焙烧温度对费托合成铁基催化剂还原动力学的影响

采用沉淀法和喷雾干燥技术制备了一个典型的费托合成铁基催化剂(100Fe/3K/6SiO_2,质量比)所得样品在不同温度下焙烧5 h.分别利用N_2吸附和穆斯保尔谱表征了催化剂的织构和物相性质,同时利用热重分析仪记录了催化剂在H2气氛中的还原过程,并利用气固反应模型对还原曲线进行了动力学模拟.结果表明,300~600℃焙烧后催化剂的还原过程可用相同的模型拟合,其中由α-Fe_2O_3还原为Fe_3O_4的过程可用一维晶相形成与生长模型或三维相界面反应模型描述,Fe_3O_4还原为α-Fe的过程受二维晶相形成与生长模型控制.而对于700℃焙烧后的催化剂,其还原过程可能受晶相形成与生长模型和收缩核模型共同影响.随着焙烧温度的提高,催化剂的还原能力减弱,还原过程活化能升高.这可能是由于焙烧温度的提高导致晶粒尺寸增大和晶格缺陷减少所致.     

高温沉淀铁基催化剂上费托合成含氧化合物生成机理的研究

采用漫反射原位红外光谱法及化学捕获方法,考察了费托合成过程中高温沉淀铁基催化剂表面吸附物种的变化,并探讨了含氧化合物的生成机理。结果表明,CO在高温沉淀铁基催化剂上有线式和桥式两种吸附态存在,同时,CO的吸附在催化剂表面生成大量含氧化合物前驱体。费托原位实验捕获到了一些较关键的中间产物:表面乙酸盐、表面酰基、甲氧基等。同时发现高温沉淀铁基催化剂表面具有以下反应共性:醇类可与表面羟基结合生成烷氧基团;催化剂表面的吸附分子具有氧化性;一些基础化学物质如OH^-、晶格氧等可以与甲醇或乙醛分子发生反应。对CH₃OH + CO及CH₃I + CO + H₂两个反应的化学捕获实验表明,酰基是C₂⁺含氧化合物的重要中间产物,酰基加氢是形成C₂⁺含氧化合物的关键步骤。根据表面中间产物及反应特性,得到了高温沉淀铁基催化剂上费托合成含氧化合物的生成机理。     

费托合成钴基催化剂微观结构研究进展

费托合成可将煤、天然气及生物质等各种非石油含碳资源通过合成气转化为各种油品和精细化学品.钴基催化剂因其水煤气变换反应活性低、费托反应活性高、碳链增长能力高的优良特点,在工业应用和相关科学研究上备受关注.钴基催化剂微观活性位的结构和费托反应过程中催化剂的表面吸附物等都会对F-T合成反应的产物分布以及催化性能有影响.本文分...     

Fe-Mn催化剂的费托合成产物分布动力学

在固定床反应器上进行了Fe-Mn超细粒子催化剂F -T合成反应动力学研究。以碳化物机理为基础推导出简化的F -T合成产物生成动力学模型 :　RCnH2n 2 =kHC5PH2 (1-α)αn在温度 5 76～ 6 10K ,压力 1 5～ 2 5MPa ,空速 2 5 0 0～ 45 0 0h-1和原料气H2 /CO比为 2 0的条件下进行动力学试验 ,通过模型拟合 ,求得动力学方程参数 :　kHC5=kHC5(5 80K)exp[EaR(1T - 15 80 ) ]其中 ,kHC5(5 80K) =2 82× 10 -6mol/ (mlcat·MPa·s) ,Ea=6 6 0 7kJ/mol结果表明 ,该模型与实验值拟合较好 ,链增长几率α与温度和反应器内H2 /CO比具有简单的关系 :α =1/ (1 ρRHC)。     

纳米线堆积的铁硅球体催化剂用于费托合成

以共沉淀法所制的工业铁硅球体催化剂(indus-FS)为原料,用改进的有机胺蒸气相传输转化法,得到了负载高分散铁的交织氧化硅纳米线球体催化剂(NW-FS),并用于费托合成反应.在所制纳米线催化剂中,原料催化剂中氧化硅在氧化铁诱导下成功地转变成纳米线交织微球载体,而氧化铁组分则高度分散在氧化硅纳米线上.用扫描电镜、透射电镜、X射线衍射、低温氮吸附、X射线光电子能谱和程序升温还原等方法对所得纳米线催化剂进行了表征.在费托合成中,纳米线铁硅催化剂由于其特殊的堆积结构所导致的低的扩散阻力和高的铁活性组分分散度,提高了低碳烯烃尤其是乙烯的选择性.纳米线铁硅催化剂上低碳产物(C2–C4)的烯烷比为3.3,高于母体工业催化剂的1.9.     

