Technical Research And Engineering Design Of Catalytic Combustion For Volatile Organic Compounds Of Finishing Process In Synthetic Leather Industry

Volatile organic compounds（VOCs）,as vital precursors of PM_2.5and O₃,are the culprit for the complex atmospheric pollution.With the develpoment of VOCs renovation in our country,how to develop economical and feasible treatment process for the emission characteristics of VOCs becomes the key to improve the efficiency and save energy.Synthetic leather is a dominating high-emissions industry in China.A large amount of VOCs containing methyl ethyl ketone（MEK）and ethyl acetate（EA）with total concentrations of 1050-3869 mg/m³were emited by a selected synthetic leather enterprise during the finishing process.It will be difficult to treat such VOCs waste gas,since the emission process of VOCs with high air volume are non-continuous and non-constant,and the enterprise has the demand of heat recovery for energy saving.In this study,taking the synthetic leather enterprise’s VOCs during finishing process as an example,the catalytic combustion pilot of MEK and EA was studied by using the monolithic honeycomb Pt-Pd/γ-Al₂O₃and Mn-Ce-Zr catalysts.The factors involved in research were intake concentration,temperature,volume space velocity（GHSV）,relative humidity（RH）,two-component coexistence and catalytic lifetime.The two catalysts were compared for engineering application.The results showed that MEK and EA could be removal effectively by both Pt-Pd/γ-Al₂O₃and Mn-Ce-Zr catalysts.The Mn-Ce-Zr catalyst had the advantages of lower cost,lower temperature and higher GHSV,but shorter lifetime and the conversion was not consistent with the initial value after 240 h of continuous reaction.In contrary,the Pt-Pd/γ-Al₂O₃catalyst had a longer catalytic lifetime and stable conversion of MEK and EA within 240 h,indicating that the Pt-Pd/γ-Al₂O₃catalyst was more suitable for practical engineering.Moreover,the conversion of MEK and EA at the same temperature decreased with the increase of intake concentration on the Pt-Pd/γ-Al₂O₃catalyst.The conversion of 2945mg/m³MEK and 1800 mg/m³EA could achieve 99.2%and 98.3%at 380^oC,respectively.The transformations of MEK and EA were obviously inhibited with the increase of GHSV and the appropriate GHSV should not exceed 20000 h^-1,which was the best choice for ensuring the maximum waste gas treatment capacity.The influence of RH and two-component coexistence could be ignored in practical engineering when the temperature was not lower than 380^oC.The screened Pt-Pd/γ-Al₂O₃catalyst was applied in a set of catalytic combustion project with an air volume of 40000 m³/h.The conventional catalytic combustion process was adopted in the project,setting the temperature of catalytic combustion at380^oC and the GHSV at 20000 h^-1.The preheating time was 15 min and the project could be quickly started or stopped.The hot air could be reused in the system through heat recovery.When the maximum air volume was operated at 40000 m³/h,the preheating cost was 414.7 yuan/time.The heat recovery could reduce operating cost by about 56%and the actual operating cost was only 80.1 yuan/（10000 m³）.The actual catalytic combustion efficiency of the project could reach more than 90%,and the concentration of non-methane total hydrocarbons meeted the requirements of Table 5 in the“Emission standard of pollutants for synthetic leather and artificial leather industry”（GB 21902—2008）.This study provides a successful case for deep reduction of VOCs and treatment of VOCs waste gas with high air volume,non-continuous and non-constant emissions,and heat recovery demand.