Methods and systems for increasing the added value of low-carbon alkanes in raffinate oil

Abstract

This invention relates to the field of petrochemical technology, specifically to a method and system for increasing the added value of low-carbon alkanes in raffinate oil. The method includes: contacting the feedstock to be treated with benzene and hydrogen under alkylation reaction conditions to carry out an alkylation reaction; wherein the feedstock to be treated is raffinate oil and / or hydrogenated raffinate oil, and the bromine index of the feedstock to be treated is ≤500 mgBr / 100g; the weight ratio of benzene to the feedstock to be treated is 1-9:1. This invention can convert raffinate oil into toluene and xylene, greatly increasing its added value, and the selectivity for toluene and xylene is high, and it can also produce high-quality olefin cracking feedstocks such as ethane and propane as byproducts; this method has the characteristics of simple process flow and high product value enhancement, successfully solving the problem of disposal of low-octane raffinate oil, and resulting in significant direct economic benefits.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, and specifically to a method and system for increasing the added value of low-carbon alkanes in raffinate. Background Technology

[0002] Alkylbenzenes have broad application prospects in the chemical industry, with toluene and xylene being important raw materials in organic chemicals. With rapid economic development, the market demand for toluene and xylene is increasing, but traditional production technologies are increasingly unable to meet current needs. Therefore, to satisfy the current market demand for toluene and xylene, it is urgent to develop new production processes.

[0003] Alkylation of low-carbon alkanes with benzene is one of the effective ways to rationally utilize resources for the production of aromatics. In recent years, more and more researchers have become interested in the direct conversion of low-carbon alkanes and benzene into light aromatics. For example, the literature Journal of Molecular Catalysis A Chemical, 2008, 279(1):128-132 reported the production of ethylbenzene from benzene and ethane under the catalysis of PtH-MFI catalyst, which has high selectivity and stability. The literature ACS Catalysis, 2015, 5(9):5512-5518 reported the production of cumene from benzene and propane under the action of a bifunctional catalyst. CN106582792A discloses a catalyst for the alkylation reaction of benzene and ethane, which mainly solves the problem of low conversion rate of benzene and ethane in the alkylation reaction between benzene and ethane using molecular sieve-supported Pt catalyst. Therefore, the rational utilization of low-carbon alkanes to produce high-value-added aromatics has very considerable economic benefits.

[0004] Rag oil is a byproduct of catalytic reforming for the production of aromatics and high-octane gasoline. It contains a large amount of alkanes and is currently mainly used in the production of solvent oils, with low added value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies in which the added value of low-carbon alkanes in raffinate oil is low, and to provide a method and system for improving the added value of low-carbon alkanes in raffinate oil. This method realizes the conversion of raffinate oil into high-value-added toluene and xylene, and the toluene and xylene have high selectivity.

[0006] The inventors of this invention discovered that directly reacting raffinate oil to generate toluene and xylene would significantly increase its added value and generate substantial direct economic benefits; however, no such reports have been found in the prior art. Further research revealed that raffinate oil contains a large amount of C5-C7 alkanes and some unsaturated hydrocarbons. Excessive unsaturated hydrocarbon content can lead to catalyst poisoning, which is detrimental to the long-cycle alkylation reaction of C5-C7 alkanes with benzene. Further research resulted in the method of this invention, which improves benzene conversion and the selectivity of alkylbenzenes (mainly toluene and xylene) by partially saturating the raffinate oil before alkylation with benzene and hydrogen. The introduced hydrogen can hydrogenate the unsaturated hydrocarbons present in the alkylation reaction, thus avoiding the adverse effects of polymerization or condensation of unsaturated hydrocarbons (including unsaturated hydrocarbons in the raffinate oil and unsaturated hydrocarbons generated by side reactions such as hydrogen transfer that may occur during the alkylation reaction) leading to carbon deposits.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for increasing the added value of low-carbon alkanes in raffinate oil, the method comprising: contacting the feedstock to be treated with benzene and hydrogen under alkylation reaction conditions to carry out an alkylation reaction; wherein the feedstock to be treated is raffinate oil and / or hydrogenated raffinate oil, the bromine index of the feedstock to be treated is ≤500mgBr / 100g; and the weight ratio of benzene to the feedstock to be treated is 1-9:1.

[0008] Preferably, the volume ratio of hydrogen to the raw material to be treated in the alkylation reaction is 500-1000:1.

[0009] Preferably, the weight ratio of benzene to the raw material to be treated is 2-9:1.

