Removal of residual hydrogen from aromatic fraction

Abstract

This disclosure describes a process for removing residual hydrogen present in an aromatic fraction that has had its Bromine Index reduced through a selective hydrogenation reaction by reacting it with the olefins and / or 2-ring aromatic components contained therein.

Description

[Technical Field]

[0001] The present disclosure relates to a process for removing residual hydrogen from an aromatic fraction. More specifically, the present disclosure relates to a process for removing residual hydrogen present in an aromatic fraction that has had its bromine index reduced through a selective hydrogenation reaction by reacting the residual hydrogen with the olefins and / or two-ring aromatic components contained therein. [Background technology]

[0002] C6+ aromatic hydrocarbons, specifically benzene, toluene, and mixed xylenes (or xylene isomers), are important sources of base fractions for the petrochemical industry. Among these, mixed xylenes, including meta-xylene (m-xylene), para-xylene (p-xylene), and ortho-xylene (o-xylene), with para-xylene being particularly important.

[0003] Known commercial methods for producing benzene, toluene, or mixed xylenes include a method for separating and recovering them from an aromatic hydrocarbon-rich fraction, and a method for synthesizing them through a reaction. Among the above-mentioned separation and recovery methods, representative examples include a method for separating them by distilling reformate produced by a catalytic reforming reaction of naphtha, and a method for separating them from thermal cracking oil obtained as a by-product during naphtha thermal cracking.

[0004] However, aromatic hydrocarbon fractions, including catalytic reformate and thermal cracking oil, contain unsaturated hydrocarbons (e.g., olefins, acetylene, and / or styrene or their derivatives), which can adversely affect the operation of downstream processes. Therefore, techniques for reducing the olefin content in the feedstock for downstream processes, such as clay pretreatment or hydrogenation, are known. Among these, hydrogenation methods use hydrogen in the presence of a catalyst to convert unsaturated hydrocarbons (i.e., olefins, acetylene, and / or styrene (including their derivatives), but excluding aromatic (benzene) rings) in the aromatic fraction into saturated hydrocarbons (i.e., paraffins), while minimizing aromatic loss. This alleviates issues associated with clay treatment methods, such as frequent replacement cycles, increased clay costs, and waste generation. In this case, well-known catalysts, such as nickel-based catalysts, precious metal catalysts (e.g., Pt, Pd), cobalt-molybdenum (Co-Mo), and nickel-molybdenum (Ni-Mo), are used as hydrogenation catalysts.

[0005] However, during the hydrogenation reaction, due to reaction characteristics, loss of aromatic fraction occurs due to excessive hydrogenation, or the input hydrogen is not fully consumed, resulting in a small amount remaining in the hydrogenated aromatic fraction. In particular, the remaining hydrogen can adversely affect the distillation performance in the downstream xylene process, cause cavitation due to bubbles in the pump, which can damage the pump, or reduce the separation performance in the para-xylene purification process.

[0006] When a catalyst with controlled hydrogenation activity, such as a NiMo sulfide catalyst, is used to selectively hydrogenate and remove unsaturated hydrocarbons such as olefins while suppressing loss of aromatic fractions, residual gases are initially contained in the hydrogenated product and then discharged. On the other hand, when a catalyst with relatively high hydrogenation activity, such as a Ni or NiMo reduced catalyst, is used, there is almost no residual hydrogen, but loss of aromatic fractions is high.

[0007] In this regard, in order to minimize the loss of aromatics, a method of combining a NiMo sulfide catalyst with a NiMo reduced catalyst can be considered. However, although there is little residual hydrogen contained initially, as the reaction proceeds for a certain period of time, the hydrogenation activity decreases and the residual hydrogen is discharged in the form of a product.

[0008] In response to this, methods have been known in which the residual hydrogen in the selective hydrogenation product is removed using physical methods such as gas-liquid separation (e.g., a flash column, a deheptanizer, a fractionator, etc.) (Korean Patent Application Publication No. 1109814, Korean Patent Application Publication No. 2005-0089010, U.S. Patent No. 6977317). However, when separate separation and recovery equipment is introduced into the process, an increase in capital investment costs is unavoidable.

[0009] Meanwhile, the present applicant has previously developed a process for performing a two-stage selective hydrogenation reaction based on a catalyst system in which two catalysts (first and second hydrogenation catalysts) with different hydrogenation activities are loaded in a stepwise loading manner or in two reactors connected in series (U.S. Patent Publication No. 2022-0073440). When operating the above process, it is possible to consider adjusting the second hydrogenation reaction conditions to remove residual hydrogen from the final hydrogenated aromatics fraction. However, even when the second hydrogenation reaction is precisely controlled, the residual hydrogen content in the final hydrogenated aromatics fraction is approximately 84 wtppm (residual hydrogen concentration in the final product after 17 days of operation) and tends to gradually increase thereafter. Furthermore, when the second hydrogenation reaction conditions are adjusted to a level that minimizes the amount of residual hydrogen in the final aromatics fraction, the loss of increased 1-ring aromatics due to excessive hydrogenation remains a problem.

[0010] As described above, even when aromatic fractions having reduced bromine index-increasing components such as olefins are produced while minimizing aromatic loss through a selective hydrogenation reaction, the remaining unreacted excess hydrogen remains a technical problem to be solved.

[0011] Therefore, there is a need for a method for effectively removing residual hydrogen present in the aromatic fraction, especially the C8+ aromatic fraction, after the selective hydrogenation reaction without losing one-ring aromatics. Summary of the Invention [Problem to be solved by the invention]

[0012] In an embodiment of the present disclosure, a method is provided that can effectively remove residual hydrogen in an aromatic fraction having a reduced bromine index through a selective hydrogenation reaction while suppressing the loss of one-ring aromatics. [Means for solving the problem]

[0013] According to one embodiment of the present disclosure,

[0014] a) conducting a selective hydrogenation reaction on an aromatic hydrocarbon-containing feedstock having a bromine index of at least 30 in the presence of a selective hydrogenation catalyst and in the presence of hydrogen to form a first aromatic hydrocarbon-containing product having a reduced bromine index and a content of unsaturated hydrocarbons, and containing up to 200 wtppm of residual hydrogen; and b) performing a hydrogenation reaction on the first aromatic hydrocarbon-containing product with the residual hydrogen in the presence of a hydrogenation catalyst to form a second aromatic hydrocarbon-containing product having reduced residual hydrogen relative to the first aromatic hydrocarbon-containing product; Including, wherein the first aromatic hydrocarbon-containing product exhibits a Bromine Index reduced by at least 20% compared to the aromatic hydrocarbon-containing feedstock; and a process for purifying aromatic hydrocarbons containing (i) unsaturated hydrocarbons, and (ii) two-ring aromatic hydrocarbons is provided.

[0015] According to an illustrative embodiment, based on the aromatic hydrocarbon-containing feedstock, the loss of total aromatics in the first aromatic hydrocarbon-containing product may be less than 0.45 wt. %, and based on the first aromatic hydrocarbon-containing product, the loss of one-ring aromatics in the second aromatic hydrocarbon-containing product may be less than 0.15 wt. %.

[0016] According to an exemplary embodiment, said step b) hydrogenation step may be carried out under reaction conditions controlled in the temperature range above 55° C. and below about 255° C., and in the pressure range from 3 bar to 60 bar.

[0017] According to an exemplary embodiment, the hydrogenation catalyst in step b) may comprise an active metal selected from at least one of nickel and platinum group metals and an inorganic oxide support.

[0018] According to an exemplary embodiment, the platinum group metal may be at least one selected from the group consisting of platinum, rhodium, and ruthenium.

[0019] According to an exemplary embodiment, the content of the active metal in the hydrogenation catalyst in step b) may be adjusted in the range of 0.1 wt % to 40 wt % on an elemental basis.

[0020] According to an exemplary embodiment, the aromatic hydrocarbon-containing feedstock can include C8+ aromatic hydrocarbons.

[0021] According to an exemplary embodiment, 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 para-xylene from the separated C8 aromatic hydrocarbon fraction; It may further include:

[0022] According to an exemplary embodiment, the method may further comprise, prior to step c), treating the second aromatic hydrocarbon-containing product with a solid acid.

[0023] According to an exemplary embodiment, the method may further include a step of e) isomerizing the remaining C aromatic hydrocarbon fraction that has not been recovered as para-xylene to form a C aromatic hydrocarbon fraction containing an increased content of para-xylene, and then recycling the resulting fraction to step c). [Effects of the Invention]

[0024] According to an embodiment of the present disclosure, a selective hydrogenation product having a reduced bromine index (BI) obtained through the selective hydrogenation of an aromatic hydrocarbon fraction is subjected to an additional hydrogenation reaction, and residual hydrogen in the selective hydrogenation product can be effectively removed by controlling the reaction conditions, selecting a catalyst, and adjusting the content of two-ring aromatic components, while minimizing the loss of aromatics, particularly one-ring aromatic hydrocarbons such as C8. By removing residual hydrogen in the aromatic hydrocarbon fraction after selective hydrotreatment in this manner, various problems that may occur in downstream processes such as pumping, xylene separation, and para-xylene purification can be prevented. [Brief explanation of the drawings]

[0025] [Figure 1a] FIG. 1 is a schematic diagram illustrating an exemplary process for treating an aromatic hydrocarbon-containing feedstock with a selective hydrogenation reaction-hydrogenation reaction sequence, and removing residual hydrogen in the selectively hydrotreated aromatic hydrocarbon-containing product through a hydrogenation reaction. [Figure 1b] FIG. 1 is a schematic diagram illustrating an exemplary process for treating an aromatic hydrocarbon-containing feedstock with a selective hydrogenation reaction-hydrogenation reaction sequence, and removing residual hydrogen in the selectively hydrotreated aromatic hydrocarbon-containing product through a hydrogenation reaction. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention can be achieved by the following description. It should be understood that the following description describes a preferred embodiment of the present invention, and the present invention is not necessarily limited thereto. It should also be understood that the attached drawings are for facilitating understanding, and the present invention is not limited thereto.

