US2921104A

US2921104A - Combination process of isomerization and selective fractionation followed by a sorption process

Info

Publication number: US2921104A
Application number: US695291A
Authority: US
Inventors: Haensel Vladimir
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1957-11-08
Filing date: 1957-11-08
Publication date: 1960-01-12
Anticipated expiration: 1977-01-12

Description

Jan. 12, 1960 V HAENSEL COMBINATION PROCESS OF ISOMERIZATION AND SELECTIVE FOLLOWED BY A SORPTION PROCESS Filed NOV. 8, 1957 FRACTIONATION Fresh Feed a 4 4 a w m \i Q m Q 58 2?, R a 2 ow v V? 5+ A a 4 S l JOJOUO/IQDJ 1 D= 1 JOJDUQIJODJJ' wv 4 M JQZ/UD/HQEU Q m 4 x Q m Q 7A" IN *u- E u g S I N h v a Q g N W I y M f INVENTOR:

V/adimir Haense/ A TTOR/VEYS:

derived from the combination process.

COMBINATION PROCESS OF ISOMERIZATION AND SELECTIVE FRACTIONATION FOLLOWED I BY A SORPTION PROCESS Vladimir Haensel, Hinsdale, Ill., assign'or, by mesne assignments, to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware Application November 8, 1957, Serial No. 695,291 3 Claims. (Cl. 260-68365) This invention relates to a process for producing a hexane having a high octane number from amixture of C paraffins and naphthenes feed stock. More particularly, this invention is concerned with a combination process whereby an isomerization reaction zone effluent is selectively fractionated followed with a sorption process so that low octane normal hexane is separated from the desired high octane number hexanes.

Normal parafiins find use as intermediates or raw materials in the production of many. petrochemical compounds and these same normal paraffins also find wide use as solvents. While normal paraflins are not particularly desirable as a motor fuel, because of their relatively low octane numbers, they may be isomerized readily to isoparaffins which have substantially higher octane numbers. Since isomerization is an equilibrium reaction, it is preferred that isoparaffins be separated from normal paraffins before subjecting the normal paraffins to isomerization. In this manner, more of the normal hexane can be isomerized than would take place in the presence of isoparaflins. In the present process the normal hexane is'removed from the fractionated reaction product there by increasing the octane number of the hexane product The normal hexane separated from the fractionation residue may be subjected to further treatment to convert it to isoparafiins of a higher octane number.

It is an object of the present invention to subject a C paraffin hydrocarbon feed stock to isomerization, selectively fractionate the isomerization reaction zone effluent, and follow this fractionation with a sorption process whereby normal hexane may be separated from the branched chain hexanes and cycloparaflins high octane number product. It is also an object of the present invention to provide a sorption zone with a means whereby the sorbed normal paraflin may be recycled to the isomerization reaction zone for the conversion of normal hexanes to isohexanes.

In one embodiment this invention relates to a process for producing a hexane having a high octane number from a C paraffin hydrocarbon feed stock which comprises subjecting said feed stock to isomerization in the presence of an isomerization catalyst at isomerization conditions within a reaction zone, passing the resulting isomerization reaction zone product to a first fractional distillation zone wherein a first overhead comprising primarily dimethyl-substituted butane is passed overhead, passing the residue from said first fractional distillation to a second fractional distillation zone and thereby separating an overhead comprising branched chain monomethylpentanes, recycling said second overhead to said isomerization reaction zone, passing the residue comprising normal hexane, branched chain and cycloparaffins from said second fractional distillation zone to a sorption zone wherein said second fractional distillation residue contacts a solid sorbent to effect the selective rejection of the branched chain hexanes and cycloparaffins, separately withdrawing from the sorption zone a product having United States Patent "ice an octane number greater than said feed stock, separately contacting spent sorbent with a desorbent stream comprising a normal paraffin of at least 4 but less than 6 carbon atoms per molecule, recovering a desorbent effluent comprising normal hexane, and passing said desorbed normal hexane to said isomerization reaction zone.

