熔铁催化剂超临界相费托合成的研究

在固定床反应器上进行了熔铁催化剂在超临界介质存在条件下的费托合成,并与气相费托合成进行对比。结果表明,由于超临界介质具有类似气体的传质速率和类似液体的溶解能力和热容,减小了催化剂床层过热,减少了催化剂床层积炭,增加了合成气在催化剂表面浓度,促进了产物的脱附,使CO转化率提高,α-烯烃选择性和C5＋选择性增加,甲烷选择性减小。实验考察了温度、压力、合成气比例、合成气空速对超临界相费托合成反应的影响。发现当反应温度或压力低于介质的临界温度及压力时,反应性能迅速下降,说明介质仅在其临界点以上才表现出优良的超临界性能。其他反应条件对超临界相费托合成反应性能的影响类似气相费托合成。     

CO2对熔铁催化剂高温费托合成反应性能影响分析

为提升高温费托反应在煤炭资源开发中应用的安全性和效率,本文以高温费托合成反应为主要研究对象,在对熔铁催化剂高温费托合成反应的应用情况进行简单介绍之后,着重通过实验的方式,进一步探究CO₂这一因素对于熔铁催化剂高温费托合成反应性能产生的影响,希望能够通过对整个还原升温反应的实验分析,为推动熔铁还原工艺的优化发展提供一定的思路。     

催化剂对费托合成的影响

本文介绍了近年来国内外费托合成研究现状,综述了近年来铁基催化剂和钴基催化剂的研究进展。     

还原条件对高温费托合成熔铁催化剂性能的影响

为了探索熔铁催化剂还原过程中物相变化及对高温费托反应性能的影响,采用SEM（扫描电子显微镜）、EDS（X射线能谱仪）、BET和原位XRD（X射线衍射）对催化剂进行了表征。并在类似工业条件（340℃、2.4MPa、H₂/CO比例为3.8）下,于固定床反应器上评价了费托反应性能。分析了不同升温过程、氢气分压、还原空速和还原时间对高温费托熔铁催化剂物相结构、晶粒尺寸、还原度等的影响。结果表明：起始升温速率影响显著,＞2.4℃/min时容易使催化剂局部温度过高进而还原速率过快,导致α-Fe晶粒快速长大并团聚。氢气分压影响还原度有转折点,＞70%时还原度变化趋势相同;对α-Fe晶粒尺寸的影响表现在低氢分压时更稳定,40h内40%H₂/Ar条件仅增加1nm。高还原空速（10000h^-1）使得还原催化剂表面孔道分布、孔径尺寸更均匀,还原效率及极限还原度更高;而低还原空速（1000~2000h^-1）则使得还原催化剂表/体相结构稳定,晶粒尺寸更稳定,费托合成反应活性高。还原时间在其他条件固定下有最佳值,420℃恒温还原到极限还原度后,α-Fe晶粒尺寸随还原时间延长继续缓慢增长。通过研究获得了适宜的还原条件为：还原升温速率0.4℃/min（200~350℃）~0.8℃/min（＜200℃）,空速5000h^-1,还原时间＜30h。     

费托合成催化剂研究进展

介绍了费脱合成的研究现状,分析了费脱合成催化剂的组成,对催化剂存在产物不集中问题,指出了ST(Fe)型催化剂的优点。     

费托合成催化剂助剂研究进展

单一Fe基或Co基催化剂的活性、选择性、稳定性均不符合工业生产的需求.为弥补其不足,在催化剂制备过程中常需引入其他金属或无机氧化物作为助剂.该文主要介绍费托合成催化剂常用助剂K、Cu、Zn、Mn、SiO2、Al2O3和介孔分子筛的研究情况;分析了费托合成催化剂助剂的效应和机理,并对今后开发新型催化剂提出建议.     

费托合成沉淀铁催化剂性能的研究进展

费托合成（F-F合成）是实现煤间接液化技术的重要环节之一,其关键是开发高活性、选择性和稳定性的催化剂。目前应用的费托合成催化剂主要有铁基和钴基催化剂。铁基催化剂因价格低廉、催化活性和水煤气变换反应（WGS）活性高以及助剂效果明显,而在费托合成催化剂中占有重要的地位。本文对近几年铁基催化剂的特点和发展状况进行了评述,着重分析了催化剂制备过程、助剂和还原活化对其活性和选择性的影响。     