[0027] Terms used herein may be defined as follows:

[0028] A "heterogeneous catalyst" can refer to a catalyst that exists in a different phase from the reactants during a catalytic reaction, for example, a catalyst that is not dissolved in the reaction medium. In the case of a heterogeneous catalyst, for a reaction to occur, at least one reactant must diffuse and adsorb onto the surface of the heterogeneous catalyst, and after the reaction, the product must desorb from the surface of the heterogeneous catalyst.

[0029] "Support" can mean a material (typically a solid phase material) with a high specific surface area to which catalytically active components are attached, which may or may not participate in the catalytic reaction.

[0030] "Unsaturated hydrocarbons" can refer to hydrocarbons containing double or triple bonds, and can typically be understood to include olefins and alkynes, more specifically olefins. However, unless otherwise specified herein, aromatic rings themselves, despite containing double bonds therein, can be understood to be excluded from the scope of unsaturated hydrocarbons removed by "selective hydrogenation." However, in the case of "hydrogenation," two-ring aromatic rings can be understood to be included in the scope of compounds removed like unsaturated hydrocarbons.

[0031] "Olefin" may be understood to include alkenes, cycloalkenes, alkenylbenzenes, and the like.

[0032] "Cn+ aromatics" can refer to aromatic hydrocarbons having a carbon number equal to or greater than Cn, and similarly, "Cn- aromatics" can refer to aromatic hydrocarbons having a carbon number equal to or less than Cn.

[0033] "Cn+ hydrocarbons" can refer to hydrocarbons having a carbon number of Cn or greater, and similarly, "Cn- hydrocarbons" can refer to hydrocarbons having a carbon number of Cn or less.

[0034] "C8 aromatics" can mean aromatic hydrocarbons including mixed xylenes (ortho-xylene, meta-xylene, and para-xylene) and / or ethylbenzene and / or styrene.

[0035] "Hydrogenation" generally refers to the reaction of an organic compound with hydrogen, typically in the presence of a catalyst. Meanwhile, "selective hydrogenation" in a narrower sense refers to the conversion of unsaturated hydrocarbons, rather than aromatic compounds, in a hydrogenation feedstock through a hydrogenation reaction. In this specification, "hydrogenation" and "selective hydrogenation" are described separately, and it can be understood that in the case of a hydrogenation reaction, saturation of one-ring aromatic rings is minimized, but saturation of aromatic rings in two-ring aromatics, which have higher hydrogenation reactivity than one-ring aromatics, is permitted, while in the case of a selective hydrogenation reaction, saturation of the aromatic ring itself is minimized.

[0036] "Bromine index (BI)" can refer to the measurement (mg) of bromine consumed by 100 g of a hydrocarbon or hydrocarbon mixture and can be used to indicate the content of unsaturated bonds present in a hydrocarbon. Bromine index can be measured, for example, by ASTM D 2710-92.

[0037] "Rich" can mean that a particular compound in a fraction or stream is contained in an amount, for example, at least about 50%, specifically at least 70%, more specifically at least about 80%, and particularly specifically at least about 90%, on a given basis (e.g., weight, volume, or molar basis).

[0038] In this specification, when a numerical range is specified by a lower limit and / or an upper limit, it can be understood that any subcombination within that numerical range is also disclosed. For example, when a numerical range is stated as "1 to 5," it can include 1, 2, 3, 4, and 5, as well as any subcombination therebetween.

[0039] In this specification, when any component or member is described as being "connected" to another component or member, unless otherwise specified, this can be understood to include not only when it is directly connected to the other component or member, but also when it is connected via another component or member.

[0040] Similarly, the term "contact" can be understood to include not only direct contact but also contact with another component or member interposed therebetween.

[0041] The expression "above" can be understood as being used to refer to a relative positional concept. Thus, not only can other components or layers be directly present on the referenced layer, but other layers (intermediate layers) or components can be interposed or present between them. Similarly, the expressions "below," "below," and "beneath," as well as the expression "between" can also be understood as a relative positional concept. Furthermore, the expression "sequentially" can also be understood as a relative positional concept.

[0042] In this specification, when an element is referred to as "comprising," this means that other elements and / or steps may also be included, unless otherwise specified.

[0043] According to one embodiment of the present disclosure, an aromatic fraction as a feedstock is treated in a multi-stage process including a selective hydrogenation stage and a hydrogenation stage, each of which is carried out in the presence of a heterogeneous catalyst (specifically, a supported catalyst in which a metal having hydrogenation activity is introduced into a support), thereby providing an aromatic hydrocarbon (specifically, a C aromatic hydrocarbon) fraction from which residual hydrogen that acts as an obstacle to the operation of subsequent processes (e.g., pumping, xylene separation, para-xylene recovery, etc.) has been removed while reducing the bromine index of the aromatic hydrocarbon fraction.

[0044] Selective Hydrogenation Step According to one embodiment of the present disclosure, an aromatic (e.g., alkylaromatic) hydrocarbon-containing fraction is first provided as a feedstock, which may typically be a C8+ aromatic hydrocarbon-containing fraction, but which also contains unsaturated hydrocarbons (e.g., olefins, diolefins, acetylene, and / or styrene (or derivatives thereof)) and exhibits a relatively high Bromine Index (BI).

[0045] In this regard, the alkylaromatic hydrocarbons in the aromatic-containing hydrocarbon fraction may be, for example, alkylaromatic hydrocarbons having about 8 to 20 carbon atoms, specifically about 8 to 18 carbon atoms, and more specifically about 8 to 16 carbon atoms. Alkylaromatics are compounds having at least one alkyl group attached to an aromatic ring, and examples of such alkyl groups include methyl, ethyl, propyl, and butyl groups. C8+ alkylaromatic hydrocarbons include not only xylene, but also, for example, ethyltoluene, propylbenzene, tetramethylbenzene, ethyldimethylbenzene, diethylbenzene, methylpropylbenzene, ethylpropylbenzene, triethylbenzene, diisopropylbenzene, and mixtures thereof.

[0046] In an exemplary embodiment, the feedstock may be a C aromatic hydrocarbon fraction from which a C hydrocarbon fraction has been previously separated. The reason for using a C aromatic hydrocarbon-containing fraction is that in commercial processes, the C aromatic hydrocarbon fraction discharged to the top of a separator (e.g., a still) that separates the aromatic fraction into a C aromatic hydrocarbon fraction and a C aromatic hydrocarbon fraction contains almost no two-ring aromatic hydrocarbon components.

[0047] The aromatic hydrocarbon-containing fraction may also contain unsaturated hydrocarbons with an increased bromine index (BI), such as monoolefins, diolefins, acetylene, and styrene (or its derivatives), which have at least one double and / or triple bond. These unsaturated hydrocarbons are the target of the selective hydrogenation reaction. The content of unsaturated hydrocarbons in the aromatic hydrocarbon-containing feedstock can also be quantified by the bromine index. In this embodiment, the bromine index of the feedstock may be, for example, at least about 30, specifically about 50 to 30,000, more specifically about 100 to 20,000, and particularly about 150 to 10,000. In certain embodiments, the bromine index may be, for example, about 300 to 3,000, specifically about 400 to 2,000, and more specifically about 500 to 1,500.

[0048] According to an exemplary embodiment, the feedstock is an aromatic hydrocarbon-rich fraction, particularly a C aromatic hydrocarbon-rich fraction, wherein the aromatic content may be, for example, at least about 50 wt%, specifically at least about 70 wt%, more specifically about 80 wt% or more, and particularly about 90 wt% or more. The aromatic hydrocarbon-containing feedstock may also contain saturated hydrocarbons, wherein the saturated hydrocarbon content may be, for example, about 50 wt% or less, specifically about 30 wt% or less, more specifically about 20 wt% or less, and particularly about 10 wt% or less.

[0049] According to an exemplary embodiment, the aromatic hydrocarbon-containing feedstock may contain, in addition to the monocyclic aromatic hydrocarbons, a dicyclic aromatic hydrocarbon (e.g., at least one selected from naphthalene, indene, and derivatives thereof). The content of such dicyclic aromatic hydrocarbons may be, for example, at least about 0.3 wt%, specifically about 0.4 wt% to 20 wt%, more specifically about 0.5 wt% to 15 wt%, and particularly specifically about 1 wt% to 10 wt%. However, the content of dicyclic aromatic hydrocarbons may vary depending on the source of the feedstock, and therefore is not limited to the above range, and lower amounts of dicyclic aromatic hydrocarbons may be present depending on the source.

[0050] According to exemplary embodiments, aromatic hydrocarbon-containing feedstocks can be derived from, for example, catalytic reforming reactions of naphtha; thermal cracking reactions of naphtha, distillates, or other hydrocarbons to produce light olefins and aromatic-rich fractions; catalytic or thermal cracking reactions of heavy fractions to produce hydrocarbons in the gasoline boiling range, and the like, and such sources can be used as feedstocks, either alone or in combination. In certain embodiments, the feedstock can be derived from catalytic reformate of naphtha.

