Catalyst for cracking and oxidizing organic flue gas generated by melting medical waste salt

Abstract

The invention relates to a catalyst for cracking and oxidizing organic flue gas generated by melting medical waste salt. According to the invention, perovskite type metal oxide is loaded on a silicon-aluminum molecular sieve by using a sol-gel method to form a catalyst with cracking oxidation characteristics, and a layer of transition metal oxide is further loaded on the catalyst by using a chemical reduction method to regulate the cracking oxidation performance of the catalyst. The prepared catalyst has rich acid sites and oxidation sites, macromolecular organic matters in the medical waste salt molten organic flue gas can be cracked into gaseous micromolecules at a relatively low temperature, and then the gaseous micromolecules are completely oxidized into harmless substances through deep oxidation; the problems of high purification temperature and low purification efficiency of the medical waste salt molten organic flue gas are effectively avoided; and the energy consumption is low, the secondary pollution is small, the application range is wide, a secondary combustion chamber can be effectively replaced to degrade macromolecular organic matters in the medical waste salt molten organic flue gas, and the concentration of non-methane total hydrocarbon in purified tail gas is reduced to be 40 mg / Nm < 3 > or below.

Description

Technical Field

[0001] The invention belongs to the field of environmental protection, and in particular relates to a catalyst for cracking and oxidizing pharmaceutical waste salt by melting organic flue gas. Technical Background

[0002] With the steady and rapid development of my country's industry, metallurgy, chemical industry, medicine, printing and dyeing and other industries inevitably produce a large amount of industrial waste salt. According to incomplete statistics, my country's industrial waste salt output exceeds 50 million tons / year, of which pharmaceutical waste salt accounts for about 10% of industrial waste salt. In view of the high content of organic pollutants in the salt produced by the pharmaceutical industry and the complex types of waste salt, it is necessary to focus on the removal of organic impurities. At present, there are two main types of waste salt treatment and utilization technologies at home and abroad, namely harmless and resource-based.

[0003] Among them, the high-temperature melting treatment method is to remove organic matter from industrial waste salt in a molten state at a high temperature of 800 to 1200°C, and the removal effect of organic matter is better. Chinese patent CN109579025A discloses "an efficient melting and incineration device for industrial waste salt", which uses a high-temperature melting method to treat industrial waste salt, so that the organic matter in industrial waste salt is completely decomposed in a molten state, but the energy consumption is high and incineration flue gas will be produced at the same time. The incineration flue gas still contains some macromolecular organic matter, mainly halogenated hydrocarbons, benzene series and condensed rings and other difficult-to-degrade organic matter. A large amount of auxiliary fuel needs to be added to the secondary combustion chamber unit to effectively burn and remove the organic matter. The tail gas after the secondary combustion of the incineration flue gas contains dioxins, which has a large secondary pollution, high energy consumption and poor effect. Therefore, a low-temperature and efficient method for replacing the secondary combustion chamber to degrade macromolecular organic matter is needed.

[0004] Catalytic combustion is widely used in the treatment of chlorinated organic matter. Its main advantages are low operating temperature, high elimination efficiency, low energy consumption, and treatment of low-concentration waste gas at relatively low temperature (<500℃). However, during the oxidation process of chlorinated organic compounds and aromatic hydrocarbons, their byproducts (especially chlorinated aromatic hydrocarbons) are likely to form more toxic and persistent polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxins (PCDDs) and biphenyls (PCBs) at 250-400℃, which cause great harm to the atmospheric environment. Catalytic hydrodechlorination refers to the hydrodechlorination of chlorinated organic compounds under mild conditions (temperature is generally room temperature <350℃), thereby converting chlorinated organic compounds into harmless HCl and hydrocarbons. The HCl produced by this reaction can be separated by absorption with NaOH lye, while hydrocarbons can be easily eliminated or recovered. Although catalytic hydrodechlorination technology is efficient and environmentally friendly, it has disadvantages such as poor catalyst selection and stability, high equipment investment, high energy consumption, and potential safety and environmental risks, and needs to be continuously optimized and improved.