[0010] Preferably, the alkylation reaction is carried out in the presence of an alkylation catalyst, wherein the silicon-to-aluminum molar ratio of the alkylation catalyst is 20-70.

[0011] A second aspect of the present invention provides a system for increasing the added value of low-carbon alkanes in raffinate oil. The system includes: a raffinate oil supply unit, a benzene supply unit, a hydrogen supply unit, and an alkylation reactor, wherein the raffinate oil supply unit, the benzene supply unit, and the hydrogen supply unit are respectively connected to the alkylation reactor.

[0012] The system may also optionally include a hydrorefining reactor disposed between the raffinate supply unit and the alkylation reactor.

[0013] Through the above technical solution, the present invention can convert raffinate into toluene and xylene, greatly increasing its added value. Moreover, the selectivity of toluene and xylene is high, and it can produce high-quality olefin cracking feedstock of at least one of ethane and propane as by-products. The method has the characteristics of simple process flow and high product value enhancement, and successfully solves the problem of disposal of low octane raffinate, resulting in significant direct economic benefits. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the system provided by the present invention.

[0015] Explanation of reference numerals in the attached figures

[0016] 1- Hydrogenation refining reactor; 2- Alkylation reactor; 3- Gas-liquid separator

[0017] 4-Benzene fractionation tower; 5-Toluene fractionation tower; 6-Xylene fractionation tower

[0018] 7-Residual oil supply unit; 8-Benzene supply unit; 9-Hydrogen supply unit Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] The first aspect of this invention provides a method for increasing the added value of low-carbon alkanes in raffinate oil. The method includes: contacting the feedstock to be treated with benzene and hydrogen under alkylation reaction conditions to carry out an alkylation reaction; wherein the feedstock to be treated is raffinate oil and / or hydrogenated raffinate oil, the bromine index of the feedstock to be treated is ≤500mgBr / 100g; and the weight ratio of benzene to the feedstock to be treated is 1-9:1.

[0021] In the above method, this invention specifically introduces hydrogen gas to react with the raw material and benzene in an alkylation reaction. This hydrogenation saturates the unsaturated hydrocarbons generated during the alkylation reaction due to side reactions such as hydrogen transfer, preventing excessive amounts of unsaturated hydrocarbons from hindering the alkylation reaction. Simultaneously, it improves the benzene conversion rate and the selectivity of alkylbenzenes (mainly toluene and xylene; the same applies to alkylbenzenes below). Existing alkylation reactions of benzene and pure alkanes (usually ethane or propane) typically involve adjusting the catalyst to control the generation of unsaturated hydrocarbons or improve the benzene conversion rate and alkylbenzene selectivity, which suffers from low single-pass conversion rates. The method provided by this invention achieves relatively good results even when using conventional alkylation catalysts (which are less expensive).

[0022] In this invention, the term "raffinate oil" has the conventional meaning in the art and will not be elaborated further here. Preferably, the raffinate oil is a non-aromatic component produced as a byproduct in the production of aromatics through catalytic reforming.

[0023] It should be noted that the term "non-aromatic" in this invention does not mean that the component contains absolutely no aromatics, but rather that it contains virtually no aromatics. When the raffinate contains trace amounts (less than 1% by weight) of aromatics, it can be referred to as a non-aromatic component.

[0024] The raffinate oil mainly contains alkanes and unsaturated hydrocarbons, including but not limited to n-alkanes, isoalkanes, and cycloalkanes, and unsaturated hydrocarbons such as at least one of alkenes and aromatics. Preferably, the raffinate oil contains 95-98% by weight of C5-C9 alkanes and 0.5-5% by weight of C6-C9 unsaturated hydrocarbons. This preferred raffinate oil is more suitable for the present invention, resulting in higher benzene conversion and higher selectivity for alkylbenzenes.

[0025] The term "C5-C9 alkanes" refers to alkanes with a total number of carbon atoms of 5-9, including straight-chain alkanes, branched alkanes, or cycloalkanes. Specifically, they can be straight-chain alkanes, branched alkanes, or cycloalkanes with a total number of carbon atoms of 5, 6, 7, 8, or 9, such as n-pentane, isopentane, cyclopentane, n-hexane, n-heptane, methylcyclohexane, ethylcyclopentane, etc.

[0026] The term "C6-C9 unsaturated hydrocarbons" refers to unsaturated hydrocarbons with a total number of carbon atoms of 6-9, including alkenes or aromatics. Specifically, they can be alkenes or aromatics with a total number of carbon atoms of 6, 7, 8, or 9, such as hexene, heptene, methylhexene, toluene, xylene, propylbenzene, etc.

