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。     

钙基吸收剂循环吸收CO2技术的研究进展

阐述了对钙基吸收剂循环吸收CO₂技术的研究现状,包括各个可能因素对CaO碳酸化反应的影响,如吸收剂成分、颗粒特性、反应温度、反应时间、CO₂浓度等,并总结了各种CaO吸收CO₂反应动力学模型。同时对钙基吸收剂循环吸收CO₂技术未来的研究方向作了简述。     

Cl含量对钙基吸收剂微观结构以及动力学性能的影响

通过浸渍法向分析纯CaCO₃中添加Cl,在双固定床反应器系统和热重分析仪上研究了其对钙基吸收剂循环捕集CO₂性能的影响,利用离子反应模型对添加Cl后吸收剂化学反应控制阶段进行动力学分析。结果显示：Cl对钙基吸收剂循环捕集CO₂性能具有不利影响。当Cl/Ca摩尔比大于0.25%后,随Cl/Ca摩尔比增加,化学反应控制阶段反应速率和持续时间均减小,导致在该阶段最终碳酸化转化率降低。对添加Cl前后吸收剂孔隙分布特性进行分析发现,添加Cl导致煅烧后吸收剂烧结加剧,比表面积降低,10~120nm范围内孔分布减少,导致CO₂在吸收剂内部扩散阻力增加,同时能与CO₂反应的CaO量减少,这是导致吸收剂化学反应控制阶段碳酸化反应速度较慢、最终碳酸化转化率较低的主要原因。鉴于Cl的不利影响,在选择钙基材料作为CO₂吸收剂或合成高活性复合吸收剂时,应避免吸收剂中Cl含量过高。     

负载型K2CO3/Al2O3吸收剂吸收CO2反应机理

利用热重分析仪、扫描电镜和氮吸附仪对不同粒径的K₂CO₃颗粒和负载型K₂CO₃/Al₂O₃二氧化碳吸收剂的碳酸化特性进行研究。负载后的吸收剂比表面积和孔隙结构得到较大改善,使得碳酸化反应速率和转化率均提高,吸收剂碳酸化特性得到改善。纯K₂CO₃颗粒吸收剂的反应速率和转化率随着粒径的增加而减小,负载型吸收剂的反应速率和转化率随着粒径的增加略增大。研究了不同粒径和反应时间对K₂CO₃/Al₂O₃颗粒微观结构的影响,结果表明K₂CO₃/Al₂O₃颗粒具有较稳定的微观结构。采用负载型粒子模型对K₂CO₃/Al₂O₃吸收剂吸收CO₂碳酸化过程进行研究,所建立的粒子模型计算结果与试验值吻合较好。利用建立的模型对不同CO₂浓度下K₂CO₃/Al₂O₃吸收剂碳酸化反应特性进行模拟计算,模拟结果具备一定的合理性和准确性,为开展进一步研究提供了基础。     

烟气中水蒸气对钙基吸收剂碳酸化的影响特性

在循环煅烧/碳酸化反应系统上考察煅烧气氛和碳酸化气氛中水蒸气含量以及CO₂分压对钙基吸收剂成型颗粒碳酸化的影响,通过对钙基吸收剂微观结构分析(扫描电镜、氮吸附分析)以理解水蒸气影响碳酸化特性的机理。结果表明,煅烧气氛和碳酸化气氛中的水蒸气均可提高钙基吸收剂的碳酸化转化率,水蒸气含量分别为10%和5%时,吸收剂的碳酸化性能较好;水蒸气在碳酸化气氛中对高铝水泥改性吸收剂的改善作用较石灰石显著。煅烧气氛中的CO₂分压越高,烧结现象越严重,降低钙基吸收剂的捕集效率;碳酸化气氛CO₂分压提高,有利于提高钙基吸收剂的碳酸化转化率。烟气中水蒸气丰富了吸收剂的微观孔隙,使得吸收剂捕集CO₂性能得到改善。     