[0005] The main advantages of photocatalytic oxidation are that pollutants are degraded more thoroughly, the reaction conditions are mild, and it can be carried out at room temperature and pressure. However, the industrial application of the catalysts currently used in photocatalysis is restricted by their wide bandgap, narrow absorption range, low solar energy utilization rate, and low activity. In addition, the decomposition products of chlorine-containing organic compounds, such as Cl, will block the active sites on the surface of the photocatalyst and reduce the catalytic activity. Summary of the invention

[0006] In order to solve the problems existing in the above conventional technologies, the present invention provides a catalyst for cracking and oxidizing molten organic flue gas of pharmaceutical waste salt, and uses a catalyst with cracking and oxidizing functions to purify the molten flue gas of pharmaceutical waste salt. The abundant acidic sites on the cracking and oxidizing catalyst of the present invention can crack the macromolecular organic matter in the molten organic flue gas of pharmaceutical waste salt into gaseous small molecules at a relatively low temperature. In addition, the oxidation sites on the catalyst can further oxidize the gaseous small molecules into harmless substances such as CO2 and H2O, thereby realizing low-temperature and efficient purification of the molten organic flue gas of pharmaceutical waste salt. Therefore, the use of a cracking and oxidizing catalyst to purify the molten organic flue gas of pharmaceutical waste salt can achieve the purpose of replacing the secondary combustion chamber to degrade macromolecular organic matter.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] In the first aspect, the present invention provides a method for preparing a catalyst for the cracking and oxidation of molten organic flue gas from pharmaceutical waste salt, wherein a metal inorganic salt, preferably a perovskite-type metal oxide, is loaded on a silica-alumina molecular sieve by a sol-gel method to form a catalyst having cracking and oxidation properties, and a transition metal oxide film is loaded on the above-mentioned catalyst by a chemical reduction method to further regulate the cracking and oxidation properties of the catalyst, thereby obtaining the catalyst for low-temperature, high-efficiency and deep purification of molten organic flue gas from pharmaceutical waste salt.

[0009] In specific embodiments, the transition metal oxide is manganese oxide.

[0010] In a specific embodiment, the method specifically comprises the following steps:

[0011] Step 1: Dilute the metal inorganic salt, citric acid monohydrate and silica-alumina molecular sieve in deionized water in proportion to form a solution, and heat and stir until a sol is formed;

[0012] Step 2: drying the sol obtained in step 1 and continuing calcination to obtain catalyst A;

[0013] Step 3: Disperse the catalyst A obtained in step 2 and potassium permanganate in deionized water and stir at room temperature, then add a metal inorganic salt, heat and stir, filter, wash three times with water and ethanol, dry at room temperature, continue to heat and dry, and finally calcine to obtain the catalyst.

[0014] In a specific embodiment, in step 1, the metal cation in the metal inorganic salt is Cu 2+ 、Ce 2+ ,La 3+ , Mn 2+ or Co 3+ Two combinations of La 3+ and Mn 2+ A combination of La 3+ and Mn 2+ The mass ratio is 0.2~5:1.

[0015] In a more specific embodiment, the perovskite metal oxide is selected from a combination of any two of copper oxide, cerium oxide, lanthanum oxide, manganese oxide, and cobalt oxide.

[0016] In a specific embodiment, in step 1, the silica-alumina molecular sieve is one of ZSM-5, HZSM-5, and HY, preferably ZSM-5. Preferably, the silica-alumina molecular sieve has a silicon-alumina ratio of 10 to 500, more preferably 25 to 100.

[0017] In a specific embodiment, in step 1, the molar ratio of the metal inorganic salt to citric acid monohydrate is 0.5-2:1, and the mass ratio of the cation in the metal inorganic salt to the silica-alumina molecular sieve is 1:4-99.

[0018] There is no specific requirement for the amount of deionized water used in step 1, and the conventional amount range in the art can be used.

[0019] In a specific embodiment, in step 1, the heating and stirring temperature is 60-90°C for 3-6 hours, preferably at 80°C for 5 hours.

[0020] In a specific embodiment, in step 2, the drying temperature is 100-120°C, and the drying time is 10-14 hours, preferably drying at 110°C for 12 hours.

[0021] In a specific embodiment, in step 2, the calcination temperature is 600-700°C, and the time is 3-5 hours, preferably calcination at 650°C for 4 hours.

