CA1314568C - Isomerization process and apparatus - Google Patents

Abstract

ISOMERIZATION
PROCESS AND APPARATUS

ABSTRACT OF THE DISCLOSURE
Processing and apparatus are provided for upgrading the octane of a mixed hydrocarbon gasoline feedstock by an integrated adsorption-isomerization process which catalytically isomerizes normal paraffinic hydrocarbons and concentrates non-normals in a product stream, in both the reactor-lead and adsorber-lead configuration.
The process includes passing an adsorber feed stream comprising hydrogen as well as hydrocarbons to an adsorbent bed to adsorb normal hydrocarbons.
The hydrogen is preferably obtained from a hot hydrogen-containing process stream which is not cooled or separated into component parts prior to forming the adsorber feed. In some embodiments, the hot-hydrogen containing stream comes from reactor effluent and in others from desorption effluent.
According to the invention, the only hydrogen which will require cooling and separation from a hydrocarbon component is that which is recycled for desorption. The invention provides improved energy efficiency and can reduce equipment size and complexity.

Description

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D-1i698 ISOMERIZATION
PROCESS AND APPARATUS

Technical Field This invention relates to improvements in processing and apparatus for upgrading the octane of a mixed hydrocarbon gasoline feedstock by an integrated adsorption-isomerization process which catalytically isomerizes normal paraffinic hydrocarbons and concentrates no~-normals in a ~roduct stream.
The ~nown technology for improving the octan~
rating of certain hydrocarbon fractions, especially mixed feedstocks containing normal and i50 pentanes and hexanes, typically involves isomerizing normal hydrocarbons in a feed stream prior to or following an adsorption-desorption cycle which isolates non-normals.
According to one widely used process, the entire feed is subjected to an initial catalytic reaction and then to a four-stage separation procedure employing molecular sieve adsorbers operating at essentially isobaric a~d isothermal conditions. Prior to the four-stage procedure, the reactor effluent is separated into an adsorber feed stream and a hydrogen-rich gas stream. The adsorber feed stream i5 passed to the adsorbers in two adsorption stages: the fir~t, di~placing void space , , 1 31 456~

gas from a prior desorption stage; and, the second, producing an adsorption effluent having a greatly reduced content of adsorbed (e.g., normal) hydrocarbons. The adsorbers are then desorbed with a hydrogen-rich gas stream in two stages: first to displace void space gas from the preceding adsorption stage; and, second to remove adsorbed hydrocarbons from the adsorbent. This is known as a reactor-lead process.
According to another known process, the feed is first passed to the adsorbers which immediately remove non-normals, again in a four-stage adsorption procedure. The normal~ from the second desorption stage are then mixed with sufficient hydroge~ to protect the isomerization reactor and are ~hen isomerized, with subsequent removal of newly-formed non-normals and recycle of normals to the reactor.
This is known in the art as an adsorber-lead process.
By operating the four-stage adsorber cycle in the manner done in the prior art, substantially all hydrogen or other purge gas is removed from the adsorber feed prior to adsorption, and the adsorption effluent varies greatly in molecular weight, from about 10 lb/lb mole at the beginning of adsorption to about 70 lb/lb mole at the end.
Because the heat e~change system must be adequate to operate at minimum heat content (i.e., lowest molecular weight), it has been necessary to exaggerate the 6ize of the heat exchangers and to waste heat from the high heat content portion. It would be desirable to produce an adsorption effluent which showed less variation in molecular weight.
The ad~orbers operate es~entially a~ a batch procedur~. To approach a co~tinuou~ flow of ad~orber efflue~t with a four-stage adsorber cycle, 1 3 1 456~

the prior art has typically employed four adsorbers operated in timed relationship. It would be desirable to reduce the capital cost of the adsorbers and related conduits, valves and controls.
While increasing ad~Qrber operating pres~ure increases the partial pressure of normals and should, therefore, improve its adsorption, increasing the pres~ure in prior art adsorbers does not give the desired increase in adsorption efficiency. The adsorbers are filled with ~olid molecular sieve adsorbent and have significant void ~pace volumes not occupied by solid material.
Operating the adsorbers as in the prior art, but at increased pressures, has the disadvantage of increasing void space ~torage of gases being processed. It would be advantageous to achieve a better proportion of adsorbed normals to void ~pace storage of hydrocarbon.
It would fur~her be desirable to decrease the total adsor~ent bed volume and to improve the energy efficiency in an integrated isomerization-adsorption process which could achieve total isomerization of all normal hydrocarbons.
Most preferably, it would be desirable to increase the degree of integration of the reactor and adsorber operations to save epergy and decrease the amount of molecular sieve materials and vessel volumes required.

Backqround Art The art ha~ produced a number of integrated isomerization-ad~orption systems for isomerizing a feed ~tream containing normal and non-~ormal hydrocarbons and producing a product ~tream which i~
u~eful as a gasoline blendi~g feed~tock.

Most of the prior art ~ystem~ totally isomerize the normals in the feed and are referred to in the art as total i omerization proces~es, i.e., TIP.
Among these are reactor-lead system~, where the fresh feed and any recycle is fed to the isomerization reactor prior to separation of non-normals, and adsorber-lead cystems, where the fre~h feed is fed to the adsorbers prior to isomerizationO As currently operated, both of these schemes typically employ three or four adsorber beds which are cycled through at least one adsorption ~tage and two desorption stages.
In Canadian Patent 1,064,056, Reber et al describe a total isomerization process wherein large fluctuation~ in the concentration of either n-pPntane or n-hexane in the reactor feed axe prevented by suitably controlling the operation of a three-bed adsorber system. According to the disclosure, no more than two beds are being desorbed at any given time and the terminal stage of desorption in one of the three beds is contemporaneous with the initial stage of desorption in another of the three beds.
Both adsorber-lead and reactor-lead processes are specifically exemplified. The adsorber-lead process calls for first separating hydrogen from the reactor effluent. Fresh feed is then combined with the reactor hydrocarbon effluent and the combined stream is pa6sed through the adsorbers to remove non-normal hydrocarbons so that the feed to the reactor is essentially normal hydrocarbons. This require~ heat exchange eguipment of significant size to handle streams of widely varying molecular weight and large energy input~ to cool the entire reactor effluent to ~eparate ~he hydrocarbon and hydrogen 1 31 456~

portion, and then to reheat both. The reactor-lead process is similar in this regard.
In US Patent 4,210,771, Holcombe de~cribes a reactor-lead total isomerization process which S reduces the recycle rate to the reactor while maintaining a sufficient reactor hydrogen partial pres~ure by reducing fluctuations in hydrocarbon flow rate~ to the reactor. However, ~hi~ reactor-lead process required cooling the entire reactor effluent to separate hydrogen from hydrocarbon portions prior to separating the normals from non-normals in a four-stage adsorption section.
The effluent from the isomerization reactor i5 conden~ed to separate a hydrocarbon fraction. This fraction is then reheated and passed as feed in the vapor tate and at superatmospheric pressure periodically in sequence through each of at least four fi~ed beds of a system containing a zeolitic molecular sieve adsorbent having effective pore diameter of substantially 5 Angstroms, each of said beds cyclically undergoing the stages of;
A-l adsorption-fill, wherein the vapor in the bed void space consists principally of a non-sorbable purge gas and the incoming feedstock forces the said non-sorbable purge gas from the bed void space out of the bed without substantial intermi~ing thereof with non-adsorbed feedstock fraction;
A-2 ad~orption, wherein the feedstock is cocurrently passed through ~aid bed and the normal con~tituents of the feedstock are selectively adsorbed into the internal cavities of the crystalline zeolitic adsorbent and the nonadsorbed constituent6 of the feedstock are removed from the bed a~ an effluent having a greatly reduced content of norm~l feedstock cons-~ituents;

