CO2 capture into aqueous solutions of piperazine activated 2-amino-2-methyl-1-propanol

In this work, experimental data and a simplified vapor–liquid equilibrium (VLE) model for the absorption of CO₂ into aqueous solutions of piperazine (PZ) activated 2-amino-2-methyl-1-propanol (AMP) are reported. The purpose of the work was to find the AMP/PZ system with the highest concentration and cyclic capacity, which could be used in the industry without forming solid precipitations at operational temperatures. The effect of the AMP/PZ ratio and the total concentration level of amine was studied. The highest possible ratio of AMP/PZ, which does not form solid precipitates during the absorption of CO₂ at 40 °C (40 wt% amine), was identified. Considering the maximum loading found in the screening tests for AMP/PZ (3+1.5 M) and for 30 wt% MEA systems, the AMP/PZ system has about 128% higher specific cyclic capacity if operating between 40 and 80 °C, and almost twice the CO₂ partial pressure at 120 °C compared to MEA.     

空气中直接捕集CO2技术研究进展

减少碳排放并推动碳中和是应对气候变化、促进经济社会绿色转型的重要途径之一,碳中和技术已成为工业界和学术界的关注焦点。目前碳捕集与封存主要对工业固定源排放的CO₂进行处置捕集,而对占CO₂总排放近50%的分布源CO₂关注度不高。直接空气捕集(direct air capture,DAC)技术不仅可对数以百万计的小型化石燃料燃烧装置以及数以亿计的交通工具等分布源排放的CO₂进行捕集处理,还可有效降低大气中CO₂浓度。介绍了DAC的发展历史、研究现状以及发展趋势,综述了已有DAC技术的工艺流程以及反应装置,对DAC现行工艺中涉及的空气捕捉模块、吸收剂或吸附剂再生模块、CO₂储存模块进行了叙述,对比了几种工艺的优缺点以及吸附剂类型和再生方式,指出DAC技术发展的关键在于研发高效低成本的吸收/吸附材料和设备。分析了DAC吸收/吸附材料的作用原理以及吸附效果,碱性溶液原料成本相对低廉,但再生过程中能耗较高。分子筛及金属有机框架吸附剂虽然再生能耗较低,但对空气中CO₂的吸附容量和吸附选择性表现一般。胺类吸附剂具有较好的吸附能力,由于其再生温度较低,可使用工业废热或少量热能为系统供能;使用胺类吸附剂时吸附和解吸在一个单元中逐步发生,具有更高的效率和操作时间,有望降低DAC系统成本。对比了DAC与其他碳捕集技术的成本并进行了技术经济性分析,DAC成本主要包含运营和维护成本(N_Q&M)、吸附剂材料成本(N_S)和工厂设备的净成本(N_bop);指出目前限制DAC工业化应用的主要因素之一在于吸收/吸附材料和相关工艺成本过高,随着阴离子交换树脂等新型吸附剂的出现和工艺的发展,DAC成本逐年下降。全面探究吸收/吸附材料稳定性、动力学、吸附容量、选择性、再生能量损失等综合性能,研发利于快速装载和卸载吸附剂的相关装置,开发成本低廉的工艺系统是目前DAC领域的发展方向和迫切需求。DAC技术将为减少全球碳排放、实现碳中和提供重要技术支撑。     

Techno-economic comparison of three technologies for pre-combustion CO2 capture from a lignite-fired IGCC