[0022] In a specific embodiment, in step 3, the mass ratio of the metal inorganic salt, catalyst A and potassium permanganate is 1:80-120:1, preferably 1:100:1. The metal cation in the metal inorganic salt is Mn 2+ .

[0023] In a specific embodiment, in step 3, the stirring time at room temperature is 20 to 40 minutes, preferably 30 minutes at room temperature.

[0024] In a specific embodiment, in step 3, the heating and stirring temperature is 60-80°C for 2-4 hours, preferably at 70°C for 3 hours.

[0025] In a specific embodiment, in step 3, the drying time at room temperature is 20 to 28 hours, preferably 24 hours at room temperature.

[0026] In a specific embodiment, in step 3, the temperature for continued drying is 60-80°C for 10-14 hours, preferably 70°C for 12 hours.

[0027] In a specific embodiment, in step 3, the calcination temperature is 300-400°C, and the time is 1-3 hours, preferably calcination at 350°C for 22 hours.

[0028] In a second aspect, the present invention provides a catalyst prepared by the above preparation method.

[0029] In a third aspect, the present invention also provides the use of the above catalyst in the pyrolysis and oxidation of molten organic flue gas from pharmaceutical waste salt.

[0030] In a fourth aspect, the present invention also provides the use of the above catalyst in the preparation of products of molten organic flue gas cracking and oxidation of pharmaceutical waste salt.

[0031] In some specific embodiments, the method for using the above catalyst comprises the following steps:

[0032] By using air flow to bring the molten organic flue gas of pharmaceutical waste salt into the cracking oxidation catalyst and controlling the reaction temperature, the macromolecular organic matter in the molten organic flue gas of pharmaceutical waste salt can be deeply purified. The concentration of non-methane total hydrocarbons in the purified tail gas is determined according to the prescribed detection method, and the change in the concentration of non-methane total hydrocarbons in the molten organic flue gas of pharmaceutical waste salt before and after purification by the cracking oxidation catalyst is determined.

[0033] In a specific embodiment, the air velocity range of the air flow is 5000 to 20000 ml / g cat h, preferably 12000 ml / g cat ·h.

[0034] In a specific embodiment, the reaction temperature ranges from 300 to 500°C, preferably 350°C.

[0035] The detection method described in the above steps comes from the regulation "Gas Chromatography for Determination of Total Hydrocarbons, Methane and Non-methane Hydrocarbons in Waste Gas from Stationary Pollution Sources" (HJ 38-2017).

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The catalyst provided by the present invention can be used to crack and oxidize the macromolecular organic matter in the molten organic flue gas of pharmaceutical waste salt at a relatively low temperature, which can effectively replace the secondary combustion chamber to degrade the macromolecular organic matter in the molten organic flue gas of pharmaceutical waste salt, and achieve deep purification of the macromolecular organic matter in the molten organic flue gas of pharmaceutical waste salt at a relatively low temperature, thereby reducing energy consumption. The preparation method of the catalyst is relatively simple and can be reused.

[0038] (2) Compared with other treatment methods for the inefficient purification of macromolecular organic matter in the molten organic flue gas of pharmaceutical waste salt, the catalyst for the cracking and oxidation of the molten organic flue gas of pharmaceutical waste salt provided by the present invention can reduce the content of non-methane total hydrocarbons in the purified tail gas to 40 mg / Nm 3 the following.

[0039] (3) In the present invention, the above-mentioned preparation method can be used to uniformly compound the silicon-aluminum molecular sieve with a large number of surface acidic sites and the perovskite-type metal oxide with a large number of oxidation sites, and the synergistic effect of cracking and oxidation is adjusted by chemical reduction to obtain a pharmaceutical waste salt molten organic flue gas cracking and oxidation catalyst, which can effectively convert the macromolecular organic matter in the pharmaceutical waste salt molten organic flue gas into benzoquinone intermediates through nucleophilic substitution reaction, and further crack it into low-carbon straight-chain organic matter, and finally oxidize it into harmless substances, and the content of non-methane total hydrocarbons in the purified tail gas is reduced to 20 mg / Nm 3 the following.

[0040] Specific implementation methods

[0041] The effect of the catalyst of the present invention on the pyrolysis and oxidation process of molten organic flue gas of pharmaceutical waste salt is further illustrated by the following examples and comparative examples.