[0051] According to an exemplary embodiment, the selective hydrogenation reaction for removing unsaturated hydrocarbons from the aromatics-containing fraction may be carried out at a temperature selected from the range of, for example, room temperature to 300°C, specifically about 40°C to 250°C, and more specifically about 50°C to 230°C. According to a specific embodiment, the selective hydrogenation reaction may be carried out at a temperature selected from, for example, about 100°C to 220°C, specifically about 120°C to 215°C, more specifically about 130°C to 210°C, and particularly specifically about 155°C to 205°C. In this case, the selective hydrogenation reaction may be carried out as a liquid-phase reaction or a three-phase reaction (trickle bed) using an excess amount of hydrogen. However, a liquid-phase reaction may be more advantageous because it reduces investment costs and can maintain the amount of residual hydrogen as low as possible after the reaction.

[0052] According to an exemplary embodiment, the amount of hydrogen supplied during the selective hydrogenation reaction may be, for example, at least about 0.5 moles, specifically about 0.7 to 20 moles, and more specifically about 1 to 10 moles per mole of unsaturated hydrocarbons contained in the feedstock. If the amount of hydrogen supplied is too small or too large, problems may occur, such as a low removal rate of unsaturated hydrocarbons or hydrogenation of aromatic rings, resulting in increased loss of aromatic hydrocarbons. However, the amount of hydrogen supplied may vary depending on the properties of the feedstock, and is not limited to the above range.

[0053] Meanwhile, according to an exemplary embodiment, the pressure in the selective hydrogenation reaction zone may be selected, for example, within the range of about 3 bar to 70 bar, specifically about 5 bar to 30 bar, and more specifically about 7 bar to 20 bar. If the pressure in the selective hydrogenation reaction zone is excessively low or high, problems may occur, such as a low removal rate of unsaturated hydrocarbons or hydrogenation of aromatic rings, resulting in increased loss of aromatic hydrocarbons. Therefore, it may be advantageous to appropriately adjust the pressure within the above range.

[0054] Additionally, the hourly space velocity (LHSV) of the aromatic-containing feedstock may be, for example, about 0.3 hr -1 ~30hr -1 , specifically about 0.5 hours -1 ~20hr -1 , more specifically about 0.5 hours -1 ~10hr -1 can be adjusted within the range.

[0055] On the other hand, the catalyst used in the selective hydrogenation step (i.e., the selective hydrogenation catalyst) can be selected from a type having a hydrogenation activity adjusted to have the property of exhibiting substantially no hydrogenation selectivity for aromatic rings (one ring and / or two or more aromatic rings) while exhibiting high hydrogenation selectivity for unsaturated hydrocarbons.

[0056] According to an exemplary embodiment, the selective hydrogenation catalyst may include a support including an inorganic oxide and at least one active metal selected from the group consisting of 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 (elemental basis) in the selective hydrogenation catalyst may be, for example, in the range of about 0.5 wt % to 40 wt %, specifically about 2 wt % to 30 wt %, and more specifically about 4 wt % to 25 wt %, based on the total catalyst weight. These metal content ranges are provided for illustrative purposes and may vary depending on the type of active metal used, its hydrogenation activity, the form of the metal, etc.

[0057] In the selective hydrogenation catalyst, the embodiments in which a plurality of metals among the active metals exemplified above are used can be combined as exemplified below: In the case of Co-Mo, the atomic ratio of cobalt:molybdenum can be adjusted, for example, within a range of 1:about 0.5 to 10, specifically 1:about 1 to 5, and more specifically 1:about 1.5 to 3. In the case of Ni-Mo, the atomic ratio of nickel:molybdenum can be adjusted, for example, within a range of 1:about 0.5 to 10, specifically 1:about 1 to 5, and more specifically 1:about 1.5 to 3. In addition, in the case of Ni-W, the atomic ratio of nickel:tungsten can be adjusted, for example, within a range of 1:about 0.5 to 10, specifically 1:about 1 to 5, and more specifically 1:about 1.5 to 3.

[0058] In one embodiment, the selective hydrogenation catalyst may be in the form of a reduced form, a sulfide form, or a combination thereof. For example, for a specific single active metal or a combination of two active metals, both the reduced form and the sulfide form may be used, and for other active metals or combinations of two active metals, the reduced form may be used. Typically, for the same active metal or combination thereof, the reduced form has higher hydrogenation activity than the sulfide form, and the state of the catalyst (reduced form, sulfide form, or oxidized form) can be determined taking into account the amount of hydrogen or hydrogen partial pressure that contacts the catalyst.

[0059] According to another exemplary embodiment, the selective hydrogenation catalyst may be loaded into a single reactor using a stage-loading method. For example, a first selective hydrogenation catalyst layer and a second selective hydrogenation catalyst layer may be arranged in this order based on the inflow direction of the feedstock. In this case, if the active metal in the first selective hydrogenation catalyst (or catalyst layer) is Re, Co, Mo, and / or Co-Mo, a reduced or sulfide catalyst layer may be arranged. Meanwhile, if the active metal in the first selective hydrogenation catalyst (or catalyst layer) is Ni, Pd, Pt, Ru, Rh, Ni-Mo, and / or Ni-W, a sulfide catalyst layer may be arranged. On the other hand, in the case of the second selective hydrogenation catalyst in the subsequent stage, a catalyst layer supporting reduced Ni-Mo and / or Ni-W may be arranged.

[0060] As a modification of the above-mentioned stepwise loading method, a plurality of reactors corresponding to the first selective hydrogenation catalyst layer and the second selective hydrogenation catalyst layer may be connected in series to carry out the selective hydrogenation reaction.

[0061] The above-described stepwise loading scheme or variations thereof are described in commonly assigned U.S. Patent Publication No. 2022-0073440, which is incorporated herein by reference.

[0062] According to an exemplary embodiment, the support for the selective hydrogenation catalyst (or the first and second selective hydrogenation catalysts) can be selected from inorganic oxides, specifically inorganic oxides having a large specific surface area. Such supports can be, for example, at least one selected from the group consisting of alumina, silica, silica-alumina, aluminum phosphate, zirconia, titania, bentonite, kaolin, clinoptilolite, and montmorillonite. According to a specific embodiment, the inorganic oxide can be amorphous, and in particular at least one selected from the group consisting of alumina, silica, and silica-alumina, particularly alumina, can be used.

[0063] According to an exemplary embodiment, the support may be cylindrical, for example, having a diameter of about 0.5 mm to 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 support may have a shape other than a cylindrical shape, such as a granule, pellet, tablet, or sphere. In order to manufacture a support of a specific shape, molding methods known in the art, such as extrusion, spray drying, pelletizing, and oil dropping, can be applied, but this should be understood for illustrative purposes only.

[0064] According to exemplary embodiments, the support may have an apparent density ranging from about 0.3 cc / g to 1.2 cc / g, specifically from about 0.4 cc / g to 1.1 cc / g, and more specifically from about 0.4 cc / g to 0.9 cc / g. The average pore diameter of the support may range, for example, from about 3 nm to 1000 nm, specifically from about 5 nm to 800 nm, and more specifically from about 7 nm to 600 nm. Additionally, the specific surface area (BET) of the support may range, for example, from about 10 m 2 / g~1000m 2 / g, specifically about 30m 2 / g~800m 2 / g, more specifically, about 50m 2 / g~600m 2 The above-mentioned ranges of the physical properties may be understood as examples.

[0065] According to an exemplary embodiment, the active metal in the hydrogenation catalyst can be supported on a support by any method known in the art, such as impregnation (e.g., incipient wetness impregnation, excess solution impregnation, and immersion), ion exchange, co-impregnation, etc.

[0066] Typically, an impregnation method can be applied, for example, a method in which a soluble metal precursor or compound (typically a water-soluble or solvent-soluble metal compound), specifically a metal salt, is added to a liquid medium selected from water, an acid aqueous solution, a basic aqueous solution, and the like, and the pores of the support are filled with the metal precursor or compound.

[0067] In an exemplary embodiment, applicable metal precursors may generally be salts, complexes, halides, etc. of active metals, and can be exemplified as follows:

[0068] The molybdenum precursor may be, but is not limited to, at least one selected from the group consisting of molybdenum(II) acetate, ammonium molybdate(VI), diammonium dimolybdate(III), ammonium heptamolybdate(VI), ammonium phosphomolybdate(VI) and analogous sodium and potassium salts, molybdenum(III) bromide, tungsten(III)-(V) chloride, molybdenum(VI) fluoride, molybdenum(VI) oxychloride, molybdenum(IV)-(VI) sulfide, molybdic acid and the corresponding ammonium, sodium and potassium salts, and molybdenum(II-VI) oxide.

[0069] The cobalt precursor may be at least one selected from the group consisting of cobalt nitrate, sulfate, carbonate, acetate, alkoxide, and halide. Specifically, the cobalt precursor may be at least one selected from the group consisting of cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt carbonate, cobalt hydroxide, cobalt alkoxide, cobalt halides (e.g., cobalt chloride, cobalt bromide, etc.), and hydrates thereof. More specifically, cobalt nitrate and / or its hydrate (e.g., Co(NO3)2·6H2O) may be used. The nickel precursor may be at least one selected from the group consisting of nickel nitrate, nickel sulfate, nickel phosphate, nickel halide, nickel carboxylate, nickel hydroxide, nickel carbonate, nickel acetylacetonate complex, and nickel acetate and its hydrate. More specifically, nickel nitrate and / or its hydrate (e.g., Ni(NO3)2·6H2O) may be used. The tungsten precursor may be at least one selected from ammonium metatungstate, ammonium tungstate, sodium tungstate, tungstic acid, tungsten chloride, etc. The palladium precursor may be at least one selected from palladium acetate, palladium chloride, palladium nitrate, palladium sulfate, etc. The platinum precursor may be at least one selected from chloroplatinic acid, ammonium chloroplatinate, dinitrodiaminoplatinum, tetrachlorodiaminoplatinum, hexachlorodiaminoplatinum, dichlorodiaminoplatinum, platinum(II) dichloride, platinum(IV) tetrachloride, etc. The ruthenium precursor may be at least one selected from ruthenium chloride, ruthenium nitrosyl nitrate, chlorohexaaminoruthenium, etc. The rhodium precursor may be at least one selected from rhodium chloride, rhodium acetate, rhodium nitrate, rhodium sulfate, etc. As the rhenium precursor, at least one selected from perrhenic acid, rhenium chloride, ammonium perrhenate, potassium perrhenate, rhenium oxide, and the like can be used.

