|Publication number||US3806443 A|
|Publication date||Apr 23, 1974|
|Filing date||May 26, 1972|
|Priority date||May 26, 1972|
|Also published as||DE2326834A1|
|Publication number||US 3806443 A, US 3806443A, US-A-3806443, US3806443 A, US3806443A|
|Original Assignee||Mobil Oil Corp|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (17), Classifications (30)|
|External Links: USPTO, USPTO Assignment, Espacenet|
April 23, 1974 J. MAZIUK 3,306,443
SELECTIVE HYDROCRACKING BEFORE AND AFTER REFORMING Filed May 26, 1972 5 m b) w w 1159 Q 0 I l no 0: \Kg l v v L v N "a W n l Nophfho Feed United States Patent US. Cl. 208-60 8 Claims ABSTRACT OF THE DISCLOSURE Processing naphtha to produce significant yields of LPG and an aromatic rich concentrate is described by the selective hydrocracking of normal parafiins to LPG material with a small pore crystalline zeolite hydrocracking catalyst before and after platinum reforming.
BACKGROUND OF THE INVENTION Reforming of hydrocarbons is a widely used process in petroleum technology for upgrading hydrocarbon fractions such as naphthas, gasolines and kerosines to improve the anti-knock characteristics thereof. Hydrocarbon fractions suitable for upgrading by reforming are composed of normal and branched parafiins, naphthenic hydrocarbons and even some aromatic hydrocarbons. During reforming a multitude of reactions take place including dehydrogenation, isomerization, dehydrocyclization, hydrocracking, and combinations thereof to yield a product of increased aromatics content and branched chain hydrocarbons. Thus in reforming it is desired to dehydrogenate the naphthenic hydrocarbons to produce aromatics, cyclize straight chain paraffins to form naphthenes, to convert C ring compounds to C ring compounds which are dehydrogenated to for maromatics, isomerize normal and branched paraffin hydrocarbons to yield higher octane branched chain hydrocarbons and effect a controlled hydrocracking of hydrocarbon constituents which are of undesired octane characteristics.
Normal and slightly branched paraflin hydrocarbons found in the above hydrocarbon fractions are generally of low octane rating. Highly branched-chain parafiin hydrocarbons, on the other hand, are characteristic of higher octane ratings. Therefore, one object of reforming is to effect isomerization of the normal and slightly branched chain parafiins to higher octane products by any one of the aforementioned reactions. The production of aromatics during reforming is accomplished by one or more of the above identified reactions leading to the production of naphthenes which are then dehydrogenated to aromatics such as benzene, toluene and xylene. One method for producing aromatics involves the isomerization of alkyl cyclopentanes to form cyclohexanes which thereafter are dehydrogenated to aromatics.
Ever since the concept of catalytic reforming was developed and commercially adopted, the refiner has been concerned with improving upon the selectivity of the product obtained and thus has strived to reduce yields of carbon and normally gaseous product materials since such materials represent a loss in desired liquid product. Thus small improvement in product selectivity has been gained with difficulty since there is a limit to the quantity of normally liquid constituents of desired octane rating that can be produced from a given charge. Consequently increases in product selectivity are viewed with considerable interest particularly if the selectivity increases can be associated with products of economic interest to the refiner. It has been found that the selectivity of a particular product slate or composition can be considerably enhanced by following the concepts and sequence of steps comprising this invention.
THE INVENTION This invention relates to a method and combination of processing steps for effecting a selective conversion and a rearrangement of petroleum hydrocarbon constituents to form aromatic enriched products and improve yields of LPG materials. In one aspect the present invention is concerned with one or more methods for selectively conducting chemical reactions with an arrangement of catalytic compositions possessing selective reaction properties with respect to different hydrocarbon components existing in the naphtha boiling range material. In yet another aspect the present invention relates to effecting a selective catalytic conversion of hydrocarbon components comprising ring, normal and isoparafiin hydrocarbon components in a sequence of hydrogenating conversion steps maintained under operating conditions selected to obtain products rich in aromatics and LPG material. More specifically, the invention is concerned with an arrangement and sequence of catalytic reactions designed to manipulate the reaction of hydrocracking, dehydrogenation, isomerization and dehydrocyclization in an amount selected to improve upon the yields of LPG products and relatively high octane aromatic components.
