US2034712A - Method of refining petroleum distillates - Google Patents

Description

March 24, 1936. c, E. DOLBEAR METHOD OF REFINING PETROLEUM DISTI-LLATES Filed Nov, 28, '1955 u INVENToR. CZUzoNEOZeaP,

B M /f/ ATTORNEYS.

vrender inactive certain o f Patented Mar. 24, 1936 'Y UNITED STATES PATENT OFFICE METHOD 0F REFININ G PETROLEUM DISTILLATES Clinton E. Dolbear, Los Angeles, Calif., assignor to Philip Wiseman,

l?. Kenneth Wiseman, and

10 Claims.

The present invention relates to a method of refining petroleum oils and pertains particularly to a vapor phase treatment process for rening and purifying petroleum distillates.

According to standard petroleum rening practice, a petroleum stock is subjected to a heating operation to vaporize certain portions thereof; the evolved vapors fractionally condensed and the several fractions treated with various reagents to eliminate certain objectionable substances mixed with these fractions. The character of these objectionable substances is subject to considerable variation, dependent upon the character and quality of the crude oil or other petroleum stock used, upon the boiling points of the distilled fractions, and the nature of the distillation process, that is, whether or not the distillation process involves a cracking or depolymerization of the stock.

The several fractions obtained from the distillation are generally classied according to their physical properties, and the following disclosure will be directed to the treatment of an oil to recover but a single fraction such as gasoline. The description of the process as directed to the recovery of gasoline will be fully illustrative, and it will be understood that the process is equally applicable in the refining of any suitable oil stock and in the recovery of any desired distillate.

Gasoline, for example, whether recovered by straight distillation of gasoline-bearing crude oil or artificially produced by cracking of higher boiling-point oils, is usualy contaminated with gums and gum-forming compounds, color and color-forming compounds, certain organic acids, and sulphur and sulphur compounds which generally have a corrosive action on metals. If the gasoline be a cracked product, it usually has a disagreeable odor as Well. According to established refining methods, the gasoline fraction from the distillation operation is subjected to a chemical treatment for the removal of the above-outlined objectionable constituents, or to at least lower the proportion of such constituents to render the-gasoline salable. This is usually accomplished by treating the gasoline, in liquid phase, with strong sulphuric acid, followed by water-washing and a caustic alkali treatment. This treatment is followed in most cases, bytreatment with a sweetening agent such as an alkaline solution of sodiiun plumbite mixed with powdered elemental sulphur to remove or the so-called corrosive sulphur compounds. The above refining steps are quite frequently combined with a treatd ment, either in the liquid or vapor phase, with adsorbent material, as with a clay or the like, to remove a further quantity of gums and gum- Y forming compounds, and color and color-form- 5 ing compounds.

It will be appreciated that the above rening operation involves a number of steps and requires handling of the stock in a series of operations, each of which generally involves the use 10 and consequent consumption of a chemical reagent, thus rendering the refining process relatively costly.

The principal object of the present invention is to provide a process for refining petroleum oils l5y in which a great proportion of all of the aboveenumerated objectionable constituents of a distilled fraction may be removed in a single relatively inexpensive rening step, and which produces a sweet, non-corrosive, color-stable and gumstable distillate which, in case the color and gums are not completely removed by the above treatment, may be made readily salable by a simple treatment with clay or other adsorbent material to improve the color and gum char- 25 acteristics.

A further and important object of the present invention is to provide a simple and highly effective step in the rening of petroleum oils which will obtain removal of all or substantially all 30 of the corrosive sulphur or sulphur compounds, and which, while it will not always remove all of the undesirable color, will remove all or substantially all of the color-forming compounds or constituents, so that removed by a suitable clay treatment or the distillate is color-stable.

The method of the present invention involves vaporizing the desired volatile constituents of a petroleum stock and passing such vapors 40 through a porous bed of reactive material inV fragmentary form, capable of adsorbing certain the like,

whereby the objectionable constituents of the 45 vaporized product are chemically and physically entrained in the reactive bed, and the treated vapors rendered physically and chemically of the desired nature, said vapors being subsequently subjected to a condensing-operation of any suit- 50 able type.

According to the preferred embodiment'of the invention, the distilled vapors are passed through a column of fragmentary reactive material comprising a partially hydrated alkaline earth metal when the color itself is 35A oxide of a porous nature having the pore surfaces suitably activated by a coating of caustic alkali metal hydrate in such proportion as to avoid clogging of the pores of the material and preserve the porous nature of the material.

