EP0295638B1 - Procédé et appareil d'isomérisation - Google Patents

Procédé et appareil d'isomérisation Download PDF

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EP0295638B1
EP0295638B1 EP88109494A EP88109494A EP0295638B1 EP 0295638 B1 EP0295638 B1 EP 0295638B1 EP 88109494 A EP88109494 A EP 88109494A EP 88109494 A EP88109494 A EP 88109494A EP 0295638 B1 EP0295638 B1 EP 0295638B1
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Prior art keywords
hydrogen
reactor
stream
adsorber
feed
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EP0295638A1 (fr
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Thomas Charles Holcome
Thomas Charles Sager
Warren Karl Volles
Andrew Stephen Zarchy
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Honeywell UOP LLC
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UOP LLC
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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G65/00—Treatment of hydrocarbon oils by two or more hydrotreatment processes only
    • C10G65/02—Treatment of hydrocarbon oils by two or more hydrotreatment processes only plural serial stages only
    • C10G65/04—Treatment of hydrocarbon oils by two or more hydrotreatment processes only plural serial stages only including only refining steps
    • C10G65/043—Treatment of hydrocarbon oils by two or more hydrotreatment processes only plural serial stages only including only refining steps at least one step being a change in the structural skeleton

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  • 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 non-normals in a product stream.
  • the known technology for improving the octane rating of certain hydrocarbon fractions, especially mixed feedstocks containing normal and iso pentanes and hexanes typically involves isomerizing normal hydrocarbons in a feed stream prior to or following an adsorption-desorption cycle which isolates non-normals.
  • 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 and isothermal conditions.
  • the reactor effluent 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 is passed to the adsorbers in two adsorption stages: the first, displacing void space 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.
  • the feed is first passed to the adsorbers which immediately remove non-normals, again in a four-stage adsorption procedure.
  • the normals from the second desorption stage are then mixed with sufficient hydrogen to protect the isomerization reactor and are then 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.
  • 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 Kg/Kg (1b/1b) mole at the beginning of adsorption to about 70 Kg/Kg (1b/1b) mole at the end.
  • the heat exchange system must be adequate to operate at minimum heat content (i.e., lowest molecular weight), it has been necessary to exaggerate the size 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 adsorbers operate essentially as a batch procedure.
  • 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.
  • the art has produced a number of integrated isomerization-adsorption systems for isomerizing a feed stream containing normal and non-normal hydrocarbons and producing a product stream which is useful as a gasoline blending feedstock.
  • TIP total isomerization processes
  • reactor-lead systems where the fresh feed and any recycle is fed to the isomerization reactor prior to separation of non-normals
  • adsorber-lead systems where the fresh feed is fed to the adsorbers prior to isomerization.
  • both of these schemes typically employ three or four adsorber beds which are cycled through at least one adsorption stage and two desorption stages.
  • 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 passed through the adsorbers to remove non-normal hydrocarbons so that the feed to the reactor is essentially normal hydrocarbons. This requires heat exchange equipment of significant size to handle streams of widely varying molecular weight and large energy inputs to cool the entire reactor effluent to separate the hydrocarbon and hydrogen portion, and then to reheat both.
  • the reactor-lead process is similar in this regard.
  • the effluent from the isomerization reactor is condensed to separate a hydrocarbon fraction.
  • This fraction is then reheated and passed as feed in the vapor state and at superatmospheric pressure periodically in sequence through each of at least four fixed beds of a system containing a zeolitic molecular sieve asorbent having effective pore diameters of substantially 0.5 nm (5 Angstroms), each of said beds cyclically undergoing the stages of:
  • A-1 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 intermixing thereof with non-adsorbed feedstock fraction;
  • A-2 adsorption wherein the feedstock is cocurrently passed through said bed and the normal constituents of the feedstock are selectively adsorbed into the internal cavities of the crystalline zeolitic adsorbent and the nonadsorbed constituents of the feedstock are removed from the bed as an effluent having a greatly reduced content of normal feedstock constituents;
  • D-1 void space purging wherein the bed, which is loaded with normals adsorbate to the extent that 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 normals and non-normals in essentially feedstock proportions, is purged countercurrently, with respect to the direction of A-2 adsorption, by passing through the bed a stream of a non-sorbable purge gas in sufficient quantity to remove said void space feedstock vapors 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 gas countercurrently with respect to A-2 adsorption through the bed until the major proportion of adsorbed normals has been desorbed and the bed void space vapors consist principally of non-sorbable purge gas.
