Process for removing residual hydrogen fractions

Abstract

The present invention relates to a process for removing residual hydrogen from an aromatic fraction having a reduced bromine index by selective hydrogenation by reacting with olefins and / or bicyclic aromatic components contained in the aromatic fraction.

Description

Technical Field

[0001] The present invention relates to a method for removing residual hydrogen from an aromatic fraction. More specifically, the present invention relates to a method for removing residual hydrogen from an aromatic fraction by reacting with olefins and / or bicyclic-aromatic components contained in the aromatic fraction, wherein the bromine index of the aromatic fraction has been reduced by preliminary (or previous) selective hydrogenation. Background Art

[0002] C6+ aromatic hydrocarbons (especially benzene, toluene or mixed xylenes (or xylene isomers)) are the main sources of basic chemicals used in the petrochemical industry. Among them, mixed xylenes including meta-xylene (m-xylene), para-xylene (p-xylene) and ortho-xylene (o-xylene) (especially para-xylene) are extremely important.

[0003] Commercial processes for producing benzene, toluene or mixed xylenes include separation / recovery methods and synthesis methods from aromatic-rich fractions. With regard to the separation / recovery method, mixed xylenes are separated by distilling reformate obtained from catalytic reforming of naphtha, or from pyrolysis oil produced as a by-product during thermal cracking of naphtha.

[0004] However, aromatic hydrocarbon fractions (e.g., catalytic reforming oil and pyrolysis oil) contain unsaturated hydrocarbons (e.g., olefins, acetylene and / or styrene or derivatives thereof), which have adverse effects on the operation of downstream processes. Therefore, it is known to reduce the olefin content in the feedstock of the downstream process by clay pre-treatment or pre-hydrogenation. Among them, hydrogenation is carried out by feeding hydrogen in the presence of a catalyst to convert unsaturated hydrocarbons (i.e., olefins, acetylene and / or styrene (including derivatives thereof, but not containing aromatic (benzene) rings)) in the aromatic fraction into saturated hydrocarbons (i.e., paraffins), but hydrogenation is carried out in order to minimize aromatic hydrocarbon losses, thereby alleviating problems associated with frequent replacement cycles, increased clay treatment, and waste generation encountered in clay treatment. In this case, a hydrogenation catalyst known in the art, such as a nickel-based catalyst, a noble metal-based catalyst (Pt, Pd, etc.), cobalt-molybdenum (Co-Mo), nickel-molybdenum (Ni-Mo), etc., is used.

[0005] However, due to the nature of the hydrogenation reaction, the aromatic fraction may be lost due to over-hydrogenation, or all the fed hydrogen may not be completely consumed and a small amount of hydrogen may remain in the hydrogenated aromatic fraction. Specifically, the residual hydrogen may adversely affect the distillation performance in the downstream xylene process, cause cavitation due to bubbles in the pump and thus damage the pump, or cause deterioration of the separation performance in the xylene purification method.

[0006] When a catalyst having controlled hydrogenation activity (e.g., NiMo sulfide catalyst) is used to selectively remove unsaturated hydrocarbons (e.g., olefins) by hydrogenation while suppressing the loss of aromatic fractions, a hydrogenation product initially containing residual hydrogen is discharged. On the other hand, a catalyst having relatively high hydrogenation activity (e.g., Ni or NiMo reduction-type catalyst) has almost no residual hydrogen but causes severe loss of aromatic fractions.

[0007] In this regard, in order to try to minimize such aromatic hydrocarbon loss, a method of combining a NiMo sulfide catalyst with a NiMo reduced catalyst may be considered. However, initially, the product contains almost no residual hydrogen, but as the reaction proceeds for a predetermined time or longer, the hydrogenation activity decreases, and thus a product containing residual hydrogen is discharged.

[0008] In this regard, a method of removing residual hydrogen from a selective hydrogenation product using a physical method (e.g., gas-liquid separation (e.g., flash column, deheptanizer, fractionator, etc.) is known (described in Korean Patent No. 1109814, Korean Patent Application Early Publication No. 2005-0089010, U.S. Patent No. 6977317, etc.). However, this method uses separate separation and recovery facilities, which inevitably increases equipment investment costs.

[0009] At the same time, the applicant has developed a secondary selective hydrogenation method based on a catalyst system, in which two types of catalysts (a first hydrogenation catalyst and a second hydrogenation catalyst) with different hydrogenation activities are loaded in a stage loading manner or loaded in two reactors connected in series (U.S. Patent Application Early Publication No. 2022-0073440). Considering the second hydrogenation reaction conditions, the method can be carried out by removing the residual hydrogen in the hydrogenated aromatic fraction finally discharged. However, even if the second hydrogenation reaction is carefully controlled, the content of residual hydrogen in the final hydrogenated aromatic fraction is still approximately 84wtppm (the concentration of residual hydrogen in the final product after 17 days of operation) and then gradually increases. In addition, when the conditions of the second hydrogenation are adjusted to minimize the amount of residual hydrogen in the final aromatic fraction, the problem of increased loss of monocyclic aromatic hydrocarbons due to over-hydrogenation has not been solved.

[0010] As described above, even if an aromatic fraction containing a reduced amount of bromine index increasing components (eg, olefins) is produced by primary selective hydrogenation while minimizing aromatic hydrocarbon losses, unreacted residual (excess) hydrogen remains a technical problem.

[0011] Therefore, there is a need for a method for effectively removing residual hydrogen present in an aromatic fraction, particularly a C8+ aromatic fraction, after selective hydrogenation without causing a loss of single-ring aromatic hydrocarbons. Summary of the invention

[0012] 1. Technical issues to be resolved

[0013] Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a method of reducing the loss of single-ring aromatic hydrocarbons while effectively removing residual hydrogen in an aromatic fraction having a reduced bromine index through selective hydrogenation.

[0014] (II) Technical solution

[0015] According to an embodiment of the present invention, a method for purifying aromatic hydrocarbons comprises:

[0016] a) selectively hydrogenating an aromatic hydrocarbon-containing feedstock having a bromine index of at least 30 in the presence of a selective hydrogenation catalyst and while supplying hydrogen to form a first aromatic hydrocarbon-containing product having a reduced bromine index and unsaturated hydrocarbon content and containing at most 200 wtppm of residual hydrogen, and

[0017] (b) hydrogenating the first aromatic-containing product using the residual hydrogen in the presence of a hydrogenation catalyst to form a second aromatic-containing product, the second aromatic-containing product containing a reduced amount of residual hydrogen compared to the first aromatic-containing product,

[0018] The first aromatic hydrocarbon-containing product has a bromine index reduced by at least 20% compared to the aromatic hydrocarbon-containing feedstock, and the first aromatic hydrocarbon-containing product contains (i) unsaturated hydrocarbons and (ii) bicyclic aromatic hydrocarbons.

[0019] According to an exemplary embodiment, the total aromatic loss in the first aromatic-containing product is less than 0.45 wt % based on the weight of the aromatic-containing feedstock, and the monocyclic aromatic loss in the second aromatic-containing product is less than 0.15 wt % based on the first aromatic-containing product.

[0020] According to an exemplary embodiment, the hydrogenation of step b) may be performed under reaction conditions controlled within a temperature range of higher than 55° C. and lower than about 255° C. and a pressure range of 3 bar to 60 bar.

[0021] According to an exemplary embodiment, the hydrogenation catalyst in step b) may comprise at least one active metal and an inorganic oxide support, wherein the at least one active metal is selected from nickel and platinum group metals.

[0022] According to an exemplary embodiment, the platinum group metal may include at least one selected from the following group: platinum, rhodium, and ruthenium.

[0023] According to an exemplary embodiment, the content of the active metal in the hydrogenation catalyst in step b) may be controlled within a range of 0.1 wt % to 40 wt % on an elemental basis.

[0024] According to an exemplary embodiment, the aromatic hydrocarbon-containing feedstock may include C8+ aromatic hydrocarbons.

[0025] According to an exemplary embodiment, the method may further comprise:

[0026] c) separating the second aromatic hydrocarbon-containing product into a C9+ aromatic hydrocarbon fraction and a C8 aromatic hydrocarbon fraction; and

[0027] d) separating and recovering p-xylene from the separated C8 aromatic hydrocarbon fraction.

[0028] According to an exemplary embodiment, the method may further comprise treating the second aromatic hydrocarbon-containing product with a solid acid before step c).

[0029] According to an exemplary embodiment, the method may further comprise:

[0030] e) isomerizing the residual C8 aromatic hydrocarbon fraction not recovered as p-xylene to form a C8 aromatic hydrocarbon fraction containing an increased p-xylene content, followed by recycling to step c).

[0031] (III) Beneficial effects

[0032] According to an embodiment of the present invention, when a selective hydrogenation product having a reduced bromine index (BI) through selective hydrogenation of an aromatic hydrocarbon fraction is additionally hydrogenated, the loss of aromatics (especially single-ring aromatic hydrocarbons, such as C8) can be minimized by controlling the reaction conditions, the selection of a catalyst, and the content of a two-ring aromatic component, while effectively removing residual hydrogen in the selective hydrogenation product. Therefore, by removing residual hydrogen in the selectively hydrogenated aromatic hydrocarbon fraction, various problems that may occur in downstream processes (such as pump-based transfer, separation of xylene, and purification of paraxylene) can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1a and Figure 1b An exemplary method of treating an aromatic hydrocarbon-containing feedstock in the order of selective hydrogenation and hydrogenation, and then removing residual hydrogen from the selectively hydrogenated aromatic hydrocarbon-containing product by hydrogenation is schematically illustrated. Best Mode for Carrying Out the Invention

[0034] The present invention can be fully implemented with reference to the following description. It should be understood that the following description illustrates preferred embodiments of the present invention, but the present invention is not necessarily limited thereto. It should also be understood that the accompanying drawings are included to provide a further understanding of the present invention and are not intended to limit the scope of the present invention.

[0035] The terms used herein are defined as follows.

[0036] The term "heterogeneous catalyst" as used herein refers to a catalyst that exists in a different phase than the reactants in a catalytic reaction. For example, a heterogeneous catalyst may remain undissolved in the reaction medium. When a heterogeneous catalyst is used, the reaction begins with the reactants diffusing and adsorbing onto the surface of the heterogeneous catalyst. After the reaction is complete, the product needs to be desorbed from the surface of the heterogeneous catalyst.

