CN114804995B - Series reaction process for preparing paraxylene by aromatic hydrocarbon alkylation - Google Patents

Series reaction process for preparing paraxylene by aromatic hydrocarbon alkylation Download PDF

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CN114804995B
CN114804995B CN202210555243.6A CN202210555243A CN114804995B CN 114804995 B CN114804995 B CN 114804995B CN 202210555243 A CN202210555243 A CN 202210555243A CN 114804995 B CN114804995 B CN 114804995B
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zsm
catalyst
reaction process
alkylation
molecular sieve
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CN114804995A (en
Inventor
侯章贵
李孝国
张安峰
王仕文
李永恒
郭新闻
韩国栋
徐仲龙
常洋
郜金平
徐冰峰
曹辉
张永坤
肖家旺
郭亮
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Dalian University of Technology
China National Offshore Oil Corp CNOOC
CNOOC Oil and Petrochemicals Co Ltd
CNOOC Research Institute of Refining and Petrochemicals Beijing Co Ltd
CNOOC Qingdao Heavy Oil Processing Engineering Technology Research Center Co Ltd
CNOOC Ningbo Daxie Petrochemical Co Ltd
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Dalian University of Technology
China National Offshore Oil Corp CNOOC
CNOOC Oil and Petrochemicals Co Ltd
CNOOC Research Institute of Refining and Petrochemicals Beijing Co Ltd
CNOOC Qingdao Heavy Oil Processing Engineering Technology Research Center Co Ltd
CNOOC Ningbo Daxie Petrochemical Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
    • C07C1/20—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon starting from organic compounds containing only oxygen atoms as heteroatoms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
    • B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
    • B01J29/44—Noble metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
    • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2529/00—Catalysts comprising molecular sieves
    • C07C2529/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites, pillared clays
    • C07C2529/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • C07C2529/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11
    • C07C2529/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11 containing iron group metals, noble metals or copper
    • C07C2529/44—Noble metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/584—Recycling of catalysts

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
  • Catalysts (AREA)

Abstract

The invention provides a series reaction process for preparing paraxylene by aromatic alkylation, which comprises the steps of coupling a modified metal/ZSM-5 catalyst with at least 3 sections of alkylation fixed bed reactors connected in series; the process adopts a modified ZSM-5 molecular sieve with high selectivity and high stability, loads metal with hydrogenation function on the molecular sieve, inhibits the conversion of reactants to carbon deposition precursors under the condition of hydrogen, thereby delaying the carbon deposition deactivation of the catalyst, simultaneously reduces the local concentration of methanol and the reaction temperature rise of a catalyst bed layer by matching with a multistage series fixed bed reaction process, inhibits side reactions such as deep alkylation of methanol to olefin, toluene and isomerization of para-xylene, obviously improves the yield of para-xylene and the service life of the catalyst, and can also realize the continuous production of the para-xylene by flexibly switching the material flow directions among different reactors.

Description

Series reaction process for preparing paraxylene by aromatic hydrocarbon alkylation
Technical Field
The invention belongs to the technical field of chemical raw material synthesis, and particularly relates to a series reaction process for preparing paraxylene by aromatic alkylation.
Background
Para-xylene (PX) is one of the basic organic raw materials of the petrochemical industry, mainly used for Preparing Terephthalic Acid (PTA), and further reacted with ethylene glycol (MEG) to produce polyethylene terephthalate (PET) by dehydration condensation, which can be used for producing polyester fibers and thus textile products.
At present, the production of paraxylene mainly depends on petroleum resources, and along with the increasing shortage of world petroleum resources, the traditional aromatic hydrocarbon production process taking naphtha as a route faces challenges, and the active development of non-petroleum routes to increase the yield of aromatic hydrocarbon is a necessary route for the development of aromatic hydrocarbon industry. The toluene and methanol alkylation process can convert the toluene with excess capacity in petrochemical industry and the methanol from coal chemical industry into paraxylene with one-step high selectivity, has short process flow and low separation energy consumption, and is one of the most promising and competitive new paraxylene production technologies at present. In view of this, many researchers have been working on developing new technologies for producing para-xylene by alkylation of toluene with methanol, and have desired to be able to synthesize para-xylene product continuously and with high selectivity, reduce separation energy consumption, and increase toluene and methanol utilization. However, since methanol is introduced into the shape selective catalytic reaction system, the methanol is easy to generate coking reaction under the alkylation reaction condition to cause the deactivation of the catalyst, and the problem is always a difficult problem for restricting the alkylation technology of toluene and methanol.
To improve the stability of the catalyst, the prior studies have been essentially conducted from two points of view, on the one hand, to develop a catalyst with more excellent performance and, on the other hand, to optimize the design of the reactor. CN105749961A discloses a high-selectivity, high-stability and low-energy-consumption synthetic para-xylene catalyst, which is prepared from a molecular sieve, a molding carrier and a modifier, wherein the molecular sieve is Fe-HZSM-5, the molding carrier is pseudo-boehmite and rare earth, and the active component of the modifier is SiO 2 MgO and B 2 O 3 Etc.; the selectivity of the para-xylene is above 98%, the selectivity of the xylene is above 95%, the toluene conversion rate is above 25%, and the reaction can be continuously carried out for 720 hours.
CN102701899a discloses an energy-saving and emission-reducing process for producing paraxylene by alkylation of toluene and methanol, which is divided into a reaction part and a separation part, wherein a plurality of fixed bed reactors are adopted in the flow, and the temperature rise of the reactors is controlled by direct chilling of methanol between reactor segments, so that the conversion rate of the methanol is increased; the heat recovery is increased by carrying out heat exchange on the materials at the outlet of the reactor and the raw materials in front of the heating furnace for a plurality of times, so that the consumption of low-grade refrigerant required by flash evaporation separation is reduced, and the heat power integration is realized; and finally, the paraxylene product is obtained through the coupling operation of rectification and melt crystallization, so that the production energy consumption is obviously reduced.
Defects and deficiencies of the prior art:
1. the conventional HZSM-5 molecular sieve can realize high paraxylene selectivity after being modified by modifying agents such as Si, P and the like, but has the advantages of reduced toluene conversion rate and poor stability due to the influence of diffusion limitation caused by reduced acid amount, and can not realize long-time operation due to deactivation of a catalyst caused by carbon deposition;
2. toluene and methanol in a conventional single-stage fixed bed reactor can only be fed once, the yield of paraxylene is low, side reactions are more, the load of toluene circulation is increased, the heat energy consumption is higher, and continuous regeneration cannot be realized after the catalyst is coked and deactivated. If a conventional fluidized bed reactor is adopted to regenerate the catalyst in real time, the construction cost of the reactor and the complexity of the reaction process are greatly increased, and extremely high requirements are put on the mechanical performance and structural stability of the catalyst.
In summary, how to provide a high-selectivity and high-stability molecular sieve catalyst and a high-efficiency supporting reaction device, so as to realize continuous and high-selectivity synthesis of paraxylene products, reduce separation energy consumption, and improve toluene and methanol utilization rate, is a current urgent problem.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention aims to provide a series reaction process for preparing paraxylene by alkylating aromatic hydrocarbon, which realizes effective management of carbon species distribution by preparing a modified metal/ZSM-5 catalyst with high selectivity and high stability and combining at least 3 sections of series-connected alkylation fixed bed reactors, thereby remarkably improving the stability of the catalyst while keeping higher paraxylene selectivity, and realizing continuous production of paraxylene by utilizing the characteristic that the multistage series-connected fixed bed reactors can flexibly switch material flow directions among different reactors.
