The Effects Of Additives On CO₂Capture By Hydrate Membrane Technology

The greenhouse effect has caused severe changes in the global climate and ecosystem. Among the greenhouse gases, CO2is the most influence one. Among all origins of CO2emissions, fossil fuels from electricity production which accounts for about30%is the major one. With the development of economy, CO2emissions in the atmosphere are increasing. Therefore developing energy-saving and effective technology to capture CO2produced in power-plants has scientific significance and broad application prospects in reducing the greenhouse effect and environmental protection.There are some obvious disadvantages of conventional CO2separation techniques. A hydrate-based gas separation process has attracted more attention recently. But there are many problems need to be investigated, such as intermittent operation and high energy consumption, rigorous temperature and pressure, low reaction rate. In this study, we proposed a new techno-logy which combined hydrate and porous membrane and thus overcame the shortages caused by intermittent operation. Sodium lauryl sulfate(SDS)-tetrahydrofuran(THF), tetra-n-butyl ammonium bromide(TBAB)-methanol(MeOH) and tetra-n-butyl ammonium fluoride(TBAF)-MeOH were chosen as additives for hydrate formation. The separation efficiency of CO2/N2mixture was investigated with them, respectively. This provided a theoretical basis for CO2capture by the hydrate membrane technology.(1) Hydrate membrane separation experiments were carried out with SDS and THF, and the effects of their concentrations on CO2separation efficiency were studied. The results showed that the better CO2separation efficiency was obtained with250ppmSDS-1.0mol%THF mixed solution. With the increase of the feed pressure, the CO2separation factor first increased and then decreased. And in the range of0.5-6.0°C, the CO2separation factor was increased with the increase of temperature. The maximum CO2separation factor was3.84at4.10MPa and6.0°C. And the permeance was in the range of1.87~4.01*10"8mol/(m2-s-Pa).(2) The process of CO2capture by hydrate membrane method with the additives of TBAB/TBAF and MeOH was studied. The effects of the TBAB、 MeOH or TBAF concentration, feed pressure, temperature and CO2composition in the feed gas were investigated. The results showed that the CO2separation efficiency with0.229mol%TBAB/TBAF-1.26mol%MeOH mixed additives was better than others. And adding additives reduced the time to reach steady state from300min to120~150min, as compared to pure water. The maximum of CO2separation factors was5.90with0.229mol%TBAB-1.26mol%MeOH and7.58with0.229mol%TBAF-1.26mol%MeOH. And the permeance was in the range of1.82-3.48*10-8mol/(m2-s-Pa). In the range of2.88-4.52MPa and0.5°C-6.0°C, the CO2separation factor first increased and then decreased. The results demonstrated that the pressure and temperature have an optimal range.(3) The mixed additives, especially TBAF-MeOH, could enhance CO2separation efficiency. And CO2could be enriched from19.71mol%to94.40mol%by three stages hydrate membrane formation process with TBAF-MeOH at4.0°C.