[0027] More preferably, the raffinate contains 90-95% by weight of C5-C7 alkanes. The C5-C7 alkanes may be, for example, n-pentane, isopentane, n-hexane, n-heptane, etc.

[0028] According to the present invention, preferably, the bromine index of the raw material to be treated is ≤200 mgBr / 100g, more preferably 100-200 mgBr / 100g. Further research by the inventors has revealed that the raw material to be treated, meeting the bromine index requirements of the preferred embodiment of the present invention, can promote the alkylation reaction, thereby improving the benzene conversion rate and alkylbenzene selectivity.

[0029] In this invention, it is understood that when the composition of the raffinate does not meet the required bromine index, the raffinate can be hydrogenated to meet the required bromine index after hydrogenation saturation; when the content of unsaturated hydrocarbons in the composition of the raffinate is low and meets the required bromine index, hydrogenation can be omitted, and the raffinate can be directly used as the raw material to be treated for subsequent alkylation reaction.

[0030] According to the present invention, preferably, the raw material to be treated is hydrogenated raffinate oil, and the hydrogenation conditions are such that the raffinate oil meets the bromine index after hydrogenation. Preferably, the hydrogenation is carried out in the presence of hydrogen gas, and the volume ratio of the hydrogen gas (understood to be understood as the hydrogen gas in the hydrogenation process) to the raffinate oil (hereinafter referred to as the hydrogen-oil ratio) is 100-500:1, more preferably 150-200:1.

[0031] According to the present invention, preferably, the hydrogenation is carried out in the presence of a hydrogenation catalyst, and the hydrogenation conditions include: the mass hourly space velocity of the raffinate is 1-8 h⁻¹. -1 More preferably 1-5h -1 The temperature is 150-200℃, more preferably 165-180℃.

[0032] In this invention, preferably, the hydrogenation conditions further include a pressure of 1-5 MPa, more preferably 3-5 MPa.

[0033] The present invention allows for a wide range of hydrogenation catalysts, as long as they can catalyze hydrogenation to achieve the desired bromine index after hydrogenation saturation of the raffinate. Preferably, the hydrogenation catalyst comprises a support and a metallic active component supported on the support. The metallic active component is selected from at least one element from Group VIII, Group VIB, Group IIB, and Group IIA. Based on the total amount of catalyst, the content of the metallic active component is 0.1-10% by weight, and the content of the support is 90-99% by weight.

[0034] Preferably, the carrier is selected from at least one of alumina, titanium dioxide, zirconium oxide and silicon dioxide; more preferably, it is alumina.

[0035] Preferably, the active metal component is selected from at least one of Group VIII, Group VIB, Group IIB, and Group IIA metals. More preferably, the active metal component is selected from at least one of Ni, Mo, W, Zn, and Mg.

[0036] The hydrogenation catalyst can be commercially available, such as RN-1 catalyst, purchased from Sinopec Catalyst Company; it can also be prepared by existing methods, which will not be described in detail here.

[0037] According to the present invention, the alkylation reaction can directionally convert more alkanes (preferably C5-C7 alkanes) in the feedstock into alkylbenzenes (mainly toluene and xylene). Preferably, the weight ratio of benzene to the feedstock is 2-9:1, more preferably 4-9:1.

[0038] In a preferred embodiment of the present invention, the volume ratio of hydrogen to the raw material to be treated in the alkylation reaction (hereinafter referred to as the hydrogen-oil volume ratio) is 500-2000:1, preferably 1000-2000:1. Under this preferred embodiment, using an appropriate amount of hydrogen can better hydrogenate the unsaturated hydrocarbons present in the alkylation reaction, thereby avoiding the adverse effects of unsaturated hydrocarbons (including unsaturated hydrocarbons in the raffinate oil and unsaturated hydrocarbons generated by side reactions such as hydrogen transfer that may occur during the alkylation reaction) potentially polymerizing or condensing to form carbon deposits, further improving the benzene conversion rate and the selectivity of alkylbenzenes (mainly toluene and xylene).

[0039] In this invention, preferably, the alkylation reaction is carried out in the presence of an alkylation catalyst.

[0040] To further promote the alkylation reaction, preferably, the alkylation catalyst is a molecular sieve catalyst. Preferably, the molecular sieve catalyst is selected from at least one of ZSM-5 molecular sieves (with or without acid modification), MCM-22 molecular sieves, MOR-structured molecular sieves, and Beta molecular sieves. More preferably, the alkylation catalyst is an acid-modified ZSM-5 molecular sieve.

