Catalytic cracking of paraffinic feedstocks with zeolite beta

Abstract

 57 Heavy hydrocarbon oils of high paraffin content are catalytically cracked using zeolite beta. The paraffin content of the oil is at least 20 weight percent or higher. The gasoline cracking products have a high octane rating and the higher boiling products a decreased pour point resulting from the dewaxing activity of the zeolite beta.

Description

[0001] This invention relates to a process for the catalytic cracking of heavy oil feeds using a cracking catalyst comprising zeolite beta. It relates more particularly to a process for the catalytic cracking of paraffinic feeds with a catalyst of this type.

[0002] The catalytic cracking of hydrocarbon oils using acidic cracking catalysts is a well established process which has, for a number of years, used a number of different types of catalytic cracking units including, in the early years, fixed bed crackers of the Houdriflow type and later, moving bed units such as the Thermofor Catalytic Cracking (TCC) units and fluidized bed catalytic cracking units (FCC). Of these, fluid catalytic cracking (FCC) has now become the predominant type of unit for catalytic cracking. In both the moving, gravitating bed and moving, fluidized bed processes, the feedstock to the unit is brought into contact with a hot, continuously circulating, cracking catalyst to effect the desired cracking reactions, after which the cracking products are separated from the catalyst which is regenerated by oxidation of the coke which accummulates on the catalyst. Oxidative regeneration in this way serves the purpose both of removing the coke which deactivates the catalyst and also brings the catalyst back up to the temperature required to maintain the endothermic cracking reactions. The hot, regenerated catalyst is then recirculated to the reactor where it is again brought into contact with the feedstock. In the moving bed (TCC) process, the catalyst is generally in the form of beads which move through the reactor and the regenerator in a solid, gravitating mass whereas in the FCC process, the catalyst is in the form of a fluant powder, typically of about 100 microns particle size.

[0003] The catalysts used in catalytic cracking, whatever the type of unit employed, possess acidic functionality in order to catalyze the cracking reactions which occur. Initially, the acidic functionality was provided by amorphous type catalysts such as alumina, silica-alumina or various acidic clays. A significant improvement in the process was provided by the introduction of crystalline, zeolitic cracking catalysts in the 1960's and this type of catalyst has now become universally employed. The zeolites which are used for this purpose can generally be characterized as large pore zeolites because it is essential that the internal pore structure of the zeolite which contains the bulk of the acidic sites on the zeolite should be accessible to the bulky, polycyclic aromatic materials which make up a large portion of the heavy oil feeds to the process. Large pore zeolites which have been used for this purpose include mordenite and the synthetic faujasite zeolites X and Y. Of these, zeolite Y has now become the zeolite of choice because of its superior stability to hydrothermal degradation, particularly when it is used in the forms of a rare earth exchanged zeolite (REY) or the so-called ultrastable Y (USY).

[0004] Although most of the feeds to catalytic cracking units contain significant amounts of high boiling aromatic constituents, some feeds, particularly from Southeast Asian and Pacific sources contain relatively large amounts of waxy paraffins which are relatively refractory towards catalytic cracking, especially in the presence of aromatics. Feedstocks of this type are generally difficult to process in conventional catalytic cracking processes regardless of the type of catalyst used: when waxy gas oils derived from crudes of this type are passed through the unit, the gasoline product tends to have a relatively low octane number and the unconverted fraction in which the refractory paraffins tend to concentrate, has a very high pour point which makes it unsuitable for use as a blending component in fuel oils. Furthermore, recycle of the unconverted fraction is of limited utility because of the refractory nature of the paraffins in this material.

