US2336505A - Process fob conversion of asphaltic - Google Patents

Description

Dec. 14, 1943. v sALMl 2,336,505

PROCESS FOR CONVERSION OF ASPHAl-TIC HYDROCARBONS Filed Jan. 27; 1941 Patented Dec. 14, 1943 arrests PROCESS FOR CONVERSION OF ASPHALTIC HYDROCARBONS Vaino A. Salmi, Los Angeles, Calif., assignor to Metallytic Corporation, Los Angeles, Calif., a corporation of California Application January 27, 1941, Serial No. 376,104 4. Claims. (or. 196- This invention relates to the conversion of high boiling hydrocarbon oils into hydrocarbon oils of lower boiling point, and particularly to the conversion cf asphaltic hydrocarbons into hydrocarbon oils of the lubricating oil boiling point range, this conversion being efiected by a simple heat treatment or pyrolysis. These asphaltic hydrocarbons occur either as such or together with lighter hydrocarbons in petroleum, in the destructive distillation products of coal, shale, peat, wood, etc.

In the pyrolytic conversion processes now knownusually referred to as cracking processes-asphaltic stocks are subjected to a more or less severe heat treatment, depending upon whether the object is to produce a maximum possible yield of lighter fractions, such as light motor fuels, or to increase the percentage of the intermediate fractions, such as gas oil and lubrieating oils.

In case of severe cracking in the processes now known, asphaltic bodies are decomposed in a manner which results in the formation of solid residues, coke, and non-condensible gases, which gases have a higher hydrogen-carbon ratio than the original oil stock, the oil stock being thus robbed of part of its valuable hydrogen content. If any lubricating oils are produced, they appear only as intermediate products and constitute at any one time only a relatively small part of the total oil stock.

In case of milder cracking, sometimes called viscosity breaking, the processes now known are capable of only a relatively low rate of conversion, if the actual asphalt content is taken into consideration. Coke and gases may not form to any appreciable extent but the residual asphalt is even more viscous and less amenable to further heat treatment apparently as a result of polymerization reactions.

As a consequence of the reactions taking place in the pyrolytic conversion processes now known,

the theory has been generall accepted that, if asphaltic hydrocarbons are subjected to pyrolysis, a multiplicity of reactions is induced simultaneously, so that lubricating oils, for instance, constitute at any one time only a part of the reaction products.

I have discovered that asphaltic hydrocarbons may be converted into lubricating oils completely, or, at any rate, to an extent not possible by other pyrolytic processes now known, if they are heated to a certain temperature range, and means are provided to rapidly introduce the endothermic heat necessary for the asphalt lubrieating oil reaction, but under such conditions that the temperature of the all stock under treatment is prevented from rising above the proper reaction temperature. Thus, the asphalt-*lubrieating oil reaction, which is endothermic and evidently capable of proceeding very rapidly under proper conditions, is favored in preference to the polymerization reactions, which are exothermic and evidently proceed relatively slowly within the same temperature. By preventing the temperature from rising beyond the asphalt-flubricating oil reaction temperature range,"reactions of other nature are prevented from tak ing place.

The extreme rapidity of the asphaltlubricating oil reaction is, in fact, an important factor to be taken into consideration in establishing and maintaining conditions favorable for said reaction. Unless the conditions prevailing in the reaction zone are sufficiently favorable for the reaction, so that it may be completed within a very shirt periodevidently within a few seconds at the mosteither no such reaction takes place or the extent of conversion is limited.

Such rapid transfer of heat into the reaction zone may be accomplished by bringing the hy-' drocarbon oils into contact Withsubstances of high heat conductivity and of high specific heat, under conditions more fully specified further on.

Most suitable as heat carriers are metals, mixture of metals, or alloys which can be kept in the molten state at the temperature to be maintained in the heat transfer medium. Employing the metals in the molten state has the advantage of further facilitating the transfer of heat, as th molten metals can be kept in motion While in contact with the oil, a condition which also prevents the formation of coatings of carbon between the metal and oil.

