US2920037A

US2920037A - Separation of normal paraffins from hydrocarbon mixtures using zeolitic molecular sieves

Info

Publication number: US2920037A
Application number: US568809A
Authority: US
Inventors: Haensel Vladimir
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1956-03-01
Filing date: 1956-03-01
Publication date: 1960-01-05
Anticipated expiration: 1977-01-05
Also published as: DE1418428B1; FR1172788A; DE1795548A1; CA1016873A; NL108239C; DE1795548B2; DE1418428C2; GB803184A; ES233939A1

Description

FROM HYDROCARBON CULAR SIEVES V. HAENSEL Filed March 1, 1956 SEPARATION OF NORMAL PARAFFINS MIXTURES USING ZEOLITIC MOLE Jan. 5,

KN MN //vv/v r155: Vladimir Haense/ 8K5 A TTORA/EYS:

2,920,037 Patented J an. 5, 1960 United States Patent Oefiice SEPARATION OF NORMAL PARAFFINS FROM HYDROCARBON MIXTURES USING ZEOLITIC MOLECULAR smvns Application March 1, 1956, Serial No. 568,809

6 Claims. (Cl. 208'310) This invention relates to a method of separating normal parafiins from a hydrocarbon mixture containing the same. It is more specifically .concerned with a sorption-desorption process which is particularly suitable for the separation of normal paraffins from a hydrocarbon mixture containing the same.

Normal paraflins find use as intermediates or raw materials in the production of many petro-chemicals. Normal paraffins also find wide use as solvents. While normal parafiins are not particularly desirable for use as a motor fuel, because of their relatively low octane numbers they may readily be isomerized to isoparaflins which have substantially higher octane numbers. Since isomerization is an equilibrium reaction, it is preferred that the normal paraffins be separated from isoparaffins before subjecting the normal parafiins to isomerization. In this manner, isomerization of the normal-paraflins occurs without theequilibrium restrictions imposedby the presence of isoparaffins in the feed.

. The process of the present invention may also be used to increase the octane number of gasolines. Forexample, a gasoline having an octane number of 85 F-l clear and containing normal parafiins, having an average octane number of zero, would have an octane improvement from 85 to 94.5 by removal of these normal paraflins, on a strictly arithmetical basis. In the present process the normal parafiins are removed from the gasoline thereby increasing the octane number. The normal parafiins separated from the gasoline may be subjected to a further treatment to convert them to aromatics and/or isoparaflins which may be blended into gasoline.

. It is an object of the present invention to separate normal paraffins from a hydrocarbon mixture containing the same. i

It is another object of the present invention to provide a sorption-desorption process, for the separation of normal paraflins from a hydrocarbon mixture containing the same, in which the heat requirements for the process are kept to a minimum.

In one embodiment the present invention relates to a process which comprises contacting in a sorption zone a hydrocarbon mixture containing normal paraffins with a solid sorbent-having a high sorbing power for normal paraffins, withdrawing and recovering from said sorption zone a hydrocarbon mixture of decreased normal paraffin content, anddesorbing the normal parafins sorbed on the solid sorbent by displacing them with a normal paraflin.

In another embodiment the present invention relates to a process which comprises contacting in a sorption zone a hydrocarbon mixture containing normal paraffins and isoparafiins with "a solid sorbent having a higher sorbing power for normal paraffins than for isoparaffins at a temperature within the range of from about 175 F. to'about 305 9 F., withdrawing from said sorption zone a hydrocarbon mixture of decreased normal parafiin content, discontinuing the introduction of the hydrocarbon mixture to said sorption zone and thereafter introducing a normal paraflin to said sorption zone, which normal parafiin selectively removes the sorbed normal paraifins from said solid sorbent and recovering the desorbed normal paraffins.

