Additives for FCC processes

Abstract

The invention includes an additive for maximizing olefin production. The additive includes a ZSM-5 molecular sieve, at least one inorganic oxide, and phosphorous oxide. The ZSM-5 molecular sieve has iron in the framework, and the additive includes at least 0.5 wt% of iron in the molecular sieve framework, measured as iron oxide. The additive can be used to maximize olefin production in an FCC process.

Description

Technical Field

[0001] This invention relates to additives for maximizing the production of light olefins, particularly propylene, in fluid catalytic cracking processes. Background Technology

[0002] Fluid catalytic cracking (“FCC”) processes produce lighter, valuable products, such as gasoline, distillates, and C2-C4 olefins and saturated hydrocarbons, through the cracking of heavy hydrocarbon fractions. The FCC process can be advantageously used for propylene production.

[0003] The FCC process is typically carried out in the presence of an FCC catalyst. Typical FCC catalysts include Y zeolites, or aluminum-deficient forms of these zeolites, such as dealuminated Y, ultrastable Y, and superhydrophobic Y. Zeolites can be stabilized with rare earth metals such as lanthanum, cerium, neodymium, and praseodymium, for example, in amounts from about 0.1 wt% to about 10 wt%. The catalyst used in the FCC process is in particulate form, typically with an average particle size ranging from 20 micrometers to 200 micrometers, and is circulated between the cracking reactor and the catalyst regenerator of the FCC unit. In the reactor, the hydrocarbon feed is contacted with a hot regenerated catalyst, which evaporates and cracks the feed at about 400°C to 700°C, typically 500°C to about 550°C.

[0004] The product distribution from current FCC processes includes a variety of components, with gasoline or diesel being of primary interest to most refiners. Light olefins and liquefied petroleum gas (“LPG”) are also present in FCC products and are attracting increasing attention from refiners as these products become more valuable. The resulting light olefins can be used for a variety of purposes; for example, they can be upgraded to high-quality alkylates via sulfuric acid or HF alkylation. LPG is used for cooking and / or heating purposes. Therefore, operators of FCC units can vary the content of their products based on the markets they serve and the value associated with each component found in FCC products.

[0005] Propylene is a specific light olefin in high demand. It is used as a feedstock in many of the world’s largest and fastest-growing synthetic materials and thermoplastics. Refiners are increasingly relying on their FCC units to meet the growing demand for propylene, and as operators seek opportunities to maximize profits, they are shifting the focus of traditional FCC units away from transportation fuels and towards petrochemical feedstock production.

[0006] Previously disclosed methods teach catalytic conversion methods for petroleum hydrocarbons, particularly catalytic conversion methods for producing light olefins in high yields from petroleum hydrocarbons. See, for example, U.S. Patent Nos. 5,997,728 and 8,658,024 and U.S. Patent Application Publications Nos. 2005 / 0020867 and 2010 / 0010279.

[0007] U.S. Patent Application Publication No. 2009 / 0134065 teaches a fluidizable catalyst composition comprising pentasilicone zeolite, at least 5% by weight of phosphorus (as P2O5), and at least about 1% of iron oxide present outside the pentasilicone zeolite framework.

[0008] Industrial facilities are constantly seeking new and improved methods for producing light olefins, particularly refiners who are also interested in producing gasoline as a primary product from their FCC units. Therefore, there is a demand for additives that offer improved olefin selectivity (e.g., propylene selectivity) per unit LPG, relative to existing additives.

[0009] The applicant has developed an additive that increases propylene yield by approximately 15% compared to additives previously used in FCC methods. Summary of the Invention

[0010] This invention includes an additive for maximizing olefin production in a fluid catalytic cracking process. The additive comprises a ZSM-5 molecular sieve, at least one inorganic oxide, and phosphorus oxide. The ZSM-5 molecular sieve has iron in its framework, and the additive contains at least 0.5% by weight of iron in the molecular sieve framework, measured as iron oxide. Attached Figure Description

[0011] Figure 1 shows a graph of propylene production versus the molar ratio of skeletal iron to skeletal aluminum (Fe:Al).

[0012] Figure 2 shows a graph of the molar ratio of propylene production to the combined amounts of phosphorus and skeletal iron and aluminum (P:(Fe+Al)). Detailed Implementation

[0013] This invention includes an additive for maximizing olefin production in a fluid catalytic cracking process. The additive comprises a ZSM-5 molecular sieve. The ZSM-5 molecular sieve has iron in its framework, and the additive contains at least 0.5% by weight of iron in the molecular sieve framework, measured as iron oxide.