The present invention is concerned with contacting a relatively wide boiling range naphtha hydrocarbon material boiling in the range of C hydrocarbons up to about 380 or 400 F. under selective hydrocracking conditions suitable for particularly removing the relatively low boiling C and C normal parafiins and not more than a minor amount of C parafiins by a selective cracking thereof to LPG (propane and butane) products. The naphtha charge remaining after the selective removal particularly of low boiling normal parafiin constituents and comprising C and higher boiling naphtha boiling range materials is subjected to reforming conditions in the presence of a platinum type reforming catalyst maintained under conditions selected to reestablish the presence of normal paraflins and thus a relationship approaching equilibrium between normal and branched compounds existing in the hydrocarbon charge encountering the reforming reactions comprising dehydrogenation of naphthenes, isomerization of isomerizable hydrocarbons and dehydrocyclization of non-aromatic hydrocarbon constituents. Thus in the reforming operation of this invention, a relationship between branched and normal paraflins is established in the normal paraffin deficient hydrocarbon material passed to reforming in combination with effecting the production of relatively high octane components and particularly relative high octane aromatic and branched components. In this reforming operation the conditions lead also to the production of relatively low octane branched and normal paraflin compounds which are available for conversion and production of additional LPG products. The reforming catalyst may be relied upon to hydrocrack these low octane compounds formed during the reforming operation by pushing the severity of the reforming operation but it is preferred that the reformate product comprising any C and higher boiling normal paraffin constituents be subjected to a selective hydrocracking operation designed to convert particularly the low boiling normal paraflins formed during the operation. Thus the present invention includes the selective cracking of low and high boiling normal paraflin components comprising the naphtha boiling material processed in the combination of catalytic contact steps comprising this invention. It therefore includes reforming a naphtha charge depleted of the relatively low boiling normal paraffins but containing higher boiling normal parafiins generally 0, and higher boiling under reforming conditions particularly selected to establish a relationship approaching equilibrium in at least the normal and branched chain hydrocarbons component along with performing the other reactions of dehydrogenation and dehydrocyclization comprising catalytic reforming. This established relationship between normal and branched chain hydrocarbon components brought about by the rearrangement of branched components provides additional normal paraffiu constituents suitable for conversion to LPG material.
In the developments leading to the concepts of this invention, it has been found that crystalline aluminosilicates of an average pore size generally less than about 6 angstroms pore diameter but greater than about 4.5 angstroms, that is, about angstroms and comprising, for example, erionite, are particularly selective for cracking of C normal parafiins to the substantial exclusion of cracking branched and ring constituents. In addition, it has been found that a nickel erionite crystalline aluminosilicate such as hereinafter described will have a preference for cracking normal C hydrocarbons to that of C C and higher boiling normal paraffin. On the other hand, a platinum type reforming catalyst including bimetallic and non-bimetallic reforming catalysts and those comprising platinum or palladium in combination with another Group VIII metal component such as rhenium, iridium, ruthenium and osmium promoted with a halogen will indiscriminately effect hydrocrac'king under elevated temperature reforming conditions of the normal and branched parafiin components comprising the hydrocarbon material in the reforming operation. Thus employing a platinum type reforming catalyst under controlled isomerizing and hydrocracking severity conditions may be relied upon to produce LPG type products or products more easily converted to LPG products with a small pore nickel erionite selective hydrocracking catalyst in another reaction zone or contact step. That is, hydrocracking reactions performed with platinum reforming catalysts are more usually rate controlled reactions wherein, for example, a normal C hydrocarbon will crack more easily than a C hydrocarbon or a lower carbon number paraffin and thus a high severity reforming operation would be required to crack, for example, a C paraflin. However, such a high severity non-selective hydrocracking operation with the platinum reforming catalyst is undesirable since cracking of branched C and C hydrocarbons will be accomplished before cracking of normal hexane. This will result in cracking desired high octane branched chain hydrocarbons. Furthermore, such an operation produces an undesired mixture of light gases particularly comprising C and C hydrocarbons rather than C and C hydrocarbons. On the other hand, using the small pore selective hydrocracking catalyst described herein, cracking the lower boiling C and C paraflins in the naphtha charge and product of reforming can be accomplished more effectively for the production of LPG products. Thus by maintaining a selective balance in rate control and equilibrium controlled hydrocracking reactions with the different catalysts described herein and particularly suitable for this purpose, an improved overall yield of LPG products can be obtained along with an aromatic rich product by the present invention.
Crystalline aluminosilicate conversion catalysts identified with the prior art which are not selective within the limits defined herein or those particularly known as methane producers rather than producers of propane and butane are of little interest in pursuing the concepts of this invention. Furthermore, high methane producing crystalline aluminosilicate catalysts generally small pore crystalline zeolites promoted with Zn, Cd and Hg or other hydrocracking catalyst compositions which non-selectively produce gaseous streams rich in methane are of little interest for practicing the concept of this invention unless they can be controlled by operating conditions to exclude the undesirable production of light gaseous hydrocarbon constituents particularly methane and ethane.
