US2081174A - Process of deasphalting and dewaxing petroleum oils - Google Patents

Description

Patented May 25, 1937 UNITED STATES PROCESS F DEASPHALTING AND DEWAX- ING PETROLEUM OILS Carleton Ellis, Montciair, N. J assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application November 11, 1931, Serial No. 574,365

6 Claims.

This invention relates to what may be termed a clarification process for the deasphalting and dewaxing treatment of hydrocarbon oils, especially heavy petroleum oils including various cylinder stocks and residuals or bottoms containing asphaltic bodies and wax, usually of the petrolatum type.

By the practice of the present invention such asphaltics, tars and related substances andv waxy components are separated from the oil by the differential or selective solvent action of a liquefiedgas hydrocarbon solvent, yielding an oil of improved quality fitted in many cases for use as a high grade lubricant; the asphaltic and waxy constituents thus segregated being utilized in other ways. Insofar as asphaltic material and wax may be considered solid bodies, the method may be looked upon as one which precipitates from the oil such solid substances leaving the oil in a clarified refined condition.

As a selective solvent of the liquefied-gas hydrocarbon type, preferably liquid propane or a mixture of liquid propane and liquid ethane is employed. Liquid butane also may be used in some cases, as also mixtures of butane with propane and/or ethane. In other words, mixed hydrocarbons of a normally gaseous character whose molecular structure contains 2, 3 and even 4 carbon atoms are preferred as the selective solvent basis. The employment of liquefied-gas containing normally gaseous olefins such as propylene is not precluded. Methane in liquid form may be used in special cases where the .resulting separations warrant the increased expense of higher pressures and more costly apparatus. In like manner methane may be admixed with liquid ethane and/or propane and/or butane, such methane usually however being present only to the extent of a few per cent. Also in some cases volatile hydrocarbons such as pentane or hexane may be incorporated with the desired active liquefied-gas, these 5 and 6 carbon com pounds serving mainly as extending agents in the operation of precipitation of asphaltics and the separation of waxy materials.

In general, however, the liquefied-gas is composed of normally gaseous hydrocarbons boiling at or below 0 C. The addition to such liquefiedgas of hydrocarbons of higher boiling point greatly diminishes the value of the solvent as a means of dissolving the desired oily components and causing the deposition of the socalled solid bodies. I

Asphaltics show a diminished solubility as the number of carbon atoms in the molecular structure of the components of the precipitation liquid isreduced. At least from the standpoint of the practical confines of the present invention this statement holds good.

The lower the specific gravity of the selective solvent the more rapid the deposition and separation of the insoluble substances, namely, the

asphaltics and wax. This has an important bearing in commercial operation, especially with respect to size of apparatus and throughput. It is an important factor in plant cost.

Hence facility of separation has to be weighed against compression expense, the cost of which will vary somewhat, depending in part on the average number of carbon atoms in the liquefiedgas precipitant.

The process of the present invention is a twostage one, involving the step of removing at least to a large degree theasphaltic and tarry material and in the second step, separating waxy bodies. The first step preferably is carriedout at. room temperature or even temperatures which are slightly elevated in order to prevent wax from being thrown down with the asphaltic bodies. The second step or stage is carried out at lower temperatures sufficient to cause a-rapid crystalli zation and deposition of the wax.

Thus a stream of the oil to be treated is caused to mingle with a stream of the liquefied-gas used' for precipitation, the proportion 'of oil and liquefied-gas varying somewhat with the. content of asphalt and wax'of the oil stock. For the first stage, namely precipitation .ofiasphaltics, one

volume of oil may be treated with 8 to 12 volumes of the liquefied-gas, this being carriedout', J

as stated, suitably atroom temperaturepThe' mixture having been made /suflicient' time Jis' I allowed for precipitation and deposition,,.such treatment being carried out in .apIessurevessel of adequate strength. In due course the-asphaltic sludge or tar as the case may. be is drawn oif at the bottom of the receptacle and the solu-v tion of the wax-bearing oil in theliquefied-gas solvent is conveyed to a dewaxing receptacle. The

tive solvent to the oil rather than, to add the oil to the liquefied-gas, since the latter procedure tends to cause a sudden precipitation of asphaltic bodies which enclose globules of oil diflicult to eliminate from. the deposit. 1

' scribed later.

