US2310524A - Solvent extraction of hyrocarbon materials - Google Patents

Description

Feb. 9, 1943. R. w. HENRY ETAL 4 I SOLVENT EXTRACTION OF HYDROCARBON MATERIALS Filed March 25, 1940 INVENTORS R.-W. HENRY 'J.V. MONTGOMER Patented Feb. 9, 1943 SOLVENT EXTRACTION OF HYROCARBON MATERIALS 5 Robert W. Henry, Bartlesville, and James V. Montgomery, Okmulgee, Okla, assignors to Phillips Petroleum Company, acorporation of Delaware Application March 25, 1940, Serial No; 325,843

4 Claims.

This invention relates to the refining of mineral oils, and more particularly to the refining of mineral oils by solvent extraction.

In some processes single solvents are used for contacting the oil undergoing refining and removing by simple solution or extraction the un desirable constituents from the parafiinic constituents of the oil. It was found that yields of the finished oils were increased by use of refrigeration. Another improvement was made wherein the solubilities of the various types of hydrocarbons were preferentially altered by the addition of a second constituent to the solvent. This operation greatly increased the flexibility of the process as well as improving the quality of the finished oil.

The use of water as a solvent modifying agent has been suggested and when used in systems in which water was at least partially soluble inthe solvent, reasonably good yields of superior quality oils resulted.

In these above mentioned processes, the undesirable constituents, such as naphthenic and asany appreciable cooling. At the same time; the

process is most flexible and may be adapted to treatment of stocks produced from crude or other oils from any source.

To obtain this maximum yield of oil or raffinate phase having the most desirable properties, that is, most nearly free from naphthenic or asphaltic constituents, it was necessary to find a selective solvent which will dissolve the entire body of oil The use of refrigeration increases thewhich is to be treated. Upon the addition of a solubility modifier such as water, the relative solubility of the hydrocarbon constituents is greatly altered. When a properly controlled amount of such solubility modifier is added, es.- sentially complete precipitation of desirable paraffinic materials into a raffinate phase is accomplished without the assistance of refrigeration or other intended cooling. Other solubility modi fying agents such as certain of the lower molecprice of high operating costs.

ular weight iso-altzohols, .or liquefied normally gaseous hydrocarbons,'may be used, but due to the normal mode of operation of these more common processes, maximum results are not obtained. Most of the solvent processes'prefer to secure only partial miscibility of the oil and sol-' vent, which process results in partial or imper fect contact between solvent and oil. Some p'rocesses employ high temperatures to effect complete solution of the oil in the solvent in an at tempt to take advantage of the more nearly perfectextraction gained therethrough. Those com mercial processes which utilize solvents completely miscible with the oils at atmospheric temperatures are forced to perform the separation We have found it poss'ible'to obtain the advantage of complete miscibility ofv oil and solvent and yet secure eificient separation of phases all at one convenient temperature. 1 1

It is an object of this invention to develop .a process in which ultimate or essentially molecular contact between the oil and the solvent is attained.

Another object is to obtain complete miscibilty between the solvent and oil at essentially atmospheric temperature.

Another object is to effect separation of the oil-solvent solution into phases by means other than changes in temperature.

Another object is to develop a process which readily adapts itself to continuous as well as to batch or intermittent operation. 1

Another object is to develop a process in which rafiinate fractions of uniformly changing properties may be separated.

Still another object is to produce a flexible process in which essentiallyany type of oil can be separated into its parafiinic and less desirable constitutents.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the process of solvent extraction of mineral oils, it is recognized that there are distinct advantages in first securing complete miscibility between the solvent and oil and then causinga separation of the rafiinate and extract phases; in that the ultimate contact of the oil with the solvent is thus secured with consequent improve- .ment of efi'iciency. We have found it practical to obtain the advantages of complete miscibility at the the pyridine type, their water-soluble homologues or derivatives. The solvent is so selected and partially or completely purified as to be miscible in all proportions with the oil at ordinary atmospheric temperatures. 'A solvent composition which meets these requirements is com--; posed of a selected fraction of commercial pyridine boiling between 260-320 F. and to which is added 1.25 per cent water, by'volume. This prepared solvent and an unextracted oil are completely miscible at a convenient operating tem-' perature, say 90 F., and thus ultimate contact of oil and solvent is secured without recourse to elevated temperatures." Afterthis above mentioned solution of oil in solvent has been effected, the solution is then mixdwith such an amount of water, or similar low miscibility liquid such as'a lower aliphatic alcohol, in a second step so asto cause partial miscibility of the solvent with the oil and consequent separation of a rafiinate from an extract phase." The relative volume of rafiinate phase which separates from the solution is dependent upon the amount of low miscibility liquid added. The rafiinate phase is separated from the extract phase," and each is freed of solvent separately by any known method, as by distillation or by absorption or by washing of the solvent from the oil. The extractph'ase from the above described extraction may be admixed with additional water; or similar low miscibility liquid, so as to cause separation of a second rafiinate phase of essentially any desired volume. This stepwise ad'- dition of water or the like and the separation of the resulting phases may be repeatedas often as desiredjand'eaJchfin-al phase product freed of solventas above. V

