April 10-14, 2016
Strategies for stabilizing atmospheric greenhouse gas concentrations will need to consider future CO2 emissions from an enormous resource of worldwide fossil fuel supplies and a diverse range of mitigation technologies. In 2013, global CO2 emissions due to fossil fuel use (and cement production) were 36 gigatonnes (Gt CO2), and are projected to increase by an additional 2.5% in 2014. Even if all emissions from large fixed sources could be captured, the roughly 30-50% of global emissions due to transportation and mobile sources would still be released into the atmosphere. To ensure the concentration of atmospheric CO2 in the scope of security, CO2 air capture, which offers the potential to be a truly carbon negative technology, is urgent.
The design and preparation of porous materials with controlled structures and functionalities is crucial to low concentration CO2 capture. In this work, two preparation approaches of CO2 adsorbents are explored. One is heterogeneous membrane preparation using porous supporting materials through phase inversion method, which is relatively simple, rapid, and inexpensive, and the other is to directly prepare the porous adsorbents through grafting method using a novel material—cellulose. For phase inversion method, anion exchange resin, which can absorb low concentration CO2 after ion exchange treatment, is mixed with Polyethersulfone (PES), N-Methyl pyrrolidone (NMP) and Macrogol 400(PEG-400) to form casting solution, and finally, the heterogeneous membrane is prepared for CO2 adsorption. For grafting method, the cellulos anion exchange fiber used for CO2 adsorption, is prepared by alkali pretreatment of sodium hydroxide and the grafting of epichlorohydrin and ethylenediamine onto fiber, and finally ion exchange treatment is made to introduce basic groups, such as carbonate ions and hydroxide ion. The surface properties of the prepared adsorption materials are characterized by SEM and BET, as can be seen in Figure 1, and the results reveal that the materials are porous and have large specific surface area, which is beneficial to the kinetics of CO2 adsorption. The absorption performances of the two kinds of adsorbents are tested on a self-made rotating bed reactor, and the absorption capacity and kinetics are compared. To optimize the kinetics performance of CO2 adsorption, the modified shrinking core model (SCM) is used to analyze the resistance during the reaction process according to the test results. The resistance during the mass transfer process includes physical diffusion resistance and chemical reaction resistance. For the heterogeneous membrane, the results reveal that the resistance of physical diffusion and chemical reaction is comparable when the saturation of CO2 adsorption is low (less than 0.3), and the physical diffusion resistance increases greatly and controls the kinetics performance when the saturation of CO2 is high, as can be seen in Figure 2. The influence of temperature and humidity on CO2 adsorption kinetics is also studied and the diffusion coefficient and reaction rate constant are obtained, and the activation energy of reaction can be determined.
Tao Wang, Jun Liu, Kun Ge, and Zhongyang Luo, "Kinetic enhancement of adsorbent for CO2 capture from atmosphere by porous material" in "CO2 Summit II: Technologies and Opportunities", Holly Krutka, Tri-State Generation & Transmission Association Inc. Frank Zhu, UOP/Honeywell Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/co2_summit2/44