The art, of employing molten metals as heat transfer mediums in the treatment of hydrocarbons is, of course, well known but, in the known processes, the object has been to maintain conditions which bring about-the well known reactions of cracking already referred to above, or condi tions merely bringing about the distillation of the volatile constituents of the oil stock, whereas, in my process, the object is to maintain condition which bring about pyroly'tic reactions of one type exclusively, or at, least relatively speaking so;

To further facilitate rapid transfer of heat from the heat transfer medium to the stock under treatment, the temperature of the heat, trans: fer medium is kept at a considerably higher level than'the temperature necessary for the reaction; also, the heat transfer medium, such as molten metal, may be kept in motion as this accelerates the transfer of heat, not only from th medium to the oil stock but from the primary heating surface to the medium.

Rapid transfer of heat is also assured by keeping the quantity of oil stock in relation to the contact surface of the medium to the minimum. In this way, the maximum possible percentage of the oil stock being heated is subjected without interruption to the condition favoring the asphalt lubricating oil reaction, in preference to the polymerization reactions. This is preferably done by floating the oil stock in the form of a thin layer or film on the surface of the medium.

This is another reason why it is preferable to While on one hand, the objectof my invention is to provide a rapid transfer of heat to the oil stock under treatment, another object is to prevent the temperature of the oil stock from rising above the range favorable for the asphaltlubricating oil reaction, as embodied in the principle disclosed above. In this respect; it is to be remembered that the asphaltlubricating oil reaction i endothermic. Conditions favoring such reaction, therefore, tend to prevent the temperature from rising in the reaction zone, while conditions favoring the polymerization of the asphaltic stock again would cause a rise in the temperature. Therefore, the more rapid the rate of conversion, the less tendency there is for the temperature in the reaction zone to rise beyond the proper range. Therefore, keeping the amount of oil present in the reaction zone to the minimum in relation to the contact surface also helps to prevent the temperature from rising during the conversion reaction.

Whether the metallic heat transfer medium also acts in the role of a catalyst is difficult to determine. At any rate. besides a possible catalytic action, conditions bringing about the type of heat transfer specified above are necessary for conversion. I have found that asphaltichydrocarbons may be brought in contact with a metallic heat transfer medium within the temperature range which would otherwise be favorable for conversion, and yet no conversion takes place unless heat is transferred under the conditions specified above. It is also to be remembered that true catalytic phenomena are specific to certain substances; certain metals, for instance being active in bringing about a certain catalytic reaction, while others at the same time are entirely inactive as far as the same reaction is concerned. Yet. from the experiments made, I have reason to believe that the conversion reaction in question can be brought about by employing as a heat transfer medium any molten metal, alloy, or mixture of metals. At any rate, I have employed lead. tin. zinc. and antimony, either singly or in a su table combination to obtain the necessary melting point.

The present application is for an improved process. which in its ori inal form was disclosed in my Patent No. 2.269.485 which issued Jan. 13, 1942. In said patent. the asphaltic stock was brought in contact with the molten metal by in troducing it either on the surface of the metal bath. or a short distance below it, such as four inches. At the same time, suihcient carrying gas. preferably steam. was introduced into the metal bath to rapidly volatil ze the oil stock so that the layer of oil on the surface of the bath was kept to the minimum. the gas at the same time keeping the oil and medium in constant motion, and thus accelerating the transfer of heat and, conseouently, the rate of conversion.

In one modification of the process. the metal bath was maintained at a temperature from 450 to 550 C. and sufficient carrying gas was passed through the medium and. oil to rapidly volatilize not only all the converted oil but any of the asphaltic stock which might remain unconverted in a single passage through the reaction zone, the unconverted asphalt then being returned into the process with fresh feed stock. As was explained, the volatilization of the unconverted asphalt under such conditions need not be considered as true vaporization but as being due to entrainment of asphalt by the lighter oil vapors or being carried over in the form of a fog.

In another modification of the process, the metal bath was maintained at a temperature of about 400 C. and sufficient carrying gas, preferably steam, was introduced to volatilize all the converted oil. The unconverted asphaltic stock, which could not be volatilized under such conditions, was drained off the surface of the bath as rapidly as possible to keep it down to the minimum, and was then treated at a higher temperature.

Now, I have been able to simplify and improve the process so that its practical and economical value has been greatly enhancedespecially when treating crudes of a high asphalt content. In case of such high asphalt crudes, the use of excessive steam would greatly affect the economical value of the process, as such oils are, as a rule, ultimately destined for the generation of power or heat. Moreover, if such oils are brought in contact with molten metals and agitated with them-especially if steam or gases are employed-part of the heavy oil will be entrapped in the metal, and will ultimately coke, forming a solid slag carrying a large percentage of clean metal, the recovery of which would result in a cumbersome and expensive operation.