To achieve the purpose, the invention adopts the following technical scheme:
the invention provides a series reaction process for preparing paraxylene by aromatic hydrocarbon alkylation, which comprises the step of coupling a modified metal/ZSM-5 catalyst with at least 3 sections of alkylation fixed bed reactors connected in series.
In the invention, aiming at the problems that the molecular sieve catalyst in the prior art has low activity, poor stability and difficult realization of continuous production while keeping high para-xylene selectivity, the invention selects the modified metal/ZSM-5 catalyst, and inhibits the conversion of reactants to carbon precursor under the hydrogen condition by loading the metal with hydrogenation function on the molecular sieve with shape selectivity, thereby delaying the carbon deposition deactivation of the catalyst; meanwhile, a multistage series fixed bed reaction process is adopted, and by reducing the local concentration of methanol and the reaction temperature rise of a catalyst bed layer, side reactions such as deep alkylation of the methanol to olefin, isomerization of the toluene and the like are inhibited, so that the yield of the paraxylene is obviously improved, and the service life of the catalyst is prolonged.
The following technical scheme is a preferred technical scheme of the invention, but is not a limitation of the technical scheme provided by the invention, and the technical purpose and beneficial effects of the invention can be better achieved and realized through the following technical scheme.
As a preferable technical scheme of the invention, the preparation method of the modified metal/ZSM-5 molecular sieve catalyst comprises the following steps:
s01: synthesis of Na-ZSM-5 molecular sieves: mixing n-butylamine, water glass, water and ZSM-5 blank molecular sieve, and marking as A solution; dissolving aluminum sulfate octadecatydrate, sodium chloride and concentrated sulfuric acid in water, and marking as solution B; dropwise adding the solution B into the solution A, and then sequentially crystallizing, washing, drying and roasting to obtain a Na-ZSM-5 molecular sieve;
wherein SiO is controlled 2 :Al 2 O 3 :Na 2 O:n-C 4 H 11 N:NaCl:H 2 The molar ratio of O is (30-150): 1 (1.8-8.): 12-47): 18-69): 833-3200, for example 120:1:1.8:47:69:3200, 30:1:5:30:43:2000, 150:8:47:52:900 or 120:1:3:33:60:2600, etc., but is not limited to the recited values, and other non-recited values within the range of values are equally applicable;
s02: preparation of H-ZSM-5 molecular sieves: mixing Na-ZSM-5 molecular sieve with pseudo-boehmite, sesbania powder and nitric acid according to the mass ratio of 100 (10-30) to 1-5 to 10-50, extruding and molding, and then placing in ammonium nitrate solution for ion exchange to obtain H-ZSM-5 molecular sieve;
Wherein the mass of the raw materials can be selected from 100:30:5:50, 100:25:3:47, 100:20:2:37 or 100:27:2:33, etc., but the raw materials are not limited to the listed values, and other non-listed values in the range of the values are equally applicable;
s03: modification of H-ZSM-5 molecular sieves: soaking H-ZSM-5 molecular sieve in silicon source, depositing SiO 2 Control of SiO 2 The deposition amount of (2) is controlled to be 6-10wt%, such as 6wt%, 8wt% or 10wt%, etc., to obtain Si/H-ZSM-5 molecular sieve; soaking Si/H-ZSM-5 molecular sieve in phosphorus source to deposit P 2 O 5 Control P 2 O 5 The deposition amount of (2) is controlled to be 5-10wt%, such as 5wt%, 8wt% or 10wt%, etc., to obtain Si-P/H-ZSM-5 molecular sieve; soaking the Si-P/H-ZSM-5 molecular sieve in a magnesium source, depositing MgO, controlling the deposition amount of MgO to be 3-5wt%, such as 3wt%, 4wt% or 5wt% and the like, so as to obtain the Si-P-Mg/H-ZSM-5 molecular sieve, which is marked as M-ZSM-5 molecular sieve; the above-mentioned selection of values is not limited to the recited values, and other non-recited values are equally applicable within the respective ranges of values;
s04: preparation of modified metal/ZSM-5 molecular sieve catalyst: immersing M-ZSM-5 molecular sieve in a metal source with hydrogenation function, controlling the deposition amount of metal to be 0.1-0.3 wt%, such as 0.1wt%, 0.2wt% or 0.3wt%, and obtaining a modified metal/ZSM-5 catalyst after sintering, wherein the selection of the values is not limited to the listed values, and other non-listed values are applicable in the range of the values;
The metal source with the hydrogenation function comprises any one or a combination of at least two of a Pt source, a Pd source, a Co source or a Ni source.
In the invention, siO is loaded on the surface of the molecular sieve 2 、P 2 O 5 The MgO oxide can passivate the acid center on the outer surface of the molecular sieve, and inhibit side reactions such as xylene isomerization, toluene disproportionation, deep alkylation and the like; meanwhile, metals Pt, pd, co or Ni and the like with hydrogenation functions are loaded on the surface of the molecular sieve, and the hydrogenation metals can activate the actions of hydrogen and carbon-carbon double bonds to realize the addition of byproduct olefins, so that the generation of carbon deposition precursors is inhibited.
By the specific method according to the invention, the preparation of the catalyst is achieved by synergistic action of various preparation conditions, in particular by controlling the concentration of three oxides (SiO 2 、P 2 O 5 And MgO) and Pt loading capacity, the modified metal/ZSM-5 catalyst with high para-selectivity and high stability of the dimethylbenzene can be obtained, and compared with the existing catalyst, the catalyst can more effectively play the role of inhibiting the conversion of reactants to carbon deposition precursors under the condition of hydrogen so as to delay the carbon deposition deactivation of the catalyst.
If three oxides (SiO 2 、P 2 O 5 And MgO) is too high or too low, the ideal shape-selective effect cannot be achieved, when the deposition amount is too high, the stability of the catalyst is deteriorated, the catalyst is rapidly deactivated, and when the deposition amount is insufficient, the higher paraxylene selectivity cannot be obtained; if the Pt loading is too high or too low, it is difficult to ensure that a higher para-xylene yield is obtained, and when the Pt loading is too high, the decomposition of methanol is aggravated, and when the Pt loading is too low, it is difficult to maintain a higher stability of the catalyst.
Preferably, the SiO is controlled 2 The deposition amount of (2) was controlled to 8wt%, and the P was controlled 2 O 5 Deposition amount control of (a)The deposition amount of MgO was controlled to be 7wt%, and the deposition amount of the metal was controlled to be 0.2wt%. In the invention, the optimal deposition amount of the four substances is controlled, so that the catalyst achieves the best effect, and the p-xylene yield and the service life of the catalyst are obviously improved by matching with the use of a serial process.
As a preferred embodiment of the present invention, the concentration of the concentrated sulfuric acid in the step S01 is 98wt%.
Preferably, the crystallization temperature in step S01 is 160 to 180 ℃, e.g., 160 ℃, 170 ℃, 180 ℃, or the like; the time is 60 to 72 hours, for example, 60 hours, 64 hours, 68 hours, 72 hours, or the like, and the selection of the above-mentioned values is not limited to the listed values, and other non-listed values are equally applicable within the respective numerical ranges.