[0041] In this invention, the acid-modified molecular sieve is a hydrogen-type molecular sieve, and the acid modification method is a method existing in the art. The acid may include at least one of citric acid, phosphoric acid, hydrochloric acid, and oxalic acid. Those skilled in the art can choose according to their needs, and will not be elaborated here.

[0042] According to a preferred embodiment of the present invention, the silicon-to-aluminum molar ratio of the alkylation catalyst is 20-70, more preferably 20-50, and even more preferably 20-40. This preferred embodiment is more conducive to the yield and selectivity of the products toluene and xylene.

[0043] In this invention, the alkylation catalyst may or may not contain a metal active component (the metal active component may be at least one of Group VIII, Group IIIA, Group IIB, and Group VIB elements, more preferably at least one of Ga, Pt, Zn, and Mo), as long as it facilitates the alkylation reaction between the raw material and benzene. The metal active component in the alkylation catalyst may be supported on a molecular sieve or on alumina; this invention has no limitations on this.

[0044] In this invention, the preparation method of the alkylation catalyst can be selected from a wide range, as long as it is conducive to the alkylation reaction. In a specific preferred embodiment, the alkylation catalyst is prepared by the following method: molding the catalyst precursor and then calcining it; the molding can be binder-free molding or binder molding, more preferably binder molding. More preferably, the preparation method of the alkylation catalyst further includes: introducing a metal active component by impregnation. The impregnation method can be carried out according to any impregnation method existing in the art, and this invention is not limited in this regard. The introduction of the metal active component can be carried out after the preparation of the catalyst precursor, specifically, for example, before the molding and calcination, or after the molding and calcination; the introduction of the metal active component can also be carried out during the preparation of the catalyst precursor, specifically, for example, the metal active component is first loaded on alumina and then the catalyst precursor is prepared, and those skilled in the art can freely choose according to their needs.

[0045] In this invention, the catalyst precursor can be a molecular sieve precursor (e.g., sodium-type ZSM-5 molecular sieve). This invention does not restrict the source of the catalyst precursor, as long as the above-mentioned alkylation catalyst can be obtained.

[0046] This invention does not impose any restrictions on the molding method of the adhesive, as long as it can achieve a good conversion effect, such as existing standard molding methods, which will not be described in detail here.

[0047] The present invention does not limit the binder, as long as it can facilitate molding; preferably, the main components of the binder may include at least one of molecular sieve, boehmite, guar gum powder and nitric acid.

[0048] In this invention, the roasting conditions can be selected from a wide range and can be conventional roasting conditions in the art. Preferably, the roasting conditions include: a roasting temperature of 500-550℃ and a roasting time of 2-5h.

[0049] According to the present invention, preferably, the alkylation reaction conditions include: the mass hourly space velocity (HHSV) of the feedstock to be treated is 0.7-4 h⁻¹. -1 More preferably 2-4h -1 .

[0050] Preferably, the alkylation reaction conditions further include: the alkylation reaction temperature is 450-560℃, more preferably 480-520℃, and even more preferably 480-510℃.

[0051] Preferably, the pressure of the alkylation reaction is 1-7 MPa, more preferably 3-5 MPa.

[0052] To further optimize the alkylation reaction and direct the conversion to alkylbenzenes (mainly toluene and xylene), such as... Figure 1 As shown, the method for increasing the added value of low-carbon alkanes in raffinate oil includes: (1) selectively hydrogenating the raffinate oil under hydrogenation conditions to obtain a feedstock to be treated, wherein the bromine index of the feedstock to be treated is ≤500mgBr / 100g; (2) alkylating the feedstock to be treated with benzene and hydrogen under alkylation reaction conditions, wherein the weight ratio of benzene to the feedstock to be treated is 1-9:1, the volume ratio of hydrogen to the feedstock to be treated is 500-2000:1, the alkylation reaction is carried out in the presence of an alkylation catalyst, wherein the silicon-aluminum molar ratio of the alkylation catalyst is 20-70, and the mass hourly space velocity of the feedstock to be treated is 0.7-4h. -1 Under this preferred scheme, the benzene conversion rate and the selectivity of alkylbenzenes (mainly toluene and xylene) are optimal, with the benzene conversion rate above 30%, the toluene selectivity above 50%, and the xylene selectivity above 6%.