In a specific embodiment the present invention relates to a process for separating normal paraflins from a hydrocarbon mixture containing normal paraflins, isoparaffins and aromatics which comprises introducing said mixture to a sorption zone and therein contacting said mixture with a crystalline alumino-silicate at a temperature within the range of from about 175 F. to about 305 F. and a pressure within the range of from about 200 to about 1000 pounds per square inch gauge, withdrawing from said sorption zone a hydrocarbon mixture of decreased normal paralfin content, discontinuing the introduction of the hyrocarbon mixture to the sorption zone, thereafter introducing normal butane to said sorption zone and displacing the sorbed normal paraffins from said crystalline alumino-silicate, reducing the pressure on said sorption zone to a pressure sufiicient to vaporize the normal butane in said zone, removing normal butane vapors therefrom and subsequently introducing a hydrocarbon mixture containing normal a the sorption zone, the hydrocarbon mixture is contacted with a solid sorbing material which has the power of sorbing normal paraffius from a hydrocarbon mixture such as a gasoline fraction. The effluent from the sorption zone, therefore, has a reduced-normal parafiin content, when compared with the charge to the sorption zone. According to the process of my invention, after the solid sorbing material has picked up, or sorbed, substantial, amounts of normal paraflins, the introduction of the hydrocarbon mixture to the sorption zone is discontinued, and the normal paraffins are removed from the sorbent.

In the operation of catalytic gasoline reforming proce'sses, it has been observed that the product, usually called reformate, contains a small amount of normal paraffins having relatively low octane numbers. The presence of these parafiins is due to the fact that under operating conditions of reforming, the equilibrium concentration represents a fair concentration of normal paraflins. The effect of the normal paraflins in the reformate is to cause a substantial depression of the octane number of the reformate. If reforming processes are operated to obtain a conversion of these normal parafiins into aromatics, or into higher octane number isomers and lower boiling paraffins, it has been found that the yield-octane number improvement relationship is such that somewhat more than one yield percent is lost for each octane number unit gained in the range of octane numbers of the order of -95 F- l clear. This is due to the conversion of normally liquid components into normally gaseous components. However, if the normal parafiins were removed the octane number would improve more favorably, for example, a reformate having an octane number of 85 F-l clear and containing 10% normal parafiins, having an average octane number of zero, would have anoctane improvement from 85 to 94.5, on a strictly' arithmetical basis. In my process the octanenumber is increased and normal paraflins are recovered as a product. These nor mal paraflins may be isomerized to isoparaffins or dehydrogenated to aromatics and reblended into gasolines.

The charge stocks that may be treated in accordance with my invention comprise hydrocarbon mixtures containing normal paraffins. The mixture may be of normal parafiins and isoparaffins; normal paraffins and cycloparafiins', normal paraflins and aromatics; normal paraftins, isoparaffins and cycloparaflins; normal paraflins, isoparaffins and aromatics; normal paraflins, cycloparaifins and aromatics; etc. It is preferred that the charge to the sorption zone does not contain hydrocarbons boiling below normal butane. The reason for this will be discussed further in the specification. Petroleum hydrocarbons, for example, gasolines, naphthas, etc. are mixtures containing normal paraffins, and these mixtures may be treated in accordance with the present invention.

The contact of the hydrocarbon mixture containing normal parafiins in the sorption zone is with a solid sorbent. which has a selective sorbing power for normal paraffins. The contact is for a time sufficient to sorb a substantial amount of the normal parafiins present in the charge. The sorption tower is maintained at a temperature andpressure so that the charge is maintained in the liquid phase. As will be hereinafter further elaborated upon, it is preferred to maintain the temperature in the sorption zone within the range of from about 175 F. to about 305 F. With a hydrocarbon charge mixture boiling substantially within the gasoline boiling range, the pressure in the sorption zone is within the range of from about 200 to about 1000 p.s.i.g., to keep the charge in the liquid phase.

Any suitable solid sorbent material may be used. Preferably the solid sorbent in the sorption zone is one that has a higher sorbing power for normal paraflins than for other hydrocarbons. Alumino-silicates such as calcium alumino-silicate, magnesium alumino-silicate, barium alumino-silicate, sodium alumino-silicate, potassium alumino-silicate, strontium alumino-silicate', etc. are suitable solid sorbents to use although they do not necessarily provide equivalent results. Crystalline calcium aluminosilicates, which have been heated to remove the water of hydration are preferred. These crystalline calcium alumina-silicates which have been heated to remove the water of hydration have pore diameters of about 5.1 angstrom units, which is slightly larger than the calculated critical diameter of normal paraflin molecules, but somewhat smaller than the critical diameter of isoparaffins, cycloparaflins and aromatics. Thus it is possible to sorb normal paraffins from the mixture.

The contact of the charge with the solid sorbent is for a time sufficient to sorb substantial quantities of the normal parafiins from the charge. After a substantial quantity of the normal paraflins are sorbed, the sorbed normal paraflins are removed and recovered from the solid sorbent.

