Classifications

• • 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
  • C10G11/00—Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
  • C10G11/02—Catalytic cracking, in the absence of hydrogen, of hydrocarbon oils characterised by the catalyst used
  • C10G11/04—Oxides
  • C10G11/05—Crystalline alumino-silicates, e.g. molecular sieves

Definitions

• 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.
• 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).
• TCC Thermofor Catalytic Cracking
• FCC fluidized bed catalytic cracking
• 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.
• the catalyst 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.
• the catalysts used in catalytic cracking possess acidic functionality in order to catalyze the cracking reactions which occur.
• 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).
• 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.
• recycle of the unconverted fraction is of limited utility because of the refractory nature of the paraffins in this material.
• 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.
• 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.
• 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.
• 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 F CC processes are disclosed in U.S. Patents Nos.
• 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.
• 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 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.
• 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.
• 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).
• 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.
• 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.
• 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.
• aromatic compounds generally polycyclic aromatics with alkyl side chains of varying lengths which will be removed during the cracking process.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 pp ⁇ w 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.
• 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.
• the catalyst 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).
• the catalyst 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.
• 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.
• 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.
• 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.
• 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).
• 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.
• 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.
• 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.
• zeolite beta 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.
• a lowering of the pour point in the converted fraction may be noted, indicating a preference for conversion of the higher molecular weight components.
• 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.
• the dewaxing of the unconverted fraction enables the end point of distillate fractions which are pour point limited to be extended.
• LFO light fuel oil
• 345°C+ about 650°F+
• HFO heavy fuel oil
• zeolite beta produces an improvement in the octane rating of the gasoline boiling range product (approx. C 5 -165 0 C, 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/ C 3 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.
• 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.
• 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.
• Gas Oil B is considerably more paraffinic than Gas Oil A.
• 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.
• 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.
• 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.
• R+O gasoline plus alkylate octane number
• the zeolite beta produced not only more gasoline, but gasoline with a higher octane number than the commercially used catalyst based on zeolite Y.
• 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.
• 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.
• 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.
• 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.
• HVGO heavy vacuum gas oils
• 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.
• 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.
• the distillates from the beta catalyst are of similar cetane quality to those from REY.

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• 1985
  • 1985-12-06 AU AU50866/85A patent/AU575451B2/en not_active Ceased
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