US2063597A - Gasoline extraction - Google Patents

Description

DEC 8, 1936- o. FlTz slMoNs ET AL' I 2,063,597

GASOLINE `EXTRACTION Filed June 29, 1953 2 sheets-sheet 2 Motor Juve/M915:- Ogden Fitj Lmomff FTan/: Cailzawroxtom ATTORNEY Patented Dec. E, 1936 UNITED STATES PATENT FFICE GASOLINE EXTBACTION diana Application June 29, 1933, Serial No. 678,112

8Claims.

This invention relates to the extraction of olefinlc hydrocarbons boiling between about 250 F. and about 400 F. from mixtures of such hydrocarbons with other hydrocarbons. More particularly it relates to an extraction of the type described in which the solvent comprises a nitrogen base, preferably a heterocyclic nitrogen base. It further relates to methods of separating nitrogen bases from mixtures with hydrocarbons.

It is an object of our invention to provide a process for the extraction of a motor fuel stock to produce a fraction having an extremely high concentration of oleinic hydrocarbons boiling between about 250 F. and about 400 F. and having an unusually high octane number or antiknock rating. Itis a further object to provide means for the removal of the solvents which we prefer to use in our extraction process from the raiiinate and extract fractions produced. Further and more detailed objects will become apparent as the description of our invention proceeds.

We have found that the heterocyclic nitrogen bases have a high selective solvent power for oleflnic hydrocarbons boiling in the gasoline range and particularly those boiling between about 250 F. and about 400 F. such as are found in pressure distillates, particularly pressure distillates from vapor phase cracking processes, synthetic gasoline fractions from the reduction of carbon monoxide with hydrogen or the hydrogenation of oil or coal under high pressures, etc. This is a matter of great importance since this particular range of oleflnic hydrocarbons is of the highest value in the production of gasolines having the highest antiknock values, or, in other words, the highest octane numbers. This selective solvent action of the heterocyclic nitrogen bases is even further enhanced by using them in conjunction with liquid sulfur dioxide.

Our invention can be more particularly described by reference to the accompanying drawings in which: y

Figure 1 shows comparative data on extraction with liquid sulfur dioxide, extraction with pyridine, which is our preferred heterocyclic nitrogen base, and extraction with a mixture of pyridine and liquid sulfur dioxide; and Figure 2 represents a conventionalized flow diagram of an illustratve process embodying our invention.

In Figure l the curve marked SO2 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. Point A gives comparable data on the use of pyridine and point B on the use of a mixture of pyridine and liquid sulfur dioxide, as will be described hereafter. The motor fuel stock used in these particular experiments was a heavy naphtha boiling between 250 F. and 450 F. and obtained by fractionally distilling a pressure distillate from a vapor phase pyrolytic cracking process. The octane number of the stock after redistillation to a 400 F. end point, was 62 and the composition was as follows: olefines 52%, aromatics 1%, paraflins and naphthenes 47%, as determined by absorption with sulfuric acid.

'I'he 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 raiiinate fraction. The solvent was then removed from the extract fraction by water washing and the octane number was then determined by the Cooperative Fuel Research engine test (Research method) after redistillation to 400 F. end point.

Point A represents an extraction with 95 volumes of pyridine to 100 volumes of the above -described heavy naphtha, 9% of an 80 octane number extract being obtained. It will be noted from the curve that when 9% of this same heavy naphtha is extracted with liquid sulfur dioxide alone the extract has an octane number of only 66.

Point B shows even better results using 215 volumes of solvent to 100 volumes of this same heavy naphtha, the composition of the solvent being 23% pyridine and 77 liquid sulfur dioxide by volume. In this case 28% of an extract having an octane number of 103 was obtained as compared with an octane number of 78 obtained by means of liquid sulfur dioxide alone.

These unusual results are, we believe, due to the fact that our new selective solvents are able to remove a very high concentration of the olenic hydrocarbons present in the motor fuel stock and more particularly those olefin hydrocarbons boiling between about 250 F. and 400 F. which seem to have a very great inuence on the antiknock properties of gasoline containing them.

