| Acrylic acid emission, generated from the direct gas-phase oxidation of propylene to production of acrylic acid, contains various kinds of poisonous volatile organic compounds such as toluene, ethanol, ethylene, acetaldehyde, propane, propylene, butane, acetic acid, acrylic acid, acrolein, acetone, carbon monoxide and so on, especially 25wt% of moisture content. If it is emitted directly, acrylic acid emission seriously endangers public health and ecological environment. In this work, acrylic acid emission was purified by catalytic combustion to meet the relevant emission standards of air pollutants in China, which is of great practical significance to improve the people's living quality and protect the ecological environment.In this work, Pd/γ-Al2O3/cordierite monolith catalysts were prepared by one-step coating or two-step impregnation methods. The mixture of propylene, acetic acid, acrylic acid, moisture and air was used for the simulated acrylic acid emission. The catalytic activity and stability for the purification of acrylic acid emission over monolith catalysts was investigated by the research on washcoat and supported palladium monolith catalysts. The following conclusions were drawn as follows:1. Research on washcoat of monolith catalyst:The coating rate was up to 19.5% by vacuum coating under the preparation conditions of pH value of 2.5 and the solid content of 37.9% of alumina slurry, and the coating time of 15min. The incorporation between washcoat and support was so strong that the lost rate of washcoat was less than 1% after the ultrasonic oscillation treatment for 15min at 60℃. Addition of small amount of non-ionic surfactants improves the thixotropism and stability of alumina slurry, and the coating rate of washcoat, in which PEG-2000 has the best effect.2. Research on supported palladium monolith catalysts:Monolith Pd catalyst, prepared by two-step impregnation method, has the best overall performance under the preparation conditions of Pd(NO3)2 as precursor, air-dry at room temperature after pros and cons impregnation and calcination at 650℃. Compared with two-step impregnation method, one-step coating method is more simple, time-saving and energy-saving. The monolith catalyst, prepared by one-step coating method, kept good activity and stability after reaction at 265℃for 100 hours, in which Pd was homogeneously dispersed in the alumina washcoat and had strong interaction with the washcaot. The monolith catalyst prepared by one-step coating method has the similar catalytic performance to that prepared by two-step impregnation method. High moisture content of acrylic acid emission inhibits the catalytic activity of monolith catalyst more and more significantly with an increase in the moisture content.3. Monolith Pd catalysts were successfully developed for purification of acylic acid emission with high moisture content from 40kt/a acrylic acid production equipment and lateral-line application experiment of MAA emission from 2kt/a MAA production workshop in Shanghai Huayi Acrylic acid Co., Ltd. The emissions meet the integrated emission standard of air pollutants (GB16297-1996). |
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