Research On Preparation Of Silicon Carbide Hollow Fiber Membranes

In addition to excellent chemical and thermal stability,high mechanical strength and long service life,the hollow fiber ceramic membranes also have the advantages of large surface-to-volume ratios,thin walls,high separation effciency,high flexibility,short manufacturing time and simple process,which are widely used in various fields,including food and drug processing,seawater desalination,wastewater and exhaust gas treatment,biological engineering,energy engineering and many other fields.The current research and report on silicon carbide（SiC）hollow fiber membranes are rare,and almost all the scientific researchers combine phase inversion and sintering process to fabricate SiC hollow fiber membranes.In order to promote the research and application of SiC hollow fiber membranes,the research topic for research on preparation of silicon carbide hollow fiber membranes.In the paper,the spherical SiC was studied by template synthetic method,mechanical ball milling and high temperature heat treatment,aiming at obtaining smooth SiC particles without crystal growth.Then SiC hollow fiber membranes with high permeability and narrow distribution were preparedby one-step through extrusion molding and sintering using SiC powder as the main raw material.The effects of sintering temperature and SiC type on the properties of SiC hollow fiber membranes were systematically studied.The main contents are described as follows:（1）Preparation of SiC by template synthetic method.SiC was prepared by template synthetic method using petroleum coke and silicon powder as the main raw material.The morphology,roundness,particle size and crystal structure of SiC paticles were analyzed under different sintering temperatures,and the effect of Ti-doped to template synthetic method was discussed.The results show that the morphology and particle size of raw petroleum coke could not effectively affect and control the morphology and particle size of SiC.Therefore,it’s not feasible to obtain smooth SiC particles without crystal growth by template synthetic method using petroleum coke and silicon powder as the main raw material.Titanium doping made the products in the form of adhesion,which had a clear crystal growth and merger behavior,so it’s not feasible to control the morphology and particle size of SiC by adding titanium powders.（2）Research on mechanical ball milling reshaping of silicon carbide powders.The irregular shape of SiC powders were reshaped by the method of mechanical ball milling.The SiC powders were analyzed under different ball milling time.The morphology,roundness,particle size and its distribution of the SiC powders before and after reshaping were characterized.The results show that the particle size distribution of SiC powders reduced in width with the increase of mechanical ball milling time,but it’s not obvious that SiC particles become spherical and ball milling reached the limit at 48h.The irregular shape of SiC powders were reshaped by the method of mechanical ball milling,which couldn’t obtain smooth SiC.Therefore,it’s not feasible to prepare SiC hollow fiber membranes on this basis.（3）Research on high temperature heat treatment reshaping of silicon carbide powders.The irregular shape of SiC powders were reshaped by the method of heat treatment.The different size of SiC powders were analyzed under different heat treatment temperatures.The morphology,roundness,particle size and its distribution of the SiC powders before and after reshaping were characterized.And the recrystallization sintering mechanism of SiC was discussed.The results show that the sphericity of the reshaping SiC powders were high at 2000℃-2050℃,with smooth surface and narrow particle size distribution.The mass transfer process of SiC powders were evaporation-condensation at high temperature.It’s proofed that SiC powders were reshaped effectively by high temperature heat treatment.Therefore,it’s feasible to prepare Si C hollow fiber membranes on this basis.（4）Preparation and characterization of silicon carbide hollow fiber membranes by extrusion molding.SiC hollow fiber membranes were prepared by one-step through extrusion molding and sintering using SiC powders as main raw material.The effects of sintering temperature and SiC type on the properties of SiC hollow fiber membranes were systematically studied.The microstructure,thermal decomposition process,crystal structure,pore size distribution,mechanical strength,open porosity,and nitrogen permeation flux were characterized.Results show that the fibrous structures are located on the completely covered cross section,it’s feasible to prepare SiC hollow fiber membranes with high permeability and narrow distribution by extrusion molding and sintering.The mechanical strength of SiC hollow fiber membranes was gradually increased with increasing temperature from 2000℃to 2200℃,but the pore size,open porosity and nitrogen permeation flux were gradually decreased.The 2200℃was the best sintering temperature,the mechanical strength,open porosity and nitrogen permeation flux respectively was 34.0MPa,41.4%,4.2×10⁶Lm^-2h^-1bar^-1.The pore size distribution of SiC hollow fiber membranes prepared by using black SiC powders as raw material was wide and disorderly,showing a multiple peak distribution.The mechanical strength of SiC hollow fiber membranes was increased with black SiC particle size decreased,the pore size and open porosity were decreased.The pore size distribution of SiC hollow fiber membranes prepared by using green SiC powders as raw material exhibited a single peak and approximated the normal distribution curve,showing an excellent mechanical strength,open porosity and nitrogen permeation flux,respectively was 18.28MPa、56.37%、8.4×10⁷Lm^-2h^-1bar^-1.