  • the present invention is based upon the discovery that considerable improvements can be achieved in terms of reduced adsorbent inventories, reduced adsorption section complexity, and improved energy efficiency, for an integrated isomerization-adsorption process for upgrading light naptha feeds by implementing 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 adorption technologies in both the adsorber-lead and reactor-lead modes.
  • the process increases 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 comprising: a) passing an adsorber feed stream comprising hydrogen and hydrocarbons to an adsorber bed containing adsorbent and having bed void space under conditions effective to adsorb normal hydrocarbons from said feed and produce an adsorption effluent stream comprising non-normal hydrocarbons and hydrogen, wherein the bed void space contains a mixture of hydrogen and unadsorbed adsorber feed comprising non-normal hydrocarbons; b) passing a hydrogen-rich purge gas through said adsorber bed to produce a desorption effluent stream comprising normal hydrocarbons and said mixture of hydrogen and unadsorbed adsorber feed comprising non-normal hydrocarbons; and c) passing a reactor feed stream comprising at least a portion of said desorption effluent stream to an isomer
  • the adsorber feed stream comprises reactor effluent, preferably prior to any significant cooling or component separation.
  • This supplies hydrogen to the adsorber bed and conserves the heat value of the hydrogen and hydrocarbon components.
  • this embodiment enables recycle of the majority of the hydrocarbon based on weight in a given cycle, without cooling to any significant degree.
  • 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 catalyst and the molecular sieve adsorbent in the same vessel.
  • the adsorber feed stream comprises fresh hydrocarbon 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.
  • the fresh feed contains normal and non-normal hydrocarbons. It is composed principally of 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 prefix notations “iso” and “i” are intended to be generic designations of all branched chain and cyclic (i.e., non-normal) forms of the indicated compound.
  • composition is typical of a feedstock suitable for processing according to the invention:
  • Suitable feedstocks 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 advantageously less than about 4 mole percent in the feedstock. Aromatic and cycloparaffin molecules have a relatively high octane number. Accordingly, the preferred feedstocks are those high in aromatic and cycloparaffinic hydrocarbons, 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 least 60, and more typically at least 75, mole percent of the feedstock, with at least 25, and preferably at least 35, mole percent of the feedstock being hydrocarbons selected from the group of iso-pentane, iso-hexane and combinations of these.
  • the feedstock will comprise no more than 40, and more preferably no more than 30 mole percent of a combination of n-pentane and n-hexane.
  • the isomerization reactor sections (21 and 27 in Figure 1) contain an isomerization catalyst which can be any of the various molecular sieve based catalyst compositions well known in the art which exhibit selective and substantial isomerization activity under the operating conditions of the process.
  • an isomerization catalyst which can be any of the various molecular sieve based catalyst compositions well known in the art which exhibit selective and substantial isomerization activity under the operating conditions of the process.
  • such catalysts comprise the crystalline zeolitic molecular sieves having an apparent pore diameter large enough to adsorb neopentane, SiO2/Al2O3 molar ratio of greater than 3; less than 60, preferably less than 15, equivalent percent alkali metal cations and having those AlO4 ⁇ tetrahedra not associated with alkali metal cations either not associated with any metal cation, or associated with divalent or other polyvalent metal cations.
  • 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 used alone or can be combined with a porous inorganic oxide diluent as a binder material.
  • the hydrogenation agent can be carried on the zeolitic component and/or on the binder.
  • inorganic oxide diluent materials are known in the art -- some of which exhibit hydrogenation activity per se .
