US2125714A - Naphtha reforming - Google Patents

Description

Aug 2, 1938. s. c. FLJLToN 2,125,714

NAPHTHA REFORMING Filed oct. 26. 1955 l cA TAL Y: r /NLET .zj/c55 rfa 25 l, Patented Aug. l 2, 1938 PATENT OFFICE 2,125,714 NAPHTHA aEFoaMlNG Stewart C. Fulton, Elizabeth, N. J., assigner to Standard Oil Development Company, a corporation of Delaware applicativa october 26, 193s, serial No. 46,847

4 Claims.

The present invention relates to a process for the improvement of the octane number of straight run naphthas and those obtained by the cracking of heavier stocks. It has for its particular object 5 the provision of a process by which straight run naphthas can be reformed so as to have the proper volatility and a satisfactory octane number without an accompanying prohibitive gas loss.

As is known, straight run naphthas are ordinarily possessed of an unusually large percentage of constituents boiling within the range of heavy naphtha and are poor in those low boiling constituents which are so essential to the proper volatility of motor fuels. In addition, these straight run naphthas, probably by reason of their poor volatility as well as by reason of their saturated nature, have anoctane number much below the standard set for commercial fuels. It has commonly been the practice to subject such straight run naphtha to a treatment, referred to as reforming, for the purpose of reducing its initial boilingI point and increasing its content of unsaturates and aromatics; thereby improving.

its octane number.

Hitherto, the reforming" of straight run naphthas has been accomplished by one of three general methods, namely, vapor-phase cracking conducted under atmospheric pressure and at a temperature above 1000* F., pressure cracking or, as it is called, pressure reforming conducted at a temperature between 800 F. and 1000 F. and

. under a pressure ranging from 250 to 1000#, and catalytic reforming conducted at a temperature between 850 F. and 1100 F. in the presence of a dehydrogenating catalyst. In` the order listed these methods will give a larger increase in octane number for a given gas loss up to a certain point after which they converge to a point where, for a maximum increase in octane number, the gas loss in each instance is about the same and is prohibitively large. In the case of vaporphase cracking the gasv loss becomes excessive for an octane number increase which is smaller than that atA which gas loss becomes excessive in pressure I reforming. In like manner catalytic reforming is superior to pressure reforming.

In the reformation of straight run naphthas, vapor phase cracking has been largely superseded by pressure reforming and catalytic reforming. Pressure reforming offers the advantage over catalytic reforming that it sufficiently increases the lightends of the naphtha. It is attended by the disadvantage, however, that in addition tothe gas loss involved it is accompanied by the formation of polymers which represent a loss of initiall material.- Thus, as between pressureA reforming `and catalytic reforming the advantages of either could not be derived without incurring the disadvantages attending each.

By any one of the methods above referred to, octane number can be increased rapidlyatV its lower levels. Thus, an increase of octane number from 40 to 65 can be readily accomplished by any one of the methods. When the octane number reaches 70, any further increase becomes more and more difiicult of attainment. It may be said without exaggeration that to increase an octane number from 75 to 76 presents a greater problem than an increase in octane number from 40 to 60. Increases in octane number in the upper range indicated above can be achieved with any one of the methods referred to, only with gas'losses which are for practical purposes prohibitive.

It has now been ascertained that increases in octane number in the upper range can be achieved by catalytic reforming with a smaller gas loss than with either ofthe other types of reforming. 'Io accomplish the full increase in octane number by catalyticreforming, however, would mean that the resulting naphtha would be deficient in light ends. According to the present invention, therefore, the desired increase in octane number is obtained with a minimum gas loss. and with a satisfactory adjustment of the distillation curve of the resulting naphtha by effecting a partial increase in the octane number by pressure reforming, conducted to a point where the content of the naphtha in light endsis nearly sufficient to satisfy'market specifications, and completing the increase by catalytic reforming. By .this combination of steps the excessive gas loss and. polymer loss incurred in effecting the total improvement in octane number by pressure reforming are avoided, and the deficiency in light ends incurred in effecting the total improvement in octane number by catalytic reforming is f avoided. This combination is based on the reali- Zationthat the greatest benefit derivable from pressure reforming is obtained when a substantial portion of the heavier constituents are converted into light constituents and before these lightconstitunts are cracked to a considerable extent to gases or to substances of a more unsaturated nature which readily polymerize to gums.' Up to the point where these undesirable byreactions occur, pressure reforming offers a distinct advantage over catalytic reforming.