In the interest of convenience to a better understanding of the concepts of the present invention the platinum type of reforming catalyst used will be referred to as catalyst A hereinafter, and the described selective crystalline aluminosilicate hydrocrackin'g catalyst relied upon particularly for the production of LPG gases will be referred to hereinafter as catalyst B.
The platinum type reforming catalyst, catalyst A, selected for use in the sequence of process steps of this invention may be selected from any one of a number of known prior art reforming catalysts suitable for accomplishing the results desired. These catalysts include generally, for example, alumina as the carrier material for one or more hydrogenation-dehydrogenation components distributed thereon with the alumina being in either the eta, chi, gamma or mixed forms thereof. The alumina carrier is promoted with, for example, one or more Group VIII metal components either with or without an acidic promoter such as silica, boron or a 'halogen. The platinum type of reforming catalyst is intended to include platinum, palladium, osmium, iridium, ruthenium, rhenium and mixtures thereof deposited on an alumina containing carrier or support with the alumina components generally being in an amount up to about by weight. Other components such as magnesium, zirconium, thorium, vanadium and titanium may also be combined or distributed in the alumina carrier. The platinum type catalyst may also include various amounts of halogen such as chlorine or fluorine in amounts ranging from about 0.1% up to about 10%; usually not more than 5 or 6%. The platinum reforming catalysts described may be one of those described in the prior art as homogeneous mixtures of metal components, alloys, and metal halide complexes thereof. A bimetal catalyst composition suitable for the reforming operation of this invention may be platinum combined with either rhenium, ruthenium, osmium or iridium and an alumina carrier promoted with chlorine to provide desired acid activity.
The selective conversion catalyst or hydrocracking catalyst herein referred to as a type B catalyst is a porous solid particle material having a majority of its pores of substantially uniform small dimension which are large enough to allow uptake and egress of normal paraflin molecules such as, for example, normal hexane and smaller carbon atoms, but too small to allow a similar uptake of either branched or ring compounds such as, for example, methylpentane, cyclohexane or benzene. In addition, those hydrocarbons comprising C and longer chain normal parafiin hydrocarbons up to about C hydrocarbons encounter ditfusion limitations which increase with length of chain and thus are slower to crack when employing the small pore crystalline aluminosilicate catalyst intended for use by this invention. Thus the selective hydrocracking catalytic material, type B, is a porous crystalline material wherein a substantial majority of its pores are of an average uniform dimension of about 5 angstroms and in the range of from about 4.5 up to about 6.0 angstrom units effective diameter. This is essentially a selective crystalline aluminosilicate of the erionite variety provided with inpore acid activity cracking sites and catalytically effective bydrogenationdehydrogenation sites. In some cases the hydrogenation-dehydrogenation functions may be associated with the small pore shape selective crystalline material but externally located to the pore and in some cases located both within and externally to the pore. On the other hand, it is contemplated providing the catalytically effective hydrogenation-dehydrogenation sites restricted substantially completely to within the pore. The hydrogenation-dehydrogenation component provided during manufacture of the catalyst involves one or more of the elements such as a transition metal. Preferably one or more of the elements of nickel, cobalt, molybdenum, iron or of the platinum or palladium family are employed. One or more of the elements employed may involve an element selected from a higher molecular weight transition metal which have hydrogenation-dehydrogenation activity, such as tungsten.
A crystalline aluminosilicate of desired porosity such as erionite may be modified to produce useful catalysts for this invention by effecting the introduction of one or more of the above identified transition elements in such a way that the final quantity of the element may be located in either the internal, external or mixed internalexternal pore structure of the crystalline aluminosilicate. Introduction of one or more of such metallic elements or components may be achieved by processes allowing the metal to penetrate the existing or preformed pore solid and be fixed therein or by formation on the pore solid itself in a compositional environment which contains the desired metal component in a form suitable to be incorporated into the porous structure in the formation thereof, or in the course of its modification to a desired pore structure.
It is preferred to impart the type B catalyst with certain limited magnitudes of acid catalytic activity. For example, when LPG product is preferred over methane, the preferred acid activity will have an alpha value in excess of 10. If the process employs the catalyst at a temperature of 900 F. or higher, a more preferred acidity level is between 5 and 300 alpha; for operations more nearly at 800 F., above about 500 alpha; for operations near 700 F., above about 200 alpha. A very practical method of assaying the alpha acidity of the type B catalyst is that of testing its n-hexane cracking activity under conditions of cracking, in the absence of hydrogen. Such a procedure is identified in Journal of Catalysis, volume 4, No. 4, August 1965.