  • an inorganic 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 per se hydrogenation catalysts.
  • Oxides suitable as diluents, which of themselves exhibit hydrogenation activity are the oxides of the metals of Group VI of the Mendeleev Periodic Table of Elements. Representative of the metals are chromium, molybdenum and tungsten.
  • 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 metals of Groups III, IV-A and IV-B of the Mendeleev Periodic Table, and cogels of silica and oxides of the metals of the 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 US 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 SiO2/Al2O3 molar ratio of about 5 by reducing the sodium cation content to less than about 15 equivalent 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.
  • a hydrogenation component 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.
  • the zeolitic molecular sieve employed in the adsorption bed must be capable of selectively adsorbing the normal paraffins of the feedstock using molecular size and configuration as the criterion. Such a molecular sieve should, therefore, have an apparent pore diameter of less than about 0.6 nm (6 Ansgroms) and greater than about 0.4 nm (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 0.5 nm (5 Anstroms), and has a very large capacity for adsorbing normal paraffins.
  • Suitable molecular sieves include zeolite R, US Patent 3,030,181; zeolite T, US 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 dimension, or the molecular species which is adsorbed by the adsorbent under normal conditions.
  • the 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, bond angles and van der Waals' radii.
  • the apparent pore diameter will always be larger than the structural pore diameter, which can be defined as the free diameter of the appropriate silicate ring in the structure of the adsorbent.
  • 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 isomerization 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.
  • fresh feed in line 10 is combined in 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 the adsorption section 22 (adsorbent bed), of vessel 23. It is of course possible to have the catalyst and adsorbent beds in different vessels if desired.
  • the reactor feed stream in line 24 is formed by combining the hot hydrocarbon stream from furnace 20 with hot reactor effluent from line 26 which contains hydrogen and hydrocarbon components (i.e., hot recycle or hot hydrogen recycle). Suitable control valves and controllers (not shown) 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.
  • the operating temperature of within vessels 23 and 29 is generally within the range of 100° to 390°C and the pressure is within the range of 1.21 to 4.14 Mpa (175 to 600 psia). Desirably, the temperature will be within the range of from 220° to 280°C and the pressure will be in the range of from 1.38 to 2.76 (200 to 400), preferably 1.52 to 2.07 Mpa (220 to 300 psia), and most preferably about 1.72 Mpa (250 psia).
  • the catalyst bed is maintained under a hydrogen partial pressure sufficient to prevent cocking of the isomerization catalyst at the conditions maintained in the reactor.
  • the hydrogen partial pressure will be within the range of from 0.69 to 1.72 (100 to 250), preferably from 0.90 to 1.31 (130 to 190), Mpa (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.g., 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. Because these are non-sorbable, they are retained in the process at some equilibrium level and circulate with the recycle stream.
  • hydrogen and hydrocarbon reactants e.g., normal and iso-pentane and hexane
  • the adsorbents in adsorbent beds 22 and 28 have effective pore diameters of substantially 0.5 nm (5 Ansgtroms).
  • bed void space for purposes of this description means any space in the bed not occupied by solid material except the intracrystalline 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 feed is intentionally mixed with hydrogen prior to introducing it to the feed and of the adsorber, then adsorbed, with product and hydrogen being withdrawn from the effluent end of the adsorber.
  • 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 exchange. (There is no A1 step.)
  • DES ⁇ hydrogen is used 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 no DI step.)
  • the presence of hydrogen in the adsorber feed improves heat exchange.
  • Heat exchange is better for a steady state system than a dynamic system such as conventional TIP.
  • the heat content of a process stream such as the adsorption effluent is a function of the molecular weight of the stream, which varies from about 10 Kg/Kg (1b/1b) mole at the beginning of the step to about 70 Kg/Kg (1b/1b) mole at the end of the step in the standard conventional TIP process. Since the heat exchange system must be designed to operate at the minimum heat content level, a significant amount of the high heat content portion cannot be utilized effectively.
  • the molecular weight of the adsorption effluent varies from about 10 to 40 Kg/Kg (1b/1b) mole.
