基于草木灰修饰Fe基载氧体的化学链燃烧实验

采用草木灰对Fe基载氧体进行修饰,并在流化床反应器上进行了气体燃料化学链燃烧实验。研究了草木灰修饰对提高Fe基载氧体还原活性的可行性,讨论了草木灰种类、草木灰的无机组分对载氧体活性的影响。结果表明,草木灰修饰能有效提高Fe载氧体的反应活性,载氧体的反应活性由草木灰中K和Si的含量共同决定。随着修饰草木灰中的K含量提高,载氧体的活性逐渐提高;但在Fe3O4/FeO的转化阶段中,同时存在碱金属K对还原反应的催化作用和低熔点碱金属硅酸盐对还原反应的抑制作用。循环实验表明,草木灰中碱金属K对载氧体活性的提高效果始终明显,载氧体中负载的K在循环过程中出现了流失现象,而生成的碱金属硅酸盐类化合物,可抑制碱金属K的流失。     

基于锰矿石载氧体的准东煤化学链气化特性

化学链气化利用循环载氧体为气化过程提供氧化剂,碱金属修饰载氧体能显著催化气化过程.本文以高钠准东煤为燃料,反应性高、稳定性好的锰矿石为载氧体,探究循环次数、比氧耗和温度对准东煤化学链气化特性的影响.结果表明,随着循环次数增加,碱金属Na逐渐沉积在锰矿石表面,载氧体无明显烧结,反应性能良好;比氧耗的变化会影响合成气各组分浓度,比氧耗为4、温度900℃时,有效气组分可达78.83%.     

基于钾盐修饰Fe基载氧体的化学链燃烧研究

采用典型的钾盐和惰性载体对Fe基载氧体进行修饰,在热重和小型流化床反应器上,采用CO/N2对其还原活性和化学链燃烧特性进行测试,考察了钾盐种类、反应温度对和惰性载体种类的影响。结果表明：钾盐修饰（KCl、K2SO4和K2CO3）能提高载氧体还原反应速率,并以K2CO3效果最好,最大还原反应速率提高约30%,载氧体完全还原时间由50 min缩短到25 min,主要归因于K2CO3修饰促进形成高活性的Fe-K-O化合物及发达的孔隙结构;对于K2CO3修饰Fe基载氧体,SiO2和高岭土载体易与K2CO3发生烧结,造成活性下降,TiO2与载氧体反应生成复杂的化合物,其氧化过程变慢,影响整个进程,而Al2O3载体展现了最好的反应活性,随着反应循环的增加其活性略有下降并趋于稳定,9个循环后CO2捕集效率高达98.0%     

CuFe_2O_4载氧体的释氧特性及其对煤化学链气化的影响

采用燃烧合成法制备了CuFe_2O_4载氧体材料,通过TGA和流化床研究了CuFe_2O_4载氧体在不同温度下的释氧特性及其对煤化学链气化的影响,并对载氧体物相组成的变化规律进行了XRD分析.结果表明,低于1 179.7℃时,CuFe_2O_4中最多有16.7%的晶格氧转化为气相氧;在750～950℃内,CuFe_2O_4晶体晶格畸变产生氧缺陷是导致释氧的主要原因,随着温度升高,载氧体的失氧度从0.033增加到0.40;与新鲜的CuFe_2O_4载氧体相比,载氧体失氧度越高越有益于H2的产生,但同时氧传输量下降,导致碳转化率的降低.     

结构型载氧体固定床化学链重整制氢的实验研究

采用浸渍法制备球形与拉西环形两种不同结构型Ni基载氧体,用于甲烷化学链重整制氢反应。在固定床中考察反应温度、进气水碳物质的量的比和空速对载氧体活性及稳定性的影响,并对比研究两种不同结构型载氧体的性能。结果表明：两种载氧体均可以保持较好的活性,相对而言球形载氧体更易积碳。在800℃以上时两种载氧体均具有较高的甲烷转化率及产物选择性,拉西环形载氧体在高温下性能下降得较慢。过高的水碳物质的量的比会抑制重整反应的进行,但拉西环形载氧体在高水碳物质的量的比下仍能保持较高的产物选择性。随着空速的增大,拉西环形载氧体的甲烷转化率降低,而对球形载氧体来说,当空速在3 500 h^-1左右时甲烷转化率和氢气产率均最高。经过20次循环稳定性测试,两种载氧体颗粒均出现了不同程度的积碳烧结,其中拉西环形载氧体结构保持得较好,积碳在氧化阶段能被部分清除。     

钙基复合载氧体反应性能的研究

采用沉淀法制备了3种钙基复合载氧体,并在固定床试验台架上对复合载氧体与CO的反应性能进行了研究.对反应前后的载氧体进行了X射线衍射(XRD)和场发射扫描电镜(FSEM)表征分析.结果表明:3种添加物均能促进CaSO4与CO的还原反应,提高载氧体的反应速率和转化率;3种添加物对COS的释放具有抑制作用,La添加物对SO2的释放有一定的抑制作用,而Ti、Ni添加物促进了SO2的释放;添加Ni的载氧体具有较高的反应活性,表现出良好的循环特性;载氧体在1次循环反应后,固相中出现了少量的CaO;在6次循环反应后,CaO的峰值比第1次循环后的峰值高,载氧体表面由平整光滑变得疏松多孔,且分布均匀.     

