CN101780417B - Catalyst for preparing p-xylene and light olefins by conversion of methanol and its preparation method and application - Google Patents

Abstract

The invention discloses a catalyst for preparing paraxylene and low-carbon olefin by methanol conversion, and a preparation method and application thereof. The catalyst provided by the invention is obtained by modifying the surface acidity and the pore structure of a zeolite molecular sieve modified by transition metal and rare earth metal by a siloxane compound; wherein, the content of the transition metal is 0.1 to 10 weight percent of the total weight of the catalyst; the content of rare earth metal is 0.1-5 wt% of the total weight of the catalyst; the loading amount of the modified siloxane-based compound counted by Si is 0.1-8 wt% of the total weight of the catalyst. The catalyst is utilized to realize the purpose of directly preparing three basic chemicals, namely ethylene, propylene and paraxylene from methanol in a reaction process; the selectivity of p-xylene in aromatic hydrocarbon in the hydrocarbon products obtained by the reaction is more than 80 wt%, and the selectivity of ethylene and propylene in C₁-C₅The medium selectivity is more than 80 wt%.

Description

Catalyst for preparing p-xylene and light olefins by conversion of methanol and its preparation method and application

technical field

The invention relates to a technology for preparing low-carbon olefins and aromatics from methanol, in particular to a catalyst for the high-selectivity preparation of p-xylene and co-production of ethylene and propylene from methanol, its preparation method and application.

Background technique

Ethylene, propylene and p-xylene are the basic raw materials of modern chemical industry. At present, p-xylene is mainly produced from toluene, _C9 aromatics and mixed xylenes through disproportionation, isomerization, adsorption separation or cryogenic separation. Because the p-xylene content in the product is controlled by thermodynamics, p-xylene only accounts for about 20% of the C ₈ mixed aromatics, and the process involves a large amount of material circulation, huge equipment, and high operating costs. In particular, the difference between the boiling points of the three isomers of xylene is very small, and high-purity p-xylene cannot be obtained by ordinary distillation techniques, but an expensive adsorption separation process must be used. Ethylene and propylene are produced from light oil (naphtha and light diesel oil) obtained from crude oil refining, liquefied petroleum gas (LPG) and ethane and propane obtained from natural gas processing. In recent years, many patents at home and abroad have disclosed new ways to produce p-xylene, in which the alkylation of toluene can produce p-xylene with high selectivity, but the above-mentioned processes are all dependent on petroleum resources.

Methanol to light olefins and methanol to aromatics are new ways to produce ethylene, propylene and aromatics by non-petroleum route. In 1976, Mobil Oil Company carried out the reaction of converting methanol into hydrocarbons on ZSM-5 molecular sieve catalyst. USP 4,035,430 discloses the process of methanol converting gasoline on ZSM-5 molecular sieve catalyst; USP4,542,252 discloses the technology of producing low-carbon olefins from methanol on ZSM-5 molecular sieve catalyst; USP 3,911,041, USP 4,049,573, USP 4,100,219, JP 60-126233, JP 61-97231, JP 62-70324 and EP 6501 disclose the use of ZSM-5 molecular sieve catalysts modified by phosphorus, magnesium, silicon or alkali metal elements to produce low-carbon olefins from methanol; USP 5,367,100 It is disclosed that Dalian Institute of Chemical Physics uses ZSM-5 molecular sieve catalyst modified by phosphorus and lanthanum to produce light olefins from methanol or dimethyl ether. The total selectivity of ethylene and propylene is only about 65wt%, and ethylene, propylene and The overall butene selectivity is greater than 85 wt%. Chinese patent CN 101244969 discloses a fluidized bed device for _C1 - _C2 hydrocarbons or methanol aromatization and catalyst regeneration. Using this device and catalyst, the coking state of the catalyst in the aromatization reactor can be adjusted at any time. Therefore, the purpose of continuously and efficiently converting C ₁ -C ₂ hydrocarbons or methanol and generating aromatics with high selectivity is achieved. Chinese patent CN 1880288 discloses a process for methanol conversion to aromatics. On the modified ZSM-5 molecular sieve catalyst, methanol is catalytically converted into aromatics-based products, which has the advantages of high overall selectivity of aromatics and flexible process operation. U.S. Patent US 4615995 discloses a ZSM-5 molecular sieve catalyst loaded with Zn and Mn, which is used for the conversion of methanol to prepare olefins and aromatics. By adjusting the content of Zn and Mn in the catalyst, the low-carbon olefins/aromatics in the product can be changed ratio.