In reforming operations it is known that as the reforming severity is increased to achieve higher and higher product octane number, the octane number increase is obtained primarily by way of paratiin aromatization and 5 carbon ring aromatization. At the relative high severity conditions parafiin to aromatic dehydrocyclization reactions become important and are accompanied by progressive and non-selective elimination of remaining paraffins to light gaseous products thus increasing octane number at the expense of substantial liquid volume loss. However, by selectively controlling the reforming operation severity the chemical reactions encountered therein are restricted to minimize the production of low octane and undesired gaseous component in favor of producing branched chain hydrocarbons in an aromatic enriched product of relatively high octane rating. Accordingly, the method and combination of process steps herein described provide significant and unusual benefits by adjusting the reaction mechanisms to implement and improve the production of LPG products and high octane aromatic products.
The operating conditions employed in the proces combination of this invention and particularly that of the reforming operation with type A catalyst are those conditions which promote dehydrogenation of naphthenes along with reactions associated with isomerization which reestablish a relationship between normal paralfins to branched paraffins and include operating temperatures selected from within the range of from about 800 F. to about 1000 F. and preferably from about 850 F. up to about 980 F., liquid hourly space velocity in the range of from about 0.1 to about 10, preferably from about 0.5 to about 5; a pressure in the range of from about atmospheric up to about 600 p.s.i.g. and preferably from about 100 to about 400 p.s.i.g.; and a hydrogen to hydrocarbon ratio selected from within the range of from about 0.5 to about 20 and preferably from about 1 to 10.
On the other hand, type B catalyst or the selective normal parafl'in conversion catalyst may be operated at conditions similar to reforming operating conditions depending on the catalyst employed therein. However, it is important that the operating conditions be selected which will particularly promote the formation of LPG gaseous material from the hydrocarbon charge material brought in contact with type B catalyst. Therefore, catalyst type B Type B, catalyst example A natural crystalline aluminosilicate identified as erionite obtained from Nevada was analyzed with the following results:
Weight percent Si0 68.4 A1 0 16.2 F6203 2.7 K 0 4.4 CaO 2.0 Na O 4.7 MgO 1.3 Silica to alumina mol ratio 7.2
A sample of the above identified erionite was crushed to provide a powder. The powder was exchanged twice with 6 ml. of 5 M ammonium chloride solution per gram (bone dry baiss) of the erionite powder for 4 hours at F. with filtering after each exchange. Thereafter the exchanged erionite is washed with 10 ml. of water per gram of erionite and filtered. Then the erionite zeolite is exchanged with 4.4 ml. of 0.5 M nickel acetate solution (adjusted to 6 pH with acetic acid) per gram of the zeolite for 4 hours at 210 F. and filtered. The nickel exchanged zeolite is then washed with 10 ml. of water per gram of zeolite and filtered. The exchanged zeolite prepared as above identified is then dried for at least 16 hours or to a constant weight at a temperature in the range of 225 to 250 F. The dried erionite zeolite promoted with nickel is then pelleted and crushed to a 10/14 mesh. The 10/14 mesh refers to passing through U.S. Standard Sieve No. 10 (Tyler equivalent 9 mesh) and retained on U.S. Standard Sieve No. 14 (Tyler equivalent 12 mesh).
SPECIFIC EMBODIMENTS In an effort to provide a better and more complete understanding of the method and process of this invention, the method of improving the yield of LPG gases comprising propane and butane finds support in the following examples. Table 1 below identifies the characteristics of a light Arabian naphtha boiling in the range of C hydrocarbons up to about 340 F. which was processed in the combination of steps of this invention comprising an initial selective hydrocracking of normal parafiins boiling below about 0, hydrocarbons to LPG products under hydrogenating conditions employing a nickel-erionite catalyst prepared as above identified before reforming of the remaining hydrocarbon material comprising C and higher boiling hydrocarbons with a platinum under conditions to produce additional normal parafiins in combination with branched and aromatic constituents in a reformate product. The naphtha charge when containing undesired levels of sulfur and nitrogen may be subjected to an initial hydrofining or pretreat operation wherein the sulfur and nitrogen constituents are reduced to less than 10 p.p.m. and more usually to about 2 p.p.m. by hydrogenation to products easily separated from a desired C or C naphtha charge. Hydrofining of the charge naphtha may be accomplished in the presence of any one of a number of different hydrofining catalysts known and available in the prior art. Suitable hydrofining catalysts include the metals and/or sulfides of Group VIII and Group VI metals of the Periodic Table employed alone or in combination with one another such as cobalt or nickel and molybdenum or tungsten. Such catalyst may be employed alone or in combination with a support or carrier material such as alumina, silica, zirconia, titania and clays or mixtures thereof. Generally the hydrofining catalyst is an amorphous base catalyst but it may also contain a small amount of a crystalline aluminosilicate in combination with the amorphous carrier component. Suitable hydrofining catalysts include cobalt-molybdenum dispersed on alumina, nickel-tungsten sulfide alone or dispersed on a carrier or support such as alumina or silica-alumina. In the hydrofining operation, temperature, pressure and space velocity conditions are selected from those well known in the prior art which will be effective in reducing the level of nitrogen and sulfur in the charge to that suitable for initial contact with the selective crystalline aluminosilicate conversion catalyst.