Although we may utilize our new selective solvents in a batch process by merely coagitating the hydrocarbon mixture and solvent and then separating the two liquid phases or by heating the solvent and hydrocarbon mixture to a point at which a single liquid phase is formed and then cooling to separate two liquid phases, we prefer to operate in countercurrent fashion and find that much more emcient results are obtained. One countercurrent process which is particularly advantageous is that illustrated in Figure 2 which will now be described.

The heterocyclic nitrogen base, for instance pyridine, is removed from storage tank II by means of pump I2 and introduced into mixer I3. Simultaneously, liquid sulfur dioxide is removed from storage tank I4 by means of pump I5 and also introduced into mixer I3. Recycle solvent from line I6 can also be added at this point, as

will be described later. The mixed solvent then passes to cooler I1 and thence to downwardly directed spray I8 located in'countercurrent ex`- traction tower I9. Simultaneously a motor fuel stock containing a substantial amount, preferably at least 25%, of olefin hydrocarbons boiling between about 250 F. and about 400 F., for instance the above mentioned heavy naphtha, is withdrawn from tank 20 by means of pump 2I and passed through cooler 22 and thence to upwardly directed spray 23 located near the bottom of countercurrent extraction tower I9. Coolers I1 and 22 are used to lower the temperatures of the two streams to the point or points found to be most eilicient for the extraction step. This must be determined by experiment for each particular solvent and each particular stock and in some cases will be found to be the prevailing atmospheric temperature, or even higher in which case one or both of the coolers can be dispensed with or even replaced by heaters. It will be found, however, in most cases, that the nitrogen base coming in contact with the liquid sulfur dioxide in mixer I3 will react chemically, with the liberation of considerable heat, and cooling is, therefore, generally necessary.

The stream of stock rising from spray 23 through tower I9 passes in countercurrent contact with a falling stream of solvent from spray I8, An extract fraction, containing an increased amount of the desired oleiinic hydrocarbons, is removed from the base of tower I9 and a raffinate fraction, containing a decreased amount of these hydrocarbons is removed from the top of the tower. Referring first to the extract fraction, this is withdrawn through line 24 and passes to upwardly directed spray 25, located near the bottom of scrubbing tower 26 where it meets a downcoming stream of water from spray 21 located near the top of the tower. This water comes in general from recycle line 28 to be described hereafter and passes through valve 29. Fresh makeup water can be introduced from time to time as needed from line 30 by means of pump 3| and valve 32. This water wash in tower 26 tends to remove the nitrogen base and sulfur dioxide. This action may be accounted for, in the case of pyridine, by the following chemical equation:

A second scrubbing tower similar to tower 26 may be used in series therewith. The extract fraction of the yoriginal hydrocarbon mixture purified by means of this scrubbing action passes oif from the top of tower 26 through valve 33 and line 34 by means of pump 35 and is blended with other materials as will be described hereafter in mixer 36, thence passing to further treatment, storage or use, as desired, through line 31.

Returning now to countercurrent contacting tower I9, the raiinate fraction passes off from the top of that tower through line 38 by means of piunp 39 and is introduced into upwardly directed spray 40 located near the bottom of scrubbing tower 4I which is similar in general to scrubbing tower 26. Water is introduced into this scrubbing tower by line 42 leading to downwardly directed spray 43 located near the top of scrubbing tower 4I. The scrubbed ramnate fraction is drawn off from the top of this tower by means of pump 44 and passes through line 45 to cracking coil 46 located in pipe still 41. Cracking coil 46 is operated under vapor phase pyrolytic cracking conditions. The material from the cracking coil is expanded through valve 48 into bubble tower 49 and cooled at the top by means of dephlegmating coil 5I. Tar is removed from the base of tower 49 through valve 52 and line 53 for further treatment or use as desired. A heavy naphtha fraction, for instance a fraction boiling preponderantly between about 250 F. and about 400 F., is withdrawn from trap-out plate 54 through valve 55 and line 56 and is recycled to stock tank 2li. This recycle stock having been subjected to vapor phase cracking conditions contains high concentrations of oleiinic hydrocarbons and is, therefore, capable of producing a very high antiknock extract by means of the use of our new selective solvents. A light naphtha fraction is removed from the top of tower 49 through line 51, is condensed in condenser 58 and passes to stabilizer 59, equipped with reboiling coil 59a and dephlegmating coil 59h. Gas is removed from the stabilizer 59 through line 60, passing to fuel lines or an absorption plant, etc., as desired. The light naphtha fraction is removed from the base of stabilizer 59 through valve 6I and line 62 by means of pump 35, and is blended with the extract heavy naphtha fraction from line 34 in mixer 36. In some cases the amount of light naphtha available from the cracking process will be more than is desired for blending with the extract fraction of the heavy naphtha and in this case the excess is removed from the system through valve 63 by means of pump 64 and passes through line 65 to storage.