[0005] The problems presented by the presence of waxy components in petroleum oils have, of course, been known for a long time and various processes have been evolved for removing the waxy components from various distillate fractions including lubricating oils, middle distillates including heating oils and jet fuels and gas oils. Various catalytic hydro-dewaxing processes have been developed for this purpose and these processes have generally removed the longer chain n-paraffins and slightly branched chain paraffins by selectively cracking these materials to produce lower molecular weight products which may be removed by distillation. In order to obtain the desired selectivity, the catalyst has usually been an intermediate pore size zeolite with pore size which admits the straight chain n-paraffins either alone or with only slightly branched chain paraffins, but which excludes more highly branched materials, naphthenes and aromatics. Catalytic hydro-dewaxing processes of this kind are described, for example, in U.S. Patents Nos. 3,668,113; 3,894,938; 4,176,050; 4,181,598; 4,222,855; 4,229,282; and 4,247,388. However, the intermediate pore size zeolites such as ZSM-5 which are highly effective as dewaxing catalysts in these hydrogenative processes using relative light feeds are generally unsuitable for use as cracking catalysts because their pores are too small to admit the bulky, polycyclic aromatics into the internal pore structure of the zeolite where cracking can take place. They have not, therefore, been used as such for catalytic cracking although they have been combined with large pore zeolites in catalytic cracking catalysts in order to improve the octane rating of the naphtha cracking product, but even when combined with a conventional cracking catalyst in this way, they are unable to function effectively as cracking catalysts for waxy feeds. The problem of dealing with feeds of this kind has therefore persisted.

[0006] It has now been found that zeolite beta is an extremely effective cracking catalyst for highly paraffinic feeds, being capable of producing gasoline of improved octane number, with greater potential alkylate yield, with reductions in the pour point (ASI_M D-97) of the higher boiling cracking product fractions. According to the present invention, therefore, a process for the catalytic cracking of a highly paraffinic hydrocarbon oil employs a cracking catalyst comprising zeolite beta.

[0007] The present catalytic cracking process is applicable to the catalytic cracking of highly paraffinic feeds, that is, to feeds which comprise at least 20% by weight paraffins. The process may be carried out in any of the conventional type of catalytic cracking units, implying that it will normally be carried out in a moving, gravitating bed (TOC) unit or a fluidized bed (FCC) catalytic cracking unit in the absence of added hydrogen. Because both the FCC and TOC processes are well established, it is not necessary to describe their individual features in detail, except to point out that both are endothermic catalytic cracking processes which are operated at elevated temperatures, typically in excess of about 550°C (about 1020°F) usually under slight superatmospheric pressure in the reactor. The catalyst passes continuously in a closed loop from the cracking reactor to the regenerator in which the coke which accummulates on the catalyst is removed oxidatively, both in order to restore activity to the catalyst and to supply heat for the endothermic cracking requirements. The oxidative regeneration is carried out in a bed of the same general type as the reactor bed so that in a TOC process, regeneration is carried out in a moving, gravitating bed in which the catalyst particles move downwards in countercurrent to the flow of regeneration gas and in the various FCC processes, regeneration is carried out in a fluidized bed, typically using a dense phase bed or a combination of dense phase bed with a dilute phase transport bed, according to the unit. Typical _FCC processes are disclosed in U.S. Patents Nos. 4,309,279; 4,309,280; 3,849,291; 3,351,548; 3,271,418; 3,140,249; 3,140,251; 3,140,252; 3,140,253; 2,906,703; 2,902,432; regeneration techniques applicable to FCC are disclosed, for example, in U.S. Patents Nos. 3,898,050, 3,893,812 and 3,843,330 to which reference is made for a description of particular details of such processes.

[0008] In general, the present catalytic cracking process will be carried out under conditions comparable to those used in existing processes, having regard to the capabilities of the cracking unit, the exact composition of the feed and the type and distribution of the products which are desired. As is well known, some feeds are more refractory than others and require the use of higher temperatures and changes in the distribution of the products, for example, depending upon whether the production of naphtha or of distillate is to be maximized, will require other changes. Other changes in operating conditions may be required according to the circulation rate -- a factor which is characteristic of the unit -- and catalyst makeup rate. 7he extent to which changes in these operating conditions will affect the products obtained in any given unit will be known for that unit.

Feedstocks

[0009] Feedstocks which are used in the present process are highly paraffinic petroleum fractions, that is, petroleum fractions which contain at least 20% by weight of waxy components. The waxy components will comprise normal paraffins and slightly branched chain paraffins with only minor degrees of short-chain branching, e.g. mono-methyl paraffins. In some cases, the petroleum fraction will contain at least 40% or even at least 60 wt. % of waxy components and indeed, the ability of the present catalysts to handle very highly paraffinic feeds enable certain refinery streams which are almost exclusively paraffinic, such as slack wax, to be cracked effectively to produce products of higher value. The presence of waxy components implies, of course, that the petroleum fraction has an initial boiling point which places the molecular weights of the paraffins in a range where they will be waxy in nature. This normally means that the fraction will have an initial boiling point above that of the naphtha boiling range materials, e.g. above about 200°C (about 390°F) and more usually the initial boiling point will be above about 300°C (about 570°F). In most cases, the initial boiling point of the fraction will be at least 345°C (about 650°F). In most cases, the end point will not be higher than 565°C (about 1050°F) although higher end points may be encountered, depending upon the distillation units being used in advance of the cracker although they may include significant amounts of heavy ends which are essentially non-distillable. Generally, therefore, the feedstocks which are used in the present process will have a boiling range within the range of 345° to 565°C (about 650° to 1050°F) although other boiling ranges, e.g. 300-500°C may also be encountered. The feeds can therefore be generally characterized as gas oils, including vacuum gas oils although other highly paraffinic refinery streams such as slack wax may also be catalytically cracked using the present catalysts.

