Application of metal-free catalyst in catalytic decomposition of methyl mercaptan in coal gasification process

Abstract

The invention discloses an application of a metal-free catalyst in catalytic decomposition of methyl mercaptan in a coal gasification process, and the metal-free catalyst is prepared by the following steps: placing cetyltrimethylammonium bromide and ammonia water in ionized water, dropwise adding tetraethoxysilane while stirring, stirring for 1-2 hours, carrying out microwave heating reaction, carrying out solid-liquid separation on the reaction product, washing the solid, and drying to obtain the metal-free catalyst. And drying and roasting. The catalyst provided by the invention is free of metal loading, and the toxicity of the catalyst and the cost of loaded metal do not need to be considered in the use process; the catalyst can efficiently catalyze and decompose methyl mercaptan at the reaction temperature meeting the coal gasification process, the reaction is carried out at the normal pressure and the temperature of 600 DEG C, and the catalyst shows good stability and water resistance.

Description

Technical Field

[0001] The invention relates to use of a metal-free catalyst in catalytic decomposition to remove methyl mercaptan generated in a coal gasification process, and belongs to the technical field of removing sulfur-containing volatile organic pollutants. Background Art

[0002] Sulfur-containing volatile organic compounds are usually highly toxic to organisms and persistent in the environment. They are considered as target pollutants that need to be strictly controlled by most countries. Among them, methyl mercaptan (CH3SH) mainly comes from industrial production, urban sewage, sludge treatment and garbage treatment facilities. Its concentration is between tens and hundreds of ppm. It has the characteristics of low olfactory threshold, volatility, high toxicity and high corrosiveness, which can cause harm to the central nervous system and cardiovascular system. At present, the removal methods of methyl mercaptan include alkali absorption method, adsorption method, direct combustion method, catalytic oxidation method, photocatalytic degradation method, biological method and catalytic decomposition method. The catalytic decomposition method has the advantages of simple operation, no need for additional additives and low pollution, and is considered to be the most effective method for degrading methyl mercaptan. In recent years, the catalysts for catalytic decomposition of methyl mercaptan mainly include four types: metal elements, metal oxides, zeolite molecular sieves and loaded molecular sieves.

[0003] So far, the main problems faced by supported metal catalysts are metal toxicity and high cost; if the metal used in the catalyst is not properly treated or discharged into the environment due to leakage, it will have a negative impact on the ecological environment; at the same time, if the metal catalyst used in industry is not properly controlled, it will enter the human body through air, water or food chain, posing a potential risk to the health of people and residents. On the other hand, metal catalysts are relatively expensive, and for large-scale applications, the use of high-cost metal catalysts will significantly increase production costs. In addition to the above problems, due to the sintering of metal catalysts under high temperature conditions, large particles of metal are formed, resulting in a decrease in specific surface area, which further leads to a decrease in its activity. At the same time, during the catalytic decomposition of methyl mercaptan by metal catalysts, there is usually a strong interaction between metal atoms and sulfur atoms, which will cause catalyst sulfur poisoning and also cause catalyst deactivation. Therefore, in order to achieve efficient removal of methyl mercaptan, it is very important to seek a catalyst with a simple preparation method and excellent performance.

[0004] In addition, a large amount of water molecules are produced during the lignite gasification process, and the presence of these water molecules will significantly affect the activity of the catalyst. Therefore, in the design of the catalyst, the effect of water molecules on the catalyst performance must be considered. Summary of the invention

[0005] The invention provides a new use of a metal-free catalyst, namely, use of the metal-free catalyst in catalytically decomposing methyl mercaptan in a coal gasification process. The metal-free catalyst is prepared by placing hexadecyltrimethylammonium bromide and ammonia water in ionized water, adding ethyl orthosilicate dropwise under stirring, stirring for 1-2 hours, performing microwave heating reaction, filtering and washing the reaction product, and then drying and roasting. The metal-free catalyst has the characteristics of simple preparation method, low cost, high stability, water resistance, and the like.

[0006] The mass volume ratio of the hexadecyltrimethylammonium bromide to aqueous ammonia is 1:3-4 g:mL, and the mass volume ratio of the hexadecyltrimethylammonium bromide to tetraethyl orthosilicate is 1:3.5-4.5 g:mL.

