CETANE UPGRADING VIA AROMATIC ALKYLATION

Abstract: A process of increasing the cetane index of a distillate pool comprising contacting a first refinery-grade feedstream of an aromatic compounds-containing heavy gasoline or distillate fuel feedstream with a second refinery-grade feedstream containing olefins in the presence of an acidic solid alkylation catalyst under alkylation conditions, wherein both the aromatic-containing feedstream and the olefin-containing feedstream are simultaneously upgraded to suitable fuel products without addition of hydrogen.

Description: CETANE UPGRADING VIA AROMATIC ALKYLATION The aromatics in both heavy naphtha and light cycle oil may be upgraded to higher cetane distillate via alkylation with olefins over a variety of acid catalysts, thus reducing the aromaticity of the distillate products and increasing the volume of distillate. As a result of clean fuels legislation, transportation fuels are undergoing dramatic changes. While much attention has centered on gasoline, diesel fuel must also meet more stringent requirements. These include U.S. EPA standards of 0.05 wt% sulfur (max.) plus 40 Cetane Index (min.) or 35 vol% aromatics (max.). Even more stringent diesel fuel requirements have been imposed in California and are anticipated in other parts of the world. Generally, permitted levels of sulfur and aromatics are being reduced while minimum cetane limits are increasing. These regulations are driven by the goal of reducing emissions, particularly NO x , from diesel engines. While Cetane Number (CN) can be increased cost effectively with additives such as isooctyl nitrate, no such additive fix exists for increasing Cetane Index (Cl), which depends on bulk properties (T 5 0 and density) of the fuel, as described in ASTM D976-91, incorporated herein by reference, which utilizes a two-variable equation for calculating Cl of various hydrocarbons. Thermal or catalytic cracking is the backbone of many refineries. It converts heavy feeds to lighter products by cracking large molecules into smaller molecules. Catalytic cracking operates at low pressures, without H 2 addition, in contrast to hydrocracking, which operates at high hydrogen partial pressures. Catalytic cracking is inherently safe as it operates with very little oil actually in inventory during the cracking process. However, some products derived from cracking processes, such as fluidized catalytic cracking (FCC) or coking, are high in aromatics content and particularly low in Cetane Index, typically with values around 20 (±5), much lower than the legislated limit of 40 or above, and contain 70-80% aromatics. Thus, finding commercial outlets for such products will become more difficult in the future. Lowered gasoline T 0 will exacerbate the situation as heavy FCC naphtha must be redefined as light cycle oil (LCO), thus increasing the volume of such products. Conventional hydroprocessing, such as hydrocracking or hydrogenation, may be used to upgrade aromatic distillates to meet the revised limits. However, conventional hydroprocessing is expensive, consuming large quantities of hydrogen, which is becoming a limited refinery resource, especially given pending gasoline aromatic, sulfur and T90 reductions. US 4,594,143 discloses alkylating aromatics in jet fuel with light olefins over large pore zeolite catalysts to produce an olefinic distillate and a high molecular weight alkyl aromatic fraction of higher boiling point than the olefinic distillate, which may be separated from the olefinic distillate and used as a blending material for diesel fuel. US 4,594,143 discloses an increase in CN of the alkylated aromatics over the non-alkylated aromatic reactants. US 4,871,444 teaches alkylating FCC cycle oils to improve cetane value. Catalysts used include ZSM-20, Y, and zeolite Beta. The cycle oils had an IBP of at least 300°F, and usually above 330°F, such as a light cut of a light cycle oil. The olefin alkylating agent preferably is a 1 -olefin having 5-7 carbon atoms. The examples disclose 1-butene and 1- hexene. Highest olefin conversion reported was 60%. US 4,992,606 discloses alkylation of aromatics such as benzene, in a reformate stream with olefins by contacting mixtures of light olefins derived from refinery streams with the reformate over MCM-22. US 5,171,916 discloses alkylation to produce functional fluids from cycle oils and achieve some desulfurization as well. As stated in the abstract, alkylated aromatic functional fluids are produced from FCC LCO by alkylation with an alkylating agent such as alpha C 14 - olefin or coker gas oil over a catalyst, preferably MCM-22. The heteroatom molecules in the LCO are apparently preferentially alkylated so that S and N containing molecules ended up in the 650°F + product, desulfurizing to some extent the 650°F " product. All of US 4,594,143, US 4,871,444, US 4,992,606 and US 5,171,916 are incorporated herein by reference in their entireties. It would be highly desirable to treat low Cetane Index value refinery-grade cracked process streams, such as aromatic distillates, so as to uplift the Cetane Index of the stream itself and/or of the distillate pool to which it is added, without addition of hydrogen. It would be further desirable to remove olefins from light naphtha refinery streams containing olefins, so as to increase oxidation resistance of the light naphtha stream. The present inventors have discovered an alternative to conventional hydroprocessing for cetane uplift, which does not produce fuel gas or consume hydrogen. Alkylation of aromatic-containing feedstreams