The figure illustrates one apparatus in which the process may be carried out, but it is not intended to limit the operation of this invention 1 to the use of this particular type of apparatus.

Referring to the diagram, tanks 1 and 3 are run or storage tanksfor untreated oil and solvent, respectively. 2 is a conventional mixing apparatus; tanks A, B, C and D are settlersor separators; 8', l3, l8 and 23 represent stills. resents a still fitted with a fractionating column which in turn is equipped-with at least'one sidedraw. Pumps, lines, valves, regulators, etc. are supplied as required.

The following discloses the operation of the processas applied to the solvent extraction of a Mid Continent residual bright stock. The operation of the process for the refining of this bright stock is given merely as one example and the process'is not intended to be limited to the refining of this type of stock. Stocks such as residuals, overhead, cylinder stocks, etc., arising from essentially any type of mineral or other oil from essentially any locality may be solvent extracted according to the process hereindisclosed or by'relatively simple alteration therein.

The residual stock" is pumped at the rate of 1,000 barrels per day from storage tank 1' into the mixing apparatus '2 in'which the oil is mixed 26 repwith solvent from storage tank 3 in the proportion of one volume of oil to three volumes of solvent. This solvent comprises the fraction of commercial pyridine boiling from 260-320 F. to which has been added 1.25 per cent water by volume. The oil and solvent are completely miscible at the operating temperature of F. and by such operation ultimate contact of oil and solvent is secured without recourse to elevated temperature.

The solution of oil and solvent is transferred through line 4 to pump 5 and thence into separatorA at the rate of 4,000 barrels per day. A sufiicient quantity of constant boiling mixture of pyridine fraction and water (consisting of approximately 40% water and 60% pyridine fraction) is added from line 6 to increase the water content of the solvent in separator A. At the convenient operating temperature this concentration of water in the solvent is sumcient to cause the separation of a raffinate phase which is then removed through line I to still 8 for separation into rafiinate oil and solvent. The former (raflinate) passes to storage through line R1, while the solvent is returned to tank 3 for reuse.

Theextract phase is transferred from separator A through line 9 and pump l0 into separator B. A sufficient quantity of constant boiling solvent mixture is added from line H to cause in .B the separation of a second rafiinate phase which is in turn separated into raffina-te N0. 2 and solvent by fractionating in still I3. The rafiinate passes to storage through line R2 and the solvent is returned to tank 3 for recycling.

i The extract phase remaining in separator B is transferred through line 14 and pump l5 into separator C and during this transfer additional constant boiling mixture from line 16 is added. In separator C, due to the increased water content of the solvent, a third raffinate phase separates, and it in turn is withdrawn through line I! to still I8 in which it is separated into oil, called rafiinate No. 3 and solvent. The oil passes to storage through line R3 and the solvent is returned to tank 3 for'recycling.

The extractphase remaining in separator C is then transferred through line [9 and pump 20 along with additional constant boling solventmixture from'line 2|, to separator D. In this settler another rafiinate phase separates and is withdrawn through line 22 to still 23 in which the oil, labelled rafiinate No. 4 and thereafter transferred to storage through line R4, is separated from the solvent. The latter is transferred to tank 3 for reuse.

