US1891108A - Method of treating cracked petroleum distillates - Google Patents

Description

'DeC- 13, 1932 R. c. osTERsTRoM ET AL 1,891,108

METHOD 0F TREATING CRAKED PETROLEUM DISTILLATES Filed Feb. 5, 1950 Patented Dec. 13, 193.2v

UNITED STATES PATENT oFF1cE RUDOLPH C. OSTERSTROM AND CARY R. WAGNER, F CHICAGO, ILLINOIS, ASSIGNORS TO T HE PURE OIL COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF OHIO METHOD OF TREATING CRACKED PETROLEUM DISTILLATES BEISSUED Application led February This invention relates to improvements in processes for treating cracked petroleum oils and similar products resulting from the cracking of heavier oils in the vapor phase 5 for the production of such lighter oils and products therefrom.

Cracked distillates obtained by the vapor phase cracking of hydrocarbon oils contain high percentages of unsaturated constituents and especially unsaturated constituents of a higher degree of unsaturation than the simple olefines. Such highly cracked distillates contain undesirable gum-forming and colorimparting compounds consisting of the highly reactive unsaturates which readily oxidize upon exposure to air, or when stored in tanks, to produce gummy or resinous bodies in such quantities as to render the cracked distillates unsuitable when not adequately treated for 2;) use as motor fuels or blending stocks. Hitherto it has been common in the art to eect the removal of the undesirable gum-forming and color-imparting bodies from cracked distillates obtained bythe vapor phase conversion of heavier hydrocarbon oils, by bringing the vapors of such cracked oils into Contact with fullers earth which apparently acts as a catalyst in effecting the polymerization of the aforesaid undesirable compounds. Again 3o the distillates have been treated with sulphuric acid and subsequently neutralized by an alkali to rid the distillates of objectionable color and gums.

It is a primary object of the present inveni tion to provide an improved process for effecting the removal of these undesirable compounds which are present in the crackedj distillates in a more economical and effective manner and to provide a system of treatment 40 wherein the use of relatively expensive treat` ing materials is reduced to a minimum and wherein only the heavier fractions of the distillates undergoing treatment require the use of a polymerizing agent, the lighter fractions 13 being thoroughly and effectively treated to re- 5, 1930. Serial No. 426,122.

move the undesirable compounds without requiring the use of any extraneous treating agent Whatever.

For a more complete understanding of the present invention reference is to be had to the accompanying drawing wherein the figure illustrates diagrammatically apparatus used in carrying out the present invention.

Referring more particularly to this drawing, the numeral 1 designates a pipe still in the setting of which there is arranged a bank of heating tubes 2. The cracked distillate delivered to the system for treatment is continuously passed through the tubes 2 and is heated to vaporizing temperatures while passing through said tubes of the order of 500 to 650o F. This distillate is obtained from a storage tank 3 and is withdrawn from the tank and forced through the coils of the tubes 2 by means of a pump 4 which places the oil passing through the pipe still under pressures of the order of from 300 to 500 pounds per square inch. These pressures, however, are not sufficient to maintain the oils in the liquid phase at the temperatures to which the oils are heated prior to their discharge from v the coils comprising the bank 2. Care is taken, however, in the operation of the still 1 to avoid heating the oils tokcracking temperatures since the object of this phase of the treatment is to vaporize the oils while the latter are maintained under super-atmospheric y pressures Without any substantial cracking of the oils. It will be understood that the oils or distillates contained in the tank 3 are obtained preferably from the operation of vapor phase systems of oil conversion wherein heavier .oils are heated to vaporizing and cracking temperatures in excess of 1000o F.

The subsequently condensed and fractionated distillates' are then delivered to the tank 3 tol removetherefrom undesirable color and gum producing compounds, and it is tothe performance of this function that the present invention is directed.

. form of a fuel oil residue. time, which isfan important factor, taken by in the tower are collected as liquids in the lower portion of the tower. In this instance, the upper portion of the tower is provided with a pressure relief valve 8 to permit of the release of abnormal pressures which may accidentally exist in the tower.

We have discovered that when cracked petroleum distillates having the boiling range of ordinary gasoline are thus vaporized to elevated but non-cracking temperatures and maintained at the same time under superatmospheric pressure conditions for relatively prolonged periods of time, the undesirable fraction of the unsaturated compounds are apparently polymerized in the treating zone indicated by the tower 6. The polymerization is evident in the production of higher boiling point oils than the boiling points of the oils initially introduced into the system by the pump 4. These high boiling point oils, obtained by polymerization inu the tower 6, are removed from the bottom of the tower by way of the valved pipe line 9 in the The period of the distillates under treatment in securing this polymerization varies, of course, with the character of the charging stock and operating conditions, since the distillates may be maintained in the system for periods of time varying between 15 minutes to three hours.