is an alternative cetane upgrading technique which consumes no hydrogen. A first object of the present invention is to upgrade a refinery-grade feedstream containing greater than 40 wt% aromatics, such as a heavy naphtha feedstream or a distillate fuel feedstream, by reducing the aromaticity of the feedstream without addition of hydrogen. A second object of the present invention is to increase the Cetane Index of a distillate pool by upgrading a refinery-grade feedstream, such as a heavy naphtha feedstream or a distillate fuel feedstream, by reducing the aromaticity of the feedstream, without addition of hydrogen, fractionating the product stream into at least a diesel fuel fraction and adding the diesel fuel fraction to the distillate pool. Another object of the invention is to upgrade a refinery-grade feedstream containing olefins, such as a light naphtha feedstream, by reducing or eliminating the olefins so as to increase oxidation resistance of the treated product. Another object of the invention is to increase the volume of a distillate fuel pool by alkylating aromatics in a refinery-grade feedstream containing aromatics with olefins derived from a refinery-grade feedstream containing olefins, thus upgrading the olefins to a distillate fuel having an increased Cetane Index. In one embodiment, the present invention is directed to a hydrocarbon conversion process of contacting a first feedstream of heavy naphtha or distillate fraction containing greater than 40 wt% aromatics with a second feedstream containing light olefins, in the presence of an acidic solid alkylation catalyst under alkylation conditions, without addition of hydrogen, to form a reaction product stream, fractionating said reaction product stream into at least a diesel fuel fraction, wherein the diesel fuel fraction is upgraded in Cetane Index relative to the first feedstream. In another embodiment, the present invention is directed to a process of increasing the oxidation resistance of a gasoline pool comprising contacting a first feedstream of heavy naphtha or distillate fraction containing greater than 40 wt% aromatics with a light cracked naphtha feedstream, in the presence of an acidic solid alkylation catalyst under alkylation conditions, without addition of hydrogen, to form a reaction product stream, fractionating said reaction product stream into at least a gasoline fuel fraction and adding said gasoline fuel fraction to a gasoline pool, wherein the gasoline fuel fraction has increased oxidation resistance relative to the light naphtha feedstream. The above and other objects, features and advantages of the present invention will be better understood from the following detailed descriptions, taken in conjunction with the accompanying drawings, all of which are given by illustration only, and are not limitative of the present invention. Figure 1 is a graph of Cetane Index vs. carbon number for various hydrocarbons. Figures 2 a-h are graphs of cetane ratings (both Cl and CN) vs. carbon number for various hydrocarbon groups. Figure 3 is a graph comparing alkylation vs. hydroprocessing of 2-methylnaphthalene, a model LCO aromatic. Figure 4 is a low-resolution chromatogram (simdis GC) of an exemplary product of the process of the present invention. Figures 5a-b, 6a-b and 7a-b are bar graphs illustrating the yield of the various products produced by the process of the present invention at varying temperatures and reactant ratios, with various catalysts. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In one embodiment, the present invention is directed to a hydrocarbon conversion process of contacting a first feedstream of heavy naphtha or distillate fraction containing greater than 40 wt% aromatics with a second feedstream containing light olefins, in the presence of an acidic solid alkylation catalyst under alkylation conditions, without addition of hydrogen, to form a reaction product stream, fractionating said reaction product stream into at least a diesel fuel fraction, wherein the diesel fuel fraction is upgraded in Cetane Index relative to the first feedstream. In another embodiment, the present invention is directed to a process of increasing the oxidation resistance of a gasoline pool comprising contacting a first feedstream of heavy naphtha or distillate fraction containing greater than 40 wt% aromatics with a light cracked naphtha feedstream, in the presence of an acidic solid alkylation catalyst under alkylation conditions, without addition of hydrogen, to form a reaction product stream, fractionating said reaction product stream into at least a gasoline fuel fraction and adding said gasoline fuel fraction to a gasoline pool, wherein the gasoline fuel fraction has increased oxidation resistance relative to the light naphtha feedstream. The first refinery-grade feedstream is suitably a thermally- or catalytically-cracked fraction, such as a FCC heavy naphtha, light cycle oil or a coker gas oil. The first feedstream may contain from 20 wt% to 80 wt% of one- and/or two-ring aromatic compounds, preferably greater than 40 wt% aromatics, and more preferably greater than 50 wt% aromatics and densities greater than 0.85 g/ml at 60°F, preferably greater than 0.87 g/ml at 60°F. FCC light cycle oil and heavy naphtha offer the most potential for overall Cetane Index upgrading. These streams are very low Cl (typically 20±5) and currently must be hydroprocessed and/or blended with straight-run distillate or kerosene to meet road diesel specifications/regulations. Accordingly, FCC LCO is a preferable first aromatic-containing feedstream for the process of the present invention. More preferably, the aromatic distillate feedstream is previously hydrotreated to reduce sulfur and nitrogen contamination. The second refinery-grade feedstream may be a light cracked naphtha, which contains olefins and may be obtained from a thermal or catalytic cracking reactor, such as an FCC cracker, a pyrolysis unit or a coker. The olefins may be present in the stream at a concentration of 10 wt.