This paper compares the techno-economic performances of three technologies for CO₂ capture from a lignite-based IGCC power plant located in the Czech Republic: (1) Physical absorption with a Rectisol-based process; (2) Polymeric CO₂-selective membrane-based capture; (3) Low-temperature capture. The evaluations show that the IGCC plant with CO₂ capture leads to costs of electricity between 91 and 120 €·MWh⁻¹, depending on the capture technology employed, compared to 65 €·MWh⁻¹ for the power plant without capture. This results in CO₂ avoidance costs ranging from 42 to 84 €·t_CO2,avoided⁻¹ , mainly linked to the losses in net power output. From both energy and cost points of view, the low-temperature and Rectisol based CO₂ capture processes are the most efficient capture technologies. Furthermore, partial CO₂ capture appears as a good mean to ensure early implementation due to the limited increase in CO₂ avoidance cost when considering partial capture. To go beyond the two specific CO₂-selective membranes considered, a cost/membrane property map for CO₂-selective membranes was developed. This map emphasise the need to develop high performance membrane to compete with solvent technology. Finally, the cost of the whole CCS chain was estimated at 54 €·t_CO2,avoided⁻¹ once pipeline transport and storage are taken into consideration.     

Experimental evaluation of Mg- and Ca-based synthetic sorbents for CO2 capture

Hydrogen with high purity can be directly derived from fossil and renewable energy sources, like natural gas, coal and biomass, by the so-called sorption-enhanced reforming (SER) and water gas shift (SEWGS) processes characterized by simultaneous CO₂ capture.     

不同钙基吸附剂捕集CO2后的硫酸化反应特性研究

钙基吸附剂进行多次CO₂捕集后,碳酸化效率会大幅衰减,此时的吸附剂能否高效脱硫利用是值得重点关注的问题。鉴于此,筛选了高性能合成钙基吸附剂和天然石灰石吸附剂,通过热重分析仪分析对比其在多循环CO₂捕集后的碳酸化和硫酸化反应性能,采用微粒模型研究其硫酸化反应动力学特征。结果发现,高性能合成钙基吸附剂的碳酸化反应速率和CO₂吸附能力明显高于石灰石吸附剂。在长达500循环的CO₂捕集试验后,高性能合成钙基吸附剂的CO₂吸附能力比石灰石高10倍以上,其SO₂吸附能力相较于石灰石提升约40%。经历多次CO₂捕集反应循环后,2种吸附剂的硫酸化能力均有提升:其中,石灰石吸附剂的提升幅度更大,硫酸化转化率从26%提升到35%,而高性能合成钙基吸附剂的硫酸化转化率则从38%提升到43%。通过微粒模型计算发现,2种吸附剂的硫酸化反应均是与SO₂浓度相关的一级反应,多循环捕集CO₂反应后,石灰石吸附剂的硫酸化反应活化能下降接近30%,而高性能合成钙基吸附剂的硫酸化反应活化能只下降了5%。研究结果说明2种不同钙基吸附剂在进行循环CO₂捕集后,脱硫能力得到了不同程度的提高,且均可以较好地应用于SO₂的脱除。     

Integrated adsorption and absorption process for post-combustion CO2 capture

This study explored the feasibility of integrating an adsorption and solvent scrubbing process for post-combustion CO₂ capture from a coal-fired power plant. This integrated process has two stages: the first is a vacuum swing adsorption (VSA) process using activated carbon as the adsorbent, and the second stage is a solvent scrubber/stripper system using monoethanolamine (30 wt-%) as the solvent. The results showed that the adsorption process could enrich CO₂ in the flue gas from 12 to 50 mol-% with a CO₂ recovery of >90%, and the concentrated CO₂ stream fed to the solvent scrubber had a significantly lower volumetric flowrate. The increased CO₂ concentration and reduced feed flow to the absorption section resulted in significant reduction in the diameter of the solvent absorber, bringing the size of the absorber from uneconomically large to readily achievable domain. In addition, the VSA process could also remove most of the oxygen initially existed in the feed gas, alleviating the downstream corrosion and degradation problems in the absorption section. The findings in this work will reduce the technical risks associated with the state-of-the art solvent absorption technology for CO₂ capture and thus accelerate the deployment of such technologies to reduce carbon emissions.     