[0014] ZSM-5 molecular sieves have a five-membered ring in their structural framework. This framework comprises tetrahedral coordinated silica and alumina. ZSM-5 molecular sieves also contain iron in the framework. Iron is added to the framework in the methods for preparing ZSM-5. "In the framework" means that iron is present in the structural framework of ZSM-5 because it replaces the silicon or aluminum in the typical silica-alumina framework of ZSM-5.

[0015] The additive preferably contains 1% to 5% iron (measured as iron oxide) in the molecular sieve framework, and even more preferably about 1% to 3% iron (measured as iron oxide).

[0016] Preferably, the molar ratio of iron to aluminum in the ZSM-5 skeleton is in the range of 0.4 to 0.67.

[0017] ZSM-5 containing iron in its framework can be produced by any known method. For example, a molecular sieve gel can be prepared by controlled mixing of alumina, silica, iron, acid, and a template source. The gel is then crystallized at high temperature (under autogenous pressure) for a period of time. The iron-containing ZSM-5 is then preferably treated by filtration, washing, ion exchange, and grinding.

[0018] Following preparation, ZSM-5 is preferably ion-exchanged with the desired cation to replace the alkali metal present in the prepared zeolite. This exchange treatment reduces the alkali metal content of the final catalyst to less than about 0.5% by weight, preferably less than about 0.1% by weight.

[0019] The additive also contains phosphorus. Phosphorus is commonly used to stabilize ZSM-5.

[0020] Preferably, phosphorus is added to the additive by impregnating ZSM-5, which has a skeletal iron structure, with a phosphorus compound. Alternatively, phosphorus may be added to an additive that contains inorganic oxides (and other possible components) in addition to ZSM-5. The additive preferably contains at least about 5% by weight of phosphorus (as P2O5), more preferably at least 8% by weight, and even more preferably at least 10% by weight.

[0021] Any phosphorus-containing compound can be used to add phosphorus to the additive. Preferably, the phosphorus-containing compound will contain a covalent or ionic component capable of reacting with hydrogen ions. Suitable phosphorus-containing compounds include acids such as phosphoric acid, phosphorous acid, and their salts. Other suitable phosphorus-containing compounds include phosphine, phosphites, phosphonates, and phosphonates, such as primary, secondary, and tertiary phosphines, such as butylphosphine; tertiary phosphine oxides such as tributylphosphine oxide; primary and secondary phosphonic acids, such as phenylphosphine; esters of phosphonic acids, such as diethylphosphonate, dialkylalkylphosphonate, and alkyldialkylphosphonates; trivalent phosphonates, such as diethyltrivalent phosphine; primary, secondary, and tertiary phosphites; and their esters, such as monopropyl esters, alkyldialkylphosphonates, and dialkylalkylphosphonates.

[0022] Preferably, the molar ratio of phosphorus to iron and aluminum in the ZSM-5 skeleton (P:(Fe+Al)) is in the range of 1 to 1.3.

[0023] In addition to ZSM-5 and phosphorus, the additive also contains one or more inorganic oxides. The inorganic oxides are preferably one or more of silica, alumina, silica-alumina, titanium dioxide, zirconium oxide, aluminum phosphate, etc. The inorganic oxides are preferably not molecular sieves. When the inorganic oxide is aluminum phosphate, the amount of phosphorus (separated from aluminum phosphate) added to the additive can be reduced.

[0024] The additive preferably also contains one or more types of clay. Preferably, the clay includes montmorillonite, kaolin, halloysite, bentonite, palygorskite, etc.

[0025] The additive preferably contains ZSM-5 with skeletal iron, such that ZSM-5 accounts for 25% to 80% by weight of the additive, more preferably 40% to 70% by weight of the additive.

[0026] The additive can be prepared by any known method, including adding ZSM-5 molecular sieves containing skeletal iron, phosphorus sources, inorganic oxides and clay to the spray dryer feed slurry and forming additive particles.

[0027] This additive can be used in a fluid catalytic cracking process for catalytic cracking hydrocarbon feedstocks, which involves contacting the feedstock with the additive under catalytic cracking conditions in the presence of an FCC catalyst.

[0028] Preferably, the catalytic cracking conditions involve reacting the hydrocarbon feedstock at a temperature of about 400°C to about 700°C. Feedstock contact typically takes place in an FCC unit comprising a riser and a reaction section, wherein the FCC catalyst contacts and evaporates the hydrocarbon feedstock. The hydrocarbon feedstock preferably enters the bottom of the riser of the FCC unit and carries the FCC catalyst and additives upwards through the riser into the reactor section. The cracked hydrocarbon products exit the top of the reactor, and the FCC catalyst particles and additives remain in a particle bed in the lower part of the reactor.