In another embodiment the present invention relates to a process for producing a hexane having a high octane number from a C paraffin hydrocarbon feed stock which comprises subjecting said feed stock to isomerization in the presence of an isomerization catalyst at isomerizing conditions within a reaction zone, passing the resulting isomerization reaction zone product to a debutanizer zone wherein low boiling hydrocarbon gases are passed overhead from said zone, passing the debutanized product from said debutanizing zone to a first fractional distillation zone wherein a first overhead comprising primarily a dimethyl-substituted butane is passed overhead, passing the residue from said first fractional distillation to a second fractional distillation zone and thereby separating an overhead comprising branched chain monomethylpentanes, recycling said second overhead to said isomerization reaction zone, passing the residue comprising normal hexane, branched chain hexanes and cycloparafiins from said second fractional distillation zone to a sorption zone wherein said second fractional distillation residue contacts a solid sorbent to effect the selective rejection of the branched chain hexanes and cycloparaffins, separately withdrawing from the sorption zone a product having an octane number greater than said feed stock, separately contacting spent sorbent with a desorbent stream comprising a normal parafiin of at least 4 but less than 6 carbon atoms per molecule, recovering a desorbent efliuent comprising normal hexane, and passing said desorbed normal hexane to said isomerization reaction zone.

In the operation of catalytic reforming processes, it has been observed that the product, usually called reformate, contains a small amount of normal parafiin having a relatively low octane number. The presence of these par'aflins is due to the fact that under operating conditions of reforming, the equilibrium concentration represents a fair concentration of normal paraffins. The presence of these normal paraflins in the reformate causes a substantial depreciation of the octane number of the reformate.

As reforming processes are operated to obtain a conversion of these normal parafiins into aromatics, or into higher octane number branched chain and lower boiling parafiins during the reforming reaction, 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 gained in the range of octane numbers in the order of -95 F-l clear. This is due to the conversion of normal liquid components into normally gaseous components. However, if the normal par aifins were removed from the reformate the octane number would improve more favorably, for example, a reformate having an octane number of 85 F-l clear and containing 10% normal paraffin, having an average octane number of 0, would have an octane number improved of 85 to 94.5, on the strictly arithmetical blending basis. In the present process, the octane number of the isomerization reaction zone eflluent is increased through selective fractionation followed by a sorption process whereby normal paraflins are sorbed and the high octane number branched chain hexanes and cycloparafiins are rejected. These normal hexanes are subjected to a desorbent stream comprising a normal paraffin of at least 4 but less than 6 gen, and alumina.

returned to the isomerization reaction zone as recycle to be isomerized to isohexanes.

The contact of the normal hexane, cycloparaflins and branched chain hexanes in the sorption zone is with a 'solid sorbent which has a selective sorbing power for normal hexane. The contact is for a time sufficient to sorb a substantial amount of the normal hexane present in the charge to the sorption zone. The sorption tower is maintained at a temperature and pressure so that the charge is maintained in the liquid phase. It is preferred to maintain the temperature in the sorption zone substantially within the range of from about 80 C. to about 152 C. The pressure in the sorption zone is within the range of from about 13.5 to about 68 atmospheres and such that the charge is kept'in the liquid phase.

Any solid sorbent material which has a high power of selectively sorbing normal paraflins from their mixtures with other hydrocarbons may be used in the present process. Crystalline metal alumino-silicates, such as calcium alumino-silicate, strontium alumino-silicate, sodium alumino-silicate, barium alumino-silicate, and potassium alumino-silicate are suitable solid sorbents to be used although they do not necessarily provide quantitatively the same results. Crystalline calcium alumino-silicate, which has been heated to remove the water of hydration is preferred. These crystalline calcium alumino-silicates which have been heated to remove the water of hydration have pore diameters of about 5.1 A. units; this diameter 'is slightly larger than the calculated critical diameter of normal parafiin molecules, but somewhat smaller than the critical diameter of isoparafiins, cycloparaffins and aromatics. Thus, it is possible to sorb normal paraffins from the mixture of branched chain hexanes and cycloparaflins.

The contact of the charge with the solid sorbent is for a time sufficient to sorb substantial quantities of the normal paraflin from the charge. After a substantial quantity of the normal parafiin is sorbed, the sorbed normal .parafiins are removed and recovered from the solid sorbent and subsequently returned as recycle to the isomerization reaction zone for further conversion to high octane number isoparafiins.