Partial O2-fired coal power plant with post-combustion CO2 capture: A retrofitting option for CO2 capture ready plants

In the work presented in this paper, an alternative process concept that can be applied as retrofitting option in coal-fired power plants for CO₂ capture is examined. The proposed concept is based on the combination of two fundamental CO₂ capture technologies, the partial oxyfuel mode in the furnace and the post-combustion solvent scrubbing. A 330 MW_el Greek lignite-fired power plant and a typical 600 MW_el hard coal plant have been examined for the process simulations. In a retrofit application of the ECO-Scrub technology, the existing power plant modifications are dominated by techno-economic restrictions regarding the boiler and the steam turbine islands. Heat integration from processes (air separation, CO₂ compression and purification and the flue gas treatment) can result in reduced energy and efficiency penalties. In the context of this work, heat integration options are illustrated and main results from thermodynamic simulations dealing with the most important features of the power plant with CO₂ capture are presented for both reference and retrofit case, providing a comparative view on the power plant net efficiency and energy consumptions for CO₂ capture. The operational characteristics as well as the main figures and diagrams of the plant’s heat balances are included.     

三元复合钙基材料CaO-Ca3Al2O6-MgO的合成及其CO2吸附性能

采用Al₂O₃和MgO同时掺杂改性的方法制备了CaO-Ca₃Al₂O₆-MgO复合钙基高温吸附CO₂材料。复合钙基材料孔隙发达,活性物相为CaO,惰性骨架物相为Ca₃Al₂O₆和MgO。Ca₃Al₂O₆/MgO质量比偏小的材料,表面微粒粒径较小。在10%（体积分数,下同）CO₂和90% N₂的混合气气氛下,采用热重分析仪测量了复合钙基材料吸附CO₂容量、碳化反应速率以及循环碳化（670℃）/煅烧（900℃）过程的稳定性。结果发现,复合钙基材料CaO-Ca₃Al₂O₆-MgO具有较好的吸附CO₂性能,提高Ca₃Al₂O₆/MgO质量比,合成材料的循环稳定性较好;降低Ca₃Al₂O₆/MgO质量比,合成材料的碳化反应速率加快,CaO转化率提高。最后,通过对不同循环次数下复合钙材料的比表面积、孔径分布、微观形貌、表面元素分布,晶相、晶粒大小进行研究分析,对合成材料的失活以及掺杂物质对烧结的抑制机理进行了讨论。     

Efficient MgO-doped CaO sorbent pellets for high temperature CO2 capture

Novel MgO-doped CaO sorbent pellets were prepared by gel-casting and wet impregnation. The effect of Na⁺ and MgO on the structure and CO₂ adsorption performance of CaO sorbent pellets was elucidated. MgO-doped CaO sorbent pellets with the diameter range of 0.5-1.5 mm exhibited an excellent capacity for CO₂ adsorption and adsorption rate due to the homogeneous dispersion of MgO in the sorbent pellets and its effects on the physical structure of sorbents. The results show that MgO can effectively inhibit the sintering of CaO and retain the adsorption capacity of sorbents during multiple adsorption-desorption cycles. The presence of mesopores and macropores resulted in appreciable change of volume from CaO (16.7 cm³∙mol⁻¹) to CaCO₃ (36.9 cm³∙mol⁻¹) over repeated operation cycles. Ca2Mg1 sorbent pellets exhibited favorable CO₂ capture capacity (9.49 mmol∙g⁻¹), average adsorption rate (0.32 mmol∙g⁻¹∙min⁻¹) and conversion rate of CaO (74.83%) after 30 cycles.     

Development of low-cost biomass-based adsorbents for postcombustion CO2 capture

In this work a series of carbon adsorbents were prepared from a low-cost biomass residue, olive stones. Two different approaches were studied: activation with CO₂ and heat treatment with gaseous ammonia. The results showed that both methods are suitable for the production of adsorbents with a high CO₂ adsorption capacity, and their potential application in VSA or TSA systems for postcombustion CO₂ capture. It was found that the presence of nitrogen functionalities enhances CO₂ adsorption capacity, especially at low partial pressures.     