  • the invention 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 is lower, and why the integration of the 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 system because there are less normal paraffins processed through the adsorbers.
  • the DI step (initial part of desorption) performs two functions: one is to prevent hydrogen lean desorption effluent from contacting the catalyst, and the other is to recycle the D1 effluent back to the adsorbers for readsorption. The effect is to minimize the adsorber size and minimize the reactor size.
  • 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. Hence, since the effluent has been further isomerized before being recycled to the adsorbers, fewer normals are ultimately recycled and the adsorbent inventory can be lower.
  • an increase in operating pressure would result in only a marginal 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.
  • an increase in operating pressure is desirable since it increases the normals partial pressure so as to be comparable to the conventional TIP system; however, since 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 as a function of the average feed rate in weight units. Since the initial portion of the desorption effluent, D1 effluent, is 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 expected that the catalyst volume required should be proportionally higher for the present invention. However, a smaller than expected catalyst volume can be effectively used in the present invention because of the high isomer content 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 the high isomer/high flow rate portion of the desorption effluent more effectively than in conventional TIP.
  • the reactor feed from line 24 is directed via suitable lines, manifolds, and valves (not shown) to vessel 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.
  • adsorbent beds in the system namely beds 22 and 28 contain a molecular sieve adsorbent in a suitable form such as cylindrical pellets.
  • the bed contains residual purge gas from the preceding desorption stroke.
  • the purge gas is preferably hydrogen-containing because of the need to maintain at least a minimum hydrogen partial pressure in the isomerization reactor. This is supplied to the adsorbent beds during desorption as a purge gas recycle stream via line 50. Feed through line 24 first flushes bed 22 of residual hydrogen-containing purge gas. This does not, however, end the stage and reactor effluent from bed 21 continues to flow as adsorber feed to adsorbent bed 22 with the production of adsorption effluent drawn off via line 16.
  • adsorption effluent i.e., hydrogen and the non-adsorbed non-normals
  • the adsorption effluent flows through line 16, heat exchanger 18, air cooler 32 and heat exchanger 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 separator 36 and combined with a similar overhead product from separator 40 which separates the reactor effluent takeoff from reactor bed 27 in line 42 into an overhead product taken off by line 44 and 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 adsorbent bed undergoing desorption.
  • appropriate valves direct flow to heat exchanger 52 and heater 54 prior to entering vessel 29, containing bed 28 for desorption.
  • the effluent from bed 28, passes directly to reactor bed 27.
  • void space adsorber feed is first purged, followed by desorption of selectively-adsorbed normal paraffins from the zeolitic molecular sieve.
  • the desorption effluent from bed 28 will, throughout the stage, comprise hydrogen and hydrocarbons.
  • the desorption effluent passes directly to isomerization reactor bed 27 as reactor feed.
  • the isomerization process will result in some hydrogen losses from the purge gas due to hydrogenation of starting materials and cracked residues. Hydrogen will also be lost due to solubility 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 hydrogen.
  • Makeup hydrogen can be supplied in impure form, e.g., via line 62, typically as an offgas from catalytic reforming or steam reforming of methane. These hydrogen sources 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 and n-hexane, and hydrogen and light hydrocarbon and other impurities which comprise the purge gas used for desorption.
  • This effluent is reactor feed and is passed to isomerization reactor 60.
  • a portion (up to 100%) of the reactor effluent from bed 27 is split off from line 64 via line 26 as a hot hydrogen-containing stream (i.e., hot recycle or hot-hydrogen recycle) for feed to the vessel 23, first to reactor bed 21 and then to adsorbent bed 22 undergoing adsorption.
  • a hot hydrogen-containing stream i.e., hot recycle or hot-hydrogen recycle
  • 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 40.
  • this hot recycle does not involve a component separation; it is 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.
  • the hot recycle carries with it a substantial portion of the reactor effluent that must ultimately be recycled to the adsobers. This mode of operation reduces the process cooling and heating requirements that would otherwise be required. It is important to note that the amount of hot recycle must 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 is different than the D1 recycle used in the conventional TIP. It is undesirable to have hydrogen present in the D1 effluent whereas in the present invention its primary purpose is to provide hydrogen.