The final extract phase is transferred from separator D through line 24 and pump 25 into still 26. This still is equipped with a fractionating column and means of creating and controlling reflux. The overhead distillate from still 26 is composed of a constant boiling mixture of the solvent and water. This mixture is stored in the run tank 29 from which it is transferred by pump 21 through line 28, and lines 6, H, l5 and 2| for reuse in the several separators. The sidestream from still 25 is composed of solvent containing a low percentage of Water, less than 1.25 per cent,

and it is returned through pump 3| and line 30' to the storage tank 3. The residue from still 25 consisting of extract oil, is transferred to extract storage.

Example A Mid-Continent residual bright stock when solvent treated in th apparatus and by the process herein described gave the following results. The particular operating conditions and solution concentrations were: 1000 barrels per day of bright stock was mixed with solvent in the mixing apparatus in the proportion of one volum of oil to three volumes of solvent. comprises the pyridine fraction boiling from 260-320 F. to which was added 1.25 percent water by volume. The mixer temperature was 90 F. vWhile transferring the solution of oil and solvent to the separator A, sufiicient constant boiling, mixture (consisting of approximately 40% water and 60% pyridine fraction), was added to increase the water content of the solvent to 2 per cent by volume. From this solution a raffinate phase separated which contained 45 per cent oil and 55 per cent solvent. This solvent contained 1.4 per cent water by volume. The solvent was removed from the rafiinate phase and returned to run storage while the rafinate N0. 1 oil comprising 20 per cent of the original stock, or 200 barrels per day, was pumped to storage.

To the extract phase from separator A was added sufficient constant boiling mixture (consisting of approximately 40% water and 60% Plridine fraction) from tank 29 to increase the water content of the solvent in separator B to 2.35 per cent. A raffinate phase separated, which contained 47 per cent of a parafiinic oil and 53 per cent solvent. This solvent contained 1.6 per cent water by volume. The raifinate oil was marked raflinate No. 2 and comprised 20 per cent by volume of the charge stock, or 200 barrels per day.

The extract phase from rafiinate No. 2 in separator B was transferred to separator C and sufficient constant boiling mixture (consisting of approximately 40% water and 60% pyridine fraction) added during transit to bring the water content of the solvent in separator C to 2.85 per cent by volume. A raffinate phase containing 52 per cent parafiinic oil and 48 per cent solvent separated in C. This solvent contained 1.8 per cent water. After separation from the solvent this rafiinate, labelled raffinate No. 3 comprised 20 per cent by volume of the original stock, or 200 barrels per day.

The extract from rafiinate No. 3 was transferred from separator C to separator D with the addition of suflicient constant boiling mixture (consisting of approximately 40% water and 60% pyridine fraction) to bring the water content of the solvent in the latter to 4.1 per cent by volume. A rafiinate phase containing 67 per cent parafilnic oil and 33 per cent solvent separated. This solvent contained 1.8 per cent water. The raffinate oil was separated from the solvent, labelled rafiinate No. 4 and transferred to storage. It comprised 20 per cent by volume of the charge stock, or 200 barrels per day.

The final extract from raffinate No. 4 in separator D was fractionated in still 26 into an extract oil bottoms, a solvent side out and a solvent overhead. This side out solvent contained a low percentage of water, less than 1.25 per cent by volume while the overhead was a constant boiling mixture of water and nitrogen base, both fractions were continuously recycled. The extract was pumped to storage.

In this example it is evident that the ratio of solvent to oil increased in each successive separator because of the fact that the solvent to 011 ratio in the raflinate phase withdrawn from each separator-was much less than the original'3zl mixture. The solventto'oil ratios were: 3:1 in

-- A, 3.521 in B, 4.421 in Cjand 6.211111 D. This in- This solvent creased ratio of solvent to oil, tended to assist in holding naphthenic materials in solution and thus to produce raflinates of good quality from each separation. The percentage of oil dissolved in the solvent of the extract phase decreased from about 22 per cent from separator A- to about 7.8 per cent of oil from that of separator D. The selectivity of the solvent increases as the concentration of dissolved oil decreases, and thus good selectivity between parafiinic and naphthenic oil was obtained.

From these data, it is evident that rafiinate No. 1 consisted of a high quality parafiinic oil of higher viscosity than the charge stock, and was an excellent bright stock. Rafiinates 2, 3 and 4 decreased in quality successively, but in all cases were improved over the original charge. The extract was a dark viscous oil of low viscosity index and contained resinous and naphthenic material.