The above method of methanol conversion to prepare low-carbon olefins or aromatics mainly focuses on methanol conversion to produce low-carbon olefins, methanol conversion to produce mixed aromatics, or methanol conversion to produce low-carbon olefins by-product mixed aromatics. The content of the main product of methanol conversion in any method is relatively low, such as the poor selectivity of ethylene and propylene in the production of low-carbon olefins from methanol conversion, and the low market value of mixed aromatics produced by direct conversion of methanol, which makes these processes difficult to industrialize. App promotion.

Contents of the invention

The object of the present invention is to provide a catalyst for preparing p-xylene and light olefins (ethylene, propylene) by converting methanol with high selectivity. The catalyst can be used to directly produce three basic chemicals ethylene, propylene and p-xylene from methanol in one reaction process.

In order to achieve the above object, the catalyst provided by the present invention is obtained by first modifying the zeolite molecular sieve with a transition metal and a rare earth metal double metal, and then modifying it with a siloxane compound;

In the catalyst, the content of the transition metal is 0.1-10% of the total mass of the catalyst, the content of the rare earth metal is 0.1-5% of the total mass of the catalyst, and the siloxane-based compound is calculated as silicon The loading amount is 0.1-8% of the total mass of the catalyst.

Further, the content of transition metals in the catalyst is 4-8% of the total mass of the catalyst, the content of rare earth metals is 2-5% of the total mass of the catalyst, and the loading of the siloxane-based compound in terms of silicon The amount is 3-6% of the total mass of the catalyst.

The transition metal can be selected from any one of the following: iron, cobalt, nickel, copper and zinc, preferably zinc or iron; the rare earth metal can be lanthanum.

Catalyst provided by the present invention is prepared according to the method comprising the following steps:

1) The zeolite molecular sieve is prepared into an acidic zeolite molecular sieve through ion exchange and roasting;

2) Immerse the acidic zeolite molecular sieve obtained in step 1) in a transition metal soluble salt or transition metal soluble oxide solution for 0.5-12 hours, take it out and dry it, and roast it at 450-650°C for 2-6 hours to obtain a single metal modified Sexual molecular sieve;

3) Put the monometallic modified molecular sieve obtained in step 2) in the rare earth metal soluble salt solution for 0.5-12 hours, take it out and dry it, and then bake it at 450-650° C. for 2-6 hours to obtain a bimetallic modified molecular sieve;

4) The bimetallic modified molecular sieve obtained in step 3) is impregnated with a siloxane compound for 0.5-12 hours, taken out and dried, and then calcined at 450-650° C. for 2-6 hours to obtain the catalyst.

Wherein, the metal in the transition metal soluble salt and the transition metal soluble oxide in step 2) is selected from any one of the following: iron, cobalt, nickel, copper and zinc, preferably zinc or iron; step 3) The soluble salt of rare earth metal mentioned in is the soluble salt of lanthanum.

The zeolite molecular sieve described in the present invention is the aluminosilicate with crystalline skeleton structure, and its structural type is MFI type or MEL type; The zeolite molecular sieve of described MFI type is preferably ZSM-5, and the zeolite molecular sieve of described MEL type is preferably ZSM-11.

The general structural formula of the siloxane-based compound is shown in formula I:

(Formula I)

Wherein, R ₁ , R ₂ , R ₃ and R ₄ are all selected from C ₁ -C ₁₀ alkyl groups; the preferred siloxane compound in the present invention is tetraethyl silicate.

Another object of the present invention is to provide the application of the above-mentioned catalyst in the conversion of methanol to produce p-xylene and the co-production of light olefins.

The method for methanol conversion to prepare p-xylene and co-produce ethylene and propylene is: adopt the catalyst provided by the present invention to react with methanol raw material to obtain p-xylene, ethylene and propylene; the reaction method can be fixed bed or fluidized bed Either form; the reaction conditions are: reaction temperature 350-550°C, preferably 400-500°C; reaction pressure 0-5MPa; methanol feeding weight space velocity 0.5-10h ^-1 .

Among the hydrocarbon products of the reaction product, the selectivity of p-xylene in aromatic hydrocarbons is greater than 80 wt%, and the selectivity of ethylene propylene in _C1 - _C5 is greater than 80 wt%.

