US2043288A - Process for solvent fractionation of motor fuel stock - Google Patents

Description

June 9, 1936. o. FITZ SIMONS 2,043,288

PROCESS FOR SOLVENT FRAOTIONATION OF MOTOR FUEL STOCK 2 Sheets-Sheet 1 Filed June 5, 1933 on W Du 0 y x m 0% 2. W Om m 09 Inventor Ogden Filfj 527710715 FD i ATTORNEY June 9, 1936. o. FITZ SIMONS 2,043,288

PROCESS FOR SOLVENT FRACTIONATION OF MOTOR FUEL STOCK Filed June 5, 1933 2 Sheets-Sheet 2 .fitripper fitripper' Cofitczctor High Fraction Inventor ATTORNEY Patented June 9, 1936 UNITED STATES,

PATENT OFFICE PROCESS FOR SOLVENT FRACTIONATION OF MOTOR FUEL STOCK ration of Indiana Application June 5, 1933, Serial No. 674,302

6 Claims. (Cl. 196-37) This invention pertains to the solvent fractionation of motor fuel stocks to form a relatively high octane number fraction and a relatively low octane number fraction.

It is an object of the invention to provide a solvent fractionation process for motor fuel stocks utilizing a new and improved mixed solvent. A further object is to provide a process of this type which will produce a higher octane number fraction than is produced by prior art processes under comparable conditions. A still further object is to provide a process in which a portion of the mixed solvent remains in the high-octane number fraction of the motor fuel stock and enhances its value as a fuel for internal combustion engines. Other and more detailed objects of our invention will become apparent as the description thereof proceeds.

It is old to fractionate a motor fuel stock by the use of liquid sulfur dioxide (S02) alone but the process suifers from the low yields of extract obtained, necessitating the use of large quantities of S02. I have found that greatly improved results can be obtained by incorporating a secondary selective solvent with the sulfur dioxide. My preferred secondary selective solvent is methanol or methyl alcohol (CHaOH).

Referring now to the drawings: Figure 1 shows a variety of curves giving data on solvent fractionation processes using my preferred mixed solvent as compared with solvent fractionation processes using sulfur dioxide alone, and

Figure 2 shows in sectional'elevation a conventionalized flow diagram of a preferred embodiment of my solvent fractionation process.

In Figure 1 the curve marked S02 illustrates the relationship between the yield of extract motor fuel fraction and the octane number of the extracted material when treating with various volumes of liquid sulfur dioxide at +5 F. Similarly the other curves give comparable data on mixed solvents composed of liquid sulfur dioxide and methanol in various ratios to each other as indicated on the various curves. The motor fuel stock used in these particular experiments was a heavy naphtha boiling between 250 F. and 460 F. obtained by fractionally distilling a pressure distillate from a vapor phase pyrolytic cracking process. The octane number of the stock, after redistillation to 400 F. end point, was 62 and the composition as follows: olefines 52% aromatics 1%, paraflins and naphthenes 47%, as determined by absorption with suitable concentrations of sulfuric acid.

The method of treating was to coagitate the motor fuel stock and the solvent very vigorously at +5 F. and then separate an extract fraction and a rafllnate fraction. The solvent was then removed from the extract fraction by fractional distillation followed by water and caustic wash- S02 alone. As is apparent from Figure 1, the maximum octane number obtainable with S02 alone, under the conditions outlined is 80, whereas with 1:1SO2-CH3OH an octane number of 89 can be obtained. 25

In general I use from 50 to 750 volumes of my mixed solvent to 100 volumes of the motor fuel stock being treated. The preferred range is from to 250 volumes of solvent per volumes of stock. The amount of mixed solvent used is determined in general by balancing the desirability of a high yield against the desirability of a high octane number.

It will be seen by reference to Figure 1 that at least up to a 40% extract yield (and with some 35 stocks this will remain true at higher yields) it is possible to produce a motor fuel having a much higher octane number by the use of SO2CH3OH than can be produced with S02 alone.

It will also be seen by reference to the curves that 1I3SO2-CH3OH and 3:1S02C'H3OH are both markedly inferior to 1:1SO2-CH3OH although still distinctly superior to S02 alone. The 1:1 mixture appears to be approximately an optimum. Thus, for example at 20% yield S02 alone gives an octane number of 70, 1:3SO2-CH3OH gives 84, 321SO2CH3OH gives 86 and gives 89. CHaOH alone gives an octane number of 75 as shown at point A on Figure 1.