[0053] According to a preferred embodiment of the present invention, such as Figure 1 As shown, the method further includes: optionally cooling the aromatic product obtained from the alkylation reaction, followed by gas-liquid separation to obtain a gaseous material (e.g., Figure 1 The dry gas and liquid phase materials are shown. In this invention, the cooling is preferably performed to below 25°C.

[0054] According to a preferred embodiment of the present invention, such as Figure 1 As shown, the method further includes: fractionating the liquid phase material to obtain benzene, toluene and xylene.

[0055] The present invention does not limit the conditions for the fractionation, as long as the desired materials can be obtained. Preferably, the fractionation process includes: first, performing a first fractionation to obtain benzene, with a distillation range of 65-85℃; then performing a second fractionation to obtain toluene, with a distillation range of 85-105℃; and then performing a third fractionation to obtain xylene, with a distillation range of 105-145℃.

[0056] According to the present invention, preferably, the benzene obtained from the fractionation is recycled for the alkylation reaction. This preferred embodiment can improve the benzene conversion rate.

[0057] More preferably, the method further includes: subjecting the liquid phase material obtained from the fractionation (which can be understood as the liquid phase material obtained after separating xylene in the third fractionation) to further fractionation to obtain heavy aromatics and olefin cracking feedstock. The olefin cracking feedstock refers to a product generated in the alkylation reaction that is suitable as a feedstock for olefin production, such as at least one of ethane, propane, isobutane, and n-butane. The further fractionation process can be a method existing in the art and will not be described in detail here.

[0058] A second aspect of the present invention provides a system for increasing the added value of low-carbon alkanes in raffinate, such as... Figure 1 As shown, the system includes: a raffinate oil supply unit 7, a benzene supply unit 8, a hydrogen supply unit 9, and an alkylation reactor 2. The raffinate oil supply unit 7, the benzene supply unit 8, and the hydrogen supply unit 9 are respectively connected to the alkylation reactor 2.

[0059] The system also optionally includes a hydrorefining reactor 1, which is disposed between the raffinate supply unit 7 and the alkylation reactor 2.

[0060] It is understood that the raffinate supply unit 7 and the alkylation reactor 2 can be directly connected; alternatively, a hydrorefining reactor 1 can be provided, that is, the raffinate supply unit 7 and the alkylation reactor 2 are respectively connected to the hydrorefining reactor 1.

[0061] According to the system provided by the present invention, preferably, the system further includes a gas-liquid separator 3, which is connected to the alkylation reactor 2. The specific device of the gas-liquid separator 3 can be freely selected by those skilled in the art; for example, it can be a high-precision separator.

[0062] According to the system provided by the present invention, preferably, the system further includes a benzene fractionation tower 4, the inlet of which is connected to the liquid phase material outlet of the gas-liquid separator 3; used to perform a first fractionation on the liquid phase material separated by the gas-liquid separator 3 to obtain benzene.

[0063] More preferably, the benzene material outlet at the top of the benzene fractionation tower 4 is connected to the alkylation reactor 2, for recycling the benzene obtained from the fractionation of the benzene fractionation tower 4 for the alkylation reaction.

[0064] According to the system provided by the present invention, preferably, the system further includes a toluene fractionation tower 5, the inlet of which is connected to the bottom outlet of the benzene fractionation tower 4; used to perform a second fractionation on the liquid phase material obtained from the bottom outlet of the benzene fractionation tower 4 to obtain toluene.

[0065] According to the system provided by the present invention, preferably, the system further includes a xylene fractionation tower 6, the inlet of which is connected to the bottom outlet of the toluene fractionation tower 5; used to perform a third fractionation on the liquid phase material obtained from the bottom outlet of the toluene fractionation tower 5 to obtain xylene.

[0066] Those skilled in the art can further fractionate the liquid material separated by the xylene fractionation tower 6 to obtain heavy aromatics and olefin cracking feed, according to actual needs. The fractionation process can be a method existing in the art, which will not be described in detail here.

[0067] The system provided by the present invention can realize the method of the first aspect mentioned above, converting raffinate into alkylbenzene (mainly toluene and xylene), which increases the added value of low-carbon alkanes in raffinate, and the benzene conversion rate and the selectivity of alkylbenzene (mainly toluene and xylene) are high, even better than the selectivity of alkylbenzene (mainly toluene and xylene) in the alkylation reaction of pure alkanes and benzene.

[0068] The present invention will be described in detail below through embodiments.

