US3723292A

US3723292A - Removal of straight chain hydrocarbons from different hydrocarbon stocks

Info

Publication number: US3723292A
Application number: US00174322A
Authority: US
Inventors: A Glessner; W Wentzheimer
Original assignee: Sun Oil Co
Current assignee: Sunoco Inc
Priority date: 1971-08-24
Filing date: 1971-08-24
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27

Abstract

A cyclic process is disclosed for sequentially treating two different naphtha stocks in the same molecular sieve adsorption bed to produce nonstraight chain hydrocarbon fractions respectively from each stock and a third product composed of straight chain hydrocarbons from both stocks. Also disclosed is the use of this procedure in conjunction with a reforming process wherein a naphtha feed is first denormalized, the denormalized naphtha is reformed and the resulting reformate is denormalized to yield high octane gasoline blending stock.

Description

United States Patent [191 Glessner et al.

REMOVAL OF STRAIGHT CHAIN HYDROCARBONS FROM DIFFERENT HYDROCARBON STOCKS Inventors: Alfred J. Glessner, Glenolden, Pa.; William Wayne Wentzheimer, Edgewood, Md.

Sun Oil Company of Pennsylvania, Philadelphia, Pa.

Filed: Aug. 24, 1971 Appl. No.: 174,322

Assigneez U.S. Cl..... ..208/85, 208/310, 260/676 MS Int. Cl. ..C10g 25/04, C10g l/00, Cl0g 35/18 Field of Search ..208/310, 85; 260/676 MS References Cited UNITED STATES PATENTS Fleck et al ..208/310 Kimberlin et al. ..260/676 MS 1 Mar. 27, 1973 2,987,471 6/1961 Eggertsen ..208/310 3,007,863 11/1961 Hess et al. ..208/31O 3,268,440 8/1966 Griesmer et a1. ..208/310 3,520,801 7/1970 Lewis et al. .208/3 10 Primary Examiner-Herbert Levine Attorney-George L. Church et a1.

[57] ABSTRACT 8 Claims, 2 Drawing Figures l6 j PURGE GAS 8 n-PARAFFINS PURGE GAS7 18 G/5L "A" RAFFINATE Q/ "B" RAFFINATE PAIEI-IIEDIIARZYIQYB PURGE GAS SHEET 1 [IF 2 FIG. I

"A" RAFFINATE ;\D "B" RAFFINATE INVENTORS ALFRED J. GLESSNER WILLIAM WAYNE WENTZHEIMER BY 7 -MWM y ATTORNEY PATEr-fliinmzmrs 3,7 3,292

SHEET 2 BF 2 FIG. 2

- 44 I 3o NAPHTHA 5 E FEED 32 SEPARATOR ADSORBER f lz n-PARAFFINS 2 s GASOLINE s z BLENDING [H2 RECYCLE 55 34 M STOCK 1 56 0 REFORMER SEPARATOR INVENTORS W. 2 -MW, F.

ATTORNEY REMOVAL OF STRAIGHT CHAIN HYDROCARBONS FROM DIFFERENT HYDROCARBON STOCKS CROSS REFERENCE TO RELATED APPLICATION Copending application Ser. No. 112,140, filed Feb. 3, 1971, by Alfred J. Glessner, William Wayne Wentzheimer and Rene F. Kress, describes a process involving denormalizing naphtha by means of molecular sieves, hydroforming the denormalized naphtha and then denormalizing the reformate by means of molecular sieves. The present invention is applicable for carrying out the two denormalization steps of that process in an improved manner.

BACKGROUND OF THE INVENTION This invention relates to an adsorption process for separating each of two different naphtha feedstocks into straight chain and nonstraight chain hydrocarbon fractions by treatment with a molecular sieve adsorbent.

It is well known that hydrocarbon stocks such as gasoline and kerosene can be treated in either vapor or liquid phase with crystalline zeolite molecular sieves having uniform pore diameters of about 5 Angstrom units to selectively adsorb n-paraffins and unbranched olefins from the other hydrocarbon components. This type of treatment has been described in numerous United States Patents of which the following are examp les: Pat. No. 2,886,508, H. V. Hess et al., issued May 12, 1959; No. 2,917,449, E. R. Christensen et al., issued Dec. 15, 1959; No. 2,945,804, C. E. Hemminger, issued July 19, 1960; No. 2,952,614, K. E. Draeger et al., issued Sept. 13, 1960; Nos. 2,958,644 and 2,958,645, C. N. Kimberlin, Jr., et al., both issued Nov. 1, 1960; and No. 3,193,490, D. B. Boughton, issued July 6, 1965.