Preferably, the washing is performed with deionized water in step S01, and is washed to neutrality.
Preferably, the temperature of the drying in step S01 is 100 to 130 ℃, for example 130 ℃, 130 ℃ or 130 ℃, etc.; the time is 12 to 24 hours, for example, 12 hours, 16 hours, 20 hours, 24 hours, or the like, and the selection of the above-mentioned values is not limited to the listed values, and other non-listed values are equally applicable within the respective numerical ranges.
Preferably, the temperature of the firing in step S01 is 520 to 560 ℃, for example 520 ℃, 530 ℃, 540 ℃, 550 ℃, 560 ℃ or the like; the time is 6 to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or the like, and the selection of the above-mentioned values is not limited to the listed values, and other non-listed values are equally applicable within the respective numerical ranges.
In a preferred embodiment of the present invention, the nitric acid concentration in step S02 is 10 to 30wt%, for example, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, or the like, but the nitric acid concentration is not limited to the values listed, and other values not listed in the range are equally applicable.
Preferably, the concentration of the ammonium nitrate solution in the step S02 is 0.5 to 1.5mol/L, for example, 0.5mol/L, 0.7mol/L, 0.9mol/L, 1.2mol/L, or 1.5mol/L, etc., but the present invention is not limited to the recited values, and other non-recited values within the range of the recited values are equally applicable.
Preferably, the solid-to-liquid ratio of the H-type ZSM-5 molecular sieve molded in step S02 to the ammonium nitrate solution is (90 to 110 g) 1L, for example, 90g to 1L, 100g to 1L or 110g to 1L, etc., but the present invention is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned ranges are equally applicable.
Preferably, the ion exchange temperature is 60 to 90 ℃, for example 60 ℃, 70 ℃, 80 ℃, 90 ℃, or the like, but is not limited to the recited values, and other values not recited in the range of values are equally applicable.
Preferably, the ion exchange time is 1 to 2 hours, for example 1 hour, 1.5 hours, 2 hours, etc., but is not limited to the recited values, and other non-recited values within the range are equally applicable.
Preferably, the number of ion exchanges is not less than 3, such as 3, 4, or 5, but is not limited to the recited values, as other non-recited values within the range are equally applicable.
As a preferred embodiment of the present invention, the silicon source in step S03 includes an ethanol solution of ethyl orthosilicate, an ethanol solution of silicone oil, an ethanol solution of trimethylsilane, an ethanol solution of ethyltrimethylsilane, an ethanol solution of trimethylethoxysilane, cyclohexane, n-hexane, benzene, or toluene.
Preferably, the phosphorus source in step S03 comprises an aqueous ammonium dihydrogen phosphate solution, an aqueous phosphoric acid solution, an aqueous metaphosphoric acid solution, an aqueous hypophosphorous acid solution or an aqueous pyrophosphoric acid solution.
Preferably, the magnesium source in step S03 comprises an aqueous solution of magnesium acetate or an ethanol solution of magnesium ethoxide.
In a preferred embodiment of the present invention, the sintering temperature in step S04 is 450 to 550 ℃, for example 450 ℃, 480 ℃, 500 ℃, 520 ℃, 550 ℃, or the like, but the present invention is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned value range are equally applicable.
Preferably, the sintering time in step S04 is 3 to 4 hours, for example, 3 hours, 3.5 hours, or 4 hours, etc., but is not limited to the recited values, and other non-recited values within the range are equally applicable.
As a preferable technical scheme of the invention, the specific operation of the series reaction process comprises the following steps:
a. mixing an aromatic hydrocarbon raw material with a carrier gas, introducing the mixture into a first alkylation reactor, introducing an alkylation reagent into the first alkylation reactor, and allowing a reactant to flow through a catalyst bed to obtain a reaction mixture M1;
b. feeding the reaction mixture M1 into a second alkylation reactor to obtain a reaction mixture M2, and the like, wherein the reaction flow sequentially flows through n alkylation reactors, wherein n is more than or equal to 3, and finally the reaction mixture Mn is obtained;
simultaneously, the alkylating reagent is respectively and independently introduced into a second alkylation reactor to an nth alkylation reactor, mixed with a corresponding reaction mixture, contacted with a modified metal/ZSM-5 catalyst for alkylation reaction, and finally a reaction product containing PX is obtained.
Preferably, the reaction mixture Mn is subjected to alkylation reaction and then is subjected to rectification and three-phase separation in sequence, and finally a reaction product rich in PX is obtained. As a preferred technical scheme of the present invention, the series reaction process further comprises:
After the modified metal/ZSM-5 catalyst in the first alkylation reactor is deactivated, cutting the first alkylation reactor out of a series reaction process by switching a valve, and performing charcoal burning regeneration on the modified metal/ZSM-5 catalyst; after the regeneration is completed, the first alkylation reactor is returned to the series reaction process again;
according to the operation, the alkylation reactor deactivated by the modified metal/ZSM-5 catalyst is cut out of the series reaction process in sequence, the modified metal/ZSM-5 catalyst is subjected to charcoal burning regeneration, and the series reaction process is returned again, so that the continuous production of the whole reaction is realized.
According to the invention, through the use of the cascade alkylation reactors and the optimization of the feeding mode, the alkylating reagent is introduced between the sections, so that on one hand, the local concentration and partial pressure of the alkylating reagent can be reduced on the premise of not influencing the conversion rate of aromatic hydrocarbon, the local reaction temperature rise of a catalyst bed layer caused in the alkylation reaction process of aromatic hydrocarbon and the alkylating reagent is avoided, and the side reactions such as ineffective conversion of the alkylating reagent are inhibited; on the other hand, by switching the feeding modes among the reactors, the deactivated catalyst can be timely switched out of the reaction system to perform in-situ regeneration or unloading agent regeneration, and the continuous operation of the whole reaction process is not influenced.
As a preferred embodiment of the present invention, the aromatic hydrocarbon feedstock comprises benzene and/or toluene.
Preferably, when the aromatic hydrocarbon feedstock is a mixture of benzene and toluene, the benzene content is 1 to 99mol.%.
Preferably, the carrier gas comprises a mixture of hydrogen and water vapor or a mixture of hydrogen, nitrogen and water vapor.
The temperature of the steam is preferably 480 to 520 ℃, for example, 480 ℃, 500 ℃, 520 ℃, or the like, but is not limited to the recited values, and other values not recited in the range of the recited values are equally applicable.
Preferably, when the carrier gas is a mixture of hydrogen, nitrogen and steam, the hydrogen accounts for 1 to 99 mol% based on 100% of the hydrogen and nitrogen.
Preferably, the alkylating agent comprises methanol or a mixture of methanol and water.
Preferably, when the alkylating agent is a mixture of methanol and water, the molar ratio of water to methanol is 1:10 to 20:1, for example 1:10, 1:2, 1:1, 10:1 or 20:1, etc., but not limited to the recited values, other non-recited values within the range are equally applicable, preferably 1:10 to 1:1.
In a preferred embodiment of the present invention, the alkylation reaction temperature is 300 to 500 ℃, for example 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, or the like, but the present invention is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned value range are applicable.
Preferably, the pressure of the alkylation reaction is 0.1 to 0.4MPa, for example, 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, etc., but is not limited to the recited values, and other non-recited values within the range are equally applicable.
