Ternary Distillation Drying Process With Pore Protection And Its Applications

Porous materials are widely applicable,and the pore properties indeed affect their applications.Drying process in preparing porous materials is a key step for preserving the materials to a great extent on pores;so choice of an appropriate drying process is very important.Although there are some drying processes with pore protection in industry,such as,supercritical drying(SCD),freeze drying,azetropic distillation drying,they have different limitations.In this work,a ternary(an exchange solvent + a modification solvent + water)distillation drying process with pore protection(TDDPP)was proposed,and applied to drying of silica and MgO.The dry porous materials were further applied and compared with those from SCD.Silica wet gel from pressurized carbonization process as the raw material was studied by using the TDDPP process.Results indicated that ethyl acetate was a good choice as the exchange solvent,while butanol was prior as the modification solvent for producing silica with large pore volume(3.3 cm3/g)and peregal as the modification solvent for silica with large pore volume(2.6 cm3/g)and reduced drying time.Ultrasound and mechanical agitation could also help to reduce drying time to some extent.On the other hand,TDDPP combined with modification is also a one-step method for surface-modified porous materials.Long modification time reduced the pore volume;when the traditional modification solvent,HMDSO,was added in advance for producing hydrophobic silica,the drying time could be reduced with relatively large pore volume(2.7 cm3/g).This ternary distillation drying method is an efficient and low-cost way for various other materials such as MgO,γ-Al2O3,and SiO2-Al2O3.When SiO2 the as dried SiO2 in this work was used as a flatting agent,the extinction ratio reached 67%.The TDDPP was applied to the drying of the precursor Mg(OH)2,which was then calcined to produce porous MgO(TDD-MgO).The TDD-MgO and SCD-MgO were compared in Pb2+ adsorption.The adsorption factors such as pH,time and temperature were tested and discussed.Results showed that at 25 ℃,when the initial Pb2+ concentration was 60 mg/L,24 h was necessary to reach adsorption equilibrium for TDD-MgO,while it needed only 4 h for SCD-MgO.The adsorption capacity declined firstly and then grew up when the temperature increased from 25 ℃ to 75 ℃.The maxium adsorption capacity of TDD-MgO was 4353 mg/L,and that of SCD-MgO was 3773 mg/L.The both adsorbents fitted the pseudo-second-order adsorption kinetic model and the Langmuir isotherm model.The XRD results were corroborative evidence which indicated that the adsorption process included both chemisorption and physical absorption behaviors.The main components after adsorption were 2PbCO3·Pb(OH)2,PbO,Mg(OH)2,and MgO.The TDD-MgO and SCD-MgO were compared in Mn2+ adsorption.The adsorption factors such as pH,time and temperature were tested and discussed.Results showed that at 25 ℃,when the initial Mn2+ concentration was 60 mg/L,it took 24 h to reach adsorption equilibrium for both TDD-MgO and SCD-MgO.The adsorption capacity increased with the temperature from 25 ℃ to 75 ℃.The maxium adsorption capacity of TDD-MgO was 1219 mg/L,and that of SCD-MgO was 1146 mg/L.The both adsorbents fitted the pseudo-second-order kinetic model and the Langmuir isotherm model.XRD results were corroborative evidence which indicated that the adsorption process included both chemisorption and physical absorption behaviors.The main components after adsorption were Mn3O4,MnO2,Mg(OH)2 and MgO.The industry wastewater treatment by using TDD-MgO was tested and the adsorption capacity was 1032 mg/L.When 15 mg TDD-MgO was added into 100 mL wastewater,the concentration of Mn2+ wastewater would be lower than the discharge standard GB 8978-1996.