The usual procedure for removal of the sorbed normal parafiins is by heating under vacuum. Such a procedure involves a considerable expenditure with respect to both initial installation and operating cost. The present invention, in its preferred embodiment, provides for a simple and essential isothermal operation of the sorption and desorption cycle. This results in a great saving in operating cost and the equipment necessary for the operation is simple and readily available.

It is thus proposed to pass a hydrocarbon mixture boiling above the boiling point of isobutane and containing normal paraflins into a sorption tower which contains an absorbent capable of selectively sorbing normal paraffins. The sorption tower is maintained at a temperature within the range of from about 175 F. to about 305 F. The sorption tower is maintained at suflicient pressure to maintain a liquid phase and for hydrocarbon charge streams boiling substantially within the gasoline range pressures of from about 200 to about 1000 pounds per square inch gauge are preferred.

. The normal paraffin which selectively removes, or displacesthe sorbed normal paraflins, may be normal buetc. although they do not necessarily produce equivalent results. Normal butane is a specifically preferred displacing agent since it is readily available. Its use has further advantages, in that it is a relatively cheap refinery product, and the process using normal butane is tane, normal pentane, normal-hexane, normal heptane, more efficient, economical and far more simple than any using the higher boiling normal paraflins. A lower temperature and generally a lower pressure may be used with normal butane which results in heat saving and a saving in investment and equipment. When normal butane is the hydrocarbon used to displace the sorbed hydrocarbon, the pressure preferably is within the range of from about 400 to about 600 pounds per square inch gauge! As hereinbefore mentioned, is is preferable to use liquid normal butane as the displacing agent in the desorption cycle of the process, and when normal butane is used, the temperature is preferably only slightly below the critical temperature of normal butane and the pressure is sufficient to maintain the normal butane as-a liquid. The critical temperature for normal butane is 305.6" F. and the critical pressure is 550 p.s.i.g. The temperature should, therefore, be below 305 F. and genarally within the 305 F. range and more preferably fromabout 250 F. to about 305 F.

In a preferred embodiment of my invention, therefore, the sorbed normal paraffins are removed from the sorbent material by passing into contact with the solid sorbent material a liquid normal paraffin which selectively removes the sorbed normal parafiins from the sorbent and the sorbed normal paratiins are removed and recovered. After the sorbent has picked up a substantial amount of normal paraffins, the sorption zone being maintained at 'a temperature within the range of from about 175 F; to about 305 F. and a pressure within the range of from about 400 to about 600 pounds per square inch, the introduction of the charge is discontinued and liquid normal butane is introduced to the sorption zone which is maintained at conditions within ranges of temperature and pressure mentioned for the sorption cycle so that the normal butane is maintained in the liquid phase. In another mode of operation, which may readily be adapted to a continuous type of process, the solid sorbent material may be removed from the sorption zone and the treatment with the normal butane may take place in a separate zone. The normal butane displaces the heavier sorbed normal parafiins and the desorbed C plus sorbed paraffins are displaced from the solid sorbent and finally recovered.

After there is a substantial removal of. the sorbed higher boiling normal parafiins (that is higher boiling than normal butane) by means of the liquid normal butane containing stream, the pressure onthe sorption tower is lowered to permit the vaporization of the normal butane from the system. Since the vaporization is conducted at nearly the critical temperature and pressure for the normal butane stream; there is essentially no heat of vaporization, and, therefore, the unit remains at essentially the same operating temperature. Following this vaporization of the normal butane, the charge may again be introduced to the sorption zone and more heavier than butane, that is more C plus normal parafiins may be sorbed on the solid sorbent material.

In the operation wherein normal butane is displacing the C plus normal parafiins from the solid sorbent material the efliuent from the zone, which is predominantly normal paraflins, is passed to a fractionator.- In the fractionator the normal butane is fractionated from the heavier hydrocarbons and from lighter hydrocarbons when they are present. The normal butane recovered from the fractionator may be passed to a sorption zone. to displace more C plus normal paraflins and this recycling of the normal butane in the process is an advantage. As hereinbefore mentioned, normal butane may;

be present in the charge to the sorption zone and this normal butane is recovered in the fractionation step following the sorption zoneand is subsequently used in the desorption cycle.