  • the hot recycle in the embodiments of Figures 1, 2 and 4 of the present invention originates from the reactor and not from the adsorbers as in the conventional TIP. This step is likewise different from the reactor effluent recycle used in the noted partial recycle process and conventional TIP since the purpose of those steps is to recycle a hydrogen-free adsorber feed.
  • a third variation of the reactor lead configuration is to combine the two reactor sections (C1 and C2) in a single vessel. This scheme might be used if it would be impractical, for some reason, to utilize the compound bed approach.
  • Figure 3 shows that there is one feed pass through 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.
  • ADS adsorption
  • DES desorption
  • FIG. 4 shows an adsorber-lead configuration which achieves the advantages of the invention 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 stream is heated by indirect heat exchange with adsorption effluent, carried by line 116 in heat exchanger 118 from which it is passed to furnace 120 where it is heated sufficiently for passage to the adsorption section 122.
  • the adsorber feed stream in line 124 is formed by combining the hot hydrocarbon stream from furnace 120 with hot reactor effluent from line 126 which contains hydrogen and hydrocarbon components. Suitable control valves and controllers (not shown) direct the adsorber feed stream directed to the appropriate bed in the adsorption section (shown here as bed 122).
  • the adsorber feed containing normal and non-normal hydrocarbons in the vapor state, is passed at superatmospheric pressure periodically in sequence through each of a plurality of fixed adsorber beds, e.g., two as shown in Figure 4. It is of course possible to employ a greater number of beds if desired; however, it is an advantage of the invention that only two are required. In a two bed system, each of the beds cyclically undergoes the two stages (ADS and DES) described with reference to Figure 1.
  • bed 122 is undergoing adsorption, and bed 128, desorption.
  • a portion of the adsorber feed from line 124 is directed via suitable lines, manifolds, and valves to adsorbent bed 122 undergoing adsorption.
  • Flow of the adsorber feed through line 124 first flushes 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.
  • adsorption effluent i.e., hydrogen and the non-adsorbed non-normals
  • the adsorption effluent flows through line 116, heat exchanger 118, air cooler 132 and heat exhanger 134 prior to separation into a hydrogen-containing overhead product for recycle and an isomerate product in separator 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 line 144 and a reactor hydrocarbon product which is withdrawn via line 114 as described above.
  • the combined stream formed from lines 138 and 144 is fed via line 146 to recycle compressor 148 for return to the adsorber section via line 150 for desorption of bed 128.
  • the hydrogen-containing purge gas stream is passed via line 150 to heat exchanger 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.
  • void space adsorber feed is first purged, followed by desorption of selectively-adsorbed normal paraffins from the zeolitic molecular sieve.
  • the desorption effluent from bed 128 will, throughout the stage, comprise hydrogen and hydrocarbons.
  • the desorption effluent is sent to isomerization reactor 160 via line 158 as reactor feed.
  • Makeup hydrogen, as needed, can be supplied, e.g., via line 162.
  • the desorption effluent in line 158 will comprise desorbed normal hydrocarbons, e.g., n-pentane and n-hexane, and hydrogen and light hydrocarbon and other impurities which comprise the purge gas used for desorption. This effluent is reactor feed and is passed to isomerization reactor 160.
  • 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 undergoing adsorption.
  • Up to 100% of the reactor effluent can be recycled in this manner to the adsorbent bed undergoing adsorption.
  • 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 exchanger 166, reactor effluent in line 142 is further cooled by air cooler 168 and water cooler 170 prior to separation as discussed above in separator 140.
  • TIP equipment can be modified to greatly increase feed throughput and final product production while still providing octane values sufficient for use as a gasoline blending stock.
  • This example illustrates the operation of a process essentially as shown in Figure 4.
  • the process design for this example is based on a charge rate of 4000 BPSD of a predominantly C5/C6 feedstock as described in the Table below, which also describes principal process streams.
