Research On Formation And Performance Of Porous Resin Adsorbent For Direct Air Capture Of CO₂

Direct air capture（DAC）of CO₂ is of great importance to global climate change mitigation,as the major component of Negative Emission Technologies（NETs）portfolio.Apart from the inherent advantage of location flexibility which reduces the need for pipelines between the capture sites and the sequestration reservoir,DAC can provide various forms of carbon sources without being affected by location,time,and space.Therefore,DAC could be deemed as a commercially-available approach to efficiently control CO₂ concentration in the atmosphere.The moisture swing adsorption technology（MSA）is incorporated into DAC,in which the adsorption and desorption processes are achieved by altering the partial pressure of water vapor in the environment.Since the regeneration of the sorbents is realized by dehydration at ambient temperature,low-grade heat could be utilized from the viewpoint of cascade utilization of energy.The state-of-art moisture swing adsorbents suffer from slow adsorption kinetics and low working capacity in comparison to the amine-based counterparts.In this paper,a novel adsorbent with fast adsorption/desorption kinetics and high working capacity was developed based on the quaternary ammonium functionalized porous resin.The rational design of DAC systems for agricultural CO₂ fertilizer with moisture-swing technique was established.For the adsorbent preparation,strong-base anion exchange porous resins with quaternary ammonium functional groups were screened and used as feedstock.Phase inversion method was adopted to prepare the heterogeneous adsorptive membranes with intrinsic pore structure.The adsorption experimental platform was set up to characterize humid CO₂ adsorption performance of the prepared adsorbents.The desorption experimental platform was established to characterize the moisture-induced CO₂ desorption performance and the dehydration process of the H2O-saturated adsorbents as well.The CO₂ adsorption properties of porous resin including D201 and D290 was preliminary studied.The pore characteristics of D201 and D290 resin were analyzed by combined nitrogen physical adsorption and mercury intrusion method.It was found that higher BET surface area and micro–mesoporosity contributes to the adsorption on the interior surface,giving rise to the increased kinetics of adsorbent.D290 resin-based adsorptive membrane showed much more rapid adsorption of ultra-dilute CO₂ and was selected for further investigation.Thermodynamic studies revealed the typical Langmuir type adsorption and desorption pattern of the D290-based adsorbents.The equilibrium constants of adsorption and desorption at different temperature and relative humidity were obtained.Kinetics studies emphasized the effect of resin particle size,temperature,and relative humidity on the adsorption kinetics,by means of the modified shrinking core model（SCM）.The adsorption rate increased with the decrease of resin particle size,thanks to the enhanced chemical reaction.The difference of the apparent adsorption rates at different temperature and relative humidity could be attributed to the discrepancy in the effect of temperature and relative humidity on the chemical reaction and product layer diffusion.The half adsorption time derived from SCM model of optimized D290-based adsorbent is determined as 4.0 minutes,which is the shortest value reported to date for MSA materials with CO₂ capacity higher than 0.70 mmol/g.The dehydration process of D290-based adsorbent could be well described by the semi-empirical model in logarithmic style.The dehydration kinetic was evidently influenced by the temperature,which indicates that the operation temperature should be carefully considered in the actual process.Based on the optimized adsorbents,we proposed the rational design of DAC systems for agricultural CO₂ fertilizer with moisture-swing technique,with the capacity scale of 10 kg CO₂ per day.The internal structure of the capture device,flow rate of the feed air,and the gas speed distribution were analyzed and decided.The requirement of adsorbent,the detailed process and operational parameters of the system was determined.Having the abovementioned information,the energy and water consumption of the system in real situation were systematically analyzed.