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

The accompanying drawing illustrates diagrammatically the process flow embodying the present combined process for producing high octane hexane fractions. Also in referring to and describing the drawing, a Skellysolve B was utilized as the charging stock, said charge having an initial boiling point of 150 F. and an end boiling point of 175 F. and containing 48% by weight normal hexane. The charge stock was passed through line 1 and commingled with a monomethylpentane recycle stream 3 and -a normal hexane recyclestream 4, the source of these latter two streams will be subsequently described. The charge stock, a monomethylpentane stream,'and a normal hexane stream are combined with a hydrogen recycle gas stream 2 and then passed'to an isomerization zone Scontaining an isomerization catalyst. The conditions utilized in reaction zone 5 willndepend upon the particular isomerization catalyst utilized therein. A preferred catalyst in the process of this invention is one comprising a platinum group metal, particularly platinum, combined halo- With such a catalyst, the pressure utilized in the reaction Zone will range from about 100 to about 1000 pounds per square inch, the temperature will range from about 100 C. to about 450 C., and the liquid hourly space velocity will range from about 0.1 to

remove. the water of hydration.

about 10. The hydrogen to hydrocarbon ratio in the reaction zonewill range from about 0.25 to about 5 mols of hydrogen per mol of hydrocarbon. When the catalyst utilized comprises platinum, alumina, and combined chlorine in an amount of from about 2.5 to about 8.0 weight percent of the latter, the reaction zone temperature will be lower than the higher part of the above set forth range, for example, from about 150 C. to about 250 C. In some instances it is desirable and/or advisable to utilize hydrogen halide along with these catalysts and thus the use of hydrogen chloride, for example, is within the generally broad scope of the present invention.

The isomerization reaction zone 5, when being charged with the above mentioned Skellysolve B charge stock, was operated at a pressure of the order of 900 p.s.i.g. and a temperature of about C. with a liquid hourly space velocity of 0.5 and a hydrogen to hydrocarbon ratio in the reaction zone of the order of 6.0. The isomerization catalyst contained in said isomerization reaction zone 5 comprises platinum, alumina, and combined chlorine, in an amount of the order of 5.5 weight percent of the latter, along with a continuous addition of hydrogen chloride to said isomerization reaction zone 5.

An isomerization reaction zone eflluent is withdrawn from said isomerization reaction zone 5 by means of line 6 and passed to a separation zone 7 wherein a separation of hydrogen from hydrocarbons is effected. A relatively high purity hydrogen recycle gas stream is withdrawn from the top of separation zone 7 by means of line 2 and is joined with a hydrogen gas makeup stream 8 and said total recycle hydrogen is passed to isomerization reaction zone 5 as hereinbefore described. A hydrocarbon efiluent stream containing of the order of 12% by weight normal hexane is withdrawn from the bottom of separation Zone 7 by means of line 9 and passed to a conventional debutanizer column 10 wherein low boiling hydrocarbon gases, in particular isobutanenormal butane, are passed overhead by means of line 11 for subsequent use in a sorption zone hereinafter described. A residue product is withdrawn from the bottom of debutanizer column 10 by means of line 12 and passed to a first fractionation zone 13. A high octane number product containing dimethylbutanes is passed overhead from said first fractionation zone 13 by means of line 14, while a residue product is withdrawn from the bottom of said first fractionation zone 13 by means of line 15 and passed to a second fractionation zone 16. The low octane number monomethylpentanes are fractionated from the product in this second fractionation Zone 16 and passed overhead by means of line 3 for further isomerization in reaction zone 5 as hereinbefore described. Aresidue product containing normal hexane, methylcyclopentane, and cyclohexane is withdrawn from the bottom of said second fractionation zone 16 by means of line 17 and passed to a sorption zone.