The lighter oils which remain in a vaporous state following travel through the tower 6 are withdrawn byway of an overhead line 10 and pass to a condenser 11 wherein the vapors are reduced to a liquid state while still maintained under super-atmospheric pressures. These condensed oils then flow by way of a pipe line 12 to a gas separator 13. The pipe line 12 contains a pressure relief valve 14 so that the products delivered into the separator `13 will be under ordinary or atmospheric pressures. Such fixed gas as may be formed fas aresult of the operation is withdrawn from 4the top of the separator 13 by way of the pipe line 15 while the treated distillate is removed from the separator by way of a pipeline 16 and lead to a storage tank 17 as finished motorfuel. y

In fa typical run, ii-rccordance with the features of the present invention, a distillate obtained by the vapor phase cracking of heavy hydrocarbon oils was delivered under a pressure' of 375 pounds to the pipe still and which distillate possessed an A. P. I. gravity of 52, an initial boiling point of 95 F., an end point of 440 F., and was of a decided lemon yellow color. This stock was heated in the still to a temperature of 550 F. and fractionated in the tower 6 and this distillate when delivered to the tank 17 was found upon analysis to possess an initial-boiling point of 95 F., an-'end boiling point of 385 an Afl). I. gravity of 56, and a clear water white color (Saybolt plus Approximately ofthe original charging distillate thus" treated was recovered as a finished motor fuel product in the tank 17. lIn addition to its water white color the motor oils collected in the tank/17 possess a low or negligible gum content which remains substantially uniform under ordinary conditions of storage andy handling.

The polymerized fractions which are removed from the bottom of the fractionating tower by way of the pipe line 9 -were foundf to possess, upon analysis, an A. P. I. gravity of 20, an initial boiling point of 420 F., and an end boiling point of 700 F. The relative differences in the matter of gravity andboil# ing range in the cracked distillate initially introduced into the pipe still 1 and the residue removed from the bottom of the tower 6 indi-- cate strongly the polymerization conditions which are set up in the tower 6' by subjecting the vapors of the cracked distillate totheA elevated temperatures and pressures for vary-y ing periods of time. f

The lower trays ofthe fractionatingtower` 6 are provided with a liquid outlet linex18f-by which oils heavier than those deliveredto the'.v tank 17 but lighter than the fuel oils removed4 by way of the pipe line 9, are discharged from the/tower 6. The oils leaving the line 18 may be termed a heavy gasoline since a typical' cut thereof discloses that they possess an 1ni tial boiling point of approximately 300uF., an end boiling point of 430 F., an 'A.1PL 'I. gravity of 43.0 and a Saybolt color varying from minus 10 to plus-5,' and comprise from 20 to 35% of the total volume of oildeliveredf to the pipe still 1. To render these that they should be treated with sulpliuric acid and a neutralizing alkali which may be heavier motor fuel oilssuitf able for commercial purposes, it 1s advisable done by extending the'Iine-18 to a mixer 19? wherein the oils are brought intorcontact with suitably regulated quantities of sul' phuric acid. Upon leaving the mixer the oils are neutralized with caustic introduced as. at 20 intothe outlet line 21 of the mixer 19.' These oils are then passed through a heater' 22 in which they are redstilled and are finally discharged into a separating tower 23.

The polymerized oils are withdrawnfrom the'.

' lbottom of the tower 23 and delivered to av tank 24, whereas the light vaporous oils pass overhead from the tower 23,.are condensed as at anddelivered as a finished motor'fuel to the tank 26. v

n By this method of treatment a large part of the cracked .distillate does not require treatment with any added polymerizing agent, since the conditions of temperature, pressure and time brought to bear on the vapors passing through the tower 6 are sufiicient of themselves to secure the desired polymerization without necessitating the aid of extraneous treating agents. This results in-a very considerable economy in operation since the expense of treating agents such as i fullers earth and sulphuric acid is reduced to a minimum, sulphuric acid treatment being only employed in connection with the heavier oils removed from the bottom of the tower by way of the outlet line 18. Moreover, the system avoids the loss of the oil or distillate itself which inevitably occurs when large quantities of treating agents are einployed, and in this respect the total percent of usable distillates recovered from the system is higher than from comparable systems of which we have knowledge. Again,-the system operates to avoid injury to the oils undergoing treatment. For example, if the lighter oils obtained from the system by way of the tank 17 were to be treated with coneentrated sulphuric acid, a large percent of the desirable compounds present in these oils as well as the undesirable constituents, would be attacked by the acid and lost as a residue or sludge. Therefore, in accordance with the present invention these lighter oils are not in any way brought into contact with an active polymerfzing agent so that there can be any injury to these light oils or loss in their total volume as a result of treatment. The heavy motor fuel oils removed from the fractionating tower 6 by the outlet line 18 are capable of withstanding treatment with sulphuric acid without injurious results or burning of the oil so that there is a large recovery of this relatively heavier fraction of the distillates as a treated, gum-free motor fuel of desired color. The polymer-containing fraction removed from the bottom of the tower 6 by way of thepipe line 9 is used preferably as a fuel oil and is not subjected to further treatment.

