Preparation And Application Of Geopolymer Based Porous Materials In Membrane Separation Field

Geopolymer is also called inorganic polymer.It is a kind of amorphous cementitious material with three-dimensional network like the zeolite structure composed of silicon-oxygen and aluminum-oxygen tetrahedron.It has the advantages of its high strength,acid resistance,alkali resistance,easy molding,high-temperature resistance and low cost.Membrane separation technology is recognized as one of the most promising high-tech fields in the 21st century,which has the advantages of high separation efficiency,low energy consumption and easy to use.Compared with the traditional inorganic ceramic membrane,geopolymer for membrane separation material has the advantages of no-sintering,low-cost and simple preparation.In this paper,there were three methods to prepare geopolymer-based porous materials for membrane separation,including the particle-stacking method（PSM）,the direct-foaming method（DFM）and the solvent-volatilization method（SVM）.Using these three methods,porous inorganic membrane separation materials with a series of pore size distribution were prepared respectively,and they were applied to the fields of petroleum sand control,paper green liquor purify,ethanol water separation and other inorganic membrane separation fields.This paper provides some new ideas for the development of geopolymer-based porous material,expands the application of traditional geopolymer-based porous material,and provides some experimental bases for the application of geopolymer-based membrane separation material in different fields.Through the systematic study of the process,ratio and properties of the geopolymer-based porous material under the three preparation methods,the main conclusions are as follows（1）Using particle-stacking method and sand as filling aggregate,the best ratio of geopolymer-based porous material was obtained of m_water-glass:m_slag=0.30,m_water:m_total=0.066,m_sand:m_total=0.825,m_thickener;m_total=4.0 ×10-3.The compressive strength and water flux were 10.33 MPa and 8.7 ×105 kg·m^-2·h^-1,respectively.The heat resistant temperature of the porous material was up to 736℃.The pore size distribution was 150-280 μm,which could intercept particles lager than 45 μm As a sand control filter of oil exploitation,the clay particles could pass through the pores without blocking them.After being placed in water or air,room temperature of 60℃ oven for 210 d,they had no obvious deformation.Compared with resin-based sand control filter,geopolymer-based filter used in oil exploitation not only had the advantages of low-cost and good durability,but also had excellent high temperature resistance（2）Using particle-stacking method,the porous material was prepared with different sizes of lab-made slag microspheres as filling aggregate and geopolymer slurry as binder.Based on the study of microstructure,particle size distribution,crystal structure,bulk density,porosity,water absorption and specific surface area of the microspheres,by adjusting the ratio of slurry,the porous material prepared by the microsphere has a certain water flux and a better compressive strength,and it could be obtained the laws of slurry dewatering volume and water demand with microsphere size and water absorption.After calcining,the specific surface area and water flux of the porous material decreased,but the compressive strength increased by 82.8%.Through the characterization of pore size distribution and separation performance,it was found that the pore size of the porous material was about 1/3 of the microsphere size,and the smallest particle size that could be retained was about 1/8 of the microsphere size（3）Using direct-foaming method and adjusting the composition of slurry,metakaolin geopolymer-based porous material was prepared and the best ratio was obtained of Mwater-glass=1.4,m_water-glass:mmetakaolin=0.80,m_water:m_total=0.30,mhydrogenperoxide:m_total=0.010,mSDS:m_total=1.0 ×10-4.The compressive strength and permeability were 5.8 MPa and 8.4×104 kg·m-2·h-1,respectively.Excessive alkali metals in the porous material could be removed by washing with magnesium ion solution.When the material was calcined at high temperature,there would be mass loss,size shrinkage and other changes.After calcining at 300℃ and cleaning,there would be no dissolved organic matter during the use,so it could be better used as membrane separation material or support material.More water-glass and a certain amount of slag could increase the stability of the material（4）Using solvent-volatilization and dip-coating method,geopolymer-based or zeolite-based separation layer was prepared on the surface of support.The composite membrane separation material was obtained by only two preparation processes.On the geopolymer-based porous material support,the metakaolin geopolymer-based composite membrane was prepared and applied to the removal of suspended solids from green liquor of papermaking.The flux and the removal rate were 340 kg·m^-2·h^-1 and 99.6%,respectively.When the ratio of slurry is 1Al₂O₃:2SiO₂:2Na₂O:15H₂O,it is the most suitable to form zeolite composite membrane after curing 24 h at 60℃ on the geopolymer-based porous material support.The NaA zeolite or sodalite zeolite was formed when the hydrothermal mother liquor was water or NaOH solution.On stainless-steel support,NaA zeolite separation layer was prepared by non-hydrothermal method,and crystal nucleus was formed at 25℃.After heat treatment above 60℃,the crystal nucleus continued to grow and form zeolite with good crystallinity.By a simple vacuum-inhalation repairing method repaired mesoporous and macroporous defect,the separation coefficient of ethanol/water could be increased by about 7-14 times.