[0037] The term "support" as used herein refers to a material (usually a solid phase material) having a catalytically active component attached thereto and having a large specific surface area, and the support may or may not participate in the catalytic reaction.

[0038] The term "unsaturated hydrocarbon" as used herein means a hydrocarbon containing a double bond or even a triple bond, and is generally intended to include alkenes and alkynes, more specifically alkenes. However, unless otherwise mentioned herein, it should be understood that aromatic rings are not included in the scope of unsaturated hydrocarbons removed by "selective hydrogenation", even if they contain double bonds. However, like unsaturated hydrocarbons, bicyclic aromatic rings fall within the scope of compounds removed by "hydrogenation".

[0039] The term "olefin" described herein may be intended to include olefins, cycloolefins, alkenylbenzenes, and the like.

[0040] The term "Cn+ aromatic" described herein refers to an aromatic hydrocarbon having Cn or more carbon atoms, and similarly, the term "Cn-aromatic" refers to an aromatic hydrocarbon having Cn or less carbon atoms.

[0041] The term "Cn+ hydrocarbon" described herein refers to a hydrocarbon having Cn or more carbon atoms, and similarly, the term "Cn- hydrocarbon" refers to a hydrocarbon having Cn or less carbon atoms.

[0042] The term "C8 aromatics" as described herein refers to aromatic hydrocarbons comprising mixed xylenes (o-xylene, m-xylene and p-xylene) and / or ethylbenzene.

[0043] The term "hydrogenation" as used herein generally refers to the reaction of an organic compound with hydrogen, wherein the reaction is generally carried out in the presence of a catalyst. Meanwhile, in a narrow sense, the term "selective hydrogenation" means preferentially converting unsaturated hydrocarbons by hydrogenation over aromatic compounds in a hydrogenated feedstock. Here, "hydrogenation" is different from "selective hydrogenation". Specifically, hydrogenation minimizes the saturation of monocyclic aromatic rings but allows saturation of aromatic rings in bicyclic aromatic hydrocarbons (which have a higher hydrogenation reactivity than monocyclic aromatic hydrocarbons), while selective hydrogenation minimizes the saturation of the aromatic rings themselves.

[0044] The term "bromine index (BI)" as used herein refers to the measurement of the amount of bromine (mg) consumed by 100 grams of hydrocarbon or hydrocarbon mixture and can be used to indicate the percentage of unsaturated bonds present in the hydrocarbon. The bromine index can be measured, for example, according to ASTM D 2710-92.

[0045] The term "enriched" as used herein means that a particular compound is present in a fraction or stream on a predetermined basis (e.g., on a weight, volume or molar basis), for example, in an amount of at least about 50%, specifically at least 70%, more specifically at least about 80%, and particularly specifically at least about 90%.

[0046] It should be understood that in the specification, when a numerical range is defined by a lower limit and / or an upper limit, the numerical range includes any subcombination thereof. For example, a range of "1 to 5" may include 1, 2, 3, 4 and 5, and any subcombination therebetween.

[0047] It will be understood that when a component or a member is referred to as being “connected to” another component or member, it can be directly connected to the other component or intervening components or members may be present therebetween, unless otherwise mentioned.

[0048] Similarly, it will be understood that when a component or member is referred to as “contacting” another component, the component or member may directly contact the other component or intervening components or members may be present therebetween.

[0049] It should also be understood that the terms "on" and "above" are used to describe positional relationships. Therefore, when a layer is referred to as being "on" or "above" another layer or component, the layer may be directly on or above the other layer, or there may be an intermediate (intermediate) layer or component sandwiched or present therebetween, unless otherwise mentioned. Similarly, expressions such as "under," "below," "beneath," and "between" may be understood as relative position terms. In addition, the expression "sequentially" may be understood as a relative position term.

[0050] It should also be understood that when the term “comprises” is used in this specification, it specifies the presence of a component but does not exclude the presence or addition of one or more other components and / or steps unless otherwise mentioned.

[0051] According to an embodiment of the present invention, an aromatic hydrocarbon fraction as a raw material is treated by a multi-step process comprising selective hydrogenation and hydrogenation, wherein the selective hydrogenation and hydrogenation are each carried out in the presence of a heterogeneous catalyst (specifically, a supported catalyst in which a metal having hydrogenation activity is introduced into a carrier). Therefore, aromatic hydrocarbons (specifically, C8+ aromatic hydrocarbons) from which residual hydrogen that hinders the operation of downstream processes (e.g., pump-based transfer, xylene separation, paraxylene recovery, etc.) are removed while reducing the bromine index of the aromatic hydrocarbon fraction can be provided.

[0052] Selective hydrogenation

[0053] According to an embodiment of the present invention, a fraction containing aromatic (specifically, alkyl aromatic) hydrocarbons is first supplied as a feedstock. In this case, the feedstock may generally be a fraction containing C8+ aromatic hydrocarbons and having a relatively high bromine index (BI) because it contains unsaturated hydrocarbons (specifically, olefins, diolefins, acetylene and / or styrene (or its derivatives)).

[0054] In this regard, the alkyl aromatic hydrocarbons in the aromatic hydrocarbon-containing fraction may be, for example, alkyl aromatic hydrocarbons having about 8 to 20 carbon atoms, specifically about 8 to 18 carbon atoms, and more specifically about 8 to 16 carbon atoms. The alkyl aromatic hydrocarbons are compounds in which at least one alkyl group is bonded to an aromatic ring, and the alkyl group may be, for example, a methyl group, an ethyl group, a propyl group, or a butyl group, etc. In addition to xylene, the C8+ alkyl aromatic hydrocarbons may include ethyltoluene, propylbenzene, tetramethylbenzene, ethyldimethylbenzene, diethylbenzene, methylpropylbenzene, ethylpropylbenzene, triethylbenzene, diisopropylbenzene, mixtures thereof, and the like.

[0055] In an exemplary embodiment, the feedstock may be a C8+ aromatic hydrocarbon fraction from which a C7- hydrocarbon fraction has been separated. The C8+ aromatic hydrocarbon-containing fraction is used because the C7-aromatic fraction discharged to the upper portion of a separator (e.g., a distillation column) for separating the aromatic fraction into a C7-aromatic fraction and a C8+ aromatic fraction in an industrial process contains almost no bicyclic aromatic hydrocarbons.

[0056] In addition, the aromatic hydrocarbon fraction may contain unsaturated hydrocarbons with increased bromine index (BI), such as hydrocarbons having at least one double bond and / or triple bond, such as monoolefins, diolefins, acetylene and styrene (or derivatives thereof), and such unsaturated hydrocarbons are subjected to selective hydrogenation. In addition, the content of unsaturated hydrocarbons in the aromatic-containing feedstock can be quantified by the bromine index. In this embodiment, the bromine index of the feedstock is, for example, at least about 30, specifically 50 to 30,000, specifically about 100 to about 20,000, especially about 150 to about 10,000, and in certain embodiments, for example, about 300 to about 3,000, specifically about 400 to about 2,000, and more specifically about 500 to 1,500.

[0057] According to an exemplary embodiment, the feedstock is a fraction rich in aromatic hydrocarbons, in particular a fraction rich in C8+ aromatic hydrocarbons, wherein the aromatic content is, for example, at least about 50% by weight, specifically at least about 70% by weight, more specifically at least about 80% by weight, and especially at least about 90% by weight. In addition, the feedstock containing aromatic hydrocarbons may contain, for example, about 50% by weight or less, specifically about 30% by weight or less, more specifically about 20% by weight or less, and particularly specifically about 10% by weight or less of saturated hydrocarbons.

[0058] According to an exemplary embodiment, in addition to the monocyclic aromatic hydrocarbons, the aromatic hydrocarbon-containing feedstock may also contain bicyclic aromatic hydrocarbons (e.g., at least one selected from naphthalene, indene, derivatives thereof, etc.). The content of such bicyclic aromatic hydrocarbons may be, for example, at least about 0.3 wt %, specifically about 0.4 wt % to about 20 wt %, more specifically about 0.5 wt % to about 15 wt %, particularly specifically about 1 wt % to about 10 wt %. However, the content of bicyclic aromatic hydrocarbons may vary widely depending on the source of the feedstock, and is not limited to the range defined above. Depending on the source, a smaller amount of bicyclic aromatic hydrocarbons may be present.

[0059] According to an exemplary embodiment, the feedstock containing aromatic hydrocarbons can be obtained by, for example, catalytic reforming of naphtha; thermal cracking of naphtha, distillates or other hydrocarbons to produce light olefins and aromatic-rich fractions; or catalytic cracking or thermal cracking of heavy oil fractions to produce hydrocarbons with boiling points similar to those of gasoline, and these sources can be used as feedstocks alone or in combination. In certain embodiments, the feedstock can be derived from catalytic reforming oil of naphtha.

[0060] According to an exemplary embodiment, the selective hydrogenation for removing unsaturated hydrocarbons from the aromatic-containing fraction is carried out, for example, in a temperature range of room temperature to 300° C., specifically in a temperature range of about 40° C. to 250° C., more specifically in a temperature range of about 50° C. to 230° C. According to a specific embodiment, the selective hydrogenation is carried out under temperature conditions of, for example, about 100° C. to 220° C., specifically about 120° C. to 215° C., more specifically about 130° C. to 210° C., and especially about 155° C. to 205° C. In this case, the selective hydrogenation can be carried out as a liquid phase reaction or a three-phase reaction (trickle bed) using excess hydrogen. However, a liquid phase reaction that can reduce investment costs and keep the amount of residual hydrogen as low as possible after the reaction may be more advantageous.

[0061] According to an exemplary embodiment, the amount of hydrogen fed during the selective hydrogenation is, for example, at least about 0.5 mol, specifically about 0.7 mol to 20 mol, more specifically about 1 mol to 10 mol, relative to 1 mol of unsaturated hydrocarbons contained in the feedstock. When the amount of hydrogen supplied is too small or too large, problems such as low removal rate of unsaturated hydrocarbons or increased loss of aromatic hydrocarbons due to hydrogenation of aromatic rings may occur. However, the supply amount of hydrogen is not limited to the above range, as it may vary depending on the properties of the feedstock.

