CRACKING OF HYDROCARBONS

Abstract: The cracking of hydrocarbons utilizing cerium and/or cerium containing compounds to passivate nickel contaminants in the hydrocarbon feedstocks.

Description: The present invention relates to the catalytic cracking of hydrocarbons, and in particular to methods of inhibiting on zeolite catalysts the detrimental effects of contamination by metals, particularly nickel, which are contained in the hydrocarbon feedstock. Major metal contaminants that are found in Fluid Catalytic Cracker (FCC) feedstocks include nickel, vanadium, iron, copper and occasionally other heavy metals. The problems associated with metal contamination, particularly nickel, during the catalytic cracking of hydrocarbons to yield light distillates such as, for example, gasoline are documented in Oil & Gas Journal of July 6, 1981 on pages 103 to 111 and of October 31, 1983 on pages 128 to 134. The problems associated with vanadium metal contamination are described in US-A- 4 432 890 and DE-A- 3 634 304. The present invention represents an innovation and improvement over those processes set forth and claimed in US-A- 4 432 890 and DE-A- 3 634 304. It is well known in the art that nickel significantly increases hydrogen and coke, and can cause decreases in catalyst activity. Vanadium primarily decreases activity and desirable gasoline selectivity by attacking and destroying the zeolite catalytic sites. Its effect on the activity is about four times greater than that of nickel. Vanadium also increases hydrogen and coke, but at only about one fourth the rate of nickel. The reducing atmosphere of hydrogen and carbon monoxide in the cracking zone reduces the nickel and vanadium to lower valency states. The nickel is an active dehydrogenating agent under these circumstances, increasing hydrogen and coke which also leads to a small decrease in conversion activity. Vanadium has been shown to destroy active catalytic sites by the movement of the volative vanadium pentoxide through the catalyst structure. Lower oxides of vanadium are not volative and are not implicated in the destruction of catalyst activity. In the cracking zone, lower oxides of vanadium will be present and vanadium pentoxide will be absent. Thus in the cracking zone, fresh vanadium from the feedstock will not reduce acitvity. When the lower valency vanadium compounds enter the regenerator where oxygen is present to combust the coke, the vanadium compounds are oxidized to vanadium pentoxide which then can migrate to active sites and destroy the active sites, leading to a large reduction in acitvity and selectivity, particularly petroleum (gasoline). An increase in hydrogen and coke due to contaminant metals translates to a decrease in yields of desirable products such as, for example, petroleum (gasoline) and light gases (propane/butanes). Also, increases in hydrogen yield require extensive processing to separate the cracked products and can result in operation and/or compressor limitations. While the coke that is produced during the catalytic cracking process is used to keep the unit in heat balance, increases in coke yields mean increased temperatures in the regenerator which can damage catalysts by destroying the zeolitic structures and thus decrease activity. As activity is destroyed by contaminant metals, conversion can be increased by changing the catalyst to oil ratio or by increasing the cracking temperature, but coke and hydrogen will also be increased in either case. For best efficiency in a FCC unit, the activity should be kept at a constant level. However, as vanadium is deposited on the catalyst over and above about a 3,000 ppm level, significant decreases in activity occur. Passivators have been used to offset the detrimental effects of nickel and of vanadium. Numerous passivating agents have been taught and claimed in various patents for nickel. Some examples include antimony in US-A- 3 711 422, US-A- 4 025 458, US-A- 4 111 845, and sundry others; bismuth in US-A- 3 997 963, and US-A- 4 141 858; tin in combination with antimony in US-A- 4 255 287; germanium in US-A- 4 334 979; gallium in US-A- 4 377 504, tellurium in US-A- 4 169 042; indium in US-A- 4 208 302; thallium in US-A- 4 238 367; manganese in US-A- 3 977 963; aluminium in US-A- 4 289 608; zinc in US-A- 4 363 720; lithium in US-A-4 364 847; barium in US-A- 4 377 494; phosphorus in US-A- 4 430 199; titanium and zirconium in