US2336056A - Method of converting oil - Google Patents

Description

7, 1943.- D. B. BELL METHOD 0F CONVERTING OIL Filed Deo. 26, 1959 gasoline.

Patented Dec. 7, 1943 METHOD 0F CONVERTING OIL `Initial E. Bell, Long Beach, Calif., assigner to Kenyon F. Lee, Los Angeles, Calif., as trustee Application necesitar ze, 1939, serial No. 310,914

e claims. (ci. 19e-c5) This invention relates to a method for conversion of hydrocarbon oils, particularly petroleum oils, into lighter oils. It is more particularly directed to a process for conversion of petroleum oils of high molecular weight into petroleum oils of lower molecularweight, as for instance, the conversion of crude oils and residual oils into gas oil and gasoline.

This invention is particularly directed to the conversion or petroleum oils and more particularly crude and residual oils by processes involving the action of oxygen or air upon such oils.

In the processing of the heavier type of oils,

v such as,` for instance, heavy gas oils ci end point in excess of about 650 F., residual oils or crude oils, the conversion which may be effected by may therefore not be heated in stills or in tubes to produce large rates of conversion', that is, Ato high cracking temperatures or ior prolonged periods of time because of such carbcni'zing tend-v ency. In the cracking oi such heavier oils it is therefore the practice to limitsuch conversion to a minor degree, especially .when causing such conversion in tubes, to produce not much more than a viscosity reductionof the heavy oil, with but a minor formation of gasoline. Where it is desired to obtain higher conversions to gasoline and to obtain higher yields of light gas oils from such crude oils and residual oils, coking operations are resorted to. In these coking processes the oil is heated to a relatively high temperature but given insumcient time'in the tubes to cause a material cracking of the oil While in' the tubes, and discharged into large soaking chambers Where the heated oil digests until it is reduced to a coke. The gas oils thus produced are re-V cracked to Obtain higheryields of gasoil and In converting heavy oils suchas residual Oils and heavy gas oils to coke, it is usual to heat the oils to about S50-950 F. `and permit the oil to digest in large chambers. The distillates which are produced are all of the heavy gasoil type;

lighter bodies with high yields of gasoline and light gas oils, valuable as cracking stock and as Diesel fuel, by so controlling the course of the reaction between the oil and air as to inhibit any substantial generation of carbon monoxide or carbo-n dioxide, with minimum formation 'of oxygenated bodies, if the course of the reaction be directed to convert the oxygen contained in the air primarily into Water. By so doing I have found that the xed gas formation from the treated oil is not greater and frequently is lower than that for treating like oils thermally to produce much lower yields of light products, and the formation of coke much less. I do not Wish to be bound by any theory of the reaction, but since large quantities of Water are formed in the reaction, it is probable that subtraction of hydrogen from the oil occurs either directly by a dehydrogenation process, or by a stage oxidation to form oxygenated bodies which then either internally or by mutual reaction produces Water by dehydration process, that is, the subtraction of HOI-I from one or more molecules. The production of gasoline of relatively low A. P. I. gravities, that is, high aromaticity, indicates that an aromatization process is also involved.

One of the characteristic features of this proc--A ess is the conversion of material proportions of the oxygen into Water. I have found that by proper control of the reaction as described above, I can direct the conversion of substantially all the oxygen employed into water. Without intending to limit myself by any theory, Ibelieve that the generation of such material proportions of water 'constituting a, material proportion, up

to substantially all of the oxygen which is fed in with the air, indicates that the oxidation proceeds either directly or indirectlygto abstract hydrogen from the molecule; The gasolines that are formed by this process are of extraordinarily low gravity, indicating that they are of highly aromatic character far in excess of what would be expected by thermal cracking at such temperatures. Iam led to believe from the fact that Water is produced, and from the generation of low A. P. I. gravity gasolines, that the process is essentially one of aromatization and cycliaation.