Using the process of my invention, therefore, the

normalparafiins may be substantially removed from hydrocarbon mixtures containing the same. The novel features of the present invention are described further in the'accom'panying diagrammatic flow drawing which illustratesl'one specific embodiment in which the invention may be practiced. The drawing is described in conjunction with a specific example of the production of a high octane number motor fuel. For the purpose of simplicity, many valves, pumps, heat exchangers, etc. have been omitted from the drawing since their illustration is not necessary for a complete understanding of the invention. I Referring now to the drawing, a Mid-Continent straight-run gasoline fraction having an initial boiling point of 197 F. andv an end boiling point of 398 F. and containing 8% normal parafiins is passed through line 1 into fractionator 2. Fractionator 2 is used since even though the charge stream has a high initial boiling point there may be some isobutane and lighter hydrocarbons dissolved in the gasoline fraction and it is desirable to remove these by fractionation prior to contact with the solid sorbent. In fractionator 2 the normally gaseous material, which includes hydracarbons containing from 1 to 4 carbon atoms per molecule, is separated from the hydrocarbon liquid comprising aromatic hydrocarb ons, cycloparafiins, isoparaffins and normal paraffins. The temperature, pressure, and reflux ratio on the fractionator 2 are regulated so as to remove isobutane and lighter components from the charge in line 1 while re taining normal butane-in the liquid bottoms.

' The gaseous material passes overhead through line 3 into cooler 4 wherein a portion of the material is condensed and the entire stream passes through line 5 into receiver 6. In receiver 6 the gas phase and the liquid phase of the overhead material separate. The gases pass through line 7 from which they may be vented to the atmosphere or otherwise used; The fractionator 2 has heat provided thereto by reboiler 10 and connecting lines 9 and 11. Fractionator 2 and receiver 6 are operated at a sufiicient pressure to liquefy at least a portion of the overhead material so that a liquid reflux stream is available to improve'the operationin fractionator 2. The'liquid reflux passes from'receiver 6 through line 8 into. upper. portion of fractionator 2. i

The bottoms which are withdrawn from fractionator 2 through line 12 contain hydrocarbons boiling above isobutane and the hydrocarbons comprise paraflinic, isoparaffinic, cycloparaflinic and aromatic hydrocarbons. The hydrocarbon mixture in line 12 may be passed through either sorption zone 19 or sorption zone 20. In this illustration it will be considered that the charge in line 12 was previously passed through sorption zone 20 and now the charge is being passed into sorption zone 19. Valve 16 in line 14 is, therefore, closed and valve 15 in line 13 is maintained open. The hydrocarbon mixture in line 12 continues through line 13, valve 15 and line 17 into sorption zone'19. In sorption zone 19 the hydrocarbon mixture is contacted with a crystalline calcium alumino-silicate which had previously been heated to remove the water of hydration. This sorption material sorbs normal parafiins from the hydrocarbon mixture and allows the isoparafiins, cycloparaffins and aromatics to pass from the sorption zone through line 21. The sorption zone is maintained at 295 F. and 550 pounds per square inch gauge. The liquid volume space velocity is 1.0.

The efiluent from the sorption zone 19 when withdrawn through line 21 has a decreased normal paraffin content when compared with the charge in line 17. The material in line 21 continues through line 23 containing open valve 25 and then through line 31. The material 6 in line 31 consists predominantly of aromaticspcycloparaffins and isoparafiins and contains less than 1% normal paraffins and when tested as a motor fuel it is found to be of higher octane number and has better road performance characteristics than the charge in line 12.

After a period of operation on this sorption cycle, the sorption material in sorption zone 19 picks up substantial amounts of normal parafins. For purposes of this illustration it will 'be considered that the charge stream in line 12 was passed through sorption zone 20 previously and that, therefore, the solid sorption material in zone 20 has substantial amounts of normal paraffins sorbed thereon. 1

Valve 35 in line 33 and valve 16 in line 14 are maintained closed and, therefore, a normal butane stream in line 50 continues through line 34, open valve 36 and line 18 into the lower portion of sorption zone 20 and the liquid normal butane displaces the C plus sorbed normal paraffius on the crystalline calcium aluminosilicate. During this desorbing operation, chamber 20 is maintained at a temperature of 295 F. and a pressure of 550 pounds per square inch gauge. The efliuent from chamber 20 which is withdrawn through line 22 during this desorbing operation, contains predominantly normal parafiinic hydrocarbons. Liquid normal butane is continued into chamber 20 through line 18 until substantially all of the C plus sorbed normal parafiins are displaced from the solid sorbent. The C plus normal paraffins continue through line 28 containing open .valve 30 and then through line 32 into fractionator 40. I