% or 5 mole% (if a fuel gas), or more. Preferably, the olefins are light olefins having from 2 to 7 carbons, with ethene being particularly preferable. Additionally, it is preferable that the olefin-containing feedstream is previously hydrotreated to reduce sulfur and nitrogen contamination. Alkylation catalysts within the scope of the present invention are acidic solid alkylation catalysts, such as acidic clays and zeolites, preferably USY, MCM-22, MCM-36, MCM-49 or MCM-56, with MCM-56 being most preferable. Alkylation conditions useful in practicing the present invention include temperatures in the range of 150 to 600°F, preferably from 250 to 550°F, and more preferably from 350 to 550°F; pressures from atmospheric up to 600 psig, preferably from 50 to 400 psig, and more preferably from 100 to 400 psig; WHSV's of 0.2 to 10 hr "1 , preferably 0.2 to 5 hr '1 and more preferably 0.2 to 2 hr "1 ; olefin/aromatic mole ratios of 0.1 to 10, preferably 0.2 to 5 and more preferably 0.2 to 2. Advantageously, according to the present invention, the hydrogen consumption is greatly reduced or eliminated by directly alkylating the aromatic compounds in the first feedstream with olefins from the second feedstream. The alkylated aromatics produced by the present process have reduced aromaticity, such that they become less aromatic and more aliphatic in character, due to the olefin-derived alkyl substituents thereon. Therefore, the negative effect that aromatics have on Cl of a distillate fuel are reduced or eliminated by the present process. Further, when a heavy gasoline fraction is used as the first feedstream, the aromatics contained therein are increased in molecular weight and therefore boiling point by the present process, resulting in easy removal from the heavy gasoline product by conventional distillation. Upgrading of the olefin-containing (second) feedstream, preferably a FCC light naphtha feedstream, occurs in a number of ways. The olefins contained in the feedstream are reacted with the aromatics in the aromatic-containing feedstream, thus facilitating conventional separation of olefin-depleted naphtha from the heavier distillate by distillation, due to the higher molecular weight and therefore boiling point of the alkylated-aromatics so formed. In this manner, the olefins, which are less suitable as gasoline components due to their low oxidation resistance, are upgraded to beneficial distillate range fuel products, which actually enhance the distillate pool due to their improved Cl. Likewise, the FCC light naphtha product is enhanced by removal of the olefins, which greatly improves the oxidation resistance of the gasoline pool to which it is ultimately added. As shown in Fig. 1, the Cl of both one- and two-ring aromatics increases significantly with molecular weight. While alkylbenzenes show a similar trend in CN, the CN of the two- ring aromatics that dominate light LCO responds only weakly to larger alkyl side chains. Thus, LCO alkylation is primarily expected to improve Cl, rather than CN. However, this limitation is of minor concern as additives such as isooctyl nitrate may be used to increase CN, while most of the regulatory limits in effect or under consideration apply to Cl. Except for decahydronaphthalenes, which behave as if they were aromatic, Cl increases with decreasing hydrocarbon aromaticity. For a given carbon number, Cl decreases in the order: n-paraffins > 2-methylparaffιns > α-olefins > n-alkyl cyclop entanes > n- alkylcyclohexanes > n-alkylbenzenes > n-alkyl decahydronaphthalenes > n-alkyl tetrahydronaphthalenes > n-alkylnaphthalenes. Cetane Number generally follows the same trend. Therefore, conventional aromatic saturation is an effective way to increase both CN and Cl. While hydrogenation of naphthalenes to tetrahydronaphthalenes increases Cl by only 2-5 numbers, saturation of tetrahydronaphthalenes to decahydronaphthalenes yields a 5-12 Cl increase. Saturation of alkylbenzenes to alkylcyclohexanes leads to an even larger Cl increase of 11-27. However, as previously discussed, hydrogenation requires large quantities of hydrogen, which is a limited commodity within a refinery. In some cases, additional hydrogen must be obtained at great expense by for instance building a hydrogen plant or increasing capacity of an existing hydrogen plant. Within a given hydrocarbon class, Figs. 2a-h, Cl increases with carbon number (or molecular weight). Cetane Number generally does likewise, with decahydronaphthalenes being a notable exception. However, for the two-ring compounds that dominate LCO, the increase in CN is significantly less than the increase in Cl. Therefore, whereas alkylation of naphthalenes or tetrahydronaphthalenes yields a Cl increase of 5-6 numbers per methylene group added, CN increases only 1-2 numbers per methylene unit. Fig. 3 is a graph comparing alkylation vs. hydroprocessing of 2-methylnaphthalene, a model LCO aromatic. Alkylation of this aromatic compound with pentene leads to an increase in Cl of 25, without hydrogen consumption. In contrast, complete saturation of this aromatic only increases Cl by 14 and requires almost 5000 