Preparation Of Metal-organic Framework CAU-10-based Membranes And Their Dehydration Performance For Ethanol Solution

Ethanol is a chemical that has been widely used in medical,chemical and fuel fields.In its application,the water content of ethanol solution is strictly required（generally≥99.37 wt%）.At present,the distillation technology is mainly used to concentrate and purify the ethanol solution.However,distillation is not effective for the separation of ethanol solution with an ethanol concentration over 85 wt%.Especially for the azeotrope of ethanol and water formed when the ethanol concentration is up to 95.6 wt%,it is difficult to separate by ordinary distillation.Therefore,it is very important to explore a separation process that is both low energy consumption and environmental friendly.Compared with the traditional separation process（distillation）,pervaporation has some advantages-small occupied area,simple process and low energy consumption and is suitable for separating azeotropes.In this thesis,metal-organic framework CAU-10 membranes,CAU-10 and chitosan composite membranes（CS@CAU-10 membranes）and CAU-10 and chitosan blend membranes（CAU-10/CS membranes）were prepared.The crystals and membranes we synthesized were characterized by X-ray diffraction and scanning electron microscopy.The prepared membranes were used as a separation membrane,and the ethanol solution was dehydrated by the pervaporation The concrete research is as follows:（1）CAU-10 membranes were prepared on alumina support by in-situ growth and secondary growth,respectively.The CAU-10 membranes prepared by in-situ growth method were continuous and dense when the concentration of the synthesis solution was 0.06 mol/L.When the concentration of the synthesis solution is too high or too low,a continuous membrane cannot be obtained.The seed layer was obtained by in-situ seeding method,and the CAU-10membrane was prepared by secondary growth.The seed layer synthesis solution containing hydrochloric acid can dissolve the aluminum element in the support alumina,and the seed layer with higher coverage on the support can be obtained.Without hydrochloric acid in the seed layer synthesis solution,the continuous seed layer cannot be obtained.The seed layer can grow into a dense membrane in either low concentration secondary growth solution（0.03 mol/L）or high concentration secondary growth solution（0.06 mol/L）.The results of N₂ single-component permeation experiment proves that the membrane obtained in the secondary growth solution with higher concentration was the densest among the membranes as prepared.（2）The pure CAU-10 membrane was broken when sealing during pervaporation for its poor mechanical performance,and the separation performance of the membrane was lost.CS@CAU-10 composite membranes were prepared by coating a layer of chitosan on their surface,and the chitosan layer can improve the mechanical performance of the membranes.The prepared composite membranes were used to separate ethanol solution.The membrane prepared by 3 wt%chitosan acetic acid water solution had the highest separation performance.During the pervaporation,increased the operating temperature from 30°C to 70°C,the total flux increased and the separation factor decreased.At 30°C,the water content of the ethanol solution increased from 5 wt%to 20 wt%,and the permeation flux increased from 91 g/（m²·h）to 450g/（m²·h）,with the separation factor decreasing from 497 to 92.（3）CAU-10 crystals with particle sizes ranging from 1μm to 4μm and 0.8μm to 1μm were synthesized,and CAU-10/CS mixed matrix membranes were obtained by using those two kinds of crystals as additive,respectively.The CAU-10/CS membranes prepared by small-sized CAU-10 crystals had better dehydration performance for ethanol solution.CAU-10/CS membranes with different additive contents were prepared.When the content of CAU-10 was lower（0 wt%―3.7 wt%）,the dispersion of CAU-10 crystals was better,and the membrane was uniform and dense without obvious defects.When the content of CAU-10 is higher（5wt%―7.5 wt%）,the aggregation of CAU-10 crystals appeared in the membrane.With the increase of CAU-10 loading,the permeation flux of the mixed matrix membrane also increased,while the separation factor first increased and then decreased.When the content of small-sized CAU-10 crystals was 3.7 wt%,the mixed matrix membrane showed the best separation performance for ethanol solution.On this mixed matrix membrane was used to separate ethanol solution,increased the operating temperature from 30°C to 70°C,the total flux increased and the separation factor decreased.At 30°C,the water content of the ethanol solution increased from 5 wt%to 20 wt%,the permeation flux increased from 81 g/（m²·h）to 401 g/（m²·h）,and the separation factor decreased from 3343 to 961.