The selective crystalline aluminosilicate hydrocracking catalyst is fairly tolerant of nitrogen and sulfur compounds and thus will assist with the removal of these contaminants during conversion of n-paraffin components in the naphtha charge. Thus the selective hydrocracking catalyst B may form a down-stream portion of the desulfurizing catalyst bed. In a particular aspect it is important that the sulfur content of the naphtha brought in contact with the platinum reforming caalyst be reduced to an acceptable level of about ppm. and preferably to about 2 p.p.m. for bimetal catalyst compositions such as platinum-rhenium dispersed on alumina. The amount of nitrogen in the naphtha reforming feed should be reduced not to exceed about 2 p.p.m.
TABLE 1 Arabian light naphtha properties (C 340 F. cut) A naphtha charge such as identified in Table 1 Was passed sequentially through the combination of catalyst contact steps comprising a selective crystalline aluminosilicate hydrocracking catalyst (SCI) for normal paraffin conversion to LPG, a platinum-aluminum reform-ing catalyst and then a final contact with a selective crystalline aluminosilicate hydrocracking catalyst (8C2). Table 2 below identifies the operating conditions employed in one particular combination and provides the results obtained with the combination of conditions recited for improving product selectivity to LPG. The SCI and SCZ catalyst steps used the nickel erionite catalyst prepared as described above in combination with 0.6 Wt. percent platinum dispersed on alumina and promoted with chlorine. Table 2 provides characteristics of the product obtained after each of the contacting steps as well as the cumulative yields obtained after traverse of the combination of processing steps. From these data it will be observed that product selectivity to LPG product comprising C and C hydrocarbons was vastly improved by the combination of selective hydrocracking before and i c r vit .72 2 :23 5 y 0 60 after reforming. It W111 also be observed that the aromatic R 41 rich high octane product of the combination process of M+ O 40 this invention has a much lower benzene content than a similar octane product of the processes compared. Thus Pona andlysls: P the combination of this invention is also unexpectedly Paraflins eifective in reducing the concentration of benzene in a Naphthenes &5 high octane product suitable for use in preparing motor Aromatics 9.5 fuels.
TABLE 2 Operating conditions S01 PtR S02 Temperature, F 800 900 800. Pressure, p si 2 500 500.-.. 500. Space velocity- 1 9 2.75. 2.1.
Total recycle ratio.. 4:0:
Catalyst Ni-erlonite. 0.6
10.0. pt. on alumina plus ch1orine- Ni-erlonite.
S01 SQ1+PtR l S1C1+PtR+S C2 PtR+SC1 PtR Wt Vol. Wt. Vol. Wt. Vol. Wt. Vol. Wt. Vol. Yields, percent on naphtha charge:
Hz. 0.6 1.2 0.1 0.8 1.1 0 4-0 2.4 5. 6 8.3 9. 1 9. 6 8x104 t73 g '5 g 22. 0 30. 5 20. 6 27. 6 a 68. 1 62. 8 68. 7 63. 4 0 composition (Wt. percent on 05+ hycs):
N-C5. 2. 6 3. 9 1. 4 2. 2 6. 5 N-C. 0. 8 4. 5 0. 5 0. 5 2. 5 NC 2. 8 0.5 0.2 1.0 N-Cg. 0. 4 0. 1 0. 2 0. 1 N-Cn 0. 0 0.0 0.0 0.0 iso-Paraflins. 28. 5 31. 4 31. 0 20. 1 Benzene. 4. 8 5. 3 5. 0 6. 3 Toluene 17. 1 18. 9 20. 0 21. 8 C gmrnafir'q 15. 4 17. 0 21. 7 23. 0 CH- m' 21. 3 23. 5 18.5 17. 8 CH- properties:
R+O 50. 8 94. 3 100 D+O 98. 3 97. 0 RVP. 4. 3 3. 9 5. 7 SPG'R 0. 7402 0. 7787 0. 7940 0. 7869 1 Based on 05+ product from S01.
To further facilitate a more complete understanding of the contributions of this invention, the data of Table 2 have been separated and rearranged to provide Tables 3 and 4 below. Table 3 below emphasizes the yield improvement in LPG material (C and C hydrocarbons) and particularly that of propane obtained by the processing combination of this invention. Furthermore, differences in the product slate obtained from the three dilferent identified operations are compared. Table 4, on the other hand, particularly emphasizes the changes in the product slate from the different processing steps of the combination (SC1-l-PtR+SC2) particularly with respect to octane rating, C and C hydrocarbons yield and the decrease yield of normal paraffins.