scf/bbl of hydrogen. Clearly, significant improvement in Cl, approximately equivalent to or greater than improvements obtainable by saturation, can be achieved by alkylation, but without the added expense of hydrogenation. Examples A number of experiments were performed utilizing both feedstocks from refinery streams and model reactant compounds, in order to demonstrate the efficacy of the inventive process. In Examples 1-8, a light cut (Cs-215°F) of FCC naphtha was used as the olefin source . Aromatic distillates used were nominal 410-490°F cuts of raw LCO, a moderately hydrotreated LCO (CHD-catalytic hydrodesulfurization effluent), and a more severely hydrotreated blend of LCO and straight-run distillate (first-stage HDC-hydrocracker effluent). Additionally, a model compound (1 -methyl-naphthalene), representative of distillate aromatics, was also used. Properties of the refinery-derived feedstocks are given in the following Table 1. TABLE 1 Feedstock Properties Lt. FCC Raw CHD First-stage Naphtha LCO Effluent HDC Effluent Composition. wt% Paraffins 28J N.A. 15.4 21.9 Olefins 62.4 N.A. - - 1-Ring Naphthenes 3.8 N.A. 6.2 12.5 2-Ring Naphthenes - N.A. 2.9 18.0 3 -Ring Naphthenes - N.A. 0.7 4J Alkylbenzenes 5.5 N.A. 15.8 14.0 Naphthene Benzenes - N.A. 27.8 25.1 Naphthalenes - N.A. 31.2 4.4 Nitrogen, ppmw 5 230 150 0.45 Sulfur, wt% 0.023 2.0 0.086 0.001 Hydrogen, wt% 14.6 N.A. 11.1 12.6 Sim. Distillation. °F 1/5 wt% off® N.A. 284/346 393/420 391/413 10/20 wt% off@ N.A. 390/434 439/457 431/454 30/40 wt% off@ N.A. 451/459 470/485 466/478 50 wt% off@ N.A. 466 497 488 60/70 wt% off® N.A. 479/490 507/516 499/510 80/90 wt% off® N.A. 500/509 526/536 520/529 95/99 wt% off® N.A. 518/527 541/549 534/541 Density @ 60°F, gm/cc 0.686 0.923 0.914 0.877 Cetane Index _ 20J 27.2 35.2 Examples 1-4 Batch studies were performed in which 1/1 (vol/vol) blends of the light FCC naphtha and aromatic distillates were converted over a USY/Al 2 O 3 or MCM-22/Al 2 O 3 catalyst at 450°F, 0.6 '1 hr olefin EWHSN and autogenous pressure. The results are shown in the following Table 2. TABLE 2 Batch Alkylation Results with Lt. FCC Naphtha 450°F, Autogenous Pressure, 0.6 hr "1 Olefin EWHSN 1/1 (vol/vol)Lt. FCC Naphtha/Distillate Ex. 1 Ex. 2 Ex. 3 Ex. 4 Catalyst MCM-22 USY USY USY Distillate Raw Raw CHD First-stage LCO LCO Effluent HDC Effluent C -C 6 Olefin Conv., % 69 51 63 81 410°F + Product/Feed, wt% 119 114 109 100 410°F + Cetane Index 26.3 25.4 29.1 38.0 Δ Cetane Index 6.0 5.1 1.9 2.8 As shown in Table 2, olefin conversion was significant (51-81%) and much of the olefin was converted to distillate-range (410°F + ) material leading to reductions in naphtha olefin levels. With the same feed (raw LCO blend), olefin conversion was greater with the MCM-22 catalyst. With the same catalyst (USY), olefin conversion increased with decreasing levels of nitrogen in the distillate feedstock, suggesting distillate hydrotreating prior to alkylation may be desirable. Cetane index of the distillates increased by 1.9-6.0 as a result of the olefin conversion. Examples 5-8 Similar studies were carried out in a fixed-bed reactor, utilizing the model aromatic compound and the first-stage HDC effluent as the aromatic-containing stream. The molar ratio of light FCC/1-methylnaphthalene was 1/1 (mol mol), and the volume ratio of the light FCC naphtha/first-stage HDC effluent feed was 1/1 (vol/vol). The results are shown in the following Table 3. TABLE 3 Fixed-Bed Alkylation Results with Lt. FCC Naphtha Distillate 1* -Methyl- First- -stage Naphthalene HDC Effluent Ex. 5 Ex. 6 Ex. 7 Ex. 8 Catalyst USY MCM-22 USY MCM-22 Temperature, °F 600 585 640 490 Pressure, psig 300 400 400 400 LHSV, hr "1 0.6 0.6 0.4 1.4 C -C 6 Olefin Conv., % 68 93 73 97 410°F + Product/Feed, wt% 121 128 128 140 410°F + Cetane Index 18.5 20.4 37.7 37.5 Δ Cetane Index 10.2 12.1 2.5 2.3 Lt. FCC naphtha olefin alkylation selectivity, % 38 25 49 23 As shown in Table 3, distillate Cl increases of up to 12.1 were obtained with a light FCC naphtha/1 -methylnaphthalene feed, and significant olefin conversion (73-97%), along with distillate yield and cetane uplift was obtained with the light FCC naphtha/HDC effluent feed. Under olefin-rich conditions, leading to maximum cetane uplift and incremental distillate yield, olefin oligomerization competes with aromatic alkylation. One approach for reducing this competing reaction is to use ethene as the alkylating agent, which is relatively difficult to oligomerize using acid catalysts. Examples 10 and 11 These experiments utilized ethene as a model reactant compound, to simulate fuel gas olefins, along with a refinery-derived aromatic distillate. The distillate was a nominal 410- 490°F cut of a severely hydrotreated blend of LCO and straight-run distillate (first-stage HDC effluent), with properties given in the following Table 4. TABLE 4 Feedstock Properties First-stage HDC Effluent Composition. wt% Paraffins 21.9 1-Ring Naphthenes 12.5 2-Ring Naphthenes 18.0 3 -Ring Naphthenes 4.1 Alkylbenzenes 14.0 Naphthene Benzenes 25.1 Naphthalenes 4.4 Nitrogen, ppmw 0.45 Sulfur, wt% 0.001 Hydrogen, wt% 12.6 Sim. Distillation. °F 1/5 wt% off® 391/413 10/20 wt% off® 431/454 30/40 wt% off® 466/478 50 wt% off® 488 60/70 wt% off® 499/510 80/90 wt% off® 520/529 95/99 wt% off® 534/541 Density @ 60°F, gm cc 0.877 Cetane Index 35.2 Fixed-bed studies were performed in which the aromatic distillate was cofed with ethene over both a USY/Al 2 O 3 and separately a MCM-22/ Al 2 O 3 catalyst at 1.0 "1 hr distillate LHSN at 500°F. Results are shown in the following Table 5. TABLE 5 