[0062] Meanwhile, according to an exemplary embodiment, the pressure in the selective hydrogenation zone may be determined in the range of, for example, about 3 bar to 70 bar, specifically about 5 bar to 30 bar, and more specifically about 7 bar to 20 bar. When the pressure in the selective hydrogenation reaction zone is too low or too high, problems such as low removal rate of unsaturated hydrocarbons or increased loss of aromatic hydrocarbons due to hydrogenation of aromatic rings may occur. Therefore, the pressure in the selective hydrogenation zone is preferably controlled within the range defined above.

[0063] In addition, the liquid hourly space velocity (LHSV) of the aromatic-containing raw material is, for example, about 0.3 hr -1 Up to 30 hours -1 , specifically about 0.5hr -1 Up to 20 hours -1 , more specifically about 0.5 hr -1 Up to 10 hours -1 .

[0064] Meanwhile, the catalyst for selective hydrogenation (i.e., selective hydrogenation catalyst) can be selected from catalysts having hydrogenation activity, which are controlled to have substantially no hydrogenation selectivity for aromatic rings (monocyclic and / or bicyclic or polycyclic aromatic rings) but have high hydrogenation selectivity for unsaturated hydrocarbons.

[0065] According to an exemplary embodiment, the selective hydrogenation catalyst may include a support containing an inorganic oxide, and an active metal, the active metal including at least one selected from the following group: Ni, Pd, Pt, Ru, Rh, Re, Co, Mo, Co-Mo, Ni-Mo and Ni-W. In an exemplary embodiment, the content of the active metal in the selective hydrogenation catalyst (calculated on an element basis) is, for example, about 0.5 wt % to about 40 wt %, specifically about 2 wt % to about 30 wt %, more specifically about 4 wt % to 25 wt %, based on the total weight of the catalyst. The range of the metal content is provided for illustrative purposes and may vary depending on the type of active metal used, its hydrogenation activity and the type of metal.

[0066] In the selective hydrogenation catalyst, the scheme of using a plurality of metals among the active metals exemplified above can be combined as exemplified below:

[0067] In Co-Mo, the atomic ratio of cobalt to molybdenum may be, for example, 1: about 0.5 to 10, specifically 1: about 1 to 5, and more specifically 1: about 1.5 to 3. In addition, in Ni-Mo, the atomic ratio of nickel to molybdenum may be, for example, 1: about 0.5 to 10, specifically 1: about 1 to 5, and more specifically 1: about 1.5 to 3. In addition, in Ni-W, the atomic ratio of nickel to tungsten may be, for example, 1: about 0.5 to 10, specifically 1: about 1 to 5, and more specifically 1: about 1.5 to 3.

[0068] In one embodiment, the selective hydrogenation catalyst may be in a reduced form, a sulfide form, or a combination thereof. As an example, a specific single active metal or a combination of two types of active metals may be in both a reduced form and a sulfide form, and different active metals or a combination of two types of active metals may be in a reduced form. Generally, in certain active metals or combinations thereof, the reduced form has a higher hydrogenation activity than the sulfide form, and the form of the catalyst (reduced, sulfide, or oxide form) may be determined in consideration of the amount or partial pressure of hydrogen in contact with the catalyst.

[0069] According to another exemplary embodiment, the selective hydrogenation catalyst can be loaded into a single reactor in a staged loading mode. For example, the first selective hydrogenation catalyst layer and the second selective hydrogenation catalyst layer can be arranged in the order described based on the inflow direction of the raw material. In this case, when the active metal in the first selective hydrogenation catalyst (or catalyst layer) is Re, Co, Mo and / or Co-Mo, a reduction or sulfide catalyst layer is provided, and when the first selective hydrogenation catalyst is Ni, Pd, Pt, Ru, Rh, Ni-Mo and / or Ni-W, a sulfide catalyst layer may be provided. On the other hand, the second selective hydrogenation catalyst of the downstream process may have a structure in which a catalyst layer of Ni-Mo and / or Ni-W loaded with a reduced form is provided.

[0070] In a modified example of the above-described staged charging method, selective hydrogenation may be performed by connecting in series a plurality of reactors corresponding to the first selective hydrogenation catalyst layer and the second selective hydrogenation catalyst layer.

[0071] A staged loading method or a modified example thereof is disclosed in U.S. Patent Application Publication No. 2022-0073440 filed by the present applicant, which is incorporated herein by reference.

[0072] According to an exemplary embodiment, the support for the selective hydrogenation catalyst (or the first selective hydrogenation catalyst and the second selective hydrogenation catalyst) can be selected from inorganic oxides, specifically inorganic oxides having a large specific surface area. Such a support may, for example, include at least one selected from the following group: alumina, silica, silica-alumina, aluminum phosphate, zirconium oxide, titanium dioxide, bentonite, kaolin, clinoptilolite, and montmorillonite. According to a specific embodiment, the inorganic oxide may be amorphous, and specifically includes at least one selected from the following group: alumina, silica, and silica-alumina, particularly specifically alumina.

[0073] According to an exemplary embodiment, the carrier may be cylindrical, and may, for example, have a diameter of about 0.5 mm to about 5 mm (specifically, about 1 mm to 3 mm), and a dimension of about 3 mm to 20 mm (specifically, about 5 mm to 15 mm). Alternatively, the carrier may have a shape other than a cylindrical shape, such as a granule, a pellet, a tablet, or a sphere. As such, a molding method, extrusion, spray drying, pelletizing, oil dropping, etc. known in the art may be applied to produce a carrier having a specific shape, but this is provided for exemplary purposes.

[0074] According to an exemplary embodiment, the carrier may have an apparent density of about 0.3 cubic centimeters per gram (cc / g) to 1.2 cubic centimeters per gram, specifically about 0.4 cubic centimeters per gram to 1.1 cubic centimeters per gram, and more specifically about 0.4 cubic centimeters per gram to 0.9 cubic centimeters per gram. In addition, the average pore size of the carrier may be, for example, about 3 nanometers to 1,000 nanometers, specifically about 5 nanometers to 800 nanometers, and more specifically about 7 nanometers to 600 nanometers. In addition, the specific surface area (BET) of the carrier may be, for example, about 10 square meters per gram (m 2 In some embodiments, the range of the physical properties is about 1000 square meters per gram (m2 / g) to 1,000 square meters per gram, specifically about 30 square meters per gram to 800 square meters per gram, and more specifically about 50 square meters per gram to 600 square meters per gram. It can be understood that the numerical ranges of the physical properties are to be understood as exemplary.

[0075] According to an exemplary embodiment, the method for loading the active metal on the support in the hydrogenation catalyst is a method known in the art, such as impregnation (e.g., incipient wetness impregnation, oversolution impregnation or immersion), ion exchange, co-precipitation, etc.

[0076] Typically, the impregnation can be performed by filling the pores of the support with a mixture of a soluble metal precursor or compound (typically a water-soluble or solvent-soluble metal compound), specifically a metal salt, and a liquid medium selected from water, an acidic aqueous solution, and an alkaline aqueous solution.

[0077] In an exemplary embodiment, useful metal precursors may generally be active metal salts, complexes, halides, and the like, and may be exemplified as follows.

[0078] For example, the molybdenum precursor includes at least one selected from molybdenum (II) acetate, ammonium (VI) molybdate, ammonium (III) dimolybdate, ammonium (VI) heptamolybdate, ammonium (VI) phosphomolybdate and similar sodium and potassium salts, molybdenum (III) bromide, molybdenum (III) chloride to molybdenum (V) chloride, molybdenum (VI) fluoride, molybdenum (VI) oxychloride, molybdenum (IV) sulfide to molybdenum (VI) sulfide, molybdic acid and its ammonium salt, sodium salt and potassium salt, and molybdenum (II-VI) oxide, but is not necessarily limited thereto.

[0079] The cobalt precursor may include at least one selected from the following groups: nitrate, sulfate, carbonate, acetate, alkoxide and halide of cobalt. Specifically, the cobalt precursor may include at least one selected from cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt carbonate, cobalt hydroxide, cobalt alkoxide, cobalt halide (e.g., cobalt chloride, cobalt bromide, etc.), hydrates thereof, etc. More specifically, the cobalt precursor may be cobalt nitrate and / or its hydrate (e.g., Co(NO3)2·6H2O). The nickel precursor may include at least one selected from nickel nitrate, nickel sulfate, nickel phosphate, nickel halide, nickel carboxylate, nickel hydroxide, nickel carbonate, acetylacetonate nickel complex, nickel acetate and hydrates thereof. More specifically, the nickel precursor may be nickel nitrate and / or its hydrate (e.g., Ni(NO3)2·6H2O). The tungsten precursor includes, for example, at least one selected from ammonium metatungstate, ammonium tungstate, sodium tungstate, tungstic acid, and tungsten chloride. The palladium precursor includes at least one selected from palladium acetate, palladium chloride, palladium nitrate, and palladium sulfate. The platinum precursor includes at least one selected from chloroplatinic acid, ammonium chloroplatinate, dinitrodiamine platinum, tetrachlorodiamine platinum, hexachlorodiamine platinum, dichlorodiamine platinum, dichloroplatinum (II), tetrachloroplatinum (IV), etc. The ruthenium precursor may include at least one selected from ruthenium chloride, ruthenium nitrosyl nitrate, and chlorohexamine ruthenium. The rhodium precursor may include at least one selected from rhodium chloride, rhodium acetate, rhodium nitrate, and rhodium sulfate. The rhenium precursor may include at least one selected from perrhenic acid, rhenium chloride, ammonium perrhenate, potassium perrhenate, and rhenium oxide.

[0080] According to an exemplary embodiment, the concentration of the active metal in the impregnation solution may be in the range of, for example, about 0.005 M to about 5 M, specifically about 0.01 M to about 3 M, and more specifically about 0.015 M to about 2 M. The conditions of the impregnation are not particularly limited, and the impregnation may be performed, for example, at about 1° C. to 100° C. (specifically, about 25° C. to 60° C.) for about 0.1 hour to 48 hours (about 0.5 hour to 12 hours), but such conditions may be understood as exemplary.

