CN101767038B - Catalyst for preparing p-xylene by conversion of methanol and its preparation method and application - Google Patents

Abstract

The invention discloses a catalyst for preparing p-xylene by converting methanol, a preparation method and application thereof. The catalyst provided by the present invention is obtained by modifying the surface acidity and pore structure of the metal-modified zeolite molecular sieve with a siloxane-based compound; wherein, the metal content is 0.1-10 wt % of the total weight of the catalyst; The loading amount calculated as Si is 0.1-8wt% of the total weight of the catalyst. The content of aromatics in hydrocarbon products obtained from the reaction is greater than 60 wt%, the selectivity of p-xylene in aromatics is greater than 85 wt%, and the selectivity of p-xylene in xylene isomers is greater than 95 wt%.

Description

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

technical field

The invention relates to a catalyst for preparing p-xylene with high selectivity of methanol, a preparation method and application thereof.

Background technique

Para-xylene is the basic raw material for the synthesis of polyester (PET). 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. In recent years, many patents at home and abroad have disclosed new ways to produce p-xylene, in which toluene methylation can produce p-xylene with high selectivity, but this process still depends on the petroleum resource - toluene.

The technology of preparing aromatics from methanol/dimethyl ether is a new way to prepare aromatics from coal or natural gas. Aromatics are prepared by direct aromatization of methanol/dimethyl ether on a metal-molecular sieve composite catalyst. ZSM-5 zeolite molecular sieve has a unique effect on converting methanol into aromatic hydrocarbons. In the methanol-to-gasoline (MTG) reaction, ZSM-5 zeolite molecular sieves can effectively convert methanol into hydrocarbons with gasoline boiling range, and the synthesized gasoline contains about 60% aromatics. On acidic molecular sieves, methanol can be converted into alkanes, alkenes and aromatics, etc. Different types of molecular sieves have different product ratios. Dehydroaromatization of alkanes and alkenes is an effective way to increase the yield of aromatics. Therefore, acidic molecular sieves are often used at present. Metal modification method to prepare methanol to aromatics catalyst.

In 1977, Chang et al. (Journal of Catalysis, 1977, 47, 249) of Mobil Corporation reported a method for the conversion of methanol and its oxygenates to prepare aromatics and other hydrocarbons on ZSM-5 molecular sieve catalysts. Studies have shown that under the action of metal components, alkanes and alkenes can be converted into aromatics under certain conditions. Therefore, modifying ZSM-5 with metal components to generate more aromatics during methanol conversion has become the main direction of current research. At present, the research on the modification of ZSM-5 mainly focuses on the modification of Zn and Ga, and the modification of other metals such as Ag and Cu have also been reported. Japan's Ono et al. (J.Chem.Soc., FaradayTrans.1, 1988,84(4), 1091; Microporous Materials, 1995,4,379) introduced Zn and Ag into ZSM-5 molecular sieves by ion exchange , investigated the catalytic performance of methanol to aromatics (MTA). After the introduction of Zn, the content of aromatics in the product is increased to about 67.4% (C%), and the yield of aromatics can reach about 80% after introducing Ag.

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 aromatics obtained in the process of methanol conversion to prepare aromatics are all mixed aromatics, the products are complicated and the market value is low.

Contents of the invention

The object of the present invention is to provide a catalyst for preparing p-xylene by converting methanol with high selectivity. The catalyst can be used to improve the selectivity of producing aromatics directly from methanol.

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

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

Further, the content of the metal in the catalyst is 2-5% of the total mass of the catalyst, and the loading amount of the siloxane-based compound calculated as silicon is 3-5% of the total mass of the catalyst.

The metal may be selected from any one of the following: iron, cobalt, nickel, copper and zinc, preferably zinc or iron.

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 metal soluble salt or 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 metal-modified molecular sieve;

3) Immerse the metal-modified molecular sieve obtained in step 2) in the 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.

Wherein, the metal in the metal soluble salt and the metal oxide in step 2) is selected from any one of the following: iron, cobalt, nickel, copper and zinc, preferably zinc or iron.

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 molecular sieve SiO ₂ /Al ₂ O ₃ ratio is 10-100.

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.

The method for preparing p-xylene with high selectivity of methanol conversion is: using the catalyst provided by the present invention to react with methanol raw material to obtain p-xylene; the conditions of the reaction are: the reaction temperature is 350-550°C, preferably 400-500°C; reaction pressure 0-5MPa; methanol feeding weight space velocity 0.5-10h ^-1 . The content of aromatics in hydrocarbon products is greater than 60 wt%, the selectivity of p-xylene in aromatics is greater than 85 wt%, and the selectivity of p-xylene in xylene isomers is greater than 95 wt%.

Detailed ways

The catalyst of the present invention uses the aluminosilicate with the structure type MFI or MEL having a crystalline skeleton structure as the active component, modifies its acidity through metal modification, and then modifies the acidity of its outer surface and pores through siloxane reagents Prepared into catalyst, its preparation process is as follows:

1) The molecular sieve raw powder is prepared into an acidic molecular sieve by exchanging and roasting;

2) impregnating the molecular sieve with metal to obtain a metal-modified molecular sieve;

3) Using a siloxane-based reagent to modify the surface of the metal-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 zeolite molecular sieve is modified with metal oxides or soluble salts, 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 present invention is described in detail below through examples, but the present invention is not limited to the following examples.