Alkali and alkaline-earth cation exchanged chabazite zeolites for adsorption based CO2 capture

In this study chabazite zeolites were prepared and exchanged with alkali cations – Li, Na, K and alkaline-earth cations – Mg, Ca, Ba and were studied to assess their potential for CO₂ capture from flue gas by vacuum swing adsorption for temperatures below 120 °C. Isotherm measurements (CO₂ and N₂) were made for all samples at 273 K, 303 K and 333 K using a volumetric apparatus and represented with the Dual-site Langmuir model for CO₂ and N₂. Henry’s constants and isosteric heats of adsorption were calculated and qualitative analyses performed for all samples. Adiabatic separation factor (ASF) and capture figure of merit (CFM) were proposed and used as indices for assessing adsorbent performance and compared with a commercial NaX-zeolite sample. It was found that NaCHA and CaCHA hold comparative advantages for high temperature CO₂ separation whilst NaX shows superior performance at relatively low temperatures.     

CO2甲烷化研究进展

CO_2是造成温室效应的主要气体,作为碳基能源使用的末端形态,CO_2也是种重要的基础碳源。因此,将CO_2转化为能源产品可以快速实现碳的循环,对环境与能源领域意义重大。介绍了CO_2的排放、回收以及资源化利用现状,从催化剂体系、反应机理、合成工艺以及工业化现状等方面系统地介绍了CO_2甲烷化的发展。针对H2供给对CO_2甲烷化应用的限制,分析了电解水制氢再与CO_2进行甲烷化反应的电制气(Pt G)技术的发展现状、工艺路线及其经济性,讨论了该技术在我国应用的可行性。提出随着CO_2捕集与新能源相关技术的发展,Pt G技术会更加成熟,将有望成为未来CO_2资源化利用的重要形式。     

Modelling reactive absorption of CO2 in packed columns for post-combustion carbon capture applications

A rate-based process model for the reactive absorption of carbon dioxide (CO₂) from a gas mixture into an aqueous monoethanolamine (MEA) solution in a packed column is developed. The model is based on the fast second-order kinetics for the CO₂-MEA reactions and takes into account the mass transfer resistances. The heat effects associated with the absorption and chemical reaction are included through energy balances in the gas and liquid phases. Appropriate correlations for the key thermodynamic and transport properties and for the gas-liquid mass transfer are incorporated into the model to ensure reliable predictions. The model predictions are validated by simulating a series of experiments conducted in pilot and industrial scale absorption columns with random and structured packings reported in the literature. Comparisons between the simulation results and the experimental data reveal good quality predictions of the gas phase CO₂ and MEA concentrations and the liquid temperature along the column height. The sensitivity studies reveal that the correlations for the gas- and liquid-film mass transfer coefficients given by Onda et al. (1968) provide better predictions than the penetration theory of Higbie (1935) and the correlation of Bravo et al. (1985).     

Post-combustion CO2 capture with chemical absorption: A state-of-the-art review

Global concentration of CO₂ in the atmosphere is increasing rapidly. CO₂ emissions have an impact on global climate change. Effective CO₂ emission abatement strategies such as Carbon Capture and Storage (CCS) are required to combat this trend. There are three major approaches for CCS: post-combustion capture, pre-combustion capture and oxyfuel process. Post-combustion capture offers some advantages as existing combustion technologies can still be used without radical changes on them. This makes post-combustion capture easier to implement as a retrofit option (to existing power plants) compared to the other two approaches. Therefore, post-combustion capture is probably the first technology that will be deployed. This paper aims to provide a state-of-the-art assessment of the research work carried out so far in post-combustion capture with chemical absorption. The technology will be introduced first, followed by required preparation of flue gas from power plants to use this technology. The important research programmes worldwide and the experimental studies based on pilot plants will be reviewed. This is followed by an overview of various studies based on modelling and simulation. Then the focus is turned to review development of different solvents and process intensification. Based on these, we try to predict challenges and potential new developments from different aspects such as new solvents, pilot plants, process heat integration (to improve efficiency), modelling and simulation, process intensification and government policy impact.     