Although my improved mixed solvent can be used in a batch process such as that used in the laboratory tests referred to above, I prefer to utilize a counter-current process. By countercurrent extraction the fresh stock comes in contact only with solvent which is already nearly saturated with oleflnic constituents. This solvent has a higher solvent power for high octane number materials than does the fresh solvent and therefore these high octane number materials are extracted to a greater extent than they would be in a batch process. The result is an even higher octane number extract than is indicated by the curves.

One counter-current process which I may use is shown inFigure 2. Liquid sulfur dioxide from tank It and methanol from tank l2 are introduced into mixer I! by means of pumps I l and II respectively and then pass to intermediate mixed solvent storage tank Ii. Other methods of obtaining a mixture of the two materials can be used. For instance sulfur dioxide gas can be bubbled into liquid methanol to form a solution. The mixed solvent can be cooled to the temperature desired for the solvent fractionation operation by any suitable means, for instance by exhausting a portion of the sulfur dioxide in vapor form through line I1 and valve It. The cooled -mixed solvent is taken by means of pump l2 and line It to a downwardly directed spray 2| located in tower 22. Simultaneously a motor fuel stock, for instance the specific stock described above is introduced through pump 23 from a source not shown, is cooled by passage through cooler 24, which may suitably be cooled by any refrigeration medium, and then passes through line 2! to upwardlydirected spray 26.

The mixed solvent passes downward in tower 22 from spray 2| and the motor fuel stock, being of lower specific gravity than the solvent, passes upward from spray 26 counter-current to the descending solvent. Tower 22 may suitably be of the disc and doughnut type as shown or of any other suitable type such as plain towers, packed towers or towers provided with mechanical agitators. The discs 21 and doughnuts 28 cause the descending and ascending streams to pursue circuitous courses and this increases the thoroughness of contact between the two streams and makes thesolvent fractionation more efficient.

- The mixed solvent carrying dissolved high octane 2! and is introduced through line 20 into an intermediate section of stripping tower II which is equipped with a heating coil 32 at the bottom to provide reboiling and a dephlegmating coil 32 at the top to provide reflux. The temperature at the top of tower II is normally controlled so that substantially all of the solvent and substantially none of the motor fuel fraction passes overhead. The solvent vapors pass out of tower ll through line 24, valve 35, compressor 3, cooling and/or condensing coil 31, drum 31a, valve 311: and line "back to intermediate storage tank I.

The motor fuel stock flowing upward in tower 22 gives up its higher octane number constituents to the downwardly flowing stream of solvent and itself dissolves a portion of the solvent. The upward stream or railinate fraction is settled in the top section of tower 22 and then passes through valve 39 into an intermediate section of stripping tower 4| which may suitably be equipped with reboiling coil 4| and dephlegmating coil 42. The mode of operation of tower 40 can be identical with that of tower 3|. Solvent vapors pass oil through line 42, valve 44, compressor 28, condensing and/or cooling coil 31, drum 21a, valve 21b, and line 38 back to intermediate storage tank to.

It will usually be desirable to insert a condenser in the line entering compressor 26, the liquid solvent from this condenser being pumped back to tank I 6 and the uncondensed gases passing to compressor 38. 10

The extract or high octane number motor fuel fraction is withdrawn from tower 2| through valve 45 to storage or to further treating processes. The rafl'inate or low octane number fraction is similarly withdrawn from tower 40 through 15 valve 48. The extract fraction is a very high grade motor fuel or motor fuel component. The rafiinate fraction can be used as a lower grade motor fuel or motor fuel component, or as a solvent naphtha or ,its octane number can be 20 increased by means of a pyrolytlc reforming operation, by blending with lead tetraethyl, etc.

Instead of controlling the temperature at the tops of towers 3i and 40 so that substantially all of the mixed solvent and substantially none of 2 the motor fuel components will pass overhead it is sometimes advantageous to control the top temperatures of one or both of these towers so that substantially all of the sulfur dioxide will pass overhead but at least a portion of the methanol will pass out with the residual motor fuel fraction. This is particularly desirable in the case of tower 3| since the quality of the extract fraction may be improved by the presence in it of from 5% to 40% of methanol. If this is 35 done the amount of fresh methanol introduced from tank l2 must, of course, be increased to balance the withdrawal of methanol from the process.

