WO2007073631A1

WO2007073631A1 - A catalytic purifying method for a waste gas containing trichloroethylene

Info

Publication number: WO2007073631A1
Application number: PCT/CN2006/000361
Authority: WO
Inventors: Xingyi Wang; Dao Li; Yi Zheng; Qiguang Dai
Original assignee: East China University Of Science And Technology
Priority date: 2005-12-29
Filing date: 2006-03-10
Publication date: 2007-07-05
Also published as: CN1806897A; CN100339152C

Abstract

A catalytic purifying method for a waste gas containing trichloroethylene is provided, which comprises introducing wet air into the waste gas to carry out reactions in the presence of a catalyst. The catalyst comprises a carrier stable in wet air, with rare metals, rare earth metals and phosphoric acid supported thereon. By the present method, the trichloroethylene contained in waste gas can be stably converted into CO2 and HCl in wet air at a lower reaction temperature and in the presence of an oxidation-decomposition catalyst for a long time, while the activity of the catalyst is not decreased. The lower amount of rare metal makes it is possible to remove hydrocarbons containing chlorine in waste gas in a very economic way, and no byproducts and second pollution are generated. Therefore the present method is very effective for treating waste gas containing chlorine hydrocarbons, and can be used widely in environmental protection.

Description

- Trichloroethylene exhaust gas catalytic purification method

The present invention relates to a process for treating a waste gas containing trichloroethylene, and more particularly to a process for catalytic combustion, and more particularly to a catalyst employed. Background technique

The hazards of chlorinated organic compounds are not only for human health, but also have a lasting, cumulative effect on biological systems, and destroy atmospheric ozone. Among the 12 international treaties on environmental projects in the United Nations, the persistent organic pollutants listed as the first are organic compounds containing chlorine ^[2] . Chlorinated hydrocarbons (CHC) are classified as aromatic hydrocarbon chlorides such as chlorobenzene, dichlorobenzene, and non-aromatic hydrocarbon chlorides such as vinyl chloride, polyvinyl chloride, chloroformam and polychloromethane, the former being derived from chlorine The bleaching of the wood pulp of the base oxidant, the heat treatment of the chlorine-containing compound and the recovery of the metal; the latter is produced by the chloro-alkali industrial oxychlorination process for the preparation of vinyl chloride. Since the above-mentioned process of producing chlorides is an industry involving China's national economy and people's livelihood at present, the discharge of a large amount of chlorine-containing compounds is inevitable. Trichloroethylene is one of the most difficult to oxidize and decompose halogenated hydrocarbons in chlorinated hydrocarbons. Therefore, the development of catalytic purification technology for trichloroethylene has important environmental protection significance.

In recent years, various methods have been adopted at home and abroad to eliminate chlorine-containing organic compounds, including heat elimination, biological treatment, photocatalytic degradation, hydrodechlorination, etc., in which catalytic elimination is the most economical with low temperature conversion and high selectivity. The most reliable method. The research team represented by Gutierrez-Ortiz has long been engaged in the catalytic elimination of chlorinated hydrocarbons. The catalytic oxidation of chlorinated alkanes and chlorinated olefins has been extensively carried out using various acidic molecular sieves and their noble metal-supporting materials as catalysts. Research, including reaction kinetics, reaction mechanisms, and development of novel catalytic elimination processes (Stud. Surf. Sci. Catal. 130 (2000) 893; Appl. Catal. B 19 (1998.189; Appl. Catal. B 30 (2001) 303; Stud. Surf. Sci. Catal. 130 (2000) 1229; J. Catal. 214 (2003) 130; ; Appl. Catal. B 41 (2003) 31); A considerable part of this work is about the elimination of oxidation of trichloroolefins, including the study of trichloroethylene and saturated hydrocarbons, unsaturated hydrocarbons, and water coexistence systems, with the aim of reducing oxidation temperatures and reducing Emission of tetrachloroethylene, improving the ability of the catalyst to resist chlorine poisoning, etc. Bert M. Weckhuysen (Phys. Chem. Phys., 6 (2004) 5256) uses a basic oxide to hydrolyze chlorinated hydrocarbons to form carbon dioxide and hydrogen chloride.

An obvious disadvantage of the above proposed chlorinated hydrocarbon elimination process is the presence of polychlorinated hydrocarbons in the process, resulting in secondary pollution. Summary of the invention

The technical problem to be solved by the present invention is to disclose a catalytic purification method of trichloroethylene exhaust gas to overcome the disadvantages of the prior art for producing polychlorinated hydrocarbons.

