Separation of $H_2/CO_2$ gas mixtures by pressure swing adsorption process

Abstract

Hydrogen and carbon dioxide, which are main components of gas in hydrogen production precesses, were separated by pressure swing adsorption(PAS) process and the effects of operating variables on product purity and recovery were investigated. For this purpose, experiments to decide adsorption equilibria isotherms and transport parameters were carried out proviously. Adsorption equilibria isotherms of hydrogen, carbon dioxide and its mixtures on actrvated carbon were determined, where pressure was 1-30 atm for the single component system and 1-20 atm for the binary component system. For the single component system, Freundlich isotherm, Langmuir isotherm, and Langmuir-Freundlich isotherm predicted experimental data fairly well. For the binary system, IAS model was best fitted to experimental data at low pressure while LRC was agreed with experimetal results at high pressure. Because of nonlinear type isotherm, mass transfer coefficient and axial dispersion coefficient were estimated by numerical analysis under various flow rates and pressures. The mass transfer coefficient was only affected by pressure such as: $$K=4.3\,P-0.9$$ But axial dispersion coefficient was affected by both pressure and flow rate. Peclet number was expressed as Reynolds and Schmidt unmber as following: $$\frac{1}{Pe}=\frac{0.25}{Re.Sc} +0.08$$ Seperation of hydrogen and carbon dioxded mixture (50/50 vol.\%) was carried out by using the PSA cycle to produce high qurity hydrogen. The effects of P/F raio, flow rate, pressure of absorption step, the end pressure of cocurrent blowdown step, and the change of time length of pressure changing steps on the product purity and recovery were investigated. When the P/F ratio was increased, product purity was also increased. Morever, higher feed flow rate in adsorption step needed higher P/F ratio. But breakthrough occurred regardless of P/F ratio when feed flow rate was very high, and product purity became down to low level. Therefore, optimal P/F rati...