  • a starting point is selected at the discharge stream from the recyle hydrogen compressor 148.
  • This stream is preheated in exchanger 152 against the reactor effluent (Stream no. 142).
  • the hydrogen recycle outlet temperature from 152 is maintained at 181°C (358°F), controlling the hydrogen recycle bypass around exchanger 152.
  • the recycle gas is then heated to 266°C (510°F) in furnace 154. From 154, the hot hydrogen passes downflow through one adsorber (in this case 128), and strips the adsorbed normals from the molecular sieve adsorbent. Hot desorption effluent (Stream no. 158) is then sent to the isomerization reactor 160.
  • the composition of this stream is shown in the Table.
  • the normal paraffins are partially converted to isoparaffins.
  • An improved distribution of isohexanes is also achieved by increasing the concentration of the more highly branched dimethylbutanes.
  • Some ring opening of naphtenes, hydrogenation of aromatics, and cracking of the hydrocarbons to butanes and lighter also occur.
  • the reactor effluent is split, with one stream (Stream no. 126) combining with the adsorber feed, and the other stream of reactor effluent takeoff (Stream no. 142) being cooled by heat exchange against the cold adsorber feed in 166 and against the recycle hydrogen stream 152.
  • the reactor effluent takeoof is further cooled to 60°C (140°F) in air cooler 168 and to 38°C (100°F) in water cooler 170. It is then sent to the reactor effluent separator 140 for separation of condensed hydrocarbons.
  • the vapor from 140 is routed to the inlet of compressor 148 where it is compressed from 1.62 to 2.18 Mpa (220 to 301 psig).
  • the condensate from 140 is pumped via pump 141 through line 114 and is mixed with the fresh feed stream (Stream No. 110) to form combined hydrocarbon stream in line 112.
  • the combined hydrocarbon stream 112 is heated against the adsorption effluent (Stream No. 116) in exchanger 118 and against the reactor effluent takeoff in exchanger 166 to the furnace at an inlet temperature of 202°C (395°F).
  • Furnace 120 the combined hydrocarbon stream is heated to 2.66°C (510°F) to provide the required temperature of 260°C (500°F) at the adsorber inlet.
  • This feed is then combined with hot recycle in line 126 and to form the total adsorber feed (Stream No. 124) passed upflow through one of two adsorbers (in this case, 122), depending on the position of the cycle, where the normals are adsorbed into the micropores of the molecular sieve adsorbent.
  • Non-normals and a small quantity of displaced hydrogen gas pass through the bed and form the adsorption effluent.
  • the adsorption effluent (Stream No. 116) is cooled against the adsorber feed in heat exchanger 118. It is then air cooled in 132 down to 60°C (140°F) 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 combined with the vapor overhead from separator 140 and is 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. Hydrogen make-up (Stream No. 162) is supplied as necessary to separator 136.
  • the two adsorbers (122 and 128) containing molecular sieve adsorbent are both used to separate the normal paraffins from the non-normals in the feedstock.
  • the adsorbers are automatically cycled through sequential steps, by a controller which operates the remote operated valves (ROVs) in the adsorber manifolds (not shown).
  • ROVs remote operated valves
  • Two cycle timers are set to give the desired step times.
  • the design step times are as follows:
  • the adsorber feed 124 enters the adsorber that is on the adsorption step.
  • the other adsorber is on the desorption step.
  • the desorption feed is totally bypassed around the adsorbers to the inlet to the isomerization reactor 160.
  • the adsorber that has just finished the desorption step now begins the adsorption step, while the other adsorber finishes the adsorption step.
  • the two adsorbers are both on the adsorption step.
  • the adsorber feed and effluent valves are opening on one bed and closing on the other bed.
  • the adsorber feed at approximately 260°C (500°F) and 1.76 Mpa (256 psia), is fed to the molecular sieve adsorbent bed, which was previously purged with hydrogen.