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D-1 void space purging, wherein the bed, which is loaded with normals adsorbate to the extent t'aat the stoichiometric point of the mass transfer zone thereof has passed between 85 and 97 percent of the length of the bed and the bed void space contains a mixture of normal~ and non-normals in essentially feed~tock proportions, is purged countercurrently, with respect to the direction of A-2 adsorption, by passing through the bed a stream cf a non-sorbable purge gas in sufficient quantity to remove ~aid void space feedstock vapor~ but not more than that which produces about 50 mole percent, preferably not more than 40 mole percent, of adsorbed feedstock normals in the bed effluent; and D-2 purge desorption, wherein the selectively adsorbed feedstock normals are desorbed as part of the desorption effluent by passing a non-sorbable purge yas countercurrently with respect to A-2 adsorption through the bed until the major proportion of adsorbed normals has been desorbed and the ~ed void space vapors consist principally of non-sorbable purge gas.
Thi~ process results in wide fluctuations in the molecular weight of the adsorption effluent, has considerable complexity and requires all recycled hydrocarbons and hydrogen to be cooled and reheated.
There is a present need for improvements in isomerization-adsorption systems which will reduce energy consumption while preferably reducing ad~orber bed volume and the overall comple~ity of the adsorption section.

Summary of the Invention The ~re~ent invention is based upon the discovery that co~iderable improvements can be achi~ved in terms of reduced ad~orbe~t inventorie~, 1 31 456~

reduced adsorption ~ection complexity, and improved energy efficiency, for an iutegrated isomerization-adsorption process for upgrading light naptha fee~s by implementiny changes which are contrary to conventional technology. The invention provides improved apparatus and methods for increasing the non-normal content of a feed stream containing normal and non-normal hydrocarbons by a new integration of isomerization and adsorption technologies in both the adsorber-lead and reactor-lead modes.
The process upgrades a hydrocarbon feed containing non-normal hydrocarbons and normal pentane and hexane to produce a hydrocarbon stream enriched in non-normals and includes: passing an adsorber feed stream, comprising hydrogen and hydrocarbons, to an ad~orption section containing an adsorbent bed to ad~orb normal hydrocarbons from said feed and to pass non-noxmal hydrocarbons and hydrogen out of the adsorption section as adsorption effluent; passing hydrogen-containing puxge gas through said adsorbent bed containing adsorbed normal hydrocarbons to produce a desorption effluent comprising hydrogen and normal hydrocarbons; and passing at least a portion of said desorption effluent to an isomerization reactor to produce a reactor effluent comprising hydrogen and a reactor hydrocarbon component co~prising an enhanced proportion of non-normal to normal hydrocarbons.
The invention enables improved integration of the two technologies of isomerization and adsorption-desorption.
When operating in the reactor-lead mode, the adsorber feed s~ream comprises reactor efflu~nt, preferably prior to any ~i~nificant cooling or compor.ent separation. This supplies hydrogen to the adsorber bed and conserves the heat value of the hydrogen and hydrocarbon components. Additionally, this embodiment enables recycle of the majority of the hydrocarbom based o~ weight in a given cycle, without cooling to any significant degree.
Preferably, the only hydrogen which will require cooling and separation from a hydrocarbon component is that which is recycled for desorption. The desorption effluent in this embodiment contains hot hydrogen and hydrocarbons and is preferably not cooled or fractionated prior to recycling for isomerization of normal hydrocarbons. This embodiment can be effectively carried out by placing the isomerization cataly~t and the molecular sieve adsorbent in the same vessel.
When operating in the adsorber-lead mode, the adsorber feed stream comprises fresh hydrccarbon feed and recycle, comprising hydrogen and hydrocarbons, from the reactor. The recycle from the reactor is preferably reactor effluent taken off directly without significant cooling or component separation. This hot recycle provides hydrogen to the adsorbent bed and conserves the heat value of the hydrogen and hydrocarbon components.
The apparatus of the invention provides means for performing the above processes.

Description of the Drawings 3Q The inventio~ will be bettex understood and its advantages will be more apparent from the following detailed description when read in connection with the accompanying drawings ~herein:

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g Figure 1 is a schematic of a reactor-lead proce6s and an apparatus arrangement which employs two pairs of reactor and adsorber sections wherein each reactor/adsorber pair is in a single vessel;
Figure 2 is a simplified ~chematic of a variation on the embodiment of Figure 1, which employs a valve manifold to maintain the same direction of flow throughout a cycle;
Figure 3 is another embodiment of a reactor-lead process and apparatus of the invention employing a single reactor vessel; and Figure 4 is a schematic of an adsorber-lead proce~s and apparatus arrangement according to the invention wherein a portio~ of the isomerization reactor effluent is combined with hydrocarbons from fresh feed and recycle to form an adsor~er feed.

SUITABLE FEEDSTOCKS ( ERESE~ FEED 1 The fresh feed contains normal and non-normal hydrocarbons~ It is composed principally o the various isomeric forms of saturated hydrocarbons having from five to six carbon atoms. The expression "the various isomeric forms" is intended to denote all the branched chain and cyclic forms of the noted compounds, as well as the straight chain forms. Also, the prefi~ notations "iso" and "i" are intended to be generic designation~- of all branched chain and cyclic (i.e., non-normal) forms of the indicated compound.
The following composition is typical of a feedstock suitable for processing according to the invention:

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Co~ponents Mole X
C4 and lower O - 7 i C5 10 - 40 i-CS lû - 40 n-C6 5 - 30 C7 and higherO - 10 Suitable feed~tocks are typically obtained by refinery distillation operations, and may contain small amounts of C7 and even higher hydrocarbons, but these are typically present, if at all, only in trace amounts. Olefinic hydrocarbons are advantag~ously less than about 4 ~ole percent in the eedstock. Aromatic and cycloparaffin molecules have a relatively high octane nu~ber. Accordingly, the preerred feed~toc~s are those high in aromatic and cycloparaffinic hydrocarbon~, e.g., at least 5, and more typically from 10 to 25 mole percent of these components combined.
The non-cyclic C5 and C6 hydrocarbons typically comprise at lea~t 60, and ~ore typically at least 75, mole percent of the feedstock, with at least 25, and prefer~ly at least 35, mole percent of the feedstock being hydrocarbons ~elected from the group of iso-pentane, iso-he~ane and combinations of these. Preferably, the feedstock will comprise no more than 40, and more preferably no more than 30 mole percent of a combination o n-pentane and n-hexane.