[0010] The feeds will usually contain varying amounts of aromatic compounds, generally polycyclic aromatics with alkyl side chains of varying lengths which will be removed during the cracking process. However, certain feeds may be so highly paraffinic that the content of aromatics will be quite small, for example, in the slack waxes mentioned above. Naphthenes will also generally be present in varying amounts, depending upon the nature of the feed and its processing prior to the catalytic cracking step. In general, the feedstocks will not contain unusually large amounts of aromatics.

[0011] The feed may be subjectd to various treatments prior to cracking, either to improve the cracking operation by providing a feed of improved crackability or to improve the distribution of the products or their properties. Hydrotreating of the feed is a particularly useful adjunct because it removes heteroatom-containing impurities and saturates aromatics; in doing so, it reduces catalyst poisoning by the heteroatom contaminants, especially nitrogen and sulfur, reduces the SO emissions from the unit and, in increasing the hydrogen content of the feed to a level which approaches that of the products, improves product distribution and feed crackability.

[0012] The compositions of two typical, waxy gas oil feeds are set out in Tables 1 and 2 below; of two hydrotreated feeds in Tables 3 and 4 and of four slack wax feeds in Table 5. These feeds, either on their own or with other feeds may be used in the present process.

Cracking Catalyst

[0013] The cracking catalyst used in the present process comprises zeolite beta as its essential cracking component. Zeolite beta is a known zeolite which is described in U.S. Patents Nos. 3,308,069 and RE 28,341, to which reference is made for a description of this zeolite, its method of preparation and its properties.

[0014] Zeolite beta may be synthesized with relatively high silica:alumina ratios, for example, in excess of 100:1 and it is possible to achieve even higher ratios by thermal treatments including steaming and acid extraction, and in this way it is possible to make highly siliceous forms of the zeolite with silica:alumina ratios ranging from the lowest ratio at which the zeolite may be synthesized up to 100:1, 1,000:1, 30,000:1 or even higher. Although these forms of the zeolite would be capable of being used in the present process, the fact that catalytic cracking requires the catalyst to possess a relatively high degree of acidity, generally implies that the more acidic materials, with silica:alumina ratios from about 15:1 to 150:1 will be preferred, with ratios from 30:1 to about 70:1 giving very good results. Because zeolite beta may be synthesized relatively easily with silica:alumina ratios of this magnitude, the zeolite may generally be used in its as-synthesized form, following calcination to remove the organic cations used in its preparation. For similar reasons, it is generally preferred not to incorporate substantial amounts of alkali or alkaline earth metal cations into the zeolite, as disclosed in U.S. Patent No. 4,411,770, because these will generally decrease the acidity of the material. If lower acidity should be desired, however, it is normally preferred to secure it by using zeolite forms of higher silica:alumina ratio rather than by adding alkali or alkaline earth metal cations to counter the acidity, because the more highly siliceous forms of the zeolite tend to be more resistant to hydrothermal degradation. Acid extraction is a preferred method of dealuminzation either on its own or with preliminary steaming; dealuminized catalysts made in this way have been found to have improved distillate (G/D) selectivity.

[0015] The acidic functionality of the zeolite at the time that it is used as fresh catalyst in the process, is typically in excess of about 0.1, as measured by the alpha activity test, with preferred alpha activities being in the range of from 1 to 500 or even higher, and more commonly in the range of 5 to 100. The method of determining alpha is described in U.S. Patent No. 4,016,218 and in J. Catalysis, VI, 278-287 (1966), to which reference is made for a description of the method. However, it should be remembered that the initial alpha value will be relatively rapidly degraded in a commercial catalytic cracking unit because the catalyst passes repeatedly through steam stripping legs to remove occluded hydrocarbons and in the regeneration process, a considerable amount of water vapor is released by the combustion of the hydrocarbonaceous coke which is deposited on the zeolite. Under these conditions, aluminum tends to be removed from the framework of the zeolite, decreasing its inherent acidic functionality.

