US2194335A - Treatment of hydrocarbon oils - Google Patents

Description

Patented Mar. 19, 1940 UNITED STATES 2,194,335 TREATMENT or nrnnocmon oms Hans Tropsch, Chicago, IlL, assignor to Universal Oil Products Company, Chicago, 111., a commation of Delaware No Drawing. Application June 21, 1985, Serial 3 Claims.

This application is a continuation-in-part of my application Serial No. 667,674 filed April 34, 1933.

This invention refers more particularly to the treatment of hydrocarbon motor fuels of low antiknock value, such as straight run gasolines produced from paramnic crudes though the process is also applicable for improving the knock rating of gasoline fractions from other sources, e. g. those from naphthenic base crudes and from cracking processes.

In a more specific sense the invention has reference to a catalytic process which constitutes an improvement over the usual high pressure 13 reforming operations on gasolines in that a minimum of cracking occurs in the ordinarily accepted sense of the term and the yields of desired product are higher under special conditions in regard to temperature, pressure and. time. Further objects and advantages will become apparent in the following description of the nature of the process.

The present process is readily distinguishable from pyrolytic or cracking processesused to reform gasolines in the employment of higher tam-- peratures, lower pressures, much shorter time factors and particular catalysts. In ordinary cracking processes conducted upon petroleum fractions of a distillate character for the pro-- duction'of high yields of gasoline of improved anti-knock value, it is current practice to employ temperatures within the approximate range of 850 to 1000 F., pressures of from'100 to 500 pounds per square inch above atmospheric and a long time factor, the .last being obtained by the employment of large vaporizing or reaction chambers following the heating elements. Under these ordinary conditions of operation an equilibrium is approached due to the use of the long time factor, and a certain amount of secondary reactions of polymerization and condensation takes place following the primary reactions of decomposition. In contra-distinction to these conditions of operation the-present process may 5 be employed to limit the decomposition reactions to the primary reactions of decompositions so that equilibria corresponding to the temperanot 'reached and the secondary polymerization 60 reactions are obviated.

As a general rule 'its content of oleflnic and cyclic (particularly aromatic)- compounds.

tures and pressures as ordinarily employed are v the antiknock'v'alue r a hydrocarbon motor fuel mixture increases with I This rule cannot bev ll stated as absolute since experiments on pure con Renewed January 12, 1938 pounds have shown that the knock rating is also a function of such factors as the length of the straight chain in the paraflin hydrocarbons, the position of the double bcnd in the corresponding olefins, the degree of partial or complete saturation of the cyclic hydrocarbons and the presence ofminor amounts of substances which may exert an accelerating or a retarding influence upon the rate of combustion of the fuel. While it may be stated generally that the antiknock value of a hydrocarbon fuel mixture is increased by loss of hydrogen in decomposition reactions of various types, other reactions may also take place such as isomerization involving the .iormation of branched chain saturated and l unsaturated hydrocarbons and the formation of hydrocarbons of a mixed straight chain and cyclic character. The reactions involved in the treatments of the present process are apparently distinct from those which occur in ordinary cracking operations.

In one specific embodiment the invention comprises vap'orizinggasoline without substantial decomposition'thereof and subjecting the vapors to pyrolysis at temperatures of from approximately .1200 to 1500 F., under sub-atmospheric pressures for times not in excess of 0.04 second in the presence of activated magnesite catalysts.

According to the .present invention an activated magnesite catalyst is employed in the zone of intensiveheating or in other words the main reaction. zone. The term "activated magnesite" is hereby defined as including the residual material resulting from the calcination of magnesium carbonate either natural or artificial and comprising principally magnesium oxide .of a .more or less porous character. Thus the calcining of the original carbonate is essentially the activating step, although the porosity may be influenced by V the presence of other gases which are passed in a 40 stream through a mass of particles of the ground carbonate to carry oif the cabon dioxide evolved. Magnesium carbonate [begins to decompose to yield the oxide at temperatures of approximately. 350? 0. (662 F.) and if heated long, enough at this temperature will be converted to the oxide.

However, the use-of higher temperatures permits 'the use of shorter'times. When employing an incompletely converted magnesite at the start of a reforming process of the present character and under the temperature conditions which characterize it, any carbonate remaining is gradually decomposed so that the essential catalyst is finally aporous and active magnesium oxide, which may be designated as activated magnesite.

The carbonate of magnesium, MgCOa, is known as magnesite as it occurs in nature, and this is the cheapest and most readily available primary source of catalyst for the present process.