Conditions best suited for pressure reforming are commonly known. In general, naphtha to preferably between 950 F. and 1050 F. In pracl tice the process is conducted under atmospheric pressure, although, if desired, elevated pressures can be employed. 'I'he catalyst employed is usually one of the known dehydrogenation catalysts, Ing( neral, refractory metal oxides, such as alumina, thoria, oxides of metals of groups and 6,

`and mixtures of such refractory oxides are suitable. Phosphates and meta-phosphates exercise particular utility in this process. vaporous catalysts, such as readily vaporizable metal halides, particularly the halides of boron, such as boron fluoride, may also be employed. A particularly eectivecatalyst is one mainly composed of a reduced mixture 'of zinc oxide and chromium oxide, preferably on a support such as pumice, refractory oxides, etc. Other catalysts of a specific nature which are suitable for this p are disclosed .in Patent Nos. 1,844,998, 1,851,726, 1,881,692, 1,900,739, 1,910,910, 1,913,940, 1,913,941, 1,937,619, 1,938,086, 1,955,829, 1,975,476.

According to the present invention the initial straight run naphtha is subjected to pressure reforming until a substantial-part, at least about one-third, of the desired octane number increase is effected, and the remainder of the increase in octane number is attained by catalytic reforming. For example, a stock having an initial octane number of about 47 may be pressure reformed to an octane number between 60 and 75 and then subjected to catalytic reforming to bring the octane number up to a value btween 75 and 80. While pressure Areforming may be employed to effect from '/3 to V. of the total desired increase in octane number, it is preferred to effect only such an increase in octane number by pressure reforming as can be obtained without any appreciable loss due to polymerization.

In the event that pressure reforming is employed to attain the maar portion of the desired increase in octane num r whereby loss through polymerization is incurred, it is advantageous to subject the vapors leaving the pressure reforming unit to a treatment suitable for removing polymerizates and highly unsaturated components which would polymerize under the conditions in the catalytic reforming unit prior to the introduction oi the vapors into the` catalytic reforming unit. The purpose of this step is to prevent deposition of the polymers on the catalyst and the consequent reduction in activity of the catalyst. Among the treatments suitable for removing polymers and readily polymerized unsaturates are scrubbing with sulfuric acid and a contact treatment of the vapors with absorbent substances, such as claysjactive carbon, etc. l

Where heat loss is not of practical signiilcance, such as where heating gases which are normally wasted are available, the process can be improved by interposing between the two reforming steps a lsolvent extraction step. 'Ihis can be performed by reducing the temperature of the vapors to a point where a solvent having selectivity. for aromatics and unsaturates, such as tricresyl phosphate, phenol, anlline, nitrobenzene, chlorex, etc., can be employed as a liquid medium for scrubbing the vapors, Jr by condensing the vapors and subjecting them to liquid phaseextraction with any of the above enumerated solvents or with liquid sulfur dioxide. Such an extraction would remove those constituents which are not substantially affected by catalytic reforming, leaving the constituents, such as naphthenes, which are extremely sensitive to catalytic reforming, in a concentrated form. By this expedient the gas loss in the catalytic reforming step can be reduced since it is undoubtedly true that this gas loss is en'- hanced by the extent of exposure of the unsaturates to the high temperatures employed. In addition, the octane` number of the naphtha resulting from the catalytic reforming step will be increased because the eiIect of the step on the substances which are sensitive to it will be greater due to the avoidance of the diluent effect of the aromatics and unsaturates.

Where such an extraction step is included in the process the vaporous mixture not absorbed by the solvent, in the case of vapor phase extraction, or the raffinate, in the 'case of liquid phase extraction, is subjected to the catalytic reforming step. The product of vthe catalytic reforming step is then ,combined with the extract of the extraction step.

A front elevation of one form of apparatus for carrying out the process according to the present invention is illustrated diagrammatically in the accompanying drawing in which I represents a heating coil in which ythe naphtha is vaporized and the vapors are brought toa temperature between 800 and 1000 F. and from which they are passed to a digester 2, which may be termed a soaker and which is maintained at a temperature betwee'n 800 and 1000 F. and under a pressure between 250 and 1000 lbs.'/sq. in. The products leaving the bottom of the soaker are introduced into a separating chamber 3 in which such tar 'as may be formed falls out and the vapors leave through line l which is provided with a pressure release valve 5 so that the catalytic reformingl may be conducted under atmospheric pressure. The line I conducts the vapors to chambers 6 and 1 which are packed with a dehydrogenation catalyst, in case the latter is a solid, or which may be packed with a solid refractory material, such as clay sherds, porcelain balls, Raschig rings or other suitable material in the event that the catalyst employed is liquid or gaseous. In the latter event the catalyst is added to the vaporous material through line l. Line 4 is provided with valves 9 and I0 which may be manipulated in conjunction wth valves II and I2 respectively, to pemiit the vapors leaving separator 3 to be shunted througheither lines I3 or I4 respectively, or both, to other treating units. Line 'I3 is provided with a cooler I5 and leads to chamber I 6 which is packed with any suitable illling material or provided with discs and doughnuts, and which at its upper end is provided with an inlet tube I1 having at its inner end a nozzle I6 through which a selective solvent may be sprayed. Condenser II is operated so asto either reduce the temperature of'the vapors to such a level that the vaporsn can be extracted byl a liquid introduced through tube I1 or may be operated so as to condense the vapors, in which event the condensed.