One of the signicant features of this process is that the conversions occur at temperatures Abelow those usually encountered in thermal cracking for like or even lower yields, or for the production of gasoline of like aromatic quality. `[Ihe yields of` gasoline and light gas oil cycle stocks obtained on processing residual stocks and crude oils on a once through basis is high, considering that the temperatures obtained in the reaction zone are below what is usually considered necessary cracking temperatures. 'This indicates the reaction occurring is not merely one of thermal cracking but probably of deep seated chemical reactions occurring between the charge and the air. Such reactions are probably not simple dehydrogenation or simple thermal cracking, but undoubtedly involve both catalytic and non-catalytic action of complex nature by the air. It is to be understood that the process as herein disclosed operates without the presence of any oxidation catalysts, although it does not exclude the possibility of the use of oxidation catalysts. For the purpose, however, of this description, it

will be understood that the process herein specically disclosed and illustrated by the examples, operates without any catalyst.

I have found that in order to prevent excessive oxidation by air and partial combustion of the oi1,that is, theV generating of carbon monoxide andcarbon dioxide, and the direction of the course of reaction to produce mainly hydrocarbons and to inhibit the production of oxygenated bodies' other than water, it is desirable to control the ratio of air to oil present in the oxygenation oil reaction zone. But also of great importance is the control of the mixing of the oil and air. If the mixture is notrproperly made there will be local zones wherein the ratio of air to oil is higher than that represented by the average, causing local Zones of partial combustion, resulting in the generation of excessive high local temperatures, causing an excessive cracking and oxygenation. `This, produces low yieldsV of gasoline and desirable gas oil fractions, and the production of lundesired oxidation products,-gas and coke, notwithstanding that the average temperatures'measured,A and average rates of oxygen and oil-are under relative control. i

. yI have. found it desirable to so design the mixing nozzles as to bring a relatively small stream of oxygen and oil togetherV and to cause a relativelyrapid reaction to take place, which is completed ina relatively short time so that the total Zone of the reaction is relatively restricted. This may bevaccomplished by mixing the oil and air in a-restricted stream in a line ofsuch diameter related to the volume ofoil and gas introduced that high turbulence and rapid mixing occurs,Y and then after passage for a short distance through said restricted stream to expand the mixture into an enlarged space many times greaterin diameterthan the mixing tube. ,I have also found it desirable, having obtained a proper control ofthe mixing, to control the air rates to a relatively low value in the neighborhood of about to 50 c ubic feet (when measured at atmospherictemperature and pressure) per liquid gallon .o oil feed. The air rate will depend upon thenature of the stock being processed and will have tobe adjusted to the temperature of the oil entering the reaction zone, but it will be found that by controlling the rate so as to limit the reaction to prevent partial combustion and to ,limit or inhibit the production of carbon dioxide'and to cause a substantially complete conversion' of the oxygen to water, having due regard for the process herein described, the proper air rate willl be capable of ascertainment by those skilled inthe art. v y 'l V I have also found it'desirabl'e to limit the temperatureof the oil yentering lthe reaction zone. It has beenY my observation that if the temperaturemofl the oil be permitted torise to the neighborhood of a normal cracking temperature before admission of air, that it is dirlicult to control the air rate and the mixing to prevent the production of large quantities of oxygenated bodies, gas, lamp black, coke and low yields of desired'products. When the feed employed is a straight run fuel oil, i. e. one produced by ordinary distillation, these precautions are particularly desirable. The reaction rate is so rapid that it is difcult for the proper mixing to occur, resulting in local Zones of overheating and excessive reaction. Y

Additionally I have found, particularly when operating with heavier types of oils, that it is desirable to limit the temperature of the oil entering the oxygen reaction zone, since the reactions occurringV with oil when at low temperatures whenadmixed with air is difierent from that which occurs when mixed with heated air or vwhen using oils heated to or approximating their thermal reaction cracking temperatures. When so heating the oil to its thermal reaction cracking temperature and admixing with either cold or preheated air, I nd that a greater percentage of oxygenated bodies and the degradation of the oil to fixed gas and coke results.