[0070] According to an exemplary embodiment, the concentration of the active metal in the impregnation solution may be, for example, in the range of about 0.005 M to 5 M, specifically about 0.01 M to 3 M, and more specifically about 0.015 M to 2 M. The conditions for the impregnation process are not particularly limited, but may be, for example, at about 1° C. to 100° C. (specifically, about 25° C. to 60° C.) for about 0.1 to 48 hours (about 0.5 to 12 hours), although such conditions may be understood as exemplary.

[0071] As described above, after the active metal is impregnated into the support, a drying process can be performed, for example, in an oxygen-containing atmosphere (e.g., air). The drying temperature can be, for example, about 60°C to 200°C, specifically about 80°C to 150°C. The drying time can be, for example, about 0.5 hours to 15 hours, specifically about 1 hour to 12 hours. Through the drying process, the metal precursor can adhere more firmly to the support.

[0072] Next, the dried catalyst is subjected to a calcination (or heat treatment) step. The calcination step may be performed in an oxygen-containing atmosphere (e.g., air) or an inert gas atmosphere (e.g., nitrogen), specifically, in an oxygen-containing atmosphere. The calcination temperature may be selected, for example, within a range of about 300°C to 800°C, specifically, about 400°C to 650°C. The calcination time may be adjusted, for example, within a range of about 0.5 hours to 24 hours, specifically, about 1 hour to 12 hours. When calcination is performed in an oxygen-containing atmosphere, the active metals may be converted into oxide forms; for example, molybdenum may be in the form of MoO3, and nickel may be in the form of NiO.

[0073] -Production of reduced catalysts According to an exemplary embodiment, if the hydrogenation catalyst is in reduced form, a reduction treatment can be carried out to convert the active metals in the catalyst in the oxide form described above into fully reduced and / or partially reduced forms.

[0074] In this regard, the reduction treatment step may be performed using hydrogen alone or hydrogen diluted in an inert gas (e.g., N, He, Ar, etc.) at a temperature of, for example, about 25° C. to 800° C., specifically about 200° C. to 700° C., more specifically about 300° C. to 550° C. The reduction treatment time is not particularly limited, but may be adjusted within a range of, for example, about 0.5 hours to 24 hours, specifically about 1 hour to 12 hours.

[0075] The reduction treatment may cause the active metal in the hydrogenation catalyst to exist in a reduced form. Illustratively, the metal contained in the catalyst may be reduced to, for example, an elemental form or a partially oxidized form (e.g., in the case of molybdenum (Mo), the maximum oxidation state of Mo). 6+ Instead of Mo 4+ It can have a partially oxidized form.

[0076] -Production of sulfide catalysts The supported metal can be optionally converted to a non-reduced sulfide form to control excessive hydrogenation activity that leads to side reactions such as loss of aromatics or to impart hydrogenation functionality (especially in the case of molybdenum).

[0077] According to exemplary embodiments, the reduced catalyst body can be sulfided to convert the metal components in the catalyst to sulfides by methods known in the art. Such sulfiding can be performed in the gas phase (contact with hydrogen sulfide or a mixture of hydrogen sulfide and an inert gas) or in the liquid phase (contact with a sulfur compound-containing solution). According to specific embodiments, the reduced catalyst can be treated with a solution containing a sulfur compound.

[0078] According to an exemplary embodiment, the sulfur compound usable in the sulfurization treatment may be at least one selected from hydrogen sulfide, hydrogen disulfide, carbon disulfide, alkyl sulfides, etc. In particular, alkyl sulfides such as methyl sulfide, dimethyl sulfide, dimethyl disulfide, diethyl sulfide, and / or dibutyl sulfide may be used. Furthermore, hydrocarbon solvents such as benzene, toluene, xylene, C9+ aromatics, hexane, and heptane may be used as the solvent during the sulfurization treatment. For example, the amount of sulfur compound in the solution for the sulfurization treatment may be determined appropriately based on an amount equal to or greater than the equivalent required to sulfurize the metal in the catalyst. For example, when molybdenum is used as the active metal, a sulfur compound equal to or greater than the equivalent required to sulfurize the molybdenum to MoS3 (which may ultimately be converted to MoS2) may be mixed into the solution. Furthermore, in the case of nickel, it may be converted to Ni3S2.

[0079] In an exemplary embodiment, the sulfurization treatment may be carried out at a temperature of, for example, room temperature to about 500°C (specifically, about 100°C to 450°C) for about 0.5 hours to 100 hours (specifically, about 1 hour to 48 hours).

[0080] Meanwhile, by selectively removing unsaturated hydrocarbons from the aromatic hydrocarbon-containing fraction through the selective hydrogenation reaction described above, the bromine index of the product (i.e., the first aromatic hydrocarbon-containing product) is reduced. For example, 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 first aromatic hydrocarbon-containing product may exhibit a bromine index that 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.

[0081] During the selective hydrogenation reaction described above, it may be preferable to hydrogenate and remove all unsaturated hydrocarbons. However, this may also increase aromatics loss, so it may be advantageous to carry out the reaction so as to have a well-balanced product distribution. In this case, the unsaturated carbon in the first aromatic hydrocarbon-containing product may not be completely removed, and a small amount may remain. In this regard, the content of unsaturated carbon in the first aromatic hydrocarbon-containing product may be, for example, up to about 2 wt%, specifically up to about 1.5 wt%, more specifically about 0.01 wt% to 1 wt%, and particularly specifically about 0.02 wt% to 0.5 wt%.

[0082] On the other hand, the hydrogen supplied during the selective hydrogenation reaction is typically used in excess relative to the unsaturated hydrocarbons. However, because there is a limit to the ability to completely remove the unsaturated hydrocarbons due to controlled hydrogenation activity, residual hydrogen is contained in the first aromatic hydrocarbon-containing product. In this regard, the concentration of residual hydrogen in the first aromatic hydrocarbon-containing product may be, for example, up to about 200 wtppm, specifically up to about 180 wtppm, and more specifically up to about 150 wtppm. According to a specific embodiment, the concentration of residual hydrogen in the first aromatic hydrocarbon-containing product may be, for example, in the range of about 50 wtppm to 120 wtppm, specifically about 60 wtppm to 110 wtppm, and more specifically about 80 wtppm to 100 wtppm.

[0083] Also, in exemplary embodiments, it is preferred to minimize aromatic compound loss during the selective hydrogenation reaction, so that total aromatic loss can be, for example, less than about 0.45 wt.%, specifically less than about 0.3 wt.%, more specifically less than about 0.1 wt.%, and most specifically less than about 0.05 wt.%.

[0084] Hydrogenation Stage According to one embodiment of the present disclosure, an additional hydrogenation step may be carried out to remove residual hydrogen contained in the first aromatic hydrocarbon-containing product formed through the selective hydrogenation of the aromatic fraction. This hydrogenation step is different from the previous selective hydrogenation reaction in that it allows the hydrogenation or saturation of aromatic rings (specifically, at least one double bond in the aromatic ring) in aromatic hydrocarbons of specific structures based on the different hydrogenation reactivities between hydrocarbon structures, whereas the previous selective hydrogenation reaction removes as little aromatic ring as possible through hydrogenation. It should also be noted that the hydrogenation step is carried out without an external hydrogen supply, since the residual hydrogen is removed by the hydrogenation reaction.

[0085] According to this example, during the hydrogenation reaction of unsaturated hydrocarbons (specifically, olefins, etc.) using the residual hydrogen in the aromatic fraction, the residual hydrogen in the first aromatic hydrocarbon-containing product (i.e., the selectively hydrotreated C aromatic hydrocarbon fraction) can be effectively removed based on the fact that the hydrogenation tendency differs depending on the hydrocarbon structure.

[0086] Specifically, the hydrogenation tendency of compounds is evaluated in the following order: olefins > 2-ring aromatics (naphthalenes → tetralins or indenes → indanes) > 1-ring aromatics. By utilizing these differences in hydrogenation tendency according to hydrocarbon structure, it is possible to maximize the content of the target product, 1-ring aromatic hydrocarbons (i.e., minimize the loss of 1-ring aromatics), while removing the remaining hydrogen in the aromatic fraction using olefins and / or 2-ring aromatics with better hydrogenation reactivity. In this regard, "2-ring aromatics" or "2-ring aromatic hydrocarbons" can refer to naphthalenes and indenes, which have two aromatic rings in their molecules.

[0087] According to this example, in the additional hydrogenation reaction, the unsaturated hydrocarbons present in the first aromatic hydrocarbon-containing product are reacted with the remaining hydrogen (hydrogenation reaction), thereby further reducing the bromine index resulting from the unsaturated hydrocarbons and simultaneously removing the remaining hydrogen in the selective hydrogenation product.