  • the molecular sieve bed contains synthetic zeolite crystals having interconnecting pores of a precisely uniform size. The pore size of molecular sieve crystals is tailored to accept only molecules with a minimum effective diameter of up to 0.5 nm (five angstroms).
  • the non-normals/purge gas interface reaches the top of the adsorber.
  • the composition of the adsorption effluent changes from being mostly purge gas to being mostly non-normals and hydrogen.
  • the adsorber feed continues to pass upflow through the adsorber and the normals continue to be adsorbed on the bed.
  • the quantity of normals adsorbed per unit of molecular sieve i.e., the loading
  • the normals adsorbing in the bed displace about 15 percent of a vessel void volume if purge gas from the micropores. This gas gradually mixes with the non-normals and passes into the adsorption effluent.
  • the purge gas establishes a residual loading of normals on the top portion of the adsorber which is in equilibrium with the normals concentration in the vapor. Since the same equilibrium is reached during the adsorption step, the minimum normals concentration in the adsorber effluent is the same as the concentration in the purge gas.
  • the liberated heat of adsorption creates a temperature front which travels 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 and reducing the isomerate purity.
  • the non-adsorbed C4+ hydrocarbons retained in the bed after completion of the adsorption step, are countercurrently displaced with hydrogen purge gas.
  • the purge gas then desorbs normals from the adsorbent by reducing the partial pressure of the normals in the vapor phase, thereby shifting the equilibrium loading to a lower value.
  • Normal pentane and hexane concentrations in the purge gas are maintained at low levels to insure efficient desorption of the adsorbed normals.
  • the desorption step proceeds, the normals loading on the bed declines and the rate at which normals leave the bed decreases.
  • the desorption step is terminated before all the normals have been removed from the bed. The amount removed during each cycle is based on an economic balance between the adsorber bed investment and the purge gas recirculating costs.
  • the desorption feed and effluent valves close and a desorption feed bypass valve opens. This bed then returns to the adsorption step and continues the sequence of steps just described.

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  • General Chemical & Material Sciences (AREA)
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Claims (7)

1. Procédé pour accroître la teneur en hydrocarbures non normaux d'une alimentation hydrocarbonée contenant des hydrocarbures non normaux et des hydrocarbures normaux, y compris de l'hexane normal et du pentane normal, selon une opération combinée d'isomérisation-adsorption comprenant:
a) le passage d'un courant d'alimentation d'adsorbeur comprenant de l'hydrogène et des hydrocarbures dans un lit d'adsorbeur contenant un adsorbant et ayant un espace mort, dans des conditions efficaces pour adsorber les hydrocarbures normaux de ladite alimentation et produire un courant effluent d'adsorption comprenant des hydrocarbures non normaux et de l'hydrogène, le volume mort du lit contenant un mélange d'hydrogène et d'alimentation de l'adsorbeur non adsorbée comprenant des hydrocarbures non normaux;
b) le passage d'un gaz de purge riche en hydrogène à travers ledit lit d'adsorbeur pour produire un courant effluent de désorption comprenant des hydrocarbures normaux et ledit mélange d'hydrogène et d'alimentation de l'adsorbeur non adsorbée comprenant des hydrocarbures non normaux; et
c) le passage d'un courant d'alimentation de réacteur comprenant au moins une portion dudit courant effluent de désorption dans un réacteur d'isomérisation pour produire un courant effluent de réacteur comprenant de l'hydrogène et des hydrocarbures non normaux et normaux, le rapport des hydrocarbures non normaux aux hydrocarbures normaux étant accru par rapport audit courant d'effluent de désorption.
2. Procédé selon la revendication 1, dans lequel ladite alimentation de l'adsorbeur comprend 30 à 65% molaires d'hydrogène.
3. Procédé selon la revendication 1, dans lequel ledit courant d'alimentation de l'adsorbeur comprend un mélange d'un courant d'alimentation hydrocarboné frais et d'un courant de recyclage comprenant au moins une portion dudit courant effluent de réacteur.