In case theasphaltic material is slow settling its coagulation and deposition may be accelerated by the addition of a small proportion of clay and the like to the oil prior to the introduction of the liquefied-gas precipitating agent. Such additions of coagulating-assistants do not, however, form a part of the present invention.

In any event, the rate of deposition of the asphalt will depend to a considerable extent on the density and proportion of the hydrocarbon precipitant. The density in turn is related to the composition of the latter. In most cases I prefer to employ the lightest gas in liquefied form which can be handled economically under the pressures imposed. Liquefied propane is in general highly suitable, a still better precipitant being a mixture of propane and ethane, the latter being present preferably to the extent of from 10 to 20 per cent. One volume of ethane to 4 volumes of propane gives a liquefied-gas of relatively low specific gravity which allows extremely rapid settling.

While a proportion of say 10 volumes of the liquefied-gas precipitant may be used in the first stage of separation for removal of asphalt, so large a proportion is not needed in the second stage of wax removal. In the latter case, depending on the content of wax, from less than 2 volumes up to perhaps 4 or 5 volumes of liquefied gas may be employed to 1 volume of oil. A desirable proportion is 3 volumes of liquefiedas to 1 volume of oil.

In the foregoing I have stated that a lowering of temperature in the second step permits of adequate wax removal. While this temperature lowering may be carried out by cooling through external, that is extraneous refrigeration, e. g. brine cooling, I may employ self-refrigeration induced by diminishing the pressure in the system to an extent which will permit evaporation (flashing) of the liquefied gas in a measure adequate to cause such self-chilling. The gases so removed preferably are kept in the operation circuit being compressed or cooled to liquefy and are duly recycled. While, as pointed out above, the step of asphaltic precipitation is carried out advantageously by the employment of a large volume of the liquid gas precipitant, the second stage of wax precipitation or deposition does not call foras large a proportion of the liquefied-gas and therefore removal of the gas to accomplish self-refrigeration does not disturb the effectiveness of the stage of wax elimination.

Finally a solution of the clarified oil free or substantially free from the so-called solids is obtained in the liquefied-gas vehicle and'the latter is removed from the oil for reuse. The removal of the gas causes chilling and if desired heat exchangers may be interposed in the system in order to supplement the lowering of temperature in the wax precipitation receptacle caused by evaporation therein of the liquefiedgas.

A specific phase of operation in the second stage is that of fractional separation of wax to obtain first crop, second crop, and so forth, at different temperatures and also to secure asphalt-free oils obtaining a regulated content of wax not in excess of that which can be easily controlled by a pour inhibitor, as will be de- Asphaltic bodies in some cases are not thrown down completely in the first stage, certain substances of a tarry or vasphaltic nature remaining in the vehicle, possibly in part in a the fourth to 0 F. and so on depending upon the type and quantity of wax present in the oil. This temperature lowering is merely illustrative of the manner in which the fractional wax separation is carried out. It will be understood that the exact temperatures used in any particular case will vary with different oils. The wax fraction separated in the first chilling step will, of course, be discolored by the asphaltic bodies present in it, but the remaining wax fractions will be substantially free from coloring matter.

The wax deposition or magma is collected and freed from the liquefied-gas vehicle. Sometimes this may be carried out by filtration or centrifugal treatment. The washing of the wax depositi'on with the fresh supply of liquefied-gas may be desirable in some cases. If decantation is employed for the separation of the oil solution and the wax magma, the liquefied-gas remaining in the latter may be removed and reused.

The oil dissolved in the liquefied gas has now been purified to the degree desired for most purposes but may be-further treated as a solution with additional clarifying or bleaching agents such, for example, as filtration through a bed of active clay, and the like. The low viscosity of the solution permits rapid passage through such clarifying beds. Such additional purification does not, however, form a part of the present invention.

The evaporation step for removal of the solvent from the oil may be conducted in a flash coil or bubble tower or other suitable evaporator, this however preferably being coordinated to heat exchange relationship as described above. If simple evaporation of the liquefied gas does not accomplish complete degasification of the oil, the latter may be further treated to remove any traces of gas which might affect the normal flash-point. For, example, the oil may be blown with inert gas such as nitrogen or with steam at ordinary or elevated temperatures or under reduced atmospheric pressure, and the like.