[0042] The sources of some components in the embodiments and comparative examples are as follows:

[0043] Pharmaceutical waste salt molten organic smoke simulation gas: The same pharmaceutical waste salt molten organic smoke simulation gas is used in the following embodiments. The pharmaceutical waste salt molten organic smoke simulation gas is obtained by blowing air into 3-methylbenzyl chloride liquid. The non-methane total hydrocarbon concentration of the pharmaceutical waste salt molten organic smoke simulation gas is about 4000 mg / Nm 3 Although the same method was used to generate the simulated gas of molten organic smoke from pharmaceutical waste salt in the following examples, due to the arrangement of experimental time and the inherent error of non-methane total hydrocarbon test, the non-methane total hydrocarbon content of the simulated gas of molten organic smoke from pharmaceutical waste salt without catalyst treatment fluctuated slightly. However, these differences are within the acceptable error range.

[0044] The number following the silica-alumina molecular sieve as the carrier of the catalyst used in the following examples and comparative examples represents the silicon-alumina ratio. For example, "ZSM-5" in ZSM-5-40 represents the silica-alumina molecular sieve, and "40" represents the silicon-alumina ratio of the silica-alumina molecular sieve.

[0045] Example 1

[0046] This embodiment provides a method for pyrolysis and oxidation of pharmaceutical waste salt melted organic flue gas, the method is as follows:

[0047] (1) Preparation of catalyst A: 0.78 g La(NO3)2·6H2O, 1.14 g Mn(NO3)2·4H2O, 1.21 g citric acid monohydrate and 5 g ZSM-5-40 carrier were weighed and added to 50 ml deionized water, heated and stirred at 80°C for 4 h until a sol was formed, then dried at 110°C for 12 h, and finally calcined in a muffle furnace at 650°C for 4 h to obtain a lanthanum manganese perovskite-type bimetallic oxide catalyst; the mass ratio of La to Mn in the catalyst was 1:1, and the mass percentage content of La and Mn in the catalyst was 100% based on the mass percentage content of the catalyst;

[0048] (2) Catalyst preparation: Weigh 1g of catalyst A and 0.01g of KMnO4 and disperse them in 25mL of deionized water and stir for 30min. Then add 0.01g of Mn(NO3)2 and stir at 70℃ for 2h. Filter and wash three times with water and ethanol. The obtained precursor is first dried at room temperature for 24h and then dried at 70℃ for 12h. Finally, the prepared sample is calcined at 350℃ for 2h.

[0049] (3) 12000ml / (g cat The simulated gas of molten organic flue gas of pharmaceutical waste salt was cracked and oxidized at a reaction space velocity of 0.10 0.1 h and a reaction temperature of 350°C, and the concentration of total non-methane hydrocarbons in the purified tail gas was determined by gas chromatography.

[0050] Example 2

[0051] This embodiment provides a method for pyrolysis and oxidation of pharmaceutical waste salt by melting organic flue gas, which is different from the embodiment 1 only in that:

[0052] The catalyst carrier ZSM-5-40 in step (1) of Example 1 was replaced with an equal mass of ZSM-5-25;

[0053] Other conditions are the same as in Example 1.

[0054] Example 3

[0055] This embodiment provides a method for pyrolysis and oxidation of pharmaceutical waste salt by melting organic flue gas, which is different from the embodiment 1 only in that:

[0056] The catalyst carrier ZSM-5-40 in step (1) of Example 1 was replaced with an equal mass of ZSM-5-60;

[0057] Other conditions are the same as in Example 1.

[0058] Example 4

[0059] This embodiment provides a method for pyrolysis and oxidation of pharmaceutical waste salt by melting organic flue gas, which is different from the embodiment 1 only in that:

[0060] The catalyst carrier ZSM-5-40 in step (1) of Example 1 was replaced with an equal mass of ZSM-5-80;

[0061] Other conditions are the same as in Example 1.

[0062] Example 5

[0063] This embodiment provides a method for pyrolysis and oxidation of pharmaceutical waste salt by melting organic flue gas, which is different from the embodiment 1 only in that:

[0064] The catalyst carrier ZSM-5-40 in step (1) of Example 1 was replaced with an equal mass of ZSM-5-100;

[0065] Other conditions are the same as in Example 1.