There are instances where in processing two different stocks in refinery operations it is desirable to separate each stock into straight chain and nonstraight chain hydrocarbon fractions. Several processes in which two different stocks are treated with zeolitic molecular sieves for this purpose have been described in the following United States Patents: No. 2,891,902, H. V. Hess et al., issued June 23, 1959; No. 2,935,467, R. N. Fleck et al., issued May 3, 1960; No. 2,944,001, C. N. Kimberlin, Jr., et al., issued July 5, 1960; No. 2,987,471, F. T. Eggertsen, issued June 6, 1961; No. 3,007,863, H. V. Hess et al., issued Nov. 7, 1961; No. 3,160,581, W. J. Mattox et al., issued Dec. 8, 1964; and No. 3,227,647, H. G. Krane, issued Jan. 4, 1966.

The present invention is applicable to such refinery operations wherein two different stocks boiling in the range of gasoline and kerosene are to be processed to selectively separate straight chain from nonstraight chain hydrocarbons. These stocks can have boiling ranges which are either substantially the same or different. The invention can be used as an improved way of practicing the adsorption operations in the several processes of the above-mentioned patents in which different stocks are treated with molecular sieve adsorbents.

SUMMARY OF THE INVENTION The invention involves a cyclic operation for the successive treatment of two naphtha stocks in an adsorption zone containing zeolitic molecular sieves and the separate recovery ofraffinate products (i.e. nonstraight chain hydrocarbons). The extract materials (i.e. straight chain hydrocarbons) from the two stocks are recovered entirely or in part in admixture with each other.

The cyclic method of utilizing the adsorbent according to the invention comprises the following steps with steps A to G, inclusive, being in sequence:

A. introducing a first'feed in vapor form into one end of a bed of molecular sieve adsorbent selective for adsorbing straight chain hydrocarbon and passing same toward the other end;

B. stopping introduction of the first feed before the amount introduced is sufficient to saturate the adsorbent with straight chain hydrocarbon;

C. introducing a purge gas into the bed in amount to purge interstitial hydrocarbons therefrom without substantial displacement of adsorbed straight chain hydrocarbon;

D. introducing a second feed in vapor form into said one end of the bed and passing same toward the other end;

E. stopping introduction of the second feed at least before straight chain hydrocarbon of highest molecular weight from the feed having the lower end boiling point appears in the effluent or, in some embodiments of the invention, before any substantial amount of any straight chain hydrocarbon appears in the effluent;

F. introducing purge gas into the bed in amount to purge interstitial hydrocarbons therefrom without substantial displacement of adsorbed straight chain hydrocarbon;

G. introducing a further quantity of purge gas into said other end of the bed until substantially all straight chain hydrocarbons have been displaced therefrom through said one end;

H. segregating the effluent from said other end of the bed into separate product fractions comprising a first product rich in nonstraight chain hydrocarbons from the first feed and a second product rich in nonstraight chain hydrocarbons from the second feed;

I. and recovering from the effluent from said one end of the bed a third product comprising straight chain hydrocarbons from both feeds.

In another aspect the invention is applicable to a process for upgrading a feed naphtha of the C C range involving treatment of the naphtha in an adsorption zone containing molecular sieves to separate same into n-paraffin-rich and n-paraffin-lean fractions in a manner preferably such that the latter still contains nparaffins of the C,,-C range, catalytically reforming the n-paraffin-lean fraction, and treating the resulting reformate in the same adsorption zone to yield denormalized reformate. In this procedure C -C n-paraffins from the feed naphtha together with any C-,-C nparaffins formed during the reforming step are obtained from the adsorption zone as a single product, while n-paraffins of the C,,C range from the feed naphtha as well as from the reformate are included in the n-paraffinlean fraction which is reformed. These C -C6 n-paraffins are converted during the reforming operation mainly to C C isoparaffins which end up as components of the denormalized reformate.

BRIEF DESCRIPTION OF DRAWINGS The invention is described in conjunction with the accompanying drawings wherein:

FIG. 1 schematically illustrates a single adsorption zone operated in a cyclic manner to denormalize two different feeds designated as A and B.

FIG. 2 is a schematic flowsheet of a reforming process wherein the invention is utilized for denormalizing the fresh feed naphtha as well as the reformate produced.

DESCRIPTION The present invention has utility in refinery operations wherein two different feed materials of either similar or different boiling ranges are to be denormalized. The term denormalize as used herein refers to removing straight chain hydrocarbons, which can be nparaffins or nonbranched aliphatic olefins or both, from nonstraight chain hydrocarbons.