Preferably, the quality of the aromatic hydrocarbon feedstock and the alkylating agentThe weight airspeed is 0.5 to 10 hours -1 For example 0.5h -1 、1h -1 、3h -1 、5h -1 、8h -1 Or 10h -1 And the like, but are not limited to the recited values, and other non-recited values within the range of values are equally applicable.
Preferably, the molar ratio of the aromatic hydrocarbon feedstock to the alkylating agent is (0.5 to 10): 1, e.g., 0.5:1, 1:1, 3:1, 5:1, 7:1, or 10:1, etc., but is not limited to the recited values, as other non-recited values within the range of values are equally applicable.
Preferably, the carrier gas is present in an amount of 1 to 6 times, for example 1, 2, 4 or 6 times, the total molar amount of the aromatic hydrocarbon feedstock and the alkylating agent, but is not limited to the recited values, and other non-recited values within this range are equally applicable.
Compared with the prior art, the invention has the following beneficial effects:
(1) The tandem reaction process of the present invention uses SiO 2 、P 2 O 5 The MgO oxide is modified, and the metal with hydrogenation function is loaded, so that para-position selectivity and reaction stability of the catalyst dimethylbenzene are improved, and the catalyst preparation process is easy to implement and suitable for large-scale production;
(2) The series reaction process disclosed by the invention is matched with at least 3 sections of alkylation fixed bed reactors connected in series on the basis of using the modified metal/ZSM-5 catalyst, optimizes the feeding mode of an alkylation reagent, effectively inhibits side reaction, can timely switch the deactivated catalyst out of a reaction system by switching valves among the reactors to perform in-situ regeneration or unloading regeneration, does not influence the continuous operation of the whole reaction process, and has a good industrial application prospect.
Drawings
FIG. 1 is a schematic diagram of the series reaction process for preparing paraxylene by alkylating aromatic hydrocarbon according to example 1 of the present invention;
wherein, R1-R6 are the serial numbers of alkylation fixed bed reactors in turn, F1 is an aromatic hydrocarbon raw material tank, F2-water tank, F3-is a feeding inlet of hydrogen carrying water vapor, F4-nitrogen is a feeding inlet, C1-C6 are corresponding methanol feeding tanks in turn, M1-M6 are serial numbers of reaction mixtures in turn, V1 is a rectifying tower, S1-is a three-phase separation device, W1 is a sewage tank, and P is a reaction product tank.
FIG. 2 is a graph showing the variation of the reaction data of each stage of alkylation fixed bed reactor in the tandem reaction process for producing paraxylene by alkylation of aromatic hydrocarbon according to example 1 of the present invention.
FIG. 3 is a graph showing the overall reaction performance of each stage of alkylation fixed bed reactor over time in a series reaction process for producing para-xylene by alkylation of aromatic hydrocarbons according to example 1 of the present invention.
FIG. 4 is a graph showing the molar ratio of each carbon-containing species in the gas phase product and the hydrogen-hydrocarbon ratio over time in a tandem reaction process for producing para-xylene by alkylating aromatic hydrocarbons according to example 1 of the present invention.
FIG. 5 is a graph showing the variation of the reaction data of each stage of alkylation fixed bed reactor in the tandem reaction process for producing paraxylene by alkylation of aromatic hydrocarbon according to example 2 of the present invention.
FIG. 6 is a graph showing the overall reaction performance of each stage of alkylation fixed bed reactor over time in a series reaction process for producing para-xylene by alkylation of aromatic hydrocarbons according to example 2 of the present invention.
FIG. 7 is a graph showing the molar ratio of each carbon-containing species in the vapor phase product and the hydrocarbon ratio over time in a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbons according to example 2 of the present invention.
FIG. 8 is a graph showing the variation of the reaction data of each stage of alkylation fixed bed reactor in the tandem reaction process for producing paraxylene by alkylation of aromatic hydrocarbon according to example 3 of the present invention.
FIG. 9 is a graph showing the overall reaction performance of each stage of alkylation fixed bed reactor over time in a series reaction process for producing para-xylene by alkylation of aromatic hydrocarbons according to example 3 of the present invention.
FIG. 10 is a graph showing the molar ratio of each carbon-containing species in the vapor phase product and the hydrocarbon ratio over time in a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbons according to example 3 of the present invention.
Detailed Description
For better illustrating the present invention, the technical scheme of the present invention is convenient to understand, and the present invention is further described in detail below. The following examples are merely illustrative of the present invention and are not intended to represent or limit the scope of the invention as defined in the claims.
In one embodiment, the invention provides a method for preparing a modified Pt/ZSM-5 catalyst, comprising the steps of:
s01: synthesis of Na-ZSM-5 molecular sieves: firstly, adding 4.8g of n-butylamine into 34.4g of water glass and 27.3g of water, uniformly mixing, adding 0.5g of ZSM-5 blank molecular sieve, mixing, stirring for 30min at 35 ℃, and recording as A solution; then 0.8g of aluminum sulfate octadecatydrate, 5.6g of sodium chloride and 3.5g of concentrated sulfuric acid (98 wt%) were dissolved in 30.0g of water, designated as solution B; slowly dripping the solution B into the solution A, vigorously stirring for 1h, filling the mixed gel into a crystallization kettle with a polytetrafluoroethylene lining, crystallizing at 170 ℃ for 72h, centrifugally separating the crystallized suspension, washing with deionized water to neutrality, drying at 120 ℃ for 12h, transferring into a muffle furnace, and roasting at 540 ℃ for 6h to obtain the Na-ZSM-5 molecular sieve;
Wherein SiO is controlled 2 :Al 2 O 3 :Na 2 O:n-C 4 H 11 N:NaCl:H 2 The molar ratio of O is 120:1:1.8:47:69:3200;
s02: preparation of H-ZSM-5 molecular sieves: mixing Na-ZSM-5 molecular sieve with pseudo-boehmite, sesbania powder and nitric acid according to the mass ratio of 100:30:5:50, extruding and molding, then placing 100g of molded Na-ZSM-5 molecular sieve into 1L of ammonium nitrate solution with the concentration of 0.5mol/L, exchanging for 1.5H at 80 ℃ for three times, exchanging for each time, washing for four to five times by deionized water after the last exchange, drying the molded catalyst for 4H at 80 ℃, and then transferring into a muffle furnace for roasting for 4H at 540 ℃ to obtain the H-ZSM-5 molecular sieve;
s03: modification of H-ZSM-5 molecular sieves: impregnating H-ZSM-5 molecular sieve in normal siliconControlling SiO in ethyl acetate ethanol solution 2 The deposition amount of the catalyst is controlled to be 8 weight percent, the catalyst is dried for 12 hours at 80 ℃ after being sealed for 24 hours, and then is transferred into a muffle furnace to be roasted for 5 hours at 550 ℃ to obtain the Si/H-ZSM-5 molecular sieve; soaking Si/H-ZSM-5 molecular sieve in aqueous solution of ammonium dihydrogen phosphate, and controlling P 2 O 5 The deposition amount of the catalyst is controlled to be 7 weight percent, and after the catalyst is dried in the shade at room temperature, the catalyst is dried for 12 hours at 80 ℃, and then is transferred into a muffle furnace to be roasted for 5 hours at 550 ℃ to obtain the Si-P/H-ZSM-5 molecular sieve; soaking Si-P/H-ZSM-5 molecular sieve in aqueous solution of magnesium acetate, controlling the deposition amount of MgO to be 4wt%, drying in the shade at room temperature, drying at 80 ℃ for 12 hours, transferring into a muffle furnace, roasting at 550 ℃ for 5 hours to obtain Si-P-Mg/H-ZSM-5 molecular sieve, and marking the Si-P-Mg/H-ZSM-5 molecular sieve as M-ZSM-5 molecular sieve;
S04: preparation of modified Pt/ZSM-5 molecular sieve catalyst: the M-ZSM-5 catalyst is immersed in an aqueous solution of chloroplatinic acid, the deposition amount of Pt is controlled to be 0.2wt%, and after being air-dried at room temperature, the catalyst is dried for 12 hours at 80 ℃, and then is transferred into a muffle furnace for roasting for 3 hours at 500 ℃ to obtain the modified Pt/ZSM-5 catalyst.