循环捕集CO2后煅烧石灰石的硫化特性

ZEC(zero emission coal)系统中,粗煤气进入碳酸化/重整炉前需先脱除H₂S,提出利用经过多次碳酸化/煅烧捕集CO₂循环的煅烧石灰石(CaO)脱除H₂S,并研究循环碳酸化/煅烧次数、硫化温度、H₂S浓度和微观结构对循环CaO硫化特性的影响。结果表明,多次循环碳酸化/煅烧捕集CO₂后CaO仍具有较高H₂S吸收性能。前20次循环,CaO硫化转化率随循环次数增加迅速降低;20次循环后,CaO硫化转化率缓慢下降。硫化120 min后,未循环CaO的硫化转化率接近100%,而经历1、20和100次循环后CaO的硫化转化率分别为94%、81%和74%。H₂S浓度对循环CaO硫化性能影响较大。硫化温度(800～1000℃)对循环CaO的硫化性能影响较小,最佳硫化温度为900℃。随循环次数增加,CaO颗粒发生高温烧结,导致比表面积降低和20～150 nm内孔隙减少,而这是与H₂S吸收密切相关的孔隙,导致CaO硫化转化率降低。     

钙循环捕集CO2后CaO的水合/脱水热化学储热性能

提出了基于CaO的钙循环捕集CO₂与CaO/Ca(OH)₂体系热化学储热耦合新工艺，在双固定床反应器上，研究了循环捕集CO₂中煅烧条件和碳酸化条件对CaO储热性能的影响，探究CaO循环捕集CO₂过程和循环水合/脱水储热过程的相互作用。研究表明，多次循环碳酸化/煅烧捕集CO₂后CaO仍具有较高储热性能，10次循环捕集CO₂后再经10次储热循环，CaO水合转化率可达0.66mol/mol。与苛刻煅烧条件相比，温和煅烧条件下经历多次循环捕集CO₂后CaO的储热性能更高。在碳酸化气氛中加入水蒸气对经历多次循环捕集CO₂后CaO储热性能的影响不大。钙循环捕集CO₂过程和水合/脱水循环储热过程能够相互促进。该工艺有望同时实现CO₂捕集和储热，具有一定的应用前景。     

硅铝比和金属离子对ZSM-5吸附CO2/N2的Monte Carlo模拟的影响

通过调节硅铝比和引入金属离子构建了Si₉₆O₁₉₂、NaAlSi₉₅O₁₉₂、Na₂Al₂Si₉₄O₁₉₂、Li₂Al₂Si₉₄O₁₉₂、K₂Al₂Si₉₄O₁₉₂分子筛模型,并用MonteCarlo模拟CO₂和N₂吸附。结果表明,硅铝比降低和金属离子量增加可提供更多的吸附位点,CO₂吸附量逐渐增加,CO₂/N₂选择性显著提高。CO₂吸附位点主要集中在Na⁺附近和孔道中。在低压力下,分子筛吸附量主要由不同金属离子与CO₂分子之间的相互作用决定;随着压力增加,吸附量由分...     

CO2矿化及吸收-矿化一体化(IAM)方法研究进展

为避免温室效应带来的负面影响,CO₂减排已成为目前的当务之急。CO₂矿物碳酸化作为一种有潜力的CO₂减排技术,受到了学者们的广泛关注。CO₂矿物碳酸化方法主要包括直接干法碳酸化、直接湿法碳酸化以及间接碳酸化等不同工艺过程。目前,CO₂直接或间接碳酸化方法面临的关键挑战是提升CO₂碳酸化反应动力学特性;反应速率慢、碳酸化效率较低是当前该技术的主要问题。传统CO₂胺类化学吸收法具有吸收速率快、吸收容量大和吸收剂能循环再生的优点,但能耗和运行成本较高。将CO₂胺类化学吸收法与CO₂碳酸化过程结合而开发的CO₂吸收-矿化一体化技术（IAM）不仅解决了传统工艺高能耗、低转化率的问题,而且使工艺流程简化、成本降低,有利于应用于工业化。本文主要综述了近年来CO₂矿化技术的研究进展,对比了各种工艺技术路线的不同特点,并分析指出加强对IAM工艺反应机理的研究以及开发出高效、经济的吸收剂和矿化原料,将是该工艺未来研究的重点和关键。     

