US2120810A - Solvent fractionation - Google Patents

Description

June 14, 1938.

G. L. PARKHURST SOLVENT FRACTIONATION Filed July 51, 1955 Patented June 14, 1938 SOLVENT FRACTIONATION George L. Parkhurst, Chicago, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Application July 31, 1933, Serial No. 682,919

2 Claims.

This invention relates to the solvent fractionation of hydrocarbon mixtures. It is an object of the invention to provide a process for the solvent fractionation of hydrocarbon mixtures which will give either higher yields of the desired fraction or a greater spread in properties between the two fractions produced than has been the case with previously known processes. In some cases both of these advantages can be secured simultaneously. Further objects will become apparent as the description of my invention proceds.

Liquid sulfur dioxide (S02) and phenol have been used separately as selective solvents for the fractionation of lubricating oil stocks. Each of these selective solvents has, however, certain disadvantages and inadequacies. Thus liquid sulfur dioxide is not highly selective. In other words, the spread in properties between the 20 two fractions produced by its use is relatively small as will be pointed out in a specific instance below. This spread can be increased by operating at higher temperatures but this involves the use of high pressures with consequent expensive equipment and high compression costs. Furthermore when the operating temperature is raised the yield of the desirable rafiinate fraction is very markedly decreased.

On the other hand, when using phenol as a selective solvent, for instance, in the fractiona tion of lubricating oil stocks, the yield of the desirable rafiinate fraction is relatively low. This can be increased by lowering the operating temperature but concomitantly there is a distinct decrease in the quality of the raffinate or in other words a decreased spread between the properties of the two fractions produced.

I have found that a mixture of liquid sulfur dioxide and phenol is very greatly superior as a selective solvent to either sulfur dioxide or phenol alone. If sulfur dioxide, phenol and a mixture of the two are compared as selective solvents under conditions such that the yields of raffinate and extract are the same in all three cases, it will be found that the rafiinate and extract produced by the use of a mixture of the two solvents have a greater spread in properties than the fractions produced by either solvent alone. In other words, the raffinate produced with sulfur dioxide plus phenol will in the case of lubricating oil extraction be more parafiinic and have a higher viscosity index, greater stability, etc. than is the case with the raflinates produced by either solvent alone. In the case of gasoline or naphtha extraction, for another example, the extract fraction will have a higher antiknock rating (octane number) and the rafiinate fraction a lower antiknock rating than the corresponding fractions produced by the use of liquid sulfur dioxide or phenol alone under conditions adapted to produce the same yields of the two fractions.

If instead of operating under conditions (temperature, ratio of volume of solvent to volume of stock, etc.) adapted to produce identical yields, the comparative tests are conducted under conditions adapted to give, for instance, a lubricating oil raiiinate of a given viscosity index (Dean and Davis, Chemical and Metallurgical Engineering, v. 36, page 618-l929) or a gasoline extract of a given octane number (National Petroleum News, June, 1930; page 35), it will be found that the yield of the desired fraction will be markedly higher in most cases when a mixture of sulfur dioxide and phenol is used than when either sulfur dioxide or phenol is used alone. cases both a higher yield and an improved product can be secured simultaneously by the use of the mixed solvent.

These facts can be illustrated by the following data relating to the solvent fractionation of lubricating oil stocks.

In some The particular stocks used where lubricating distillates from midcontinent crude.

The methodof test was to agitate the stock and solvent together until equilibrium was attained at the optimum temperature for the particular solvent being used, separate the raflinate and extract, and remove the solvent from both fractions by fractional distillation and water and caustic washing.

After percolation of the rainnate fraction through clay its viscosity in seconds b Saybolt at 210 F. and Dean and Davis viscosity index were determined and compared with those of the original stock. The results are tabulated The SOz-phenol mixture thus gives a 9% higher 0 yield with less loss in viscosity and a slightly greater increase in viscosity index as compared with an equal volume of phenol alone. crease in yield will in many cases make all the difference between commercial success and commer- A 9% incial failure. The yield with phenol can be increased, to be sure, by lowering the fractionation temperature but if this is done the viscosity index of the raflinate drops very rapidly, the loss in viscosity increases, the sludge and oxidation stabilities deteriorate rapidly, etc. so that if one operates with phenol at a temperature which will give the same yield of raflinate as with SOz-phenol the rafiinate produced will be very inferior.

Sulfur dioxide alone on the other hand gives a high yield and a small loss in viscosity but the rafflnate is, relatively speaking, but little better than the original stock. The best measure of the improvement in a lubricating oil raifinate is probably the viscosity index. It will be noted that the improvement in viscosity index when using S02 alone was only slightly more than half that secured by the use of the Sz-phenol mixture. By raising the fractionation temperature more improvement could be obtained with S02 alone but it is found that although the yield drops off rapidly as the temperature is raised, the improvement in the ramnate is only slight. Moreover the use of high temperatures with S02 alone involves the use of pressure equipment, high compression costs, etc. This is avoided when using S02-phenol sincethe phenol tends to keep theS02 in the liquid phase and greatly reduces its partial vapor pressure.

