OF LIGHT CYCLE OIL

Mi l l) OF THE INVENTION

[0001] The invention generally concerns methods for converting a polyaromatic hydrocarbon feedstock into higher-value monoaromatic compounds like benzene, toluene, ethylbenzene, and xylenes by a catalytic hydrocracking process.

BACKGROUND

[0002] Light Cycle Oil (LCO) is low-value liquid residue produced when using catalytic cracking to convert heavy hydrocarbon fractions from earlier stages of refining into lighter, more valuable products. In refineries and chemical industries, LCO is produced in large quantities as side streams or by-products. These feedstock contains high amounts of heteroatoms like sulfur and nitrogen-containing compounds, and polyaromatics like di and tri aromatic compounds.

[0003] LCO typically has high sulfur content and exhibits poor engine ignition performance. Because LCO is unattractive as a stand-alone fuel, it has been used as a blending component for increasing the cetane number of diesel, and for adjusting the viscosity of heating oil and fuel oil. In some plants, LCO is recycled and re-introduced into the refining process.

[0004] As refiners face increasing regulations for cleaner fuels, one of the many considerations is the future of LCO. Because the polyaromatic content of diesel fuel is correlated with diesel engine particulate and NOx emissions, the trend in diesel fuels has been to lower the polyaromatic content. Demand for fuel oil, which employs LCO as a viscosity- adjuster, has been decreasing as a result of refineries looking to maximize production of high- value products. While there have been many attempts to make use of LCO by blending into fuel oil or diesel, high levels of sulfur, nitrogen and aromatics often make this an unattractive choice.

SUMMARY OF THE INVENTION

[0005] The high levels of aromatics in LCO make it economically attractive as a source for conversion into high-value aromatics feedstocks - specifically, benzene, toluene, ethylbenzene, and xylenes (BTEX). The methods disclosed herein provide a method and system for converting low-value LCO into higher-value aromatics in high yields. The methods are premised on the use of a two stage process for converting polyaromatic hydrocarbons into monoaromatics, such as benzene, toluene, ethylbenzene, and xylenes. The two stage process comprises a hydrocracking component having a dual catalyst bed system in which the first catalyst bed catalyst is different from the second catalyst bed catalyst.

[0006] In some embodiments, a process for preparing monoaromatic compounds from a polyaromatic feedstock is disclosed. The process comprises contacting the hydrotreated polyaromatic feedstock with a catalyst under conditions sufficient to hydrocrack the polyaromatic feedstock. The polyaromatic feedstock may be hydrotreated before the contacting. The catalyst comprises a first catalyst bed comprising cobalt, molybdenum, a zeolite, and a support material, and a second catalyst bed comprising molybdenum on zeolites. The zeolites of the second catalyst bed may comprise 8-, 10-, l2-membered rings like ZSM-5, ZSM-12, mordenite, MCM-22, b-zeolite, or combinations thereof. In a particular aspect, the first catalyst bed catalyst comprises C0M0/AI2O3 and b-zeolite, and the second catalyst bed catalyst comprises Mo on mordenite.

[0007] In certain aspects, the first catalyst bed may comprise transition metals including Co (cobalt), Ni (nickel), W (tungsten), Mo (molybdenum) supported on a inorganic support material including alumina, silica, zeolites including 8-, 10-, l2-membered ring like ZSM-5, ZSM-12, mordenite, MCM-22, b-zeolite, or combinations thereof. The second catalyst bed may comprise Ni, Mo, Re (rhenium), Pt (platinum), or combinations thereof supported on zeolites comprising 8-, 10-, l2-membered ring like ZSM-5, ZSM-12, mordenite, MCM-22, Y- and b-zeolite, or combinations thereof.