The reactive material is preferably prepared by calcining an alkaline earth metal carbonate, such as calcium carbonate, in the form of lumps or fragments of suitable size, to a temperature such as to drive off the principal proportion of CO2, without producing a dead-burned material, and leave the calcined material in a highly porous state. The calcined material, now consisting principally of alkaline earth metal oxide, is then immersed in an aqueous solution of an alkali metal hydrate, such as caustic soda, of suitable concentration, for example, a concentration in excess of 27 B. and below 50 B. and preferably about 39'Be. Upon immersion, the alkaline earth oxide will begin to hydrate, and according to my preferred practice I quickly remove the oxide material from contact with the caustic solution, whereby the hydration o-f the oxide is allowed to progress only slightly, and the evolved heat is thus effective in drying the partially hydrated oxide. The caustic alkali con.- tained in the solution taken up by the oxide material is thus dried on the surfaces of the oxide material including the pore surfaces thereof, in intimate mixture with the hydrated oxide, and, due to the high porosity of the oxide material, the caustic alkali and the hydrated alkaline earth oxide are quite thoromghly distributed over the oxide matrix, both supercially and on the pore walls.

While the above example calls for activation with caustic soda solution, I have found that caustic potash solutions of a concentration in excess of 22 B., but below 51 B. and preferably about 36" B., are also very effective in activation. Moreover, mixtures of caustic soda and caustic potash may be used, though in general, activation solely with caustic soda is to be preferred by reason of the lower cost thereof. The concentration of caustic used will be governed in general by the physical condition of the oxide material, that is, the porosity, and will in general be greater with a highly porous oxide.

According to the above-outlined procedure, a highly porous reactive material is obtained, substantially the entire pore surface area of which is provided with a coating of a mixture of caustic alkali and hydrated alkaline earth metal hydrate. It will be of course apparent, however, that it is not necessary to Coat the entire pore surface of the base material, and in fact it is almost impossible to actually accomplish this end, but the more complete coating obtained, the more efficient is the activation of the oxide material. It is essential that the treatment with caustic alkali solution be carried out under such conditions that the oxide. material is not unduly hydrated or slaked, and so that the caustic alkali material does not clog the pores of the oxide base material. It has been found that very little rening action is obtained by the reactive material if the pores thereof are clogged with caustic soda or potash, though its activity is very pronounced if sufficient caustic alkali has been absorbed by the oxide material to activate it without materially diminishing the porosity thereof.

The value of the above-described material in petroleum refining appears to lie in its combined -adsorbent and chemically reactive properties. ItA

is my conclusion that the gum and gum-forming impurities of a petroleum vapor, as well as the color and color-forming impurities, are chiefly adsorbed by the reactive material, and the acid impurities, elemental sulphur, and perhaps some sulphur compounds of an organic character, are removed chiefly through a chemical reaction of the reactive material, but it will be understood that the invention is not restricted to this precise theory of performance of the material.

The accompanying drawing illustrates the manner of carrying out the present invention, and referring thereto:

Fig. 1 is a diagrammatic flow sheet showing the treating procedure; and

Fig. 2 is a vertical section of a form of treating chamber which may be used in the present process.

Referring to the drawing, In Fig. l I have shown a still I provided with an oil inlet 2 and a vapor outlet 3. The still I is provided with heating means such as burner means 4 provided with fuel supply means such as gas connection 5. A treating tower 6, is provided connected to the vapor outlet line 3, and the treating tower is also provided with a vapor outlet connection 1 communicating with a suitable condenser means 8.

In Fig. 2 I have illustrated a form of reaction or treating tower 6 which is admirably suited to the present process, and this tower may comprise an outer shell or casing 2| preferably provided with an insulating coating 22 and a vapor inlet line 23 which, in Fig. 1, would communicate with the vapor line 3. The shell 2| is preferably provided with a conical lower end portion 24 to which is secured a suitable discharge door 25 covering a discharge opening 26. The shell 2I is provided with an inner shell or casing 21 spaced from said shell 2| to provide an annular vapor space 28, and said inner shell 21 is provided with a pervious conical bottom 29 formed of perforated metal or of a heavy screen as shown, and terminating in a discharge opening 3| adjacent the discharge opening 26 in the shell 2|. The upper end of the shell 21 is secured to the upper wall 32 of the tower, so as to be substantially vapor-tight at said upper end, and

means are provided for supply of reactive material to within the inner shell 21 through said upper wall, as by means of a hopper shown at 33. suitable plug or valve means 34 being provided at the bottom of said hopper for charging the said inner shell with material upon occasion.