The method of the invention comprises the following steps:

In the presence of a catalyst, a humid air is introduced into the exhaust gas containing trichloroethylene to carry out a reaction to convert trichloroethylene into a non-toxic gas of carbon dioxide and hydrogen chloride, thereby eliminating chlorine gas generated during the process, so that the catalyst can stably maintain oxidation activity for a long period of time. . When the reaction temperature is 450 ° C, the conversion of trichloroethylene can reach more than 95%, and no polychlorinated hydrocarbons are formed.

The reaction pressure is 0.1-lMpa, preferably 0.1-0.5 Mpa, especially 0.1 Mpa, which is close to normal pressure, and the temperature is 300 to 600 ° C, preferably 400 to 500 ° C, especially 450 ° C.

Said catalyst consists of a carrier which is stable in moist air and a rare metal, rare earth oxide and phosphoric acid supported on the carrier;

The rare metal comprises one or more of palladium or platinum, preferably platinum, in an amount of from 0.08 to 5% by weight based on the total weight of the catalyst;

The rare earth oxide is one or more of an oxide of cerium or an oxide of cerium, in an amount of from 1 to 10% by weight based on the total weight of the catalyst;

Said carrier is a carrier well known in the art, preferably mesoporous silica, silica or he The pure silicon molecular sieve material, the preferred carrier is a large surface mesoporous silica material.

The mesoporous silica MCM-41 can be prepared by a method disclosed in the literature (Nature, 1992, 359: 710);

The preferred components and weight levels of the catalyst are:

Palladium 0.1-2% by weight, platinum 0.08-2% by weight, cerium oxide 3-10% by weight, cerium oxide 3-10% by weight, phosphoric acid 1% by weight to 20% by weight, and the balance being carrier silica.

The preparation of the catalyst can be divided into two steps. The first step is to impregnate the silica with a phosphoric acid solution, dry, and calcine. The process can be carried out by an isometric impregnation method well known in the art, such as the literature (J. Mater. Chem., 2002, 12: 1582) Method of public gong; The second step is to load rare metals with rare earth elements, such as the salt solution impregnation method commonly mentioned in the literature.

The amount of catalyst must be sufficient to convert trichloroethylene into carbon dioxide and hydrogen chloride in the presence of moist air. In general, the concentration of trichloroethylene in the exhaust of trichloroethylene is 0.05-0.2 vol%, per gram of catalyst treatment. The amount of exhaust gas is 10-30L per hour.

The humid air is air containing water vapor, and the water concentration must be such that all the chlorine gas generated by the reaction is converted into hydrogen chloride, but the water cannot be the inhibitor of the reaction. In the air, the suitable water concentration is 0.1~lvol. %;

The molar ratio of water to trichloroethylene is 2~5:1;

By using the method of the present invention, in a humid air, at a lower reaction temperature, in the presence of an oxidative decomposition catalyst, the trichloroethylene in the exhaust gas can be stably converted into carbon dioxide and hydrogen chloride for a long time, and the activity of the catalyst is not lowered. The content of precious metals in the catalyst is particularly low, and the chlorine-containing hydrocarbons in the exhaust gas are eliminated in a particularly economical manner, and no polychlorinated hydrocarbon by-products are formed, which does not cause secondary pollution, and is a very effective method for treating uranium-containing hydrocarbon waste gas. , has a greater prospect of environmental protection applications. detailed description Example 1

3.0 g of cetyltrimethylammonium bromide (CTMAB) was added to 105 ml of deionized water and dissolved at 30 ° C to produce a transparent template solution; then 35 ml of ethylenediamine (EDA) was stirred. In the case, it was added to the flask together with the templating solution solution, and maintained at 30 ° C _; then 15 ml of tetraethyl orthosilicate (TEOS) and 50 ml of deionized water mixture were slowly dropped into the above system containing the templating agent, ethylenediamine and water. In the process, the quality of the system is satisfied: n (TEOS): n (CTMAB): n (EDA): n (H ₂ 0) = 1 : 0.12: 9.7: 130, stirred for 15 min, the pH of the system is adjusted to 10.5 with acetic acid. After stirring for 1.5 h, the sol mixture was transferred into a 100 ml stainless steel autoclave with a Teflon liner, and statically crystallized at 120 ° C in an oven at its own pressure for 72 h, taken out and cooled, and washed with deionized water. It was suction filtered, washed with absolute ethanol, suction filtered, and dried at 50 ° C overnight to obtain a mesoporous molecular sieve sample without removing the template. The sample from which the templating agent was not removed was calcined in a muffle furnace at 50 ° C to start heating, and the temperature was raised by 50 ° C every 0.5 h until 550 ° C, and then maintained at 550 ° C for 8 h to obtain a MCM-41 mesoporous molecular sieve.