Returning now to the solvent extracted by the water scrubbing conducted in towers 26 and 4I, these water extracts pass through valves 66 and 61 by means of pump 68 to a fractionating column 69, the object of which is to split up this material into sulfur dioxide, nitrogen base and water. Reboiling coil 10 located in the base of tower 69 is operated at such a temperature that practically nothing except nitrogen base is withdrawn from the bottom of tower 69. Sulfur dioxide being the lightest component, is removed from the top of the tower, water and nitrogen base being reiiuxed by means of dephlegmating coil 'l I. The nitrogen base is withdrawn from the bottom of the tower through valve 12 and pump 13 and line i6 back to mixer I3 where it re-enters the extraction process. Alternatively, it may of course be returned to tank Il. The water being the component of intermediate boiling points is withdrawn from tower 69 at an intermediate level by means of trap-outplate 14 and pump 15. This water is then recycled to spray 21 and/or spray 43 by means of valve 16 and/or valve 11. Any sulfur dioxide or nitrogen base in this water is thus recycled and is not lost to the system. The sulfur dioxide passes overhead from tower 69 through line 18 to spray 19 located near the bottom of drying tower where it comes in contact with a downward stream of sulfuric acid introduced through spray 8|. Sulfuric acid is removed from the base of the tower by means of pump 82 and recycled to spray 8I by means of aocaser valve 83. When the supply of sulfuric acid becomes too dilute for efcient drying it can be removed through valve 84 by means of pump 82 and line 85 and fresh sulfuric acid introduced at this same point. Alternatively, continuous concentration apparatus for the sulfuric acid can be installed in the system. The dry sulfur dioxide is removed from the top of drying tower 80 through line 86 and passes back to storage tank I4 by way of compressor 81 and condenser 88. As alternatives to the use of a sulfuric acid drying tower, drying can be accomplished by other drying agents, or by cooling to precipitate moisture or by continued redistillation, etc.

Fresh stock can be introduced into our apparatus from a supply not shown through valve 89 or preferably, as charging stock to the cracking step by means of valve 90, and a pump not shown.

It will be seen that an important feature of our process is the removal of the nitrogen base and liquid sulfur dioxide from the hydrocarbons following the solvent fractionation by means of a water wash followed by fractional distillation of the water extract. This step can of course be applied to processes other than our preferred solvent extraction process, for instance, it can be applied to the solvent extraction of lubricating oils or kerosene with nitrogen bases or to the removal of nitrogen bases from coal tar distillates, petroleum distillates, etc., by means of treatment with sulfur dioxide and water.

As aforementioned, our preferred selective solvents for, the removal of the desired oleflnic hydrocarbons boiling between about 250 F. and about 400 F. are the heterocyclic nitrogen bases.

The preferred example, as aforementioned, is

pyridine. Other heterocyclic nitrogen bases which can suitably be used are quinoline, quinaldine, the picolines, the lutidines, the collidines, pyrrol, piperidine, etc. These may be used alone or may be combined with various secondary selective solvents. A preferred secondary selective solvent is liquid sulfur dioxide. Liquid carbon dioxide is also suitable. From 50 to 1000 volumes of the solvent or a mixed solvent can be used per 100 volumes of thehydrocarbon mixture to be extracted, but, in general, we prefer to use from '15 volumes to 500 volumes of solvent per 100 volumes of hydrocarbon mixture. The heterocyclic nitrogen base or heterocyclic nitrogen bases used in a solvent mixture may suitably constitute from 20% to 100% and the liquid sulfur dioxide or carbon dioxide from 20% to 80% by volume of the total mixture.