PtR PtR-l-SC2 SC1+PtR+SC2 Volume yield, percent of naphtha charge:
63. 4 62. 8 53. 7 Cs+C 27. 6 30. 5 45. 2 03-..- 13. 3 22.0 35. 3 i-C4 5. 8 4. 9 3. 1 n-Cr 8. 5 3. 6 6. 8 Weight yield, percent:
n-Ca 1.7 0.3 0. 3 Aromatics 47. 2 44. 4 38. 1
TABLE 4 Weight yield percent of Naphtha S01 PtR SC2 naphtha charge charge product product product n-C 6. 4 0. 6 2.8 0.3 i-Paraflins 44. 9 44. 9 18. 5 18.5 Aromatics. 11. 6 l1. 6 38. 1 38. 1 05+ (R+O) 41 50.8 94.3 100 Vol. percent Os+C 1 24. 7 37. 7 45. 2
It will be recognized by those skilled in the art that the combination of processing steps comprising this invention and the product slate obtained therefrom can be varied by varying, for example, the reforming operating conditions and/or the catalyst employed therein. For example, reforming catalysts of different composition are known to influence the various reforming reactions. Catalyst acidity may be employed to influence the various reactions of isomerization in the direction desired. That is, acidic reforming catalyst may be relied upon to enhance isomen'zing reactions which change the balance between normal and branched parafiins and/or the cracking reactions encountered depending upon the temperature and space velocity employed. A silica promoted reforming catalyst may be selected to enhance dehydrocylization reactions for example at temperatures less suitable for isomerizing reactions. Thus in the plurality of catalytic reaction zones comprising the reforming operation, a catalyst of very low acidity may be employed in the first reaction zone with subsequent reaction zones provided with catalyst compositions of the same or diiferent acid activity to promote desired reactions.
The processing combination of this invention contemplates the use of the selective crystalline aluminosilicate conversion catalyst (SCl) to effect a part of the desulfurizing of the naphtha charged to the process. It also contempltes use of the crystalline selective hydrocracking catalyst as a down stream portion of the hydrofining catalyst bed of a different composition such as CoMo on alumina or the selective hydrocracking catalyst (SCI) may be in admixture with the desulfurizing catalyst. Under some circumstances it may be desirable to maintain the hydrofining, catalyst and the selective nickel erionite conversion catalyst in separate reactor beds with means between beds for removing undesired gaseous constituent with or without means for altering the temperature between catalyst beds as required. In any event means are provided between the initial selective nickel erionite hydrocracking catalyst conversion step and the reforming step to separate, for example, sulfur and nitrogen before passing the naphtha charge depleted of sulfur to a heating zone wherein it is heated either alone or in the presence of hydrogen to a temperature sufiiciently elevated to effect primarily dehydrogenation of naphthenes therein upon contact with the chlorine promoted platinum alumina reforming catalyst. The total product of the reforming operation may be passed in contact with a selective crystalline aluminosilicate (CAS) conversion catalyst such as nickel promoted erionite for the purpose of selectively cracking to LPG products only the n-parafiins found in the reformate product. On the other hand the reformate product may be first, separated to recover C and h1gher boiling material from gaseous material lowei' boilmg than C hydrocarbons. Thereafter the C and higher boiling material and comprising normal paraifin components therein formed during the reforming operation is passed in contact with the selective nickel erionite hydrocracking catalyst defined herein under desired temperature and pressure hydrocracking conditions selected toachieve the further production of LPG products comprising C and C hydrocarbons as described herein. The selective hydrocracking catalyst SC2 relied upon to convert normal paraffins in the C reformate may be the same catalyst relied upon initially to remove nparafiins and sulfur from the naphtha charge. Other catalyst suitable for accomplishing this purpose may also be relied upon provided the catalyst does not hydrogenate or otherwise destroy aromatics existing therein. Under some conditions a crystalline aluminosilicate hydrocracking catalyst of larger pore diameter than the particular selective catalyst herein defined may be used provided it will convert normal and some branched parafiin to form LPG products without destroying aromatics formed in the combmation.