[0029] The used FCC catalyst and additives are then fed into the regenerator of the FCC unit. As used herein, the term "regenerator" also includes the combination of a regenerator and a CO boiler, particularly when the regenerator itself operates under partial combustion conditions. In the regenerator, the coke on the FCC catalyst and the additives are burned off in a fluidized bed in the presence of oxygen and fluidizing gas, which is typically supplied through the bottom of the regenerator. The regenerated FCC catalyst and additives are then removed from the regenerator and returned to the riser for reuse in the cracking process.

[0030] Preferably, the recycled stock of FCC catalyst and additives is recycled in the catalytic cracking process, wherein about 2% to about 20% by weight of the recycled stock contains the additives as described above.

[0031] The range of hydrocarbon feedstocks used in catalytic cracking processes can include petroleum distillates or residual feedstocks (raw or partially refined), coal tar and shale oil, gas oil, vacuum gas oil, atmospheric residue, vacuum residue, biomass, coking gas oil, lubricating oil extracts, hydrocracking bottom products, wild naphtha, sludge, etc. Feedstocks may contain recycled hydrocarbons, such as already cracked light and heavy cycle oils. Preferred feedstocks include gas oil, vacuum gas oil, atmospheric residue, and vacuum residue.

[0032] Additives and FCC catalysts can be added to the FCC unit separately or together. Additives are preferably, but not exclusively, added to the regenerator of the FCC unit.

[0033] Additives and FCC catalysts can be introduced into the FCC unit manually from a hopper, bag, or drum, or using an automated addition system, as described, for example, in U.S. Patent No. 5,389,236. To introduce additives into the FCC unit, the additives can also be premixed with the FCC catalyst and introduced into the unit as an admixture. Alternatively, the additives and FCC catalysts can be introduced into the FCC unit via a separate injection system. In another embodiment, the additives can be added to the FCC catalyst at different ratios. For example, to optimize the addition rate of the additives, the varying ratios can be determined when adding them to the FCC unit.

[0034] Conventional and high-severity FCC riser or downcomer cracking conditions, or older types of FCC fluidized bed reactor cracking conditions, can be used. Cracking reaction conditions include a catalyst / oil ratio of about 1:1 to about 30:1 and a catalyst contact time of about 0.1 seconds to about 360 seconds, and a riser top / reactor bed temperature of about 425°C to about 750°C.

[0035] The additive of this invention can be added to any conventional fluidized bed reactor-regenerator system, to a fluidized bed catalyst system, or to a system involving the continuous transport or circulation of catalyst / additive between a reaction zone and a regeneration zone. In one embodiment, the system is a circulating bed system. Typical circulating bed systems are conventional moving bed and fluidized bed reactor-regenerator systems. Both of these circulating bed systems are commonly used for hydrocarbon conversion (e.g., hydrocarbon cracking) operations. In one embodiment, the system is a fluidized bed catalyst reactor-regenerator system.

[0036] Other dedicated riser-regenerator systems that can be used in this paper include deep catalytic cracking (DCC), millisecond catalytic cracking (MSCC), high-severity petrochemical FCC residual fluid catalytic cracking (RFCC) systems, Superflex, and advanced catalytic olefins.

[0037] The FCC catalyst of this invention refers to any catalyst that can be used to operate an FCC unit under all types of catalytic cracking conditions. Any commercially available FCC catalyst can be used as an FCC catalyst. The FCC catalyst can be 100% amorphous, but in one embodiment, some zeolite can be included in a porous refractory matrix such as silica-alumina, clay, etc. The zeolite typically comprises about 5% to about 70% by weight of the catalyst, with the remainder being the matrix. Conventional zeolites such as Y zeolite, or aluminum-deficient forms of these zeolites such as dealuminated Y, superstable Y, and superhydrophobic Y, can be used. The zeolite can be stabilized with magnesium or rare earth elements, for example, in an amount from about 0.1% to about 10% by weight.

[0038] The zeolites that can be used in this article include both natural and synthetic zeolites.

[0039] Catalysts containing relatively high levels of silica zeolite can be used in this invention. They can withstand the high temperatures typically associated with the complete combustion of coke into CO2 in an FCC regenerator. Such catalysts include those that typically contain about 10% to about 70% ultrastable Y or rare-earth ultrastable Y.