The present invention thus provides for the vaporizing of the cracked distillates and the fractionation thereof at high pressures by which the necessary time factor 1n obtaining polymerization reactions is secured in a tower of ordinary size. The use of pressure is alsoV advantageous in promoting the desired poly merization reactions, because one molecule of a polymerized product occupies no more space than al single molecule of the compounds entering into the polymerizing reaction, the reactions being speeded up, as it were, by the use of higher pressures.

When an ordinary cracked vapor phase distillate is fractionated at low pressures and in the usual manner, and where the vapors have a velocity of approximately one foot, per second through a fractionating tower of the usual type, the resulting product is yellow in color from the beginning of the distillation tothe end. lVe have discovered that when the fractionation-is slowed down so that the vapors are subjected to temperatures above 200 F. for a period of minutes in an ordinary fractionating tower colorless products distill over, and from this basis We have continued to increase the elements of time, pressure and temperature to secure the most practical conditions for commercial operation. 1n ordinary operations less than 2% of the cracked distillate under treatment is lost as a result of polymerization reactions, and fully 50% of the distillate so treated may be recovered in the form of a gum-free and colorless liquld which requires no treatment with catalyzing agents. Ordinarily, between 50 and 75% of the distillate under treatment may be so recovered after treatment without a catalyzing agent, thus leaving only the high boiling fractions with a distillation range of between 300 F. and 430 F. which require polymerization treatment with, for example, sulphuric acid. 0f this latter fraction, approximately 95%thereof is obtained as a salable motor fuel product of desired color and freedom from gums.

`What is claimed is:

1. The method of treating cracked low boiling petroleum oils containing unsaturated compounds to remove therefrom gumforming and color-imparting bodles, which comprisesU heating such oils to temperatures above their normal vaporizing temperatures but insuiiicient to effect any substantial cracking thereof, introducing such heated oils alone and unmixed withk other substances into a fractionating zone wherein said oils in a yvapor state are maintained under superatmospheric pressures, retaining the 011s 1n said zone while in substantially the vapor state and under the influence of said pressures for a suiiicient period of time not in ex-` cess of thirty minutes to effect the formation of compounds having a higher boilin range than that of the oils originally heate Withdrawing from one portion of said fractionating zone the treated vaporized oils, and separately withdrawing .from another portion of said fractionating zone as liquids the oils containing the high boiling compounds.

2. The method of treating cracked low boilng petroleum oils containing unsaturated compounds to remove therefrom gumforming and color-imparting bodies, which comprises subjecting such oils alone while under superatmospheric pressures to temperatures above theirl normal vaporizing temperatures but below those at which vany appreciable cracking thereof is effected, introducin such vaporized oils alone and unmixed with other substances into a fractionating zone wherein the oils are maintained under said superatmospheric pressures, re taining the oils in said zone while in substantially the vapor state and under the influence of said pressures for a suiiicient period of time not in excess of thirty minutes to eiiect the formation of compounds of higher boiling point than the oils originally heated, withdrawing said h/igh boiling compounds as liquid oils from said fractionating zone, separately removing the vaporfzed oils from another portion of said fractlonating zoneand condensing the same without release of pressure, releasing the pressure on said condensed oils and removing lighter gaseous products therefrom.

3. The method of treating cracked low boiling petroleum oils containing unsaturated compounds to remove therefrom forming and color-imparting bodies, -w ich comprises subjecting such oilsalone and unmixed with other substances to temperatures suiticientlyf'highto effect their complete vaporization without any material cracking of the same, introducing such vaporized 011s alone into a fractlonatmg zone whereln the oils are maintained under superatmospheric pressures, retaining the oils in said zone while in substantially the vapor state and under the inluence of said pressures for a suiic'ient period of time not in excess of thirty minutes to effect polymerization of the undesired unsaturated compounds conltained therein, removing from one point of said fractionating zone the undesired com- -pounds in the form of a heavy liquid oil, and

in removing from another point of said fractionatin zone .the desired treated vapors, and con ensing and collecting said vapors.

4. The method of treating cracked low boiling petroleum oils containing unsaturated compounds to remove therefrom gumorming and color-impartingbodies, which comprises subjecting such oils alone and unmixed with other substances to temperatures sufficiently high to effect substantially their complete vaporization without any material cracking of the same, introducing such vaporized oils alone into a fractionatlng zone whereln the 011s aremalntalned under superatmospherlc pressures and held in said zone for a suicient period of time Y varyin between fifteen minutes and three hours 1n substantially the vapor state to effect -the polymerization of the undesired compounds contained therein, withdrawing 'the treated vapors from the upper portion of said fractionating zone and condensing and collecting the same, separately7 withdrawing from the *lower portion of said actionating zone a-heavy liquid oil containing the undesired polymerized compounds, and withdrawing from an intermediate portion of said z one an intermediate fraction of said liquid tures.

RUDOLPH C. OSTERSTROM. CARY R. WAGNER.

Images