[0066] Comparative Example 1

[0067] This comparative example provides a method for the pyrolysis and oxidation of pharmaceutical waste salt melted organic flue gas, the method being as follows:

[0068] (1) Preparation of catalyst A: 0.78 g La(NO3)2·6H2O, 1.14 g Mn(NO3)2·4H2O, 1.21 g citric acid monohydrate and 5 g HZSM-5-40 carrier were weighed and added to 50 ml deionized water, heated and stirred at 80°C for 4 h until a sol was formed, then dried at 110°C for 12 h, and finally calcined in a muffle furnace at 650°C for 4 h to obtain a lanthanum manganese perovskite-type bimetallic oxide catalyst; the mass ratio of La to Mn in the catalyst was 1:1, and the mass percentage content of La and Mn in the catalyst was 100% based on the mass percentage content of the catalyst;

[0069] (2) Catalyst preparation: Weigh 1g of catalyst A and 0.01g of KMnO4 and disperse them in 25mL of deionized water and stir for 30min. Then add 0.01g of Mn(NO3)2 and stir at 70℃ for 2h. Filter and wash three times with water and ethanol. The obtained precursor is first dried at room temperature for 24h and then dried at 70℃ for 12h. Finally, the prepared sample is calcined at 350℃ for 2h.

[0070] (3) 12000ml / (g cat The simulated gas of molten organic flue gas of pharmaceutical waste salt was cracked and oxidized at a reaction space velocity of 0.10 0.1 h and a reaction temperature of 350°C, and the concentration of total non-methane hydrocarbons in the purified tail gas was determined by gas chromatography.

[0071] Comparative Example 2

[0072] This embodiment provides a method for pyrolysis and oxidation of pharmaceutical waste salt melted organic flue gas, the method is as follows:

[0073] (1) Preparation of catalyst A: 0.78 g La(NO3)2·6H2O, 1.14 g Mn(NO3)2·4H2O, 1.21 g citric acid monohydrate and 5 g HY-40 carrier were weighed and added to 50 ml deionized water, heated and stirred at 80°C for 4 h until a sol was formed, then dried at 110°C for 12 h, and finally calcined in a muffle furnace at 650°C for 4 h to obtain a lanthanum manganese perovskite-type bimetallic oxide catalyst; the mass ratio of La to Mn in the catalyst was 1:1, and the mass percentage content of La and Mn in the catalyst was 100% based on the mass percentage content of the catalyst;

[0074] (2) Catalyst preparation: Weigh 1g of catalyst A and 0.01g of KMnO4 and disperse them in 25mL of deionized water and stir for 30min. Then add 0.01g of Mn(NO3)2 and stir at 70℃ for 2h. Filter and wash three times with water and ethanol. The obtained precursor is first dried at room temperature for 24h and then dried at 70℃ for 12h. Finally, the prepared sample is calcined at 350℃ for 2h.

[0075] (3) 12000ml / (g cat The simulated gas of molten organic flue gas of pharmaceutical waste salt was cracked and oxidized at a reaction space velocity of 0.10 0.1 h and a reaction temperature of 350°C, and the concentration of total non-methane hydrocarbons in the purified tail gas was determined by gas chromatography.

[0076] The concentration of non-methane total hydrocarbons was measured on the simulated organic flue gas of the molten pharmaceutical waste salt before and after cracking and oxidation in the above embodiment, and the results are shown in Table 1 below.

[0077] Table 1

[0078]

[0079]

[0080] The protection content of the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be thought of by those skilled in the art are included in the present invention and are protected by the attached claims.

Claims

1. A method for preparing a catalyst for the pyrolysis and oxidation of pharmaceutical waste salt melted organic flue gas, characterized in that: The catalyst is obtained by loading a metal inorganic salt onto a silicon-aluminum molecular sieve by a sol-gel method to form a catalyst having cracking and oxidation properties, and loading a transition metal oxide film onto the catalyst by a chemical reduction method to further regulate the cracking and oxidation properties of the catalyst; Preferably, the method specifically comprises the following steps: Step 1: Dilute the metal inorganic salt, citric acid monohydrate and silica-alumina molecular sieve in deionized water in proportion to form a solution, and heat and stir until a sol is formed; Step 2: drying the sol obtained in step 1 and continuing calcination to obtain catalyst A; Step 3: Disperse the catalyst A obtained in step 2 and potassium permanganate in deionized water and stir at room temperature, then add a metal inorganic salt, heat and stir, filter, wash three times with water and ethanol, dry at room temperature, continue to heat and dry, and finally calcine to obtain the catalyst.

