Preparation Of Polyacrylonitrile Hollow Fiber Membrane And Study On Separation Performance Of Acetylene

Acetylene is a basic chemical raw materials, it has an important position in the industrial production. The separation and purification of acetylene obtained widely attention. Compared with the traditional separation methods, membrane absorption technology exhibited good prospect due to its highly efficient, energy-saving. In this paper, separation of acetylene from gas mixture was investigated by membrane absorption method and 1-Methyl-2-Pyrrlione（NMP） as absorbent. Polyacrylonitrile（PAN） as membrane material, through heat treatment, hybrid and hydrophobic modified to manipulate the structure of PAN membrane. Intensification of acetylene mass transfer from the gas permeation rate and reduce membrane wetting. The major studies were as below:The PAN hollow fiber membranes were prepared by phase inversion, and then heating it under air atmospheres results in crosslinking reaction between two nitrile groups, which imparts PAN with excellent solvent and insoluble in NMP. As-prepared membranes were used for acetylene absorption. The effects of gas and liquid velocity, the feed gas concentration and fiber length on acetylene mass transfer were investigated. And mathematical model was established to analysis and forecasting of mass transfer. The results showed that the heat-treated PAN hollow fiber membrane can be successfully used for the acetylene absorption. The acetylene mass transfer flux and absorption efficiency increased with increasing liquid velocity then decreased; the acetylene mass transfer flux increased with increasing gas velocity, the absorption efficiency decreased with increasing gas velocity; the acetylene mass transfer flux increased with increasing the feed gas concentration, the absorption efficiency increased with increasing the feed gas concentration then decreased. When the gas velocity was 0.327 m/s and liquid velocity was 0.00927 m/s, the acetylene concentration in the feed gas was 9%, the one-way acetylene absorption efficiency and mass flux are 41.11% and 1.63×10-4 mol·m-2·s-1, respectively.To avoid the densification and deformation caused by heat treatment in membranes, inorganic fillers were incorporated into polymer matrix to manipulate the membrane structure and enhance gas permeation properties. The heat-treated PAN/SiO₂ hollow fiber membranes were prepared through combining organic/inorganic blend and heat treatment methods for acetylene absorption process. The effect of SiO₂ contents, heat treatment temperature on the membrane morphology, structure and performance were investigated. The results showed that the hybrid membranes had higher gas permeation properties due to their high pore sizes, porosities and thin skin layer. The membranes were further investigated as a membrane contactor for acetylene absorption using NMP as absorbent. The acetylene absorption performance increased with increasing SiO₂ loading, and the acetylene mass transfer flux and absorption efficiency of the hybrid membrane contain 1 wt% SiO₂ were about 101% and 107% higher than the plain membrane at the same operating conditions, respectively. By adjusting the operating conditions, when the gas velocity was 0.496 m/s and liquid velocity was 0.0125 m/s, the acetylene concentration in the feed gas was 9%, the one-way acetylene absorption efficiency up to 79.35% and mass flux is 5.85×10-4 mol·m-2·s-1.To reduced membrane wetting and further optimize the performance of membrane, the highly hydrophobic hollow fiber membrane was prepared by incorporating the fluorinated silica（f SiO₂） inorganic layer on the surface of PAN/SiO₂ membrane for acetylene absorption. The f SiO₂ layer was tightly bonded to the surface of PAN/SiO₂ membrane through silane chemical reactions. The effects of silane concentration and treatment time on the hydrophobicity of membrane, mechanical properties and gas permeability were investigated. The experimental results revealed that the incorporation of the f SiO₂ layer on the membrane surface could enhance the surface roughness and greatly reduce the surface free energy due to the hydrophobic compound. The water contact angle of membrane surface was increased from 52° to 142°. When the gas velocity was 0.496 m/s and liquid velocity was 0.0125 m/s, the acetylene concentration in the feed gas was 9%, the acetylene absorption efficiency is 77.17% and mass flux is 5.69×10-4 mol·m-2·s-1.Moreover, the membrane contactor showed a reasonably stable performance throughout the 90 h long-term operation, the attenuation of mass transfer flux only 10%. Compared with PAN/SiO₂ membrane, the wetting fraction of PAN/SiO₂-f SiO₂ membrane is reduced 6%.