[0040] In addition to the FCC catalyst and the additives of this invention, other additives may also be used in the method of this invention. Preferably, these additional additives may be added to increase the octane number; capture metals; promote CO combustion; and reduce SO₂. x Emissions, NO x Emissions and / or CO emissions; promote catalysis; or reduce gasoline sulfur.

[0041] Compared to similar methods using ZSM-5 without added iron or using ZSM-5 additives containing non-skeleton iron (added iron via ion exchange, wet impregnation, spray dryer feed slurry, and / or impregnation), the use of the additives of the present invention in the FCC process results in an increase in the yield of light olefins.

[0042] The following examples are merely illustrative of the invention. Those skilled in the art will recognize the spirit of the invention and many variations within the scope of the claims.

[0043] Comparative Example 1: Preparation of ZSM-5

[0044] Water (approximately 42 kg) was added to the tank, followed by the addition of tetrapropylammonium bromide template (TPABr, 280 g). Then, water glass (72 kg; 28.9 wt% SiO2, 8.9 wt% Na2O), aluminum sulfate (12.5 kg; 8.2% Al2O3), and sulfuric acid (4.45 kg) were simultaneously added to the tank to maintain a pH of approximately 9.5. After the addition of the raw materials, the gel was transferred to a reactor and hydrothermally crystallized at a high temperature (~160 °C) until the relative crystallinity of the zeolite reached 95% or higher (based on standard ZSM-5 crystals). After crystallization, the zeolite was washed and subjected to ion exchange to remove sodium. This zeolite was designated Zeolite 1.

[0045] Example 2: Preparation of the zeolite of the present invention containing iron in its framework

[0046] Except that ferric sulfate (3.65 kg; 18.2 wt% Fe₂O₃) was added to the tank along with water glass, aluminum sulfate, and sulfuric acid, the procedure was followed according to Comparative Example 1; and only 2.8 kg of sulfuric acid was used. After all the raw materials were added, the gel was then transferred to a reactor and hydrothermally crystallized at a high temperature (~160°C) until the relative crystallinity of the zeolite was greater than 95%. This zeolite was named zeolite 2.

[0047] Table 1: The properties of zeolite 1 and zeolite 2 are shown in Table 1.

[0048]

[0049] Comparative Example 3: Preparation of a comparative catalyst containing ZSM-5

[0050] False boehmite alumina (116.3 g; 78 wt% solids) was added to 630 g of water, and the mixture was stirred for 10 minutes. Formic acid (10.9 g; 90% concentration) was then added, and the mixture was stirred for 1 hour. The degelatinated alumina mixture was then transferred to a mixing tank, followed by silica sol (263.8 g; 41.3 wt% solids), clay (1177.9 g; 51.6 wt% solids), zeolite 1 (2335.8 g; 35.0 wt% solids), and 85% phosphoric acid (350.5 g). The slurry was stirred for half an hour and then spray-dried to form catalyst 3.

[0051] Example 4: Preparation of the catalyst of the present invention

[0052] The catalyst B of the present invention was prepared in a manner similar to that of Example 3, except that 1142.8 g of clay (51.6 wt% solids) and 383.8 g of 85% phosphoric acid were used, by using zeolite 2 instead of zeolite 1.

[0053] Comparative Example 5: Preparation of a comparative catalyst with added iron in the form of ferric nitrate

[0054] Catalyst C was prepared in a manner similar to that of Example 4, except that zeolite 1 (2249.8 g) was used instead of zeolite 2 and 296.2 g of ferric nitrate (9.8 wt% solids) was added to the spray dryer feed slurry.

[0055] Comparative Example 6: Preparation of a comparative catalyst with added iron oxide.

[0056] Catalyst D was prepared in a similar manner to Comparative Example 5, but 29.2 g of iron oxide (99.5% by weight solids) was added to the spray dryer feed slurry instead of ferric nitrate.

[0057] Table 2: Characteristics of catalysts A, B, C and D

[0058]

[0059] Example 7: Testing of catalyst AD

[0060] The catalyst AD was calcined at 732°C for 1 hour and then deactivated by steam. Deactivation was performed by steaming at 815°C for 20 hours with 95% steam. Catalyst testing was conducted using an Advanced Cracking Evaluation (ACE) unit. The catalyst was blended with a commercially available balanced catalyst (Ecat) at 4 wt% using a mixture of vacuum gas oil (80%) and atmospheric residue (20%) as feed. The conversion rate was varied by changing the feed rate (at a constant injection rate) while keeping the catalyst amount constant.