By reacting the oil with oxygenV at temperatures below thermal cracking temperature, I find that it is possible to inhibit the conversion of the oil to substantial quantities of carbon dioxide and carbon monoxide, and also to limit the degradation of the o-il to hydrocarbon fragments of molecular weight lower than that required for the gasoline boiling range.r Without intending to limit myself to any theory, I believe that the probable explanation of this phenomenon resides in the fact that if the oxygen is reacted with oil after exposure to cracking temperatures and other cracking conditions, the oxygen also reacts with the hydrocarbon fractions lighter than the charge which are generated by the cracking, as for instance,rthe light gas oils and the gasoline fractions, causingtheir degradation with a subsequent reduction in yield and increase in f gas formation. Additionally it is also probable that the products formed by reaction of heavy oil with oxygen at high temperatures will form a greater proportion of gas and coke than will the reaction of oil at lower temperatures. v,

I therefore find it desirable to cause the commingling of the oil and the oxygen-containing gas, such as air, by preheating the oil to an oxygen reaction temperature but not to a temperature at which any material cracking of the oil will occur under conditions of heating, and thereafter commingling the oil with air, and byso doing I am able to cause the commingling of the oil and the air in an intimate manner and to permit the reaction temperature to rise to conversion temperature without excessive generation of fixed gas and to obtain a high yield of motor fuel with the concomitant generation oflight gas oils available as cycle stock for cracking or as Diesel fuel.

I have found it desirable to maintain the reaction mixture at about its reaction temperature for a period of time topermit a further-reaction and conversion of the oil-into lighter bodies. This may be advantageously accomplished by passing the oil from the restricted reactionzone into an enlarged reaction chamber wherethegvapors' and unvaporized oil are permitted to digest `for a. period of time while passing-throughthereaction' zone. l l' lI have found it sufficient and desirable -to nreheat the oil to about the incipient vaporization point of the lighter fractions of the oil. The oil, in a substantially unvaporized state, is admixed with the air. The minimum temperature permissible is that at which air will react rapidly with the oil, that is, its catch point or the oxidizing temperature. This temperature limitation, it will be found, for fuel oils, heavy gas oils and-crude oils, will be met by temperatures ranging from 450 F. upwards and for practical purposes it will be found that temperatures within the range of 50G-700 F. will be found practicable. For fuel oils which contain but minor proportions of products vaporizable in the range of 550-650 F., Ifhavefound that the preheat temperatures of about 55u-650 F. are usefully employed. The proper temperature of preheat will depend upon the oil employed, the rates of oxygen used and the controls established in the process, as will be understood by those skilled in the art. By employing the principles herein described, those skilled in the art will be able to choose the most economical temperature of preheat to give the best results in this process.

Heavy gas oil and fuel oils may be converted by this process to produce a maximum of light distillates and coke as a final product. Thus if the oil at the chosen temperature of Preheat, i. e. 550-650F., is commingled with air under conditions of mixing previously specified, the oil may be raised to 850-950 F. The temperatures of S75-900 F. will be found useful for most residual oils.

The oil will thus be converted to produce maximum yields of gasoline and be raised to a desiri able coking temperature with a minimum or substantially no combustion of the oil and generation of carbon monoxide and carbon dioxide, and with the production of substantially no oxygenated products other than water. The oil is converted into large yields of gasoline and light gas oil and is introduced into an enlarged coking chamber in which the oil digests at a temperature of about 900 F. until it is reduced to coke.

It is an object of this invention to convert oil residuums to produce light bodies and coke.

'It is an additional object of this invention to process oils and particularly residual oils to convert 'said oils into gasoline, other distillate products and coke by reaction of the oil with oxygen or oxygen-containing gas.