The invention is especially useful when it is desired to denormalize one of the stocks substantially completely while exhaustive removal of straight chain hydrocarbons from the other stock is not essential. An example of such a situation in refinery practice is when one of the stocks is to be employed in a low octane gasoline pool while the other is to be used for making gasoline of high antiknock quality, for example, lOO or more F-l clear octane number. In such case the presence of a small amount of n-paraffins in the firstmentioned blending stock can readily be tolerated whereas even a small percentage of n-paraffins in the other may be highly detrimental.

The invention also has special applicability in conjunction with the reforming process described in aforesaid application Ser. No. 112,140.

FIG. 1 illustrates an adsorption zone 10 containing a bed of crystalline zeolite molecular sieves having uniform pore diameter of about 5 Angstrom units. The adsorption zone is utilized in a cyclic operation in which feed naphthas A and B are sequentially treated in vapor phase and adsorbed straight chain hydrocarbons from both feeds are then desorbed by means of a purge gas. More specifically, feed A at elevated temperature is first introduced through line 11 and valve 12 into the top of the bed and passed downwardly toward the bottom. The temperature in the adsorbent can be in the range of 300-800F. (l49427 C.), more preferably 350750F. (177-399C.), and is sufficiently high to maintain the feed as a vapor at the prevailing pressure but not so high as to cause cracking. In each cycle the amount of feed A introduced is substantially less than that amount which would saturate the adsorbent with straight chain hydrocarbons. For example the amount introduced per cycle generally will be between 5 percent and 80 percent of the amount which would fully saturate the adsorbent with straight chain hydrocarbons. For purpose of description the latter here are considered to be n-paraffins. As the feed A material passes downwardly in the bed the n-paraffins are retained in the upper portion of the adsorbent while branched and cyclic hydrocarbons pass on down the bed and out of the bottom, from which they are collected through valve 17 and line 18 as A raffinate. This product is of especially high purity since it has passed through a considerable amount of adsorbent that has not been saturated with n-paraffins.

After the desired amount of feed A has been introduced, its flow to the bed is stopped and a heated purge gas is introduced in amount sufficient only to force interstital hydrocarbons from the bed without substantial displacement of the adsorbed n-paraffins. Any suitable gas can be used as the purge gas, such as hydrogen, methane, ethane, propane, nitrogen, carbon dioxide, carbon monoxide and the like. The purge gas can be introduced at the top or bottom of the bed so as to force the interstitial hydrocarbons toward either end, but it is distinctly preferable that it be introduced at the bottom in order to displace the interstitial hydrocarbons in the opposite direction from which they entered. This permits the displaced hydrocarbons to be sent back through valve 12 into feed line 11 and eliminates any need for separately collecting this material in order to avoid product contamination. Thus the displaced hydrocarbons will again enter adsorption zone 10 in a subsequent cycle of operation along with additional feed A.

Feed B is next introduced in vapor phase and likewise at elevated temperature into the top of adsorption zone 10 through line 13 and valve 14 and passed downwardly in the bed. The bed temperature again is maintained in the ranges previously specified. Preferable the addition of feed B is continued until the adsorbent has become saturated with n-paraffins substantially throughout its entire mass, as this permits most efficient utilization of the adsorbent in each cycle. In any event introduction of feed B is stopped at least before the n-paraffin of highest molecular weight of the feed having the lower end boiling point appears in the effluent from the bottom of the bed. For example, if feed A contains n-paraffms through the range of C -C while feed B contains those of the higher boiling range that includes C C then the introduction of feed B would be stopped at least before n-octane appears in the effluent. In some embodiments of the invention, introduction of feed B is stopped before effluent from the bottom of the bed exhibits substantial content of any nparaffins. During this stage the effluent passing from the bottom of zone 10 is separately collected through valve 19 and line 20 as B raffinate. This product may not have as high purity as A raffinate but in any event itsn-paraffin content will be low.

The next step in the cycle involves again introducing heated purge gas to adsorber 10 to remove interstitial hydrocarbons from the bed without substantial displacement of the n-paraffins. Preferably this is also done by passing purge gas from line 21 and valve 22 into the bottom of the adsorber to push the interstitial hydrocarbons upwardly through the bed. Again the amount of purge gas used is just sufficient to purge out the interstitial hydrocarbons without substantial displacement of the n-paraff'ms from the bed. The removed hydrocarbons preferably are allowed to flow back through valve 14 into line 13, from which they will thereafter be fed along with additional feed B to adsorber 10 in a subsequent operating cycle.