Zn对沉淀铁催化剂结构及其F-T合成性能的影响

采用低温N₂吸附、XRD、MES、CO-TPR和H₂-DTG研究了Zn(100 gFe/x gZn, x=7～100)助剂对 Fischer-Tropsch (F-T) 合成Fe基催化剂的织构性质、还原行为以及相变结构的影响;在H₂/CO=2.0、260 ℃、1.5 MPa和4000 mL/(g·h) 条件下在固定床反应器上考察了Zn助剂含量对Fe基催化剂F-T合成反应活性、烃产物选择性和运行稳定性的影响。研究结果表明,随着Zn含量的增加,氧化态催化剂的物相由α-Fe₂O₃和ZnFe₂O₄逐渐向ZnFe₂O₄和ZnO转变,ZnFe₂O₄在催化剂中优先生成,只有在超出其计量比1∶2之后才有ZnO出现。由于ZnFe₂O₄较为稳定,能够促进催化剂中Fe物相的分散,导致比表面积增加。在还原和反应态催化剂中,ZnFe₂O₄一方面抑制催化剂的过度还原和碳化;另一方面表现为稳定活性相铁碳化物。催化剂的F-T反应性能评价结果表明,纯铁催化剂由于铁碳化物氧化而迅速失活,而Zn助剂催化剂却由于ZnFe₂O₄的稳定作用,活性较为稳定。同时,由于催化剂在反应初相变的影响,导致Zn助剂催化剂的初始烯烃选择性随着Zn含量的增加而增加,在相态稳定之后选择性趋于一致。     

Cu助剂对聚乙烯醇辅助沉淀铁催化剂费托合成反应性能的影响

通过共沉淀法或聚乙烯醇（PVA）辅助共沉淀法分别制备了Fe₂O₃和FeCu催化剂,结合BET、XRD、SEM、H₂-TPR等表征手段,研究了Cu助剂对PVA辅助的沉淀铁催化剂的织构性质、物相结构、形貌特征、还原行为以及F-T合成反应性能的影响。结果表明,Cu助剂的加入增大了铁基催化剂中α-Fe₂O₃的晶粒,减小了催化剂的BET比表面积和孔容,增大了孔径;改变了铁基催化剂的形貌;促进了铁基催化剂在H₂中的还原。反应过程中,在催化剂中只添加Cu助剂时,有利于提高催化剂的反应活性,而当同时加入Cu助剂和PVA时,由于Cu助剂与PVA较强的相互作用,反而降低了催化剂的反应活性,且催化剂的选择性向轻质烃方向偏移。     

不同处理方法对氮化硼负载铁基催化剂费托合成性能的影响

采用等体积浸渍法制备了三种氮化硼(BN)负载的铁基催化剂,将其用于费托合成反应中;结合XRD、TEM、FT-IR和H2-TPR等表征手段,研究了催化剂的物相结构、形貌特征、还原性能以及F-T合成反应性能。结果表明,Cu助剂加入不会破坏载体BN的物相结构,而硼砂的加入会提高载体BN的结晶度; Cu助剂和硼砂加入对催化剂形貌的影响不明显,但都会使所制备的负载型铁基催化剂还原温度降低。在n(H2_)/n(CO)=2.0、340℃、2 MPa和GHSV=1500 h~(-1)的条件下,三种催化剂Fe/BN、Fe/BNM和Fe-Cu/BN上的CO的转化率分别为12.3%、36.2%和31.6%,产物中甲烷选择性为57.9%、26.8%和44.7%。Fe-Cu/BN和Fe/BNM两种催化剂活性均比Fe/BN催化剂有所提高,表明BN负载的铁基催化剂可以通过加入助剂以及改善载体与活性组分之间的相互作用来提升其对F-T合成反应的催化活性。相关结果可为探索制备高活性的氮化硼基FT合成催化剂提供思路。     

低温高活性熔铁催化剂上的超临界相费托合成反应

在固定床反应器中超临界相条件下研究了熔铁催化剂上的费托合成反应,发现在超临界介质中反应物和产物更容易扩散,较好地抑制了催化剂表面非活性碳的沉积,从而提高了费托合成反应中的CO转化率和烯烃选择性,增加了链增长因子,降低了甲烷选择性.同时,考察了超临界介质、反应温度、压力、H2/CO比和空速等条件对费托合成反应的影响.结果表明,C5-8正构烷烃在催化剂活性温度下都是适宜的超临界介质.当温度和压力都在介质的临界点以上时,介质表现出较好的传质与传热性能,可改善费托合成反应性能.     