vapors pass through chamber Il in countercurrent to the selective solvent. In either event, the solvent containing the extracted components is drawn 0E through outlet I9 and the vapors or the rainate, as -the case may be, is led' off through line 20 back to line l.

Line I4 is connected to a clay treating tower 2l which is ordinarily operated at a temperature of about 500 F. and which contains Attapulgus clay or a similar absorbent clay or other absorbent material.

Since either of the above mentioned intermediate treatments would require a reduction in temperature of the vapors, a heating coil 22 is provided in line 4 for bringing the vapors to the proper temperature for the catalytic reforming.

The catalytically reformed vapors leave tower 1 through line 23 and are condensed in condenser 2l.

In a practical embodiment of the'process according to the present invention a west Texas heavy naphtha wasA reformed in soaker 2 at a temperature of 950 F. and under a pressure of 800 lbs/sq, in., the feed rate being about 18 gallons per hour per cubic foot of soaker space. In this step there was incurred a 13.3% gas loss and a 5% polymer loss. The vapors leaving separator 3 were conducted to towers 6 and 1 which were packed with a catalyst composed of a reduced mixture of zinc oxide and chromium oxide supported on alumina. At this stage the naphtha was fed through the catalyst at a rate of .8 volume of liquid naphtha by volume of catalyst per hour. The towers were maintained under atmospheric pressure and at a temperature of 1000 F. .In this step a 4.6% gas loss was incurred. The inspections of the initial naphtha, the pressure reformed naphtha, and the catalytically reformed pressure reformed naphtha `are as follows:

Catalytic re- Orlginal West fopglslrgv't forming of pres- Texas heavy Texas heavy sure reformed naphtha naphtha West Texas heavy naphtha l Init. 248 99 186 90 04 0. 5 2. 5 it $2 11.0 158 11. 5 15. 0 176 15. 5 19. 5 194 20. 0 24. 5 212 25. 5 30. 0 221 29. 33. 5 230 32. 0 37. 0 245 39. 0 45. 0 257 43. 49. 0 266 3. 5 48. 0 53. 5 284 23. 0 57. 0 62. 0 302 4l. 5 86. 5 70. 0 320 57. 5 73. 0 77. 5 338 72. 5 79. 5 84. 0 356 84. 0 84. 5 88.0 374 91. 0 89. 0 9l. 0 392 95. 0 91. 5 92. 0 410 97. 0 94. 5 F. B. P 414 437 403 90% at 370 383 371 ec. 98 95 93 Loss 3. 7 6. 0 Res. 1. 0 1. 3 1./0 Grav. 48. 9 52. 3 52. 9 An. Pt. 127.0 79 70 Octane 47. 0 72. 5 77 (C. F. 11.-M. M.)

It may be noted from the above table that whereas the pressure reforming affected only that increase in octane number which is most easily obtained, it reduced the initial point of the naphtha from 248 to 99 and increased the amount going over at 266 F. from 3.5 to 48%. Catalytic reforming, on the other hand, while it raised the octane number through that range in which the' l attainment of an increase is most diiicult, de-

creased the initial point only to 90 and increased the amount going over at 266 only from 48% to 53.5%. The figures given under loss must not be confused with gas loss or polymerization loss` The loss listed in the table is the loss incurred in` distillation.

Where the vapors lresulting from the pressure reforming are subjected to extraction With'tricresyl phosphate an extract is obtained having an octane number of 76. The vapors not absorbed are subjected to the catalytic reforming step and yield a product having an octane number of 80. This product, upon being blended with the constituents extracted by the tricresyl phosphate, gives a naphtha having an octane number of 78.5.