SUITABLE ISOMERIZATION CATALYSTS

The i~o~eri~atio~ ~eactor 6~ctions (21 and 27 in Figure 1) co~ain an i~o~eriz~tion cataly~t which can be any of the various molecular sieve based catalyst compositions well known in the a:t which exhibit ~elective and substantial isomerization activity under the operating conditions of the process. As a general cla~s, such catalysts comprise the crystalline zeolitic molecular sieves having an apparent pore diameter large enough to adsorb neopentane, SiO2/Al203 molar ratio of greater than 3; less than 60, preferably less than 15, equivalent percent alkali metal cations and having those A104 - tetrahedra not associated with alkali metal cations either not a~sociated with any metal cation, or associated with divalent or other polyvalent metal cations.
Because the feedstock may contain some olefins and will undergo at least some cracking, the zeolitic catalyst is preferably combined with a hydrogenation catalyst component, preferably a noble metal of group VIII of the Periodic classification of the Elements. The catalyst composition can be use~ alone or can ~e combined with a porous inorganic oxide diluen 3s a binder material. The hydrogenation agent can be carried on the zeolitic component and/or on the binder. A wide variety of inorganic oxide diluent materials are known in the art -- some of which exhibit hydrogenation activity per se. It will, accordingly, be understood that the expression "an inorqanic diluent having a hydrogenation agent thereon" is meant to include both diluents which have no hydrogenation activity per se and carry a separate hydrogenation agent and those diluents which are pe~ se hydrogenation catalysts. Oxides suit~ble as diluent6, which of themselves e~hibit hydrogenation activity, are the oxides of the metal~ of Group VI of the M~ndeleev 12 1 31 45~,`Q, Periodic Table of Elements. Representative of the metals are chromium, molybdenum and tungsten.
It is preferred that the diluent material possess no pronounced catalytic cracking activity. The diluent should not exhibit a greater quantitative degree of cracking activity than the zeolitic component of the overall isomerization catalyst composition. Suitable oxides of this latter class are the aluminas, silicas, the oxides of this latter class are the aluminas, silicas, the oxides of metals of Groups III, IV-A and Iv-B of the Mendeleev Periodic Table, and cogels of silica and oxides of metals of Groups III, IV-A and IV-B, especially alumina, zirconia, titania, thoria and combinations thereof. Aluminosilicate clays such as kaolin, attapulgite, sepiolite, polygarskite, bentonite, montmorillonite, and the like, when rendered in a pliant plastic-like condition by intimate admixture with water are also suitable diluent materials, particularly when said clays have not been acid-washed to remove substantial quantities of alumina.
Suitable catalysts for isomerization reactions are disclosed in detail in U.S. Patents 3,236,761 and 3,236,762. A particularly preferred catalyst is one prepared from a zeolite Y (US Patent 3,130,007~ having a SiO~/A1203 molar ratio of about 5 by reducing the sodium cation content to less than about 15 equivalenk percent by ammonium cation exchange, then introducing between about 35 and 50 equivalent percent of rare earth metal cations by ion exchange and thereafter calcining the zeolite to effect substantial deammination. As a hydrogen c~mponent, platinum or palladium in an amount of about 0.1 to 1.0 weight percent, can be placed on the zeolite by any conventional method.
SUITABLE ADSORBENTS
The zeolitic molecular sieve employed in the adsorption bed must be capable of selectively adsorbing D

1 31 456~3 the normal paraffins of the feedstock using molecular si~e and confiquration as the criterion. Such a molecular sieve should, therefore, have an apparent pore diameter of less than about 6 Angstroms and greater than about 4 Angstroms. A particularly suitable zeolite of this type is zeolite A, described in U.S. Patent 2,883,243, which in several of its divalent exchanged forms, notably the calcium cation form, has an apparent pore diameter of about 5 Angstroms, and has a very large capacity for adsorbing normal paraffins. Other suitable molecular sieves include zeolite R, U.S. Patent 3,030,181; zeolite T, U.S. Patent 2,950,952, and the naturally occurring zeolitic molecular sieves chabazite and erionite.
The term "apparent pore diameter" as used herein may be defined as the maximum critical dimen~ion, or the molecular species which is adsorbed by the adsorbent under normal conditions. ~he critical dimension is defined as the diameter of the smallest cylinder which will accommodate a model of the molecule constructed using the available values of bond distances, kond angles and van der Waals' radii. The apparent pore diameter will always be laxger than the structural pore diameter, which can be defined as the free diameter of the r~

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appropriate silicate ring in khe structure of the adsorbent.

Detailed Description The invention will be described primarily according to a preferred embodiment wherein a mixed hydrocarbon feedstock (fresh feed) is upgraded for use as a gasoline blending stock by an integrated combination of adsorption and isomerization.
The invention will first be described in terms of the reactor-lead configuration in conjunction with Figure 1 which, as a virtual total integration of i~omerization and adsorption technologies, enables adsorber and reactor beds to be in the same vessel. This configuration combines the benefits of both reactor-lead and adsorber-lead systems.
Normals in the feed can be partially isomerized before adsorption as in the reactor-lead system, thereby making the adsorption section smaller. On desorption, the benefits of adsorber-lead are appreciated. Since essentially normals are fed to the reactor section on desorption, the catalyst volume is utilized more effectively.
Referr:ing to Figure 1, fresh feed in line 10 is combined i~ line 12 with hydrocarbon recycle from line 14. This combined hydrocarbon stream is heated by indirect heat exchange with adsorption effluent, carried by line 16 in heat exchanger 18 from which it is passed to furnace 20 where it is heated sufficiently for passage to isomerization reactor section 21 (catalyst bed) and then ~he adsorption section 22 (adsorbent bed), of vessel 23. It is of course pos~ible to have the catalyst and adsorbent beds i~ different ve#sel~ if de ired.

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The reactor feed stream in line 24 is formed by combining the hot hydrocarbon 6tream from furnace 20 with hot reactor effluent rom line 26 which contains hydrogen and hydrocarbon components (i.e., hot recycle or hot hydrogen recycle). Suitable control valves and controller~ (not ~hown) direct feed stream 24 to the appropriate one of vessels 23 and 29, which will alternate between the two functions now represented in Figure 1 as being performed by each of the vessels.
Depending on the particular catalyst composition employed, the operating temperature of ~ithin vessels 23 and 29 is generally withln the range of 100 to 390C and the pressure is within 15 the range of 175 to 600 psia. Desirably, the temperature will be within the range of from 220 to 280C and the pressure will be in the range of from 200 to 400, preferably 220 to 300 psia, and most preferably about 2.50 psia. The catalyst bed is maintained under a hydxogen partial pressure sufficient to prevent co~ing of the isomerization catalyst at the conditions maintained in the reactor. Typically, the hydrogen partial pressure will be within the range of from 100 to 250, preferably from 130 to 190, psia with the hydrogen, comprising from 10 to 90, preferably from 35 to 75 and most preferably from 45 to 65, mole percent of the reactor contents which are maintained in a gaseous state.
The feed to the reactor will contain, in addition to hydrogen and hydrocarbon reactants, e.~., normal and iso-pentane and hexane, a quantity of light hydrocarbons which are produced during the reaction and possibly as part of feed and makeup.
Becau~e the~e are ~on-~orbable, they are retained in the process at some equilibrium level and circulate with the recycle stream.
Preferably, the adsorbents in adsorbent beds 22 and 28 have effective pore diameters of substantially 5 Angstroms. The term "bed void space" for purposes of this description means any space in the bed not occupied by ~olid material except the i~tracrystalline cavities of the zeolite crystals. The pores within any binder material which may be used to form agglomerates of the zeolite crystals is considered to be bed void space.
The two adsorbent beds hown in the system of Figure 1, each cyclically undergo the two stages of:
ADS - The feed is intentionally mixed with hydrogen prior to introducing it to the feed end of the adsorber, then ad~orbed, with product a~d hydrogen being withdrawn from the effluent end of the adsor~er. The hydrogen will typically comprise from 10 to 90 mole percent of the adsorber feed, preferably, from 35 to 65; and most preferably, from 45 to 55 mole percent. Since there is hydrogen present in the feed as well as the product, there is proportionally less variation in the molecular weight of the product and therefore more efficient heat e~change. (There is no Al ~tep.~
DES - hydrogen is uced to desorb the bed in a direction countercurrent to the feed and the total effluent is sent to the isomerization reactor as feed with no internal recycle. ~There is ~o Dl step.) The presence of hydrogen in the adsorber feed improves heat e~change. ~eat e~change is better for a 6teady ~tate system than a dynamic system such as conventional TIP. The heat conte~t of a process ~tream such as the adsorption effluent i~ a function 1 31 456~

of the molecular weight of the stream, which varies from about 10 lb/lb mole at the beginning of the step to about 70 lb/lb mole at the end of the ~tep in the standard conventional TIP proce~s. Since the heat exchange system must be de6igned to operate at the minimum heat content level, a significant amount of the high heat content portion cannot be utilized effectively. In the present invention, the molecular weight of the adsorption effluent varies from about 10 to 40 lb/lb mole.
In a steady state system there would be no variation in molecular weight. ~ence, a mathematical relationship showing the approach to a steady state system can be developed as follows:

% SS = ( AMW - Deviation from AMW ) / AMW

where, A~W = average molecular weight Deviation from AMW = (Maximum molecular weight - AMW) For the standard conventional TIP the % SS is 2Q calculated as follows:

% SS = ( 40 - (70~40)) / 40 = 25%

Similarly, for the present invention the % SS
is:

% SS = ( 25 - (40-25)) / 25 = 40%

It can be seen that the 40% value for the present invention ~ystem is significantly closer to the theoretical ~teady ~tate valu~ of 100~ than the ~tandard conventional value of 25%.

