CN101797517A - Preparation method of zinc doping zeolite molecular sieve catalyst - Google Patents

Abstract

The invention discloses a preparation method of a zinc-doped zeolite molecular sieve catalyst. The steps are: a) dehydrating the carrier hydrogen type ZSM-5 molecular sieve at a high temperature, the temperature is controlled between 300-500°C, and the temperature is increased by a program to reach Target temperature, and keep at this temperature for 8-12 hours, vacuumize, and the vacuum degree is less than 10 ^-5 torr to remove the water molecules adsorbed by the carrier; b) add Zn element according to the content of the active component of the catalyst, the content range is 0.5% ~8%, sublimation to the surface of the carrier ZSM-5 treated in step (a) at high temperature, the temperature is controlled at 400-550°C, and the sublimation time is kept for 1-5h to obtain the catalyst ZnZSM-5 supported by the active component Zn. The invention has the characteristics of low production cost and simple preparation process, and the prepared catalyst has high and low-temperature activity to alkanes such as methane and high product selectivity.

Description

A kind of preparation method of zinc-doped zeolite molecular sieve catalyst

technical field

The invention relates to the fields of petrochemical industry and natural gas chemical industry, and more specifically relates to a preparation method of a zinc-doped zeolite molecular sieve catalyst. The zinc-doped zeolite molecular sieve catalyst prepared by the invention can be used for catalytic conversion of methane and other alkanes.

Background technique

With the gradual development of social economy, the contradiction between the increasing energy demand of industrialization and the continuous decrease of oil resources as the main energy has become increasingly prominent. Natural gas reserves are extremely rich, and it is speculated that in the next 10-20 years it will replace oil as the world's number one energy source. Natural gas is not only a clean fuel but also an important chemical raw material. Since the 1980s, it has been paid more and more attention by countries all over the world. The main component of natural gas is methane, so the activation and conversion of methane is the core issue of natural gas chemical industry and the key to develop non-oil-based chemical process. As we all know, methane is the most stable organic molecule in nature, and its C-H bond energy is as high as 435KJ/mol, which brings great difficulties to the activation of methane. At present, the industrial activation method is generally to first convert synthetic gas through steam reforming, and then prepare methanol, paraffin and other chemical raw materials through Fischer-Tropsch processes, and then produce high-addition gas from methanol through MTG, MTP, MTO and other processes. valuable industrial products. This multi-step indirect conversion method not only requires large investment but also high energy consumption. Therefore, although this process has a history of more than 70 years, large-scale production is still restricted by high costs. At present, the direct conversion of methane is the focus of research, such as hydrogen production by cracking, ethylene by oxidative coupling, aromatics by aromatization, and methyl chloride by chlorination. There have been many public patent reports on this aspect of research at home and abroad, such as USP 6,552,243, USP 5,877,387, USP 5,670,442, etc. and Chinese patents CN 99122642, CN 99101924, CN 01138890, CN 02131609, etc. Molecular sieves modified by metal tungsten or molybdenum can convert methane into hydrocarbons above C2 in one step. Although the conversion rate of methane and product selectivity continue to increase, all catalytic processes must be carried out at high temperatures (600 ° C ~ 800 ° C or even 1000 ° C ) under heating, this high-energy-consuming process brings great difficulties to industrial applications and is inconsistent with China's industrial production energy-saving and emission-reduction policies. Therefore, the development of catalysts with high and low temperature activity, high product selectivity and simple process flow has important theoretical significance and practical application value.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a zinc-doped zeolite molecular sieve catalyst. The present invention has the advantages of low production cost, simple preparation process, and the prepared catalyst has high and low temperature activity and high product selectivity for alkanes such as methane. features.

In order to achieve the above object, the present invention adopts the following technical measures:

The methane conversion catalyst of the present invention is composed of an active component and a carrier, the active component is Zn (purchased from the market) element, and the carrier is zeolite ZSM-5 (purchased from the market) molecular sieve. By mass percentage, the content range of Zn is 0.5%～8%, and the preferred range is 1～6%, and the balance is zeolite molecular sieve ZSM-5 carrier (92～99.5%), molecular sieve framework molar ratio silicon dioxide: trioxide Dialuminum (SiO ₂ :Al ₂ O ₃ ) is preferably 10-200.

A preparation method of a zinc-doped zeolite molecular sieve catalyst, comprising the following steps:

1) Carrier hydrogen type ZSM-5, wherein: silicon dioxide: aluminum oxide molar ratio = 10-200 molecular sieve dehydration at high temperature, the temperature is controlled between 300-500 ° C, the preferred range of temperature control is 350-450 ℃, using a program (0.5-1 ℃/min) to raise the temperature to reach the target temperature within 8-12 hours, and keep at this temperature for 8-12 hours. Vacuumize (vacuum degree less than 10 ^-5 Torr) to remove water molecules adsorbed by the carrier.

2) according to the content of the catalyst active component, the Zn element is sublimated to the surface of the carrier ZSM-5 treated in step 1 at high temperature, the content range is 0.5%～8%, the preferred range is 1～6%, and the temperature is controlled at 400-550° C., the preferred range of temperature control is 420-500° C., and the sublimation time is maintained for 1-5 hours to obtain the catalyst ZnZSM-5 supported by the active component Zn.