, It iis an object of this invention to cause the conversion of oil such as residual oils to produce gasoline and heavier oils by reaction of oil when brought to a temperature below its normal thermal cracking temperature with oxygen-containing gasto raise such oil to a coking temperature Without any substantial combustion of the oil.

This invention will be better understood by reference to the figure, which is a schematic showing of the invention.

' ,Oil from a source of supply is passed through line I bypump 2 and through heater 3 and transfer line f4 to the evaporator 5. Vapors are removed from the evaporator by vapor line 6 and condensed in 1. The distillate is separated in separator 8 and the uncondensed gases are removed through valved line 9. Part of the condensate is passed through line I0 and pumped by pump II through the reiiux line I2. The unvaporized portion is withdrawn by pump I3 and passed to line I4. Oil may be passed either through valves I4a or I4b as desired. If passed through I4a with I4b closed or partially open as desired, theoil is passed into the mixing T I5 -where it meets a stream of air controlled by valve I6. The commingled air and oil passes through line I1 into reaction chamber I8. If the reaction chamber is desired to be by-passed, valve |4a is closed as is the valved outlet from I8, andthe oil is passed through v|41) into T I5a. Air may be passed through valved line I6a. In either circumstance, the commingled air and oil passes through I9 and by proper manipulation of the valves 2I and 25 and 21 and 28 are introduced either into the coking chamber 22 by line 20 or into the coking chamber 26 by line 24. The vapors passing either through 22 or 26 by proper control of 2'I and 28 pass through 29 into rectiiier 30, Where they are separated into a heavy gas oil fraction which is Withdrawn through 3l and line 32, or a light gas oil fraction which is Withdrawn through line'40 by control of valve 4I, and gasoline which passes through line 33 is condensed in 34, separated from the uncondensed gases in 35 and part removed via line 42 controlled by valve 43 returned through line 31, pump 38 and line 33 as a reflux in rectifier 30. The uncondensed gases are withdrawn through 36 and they may be passed to an absorption system for recovery of gasoline in the gases. No illustration is here made of the method of removal of coke from chambers 22 and 26, since these `are now conventional. Such means are either the use of chains which are positioned in the chamber, which onwithdrawal remove the coke, or boring tools or rotating sprays for cutting out the coke; as'will be understood by those skilled in the art.

As an illustration of the application of this process, the following may be taken as an example. Oil, which may be crude oil, may be passed through heater 3 into evaporator 5 and the temperature maintained so as to remove the light gas oils and gasoline and to leave a bottoms at,V for instance, a temperature of 60G-650 F; This temperature is below the normal cracking temperature of the residual oil. It is at substantially the incipient vaporization temperature of the bottoms, since they have been stripped at this temperature. It is passed to the air reaction zone. The pressure on the system at this point will be sufficient merely to pass the oil and vapors through the system, say at a pressure of 25 to 100 pounds. In T I5 the oil meets air at a pressure sufficient to introduce it into the system at proper velocity. which of course depends upon the back pressure in the system.`

.Thelair rate will be in the neighborhood of 25 to`100.cubic feet per gallon of feed, or sufficient toV raise` the temperature of the oil to about S50-950 F., preferably around 900 F. The air is here specified at normal atmospheric temperature and pressures. The oil is then passed through the short section of pipe I'I and then through enlarged reaction zone I 8, where it is given additional reaction time. Frequently with some oils, the reaction caused by the mixing of the oil in the T and the pipe sections connecting it to the coking chambers 22 are suiiicient, in which case the reaction zone may be by-passed by closing valves Illa and by-passing the oil through I4b into the mixing zone I5a, where it meets a stream of air under the proper conditions and proper rates, and then is passed into line I9.