The figure provided herewith presents one arrangement of a combination of processing steps for practicing the present invention. In the figure a naphtha boiling range material such as used in the above examples and boiling from about C hydrocarbons up to about 340 F. is introduced to the process by conduit 2. Hydrogen such as hydrogen rich gaseous product of reforming is introduced by conduit 4 for admixture with the naphtha charge being passed to a preheat furnace 6. In furnace 6 the mixture is preheated to an elevated temperature in the range of 600 F. up to about 800 F., or higher and sufiicient to effect desulfurization of the naphtha upon contact with the desulfurizing catalyst or the combination of catalysts provided in reactor 10 in this specific embodiment. The preheated naphtha boiling charge is passed by conduit 8 to reactor 10 wherein is housed, in this specific embodi ment, an amorphous base desulfurization catalyst 12 such as cobalt-molybdenum on alumina in an upper portion of the reactor and a selective crystalline aluminosilicate (CAS) hydrocracking catalyst (SCI or nickel erionite) 14 in the lower portion of the reactor. When the naphtha charge contains only a small amount of sulfur, then the sole fill of reactor 10, for example, may be the selective catalyst (SCI) defined hereinbefore and having a pore size of about 5 A. and generally in the range of from about 4 to about 6 angstroms since such material has been found to be a very acceptable material for desulfurizing the naphtha charge In reactor 10, desulfurization of the naphtha charge is accomplished along with the selective cracking of low boiling normal paraffins to the substantial exclusion of cracking higher boiling long chain normal parafiins, branched and ring compounds. In this selective cracking operation, a temperature of about 800 F. at a pressure of about 500 p.s.i.g. was found acceptable. The effluent of the catalyst reactions of reactor 10 is then passed by conduit 16 to a separator 18. In separator 18 gaseous products comprising LPG material such as C and C hydrocarbons along with lower boiling hydrocarbons, hydrogen sulfide and ammonia as well as unconsumed hydrogen is removed from the upper portion thereof 'by conduit 20. This gaseous product is passed through equipment not shown to obtain a separation and recovery of LPG materials from the remaining gaseous product. Higher boiling hydrocarbon material and more usually comprising and higher boiling hydrocarbons are removed from separation step 18 by conduit 22 for passage through a platinum catalyst reforming operation. The platinum catalyst reforming operation depicted comprises a plurality of sequentially arranged catalytic reactors pro vided with furnace means for preheating the hydrocarbon charge passed to each reactor to provide an inlet temperature of about 900 F. so that primarily dehydrogenation of naphthenes to form aromatics will be accomplished in reactor 1 and 2 with the remaining reforming reactions of isomerization, dehydrocyclization and hydrocracking being performed in reactors 2 and 3 under selected temperature reforming conditions. The reforming reactors may be maintained at a pressure selected from within the range of 100 p.s.i.g. up to about 600 p.s.i.g. relying upon temperatures selected from within the range of from about 800 R, up to about 1000 F. Thus in the specific combination of the process represented by the figure the hydrocarbon material in conduit 22 is passed to furnace 24 in admixture with hydrogen containing gas admitted by conduit 23, wherein the mixture is preheated to an elevated temperature particularly suitable for effecting dehydrogenation of naphthenes in the mixture upon contact with a suitable platinum reforming catalyst in Pt. R1 or reactor 28. The effiuent of reactor 28 is then passed by conduit 30 to furnace 32 wherein its temperature is elevated to that suitable for passage to PtRZ by conduit 34. In reactor 36 dehydrogenation, isomerization and even some dehydrocyclization reactions may occur. The eflluent from reactor 36 may be passed, if desired, by conduit 38 to furnace 40 for reheating thereof as required and before passage by conduit 42 to PtR3 or reactor 44. In reactor PtR3 (44) reactions of dehydrocyclization and hydrocracking are promoted and controlled by the reaction conditions and catalyst composition employed therein. Under some circumstances it may be desirable to replace all or a portion of the platinum reforming catalyst in reactor 44 with the shape selective conversion catalyst. In this arrangement the recovery of product could be effected similarly to that disclosed in US. Pats. 3,395,094 or 3,432,- 425. The reformate product, on the other hand, and comprising the efiluent of reactor 44, as shown in the figure in this embodiment, is then passed by conduit 46 to one or more separator vessels represented by vessl 48. In separator 48, gaseous products of reforming and comprising hydrogen are separated from higher boiling reformate material comprising C and higher boiling hydrocarbons including aromatic enriched product of the process. The gaseous product of reforming boiling below C hydrocarbons is removed by conduit 50 and passed to suitable recovery equipment not shown wherein hydrogen rich gases are recovered from higher boiling hydrocarbons such as those forming LPG products. The higher boiling portion of the reformer effluent separated in separator 48 is removed by conduit 52 and sentto furnace 54 in admixture with hydrogen containing gas introduced by conduit 56. In furnace 54 the reformer effluent higher boiling than LPG material is reheated to an elevated temperature before it is passed by conduit 58 to reactor 60 containing a selective conversion catalyst represented as 5C2. In reactor 60 the reformer effluent boiling above LPG material and containing some formed normal paraffins during the platinum catalyst reforming operation is subjected to a further selective cracking operation for the conversion of normal paraffin components to additional LPG material. The selective cracking of normal parafi'ins may be effected at temperatures below the reforming temperatures relying upon pressures below, equal to or above the reforming pressure.