[0088] According to another exemplary embodiment, the first aromatic hydrocarbon-containing product further contains two-ring aromatic hydrocarbons in addition to unsaturated hydrocarbons. Specifically, when the feedstock (specifically, the C aromatic hydrocarbon-containing fraction) contains two-ring aromatic hydrocarbons in addition to one-ring aromatic hydrocarbons, the first aromatic hydrocarbon-containing product may still contain two-ring aromatic hydrocarbons because the selective hydrogenation reaction in the previous stage is carried out to maximize the maintenance of aromatic rings (i.e., minimize the hydrogenation or saturation of aromatic rings). In this case, the content of two-ring aromatic hydrocarbons in the first aromatic hydrocarbon-containing product may be adjusted to, for example, at least about 0.3 wt%, specifically 0.4 wt% to 15 wt%, more specifically about 0.5 wt% to 10 wt%, and particularly specifically about 1 wt% to 5 wt%.

[0089] If the total amount of unsaturated hydrocarbons and / or bicyclic aromatic hydrocarbons in the first aromatic hydrocarbon-containing product does not reach the level required for removing residual hydrogen, bicyclic aromatic hydrocarbons can be added to the reaction system, e.g., the first aromatic hydrocarbon-containing product, before or during the hydrogenation reaction to adjust the amount to the above range. The amount of bicyclic aromatic hydrocarbons added can vary depending on the content of residual hydrogen and is not necessarily limited thereto. In this way, bicyclic aromatic hydrocarbons are preferentially hydrogenated compared to monocyclic aromatic hydrocarbons due to their structural characteristics, thereby effectively suppressing the loss of monocyclic aromatic hydrocarbons such as C8 aromatics.

[0090] In this example, in the hydrogenation step, hydrogenation of not only unsaturated hydrocarbons but also bicyclic aromatic rings is permitted, and it is necessary to reduce the trace amount of remaining hydrogen as much as possible through the hydrogenation reaction. Therefore, a catalyst exhibiting stronger hydrogenation activity than that in the preceding selective hydrogenation step can be used.

[0091] According to an exemplary embodiment, the hydrogenation catalyst may be prepared in the same manner as the metal-supported catalyst used in the selective hydrogenation reaction described above, with the same catalyst shape and preparation method. In this regard, the active metal in the hydrogenation catalyst may be 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 be at least one selected from the group consisting of platinum, rhodium, and ruthenium. The active metal in the hydrogenation catalyst may be in a reduced form, which is because it exhibits a higher hydrogenation activity than a sulfide form. In particular, among platinum group metals, palladium may be undesirable because a palladium catalyst may not provide sufficient hydrogenation activity for removing residual hydrogen compared to other platinum group metal catalysts.

[0092] The content (elemental basis) of the active metal in the hydrogenation catalyst may be, 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 particularly specifically about 1 wt % to 20 wt %, based on the total catalyst weight. These metal content ranges are provided for illustrative purposes and can be changed depending on the type of active metal used, its hydrogenation activity, metal form, etc.

[0093] On the other hand, the support for supporting the active metal in the hydrogenation catalyst can be selected from the range of supports used in the selective hydrogenation catalysts described above, and specifically, alumina can be used.

[0094] According to this embodiment, most of the unsaturated hydrocarbons are removed in the first selective hydrogenation step to produce a selective hydrogenation product containing a trace amount of residual hydrogen, and the second hydrogenation step involves a process of using the unsaturated hydrocarbons (and / or bicyclic aromatic hydrocarbons) remaining in the selective hydrogenation product to react with the trace amount of residual hydrogen without external hydrogen supply. Therefore, more precise control of the reaction conditions may be required compared to the hydrogenation reaction of a typical hydrocarbon fraction.

[0095] For example, the hydrogenation reaction temperature may be adjusted to, for example, a range greater than about 55° C. and less than about 255° C., specifically between about 60° C. and 230° C., and more specifically between about 70° C. and 225° C. According to a particular embodiment, the hydrogenation reaction temperature may be set to a range of about 80° C. and 185° C., specifically between about 90° C. and 175° C., more specifically between about 95° C. and 155° C., and particularly specifically between about 100° C. and 130° C.

[0096] If the hydrogenation reaction temperature is too low, it may be difficult to remove substantially all of the residual hydrogen. On the other hand, if the hydrogenation reaction temperature is too high, the loss of monocyclic aromatic hydrocarbons and the bromine index (BI) of the product may tend to increase. In particular, as the hydrogenation reaction temperature increases, the difference in hydrogenation tendency depending on the hydrocarbon structure may decrease. Furthermore, if the hydrogenation reaction temperature is too high, the conversion of bicyclic aromatic hydrocarbons, which are useful for removing residual hydrogen, may not increase, and instead the loss of the target monocyclic aromatic hydrocarbons may increase. Taking this into consideration, it may be advantageous to appropriately adjust the reaction temperature within the above-mentioned range.

[0097] On the other hand, the pressure conditions during the hydrogenation reaction can increase the hydrogenation tendency, but as the reaction pressure increases, the loss of aromatics, especially monocyclic aromatic hydrocarbons, can increase. Taking this into consideration, the reaction pressure can be adjusted, for example, in the range of about 3 bar to 60 bar, specifically about 4 bar to 30 bar, more specifically about 5 bar to 15 bar.

[0098] According to an exemplary embodiment, the hourly 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 ~30hr -1 , specifically about 0.5 hours -1 ~20hr -1 , more specifically about 0.5 hours -1 ~10hr - can be adjusted within the range.

[0099] As described above, a second aromatic hydrocarbon-containing product having reduced contents of residual hydrogen and unsaturated hydrocarbons (and additionally bicyclic aromatic hydrocarbons) can be formed through the hydrogenation reaction after the selective hydrogenation reaction. In this case, the amount of hydrogen (residual hydrogen) in the second aromatic hydrocarbon-containing product can be less than about 6 wtppm, specifically less than about 3 wtppm, and more specifically less than about 1 wtppm. The reason for adjusting the amount of residual hydrogen to less than about 6 wtppm is that the amount of residual hydrogen corresponds to the saturated solubility of hydrogen in aromatic hydrocarbons at 1 atmosphere. If the amount of residual hydrogen exceeds this amount, bubbles will form, which, as mentioned above, can have an adverse effect on downstream equipment or processes. In this case, the saturated solubility of hydrogen can be measured with reference to the descriptions in de Wet, WJJSAfr. Chem. Inst. 1964, 17, 9-13 and Satterfield, CNI Chem. E. Symp. Ser. 1968, No. 28, 22-29, which are incorporated herein by reference.

[0100] In addition, the loss of monocyclic aromatic hydrocarbons during the hydrogenation reaction of the first aromatic hydrocarbon-containing product can be controlled, for example, to a range of 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.

[0101] According to illustrative examples, the bromine index of the second aromatic hydrocarbon-containing product may be reduced compared to the first aromatic hydrocarbon-containing product due to the removal of unsaturated hydrocarbons contained in the first aromatic hydrocarbon-containing product, which is a reactant. For example, it is preferable that the bromine index of xylene obtained by distilling the second aromatic hydrocarbon-containing product is low. In this regard, the bromine index of xylene separated by distillation of the second aromatic hydrocarbon-containing product may be advantageously, for example, less than about 20, specifically less than about 15, and more specifically less than about 10. Such properties are advantageous for use in downstream processes that use xylene with a bromine index of 20 or less as a raw material, particularly xylene separation and recovery processes (e.g., PAREX processes).

[0102] Selective Hydrogenation - Hydrogenation Reaction and Integration with Subsequent Processes According to one embodiment, in a refining process in which an aromatic hydrocarbon-containing feedstock is subjected to a selective hydrogenation reaction followed by a hydrogenation reaction, the remaining hydrogen in the aromatic hydrocarbon-containing product obtained through the selective hydrogenation reaction is removed by a subsequent hydrogenation reaction. An exemplary embodiment is shown in FIGS. 1a and 1b, respectively.

[0103] According to the illustrated embodiment, the overall process 100, 200 can be carried out in two ways: using multiple reactors connected in series (using two reactors in Figure 1a) and using a staged loading scheme (using two catalyst layers stacked sequentially in Figure 1b).

[0104] Referring to FIG. 1a, the first reactor A and the second reactor B correspond to a selective hydrogenation reactor and a hydrogenation reactor, respectively. The aromatic hydrocarbon-containing fraction 101, which is the feedstock, is combined with hydrogen 102 supplied from an external source, and at least a portion of the supplied hydrogen is dissolved in the feedstock to form stream 103, which is introduced into the first reactor A. As described above, the first reactor A selectively hydrogenates unsaturated hydrocarbons (e.g., olefins) while preserving the aromatic rings in the feedstock. The selective hydrogenation product discharged from this, i.e., the first aromatic hydrocarbon-containing product 104, is introduced into reactor B. Unlike reactor A, reactor B removes the remaining hydrogen in product 104 by a hydrogenation reaction using unsaturated hydrocarbons and / or two-ring aromatic hydrocarbons, while maximizing the preservation of monocyclic aromatic hydrocarbons in product 104. As a result, the hydrogenation product discharged from reactor B, i.e., the second aromatic hydrocarbon-containing product 105, can be obtained as a purified aromatic fraction.

[0105] In the embodiment shown in Figure 1b, a first catalyst layer A' and a second catalyst layer B' are stacked in this order in a single reactor based on the flow direction of the feedstock (i.e., a staged loading method). As in Figure 1a, aromatic-containing feedstock 201 is combined with hydrogen 202 to form stream 203, which is then contacted with multiple catalyst layers stacked sequentially in the reactor. At this time, this stream contacts selective hydrogenation catalyst layer A' and then hydrogenation catalyst layer B', and a second aromatic hydrocarbon-containing product 205 containing substantially no residual hydrogen and having a reduced bromine index (BI) is discharged.

[0106] When multiple reactors connected in series as shown in FIG. 1a are used, it is possible to provide an advantage in that the loss of aromatics (especially monocyclic aromatic hydrocarbons such as C8 aromatics) can be minimized by varying the operating conditions for each reactor, but it may be disadvantageous compared to the embodiment shown in FIG. 1b in terms of increased capital investment costs.