Theoretical and experimental study on the fluidity performance of hard-to-fluidize carbon nanotubes-based CO2 capture sorbents

Carbon nanotubes-based materials have been identified as promising sorbents for efficient CO₂ capture in fluidized beds, suffering from insufficient contact with CO₂ for the high-level CO₂ capture capacity. This study focuses on promoting the fluidizability of hard-to-fluidize pure and synthesized silica-coated amine-functionalized carbon nanotubes. The novel synthesized sorbent presents a superior sorption capacity of about 25 times higher than pure carbon nanotubes during 5 consecutive adsorption/regeneration cycles. The low-cost fluidizable-SiO₂ nanoparticles are used as assistant material to improve the fluidity of carbon nanotubes-based sorbents. Results reveal that a minimum amount of 7.5 and 5 wt% SiO₂ nanoparticles are required to achieve an agglomerate particulate fluidization behavior for pure and synthesized carbon nanotubes, respectively. Pure carbon nanotubes + 7.5 wt% SiO₂ and synthesized carbon nanotubes + 5 wt% SiO₂ indicates an agglomerate particulate fluidization characteristic, including the high-level bed expansion ratio, low minimum fluidization velocity (1.5 and 1.6 cm·s^–1), high Richardson−Zakin index (5.2 and 5.3 > 5), and low Π value (83.2 and 84.8 < 100, respectively). Chemical modification of carbon nanotubes causes not only enhanced CO ₂ uptake capacity but also decreases the required amount of silica additive to reach a homogeneous fluidization behavior for synthesized carbon nanotubes sorbent.     

CO2 capture by adsorption with nitrogen enriched carbons

The success of CO₂ capture with solid sorbents is dependent on the development of a low cost sorbent with high CO₂ selectivity and adsorption capacity. Immobilised amines are expected to offer the benefits of liquid amines in the typical absorption process, with the added advantages that solids are easy to handle and that they do not give rise to corrosion problems. In this work, different alkylamines were evaluated as a potential source of basic sites for CO₂ capture, and a commercial activated carbon was used as a preliminary support in order to study the effect of the impregnation. The amine coating increased the basicity and nitrogen content of the carbon. However, it drastically reduced the microporous volume of the activated carbon, which is chiefly responsible for CO₂ physisorption, thus decreasing the capacity of raw carbon at room temperature.     

Microporous phenol-formaldehyde resin-based adsorbents for pre-combustion CO2 capture

Different types of phenolic resins were used as precursor materials to prepare adsorbents for the separation of CO₂ in pre-combustion processes. In order to obtain highly microporous carbons with suitable characteristics for the separation of CO₂ and H₂ under high pressure conditions, phenol-formaldehyde resins were synthesised under different conditions. Resol resins were obtained by using an alkaline environment while Novolac resins were synthesised in the presence of acid catalysts. In addition, two organic additives, ethylene glycol (E) and polyethylene glycol (PE) were included in the synthesis. The phenolic resins thus prepared were carbonised at different temperatures and then physically activated with CO₂. The carbons produced were characterised in terms of texture, chemical composition and surface chemistry. Maximum CO₂ adsorption capacities at atmospheric pressure were determined in a thermogravimetric analyser. Values of up to 10.8 wt.% were achieved. The high-pressure adsorption of CO₂ at room temperature was determined in a high-pressure magnetic suspension balance. The carbons tested showed enhanced CO₂ uptakes at high pressures (up to 44.7 wt.% at 25 bar). In addition, it was confirmed that capture capacities depend highly on the microporosity of the samples, the narrow micropores (pore widths of less than 0.7 nm) being the most active in CO₂ adsorption at atmospheric pressure. The results presented in this work suggest that phenol-formaldehyde resin-derived activated carbons, particularly those prepared with the addition of ethylene glycol, show great potential as adsorbents for pre-combustion CO₂ capture.     

