Preparation Of Hydrophobic Microporous Membrane And Study On The Performance Of Separating N₂O From Aqueous Solution

N₂O is a potential renewable energy source,when it replaces O₂and combusts with CH₄,the calorific value can be increased by about 37 percent.Moreover,the research shows that the N₂O release of sewage treatment process is large,accounting for 2.5%-25%of the total release of global N₂O.In the enriched N₂O bioprocessing process,the soluble N₂O concentration is as high as 35mg N/L,and realizing its high-efficiency separation can provide a theoretical basis for nitrogen energy recovery in sewage treatment.This paper studies the feasibility of N₂O aqueous solution separation of hollow fiber membrane contactors,and on this basis,hydrophobic microporous membranes are prepared,a flat film separation contactor for circulating fluid separation is constructed,and the separation properties of N₂O aqueous solutions are studied.The following results were obtained:（1）Using the circulating flow hollow fiber membrane contactor,the separation performance and influencing factors of N₂O aqueous solution were studied.It was found that the initial concentration,negative pressure and liquid flow rate had a positive correlation with the separation performance;while the pH and salinity of the solution had little effect on the separation performance.When the initial concentration is 35mg/L,the negative pressure is 0.05MPa,and the liquid flow rate is 7L/h,a separation efficiency of 92.12%and a flux of 7.47μmol·m^-2·s^-1can be obtained in 10minutes;at a pH of 5-9,the salinity is in the range of 0-10g/L,and the separation efficiency of low-concentration N₂O is not significantly affected by the two.（2）The hydrophobic microporous flat membrane was prepared by thermally induced phase separation method.The best preparation parameters are as follows:30wt%polypropylene as raw material,7:3 ratio of DBP to soybean oil as mixed diluent,0.2wt%adipic acid as nucleating agent,and Irganox 1010 as antioxidant.Further characterization found that the contact angle of the membrane surface was more than 90°;the membrane pore size was 3-5μm,and the distribution was relatively uniform;the membrane surface potential was negatively charged.（3）A gas-liquid separation flat membrane contactor with a circulation loop was constructed,and the self-made hydrophobic microporous membrane was used to study the factors affecting the separation performance of the N₂O aqueous solution.The results are as follows:（1）The initial concentration of N₂O,negative pressure and liquid flow have a positive effect on the separation efficiency.When the initial concentration is 30 mg/L,the negative pressure is 0.07 MPa,and the liquid flow rate is 300 m L/min,the separation efficiency within 30 minutes is 59.57%.Among them,the initial concentration of N₂O has the greatest influence on the separation efficiency,followed by the influence of liquid flow and negative pressure.（2）There is no significant correlation between the pH of the solution and the separation efficiency.The pH value is in the range of 5 to 9,and the N₂O separation efficiency is between 56.24%and 59.07%.Compared with the initial concentration,negative pressure,and liquid flow rate,the solution pH value has little effect on the N₂O separation efficiency.（3）When the salinity is in the range of 0g/L to 35g/L,the N₂O separation efficiency is 58.23%-59.49%.Indicating that the solution salinity has little effect on the N₂O separation efficiency.（4）With the hydrophobic flat microporous membrane as the carrier,by attaching and growing a uniform biofilm on the surface of the microporous membrane,a biofilm-microporous membrane gas-liquid separation system was constructed,and the separation performance and influencing factors of the N₂O aqueous solution were studied,ang it is expected to provide a basis for the in-situ separation of N₂O in the biological reaction system.The results are as follows:（1）The initial concentration,negative pressure and liquid flow rate are positively correlated with the separation efficiency of N₂O,which is consistent with the impact characteristics of the unattached biofilm system.The pH and salinity of the solution have little effect on the separation efficiency.（2）Compared with the hydrophobic flat microporous membrane contactor,the N₂O separation efficiency of this system has decreased by about 10%-20%,which is presumably due to the clogging of the microporous membrane caused by the growth of microorganisms;it may also be due to the use of part of the N₂O by the microorganisms.