[0107] According to an exemplary embodiment, the second aromatic hydrocarbon-containing product is applied to a subsequent process, specifically a xylene production process, especially a para-xylene recovery process, and a purification process by a two-stage hydrogenation reaction can be integrated with the xylene production process.

[0108] For example, the second aromatic hydrocarbon-containing product can be transferred to a xylene column and separated into an upstream C aromatic hydrocarbon fraction and a bottoms C aromatic hydrocarbon fraction. The separated C aromatic hydrocarbon fraction is then transferred to a para-xylene separation / recovery unit to recover para-xylene. Representative examples of such para-xylene recovery technologies include Parex from UOP, Eluxyl from IFP, and Aromax from Toray.

[0109] According to an exemplary embodiment, prior to separating the second aromatic hydrocarbon-containing product, a step of treating the product with a solid acid (solid acid catalyst) can be optionally performed. The solid acid can typically be clay (natural and / or synthetic clay) and / or zeolite. This subsequent treatment can decompose the alkyl groups of the C9+ aromatic hydrocarbons and partially increase the content of C8- aromatic hydrocarbons. The clay can be of the type used in clay treatment methods for aromatic hydrocarbons known in the art, such as at least one selected from bentonite, montmorillonite, kaolin, etc. The zeolite can be 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 treatment temperature of the solid acid may be adjusted within a range in which the second aromatic hydrocarbon-containing product maintains a liquid phase, for example, about 120°C to 350°C (specifically, about 160°C to 300°C). The treatment pressure of the solid acid may be adjusted within a range of, for example, about 3 bar to 60 bar (specifically, about 5 bar to 30 bar). In addition, the space velocity may be adjusted within a range of, for example, about 0.2 hr -1 ~20hr -1 (approx. 0.5 hours -1 ~10hr -1 ) range, but such processing conditions should be understood as illustrative.

[0110] The C8 aromatic hydrocarbon fraction remaining after separation of para-xylene from the xylene recovery unit may contain mainly ortho-xylene and / or meta-xylene and is transferred to a xylene isomerization unit to form a xylene mixture with an increased para-xylene content. The reaction in the xylene isomerization unit can be carried out using known reaction conditions and catalysts, and detailed description thereof will be omitted. The C8 isomerization product discharged from the xylene isomerization reaction is separated into a light fraction (e.g., a C7 hydrocarbon fraction (upstream)) and a C8 aromatic hydrocarbon fraction (bottoms stream) in a separation column. At this time, the C8 aromatic hydrocarbon fraction can be transferred to a xylene column.

[0111] The present invention can be more clearly understood from the following examples, which are intended to illustrate the present invention only and are not intended to limit the scope of the invention. [Example]

[0112] The materials used in the examples and comparative examples are as follows.

[0113] Xylene, naphthalene, and metal compounds were ACS Reagent Grade from Sigma-Aldrich, and inorganic oxides were purchased from Sigma-Aldrich. The aromatic hydrocarbon fraction used as the feedstock was obtained from a commercial process and used as a C8+ aromatic fraction with a bromine index (BI) of 748.

[0114] Evaluation and comparison of xylene hydrogenation activity among catalysts In Comparative Examples 1 to 11, catalysts were produced to select catalysts suitable for the selective hydrogenation reaction and the subsequent hydrogenation reaction (removal of residual hydrogen), and their hydrogenation activities were evaluated.

[0115] Comparative Example 1 Xylene hydrogenation using Co reduction catalysts Cobalt nitrate was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After being kept at room temperature for about 1 hour, the mixture was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours to prepare a 7 wt% Co-loaded catalyst.

[0116] 40 cc of the CoO / alumina catalyst (catalyst size distribution: 20 mesh to 40 mesh) was packed into a fixed-bed continuous reactor. Then, the atmosphere in the reactor was replaced with nitrogen, and the pressure was increased to 10 kgf / cm. 2 Next, the nitrogen was replaced with hydrogen, and the temperature was raised to 450°C while hydrogen was flowing at 500 cc / min, and reduction treatment was carried out for 2 hours.

[0117] After that, the temperature in the reactor was lowered to 100°C, and the hydrogen / C8 aromatic molar ratio was set to 6.0, and the hydrocarbon fraction (xylene:dimethylcyclohexane=1:7) was heated at a space velocity of 15 h -1 The xylene hydrogenation reaction was carried out under the conditions above, and the results are shown in Table 1 below.

[0118] Comparative Example 2 Xylene hydrogenation using Mo sulfide catalysts Ammonium heptamolybdate was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After being maintained at room temperature for approximately 1 hour, the support was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours to prepare a 15 wt% Mo-loaded catalyst.

[0119] 40 cc of the catalyst (catalyst size distribution: 20 mesh to 40 mesh) was packed into a fixed-bed continuous reactor. Then, the atmosphere in the reactor was replaced with nitrogen, and the pressure was increased to 10 kgf / cm. 2The pressure was then increased to 500 cc / min. The nitrogen was then replaced with hydrogen, and hydrogen was flowed at 500 cc / min while toluene containing 2 wt% DMDS was flowed at 0.7 cc / min. This was maintained for 5 hours, and the temperature was then increased to 350°C, whereupon the sulfurization treatment was carried out 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.

[0120] Comparative Example 3 Xylene hydrogenation using CoMo sulfided catalysts. Ammonium heptamolybdate was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After maintaining at room temperature for approximately 1 hour, the support was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours. Cobalt nitrate was then dissolved in distilled water, and nickel was additionally loaded onto the molybdenum-loaded alumina support by incipient wetness impregnation. The support was then dried and calcined under the same conditions to produce a 3.5 wt% Co and 12 wt% Mo loaded catalyst.

[0121] Thereafter, an experiment was carried out in the same manner as in Comparative Example 2, and the results are shown in Table 1 below.

[0122] Comparative Example 4 Xylene hydrogenation using NiMo sulfided catalysts. Ammonium heptamolybdate was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After maintaining at room temperature for approximately 1 hour, the support was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours. Nickel nitrate was then dissolved in distilled water, and additional nickel was loaded onto the molybdenum-loaded alumina support by incipient wetness impregnation. The support was then dried and calcined under the same conditions to produce a 3.5 wt% Ni and 12 wt% Mo loaded catalyst.

[0123] Thereafter, an experiment was carried out in the same manner as in Comparative Example 2, and the results are shown in Table 1 below.

[0124] Comparative Example 5 Xylene hydrogenation using Mo-reduced catalysts Ammonium heptamolybdate was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After being maintained at room temperature for approximately 1 hour, the support was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours to prepare a 15 wt% Mo-loaded catalyst.

[0125] Thereafter, an experiment was carried out in the same manner as in Comparative Example 1, and the results are shown in Table 1 below.

[0126] Comparative Example 6 Xylene hydrogenation using Ni-reduced catalysts Nickel nitrate was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After being kept at room temperature for about 1 hour, the mixture was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours to prepare a 7 wt% Ni-loaded catalyst. The experiment was then carried out in the same manner as in Comparative Example 1, and the results are shown in Table 1 below.

[0127] Comparative Example 7 Xylene hydrogenation using Pd-reduced catalysts Palladium chloride was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After being kept at room temperature for about 1 hour, the mixture was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours to prepare a 7 wt% Pd-loaded catalyst. The experiment was then carried out in the same manner as in Comparative Example 1, and the results are shown in Table 1 below.

[0128] Comparative Example 8 Xylene hydrogenation using reduced Pt catalysts Chloroplatinic acid was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After being kept at room temperature for about 1 hour, the mixture was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours to prepare a 7 wt% Pt-loaded catalyst. The experiment was then carried out in the same manner as in Comparative Example 1, and the results are shown in Table 1 below.

[0129] Comparative Example 9 Xylene hydrogenation using Ru-reduced catalysts Ruthenium chloride was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After being maintained at room temperature for approximately 1 hour, the mixture was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours to prepare a 7 wt% Ru-loaded catalyst. The experiment was then carried out in the same manner as in Comparative Example 1, and the results are shown in Table 1 below.

[0130] Comparative Example 10 Xylene hydrogenation using Rh-reduced catalysts Rhodium chloride was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After being kept at room temperature for about 1 hour, the mixture was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours to prepare a 7 wt% Rh-loaded catalyst. The experiment was then carried out in the same manner as in Comparative Example 1, and the results are shown in Table 1 below.

[0131] Comparative Example 11 Xylene hydrogenation using NiMo reduction catalysts The catalyst prepared in the same manner as in Comparative Example 4 was reduced in the same manner as in Comparative Example 1, and the reaction results are shown in Table 1 below.

[0132] [Table 1]

[0133] According to the table, platinum-based catalysts, excluding nickel and palladium, have strong hydrogenation activity, resulting in large xylene hydrogenation conversions (losses). However, the Co reduction, Mo sulfidation, CoMo sulfidation, NiMo sulfidation, Mo reduction, Pd reduction, and NiMo reduction catalysts were evaluated to have xylene hydrogenation conversions of 2.1% or less. Of these, a catalyst with a xylene hydrogenation conversion of 0.1% by weight or less was used as the first catalyst for the "selective hydrogenation reaction." Meanwhile, for the second catalyst for the subsequent "hydrogenation reaction," trace amounts of hydrogen must be completely removed, so a catalyst with strong hydrogenation activity and a xylene hydrogenation conversion of 20% or more was selected and used.