铁钴修饰镍基复合载氧体化学链重整制氢研究

采用浸渍法制备Fe₂O₃-NiO-CeO₂/γ-Al₂O₃和CoO-NiO-CeO₂/γ-Al₂O₃复合载氧体,研究了不同复合载氧体对化学链重整制氢反应性能的影响。固定床活性测试实验表明,在镍铈载氧体中加入质量分数为5%的Fe₂O₃复合载氧体(5%Fe-Ni-Ce)的H₂选择性和H₂体积分数最大;在镍铈载氧体中加入CoO后,其复合载氧体的反应性能下降。循环实验表明,5%Fe-Ni-Ce复合载氧体在经过20次循环后仍保持高活性。X射线衍射(XRD)结果表明,5%Fe-Ni-Ce复合载氧体中有固溶体形成,进一步的XRD分析发现5%Fe-Ni-Ce晶粒粒径较小。扫描电子显微镜分析发现,反应前5%Fe-Ni-Ce复合载氧体的颗粒分散度最优,在经过20次循环后复合载氧体仍能保持较好的形貌。进一步的固定床实验研究表明,5%Fe-Ni-Ce...     

化学链过程铁基载氧体的研究进展

在化学链过程中,载氧体通过晶格氧的生成和释放避免了燃料和氧气的直接接触,降低了分离的成本,故其在化学链反应中起到重要的作用。铁基载氧体因成本低、环境友好的特性成为一种有吸引力的选择。总结了铁基载氧体在化学链过程中的相关研究。活性氧化铁因其较低的还原能力通常需要掺杂其他金属,目前主要采用碱性金属（Na、K、Ca）和过渡金属（Cu、Co、Ni等）来进行改性。研究的重点是复合金属载氧体（钙钛矿、铁酸盐、六铝酸盐、CeO₂型载氧体等）,其中钙钛矿型载氧体传氧能力优异,热稳定性和机械强度高,因此以不同的A/B位离子取代,或将钙钛矿与其他材料复合成为近年来的研究热点。     

流化床上铜基载氧体的反应特性和积碳特性研究

利用小型流化床实验台对机械制备的Cu基载氧体在4个反应温度(650℃、750℃、850℃和950℃)和两种气氛(CH4和CO+H2)下进行了实验研究,结果表明:两种气氛下Cu基载氧体的还原转化率并不随温度的升高而单调递增,而是有个最佳反应温度,分别为750℃和850℃;由于CH4气氛下Cu基载氧体表面的积碳比CO+H2气氛下严重,因此4个温度下Cu基载氧体的还原转化率都比CO+H2气氛下低,这也说明CO+H2比CH4更适合Cu基载氧体的化学链燃烧。为了避免因积碳而带来的载氧体失活,在管式炉内进行CO和载氧体的燃烧反应时,向炉内通入水蒸气,结果发现Cu基载氧体表面的积碳得到有效抑制。     

氧缺陷影响铁基载氧体氧化-还原行为的分子动力学模拟

铁基载氧体是化学链燃烧中最受青睐的金属载氧体。构造了氧化铁载氧体的S完整表面和S^1*、S^2*、S^3*三种代表性缺陷表面,基于密度泛函理论(density function theory, DFT),首先计算分析了氧缺陷对CO在α-Fe₂O₃表面上吸附反应的影响,即对比了完整和缺陷α-Fe₂O₃(0 0 1)表面上CO的吸附和生成物CO₂的解离;其次将反应后的载氧体构型表面进行O₂吸附反应的模拟;继而对此载氧体一个循环及过程中铁基载氧体表面的积碳趋势进行了模拟分析。通过吸附能、反应能垒和反应能等参数的比较,结果显示,在铁基载氧体表面还原、积碳、氧化反应中,S^1*类氧缺陷具有更好的反应活性和抗积碳性能,具有良好的循环反应性能。该模拟研究为缺陷类型铁基载氧体的制备及其反应条件的确定提供指导。     