In general, I prefer to use from 0.5 to 10.0 volumes of my mixed solvent to each volume of the hydrocarbon mixture or stock to be fractionated. The solvent mixture may suitably comprise from 20% to 75% of phenol by volume and from 25% to 80% of sulfur dioxide by volume. The optimum fractionation temperature will Vary with the stock to be fractionated, the results desired, the composition of the solvent mixture, etc. and can be determined readily by experiment in each case. For the solvent fractionation of lubricating oil stocks, I prefer in general to fractionate at from 50 F. to 100 F.

It is highly preferable that the phenol used be substantially anhydrous since the presence of any substantial amount of water decreases yields markedly and has other undesirable results.

Although I can utilize my new mixed solvent efficiently in a batch process such as is described with regard to the above experiments or in a batch process wherein the solvent and hydrocarbon mixtures are heated to a temperature at which they are completely miscible and then cooled to a temperature at which the desired raifinate and extract fractions separate, I prefer to utilize a continuous process in which a much better fractionation can be accomplished and in which provision is made for the continuous recovery of the components of the solvent mixture and in which they are returned to the process.

One such continuous process is shown in the drawing which is a conventionalized flow diagram. The hydrocarbon mixture to be fractionated, for instance a lubricating oil stock, is removed from storage tank II through valve l2. Simultaneously anhydrous phenol is removed from storage tank l3 through valve l4 and sulfur dioxide, preferably liquid sulfur dioxide, is removed from tank l5 through valve l6. All of this is accomplished by means of pump I! and the various materials are pumped through heat exchanger IS in which their temperature is raised. If the lubricating oil stock is too viscous to flow readily, its temperature can be raised by means of steam coil 19. Similarly the phenol can be heated by means of steam coil if necessary. The various materials then pass through heater 2| where they come in contact with an indirect heating medium introduced through line 22 and withdrawn through line 23. The heated materials pass through mixer 24, wherein homogeneity is obtained, and through line 25 to heat exchanger l8 where they are cooled by contact with the incoming materials and thence to cooler 26 where they come in indirect contact with cooling medium introduced through line 21 and withdrawn through line 28. The purpose of the steps thus far is to heat the two solvent components and the stock to a temperature at which they can be homogenized and then cool them to a temperature at which the desired fractionation will occur. This insures complete contact between the stock and the solvents prior to fractionation. This is not essential, however, and alternatively the stock and the solvent mixture can merely be agitated together at the desired temperature and then separated or they can be passed in countercurrent relationship to each other, for instance, in a vertical tower.

The materials passing out through cooler 26 pass through line 29 and enter separator 30 at an intermediate level therein. In separator 30 raflinate and extract fractions separate, the former passing upward and the latter passing downward continuously. The rafiinate fraction is removed continuously from the top of separator 30 through valve 3| and enters fractionating column 32 at an intermediate point. Fractionating column 32 is provided with re-boiling coil 33 and dephlegmating coil 34 which are used to adjust the temperatures at the bottom and top of the tower so that at least the greater part of the sulfur dioxide passes overhead and substantially all of the hydrocarbons and phenol pass out at the bottom of the tower. The sulfur dioxide vapors leave tower 32 through valve 35 and pass through line 36, condenser 3'1, surge chamber 38 and compressor 39 back to storage tank I5. Simultaneously, the bottoms from tower 32 pass out through valve 40 by means of pump 4| and enter upwardly directed spray 42 located near the bottom of scrubbing tower 43. In this tower the rafiinate fraction comes in contact with a downwardly flowing stream of water, preferably hot water under pressure, from spray 44. This scrubbing removes the phenol and any residual sulfur dioxide. The purified raffinate passes out from the top of the tower through valve 45 and, if necessary to remove residual phenol, can again be scrubbed in a second tower similar to tower 43. It then passes through line 46 to storage tank 4! from which it can be removed for further treatment for use as desired.

Simultaneously, the aqueous materials from tower 43 pass out of the tower through valve 48 and are introduced into fractionating tower 49 at an intermediate level therein. Tower 49 is provided with reboiling coil 50 and dephlegmating coil 5| which are used to control the bottom and top temperatures so that water will pass overhead and phenol will be removed at the bottom. The water vapor passes out of tower 49 through valve 52, condenser 53, separator 54, valve 55, line 56, pump 51, valve 58 and heater 59 back to spray 44. Heater 59 is operated by means of a heating medium introduced through line 60 and removed through line 6|. Any sulfur dioxide or phenol passing out of the top of tower 49 is thus recycled with the water back to the process and is not lost. Fresh makeup water can be introduced through line 62 by means of valve 63.

While water vapor is being withdrawn through valve 52, phenol is withdrawn through valve 64 by means of pump 65 and passes through line 66 back to storage tank I3. Instead of recycling the phenol and sulfur dioxide back to their respective storage tanks it is, of course, possible to recycle them back to heater l8, mixer 24 or some other point in the process.