急冷骨架铁费托合成催化剂的研究

利用急冷方法制备了骨架Fe50Al50合金催化剂,详细研究了其物化性质以及引入金属Mn和K对催化剂物化性质和费托合成催化性能的影响。与传统Raney Fe催化剂相比,急冷Fe催化剂具有较大的比表面积、孔体积,较小的平均孔径,双孔分布中的大孔孔径相对较小,铁的晶粒较小,具有更多桥式CO活性吸附中心。与相近组成的沉淀铁催化剂对比结果表明:急冷FeMnK催化剂具有较小的比表面积和平均孔径,更大的颗粒密度,更高的F-T合成反应活性。在543 K、1.5 MPa、2.0 NL/(g-Fe.h)、H2/CO比为1的反应条件下,在1000 h运转期内,CO转化率达到了90%以上,甲烷选择性为7%左右,C5+选择性为70%左右。     

费托合成催化剂的研究进展

介绍了费托合成的研究现状,分析了费托合成催化剂的组成,重点评述了恬性组分、载体、助剂等因素在催化剂制备过程中对催化剂的活性、选择性等方面的影响,并对费托合成催化剂研究领域存在的问题进行了探讨。     

操作参数对费托合成液态烃影响的研究

熔铁催化剂对 F- T( Fischer- Tropsch)合成具有较高的活性 ,耐磨强度好 ,价格低廉 ,至今在 F- T合成中仍具有相当重要的地位 .F- T合成液相产物中的化学族组分的相对含量及烷、烯烃的分布是考察操作条件的重要指标 ,通过熔铁催化剂在单管固定床反应器中的 F- T合成反应 ,对不同工艺参数条件下所得产物中的液态烃进行色谱分析后 ,得到了合成的液态烃产物随操作参数的变化规律 ,尤其是得出了液态烃产物中的烯 /烷的相对变化的规律 .     

Potassium-Promoted Carbon-Based Iron Catalyst for Ammonia Synthesis. Effect of Fe Dispersion

Potassium-promoted iron catalysts supported on thermally modified, partly graphitized carbon were studied in the ammonia synthesis reaction. Iron nitrate was used as a precursor of the active phase and KOH or KNO₃ were used as promoters. The kinetic studies of NH₃ synthesis were carried out in a differential reactor under 63 bar and 90 bar pressure. Hydrogen chemisorption, X-ray diffraction and transmission electron microscopy experiments were performed to determine the dispersion of iron in the specimens. All the K⁺–Fe/C catalysts proved to be sensitive to ammonia, the NH₃ partial pressure dependencies of their reaction rates being close to that of the commercial magnetite catalyst (KM I, H. Topsoe). The catalytic properties of the promoted Fe particles on carbon were shown to be dependent upon the iron dispersion, i.e. smaller particles exhibited higher turnover frequency in NH₃ synthesis. It is suggested that either small Fe crystallites expose more highly active sites, e.g. C-7 (B-5) or the promotion of small crystallites by the alkali is more efficient.     

氨合成催化剂浸锰研究

本文以简单易行的方法, 在熔铁催化剂中加入活性组分锰, 使催化剂活性有明显提高。初步探讨了浸渍液浓度和K⁺/Mn²⁺,摩尔比对催化剂活性的影响, 并对催化剂作了X-射线衍射分析。     

液相合成甲醇催化剂活性的研究

The effects of reduction procedure, reaction temperature and composition of feed gas on the activity of a CuO-ZnO-Al2O3 catalyst for liquid phase methanol synthesis were studied. An optimized procedure different from conventional ones was developed to obtain higher activity and better stability of the catalyst. Both CO and CO2 in the feed gas were found to be necessary to maintain the activity of catalyst in the synthesis process. Reaction temperature was limited up to 523K, otherwise the catalyst will be deactivated rapidly. Experimental results show that the catalyst deactivation is caused by sintering and fouling, and the effects of CO and CO2 on the catalyst activity are also investigated. The experimental results indicate that the formation of water in the methanol synthesis is negligible when the feed gas contains both CO and CO2. The mechanism for liquid-phase methanol synthesis was discussed and it differed slightly from that for gas-phase synthesis.     

维氏体铁基氨合成催化剂动力学分析

Wiistite-based catalyst for ammonia synthesis exhibits extremely high activity and easy to reductionunder a wide range of conditions. The reaction kinetics of ammonia synthesis can be illustrated perfectly by boththe classical Temkin-Pyzhev and modified Temkin equations with optimized α of 0.5. The pre-exponent factors andactivation energies at the pressures of 8.0 and 15.0MPa are respectively ko = 1.09 × 1015, 7.35 × 1014 Pa0.5.s-1,and E = 156.6, 155.5kJ@mol-1 derived from the classical Temkin-Phyzhev equation, as well as ko = 2.45 × 1014,1.83 × 1014pa0.5.s-1, and E = 147.7, 147.2kJ.mol-1 derived from the modified Temkin equation. Although thedegree of reduction under isothermal condition is primarily dependent upon temperature, low pressure seems to beimperative for reduction under high temperature and low space velocity to be considered as a high activity catalyst.The reduction behavior with dry feed gas can be illustrated perfectly by the shrinking-sphere- particle model, bywhich the reduction-rate constants of 4248exp (-71680/RT) and 644exp (- 87260/RT) were obtained for the powder(0.045-0.054 mm) and irregular shape (nominal diameter 3.17 mm) catalysts respectively. The significant effect ofparticle size on reduction rate was observed, therefore, it is important to take into account the influence of particlesize on reduction for the optimization of reduction process in industry.     