[0134] Comparative Example 12 Selective hydrogenation process using Ni-Mo sulfide catalyst Ammonium heptamolybdate was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After maintaining at room temperature for approximately 1 hour, the support was dried in an air atmosphere at 150°C for 2 hours and calcined at 500°C for 2 hours. Nickel nitrate was then dissolved in distilled water, and additional nickel was loaded onto the molybdenum-loaded alumina support by incipient wetness impregnation. The support was then dried and calcined under the same conditions to produce a 3.5 wt% Ni and 12 wt% Mo loaded catalyst.

[0135] 40 cc of the catalyst (catalyst size distribution: 20 mesh to 40 mesh) was packed into a fixed-bed continuous reactor. Then, the atmosphere in the reactor was replaced with nitrogen, and the pressure was increased to 10 kgf / cm. 2 Next, the nitrogen was replaced with hydrogen, and hydrogen was flowed at 500 cc / min, and toluene containing 2 wt% DMDS was flowed at 0.7 cc / min, while maintaining this for 5 hours. Then, the temperature was raised to 350°C, and sulfurization treatment was carried out for 6 hours.

[0136] The temperature in the reactor was then lowered to 185°C, and the hydrogenation reaction was carried out by adjusting the H2 flow rate to 3.5 cc / min and flowing the C8+ aromatic fraction (BI: 748) at 1.3 cc / min. After the reaction was carried out for two days, the bromine index (BI) and gas chromatography were measured by sampling. At this time, the bromine index of the product was 96, and the loss of aromatics was 0.03 wt%.

[0137] After the reaction, to check whether excess hydrogen remained, the excess hydrogen was discharged along with the product fraction into the connected glass line under room temperature / atmospheric pressure conditions, and the volume of the collected bubbles and the increase in the fraction were measured over a certain period of time. As a result, the excess (residual) hydrogen content was found to be about 120 wtppm.

[0138] Comparative Example 13 Selective hydrogenation process using Ni-Mo sulfide catalyst In order to prevent excess hydrogen from remaining in the selective hydrogenation product, the reactant input rate was reduced to half that of Comparative Example 12. Specifically, the selective hydrogenation reaction was carried out under the same conditions as Comparative Example 12, except that the flow rate of H2 was changed to 1.75 cc / min and the flow rate of the C8+ aromatic fraction (BI: 748) was changed to 0.65 cc / min. The bromine index (BI) of the product was 94, and the loss of aromatics was 0.03 wt%. It was also confirmed that unreacted excess hydrogen was discharged together with the product fraction into the connected glass line.

[0139] As described above, when a catalyst with weak hydrogenation function is used, there is almost no loss due to aromatic hydrogenation and the olefin content can be reduced, but it has been confirmed that there is a limit to completely consuming the introduced hydrogen.

[0140] Comparative Example 14 Selective hydrogenation process using Ni-reduced catalyst Nickel nitrate was dissolved in distilled water and then loaded onto an alumina support by incipient wetness impregnation. After maintaining at room temperature for approximately 1 hour, the mixture was dried in an air atmosphere at 150°C for 2 hours and then calcined at 500°C for 2 hours. The heating rate was controlled at 3°C ​​per minute. As a result, a NiO / alumina catalyst with a Ni content of 10 wt% was prepared.

[0141] 40 cc of the prepared NiO / alumina catalyst (catalyst size distribution: 20 mesh to 40 mesh) was packed into a fixed-bed continuous reactor. Then, the atmosphere inside the reactor was replaced with nitrogen, and the pressure was increased to 10 kgf / cm. 2 Next, the nitrogen was replaced with hydrogen, and the temperature was raised to 450°C while hydrogen was flowing at 500 cc / min, and reduction treatment was carried out for 2 hours.

[0142] The temperature inside the reactor was then lowered to 185°C, and the hydrogenation reaction was carried out by adjusting the H2 flow rate to 3.5 cc / min and flowing a C8+ aromatic fraction (BI: 748) at 1.3 cc / min. After the reaction was carried out for two days, samples were taken and analyzed by BI and gas chromatography. The olefin conversion rate was 80%, and the loss of aromatics was 0.3 wt% (H2 / olefin = 2.7). After the reaction, the product fraction was discharged into a connected glass line maintained at room temperature and pressure to check for residual hydrogen. Unreacted excess hydrogen was not discharged.

[0143] Example 1 Selective hydrogenation (Ni-Mo sulfide catalyst) - Hydrogenation (Ni reduced catalyst) two-step process First, the selective hydrogenation product prepared in Comparative Example 12 was collected and used as a reactant (content of 2-ring aromatic hydrocarbons: 1.1 wt%) to carry out a hydrogenation reaction. The catalyst used in the hydrogenation reaction was the nickel (reduced) catalyst (40, catalyst size distribution: 20 mesh to 40 mesh) used in Comparative Example 6, and the reaction pressure was 10 kgf / cm. 2The hydrogenation reaction was carried out at a pressure of approximately 9.8 bar while flowing a C8+ aromatic fraction (BI:96) at a rate of 1.3 cc / min. In order to simulate the inclusion of residual hydrogen in the selective hydrogenation product (product of Comparative Example 12) and to conduct the experiment under conditions of a constant residual hydrogen amount, hydrogen was injected to adjust the residual hydrogen amount to 120 wtppm.

[0144] After the hydrogenation reaction was carried out for two days, the bromine index (BI) and gas chromatography were measured by sampling to confirm whether or not excess hydrogen remained. The results are shown in Table 2 below.

[0145] Examples 2 to 4 and Comparative Examples 15 to 17 In order to confirm the hydrogenation tendency of each hydrocarbon structure depending on the reaction temperature, an experiment was carried out in the same manner as in Example 1, and the results are shown in Table 2 below.

[0146] [Table 2]

[0147] According to the table, when the residual amount of hydrogen on the Ni catalyst was 120 wtppm and the reaction temperature was 55°C or lower (Comparative Examples 15 and 16), residual hydrogen was still detected after the hydrogenation reaction. On the other hand, when the reaction temperature was 255°C, the loss of aromatics increased significantly, and the bromine index (BI) in the hydrogenation product also increased. In particular, at a reaction temperature of 255°C (Comparative Example 17), the conversion rate of 2-ring aromatics did not increase, and instead the loss of C8 aromatics increased significantly.

[0148] It is believed that the above results are due to the fact that the difference in hydrogenation tendency due to the hydrocarbon structure decreases as the reaction temperature increases.

[0149] Comparative Example 18 Selective hydrogenation (Ni-Mo sulfide catalyst) - hydrogenation (Pd reduced catalyst) two-step process The Pd reduction catalyst prepared in Comparative Example 7 was used to carry out an experiment in the same manner as in Example 1, and the results are shown in Table 3 below.

[0150] Example 5 Selective hydrogenation (Ni-Mo sulfide catalyst) - hydrogenation (Rh reduction catalyst) two-step process The Rh reduction catalyst prepared in Comparative Example 10 was used to carry out an experiment in the same manner as in Example 1, and the results are shown in Table 3 below.

[0151] Example 6 Selective hydrogenation (Ni-Mo sulfide catalyst) - hydrogenation (Ru reduced catalyst) two-step process The Ru reduction catalyst prepared in Comparative Example 9 was used to carry out an experiment in the same manner as in Example 1, and the results are shown in Table 3 below.

[0152] Example 7 Selective hydrogenation (Ni-Mo sulfide catalyst) - hydrogenation (Pt reduced catalyst) two-step process The Pt reduction catalyst prepared in Comparative Example 8 was used to carry out an experiment in the same manner as in Example 1, and the results are shown in Table 3 below.

[0153] [Table 3]

[0154] As can be seen from the table above, with catalysts with strong hydrogenation activity (reduced catalysts of Ni, Rh, Ru, and Pt), no residual hydrogen was found at a reaction temperature of 105°C, but with the Pd reduced catalyst, which has low hydrogenation activity, it was difficult to sufficiently remove the residual hydrogen.

[0155] Comparison of long-term durability Comparative Example 19 Selective hydrogenation (Ni-Mo sulfide catalyst) - Hydrogenation (Ni-Mo reduced catalyst) two-step process The Ni-Mo oxide catalyst prepared during the implementation of Comparative Example 4 was subjected to a reduction pretreatment in the same manner as in Comparative Example 1, and the presence or absence of residual excess hydrogen was compared with the lapse of reaction time.

[0156] Since the purpose of this experiment was to compare the durability of each hydrogenation catalyst in the two-stage process, a doubled throughput was applied compared to Example 2. Specifically, the temperature inside the reactor was adjusted to 155°C, the H2 flow rate was adjusted to 7.0 cc / min, and the hydrogenation reaction was carried out while flowing the C8+ aromatic fraction (BI:748) at 2.6 cc / min. The presence or absence of residual hydrogen and the loss of C8- aromatics (wt%) over the reaction time are shown in Table 4 below.

[0157] Example 8 Selective hydrogenation (Ni-Mo sulfide catalyst) - Hydrogenation (Ni reduced catalyst) two-step process The Ni-Mo oxide catalyst prepared during the procedure of Comparative Example 4 was subjected to a reduction pretreatment in the same manner as in Comparative Example 1, and then reacted in the same manner as in Comparative Example 19. The results are shown in Table 4 below.

[0158] [Table 4]

[0159] As can be seen from the table, in Example 8, where a Ni-reduced catalyst was used as the hydrogenation catalyst in the latter hydrogenation reaction of the two-stage process, no residual hydrogen was observed even after 60 days, whereas in Comparative Example 19, where a Ni-Mo-reduced catalyst was used as the hydrogenation catalyst, residual hydrogen was observed even after 17 days, which poses a problem of frequent catalyst replacement.