[0061] The activity results are shown in Table 3, with Δ yield shown after interpolation at a constant conversion rate of 70%, and after subtracting from the Ecat value.

[0062] Table 3: Tests for catalyst AD

[0063]

[0064] As shown in Table 3, compared with the corresponding comparative catalyst A which does not contain isomorphous framework iron, catalyst B with isomorphous framework iron makes propylene (C3) ＝ The content was 52.2% higher by weight, and compared with impregnation / mixing catalysts C and D, it also increased the content of C3. ＝ More than 29.1% by weight.

[0065] Example 8: Preparation of zeolites with different amounts of skeletal iron

[0066] Zeolites with different aluminum and iron ratios were prepared in the same manner as in Example 2, except for the amount of aluminum and / or iron used. Sulfuric acid was adjusted in proportion to the aluminum and iron.

[0067] Table 4: The properties of the prepared zeolite are shown in Table 4.

[0068]

[0069] Example 9: Preparation of catalysts with different amounts of skeletal iron

[0070] Zeolites 3, 4, and 5 were formulated into catalysts E, F, and G, respectively, in a manner similar to that used in Example 4. Their properties are shown in Table 5.

[0071] Table 5: Characteristics of catalyst EG

[0072]

[0073] Example 10: Testing of catalysts with different amounts of skeletal iron

[0074] Catalysts B, E, F, and G were calcined, steam-deactivated, and tested in a manner similar to that of Example 7. The activity results are shown in Table 6.

[0075] Table 6: Tests for catalysts B and EG

[0076]

[0077] The test results of Example 10 are plotted in Figure 1, showing that the greatest benefit of skeletal iron ZSM-5 (highest propylene yield) depends on the ratio of skeletal aluminum to iron in the zeolite.

[0078] Example 11: Preparation of catalysts with different amounts of phosphorus

[0079] Zeolite 2 (prepared as in Example 2) was formulated into a catalyst in the same manner as in Example 4, but with different phosphorus contents (9.5 wt% to 13.5 wt% P2O5). The differences stemmed from the clay. The properties of the prepared catalysts are shown in Table 7.

[0080] Table 7: Characteristics of Catalyst HK

[0081]

[0082] Example 12: Testing of catalysts with different amounts of phosphorus

[0083] Catalysts B, H, I, J, and K were calcined, deactivated, and tested in a manner similar to that of Example 7.

[0084] As shown in Table 8, in addition to the dependence of activity on the Fe / Al ratio of the skeleton, there are other optimization processes required for optimal activity.

[0085] Table 8: Test results of catalysts B and HK

[0086]

[0087] The results of Example 12 are plotted in Figure 2, showing that maximum activity was observed at a P / (Fe+Al) molar ratio of approximately 1.23 (where Fe and Al are the framework).

[0088] In summary, ZSM-5 containing isomorphous framework iron showed an additional propylene content of over 50%, which is significantly higher than when iron is introduced in amorphous forms (cation exchange or impregnation / mixing). The Fe / Al ratio and P / (Fe+Al) ratio play a key role in maximizing performance benefits.

Claims

1. An additive for maximizing olefin production in a fluid catalytic cracking process, the additive comprising a ZSM-5 molecular sieve, at least one inorganic oxide and phosphorus oxide, wherein the ZSM-5 molecular sieve has iron in its framework and the additive has a molar ratio P:(Fe+Al) of phosphorus to the combined amount of framework iron and framework aluminum in the range of 1 to 1.3, and the additive contains at least 0.5% by weight of iron in the molecular sieve framework, measured as iron oxide.

2. The additive according to claim 1, wherein the additive contains at least 5% by weight of phosphorus, calculated as P2O5.

3. The additive according to claim 1, wherein the ZSM-5 molecular sieve comprises 1% to 5% by weight of iron oxide.

4. The additive according to claim 1, wherein the inorganic oxide is selected from silicon dioxide, aluminum oxide, silicon dioxide-alumina, titanium dioxide, zirconium oxide, and combinations thereof.

5. The additive according to claim 1, wherein the additive further comprises clay.

6. The additive according to claim 1, wherein the ZSM-5 molecular sieve accounts for 25% to 80% by weight of the additive.

7. The additive according to claim 1, wherein the ZSM-5 molecular sieve accounts for 40% to 70% by weight of the additive.

8. The additive according to claim 1, wherein the inorganic oxide is replaced with aluminum phosphate.

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