基于密度泛函理论的CuO氧载体释氧机理研究

化学链氧解耦（CLOU）是基于化学链燃烧（CLC）技术的一种新型燃烧方式,具有CO2内分离的优良特性。具有良好吸氧释氧性能的氧载体是CLOU技术的关键,其宏观层面的反应性决定于其微观层面的晶格氧传输机理,但目前对这种微观机理的研究非常缺乏。本文采用量子化学计算方法——密度泛函理论（DFT）研究CuO氧载体释氧的微观机理,构建了CuO团簇及CuO平板模型,模拟团簇及表面的释氧过程。CuO平板模型释氧包括O原子在CuO内部扩散、表面O2的形成及释放过程。结果表明：CuO(111)表面释氧过程的最高能量势垒为3.16 eV,与实验值3.39 eV接近,低于CuO团簇模型的释氧能量势垒3.51 eV;此外,O原子在CuO(111)内部的扩散势垒仅为0.87 eV,说明CuO(111) 释氧的限制步骤是表面O2的形成过程。     

赤泥-铜矿石复合载氧体用于煤化学链气化性能研究

煤化学链气化制合成气是一种资源利用率高、环境污染低、节能环保的新型气化技术,而高效载氧体的设计开发是化学链气化技术的关键。本文以铜矿石和赤泥为原料采用挤出滚圆法制备R-Cu-10M（蒙脱石质量分数为10%）复合金属载氧体,实现载氧体颗粒内粉末的物理均匀混合、颗粒一次成型以及活性组分间的协同效应。围绕反应温度、氧煤比、水蒸气输入量三个关键操作变量,测试了R-Cu-10M载氧体与褐煤气化反应特性。表征结果表明,R-Cu-10M载氧体具有较好的还原性,赤泥与铜矿石中Cu-Fe金属间的协同效应有助于晶格氧释放以及还原性的提升。R-Cu-10M载氧体与褐煤发生气化反应的最佳温度为950℃,在氧煤比为3∶1、水蒸气通量为0.08 mL/min的最优工况下,合成气产量可以达到50 mmol/g载氧体,合成气选择性和碳转化率分别为75.9%和71.2%。     

Chemical looping gasification of cotton stalk with bimetallic Cu/Ni/olivine as oxygen carrier

Bimetallic Cu/Ni/olivine oxygen carriers (OCs) were prepared using olivine as support material for chemical looping gasification (CLG). The cyclic redox behaviors and oxygen carrying capacity (R_o) of OCs were evaluated by thermo-gravimetric analysis. The effect of Cu/Ni ratio, gasification temperature, steam to biomass ratio (S/B), oxygen carrier to biomass ratio (OC/B) on CLG of cotton stalk has been studied in a fixed bed. The OCs characterized using BET surface area, scanning electron microscopy (SEM), X-ray diffraction (XRD), temperature-programmed reduction (TPR) to investigate the physicochemical property of OCs during CLG. Result shows that the sintering problem of OC was progressively alleviated with the increasing Cu/Ni ratio. The olivine behaves as suitable OC support with oxygen carrying capacity of 1.07%. The redox reactivity of all of the OCs kept well during multiple redox cycles. The R_o of OCs progressively increased with the Cu/Ni ratio. By comparing the product gas concentration, carbon conversion, H₂ + CO yield and gas yield over the invested OCs, the Cu9/Ni6/O was found to demonstrate better comprehensive CLG performance due to the synergistic effect of Cu and Ni. The maximum gas yield, H₂ + CO yield and carbon conversion with Cu9/Ni6/O can be obtained at the S/B of 0.8 and OC/B of 2. Compared to theoretical value, 65% of lattice oxygen has been supplied by Cu9/Ni6/O during actual CLG process. The OC displayed better reactivity due to basic crystalline phase being preserved well during multiple CLG cycles.     

pH和溶解氧对上海蕴藻浜河道沉积物重金属的影响

通过改变上覆水体pH和溶解氧,并采用改进的由欧共标准测量与检测局(BCR)提出的连续提取法,研究pH和溶解氧对蕴藻浜沉积物中Cu、Cr释放的影响,以及沉积物释放前后Cu、Cr形态的变化,探索沉积物中重金属释放的机理.结果表明:随着pH增加,沉积物中重金属释放量下降,可还原态在沉积物中的含量上升,可氧化态与酸可提取态含量均有下降,这主要和H~+与重金属离子的竞争以及沉积物中自然胶体的吸附有关;随着溶解氧含量增加,沉积物中重金属释放量升高,可氧化态含量呈明显下降趋势,而可还原态含量略有上升趋势,这主要与沉积物的还原性、硫化物及铁锰氧化态重金属有关.     