US-A- 4 437 981; silicon in US-A- 4 319 983; tungsten in US-A- 4 290 919; and boron in US-A- 4 295 955. Examples of vanadium passivating agents are fewer, but include tin in US-A- 4 101 417 and US-A- 4 601 815; titanium, zirconium, manganese, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanides, rare earths, actinides, hafnium, tantalum, nickel, indium, bismuth, and tellurium in US-A- 4 432 890 and US-A- 4 513 093; yttrium, lanthanum, cerium and the other rare earths in DE-A- 3 634 304. In general, the passivating agents have been added to the catalyst during manufacture, to the catalyst after manufacture by impregnation, to the feedstock before or during processing, to the regenerator, and/or any combination of the above methods. It has now been found that when a zeolite catalyst contaminated with metals, including nickel, is treated with cerium compounds, the hydrogen-forming property of the nickel is mitigated to a great extent. According to the present invention there is provided a method for cracking a hydrocarbon comprising: (a) contacting a hydrocarbon feedstock with a fluidized zeolite-containing cracking catalyst in a cracking zone under cracking conditions; (b) recovering the cracked products; (c) passing the cracking catalyst from the cracking zone to a regeneration zone; (d) regenerating the cracking catalyst in the regeneration zone by contact with oxygen-containing gas under regeneration conditions to produce a regenerated catalyst; and (e) introducing the regenerated catalyst to the cracking zone for contact with the hydrocarbon feedstock; the catalyst during the cracking process being contaminated with from 100 to 5000 parts nickel per million parts of catalyst, with nickel being contained in a feedstock at concentrations of up to 100 ppm and the catalyst containing less than 3000 ppm of vanadium; which comprises treating the feedstock containing the nickel contamination with from 0.005 to 240 ppm cerium, and the atomic ratios of cerium/nickel in the feedstock being from 1:1 to 0.05:1. While cerium passivates vanadium, it was quite unexpectedly found that cerium also passivates the adverse effects of nickel. US-A- 4 432 890 and US-A- 4 513 093 teach that numerous metallic compounds (titanium, zirconium, manganese, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanides, rare earths, actinides, hafnium, tantalum, nickel, indium, bismuth, and tellurium act as vanadium passivators. DE-A- 3 634 304 claims that yttrium, lanthanides, cerium, and other rare earth compounds passivate the adverse effects of vanadium. In US-A- 4 432 890, only titanium is used on an FCC catalyst to show the effects of the various claimed metals on passivating vanadium. Cerium is not specifically mentioned. In each of these Patent Specifications, nickel is not added to the catalyst undergoing testing and so the effects on hydrogen-make by nickel with cerium passivation could not be observed. In addition, the only vanadium levels tested in these two Patent Specifications is 5,500 and 3,800 ppm, respectively. Although nickel and vanadium contamination of FCC catalysts is discussed in great depth in the art and in the same context, it is equally clear from the specifics of the art, that each represents its own separate problem as well as solution. It is not evident or expected that any treatment for vanadium would also be effective for nickel or vice-versa. It is well documented in the art that a certain level of vanadium is necessary on the catalyst to observe a loss of catalyst activity. This level varies with the type of catalyst. In one report the level of vanadium below which catalyst activity is not degraded is 1,000 ppm for that catalyst (see the newsletter Catalagram published by Davision Chemical in 1982, Issue Number 64). In another article (R.F. Wormsbecher, et al., J. Catal./, 100, 130 to 137 (1986)), only above 2000 ppm vanadium are catalyst activity and selectivity lost. Other catalysts such as, for example metal resistant catalysts need high levels (above about 3000 ppm) of vanadium where loss of catalyst activity can be observed (Oil & Gas Journal, 103-111, July 6, 1981). From these articles, it can be seen that not all catalysts are significantly affected by lower levels of vanadium contaminant. Thus, the treatment of specific catalysts containing less than a significant level of vanadium would show very small to insignificant changes in activity