Competitive adsorption of VOCs and water on the surface of Y molecular sieve

Ultra-stable Y-type molecular sieves with different silicon-to-aluminum ratios were synthesized by hydrothermal treatment, and the competitive adsorption of benzene, toluene, xylene, styrene and ethyl acetate with water on the surface of Y molecular sieve was investigated. The results show that as the Si/Al ratio increases, the number of selective adsorption sites for organic molecules on the surface of the Y molecular sieve increases, and the competitive adsorption capacity of organic molecules increases. Low-silica Y-type molecular sieves can compete strongly with water molecules only when they adsorb high-polarity organic molecules with a dipole distance> 1.0, while high-silica ultra-stable Y molecular sieves are for organic molecules with a dipole distance in the range of 0 to 0.5. The molecules show strong competitive adsorption capacity.



Volatile organic waste gas (VOCs) has become one of the most important air pollutants at present, and the adsorption method has the characteristics of energy saving and low operating cost, and has been regarded as one of the most effective treatment technologies for low concentration VOCs [1, 2 ]. Activated carbon occupies a dominant position by virtue of its low price, large adsorption capacity, strong adsorption capacity, and strong applicability to various organic molecules [3, 4]. However, activated carbon is flammable, and there is a safety hazard of explosion when adsorbing ketones and aldehydes VOCs. The zeolite molecular sieve has the advantages of high temperature resistance, non-flammability, and good thermal stability, and it is an alternative adsorbent for excellent activated carbon [5-8]. Earlier studies have found that among many zeolite molecular sieves, Y-type zeolite molecular sieves have a 12-membered ring pore structure with a pore size of 0.74 nm, which is suitable for larger organic molecules (such as common toluene, ethyl acetate and xylene). Other organic waste gas) diffuse in the pores, and Y molecular sieve has a larger specific surface area (more than 800 m2/g) and organic molecule adsorption capacity. The adsorption capacity is greater than activated carbon in low concentration organic molecules. However, the strong hydrophilicity of Y molecular sieve is the biggest obstacle to its further industrial application. In the case of coexistence of water and vapor, organic molecules can hardly be adsorbed on the surface of NaY [9-11]. In order to improve the hydrophobicity of Y molecular sieve and the selective adsorption of organic molecules, it is one of the more effective technologies to modify the framework of Y molecular sieve to form ultra-stable Y molecular sieve (USY) [6,12]. Studies have found that [6, 8, 13-15], when Y molecular sieve framework aluminum is removed, it can effectively reduce the number of surface charges and surface balance cations of molecular sieve, and improve the hydrothermal stability of Y molecular sieve. In this study, NaY molecular sieves were used as raw materials, and two ultra-stable Y molecular sieves with different Si/Al ratios were prepared by ion exchange and high temperature hydrothermal treatment. The competitive adsorption of VOCs and water molecules on the surface of NaY and ultra-stable Y molecular sieves was investigated, which is an industrial VOCs. Adsorption treatment provides reference.