[0016] Zeolite beta may be synthesized with trivalent framework atoms other than aluminum to form, for example, borosilicates, boroaluminosilicates, gallosilicates or galloaluminosilicate structural isotypes. These structural isotypes are considered to constitute forms of zeolite beta, the term zeolite beta being used to refer to materials of ordered crystalline structure possessing the characteristic X-ray diffraction of zeolite beta. The zeolite may be partially exchanged with certain cations in order to improve hydrothermal stability, including rare earths and Group 1B metals.

[0017] The zeolite beta is capable of catalyzing the desired cracking reactions on its own but in order to resist the crushing forces and attrition which are encountered in a commercial catalytic cracking unit, it will generally be formulated with a matrix or binder in order to improve its crushing strength and attrition resistance. The zeolite will therefore generally be incorporated in a clay or other matrix material such as silica, alumina, silica/alumina or other conventional binders. The binder material imparts physcial strength to the catalyst particle and also enables the density of the catalyst particles to be regulated for consistant fluidization in FCC units. Generally, the amount of zeolite in the catalyst particles will be in the range of 5 to 95 wt. percent, with amounts from 10 to 60 wt. percent being preferred.

[0018] The binder may, and usually does, have some significant catalytic activity of its own but it will generally be preferred that the total acidic functionality provided by the binder will be only a minor amount of the total catalyst activity, as determined by the alpha test, because it is the zeolite which provides the particular, selective cracking characteristics which are desired with the paraffinic feeds.

[0019] Because catalytic cracking, which is generally carried out in the absence of added hydrogen, does not require the presence of a hydrogenation-dehydrogenation component as does hydrocracking, there is no need for any such component in the present cracking catalysts. Nevertheless, metal components may be present for other purposes, notably to promote the oxidation of carbon monoxide to carbon dioxide in the regenerator, as described in U.S. Patents Nos. 4,473,658; 4,350,614; 4,174,272; 4,159,239; 4,093,568; 4,072,600; 4,541,921; 4,435,282; 4,341,660 and 4,341,623 to which reference is made for a description of the use of oxidation promoters for this purpose. Typical oxidation promoters are the noble metals, especially platinum, and generally they will be present, if at all, in amounts which do not exceed 1,000 ppmw, preferably not more than 500 ppτw with about 100 ppmw being a typical maximum. In certain cases, extremely small amounts of promoter down to 0.1 ppmw may be sufficient and amounts of 0.1-100 ppmw are by no means uncommon. The oxidation promoter may be present on the catalyst or as a separate component.

[0020] Other zeolites in addition to the zeolite beta may be present in the catalyst. If other zeolites, such as ZSM-5, are included in'the catalyst for the purpose of octane improvement, they will be used in amounts less than that of the zeolite beta, for example, usually less than 50 wt. percent of the amount of the zeolite beta and typically from 10 to about 30 percent by weight of the zeolite beta, as described, for example, in U.S. Patents Nos. 3,769,202; 3,758,403; 3,894,931; 3,894,933 and 3,894,934, although even smaller amounts, for example, 0.1 to 0.5 wt. percent may be used, as described in U.S. Patent No. 4,309,279, to which reference is made for a description of the use of intermediate pore zeolites in cracking catalysts for this purpose.

[0021] When the catalyst is to be used in a moving bed process, it will usually be formed into pills, extrudates or oil-dropped spheres with an equivalent particle diameter of 1/32 to 1/4 inch, preferably about 1/8 inch (about 1 to 6 millimeters, preferably about 2 millimeters). When the catalyst is intended for use in a fluid catalytic cracking process, it will usually be used in the form of fine powder, typically of 10 to 300 microns particle size, typically about 100 microns.