4. Procédé selon la revendication 3, dans lequel au moins une portion dudit courant effluent de réacteur est recyclée sans être sensiblement refroidie pour fournir ledit hydrogène dudit courant d'alimentation de l'adsorbeur.
5. Procédé selon la revendication 1, dans lequel ledit courant d'alimentation du réacteur comprend un mélange d'un courant d'alimentation hydrocarboné frais et d'un courant de recyclage comprenant au moins une portion dudit courant effluent de désorption.
6. Procédé selon la revendication 5, dans lequel au moins une portion dudit courant effluent de désorption est recyclée sans être sensiblement refroidie pour fournir ledit hydrogène dudit courant d'alimentation de l'adsorbeur.
7. Procédé pour améliorer l'indice d'octane d'un courant d'alimentation hydrocarboné contenant des hydrocarbures non normaux et du pentane et de l'hexane selon un procédé combiné d'isomérisation-adsorption comprenant:
a) le passage d'un courant d'alimentation de réacteur comprenant une alimentation hydrocarbonée et de l'hydrogène à travers un lit de catalyseur d'isomérisation pour transformer au moins une portion des hydrocarbures normaux dudit courant d'alimentation de réacteur en hydrocarbures non normaux que l'on fait sortir dudit lit comme premier courant effluent de réacteur;
b) le passage dudit premier courant effluent de réacteur à travers un lit adsorbeur contenant un adsorbant et ayant un espace mort de lit, dans des conditions efficaces pour adsorber les hydrocarbures normaux et produire un courant effluent d'adsorption comprenant des hydrocarbures non normaux et de l'hydrogène, l'espace mort du lit contenant un mélange d'hydrogène et d'alimentation non adsorbée de l'adsorbeur comprenant des hydrocarbures non normaux;
c) le passage d'un gaz de purge riche en hydrogène à travers ledit lit d'adsorbeur pour produire un courant effluent de désorption comprenant des hydrocarbures normaux et ledit mélange d'hydrogène et d'alimentation non adsorbée de l'adsorbeur comprenant des hydrocarbures non normaux; et
d) le passage dudit courant effluent de désorption à travers un lit catalyseur d'isomérisation pour transformer au moins une portion des hydrocarbures normaux dudit courant effluent de désorption en hydrocarbures non normaux que l'on fait sortir dudit lit de catalyseur comme second courant effluent de réacteur.
EP88109494A 1987-06-15 1988-06-14 Procédé et appareil d'isomérisation Expired - Lifetime EP0295638B1 (fr)

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AT88109494T ATE67234T1 (de) 1987-06-15 1988-06-14 Verfahren und apparat zum isomerisieren.

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US62762 1987-06-15

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FR2799202B1 (fr) 1999-09-30 2002-04-26 Inst Francais Du Petrole Procede de production d'essences a indice d'octane ameliore
US20050137443A1 (en) * 2003-12-19 2005-06-23 Gorawara Jayant K. Regenerative removal of trace carbon monoxide
US7687674B2 (en) * 2006-12-28 2010-03-30 Uop Llc Low temperature process for recovering and producing para-xylene and heat exchange network therefore
US9669382B2 (en) * 2013-12-20 2017-06-06 Uop Llc Methods and apparatuses for isomerizing hydrocarbons

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US4210771A (en) * 1978-11-02 1980-07-01 Union Carbide Corporation Total isomerization process
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JPH0639406B2 (ja) 1994-05-25
JPH01221334A (ja) 1989-09-04
EP0295638A1 (fr) 1988-12-21
DK322788D0 (da) 1988-06-14
ATE67234T1 (de) 1991-09-15
CA1314568C (fr) 1993-03-16
GR3002763T3 (en) 1993-01-25
NO882612D0 (no) 1988-06-14
IN171273B (fr) 1992-08-29
AU1765588A (en) 1988-12-15
AU602587B2 (en) 1990-10-18
DE3864755D1 (de) 1991-10-17
NO882612L (no) 1988-12-16
ES2024591B3 (es) 1992-03-01
DK322788A (da) 1988-12-16

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