The preparation of MCM-41/P0 ₃ H is prepared by the traditional impregnation method: The procedure is as follows: Weigh the above-mentioned calcined mesoporous molecular sieve MCM-41, and add 1.25, 1.5, 2.25, 4.5, 11.25 ml of H ₃ P0 respectively. _{4 The} solution is stirred vigorously to maintain the system to quickly evaporate the water at a certain temperature. Then, it was dried at 100 ° C for 8 h and calcined at 400 ° C for 3 h to obtain MCM-41/P0 ₃ H to obtain a carrier carrying phosphoric acid, and the Si/P (atom) ratio was 100, 75, 50, 25, 15 respectively. , 10. The acid amount of the different Si/P ratio carriers was tested according to the method H ₃ -TPD well known in the art, and the results are shown in Table 1. The in situ pyridine test of pyridine can confirm that the acidity caused by the phosphoric acid modification is B acid.

The noble metal active component is impregnated on the above carrier, firstly, chloroplatinic acid is formulated into an aqueous solution having a concentration of 0.00638 M, and then the pH is adjusted to 4.7 with aqueous ammonia, and each of the above carriers is taken as lg, and each is stirred with 2 mL of chloroplatinum. The aqueous acid solution was slowly added to the carrier, and then allowed to stand overnight at room temperature in air, dried at 50 ° C, and calcined at 550 ° C for 4 hours to obtain various supported Pt catalysts. The amount of Pt contained in each catalyst was determined by atomic absorption spectroscopy to be about 0.16 wt%. In the same way, Another series of catalysts were prepared with a concentration of 0.00319 M chloroplatinic acid aqueous solution, and the Pt content was 0.08.

%about.

Catalyst activity evaluation was carried out in a fixed bed reactor. All catalysts were tested for trichloroethylene (TCE) combustion activity in a U-shaped quartz micro-reverse (inner diameter 6 mm) with a catalyst dosage of 200 mg and a reaction temperature of 500 ° C. The temperature was automatically controlled by a K-type thermocouple. Trichloroethylene was injected into the vaporization chamber using a 100 series KDS120 microinjection pump from StoeMng, USA, and then mixed with humid air having a water concentration of 0.15 vd% into the reactor for combustion. The total flow of humid air is controlled by a mass flow meter. The concentration of trichloroethylene is controlled at 0.05 vol%, the amount of exhaust gas per gram of catalyst is 15 L per hour, and the gas velocity through the reactor is 120 m h. The molar ratio of water to trichloroethylene is 3:1; the reaction pressure is O.lMpa, and the temperature is 450 °C. The conversion of trichloroethylene is shown in Table 1. The reaction products are carbon dioxide, hydrogen chloride and traces of chlorine.

Table 1 Acid content of MCM-41 carrier with different Si/P ratio and its conversion of trichloroethylene after Pt (500 °C)

Example 2

1 ml of a concentration of 0.00319 M chloroplatinic acid aqueous solution and 1 ml of a 0.01275 M palladium chloride aqueous solution were mixed, and each of the phosphoric acid-containing MCM-41/P0 ₃ H carriers prepared in Example 1 was impregnated with 2 mL of the mixed solution, respectively. Subsequent treatment According to the method of Example 1, 0.08 wt% of Pt-0.5 wt% Pd / MCM-41 / P0 ₃ H series catalyst was obtained. Weigh 100 mg of the catalyst, the reaction temperature is 500 ° C, the moisture content in humid air is 0.2 vol%, the concentration of trichloroethylene is 0.1 vol%, and the molar ratio of water to trichloroethylene is 2:1; per gram The catalyst was treated with an amount of exhaust gas of 30 L per hour and a reaction pressure of 0.1 MPa. The rest of the reaction conditions were the same as those in Example 1. The conversion of trichloroethylene is shown in Table 2. The reaction products were carbon dioxide, hydrogen chloride and traces of chlorine. Table 2 Acid content of MCM-41 carrier with different Si/P ratio and conversion of trichloroethylene after loading Pt (500Ό)

Example 3

₀₂ using a commercially available surface area of 303m ² / g, as in Example 1 was immersed phosphate embodiment, to obtain various Si0 ₂ / P0 ₃ H phosphate content of the carrier. 2 ml of a 0.00319 M aqueous solution of chloroplatinic acid was separately impregnated on various supports, and subsequent treatment was carried out in the same manner as in Example 1 to obtain a 0.08 wt% Pt/SiO ₂ /PO ₃ H catalyst. Weigh 200mg of each series of catalysts, the reaction temperature is 450 ° C, the reaction pressure is 0.5Mpa, the moisture content in humid air is 0.15vpl%, the concentration of trichloroethylene is 0.05vol%, and the exhaust gas is treated per gram of catalyst per hour. The amount of the reaction was 15 L, and the rest of the reaction conditions were the same as those in Example 1. The conversion of trichloroethylene is shown in Table 3. The reaction products were carbon dioxide, hydrogen chloride and a trace amount of chlorine.