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 .

Embodiment 1, Zn-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 6 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 3wt%.

Embodiment 2, Fe-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% Fe(NO ₃ ) ₃ aqueous solution for 10 hours, dry it, and roast it at 550° C. for 3 hours to obtain Fe-HZSM-5 zeolite molecular sieve , wherein the Fe loading amount is 5wt%.

Embodiment 3, preparation catalyst

Zn-HZSM-5, Fe-HZSM-5 zeolite molecular sieves obtained in embodiment 1 and embodiment 2 are carried out surface modification using siloxane reagent tetraethyl silicate:

(1) Immerse 10 grams of Zn-HZSM-5 in 20 grams of tetraethyl silicate for 5 hours, pour out the liquid, dry at 120°C, and bake at 550°C for 3 hours to obtain modified Zn-HZSM -5 catalyst, wherein, the mass content of Zn is 2.9%, and the loading amount of tetraethyl silicate calculated as silicon is 4.3% of the total mass of the catalyst. The number is MTAC-01;

(2) Put 10 grams of Fe-HZSM-5 into 20 grams of tetraethyl silicate and immerse it for 8 hours, pour out the liquid, dry it at 120°C, and bake it at 550°C for 3 hours to obtain the modified Fe-HZSM -5 catalyst, numbered MTAC-02; wherein, the mass content of Fe is 4.8%, and the loading amount of tetraethyl silicate calculated as silicon is 4.6% 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.

Table 1, product analysis table

Catalyst MTAC-01 MTAC-02 Reaction temperature (°C) 450 450 Feeding time (min) 30 30 Methanol conversion rate (%) 85.35 96.42 Selectivity of aromatics in hydrocarbons (wt%) 63.69 65.51 Selectivity of p-xylene in aromatics (wt%) 85.27 86.83 Selectivity of p-xylene among xylene isomers (wt%) 97.19 96.62 Product distribution (wt%) C1-C5 36.31 34.49 Benzene 0.22 0.39 Ethylbenzene 1.36 1.21 p-Xylene 54.31 56.88 m-xylene 0.32 0.34 O-xylene 1.25 1.65 ≥C ₉ 6.23 5.04 Total 100.00 100.00

Embodiment 5, preparation catalyst

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 10wt% concentration Fe(NO ₃ ) ₃ aqueous solution to impregnate for 8 hours, after drying, roast at 550°C for 3 hours to obtain Fe-HZSM-5 zeolite molecular sieve, wherein the Fe loading capacity is 5wt %.

The surface modification of Fe-HZSM-11 zeolite molecular sieves was carried out using the siloxane reagent tetraethyl silicate. The steps are as follows: put 10 grams of Fe-HZSM-11 into 20 grams of tetraethyl silicate and soak for 12 hours, pour out the liquid, dry at 120°C, and roast at 550°C for 3 hours to obtain the modified Fe-HZSM-11 In the HZSM-11 catalyst, the mass content of Fe is 4.7%, and the loading amount of tetraethyl silicate calculated as silicon is 4.8% of the total mass of the catalyst. The serial number is MTAC-03.

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: 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 2.

Table 2, product analysis

Claims (4)

1. a methanol conversion prepares the catalyst of paraxylene, be zeolite molecular sieve earlier after metal-modified, obtain through siloxy group is compound modified again; In the said catalyst, said tenor is the 0.1-10% of said catalyst gross mass, and said siloxy group compound is the 0.1-8% of catalyst gross mass in the loading of silicon;

Said zeolite molecular sieve is ZSM-5 or ZSM-11;

Said metal is zinc or iron;

Said siloxy group structural general formula is suc as formula shown in the I:

Wherein, R ₁, R ₂, R ₃And R ₄Be ethyl.

2. catalyst according to claim 1 is characterized in that: in the said catalyst, said tenor is the 2-5% of said catalyst gross mass, and said siloxy group compound is the 3-5% of catalyst gross mass in the loading of silicon.

3. a method for preparing the said catalyst of claim 1 comprises the steps:

1) zeolite molecular sieve is prepared into acidic zeolite through ion-exchange, roasting; Wherein, said zeolite molecular sieve is ZSM-5 or ZSM-11;

2) acidic zeolite that step 1) is obtained flooded 0.5-12 hour in metal soluble-salt or metal dissolvable oxides solution, after the taking-up oven dry, at 450-650 ℃ of roasting 2-6 hour, obtained metal-modified molecular sieve; Wherein, the metal in said metal soluble-salt and the said metal dissolvable oxides is zinc or iron;

3) with step 2) the metal-modified molecular sieve that obtains flooded 0.5-12 hour in the siloxy group compound, took out the oven dry back at 450-650 ℃ of roasting 2-6 hour, obtained the said catalyst of claim 1;

Said siloxy group structural general formula is suc as formula shown in the I:

(formula I)

Wherein, R ₁, R ₂, R ₃And R ₄Be ethyl.

4. claim 1 or 2 described catalyst prepare the application in the paraxylene in methanol conversion.