[0069] Example 1

[0070] (1) Adopting as follows Figure 1 The system shown involves contacting raffinate (composition as shown in Table 1) with a hydrotreating catalyst (RN-1 catalyst, W-Ni / alumina, purchased from Sinopec Catalyst Co., Ltd.) in hydrotreating reactor 1 to remove unsaturated hydrocarbons, yielding hydrotreated raffinate with a bromine index of 123 mgBr / 100 g. The hydrotreating conditions are: a hydrogen-to-oil volume ratio of 150:1 and a mass hourly space velocity (WHSV) of 5 h⁻¹ for the raffinate. -1 The temperature is 165℃ and the pressure is 3MPa.

[0071] (2) Preparation of alkylation catalyst: Sodium-type ZSM-5 (SiO2 / Al2O3 molar ratio = 25, purchased from Sinopec Catalyst Co., Ltd.) molecular sieve was exchanged four times with 1M ammonium nitrate and then calcined in a muffle furnace at 550℃ for 2 hours to obtain HZSM-5. Then, boehmite was used as a binder for molding, and then calcined in a muffle furnace at 550℃ for 4 hours to obtain the catalyst, which was named ARM-1.

[0072] Then, the raffinate oil after hydrogenation in step (1) is mixed with hydrogen and pure benzene in alkylation reactor 2, and then contacted with ARM-1 catalyst for alkylation reaction. The alkylation reaction conditions are: hydrogen-to-oil volume ratio 1000:1, and mass hourly space velocity (WHSV) of the raffinate oil after hydrogenation is 2.0 h⁻¹. -1 The mass ratio of benzene to hydrogenated raffinate was 4:1, the reaction temperature was 500℃, and the pressure was 3.0MPa.

[0073] The alkylation reaction product, after cooling, enters a high-precision separator (i.e., gas-liquid separator 3) for gas-liquid separation, separating dry gas. The bottom material enters a benzene fractionation tower 4 for first fractionation (distillation range 65-85℃), separating benzene, which is then returned to the alkylation reaction. The bottom material from benzene fractionation tower 4 then enters a toluene fractionation tower 5 (distillation conditions 85-105℃), separating toluene. Finally, the bottom material from toluene fractionation tower 5 enters a xylene fractionation tower 6 (distillation range 105-145℃), separating xylene.

[0074] The above process parameters are listed in Table 2.

[0075] The product content was determined by gas chromatography, and the benzene conversion rate and product (toluene and xylene) selectivity were calculated, as shown in Table 3. The product selectivity was calculated as: target product yield (toluene or xylene) / benzene conversion rate * 100%, where xylene refers to a mixture of o-xylene, p-xylene, and m-xylene.

[0076] Example 2

[0077] The procedure was carried out according to Example 1, except that the molar ratio of SiO2 / Al2O3 in sodium-type ZSM-5 was 38 (purchased from Sinopec Catalyst Co., Ltd.), and the catalyst was named ARM-2.

[0078] Example 3

[0079] The procedure was carried out according to Example 1, except that the molar ratio of SiO2 / Al2O3 in the sodium-type ZSM-5 was 50 (purchased from Sinopec Catalyst Co., Ltd.), and the catalyst was named ARM-3.

[0080] Example 4

[0081] The method of Example 1 was followed, except that the alkylation reaction was carried out at a temperature of 520°C.

[0082] Example 5

[0083] The method of Example 1 was followed, except that the alkylation reaction was carried out at a temperature of 540°C.

[0084] Example 6

[0085] The method of Example 1 was followed, except that the alkylation reaction was carried out at a temperature of 560°C.

[0086] Example 7

[0087] The procedure was carried out according to Example 1, except that the type of alkylation catalyst precursor was different. Specifically, sodium ZSM-5 (same as in Example 1) and Beta molecular sieve (SiO2 / Al2O3 molar ratio = 70, purchased from Sinopec Catalyst Co., Ltd.) were used instead of sodium ZSM-5 in Example 1, with a mass ratio of 2:1. Other aspects were the same as in Example 1.

[0088] Example 8

[0089] The procedure was carried out according to Example 1, except that the weight ratio of benzene to hydrogenated raffinate was 5:1.

[0090] Example 9

[0091] The method was carried out according to Example 1, except that the volume ratio of hydrogen to hydrogenated raffinate in the alkylation reaction was 2000:1.

[0092] Example 10

[0093] The method was carried out according to Example 1, except that the hydrogenation conditions were different. Specifically, the hydrogenation conditions were such that the bromine index of the hydrogenated raffinate was 50 mgBr / 100g.

[0094] Examples 11-12

[0095] The method of Example 1 is followed, except that the process parameters are different, and the process parameters shown in Table 2 are used.

