitated because of the mobility of the hydrogen molecule and because of the high specific heat of hydrogen as compared with hydrocarbon vapors.

My invention is applicable to the formation by pyrolysis of motor fuels from distilled charging stocks and my invention is also applicable to the formation of motor fuel and gas oil from heavy asphaltic residual charging stocks.

It is well known that improved products may be obtained by contacting hydrocarbon material with hydrogen under conditions of temperature, pressure, and catalysis favorable to the hydrogenation of the hydrocarbon. Such hydrogenation has for its object the improvement of yields and 5 qualities by the addition of hydrogen. But I have found that certain desirable effects such as those listed above can be secured by heating hydrocarbon material in the presence of an excess of hydrogen under conditions of temperature, pres- 10.

sure, and catalysis distinctly unfavorable to hydrogenation. Because of the dehydrogenation that may occur in my process, the total liquid hydrocarbon products of pyrolysis may contain less hydrogen than the hydrocarbon material used 15 as the charge.

In the practice of my invention, oil, with or without a catalyst, is pumped, under suitable pressure together with compressed hydrogen, through a tubular heating element where the oil- 20 hydrogen mixture is subjected to cracking temperatures. After leaving the tubes of the heating element, the oil-hydrogen mixture is cooled and separated. The hydrogen may be recirculated through the heating element if desired, but 25 such recirculation will be attended by a progressive dilution of hydrogen by the gaseous hydrocarbons, such as methane, ethane, etc., formed by pyrolytic decomposition of the liquid charging stocks. I have found that in order to secure the 30 specific results of this invention, it is desirable that the circulating fixed gas contain sufficient free hydrogen to make the weight of free hydrogen not less than one-half of one per cent of the weight of the oil with which it is in contact. In 35 recirculating the gas, therefore, it is desirable to withdraw or bleed off from the system a sufficient proportion of the gas to maintain the above described condition with a corresponding addition of hydrogen to the system if neces- 40 sary. The withdrawn mixture of hydrogen and other gases can be (1) fractionated, or (2) treated by known methods for the conversion of hydrocarbon gases to hydrogen, or (3) burned as fuel. 45

By promptly cooling the oil-hydrogen mixture from high temperatures through the range of temperatures in which hydrogenation is active, hydrogenation is avoided and the particular objects of my invention are secured. 50

In the practice of my invention it is obviously essential that the temperatures to which the oilhydrogen mixture is heated must be above the temperature favorable to the hydrogenation equilibrium. Temperatures favorable to pyro- 55 lytic decomposition of petroleum are also favorable to dehydrogenation. I have, therefore, preferred to use the range of temperatures between 800 F. and 1050 F. At temperatures substantially below 800 F. it is possible for hydrogenation to take place and at temperatures substantially above 1050 F. pyrolytic decomposition is likely to be attended by the formation of coke.

In the practice of my invention I prefer to use a pressure between 1000 pounds and 5000 pounds per square inch, but satisfactory results can be secured at moderate pressures.

In the practice of my invention, the best results are secured by the maintenance in the circulating gases of an amount of free hydrogen between 2 per cent and 10 per cent by weight of the oil being processed, but satisfactory results can be secured by the use of smaller proportions of hydrogen down to the above described minimum of one-half of one per cent. Since the process involves no determinable consumption of hydrogen by reaction, the amount of hydrogen in the system tends to increase through a dehydrogenation of hydrocarbons, and makeup hydrogen is required only to replace physical losses and losses caused by the association of hydrogen with hydrocarbon gases withdrawn from the system.

The process is not sensitive to the rate of cool ing of the oil-hydrogen mixture leaving the tubes of the heating element unless an active hydrogenation catalyst is present, for the reason that the rate of hydrogenation is low in the absence of catalysts. In practice measurable hydrogenation can be avoided merely by avoiding the use of an active hydrogenation catalyst if the oilhydrogen mixture is not held in the temperature zone between 500 F. and 800 F. for more than one hour.