[0081] As described above, the support may be impregnated with the active metal and then dried. For example, the drying is performed under an oxygen-containing atmosphere (specifically, air) at a drying temperature of, for example, about 60° C. to about 200° C., specifically about 80° C. to about 150° C. In addition, the drying time may be determined in the range of, for example, about 0.5 hours to 15 hours, specifically about 1 hour to 12 hours. Drying enables the metal precursor to be more closely attached to the support.

[0082] Then, the dried catalyst is fired (or heat treated), and the firing is carried out in an oxygen-containing atmosphere (e.g., air) or an inert gas (e.g., nitrogen) atmosphere, specifically in an oxygen-containing atmosphere. In addition, the firing temperature can be selected in the range of, for example, about 300° C. to 800° C., specifically about 400° C. to 650° C. In addition, the firing time can be controlled in the range of, for example, about 0.5 hours to 24 hours, specifically about 1 hour to 12 hours. When firing in an oxygen-containing atmosphere, the active metal can be converted into an oxide, for example, molybdenum can be converted into MoO3, and nickel can be converted into NiO.

[0083] — Preparation of reduced-type catalyst

[0084] According to an exemplary embodiment, when the hydrogenation catalyst is a reduced type, a reduction treatment may be performed to convert the active metal in the oxide type catalyst into a completely reduced type and / or a partially reduced type.

[0085] In this regard, the reduction treatment can be carried out using hydrogen alone or a dilution of hydrogen in an inert gas (e.g., N2, He, Ar, etc.) at a temperature of, for example, about 25°C to 800°C, specifically, about 200°C to about 700°C, more specifically, about 300°C to about 550°C, and the reduction treatment time is not particularly limited and can be adjusted within the range of, for example, about 0.5 hours to 24 hours, specifically, about 1 hour to 12 hours.

[0086] The reduction treatment allows the active metal in the hydrogenation catalyst to be present in a reduced form. Illustratively, the metal contained in the catalyst may be in elemental form or in a partially oxidized form (e.g., molybdenum (Mo) in Mo4+ exists in a partially oxidized form rather than in the form of Mo 6+ exists in the form of 6+ is the maximum oxidation state).

[0087] — Preparation of sulfide-type catalysts

[0088] In order to control excessive hydrogenation activity causing side reactions (e.g., loss of aromaticity), or to impart hydrogenation functionality (particularly in the case of molybdenum), depending on the supported metal, the catalyst is converted to a sulfide form instead of a reduced form as appropriate.

[0089] According to an exemplary embodiment, the reduced catalyst can be sulfided, and the metal components in the catalyst can be converted into sulfides using methods known in the art. Such sulfidation can be performed using a gas phase method (including contacting hydrogen sulfide or a mixture thereof with an inert gas) or a liquid phase method (including contacting with a solution containing a sulfur compound). According to certain embodiments, the reduced catalyst can be treated with a solution containing a sulfur compound.

[0090] According to an exemplary embodiment, the sulfur compound that can be used for sulfidation may include at least one selected from hydrogen sulfide, hydrogen disulfide, carbon disulfide, alkyl sulfide, etc. Specifically, the alkyl sulfide may be, for example, methyl sulfide, dimethyl sulfide, dimethyl disufide (DMDS), diethyl sulfide and / or dibutyl sulfide. In addition, a hydrocarbon solvent (e.g., benzene, toluene, xylene, C9+ aromatics, hexane or heptane) may be used as a solvent during sulfidation. For example, the amount of the sulfur compound in the solution used for sulfidation may be appropriately determined within a range equal to or greater than the amount required to sulfidate the metal in the catalyst. For example, when molybdenum is used as an active metal, the sulfur compound may be mixed with the solution in an amount equal to or greater than the amount required to sulfidate molybdenum to MoS3 (which may ultimately be converted into MoS2). In addition, nickel may be converted into Ni3S2.

[0091] In an exemplary embodiment, the vulcanization may be performed at room temperature to about 500° C. (specifically, about 100° C. to about 450° C.) for about 0.5 hour to 100 hours (specifically, about 1 hour to about 48 hours).

[0092] At the same time, as the unsaturated hydrocarbons in the aromatic hydrocarbon-containing fraction are selectively removed by selective hydrogenation, the bromine index of the product (i.e., the first aromatic hydrocarbon-containing product) is reduced. In one embodiment, the bromine index of the first aromatic hydrocarbon-containing product may be, for example, less than about 2,000, specifically less than about 1,000, and more specifically less than about 500. In this case, the bromine index of the first aromatic hydrocarbon-containing product is reduced by at least about 20%, specifically about 30% to 99%, more specifically about 35% to 95%, and even more specifically about 40% to 90% compared to the feedstock.

[0093] It may be preferred to hydrogenate and remove all unsaturated hydrocarbons during the above-mentioned selective hydrogenation. In this case, aromatic hydrocarbon losses may also increase. Therefore, it may be advantageous to react so as to have a properly balanced product distribution. In this case, the unsaturated carbons in the first aromatic hydrocarbon-containing product may not be completely removed, and a small amount of unsaturated carbons may remain. In this regard, the content of unsaturated carbons in the first aromatic hydrocarbon-containing product is, for example, present in an amount of up to about 2% by weight, specifically up to about 1.5% by weight, more specifically about 0.01% by weight to 1% by weight, and particularly specifically about 0.02% by weight to 0.5% by weight.

[0094] At the same time, the hydrogen supplied during the selective hydrogenation can usually be used in excess relative to the unsaturated hydrocarbons, and due to factors such as controlled hydrogenation activity, there are limitations in removing all unsaturated hydrocarbons. Therefore, there is residual hydrogen in the first aromatic hydrocarbon-containing product. In this regard, the concentration of residual hydrogen in the first aromatic hydrocarbon-containing product can be, for example, at most about 200wtppm, specifically at most about 180wtppm, and more specifically at most about 150wtppm. According to certain embodiments, the concentration of residual hydrogen in the first aromatic hydrocarbon-containing product can be, for example, between about 50wtppm and 120wtppm, specifically about 60wtppm to 110wtppm, and more specifically about 80wtppm to 100wtppm.

[0095] In addition, in an exemplary embodiment, it is preferred to minimize the loss of aromatic compounds during the selective hydrogenation. The total aromatic hydrocarbon loss is, for example, less than about 0.45 wt %, specifically less than about 0.3 wt %, more specifically less than about 0.1 wt %, and particularly less than about 0.05 wt %.

[0096] hydrogenation

[0097] According to an embodiment of the present invention, additional hydrogenation may be performed to remove residual hydrogen present in the first aromatic hydrocarbon-containing product formed by the selective hydrogenation of the aromatic fraction. This hydrogenation is different from the upstream selective hydrogenation in that, based on the different hydrogenation reactivity between hydrocarbon structures, the hydrogenation allows the hydrogenation or saturation of aromatic rings with specific structures in aromatic hydrocarbons (specifically, at least one double bond in the aromatic ring), which is different from the upstream selective hydrogenation, in which the loss of aromatic rings (monocyclic or polycyclic aromatic rings) due to hydrogenation is minimized. In addition, it should be noted that the hydrogenation is performed without supplying hydrogen from an external source because the residual hydrogen is removed by hydrogenation.

[0098] According to the present embodiment, based on the fact that the hydrogenation active end during the hydrogenation of unsaturated hydrocarbons (specifically, olefins, etc.) utilizing the residual hydrogen in the aromatic fraction varies depending on the structure of the hydrocarbons, the residual hydrogen in the first aromatic hydrocarbon-containing product (i.e., the selectively hydrogenated C8+ aromatic hydrocarbon fraction) can be effectively removed.

[0099] Specifically, the hydrogenation activity of the compounds is evaluated to have the following order: olefins>bicyclic aromatics (naphthalene→tetralin or indene→indane)>monocyclic aromatics. Based on the difference in hydrogenation activity between hydrocarbon structures, olefins and / or bicyclic aromatic hydrocarbons having better hydrogenation reactivity may be used to remove residual hydrogen in the aromatic fraction while maintaining the content of monocyclic aromatic hydrocarbons as target products (i.e., minimizing the loss of monocyclic aromatic hydrocarbons). In this regard, the term "bicyclic aromatic" or "bicyclic aromatic hydrocarbon" may refer to naphthalene and indene having two aromatic rings in the molecule.

[0100] According to this embodiment, the bromine index generated by unsaturated hydrocarbons can be further reduced in the additional hydrogenation, and residual hydrogen present in the selectively hydrogenated product can be removed by reacting (hydrogenating) the unsaturated hydrocarbons present in the first aromatic hydrocarbon-containing product with residual hydrogen.

[0101] According to another exemplary embodiment, in addition to unsaturated hydrocarbons, the first aromatic hydrocarbon-containing product also contains bicyclic aromatic hydrocarbons. Specifically, when the feedstock (specifically, the fraction containing C8+ aromatic hydrocarbons) contains bicyclic aromatic hydrocarbons in addition to monocyclic aromatic hydrocarbons, the aromatic rings are retained as much as possible in the upstream selective hydrogenation (that is, the hydrogenation or saturation of the aromatic rings is suppressed as much as possible), and thus bicyclic aromatic hydrocarbons may still be present in the first aromatic hydrocarbon-containing product. In this case, the content of bicyclic aromatic hydrocarbons in the first aromatic hydrocarbon-containing product is, for example, at least about 0.3% by weight, specifically 0.4% to 15% by weight, more specifically about 0.5% to about 10% by weight, and particularly specifically about 1% to about 5% by weight.

[0102] When the total amount of unsaturated hydrocarbons and / or bicyclic aromatic hydrocarbons in the first aromatic hydrocarbon-containing product is less than the level required to remove residual hydrogen, bicyclic aromatic hydrocarbons may be further incorporated or added to the reaction system (e.g., the first aromatic hydrocarbon-containing product) before or during the hydrogenation reaction, for example, so as to adjust the total amount to the above range. There is no need to limit the amount of bicyclic aromatic hydrocarbons added, because it can be varied depending on the content of residual hydrogen. Therefore, in terms of structural characteristics, bicyclic aromatic hydrocarbons are preferentially hydrogenated compared to monocyclic aromatic hydrocarbons, so that the loss of monocyclic aromatic hydrocarbons (e.g., C8 aromatic hydrocarbons) can be effectively suppressed.