[0007] The calcination is carried out by keeping the temperature at 300-400° C. for 0.8-1.2 hours, then heating to 500-600° C. and keeping the temperature for 5-7 hours.

[0008] The microwave heating time is 4-6 min.

[0009] The metal-free catalyst performs a catalytic decomposition reaction of methyl mercaptan at 600°C.

[0010] Advantages and technical effects of the present invention: the preparation method of the metal-free catalyst of the present invention is simple, low in cost and short in preparation time; the metal-free catalyst of the present invention has excellent stability and water resistance; the catalyst of the present invention has no metal loading, and the toxicity of the catalyst and the cost of the loaded metal do not need to be considered during use; the catalyst of the present invention can catalyze and decompose methyl mercaptan efficiently at a reaction temperature that meets the reaction temperature of the coal gasification process. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is the catalytic activity diagram of metal-free catalyst MCM-41-S and empty tube at 250-600℃; Figure 2 This is a graph showing the tolerance of metal-free catalyst MCM-41-S to water. DETAILED DESCRIPTION

[0012] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is limited to the contents described above. The methods in the implementation are conventional methods unless otherwise specified, and the reagents are conventional reagents or reagents prepared according to conventional methods unless otherwise specified; Example 1: Preparation of metal-free catalyst and its application in decomposing methyl mercaptan 1. Add 14 g of hexadecyltrimethylammonium bromide and 54 mL of ammonia water to 635 mL of deionized water, stir evenly, then drop 57.6 mL of ethyl orthosilicate, stir for 1 hour after the addition is complete, microwave heating for 5 minutes, filter the reaction product, wash the solid with deionized water 3 times, dry it at 105°C for 24 hours, place the dried product in a muffle furnace and heat it to 350°C at a heating rate of 1°C / min, keep it warm for 1 hour, then continue to heat it to 550°C, keep it warm for 6 hours, press the obtained powder into tablets, crush and sieve to obtain a 40-60 mesh metal-free catalyst; 2. Take 0.2g of metal-free catalyst and load it into the reactor. Pass N2 containing 5000ppm of methyl mercaptan at a total flow rate of 30mL / min and a space velocity of 9000mL / (g•h). The reaction is carried out at normal pressure and 250-600℃. At the same time, an experiment without adding catalyst is set as a control. The results are as follows Figure 1 As shown, the activity of the metal-free catalyst gradually increases with the increase of temperature. When the temperature reaches 600°C, the conversion rate of methyl mercaptan reaches 100%.

[0013] Example 2: Water resistance test of catalytic decomposition of methyl mercaptan without metal catalyst 1. The preparation of the metal-free catalyst in this example is the same as that in Example 1; 2. Take 0.2g of catalyst and put it into the reactor. Pass a mixed gas containing 5000ppm of methyl mercaptan and N2 as the balance gas at a flow rate of 30mL / min. React at normal pressure and 600℃ for 2h. Then change the flow rate of the methyl mercaptan mixed gas to 27mL / min and introduce 3mL / min of water vapor. React for 30min. Then stop passing water vapor and change the flow rate of the methyl mercaptan mixed gas to 30mL / min. React again for 2h. Repeat this process to test the water resistance of the metal-free catalyst. The results are as follows: Figure 2 As shown, after 8 water resistance cycle tests, the catalyst still maintained a 100% conversion rate.

Claims

1. Application of a metal-free catalyst in the catalytic decomposition of methyl mercaptan during coal gasification.

2. The use according to claim 1, characterized in that: The metal-free catalyst is prepared by placing hexadecyltrimethylammonium bromide and ammonia water in ionized water, adding ethyl orthosilicate dropwise under stirring, stirring for 1-2 hours, heating with microwaves for reaction, separating the reaction product into solid and liquid, washing the solid, and drying and calcining the solid.

3. The use according to claim 1, characterized in that: The calcination is carried out by keeping the temperature at 300-400°C for 0.8-1.2 hours, then raising the temperature to 500-600°C and keeping the temperature for 5-7 hours.

4. The use according to claim 1, characterized in that: The mass volume ratio of hexadecyltrimethylammonium bromide to ammonia water is 1:3-4 g:mL, and the mass volume ratio of hexadecyltrimethylammonium bromide to tetraethyl orthosilicate is 1:3.5-4.5 g:mL.

5. The use according to claim 1, characterized in that: The catalytic decomposition reaction was carried out at 600°C.

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