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The i~vention also provides better adsorber and reactor integration which results in further advantages. Although it is clear that the number of adsorbers in the present invention is advantageously reduced from 4 to 2, it is not obvious why the adsorbent inventory i~ lower, a~d why ~he integration of ~he adsorber and catalyst is necessarily better in light of the increased flow to the catalyst section.
The adsorbent inventory of the present invention is lower than for an equivalent standard conventional TIP sy~tem because there are less normal paraffins processed through the adsorbers.
In a conventional TIP system, the Dl step (initial part of desorption) performs two function~: one is to prevent hydrogen lean desorption ~ffluent from contacting the catalyst, and the other is to recycle the D1 effluent back to the adsorbers for readsorption. The effect is to maximize the adsorber size and minimize the reactor ~ize. In the present invention, the portion of the desorption effluent that would be D1 is passed directly to the isomerization reactor where it is further isomerized and then recycled back to the adsorbers. ~ence, since the eEfluent has been further isomerized before being recycled to the adsorbers, fewer normals are ultimately recycled and the adsorbent inventory can be lowerO
Since there is hydrogen present in the adsorber feed, and since adsorber capacity is a function of the normals partial pressure in the feed, it would be expected that the adsorber capacity ~hould be ~lightly lower in the present invention (the effect i~ slight because at the normal partial pres~ure~ of the two cases, at greater than 50 psia, the ad~orbent loadi~g i8 about 90% of total capacity).

131456~3 ~ 19 --~owever, this can be compensated for by operating the adsorbers at a higher pressure in order to increase the normals partial pressure. In fact, higher pressure operation is an advantage in the S present invention but cannot conveniently be utilized in the conventional TIP system. In the conventional TIP sy~tem, an increa~e in operating pressure would result in only a ~arginal increase in adsorption capacity but would substantially increase the unwanted void space storage since it is directly proportional to the total pressure. Further, an increase in operating pressure would require a corresponding increase in operating temperature in order to prevent condensation. In the present lS invention, an increase in operating pressure i~
desirable since it increases the normals partial pressure so a~ to be comparable to the conventional TIP system; however, 6ince the hydrogen is present, the pressure increase does not have as great a detrimental effect on void storage. In addition, a corresponding temperature increase would not be required since the condensation temperature is much lower for the hydrogen-containing feed.
The catalyst volume in a conventional TIP
system is calculated a6 a function of the average feed rate in weight units. Since the initial portion of the desorption effluent, Dl effluent, i~
recycled to the adsorbers before being fed to the reactor, the average flow rate for the conventional TIP system is lower than for the present invention.
It would be e~pected that the catalyst volume required should be proportionally higher for the pre~ent invention. ~owever, a smaller than e~pected catalyst volume can be effectively used in the present invention becaul3e of the high iso~er content 1 31 456~

of the initial portion of the desorption effluent.
That is, some portion of the initial effluent can be passed through at a feed rate higher than usual since it is already partially isomerized. The remainder of the desorption effluent, which is low in isomer content, can be passed through the reactor at a more typical feed rate. The net result is that even though the reactor feed rate is significantly higher in the present invention, the increase in catalyst volume is not proportional since the invention makes it possible to utilize ~he high isomer/high flow rate portion of the desorption effluent more effectively than in conventional TIP.
The following description details an operation wherein bed 22 is undergoing adsorption, and bed 28, desorption. The reactor feed from line 24 is directed via suitable lines, manifolds, and valves (not shown) to ve~sel 23 for isomerization in catalyst bed 21 to produce a reactor effluent enriched in non-normals which is passed to adsorbent bed 22 undergoing adsorption. Each of the adsorbent beds in the ~ys~em, namely beds 22 and 28 contain a molecular sieve adsorbent in a ~uitable form such as cylindrical pellets.
At the time that reactor effluent from catalyst bed 21 ~tarts entering adsorbent bed 22, the bed contain~ re~idual purge gas from the preceding desorption 6troke. The purge ga~ is preferably hydrogen-containing because of the need to maintain at least a minimum hydrogen p~rtial pres~ure in the i~omerization reactor. This is supplied to the ad~orbent beds during desorption as a purge gas recycle strea~ via line 50. Feed through line 24 fir~t flushes bed 22 of residual hydrogen-containing purge gax. Thi~ doe6 not, however, e~d the ~tage ~ 21 I s 1 4 5 6 ~
and reactor effluent from bed 21 continue~ to flow as ad~orber feed to ad~orbent. bed 22 with the production of adsorption effluent drawn off via line 16.
As ad~orption continues, ~he normal paraffins in the feed are adsorbed by bed 22, and an adsorption effluent, i.e., hydrogen and the non-adsorbed non-noxmals, emerges from the bed through suitable ~alves and manifold arrangement ~not shown). The adsorption effluent flows ~hrough line 16, heat exchanger 18, air cooler 32 and heat exhanger 34 prior to separation into a hydrogen-containing overhead product for recycle and an isomerate product in separator 36.
The overhead gas is recovered by se2arator 36 and combined with a similar cverhead product from separator 40 which separates the reactor effluent takeoff from reactor bed 27 in line 42 into an overhead product taken of by line 44 ~nd a reactor hydrocarbon product which is withdrawn via line 14 as described above. The combined stream formed from lines 38 and 44 is fed via line 46 to recycle compressor 48 for return via line 50 to the vessel having the ad~orbent bed undergoing desorption. In this case appropriate valves direct flow to to heat e~changer 52 and heater 54 prior to entering vessel 29, containing bed 28 for desorption.
The effluent from bed 28, pafises directly to reactor bed 27. During the de~orption stage, void space adsorber feed is first purged, followed by desorption of selectively-adsorbed normal paraffins from the zeolitic molecular sieve. The deso~ption effluent rom bed 28 will, throughout the ~tage, compri~e hydrogen and hydrocarbons. The desorption effluent pa~ses directly to i~omerization reactor bed 27 as reactor feed.