The pressure on sorption zone 20 is then reduced to 300 pounds per square inch gauge, thereby vaporizing the liquid normal butane in chamber 201' After this desorbing operation, the charge in line 12 may be introduced into chamber 20 and a desorbing operation started on chamber 19. This may be accomplished by closing valve 36 in line 34 and closing

valves

15 and 30 and opening valves 16 and 26. In this operation the charge passes through line 14, open valve 16 and line 18 into sorption zone 20. The effluent from sorption zone 20 continues through line 22, line 24: containing open valve 26 and then through line 31 from which the material has recovered as product.

Sorption zone 19 is now ready for the desorption cycle. When chamber 19 is on the desorption cycle valves 15 and 25 are closed and valves 35 and 29 are maintained in an open position. In this desorption cycle, theliquid normal butane in line 50 continues through line 33, open valve 35, line 17 and into zone 19. The eflluent, which comprises chiefly normal paraflinic hydrocarbons during the desorption cycle, is withdrawn through line 21, con tinues'throu'gh line 27 containing open valve 29 and then through line 32 into fractionator 40. After the pressure is reduced on zone 19 so as to vaporize the liquid normal butane, zone 19 is again ready for a sorption cycle.

The normal paraffins in line 32 are introduced into fractionator 40. Fractionator 40 is operated as a debutanizer. Since fractionator 2 was operated so as to remove isobutane and lighter materials, normal butane is the lightest hydrocarbon material present in the feed in line 32. Fractionator 40 has heat provided thereto by reboiler 52 and connecting

lines

51 and 53. The overhead material is withdrawn from fractionator 40 through line 41 and continues through cooler 42 wherein the entire normal butane fraction is condensed and the liquid fraction in line 43 is passed into overhead receiver 44. The liquid normal butane is withdrawn from receiver 44 through line 45. A portion of this material may be used as reflux on column 40 and passes to an upper portion of fractionator 40 through line 46. A portion of the normal butane in line 47 may be withdrawn through line 48 containing valve 49. The remainder of the liquid normal butane stream continues through line 50 and is used as the desorbing liquid. In

the first embodiment herein described wherein zone 20 was on a desorption cycle while zone 19 was on a sorption' cycle, valve 35 in line 33 was maintained closed and valve 36 was open. The liquid normal butane material, therefore, continued through line 34, open valve 36 and line 18 into zone 20, wherein the liquid normal butane is used to displace C and heavier paraffins.

A C plus normal paraflin stream is withdrawn from fractionator 40 through line 54. This normal paraffin stream may be used directly as a product or may be subjected to further chemical or catalytic treatment.

The foregoing is an illustration of a specific method of operating the process of my invention and this illustration was described in conjunction with a specific example of the process.

I claim as my invention:

1. A process for separating a normal paraffin from a hydrocarbon mixture boiling in the gasoline range containing said normal paraifin and a hydrocarbon selected from the group consisting of branched chain and cyclic hydrocarbons which comprises contacting said mixture at a pressure sufficient to maintain the same in a substantially liquid phase with a dehydrated metal aluminosilicate sorbent having pores of about 5 Angstrom units in cross-sectional diameter, capable of selectively sorbing normal paraflins and of rejecting branched chain and cyclic hydrocarbons, withdrawing a non-sorbed liquid hydrocarbon stream of decreased normal paraflin content from a resulting sorbent containing sorbed normal parafiin, thereafter contacting said sorbent containing sorbed normal paraflin with a desorbent normal paramn of at least 4 carbon atoms per molecule and of lower molecular weight than said first-mentioned normal paraflin at a pressure at which said desorbent normal paraflin is maintained in substantially liquid phase to thereby. displace the first-mentioned normal parafiin in the sorbent with said desorbent normal paraffin and withdrawing from the sorbent containing desorbent normal paraffin a liquid mixture of said first-mentioned normal paraffin and said desorbent normal parafiin.

' 2. The process of claim 1 further characterized in that both said sorption and desorption contacting steps are effected at substantially the same temperature, within the range of from about 175 to about 305 F. and at a pressure sufiicient to maintain said mixture and said desorbent hydrocarbon in substantially liquid phase.