[0103] In this embodiment, hydrogenation of bicyclic aromatic rings as well as unsaturated hydrocarbons is allowed in the hydrogenation, and trace amounts of residual hydrogen need to be minimized by the hydrogenation. For this reason, a catalyst having a higher hydrogenation activity than the downstream selective hydrogenation can be used.

[0104] According to an exemplary embodiment, the hydrogenation catalyst may be prepared in a manner similar to the metal-supported catalyst, catalyst shape, etc. used in the selective hydrogenation described above. In this regard, the active metal in the hydrogenation catalyst may include at least one selected from nickel and platinum group metals in the periodic table. When a platinum group metal is used as the active metal, the platinum group metal may include at least one selected from the following groups: platinum, rhodium, and ruthenium. In addition, the active metal in the hydrogenation catalyst may be a reduced type, which is determined in consideration of the fact that the reduced type exhibits higher hydrogenation activity than the sulfide type. Specifically, among the platinum group metals, palladium may not be preferred because the palladium catalyst may not provide sufficient hydrogenation activity to remove residual hydrogen compared to other platinum group metal catalysts.

[0105] In addition, the content of the active metal in the hydrogenation catalyst (calculated on an elemental basis) is, for example, about 0.1 wt % to 40 wt %, specifically about 0.2 wt % to 30 wt %, more specifically about 0.5 wt % to 25 wt %, and especially about 1 wt % to 20 wt %, based on the total weight of the catalyst. The range of metal content is provided for exemplary purposes and may vary depending on the type of active metal used, its hydrogenation activity, and the type of metal.

[0106] Meanwhile, the carrier for supporting the active metal in the hydrogenation catalyst may be selected from the carrier used in the selective hydrogenation catalyst, and may specifically be alumina.

[0107] According to the present embodiment, most of the unsaturated hydrocarbons are removed in the upstream selective hydrogenation to produce a selective hydrogenation product containing a trace amount of residual hydrogen, and in the downstream hydrogenation, the unsaturated hydrocarbons (and / or bicyclic aromatic hydrocarbons) remaining in the selective hydrogenation product are reacted with the trace amount of residual hydrogen without supplying hydrogen from an external source. Therefore, the reaction conditions should be precisely controlled compared to the general hydrogenation of hydrocarbon fractions.

[0108] For example, the hydrogenation temperature may be controlled within a range of, for example, greater than about 55° C. and less than about 255° C., specifically about 60° C. to 230° C., and more specifically 70° C. to 225° C. According to certain embodiments, the hydrogenation temperature may be determined within a range of about 80° C. to 185° C., specifically about 90° C. to 175° C., more specifically about 95° C. to 155° C., and particularly specifically about 100° C. to 130° C.

[0109] When the hydrogenation temperature is too low, it may be difficult to substantially remove all residual hydrogen. At the same time, when the hydrogenation temperature is too high, the loss of monocyclic aromatic hydrocarbons and the bromine index (BI) of the product may increase. Specifically, as the hydrogenation temperature increases, the difference in hydrogenation activity depending on the hydrocarbon structure may decrease. In addition, at too high a hydrogenation temperature, the conversion rate of bicyclic aromatic hydrocarbons useful for removing residual hydrogen will not increase, and on the contrary, the loss of monocyclic aromatic hydrocarbons as the target component may increase. In view of this factor, it may be advantageous to appropriately adjust the reaction temperature within the range defined above.

[0110] At the same time, the pressure during hydrogenation can increase the hydrogenation activity. As the reaction pressure increases, the loss of aromatic hydrocarbons (especially monocyclic aromatic hydrocarbons) may increase. Taking this factor into consideration, the reaction pressure can be adjusted in the range of, for example, about 3 bar to 60 bar, specifically about 4 to 30 bar, and more specifically about 5 to 15 bar.

[0111] According to an exemplary embodiment, the liquid space velocity (LHSV) of the first aromatic hydrocarbon-containing product introduced into the hydrogenation reaction zone or reactor is, for example, about 0.3 hr -1 About 30 hours -1 , specifically about 0.5hr -1 About 20 hours -1 , more specifically about 0.5 hr -1 About 10 hours -1 can be adjusted within the range of

[0112] As described above, the subsequent hydrogenation performed after the selective hydrogenation enables the formation of a second aromatic hydrocarbon-containing product in which the content of each of residual hydrogen and unsaturated hydrocarbons (in addition, bicyclic aromatic hydrocarbons) is reduced. At this time, the amount of hydrogen (residual hydrogen) in the second aromatic hydrocarbon-containing product may be less than about 6 wtppm, specifically less than about 3 wtppm, and more specifically less than about 1 wtppm. In this regard, the reason for adjusting the amount of residual hydrogen to less than about 6 wtppm is as follows. The amount of residual hydrogen corresponding to the saturated solubility of hydrogen in aromatic hydrocarbons at 1 atmosphere (atm) is 6 wtppm, and when the amount of residual hydrogen is higher than this value, air bubbles may be formed, which may have an adverse effect on downstream equipment or processes as described above. In this case, the saturated solubility of hydrogen can be measured with reference to de Wet, WJJS Afr. Chem. Inst. 1964, 17, 9-13 and Satterfield, CNI Chem. E. Symp. Ser. 1968, no. 28, 22-29, which are incorporated herein by reference.

[0113] Furthermore, the loss of single-ring aromatic hydrocarbons during the hydrogenation of the first aromatic hydrocarbon-containing product is, for example, less than about 0.15 wt %, specifically about 0.12 wt % or less, more specifically about 0.03 wt % or less, and particularly specifically about 0.01 wt % or less.

[0114] According to an exemplary embodiment, the bromine index of the second aromatic hydrocarbon-containing product is reduced compared to the first aromatic hydrocarbon-containing product because the unsaturated hydrocarbons and the like contained in the first aromatic hydrocarbon-containing product as reactants are removed. For example, the bromine index of xylene obtained by distilling the second aromatic hydrocarbon-containing product is preferably low. In this regard, the bromine index level of xylene separated by distilling the second aromatic hydrocarbon-containing product is preferably less than about 20, specifically less than about 15, and more specifically less than about 10, and this is advantageously applied to a downstream process using xylene having a bromine index of 20 or less as a raw material, specifically advantageously applied to a xylene separation and recovery process (e.g., a PAREX process).

[0115] Integration with selective hydrogenation-hydrogenation and subsequent methods

[0116] According to one embodiment, in a purification method for treating an aromatic hydrocarbon-containing feedstock in the order of selective hydrogenation and hydrogenation, an exemplary embodiment of removing residual hydrogen in the selectively hydrogenated aromatic hydrocarbon-containing product by downstream hydrogenation is shown in Figure 1a and Figure 1b middle.

[0117] According to the embodiment shown, the entire process 100 or 200 can be carried out in two schemes: a plurality of reactors connected in series (in Figure 1a using two reactors) and a staged loading method (in Figure 1b The two catalyst layers in are stacked sequentially).

[0118] Reference Figure 1a , the first reactor A and the second reactor B correspond to the selective hydrogenation reactor and the hydrogenation reactor, respectively. The aromatic hydrocarbon-containing fraction 101 as a raw material is combined with the hydrogen 102 supplied from an external source and introduced into the first reactor A as a stream 103, wherein at least a portion of the supplied hydrogen is dissolved in the raw material. As described above, in the first reactor A, a reaction of selectively hydrogenating unsaturated hydrocarbons (olefins, etc.) while maintaining the aromatic rings in the raw material is carried out, and the selective hydrogenation product discharged therefrom (i.e., the first aromatic hydrocarbon-containing product 104) is introduced into the second reactor B. In the second reactor B, unlike the first reactor A, the residual hydrogen in the product 104 is removed by hydrogenation using unsaturated hydrocarbons and / or bicyclic aromatic hydrocarbons, while the monocyclic aromatic hydrocarbons in the product 104 are maintained as much as possible. Therefore, the hydrogenation product discharged from the second reactor B (i.e., the second aromatic hydrocarbon-containing product 105) can be obtained as a purified aromatic fraction.

[0119] exist Figure 1b In the illustrated embodiment, the first catalyst layer A' and the second catalyst layer B' are stacked in the order described (ie, staged loading) based on the flow direction of the feedstock in a single reactor. Figure 1a , an aromatic-containing feedstock 201 is combined with hydrogen 202 to form a stream 203, and the stream contacts a plurality of catalyst layers stacked sequentially in the reactor. In this case, the stream contacts a first catalyst layer A' for selective hydrogenation, and then contacts a second catalyst layer B' for hydrogenation to produce a second aromatic hydrocarbon-containing product 205 that is substantially free of residual hydrogen.

[0120] Compared to Figure 1b The embodiment shown uses Figure 1a The advantage of the plurality of reactors connected in series as shown is that the loss of aromatics (specifically, single-ring aromatic hydrocarbons, such as C8 aromatic hydrocarbons) can be minimized by using different operating conditions for each reactor, but there may be a disadvantage of increasing facility investment costs.

[0121] According to an exemplary embodiment, the second aromatic hydrocarbon-containing product is applied to a downstream process, specifically to a xylene production process, especially to a paraxylene recovery process, and the purification method by secondary hydrogenation can be integrated with the xylene production process.

[0122] As an example, the second aromatic hydrocarbon-containing product can be transferred to a xylene column and separated into a C8 aromatic hydrocarbon stream as an upstream and a C9+ aromatic hydrocarbon stream as a downstream. Then, the separated C8 aromatic hydrocarbon fraction is transferred to a para-xylene separation / recovery unit, and then para-xylene is recovered therefrom. Representative examples of such para-xylene recovery technology include Parex of UOP, Eluxyl of IFP, Aromax of Toray, etc.