- 2~ - l 3 1 4 5 6 ~
The foregoing description is for a single ~tage of a total two stage cycle for the system. For the next stage, appropriate valves are operated 60 that vessel 29, containing cataly6t bed 27 and adsorbent bed 28 receives feed to the reactor bed which passes reactor effluent to bed 28 fox adsorption, and bed 22 in vessel 23 begins desorption with the desorption effluent passing directly to catalyst bed 21. At the end of two ~tages, both adsorbent beds have gone through the stages of adsorption and desorption.
The isomerization process will result in some hydrogen losses from the purge ga~ due to hydrogenation of starting materials and cracked residues. ~ydrogen will also be lost due to ~olubility in product, and possibly a vent from line 50 (not shown) which can be controlled by suitable valve means. These losses require the addition of makeup hydrog~n. Makeup hydrogen can ~e supplied in i~pure form, e.g., via line 62, typically as an offgas from catalytic reforming or steam reforming of methane. These hydrogen 60urces are suitably pure for isomerization processes which typically have a vent from the recycle stream. Refinery streams of lesser purity may also be satisfactory.
The desorption effluent in line 58 will comprise desorbed normal hydrocarbons, e.g., n-pentane a~d n-hexane, and hydrogen and light hydrocarbon and other impurities which comprise the purge gas u~ed for desorption. This effluent is reactor feed and is pa~sed to isomerization reactor 60.
A portion (up to 100%) of the reactor effluent from bed 27 i~ split off from line 64 via line 26 as a hot hydrogen-containing stream (i.e., hot re~ycle or hot-hydrogen recycle)- for feed to the ves~el 23, fir~t to reactor bed 21 and then to adsorbent bed 22 undergoing adsorption. Preferably! 31t ~éast 10% and most preferably from 25 to 75%, on a weight basis, will be recycled to the first reactor in this manner. The remainder of the reactor effluent is passed to heat exchanger 66 where its sensible heat is used to heat the combined hydrocarbon stream in line 12 which includes fresh feed. From the heat exchanger 66, reactor effluent in line 42 is further cooled by air cooler 68 and water cooler 70 prior to separation as discussed above in separator ~0.
The advantages of this invention can be appreciated in a number of ways. An important concept in all of the schemes is that some or all of the hydrogen used in the desorption step is fed to an adsorber bed undergoing adsorption as hot recycle from either the reactor effluent or the desorption effluent, depending on the particular configuration used. The term, hot recycle or hot-hydrogen recycle, means hydrogen-rich gas which has been previously heated for some purpose and is utilized a second time to improve the thermal efficiency of the process. It should also be noted that the invention also applies to the partial recycle process as descri~ed in the U.S. Patent No. 4,709,116.
As discussed above this hot recycle does not involve a component separation; it i~ simply a stream or stream division. One of its major functions is to provide the necessary hydrogen in the adsorption step to prevent catalyst coking when the desorption effluent is passed to the reactor. In addition to providing the necessary hydrogen, the hot recycle carries with it a substantial portion of the reactor effluent that must ultimately be recycled to the adsorbers. This mode of operation t.
S', ~

- 24 - 13145h~
reduces the process cooling and heating requirements that would otherwise be required. It is important to note tha~ the amount of hot recycle MU6t be balanced between maximizing the amount of hydrocarbon reactor effluent recycled and minimizing the amount of hydrogen recycled. (Maximizing the hydrocarbon recycle reduces energy consumption and minimizing hydrogen recycle increases the adsorption capacity.) This hot recycle i~ different than the Dl recycle used in the conventional TIP. It is unde~irable to have hydrogen present in the Dl effluent whereas in the present i~vention its primary purpose is to provide hydrogen. In addition, the hot recycle in the embodiments of Figure~ 1, 2 and 4 of the present i~vention originates from the reactor and not from the adsorber~ as in the conventional TIP. This step is likewise different from the reactor effluent recycle u~ed in the noted partial recycle process and conventional TIP since the purpo~e of those steps is to recycle a hydrogen-free adsorber feed.
Conside:ring the reactor-lead configuration, at least two more variations are possible. In certain cases it may be more beneficial to maintain the flow through the catalyst (beds C1 and C2) in one direction ra~her than alternating between both directions a6 de~cribed in the configuration of Figure 1. Figure 2 illustrates one way that this can be accomplished with a simple v~lve manifold, which alternates the flow through beds Cl a~d C2 but maintains flow in the same direction through adsorbent bed~ ADS and DES. Other method~ ~uch as a 8ide draw port mlght be feasible when a compound bed 3s a8 in Figure 1 i8 used.

- 25 - 13145~
A third variation of the reactor lead confi~uration is to combine the two reactor s~ctions (Cl and C2) in a ~ingle ve~el. This scheme might be used if it would be impractical, for some rea~on, to utilize the compound bed approach. Figure 3 shows that there is one feed pa~s ~hrough the larger reactor, followed by adsorption (ADS~ then desorption (DES) with hydrogen. In this case, the hot hydrogen recycle is provided by the desorption effluent and not the reactor effluent.
Fi~ure 4 shows an adsorber-lead configuration which achieves the advantages of the inYention and is characterized by a two stage adsorber cycle and the use of a hot hydrogen recycle which employs reactor effluent, without substantial cooling or separation of components, as a portion of adsorber feed. Fresh feed in line 110 is combined in line 112 with reactor hydrocarbon product from line 114.
This combined hydrocarbon ~tream i6 heated by indirect heat e~change with adsorption effluent, carried by line 116 in heat exchanger 118 from which it i~ pas~ed to furnace 120 where it is heated sufficiently for passage to the adsorption section 122.
~5 The ads;orber feed stream in line 124 is formed by combining the hot hydrocarbon ~tream from furnace 120 with hot reactor effluent from line 126 which contains hydrogen and hydrocarbon component~.
Suitable control valves and controllers (not shown) direct the adsorber feed ~tream directed to the appropriate bed in the adsorption section (~hown here a~ bed 122).
The adsorber feed, containing normal and non-normal hydrocarbons in the vapor state, is passed at ~uperat~ospheric pressure periodically in - 26 - l 3 1 45~g 6equence through each of a plurality of fi~ed adsorber beds, e.g., two .s 6hown in Figure 4. It is of course possible to employ a greater number of beds if desired; however, it is an a~vantage of the invention that only two are required. In a two bed system, each of the beds cyclically undergoe~ the t~o stage~ (ADS and DES) described with reference to Figure 1.
Referring again to the adsorption ~ection in particular, the following description details an operation wherein bed 122 is undergoing ad~orption, and bed 128, desorption. A portion of the adsorber feed from line 124 is directed via suitable lines, manifolds, and valve~ to adsorbent bed 122 undergoing adsorption.
Flow of the adsorber feed through line 124 first 1ushes bed 122 of residual hydrogen-containing purge gas, and adsorber feed continues to flow to adsorbent bed 122 with the production of adsorption effluent drawn off via line 116.
As adsorption continues, the normal paraffin~
in the feed are adsorbed by bed 1~2, and an adsorption effluent, i.e., hydrogen and the non-adsor~ed non-nor~als, e~erges rom the bed 2S through suitable valves and manifold arrangement (not shown). The adsorption effluent flow~ through line 116, heat exchanger 118, air cooler 132 and heat exhanger 134 priox to ~eparation into a hydrogen containing overhead product for recycle and an i~omerate product in ~eparator 136.
The overhead gas can be recovered by separator 136 is combined with a similar overhead product from separator 140 which separates the reactor effluent takeoff in line 142 into an overhead product recovered in li~e 144 and a reactor hydrocarbon ~roduct ~hich i~ withdrawn via line 114 as described - 27 - 1 3 1 456~
above. The combined stream formed from lines 138 and ~44 is fed via line 146 to recycle compressor 148 for return to the adsorber section via line 150 for desorption of bed 128.
From compressor 148, the hydrogen-containing pur~e gas stream i~ pas~ed via line 150 to heat exchan~er 152 and heater 154, wherein it is heated and then passed to bed 128 which is undergoing desorption.
The effluent from bed 128, passes through suitable valves and manifold (not shown) to reactor 160 via line 158. During the desorption stage, void space ad~orber feed is first purged, followed by desorption of selectively-adsorbed normal paxaffins from the zeolitic molecular sieve. The desorption effluent from bed 128 will, throughout the stage, compri e hydrogen and hydrocarbonc. The desorption effluent is sent to isomerization reactor 160 via line 158 as reactor feed.
The foregoing description is for a single adsorber stage time period of a total two stage cycle for the system. For the next adsor~es stage time period, appropriate valves are operated so that bed 128 begins adsorption and bed 122 begin~
desorption. Similarly, a ~ew cycle begins after each adsorber stage time period; and, at the end of the two cycle time period~, both beds have gone through tbe stages of adsorption and desorption.
Makeup hydrogen, a~ needed, can be supplied, e.g., via line 162. The desorption effluent in line 158 will comprise desorbed normal hydrocarbons, e . q ., n-pentane and ~-hexane, and hydxo~en a~d light hydrocarbon and othe~ impurities which co~prise the purge gas uEed for de~orption. This e~flue~t is reactor eed and i~ passed to isomerization reactor 160.

