Post-combustion Co₂ Capture Using Liquid Nano-absorbents And Novel Solvent Regeneration Process

To deal the issues caused by global climate change,the control of CO₂ emitted from large point sources such as coal-fired power stations exhibites important environmental and strategic significance.Chemisorption method of post-combustion carbon capture technology is one of the best-understood and the most promising decarburization technologies,which has made great progress in recent decades,but the high investment cost and high operating energy consumption have hindered the large-scale application of this technology.The development of new absorbents and the optimization of existing chemical absorption processes are the main ways to improve the overall performance of chemisorption technology.This paper focuses on the key problems of chemsorption technology,from the nanoparticle-reinforced absorbent and the novel non-aqueous gas stripping process,in order to provide new ideas for the further development of chemisorption method.In this paper,two new types of nanoparticle-reinforced absorbents were studied:nanoparticle-organic amine mixed absorbents and nanoparticle-organic-hybrid-material-based capsule absorbents.Firstly,a stable nanoparticle-organic amine mixed absorbent with uniform particle size distribution and long-term stability was prepared by the improved"two-step method".On this basis,the effects of nanoparticles and absorbents on the gas-liquid mass transfer process of CO₂ absorption were studied by using a wetted-wall column reactor.It was found that the enhanced mass transfer of nanoparticles increased first and then decreased with the increase of particle mass fraction.Nano-SiO₂ has better enhancement effect than nano-Al₂O₃.The enhanced absorption of the nanoparticles by the nanoparticles with faster reaction rate is better than that of the slow reaction rate:PZ>MEA>MDEA.The experimental results of the bubbling reactor show that at low nanoparticle concentration,the transport mechanism and the boundary layer mixing mechanism dominate the enhanced absorption;at high nanoparticle concentrations,the bubble disruption mechanism plays a dominant role.The local microconvection in the liquid phase caused by the Brownian motion of the nanoparticles is the main reason for the increase of the CO₂ diffusion coefficient.The experimental results show that under the optimized experimental conditions,the nanoparticles can increase the liquid chromatography mass transfer coefficient of CO₂by about 15%.A heat-aided glass double capillary device for microcapsule fabrication was developed for the first time.Microcapsules based on nanoparticles organic hybrid materials with controlled particle size,shell thickness and absorbent concentration was successfully prepared.Through the characterization of the capsule absorbents,they are found to have good thermal stability and can adapt to the flue gas environment of different humidity conditions.The CO₂ absorption rate of the capsules is increased by more than 30 times compared to the unpackaged absorbent,which is mainly caused by the substantially increased specific surface area of the capsule absorbent.The shell thickness of the capsule absorbent has little effect on the CO₂ absorption and mass transfer process,and the concentration of the absorbent significantly affects the absorption rate and absorption capacity of CO₂.For NOHM-I-PEI absorbents,a 30%mass concentration is preferred.The capsule absorbent prepared herein has long-term stability and has a high CO₂ absorption capacity and a stable structure after repeated absorption and regeneration cycles.Studies on mass transfer models of CO₂ absorption by capsule absorbents have shown that capsule absorbent technology is more suitable for absorbents with a slower CO₂ reaction rate,such as carbonate and ionic liquid absorbents,and for absorbents with a fast CO₂ absorbent rate,for example The organic amine absorbent,the extra mass transfer resistance brought by the outer shell of the capsule,can significantly hinder the mass transfer process of CO₂.In this paper,novel direct non-aqueous gas stripping process was proposed for the first time,and the system design and experimental verification were carried out to explore the key operating parameters in the actual application process.Firstly,a variety of common organic substances were screened in detail.Through the analysis of parameters such as boiling point,latent heat of vaporization,density,solubility and toxicity,pentane,hexane and cyclohexane were obtained as organic stripping materials.In this paper,30%MEA was selected as the research object.The experimental results show that the organic working fluid stripping can significantly improve the mass transfer driving force of the absorbent regeneration,and exhibits the characteristics of low temperature regeneration.The regeneration effect of pentane stripping is better than that of hexane and cyclohexane.The minimum regenerative energy consumption of the pentane as stripping gas is 2.38MJ·kg^-1CO₂,which is 38.8%lower than the traditional regeneration mode(3.88MJ·kg^-1CO₂).The minimum regenerative energy consumption of hexane and cyclohexane was 2.86 and 3.16 MJ·kg^-1CO₂,respectively,which was26.5%and 18.8%lower than the conventional regeneration mode.This paper proposes an improved process based on "two-stage compression",which can achieve over 98%stripping gas recovery.Finally,the regeneration properties of nanoparticle-organic amine mixed absorbent and nanoparticle-organic-hybrid material-basd capsule absorbent were studied.The experimental results show that the enhanced regeneration of nano-TiO₂ is better than that of nano-SiO₂ and nano-Al₂O₃.When the absorbent was regenerated from 0.4 mol CO₂·mol^-1 MEA to 0.25 mol CO₂·mol^-1 MEA,the addition of 0.1%TiO₂ absorbent saved 42%of the regeneration time compared to the pure 30%MEA absorbent.The problem of nanoparticle agglomeration in the regeneration process can be dealt with by controlling the CO₂ loading of the absorbent.When the CO₂ loading of the absorbent is less than 0.4 mol CO_2·mol^-1 MEA,a stable nanofluid absorbent can be obtained.The results of direct organic vapor extraction and regeneration experiments of nanofluid absorbents show that the energy consumption of absorbent regeneration of 30%MEA absorbent with 0.1%TiO₂ under optimal conditions is 2.32MJ·kg^-1 CO₂,compared with the traditional The regeneration process was reduced by 40.4%.The results of the regeneration of capsule show that they can maintain structural stability and CO₂ capture performance after repeated cycles,and can maintain an initial absorption rate of 90%and an absorption capacity of 80%.