After purging of the interstitial hydrocarbons from the bed, a further quantity of hot purge gas is then passed through line 21 and valve 22 upwardly through the bed in amount to desorb and displace from the adsorbent substantially all n-paraffins which were adsorbed from feeds A and B during the present cycle. The effluent from the top of the bed, containing the displaced n-paraffins and purge gas, is separately collected through valve and line 16. The n-paraffins, which can be recovered by condensation from this stream upon cooling are a mixture of the n-paraffin components of both feed A and feed B.

The above-described procedure, wherein the adsorbent bed is desorbed in a direction opposite from instead of the same as that in which the feed materials were introduced, is particularly advantageous when the feeds contain a plurality of n-paraffins. As the number of carbon atoms per molecule increases the adsorbability thereof by molecular sieves likewise increases. Consequently n-paraffins of different molecular weights will progress through the adsorbent bed at different rates and tend to segregate into adjacent zones. After the feed materials have been introduced, the heaviest n-paraffin will be nearest the inlet end while the lightest will concentrate toward the opposite end. Desorbing these components in a direction opposite to that at which they entered facilitates their removal from the bed, since the most strongly adsorbed component has to travel the least distance to leave the bed. This results in a saving in amount of desorbing gas and time needed for desorption.

Another improvement in the desorption efficiency can be effected by desorbing only part of the n-paraffins from the bed when the cyclic operation is first started and thereafter desorbing only to this same ex tent during each cycle. This leaves a residual amount of n-paraffins in the bed in each cycle, which residue will be mainly the n-paraffin of highest molecular weight that was present in feeds A and B. The amount of purge gas then used in each cycle is that necessary for keeping the amounts of n-paraffins charged to and removed from the bed in the same cycle in balance. In other words the amount of purge gas introduced during a cycle is such that the quantity of n-paraffins desorbed is about the same as the total quantity adsorbed from the portions of feeds A and B just introduced and not such amount as to displace all n-paraffins from the bed. By leaving this n-paraffin residue, less purge gas is required than otherwise would be needed.

While FIG'. 1 shows only one adsorber 10, in practice a plurality of adsorber beds normally would be used in parallel so that the naphtha feeds could be fed from a common manifold alternately to the beds in timed sequence to permit continuous introduction of each naphtha to the system. Each bed would operate on a time cycle involving stages of adsorption of the straight chain hydrocarbons from the two feed materials, purging stages for removing interstitial hydrocarbons and the desorption stage for displacing the n-paraffins from the adsorbent, all as above described. In each cycle predetermined amounts of each feed would be introduced to each bed such that the total quantity of straight chain hydrocarbons so introduced preferably would be enough to approximately saturate the molecular sieve adsorbent. The relative amounts of the feed naphthas introduced per cycle can be calculated from their straight chain hydrocarbon contents and the quantities of each feed to be processed per unit time. For example, if feed A and feed B will supply, respectively, 30 percent and percent of the total quantity of n-paraffins to be removed per day, then the amount of feed A introduced to a bed per cycle preferably is that which would saturate 30 percent of the adsorbent, while the amount of feed B is that which will approximately saturate the remaining 70 percent of the adsorbent.

FIG. 2 illustrates a process wherein a feed naphtha composed of n-paraffins and non-n-paraffins of the C -C range is first treated with molecular sieves, raffinate so obtained is then hydroformed whereby a minor but significant amount of n-paraffins is produced, and the resulting reformate is then treated with the same molecular sieves to obtain fully denormalized product of high antiknock value. A feature of one embodiment of the process of FIG. 2 is that the adsorption operation is conducted in such a manner that n-paraffins of the C .,C range remain with the raffinate which is fed to the reformer, while n-paraffins of the C C range are segregated as a separate product. This is advantageous, as the C C n-paraffins will isomerize during the reforming step to isomers useful as gasoline components whereas the higher n-paraffins tend to react adversely, eg by cracking, and are undesirable as components of the reformer feed.

The feed to the process of FIG. 2 can be any naphtha fraction containing n-paraffins and other hydrocarbons of the C .,C, range including one or more n-paraffins of the C C range. The feed can be a wide boiling or narrow boiling fraction and may, for example, have an initial boiling point in the range of 50300F. (l0'l49 C.) and an endpoint in the range of 210475F. (99-246C.). The n-paraffin content of the feed can vary widely, e.g. 3-50 percent by weight. The feed can, for example, include all of the n-paraffins of the C C range, or it can be narrower boiling so as to include only portions of the range such as C .,C n-paraffins or C --C n-paraffins or C C n-paraffins. The feed enters the system through line 30 and is passed to heater 31 wherein it is vaporized and heated to a temperature in the range of 300800F. (l49427C.), more preferably 350750F. l77-399C.). The vapors then pass to a manifold or surge zone (not shown) from which a plurality of adsorber beds can be alternately fed in timed sequence so that a continuous flow of vapors from the manifold to an adsorber will occur. For simplicity the adsorption operation is illustrated by the singly adsorber 33 to which the feed naphtha is introduced via line 32.