Fixed-Bed Alkvlation Results with Ethene Ex. 10 Ex. 11 Catalyst USY MCM-22 Temperature, °F 500 500 Pressure, psig 150 300 Distillate LHSN, hr "1 1.0 1.0 Ethene/Distillate Arom. 5/1 3/1 (mol/mol) Ethene Conversion 31 69 410°F + Product/Feed, wt% _ 112 109 410°F + Cetane Index 38.1 39J ΔCetane Index 2.9 4.1 As shown in Table 5, ethene conversion to distillate was significant as indicated by an increase in distillate (410°F + ) yields. Cetane Index of the distillate increased by 2.9-4J due to ethylation of the distillate aromatics, as confirmed by ΝMR analysis. Batch alkylation of distillate aromatics with various catalysts, including MCM- 56/Al 2 O 3 was conducted at varying temperatures (350-400°F), in batch autoclave reactors, using both model compounds and refinery-derived feedstocks. Model compound studies utilized 1-methylnaphthalene as representative of the distillate aromatic feedstream and 2- methyl-1-pentene as the alkylating olefin feedstream. A light FCC naphtha cut and a hydrotreated LCO cut with properties given in the following Table 6 were used as the refinery- derived feedstocks. TABLE 6 Feedstock Properties Light FCC Hydrotreated Naphtha Light LCO Composition. wt% Paraffins 26.9 20.5 Olefins 58J - 1-Ring Naphthenes 6.4 8.1 2-Ring Naphthenes - 2.4 Alkylbenzenes 8.5 28.0 Naphthene Benzenes - 24.5 Naphthalenes - 16.6 Nitrogen, ppmw 2.6 6 Sulfur, wt% 0.030 0.002 Hydrogen, wt% 14.1 11.5 Sim. Distillation. °F 1/5 wt% off® 91/102 291/331 10/20 wt% off® 110/124 358/393 30/40 wt% off® 154/169 412/436 50 wt% off® 177 450 60/70 wt% off® 189/208 462/482 80/90 wt% off® 222/242 494/515 95/99 wt% off® 265/466 527/546 Density @ 60°F, gm/cc 0.716 0.887 Examples 12-19 Results from batch autoclave studies with model compounds at 350°F and 400°F and autogenous pressure are given in Table 7. The feed was a 1/1 molar blend of 1- methylnaphthalene and 2-methyl-l-pentene (hexene) processed at 10 cm 3 /g of catalyst for three hours at the given temperature. For comparison, results are also given for USY/Al 2 O 3 , beta/Al 2 O 3 and MCM-22/Al 2 O 3 . As shown in Table 7, MCM-56 was unexpectedly both the most active and most selective of the four catalysts tested. TABLE 7 Batch Alkvlation Results with Model Feeds Ex. 12 Ex. 13 Ex. 14 Ex. 15 ExJ6 Ex.17 Ex. 18 Ex. 19 Temperature, °F 350 350 350 350 400 400 400 400 Catalyst USY Beta MCM22 MCM56 USY Beta MCM22 MCM56 Hexene Conversion, % 94.7 96.8 97.6 99.9 81.3 99J 99.1 99.5 1 -Methyl-Naphthalene Conversion, % 32 18 32 44 25 20 40 42 Alkylation Selectivity (1) ,% 34 19 33 44 31 20 40 42 (i) 100% x Ratio of moles naphthalene converted to moles hexene converted. For a 1/1 molar feed, simply 100% x conversion ratio. Examples 20-27 Similar experiments were performed with the above-mentioned refinery feeds at a 1/1 volumetric ratio of light FCC naphtha to hydrotreated LCO. The results are given in the following Table 8. TABLE 8 Batch Alkylation Results with Refinery Feeds Ex. 20 Ex. 21 Ex. 22 Ex. 23 Ex.24 Ex.25 Ex. 26 Ex. 27 Temperature, °F 350 350 350 350 400 400 400 400 Catalyst USY Beta MCM22 MCM56 USY Beta MCM22 MCM56 C -Cβ Olefin Conversion, % 25.1 46.6 28J 42.7 30.9 56.4 47.9 12.1 TLP Wt% > 550°F 1.6 2.0 2.2 3.5 3.3 4.7 5.3 9.1 As shown in Table 8, MCM-56 was again one of the most active catalysts tested. Because the feedstocks were more complex, alkylation selectivity was much harder to quantify in these experiments. Since the feedstocks contain very little (<1 wt%) material boiling above 550°F, the amount of 550°F + formed (TLP-total liquid product) was used as a qualitative measure of alkylation selectivity. Using this quantity, MCM-56 was demonstrated to be one of the most selective of the four catalysts with refinery feedstocks. Batch experiments were performed in autoclaves at 250-450°F and autogenous pressure. The liquid product was cut at 410°F into naphtha and distillate fractions. Model feedstocks were 1 -hexene (97%) and 1-methylnaphthalene (98%) and were obtained from Aldrich and used without further purification. Refinery feedstocks included a 210°F- cut of FCC naphtha as the olefin-containing feedstream, and three LCO-derived 410- 490°F distillate cuts: 1) raw LCO; 2) CHD effluent; and 3) HDC stripper downcomer. The light FCC naphtha had properties as described in Table 9, and the LCO distillate cuts in Table 10, below. TABLE 9 210°F- FCC Naphtha Composition and Properties Research Octane 93.9 Motor Octane 81.0 Density @ 60°F, gm/cc 0.6863 Rvp, psi 10.6 Bromine Number 87.8 Dienes, mmol gm 0.20 Total Sulfur, wt% 0.023 Mercaptan Sulfur, ppmw 33 Nitrogen, ppmw 5 Basic Nitrogen, ppmw <5 Composition. wt% Olefin Trap Method 00 FID^ Butanes 0.2 0.1 Butenes 1.3 1.0 N-Pentane 2.2 1.9 Isopentane 11.7 9.8 1-Pentene 3.1 2.1 C-2-Pentene 3.8 3.3 T-2-Pentene 6.7 6.0 2-Me-l-Butene 5.1 4.4 3-Me-l-Butene 1.0 0.9 2-Me-2-Butene 8.7 7.8 Cyclopentane 0.3 0.3 Other C 5 0.4 1.8 N-Hexane 1.2 1.3 Isohexanes 8.3 8.2 C 6 Olefins 20.9 19.7 Me-Cyclopentane 1.8 2.1 TABLE 9 (CONT.) Olefin Trap Method 00 FID ,<">> Cyclohexane 0J 0.2 Benzene 3.4 3.7 Total C 7 + 19.9 24.9 C 7 -C 8 N-Paraffins 0.5 N.A. C -C 8 Isoparaffins 4.2 N.A. C 7 -C 8 Olefins 11.5 N.A. C 7 -C 8 Naphthenes 1.5 N.A. C -C 8 Aromatics 2.1 N.A. C 9 + 0.1 N.A. (a) Differential capillary column GC where olefin peaks are identified by comparing the normal chromatogram to the chromatogram generated after passing the sample over sulfuric acid. (b) Flame Ionization Detector TABLE 10 Light Distillate Compositions and Properties CHD First-stage Raw LCO Effluent HDC Effluent Sulfur, wt% 2.0 0.086 0.0014 Nitrogen, ppmw 230 150 0.45 Basic N, ppmw 89 69 N.A. Hydrogen, wt% N.A. 11.1 12.6 Composition. wt% Paraffins N.A. 15.4 21.9 1-Ring Naphthenes N.A. 6.2 12.5 2-Ring Naphthenes N.A. 2.9 18.0 3-Ring Naphthenes N.A. 0.7 4J Alkylbenzenes N.A. 15.8 14.0 Naphthene Benzenes N.A. 27.8 25.1 Naphthalenes N.A. 31.2 4.4 Distillation (D86/D2887). °F IBP 363/270 N.A./376 373/375 5 vol%/wt%off@ 411/346 N.A./420 465/413 10vol% wt%off@ 423/390 N.A./439 465/431 30 vol%/wt%off@ 447/451 N.A./470 469/466 50vol%/wt%off@ 459/466 N.A./497 474/488 70vol%/wt%off@ 468/490 N.A./516 482/510 90vol% wt%off@ 479/509 N.A./536 495/529 95 vol%/wt%of @ 485/518 N.A./541 501/534 EP 500/531 N.A./555 516/544 Weighted Tso w , °F 456 489 483 Density @ 60°F, gm/cc 0.923 0.914 0.877 Cetane Index (c) 20.3 27.2 35.2 N.A. - Not Available. Sulfur by D3120. 