I have found that it is possible to greatly reduce the amount of steam or other carrying gas, and even entirely to eliminate it if necessary, and in any case to operate under conditions where the formation of slag referred to above is prevented.

It is a general object of the present invention to provide an improved method and apparatus for the conversion of asphaltic hydrocarbons into lubricating oils.

Further objects and aspects of the invention will become apparent in the following description made with particular reference to the drawing, in which:

Fig. 1 is a vertical section of apparatus suitable for embodying the present invention;

Fig. 2 is a section taken along the line 2-2 of Fig. 1; and

Fig. 3 is a section of a reaction vessel alternative in form to that shown in Fig. 1.

Referring more particularly to Fig. 1, the crude asphaltic stock is brought from any suitable source into a pipe in and preheater coil I l adapted to be heated by furnace gases, and thence through a second preheater coil l2 arranged to be fired by a burner l3, and thence into a pipe 14 provided with a thermometer l5, a pressure gauge is, and a valved inlet pip I! serving for the introduction of steam, mixed gases, or other ancillary material, if desired. The preheated stock is then fed into a converter 2c. This converter comprises essentially a shallow cylindrical vessel 2|, the bottom of which is preferably provided with circular ribs 22 to reinforce it and to increase the area of heat transfer surface. The bottom of the vessel 2| is heated in any suitable manner, such as that indicated in the drawing Where a furnace 25 is constructed underneath the converter and provided with burners 26 spaced around the outer edges, the gases of combustion being led toward the interior of the furnace, subject to alternate deflection by the ribs 22 and a series of fire walls 2?, to be ultimately Withdrawn and passed in heat-exchange relationship with the preheater coil H by means of a flue 23.

A relatively thin layer of molten metal is kept in the vessel 2!, suitably an inch or so in depth, as indicated by the molten surface S-il. The vessel 2! is provided with a cover 2 3! to which is secured a spiral-formed band 32, mor clearly indicated in Fig. 2. This spiral band extends below the surface 33 of the molten metal, and in this manner an extended passage or duct is formed beginning at the center of the apparatus and ending at the outside circumference. At or near the outer termination of this duct a horizontal slot 35 is provided, this slot piercing the outside Wall of the vessel 2i and being vertically positioned as close as possible to the surface of the molten metal, in order to keep the oil layer on the metal surface to a depth. In operation, the asphaltic oil i fed in at the center by means of the pipe i l; the oil and vapors formed pass through the extended spiral duct and finally through the outlet slot By passing the oil stock containing asphalt, such as crude petroleum, through such an extended restricted duct or passage, the door of which is formed by the fiat smooth surface of the metal bath, the oil stock or asphalt is rapidly spread out into a thin layer and is constantly kept in motion in contact with the molten metal, a condition which favors the asphalt e lubricating oil reaction as claimed above.

As only a relatively thin layer of metal, such as an inch or two, is kept in the apparatus, the heat transfer from the outer heat transfer surface to the oil layer or film is rapid despite the fact that the metal is not excessively agitated.

The width and height of the duct is so designed that the vapors generated by volatilization of the light oils present in the crude feed stock or vapors formed by conversion will have enough velocity to force the oil stock into a thin layer and to keep it moving rapidly in contact with the molten metal. The cross section of the duct should be small enough to create this necessary velocity of vapors but not so restricted that a violent, turbulent movement of the oil stock and molten metal is brought about. A certain motion is, of course, imparted also to the molten metal; this is an advanta e as it assists in the rapid transfer of heat and prevents the formation of protective coatings of carbon on the heat transfor medium. As the molten metal is in free intercommunication under the spiral wall forming the duct, a free circular movement back to the center of the apparatus is possible.

If the oil stock worked upon does not contain a sufiicient amount of light fractions to produce the conditions necessary as regards vapor velocity, etc., gases or steam can be added, introducing it either all in the center of the apparatus or distributing it in different parts of the duct. The oil feed can also be distributed, preferably as evenly divided along the extent of the duct as possible.