For the purpose of describing a cycle of operation of adsorber 33, it is considered that the cycle begins with the introduction thereto of reformate rather than naphtha. At this time the molecular sieve adsorbent has just been desorbed and is substantially free of hydrocarbons. The reformate, obtained as hereinafter described, is passed through line 35 and heater 36 wherein it is vaporized and heated to a similar temperature level as already stated above for the naphtha feed. The hot vapors then flow into another mainfold (not shown) from which they are fed to adsorber 33 through line 37. The reformate typically contains C,,C n-

paraffins as well as higher n-paraffins formed during the reforming reactions, and these n-paraffins are selectively adsorbed by the molecular sieves as the reformate flows down through the bed. The nonadsorbed raffinate fraction, constituting the n-paraffinlean reformate material, is separately collected as a product through line 39. This material has high antiknock value and is an excellent blending stock for high quality gasoline.

Within the adsorbent bed a gradation in composition of the adsorbate occurs due to the fact that, as previously explained, a higher molecular weight n-paraffin is more strongly adsorbed than a lower molecular weight n-paraffin. Consequently, in passing through the bed, the C -C n-paraffins will forge ahead of the higher nparaffins. The amount of reformate introduced per cycle is insufficient to saturate the molecular sieve adsorbent with C C, n-paraffins and consequently the C ,-C n-paraffins do not reach the outlet until a later phase of the cycle. During the present phase the gaseous effluent which leaves the bottom of adsorber 33 through line 39 is composed essentially of branched and cyclic hydrocarbons. This is the denormalized reformate product of the process.

After the introduction of reformate has been stopped, purge gas, which is a portion of the hydrogen recycle stream from the reforming step, is passed into the bottom of adsorber 33 by means of line 34. The amount of purge gas introduced is just sufficient to push the interstitial hydrocarbons out the top of the bed and back through line 37 to the manifold. Essentially no removal of n-paraffins from the adsorbent occurs during this purging step.

In the next phase of the cycle, hot naphtha feed from line 32 is introduced into the top of the bed and flows downwardly. Nonstraight chain hydrocarbons pass out of the bed through line 38 to the appropriate manifold, while the C -C n-paraffins are adsorbed and become distributed in accordance with molecular weight variations along the length of the bed together with corresponding n-paraffins from the reformate. In one embodiment, addition of naphtha feed is stopped before the lightest n-paraffin appears in the effluent and subsequently all n-paraffins of the C C are desorbed and collected together as a separate fraction. However, in the preferred embodiment of the process of FIG. 2, feed naphtha is introduced through line 32 in amount sufficient to displace at least most of the C C n-paraffins from the bed through line 38 but insufficient to displace C,-C n-paraffins. The C,,C n-paraffins mixed with nonstraight chain hydrocarbons of the feed naphtha pass from line 38 to a manifold or surge zone (not shown), thus all becoming constituents of the nparaffin-lean material collected therein for use as reformer feed.

After addition of feed naphtha to adsorber 33 has been stopped, purge gas is again introduced through line 34 in amountjust sufficient to push the interstitial hydrocarbons out of the bed. The displaced hydrocarbons flow from the top back through line 32 to the corresponding manifold.

Finally, to complete the cycle, a large quantity of purge gas is fed through line 34 and passes upwardly through the bed in order to desorb all of the n-paraffins. A mixture of purge gas and n-paraffins leaves the top of the adsorber via line 40 and goes through cooler 41 wherein the n-paraffms are condensed and then into gas-liquid separator 42. Recovered purge gas is removed from the top of the separator and sent through line 44 back to the hydrogen recycle gas system. From the bottom of separator 42 a C -C n-paraffin product is withdrawn through line 43. If desired, this product can be passed to a catalytic dehydrocyclizing operation (not shown) for upgrading to high quality aromatic blending stock.