[0160] Analysis of the influence of dicyclic aromatic hydrocarbons in the selective hydrogenation product on the removal of residual hydrogen during the hydrogenation reaction Comparative Example 20 A hydrogenation experiment to remove residual hydrogen was carried out under the same conditions as in Example 2, except that a C8 aromatic hydrocarbon fraction having a bromine index (BI) of 65 and not containing 2-ring aromatic hydrocarbons was used, and the results are shown in Table 5 below.

[0161] [Table 5]

[0162] Referring to the table above, in Example 2, the reactants contained 2-ring aromatic hydrocarbons, which have a higher tendency to hydrogenate than 1-ring aromatic hydrocarbons, and the 2-ring aromatic hydrocarbons were preferentially hydrogenated (0.33 wt %, or about 30% of the 2-ring aromatic hydrocarbons in the reactants, were consumed).

[0163] As a result, the loss of C8 aromatics, which are monocyclic aromatic hydrocarbons, was at a significantly lower level than in Comparative Example 20.

[0164] Analysis of the effect of the amount of residual hydrogen in the selective hydrogenation product on the hydrogenation reaction Comparative Example 21 The experiment was carried out under the same conditions as in Example 3, except that hydrogen was injected so that the amount of residual hydrogen in the reactant (the product of Comparative Example 1) was 210 wtppm. The results are shown in Table 6 below.

[0165] [Table 6]

[0166] According to the table, when the residual hydrogen amount increased to 210 wtppm, the hydrogen partial pressure in the reactant (i.e., the product of Comparative Example 1) increased, and the loss of aromatics increased significantly to 0.151 wt%.

[0167] The above results are believed to be due to the fact that when the residual hydrogen content in the selective hydrogenation product exceeds a certain level, the difference in hydrogenation tendency due to the hydrocarbon structure also decreases due to the increased hydrogen partial pressure in the fraction. In particular, it is noteworthy that in Comparative Example 21 (residual hydrogen content: 210 wtppm), the increase in the loss of C8 aromatics is significantly greater than the increase in the conversion rate of 2-ring aromatics compared to Example 3 (residual hydrogen content: 120 wtppm).

[0168] Analysis of the effect of reaction pressure on hydrogenation reactions Examples 9 and 10 The reaction pressure was 5 kgf / cm 2 (approximately 4.9 bar) and 30 kgf / cm 2The hydrogenation reaction was carried out according to the same procedure as in Example 2, except that the pressure was changed to (about 29.4 bar). The results are shown in Table 7 below.

[0169] [Table 7]

[0170] According to the table, as the reaction pressure increases, the loss of C8 aromatics (single-ring aromatics) tends to increase. However, when the reaction pressure is 30 kgf / cm 2 Despite the large increase in the concentration of C8 aromatics, the loss of C8 aromatics was relatively low.

[0171] Example 11 Selective hydrogenation-hydrogenation process using two reactors connected in series Considering the experimental results of Examples 1 to 10 and Comparative Examples 12 to 19, a catalyst was loaded into each of two reactors connected in series (first reactor: selective hydrogenation reactor; second reactor: hydrogenation reactor), and a C aromatic fraction (BI: 748) was purified.

[0172] The first reactor was filled with 40 cc of catalyst as in Comparative Example 12 and then subjected to sulfidation treatment, while the second reactor was filled with 40 cc of catalyst as in Comparative Example 14 and then subjected to reduction treatment. Two reactors filled with individually pretreated catalysts were connected in series, and selective hydrogenation and hydrogenation reactions were carried out 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.

[0173] In order to confirm whether excess (residual) hydrogen in the fraction discharged from the first reactor is removed in the second reactor connected in series, an experiment was conducted while injecting hydrogen and aromatic fraction only into the first reactor, and the results are shown in Table 8 below.

[0174] Example 12 Selective hydrogenation-hydrogenation process using a reactor packed with two catalyst beds in a stepwise loading method The catalysts used in Comparative Example 12 and Comparative Example 14 were loaded into the same reactor. The catalyst used in Comparative Example 12 (40 cc; selective hydrogenation catalyst) was placed in the upper part of the reactor, and the catalyst used in Comparative Example 14 (40 cc; hydrogenation catalyst) was placed in the lower part of the reactor. Selective hydrogenation and hydrogenation reactions were carried out under the same conditions as in Comparative Example 12, and the results are shown in Table 8 below.

[0175] [Table 8]

[0176] According to the table, no differences were observed in the reduction of bromine index, removal of residual hydrogen, loss of C8 aromatics, etc. depending on the type of reactor.

[0177] As described above, when a selective hydrogenation reaction is performed to remove unsaturated hydrocarbons contained in an aromatic hydrocarbon-containing fraction, particularly a C aromatic hydrocarbon fraction, residual hydrogen in the product can be removed by adjusting the reaction conditions (temperature and pressure) based on the different hydrogenation tendencies of the hydrocarbons (i.e., olefins, bicyclic aromatic hydrocarbons, and monocyclic aromatic hydrocarbons) present in the product, and further adjusting the content of bicyclic aromatic hydrocarbons. This allows for effective removal of residual hydrogen while minimizing loss of monocyclic aromatic hydrocarbons (particularly C aromatics) in the selective hydrogenation product.

[0178] Simple variations or modifications of the present invention are readily available to those skilled in the art, and all such variations and modifications can be considered to be within the scope of the present invention.

Claims

1. a) conducting a selective hydrogenation reaction on an aromatic hydrocarbon-containing feedstock having a bromine index of at least 30 in the presence of a selective hydrogenation catalyst and in the presence of hydrogen to form a first aromatic hydrocarbon-containing product having a reduced bromine index and a content of unsaturated hydrocarbons and containing up to 200 wtppm of residual hydrogen; and b) performing a hydrogenation reaction on the first aromatic hydrocarbon-containing product with the residual hydrogen in the presence of a hydrogenation catalyst to form a second aromatic hydrocarbon-containing product having reduced residual hydrogen relative to the first aromatic hydrocarbon-containing product; Including, wherein the first aromatic hydrocarbon-containing product exhibits a Bromine Index that is reduced by at least 20% compared to the aromatic hydrocarbon-containing feedstock, and wherein the first aromatic hydrocarbon-containing product contains (i) unsaturated hydrocarbons, and (ii) two-ring aromatic hydrocarbons.

2. 10. The process of claim 1, wherein the content of 2-ring aromatic hydrocarbons in the first aromatic hydrocarbon-containing product is at least 0.3 wt.%.

3. 3. The process according to claim 2, characterized in that, if the content of 2-ring aromatic hydrocarbons in the first aromatic hydrocarbon-containing product has not reached at least 0.3 wt%, 2-ring aromatic hydrocarbons are added to the first aromatic hydrocarbon-containing product, and the hydrogenation reaction of step b) is carried out.

4. 2. The process according to claim 1, wherein the bicyclic aromatic hydrocarbon is at least one selected from the group consisting of naphthalene, indene, and derivatives thereof.

5. 2. The process of claim 1, wherein the loss of total aromatics in the first aromatic hydrocarbon-containing product is less than 0.45 wt. %, based on the aromatic hydrocarbon-containing feedstock, and the loss of one-ring aromatics in the second aromatic hydrocarbon-containing product is less than 0.15 wt. %, based on the first aromatic hydrocarbon-containing product.

6. 2. The process of claim 1, wherein steps a) and b) are carried out in a first reactor and a second reactor, respectively, and wherein the first reactor and the second reactor are connected in series.

7. The process according to claim 1, wherein steps a) and b) are carried out in the presence of a first catalyst layer and a second catalyst layer, respectively, packed in a single reactor in a stepwise loading manner, and wherein the first catalyst layer and the second catalyst layer are arranged in this order based on the flow direction of the aromatic hydrocarbon-containing feedstock.

8. 2. The process according to claim 1, characterized in that the hydrogenation step of step b) is carried out under reaction conditions adjusted in the temperature range above 55° C. and below about 255° C. and in the pressure range from 3 bar to 60 bar.

9. The selective hydrogenation step of step a) is carried out at a temperature controlled in the range of 130°C to 210°C; 9. The process according to claim 8, wherein the hydrogenation step of step b) is carried out at a temperature controlled in the range of 80°C to 130°C.

10. 2. The process of claim 1, wherein the hydrogenation catalyst in step b) comprises at least one active metal selected from nickel and platinum group metals and an inorganic oxide support.

11. 11. The process of claim 10, wherein the active metal in the hydrogenation catalyst in step b) is at least one selected from the group consisting of nickel, platinum, rhodium, and ruthenium.

12. 11. The process of claim 10, wherein the hydrogenation catalyst is in reduced form.

13. 11. The process according to claim 10, wherein the content of the active metal in the hydrogenation catalyst in step b) is in the range of 0.1 wt % to 40 wt % on an elemental basis.

14. 10. The process of claim 1, wherein the aromatic hydrocarbon-containing feedstock comprises C8+ aromatic hydrocarbons.

15. 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 para-xylene from the separated C8 aromatic hydrocarbon fraction; 10. The process of claim 1 further comprising:

16. 16. The process of claim 15, further comprising, prior to step c), treating the second aromatic hydrocarbon-containing product with a solid acid.

17. 16. The process according to claim 15, further comprising the step of: e) isomerizing the remaining C8 aromatic hydrocarbon fraction not recovered as para-xylene to form a C8 aromatic hydrocarbon fraction containing an increased content of para-xylene, and then recycling it to step c).

18. 2. The process of claim 1, wherein the content of unsaturated hydrocarbons in the first aromatic hydrocarbon-containing product is up to 2 wt. %.

19. 10. The process of claim 1, wherein the content of hydrogen in the second aromatic hydrocarbon-containing product is less than 6 wtppm.

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