[0096] Example 13

[0097] The method of Example 1 was followed, except that the weight ratio of benzene to the raw material to be treated was 9:1.

[0098] Example 14

[0099] The procedure was carried out according to Example 1, except that the raffinate was not hydrogenated, and the bromine index of the raffinate was 475 mgBr / 100g. The results are shown in Table 3.

[0100] Comparative Example 1

[0101] The procedure was carried out according to Example 1, except that hydrogen was not introduced into the alkylation reaction; otherwise, it was the same as in Example 1. The results are shown in Table 3.

[0102] Table 1

[0103] carbon number n-Alkanes Isoalkanes Olefins Cycloalkanes Aromatics total 5 0.22 0.02 / 4.68 / 4.92 6 11.09 14.75 / 14.08 0.04 39.96 7 2.82 32.76 / 9.90 0.01 45.49 8 / 0.07 / 7.15 0.25 7.47 9 / / / 1.84 0.32 2.16 total 14.13 47.60 0.00 37.65 0.62 100.00

[0104] Table 2

[0105]

[0106]

[0107] Table 3

[0108] Example Benzene conversion rate, % Toluene selectivity, % Xylene selectivity, % Example 1 40.57 60.97 10.56 Example 2 38.13 63.56 13.31 Example 3 33.42 59.76 10.9 Example 4 42.12 57.14 9.5 Example 5 42.34 57.34 9.0 Example 6 43.68 56.47 8.7 Example 7 36.12 52.10 7.5 Example 8 30.21 55.30 8.4 Example 9 40.47 61.15 11.21 Example 10 40.12 45.12 6.7 Example 11 33.13 58.13 9.1 Example 12 34.45 58.99 9.7 Example 13 30.12 65.12 14.12 Example 14 32.14 41.2 5.6 Comparative Example 1 28.12 35.12 5.1

[0109] As can be seen from Tables 1-3, the embodiments employing the specific method of the present invention exhibit higher benzene conversion rates and higher selectivity for toluene and xylene, resulting in higher added value. Comparative examples and Comparative Example 1 show that a hydrogen atmosphere is more conducive to the reaction producing toluene and xylene.

[0110] Comparing Examples 1 and 5-6, and Example 8, it is evident that the preferred alkylation reaction conditions of this invention, while maintaining a high benzene conversion rate, further improve the selectivity for toluene and xylene. Comparing Examples 1 and 7, it is evident that the preferred alkylation catalyst of this invention results in a higher benzene conversion rate and higher selectivity for toluene and xylene. Comparing Examples 1 and 10, it is evident that the preferred hydrogenation scheme satisfying a specific bromine index exhibits a superior benzene conversion rate and higher selectivity for toluene and xylene. Comparing Examples 1 and 14, it is evident that the preferred hydrogenation scheme satisfying a specific bromine index of this invention, while maintaining a high benzene conversion rate, exhibits even higher selectivity for toluene and xylene.

[0111] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for increasing the added value of low-carbon alkanes in raffinate, the method comprising: Under alkylation reaction conditions, the feedstock to be treated is contacted with benzene and hydrogen to carry out an alkylation reaction; wherein the feedstock to be treated is raffinate oil and / or hydrogenated raffinate oil, and the bromine index of the feedstock to be treated is ≤500mgBr / 100g; the weight ratio of benzene to the feedstock to be treated is 1-9:1; The raffinate contains 95-98% by weight of C5-C9 alkanes and 0.5-5% by weight of C5-C9 unsaturated hydrocarbons; The alkylation reaction is carried out in the presence of an alkylation catalyst, which is a molecular sieve catalyst. The method further includes: cooling the aromatic product obtained from the alkylation reaction, and then performing gas-liquid separation to obtain gaseous and liquid phase materials; The method further includes fractionating the liquid phase material to obtain benzene, toluene, and xylene.

2. The method according to claim 1, wherein, The raffinate is a non-aromatic component produced as a byproduct of aromatic hydrocarbon production via catalytic reforming.

3. The method according to claim 1 or 2, wherein, The raffinate contains 90-95% by weight of C5-C7 alkanes.

4. The method according to claim 1 or 2, wherein, The bromine index of the raw material to be treated is ≤200mgBr / 100g.

5. The method according to claim 1 or 2, wherein, The hydrogenation is carried out in the presence of hydrogen gas, and the volume ratio of the hydrogen gas to the raffinate oil is 100-500:

1.

6. The method according to claim 5, wherein, The volume ratio of hydrogen to raffinate is 150-200:

1.