Compared with the prior art, the present invention has the following advantages and effects:

The active components and carrier raw materials are easy to obtain and the price is low; the preparation process is simple, the loading of the active components is easy to control, the dispersion degree on the carrier surface is high, and it is easy to form high active centers; the low-temperature activity for methane is high, and it can be transformed at room temperature and normal pressure The efficiency is higher than 80%, and the stable active intermediates generated can be converted into high value-added products such as methanol with high selectivity.

Detailed ways

The present invention is described in detail below through specific examples.

Embodiment 1: the preparation of catalyst

A preparation method of a zinc-doped zeolite molecular sieve catalyst, comprising the following steps:

1) Dehydrate 1g of hydrogen ZSM-5, wherein: silicon dioxide: aluminum oxide = 10-200 molecular sieve carrier, dehydrate at high temperature, control the temperature between 380°C, and use the program (0.8°C/min) to increase the temperature within 8h The target temperature of 380°C was reached and kept at 380°C for 8h. Vacuumize (the degree of vacuum is 10 ^-6 Torr) to remove the water molecules adsorbed by the carrier.

2) Weigh 0.015g of zinc powder, use the above step (1) to degas at room temperature (the same as below 20-25°C) for 8h, then sublime at 450°C to the hydrogen-form HZSM- 5 on the surface of the carrier, the sublimation time was maintained for 3 hours, and the Zn-loaded catalyst ZnZSM-5 was obtained.

Embodiment 2: the preparation of catalyst

Using the same steps as in Example 1, 0.02g or 0.04g of zinc powder was sublimated onto the surface of the ZSM-5 molecular sieve carrier to obtain the catalyst ZnZSM-5.

Embodiment 3: the preparation of catalyst

Utilize the same steps as in Example 1 to sublimate 0.03g or 0.06g zinc powder to the carrier surface to obtain catalyst ZnZSM-5

Embodiment 4: the preparation of contrast catalyst

In this example, ZnZSM-5 catalyst was prepared by impregnation method. Weigh 5g HZSM-5, dissolve it in 33ml deionized water and stir. Weigh 1.26 g of zinc nitrate and add it into the solution and raise the temperature to 80° C. and continue to stir for 5 h. After the stirring is completed, put it in an oven and dry it overnight at 110°C. The comparative catalyst was obtained after the dried sample was calcined at 550° C. for 4 h in an air atmosphere in a tube furnace.

Embodiment 5: the preparation of contrast catalyst

This example uses the exchange method to prepare ZnZSM-5 catalyst. Weigh 5g of the hydrogen-form ZSM-5 catalyst, dissolve it in 15ml of deionized water and stir. Weigh 0.35g of zinc acetate and add it to the solution, heat to reflux at 90°C for 8h, filter after the reflux, and dry at 110°C overnight. The above process was repeated twice, and the dried sample was calcined in an air atmosphere at 550° C. for 7 hours to obtain a comparative catalyst.

Embodiment 6: Catalyst is measured to methane catalytic activity

The activity and methane conversion products of the catalysts in Examples 1-5 were detected by solid-state nuclear magnetic resonance. ¹³ CH ₄ ( ¹³ C>90%) was adsorbed into the catalyst in a vacuum system, and the adsorption amount was 150 μmol/g. The adsorbed sample was transferred to a solid-state nuclear magnetic resonance spectrometer at room temperature, and the product was detected using a cross-polarization pulse sequence. The reaction temperature was room temperature (25° C.) and the reaction time was 2 h. The results are shown in Table 1.

Table 1

Y: yes, N: no

Embodiment 7: methane is converted into methanol determination

Utilize the catalyst in Example 2 to convert methane into intermediate methoxy at different temperatures, then react with water at room temperature (25° C.) to generate methanol, extract with acetonitrile, and analyze the product by gas chromatography. The results are shown in Table 2

Table 2

The above examples show that the zinc-doped ZnZSM-5 catalyst prepared by this method has high catalytic activity for methane, and can activate methane at room temperature to generate methoxy active species, which can be further converted into methanol and other high value-added chemical products.

Claims (2)

1. a preparation method of a zinc-doped zeolite molecular sieve catalyst, the steps are: a) Carrier hydrogen type ZSM-5, wherein: silicon dioxide: aluminum oxide molar ratio = 10-200, molecular sieves are dehydrated at high temperature, the temperature is controlled between 300-500 °C, and the program is 0.5-1 °C/ Raise the temperature within 8 to 12 hours to reach the target temperature, and keep it at this temperature for 8 to 12 hours, vacuumize, and the vacuum degree is less than 10 ^-5 Torr to remove the water molecules adsorbed by the carrier; b) according to the content of the catalyst active component, the Zn element is sublimated to the surface of the carrier ZSM-5 treated in step (a) at a high temperature, the temperature is controlled at 400-550 ° C, and the content range is 0.5% to 8%. The time is maintained for 1-5 hours, and the catalyst ZnZSM-5 supported by the active component Zn is obtained. 2. The preparation method of a zinc-doped zeolite molecular sieve catalyst according to claim 1, characterized in that: the content of Zn is 1-6%.