Although I have found that methanol is peculiarly advantageous as a secondary selective solvent for enhancing the selectivity of sulfur dioxide as a solvent for the oleflnic constituents of motor fuel stocks, ethanol or ethyl alcohol (CzHsOH), isopropanol or isopropyl alcohol (CSH'IOH) and benzol or benzene (com) have a somewhat similar effect. For instance when 100 volumes of the heavy naphtha described above was treated with 60 volumes of a 5:1 mixture of SO: and CzHsOH under precisely the same conditions as in the case of the experiments described above and illustrated in Figure 1, 22.7% of an extract fraction having an octane number of was obtained. These results are shown at point 3" on Figure 1 and it is apparent that although 55 this mixture is inferior to SO:CH:OH it is considerably superior to S0: alone.

In the case of benzol mixtures somewhat lower solvent fractionation temperatures are desirable in order to lower the miscibility effect of the 60 benzol. A good operating temperature is 10 F., but temperatures from --30 F. or lower up to +10 F. canbe used. The amount of benzol used is also generally lower than in the case of methanol. Benzol in an amount from 3% to 35% of 65 the sulfur dioxide is suitable. Using '15 volumes of l0%benzol90% sulfur dioxide and volumes of the above heavy naphtha at l0 F, 24.3% of an extract having an octane number of 86 was obtained. This is shown at point C" on Figure l and is seen to approach the highest SOs-CHsOI-I curve. At this same temperature and degree of extraction the octane number of the extract using SO: alone is about 79.

When using ethanol or benzol it mav be ad- 75 vantageous to operate tower ll and/or tower 40 with a top temperature such that at least a part of the ethanol and/or benzol remains in the motor fuel fraction. This is especially desirable in the case of tower 3| since the ethanol and/or benzol may be desirable in the extract motor fuel fraction. Furthermore, this mode of operation makes possible the use of these solvent mixtures with many motor fuel stocks which could nototherwise be treated with them due to the presence of low boiling constituents which cannot be separated from ethanol or benzol by fractional distillation. Also, where the ethanol contains a small percentage of water up to 4 or 5%, this may be distilled off leaving a fuel which contains substantially anhydrous ethanol or ethanol and benzol in case the latter solvent is also present.

Mixtures of methanol, ethanol and benzol or any two of these can be used in conjunction with S02 as a mixed solvent for motor fuel stocks. The three component solvents and SO2C2H5OH-C6H5 are particularly useful since the alcohol and benzol can be left in the finished motor fuel, at least in part, and the bennol acts as a miscibility agent retaining the alcohol in solution in the finished fuel after the sulfur dioxide has been removed.

In the solvent fractionation of lubricating oils the purpose is to extract the naphthenic hydrocarbons, leaving as a rafllnate the more desirable paraffinic hydrocarbons (Industrial and Engineering Chemistry, July, 1931, page 753). In the solvent fractionation of kerosene, burning oils, etc. the principal object is to extract the smoky aromatic hydrocarbons,'agaln leaving a paraflinic raflinate (Petroleum Zeitschrift, January 8, 1930, page 47). My process, on the other hand, is found to be particularly suitable for the extraction of low boiling olefinic hydrocarbons such as are found in cracked motor fuel stocks. Paraflinic and naphthenic constituents together form the rafllnate and are not separated as in the case of lubricating oil extraction.

I have found that my mixed solvents are peculiarly advantageous in the solvent fractionation of highly olefinic motor fuel stocks, particularly those containing at least 30% of olefinic hydrocarbons and which do not normally contain substantial amounts of aromatics. By the term motor fuel stock I refer to any petroleum distillate lying predominantly within the gasoline boiling point range. Motor fuel stocks from vapor phase cracking processes contain very high concentrations of olefinic hydrocarbons; those produced from liquid phase cracking processes contain somewhat lower concentrations; virgin or uncracked motor fuel stocks contain relatively little of these desirable constituents. Since I find that my mixed solvents are peculiarly adapted to the selective extraction of these olefinic hydrocarbons it is desirable to select a motor fuel stock containing a high percentage of them and therefore my process is peculiarly applicable to motor fuel stocks such as pressure distillates, naphthas, and refined or unrefined gasolines produced by cracking processes and particularly vapor phase cracking processes. The content of oleflnic hydrocarbons seems to be roughly measured by the octane number of the motor fuel or motor fuel stock and since this is also a measure of the antiknock characteristics of the fuel it is apparent that it is desirable in the production of a high grade antiknock fuel to start with a motor fuel stock having a fairly high octane number, which is indicative of a fairly high concentration of olefinic hydrocarbons, and then selectively fractionate to segregate an extract having as high an octane number as may be consistent with reasonably high yields. This, I find, can be accomplished with unprecedented efllciency by the use of the mixed solvents which I have discovered. In general I find it desirable to start with a motor fuel stock having an octane number of at least 50 and preferably 55 to 70 and I usually obtain an extract motor fuel having an octane number of 75 or better and preferably 80 or better.