The gas fractions obtained from the "oil stills of the petroleum refinery may be used in carrying out the process herein described, gas fractions derived from debutanizer and stabilizer plants being appropriate. able form of the gas is that which having been fractionated in the debutanizer-stabilizer system is washed with an alkaline solution to remove h'ydrogen sulfide and is then treated with An especially desirsulfuric acid to absorb a greater part of the propylene and any higher olefins which may be ethane, are particularly serviceable. vIt should be noted that the sulfuric acid treatment for absorption oi olefins is a step in the production of secondary alcohols, therefore a refinery equipped with an alcohol plant of this character has avail- E able a supply of purified gas containing eifective proportions of ethane and propane.

By the foregoing process there can be obtained economically various types of high grade lubricating oils adequately free of asphaltic impurities of excellent color and low Conradson carbon and suitably dewaxed or containing at the most a very low percentage of wax, preferably controlled as to pour point by the addition of a pour inhibitor or wax-conditioning agent, the latter preferably being of the naphthalene paraflin wax compound type (e. g. naphthalene and chlorin ated parafiin wax brought into combination by the action of aluminum chloride). Except for increase in pour point, the presence of a moderate proportion of wax in a lubricant sometimes is beneficial. By controlling the wax content of finished oil through the method of liquefied gas treatment described above so that wax is present only in small proportion, the addition of such pour inhibitor serves to condition the wax to avail of any utility it may possess as a lubricant.

From the heavy oil such as bottoms containing some asphalt and wax there may be made a heavy lubricating oil in the manner herein described and involving the following steps:

1. Deasphalting.

2. Dewaxing, including partial removal of wax leaving in the oil a definite proportion of wax which is capable of being conditioned by apour inhibitor according to step 5.

3. Desolventizing (and heat exchange).

4. Flash raising.

5. Wax conditioning.

Of these steps certain may be used and others be unused as conditions of manufacture and market define or dictate. Removal of solvent (step 3) with or without heat exchange is essential. Step 4 may be omitted in many cases or combined to form a part of step 3. When a part of the wax in the oil can be thrown out, particularly when such portion serves as a clarifying agent to remove the last traces of asphalt leaving a residue of wax nicely susceptible to the conditioning effect of pour inhibitors, the fullest advantage may be taken of optional step 5.

The procedure herein described may be carried out as an intermittent or batch process or may be conducted as a continuous process, that is, one which is non-cumulative. The latter is preferred for large scale operation on account of -stage while it'is still in solution in the liquid gas. If a sufilciency of the latter is present the oil, phenol and liquid gas form a homogeneous appearing solution. On or during removal of the liquid gas the formation of two liquid phases may be brought about, one containing the phenol and dissolved oil, the other being a high grade oil raffinate. Such complete contact as the phenol secures by use of a blending solvent would permit its action to be exerted efl'icaciously. The phenol or other extraction agent of the phenol type or any other suitable heavy extraction agent or semi-solvent may be used in various proportions with respect to the volume of oil, for example, one-half the volume of the latter up to perhaps two volumes as conditions require.

'Since wax fractions of various grades and qualities are obtainable by specific procedures under the present process, the invention also includes as products wax fractions selectively fractionated from a heavy oil dissolved in a liquefied gas precipitant.

Likewise the invention includes as a product a heavy lubricating oil, for example of the cylinder oil type whose normal wax content has been reduced by fractional separation in the presence of a liquid gas precipitant leaving in the oil that part of the wax more soluble in said liquid gas precipitant under the conditions of such treatment.

Further, the invention contemplates as a product such oil containing a reduced amount of wax and that of a kind more soluble in liquid hydrocarbon gas than the total wax normal to such oil inits original state, together with a very small proportion of a wax conditioning agent specifically a synthetic lubricant of the wax and naphthalene complex'type normally present in proportion only sufflcient to materially depress the pour point of said oil.