The temperature of the molten bath may be conveniently indicated by means of a thermometer or other pyro-metric element lil. It is also desirable to employ a thermometer 4! to indicate the temperature of the hydrocarbon material issuing from the slot 35, since, as a rule, this temperature or at least the temperature of the vaporized constituents, should not greatly exceed 350 C.

The efiluent hydrocarbons are transferred by means of a conduit 42 into a separating vessel 43 in which liquid material, consisting largely of a relatively small quantity of unconverted asphalt, is separated from the vapors and withdrawn by means of a trapped Withdrawal pipe 44. A steam pipe 35 may be employed, if desired, to aid in the complete stripping of all vaporous materials from theliquid residue by the direct iniection of steam.

The vaporous constituents comprising the lubricating oil fraction formed by conversion of the asphalt are removed from the separator 43 by means of a vapor line 58 for segregation into fractions of diiierent boiling point. This may be conventionally accomplished, as by the illustrated partial condenser and rectifier 5 l, in which the lubricating oil fractions are condensed for withdrawal through a bottom line 52 and a partial condenser and rectifier 53 in which the light oils, such as gasoline and kerosene, may be condensed for withdrawal through a bottom line 54. The fixed gases which are normally produced only in slight quantity are preferably vented from the system by a valve 55, which may be set to maintain any desired back pressure on the system, although for the most part atmospheric pressure need not be widely departed from in order to obtain very good results.

Since it is always desirable to maintain the quantity of liquid hydrocarbon on the surface of the molten metal to the minimum quantity possible, i. e., to maintain the oily film on the surface of the metal as thin as possible, it is sometimes advantageous to conduct the eiiiuent hydrocarbon material underneath a ballie forming a boundary of the reaction zone, whereby the vapor constituents in the hydrocarbon effluent can skim the oil film from the surface by a process of aspiration.

Apparatus embodying this feature is shown in Fig. 3, in which a shallow cylindrical vessel 6% is placed over a furnace the details of which are not shown. In the vessel 5i) is kept a thin layer of molten metal having an upper surface bl. The entire vessel is closed by a cover c2, to which is securely fixed a spiral band 63, forming spiral passageways as described above in connection with Fig. 1. In the present embodiment, however, oil is introduced not at the center but near the outer periphery of the spiral passage by means or" an oil inlet pipe 64. Additional vapors, such as steam, may be added to the incoming fluid order to appropriately control the film velocity through the spiral passageway, such steam eing conveniently added by means of a valved inlet pipe 55. The moving film of liquid hydrocarbon, together with the overlying vapors, is disengaged from the conversion surface iii by means of a collecting stack 63 positioned at the center of the vessel. This stack comprises a cylindrical shell 61 terminating-in a lower sawtoothed edge 68. I

The triangular apertures afforded by the toothed edge E8 in eiTect determine the level iii of the molten metal since this level must sink under the pressure of incoming gases and fluids until the aper ures are uncovered by emergence from the molten metal, the excess rising to form a lead level 69 at a somewhat higher height in the collecting stack 66.

The vapors and liquid oil accumulating on the surface to in the stack 65 are removed by means of a drawoff line 10 for separation by distillation, etc., suitably as shown in Fig. 1.

It is desirable to link the drawoff it as close as possible to the upper molten metal level 69 in order to remove the oil as rapidly as it accumulates in the stack 66, but, on the other hand, sufficient difference in elevation between the level 59 and the drawoff 10 should be maintained to insure that fluctuations in molten metal levels, such as are always present to a greater or less degree during operation, will not result in loss of lead through the overflow pipe I9. I find that, in this connection, it is very advantageous to use a float 80 in the collecting stack, which float is of sufiicient bulk to greatly reduce the volume of oil corresponding to a given height of oil, the oil collecting between the float 80 and the inner wall of the stack 56. The float is preferably of such effective density as to float partly submerged in the molten lead or other metal so that it may rise and fall with variations in metal level, thus permitting such variations and fluctuations to take place without a violent uprush of lead through the annular oil-collecting zone surrormding the float.

It is sometimes advantageous to provide steam or flushing oil by means of a valved inlet line ill for the purpose of continually scavenging, or flushing, or cooling the interior of the collecting tack 55 and the molten metal surfaces therein.