Detailed ways

The catalyst of the present invention is based on the structure type of MFI or MEL aluminosilicate having a crystalline skeleton structure as the active component, and its acidity is modulated by a transition metal or a rare earth metal bimetal, and then its outer surface is acidified by a siloxane reagent. and pores are modified to prepare catalysts, and the preparation process is as follows:

1) The raw molecular sieve powder is exchanged and roasted to prepare an acidic molecular sieve.

2) impregnating the molecular sieve with transition metals and rare earth metals to obtain modified molecular sieves.

4) Using a siloxane-based reagent to modify the surface of the modified molecular sieve to adjust the acidity and pore structure of the outer surface of the catalyst to obtain a catalyst.

In the above preparation process, the oxides and soluble salts of transition metals and rare earth metals are used to modify the zeolite molecular sieve, the purpose of which is to improve the selectivity of aromatic hydrocarbons in the methanol conversion reaction of the catalyst. The surface acidity and pore structure modification of the modified molecular sieve are carried out by using a siloxane-based reagent, and the purpose is to improve the p-xylene selectivity of the methanol conversion reaction of the catalyst.

The experimental methods described in the following examples, if no special instructions, are conventional methods; the reagents and materials, if no special instructions, can be obtained from commercial sources; "wt%" in the examples means mass percentage content .

The present invention is described in detail below through examples, but the present invention is not limited to the following examples.

Embodiment 1, Zn-La-HZSM-5 zeolite molecular sieve

1) Roast ZSM-5 zeolite molecular sieve raw powder (SiO ₂ /Al ₂ O ₃ =61, Fushun Catalyst Factory) at 550°C to remove the template agent, and exchange it with 0.5 molar equivalent ammonium nitrate solution in a water bath at 80°C for 4 times , dried in air at 120°C after exchange, and calcined at 550°C for 3 hours to obtain HZSM-5 zeolite molecular sieve.

2) Take 50 g of the HZSM-5 zeolite molecular sieve prepared in step 1), impregnate it with a 10 wt% Zn(NO ₃ ) ₂ aqueous solution for 10 hours, dry it, and roast it at 550° C. for 3 hours to obtain the Zn-HZSM-5 zeolite molecular sieve , wherein the Zn loading amount is 5wt%.

3) Take 20 g of Zn-HZSM-5 zeolite molecular sieve, use 10wt% La(NO ₃ ) ₃ aqueous solution to impregnate for 10 hours, after drying, roast at 550° C. for 3 hours to obtain Zn-La-HZSM-5 zeolite molecular sieve , wherein the La loading amount is 3wt%.

Embodiment 2, Fe-La-HZSM-5 zeolite molecular sieve

1) Roast ZSM-5 zeolite molecular sieve raw powder (SiO ₂ /Al ₂ O ₃ =61, Fushun Catalyst Factory) at 550°C to remove the template agent, and exchange it with 0.5 molar equivalent ammonium nitrate solution in a water bath at 80°C for 4 times , dried in air at 120°C after exchange, and calcined at 550°C for 3 hours to obtain HZSM-5 zeolite molecular sieve.

2) Take 50 g of the HZSM-5 zeolite molecular sieve prepared in step 1), impregnate it with 12 wt% Fe(NO ₃ ) ₃ aqueous solution for 12 hours, dry it, and roast it at 550° C. for 3 hours to obtain Fe-HZSM-5 zeolite molecular sieve , wherein, Fe loading 6wt%.

3) Take 20 g of Fe-HZSM-5 zeolite molecular sieve, impregnate it with 10 wt% La(NO ₃ ) ₃ aqueous solution for 10 hours, dry it, and roast it at 550° C. for 3 hours to obtain Fe-La-HZSM-5 zeolite molecular sieve , wherein the La loading amount is 3wt%.

Example 3, Preparation of Catalyst for Preparing p-Xylene and Light Olefins with High Selectivity in Methanol Conversion

Zn-La-HZSM-5, Fe-La-HZSM-5 zeolite molecular sieves obtained in Example 1 and Example 2 are surface-modified using siloxane reagent tetraethyl silicate:

(1) Immerse 10 grams of Zn-La-HZSM-5 in 20 grams of tetraethyl silicate for 12 hours, pour out the liquid, dry at 120°C, and bake at 550°C for 3 hours to obtain modified Zn - La-HZSM-5 zeolite molecular sieve, numbered MTAC-11; wherein, the mass content of Zn is 4.7%, the mass content of La is 2.9%, and the loading amount of silicon is 4.2% of the total mass of the catalyst.