Ni/Al2O3催化剂作用下乙酸水蒸气催化重整制氢研究

采用浸渍法制备Ni/Al₂O₃催化剂,并利用BET、XRD、GC-MS、TG等对反应前后催化剂及液态产物进行了表征。采用固定床反应器考察了Ni/Al₂O₃催化剂作用下乙酸水蒸气重整制氢的反应性能,研究了反应温度、水碳比、CaO吸收剂等因素对气体组分体积分数变化以及氢气收率的影响。结果表明,在重整反应温度为600℃、水碳比为5的条件下,氢气体积分数可达92.9%,其收率为97.9%;添加CaO吸收剂后,氢气体积分数增加了6.1%,但其收率下降15%。反应后催化剂的XRD和TG表征结果表明,CaO吸收剂的加入抑制了催化剂表面消碳反应的进行,进而造成Ni/Al₂O₃催化剂作用下氢气收率的下降。     

Fabrication of rigid media tube filter bound with aluminum borate using Al2O3–B2O3–MgO frit for filtration of molten aluminum

We performed a study of a tube filter binding agent for molten aluminum (rigid media tube filter, RMF). In this study, we examined the formation mechanism of aluminum borate (9Al₂O₃·2B₂O₃; 9A2B) from Al₂O₃–B₂O₃–MgO frit composition, which used MgO instead of CaO in the Al₂O₃–B₂O₃–CaO frit in our previous report. The results indicated that crystallization of 9A2B is easier in Al₂O₃–B₂O₃–MgO compared to Al₂O₃–B₂O₃–CaO, in that crystals are formed with only a heating process, and the amount of crystallization increases depending on the calcination temperature and the heat load over the retention time. A tube filter made of Al₂O₃–B₂O₃–MgO frit contained a larger amount of 9A2B crystals and therefore its strength did not deteriorate until a very high temperature of 1200 °C was reached, and its coefficient of thermal expansion was low. This is an advantageous property for RMF used under constraints and high temperatures. In addition, when the amount of 9A2B crystal formation increases, the wettability of molten aluminum decreases, and it becomes more difficult for molten aluminum to impregnate the filter material, but we found that corrosion resistance was high.     

Effect of rice husk ash addition on CO2 capture behavior of calcium-based sorbent during calcium looping cycle

Rice husk ash/CaO was proposed as a CO₂ sorbent which was prepared by rice husk ash and CaO hydration together. The CO₂ capture behavior of rice husk ash/CaO sorbent was investigated in a twin fixed bed reactor system, and its apparent morphology, pore structure characteristics and phase variation during cyclic carbonation/calcination reactions were examined by SEM-EDX, N₂ adsorption and XRD, respectively. The optimum preparation conditions for rice husk ash/CaO sorbent are hydration temperature of 75 °C, hydration time of 8 h, and mole ratio of SiO₂ in rice husk ash to CaO of 1.0. The cyclic carbonation performances of rice husk ash/CaO at these preparation conditions were compared with those of hydrated CaO and original CaO. The temperature at 660 °C–710 °C is beneficial to CO₂ absorption of rice husk ash/CaO, and it exhibits higher carbonation conversions than hydrated CaO and original CaO during multiple cycles at the same reaction conditions. Rice husk ash/CaO possesses better anti-sintering behavior than the other sorbents. Rice husk ash exhibits better effect on improving cyclic carbonation conversion of CaO than pure SiO₂ and diatomite. Rice husk ash/CaO maintains higher surface area and more abundant pores after calcination during the multiple cycles; however, the other sorbents show a sharp decay at the same reaction conditions. Ca₂SiO₄ found by XRD detection after calcination of rice husk ash/CaO is possibly a key factor in determining the cyclic CO₂ capture behavior of rice husk ash/CaO.     