00 Average of Simdis (D2887) T 0 , T 5 , T 10 , T 15 ,..., T 85 , T 90 , T 95 , T 10 o. Calculated using two-parameter model (ASTM D976) with weighted T5 0 . Catalysts used in these examples were US Y/Al 2 O 3 and MCM-22, either unsupported or supported on Al 2 O 3 . The same USY/Al 2 O 3 catalyst was used as indicated in examples 28-67, while MCM-22 crystals were used in examples 28-45, as indicated and supported MCM- 22/ Al 2 O 3 was used as indicated in examples 46-67. All catalysts were sized to 14/24 mesh and freshly calcined before use. Catalyst properties are given in Table 11, below. TABLE 11 Catalvst Properties USY/AbOi MCM-22 MCM-22/AI7O1 Zeolite Loading, % 75 100 55 Alpha 206 N.A. 259 Sodium, ppmw 965 135 256 Surface Area, 555 471 374 m 2 /gm Pore Volume, cc/gm 0.75 N.A. 0.91 Density, gm/cc Real 2.38 N.A. 2.59 Particle 0.868 N.A. 0.772 N.A. - Not Available Rapid, low resolution chromatography on a simulated distillation (simdis) GC and capillary GC (60m DB-1 column) were used as the principle analytical methods for all runs. Naphthalenes were identified from spiking studies with pure compounds and Cl was calculated using the two-parameter model (ASTM D976) with a "weighted" T 50 . Weighting was necessary because alkylation of LCO aromatics often leads to a product with a bimodal boiling point distribution—an unconverted feed "lump" and an alkylated product "lump". Therefore, the measured T50 does not change until the amount of alkylated product exceeds the amount of unconverted feed. In the present case, Cl from an average boiling point of the product should be more representative than that from the actual T 50 . Examples 28-45 Alkylation of 1-methylnaphthalene (model aromatic compound) with 1 -hexene (model olefin compound) was used as a model for LCO alkylation with FCC naphtha olefins. Both MCM-22 and USY were evaluated at 250-450°F with 5/1 and 2/1 (mol/mol) aromatic/olefin feeds. Results are shown in Table 12, below. TABLE 12 Aromatic/olefin Olefin Aromatic Monoalkylation Ex. Temp °F ratio (mol) Catalyst Conversion % (a) Conversion % (b) Selectivity. wt% £s) 28 250 5 MCM-22 79 11 43 29 250 5 USY 32 2 77 30 300 5 MCM-22 88 17 79 31 300 5 USY 88 18 87 32 350 5 MCM-22 100 24 84 33 350 5 USY 96 30 72 34 400 5 MCM-22 96 28 71 35 400 5 USY 88 22 72 36 250 2 MCM-22 82 35 72 37 250 2 USY 19 1 76 38 300 2 MCM-22 53 16 67 39 300 2 USY 39 10 82 40 350 2 MCM-22 98 52 66 41 350 2 USY 90 47 81 42 400 2 MCM-22 82 34 70 43 400 2 USY 95 61 76 44 450 2 MCM-22 94 53 65 45 450 2 USY - - - (a) Calculated from simdis GC's assuming all 300°F " material was hexene. ( ) Calculated from simdis GC's assuming all 300-560°F material was 1-me-naph. (c) -fivxr-ri rα+ir v n f m o + Λfi nl i »-i oi -m ,A;« nr" As shown in Table 12, 1 -hexene conversion was nearly complete at temperatures of 350°F and above for both feeds over both catalysts. At low temperatures of 250-300°F, MCM- 22 led to higher olefin conversions. Analysis of the products indicates that hexene was converted almost exclusively via aromatic alkylation reactions rather than by oligomerization. As shown in Fig. 4, the low- resolution chromatograms (simdis GC) showed four distinct peaks classified as: 1) hexene (300°F " ); 2) 1-methylnaphthalene (300-560°F); 3) monoalkylated product (560-665°F); and 4) multi-alkylated product (665°F + ). The distribution of these four peaks are shown in Figs. 5a-b and 6a-b as a function of temperature for 5/1 and 2/1 mol/mol 1-methylnaphthalene/l -hexene feeds, respectively. Since hexene dimerization would produce 300-560°F material (1- dodecene has a 416°F boiling point), the observed decrease with temperature is inconsistent with oligomerization. Indeed, as shown in Table 12, 1-methylnaphthalene conversions at nearly complete 1 -hexene conversion were near stoichiometric with respect to both feeds. Neither the catalyst nor the aromatic/olefin feed ratio appear to strongly affect alkylation selectivity. Examples 46-52 Examples 46-52 were conducted with real refinery feeds as at least one of the reactants, and were conducted at autogenous pressure with 1.5 mL charge of feedstock blends over various catalysts for three hours, under temperature conditions as indicated in Table 13, below. TABLE 13 Results of Alkylation Studies with Refinery Feedstocks Aromatic Lt. LCO 1 -Methyl Naphthalene Olefin 1 -Hexene Lt FCC Aromatic/ Olefin. (vol/vol) 4/1 2/1 C 1 0-C 1 2 Naphthalenes/ C4-C7 Olefins ( mol/mol) 0.9 2.1 Feed Ex.46 Ex.47 Ex. 8 Ex.49 Feed Ex. 50 Catalyst - MCM- MCM-22 MCM- USY MCM-22 22 22 Temp., °F - 250 350 450 350 450 Conversions. % C 4 -C 6 Olefin - (1) 26 92 32 - 97 C 10 -C 1 2 Naphthalenes (,) - (2) (4) 10 0 - 10 Composition. wt% C-Cs Olefins 22.9 23.1 16.9 1.9 15.5 15.0 0.4 CfPNA 0.5 0.3 0.9 4.9 1.1 7.7 6.0 CrC. 1.7 1.7 1.6 2.2 1.8 6.5 3.4 C 9 -424°F(Naph.) 8.2 8.2 8.3 9.8 8.6 0.0 1.1 Naphthalenes ^ 1.3 1.3 1.2 0.8 1.1 0.0 0.3 M-Naphthalenes (,) 15.5 16.0 16.2 13.2 15.2 69.4 62.3 CrNaphthalenes ω 19.0 19.3 20.0 18.3 19.5 0.0 0.0 Other 424°F+ 30.9 30.1 34.9 48.9 37.2 1.4 26.5 (a) Estimated from GC; naphthalenes may coelute in GC with other compounds. CETANE UPLIFT Examples 53-57 Experiments were performed using refinery feeds to quantify cetane uplift potential. Light FCC naphtha was blended in 1/1 volume ratios with the three distillate cuts (Table 10) and run over 25 g of catalyst (MCM-22 or USY) at 450°F for 5.6 hours. The liquid product was analyzed by GC then cut at 410°F into distillate and naphtha fractions. Results are in Table 14, below. TABLE 14 Batch Alkylation Studies with Lt. FCC and Light Distillates Example No. 52 SJ 55 56 Distillate ] Lt. LCO Lt. LCO Lt.LCO CHD Catalyst USY ( ») MCM-22 USY USY Conversions. % C-Cβ Olefin 46 69 Φ) 51 63 C,o-C 12 Naph.- <c) 9 8 7 Composition. wt% Feed TLP Feed TLP Feed TLP Feed TLP C-C 6 Olefins 22.1 11.8 N.A. 6.3 20.5 10.1 17.2 6.3 PNA 13.2 14.8 N.A. 13.0 12.3 13.0 10.9 13.0 C 7 -Cj 11.2 10.3 N.A. 9.0 10.6 9.5 8.2 7.3 Csr424°F (Naph.) 6.0 10.1 N.A. 12.6 6.7 10.6 1.4 5.2 Naphthalene* 0 0.9 0.9 N.A. 0.9 1.0 0.9 0.2 0.3 Me-Naphthalenes <c) 11.7 10.4 N.A. 12.0 12.4 11.1 5.2 4.5 C 2 -Naphthalenes <c) 13.9 12.9 N.A. 14.5 14.5 13.8 17.8 16.9 Other 424°F+ 21.0 28.8 N.A. 31.7 22.0 31.0 39.1 46.5 410°F + Prooerties Bromine Number (Dl 159) 13.8 21.0 13.8 22.0 13.8 21.4 N.A. 9.9 Weighted T S0 W ,°F 456 499 456 505 456 497 489 499 Density @ 60°F, gm/cc 0.923 0.928 0.923 0.928 0.928 0.928 0.914 0.911 Cetane Inde (e) 20.3 25.6 20.3 26.3 20.3 25.4 27.2 29.1 (a) One run at 100 psig N 2 for 3 hours. ( ) No feed GC; conversions estimated from another run with same nominal feed composition. (<=) Estimated from GC; naphthalenes may coelute in GC with other compounds. (d) Average of Simdis (D2887) T 0 , T 5 , T 10 , T 15 ,..., T 85 , T 90 , T 95 , T 100 . (e) Calculated using two-parameter model (ASTM D976) with weighted T50. As shown in Table 14, Cl increased by 5-6 for the raw LCO cut, 2 for the CHD cut, and 3 for the HDC stripper downcomer cut. As density changed very little, this increase in Cl was due almost exclusively to an increase in distillate T 50 . It is clear from the data that Cl uplift diminishes with increased severity of LCO hydrotreating, and/or with higher Cl feed. Therefore, as suggested by distillate naphthalene levels in Table 10, severe hydrotreating is expected to lead to more saturation of naphthalene to tetrahydronaphthalenes and decahydronaphthalenes and thus less Cl uplift during subsequent alkylation. Similarly, higher Cl of the distillate feed implies low aromaticity and lower potential for improvement via alkylation. Lower olefin conversions were not responsible for the low cetane uplifts with the hydrotreated distillates. As shown in Table 14, the C 4 -C 6 olefin conversion over USY increased with decreasing nitrogen content of the distillate feed. Detailed compositional analyses show conversions of C 4 -C 6 olefins to both heavy naphtha (C 9 -424°F) and distillate (424°F + ). Naphthalene conversions of 2-19% were also observed as shown in Table 15. These levels are 10-fold lower than expected by assuming monoalkylation reaction stoichiometry. These conversion data have a somewhat high degree of uncertainty due to peak overlap (coelution) in GC analysis. For example, 25 wt% C10-C12 naphthalenes were identified in the HDC stripper downcomer cut by GC, while mass spectrometer analysis indicates that this hydrotreated distillate contains only 4 wt% naphthalenes (Table 10). Thus, actual naphthalene conversions may be up to 5-fold higher than indicated in Table 14. ETHENE STUDIES As previously stated, the use of ethene as an olefin source was expected to reduce oligomerization products, since ethene is relatively difficult to oligomerize via acid catalysis. The following examples were experiments performed using ethene as the olefin-containing stream. Examples 58-68 Isothermal, fixed-bed experiments cofeeding ethene and hydrotreated aromatic- containing streams were performed at nominal liquid feed rates of 1 hr "1 LHSN, over 15 cm 3 of 14/24 mesh USY/AL 2 O 3 catalyst. The hydrotreated aromatic-containing stream was a 410- 490°F cut of first-stage HDC effluent (properties listed in Table 15). Experimental design was a two-level factorial with three variables (2 3 ): 1) pressure (150-450 psig); 2) temperature (300- 500°F); and 3) ethene/aromatic (E/A) molar feed ratio (1-5 mol/mol). Individual example parameters and results are as listed in Table 16, below. Examples 69-75 The same feed as in Examples 58-68 was used in a 300 psig run over 15 cm 3 of 14/24 mesh MCM-22/ AL 2 O 3 , in which only temperatures (400-600°F) and E/A feed ratio (1-5 mol/mol) were varied. Individual example parameters and results are reported in Table 16. Examples 76-91 Two different aromatic-containing feedstreams, a hydrotreated heavy FCC naphtha (Examples 76-82) and a hydrotreated light LCO (Examples 83-91), the properties of which are described in Table 15, were fed to a reactor under similar conditions to Examples 69-75, but the catalyst amount was reduced to 10 cm 3 and pressure was fixed at 400 psig. The E/A feed ratios and the temperatures of the heavy naphtha feed were varied as given in Table 16. TABLE 15 Feed Properties Hydrotreated First-Stage Heavy FCC Hydrotreated HDC Effluent Naphtha Light LCO Nitrogen, ppmw 0.45 0.50 0.60 Sulfur, ppmw 14 1200 460 Hydrogen, wt% 12.58 11.38 11.82 Composition. wt% Paraffins 