on addition of cerium. However, the practical effects of nickel can be observed at levels as low as about 300 ppm, with the amount of hydrogen and coke increasing proportional to the amount of nickel present. Preferably the atomic ratio of cerium to nickel is from 0.66: 1 to 0.1: 1. Although it is not important as to the form in which the cerium is added to the feedstock, examples of cerium compounds which can be used include cerium in the cerous or ceric state with anions of nitrate (designated NO₃ in the Examples), ammonium nitrate, acetate, proprionate, butyrate, neopentoate, octoate (Oct), laurate, neodecanoate, stearate, naphthenate, oxalate, maleate, benzoate, acrylate, salicylate, versalate, terephthalate, carbonate, hydroxide, sulphate, fluoride, organosulphonate, acetylacetonate, beta-diketones, oxide (designated either as O₂ for a water based suspension or as Org for a hydrocarbon based suspension in the Examples, ortho-phosphate, or combinations of the above. Particularly useful cerium compounds are the octoate, nitrate and oxide. Generally the cerium compound is fed to the feedstock on a continuous basis so that enough cerium is present in the feedstock to passivate the nickel contained therein. The cerium concentration in the feedstock will be 0.005 to 240 ppm based on 0.1 to 100 ppm nickel in the feedstock. The most desirable manner of treating the cracking catalyst with the cerium will be adding a solution or suspension containing the cerium to the feedstock. The medium used to solubilize or suspend the cerium compound can be water or an organic medium, preferably a hydrocarbon medium similar to the hydrocarbon feedstock. The concentration of the cerium in the medium can be any concentration that makes it convenient to add the cerium to the feedstock. The present invention will now be more particularly described with reference to, but is in no manner limited to, the following Examples. In the Examples shown, commercially available zeolite crystalline aluminosilicate cracking catalysts were used. The catalytic cracking runs were conducted employing a fixed catalyst bed, a temperature of 482 o C, a contact time of 75 seconds, and a catalyst to oil ratio of about 3:1 or greater as detailed under the catalysts to oil ratio (C/O) in the individual Tables. The feedstock used for these cracking runs was a gas oil feedstock having a boiling range of approximately 260 to 538 o C (500 to 1000 o F). The four zeolitic cracking catalysts that were used are all commercial catalysts that are described as; Catalyst A -- yielding maximum octane enhancement and lowest coke and gas, Catalyst B -- yielding highest liquid product selectivity and low gas and coke make, Catalyst C -- yielding highest activity for octane enhancement and stability with low coke and gas make, and Catalyst D -- yielding octane enhancement and high stability with low coke and gas make. Each of the four catalysts were conditioned similarly. The fresh Catalysts A, C, and D were heated in air to 649 o C for 0.5 hour before metals were added. To these conditioned catalysts were added the appropriate ppms of vanadium, and/or nickel, and/or cerium (as designated in the Tables) followed by heating the metals contaminated catalysts in air for 1 hour at 649 o C and then for 6.5 hours in steam at 732 o C, or 760 o C, or 788 o C. Catalysts B was heated in air at 649 o C for 0.5 hour before metals were added. To the conditioned catalyst was added the appropriate ppms of vanadium and/or nickel and/or cerium (as designated in Table 2) followed by heating the metals contaminated catalyst in air for 1 hour at 649 o C and then for 19.5 hours at 732 o C in steam. The procedure utilzied to test the efficacy of the zeolite catalysts treated in accordance with the present invention is that which is outlined in the ASTM-D-3907. The weight percent changes in conversion were calculated in the following manner: Weight % Change Conversion = Wt. % conv. Ce run - Avg. Wt. % conv. metals contaminant runs The percent changes in hydrogen make were calculated in the following manner: Predicted hydrogen weight percent data were determined by a least squares linear fit of the vanadium and/or nickel contaminated catalyst runs for each catalyst. Predicted catalyst hydrogen weight percent data were determined by a least squares fit of the fresh catalysts only. The equations determined in each case are given in the appropriate