[0008] In some aspects, the polyaromatic feedstock has a boiling point in the range of about 180 to about 430 °C, preferably in the range of about 180 to about 350 °C. In some aspects, the polyaromatic feedstock is light cycle oil (LCO). The polyaromatic feedstock may be subjected to a hydrotreating step prior to hydrocracking. The hydrotreating step is employed to hydrogenate at least a portion of the carbon-carbon double bonds present in the feedstock, and to remove heteroatom impurities. The hydrotreating step comprises subjecting the polyaromatic feedstock to a temperature ranging from about 300 to about 400 °C, preferably from about 320 to 380 °C; a pressure ranging from about 40 to about 80 bar, preferably from about 50 bar to about 70 bar; a weight hourly space velocity (WHSV) ranging from about 0.5 to about 2.0 h ¹ , preferably from about 0.6 to about 1.4 h ¹ ; and a Lb to hydrocarbon ratio ranging from about 5 to about 12 mol/mol, preferably from about 8 to about 10 mol/mol. In some aspects, conditions sufficient to hydrocrack the polyaromatic feedstock comprise a reaction temperature ranging from about 380 to 450 °C, preferably ranging from about 380 to 425 °C.

[0009] Some aspects of the disclosure are directed towards a process for preparing monoaromatic compounds from a polyaromatic feedstock. In some embodiments, the process comprises treating the polyaromatic feedstock with hydrogen gas under conditions sufficient to hydrogenate the polyaromatic feedstock and contacting the hydrogenated polyaromatic feedstock with a catalyst under conditions sufficient to hydrocrack the hydrogenated polyaromatic feedstock. The catalyst comprises a first catalyst bed comprising cobalt, molybdenum, a zeolite, and a support material, and a second catalyst bed comprising molybdenum supported on a zeolite. In certain aspects, the zeolite of the second catalyst bed comprises mordenite. In certain aspects, the first catalyst bed is different from the second catalyst bed. In a particular aspect, the first catalyst bed catalyst comprises C0M0/AI2O3 and b-zeolite, and the second catalyst bed catalyst comprises Mo on mordenite. In some embodiments, the polyaromatic feedstock has a boiling point in the range of about 180 to about 430 °C, preferably about 180 to about 350 °C. In a preferred embodiment, the polyaromatic feedstock is light cycle oil (LCO). Hydrogenating the polyaromatic feedstock comprises hydrogenating at least a portion of the carbon-carbon double bonds present in the feedstock, and removing at least some heteroatom impurities. In some aspects, conditions sufficient to hydrogenate the polyaromatic feedstock comprise a temperature ranging from about 300 to about 400 °C, preferably from about 320 to 380 °C; a pressure ranging from about 40 to about 80 bar, preferably from about 50 bar to about 70 bar; a WHSV ranging from about 0.5 to about 2.0 h ¹ , preferably from about 0.6 to about 1.4 h ¹ ; and a H2 to hydrocarbon ratio ranging from about 5 to about 12 mol/mol, preferably ranging from about 8 to about 10 mol/mol. In some embodiments, conditions sufficient to hydrocrack the hydrogenated polyaromatic feedstock comprise a reaction temperature ranging from about 380 to 450 °C, preferably from about 380 to 425 °C.

[0010] In some aspects of the disclosure, a system for preparing monoaromatic compounds from a polyaromatic feedstock is provided. The system comprises an inlet for a reactant feed comprising the polyaromatic feedstock, a reaction zone that is configured to be in fluid communication with the inlet, and an outlet configured to be in fluid communication with the reaction zone and remove a first product stream comprising monoaromatic compounds from the reaction zone. The reaction zone comprises a catalyst having a first catalyst bed comprising cobalt, molybdenum, a zeolite, and a support material, and a second catalyst bed comprising molybdenum and mordenite. In a particular aspect, the first catalyst bed catalyst comprises C0M0/AI2O3 and b-zeolite, and the second catalyst bed catalyst comprises Mo on a zeolite. In certain aspects, the zeolite of the second catalyst bed comprises mordenite. In some embodiments, the system further comprises a hydrotreating zone upstream of the reaction zone. The hydrotreating zone has an inlet, and an outlet that is in fluid communication with the reaction zone. The hydrotreating zone comprises a hydrotreating reactor for hydrogenating at least a portion of the carbon-carbon double bonds present in the feedstock and removing at least some heteroatom impurities. In some embodiments, the hydrotreating reactor comprises a catalyst comprising cobalt, molybdenum, and a support material. In some embodiments, the hydrotreating catalyst is activated by a polysulfide compound, preferably /er/-butyl polysulfide.