Process Conditions

[0022] As mentioned above, the catalytic cracking process is an endothermic process which is carried out under high temperatures, with the heat required for the process supplied by the oxidation of the carbon (coke) which accumulates on the catalyst during the cracking part of the cycle. Thus, the process as a whole, including the regeneration, is operated in a heat-balanced mode, with the regenerated catalyst serving as the medium for transferring the heat produced in the regenerator to the endothermic cracking process. Each cracking unit will have its own particular operating characteristics, as noted above, and these will determine the exact conditions used in the unit. Generally, however, the conditions will be characterized as being of elevated temperature, typically in excess of about 550°C (about 1020°F) and frequently even higher, although temperatures above about 760°C (about 1400°F) are infrequently encountered because they tend to cause sintering of the catalyst and are close to the metallurgical limits on most units. In riser type crackers, the quoted temperatures will be those prevailing at the top of the riser. Pressures, as noted above, are usually only slightly above atmospheric typically up to about 1000 kPa (abs.) (about 130 psig), more commonly up to about 500 kPa (abss.) (about 58 psig). Catalyst/oil ratios will generally be in the range 0.1-10, more commonly 0.2-5 (by weight, catalyst:oil).

[0023] Conversion, that is, the proportion of the feed converted to lower boiling products, is a significant process parameter and generally will be at least 50 percent by weight. So, in a 345°C+ (about 650°F+) gas oil, at least 50 percent by weight of the feed will be converted to fractions boiling below 345°C (about 650°F). Usually, conversion will be in the range 50-80 weight percent or even higher, up to 90 weight percent. It may, however, be necessary to limit conversion because of downstream limitations, especially distillation capacity. One characteristic of the present process using highly paraffinic feedstocks with the zeolite beta cracking catalyst is that large quantities of light olefins are produced and although these are desirable because they can be converted to high octane naphtha in conventional alkylation units, the fractionators connected to the cracking unit may not be large enough to handle these quantities of light olefins.

Process Characteristics

[0024] In use, zeolite beta has shown itself to be a stable cracking catalyst which, especially in its dealuminized forms with higher silica:alumina ratios, has good hydrothermal stability and in this respect has good potential for use in commercial cracking units in which the catalyst circulates through steam stripping zones and is subjected to water vapor at high temperature during the regeneration. In addition, zeolite beta is notable for its ability to crack paraffins in preference to aromatics and it is the n-paraffins which are cracked in preference to iso-paraffins. Zeolite Y, by contrast, is more selective towards naphthenes and aromatics so that highly paraffinic stocks have been considered refractory towards cracking with this zeolite. Zeolite beta is well able to convert these materials to lower boiling products but if significant quantities of aromatics are present with a correspondingly lower paraffin content, the use of a mixed catalyst comprising zeolite beta and a faujasite type zeolite may be desirable, as described in co-pending application Serial No. 775,189, to which reference is made for a description of a process using combination cracking catalysis of this type.

[0025] By preferentially cracking the waxy paraffins in the feed, zeolite beta effectively dewaxes the feed, so producing a lowering of the pour point in the unconverted fraction, e.g. the 345°C+ (about 650°F+) fraction. The present cracking process may therefore be employed for non-hydrogenative gas oil dewaxing in circumstances where an aromatic product is acceptable. At higher conversion levels, typically greater than 60 or 70 weight percent, a lowering of the pour point in the converted fraction may be noted, indicating a preference for conversion of the higher molecular weight components. Although zeolite beta has a distillate selectivity comparable to that of dealuminized zeolite Y at comparable silica:alumina ratios, it has been found that as the paraffin content of the feed increases, zeolite beta becomes progressively more effective in removal of the waxy paraffinic components, as indicated by the pour point of the unconverted fraction.

[0026] The dewaxing of the unconverted fraction enables the end point of distillate fractions which are pour point limited to be extended. For example, it is possible to extend the light fuel oil (LFO) fraction into the 345°C+ (about 650°F+) range because of the dewaxing effect of the catalyst, thereby enlarging the size of the IFO pool. Similarly, the pour point reduction of the 345°C+ (650°F+) fraction may permit the end point of heavy fractions, e.g. heavy fuel oil (HFO) to be extended.