Examples of the application of my process are as follows:

Example 1.--Venezuela gas oil, 33.7 A. P. I. is pumped through the tubes of a heating element under a pressure of 3000 pounds per square inch. At the same time hydrogen, in the proportion of 6 per cent by weight of the gas oil, is circulated through the tubes of the heating element. With an oil exit temperature of 850 F., 100 barrels of gas oil charged yield 46 barrels of a distillate boiling up to 392 F. and 53.8 barrels of liquid residue, making a total of 99.8 barrels of liquid products. The weight of the gas formed is 6.3 per cent of the weight of the charge. No coke is observed in the tubes of the heating element nor is suspended in the residue. The weight of the 53.8 barrels of residuum equals the weight of 51.2 barrels of charge.

Example 2.-Venezue1a gas oil,34.4 A. P. I. is pumped under a pressure of 200 pounds per square inch through a cracking coil while circulating 5 per cent by weight of hydrogen. With an oil exit temperature of 820 F. from 100 barrels of Venezuela gas oil is obtained 15 barrels of distillate boiling up to 392 F. and barrels of liquid residue, making a total of barrels of liquid products' No' measurable quantity of fixed gas is formed. No coke is deposited in the tubes of the heating element.

Example 3.Cracking still tar, 9.6 A. P. I. is pumped under a pressure of 3000 pounds per square inch through the tubes of the heating element while circulating 1.0 per cent by weight of hydrogen. With an oil exit temperature of .900 F. from 100 barrels of charge is obtained 10.7 barrels of distillate boiling up to 392 F. and

93.9 barrels of liquid residue making a total of 104.6 barrels of liquid products. The 93.9 barrels of residue contains an amount of residue boiling above 590 F. which is 36 barrels less than the amount of such high boiling residue in the charge. The .amount of fixed gas formed is 0.5 per cent by weight of the charge. No coke is deposited in the tubes of the heating element.

In all of the above examples the reaction products were cooled through the temperature zone promoting hydrogenation (500 F. to 800 F.) in somewhat less than an hour. This prevented appreciable hydrogenation of the products obtained in the various processes.

In the above examples cracking is conducted under conditions of temperature and time of heating such that objectionable quantities of tar and carbon would be formed were it not for the presence within the cracking tubes of hydrogen under high pressure. Carbon deposition can not be prevented by the use of an inert gas under pressure, hydrogen with a mmimum concentration of 0.5 per cent is required. It would be impossible to obtain the yield of Example 1, for example, in an operative commercial process without using hydrogen in accordance with the present invention. Carbon would quickly form in the cracking tubes stopping the operation of such a process. By use of the present invention higher yields of .a light distillate can be obtained without any tendency toward the formation of tar or carbon, in fact the amount of high boiling residue found in the residual product is usually somewhat less than that found in the charge.

The interesting yield characteristics illustrated by the above examples are believed to result from molecular transformations of hydrocarbons.

It is possible that the reason for the beneficial effect of added hydrogen in this process is the effect of the hydrogen on the equilibria of condensaticn reactions between the hydrocarbons, but such an explanation is purely hypothetical.

In the accompanying drawing I have shown more or less diagrammatically an assemblage of apparatus elements useful in the performance of my process. The figure is a view partly in elevation and partly in section of the compressor, pump, heating coil, cooler, and separator with the necessary valves and pipe connections.

In accordance with a specific embodiment of my invention hydrogen is admitted to the compressor I through pipe and is delivered by pipe 8 leading from the compressor past valve 4 and globe 5 to T' 6. At the same time the oil which is to be subjected to pyrolysis, say Venezuela gas oil, 33.7 A. P. I., is admitted to pump 1 through pipe 8, discharged through pipe 9 equipped with pressure gage l0, orifice meter H, relief valve l2, check valve 13, and globe valve I l, to the T S. The mixture of oil and hydrogen passes through the pipe 15 to the coil l6 located within the furnace ll fired by suitable burner l8. While satisfactory results may be obtained at moderate pressures, I prefer to operate between 1000 to 5000 pounds pressure. With Venezuela gas oil I have secured good results while operating under a pressure of 3000 pounds per square inch. The hydrogen is admitted in the proportion of 6 per cent by weight of the gas oil.