[0011] In some aspects, a feedstock passes over the hydrocracker catalyst beds in series, that is, a feedstock passes over the first catalyst bed then passes over the second catalyst bed. In other aspects, a feedstock may be simultaneously exposed to both catalyst beds. In some embodiments, the feedstock is hydrotreated or hydrogenated prior to passing over the hydrocracker catalyst beds. The feedstock may be hydrotreated to hydrogenate at least a portion of the carbon-carbon double bonds and carbon-carbon triple bonds, hydrogenate at least one aromatic ring of a polyaromatic compound, and/or to remove at least some heteroatom impurities. Heteroatom impurities include molecules having heteroatoms including but not limited to nitrogen, oxygen, sulfur, and metals. In some aspects, hydrotreating acts to desulfurize, denitrogenate, deoxygenate, and de-metallate the feedstock. In some aspects, a hydrotreated feedstock comprises monoaromatic compounds. In some embodiments, the hydrotreated feedstock passes over the first hydrocracking catalyst bed where hydrogenated rings are opened and some C6 to C9+ aromatics are produced. This stream is passed over the second hydrocracking catalyst bed where C6 to C8 aromatic yield is increased. Because some carbon-carbon bonds are broken during the hydrocracking step, e.g., opening of hydrogenated rings, the average molecular weight of compounds in the hydrocracking stream is reduced.

[0012] The terms“about” or“approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0013] The terms“wt.%”,“vol.%”, or“mol.%” refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or total moles of a material, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component.

[0014] The term“substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0015] The term“Cn+ hydrocarbon” wherein n is a positive integer, e.g. 1, 2, 3, 4, or 5, as that term is used in the specification and/or claims, means any hydrocarbon having at least n number of carbon atom(s) per molecule.

[0016] The use of the words“a” or“an” when used in conjunction with any of the terms “comprising,”“including,”“containing,” or“having” in the claims, or the specification, may mean“one,” but it is also consistent with the meaning of“one or more,”“at least one,” and “one or more than one.” The words“comprising” (and any form of comprising, such as “comprise” and“comprises”),“having” (and any form of having, such as“have” and“has”), “including” (and any form of including, such as“includes” and“include”) or“containing” (and any form of containing, such as“contains” and“contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0017] The methods of the present invention can“comprise,”“consist essentially of,” or “consist of’ particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phase“consisting essentially of,” in one non limiting aspect, a basic and novel characteristic of the methods of the present invention are their abilities to hydrocrack a polyaromatic feedstock into a product comprising monoaromatic compounds.

[0018] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that 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 further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0020] FIG. 1 show a schematic diagram for preparing monoaromatic compounds from a polyaromatic feedstock, according to embodiments of the invention.

DETATEED DESCRIPTION OF THE INVENTION

[0021] In the present disclosure, a refinery feedstock like LCO is processed in two steps to produce mono-aromatics as a major fraction. In the first hydrotreating step, unwanted impurities such as sulfur, nitrogen, and metals are removed by reacting with hydrogen in the presence of a catalyst. Hydrotreating conditions are adjusted in such a way that monoaromatic compounds produced and/or preserved while decreasing sulfur content significantly. In the second hydrocracking step, the partially hydrogenated feed molecules are broken down into simpler ones by using a distinct, dual catalyst bed arrangement and an elevated partial pressure of hydrogen gas. The dual catalyst bed arrangement allows for production of mono-aromatic compounds as major products in increased yields.