7. The method according to claim 1 or 2, wherein, The hydrogenation is carried out in the presence of a hydrogenation catalyst, and the hydrogenation conditions include: The mass hourly space velocity of the raffinate is 1-8 h⁻¹. -1 The temperature is 150-200℃; And / or, the pressure is 1-5 MPa.

8. The method according to claim 7, wherein, The hydrogenation catalyst comprises a support and a metal active component supported on the support. The metal active component is selected from at least one of Group VIII, Group VIB, Group IIB and Group IIA elements. Based on the total amount of the catalyst, the content of the metal active component is 0.1-10% by weight and the content of the support is 90-99% by weight.

9. The method according to claim 8, wherein, The active metal component is selected from at least one of Ni, Mo, W, Zn and Mg.

10. The method according to claim 8, wherein, The carrier is selected from at least one of alumina, titanium dioxide, zirconium oxide, and silicon dioxide.

11. The method according to claim 7, wherein, The hydrogenation conditions include: The mass hourly space velocity of the raffinate is 1-8 h⁻¹. -1 The temperature is 165-180℃.

12. The method according to claim 7, wherein, The pressure is 3-5 MPa.

13. The method according to claim 1 or 2, wherein, The weight ratio of benzene to the raw material to be treated is 2-9:1; And / or, the volume ratio of hydrogen to the raw material to be treated in the alkylation reaction is 500-2000:

1.

14. The method according to claim 13, wherein, The weight ratio of benzene to the raw material to be treated is 4-9:

1.

15. The method according to claim 13, wherein, In the alkylation reaction, the volume ratio of hydrogen to the raw material to be treated is 1000-2000:

1.

16. The method according to claim 1 or 2, wherein, The molecular sieve catalyst is selected from at least one of ZSM-5 molecular sieve, MCM-22 molecular sieve, MOR structured molecular sieve and Beta molecular sieve, with or without acid modification. And / or, the silicon-to-aluminum molar ratio of the alkylation catalyst is 20-70.

17. The method according to claim 16, wherein, The molecular sieve catalyst is an acid-modified ZSM-5 molecular sieve.

18. The method according to claim 16, wherein, The silicon-aluminum molar ratio of the alkylation catalyst is 20-50.

19. The method according to claim 1 or 2, wherein, The alkylation reaction conditions include: the mass hourly space velocity (HHSV) of the feedstock to be treated is 0.7-4 h⁻¹. -1 ; And / or, the alkylation reaction is carried out at a pressure of 1-7 MPa.

20. The method according to claim 19, wherein, The alkylation reaction conditions include: the mass hourly space velocity (WHSV) of the feedstock is 2-4 h⁻¹. -1 .

21. The method according to claim 1 or 2, wherein, The alkylation reaction conditions also include: the alkylation reaction temperature is 450-560℃.

22. The method according to claim 21, wherein, The alkylation reaction conditions also include: the alkylation reaction temperature is 480-520℃.

23. The method according to claim 1 or 2, wherein, The pressure for the alkylation reaction is 3-5 MPa.

24. The method according to claim 1 or 2, wherein, The fractionation process includes: first, a first fractionation to obtain benzene, with a distillation range of 65-85℃; then, a second fractionation to obtain toluene, with a distillation range of 85-105℃; and then, a third fractionation to obtain xylene, with a distillation range of 105-145℃.

25. The method according to claim 24, wherein, The benzene obtained from the fractionation is recycled for use in the alkylation reaction.

26. A system applicable to the method for increasing the added value of low-carbon alkanes in raffinate as described in any one of claims 1-25, the system comprising: The system includes a raffinate supply unit, a benzene supply unit, a hydrogen supply unit, and an alkylation reactor, wherein the raffinate supply unit, the benzene supply unit, and the hydrogen supply unit are respectively connected to the alkylation reactor; The system may also optionally include a hydrorefining reactor disposed between the raffinate supply unit and the alkylation reactor; The system also includes a gas-liquid separator connected to the alkylation reactor; The system also includes a benzene fractionation tower, the inlet of which is connected to the liquid phase material outlet of the gas-liquid separator; The system also includes a toluene fractionation tower, the inlet of which is connected to the bottom outlet of the benzene fractionation tower; The system also includes a xylene fractionation tower, the inlet of which is connected to the bottom outlet of the toluene fractionation tower.

27. The system according to claim 26, wherein, The benzene product outlet at the top of the benzene fractionation tower is connected to the alkylation reactor.

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