It is to be understood that while the constant boiling point mixture of pyridine and water has been described as to the precipitant, it has been found the low boiling alcohols such as methyl, ethyl, propyl and iso-propyl or mixtures of water and low boiling alcohols are effective precipitants in similar manner.

It should be realizedthat the process herein described in sufliciently flexible as to cover a wide range of operation. Practically any mineral or other oil may be charged and any desired number of fractions obtained therefrom. A treated oil may be separated into cuts of varying paraffinicity, as shown in the above given example or an untreated cylinder stock may be separated into fractions consisting of tar, resins, naphthenic oil, and parafiinic oil, in which case the extract would contain the tar fraction. We have shown the separators to be simple vertical settlers. They may be horizontal if desired. Each separation may be improved by counter current washing, reflux of extract, etc., in conventional manner, although such improvements are not as necessary in our process as in conventional solvent extraction since we obtain complete miscibility of oil and solvent prior to each separation.

We claim:

1. The method of refining and purifying mineral oil to separate the asphaltic and other undesirable bodies from the relatively more desirable paraffinic portion of the oil including the steps of mixing the mineral oil with a water soluble solvent comprising a commercial pyridine fraction boiling between 260 F. to 320 F., to form substantially one homogeneous solution, adding to the solution a constant boiling point mixture of water in a fraction of commercial pyridine boiling between 260 F. to 320 F. as a precipitant to separate the solution into a desirable rafiinate phase and;a lessdesirable extract phase, separating the'two phases, adding to the extract phase additional constant boiling point mixture of water in a fraction of commercial pyridine boiling between 260 F. to 320 F. as a precipitant to separate the extract into a second rafiinate phase and a second extract phase, again separating the two phases and then separating from the second extract phase previously added solvent and previously added constant, boiling point precipitant in one operation.

2. The method of refining and purifying mineral oil to separate the asphaltic and other undesirable bodies from the relatively more desirable parafiinic portion of the oil including the steps of mixing the mineral oil with a water soluble sol vent comprising a commercial pyridine fraction boiling between 260 F. to 320 F., to form substantiall one homogeneous solution, adding to the solution a constant boiling point mixture of water in a fraction of commercial pyridine boiling between 260 F. to 320 F. as a precipitant to separate the solution into a desirable rafiinate phase and a less desirable extract phase, separatin the two phases, adding to the extract phase additional constant boiling point mixture of water in a fraction of commercial pyridine boiling between 260 F. to 320 F. as a precipitant to separate the extract into a second raffinate phase and a'second extract phase, again separating the two phases, then separating from the second extract phase previously added solvent and previously added constant boiling point precipitant in one operation and recycling the solvent and precipitant.

3. The method of refining and purifying mineral oil to separate the asphaltic and other undesirable bodies from the relatively more desirable parafinic portion of the oil which comprises mixing the mineral oil with a water soluble solvent comprising a fraction of commercial pyridine boiling between 260-320 F. to form substantially one homogeneous solution, adding to the solution as a precipitanta constant boiling point mixture of Water in a fraction of commercial pyridine boiling between 260-320 F. to separate the solution into a desirable rafiinate phase and a less desirable extract phase, and controlling the precipitation by controlling the amountof the said constant boiling point mixture added, separating the two phases, adding to the extract phase an additional controlled amount of said constant boiling point mixture to separate the extract phase into a second raflinate phase and a second extract phase, again separating the two phases, then separating from the second extract phase previously added solvent and previously added constant boiling point mixture in one operation.

4. The method of refining and purifying mineral oil to separate the, asphaltic and other undesirable bodies from the relatively more desirable parafiinic portion ofthe oil which comprises mixing the mineral oil with a water soluble solvent comprising a fraction of commercial pyridine boiling between 260-320 F., to form substan tially one homogeneous solution, adding to the solution as a precipitant a constant boiling point mixture of water in a fraction of commercial pyridine boiling between 260-329 F. to separate the solution into a desirable raflinate phase and a less desirable extract phase, and controlling the precipitation b controlling the amount of the said constant boiling point mixture added, separating the two phases, adding to the extract phase an additional controlled amountof said constant boiling point mixture to separate the extract phase into a second raflinate phase and a second extract phase, again separating the two phases, then separating from the second extract phase previously added solvent and. previously added constant boiling point mixture in one operation and recycling the solvent and constant boiling point mixture.

ROBERT W. HENRY. JAMES V. MONTGOMERY.

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