In order to save the heating capacity of the main reaction vessel, the crude feed stock may be preheated, a preheat of about 300 C. being, as a rule, most advantageous. Regarding the temperature at which the heat transfer medium or molten metal is to be maintained, this depends largely on the nature of the stock to be worked upon, but temperatures from 425 to 525 C. may be considered most advantageous.

As is apparent from the description given above, the process is of extreme simplicityboth as to design of apparatus employed and cost of operation. No pressure or vacuum is necessary and even steam can be dispensed with entirely in many cases. The process can be employed as a primary topping or distillation process of crude oil stocks, such as petroleum, whereas, with processes now known, supposed to reduce the asphalt content of the crude oils, a preliminary topping step is necessary.

The process is, therefore, useful in producing higher yields of superior fuel oils and cracking stock; also, in converting residues from ordinary cracking processes into overhead distillates,

which then can be returned into the cracking unit. I have also found that, if high grade crude oils which are used for the manufacture of lubricating oils and which, as a rule, contain a relatively small percentage of asphaltic residue, are heated and distilled by the method disclosed, an improved type of lubricating oil distillate is obtained, which can be refined more economically than the lubricating oil distillates from ordinary distillation processes.

I claim as my invention:

1. A process for the conversion of asphaltic hydrocarbons into lubricating oil by contact with molten metal maintained at or above the conversion temperature of said hydrocarbons, Which comprises: forming a continuously advancing stream comprising the asphaltic hydrocarbons; providing two free surfaces of molten metal for contact and separation, respectively, said surfaces being separated by a baffle permissive of fluid flow therebetween under sufficient pressure differential; contacting the first surface with said stream whereby conversion of asphaltic hydrocarbons to lubricating oil is effected; maintaining a pressure on the first surface sufficient to cause the converted asphaltic material to transfer to the second surface; and separating the hydrocarbon material from the second surface, said second surface being smaller in area than the first surface.

2. A process for the conversion of asphaltic hydrocarbons into lubricating oil by contact with molten metal maintained at or above the conversion temperature of said hydrocarbons, which comprises: forming a continuously advancing stream comprising the asphaltic hydrocarbons; providing two free surfaces of molten metal for contact and separation, respectively, said surfaces being separated by a baffle permissive of fluid flow therebetween under sufficient pressure differential; contacting the first surface with said stream whereby conversion of asphaltic hydrocarbons to lubricating oil is effected; maintaining a pressure on the first surface suflicient to cause the converted asphaltic material to transfer to the second surface; and separating the hydrocarbon material from the second surface, said second surface being continuously flushed with a fluid adapted to facilitate separation.

3. A process for the conversion of asphaltic hydrocarbons into lubricating oil by contact with molten metal maintained at or above the conversion temperature of said hydrocarbons, which comprises: forming a continuously advancing stream comprising the asphaltic hydrocarbons; providing two free surfaces of molten metal for contact and separation, respectively, said surfaces being separated by a baffle permissive of fluid flow therebetween under sufficient pressure differential; contacting the first surface with said stream whereby conversion of asphaltic hydrocarbons to lubricating oil is effected; maintaining a pressure on the first surface sufficient to cause the converted asphaltic material to transfer to the second surface; and separating the hydrocarbon material from the second surface, said material being subjected to cooling immediately upon arrived at the disengaging surface.

4. A process for the manufacture of lubricating oils, fuel oils and the like from asphaltic hydrocarbons which are initially convertible into lubricating oils on contact with hot molten metal, but which on more protracted contact yield less convertible asphaltic bodies, coke, and the like, comprising the steps of: contacting a free surface of hot molten metal with a stream of asphaltic hydrocarbons to form a thin film of the asphaltic hydrocarbons on the molten surface, whereby the asphaltic hydrocarbons are uniformly and rapidly exposed to the desired conversion conditions; moving said film across said surface to and beneath a baffle forming a boundary of said conversion surface; adjusting the rate of the film flow to provide a short period of contact between said film and the free surface of the molten metal sufiicient to effect at least substantial conversion of asphaltic hydrocarbons to lubricating oil but insufficient to cause substantial coking or polymerization to less convertible asphaltic bodies; causing the material thus disengaged from the molten surface to rise through a column of molten metal terminating in a surface of restricted area; and continuously flowing a flushing fluid across said surface of restricted area to continuously remove both volatile and non-volatile hydrocarbons.

VAINO A. SALMI.

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