[0123] According to an exemplary embodiment, before separating the second aromatic hydrocarbon-containing product, a treatment using a solid acid (solid acid catalyst) may be performed as appropriate. The solid acid is generally clay (natural and / or synthetic clay) and / or zeolite. This subsequent treatment enables the alkyl groups of C9+ aromatic hydrocarbons to decompose to partially increase the content of C8-aromatic hydrocarbons. In this case, clay can be used for clay treatment of aromatic hydrocarbons known in the art, and may, for example, include at least one selected from bentonite, montmorillonite, kaolin, etc. At the same time, the zeolite may, for example, include at least one selected from zeolite Y, zeolite X, ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-385, ZSM-48, ZSM-50, ZSM-57, etc. In this case, the temperature for the solid acid treatment can be adjusted within the range of keeping the second aromatic hydrocarbon-containing product in the liquid phase, for example, within the range of about 120° C. to about 350° C. (specifically, about 160° C. to about 300° C.). In addition, the solid acid treatment pressure can be adjusted within the range of, for example, about 3 bar to 60 bar (specifically, about 5 bar to 30 bar). In addition, the space velocity can be, for example, about 0.2 hr -1 About 20 hours -1 (About 0.5hr -1 About 10 hours -1 However, the processing conditions can be understood as exemplary.

[0124] The C8 aromatic hydrocarbon fraction left after the separation of para-xylene from the xylene recovery unit may contain mainly o-xylene and / or m-xylene, and may be transferred to a xylene isomerization unit to form a xylene mixture with an increased para-xylene content. The reaction in the xylene isomerization unit may be carried out using known reaction conditions and catalysts, and therefore no further description is given. Therefore, the C8 isomerized product discharged via the xylene isomerization reaction is separated into a light fraction (e.g., a C7 hydrocarbon fraction (upstream)) and a C8 aromatic hydrocarbon fraction (downstream) in a separation tower. In this case, the C8 aromatic hydrocarbon fraction may be transferred to a xylene tower.

[0125] The present invention will be further clearly understood with reference to the following examples. However, the following examples are only provided to illustrate the present invention and therefore should not be construed as limiting the scope of the present invention. DETAILED DESCRIPTION

[0126] Example

[0127] The materials used in Examples and Comparative Examples are as follows.

[0128] ACS reagent-grade xylene, naphthalene and metal compounds were purchased from Sigma-Aldrich. Inorganic oxides are commercially available products from Sigma-Aldrich. In addition, aromatic hydrocarbon-containing fractions were obtained as raw materials obtained by commercial methods, and a C8+ aromatic fraction with a bromine index (BI) of 748 was used.

[0129] Evaluation and comparison of xylene hydrogenation activity of various catalysts

[0130] In Comparative Examples 1 to 11, catalysts were prepared to select a catalyst suitable for each of the selective hydrogenation and the subsequent hydrogenation (removal of residual hydrogen), and the hydrogenation activity thereof was evaluated.

[0131] Comparative Example 1

[0132] Xylene hydrogenation using Co reduced catalyst

[0133] Cobalt nitrate was dissolved in distilled water and loaded on an aluminum support by initial wetness impregnation. The impregnated support was then kept at room temperature for about 1 hour, dried at 150°C for 2 hours in an air atmosphere, and fired at 500°C for 2 hours to prepare a Co / O supported catalyst having a Co content of 7 wt%.

[0134] 40 cc of CoO / alumina catalyst (catalyst particle size distribution: 20 to 40 mesh) was loaded into a continuous fixed-bed reactor. Then, the atmosphere in the reactor was purged with nitrogen and the pressure was increased to 10 kgf / cm2. 2 ). Then, the nitrogen gas was replaced with hydrogen gas, and the reduction treatment was performed at a high temperature of 450° C. for 2 hours while feeding the hydrogen gas at a rate of 500 cubic centimeters per minute (cc / min).

[0135] Then, the temperature in the reactor was lowered to 100°C, and then the reactor was heated at a hydrogen / C8 aromatic molar ratio of 6.0 and a space velocity of 15 hr -1 The hydrocarbon fraction (xylene: dimethylcyclohexane = 1:7) was subjected to xylene hydrogenation under the conditions of . The results are shown in Table 1 below.

[0136] Comparative Example 2

[0137] Xylene Hydrogenation Using Molybdenum Sulfide Catalyst

[0138] Ammonium heptamolybdate was dissolved in distilled water and the resultant was supported on an aluminum support by initial wetness impregnation. The impregnated support was then kept at room temperature for about 1 hour, dried at 150° C. for 2 hours in an air atmosphere, and fired at 500° C. for 2 hours to prepare a Mo supported catalyst having a Mo content of 15 wt %.

[0139] 40 cubic centimeters of the prepared catalyst (catalyst particle size distribution: 20 to 40 meshes) were loaded into a continuous fixed bed reactor. Then, the atmosphere in the reactor was purged with nitrogen and the pressure was increased to 10 kgf / cm2. Then, hydrogen was used to replace nitrogen, and hydrogen was fed at a flow rate of 500 cubic centimeters / minute, while toluene mixed with 2% by weight DMDS was continuously fed at a speed of 0.7 cubic centimeters / minute for 5 hours, and sulfurized at a high temperature of 350°C for 6 hours. The reaction was carried out under the same conditions as in Comparative Example 1, and the results are shown in Table 1 below.

[0140] Comparative Example 3

[0141] Xylene Hydrogenation Using CoMo Sulfide Catalyst

[0142] Ammonium heptamolybdate was dissolved in distilled water, and the resultant was loaded on an aluminum support by initial wetness impregnation. The impregnated support was then kept at room temperature for about 1 hour, dried at 150°C for 2 hours in an air atmosphere, and fired at 500°C for 2 hours. Cobalt nitrate was then dissolved in distilled water, and nickel was further loaded on the aluminum support loaded with molybdenum by initial wetness impregnation, followed by drying and firing under the same conditions as above to prepare a supported catalyst having a Co content of 3.5 wt% and a Mo content of 12 wt%.

[0143] Then, a reaction was performed under the same conditions as in Comparative Example 2, and the results are shown in Table 1 below.

[0144] Comparative Example 4

[0145] Xylene Hydrogenation Using NiMo Sulfide Catalyst

[0146] Ammonium heptamolybdate was dissolved in distilled water, and the resultant was loaded on an aluminum support by initial wetness impregnation. The impregnated support was then kept at room temperature for about 1 hour, dried at 150° C. for 2 hours in an air atmosphere, and fired at 500° C. for 2 hours. Nickel nitrate was then dissolved in distilled water, and nickel was further loaded on the aluminum support loaded with molybdenum by initial wetness impregnation, followed by drying and firing under the same conditions as above to prepare a supported catalyst having a Ni content of 3.5 wt % and a Mo content of 12 wt %.

[0147] The reaction was carried out under the same conditions as in Comparative Example 2, and the results are shown in Table 1 below.

[0148] Comparative Example 5

[0149] Xylene hydrogenation using Mo reduced catalyst

[0150] Ammonium heptamolybdate was dissolved in distilled water and the resultant was supported on an aluminum support by initial wetness impregnation. The impregnated support was then kept at room temperature for about 1 hour, dried at 150° C. for 2 hours in an air atmosphere, and fired at 500° C. for 2 hours to prepare a Mo-supported catalyst having a Mo content of 15 wt %.

[0151] The reaction was carried out under the same conditions as in Comparative Example 1, and the results are shown in Table 1 below.

[0152] Comparative Example 6

[0153] Xylene hydrogenation using Ni reduced catalyst

[0154] Nickel nitrate was dissolved in distilled water and the resultant was loaded on an aluminum support by initial wetness impregnation. Then, the impregnated support was kept at room temperature for about 1 hour, dried at 150° C. for 2 hours in an air atmosphere, and fired at 500° C. for 2 hours to prepare a Ni-supported catalyst having a Ni content of 7% by weight. The reaction was carried out under the same conditions as in Comparative Example 1, and the results are shown in Table 1 below.

[0155] Comparative Example 7

[0156] Xylene hydrogenation using Pd reduced catalyst

[0157] Palladium chloride was dissolved in distilled water, and the resultant was supported on an aluminum support by initial wetness impregnation. Then, the impregnated support was kept at room temperature for about 1 hour, dried at 150° C. for 2 hours in an air atmosphere, and fired at 500° C. for 2 hours to prepare a Pd-supported catalyst having a Pd content of 7% by weight. The reaction was carried out under the same conditions as in Comparative Example 1, and the results are shown in Table 1 below.

[0158] Comparative Example 8

[0159] Xylene hydrogenation using Pt reduced catalyst

[0160] Chloroplatinic acid was dissolved in distilled water, and the resultant was supported on an aluminum support by initial wetness impregnation. Then, the impregnated support was kept at room temperature for about 1 hour, dried at 150° C. for 2 hours in an air atmosphere, and fired at 500° C. for 2 hours to prepare a Pt-supported catalyst having a Pt content of 7 wt %. The reaction was carried out under the same conditions as in Comparative Example 1, and the results are shown in Table 1 below.

[0161] Comparative Example 9

[0162] Xylene hydrogenation using Ru reduced catalyst

[0163] Ruthenium chloride was dissolved in distilled water, and the resultant was loaded on an aluminum support by initial wetness impregnation. Then, the impregnated support was kept at room temperature for about 1 hour, dried at 150° C. for 2 hours in an air atmosphere, and fired at 500° C. for 2 hours to prepare a Ru-supported catalyst having a Ru content of 7% by weight. The reaction was carried out under the same conditions as in Comparative Example 1, and the results are shown in Table 1 below.

[0164] Comparative Example 10

[0165] Xylene hydrogenation using Rh reduced catalyst

[0166] Rhodium chloride was dissolved in distilled water, and the resultant was loaded on an aluminum support by initial wetness impregnation. Then, the impregnated support was kept at room temperature for about 1 hour, dried at 150° C. for 2 hours in an air atmosphere, and fired at 500° C. for 2 hours to prepare a Rh-supported catalyst having a Rh content of 7% by weight. The reaction was carried out in the same manner as in Comparative Example 1, and the results are shown in Table 1 below.

[0167] Comparative Example 11

[0168] Xylene Hydrogenation Using NiMo Reduction Catalyst

[0169] The catalyst prepared in the same manner as in Comparative Example 4 was reduced and reacted in the same manner as in Comparative Example 1. The results are shown in Table 1 below.

[0170] [Table 1]

[0171]

[0172] As can be seen from the above table, nickel-based catalysts and platinum-based catalysts (excluding palladium) have high hydrogenation activity and therefore have high xylene hydrogenation conversion (loss), while Co reduction catalysts, Mo sulfide catalysts, CoMo sulfide catalysts, NiMo sulfide catalysts, Mo reduction catalysts, Pd reduction catalysts, and NiMo reduction catalysts have xylene hydrogenation conversions of 2.1% or less. Among them, a catalyst having a xylene hydrogenation conversion of 0.1% by weight or less than 0.1% by weight is used as the first catalyst for "selective hydrogenation". At the same time, the second catalyst used for "hydrogenation" in the downstream stage should completely remove a small amount of hydrogen, and therefore a catalyst with a high hydrogenation activity having a xylene hydrogenation conversion of 20% or more is selected and used.