In one embodiment, the invention also provides a tandem reaction process for preparing paraxylene by alkylating aromatic hydrocarbon, which comprises the following specific operations:
a. mixing an aromatic hydrocarbon raw material with a carrier gas, introducing the mixture into a first alkylation reactor R1, introducing an alkylation reagent into the first alkylation reactor R1, and allowing a reactant to flow through a catalyst bed to obtain a reaction mixture M1;
b. feeding the reaction mixture M1 into a second alkylation reactor R2 to obtain a reaction mixture M2, and the like, wherein the reaction flow sequentially flows through n alkylation reactors, wherein n is more than or equal to 3, and finally a reaction mixture Mn is obtained;
simultaneously, the alkylating reagent is respectively and independently introduced into a second alkylation reactor R2 to an nth alkylation reactor Rn, mixed with a corresponding reaction mixture, contacted with a modified metal/ZSM-5 catalyst for alkylation reaction, and then sequentially subjected to rectification and three-phase separation to finally obtain a reaction product containing PX;
c. After the modified metal/ZSM-5 catalyst in the first alkylation reactor R1 is deactivated, cutting the first alkylation reactor R1 out of a series reaction process by switching a valve, and performing charcoal burning regeneration on the modified metal/ZSM-5 catalyst; after the regeneration is completed, the first alkylation reactor R1 is returned to the tandem reaction process again;
according to the operation, the alkylation reactor deactivated by the modified metal/ZSM-5 catalyst is cut out of the series reaction process in sequence, the modified metal/ZSM-5 catalyst is subjected to charcoal burning regeneration, and the series reaction process is returned again, so that the continuous production of the whole reaction is realized.
Further, the aromatic hydrocarbon feedstock comprises benzene and/or toluene; when the aromatic hydrocarbon raw material is a mixture of benzene and toluene, the benzene content is 1-99 mol%;
further, the carrier gas comprises a mixture of hydrogen and water vapor or a mixture of hydrogen, nitrogen and water vapor; the temperature of the water vapor is 480-520 ℃; when the carrier gas is a mixed gas of hydrogen, nitrogen and steam, the ratio of the hydrogen to the nitrogen is 1-99 mol percent based on 100 percent of the hydrogen and the nitrogen;
further, the alkylating agent comprises methanol or a mixture of methanol and water; when the alkylating agent is a mixture of methanol and water, the molar ratio of water to methanol is 1:10-20:1, preferably 1:10-1:1.
Further, the alkylation reaction temperature is 300-500 ℃ and the pressure is 0.1-0.4 MPa;
further, the mass space velocity of the aromatic hydrocarbon raw material and the alkylating agent is independently 0.5-10 h -1 ；
Further, the molar ratio of the aromatic hydrocarbon raw material to the alkylating agent is (0.5-10): 1;
further, the carrier gas is present in an amount of 1 to 6 times the total molar amount of the aromatic hydrocarbon feedstock and the alkylating agent.
In addition, the specific performance indicators of the alkylation reaction involved in the present invention are defined as follows:
toluene conversion (X) T ) = (toluene concentration in feed-toluene concentration in product)/toluene concentration in feed x 100%
Xylene selectivity (S) X ) Total concentration of xylenes in product/(toluene concentration in feedstock-toluene concentration in product) ×100%
Para-xylene selectivity (S) PX ) P-xylene concentration in product/total xylene concentration in product x 100%
Xylene yield (Y) X ) Toluene conversion x xylene selectivity
Para-xylene yield (Y) PX ) Toluene conversion x xylene selectivity
The following are exemplary but non-limiting examples of the invention:
example 1:
the present example provides a series reaction process for the alkylation of aromatic hydrocarbons to para-xylene comprising coupling a modified Pt/ZSM-5 catalyst with a 6-stage series of alkylation fixed bed reactors. The schematic of the system flow of the series reaction process is shown in fig. 1, wherein the nitrogen feed inlet F4 is shown in the schematic of the system flow, but in this embodiment, it is not opened.
The modified Pt/ZSM-5 catalyst is prepared by adopting a preparation method in a specific embodiment.
The series reaction process is based on the process flow in the specific embodiment, and specific alkylation reaction conditions are as follows:
before the reaction, the catalyst is reduced for 2 hours under the hydrogen atmosphere with the temperature of 500 ℃, the hydrogen flow is 50mL/min, and when the reaction is evaluated, 720g of modified Pt/ZSM-5 catalyst is divided into 6 parts and is respectively filled into 6 sections of alkylation fixed bed reactors, the concrete filling amounts are respectively 130g, 120g and 90g according to the sequence of the reactor numbers, and the upper section and the lower section of the catalyst are respectively filled with phi 3 porcelain balls.
The reaction temperature is 460 ℃; the carrier gas is hydrogen carrying 500 ℃ water vapor, and the reaction pressure is 0.2MPa; the arene raw material is toluene, and the mass airspeed of the toluene is 1h -1 The method comprises the steps of carrying out a first treatment on the surface of the The alkylating agent is a mixture of methanol and water (water is fed only from the first alkylation reactor R1), the total feed molar ratio of toluene to methanol being 1.4:1, i.e. nT/nm=1.4; water and hydrocarbon feedstockMolar ratio of 2, i.e.nH 2 O/(nt+nm) =2; the molar ratio of hydrogen to hydrocarbon feedstock is 2, i.e. nH 2 /(nt+nm) =2; hydrogen carries superheated steam, toluene and methanol into the reaction system.
In this example, the change in reaction data for each stage of the alkylation fixed bed reactor is shown in FIG. 2. As can be seen from fig. 2, toluene conversion continues to increase from 8.9% for R1 to 27.3% for R6 as the reactants pass through each reactor step by step, with the increase in magnitude being most pronounced between R1 and R4; the selectivity of the dimethylbenzene is between 95.4% and 93.4%, the selectivity of the PX is gradually reduced, the selectivity is reduced from 97.1% of R1 to 91.9% of R6, and the selectivity of the PX is reduced by 0.87% when one reactor is added. However, the xylene yield and PX yield remained almost the same and increased continuously from the yield of the target product, indicating that the vast majority of the alkylation product of toluene and methanol alkylation reactions was PX on multi-stage series fixed bed reactors, with PX yield increasing from 8.7% for R1 to 25.1% for R6, with a particularly significant increase between R1 and R4, with a smaller increase in R5 and R6. The composition of the liquid phase product flowing out of each reactor is shown in Table 1, and it can be seen from Table 1 that as the number of reactor stages increases, the toluene content continuously decreases, the paraxylene content continuously increases, and small amounts of benzene, ethylbenzene, metaxylene, orthoxylene, methylethylbenzene, trimethylbenzene and aromatics above C9 are by-produced during the reaction, wherein the molar composition of all by-products is not more than 3.8% from the view of the composition distribution of R6, indicating that the proportion of by-products can be effectively reduced by using a multistage reactor.