However reacted, the mixture passes through line I9 and either into chamber 22 or chamber mixture is passed into 22. The unvaporized oil f accumulates at the bottom of the chamber 22 and being at the coking temperature continues coking. The vapors caused by the oxygen reaction and the vapors generated by the coking of the oil are given some digestion time in the top portion of the coker 22 and are passed into the rectifying Zone 39 where they areseparated by rectification into a, heavy gas oil whichis removed from 32 and light gas oil which is removed through 40, and the gasoline which lis collected in 35, part being used for reuxing and part withdrawn from the system. When A22 has been lled with oil and coke it is cut from the system by valve 2| and the oil is passed to 26. Evaporator ecker Z2 may be allowed time to finish digestion and coking and then may be opened to discharge coke. l

It will be seen that while this system Vhas Ybeen described ras operating on a reduced crude which is removed from the evaporator 5 at the required reaction temperature, other residuums such as cracked residuum and residuuin from vother air conversion` processes may be passed to this s-ystem. These oils are conveniently -raisedl to a temperature substantially similar to that illustrated above, that is, to a temperature of about 550-650 F., and reacted in substantially .the same way. It will be preferable in certain circumstances not to raise the temperature ofthe oil `to cracking temperatures or to a temperature substantially approaching such temperatures, because the conversion -occurring with Iair Yin `the reaction Ts will be so excessive' as to cause coking of the lines and plugging of the T"s. Thus residual oil which has been heated to a temperature of about 800 F., especially if containing quantities of coky material, when 'reacted with air under conditions tov cause the conversion here described, and to obtain the coking temperatures, will cause-a plugging of the lines, that is, andexcessive conversion to coke .in the constricted transfer passages. 1t is therefore desirable inthis process that the 'stock entering the reaction lZone, particularly iffa cracked stock, be passed to the reaction Zone at a temperature considerably below 800 F., and preferably at a temperature of about S50-650 F. In -so doing the reaction will proceed as described with a minimum of coking difculties in that portion of the system where coking Would'be undesirable. VIt is likewise desirable Vthatthe charge to the reactor be one which contains but a minimum amount of 'coke or coke-like materials, since the conversion causes a con-centration of these coke materials in theunvapori-zed i modifications may be made therein within the scope of the appended claims.

I`claim:

1. A method for converting residual oils into lighter fractions and coke which comprises .preheating relatively heavy liquid oil Yto a temper'ature below the cracking temperature of said oil to `a temperature not exceeding 700 F., mixing said preheated liquid oil with air while substantially in the unvaporized state in a restricted stream and without further external heating -of said oil, passing said mixture beforeV a, gasoline forming or combustion reaction takes place into an enlarged reaction space yWhere the mixture is allowed to react for a period of time in commingled state without separation of component parts of said mixture to attain a temperature of about SDU-950 F. solely by reaction of the air introduced into the mixing zone with the oil Vin said expansion zone andY without combustion thereof, controlling the rate of feed of oil and air to cause said conversion without forming any substantial amounts of carbon monoxide and carbon dioxide, regulating said temperature of preheat and said rate of feed of oil and air to cause said reaction to rise to a coking temperature, introducing said mixture from said reaction space into a digestion zone where the oil accumulates at a coking temperature and is converted into coke and vaporous products substantially free of carbon monoxide and carbon dioxide, separating saidvaporous products from said coke, and separatingV gasoline from said vaporous products.

2. A method for converting residual oils into lighter fractions and coke which comprises preheating relatively heavy liquid oil to a temperature below the cracking temperature of said oil, up to about 650 toV '700 F., mixingsaid preheated liquid oil with air while substantially in the unvaporized state in a restricted stream Yand without further external heating -of said oil, passing said mixture before a gasoline forming or combustion reaction takes place into an enlarged reaction space Where the mixture is allowedy to react for a period of time in commingled state without separation of component parts of said mixture, controlling the rate of feed of oil and air to said mixing zone at the rate of about 25 to 100 cubic feet, measured at atmospheric temperatures and pressures, per gal- Y lon of oil to cause said conversion, regulating

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