(2) Put 10 grams of Fe-La-HZSM-5 into 20 grams of tetraethyl silicate and soak for 12 hours. After pouring out the liquid, dry it at 120°C and bake it at 550°C for 3 hours to obtain the modified Fe - La-HZSM-5 zeolite molecular sieve, numbered MTAC-12; wherein, the mass content of Fe is 5.6%, the mass content of La is 2.9%, and the loading amount of silicon is 4.3% of the total mass of the catalyst.

Embodiment 4 fixed bed reaction evaluation

The methanol conversion reaction was carried out in a fixed-bed reactor, using the catalyst in Example 3, and the reaction conditions were: the methanol weight space velocity was 2 h ⁻¹ , and the temperature was 450° C. The products were analyzed online by gas chromatography (normalized after removal of methanol), as shown in Table 1. Among them, the C ₁ -C ₅ composition analysis was performed by gas chromatography off-line analysis, and the results are shown in Table 2.

Table 1, product analysis table

catalyst MTAC-11 MTAC-12 Reaction temperature (℃) 450 450 Feeding time (min) 30 30 Methanol conversion rate (%) 85.23 96.21 p-xylene selectivity (%) ^* 83.42 83.58 Product distribution (%) C ₁ -C ₅ 48.31 47.32 Benzene 0.06 0.07 Ethylbenzene 0.24 0.3 p-xylene 43.12 44.03 m-xylene 0.89 0.76 O-xylene 1.18 1.09 ≥C ₉ 6.20 6.43 Total 100.00 100.00

^* Selectivity of p-xylene in aromatics

Table 2, product analysis table

Catalyst MTAC-11 MTAC-12 Reaction temperature (°C) 450 450 Feeding time (min) 20-40 20-40 CH ₄ 2.12 2.36 C ₂ H ₄ 46.82 45.56 C ₂ H ₆ 0.21 0.28 C ₃ H ₆ 33.49 34.59 C ₃ H ₈ 0.45 0.43 ^C ₄₊ 11.72 12.01 _C5 ⁺ 5.19 4.77 Total 100.00 100.00 C ₂ H ₄ +C ₃ H ₆ 80.31 80.15

Example 5, Preparation of Catalysts for Preparing p-Xylene and Light Olefins with High Selectivity in Methanol Conversion

The original powder of ZSM-11 zeolite molecular sieve (SiO ₂ /Al ₂ O ₃ =65, Fushun Catalyst Factory) was calcined at 550°C to remove the template agent, and exchanged with 0.5 molar equivalent ammonium nitrate solution in a water bath at 80°C for 4 times, After the exchange, it was calcined at 550° C. for 3 hours to obtain HZSM-11 zeolite molecular sieve.

Take 50g of HZSM-11 zeolite molecular sieve, use 12wt% Fe(NO ₃ ) ₃ aqueous solution to impregnate for 12 hours. %.

Take 20g of Fe-HZSM-11 zeolite molecular sieve, use 10wt% La(NO ₃ ) ₃ aqueous solution to impregnate for 12 hours, after drying, roast at 550°C for 3 hours to obtain Fe-La-HZSM-11 zeolite molecular sieve, wherein The loading amount of La was 5 wt%.

The surface modification of Fe-La-HZSM-11 zeolite molecular sieves was carried out using the siloxane reagent tetraethyl silicate. The steps are as follows: immerse 10 grams of Fe-La-HZSM-11 in 20 grams of tetraethyl silicate overnight, pour out the liquid, dry at 120°C, and roast at 550°C for 3 hours to obtain the modified Fe -La-HZSM-11 zeolite molecular sieve, numbered MTAC-13, wherein the mass content of Fe is 7.6%, the mass content of La is 4.8%, and the loading amount of silicon is 4.4% of the total mass of the catalyst.

Embodiment 6, fixed bed reaction evaluation

The methanol conversion reaction was carried out in a fixed-bed reactor using the catalyst in Example 5, the reaction conditions were: the methanol weight space velocity was 4h ^-1 , and the temperatures were 450°C and 500°C respectively. The products were analyzed online by gas chromatography (normalized after removal of methanol), as shown in Table 3. Among them, the composition analysis of C ₁ -C ₅ adopts gas chromatography offline analysis, and the results are shown in Table 4.