~ 28 - 131456~
The effluent from the reactor 160 flows via line 164. A portion of the reactor effluent is split off of line 164 via line 126 as a hot hydrogen-recycle for feed to the adsorbent bed undergoi~g adsorption. Up to lOG% of the reactor effluent can be recycled in this manner to the adsorbent bed undergoing adsorption. Preferably, at least loX, and most preferably from 25 to 75% will be recycled. The remainder of the reactor effluent is then passed to heat exchanger 166 where its sensible heat is used to heat the combined hydrocarbon stream in line 112 which includes fresh feed. From the heat e~changer 166, reactor effluent in line 142 i~ fuxther cooled by air cooler 168 and water cooler 170 prior to separation as discussed above in ~eparator 140.
It is an advanta~e of the invention that existing TIP equipment can be modified to greatly increase feed throughput and final product production while still providing octa~e values sufficient for use as a ga601ine blending stock.
The followi~g example will help to illustlate and explain the invention, but is not meant to be li~iting in any regard. Unless otherwise indicated, all parts and percentage~ are on a molar basis.

= LE 1 This example illustrates the operation of a proce~s essentially as shown in Figure 4. The process design for this e~a~ple i6 based on a charge rate of 40Q0 BPSD of a predominantly C5/C6 feedstock a~ described in the Table below, ~hich also de~cribes principal process ~tream~.

ll o~ C~ o o ~ X
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1 31 456~

A starting point is selected at the discharge stream from the recyle hydrogen compressor 148.
This stream is preheated in e~changer 152 against the reactor effluent (Stream No. 142). The hydrogen recycle outlet temperature from 152 i8 ~aintained at 358F, con~rolling the hydrogen recy~le bypass around exchanger 152. The recycle gas is then heated to 510F in furnace 154. From 154, the hot hydrogen pa~ses downflow through one adsorber (in this case 128), and strips the adsorbed normals from the molecular ~ieve adsorbent. ~ot desorption effluent (Stream No. 158) is then sent to ~he isomerization reactor 160. The composition of this 6tream is ~hown in the Table.
In the isomerization reactor, the normal paraffins are partially converted to isoparaffins.
An improved distribution of isohexaGes is also achieved by increa~ing the concentration of the more highly branc~ed dimethylbutanes. Some ring opening of naphtenes, hydrogenation of aromatics, and crackinq of the hydrocarbons to butane~ and lighter also occur. The reactor efflue~t is split, with one ~tream ~Stream No. 126) combining with the adsorber feed, and the other ~tream of reactor effluent takeoff (Stream No. 142) being cooled by heat exchange again~t the cold adsorber feed in 166 and against ~h,e recycle hydro~en stream 152. The reactor effluent takeoff is further cooled to 140F
in air cooler 168 and to 100F in water cooler 170.
It is then sent to the reactor effluent separator 140 for ~eparation of condensed hydrocarbons. The vapor from 140 is routed to the inlet of co~pre~cor 148 where it is compre6sed from 220 to 301 psig.
The condensate from 140 i~ pumped via pu~p 141 through line 114 and i8 ~ixed with the fxe~h feed 1 3 1 456~3 stream (Stream No. 110) to form combined hydrocarbon stream in line 112.
~ he combined hydrocarbon stream 112 is heated against the adsorption effluent (Stream No. 116) in e~changer lla and against the reactor effluent takeoff in exchanger 166 to the furnace at an inlet temperature of 395F. In Furnace 120 the co~bined hydrocarbon stream is heated to 510F to provide the required temperature of 500F at the adsorber inlet.
This feed i5 then combined with hot recycle in line 126 and to form the total adsorber feed lStream No.
124) pa~sed upflow through one of two adsorbers tin this case, 122), depending on the position of the cycle, where the normals are adsorbed into the micropores of the ~olecular sieve adsorbent.
Non-normals and a small quantity of displaced hydrogen gas pass throuqh the bed and form the adsorption effluent. The adcorption effluent (Stream No. 116~ is cooled against the adsorber feed in heat exchanger 118. It is then air cooled in 132 down to 140F, and water cooled in 134 down to the temperature of the adsorption effluent receiver 166.
The vapor overhead from separator 136 (Stream No.
138) is co~bined with the vapor overhead from separator 140 and i~ routed to the inlet to compressor 148. The condensed hydrocarbons from separator 136 form the unstabilized isomerate product. The unstabilized isomerate (Stream No.
137) is sent to stabilization facilities. ~ydrogen make-up (Stream No. 162) is ~upplied as neces~ary to separator 136.
The two adsorbers (122 and 128) containing molecular sieve ad~orbent are bo~h used to separate the normal paraffins fro~ the non-nor~als in the feed~tock. The adsoxbers are automatically cycled 1 3 1 456 ~

through ~equential steps, by a controller which operates the remote operated valves (ROVs) in the adsorber manifolds (not shown ) . At any given mo~ent either the two adsorber~ are both on the adsorption step or one adsorber is on the adsorption step and one ad~orber is on the desorption ~tep. Two cycle timers are ~et to give the desired step times. The design step times are as follows:

Adsorption Step 110 seconds Desorption Step 90 ~econds Valve Changing 40 seconds Total Cycle Time 240 seconds The adsorber feed 124 enters the adsorber that i6 on the adsorption step. The other adsorber is on the desorption ~tep. As the desorption step finishes, the desorption feed is totally bypassed around the adsorber~ to the inlet to the isomerization reactor 160. The ad~orber that has just finished the desorption step now begins the adsorption step, while the other adsorber finishes the adsorption step. Thus, for a short period of time (20 sleconds during valve changes in the four-minute cycle), the two adsorbers are both on the ad~orption ~tep.
At the beginning of the adsorption ~tep, the adsorber feed and effluent valves are opening on one bed and clo~ing on the other bed. The adsorber feed, at approximately 500F and 256 psia, is fed to the molecular sieve adsorbent bed, which was previously purged with hydrogen. The molec~lar ~ieve bed contains synthetic zeolite cry~tals having interconnecting pore~ of a preci~ely uniform size.
The pore 3ize of ~olecular ~ieve cry~tals i6 tailored to accept only ~olecules with a mini~um ~ 33 ~ 563 effective diameter of up to five angstroms. Since the effective molecular diameters of the non-normals in the feed are too large to pass through the pore~
into the main ad~orption site~, only the normals are adsorbed on the bed. The non-normals remain in the void space6 of the bed and displace the purge gas (retained from the previous desorption step) out through the top of the adsorber into the adsorption ~anifold.
As the adsorption ~tep continues, the non-normals/purge gas interface reaches the top of the adsorber. The composition of the adsorption effluent changes from being mo6tly purge gas to being mo~tly non~normal6 and hydrogen. The adsorber feed continues to pa6s upflow through the adsorber and the normals continue to be adsorbed on the bed.
The quantity of normals adsorbed per unit of molecular ~ieve (i.e., the loading ) approaches an eguilibrium level determined by the partial pres~-ure and molecular weiqht of the normals and by ~he adsorption temperature. Thi~ relationshlp is illustrated by plotting the isotherms of loading versus partial pressure. The non-nor~als and hydrogen in the feed, together with some purge gas and a ~mall guantity of normals, pass out of the top of the adsorber into the adsorption effluent manifold. The normals adsorbing in the bed displace a`bout 15 percent of a vessel void volume of purge gas from the micropore~. This gas gradually mixes with the non-normal and pas~es into the ~dsorption effluent. During the desorption ~teps, the purge gas e~tabli~hes a re~idual loading of normals on the top portion of the ad~orber which i~ in eguilibrium with the normal~ conce~tration i~ ~he vapor. Since the ff~ eguilibriu~ i~ reached duri~g the ~d80rptio~ 3tep, the minimum normal~ concentxation 1 31 456~