Dynamic modelling of CO2 absorption for post combustion capture in coal-fired power plants

Power generation from fossil fuel-fired power plants is the largest single source of CO₂ emissions. Post combustion capture via chemical absorption is viewed as the most mature CO₂ capture technique. This paper presents a study of the post combustion CO₂ capture with monoethanolamine (MEA) based on dynamic modelling of the process. The aims of the project were to compare two different approaches (the equilibrium-based approach versus the rate-based approach) in modelling the absorber dynamically and to understand the dynamic behaviour of the absorber during part load operation and with disturbances from the stripper. A powerful modelling and simulation tool gPROMS was chosen to implement the proposed work. The study indicates that the rate-based model gives a better prediction of the chemical absorption process than the equilibrium-based model. The dynamic simulation of the absorber indicates normal absorber column operation could be maintained during part load operation by maintaining the ratio of the flow rates of the lean solvent and flue gas to the absorber. Disturbances in the CO₂ loading of the lean solvent to the absorber significantly affect absorber performance. Further work will extend the dynamic modelling to the stripper for whole plant analysis.     

Preliminary analysis of process flow sheet modifications for energy efficient CO2 capture from flue gases using chemical absorption

The energy penalty associated with solvent based capture of CO₂ from power station flue gases can be reduced by incorporating process flow sheet modifications into the standard process. A review of modifications suggested in the open and patent literature identified several options, primarily intended for use in the gas processing industry. It was not immediately clear whether these options would have the same benefits when applied to CO₂ capture from near atmospheric pressure combustion flue gases. Process flow sheet modifications, including split flow, rich split, vapour recompression, and inter-stage cooling, were therefore modelled using a commercial rate-based simulation package. The models were completed for a Queensland (Australia) based pilot plant running on 30% MEA as the solvent. The preliminary modelling results showed considerable benefits in reducing the energy penalty of capturing CO₂ from combustion flue gases. Further work will focus on optimising and validating the most relevant process flow sheet modifications in a pilot plant.     

Reactivation and remaking of calcium aluminate pellets for CO2 capture

CaO-based pellets supported with aluminate cements show superior performance in carbonation/calcination cycles for high-temperature CO₂ capture. However, like other CaO-based sorbents, their CO₂ carrying activity is reduced after increasing numbers of cycles under high-temperature, high-CO₂ concentration conditions. In this work the feasibility of their reactivation by steam or water and remaking (reshaping) was investigated. The pellets, prepared from three limestones, Cadomin and Havelock (Canada) and Katowice (Poland, Upper Silesia), were tested in a thermogravimetric analyzer (TGA). The cycles were performed under realistic CO₂ capture conditions, which included calcination in 100% CO₂ at temperatures up to 950 °C. Typically, after 30 cycles, samples were hydrated for 5 min with saturated steam at 100 °C in a laboratory steam reactor (SR). Moreover, larger amounts of pellets were cycled in a tube furnace (TF), hydrated with water and reshaped, and tested to determine their CO₂ capture activity in the TGA. It was found that, after the hydration stage, pellets recovered their activity, and more interestingly, pellets that had experienced a longer series of cycles responded more favorably to reactivation. Moreover, it was found that conversion of pellets increased after about 70 cycles (23%), reaching 33% by about cycle 210, with no reactivation step. Scanning electron microscope (SEM) analyses showed that the morphology of the low-porosity shell formed at the pellet surface during cycles, which limits conversion, was eliminated after a short period (5 min) of steam hydration. The nitrogen physisorption analyses (BET, BJH) of reshaped spent pellets from cycles in the TF confirmed that sorbent surface area and pore size distribution were similar to those of the original pellets. The main alumina compound in remade pellets as determined by XRD was mayenite (Ca₁₂Al₁₄O₃₃). These results showed that, with periodic hydration/remaking steps, pellets can be used for extended times in CO₂ looping cycles, regardless of capture/regeneration conditions.