[0173] Comparative Example 12

[0174] Selective hydrogenation using Ni-Mo sulfide catalysts

[0175] Ammonium heptamolybdate was dissolved in distilled water and loaded on an aluminum support by initial wetness impregnation. The impregnated support was then kept at room temperature for about 1 hour, dried at 150°C for 2 hours in an air atmosphere, and fired at 500°C for 2 hours. Nickel nitrate was then dissolved in distilled water and nickel was further loaded on the aluminum support loaded with molybdenum by initial wetness impregnation, followed by drying and firing under the same conditions as above to prepare a catalyst having a Ni content of 3.5 wt% and a Mo content of 12 wt%.

[0176] 40 cubic centimeters of the prepared catalyst (catalyst particle size distribution: 20 to 40 mesh) were loaded into a continuous fixed bed reactor. Then, the atmosphere in the reactor was purged with nitrogen and the pressure was increased to 10 kgf / cm2. Then, hydrogen was used to replace the nitrogen, and hydrogen was fed at a flow rate of 500 cubic centimeters / minute, while toluene mixed with 2 wt% DMDS was continuously fed at a rate of 0.7 cubic centimeters / minute for 5 hours, and sulfurization was performed at a high temperature of 350°C for 6 hours.

[0177] Then, the temperature in the reactor was lowered to 185° C., the flow rate of H 2 was adjusted to 3.5 cubic centimeters per minute, and a C8+ aromatic fraction (BI: 748) was fed at a rate of 1.3 cubic centimeters per minute for hydrogenation. The reaction was allowed to proceed for 2 days, and BI measurement and gas chromatography were performed on each of the obtained samples. At this time, the bromine index of the product was 96, and the aromatic loss was 0.03% by weight.

[0178] In order to determine whether there is residual hydrogen after the reaction, the residual hydrogen under normal temperature / pressure conditions is observed to be discharged together with the product fraction through the connected glass pipe, and the bubble volume and fraction increase collected within a predetermined time are measured. The result is that the residual hydrogen content is about 120wtppm.

[0179] Comparative Example 13

[0180] Selective hydrogenation using Ni-Mo sulfide catalysts

[0181] In order to suppress the presence of residual hydrogen in the selective hydrogenation product, the experiment was conducted while reducing the amount of the feed reactant to 1 / 2 compared to Comparative Example 12. Specifically, the selective hydrogenation was conducted under the same conditions as in Comparative Example 12, except that the flow rate of H2 was changed to 1.75 cubic centimeters per minute and the flow rate of the C8+ aromatic fraction (BI: 748) was changed to 0.65 cubic centimeters per minute. At this time, the bromine index (BI) of the product was 94, and the loss of aromatic hydrocarbons was 0.03% by weight. In addition, it was found that unreacted residual hydrogen was discharged together with the product fraction through the connected glass line.

[0182] Therefore, when a catalyst having a relatively weak hydrogenation function is used, the olefin content can be reduced while causing almost no loss of aromatic hydrocarbons due to hydrogenation, but there is a limitation in completely consuming the introduced hydrogen.

[0183] Comparative Example 14

[0184] Selective hydrogenation using Ni-reduced catalysts

[0185] Nickel nitrate was dissolved in distilled water and the resultant was loaded on an aluminum support by initial wetness impregnation. Then, the impregnated support was kept at room temperature for about 1 hour, dried at 150°C for 2 hours in an air atmosphere, and fired at 500°C for 2 hours. At this time, the heating rate was adjusted to 3°C / min. Thus, a NiO / alumina catalyst with a Ni content of 10 wt% was prepared.

[0186] 40 cm3 of the prepared NiO / alumina catalyst (catalyst particle size distribution: 20 to 40 mesh) was loaded into a continuous fixed bed reactor. Then, the atmosphere in the reactor was purged with nitrogen and the pressure was increased to 10 kgf / cm2. Then, the nitrogen was replaced with hydrogen and a reduction treatment was performed at a high temperature of 450°C for 2 hours while feeding hydrogen at a flow rate of 500 cm3 / min.

[0187] Then, the temperature in the reactor was lowered to 185°C, the flow rate of H2 was adjusted to 3.5 cubic centimeters per minute, and the C8+ aromatic fraction (BI: 748) was fed at a rate of 1.3 cubic centimeters per minute for hydrogenation. The reaction was allowed to proceed for 2 days, and BI measurement and gas chromatography were performed on each sample obtained. At this time, the olefin conversion was 80%, and the aromatic hydrocarbon loss was 0.3 wt% (H2 / olefin=2.7). In order to determine whether there was residual hydrogen after the reaction, the product fraction was discharged through the connected glass pipeline under normal temperature / pressure conditions. At this time, unreacted residual hydrogen was not discharged.

[0188] Example 1

[0189] Selective hydrogenation (Ni-Mo sulfide catalyst)-hydrogenation (Ni reduction catalyst) two-step process

[0190] First, the selective hydrogenation product prepared according to Comparative Example 12 was used as a reactant (bicyclic aromatic hydrocarbon content: 1.1% by weight), and then hydrogenation was performed. The catalyst used for hydrogenation was the nickel (reduction) catalyst used in Comparative Example 6 (40 cm3, catalyst particle size distribution: 20 to 40 mesh), the reaction pressure was 10 kgf / cm2 (about 9.8 bar), and the C8+ aromatic fraction (BI: 96) was flowed at a rate of 1.3 cm3 / min for hydrogenation. At this time, in order to simulate the incorporation of residual hydrogen into the selective hydrogenation product (product of Comparative Example 12) and to conduct the experiment under the condition of a predetermined amount of residual hydrogen, hydrogen was injected to adjust the amount of residual hydrogen to 120 wtppm.

[0191] The hydrogenation was carried out for 2 days, and then sampling, bromine index (BI) measurement and gas chromatography were performed. In addition, it was determined whether there was residual hydrogen, and the results are shown in Table 2 below.

[0192] Examples 2 to 4 and Comparative Examples 15 to 17

[0193] In order to determine the hydrogenation activity of each hydrocarbon structure according to the reaction temperature, an experiment was conducted in the same manner as in Example 1, and the results are shown in Table 2 below.

[0194] [Table 2]

[0195]

[0196] As can be seen from the above table, when the reaction temperature is 55°C or less (Comparative Examples 15 and 16), residual hydrogen is still detected even after 120 wtppm of residual hydrogen is hydrogenated using a Ni catalyst. On the other hand, when the reaction temperature is 255°C, the loss of aromatic hydrocarbons is greatly increased, and the bromine index (BI) in the hydrogenated product is also increased. In particular, at a reaction temperature of 255°C (Comparative Example 17), the conversion rate of bicyclic aromatics is not increased, but the loss of C8 aromatics is greatly increased.

[0197] This result is considered to be due to the fact that the difference in hydrogenation activity depending on the hydrocarbon structure decreases as the reaction temperature increases.

[0198] Comparative Example 18

[0199] Selective hydrogenation (Ni-Mo sulfide catalyst)-hydrogenation (Pd reduction catalyst) two-step process

[0200] Using the Pd reduction catalyst prepared in Comparative Example 7, an experiment was conducted in the same manner as in Example 1, and the results are shown in Table 3 below.

[0201] Example 5

[0202] Selective hydrogenation (Ni-Mo sulfide catalyst)-hydrogenation (Rh reduction catalyst) two-step process

[0203] Using the Rh reduction catalyst prepared in Comparative Example 10, an experiment was conducted in the same manner as in Example 1, and the results are shown in Table 3 below.

[0204] Example 6

[0205] Selective hydrogenation (Ni-Mo sulfide catalyst)-hydrogenation (Ru reduction catalyst) two-step process

[0206] Using the Ru reduction catalyst prepared in Comparative Example 9, an experiment was conducted in the same manner as in Example 1, and the results are shown in Table 3 below.

[0207] Example 7

[0208] Selective hydrogenation (Ni-Mo sulfide catalyst)-hydrogenation (Pt reduction catalyst) two-step process

[0209] Using the Pt reduction catalyst prepared in Comparative Example 8, an experiment was performed in the same manner as in Example 1, and the results are shown in Table 3 below.

[0210] [Table 3]

[0211]

[0212] As can be seen from the above table, the catalysts with high hydrogenation activity (Ni, Rh, Ru and Pt reduction catalysts) have no residual hydrogen at a reaction temperature of 105° C., but the Pd reduction catalyst with relatively low hydrogenation activity cannot sufficiently remove the residual hydrogen.

[0213] Long-term durability comparison

[0214] Comparative Example 19

[0215] Selective hydrogenation (Ni-Mo sulfide catalyst)-hydrogenation (Ni-Mo reduction catalyst) two-step process

[0216] The Ni-Mo oxide catalyst synthesized in the practice of Comparative Example 4 was subjected to reduction pretreatment to give a Ni-Mo reduced catalyst in the same manner as in Comparative Example 1. The obtained Ni-Mo reduced catalyst was used as a hydrogenation catalyst in a selective hydrogenation-hydrogenation two-step process, and the presence or absence of residual hydrogen was compared during the reaction time.

[0217] In order to compare the durability of the hydrogenation catalyst in the two-step process, the reactants were used in twice the amount compared to Example 2. Specifically, the temperature in the reactor was adjusted to 155° C., the flow rate of H2 was adjusted to 7.0 cubic centimeters per minute, and the C8+ aromatic fraction (BI: 748) was flowed at a rate of 2.6 cubic centimeters per minute for hydrogenation. The presence or absence of residual hydrogen and the C8 aromatic loss (weight %) during the reaction time are shown in Table 4 below.

[0218] Example 8

[0219] Selective hydrogenation (Ni-Mo sulfide catalyst)-hydrogenation (Ni reduction catalyst) two-step process

[0220] The Ni reduction catalyst prepared in Comparative Example 6 was used as a hydrogenation catalyst in the selective hydrogenation-hydrogenation two-step method. The results are shown in Table 4 below.