The effect of oxygen carrier content and temperature on chemical looping gasification of microalgae for syngas production

The study of the effect of oxygen carrier content and temperature on chemical looping gasification (CLG) of Chlorella vulgaris was carried out in a fixed bed reactor. In order to obtain the characterization and optimal conditions of CLG for syngas production, this paper analyzed the product fractional yields, gaseous yields, conversion efficiency, SEM, XRD and composition analysis of oxygen carriers. The results indicated that CLG had a greater performance on gasification characteristics. When O/C increased from 0.5 to 3.0, gas yield, CO₂ yield and carbon conversion efficiency increased gradually, but LHV, H₂ and CH₄ yields decreased. Meanwhile, CO yield and gasification efficiency increased firstly and then decreased. Oxygen carrier Fe₂O₃ exhibited the characteristics of step-wise reduction (Fe₂O₃ → Fe₃O₄ → FeO) in CLG process. More FeO were generated at O/C of 0.5 and then caused serious sintering and agglomeration. High temperature was helpful to improve gas yield, carbon conversion efficiency and gasification efficiency. However, higher temperature would cause sintering and then weaken the activity of oxygen carrier. Moreover, under the experimental condition, O/C of 1.0 and 800 °C were the optimal parameters to obtain a high conversion efficiency of biomass, high products yield, good LHV and great reducibility of oxygen carrier.     

Interaction between bimetallic composite oxygen carriers and coal and its contribution to coal direct chemical looping gasification

Coal direct chemical looping gasification (CDCLG) to produce synthesis gas was investigated with Fe-based bimetallic composite oxygen carriers (Fe–M oxides, M = Ba, Ca, Cu, Ni and Co). Thermogravimetric-mass spectrum analysis and fixed-bed tests indicated that reaction between coal and Fe-based composite oxygen carriers via direct contact could not be negligible in the CDCLG process. The contribution of the reaction between the two solid particles to the carbon conversion was estimated. Furthermore, the yields of synthesis gas production were also conducted to evaluate performance for the prepared samples. Of the five investigated Fe-based bimetallic composite oxygen carriers (OCs), Fe–Ni oxides/Al₂O₃ presented high reactivity with coal and high selectivity for synthesis gas during coal-OC steam gasification, which made it attractive for the CDCLG process. By comparing with the main phases of the Fe-based OCs after cycling and the raw samples before test, it could be observed that there were no significant changes in material phases. Combined with the SEM images of the Fe-based OCs samples, we can conclude that the prepared OCs showed a good heat-resistant property, which was beneficial for keeping a stable performance in the CDCLG experiment.     

Effect of the carbon on the electrochemical performance of rechargeable Zn-air batteries

Carbon materials as catalyst substrates play key roles in Zn-air batteries which not only construct abundant tri-phase interfaces for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) to take place but also enable the diffusion of reactants. Carbon corrosion is known to occur in the aqueous electrolyte which leads to catalysts dissolution, electrode flooding, and rapid performance degradation. In this study, rechargeable Zn-air batteries with MnO₂ as the bifunctional catalysts and different carbon as catalyst carriers, such as carbon black, CNTs, and graphene have been assembled with their electrochemical performance systematically evaluated. The correlation between the graphitization, surface, structure properties of the carbon, and the electrochemical performance of air-electrodes has been elucidated. The electrolyte composition change during cycling and the underlying corrosion mechanism of carbon have been explored. CNTs with high crystallinity and less edge exposure is an excellent candidate over activated carbon and graphene as a catalyst carrier for metal-air batteries.     

Chemical looping gasification of rice husk to produce hydrogen-rich syngas under different oxygen carrier preparation methods

The chemical looping gasification (CLG) of rice husk was conducted in a small fixed-bed reactor to investigate the effects of oxygen carrier preparation methods, active components, Fe loadings, water inflow and successive redox cycles. The gas content, the relative gas concentration, lower heating value of syngas (LHV), carbon conversion efficiency, gasification efficiency, H₂-TPR, XRD, BET and SEM were analyzed to obtain CLG reaction characterization and comprehensive performance of oxygen carrier. The results showed that compared with several methods and active components, the coprecipitation method with a Fe:Al ratio of 2 was the best preparation method for oxygen carrier. Furthermore, the H₂ concentration was 57.29%, while the gasification efficiency and carbon conversion efficiency were 95.79% and 51.56%. Meanwhile, the oxygen carrier prepared by coprecipitation had a greater performance of oxygen release and reduction. There was an optimal water inflow to obtain the highest gas content, carbon conversion efficiency and gasification efficiency. Thereinto, the H₂ concentration was stable at 54.07–57.65%. And the highest gas content of 78.33% and carbon conversion efficiency of 54.42% were obtained at a water inflow of 14.0 mL/h, while the highest gasification efficiency of 95.79% was obtained at 16.8 mL/h. In addition, after ten successive redox cycles, the gasification performance, crystal size, specific surface area and pore structure were relatively stable. Moreover, the material composition remained basically unchanged.