Analysis on Ammonia Synthesis over Wustite-Based Iron Catalyst

Wustite-based catalyst for ammonia synthesis exhibits extremely high activity and easy to reduction under a wide range of conditions. The reaction kinetics of ammonia synthesis can be illustrated perfectly by both the classical Temkin-Pyzhev and modified Temkin equations with optimized a of 0.5. The pre-exponent factors and activation energies at the pressures of 8.0 and 15.0MPa are respectively k0 = 1.09 x 1015, 7.35 X 1014Pa0.5.s-1, and E = 156.6, 155.5kJ-mol-1 derived from the classical Temkin-Phyzhev equation, as well as k0 = 2.45 X 1014, 1.83 X 1014Pa0.5s-1, and E = 147.7, 147.2kJ-mol-1 derived from the modified Temkin equation. Although the degree of reduction under isothermal condition is primarily dependent upon temperature, low pressure seems to be imperative for reduction under high temperature and low space velocity to be considered as a high activity catalyst. The reduction behavior with dry feed gas can be illustrated perfectly by the shrinking-sphere-particle model, by which the reduction-     

焙烧温度对碳纳米管钴基费托合成催化剂的影响

通过浸渍法制备了不同焙烧温度的碳纳米管钴基费托合成催化剂[CAT(X),X=250、300、350、400、450、500],利用热重分析、氮气物理吸附-脱附、X射线衍射、氢气程序升温还原、扫描电镜、透射电镜和X射线光电子能谱等考察了焙烧温度对催化剂热稳定性、结构、物相、还原度及费托合成反应性能的影响。结果表明:载体碳纳米管在500℃以下可以稳定存在;焙烧温度在250~500℃时,催化剂的比表面积在79.78~85.23 m2/g,孔容在0.60~0.68 m3/g,孔径在28.9~33.4 nm。其中,经350℃焙烧的催化剂CAT(350)比表面积为79.78 m2/g,孔容为0.67 m3/g,孔径为33.4 nm;在350℃焙烧后,催化剂表面钴主要有Co3O4和Co O两种存在形式,晶粒细小,尺寸分布窄。程序升温还原测试和费托合成反应性能评价结果显示,350℃焙烧的催化剂CAT(350)还原温度最低,一氧化碳转化率最高,为12.5%。     

无助剂沉淀铁催化剂上F-T合成的研究

研究了高温条件下无助剂沉淀铁催化剂在固定床积分反应器中的F-T合成反应。实验结果表明在实验条件下,随着温度的升高,CO和H2的转化率明显增大;而空速的增加,H2和CO的转化率下降。在压力2.6MPa,空速0.86L·h-1·(g-Fe)-1,H2／CO=2／3,温度260-280℃时,产物中的烃类主要是C5-11,约占烃类总质量的50％,其次是C2-4,约占烃类总质量的25％,再次是C12+,约占烃类总质量的18％,C1占7％。     

TiO2对电熔合成镁铝尖晶石的影响

以轻烧氧化镁粉、工业氧化铝为原料合成电熔镁铝尖晶石材料,重点研究二氧化钛为添加剂对电熔合成镁铝尖晶石的物相组成,显微结构的影响,通过XRD,SEM分析试样的物相组成、晶胞参数和断口的微观形貌.研究发现:二氧化钛为外加剂可以增大镁铝尖晶石的晶胞参数、提高材料的体积密度进而改善材料的烧结性能,并且随着二氧化钛加入量的增加镁铝尖晶石的晶胞参数和晶胞体积呈现先增大后减小的变化规律.分析认为由于二氧化钛、钛酸镁固溶到镁铝尖晶石中促使镁铝尖晶石的晶胞参数和晶胞体积增大,而过量的钛酸镁位于晶界阻碍镁铝尖晶石的长大,导致镁铝尖晶石的晶胞参数和晶胞体积减小.在电熔法制备镁铝尖晶石时,二氧化钛的加入量不宜超过5wt%.     

合成2,3,5-三甲酚催化剂的研究

采用等体积浸渍法制备负载型催化剂用于3,5-二甲酚甲基化反应,在固定床反应器中考察了载体的焙烧温度、助剂、催化剂的焙烧温度和焙烧时间等因素对催化剂活性影响分析。结果表明:Fe2O3-Cr2O3/Al2O3催化剂在反应中具有较高的反应活性和选择性。