Table 3 The acidity of MCM-41 carrier with different Si/P ratio and its conversion to trichloroethylene after loading Pt (450 °C)

Example 4

The MCM-41 carrier prepared in Example 1 was excessively impregnated with 5 mL of a 0.1 M aqueous solution of cerium nitrate and cerium nitrate, and the solution was slowly added to the carrier under stirring; The mixture was dried (50 ° C) and calcined at 550 ° C for 4 h to obtain a MCM-41 carrier modified with La and Ce. The loading of La and Ce was about 10% by weight. 2 ml of a 0.00319 M aqueous solution of chloroplatinic acid was separately impregnated on the above-prepared Ce-MCM-41 and La-MCM-41 supports, and subjected to subsequent treatment in the same manner as in Example 1 to obtain 0.08 wt% of a Pt catalyst. Weigh 200mg of each series of catalysts, the reaction temperature is 450 ° C, the moisture content in humid air is 0.1 vol%, the concentration of trichloroethylene is 0.5ol%, the amount of exhaust gas per gram of catalyst per hour is 15L, the rest of the reaction The conditions are the same as those in Example 1. The conversion of trichloroethylene is shown in Table 4. The reaction product It is carbon dioxide, hydrogen chloride and traces of chlorine.

Table 4 Acid content of MCM-41 carrier with different Si/P ratio and conversion of trichloroethylene after loading Pt (450Ό)

Example 5

The MCM-41 P0 ₃ H series carrier prepared in Example 1 was excessively impregnated with 5 mL of a 0.1 M aqueous solution of cerium nitrate and cerium nitrate, and the solution was slowly added to the carrier under stirring; then at room temperature in air. The mixture was allowed to stand overnight, dried at a low temperature (50 ° C), and calcined at 550 ° C for 4 hours to obtain two series of carriers of MCM-41/P0 ₃ H modified with La and Ce. The loading of La and Ce was about 10% by weight. O. 08wt%R催化剂。 The catalyst was then impregnated with a solution of 0. 08wt% R catalyst. Weigh 100mg of each of the two series of catalysts, the reaction temperature is 450 ° C, the moisture content in humid air is 0.5 vol%, the concentration of trichloroethylene is 0.1 vd%, and the amount of exhaust gas per gram of catalyst per hour is 30 L. The conditions were the same as those in Example 1. The conversion of trichloroethylene is shown in Table 5. The reaction products were carbon dioxide, hydrogen chloride and traces of chlorine.

Table 5 Example 5 Preparation of Trichloroethylene Conversion Rate on Each Catalyst (450 ° C)

Example 6

The respective phosphoric acid content of MCM-41/P0 ₃ H carrier prepared in Example 1 was impregnated with 2 ml of a concentration of 0.01275 M and 0.0255 M palladium chloride aqueous solution, respectively, and the subsequent treatment was carried out according to Example 1, to obtain 0.5 wt. Two series of catalysts, %Pd /MCM-41/PO ₃ H and 1wt% Pd /MCM-41/P0 ₃ H. Weigh 200mg of each series of catalysts, the reaction temperature is 450 ° C, the moisture content in humid air is 0.2 vol%, the concentration of trichloroethylene is 0.1 vol%, per gram of catalyst per hour The amount of waste gas was 15 L, and the rest of the reaction conditions were the same as those in Example 1. The conversion of trichloroethylene is shown in Table 6. The reaction products were carbon dioxide, hydrogen chloride and traces of chlorine.

Table 6 Acid content of MCM-41 carrier with different Si P ratio and its conversion of trichloroethylene after Pd (450 ° C)

Si/P(atom) 100 75 50 25 15 10

0.5wt% Pd /MCM-41/P0 ₃ H 75 81 90 86 77 32 lwt Pd /MCM-4I/PO3H 80 87 93 89 78 40

Claims

Rights request

A method for catalytically purifying a waste gas of trichloroethylene, which comprises the steps of: reacting a humidified air into an exhaust gas containing trichloroethylene in the presence of a catalyst;

The rare metal includes one or more of palladium or platinum in an amount of 0.1 to 5% by weight based on the total weight of the catalyst;

The method according to claim 1, wherein the reaction pressure is 0.1 to 1 MPa, preferably 0.1 to 0.5 MPa, and the temperature is 300 to 600 °C.

3. The method of claim 1 wherein said rare metal is platinum.

4. A method according to claim 1, 2 or 3, characterized in that the support is selected from mesoporous silica, silica or other pure silicon molecular sieve material.

The method according to claim 4, wherein the composition and weight of the catalyst are 0.1 to 2 wt% of palladium, 0.08 to 2 wt% of platinum, and 3 to 10 wt% of ruthenium oxide. , cerium oxide 3-10wt%, phosphoric acid lwt%~20wt%, and the rest is carrier silica.