When a heterocyclic nitrogen base is used alone, it can be recovered from the extract and raffinate phases by distillation or by extraction with liquid sulfur dioxide or aqueous sulfur dioxide and recovered as above described.

Although as aforementioned, we nd that heterocyclic nitrogen bases are peculiarly suitable for the extraction of the desired range of olenic hydrocarbons fromy their mixtures with other hydrocarbons, other nitrogen bases can also be used. Thus, for instance, the aromatic nitrogen bases, such as aniline, chloraniline, diphenyl amine, benzyl aniline, diethyl aniline, dimethyl naphthyl amine, etc., can be used. Aliphatic nitrogen bases, such as the diand tri-butyl amines, the mono-, di and tri-amyl amines and polymethylene amines, such as cyclo hexyl amine, can also be used alone, in mixtures with each other or in mixtures with liquid sulfur dioxide orA liquid carbon dioxide as above described.

Although we have described our invention in connection with certain specific embodiments thereof, we dovnot desire to be limited thereby but only to the scope of the appended claims which set forth the novel features inherent in our invention.

We claim:

1. The method of producing a high antiknock motor fuel from a motor fuel stock containing a substantial amount of oleilnic hydrocarbons boiling between about 250 F. and about 400 F., comprising extracting said stock with a substantial amount of a solvent comprising a substantial amount of a heterocyclic nitrogen base and a substantial amount of liquid sulfur dioxide, forming an extract phase containing a substantially higher concentration of said olenic hydrocarbons than said stock and a railinate phase containing a substantially lower concentration of said oleflnic hydrocarbons than said stock, separating said extract and raffinate phases from each other, and removing said heterocyclic nitrogen base and liquid sulfur dioxide from each of said phases.

2. In a process for the solvent extraction of olefinic hydrocarbons boiling between about 250 F. and about 400 F. from a mixture of such hydrocarbons with other hydrocarbons the step which comprises contacting said mixture with a solvent comprising a substantial amount of a liquid selected from the group consisting of the nitrogen bases and a substantial amount of liquid sulfur dioxide.

3. In the solvent fractionation of a hydrocarbon mixture the steps which comprise contacting said mixture with a solvent comprising a sub- 3 stantial amount of a liquid selected from the group consisting of the nitrogen bases and a substantial amount of liquid sulfur dioxide, separating a raffinate phase and an extract phase, scrubbing at least one of said phases with water and fractionally distilling the water extract into a predominantly sulfur dioxide fraction, a predominantly aqueous fraction and a predominantly nitrogen base fraction.

4. In the solvent fractionation of a hydrocarbon mixture the steps which comprise contacting said mixture with a solvent comprising a substantial amount of a liquid selected from the group consisting of the nitrogen bases and a .substantial amount of liquid sulfur dioxide, separating a raffinate phase and an extract phase, scrubbing at least one of said phases with water, fractionally distilling the water extract into a predominantly sulfur dioxide fraction. a predominantly aqueous fraction and a predominantly nitrogen base fraction, recycling said predominantly sulfur dioxide fraction and said predominantly nitrogen base fraction back to the contacting step and recycling said predominantly aqueous fraction back to the scrubbing step.

5. In the solvent fractionation of a hydrocarbon mixture the steps which comprise contacting said mixture with a solvent comprising a substantial amount of a liquid selected from the group consisting of the nitrogen bases separating a ralnate phase and an extract phase, scrubbing at least one of said phases with water in the presence of sulfur dioxide, fractionally distilling the water extract into a predominantly sulfur dioxide fraction, a predominantly aqueous fraction, and a predominantly nitrogen base fraction and recycling said fractions to the process.

y6. 'Ihe process of separating from a hydrocarbon distillate boiling substantially within the range of gasoline, a fraction having a higher antiknock value than that of the original distillate, comprising extracting the distillate with a mixture of pyridine and liquid sulfur dioxide, and recovering the pyridine and sulfur dioxide from the extracted gasoline.

7. The process of claim 6 wherein the major part of the sulfur dioxide is recovered by distilling directly from the extract, and the remaining sulfur dioxide and the pyridine are recovered by 10 extracting with water.

A 8. 'I'he process of separating from a hydro-

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