[0022] In the first step, a polyaromatic-containing feedstock 1 like LCO is hydrotreated in hydrotreating reactor 102 to partially hydrogenate polyaromatic compounds and remove heteroatom impurities. The hydrotreating catalysts employed herein comprise cobalt and molybdenum on a support material such as gamma alumina. In certain aspects, the hydrotreating catalysts comprise transition metals including Co, Ni, W, Mo, or a combination thereof supported on a supporting material including alumina and/or silica. Non-limiting examples of the hydrotreating catalyst include C0M0/Y-AI2O3, N1M0/Y-AI2O3, NiMo/Silica- AI2O3, MW/Y-AI2O3, C0MM0/Y-AI2O3, and combinations thereof. In the second step, the partially hydrogenated hydrotreated stream is subjected to hydrocracking over two distinct catalyst beds. [0023] The two-step process may be implemented in a system shown in FIG. 1. According to embodiments of the invneiton, the system may include pump 2 in fluid communication with hydrotreating reactor 5 such that poly aromatic-containing feedstock stream 1 is feed to hydrotreating reactor 5 via pump 2. Hydrotreating reactor 5 may include hydrotreating catalyst bed 7 comprising transition metals including Co, Ni, W, Mo, or a combination thereof. The transition metals may be supported on a supporting material including alumina and/or silica.

[0024] In embodiments of the invention, an outlet of hydrotreating reactor 5 may be in fluid communication with hydrocracking reactor 6 such that hydrotreated feedstock 10 flows from hydrotreating reactor 5 to hydrocracking reactor 6. Hydrocracking reactor 6 may include first catalyst bed 8 and second catalyst bed 9. In certain aspects, first catalyst bed 8 may comprise transition metals including Co (cobalt), Ni (nickel), W (tungsten), Mo (molybdenum) supported on a inorganic support material including alumina, silica, zeolites including 8-, 10-, l2-membered ring like ZSM-5, ZSM-12, mordenite, MCM-22, b-zeolite, or combinations thereof. Second catalyst bed 9 may comprise Ni, Mo, Re (rhenium), Pt (platinum), or combinations thereof supported on zeolites comprising 8-, 10-, l2-membered ring like ZSM- 5, ZSM-12, mordenite, MCM-22, Y- and b-zeolite, or combinations thereof.

[0025] In embodiments of the invention, an outlet of hydrocracking reactor 6 may be in fluid communication with high pressure separator 12 such that effluent stream 11 flows from hydrocracking reactor 6 to high pressure separator 12. In embodiments of the invention, high pressure separator 12 may include a top outlet in fluid communication with recycle compressor 14, and a bottom outlet in fluid communication with low pressure separator 13. Recycle compressor 14 may be in fluid communication with an inlet of hydrocracking reactor 6 such that hydrogen gas from high pressure separator 12 is compressed and recycled back to hydrotreating reactor 5 and/or hydrocracking reactor 6. The bottom fraction from high pressure separator 12 may be separated in low pressure separator 13 to form product stream 17 and a gas stream 16.

EXAMPLES

[0026] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results. [0027] The experiments were carried out in a fixed bed catalytic reactor. The light cycle oil refinery stream was subjected to hydrotreating in a hydrofining reactor, followed by hydrocracking the liquid effluent of hydrofining reactor.

[0028] Step 1. The hydrotreating step was carried out by mixing heavy aromatic rich light cycle oil with hydrogen and exposing the mixture to a hydrogenation catalyst at elevated temperature. The hydrotreating process removed sulfur and nitrogen impurities in the mixture.