From the above table it is to be noted that the octane number vof the initial naphtha was raised from 47 to 77 with a gas loss of 17.9 and a polymer loss of 5%. To eiect a similar improvement by pressure reforming alone would `entail a gas loss of 21% and a polymer loss of 8.5%. A similar improvement in octane number could lbe eiected by catalytic reforming alone with a gasloss of about 19%, but the product obtained would have a distillation curve such that light ends would have to be blended with it to meet market specilication.

The present invention is also applicable to the improvement of the octane number of a cracked naphtha from any source providing the naphtha has approximately the nal desired content of light ends, and particularly if it has a relatively 'high octane number'with respect to straight lrun distillation curve.` A naphtha obtained from a Quire-Quire crude by cracking was passed at a` temperature of 1000 F. over acatalystcomposed of magnesite combined with zinc sulphate and lead chromate. The inspections of the feed stock and the ilnal product are given in the following I table:

Reforming of Qure-Quire cracked distillate Reformed ggg product run RU74 Gas loss. 6. 2% Thru-put- 0. 82 Block temp. 1000 F.

Percent oif at F.:

l04 1. 0 2. 0 4. 5 6. 0 9. 0 10. 0 14. 0 14. 0 19. 0 1B. 0 24. 0 22. 5 28. 5 27. 0 3l. 0 29. 5` 34. 0 32. 5 40. 0 38. 5 43. 5 4l. 5 46. 5 45. 0 54. 0 52. 5 62. 0 01. 5 70. 5 67. 5 78. 0 75. 0 86. 0 82. 0 92. 0 87. 5 95. 0 91. 0 96. 5 93. 0

99 93 412 455 369 388 97 97 77 53 52. 4 48 .M. M. octane No 77.0 79

Kauri butanol No 47. 7 55. 8

While the improvement in octane number o1' a naphtha from any source is contemplated by the present invention, it is to be understood that in its preferred embodiment the present invention resides in the combination ofpressure reforming with catalytic reforming of straight run naphthas in such-a manner as to utilise the most advantageous features of both while minimizingthe objectionable features of both. the pressure reforming being used only to the extent that gas loss and polymer loss do not become objectionable and that the content of light ends in the naphtha approaches that desired in the nnal product. Various types of apparatus, other than that illustrated, can be employed for carrying out the process. No novelty is alleged in the specific conditions employed in `each step of the process or in the specinc catalyst employed in the catalytic reforming step, except insofar as these conditions and catalyst represent the preferred mode of operation. y

The term reforming" as employed in the specincation and claims is here defined to mean a treatment wherein the chemical composition of the naphtha is changed without being combined with any other reagents.

The nature and objects of the present invention having been thus described and a specinc embodiment of the same having been given without any intention, however, of limiting the invention to that specific embodiment. what is claimed as new and useful`and desired to be secured b! Letters Patent is: A

i. Aprocsssforimprovingtheoctanenumber and distiilationeurve of a heavy straight run naphtha which comprises subjecting said naphthatoanon-catalyticpressurereforming fora length of time sumcient to substantially increase octane number thereof and to increase ltr t in'light ends to a quantity approximattdesiredinthefinalproduct, and comtheincreaseinoctanenumberbysubjectthe pressure reformed naphtha to a dehydrogenating catalytic reforming and for a time limitedsothatnosubstantial increaseinlight ends is obtained.

2. A process according to claim 1 in which the pressure reformed naphtha is subjected to extraction with a solvent having a selective solvent action'for cyclic hydrocarbons and only the portion not dissolved in the selective solvent is subjected to the catalytic reforming.

. 3. A process for improving the octane number and distillation curve of a heavy straight run naphtha which comprises subjecting saidnaphtha. to non-catalytic pressure reforming for a length of time suiiicient to effect at least l.; of'the desired increase in octane number and to increase its content in light ends to a quantity of that approximating that desired in the i'inal product and completing the increase in octane number by subjecting naphtha so reformed to a dehydrogenating catalytic reforming maintained under conditions such that the ratio of the amount of octane improvement to the amountvof lower boiling hydrocarbons formed is substantially higher than in the pressure-reforming treatment and for a time limited so that no substantial increase in light e'nds is obtained.

4. A method of producing a motor fuel having improved volatility and octane number which comprises subjecting a low octane heavy naphtha fraction of low volatility to a non-catalytic pres; sure reforming to produce a relatively low ratio of octane improvement to lower boiling hydrocarbon formation to thereby materially improve the volatility of said fraction, thereafter subject-v ing naphtha so reformed to a dehydrogenating catalytic reforming treatment controlled rto produce a relatively higher ratio of octane number improvement to the amount of lower boiling hy drocarbons formed than in said first mentioned reforming treatment.

BTIWART C. FULTON.

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