Table 3, product analysis

^* Selectivity of p-xylene in aromatics

Table 4, product analysis

Claims (5)

1. A catalyst for methanol conversion to prepare p-xylene and co-produce low-carbon olefins, obtained by zeolite molecular sieve first modified by transition metals and rare earth metals, and then modified by siloxane compounds; In the catalyst, the content of the transition metal is 0.1-10% of the total mass of the catalyst, the content of the rare earth metal is 0.1-5% of the total mass of the catalyst, and the siloxane-based compound is calculated as silicon The loading amount is 0.1-8% of the total mass of the catalyst; The low carbon olefins are ethylene and propylene; The zeolite molecular sieve is ZSM-5 or ZSM-11; The transition metal is zinc or iron; the rare earth metal is lanthanum; The general structural formula of the siloxane-based compound is shown in formula I:

(Formula I) Wherein, R ₁ , R ₂ , R ₃ and R ₄ are all ethyl groups. 2. The catalyst according to claim 1, characterized in that: in the catalyst, the transition metal content is 4-8% of the total mass of the catalyst, and the rare earth metal content is 2% of the total mass of the catalyst. -5%, the loading amount of the siloxane-based compound in terms of silicon is 3-6% of the total mass of the catalyst; the low-carbon olefins are ethylene and propylene. 3. catalyzer according to claim 1 or 2, is characterized in that: described catalyzer is prepared according to the method comprising the following steps: 1) The zeolite molecular sieve is prepared into an acidic zeolite molecular sieve through ion exchange and roasting; wherein, the zeolite molecular sieve is ZSM-5 or ZSM-11; 2) Immerse the acidic zeolite molecular sieve obtained in step 1) in a transition metal soluble salt or transition metal soluble oxide solution for 0.5-12 hours, take it out and dry it, and roast it at 450-650°C for 2-6 hours to obtain a transition metal modified A molecular sieve with properties; wherein, the metal in the transition metal soluble salt and the transition metal soluble oxide is zinc or iron; 3) Immerse the transition metal-modified molecular sieve obtained in step 2) in a rare earth metal soluble salt solution for 0.5-12 hours, take it out and dry it, and then bake it at 450-650° C. for 2-6 hours to obtain a transition metal and rare earth metal bimetallic Modified molecular sieve; wherein, the rare earth metal soluble salt is a lanthanum soluble salt; 4) immerse the bimetallic modified molecular sieve obtained in step 3) in a siloxane compound for 0.5-12 hours, take it out and dry it, and then bake it at 450-650° C. for 2-6 hours to obtain the catalyst; The general structural formula of the siloxane-based compound is shown in formula I:

(Formula I) Wherein, R ₁ , R ₂ , R ₃ and R ₄ are all ethyl groups. 4. A method for preparing the catalyst as claimed in claim 1, comprising the steps of: 1) The zeolite molecular sieve is prepared into an acidic zeolite molecular sieve through ion exchange and roasting; wherein, the zeolite molecular sieve is ZSM-5 or ZSM-11; 2) Immerse the acidic zeolite molecular sieve obtained in step 1) in a transition metal soluble salt or transition metal soluble oxide solution for 0.5-12 hours, take it out and dry it, and roast it at 450-650°C for 2-6 hours to obtain a transition metal modified A molecular sieve with properties; wherein, the metal in the transition metal soluble salt and the transition metal soluble oxide is zinc or iron; 3) Immerse the transition metal-modified molecular sieve obtained in step 2) in a rare earth metal soluble salt solution for 0.5-12 hours, take it out and dry it, and then bake it at 450-650° C. for 2-6 hours to obtain a transition metal and rare earth metal bimetallic Modified molecular sieve; wherein, the rare earth metal soluble salt is a lanthanum soluble salt; 4) immerse the bimetallic modified molecular sieve obtained in step 3) in a siloxane-based compound for 0.5-12 hours, take it out and dry it, and then bake it at 450-650° C. for 2-6 hours to obtain the catalyst according to claim 1; The general structural formula of the siloxane-based compound is shown in formula I:

(Formula I) Wherein, R ₁ , R ₂ , R ₃ and R ₄ are all ethyl groups. 5. The application of the catalyst described in any one of claims 1-3 in methanol conversion to prepare p-xylene and co-production of light olefins.