Returning now to separator 39, the extract fraction is withdrawn from the base of the separator through line 6'! and is passed through heat exchanger 98 where its temperature is raised, as Will be described hereafter. It then passes through line 69 into tower ill at an intermediate point therein. It will be found in general that the extract fraction contains considerably more phenol than does the raffinate fraction and it is, therefore, desirable to provide somewhat more efiicient means for its removal. This is done in tower l0 and the subsequent apparatus now to be described. Tower 19 is provided with reboiler coil II and dephlegmating coil 12 used to control the bottom and top temperatures in such manner that a maximum amount of the phenol and sulfur dioxide will pass overhead and the hydrocarbons will pass out of the base of the tower in liquid form. Sulfur dioxide vapors are removed from the dome of tank l5 through valve 13 and line 14 and are introduced into fractionating column ill by means of a perforate pipe 15 located near the bottom of the tower. Sulfur dioxide vapors carrying with them the great bulk of the sulfur dioxide and phenol present in the material introduced through line 69 pass out of tower 19 through valve 16 and give up a portion of their heat to the incoming material. These vapors are then further condensed by means of condenser 11 and passed to trap '18. Phenol is removed from the base of this trap through valve 19 and passes back to storage tank I3 by means of pump 65 and line 66. This phenol will in most cases contain. some sulfur dioxide, but since it is recycled to the process this is not a matter of importance. The bulk of the sulfur dioxide passes off from trap 18 in vapor form through valve 89 to line 36, condenser 31, surge chamber 39 and compressor 39 back to storage tank I5.

Simultaneously, the extract hydrocarbons re moved from the base of tower, 19 through valve 8| by means of pump 82, are introduced at an intermediate level into fractionating tower 83 provided with reboiling coil 84 and dephlegmating coil 85. The residual sulfur dioxide is re moved in vapor form through valve 99, passes into line 36 and thence back to storage tank 15. At the same time, the hydrocarbon material containing some residual phenol is removed from the base of tower 83 through valve 9'! and line 89 by means of pump 89 and is introduced into upwardly directed spray 99 located near the bottom of scrubber 9| where it comes in contact with hot water under pressure introduced through downwardly directed spray 92 by means of valve 93 and the water circulating system previously described in the case of scrubbing tower 43. Ihe aqueous extract passes out from the base of tower 9| through valve 94 and/or valve 95. Valve 94 leads by way of line 56 back to the water circulating system. By this method phenol is only indirectly removed after passing through scrubbing tower 43 and into fractionating tower 49 and it should therefore not be used unless the phenol content of the aqueous material leaving the base of tower 9| is low. If the phenol content is high, valve 95 should be used and the aqueous material then passes through pump 96 to fractionating tower 49 where water and phenol are separated and recycled to the system.

The purified extract material is removed from tower 9! through valve 91 and passes to storage tank 93 for further treatment or use as desired. Although different systems for the recovery of solvents have been shown for the extract and raflinate fractions, it will be understood that either can be used in either case. In general, I prefer, however, to use the recovery system shown with reference to the extract fraction since it is the more efficient of the two.

Although I have described the use of my process and of my new solvent mixture with particular reference to the fractionation of the hydrocarbon mixtures present in lubricating oil stocks and although it is particularly useful in that regard, it will be understood that the process and the solvent mixture can be used for the removal of smoky materials from kerosenes and burning 1 oils, for the solvent fractionation of motor fuel stocks to produce an extract fraction having a high antiknock rating (octane number), etc.

Furthermore, although I have described my invention with particular reference to the use of phenol and sulfur dioxide, other phenolic compounds such as cresol, the ortho, meta and para cresylic acids, wood tar creosotes such as beechwood cresote, etc. can be used to replace all or part of the phenol. The phenolic compound used should be substantially anhydrous. Liquid carbon dioxide can be used to replace all or part of the liquid sulfur dioxide.

In the appended claims I have set forth the novelty residing in my invention.

I claim:

1. A process for the solvent fractionation of hydrocarbon mixtures comprising contacting 100 volumes of said mixture with from 50 volumes to 1000 volumes of a solvent mixture comprising from about 20% to about of phenol by volume and from about 25% to about of liquid sulfur dioxide by volume, separating a raffinate fraction and an extract fraction and removing solvent from at least one of said fractions by stripping with sulfur dioxide gas.

2. A process for the solvent fractionation of hydrocarbon mixtures comprising contacting said mixture with a solvent mixture comprising at least 20% phenol and at least 25% liquefied sulfur dioxide, separating said solvent and hydrocarbon mixture into a raflinate fraction and an extract fraction and removing solvent from at least one of said fractions by stripping with said sulfur dioxide in gaseous form.

GEORGE L. PARKHURST.

CERTIFICATE OF CORRECTION.

Patent No. 2,120,810.. June it, 19 8..

GEORGE L. PARKHURST.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page .1, first column, line 12, for "precede" read proceeds; and second column, line 1 5, in the table, strike out the word "Percent" over last column; and that the said Letters Patent shouldbe read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 19th day of July, A. D, 1958.

Henry 'Van Arsdale, (Seal) Acting Commissioner of Patents.

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