The n-paraffin-lean naphtha fraction from the adsorber, which also contains the C -C n-paraffins as shown above, is passed through line 50 to heater 51 wherein it is heated to a suitable reforming temperature, after which it is subjected to hydroforming as indicated by reformer 52. Any suitable reforming catalyst and conditions can be employed in this step. Typically the reforming reaction is carried out by means of a platinum-containing reforming catalyst in the presence of hydrogen at suitable reforming temperatures in the range of 750-l000F. and pressures of from or 200 p.s.i.g. to 700 p.s.i.g. A space velocity generally in the range of 05-20 liquid volumes per hour per volume of catalyst (v/hr./v) and usually of 2 or more, e.g. 3 v/hr./v, is utilized. Average temperatures in the reformer 52 may be, for example, in the range of 875-975F. A plurality of reactors in series generally is used in this type of operation, with heaters between reactors for reheating the hydrocarbon reactants to compensate for reductions in temperature that occur due to the endothermic reactions which take place. Under these reforming conditions naphthenes dehydrogenate to aromatics, substantial isomerization of the C -C n-paraffins occurs, a significant portion of the C C or higher singly branched paraffins disappear by being converted to other components, and also C and higher n-paraffins are formed in substantial amount.

The effluent from reformer 52 is withdrawn through cooler 53 and passes to gas-liquid separator 54. The hydrogen-containing gas phase is in part recycled from the top of separator 54 through

lines

55 and 50 and heater 51 back to reformer 52 and in part is withdrawn through line 34 for use as purge gas. A hydrogen recycle rate typically in the range of 3,0009,000 SCF/bbl. of reformer feed is used and the hydrogen content of the recycle stream is generally in the range of 60-98 percent by volume. Any excess hydrogen can be removed from the system as indicated by line 56.

Platinum-containing reforming catalysts are preferred for effecting the hydroforming reaction in reformer 52. Such catalysts have been described in numerous prior art references and need not be described herein. Reference can be made, for example, to the following: CATALYTIC PROCESSES AND PROVEN CATALYSTS by C. L. Thomas, pages 54-57, Academic Press (1970); US Pat. No. 2,479,109, V. Haensel, issued Aug. I6, 1949; and US. Pat. No. 2,478,9I6, V. Haensel et al., issued Aug. 16, I949. The platinum-containing catalyst can also contain other metals, such as rhenium, ruthenium, rhodium or iridium, which are beneficial. The pIatinum-rhenium reforming catalysts are particularly desirable and such catalysts have been described in US. Pat. No. 3,415,737, H. E. Kluksdahl, issued Dec. 10. I968 and U.S. Pat. No. 3,434,960, R. L. Jacobsenson, issued Mar. 25, 1969. Platinum-iridium reforming catalysts are disclosed in US. Pat. No. 3,554,902, W. C. Buss, issuedJan. 12,1971.

The liquid reformate which passes from the bottom of separator 54 through line 35 contains C:,C n-paraffins which have not isomerized or which were produced by the reforming reactions and a significant amount of C and higher n-paraffins but is substantially depleted of singly branched paraffms of the C C range or higher as compared to the charge to reformer 52. This reformate is then treated in adsorber 33 in the manner previously described to selectively remove the n-paraffin components and yield blending stock of high antiknock value. v

The following is a specific example of processing in the manner of FIG. 2 but without segregating C,,C from the higher paraffins. in this case the process handles 10,000 bbls./day of a fresh naphtha cut containing -25 percent by volume of n-paraffins all of which are of the C C range. This amount per day of naphtha feed enters the adsorption zone 33 and 7,500 bbls./day of denormalized naphtha substantially free of any n-paraffins are produced through line 38. The denormalized naphtha is processed in reformer 52 utilizing a platinum-containing reforming catalyst at an average temperature of 910F. and pressure of 350 p.s.i.g. The reformate product obtained from separator 54 through line 35 amounts to 6,375 bbls./day, has an R1 clear octane rating of about 100 and contains a total of 6 percent-n-paraffins made up of 3.2 percent C,-,--C n-paraffins and 2.8% C and higher n-paraffins. This shows that n-paraffins are produced during the reforming operation. This reformate is fed to adsorber 33 through line 37 at the beginning of each cycle in the manner previously described. After the phase of introducing reformate to the adsorption zone, each cycle includes the sequential phases of purging interstitial hydrocarbons, feed fresh naphtha in amount insufficient to cause any n-paraffins to appear in the effluent, purging again and finally desorption of the n-paraffins from the bed in the opposite direction from which they were introduced. This procedure results in a denormalized reformate, obtained through line 39 in amount of 5,990 bbls./day having an F-l clear octane number of about 103. Also obtained is a product composed of n-paraffins of the C,,C range, which is removed from separator 42 through line 43 in amount of 2,885 bbls./day.