in the adsorber effluent is the same as the concentration in the purge gas. A~ the normal~ are adsorbed from the incoming adsorber feed, the liberated heat of adsorption create6 a temperature S front which travel~ up the bed coincident with the adsorption mass transfer front. The adsorption step is terminated before the mass transfer front reaches the top of the bed (approximately 90 percent bed utilization), thereby preventing a large concentration of normals from breaking into the adsorption effluent a~d reducing the isomerate purity.
During the beginning of the desorption step, the non-ad60rbed C4+ hydrocarbons, retained in the bed after completion of the ad~orption ~tep, are countercurrently difiplaced with hydrogen purge gas.
The displaced hydrocarbons, along with some purge gas, pass out of the botto~ of the bed to the Isomerization Reactor.
The purge gas then desorbs normals from the adsorbent by reducing the partial pressure of the normals in the vapor phase, thereby shifting the eguilibrium loading to a lower value. Normal pentane and he~ane concentrations in the purge gas are maintained at lvw levels to insure efficient desorption of the adsorbed normals. As the desorption step proceeds, the normals loading on the bed declines and the rate at which ~ormals leave the bed decreases. The desorption step is ter~inated before all the normals have been removed from the bed. The amo~nt removed durinq each cycle is based on an economic balance between the adsorber bed inve~tment and the purge gas recirculating costs.
Following the completion of ~he desorption ~tep, the desorption feed and efflue~t valves clo~e and a desorption feed bypa~s valve opens. Tbi8 bed then l Jl 456~

returns to the adsorption ~tep and continues the sequence of step6 just de~cribed.
In the isomerization reactor, normal paraffins are partially converted to isoparaffins. A higher octane distribution of isohexane is also achieved by increasing the relative concentration of dimethylbutanes. Some ring opening of naphthenes, hydrogenation of aromatics and feed cracking to butane~ and lighter also occur. The performance of the reactor (i.e., conversion and yield) is dependent on space velocity, feed composition, operating temperature and hydrogen partial pressure.
The above description is for the purpose of teaching the person of ordinary skill in the art how to practice the present invention and is ~ot intended to detail all of tho~e obvious modifications and variations of it which will become apparent to ~he skilled worker upon reading the description. It is intended, however, that all such ~odifications and variations be included within the scope of the present invention which is defined by the following claims.

Claims (46)

1. A process for increasing the non-normal content of a hydrocarbon feed containing non-normal hydrocarbons and normal hydrocarbons including normal hexane and normal pentane by a combined isomerization-adsorption process in either the adsorber-lead or reactor-lead configuration, comprising:
(a) passing an adsorber feed stream, comprising hydrogen and hydrocarbons, to an adsorber bed to adsorb normal hydrocarbons from said feed and to pass non-normal hydrocarbons and hydrogen out of the adsorber bed as adsorption effluent;
(b) passing hydrogen-containing purge gas through said adsorber bed containing adsorbed normal hydrocarbons to produce a desorption effluent comprising hydrogen and normal hydrocarbons; and (c) passing at least a portion of said desorption effluent to an isomerization reactor to produce a reactor effluent comprising hydrogen and a reactor hydrocarbon component comprising non-normal and normal hydrocarbons.

2. A process according to claim 1 wherein said adsorber feed stream is formed by admixing a hot hydrocarbon-containing process stream with a hydrocarbon-containing process stream without any substantial cooling of said hydrogen-containing stream prior to admixing.

3. A process according to claim 1 wherein said adsorber feed comprises from 10 to 90 mole percent hydrogen.

4. A process according to claim 3 wherein said adsorber feed comprises from 30 to 65 mole percent hydrogen.

5. A process according to claim 4 wherein said adsorber feed comprises from 45 to 55 mole percent hydrogen.

6. A process according to claim 1 wherein said adsorber feed stream comprises hydrocarbon feed and recycle, comprising hydrogen and hydrocarbons, from a reactor bed.

7. A process according to claim 1 wherein said adsorber feed stream comprises reactor effluent.

8. A process according to claim 7 wherein said adsorber feed stream consists of reactor effluent.

9. A process according to claim 8 wherein said adsorber feed comprises from 30 to 65 mole percent hydrogen.

10. A process according to claim 9 wherein the process is performed in two combined beds, each containing a catalyst section and an adsorption section.

11. A process for upgrading the octane of a hydrocarbon feed containing non-normal hydrocarbon compounds and normal pentane and hexane by a combined isomerization-adsorption process in the adsorber-lead configuration, comprising:
(a) passing an adsorber feed stream comprising hydrogen and said hydrocarbon feed to an adsorber bed to adsorb normal hydrocarbons from said feed and pass non-normal hydrocarbons out of the adsorber bed as adsorption effluent;
(b) passing hydrogen-containing purge gas through said adsorber bed containing adsorbed normal hydrocarbons to produce a desorption effluent comprising purge gas and normal hydrocarbons; and (c) passing said desorption effluent through an isomerization reactor to produce a reactor effluent comprising purge gas and reactor hydrocarbon product comprising non-normal and normal hydrocarbons.

12. A process according to claim 11 wherein the adsorber feed comprises from 10 to 90 mole percent hydrogen.

13. A process according to claim 12 wherein the adsorber feed comprises from 30 to 65 mole percent hydrogen.

14. A process according to claim 13 wherein the adsorber feed comprises from 45 to 55 mole percent hydrogen.

15. A process according to claim 11 wherein a portion of said reactor effluent is combined with a hydrocarbon stream comprising said hydrocarbon feed to form said adsorber feed stream.

16. A process according to claim 15 wherein said portion of said reactor effluent is combined with said hydrocarbon stream at substantially the temperature taken from the reactor without cooling or separation of components.

17. A process for upgrading the octane of a hydrocarbon feed containing non-normal hydrocarbons and normal pentane and hexane by a combined isomerization-adsorption process in the reactor-lead configuration, comprising:
(a) passing a reactor feed comprising said feed stream and a desorption effluent, as hereinafter delineated, through an isomerization reactor to convert at least a portion of the normal hydrocarbons in said reactor feed to non-normal hydrocarbons which are withdrawn from the reactor in a reactor effluent;
(b) passing at least a portion of said reactor effluent, containing hydrogen and hydrocarbons, without substantial cooling as adsorber feed to an adsorber bed to adsorb normal hydrocarbons and pass hydrogen and non-normal hydrocarbons out as adsorption effluent;
(c) passing a hydrogen-containing purge gas through said adsorber bed containing adsorbed normal hydrocarbons to produce said desorption effluent which comprises hydrogen and normal hydrocarbons;
and (d) passing at least a portion of said desorption effluent to said isomerization reactor.

18. A process according to claim 17 wherein the adsorber feed comprises from 10 to 90 mole percent hydrogen.

19. A process according to claim 18 wherein the adsorber feed comprises from 30 to 65 mole percent hydrogen.

20. A process according to claim 19 wherein the adsorber feed comprises from 45 to 55 mole percent hydrogen.

21. A process according to claim 17 wherein at least portion of said desorption effluent is combined with said hydrocarbon feed stream and passed to said reactor without separating the hydrogen and normal hydrocarbon components.