[0027] Another particular advantage of zeolite beta is that it produces an improvement in the octane rating of the gasoline boiling range product (approx. C₅-165⁰C, C_S-330°F). Improvements of at least 2 and typically of 3 to 5 octane numbers (R+O) may be noted with cracking of highly paraffinic feeds over zeolite beta, as compared to cracking over conventional cracking catalysts based on zeolite Y. Octane ratings in excess of 90 (R+O) may be achieved. Furthermore, when the octane contribution from the alkylate fraction is considered, the improvement is even more marked: zeolite beta produces larger quantities of alkylate with a higher C_4/C₃ ratio than zeolite Y. These characteristics make for a higher alkylate yield and alkylate quality for a further improvement in gasoline quality. Octane quality of the naphtha and of the alkylate is relatively constant with conversion although slight increases do occur at higher conversion levels, as is customary.

Examples 1-4

[0028] These Examples compare the performances of two different cracking catalysts on two different feeds. One catalyst was a conventional catalyst based on zeolite Y and the other is based on zeolite beta.

[0029] The conventional catalyst was a sample of equilibrium Durabead 9A (trademark), a moving bed catalytic cracking catalyst removed from an operating refinery. It consisted of a conventional 12 wt.percent REY zeolite in a silica/alumina binder in bead form.

[0030] The zeolite beta catalyst consisted of 50 wt. percent zeolite beta (zeolite silica/alumina ratio of 40:1, alpha activity of 400 in the hydrogen form) and 50 wt. percent alumina binder mixed together and extruded. The catalyst was aried and calcined for 3 hours at 540°C (1000°F) in nitrogen followed by 3 hrs. at 540°C (1000°F) in air. The sodium content of the catalyst was 495 ppm. The zeolite beta catalyst was then steamed at 700°C (1290°F) for 4 hrs., in 100% steam at atmospheric pressure to an alpha activity of 6.

[0031] The two catalysts were then tested for the catalytic cracking of two different gas oil feeds, whose properties are shown in Table 6 below.

[0032] As is apparent, Gas Oil B is considerably more paraffinic than Gas Oil A.

[0033] The catalysts were each placed in a laboratory sized, fixed-bed cracking unit which simulates moving bed cracking and used to crack the two gas oil feeds. The conditions used and the results obtained are given in Tables 7 and 8 below.

[0034] As shown in Tables 7 and 8, zeolite beta provides only marginal benefits over the conventional zeolite Y cracking catalyst when relatively non-paraffinic feeds such as Gas Oil A are used. Although the octane number of the gasoline produced is about the same, the zeolite beta cracking produces a 0.9 higher gasoline and alkylate octane number and 5 vol. percent higher gasoline and alkylate. These benefits increase substantially when the feed is highly paraffinic. As shown in Table 8, zeolite beta cracking of the paraffinic Gas Oil B results in the production of significantly more gasoline plus alkylate (75.0 vol. percent, as compared to 64.0 vol. percent). Furthermore, the improved pour points of the heavier fractions is notable.

[0035] Somewhat surprisingly, the octane number of the gasoline and alkylate fraction produced by zeolite beta cracking is also significantly higher, a gasoline plus alkylate octane number (R+O) of 91.9 as compared to the 88.3 (RrO) of the gasoline and alkylate produced from zeolite Y catalytic cracking. Thus, the zeolite beta produced not only more gasoline, but gasoline with a higher octane number than the commercially used catalyst based on zeolite Y.

Examples 5-13

[0036] In these Examples, two catalysts were tested on three different waxy gas oils of high paraffin content.

[0037] The first catalyst was a dealuminized zeolite Y catalyst prepared by the acid extraction of zeolite Y, followed by steaming at 650°C (1200°F) at atmospheric pressure in 100% steam for 24 hours. The final, steamed zeolite had a silica:alumina ratio of 226:1.

[0038] The second catalyst was a calcined zeolite beta catalyst (30:1 silica:alumina) which had been subjected to the same steaming treatment to increase the silica:alumina ratio to about 228:1.

[0039] The catalysts were used for the fluidized bed cracking of the three gas oils described below, using a small scale, dense fluidized bed reactor operated in a cyclic mode to give 10 minutes cracking and 5 minutes helium purge followed by oxidative regeneration to completion (40_% oxygen:60% nitrogen), with a final 1 minute helium purge. The catalyst was used in the form of the pure zeolite (50cc) crushed to 60-80 mesh (U.S. Standard), mixed with 30cc of acid-washed, calcined quartz chips (80-120 mesh, U.S. Standard, "Vycor" - trademark). Comparison runs to show the extent of thermal cracking were carried out with 80cc of crushed "Vycor" chips. The reaction temperature in each case was 510°C (950°F) with space velocity (IHSV) varying from 1.5 to 12 hr^-1. Product was accummulated over a series of 10 cycles; mass balances in all cases were greater than 95%. All products were analyzed by gas chromatograph.