It is most commonly encountered in a massive or earthy variety and rarely in crystal form, the crystals being usually rhombohedral. In many natural magnesites, the magnesium oxide may be replaced to the extent of several per cent by ferrous oxide. The mineral is of quite common occurrence and its use is economical. This minera] is related to dolomite, the mixed carbonate of calcium and magnesium. Dolomite, however, is not of as good service as the relatively pure magnesite in the present instance but under certain conditions depending on results desired it may be employed.

In the activation of this material it is preliminarily heated to a temperature-and at a pressure in the neighborhood of that preferred for the cracking and reforming operations for a period of time suiiicient to convert substantially all of the magnesite to magnesium oxide of high porosity. -In the preliminary activating treat- 1 ment a stream of gas may be conducted through the material to assist in flushing out the carbon dioxide evolved and produce other efiects upon the structure and surface characteristics of the contact material. In some cases air may be used,

' in other cases hydrogen, carbon dioxide or even hydrocarbon gas mixtures such as natural gas or the vapors of the oil to be treated. When using oil vapors the process of treatment for increasing antiknock value may be started after the magnesite has attained a proper degree 01 activation as evidenced by the results obtained in the direction of increased antiknock rating without high losses.

Precipitated magnesium carbonate may be employed alternatively with the natural mineral as a source of catalytic material. While catalysts of varying activity may be prepared from either magnesite or the precipitated carbonate their in-' 1 fiuence upon the reactions of decomposition will 1 vary with the starting material and the exact manner of its preparation so that alternative but not exactly equivalent catalysts may be prepared.

It has been observed that, whenactivation by the hydrocarbon vapors is practiced, increase in activity seems to follow the deposition of a certain amount of carbon on the surface of the catalyst though it is not known at the present time whether the increase in activity of the mass is definitely related to thisdeposit of carbon. The general steps thus briefly enumerated for the activation of contact masses may be employed in many cases also to eflect its regeneration after it has become coated with tarry polymers after a certain period of use, e. g. the use of air to burn or oxidize the carbonaceous and tarry matter deposited 'on the catalyst to cleanse its surface. v

The exact course of the chemical reactions involved infthe decomposition by heat of hydrocarbon oil mixtures having the complex composition of gasoline is difllcult to follow, on account .Of' the extremely large number of hydrocarbon compounds present. In the case of normal straight-chain paraflin hydrocarbons there is decane i s' -.cracke'd. apparently the primary re resistance to flow.

The present invention is especially characterof the equipment.

actions of decomposition are followed by secondary reactions involving polymerization of oleflns from the primary decompositions and with increased pressure and long time factor some ring-closures occur to form naphthenic and aromatic compounds. Obviously the exact nature of the decomposiitons is much more complicated but from a practical standpoint in the cracking of hydrocarbon oil mixtures such as gasolines, it seems probable that the formation of coke and gas which constitute undesirable byproducts of the cracking reactions is a phenomenon accompanying the secondary reactions, so that if conditions are properly controlled to prevent polymerization, coke formation will, .also be prevented. The ratio of coke to gas in the extent to the ratio of carbon to hydrogen by weight in the stock cracked and to a lesser extent by the form of their combination.

In applying the process of the invention to the treatment of gasolines for the improvement of their antiknock characteristics they are vaporized in any convenient manner, for example, during passage through tubular heating elements and are then passed through a highly heated zone containing granular activated magnesite and maintained at some optimum temperature within the range previously speciijed for a very shbrt time period corresponding usually to less than 0.04 second and sometimes as low as 0.001 second. When under these high temperatures subatmospheric pressures are preferably maintained by withdrawing the gaseous products of the reactions from the receiver of the process at a suitable rate, the preferred pressures in the high temperature zone being of the order of 50 mm. of mercury absolute. The catalyst may be distributed throughout the zone of intensive heating and in a state of subdivision which presents sumcient contact surface without causing too great ized by the fact that extensive decomposition of gasolines may be brought about without the formation of heavy hydrocarbon polymers of a high boiling or tarry', character and without separation or decomposition of any material amounts of carbon in the reaction zone or in succeeding portions Owing to the avoidance of polymer formation the yields of desired products are higher and runs in commercial equipment are lengthened on account of the lack of coke deposition which ordinarily causes hazards, duev to over-heating of tubes and clogging of equipment. It is to be specifically pointed out that the present process of making high antiknock hydrocarbons from thosepresent in gasolines.

produces substantially nooke and/or pitchy or tarry substances especially in comparison withthe well known reforming processes of the prior art. Apparently the character of the reactions induced by'the use of the catalysts mentioned is in the direction of splitting 05 of hydrogen and rearrangement of branched chains so that the content of unsaturatedflsomeric straight chainand cyclic hydrocarbons, is increased, without extensive cracking in the ordinary sense of the;

are characterized of more heavy polymers and tar word since cracking reactions by the formation as well as gas. I

While the invention is particularly directed to the pyrolysis of straight-run or uncracked distillates,'it is furtlier comprised within its'scope to .employ' corresponding liquid products from cracktion.

ing processes as the term is ordinarily used in r the trade and to crack oil vapors if necessary or desirable prior to their passage through the main reaction zone in which the reactions of gas and liquid formation are brought about.