TABLE 1
C6 － Non-aromatic refers to non-aromatic species of 6 carbons or less; C9C 9 + Aromatic hydrocarbon refers to aromatic hydrocarbon substances with more than 9 carbons.
The overall reaction performance of the 6-stage alkylation fixed bed reactor is shown in FIG. 3 as a function of time. As can be seen from FIG. 3, the toluene conversion rate is kept at 27% basically within 90h, the selectivity of xylene is not lower than 92%, the selectivity of PX is not lower than 91.8%, and the activity of the catalyst is kept unchanged basically while the selectivity of PX is higher, which indicates that the catalyst and the reaction process provided by the invention can realize stable operation of the shape-selective catalytic reaction of toluene and methanol.
The molar ratio of each carbon-containing species in the gas phase product and the hydrogen-to-hydrocarbon ratio as a function of time are shown in FIG. 4. As can be seen from FIG. 4, after 30 hours from the reaction to the stationary phase, the main by-products in the gas phase product include H 2 、CO、CO 2 Methane, ethane, ethylene, propane, propylene, and C4-C6 hydrocarbons. Wherein the hydrogen accounts for about 90% -95% of the total composition of the gas phase; in the carbon-containing species, methane, ethane and propane form main hydrocarbon byproducts, the sum of which is close to 75 percent, and the carbon monoxide also contain about 15 to 20 percent 2 . The results show that the catalyst provided by the invention can effectively reduce the proportion of carbon deposition precursors such as ethylene, propylene and the like in gas-phase products under the hydrogen condition, and delay the carbon deposition process of the catalyst, so that the modified Pt/ZSM-5 catalyst has higher stability.
Example 2:
the present example provides a series reaction process for the alkylation of aromatic hydrocarbons to para-xylene comprising coupling a modified Pt/ZSM-5 catalyst with a 5-stage series of alkylation fixed bed reactors.
The modified Pt/ZSM-5 catalyst is prepared by adopting a preparation method in a specific embodiment.
The series reaction process is based on the process flow in the specific embodiment, and specific alkylation reaction conditions are as follows:
before the reaction, the catalyst is reduced for 2 hours under the hydrogen atmosphere with the temperature of 500 ℃ and the hydrogen flow rate of 50mL/min, and when the reaction is evaluated, 600g of modified Pt/ZSM-5 catalyst is divided into 5 parts and respectively filled into 5 sections of alkylation fixed bed reactors, the specific filling amounts are 130g, 120g and 100g according to the sequence of the reactor numbers, and the upper section and the lower section of the catalyst are respectively filled with phi 3 porcelain balls.
The reaction temperature is 460 ℃; the carrier gas is carried with 500 ℃ water vaporThe reaction pressure is 0.2Mpa; the arene raw material is toluene, and the mass airspeed of the toluene is 1h -1 The method comprises the steps of carrying out a first treatment on the surface of the The alkylating agent is a mixture of methanol and water (water is fed only from the first alkylation reactor R1), the total feed molar ratio of toluene to methanol being 1.4:1, i.e. nT/nm=1.4; the molar ratio of water to hydrocarbon feedstock is 2, i.e. nH 2 O/(nt+nm) =2; the molar ratio of hydrogen to hydrocarbon feedstock is 2, i.e. nH 2 /(nt+nm) =2; hydrogen carries superheated steam, toluene and methanol into the reactor.
In this example, the reaction data for each stage of the alkylation fixed bed reactor is shown in FIG. 5. As can be seen from FIG. 5, with the same reaction conditions, the overall toluene conversion can reach 22.4% with 94.6% xylene selectivity and 93.1% PX selectivity for the five-stage series reactor. The law of the reactant flowing through each reactor is similar to that of the six-stage reactor, namely, the toluene conversion rate is gradually increased, and the xylene and paraxylene selectivity is gradually reduced. Wherein the xylene yield increases from 3.2% for R1 to 21.2% for R5 and the PX yield increases from 3.2% for R1 to 20.9% for R5. The liquid phase product distribution of each reactor effluent is shown in table 2, and it can be seen from table 2 that PX is the main alkylation product.
TABLE 2
The overall reaction performance of the 5-stage series alkylation fixed bed reactor is shown in FIG. 6 as a function of time, and it can be seen from FIG. 6 that the entire reaction can be stably operated for 120 hours. FIG. 7 shows the molar ratio of each carbon-containing species and the hydrogen-to-hydrocarbon ratio in the gas phase product with time, with the main by-products being CO, CO 2 Methane, ethane and propane, and a small amount of carbon precursor such as ethylene and propylene, show a similar reaction law to example 1.
Example 3:
the present example provides a series reaction process for the alkylation of aromatic hydrocarbons to para-xylene comprising coupling a modified Pt/ZSM-5 catalyst with a 6-stage series of alkylation fixed bed reactors.
The modified Pt/ZSM-5 catalyst is prepared by adopting a preparation method in a specific embodiment.
The series reaction process is based on the process flow in the specific embodiment, and specific alkylation reaction conditions are as follows:
before the reaction, the catalyst is reduced for 2 hours in a hydrogen atmosphere at 500 ℃, the hydrogen flow is 50mL/min, and when the reaction is evaluated, 720g of modified Pt/ZSM-5 catalyst is divided into 6 parts and is respectively filled into 6 sections of alkylation fixed bed reactors, the specific filling amount is 120g according to the sequence of the serial numbers of the reactors, and the upper section and the lower section of the catalyst are respectively filled with phi 3 porcelain balls.
The reaction temperature is 460 ℃; the carrier gas is hydrogen carrying 500 ℃ water vapor, and the reaction pressure is 0.2MPa; the arene raw material is toluene, and the mass airspeed of the toluene is 1h -1 The method comprises the steps of carrying out a first treatment on the surface of the The alkylating agent is a mixture of methanol and water (water is fed only from the first alkylation reactor R1), the total feed molar ratio of toluene to methanol being 1.26:1, i.e. nT/nm=1.26; the molar ratio of water to hydrocarbon feedstock was 1.3, i.e. nH 2 O/(nt+nm) =1.3; the molar ratio of hydrogen to hydrocarbon feedstock was 1.3, i.e. nH 2 /(nt+nm) =1.3; hydrogen carries superheated steam, toluene and methanol into the reaction system.
In this example, the reaction data for each stage of the alkylation fixed bed reactor is shown in FIG. 8. As can be seen from FIG. 8, maintaining the same reaction temperature, pressure and space velocity of toluene, reducing the molar ratio of toluene to methanol to 1.26, and reducing the hydrogen to hydrocarbon ratio and the water to hydrocarbon ratio to 1.3, the overall toluene conversion can reach 19.1%, the xylene selectivity 94.0% and the PX selectivity 97.9% using six-stage reactors in series. The reaction flow through each reactor showed a similar pattern as in example 1, i.e., toluene conversion was progressively higher and xylene and para-xylene selectivity was progressively lower. Wherein the xylene yield increases from 7.1% of R1 to 17.9% of R6 and the PX yield increases from 7.4% of R1 to 18.7% of R6. The liquid phase product composition of each reactor effluent is set forth in Table 3, and from Table 3 it can be seen that PX is the predominant alkylation product and the total composition of other hydrocarbons is no greater than 1.52%.
