Study On The Resourcing Silicoaluminophosphate Zeolite SAPO-34 Crystallization Mother Liquor And The Application Performance Of Its Products

Silicoaluminophosphate zeolite SAPO-34 is an important catalyst for methanol-to-olefin reaction.In synthesizing SAPO-34 molecular sieve by hydrothermal method,the crystallization mother liquor,an industrial wastewater is produced,it contains template agent(triethylamine),species of aluminum(Al2O3),phosphorus(phosphoric acid),silicon(SiO2)and residual SAPO-34 molecular sieve.Direct drainage of the mother liquor will pollute the environment,and waste the recyclable raw materials,so it is necessary to recycle the mother liquor.At present,the reuse study mainly focus on circulating mother liquor for synthesis of SAPO-34,few studies focus on other aspects.In this thesis,one way of resourcing is recovering triethylamine(TEA)in mother liquor by distillation,then inorganic coagulant was prepared using the remaining inorganic elements.The prepared coagulant was applied in treatment of municipal wastewater;Another way of resourcing the mother liquor is SAPO-34 molecular sieve synthesis.Using the synthesized SAPO-34 molecular sieve,the supported catalysts were prepared and applied to the catalytic ozonation of NO.Furthermore,a new method of simultaneous desulfurization and denitrification by coupling ammonium persulfate with catalytic ozonation was proposed.Specific contents and conclusions are below:(1)Triethylamine in the SAPO-34 mother liquor was recovered by the fractional distillation,and the remaining inorganic elements were used to prepare polyaluminum phosphoric sulfate coagulant.The results showed that 80.5%of triethylamine in the mother liquor was recovered,while the residual was dissolved by washing and then decomposed by catalytic ozonation.The optimal conditions for preparing coagulant are obtained using response surface methodology,where[P]/[Al]and[OH]/[Al]molar ratios were 0.25 and 1.05 respectively,reaction temperature was 85°C.Polyaluminum phosphoric sulfate coagulant mainly contains Al,O,P,Na and S,forming amorphous polymer.The optimal dosage of polyaluminum phosphoric sulfate coagulant was 40 mg·L-1,the removal efficiencies of turbidity,COD and total phosphorus were 89.3%,79.7%and 72.6%respectively.What's more,the optimal dosage of polyaluminum phosphoric sulfate was 20 mg·L-1 lower than that of polymeric aluminum chloride.(2)Resourcing SAPO-34 mother liquor,the effects of the molar ratios of[SiO2]/[Al2O3],[TEA]/[Al2O3]and crystallization time on the synthesis of SAPO-34 molecular sieve were studied.The Al2O3:P2O5:SiO2:TEA molar ratio of the resulting mixture was 1.00:1.00:0.16:3.00,the gel was heated at 20? for 6 h,SAPO-34 molecular sieve with a higher crystallinity and an average particle size of 2-3 ?m can be obtained.Compared with the commercial SAPO-34,the prepared SAPO-34 molecular sieve had larger specific surface area,smaller grain size and more moderate acid centers.In addition,the catalyst life time of the prepared SAPO-34 was 2.2 times that of commercial SAPO-34 in methanol-to-olefin reaction.(3)FeOx/SAPO-34 catalyst was prepared with the synthesized SAPO-34 as support,it was applied to the catalytic ozonation of NO.The optimal preparation conditions of the ozonation catalyst were that allowing NH4+/SAPO-34 reacting in 0.05 mol·L-1 iron nitrate solution for 15 h.The mechanism of catalytic ozonation of NO was studied by electron paramagnetic resonance and other technologies,the results showed that oxygen vacancies were the active sites of the catalyst and the formation of superoxide and hydroxyl radicals were detected.The effects of the molar ratio of[O3]/[NO],the residence time,the volume fraction of water vapor and the concentration of SO2 on the NO oxidation rate were studied.An oxidation rate of 55.0%for NO was obtained under the optimal experimental conditions.The NO oxidation rate decreased only 10.2%after 50 h of continuous reaction,suggesting that the FeOx/SAPO-34 catalyst had certain resistance to water and sulfur.(4)An integrated method of simultaneous desulfurization and denitrification of flue gas by coupling ammonium persulfate with catalytic ozonation was developed.As the gas passed sequentially through the ozonation reactor and ammonia/ammonium persulfate solution,NO conversion rate of 92.6%and SO2 absorption rate of 100.0%were obtained under the optimum conditions:the initial pH value of 9.0,ammonium persulfate solution concentration of 0.20 mol·L-1,the volume fraction of ammonia solution of 0.8%,the reaction temperature of 15? and the volume of absorbent of 150 mL.The reaction of simultaneous desulfurization and denitrification were studied in detail:when the solution pH ranged from 7.0 to 9.0,hydroxyl and sulfate radicals played a main role;when pH was less than 7.0,ozone and persulfate served as the main oxidants.After 10 cycles of simultaneous absorptions of NO and SO2,the compound fertilizer from reaction products,with total nitrogen of 24.5%was prepared.