tables. The percent changes in coke were calculated in the following manner: It is apparent from the percent change of hydrogen data in Table 1 that cerium in the form of the octoate (Oct) greatly decreases the amount of hydrogen make that is attributed to the nickel contamination. Additionally, the weight percent changes in the conversions are relatively small. Also, the catalysts passivated with cerium resulted in lower coke values when steamed at 732 o C or 788 o C. From the data in Table 2, it is apparent that cerium reduces hydrogen make especially when the cerium is in the form of an organic compound, and in particular the octoate. At the same time, the increases in conversion are small, except when 3000 to 5000 ppm cerium for various compounds was used. Considering the 3000 ppm of vanadium on the present Catalyst B versus the 3800 ppm of vanadium on the catalyst in DE-A-3 634 304, the change in percent conversion is much smaller in our case (about 12%) versus the case (about 24%) in DE-A- 3 634 304. Thus, the cerium is a better passivator of nickel than vanadium. Also, the catalysts passivated with cerium had some effects on coke reduction in these experiments. For the data in Table 3, only slight improvements can be noted in reducing hydrogen make. It should be noted that when cerium alone was added to the catalyst, large increases in hydrogen make were observed and small decreases in activity were also noted. Thus, overfeeding of cerium could be detrimental to catalyst activity and hydrogen make. For Catalyst D, the percent changes in hydrogen and coke were reduced when passivated with cerium compounds. For completeness, all data obtained during these experiments have been included. Efforts to exclude any value outside acceptable test error limits have not been made. It is believed that, during the course of these experiments, possible errors in preparing samples and in making measurements may have been made which may account for the occasional data point that is not supportive of this art. It is apparent from the foregoing that catalysts treated in accordance with the procedures and treatment levels as prescribed by the present innovation permitted reduction in hydrogen attributed primarily to the nickel contaminant.

Claims: A method for cracking a hydrocarbon comprising: (a) contacting a hydrocarbon feedstock with a fluidized zeolite-containing cracking catalyst in a cracking zone under cracking conditions; (b) recovering the cracked products; (c) passing the cracking catalyst from the cracking zone to a regeneration zone; (d) regenerating the cracking catalyst in the regeneration zone by contact with oxygen-containing gas under regeneration conditions to produce a regenerated catalyst; and (e) introducing the regenerated catalyst to the cracking zone for contact with the hydrocarbon feedstock; the catalyst during the cracking process being contaminated with from 100 to 5000 parts nickel per million parts of catalyst, with nickel being contained in a feedstock at concentrations of up to 100 ppm and the catalyst containing less than 3000 ppm of vanadium; which comprises treating the feedstock containing the nickel contamination with from 0.005 to 240 ppm cerium, and the atomic ratios of cerium/nickel in the feedstock being of from 1:1 to 0.05:1. A method according to claim 1, wherein the cerium to nickel atomic ratio is 0.66:1 to 0.1:1. A method according to claim 1 or 2, wherein the feedstock is treated with the cerium on a continuous basis. A method according to any of claims 1 to 3, wherein the cerium is provided through the treatment of the feedstock with cerium octoate. A method according to any of claims 1 to 3, wherein the cerium is provided through the treatment of the feedstock with cerium nitrate. A method according to any of claims 1 to 3, wherein the cerium is provided through the treatment of the feedstock with cerium oxide. A method according to any of claims 1 to 6, wherein the cerium is provided through treatment of the feedstock with cerium as a compound in a solution or suspension. A method according to claim 7, wherein the medium used to solubilize or suspend the cerium compound is water or an organic solvent. A method according to claim 8, wherein the organic medium is a hydrocarbon medium.

Inventors: FORESTER, DAVID ROGER
Applicants: BETZ EUROPE, INC.
Application year: 1989
Main classification: C10G11
IPC codes: C10G11