Preparation Of ZIF-L（NH₂）/PEBA2533/PTFE Membranes And Their Dephenolization Performance For Phenol Solution

In the development of coal chemical industry,wastewater treatment has always been a difficult problem.In particular,the coal gasification wastewater contains a variety of organic pollutants,which are badly toxic and harmful.The content of phenol is high in the coal gasification wastewater,and phenol is an important chemical raw material,so it is of great significance to separate and recover phenol from coal gasification wastewater.At present,adsorption dephenolization and extractive distillation dephenolization the are two mainly processes applied to separate and recycle phenol from wastewater in industrial.Adsorbents used in adsorption process are difficult to regenerate.Extraction agents used in extraction distillation dephenolization process are often toxic,easy to cause secondary pollution,and the process is energy intensive.In contrast,pervaporation membrane separation process has become one of the most promising technologies for phenol separation and recovery from wastewater due to its advantages of low energy consumption,no need for regeneration,continuous operation,clean and friendly to environment.In this paper,the hydrophobic ZIF-L crystals with suitable pore size for phenol permeation were introduced into PEBA2533 matrix,which has a good affinity to phenol,and the mixed matrix membranes were improved from two aspects.On the one hand,to make the ZIF-L crystals disperse in PEBA2533 more uniform and to restrain the agglomeration of the crystals,small-sized ZIF-L crystals were prepared,and the casting solution was prepared by precoating the ZIF-L crystals method.On the other hand,to decrease the interface defects between the additive and the polymer,Amino functional groups were introduced into ZIF-L crystals.Hydrogen bonding between amino functional groups and amide functional groups in the polymer matrix enhanced the force strength between the two phases,and restrained the forming of the interface defects.The dephenolizaton of phenol solution by the prepared mixed matrix membranes was investigated.The specific research content is as follows:1.The size of the ZIF-L crystals were controlled by polyvinyl pyrrolidone（PVP）as an end-capping reagent.The mono-dispersed rod-like ZIF-L crystals were obtained.With the increase of the PVP content in the synthesis solution,the crystal size decreased to 1.5μm.At25℃,the adsorption capacity of 1.5μm rod-like ZIF-L crystals for phenol reaches 21.9 mg/g,which is competitive compared with other materials with adsorption capacity for phenol reported in the literature.2.ZIF-L/PEBA2533/PTFE mixed matrix membranes with different doping amounts were prepared by precoating method with small particle size ZIF-L crystals as additive,PEBA2533 as organic matrix and PTFE as support.Compared with ZIF-L crystals doped with large particle size,ZIF-L crystals with small particle size in organic matrix PEBA2533 were dispersed unifromly and had good interface compatibility,which improved the separation performance of phenol solution.At high doping content（20 wt.%–30 wt.%）,there were still some non-selective gaps between the two phases.With the increase of doping amount from 0wt.%to 30 wt.%,the separation factor first increased and then decreased,and the flux increased.When the doping amount is 15wt.%,the membrane shows the best separation performance for phenol solution.As the feed temperature increased from 30℃to 80℃,the total flux,water flux and phenol flux increased,and the separation factor increased.At 80℃,as the feed concentration increased from 1000 ppm to 8000 ppm,the total flux increased slightly,while the water flux almost unchanged.The phenol flux increased with the increase of the concentration of phenol solution from 169.9 g/（m²·h）to 608.83 g/（m²·h）,and the separation factor decreased from 71.67 to 32.19.3.ZIF-L-NH₂ crystals with different degree of amino substitution were prepared by using 2-methylimidazole and 2-aminobenzimidazole as mixed ligands.The phase structure of ZIF-L-NH₂ crystals was not changed when the degree of amino substitution was 5%–10%.ZIF-L-NH₂/PEBA2533/PTFE mixed matrix membranes were prepared by incorporatiing ZIF-L-NH₂ crystals into the organic matrix.Hydrogen bonding between ZIF-L-NH₂and H–N–C=O functional groups in PEBA2533 was formed,which enhanced the force strength between the two phases.The separation performance of the prepared mixed matrix membranes for phenol solution was investigated.The results showed that the separation effect of the mixed matrix membranes prepared by ZIF-L-NH₂ with a substitution degree of 7.5%was the best.At 80℃,the separation factor was 41.49 and the permeation flux was 2420.41g/（m²·h）for phenol solution with a concentration of 5000 ppm.The separation factor increased,the total flux decreased,and the phenol flux increased.Due to the decrease of the interface defects,the non-selective diffusion of water was inhibited and the water flux was reduced.The amino modified ZIF-L crystals play a role in promoting the performance of the membrane.