21.9 13.0 20.9 1-Ring Naphthenes 12.5 5.9 10.9 2-Ring Naphthenes 18.0 2.4 5.1 3-Ring Naphthenes 4.1 - 0.3 Alkylbenzenes 14.0 34.3 28.7 Naphthene Benzenes 25.1 35.3 24.8 Naphthalenes 4.4 6.6 9.3 Other - 2.5 - Distillation (D86/D2887). °F l/5 wt% off@ 391/413 232/301 246/305 10/20 wt% off@ 431/454 328/373 333/372 30/40 wt% off® 466/478 400/413 400/422 50 wt% off@ 488 428 443 60/70 wt% off@ 499/510 444/456 459/473 80/90 wt% off@ 520/529 468/486 491/509 95/99 wt% off@ 534/5413 500/534 524/541 Weighted T 50 , °F 483 417 429 Density @ 60°F, gm/cc 0.8768 0.8839 0.8744 Cetane Index 35.2 21.8 26.7 TABLE 16 Cetane Uplift Results E/A Ex No. Temperature. °F mol/mol Pressure, psig Catalyst Aee. DOS ACI Ethene Conv. 58 397 3 292 1.9 0.1 0.0 59 477 5 143 3.9 2.9 33.4 60 302 1 441 6.9 0.7 0.0 61 537 5 441 8.9 3.0 33.8 62 480 1 441 12.0 0.6 0.0 63 501 1 143 13.9 0.0 0.0 64 289 5 143 15.9 0.0 0.0 65 300 1 143 17.9 0.4 9.9 66 301 5 441 22.2 0.1 16.5 67 405 3 292 24.2 -0J 31.1 68 626 5 441 26.2 0.9 37.5 69 501 3 266 3.2 4.1 68.1 70 592 1 254 6.2 -1.9 64.9 71 407 1 240 8.3 2.2 0.0 72 407 5 280 10.3 1.3 2.1 73 632 5 282 12.3 3.6 77.4 74 501 3 297 14.3 1.8 24.2 75 400 1 291 16.2 0.7 2.9 76 499 3 400 1.1 4.1 17.7 77 397 1 400 2.1 -1.1 0.0 78 602 1 400 3.8 6.3 100.0 79 489 3 400 4.8 1.5 8.5 80 609 5 400 5.7 9.8 30.3 TABLE 16 (COKT., E/A Ex. No. Temperature. C F mol mol Pressure, psig Catalyst Age. DOS ACI Ethene Conv. 81 395 5 400 6.7 -0.3 3.5 82 494 3 400 7.8 0.2 3.6 83 622 3 400 8.9 10.2 90.3 84 553 1 400 9.8 3.0 3.5 85 662 1 400 10.8 3.9 99.9 86 607 3 400 11.7 1.1 71.9 87 652 5 400 12.7 8.3 79.9 88 565 5 400 13.7 5.3 26.3 89 605 3 400 14.7 8.3 63.2 90 645 1 400 15.7 5.8 99.7 91 615 5 410 16.9 8.0 44.8 As shown in Table 16, increasing the molecular weight of distillate aromatics via alkylation with ethene increased the Cl by as much as 10 above the hydrotreated feed Cl. Cetane uplift was found to be a function of temperature, feed composition and to some degree catalyst age. Generally, ΔCI was greater at high temperatures (600-650°F) due to higher ethene conversions as discussed below. There was little or no increase in cetane at low temperatures (300-400°F) due to little or no ethene conversion. Feed composition influenced cetane uplift in two ways: 1) ΔCI increased with the amount of ethene in the feed, and 2) distillate cracking somewhat offset Cl increases for the straight-run containing hydrocracker effluent feedstock. Catalyst aging reduced ethene conversion and subsequently ΔCI somewhat. Unlike most other cetane upgrading processes, distillate yield generally increases during alkylation with ethene. As shown in Table 16, 330°F + yields were as high as 134 wt% and as low as 77 wt%, depending on temperature, feedstock composition and, to some extent catalyst age. Distillate yield closely mirrors cetane uplift. Low incremental distillate yields or even yield loss was most likely at high temperature and low E/A conditions, where ethene conversion to distillate competed less favorably with distillate cracking. Further, yield losses due to cracking were most evident with the first-stage HDC effluent, with high straight-run distillate content. At 600°F and 1 E/A, a 330°F + yield loss of 23 wt% was observed due to cracking of the straight-run containing feed, while no such losses were evident with the more aromatic light LCO or heavy FCC naphtha feeds. The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims: CLAIMS: 1. A hydrocarbon fuels upgrading process for producing fuel of improved characteristics, comprising contacting a first feedstream of heavy naphtha or a distillate fraction containing greater than 40 wt% aromatics with a second feedstream containing light olefins, in the presence of an acidic solid alkylation catalyst under alkylation conditions, without addition of hydrogen, to form a reaction product stream; and fractionating said reaction product stream to form a fuel product fraction of improved properties. 2. A process according to Claim 1 in which the product fraction is a diesel fuel fraction which is upgraded in Cetane Index relative to the first feedstream. 3. The process according to Claim 2 in which the second feedstream is a fuel gas containing greater than 5 mole % light olefins. 4. A process according to Claim 1 in which the product fraction is a gasoline fraction of improved oxidation resistance relative to a light naphtha fraction which comprises the second feedstream. 5. The process according to Claim 3 in which the second feedstream is a light naphtha cut containing greater than 10 wt% light olefins. 6. The process according to any of Claims 1 to 5 in which the first feedstream is a FCC heavy naphtha, light cycle oil or a coker gas oil. 7. The process according to any of Claims 1 to 5 in which the first feedstream contains greater than 50 % by weight of one- or two-ring aromatic compounds. 8. The process according to Claim 1 in which the acidic solid alkylation catalyst comprises USY, MCM-22 and MCM-56. 9. The process according to Claim 1 in which the reaction product stream is upgraded in reduced aromaticity relative to said first feedstream. 10. The process according to Claim 1 in which the reaction product stream is upgraded in increased oxidation resistance relative to said second feedstream.

Inventors: COLLINS NICK ALLEN, LANDIS MICHAEL E, TIMKEN HYE KYUNG CHO, TREWELLA JEFFREY C, COLLINS, NICK, ALLEN, LANDIS, MICHAEL, E., TIMKEN, HYE, KYUNG, CHO, TREWELLA, JEFFREY, C.
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION
Application year: 1999
Main classification: C10G35
IPC codes: C10G29