The inner shell 21 is filled with fragmentary reactive material of the type described, as shown at 35, and petroleum vapors are admitted to said tower through the vapor inlet line. The vapors pass downwardly through the space 28 around the inner shell 21 and thence upwardly through the perforated bottom 29 of the inner shell and through the column of reactive. material 35, and thence outwardly of the inner shell through a suitable outlet line 36, said line 36 connecting with the line 1 shown in Fig. 1.

In order to provide for preheating the treating tower 6 and the contained reactive material 35 to a temperature somewhat above the dewpoint of the still vapors, I provide a gas line communicating with the line 3 as at 9, said line being provided with a heating coil I I disposed in heatreceiving relation to the burner means 4 and being also provided with connection to the gas connection 5. A gas return line I2 is preferably to feed the burners also provided leading from the treating tower vapor outlet l to the burner means 4 whereby the gas which is used to heat the tower 6 may also be used to provide combustion at the burner means 4.

Assuming the still I to be properly filled with the petroleum stock which is to be distilled and treated, the gas valve I3 in the gas line 5, the valve I4 in the supply line of the heating coil I I, the valve I5 in the connection 9 and the valve I6 in the line I2 may be opened, allowing gas to fiow through the coil into andv through the tower 6. The valve I'I in the line 3 and the valve I8 in the supply line between the burners 4-and the connection 5 may be closed. In this manner, the

gas passing through the coil and the treating tower is brought to the burners 4 and burned to provide heat for both the coil and the still, the heated gas passing through the tower 6 serving to heat the reactive material and drive off moisture from the mass, though the temperature of preheating is always lower than the dissociation temperature of the alkaline earth metal hydrate. After the tower 6 is heated to the desired temperature (for example, to approximately t50 F. above the dewpo-int of the vapors to be passed from the still), the valves I4, I5, and I 6 may be closed, and the valves I'I and I 8 opened, allowing vapors to pass from the still I into the tower 6, and using gas directly from the gas line 4.- The vapors from the still I thus pass through the tower 6 and thence into the condenser 8, from which the desired fractionated distillate may be withdrawn through any of the outlets 20. The above-described flow 1,1; is offered merely as an example, Vshowing a simplearrangement whereby the treating tower 6 and the reactive material may be brought to the desired temperature, and the vapors from the still passed through said tower. It will be appreciated that, if desired, any suitable means maybe used for heating the tower 6, but I have found that the above arrangement is quite satisfactory. Natural gas, refinerygas, or even air may be used, it being preferable to use a non-condensing or fixed gas however, to forego any disintegrating effect on the reactive material by the formation of condensate in contact therewith.

If desired, the vapors obtained from the still I may be superheated by passing the same through a coil 4I before passage thereof through the tower 6, whereby condensation of vapors in the tower 6 is substantially prevented. In the event that some condensation does occur within the tower 5, I preferably provide a bleeder line 42 at the bottom of said tower for removal of such condensate. In general no substantial amount of condensate is permitted to form in the tower as it has been found that the presence of such condensate has a disintegrating effect upon the reactive material.

As the petroleum vapor, carrying the abovereferred-to impurities, passes through the column of reactive material the vapors will be brought into intimate contact with the porous lumps of activated alkaline eaith metal oxide. This contact results in a removal of the principal proportion of the impurities from the vapors. Certain of the impurities react directly with the purifying agent and the reaction compounds are formed in place in the reactive material, being absorbed and caused to penetrate the individual lumps. Other constituents such as the gums, and gumforming compounds are apparently not chemically reacted with the reactive material but are adsorbed thereby and effectively removed from the vapor stream. The temperature maintained Within the treating tower 6, that is, the temperature at which the vapors and reactive material are brought into contact, is preferably about 50 or more above the boiling-point of the highest boiling constituent of the vapors, and should be below theI cracking temperature of the vapors; in

` general, I prefer to use temperatures below about 800 F., and for most vapors temperatures below 700 F. are found to be most satisfactory. In the event that the process is to be used in the purifying treatment of relatively heavy distillates, such as those obtained in the refining of lubricating oils, the purifying step may be conducted at a reduced pressure so that the temperature may be maintained near and preferably below the abovementionedmaximum. The purifying treatment may also be applied to vapors at super-atmospheric pressure, if desired. I have found that prolonged contact of the vapors with the reactive material is not necessary, practically all of the refining action taking place during the first few seconds of contact of the vapors with the reactive material, this time of contact being dependent upon the temperature at which the reaction is conducted and the size of the fragments with which the apparatus is filled, but in general I have found a time of contact of from 2 to 4 seconds to be sufficient. This means that with a column of conventional size, an extremely high rate of passage of the distillate vapor through the agent may be obtained, and consequently vprovides large treating capacity in equipment of relatively smal-l size.

