PU is an abbreviation of English Polyurethan, the Chinese name Polyure. PU leather is the epidermis of polyurethane ingredients. It is widely used in the decoration of luggage, clothing, shoes, vehicles, and furniture. Its widely used range, large quantity, and variety are unsatisfactory.
PU leather production has a wet method and a dry method. The wet process uses a single DMF solvent (di metamimam); the dried method is in addition to the DMF solvent, which also contains butthom and toluene. The wet process DMF solvent is mainly in the water body, and the dry method uses a wet washing tower to absorb soluble DMFs with water. Regardless of whether the wet method or the dry method, the high concentration DMF dissolved in the water can be recovered by the psychic. However, DMF is prone to heat and decomposition during the recycling recycling process to produce dihamine and methic acid. DMF generates a diemine from the top of the tower in the phee recycling process, and methic acid is divided with DMF. The exhaust gas generated by the PU leather process is DMF, butthone and toluene. Although dihylamine only accounts for 0.1%of DMF, due to the large amount of DMF recycling, dysyamine has a bad odor and has a great impact on the environment. It must be further treated with dihylamine.
Although the dyshamine is not toxic, the boiling point is low, it is easy to volatilize, and it has a odor smell, making people feel unpleasant. Environmental impact. At present, the gas is usually sent to the boiler to burn after condensing the gas, but in the case of immature equipment, technology and technology, environmental protection requirements cannot be met. Therefore, DMF distilled dihylamine, as well as taitone and toluene, is a top priority.
There are many ways to deal with dysyle, butthone, and toluene. Theoretically, further distillation can be separated and recycled. Di metamine, butthonone, and toluene waste gas without recycling value can be treated with plasma treatment, direct incineration, catalytic combustion, direct burning of heat storage (RTO), heat storage catalytic combustion (RCO), etc. (RCO), etc. Wait for technology to deal with. Today, the core of catalytic combustion, catalyst, is the purification catalyst of nitrogen-containing organic exhaust gas (NVOCs).
1. Research history of nitrogen -containing organic exhaust gas (NVOCS) catalyst
I have participated in PU leather related since graduating from college (1983) R u0026 D of nitrogen -containing organic exhaust gas catalysts. The unit is the Institute of Catalytic Research of the Department of Chemistry of Hangzhou University. At that time, the Institute of the Institute undertaken the project of the Zhejiang Provincial Department of Science and Technology. The representative pollutants DMF, buttholone, and toluene of leather production did a lot of laboratory research. In 1985, they cooperated with Hangzhou Dahe Shipyard to conduct a catalyst. In 1986, they won the second prize of scientific and technological progress in Zhejiang Province. It is estimated that it is the earliest domestic PU leather tail gas catalystPick up. Then a few years of reaction performance of the catalyst has been studied in detail and published some research papers. For nitrogen -containing organic matter, the nitrogen in organic matter must be converted into NOX in the reaction process, and NOX increases as the reaction temperature increases. In the laboratory, the reaction temperature can be transformed into N2 by controlling the reaction temperature. If you are interested, you can check the relevant literature.
2. The latest study of nitrogen -containing organic exhaust gas (NVOCS) catalyst
Due to a long period of time, domestic environmental protection for environmental protection Without attention, many PU leather manufacturers have not processed the emission VOCs. Even if the processing is processed, VOCS is sent directly into the boiler to burn. Although the stench has decreased, it cannot meet environmental protection requirements. Twenty -five years ago, the catalyst was catalyst with natural silk -light zigzag particles as the carrier. Now it is a honeycomb catalyst, and the emission standards of NOX have also been greatly improved, which can no longer meet the current needs. In order to adapt to the new situation, high -performance nitrogen -containing organic waste gas purification catalysts need to be developed. Taking dihamine as an example, the dihyramine molecular structure is (CH3) 2nh. Under the action of a catalyst, the following reactions can occur:
For the treatment of nitrogen -containing VOCs, the ideal state It is to convert all N elements to N2. However, in fact, the generation of NOX is inevitable. NOX concentration is related to the reaction temperature. If the catalyst temperature is high, more NOX will be generated. Previous studies showed that the use of transition metal oxide catalysts to control NOX is better, but the defects that the transitional metal oxide catalyst is difficult to overcome is that the activity of the catalyst is low, and the thermal stability of the catalyst is poor, and the service life is relatively short. In the catalytic combustion engineering equipment, the amount of catalysts is large and the volume of the reactor is large, which is difficult to achieve the uniform temperature of the catalyst bed layer. In order to ensure the catalytic effect of the dihamine, the temperature of the catalyst will be higher than the laboratory temperature. It is difficult to avoid NOX.
According to the revised Beijing Boiler Atmospheric Pollution Emissions Standards. The discharge standards of nitrogen oxides of industrial boilers have been improved, and they will be implemented in two stages: from the date of implementation until March 31, 2017, newly built, nitrogen oxide emissions must be less than 80 mg/cubic meter. In 150 mg/cubic meter; the second stage is from April 1, 2017, the new boiler must be less than 30 mg/cubic meter, and the use of 80 mg/cubic meters must be used. Some information also shows that the nitrogen oxide emissions standards are now 100 mg/cubic meter, and 50 mg/cubic meters in developed areas.
Calculated at 2000 mg/m3 according to the concentration of dihamine (molecular weight 45). To reach NOX (NO2 molecular weight 46) emission standard 80mg/m3, it is difficult to achieve 96%of N elements to N2. therefore,I think it should increase the denitration device to deal with NOX generated by the combustion process.If NOX is not considered, the catalytic combustion of dihylamine is relatively simple.
We have developed PU leather exhaust purification special catalysts with ceramic honeycomb as a carrier, precious metal as active components, and the performance of catalysts under the condition of 20000H-1 condition is shown in Table 1.1 It can be seen that catalysts have good catalytic performance for dihylline, DMF, butthonone, and toluene. At the same time, they have good thermal stability and can meet the requirements of processing PU tail gas.
Table 2 is the relationship between the generication and reaction temperature of the NOX catalytic combustion process in Table 2.The product is mainly NO, and the total concentration of NOX increases with the temperature.