TABLE 3 Table 3
The overall reaction performance of the 6-stage alkylation fixed bed reactor is shown in FIG. 9 as a function of time. As can be seen from fig. 9, the whole reaction can be stably operated within 225h, the total toluene conversion reaches the highest value of 22.3% at 50h, and the total toluene conversion is reduced to 17.1% after 225 h.
The molar ratio of each carbon-containing species in the gas phase product and the hydrogen-hydrocarbon ratio as a function of time are shown in FIG. 10. As can be seen from FIG. 10, the main byproducts in the gas phase product are CO and CO 2 Methane, ethane and propane, and small amounts of carbon precursors such as ethylene and propylene.
Example 4:
this example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: in the process of preparing the modified Pt/ZSM-5 catalyst, in step S03, siO is controlled 2 The deposition amount of (2) was controlled to 3wt%.
In this example, the loading of silicon in the resulting modified Pt/ZSM-5 catalyst was too small, resulting in a high toluene conversion of 30.1%, but a PX selectivity of only 66.7% was too low.
Example 5:
this example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: in the process of preparing the modified Pt/ZSM-5 catalyst, in step S03, siO is controlled 2 The deposition amount of (2) was controlled to 15wt%.
In this example, a modified Pt/ZSM-5 catalyst was prepared In the process, the silicon loading is excessive, so that the conversion rate and the selectivity of PX are reduced simultaneously, the average conversion rate is 16.9%, and the selectivity is lower than that of the optimal SiO 2 The deposition amount was 92.1%.
Example 6:
this example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: in the process of preparing the modified Pt/ZSM-5 catalyst, in step S03, P is controlled 2 O 5 The deposition amount of (2) was controlled to 1wt%.
In the modified Pt/ZSM-5 catalyst prepared in this example, the phosphorus loading is too small, so that the toluene conversion rate is improved to a certain extent, the average conversion rate is 27.2%, but the selectivity is only 54.7%.
Example 7:
this example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: in the process of preparing the modified Pt/ZSM-5 catalyst, in step S03, P is controlled 2 O 5 The deposition amount of (2) was controlled to 15wt%.
In the modified Pt/ZSM-5 catalyst prepared in this example, the phosphorus loading is too large, resulting in a significant reduction in toluene conversion of only 18.1%, and the selectivity is improved to some extent but less than 90%, about 83.7%.
Example 8:
this example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: in the process of preparing the modified Pt/ZSM-5 catalyst, in the step S03, the deposition amount of MgO is controlled to be 1wt%.
In this example, the loading of magnesium in the modified Pt/ZSM-5 catalyst prepared was too small, resulting in too low selectivity for PX, only 66.5%, and a toluene conversion of 25.8%.
Example 9:
this example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: in the process of preparing the modified Pt/ZSM-5 catalyst, in the step S03, the deposition amount of MgO is controlled to be 15wt%.
In the modified Pt/ZSM-5 catalyst prepared in the embodiment, the magnesium loading is excessive, so that the selectivity of PX is improved to a certain extent, but the selectivity shows a tendency of declining along with the improvement of the Mg loading compared with the optimal loading, and the conversion rate is not changed greatly.
Example 10:
this example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: in the process of preparing the modified Pt/ZSM-5 catalyst, in step S04, the deposition amount of Pt is controlled to be 0.01wt%.
In the modified Pt/ZSM-5 catalyst prepared in the embodiment, the loading of Pt is too small, so that the catalyst has certain hydrogenation performance, but the catalyst does not have ideal hydrogenation performance due to the too small loading of metal, and finally the catalyst carbon deposit is deactivated.
Example 11:
this example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: in the process of preparing the modified Pt/ZSM-5 catalyst, in step S04, the deposition amount of Pt is controlled to be 1wt%.
In the modified Pt/ZSM-5 catalyst prepared in the embodiment, the loading of Pt is too large, so that the catalyst has better stability, but the loading of Pt is too high, so that the methanol is decomposed in an ineffective way, and the toluene conversion rate is only kept at about 15.3%.
Comparative example 1:
this comparative example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: the catalyst used was a modified ZSM-5 catalyst, i.e.the procedure of step S04 was not performed during the preparation of the catalyst.
Since in this comparative example, there was no metal having a hydrogenation function to the catalyst support, the catalyst was deactivated by rapid carbon deposition, the conversion rate was rapidly decreased within 10 hours, and the selectivity was simultaneously decreased.
Comparative example 2:
this comparative example provides a tandem reaction process for producing para-xylene by alkylation of aromatic hydrocarbon, which is different from that of example 1 only in that: methanol is fed entirely from the first alkylation reactor R1 and is no longer fed separately from each reactor.
This feed mode resulted in toluene conversion of only 18% below 27% for methanol staged feed; in addition, the catalyst in the first stage reactor is rapidly deactivated, and it is difficult for the catalyst to remain stable.
As can be seen from a combination of the above examples and comparative examples, the tandem reaction process of the present invention is carried out by using SiO 2 、P 2 O 5 The MgO oxide is modified, and the metal with hydrogenation function is loaded, so that para-position selectivity and reaction stability of the catalyst dimethylbenzene are improved; on the basis of using the modified metal/ZSM-5 catalyst, at least 3 sections of alkylation fixed bed reactors connected in series are matched, the feeding mode of an alkylation reagent is optimized, and side reactions are effectively inhibited; in addition, by switching the valves among the reactors, the deactivated catalyst can be timely switched out of the reaction system to perform in-situ regeneration or unloading regeneration, the continuous operation of the whole reaction process is not influenced, and the method has good industrial application prospect.
The applicant states that the detailed method of the present invention is illustrated by the above examples, but the present invention is not limited to the detailed method described above, i.e. it does not mean that the present invention must be practiced in dependence upon the detailed method described above. It should be apparent to those skilled in the art that any modifications, equivalent substitutions for operation of the present invention, addition of auxiliary operations, selection of specific modes, etc., are intended to fall within the scope of the present invention and the scope of the disclosure.