The invention claimed is:

1. In a process wherein two different naphtha feeds are separated into straight chain and nonstraight chain hydrocarbon fractions by treatment with a molecular sieve adsorbent selective for adsorbing straight chain hydrocarbons, the method of utilizing the adsorbent in a cyclic manner comprising the following steps with steps A to G, inclusive, being in sequence:

A. introducing a first feed in vapor form into one end of a bed of said molecular sieve adsorbent and passing same toward the other end;

D. introducing a second feed in vapor form into said one-end of the bed and passing same toward the other end;

E. stopping introduction of the second feed at least before straight chain hydrocarbon of highest molecular weight from the feed having the lower end boiling point appears in the effluent from said other end of the bed;

G. introducing a further quantity of purge gas into said other endof the bed until substantially all straight chain hydrocarbons have been displaced therefrom through said one end;

. and recovering from the effluent from said one end of the bed a third product comprising straight chain hydrocarbons from both feeds.

2. A process according to claim 1 wherein in each of steps C and F the purge gas is introduced into the said other end of the bed to purge interstitial hydrocarbons from said one end.

3. A process according to claim 2 wherein in step E the introduction of said second feed is stopped before any substantial amount of any straight chain hydrocarbon appears in said effluent.

4. A process according to claim 1 wherein in step E the introduction of said second feed is stopped before any substantial amount of any straight chain hydrocarbon appears in said effluent.

5. In a process for upgrading a feed naphtha composed of n-paraffin and non-n-paraffin hydrocarbons of the C,,C range by separating the feed naphtha into nparaffin-rich and n-paraffin-lean fractions and catalytically reforming the n-paraffin-lean fraction to product a reformate, the steps comprising:

a. subjecting said n-paraffin-lean fraction to reforming conditions in the presence of hydrogen and a reforming catalyst, whereby reforming reactions occur and a reformate is obtained containing C C n-paraffins;

. introducing said reformate in vapor phase to one end of an adsorption zone containing a bed of molecular sieve adsorbent to selectively adsorb nparaffins and recovering from the other end of said zone an n-paraffin-lean reformate, the amount of reformate so introduced being insufficient to saturate the molecular sieve adsorbent with C -C nparaffins;

c. purging interstitial vapor from the adsorbent without substantial removal of C r,--C n-paraffins therefrom;

. introducing feed naphtha in vapor phase to said one end of the adsorption zone to selectively adsorb n-paraffins therefrom, the amount so introduced being insufficient to displace C,,C nparaffins from the adsorbent bed;

e. recovering from said other end of the adsorption zone an effluent constituting said n-paraffin-lean fraction and utilizing same as specified in step (a);

f. purging interstitial vapor from the adsorbent without substantial removal of C C, n-paraffins therefrom;

g. and desorbing the C,,C n-paraffins from the bed zone an nparaffin-lcan reformate, the amount of reformate so introduced being insufficient to saturate the molecular sieve adsorbent with C .,C nparaffins;

t reC Bl' Said n-p affinic fraCKiOn and c. purging interstitial vapor from the adsorbent rfig nfi the adsorbent for in p without substantial removal of C C n-paraffins 6. A process according to claim 5 wherein each of h f R and is Carried out y lmroducing P g d. introducing feed naphtha in vapor phase to said 5 l l d the 5 ofther f d the d to Purge mterst" one end of the adsorption zone to selectively ad- Y one en 10 sorb n-parafflns therefrom, the amount so in- 7. In a process for upgrading a feed naphtha comtroduced being Sufficient to displace CYC6 posed of n-paraffin and non-n-paraffin hydrocarbons of paraffins from the adsorbent bed but insufficient the C -C range by separating the feed naphtha into nto displace crclz therefrom. paraffin-rich and n-paraffin-lean fractions and catalytirecovering from Said other of the adsorption zigotiz r e s lz s'sgiz i zf fracton to produce 15 zone an effluent constituting said n-paraffin-lean 1 1 a subjecting saig n par affin l ean fraction substan fracflon contammg C5-C6 mpamffms and uuhzmg tially free of C C n-paraffins but containing p i ep(a) h I C C n-paraffins and derived as hereinafter Purging mterstiua vapor from t e adsorbent specified, to reforming conditions in the presence without slibstamlal remqval of n-paraffins of hydrogen and a reforming catalyst whereby therefrom and desorbmgthe n-Paraffins reforming reactions occur with C -50 C n-paraf- F the bed to recover said n-paraffm-nch fins partially isomerizing to C -C isoparaffins and a regenerate the adsorbent for re-use m a reformate is obtained containing C C n-paraf- Step fins. 8. A process according to claim 7 wherein each of b. introducing said reformate in vapor phase to one Step? (c) and earned out by lmmducmg Purge end of an adsorption Zone containing a bed of gas into the said other end of the bed to purge interstimolecular sieve adsorbent to selectively adsorb nhydrocarbons from Sam one paraffins and recovering from the other end of said