The hydrocarbon mixture in line 17 may pass through either sorption zone 24 or sorption zone 25. By way of example, it will be considered that the charge from line 17 was previously directed to sorption zone 25 and that now the charge is being passed into sorption zone 24. Valve 21 in line 19 is closed and valve 20 in line 18.is opened. The hydrocarbon mixture from line 17 continues through line 18, valve 20 and line 22 into sorption zone 24. In sorption zone 24 the hydrocarbon mixture is contacted with a crystalline calcium alumino-silicate which had previously been heated to This sorption zone material sorbs normal hexane from the hydrocarbon mixture and allows the cyclohexane, methylcyclopentane, and aromatics to pass from the sorption zone through line 26. The sorption zone is maintained at 156 C. and

37.5 atmospheres. The liquid hourly space velocity is 1.0, that is, the volume of liquid hydrocarbon charge per volume of sorption material per hour.

The efiluent from sorption zone 24 when withdrawn through line 26 has a decreased normal hexane content when compared with the charge in line 17. The material in line 26 continues through line 28 containing open valve 30 and then through line 36. The material in line 36 consists predominately of cyclohexane and methylclopentane and is combined with the dimethylbutanes contained in line 14 to form a high octane number hydrocarbon product.

After a period of operation on this sorption cycle, the sorption material in sorption zone 24 has picked up a substantial amount of normal hexane. For the purposes of this illustration it will be considered that the charge in line 17 was passed through sorption zone 25 previously and that, therefore, the solid sorption material in zone 25 has substantial amounts of normal hexane sorbed therein.

A normal butane stream from a source other than the process itself will be used in illustrating the desorbing operation of the process. Therefore, valve 45 in line 42 is maintained closed while valve 46 in line 11 is opened so that the overhead product from the conventional debutanizing zone is discharged from the process as a product stream of said process. The liquid normal butane stream is introduced into line 43 containing open valve 44 from where said liquid normal butane stream flows through line 42. Valve 40 in line 38 and valve 21 in line 19 are maintained closed and a normal butane stream flows from line 42 through valve 41 and line 39 and line 23 into sorption zone 25. This liquid normal butane displaces the normal hexane sorbed on the crystalline calcium alumino-silicate. During this desorbing operation, chamber 25 is maintained at a temperature of about 156 C. and a pressure of about 37.5 atmospheres. The effluent from chamber 25 which is withdrawn through line 27 during this desorbing operation contains predominately normal hexane hydrocarbons. The flow of liquid normal butane into chamber 25 through line 23 is continued until substantially all of the normal hexanes are displaced from the solid sorbent. The normal hexanes continue through line 33 conitaining open valve 35 and then through line 37 and into line 4 which returns the normal hexane as recycle to the isomerization reaction zone hereinabove described. The normal hexane is subsequently isomerized to the higher octane number isohexanes in the isomerization reaction zone 5. When the normal hexanes have been substantially displaced from the solid sorbent in chamber 25 by liquid normal butane, the pressure on chamber 25 is reduced to the order of 20.4 atmospheres, thereby vaporizing the liquid normal butane in this chamber.

A convenient source for the liquid normal butane used in the desorbing step of the sorption zone is overhead product 11 from the conventional debutanizer 10. When the overhead product 11 is to be used in the desorbing step, valve 46 in line 11 and valve 44 in line 43 are closed while valve 45 in line 42 is maintained open. The liquid butane stream from column 10 passes through line 11 and open valve 45 in line 42 and then into the sorption zone of the process. Any other source of the liquid normal butane which may be readily available can also be used in the desorption step.

After this desorbing operation the charge in line 17 may be introduced into chamber 25 and a desorbing operation started on chamber 24. This may be accomplished by closing valve 41 in line 39 and closing

valves

20 and 35 and opening

valves

21 and 3 1. In this operation the charge passes through line '19, open valve 21 and line 23 into sorption zone 25. The effluent from sorption zone 25 continues through line 27 containing open valve 31 and then into line 29 from which the hydrocarbon material of decreased normal hexane content is recovered as product. The product in line 29 is then passed into line 36 and combined with the dimethylbutane contained in line 14 and a resulting high octane number hydrocarbon product results thereform.