Altho it is quite possible to use a complete pressure distillate or gasoline as a stock for my process I find that it is often preferable to use a heavy naphtha such as can be produced by the fractional condensation or fractional distillation of a pressure distillate. Such a heavy naphtha may suitably have an initial boiling point of from 200 F. to 300 F. and a maximum boiling point of from 350 F. to 500? F. Any material present having a boiling point in excess of about 400 F. will, in general, be removed by redistillation following the solvent fractionation. The elimination of the light constituents, boiling below 200 F. to 300 F. is highly advantageous since it greatly reduces vapor losses, enhances the separation of the solvent from the motor fuel fractions produced by the process and permits the production of a higher octane number extract fraction. The light constituents are normally of high octane number and can be blended with the high octanr number material recovered from the extract fraction to give a maximum yield of a highly superior antiknock motor fuel.

Although I have described my invention in terms of certain specific embodiments thereof numerous modifications will be apparent in the light of my specification to those skilled in the art and I do not desire to limit my invention except to the scope of the appended claims. I have also mentioned certain theories in connectior with my invention but it is to be understood tha. the invention is a matter of fact and is not dependent on the theories advanced.

I claim:

1. In a process for the solvent fractionation of a motor fuel stock to produce a high octane number motor fuel the steps which comprise mixing said stock with a selective solvent comprising at least sulfur dioxide and at least 25% methanol and separating a rafiinate fraction and a' extract fraction.

2. In a process for the solvent fractionation of a motor fuel stock having an octane number within the range 50 to '70 the steps which comprise mixing said stock with a selective solven comprising a susbtantial amount of sulfur dioxide and a substantial amount of methanol, separatirig a rafliniate fraction, and separating an extract fraction comprising a fraction of said motor fuel stock having an octane number in ex cess of '75.

3. In a process for the solvent fractionation of a motor fuel stock to produce a high octane number motor fuel the steps which comprise passing a stream of said stock in contact with an oppo' sitely flowing stream of a mixed selective solvent comprising a substantial amount of sulfur dioxide and a substantial amount of methanol, dissolving not more than about 40% of said stream of sai: stock in said stream of said mixed solvent ant separating the two resultant streams.

4. In a process for the solvent fractionation of a motor fuel stock to produce a high octane number motor fuel, the steps which comprise passing a stream of said stock in contact with an oppositely flowing stream of a mixed selective solvent consisting essentially of sulfur dioxide and methanol in the ratio of-from about 1:3 to about 3:1, dissolving not more than about 40% of said stream of said stock in said stream of said mixed solvent and separating the two resultant streams.

5. In a process for the solvent fractionation of a motor fuel stock to produce a high octane number motor fuel the steps which comprise mixing said stock with a selective solvent comprising a substantial amount of sulfur dioxide and a substantial amount of methanol; separately recovering a rafllnate fraction; separately recovering an extract fraction containing the major portion of said sulfur dioxide, a portion of said methanol and an extract fraction of said stock having an octane number substantially higher than that of said stock; and fractionally distilling said extract fraction into an overhead fraction comprising substantially all of said sulfur dioxide and a residual motor fuel fraction comprising substantially all of said extract fraction of said stock and at least a substantial portion of said methanol.

6. The method of obtaining maximum yields of high antiknock motor fuel from cracked hydrocarbon distillates which comprises fractionating said distillates into one boiling below about 200-300 I and one boiling from these temperatures to about 400-500 F., selectively extracting the latter fraction with a solvent mixture of sulfur dioxide and methanol to yield a ramnate phase and an extract phase, removing substantially all of said sulfur dioxide and a substantial part but substantially less than all of said methanol from said extract phase and blending at least a substantial part of the remainder of said extract phase with at least a substantial part of said first-named fraction.

OGDEN FITZ SMONS.

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