[0040] The properties of the three heavy vacuum gas oils (HVGO) used in these experiments are given in Table 9 below.

[0041] The results are given in Tables 10-12 below, the reported pour points being for the 345°C+ (650°F+) fractions.

[0042] Comparison of Table 10-12 shows that the dewaxing ability of the zeolite beta is related to the paraffin content of the feed. For relatively less waxy HVGO-C (31% paraffins) there is no improvement in the pour point of the 345°C+ fraction, either by thermal cracking, cracking over the zeolite Y catalyst or over zeolite beta. As the content of the feeds increases in gas oils D and E (52 and 81% paraffins, respectively), so does the spread between the 345°C+ pour points for the products obtained with the zeolite Y and the zeolite beta catalysts. Although product distillate selectivities for the two zeolites are similar, the possibility of extending the distillate end point above 345°C by reason of the reduced pour point permits an increase in distillate selectivity for the zeolite beta to be achieved.

Examples 14-15

[0043] A steamed zeolite beta catalyst was used in these Examples with another waxy feed. The catalyst was prepared by the same method as in Examples 5-13 and used for cracking according to the same procedure as described there.

[0044] The properties of the mixed-phase feed used are shown in Table 13 below.

[0045] The results of the cracking of the mixed-phase feed at two different severities are shown in Table 14 below, the pour point being of the 315°C+ (600°F+) fractions.

These results show that the zeolite beta effectively dewaxes the high boiling fraction with increasingly lower pour point being obtained at higher conversions.

Examples 16-19

[0046] Gas Oil _D was cracked in a fixed bed at 500°C (925°F) over an REY cracking (12% REY on silica-alumina) catalyst and a steamed zeolite beta cracking catalyst, prepared by the same method as in Examples 5-13. The LFO (230°-365°C, 450°-690°F) distillate yield and cetane index were determined at two different conversion levels for each catalyst. The results are shown in Table 15 below.

[0047] The distillates from the beta catalyst are of similar cetane quality to those from REY.

Claims

1. A process for catalytically cracking a hydrocarbon oil having an initial boiling point above 200⁰C comprising contacting the oil with a circulating hot cracking catalyst in the absence of added hydrogen to produce cracking products which are separated from the catalyst, and continuously regenerating the catalyst on a cyclic basis by oxidative removal of the carbon deposited on the cracking catalyst during the cracking, characterised in that feedstock comprises at least 20 weight percent paraffins and the cracking catalyst comprises zeolite beta.

2. A process according to claim 1 in which the feedstock boils within the range of 300 to 500⁰C.

3. A process according to claim 1 or claim 2 in which the feedstock comprises at least 40 wt.% paraffinic components.

4. A process according to any preceding claim in which the feedstock comprises at least 60 wt.% paraffinic components.

5. A process according to any preceding claim in which the catalyst comprises 5 to 95 wt.% zeolite beta.

6. A process according to any preceding claim in which the zeolite beta has a silica:alumina ratio of 15:1 to 150:1.

7. A process according to any preceding claim in which the zeolite beta has an alpha activity of 1 to 500.

8. A process according to any preceding claim in which the catalytic cracking process is a fluidized catalytic cracking process.

9. A process according to any of claims 1 to 7 in which the catalytic cracking process is a moving, gravitating bed catalytic cracking process.

10. A process according to any preceding claim in which zeolite beta is the sole zeolite cracking component in the catalyst.

11. A process according to any preceding claim in which the cracking catalyst includes no metal components in excess of 1000 ppmw.

12. A process according to any preceding claim in which the cracking catalyst includes a carbon monoxide oxidation promoter as a metal component in an amount from 0.1 to 1000 ppmw.

13. A process according to claim 12 in which the oxidation promoter is present in an amount of 0.1 to 100 ppmw.

14. A process according to claim 12 or claim 13 in which the oxidation promoter comprises platinum.

15. A process according to any preceding claim in which the conversion to lower boiling products is at least 50 weight percent.

16. A process according to any preceding claim in which the conversion to lower boiling products is 50 to 90 weight percent.

17. A process according to any preceding claim in which the feedstock has an initial boiling point of at least 345^oC.