The following example illustrates the practical application of the process:

A heavy, viscous, dark-colored bottoms obtained from a Ranger-Burbank crude oil and having the following characteristics:

Gravity, A. P. I 23.1 Saybolt viscosity at130 F 1463 Secs. Saybolt viscosity at 210 F 187.5 Secs. Carbon 5.31% Pour point 65 F. Flash point 505 F. Color Brown-black is, diluted with '75 volumes of liquid propane and 2.5 volumes of liquid ethane while maintained under'pressure, of 20 atmospheres and at'room temperature (about 75 F.). A dark-colored material is thrown out. This is allowed to settle and the supernatant liquid is drawn off. A yield of, 15% tarry material isobtained.

The clear liquid consisting of oil and wax dissolved in liquid propane and ethane is then chilled by external means to a temperature of F. and allowed to stand for hours. At the end of this time the wax has settled and the remaining liquid is decanted. The yield of wax is 10%. The propane and ethane are flashed off of the liquid and a yield of 75% of oil of the following characteristics is recovered:

Gravity, A. P. I 23.1 Saybolt viscosity at 100 F 2566 Secs. Saybolt viscosity at 210 F 137 Secs. Carbon). i 2.02% Pour point 30 F. Color, Robinson 2% (diluted) out at reduced temperatures sumcient to cause rapid crystallization and deposition of wax but I wish to point out that with many oils, especially when the liquefied gas contains a proportion of ethane and/or methane reduction of temperature to a very low point (e. g. F.) would tend also to cause separation of oil constituents. In consequence, a loss of yield of oil would result. The wax likewise would be softer.

The preferred form of the invention, therefore, contemplates for wax separation a temperature reduction adequate for the purpose while avoiding over-cooling that would cause the liquefied gas to become a non-solvent for the oil.

What I claim is:

1. The process of treating a hydrocarbon oil containing asphaltic bodies and wax which comprises mixing such oil with a liquefied gas precipitant of the group comprising methane, ethane, propane and butane, and a heavy extraction solvent of the phenol type at a tempera ture which permits the asphaltic bodies but substantially no wax to separate, removing the precipitated asphaltic bodies, lowering the temperature of the solution in said liquefied precipitant whereby a substantial portion of the wax is caused to separate, removing said wax, removing the liquefied gas precipitant and the heavy extraction solvent from the oil and adding a pour point inhibitor to the oil to condition the residue of wax remaining therein.

2. The process of treating a hydrocarbon oil containing asphaltic bodies and wax which comprises mixing said oil with a liquefied gas precipitant of the group comprising methane, ethane, propane and butane, and a heavy extraction solvent of the phenol type at a temperature which permits the asphaltic bodies but substantially no wax to separate, removing the precipitated as-' phaltic bodies, lowering the temperature of the solution in said liquid precipitant whereby a substantial portion of the wax is caused to separate,

removing said wax, removing the liquefied gas precipitant and the heavy extraction solvent from the oil, and adding a pour point inhibitor to the oil to condition the residue of wax remaining therein; the steps of asphaltic body precipitation and wax precipitation being conducted in continuous non-cumulative manner.

3. The process of treating a hydrocarbon oil containing asphaltic bodies and wax which comprises mixing such oil with a liquefied gas pre-- cipitant for asphaltic bodies at a temperature which permits the major portion of the asphaltic bodies, but substantially no .wax, to separate,

. tion the residue of wax remaining in the oil.

4. The process of treating a hydrocarbon oil containing asphaltic bodies and wax which comprises mixing a stream of such oil with a. stream of a liquefied gas precipitant for asphaltic bodies at a temperature which permits the major portion of the asphaltic bodies but substantially no wax to separate, collecting the precipitated asphaltic bodies, lowering the temperature of the solution of oil in said liquid precipitant whereby a small amount of wax and the remaining asphaltic bodies are separated, removing the precipitated wax and asphaltic bodies, further lowering the temperature of the solution whereby a substantial portion of the wax free from asphaltic bodies is separated, collecting the wax and removing the liquefied gas from said oil; the steps of asphaltic body precipitation and wax deposition being conducted in a continuous noncumulative manner; thereafter adding a pour point inhibitor to the oil to condition the residue of wax remaining therein.

5. Process according to claim 3 in which a heavy extraction solvent of the phenol type is added to the charge and subsequently removed with its extracted materials.

6. Process according to claim 4 in which a heavy extraction solvent of the phenol type is added to the charge and subsequently removed with its extracted materials.

CARLETON ELLIS.