In the combination of processing steps comprising this invention and diagrammatically depicted in the figure, a
considerable amount of equipment such as values, compressors, separator equipment and recycle conduits are not shown for the purpose of simplifying the process depicted but are contemplated being used in such as process combination. It should be understood furthermore that recycling of hydrogen rich gasses recovered from the gaseous product of reforming to the reforming step and to either or both of the selective conversion steps is also contemplated. Other processing schemes for handling the efiluent of the reforming operation and contacting portions thereof with a selective conversion catalyst are discussed in US. Pat. 3,432,425 and the use of such schemes are contemplated where appropriate by this invention. In the figure presented herewith, the efiluent of the nickel erionite selective hydrocracking operation is passed by conduit 62 to separator 64. In separator 64, gaseous products comprising LPG material such as propane and butane are separated and removed by conduit 66 from a higher boiling aromatic enriched product removed by conduit 68. The LPG material produced by the process combination of this invention is combined for further use as desired. The aromatic enriched product formed by the combination and being of a high octane rating and relatively low benzene content is thereafter used, for example, in gasoline blending operations.
Having thus provided a general discusion of the present invention and discussed specific examples in support thereof, it is to be understood that no undue restrictions are to be imposed by reason thereof except as provided by the following claims.
1. A method for upgrading naphtha boiling in the range of to 400 F. to produce propane and a liquid product of high aromatic content which comprises,
(a) contacting a desulfurized naphtha and hydrogen with a selective hydrocracking catalyst comprising acid erionite at a temperature in the range of 700 to 850 F. at a pressure in the range of 100 to 600 p.s.i.,
(b) separating C and lower boiling gasiform material from a higher boiling normally liquid naphtha material comprising C7 hydrocarbons,
(c) contacting the normally liquid naphtha material with a platinum containing reforming catalyst under reforming conditions selected to produce a product comprising aromatics, branched and normal paraffins and a normally gaseous stream comprising C and lower boiling hydrocarbons,
(d) separating a normally liquid reformate product stream comprising C and higher boiling reformate product from lower boiling gasiforrn material,
(e) contacting the normally liquid reformate product stream with a hydrocracking catalyst comprising acid erionite under conditions selective for converting nparafiins to LPG product gas and (f) recovering from each of said selective hydrocracking a product rich in propane and an aromatic rich product from said second selective hydrocracking operation.
2. The method of claim 1 wherein the selective hydrocracking is restricted primarily to C normal paraffins.
3. The method of claim 1 wherein the selective hydrocracking of normal parafiins is controlled by pressure, space velocity and use of a crystalline zeolite of about 5 angstrom average pore size provided with in pore hydrogenation-dehydrogenation activity.
4. The method of claim 3 wherein the hydrocracking catalyst comprises acid nickel erionite.
5. The method of claim 1 wherein the selective hydrocracking of the naphthas charge is accomplished in a downstream portion of a naphtha desulfurizing zone and the selective hydrocracking of liquid reformate product is accomplished in a downstream portion of the last reforming zone.
6. The method of claim 1 wherein the selective hydrocracking of the naphtha charge occurs at a temperature in the range of 700 to 850 F. at a pressure within the range of 100 to 600 p.s.i. and the selective hydrocracking of the liquid reformate occurs at a temperature within the range of 800 to 1000 F. at a pressure within the range of 100 to 600 p.s.i.
7. The method of claim 1 wherein the reforming operation is accomplished at a higher temperature than the selective hydrocracking steps.
8. The method of claim 1 wherein the selective hydrocracking steps are accomplished in separate reaction zones.
References Cited UNITED STATES PATENTS 0 HERBERT LEVINE, Primary Examiner 208-65, DIG. 2
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|U.S. Classification||208/60, 208/DIG.200, 208/65|
|International Classification||C07C67/00, C10G59/02, B01J23/00, C10G47/16, C07C5/373, C10G69/08, C07C4/06, C10G45/64, C10G35/06, C10G69/10, C10G47/00, C10G50/00, C10L1/02, C07C9/02, C07C1/00, C07B61/00, C10G35/095, B01J29/56, C10L10/10, C07C15/02, B01J29/00|
|Cooperative Classification||C10G2400/02, Y10S208/02, B01J29/56, C10G59/02|
|European Classification||C10G59/02, B01J29/56|