The oil and hydrogen in the coil l6 are heated rapidly to 800 F. or slightly higher. With an oil exit temperature of 850 F. an extremely satisfactory distillate in large quantities is secured. The oil leaves the coil 16 through the pipe l8 equipped with pyrometer connection and pyrometer 20 and passes through pipe 2| to cooler 22 where the mixture is promptly cooled to a temperature below 500 F. This cooler 22 is diagrammatically shown but it may be of any ordinary type such as water cooled, air cooled and the like. The cooled mixture passes into the separator 23 from which the liquid resultants of pyrolysis are Withdrawn through pipe 24 equipped with globe valve 25 and slide valve 20, while the hydrogen with whatever hydrogen gas has been formed is withdrawn from the top of the separator through a line equipped with a pressure gage 2?, relief valve 28, globe valve 20 and slide valve 30. The distillate removed past valve 20 is sent to storage.

The hydrogen and the hydrocarbon gases which have been formed are sent to storage and the hydrogen may be recirculated through the heating element. Ordinarily I do not continuously circulate the hydrogen since there would be a progressive dilution by gaseous hydrocarbons. As before stated, the circulated gas should contain sufficient free hydrogen to make the weight of free hydrogen not less than one-half of one per cent of the weight of the oil with which it is in contact.

The apparatus described may be used to perform the process of the examples previously given and of course obvious modifications are possible.

What I claim is:

1. In the manufacture of motor fuels, the process which comprises cracking a hydrocarbon oil in a constricted reaction zone at temperatures ranging between about 800 and 1050 F., without the use of catalysts, in the presence of a pressure of 1000 to 5000 pounds per square inch of added hydrogen amounting to from about 0.5 to 1.0 per cent by weight of the oil, and conducting the process in such manner that said hydrocarbon oil will not be subjected to temperatures within the range of 500 to 800 F. for a period substantially longer than one hour, substantially no hydrogen being consumed or produced and substantially no coke being formed during the process; the conditions of temperature and pressure being such that a substantial proportion of the said oil is maintained in the liquid state.

2. In the manufacture of motor fuels, the process which comprises quickly heating in a restricted reaction zone an oil-hydrogen mixture, containing an amount of added hydrogen suiiicient to produce pressures ranging from about 1000 to 5000 pounds per square inch amounting to from 0.5 to 10 per cent by weight of the oil present, to temperatures between 800 and 1050 F., in the absence of hydrogenating and dehydrogenating catalysts, holding said mixture under the stated conditions thereby effecting cracking without substantial production of hydrogen and Without the formation of coke and then charge, no consumption of hydrogen taking place and substantially no coke being formed in the process.

4. In the continuous manufacture of motor fuels, the process which comprises quickly heating in a reaction zone of restricted cross sectional area an oil-hydrogen mixture, containing an amount of hydrogen sumcient but not substantially exceeding the amount required to prevent coke or carbon formation from the oil or its derivatives under the conditions of reaction, maintaining a pressure between 100 and 300 atmospheres and a temperature between 878 and 950 F. in the reaction zone in the absence of hydrogenating or dehydrogenating catalysts, maintaining said mixture under the stated conditions as the mixture passes through the reaction zone, thereby effecting cracking of the oil Without substantial production of hydrogen and without the formation of coke, and then immediately thereafter quickly cooling the reaction mixture to a temperature substantially below the reaction temperature, the heating and cooling occupying a period such that substantial consumption of hydrogen in the process is avoided.

5. In the manufacture of motor fuels, the process which comprises continuously passing through a heating zone in a flowing stream of restricted cross-sectional area an oil-hydrogen mixture containing an amount of hydrogen sufiicient but not substantially exceeding the amount required to prevent coke or carbon formation from the oil or its derivatives under the conditions of reaction, quickly heating the mixture during its passage through said heating zone to a temperature between about 800 and 950 F., then passing the mixture through a reaction zone of restricted cross-sectional area wherein the mixture is maintained under high superatmospheric pressure and at a temperature between about 800 and 950 F. in the absence of hydrogenating or dehydrogenating catalysts, and immediately thereafter quickly cooling the reaction mixture to a temperature substantially below the reaction temperature, the heating, reacting and cooling times occupying periods such that substantial cracking will be effected and substantial production or consumption of hydrogen avoided.

EUGENE E. AYRES.

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