Claims

2. A process according to claim 1 wherein in each of steps C and F the purge gas is introduced into the said other end of the bed to purge interstitial hydrocarbons from said one end.
3. A process according to claim 2 wherein in step E the introduction of said second feed is stopped before any substantial amount of any straight chain hydrocarbon appears in said effluent.
4. A process according to claim 1 wherein in step E the introduction of said second feed is stopped before any substantial amount of any straight chain hydrocarbon appears in said effluent.
5. In a process for upgrading a feed naphtha composed of n-paraffin and non-n-paraffin hydrocarbons of the C5-C12 range by separating the feed naphtha into n-paraffin-rich and n-paraffin-lean fractions and catalytically reforming the n-paraffin-lean fraction to product a reformate, the steps comprising: a. subjecting said n-paraffin-lean fraction to reforming conditions in the presence of hydrogen and a reforming catalyst, whereby reforming reactions occur and a reformate is obtained containing C5-C12 n-paraffins; b. introducing said reformate in vapor phase to one end of an adsorption zone containing a bed of molecular sieve adsorbent to selectively adsorb n-paraffins and recovering from the other end of said zone an n-paraffin-lean reformate, the amount of reformate so introduced being insufficient to saturate the molecular sieve adsorbent with C5-C12 n-paraffins; c. purging interstitial vapor from the adsorbent without substantial removal of C5-C12 n-paraffins therefrom; d. introducing feed naphtha in vapor phase to said one end of the adsorption zone to selectively adsorb n-paraffins therefrom, the amount so introduced being insufficient to displace C5-C12 n-paraffins from the adsorbent bed; e. recovering from said other end of the adsorption zone an effluent constituting said n-paraffin-lean fraction and utilizing same as specified in step (a); f. purging interstitial vapor from the adsorbent without substantial removal of C5-C12 n-paraffins therefrom; g. and desorbing the C5-C12 n-paraffins from the bed to recover said n-paraffin-rich fraction and regenerate the adsorbent for re-use in step (b).
6. A process according to claim 5 wherein each of steps (c) and (f) is carried out by introducing a purge gas into the said other end of the bed to purge interstitial hydrocarbons from said one end.
7. In a process for upgrading a feed naphtha composed of n-paraffin and non-n-paraffin hydrocarbons of the C5-C12 range by separating the feed naphtha into n-paraffin-rich and n-paraffin-lean fractions and catalytically reforming the n-paraffin-lean fraction to produce a reformate, the steps comprising: a. subjecting said n-paraffin-lean fraction, substantially free of C7-C12 n-paraffins but containing C5-C6 n-paraffins and derived as hereinafter specified, to reforming conditions in the presence of hydrogen and a reforming catalyst, whereby reforming reactions occur with C5-50 C6 n-paraffins partially isomerizing to C5-C6 isoparaffins and a reformate is obtained containing C5-C12 n-paraffins; b. introducing said reformate in vapor phase to one end of an adsorption zone containing a bed of molecular sieve adsorbent to selectively adsorb n-paraffins and recovering from the other end of said zone an n-paraffin-lean reformate, the amount of reformate so introduced being insufficient to saturate the molecular sieve adsorbent with C5-C12 n-paraffins; c. purging interstitial vapor from the adsorbent without substantial removal of C5-C12 n-paraffins therefrom; d. introducing feed naphtha in vapor phase to said one end of the adsorption zone to selectively adsorb n-paraffins therefrom, the amount so introduced being sufficient to displace C5-C6 n-paraffins from the adsorbent bed but insufficient to displace C7-C12 therefrom; e. recovering from said other end of the adsorption zone an effluent constituting said n-paraffin-lean fraction containing C5-C6 n-paraffins and utilizing same as specified in step (a); f. purging interstitial vapor from the adsorbent without substantial removal of C7-C12 n-paraffins therefrom; g. and desorbing the C7-C12 n-paraffins from the bed to recover said n-paraffin-rich fraction and regenerate the adsorbent for re-use in step (b).
8. A process according to claim 7 wherein each of steps (c) and (f) is carried out by introducing a purge gas into the said other end of the bed to purge interstitial hydrocarbons from said one end.