Obviously the proportioning of relative sizes of parts of different types of equipment which may be used to carry out the process will depend upon many factors such as the character of the oil which it is desired to treat, the increase in knock rating deisred, the heats of vaporization and decomposition of the vapors involved and other factors. The matter of deisgn of commercial units may be based to some extent on the operation of small scale experimental units, as is done in many other commercial development projects.

The materials entering into the construction of the reaction zone of the process will require some consideration since temperatures above those to which the ordinary materials of construction are ordinarily subjected are employed in many instances at this point. Thus temperatures in the neighborhood of 1200 to 1300 F are high enough so that the tensile and compressive strength of ordinary steels is definitely reduced and they possess greatly lessened resistance to deformation, which must be reckoned with in view of the fact that there is external pressure upon any tube or arrangement of tubes which -may be employed corresponding to the degree of vacuum in use which may at times be that equivalent to 50 mm. of mercury absolute-or lower. There is a further reason for avoiding the use of ferrous metals as materials for the main reaction zone in that many of these metals may exert not only an undesirable and difilcultly controllable catalytic action but that they also tend to form carbides by direct combination with the carbon in the oils and further the tendency toward cokeformation, the avoidance of which constitutes one of the primary advantages of the present invention.

In place of metals such materials as silica, firebrick, carborundum, sillimanite, alundum, corundum and other high melting point refractory materials are preferred for materials to constitute the main reaction zone. The tube or tubes of the reaction zone may be heated by any convenient economical method, heat being supplied in some instances by electrical resistors which are wound around the tubes and protect them from unnecessary radiation loss by being embedded in suitable insulating materials surrounding the tubes. A somewhat cheaper method, although not always capable of effecting the same exact control of temperature, may

consist in heating the reaction zone by the direct impingement ofoil or gas flames thereon. Evidently the greatest overall heat efficiency of the process will be attained by preliminary heating of the vapors by ordinary means to the maximum temperature consistent with the decomposition reactions desired prior to their passage through the reaction zone which is thus relieved of excess burden,

The following example is illustrative of improvement of gasoline quality, while operating according to the process of the present inven- The data in the tabulation shows the principal characteristics of the stock charged to the'process (which was the'straight run Pennsylvania gasoline) and shows also the corresponding properties of the product obtained by treating the vapors ofthis gasoline at 1300 F. and 50 mm. absolute pressure in the presence of a catalyst prepared by calcining granular magnesite at a temperature of about 1500 F., the time that the vapors were under these conditions being approximately 0.04 second.

Comparison of straight run and treated gasolines Properties Charge Product by ordinary re-forming operations, particularly in the relatively low loss incurred for the improvement in antiknock value shown and in the absence of heavy polymerized oils. The present process is operable also in more compact apparatus than that commonly employed in re-forming operations.

The invention is sufficiently disclosed and described in the foregoing specification and the single instance of results obtained but the invention is to be in no way limited to the exact details of the description orthe particular numerical data introduced.

I claim as my invention:

1. A process for the reforming of low antiknock hydrocarbon distillates containing straight chain parafiins within the boiling range of gasoline to improve the antiknock'quality thereof without substantial decomposition, which comprises subjecting the distillate while in heated vaporous condition at a temperature between 1200 F. and 1500 F., and'for the period of time not in excess of four one-hundredthsof a second and under a subatmospheric pressure of less than millimeters, to the action of a catalyst comprising essentially activated magnesite.

2. A process for the reforming of low antiknock hydrocarbon distillates containing straight chain parafflns within the boiling range of gasoline to improve the antiknock quality thereof without substantial decomposition, which comprises subjecting the distillate while in heated vaporous condition at a temperature in excess of 1200 F., and less than 1500 F. and for a time not in excess of four one-hundredths of a second and under subatmospheric pressure to the action of a cataylst comprising essentially activated magnesite.

3. A process for reforming straight chain par,- aflins boiling within the gasoline range which comprises subjecting the parafiins, in vapor phase HANS TROPSCH.