铵基循环碳酸化固定CO2

引言由煤等化石燃料燃烧产生的温室气体CO2的捕集与封存已引起国际社会的广泛关注[1-2];其中,模仿自然界钙镁硅酸盐矿物风化过程的碳酸化固定是实现大规模封存CO2的重要途径,与其他封存技术相比,碳酸化固定CO2环境风险性小,并可     

负载型K2CO3/Al2O3二氧化碳吸收剂的碳酸化反应特性

The carbonation characteristics of K₂CO₃/Al₂O₃ supported sorbent for CO₂ capture was investigated with thermogravimetric apparatus（TGA）,X-ray diffraction（XRD）,scanning electron microscopy analysis（SEM）and N₂ adsorption.The results showed that the carbonation rate of K₂CO₃ before being loaded on Al₂O₃ was slow.However,the K₂CO₃/Al₂O₃ upported sorbent showed excellent carbonation performance.The difference in carbonation behavior between K₂CO₃ nd K₂CO₃/Al₂O₃ supported sorbent was analyzed from the microscopic view.The analytical reagent K₂CO₃ sample was of monoclinic crystal structure and could react quickly with H₂O in the experimental carbonation environment to produce K₂CO₃•1.5H₂O,which was unfavorable to carbonation reaction.When K₂CO₃was loaded on Al₂O₃,the surface area and porosity of the sorbent was improved greatly.So the carbonation properties of the K₂CO₃/Al₂O₃ supported sorbent was also improved.     

UV/H2O2氧化联合Ca(OH)2吸收同时脱硫脱硝

在小型紫外光-鼓泡床反应器中,对UV/H₂O₂氧化联合Ca(OH)₂吸收同时脱除燃煤烟气中NO与SO₂的主要影响因素[H₂O₂浓度、紫外光辐射强度、Ca(OH)₂浓度、NO浓度、溶液温度、烟气流量以及SO₂浓度]进行了考察。采用烟气分析仪和离子色谱仪分别对尾气中的NO₂和液相阴离子作了检测分析。结果显示:在本文所有实验条件下,SO₂均能实现完全脱除。随着H₂O₂浓度、紫外光辐射强度和Ca(OH)₂浓度的增加,NO的脱除效率均呈现先大幅度增加后轻微变化的趋势。NO脱除效率随烟气流量和NO浓度的增加均有大幅度下降。随着溶液温度和SO₂浓度的增加,NO脱除效率仅有微小的下降。离子色谱分析表明,反应产物主要是SO₄^2-和NO₃^-,同时有少量的NO₂^-产生。尾气中未能检测到有害气体NO₂。     

CO2 capture from syngas via cyclic carbonation/calcination for a naturally occurring limestone: Modelling and bench-scale testing

The intrinsic rate constants of the CaO-CO₂ reaction, in the presence of syngas, were studied using a grain model for a naturally occurring calcium oxide-based sorbent using a thermogravimetric analyzer. Over temperatures ranging from 580 to 700 °C, it was observed that the presence of CO and H₂ (with steam) during carbonation caused a significant increase in the initial rate of carbonation, which has been attributed to the CaO surface sites catalyzing the water-gas shift reaction, increasing the local CO₂ concentration. The water-gas shift reaction was assumed to be responsible for the increase in activation energy from 29.7 to 60.3 kJ/mol for limestone based on the formation of intermediate complexes. Changes in microporosity due to particle sintering during calcination have been credited with the rapid initial decrease in cyclic CaO maximum conversion for limestone particles, whereas the presence of steam during carbonation has been shown to improve the long-term maximum conversion in comparison to previous studies without steam present.     