[0029] The hydrotreating catalyst was a CoMoS on AI2O3. The catalyst was activated by presulfidation using /er/-butyl polysulfide (TBPS). The hydrotreating reaction was carried out at 360 °C, 60 bar, and 0.7 h ¹ WHSV. The H2 to hydrocarbon ratio was maintained at 10 mol/mol. The hydrotreating catalyst was sized and sieved to a particle size range of 300 - 500 pm. Gas and liquid samples were taken after steady state was reached, and were analyzed using gas chromatography mass spectroscopy (GC-MS). The different components are categorized as per their group types as shown in Table 1. The carbon number of the LCO feed was in the range of C6+ to C14+. During hydrotreating, hydrogen was added to aromatic components to partially saturate the aromatic rings, and no hydrocracking was observed. Table

1 shows that diaromatics are converted to partially saturated mono-aromatics (monoaromatics- 2R) like tetralin, and tri-aromatics are completely converted to partially saturated products (diaromatics-3R). HDT-LCO is hydrotreated LCO. Monoaromatics-2R are dual ring compounds having a single aromatic ring. Monoaromatics-lR are single-ring, aromatic compounds. Diaromatics-3R are triple ring compounds having two aromatic rings. Diaromatics are dual aromatic ring compounds. Triaromatics are triple aromatic ring compounds.

Table 1 Hydrotreating of Refinery LCO on C0M0S/AI ₂ O ₃

[0030] Step 2. The hydrocracking step was carried out on the hydrotreated feed from Step 1 above. The feed was subjected to hydrocracking conditions over two different catalysts beds. Bed-l consisted of a 1 :1 w/w mixture of hydrotreating catalyst (CoMoS on A12O3) and hydrocracking catalyst (b-zeolite), followed by bed-2 hydrocracking catalyst (Mo on mordenite). The catalyst were sized and sieved in a particle size range of 300 - 500 pm. The zeolites in powder form were extruded using alumina as binder followed by sizing the extrudates to required size.

[0031] Hydrocracking catalyst bed: Glass beads were charged to the reactor followed by Bed-2 catalyst (Mo on mordenite). Bed-l catalyst components (C0M0/AI2O3 and b-zeolite) were mixed to have uniform distribution into the reactor above the Bed-2 catalyst. As a control, a reactor was loaded with Bed-l catalyst only. The hydrotreated feed was passed over the catalyst beds at predetermined process conditions. The products were analyzed by gas chromatograph, and components categorized into different groups. The product composition as given in Table-2 indicate that dual -bed catalyst combination of CoMoS on AI2O3 with b- zeolite and Mo/Mordemite catalysts showed BTEX gain of 23.59 wt%. By contrast, the single bed, Bed-l catalyst (combination of CoMoS on AI2O3 and b-zeolite) showed BTEX gain of 17.86 wt%. The alkyl -naphthalene and naphthalene formation (Table 2, bottom row) was higher for the dual-bed catalyst combination (3.76 wt%), as compared to the single-bed catalyst (3.17 wt%), which is attributed to reversible reactions of hydrogenated products in the presence of higher acidity catalysts.

Table 2 Composition of Hydrocracked Product Stream, Single Versus Dual-Bed

Catalyst (sampling time = 24 hr)

[0032] The results in Table 2 demonstrate that benzene yields are greater when hydrocracking was carried out on the dual-bed catalyst combination (4.08% vs 2.78% for single bed catalyst). The single bed catalyst hydrocracks LCO components ranging from C10+ to Cl 4+ to lower carbon numbers C6+ to C10+. The dual -bed catalyst combination increases the yields of BETX from 17.86 wt.% (single bed) to 23.59 wt.%. The product stream emanating from the dual-bed catalyst combination is enriched in C6 to C8 products. The composition of gases in the product stream (Table-2, dual -bed catalyst combination) indicates that ethane and propane are major products, which and can be utilized as cracker feedstock. Thus the dual -bed catalyst combination process provides improved BTEX yields from an LCO stream, and provides cracker feed gases like ethane and propane as well.

Table 3 Dual-bed Catalyst Combination vs Single-Catalyst Bed: Composition of

Different Streams

[0033] The results in Table 3 demonstrate that single-ring monoaromatic yields are greater when hydrocracking was carried out on the dual-bed catalyst combination (32.09% vs 27.36% for single bed catalyst). [0034] In the context of the present invention, embodiments 1-14 are described.