3. The process of claim 1 further characterized in that said metal aluminosilicate is calcium aluminosilicate.

4. A process for separating normal pentane from a hydrocarbon mixture containing the same and isopentane which comprises contacting said mixture with a dehydrated crystalline calcium aluminosilicate containing pores having a cross-sectional diameter of about 5 angstrorn units, capable of selectively sorbing said normal pentane while rejecting said isopentane at a pressure at which said mixture is maintained in substantially liquid phase, withdrawing a hydrocarbon product of decreased normal pentane content from the resulting calcium aluminosilicate containing sorbed normal pentane, thereafter contacting the silicate containing sorbed normal pentane with normal butane at substantially the temperature maintained in the foregoing separating step and at a pressure at which said normal butane is maintained in subtantially liquid phase, and withdrawing from the resulting calcium aluminosilicate a stream comprising normal pentane displaced from said silicate by normal butane in admixture with normal butane.

5. A process for separating normal hexane from a hydrocarbon mixture containing the same and at least one other hydrocarbon selected from the group consisting of branched chain hexanes and cyclic hydrocarbons which comprises contacting said mixture with a dehydrated crystalline calcium alurninosilicate containing pores having a cross-sectional diameter of about 5 augstrom units, capable of selectively sorbing said normal hexane while rejecting said other hydrocarbon, at a pressure at which said mixture is maintained in substantially liquid phase, withdrawing a hydrocarbon stream of decreased normal hexane content from the resulting calcium aluminosilicate containing sorbed normal hexane, thereafter contacting the silicate containing sorbed normal hexane with normal butane at substantially the tempera-,

References Cited in the file of this patent UNITED STATES PATENTS 2,306,610 Barret Dec. 29, 1942 2,376,425 Frey May 22, 1945 2,425,535 Hibishman Aug. 12, 1947 2,574,434 Greentree et al. Nov. 6, 1951 2,586,889 Vesterdal et al Feb. 26, 1952 2,818,137 Richmond et al. Dec. 31, 1957 2,818,455 Ballard et al. Dec. 31, 1957 2,859,256

Hess et al. Nov. 4,1958

Claims

1. A PROCESS FOR SEPARATING A NORMAL PARAFFIN FROM A HYDROCARBON MIXTURE BOILING IN THE GASOLINE RANGE CONTAINING SAID NORMAL PARAFFIN AND A HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF BRANCHED CHAIN AND CYCLIC HYDROCARBONS WHICH COMPRISES CONTACTING SAID MIXTURE AT A PRESSURE SUFFICIENT TO MAINTAIN THE SAME IN A SUBSTANTIALLY LIQUID PHASE WITH A DEHYDRATED METAL ALUMINOSILICATE SORBENT HAVING PORES OF ABOUT 5 ANGSTROM UNITS IN CROSS-SECTIONAL DIAMETER, CAPABLE OF SELECTIVELY SORBING NORMAL PARAFFINS AND OF REJECTING BRANCHED CHAIN AND CYCLIC HYDROCARBONS, WITHDRAWING A NON-SORBED LIQUID HYDROCARBON STREAM OF DECREASED NORMAL PARAFFIN CONTENT FROM A RESULTING SORBENT CONTAINING SORBED NORMAL PARAFFIN, THEREAFTER CONTACTING SAID SORBENT CONTAINING SORBED NORMAL PARAFIN WITH A DESORBENT NORMAL PARAFFIN OF AT LEAST 4 CARBON ATOMS PER MOLECULE AND OF LOWER MOLECULAR WEIGHT THAN SAID FIRST-MENTIONED NORMAL PARAFFIN AT A PRESSURE AT WHICH SAID DESORBENT NORMAL PARAFFIN IS MAINTAINED IN SUBSTANTIALLY LIQUID PHASE TO THEREBY DISPLACE THE FIRST-MENTIONED NORMAL PARAFFIN IN THE SORBENT WITH SAID DESORBENT NORMAL PARAFFIN AND WITHDRAWING FROM THE SORBENT CONTAINING DESORBENT NORMAL PARAFFIN A LIQUID MIXTURE OF SAID FIRST-MENTIONED NORMAL PARAFFIN AND SAID DESORBENT NORMAL PARAFFIN.