Development of new alumina-modified sorbents for CO2 sorption and regeneration at temperatures below 200 °C

A new regenerable alumina-modified sorbent was developed for CO₂ capture at temperatures below 200 °C. The CO₂ capture capacity of a potassium-based sorbent containing Al₂O₃ (KAlI) decreased during multiple CO₂ sorption (60 °C) and regeneration (200 °C) tests due to the formation of the KAl(CO₃)(OH)₂ phase, which could be converted into the original K₂CO₃ phase above 300 °C. However, the new regenerable potassium-based sorbent (Re-KAl(I)) maintained its CO₂ capture capacity during multiple tests even at a regeneration temperature of 130 °C. In particular, the CO₂ capture capacity of the Re-KAl(I)60 sorbent which was prepared by the impregnation of Al₂O₃ with 60 wt.% K₂CO₃ was about 128 mg CO₂/g sorbent. This excellent CO₂ capture capacity and regeneration property were due to the characteristics of the Re-KAl(I) sorbent producing only a KHCO₃ phase during CO₂ sorption, unlike the KAlI30 sorbent which formed the KHCO₃ and KAl(CO₃)(OH)₂ phases even at 60 °C. This result was explained through the structural effect of the support containing the KAl(CO₃)(OH)₂ phase which was prepared by impregnation of Al₂O₃ with K₂CO₃ in the presence of CO₂.     

Fuel mixture approach for solution combustion synthesis of Ca3Al2O6 powders

Single-phase 3CaO·Al₂O₃ powders were prepared via solution combustion synthesis using a fuel mixture of urea and β-alanine. The concept of using this fuel mixture comes from the individual reactivity of calcium nitrate and aluminum nitrate with respect to urea and β-alanine. It was proved that urea is the optimum fuel for Al(NO₃)₃ whereas β-alanine is the most suitable fuel for Ca(NO₃)₂. X-ray diffraction and thermal analysis investigations revealed that heating at 300 °C the precursor mixture containing the desired metal nitrates, urea and β-alanine triggers a vigorous combustion reaction, which yields single-phase nanocrystalline 3CaO·Al₂O₃ powder (33.3 nm). In this case additional annealing was no longer required. The use of a single fuel failed to ensure the formation of 3CaO·Al₂O₃ directly from the combustion reaction. After annealing at 900 °C for 1 h, the powders obtained by using a single fuel (urea or β-alanine) developed a phase composition comprising of 3CaO·Al₂O₃, 12CaO·7Al₂O₃ and CaO.     

Cyclic CO2 capture behavior of KMnO4-doped CaO-based sorbent

This study examines the CO₂ capture behavior of KMnO₄-doped CaO-based sorbent during the multiple calcination/carbonation cycles. The cyclic carbonation behavior of CaCO₃ doped with KMnO₄ and the untreated CaCO₃ was investigated. The addition of KMnO₄ improves the cyclic carbonation rate of the sorbent above carbonation time of 257 s at each carbonation cycle. When the mass ratio of KMnO₄/CaCO₃ is about 0.5-0.8 wt.%, the sorbent can achieve an optimum carbonation conversion during the long-term cycles. The carbonation temperature of 660-710 °C is beneficial to cyclic carbonation of KMnO₄-doped CaCO₃. The addition of KMnO₄ improves the long-term performance of CaCO₃, resulting in directly measured conversion as high as 0.35 after 100 cycles, while the untreated CaCO₃ retains conversion less than 0.16 at the same reaction conditions. The addition of KMnO₄ decreases the surface area and pore volume of CaCO₃ after 1 cycle, but it maintains the surface area and pores between 26 nm and 175 nm of the sorbent during the multiple cycles. Calculation reveals that the addition of KMnO₄ improves the CO₂ capture efficiency significantly using a CaCO₃ calcination/carbonation cycle and decreases the amount of the fresh sorbent.