[0221] [Table 4]

[0222]

[0223] As can be seen from the above table, in Example 8 where the Ni-reduced catalyst was used as the hydrogenation catalyst in the two-step hydrogenation, residual hydrogen was not observed even after 60 days, but in Comparative Example 19 where the Ni-Mo-reduced catalyst was used as the hydrogenation catalyst, residual hydrogen was observed after 17 days. In this case, the catalyst needs to be frequently replaced.

[0224] Analysis of the effect of bicyclic aromatic hydrocarbons in the selective hydrogenation product on the removal of residual hydrogen during hydrogenation

[0225] Comparative Example 20

[0226] A hydrogenation experiment was conducted under the same conditions as in Example 2 except that a C8 aromatic hydrocarbon fraction having a bromine index (BI) of 65 and containing no double-ring aromatic hydrocarbons was used to remove residual hydrogen, and the results are shown in Table 5 below.

[0227] [Table 5]

[0228]

[0229] As can be seen from the above table, in Example 2, the reactants contained bicyclic aromatic hydrocarbons having higher hydrogenation activity than monocyclic aromatic hydrocarbons, and thus the bicyclic aromatic hydrocarbons were preferentially hydrogenated (0.33 wt % corresponding to about 30 wt % of the bicyclic aromatic hydrocarbons in the reactants were consumed).

[0230] Therefore, compared with Comparative Example 20, the loss of C8 aromatic hydrocarbons, which are single-ring aromatic hydrocarbons, is much lower.

[0231] Analysis of the effect of residual hydrogen in the selective hydrogenation product on hydrogenation

[0232] Comparative Example 21

[0233] The experiment was conducted under the same conditions as in Example 3, except that hydrogen gas was injected so that the amount of residual hydrogen in the reactant (product of Comparative Example 1) was 210 wtppm. The results are shown in Table 6 below.

[0234] [Table 6]

[0235]

[0236] It can be seen from the above table that when the amount of residual hydrogen increases to 210 wtppm, the partial pressure of hydrogen in the reactant (ie, the product of Comparative Example 1) increases, resulting in an increase in aromatic loss to 0.151 wt%.

[0237] This result is considered to be due to the fact that when the amount of residual hydrogen in the selective hydrogenation product is higher than a predetermined level, the difference in hydrogenation activity depending on the structure of the hydrocarbon is also reduced due to the increase in the hydrogen partial pressure in the fraction. In particular, it should be noted that, compared with Example 3 (the amount of residual hydrogen: 120 wtppm), Comparative Example 21 (the amount of residual hydrogen: 210 wtppm) showed a greater increase in C8 aromatic loss than an increase in two-ring aromatic conversion.

[0238] Analysis of the influence of reaction pressure on hydrogenation

[0239] Embodiment 9 and Embodiment 10

[0240] Hydrogenation was performed in the same manner as in Example 2, except that the reaction pressure was changed to 5 kgf / cm2 (about 4.9 bar) and 30 kgf / cm2 (about 29.4 bar). The results are shown in Table 7 below.

[0241] [Table 7]

[0242]

[0243] As can be seen from the above table, as the reaction pressure increases, the loss of C8 aromatics (single-ring aromatics) increases. However, although the reaction pressure is greatly increased to 30 kgf / cm2, the loss of C8 aromatics is relatively low.

[0244] Embodiment 11

[0245] Selective hydrogenation using two reactors connected in series - hydrogenation

[0246] Considering the experimental results according to Examples 1 to 10 and Comparative Examples 12 to 19, a catalyst was filled in each of two reactors connected in series (first reactor: selective hydrogenation; second reactor: hydrogenation), and the C8+ aromatic fraction (BI: 748) was purified.

[0247] As in Comparative Example 12, 40 cubic centimeters of catalyst were filled in the first reactor and then sulfided, and as in Comparative Example 14, 40 cubic centimeters of catalyst were filled in the second reactor and then reduced. The two reactors filled with the catalysts that were respectively pretreated were connected in series to perform selective hydrogenation and hydrogenation under the same conditions as in Comparative Example 12. The product discharged from the second reactor was analyzed, and the results are shown in Table 8 below.

[0248] At this time, in order to determine whether the second reactor connected in series removes excess (residual) hydrogen present in the fraction discharged from the first reactor, only hydrogen and the aromatic fraction were injected into the first reactor and the experiment was conducted. The results are shown in Table 8 below.

[0249] Example 12

[0250] Selective hydrogenation using a reactor filled with two catalyst layers in a staged loading mode - hydrogenation

[0251] The catalyst used in Comparative Example 12 and Comparative Example 14 was filled in the same reactor. At this time, the catalyst used in Comparative Example 12 (40 cubic centimeters; selective hydrogenation catalyst) was placed at the top of the reactor, and the catalyst used in Comparative Example 14 (40 cubic centimeters; hydrogenation catalyst) was placed at the bottom of the reactor. Selective hydrogenation and hydrogenation were performed under the same conditions as in Comparative Example 12. The results are shown in Table 8 below.

[0252] [Table 8]

[0253]

[0254] As can be seen from the above table, no differences were observed in bromine index reduction, residual hydrogen removal, C8 aromatic loss, etc. according to the type of reactor.

[0255] As described above, when selective hydrogenation is performed to remove unsaturated hydrocarbons contained in an aromatic hydrocarbon-containing fraction (particularly a C8+ aromatic hydrocarbon fraction), by controlling the reaction conditions (e.g., temperature and pressure) and additionally controlling the content of double-ring aromatic hydrocarbons, residual hydrogen in the product can be effectively removed while minimizing the loss of single-ring aromatic hydrocarbons (particularly C8 aromatics) in the selective hydrogenation product.

[0256] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A method for purifying aromatic hydrocarbons, comprising: (a) selectively hydrogenating an aromatic hydrocarbon-containing feedstock having a bromine index of at least 30 in the presence of a selective hydrogenation catalyst and while supplying hydrogen to form a first aromatic hydrocarbon-containing product having a reduced bromine index and unsaturated hydrocarbon content and containing at most 200 wtppm of residual hydrogen, and (b) hydrogenating the first aromatic-containing product using the residual hydrogen in the presence of a hydrogenation catalyst to form a second aromatic-containing product, the second aromatic-containing product containing a reduced amount of residual hydrogen compared to the first aromatic-containing product, The first aromatic hydrocarbon-containing product has a bromine index reduced by at least 20% compared to the aromatic hydrocarbon-containing feedstock, and the first aromatic hydrocarbon-containing product contains (i) unsaturated hydrocarbons and (ii) bicyclic aromatic hydrocarbons.

2. The method according to claim 1, characterized in that The bicyclic aromatic hydrocarbon is present in the first aromatic hydrocarbon-containing product in an amount of at least 0.3 wt%.

3. The method according to claim 2, characterized in that When the amount of the bicyclic aromatic hydrocarbons in the first aromatic hydrocarbon-containing product is less than 0.3 wt %, the hydrogenation of step (b) is performed by adding the bicyclic aromatic hydrocarbons to the first aromatic hydrocarbon-containing product.

4. The method according to claim 1, characterized in that The bicyclic aromatic hydrocarbon includes at least one selected from the following group: naphthalene, indene, and derivatives thereof.

5. The method according to claim 1, characterized in that The total aromatic loss in the first aromatic-containing product is less than 0.45 wt% based on the weight of the aromatic-containing feedstock, and the single-ring aromatic loss in the second aromatic-containing product is less than 0.15 wt% based on the weight of the first aromatic-containing product.

6. The method according to claim 1, characterized in that Step (a) and step (b) are carried out in a first reactor and a second reactor respectively, The first reactor and the second reactor are connected in series.

7. The method according to claim 1, characterized in that Step (a) and step (b) are each performed in the presence of a first catalyst layer and a second catalyst layer, wherein the first catalyst layer and the second catalyst layer are filled in a single reactor in a staged loading mode, The first catalyst layer and the second catalyst layer are arranged in sequence based on the flow direction of the aromatic hydrocarbon-containing feedstock.

8. The method according to claim 1, characterized in that The hydrogenation of step (b) is carried out under reaction conditions controlled at a temperature above 55° C. and below about 255° C. and a pressure of 3 bar to 60 bar.

9. The method according to claim 8, characterized in that The selective hydrogenation of step (a) is carried out at a temperature controlled within a range of 130°C to 210°C, and The hydrogenation of step (b) is carried out at a temperature controlled within a range of 80°C to 130°C.

10. The method according to claim 1, characterized in that The hydrogenation catalyst in step (b) comprises an active metal and an inorganic oxide support, wherein the active metal is selected from at least one of nickel and platinum group metals.

11. The method according to claim 10, characterized in that The active metal in the hydrogenation catalyst of step (b) comprises at least one selected from the group consisting of nickel, platinum, rhodium and ruthenium.

12. The method according to claim 10, characterized in that The hydrogenation catalyst is in reduced form.

13. The method according to claim 10, characterized in that The amount of active metal in the hydrogenation catalyst of step (b) is determined to be in the range of 0.1 wt% to 40 wt% on an elemental basis.

14. The method according to claim 1, characterized in that The aromatic hydrocarbon-containing feedstock comprises C8+ aromatic hydrocarbons.

15. The method according to claim 1, characterized in that Also includes: (c) separating the second aromatic hydrocarbon-containing product into a C9+ aromatic hydrocarbon fraction and a C8 aromatic hydrocarbon fraction; and (d) separating and recovering p-xylene from the separated C8 aromatic hydrocarbon fraction.

16. The method according to claim 15, characterized in that The method further comprises treating the second aromatic hydrocarbon-containing product with a solid acid before step (c).

17. The method according to claim 15, characterized in that Also includes: (e) isomerizing the residual C8 aromatic hydrocarbon fraction not recovered as paraxylene to form a C8 aromatic hydrocarbon fraction containing an increased paraxylene content, which is then reinjected into step (c).

18. The method according to claim 1, characterized in that The unsaturated hydrocarbons in the first aromatic hydrocarbon-containing product are present in an amount of 2 wt% or less.

19. The method according to claim 1, characterized in that Hydrogen is present in the second aromatic-containing product in an amount less than 6 wtppm.

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