Embodiment 1 is a process for preparing monoaromatic compounds from a polyaromatic feedstock. The process includes treating the polyaromatic feedstock with hydrogen gas under conditions sufficient to hydrogenate the polyaromatic feedstock, and contacting the hydrogenated polyaromatic feedstock with a catalyst under conditions sufficient to hydrocrack the hydrogenated polyaromatic feedstock. The catalyst includes a first catalyst bed comprising cobalt, molybdenum, a zeolite, and a support material, and a second catalyst bed comprising molybdenum supported on a zeolite. Embodiment 2 is the process of embodiment 1, wherein the polyaromatic feedstock has a boiling point in the range of about 180 to about 430 °C. Embodiment 3 is the process of embodiment 1, wherein the polyaromatic feedstock has a boiling point in the range of about 180 to about 350 °C. Embodiment 4 is the process of any of embodiments 1 to 3, wherein hydrogenating the polyaromatic feedstock includes hydrogenating at least a portion of the carbon-carbon double bonds present in the feedstock and removing at least some heteroatom impurities from the feedstock. Embodiment 5 is the process of any of embodiments 1 to 4, wherein conditions sufficient to hydrogenate the polyaromatic feedstock include a temperature ranging from about 300 to about 400 °C, a pressure ranging from about 40 to about 80 bar, a WHSV ranging from about 0.5 to about 1.4 h-l, and a Eb to hydrocarbon ratio ranging from about 5 to about 12 mol/mol. Embodiment 6 is the process of any of embodiments 1 to 5, wherein conditions sufficient to hydrocrack the hydrogenated polyaromatic feedstock have a reaction temperature ranging from about 380 to about 450 °C. Embodiment 7 is the process of any of embodiments 1 to 6, wherein the zeolite of the second catalyst bed comprises mordenite. Embodiment 8 is the process of any of embodiments 1 to 7, wherein the first catalyst bed is different from the second catalyst bed. [0035] Embodiment 9 is a system for preparing monoaromatic compounds from a polyaromatic feedstock. The system includes an inlet for a reactant feed comprising the polyaromatic feedstock and a reaction zone that is configured to be in fluid communication with the inlet, wherein the reaction zone comprises a catalyst. The catalyst includes a first catalyst bed comprising cobalt, molybdenum, a zeolite, and a support material, and a second catalyst bed comprising molybdenum supported on a zeolite. The system further includes an outlet that is configured to be in fluid communication with the reaction zone and configured to remove a first product stream comprising monoaromatic compounds from the reaction zone. Embodiment 10 is the system of embodiment 9, further including a hydrotreating zone upstream of the reaction zone having an inlet and an outlet that is in fluid communication with the reaction zone. Embodiment 11 is the system of embodiment 10, wherein the hydrotreating zone includes a hydrotreating reactor for hydrogenating at least a portion of the carbon-carbon double bonds present in the feedstock and removing at least some heteroatom impurities. Embodiment 12 is the system of embodiment 11, wherein the hydrotreating reactor comprises a CoMo hydrotreating catalyst. Embodiment 13 is the system of embodiment 11, wherein the hydrotreating reactor contains a catalyst that comprises a transition metal selected from the group consisting of Co, Ni, W, Mo, and combinations thereof. Embodiment 14 is the system of embodiment 13, wherein the catalyst of the hydrotreating reactor includes C0M0/Y-AI2O3, NiMo/ Y-AI2O3, NiMo/Silica - AI2O3, NiW/ Y-AI2O3, CoNiMo/ Y-AI2O3, or combinations thereof. Embodiment 15 is the system of embodiments 9-14, wherein the zeolite of the second catalyst bed comprises mordenite. Embodiment 16 is the system of embodiments 9-15, wherein the first catalyst bed is different from the second catalyst bed.