22. A process for upgrading the octane of a hydrocarbon feed containing non-normal hydrocarbons and pentane and hexane by a combined isomerization-adsorption process in the reactor-lead configuration, comprising:
(a) passing a reactor feed, comprising hydrocarbon feed and hydrogen, through a first isomerization catalyst bed to convert at least a portion of the normal hydrocarbons in said reactor feed to non-normal hydrocarbons which are passed from said bed as first reactor effluent;
(b) passing said first reactor effluent through a adsorber bed to adsorb normal hydrocarbons and pass non-normal hydrocarbons out as adsorption effluent;
(c) passing hydrogen-containing purge gas through said adsorber bed containing adsorbed normal hydrocarbons to produce a desorption effluent comprising hydrogen and normal hydrocarbons; and (d) passing said desorption effluent through a second isomerization catalyst bed to convert at least a portion of the normal hydrocarbons in said desorption effluent to non-normal hydrocarbons which are passed from said second catalyst bed as second reactor effluent.

23. A process according to claim 22 wherein at least a portion of said second reactor effluent is combined with said hydrocarbon feed prior to substantial cooling.

24. A process according to claim 22 wherein a complete cycle comprises two passes through each catalyst bed, with the flow reversed after each path.

25. A process according to claim 24 wherein catalyst bed and an adsorber bed are included within a single vessel.

26. A process according to claim 22 wherein a complete cycle comprises two passes through each catalyst bed, with the flow being in the same direction for each pass.

27. A process according to claim 22 wherein hydrogen comprises from 10 to 90 mole percent of the first reactor effluent.

28. A process according to claim 27 wherein hydrogen comprises from 30 to 65 mole percent of the first reactor effluent.

29. A process according to claim 28 wherein hydrogen comprises from 45 to 50 mole percent of the first reactor effluent.

30. A process according to claim 29 wherein a complete cycle comprises two passes through each catalyst bed, with the flow reversed after each path.

31. A process according to claim 30 wherein catalyst bed and an adsorber bed are included within a single vessel.

32. An apparatus for increasing the non-normal content of a hydrocarbon feed containing non-normal hydrocarbons and normal hydrocarbons including normal hexane and normal pentane by a combined isomerization-adsorption process in either the adsorber-lead or reactor-lead configuration, comprising:
(a) an adsorber bed capable of selectively adsorbing normal hexane and normal pentane;
(b) means for passing an adsorber feed stream, comprising hydrogen and hydrocarbons, to the adsorber bed to adsorb normal hydrocarbons from said feed and to pass non-normal hydrocarbons and hydrogen out of the adsorber bed as adsorption effluent;
(c) means for passing hydrogen-containing purge gas through said adsorber bed containing adsorbed normal hydrocarbons to produce a desorption effluent comprising hydrogen and normal hydrocarbons;
(d) an isomerization reactor containing a catalyst capable of isomerizing normal hexane and normal pentane;
and (e) means for passing at least a portion of said desorption effluent to an isomerization reactor to produce a reactor effluent comprising hydrogen and a reactor hydrocarbon component comprising non-normal and normal hydrocarbons.

33. An apparatus according to claim 32 wherein means are provided for forming said adsorber feed stream by admixing a hot hydrogen-containing process stream with a hydrocarbon-containing process stream without any substantial cooling of said hydrogen-containing stream prior to admixing.

34. An apparatus according to claim 33 wherein said adsorber feed comprises from 10 to 90 mole percent hydrogen.

35. An apparatus according to claim 34 wherein said adsorber feed comprises from 30 to 65 mole percent hydrogen.

36. An apparatus according to claim 35 wherein said adsorber feed comprises from 45 to 55 mole percent hydrogen.

37. An apparatus according to claim 32 wherein said adsorber feed stream comprises hydrocarbon feed and recycle, comprising hydrogen and hydrocarbons, from a reactor bed.

38. An apparatus according to claim 32 wherein said adsorber feed stream comprises reactor effluent.

39. An apparatus according to claim 38 wherein said adsorber feed stream consists of reactor effluent.

40. An apparatus according to claim 39 wherein said adsorber feed comprises from 30 to 65 mole percent hydrogen.

41. An apparatus according to claim 40 including two combined beds, each containing a catalyst section and an adsorption section.

42. An apparatus for upgrading the octane of a hydrocarbon feed containing non-normal hydrocarbon compounds and normal pentane and hexane by a combined isomerization-adsorption process in the adsorber-lead configuration, comprising:
(a) an adsorber bed capable of selectively adsorbing normal hexane and normal pentane;
(b) means for passing an adsorber feed stream comprising hydrogen and said hydrocarbon feed to an adsorber bed to adsorb normal hydrocarbons from said feed and pass non-normal hydrocarbons out of the adsorber bed as adsorption effluent;
(c) means for passing hydrogen-containing purge gas through said adsorber bed containing adsorbed normal hydrocarbons to produce a desorption effluent comprising purge gas and normal hydrocarbons;
(d) an isomerization reactor containing a catalyst capable of isomerizing normal hexane and normal pentane; and (e) means for passing said desorption effluent through an isomerization reactor to produce a reactor effluent comprising purge gas and reactor hydrocarbon product comprising non-normal and normal hydrocarbons.

43. A process according to claim 42 wherein means are provided for combining a portion of said reactor effluent, at substantially the temperature taken from the reactor without cooling or separation of components, with a hydrocarbon stream comprising said hydrocarbon feed to form said adsorber feed stream.

44. An apparatus for upgrading the octane of a hydrocarbon feed containing non-normal hydrocarbons and normal pentane and hexane by a combined isomerization-adsorption process in the reactor-lead configuration, comprising:
(a) an isomerization reactor containing a catalyst capable of isomerizing normal hexane and normal pentane;
(b) means for passing a reactor feed comprising said feed stream and a desorption effluent, as hereinafter delineated, through an isomerization reactor to convert at least a portion of the normal hydrocarbons in said reactor feed to non-normal hydrocarbons which are withdrawn from the reactor in a reactor effluent;
(c) means for passing at least a portion of said reactor effluent, containing hydrogen and hydrocarbons, without substantial cooling, as adsorber feed to an adsorber bed to adsorb normal hydrocarbons and pass hydrogen and non-normal hydrocarbons out as adsorption effluent;
(d) an adsorber bed capable of selectively adsorbing normal hexane and normal pentane;
(e) means for passing a hydrogen-containing purge gas through said adsorber bed containing adsorbed normal hydrocarbons to produce said desorption effluent which comprises hydrogen and normal hydrocarbons; and (f) means for passing at least a portion of said desorption effluent to said isomerization reactor.

45. An apparatus according to claim 43, which further includes means for combining at least a portion of said desorption effluent with said hydrocarbon feed stream and passing the combined stream to said reactor without separating the hydrogen and hydrocarbon components.

46. An apparatus for upgrading the octane of a hydrocarbon feed containing non-normal hydrocarbons and pentane and hexane, comprising:
(a) a first catalyst bed containing a catalyst capable of isomerizing normal pentane and normal hexane;
(b) means for passing a reactor feed, comprising hydrocarbon feed and hydrogen, through a first isomerization catalyst bed to convert at least a portion of the normal hydrocarbons in said reactor feed to non-normal hydrocarbons which are passed from said bed as first reactor effluent;
(c) an adsorber bed comprising an adsorbent capable of selectively adsorbing normal pentane and normal hexane;
(d) means for passing said first reactor effluent through a adsorber bed to adsorb normal hydrocarbons and pass non-normal hydrocarbons out as adsorption effluent;
(e) means for passing hydrogen-containing purge gas through said adsorber bed containing adsorbed normal hydrocarbons to produce a desorption effluent comprising hydrogen and normal hydrocarbons;
(f) a second catalyst bed; and (g) means for passing said desorption effluent through a second isomerization catalyst bed to convert at least a portion of the normal hydrocarbons in said desorption effluent to non-normal hydrocarbons which are passed from said second catalyst bed as second reactor effluent.