2. The method for preparing a catalyst for the pyrolysis and oxidation of pharmaceutical waste salt melted organic flue gas according to claim 1, characterized in that: In step 1, the metal cation in the metal inorganic salt is Cu 2+ 、Ce 2+ ,La 3+ , Mn 2+ or Co 3+ One or a combination of two, preferably La 3+ and Mn 2+ A combination of La 3+ and Mn 2+ The mass ratio is 0.2~5:

1. Preferably, the metal inorganic salt is a perovskite-type metal oxide. More preferably, the perovskite-type metal oxide is selected from a combination of any two of copper oxide, cerium oxide, lanthanum oxide, manganese oxide, and cobalt oxide.

3. The method for preparing a catalyst for the molten organic flue gas cracking and oxidation of pharmaceutical waste salt according to claim 1, characterized in that: In step 1, the silica-alumina molecular sieve is one of ZSM-5, HZSM-5, and HY, preferably ZSM-5; more preferably, the silica-alumina ratio of the silica-alumina molecular sieve is 10 to 500, more preferably 25 to 100; In step 1, the molar ratio of the metal inorganic salt to citric acid monohydrate is 0.5-2:1, and the mass ratio of the cation in the metal inorganic salt to the silicon-aluminum molecular sieve is 1:4-99.

4. The method for preparing a catalyst for the pyrolysis and oxidation of pharmaceutical waste salt melted organic flue gas according to claim 1, characterized in that: In step 1, the heating and stirring temperature is 60-90° C., and the time is 3-6 hours, preferably stirring at 80° C. for 5 hours.

5. The method for preparing a catalyst for the pyrolysis and oxidation of pharmaceutical waste salt melted organic flue gas according to claim 1, characterized in that: In step 2, the drying temperature is 100-120°C, the time is 10-14h, preferably drying at 110°C for 12h; preferably, in step 2, the calcination temperature is 600-700°C, the time is 3-5h, preferably calcining at 650°C for 4h.

6. The method for preparing a catalyst for the pyrolysis and oxidation of pharmaceutical waste salt melted organic flue gas according to claim 1, characterized in that: In step 3, the mass ratio of the metal inorganic salt, catalyst A and potassium permanganate is 1:80-120:1, preferably 1:100:

1. The metal cation in the metal inorganic salt is Mn 2+ .

7. The method for preparing a catalyst for the pyrolysis and oxidation of pharmaceutical waste salt melted organic flue gas according to claim 1, characterized in that: In step 3, the stirring time at room temperature is 20 to 40 minutes, preferably 30 minutes at room temperature; Preferably, in step 3, the heating and stirring temperature is 60-80°C for 2-4 hours, preferably 70°C for 3 hours; preferably, in step 3, the drying time at room temperature is 20-28 hours, preferably 24 hours at room temperature; Preferably, in step 3, the temperature for further drying is 60-80°C for 10-14 hours, preferably 70°C for 12 hours; Preferably, in step 3, the calcination temperature is 300-400° C., and the time is 1-3 h, preferably calcination at 350° C. for 22 h.

8. A catalyst obtained by any preparation method according to claim 1.

9. The catalyst according to claim 8 is used in any one of the following (A1)-(A2): (A1) Application of pharmaceutical waste salt in molten organic flue gas pyrolysis and oxidation; (A2) Application in the preparation of products of molten organic flue gas cracking and oxidation of pharmaceutical waste salt.

10. The use according to claim 9, characterized in that: The method for using the catalyst comprises the following steps: The air flow is used to bring the molten organic flue gas of pharmaceutical waste salt into the molten organic flue gas and pass through the cracking oxidation catalyst to control the reaction temperature, so as to deeply purify the macromolecular organic matter in the molten organic flue gas of pharmaceutical waste salt; Preferably, the air velocity range is 5000~20000ml / g cat h, preferably 12000 ml / g cat ·h. Preferably, the reaction temperature ranges from 300 to 500°C, preferably 350°C.

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