磁性微球固定化CA酶强化IVCAP工艺捕集CO2的应用基础研究

Carbon dioxide (CO2) is a greenhouse gas that has been shown.to be a major contributor to global warming. The attention of many researchers has been attracted to develop efficient and low energy-consuming technologies for capturing the CO2 emitted from fossil fuel-fired power plants.Recently, a novel integrated vacuum carbonate absorption process (IVCAP), which employs a potassium carbonate (K2CO3) aqueous solution as a solvent, has been proposed to reduce the energy usage for CO2 stripping. However, K2CO3 is only weakly alkaline and thus a K2CO3-based system has a slow CO2 absorption rate, which become the rate-control step of this process. Carbonic anhydrase(CA), a zinc metallo enzyme that can efficiently catalyze the hydration of CO2 to form bicarbonate, can be employed as a catalyst to accelerate the absorption rate in the IVCAP without changing the phase equilibrium of the system. However, how to design an efficient bioreactor, to improve the mass transfer rate and to keep the activity and stability of the enzyme are the key problems. Based on the present research background, in this proposal, a new approach is proposed to improve the CO2 stripping efficiency of IVCAP by using a magnetically stabilized fluidized bed (MSFB) reactor with magnetic microspheres immobilized CA enzyme. The aim of this proposal is to investigate the stripping efficiency,the mass transfer reaction kinetics and mechanism of the chemical absorption combined with enzyme catalysis in magnetic field,and to investigate the effect of the integrated absorption-desorption process for CO2 capture in the long-run and then assess the economy and stability of this process.

碳酸盐溶液吸收-真空解吸集成工艺（IVCAP) 是近年来开发的一种低再生能耗的CO2捕集新工艺，但由于碳酸盐是弱碱，吸收CO2的速率较低，吸收过程为该工艺的速率控制步骤。碳酸酐酶（CA）是一种CO2水合酶，将其添加至吸收液中，可大大促进CO2吸收速率，但如何设计高效稳定的生物反应器、增强气液固三相传质效果、保持酶的活性和稳定性是待解决的关键问题。针对上述研究背景和存在的问题，本申请提出采用磁性微球固定化CA酶促进IVCAP工艺捕集CO2的新思路，将磁性微球固定化CA酶置于与之匹配的磁性稳态流化床反应器中，强化CO2捕集效果，弥补IVCAP工艺的缺陷，构建磁场作用下酶催化与化学反应耦合吸收-真空解吸的CO2捕集新工艺；深入研究其耦合吸收CO2的机理及该体系捕集CO2的传质-反应动力学；优化工艺参数，考察模拟烟气条件下该工艺捕集CO2的效能，并评价其经济性和稳定性。

本项目制备了表面羧基化Fe3O4磁性微球和聚(GMA-DVB)复合Fe3O4磁性微球，并将碳酸酐酶（CA）固定化到磁性微球上，用于强化碳酸盐溶液吸收-真空解吸集成新工艺（IVCAP）工艺捕集CO2。表征结果显示，这两种微球粒径分别约为10 nm和200-350 nm，都具超顺磁性，载体与酶分子间形成酰胺键（-CO-NH-）实现共价结合。将上述两种磁性微球作为载体固定化CA酶，采用单因素法考察载体用量、pH、摇床转数、加酶量、时间、温度等因素对CA酶在Fe3O4磁性微球上固定化效果的影响，最终确定了最佳的CA酶固定化条件。对比两种磁性微球，聚(GMA-DVB)复合Fe3O4磁性微球的产率高于表面羧基化Fe3O4磁性微球，且最佳条件下，CA酶固定化效果也略高于后者，其酶活力回收率达69.2%，固定化酶的比活力达1.462 U/g（游离酶的比活力为528.321 U/g）。随后，在最适固定化条件下，通过 p-NPA法，对比游离酶和由聚(GMA-DVB)复合Fe3O4磁性微球制备得到的固定化酶，考察两种酶的最适温度、最适pH、热稳定性、贮藏稳定性以及重复利用性等酶学特性，证明固定化CA酶比具有比游离酶更高的稳定性和耐受性。并以p-NPA为底物，根据米门方程（M-M 方程）得出固定化酶的酶催化反应动力学模型，游离酶的Km为6.091 mM，固定化酶的Km为8.077 mM。在双搅拌釜中，缓冲液为吸收液，考察固定化酶和游离酶催化 CO2水合作用大小，并基于双膜理论，分析了酶催化下的CO2水合反应的传质-反应模型，获得反应速率常数k2及增强因子E等重要的参数，其Arrhenius关系式为k2CA=1225.59exp(-3175.9/T)。