Sorption zone 24 is now ready for the desorption cycle. Chamber '24 is placed on the desorption cycle by closing

valves

20 and 30 and opening

valves

40 and 34. In this desorption cycle valve 45 in line 42 is closed while valve 46 in line 11 is open so that the overhead product from the conventional debutanizer 10 is discharged from the process as a product stream of said process. The liquid normal butane stream is introduced into line 43 containing open valve 44 from where said liquid normal butane stream flows through line 42. The liquid normal butane in line 42 continues through line 38, open valve 40, line 22 and into sorption zone 24. The eifiuent which comprises chiefly normal hexanes during the desorption cycle is withdrawn through line 26 containing open valve 34 and then into line 4. The normal hexane in line 4 is subsequently recycled to isomerization zone 5 for further isomerization to the higher octane number isohexanes. After the pressure is reduced on zone 24 so as to vaporize the liquid normal butane, zone 24 is again ready for a sorption cycle.

In the above illustration the combination process of this invention has been set forth. As stated hereinabove, the combination of isomerization, selective fractionation, and sorption are combined to produce a high octane number hydrocarbon product by the removal of the normal hexanes from the product stream. .It is also shown that the normal hexane, when withdrawn from the product stream, is returned for further isomerization along with the monomethylpentane in an isomerization reaction zone containing isomerization catalyst.

I claim as my invention:

1. A process for producing a high octane number product from a feed stock containing C parafiins and naphthenes, which comprises subjecting said feed stock to isomerization, separating from the resultant products a dimethyl'butane fraction, a monomethylpentane fraction and a heavier fraction containing n-hexane and branched chain and cyclic hydrocarbons, supplying the second-mentioned fraction to the isomerizing step, contacting said heavier fraction with a solid sorbent capable of selectively sorbing n-hexane while rejecting branched chain and cyclic hydrocarbons, commingling at least a portion of the thus rejected branched chain and cyclic hydrocarbon content of said heavier fraction with said dimethylbutane fraction and recovering the resultant mixture as said high octane number product, desorbing n-hexane from said solid sorbent and supplying the same to the isomerizing step.

2 The process of claim 1 further characterized in that the n-hexane is desorbed from the solid sorbent by being displaced with a liquid normal paraflin of from 4 to 5 carbon atoms per molecule.

3. The process of claim 1 further characterized in that the n-hexane is desorbed from the solid sorbent by being displaced with liquid n-butane.

References Cited in the file of this patent UNITED STATES PATENTS 2,394,797 McAilister et a1. Feb. 12, 1946 2,395,022 Sutton et a1. Feb. 19, 1946 2,425,535 Hibshman Aug. 12, 1947 2,766,302 Elkins Oct. 9, 1956 2,818,449 Christensen et a1. Dec. 31, 1957

Claims

1. A PROCESS FOR PRODUCING A HIGH OCTANE NUMBER PRODUCT FROM A FEED STOCK CONTAINING C6 PARAFFINS AND NAPHTHENES, WHICH COMPRISES SUBJECTING SAID FEED STOCK TO ISOMERIZATION, SEPARATING FROM THE RESULTANT PRODUCTS A DIMETHYLBUTANE FRACTION, A MONOMETHYLPENTANE FRACTION AND A HEAVIER FRACTION CONTAINING N-HEXANE AND BRANCHED CHAIN AND CYCLIC HYDROCARBONS, SUPPLYING THE SECOND-MENTIONED FRACTION TO THE ISOMERIZING STEP, CONTACTING SAID HEAVIER FRACTION WITH A SOLID SORBENT CAPABLE OF SELECTIVELY SORBING N-HEXANE WHILE REJECTING BRANCHED CHAIN AND CYCLIC HYDROCARBONS, COMMINGLING AT LEAST A PORTION OF THE THUS REJECTED BRANCHED CHAIN AND CYCLIC HYDROCARBON CONTENT OF SAID HEAVIER FRACTION WITH SAID DIMETHYLBUTANE FRACTION AND RECOVERING THE RESULTANT MIXTURE AS SAID HIGH OCTANE NUMBER PRODUCT, DESORBING N-HEXANE FROM SAID SOLID SORBENT AND SUPPLYING THE SAME TO THE ISOMERIZING STEP.