| Summary: | 碩士 === 國立高雄應用科技大學 === 化學工程與材料工程系碩士在職專班 === 102 === When the gas on either side of a membrane has pressure difference, it is driven by dissolving, permeating, diffusing, and desorbing steps to move from the higher pressure side across the membrane to the lower pressure side. Higher pressure difference across the membrane leads to stronger driving force to diffuse the gas across the membrane. Additionally, the gas diffusivity depends on the gas molecular diameter; smaller gas molecules have higher diffusivity. Hydrogen gas has smaller molecular diameter than methane gas, and it has higher diffusivity than the latter. When a hollow fiber member is used to recover hydrogen gas from a mixture of H2/CH4 (50:50), the hydrogen is effectively separated from the mixture; its concentration is raised from 50 mol% to 92% with pressure controlled at 5 kg/cm2 pressure, and to 96 mole% without pressure control. If the mixture contains H2/CH4/C3H8 (40:30:30) is treated using the same membrane, the hydrogen concentration is raised to 91.5 mole% with the pressure controlled at 3.5 kg/cm2, and to 95.4% without pressure control. Changing the membrane set arrangement to parallel mode, the hydrogen concentration can be raised further to 97.1%. Under conditions of similar input gas pressure and flow rate, the magnitude of degree for various parameters to influence the gas permeate rate across the member is parallel operating mode>free permeate>pressure control. Using the input gas pressure of 3 kg/cm2 as an example, the magnitude of gas permeate flow rate is 12.1 ml/min (parallel operating mode) > 7.0 ml/min (free permeation) > 3.5 ml/min( (pressure control). On the other hand, if the membrane module is operated in series mode instead of parallel mode with the input gas pressure and flow rate maintained at 3-11 kg/cm2 and 133-136 ml/min, respectively, laboratory results show that the series operation mode will concentrate the hydrogen concentration from 65.5 mole% to 82.2 mol% whereas the parallel operation mode will raise the hydrogen concentration from 60.1% to 73.1%. Therefore, the operation of hollow fiber polysulfone membrane at low pressure will be efficient to separate and concentrate hydrogen gas, and the recovered hydrogen gas can be used as either fuel or raw material for products with higher value. This type of membrane system is low in initial cost, easy to operate, consumes insignificant quantity of energy but produces hydrogen with high purity.
Keywords: Hollow fiber polysulfone membrane, Dissolving, Diffusion,Series operating mode,
Parallel operating mode, Hydrogen gas
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