After passing through the column of reactive material, the distillate obtained under preferred operating conditions is found to be entirely free of objectionable odor even though the stock be cracked, is gum stable and generally low in gums, color stable, non-corrosive to metals, sweet to the Doctor test, completely depleted of active sulphur compounds, elemental sulphur and acids, and relieved of a material portion of the color and of theinactive sulphur compounds. The color of the product may or may not be water-white, but simple filtration through an adsorbent material such as fullers earth will remove any remaining color and gums, thus producing a waterwhite substantially gum-free distillate which will remain definitely color stable and gum stable, whether or not exposed to direct sunlight.

'Ihe reactive material used in the present process has been found to be many times more effective than either an alkaline earth metal oxide or hydrate when used alone. 'Ihe caustic alkali metal hydrate appears to have an activating effect on the alkaline earth metal oxide and makes possible a highly effective removal of detrimental constituents of a petroleum vapor by a combined absorptive and chemically reactive action. -The material doesnot appear to lose its efficiency until it is quite saturated with reaction products, and may be revivified or reclaimed in any suitable manner, as for example, by extraction with a suitable solvent to remove the adsorbed and chemically reacted impurities, by calcining in an oxidizing atmosphere at a temperature sufiicient to burn off the containedimpurities, or by treating with superheated steam at a temperature high enough to distill off the major portion of the adsorbed and chemically reacted compounds, with or without further hydration or caustic treatment.

It will be appreciated that alkaline earth metal oxides other than quicklime may be employed in the present process,v such as barium and strontium oxides, but in general such materials will be too expensive to allow an economic practice of the invention. At the same time, however, oxides such as calcined dolomite or calcined dolomitic limestone have been found to be practically ast eicient as calcined calcium carbonate. The siliceous limestones, on the other hand, are not particularly suitable inasmuch as these minerals,

upon calcination, are not suiiiciently porous to obtain the desired characteristics inthe activated products.

I claim:

I. In a method of refining petroleum distillate, the step which comprises passing hydrocarbon vapors into contact with aV hot fragmentary porous material comprising a partially hydrated alkaline earth metal oxide having its surface activated with an alkali metal hydrate.

2. In a method of refining petroleum distillate, the step which comprises passing heated hydrocarbon vapors through a fragmentary mass of porous alkaline earth metal oxide havingv its pore surfaces partially hydrated and activated by a coating of alkali metal hydrate.

3. In a method of refining petroleum distillate, the step which comprises passing heated hydrocarbon vapors through a heated fragmentary mass of alkaline earth metal oxide in porous condition having its pore surfaces activated by treatment with a caustic alkali solution.

4. In a method of refining petroleum distillate, the step which comprises passing petroleum vapors through a heated fragmentary mass of porous quicklime having its pore surfaces activated with a caustic alkali.

5. In a method of rening petroleum distillate, the step which comprises passing petroleum vapors through a heated fragmentary mass of individually porous lumps of quicklime having their external and pore surfaces coated with sodium hydroxide.

6. In a method of refining petroleum distillate, the step which compris-es passing hydrocarbon vapors into contact with a hot fragmentary porous material comprising a partially hydrated calcium oxide having its surface activated with an alkali metal hydrate.

7. lIn a method of refining petroleum distillate, the step which comprisesl passing heated hydrocarbon vapors through a fragmentary mass of porous calcium oxide having its pore surfaces partially hydrated and activated by a coating of alkali metal hydrate.

8. In a method of refining petroleum distillates, the step which comprises: passing petroleum vapors, at a temperature above the boiling point of the least volatile constituent thereof and below 800 F., through a pervious bed of reactive adsorbent material, in fragmentary condition, each fragment of said material consisting substantially Wholly of a porous body of partially hydrated alkaline earth metal oxide having its pore surfaces coated with an alkali metal hydroxide.

9. In a method of refining petroleum distillates, the step which comprises: passing petroleum vapors, at a temperature above the boiling point of the least volatile constituent thereof and belo-w 800 F., through a pervious bed of reactive adsorbent material, in fragmentary condition, each fragment of said material consisting substantially Wholly of a porous body of partially hydrated calcium oxide having its pore surfaces coated with an alkali metal hydroxide.

10. In a method of refining petroleum distillates, the step which comprises: passing petroleum vapors, at a temperature above the boiling point of the least volatile constituent thereof and below 800 F., through a pervious bed of reactive adsorbent material, in fragmentary condition, each fragment of said material consisting substantially wholly of a porous body of partially hydrated calcium oxide having its pore surfaces coated with sodiumhydroxide and potassium hydroxide.

CLINTON E. DOLBEAR.

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