Claims (19)

1. A tandem reaction process for preparing paraxylene by aromatic alkylation, which is characterized by comprising the following steps:
a. mixing an aromatic hydrocarbon raw material with a carrier gas, introducing the mixture into a first alkylation reactor, introducing an alkylation reagent into the first alkylation reactor, and allowing a reactant to flow through a catalyst bed to obtain a reaction mixture M1; the aromatic hydrocarbon feedstock comprises benzene and/or toluene; the carrier gas comprises a mixed gas of hydrogen and water vapor or a mixed gas of hydrogen, nitrogen and water vapor; the alkylating agent comprises methanol or a mixture of methanol and water;
b. feeding the reaction mixture M1 into a second alkylation reactor to obtain a reaction mixture M2, and the like, wherein the reaction flow sequentially flows through n alkylation reactors, wherein n is more than or equal to 6 and more than or equal to 3, and finally the reaction mixture Mn is obtained;
Simultaneously, the alkylating reagent is respectively and independently introduced into a second alkylation reactor to an nth alkylation reactor, mixed with a corresponding reaction mixture, contacted with a modified metal/ZSM-5 catalyst for alkylation reaction, and sequentially subjected to rectification and three-phase separation to finally obtain a reaction product containing PX; the temperature of the alkylation reaction is 300-500 ℃; the pressure of the alkylation reaction is 0.1-0.4 MPa;
c. after the modified metal/ZSM-5 catalyst in the first alkylation reactor is deactivated, cutting the first alkylation reactor out of a series reaction process by switching a valve, and performing charcoal burning regeneration on the modified metal/ZSM-5 catalyst; after the regeneration is completed, the first alkylation reactor is returned to the series reaction process again;
according to the operation, the alkylation reactor deactivated by the modified metal/ZSM-5 catalyst is cut into a series reaction process in sequence, the modified metal/ZSM-5 catalyst is subjected to charcoal burning regeneration, and the series reaction process is returned again to realize continuous production of the whole reaction;
the preparation method of the modified metal/ZSM-5 molecular sieve catalyst comprises the following steps:
s01: synthesis of Na-ZSM-5 molecular sieves: mixing n-butylamine, water glass, water and ZSM-5 blank molecular sieve, and marking as A solution; dissolving aluminum sulfate octadecatydrate, sodium chloride and concentrated sulfuric acid in water, and marking as solution B; dropwise adding the solution B into the solution A, and then sequentially crystallizing, washing, drying and roasting to obtain a Na-ZSM-5 molecular sieve; the crystallization temperature is 160-180 ℃ and the crystallization time is 60-72 h; the roasting temperature is 520-560 ℃ and the roasting time is 6-10 hours;
Wherein SiO is controlled 2 :Al 2 O 3 :Na 2 O:n-C 4 H 11 N:NaCl:H 2 The mol ratio of O is (30-150): 1 (1.8-8): 12-47): 18-69): 833-3200;
s02: preparation of H-ZSM-5 molecular sieves: mixing Na-ZSM-5 molecular sieve with pseudo-boehmite, sesbania powder and nitric acid according to the mass ratio of 100 (10-30): 1-5): 10-50, extruding and molding, and then placing in ammonium nitrate solution for ion exchange to obtain H-ZSM-5 molecular sieve;
s03: modification of H-ZSM-5 molecular sieves: soaking H-ZSM-5 molecular sieve in silicon source, depositing SiO 2 Control of SiO 2 The deposition amount of the catalyst is controlled to be 6-10wt% to obtain the Si/H-ZSM-5 molecular sieve; soaking Si/H-ZSM-5 molecular sieve in phosphorus source to deposit P 2 O 5 Control P 2 O 5 The deposition amount of the catalyst is controlled to be 5-10wt% to obtain the Si-P/H-ZSM-5 molecular sieve; soaking a Si-P/H-ZSM-5 molecular sieve in a magnesium source, depositing MgO, controlling the deposition amount of MgO to be 3-5wt%, and obtaining the Si-P-Mg/H-ZSM-5 molecular sieve, namely an M-ZSM-5 molecular sieve;
the silicon source comprises an ethanol solution of ethyl orthosilicate, an ethanol solution of silicone oil, an ethanol solution of trimethylsilane, an ethanol solution of ethyltrimethylsilane, an ethanol solution of trimethylethoxysilane, a cyclohexane solution of ethyl orthosilicate and an n-hexane solution of ethyl orthosilicate;
the phosphorus source comprises an aqueous ammonium dihydrogen phosphate solution, an aqueous phosphoric acid solution, an aqueous metaphosphoric acid solution, an aqueous hypophosphorous acid solution or an aqueous pyrophosphoric acid solution;
The magnesium source comprises an aqueous solution of magnesium acetate or an ethanol solution of magnesium ethoxide; s04: preparation of modified metal/ZSM-5 molecular sieve catalyst: dipping an M-ZSM-5 molecular sieve in a metal source with a hydrogenation function, controlling the deposition amount of metal to be 0.1-0.3wt%, and sintering to obtain a modified metal/ZSM-5 catalyst;
the metal source with the hydrogenation function comprises any one or a combination of at least two of a Pt source, a Pd source, a Co source and a Ni source;
the sintering temperature is 450-550 ℃; the sintering time is 3-4 hours.
2. The tandem reaction process according to claim 1, wherein the SiO is controlled 2 The deposition amount of (2) was controlled to 8wt%, and the P was controlled 2 O 5 The deposition amount of MgO is controlled to 7wt%, the deposition amount of MgO is controlled to 4wt%, and the deposition amount of the metal is controlled to 0.2wt%.
3. The tandem reaction process according to claim 1, wherein the concentration of said concentrated sulfuric acid in step S01 is 98wt%.
4. The tandem reaction process according to claim 1, wherein the washing is performed with deionized water and washed to neutrality in step S01.
5. The tandem reaction process according to claim 1, wherein the drying temperature in step S01 is 100 to 130 ℃ for 12 to 24 hours.
6. The tandem reaction process according to claim 1, wherein the nitric acid concentration in step S02 is 10 to 30wt%.
7. The tandem reaction process according to claim 1, wherein the concentration of the ammonium nitrate solution in step S02 is 0.5 to 1.5mol/L.
8. The tandem reaction process according to claim 1, wherein the solid-to-liquid ratio of the H-type ZSM-5 molecular sieve molded in step S02 to the ammonium nitrate solution is (90 to 110 g): 1L.
9. The tandem reaction process according to claim 1, wherein the ion exchange temperature is 60 to 90 ℃.
10. The tandem reaction process according to claim 1, wherein the time of the ion exchange is 1 to 2 hours.
11. The tandem reaction process according to claim 1, wherein the number of times of ion exchange is not less than 3.
12. The tandem reaction process according to claim 1, wherein when the aromatic hydrocarbon raw material is a mixture of benzene and toluene, the benzene content is 1 to 99 mol%.
13. The tandem reaction process according to claim 1, wherein the temperature of the water vapor is 480 to 520 ℃.
14. The tandem reaction process according to claim 1, wherein when the carrier gas is a mixture of hydrogen, nitrogen and steam, the ratio of hydrogen is 1 to 99 mol%, based on 100% of hydrogen and nitrogen.
15. The tandem reaction process of claim 1, wherein when the alkylating agent is a mixture of methanol and water, the molar ratio of water to methanol is 1:10 to 20:1.
16. The tandem reaction process of claim 15, wherein when the alkylating agent is a mixture of methanol and water, the molar ratio of water to methanol is 1:10 to 1:1.
17. The tandem reaction process of claim 1, wherein the mass space velocity of the aromatic hydrocarbon feedstock and the alkylating agent is independently 0.5 to 10h -1 。
18. The tandem reaction process according to claim 1, wherein the molar ratio of the aromatic hydrocarbon feedstock to the alkylating agent is (0.5-10): 1.
19. The tandem reaction process according to claim 1, wherein the amount of the carrier gas is 1 to 6 times the total molar amount of the aromatic hydrocarbon feedstock and the alkylating agent.
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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5240892A (en) * 1987-09-02 1993-08-31 Mobil Oil Corporation Small crystal ZSM-5, as a catalyst

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5240892A (en) * 1987-09-02 1993-08-31 Mobil Oil Corporation Small crystal ZSM-5, as a catalyst

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