焙烧温度对含Mg助剂的铁基催化剂F-T合成反应性能的影响

采用连续共沉淀和喷雾干燥技术相结合的方法制备了Mg助剂的Fe/Cu/K/SiO2催化剂,采用N2物理吸附、XRD、MES 和H2-TPR等表征手段,考察了焙烧温度对催化剂比表面积、体相结构和还原性能的影响。结果表明,随着焙烧温度的升高,催化剂的比表面积降低,平均孔径增大,体相中α-Fe2O3晶粒逐渐增大,催化剂变的越来越难还原,其结构更加稳定。在H2/CO （摩尔比）= 2.2、250 ℃、2.0 MPa和2 000 h－1于固定床反应器考察了焙烧温度对该催化剂F-T合成反应性能的影响,结果表明,随着焙烧温度的升高,催化剂的F-T合成反应活性降低,在运行过程中反应活性逐渐增加直至达到平稳,但达到平稳所需的诱导期越来越长;提高焙烧温度使烃产物分布向重质烃方向转移,有利于降低CH4的选择性,促进重质烃的生成。     

焙烧温度对Fe-Mn催化剂结构和F-T合成性能影响

研究了焙烧温度对Fischer-Tropsch(F-T)合成Fe-Mn催化剂的织构性质、还原行为以及在还原和反应过程中结构变化的影响；在H2/CO=2.0、260 ℃、2.5 MPa和1 000 h－1条件下在固定床反应器上考察了焙烧温度对Fe-Mn催化剂F-T合成反应活性、烃产物选择性和运行稳定性的影响。XRD和TPR结果表明，随着焙烧温度的升高，催化剂中α-Fe2O3晶粒增大，催化剂比表面积降低，促进Mn3+渗入α-Fe2O3晶格中，形成了铁锰固溶体物相，使得催化剂难于还原，当焙烧温度升高到700 ℃时，催化剂中的α-Mn2O3相完全消失。催化剂F-T合成反应评价表明，在不降低催化剂活性的同时，焙烧温度的升高可显著地提高催化剂的反应运行稳定性，并促使烃产物分布向高碳数方向偏移；600 ℃焙烧的Fe-Mn催化剂运行200 h，总体活性高，失活速率较低，对低碳烯烃和中间馏分油段产物选择性好。     

Fischer-Tropsch synthesis by nano-structured iron catalyst

Effects of nanoscale iron oxide particles on textural structure, reduction, carburization and catalytic behavior of precipitated iron catalyst in Fischer-Tropsch synthesis (FTS) are investigated. Nanostructured iron catalysts were prepared by microemulsion method in two series. Firstly, Fe2O3, CuO and La2O3 nanoparticles were prepared separately and were mixed to attain Fe/Cu/La nanostructured catalyst (sep-nano catalyst); Secondly nanostructured catalyst was prepared by co-precipitation in a water-in-oil microemulsion method (mix-nano catalyst). Also, conventional iron catalyst was prepared with common co-precipitation method. Structural characterizations of the catalysts were performed by TEM, XRD, H2 and CO-TPR tests. Particle size of iron oxides for sep-nano and mix-nano catalysts, which were determined by XRD pattern (Scherrer equation) and TEM images was about 20 and 21.6 nm, respectively. Catalyst evaluation was conducted in a fixed-bed stainless steel reactor and compared with conventional iron catalyst. The results revealed that FTS reaction increased while WGS reaction and olefin/paraffin ratio decreased in nanostructured iron catalysts.     

Deactivation studies of nano-structured iron catalyst in Fischer-Tropsch synthesis

A nano-structured iron catalyst for syngas conversion to hydrocarbons in Fischer-Tropsch synthesis (FTS) was prepared by micro-emulsion method. Compositions of bulk iron phase and phase transformations of carbonaceous species during catalyst deactivation in FTS reaction were characterized by temperature-programmed surface reaction with hydrogen (TPSR-H2), and XRD techniques. Many carbonaceous species on surface and bulk of the nano-structured iron catalysts were completely identified by combined TPSR-H2 and XRD spectra and which were compared with those recorded on conventional co-precipitated iron catalyst. The results reveal that the catalyst deactivation results from the formation of inactive carbide phases and surface carbonaceous species like graphite, and it will be increased when the particle size of iron oxides was reduced in FTS iron catalyst.     

Partially hydrated iron–chromium oxide catalyst for the Fischer-Tropsch synthesis

Due to their well-developed surface, partially hydrated iron–chromium oxides with the ferrihydrite structure exhibit much higher activity in the Fischer-Tropsch synthesis than those that have the hematite structure.     

Deactivation studies of bifunctional Fe-HZSM5 catalyst in Fischer-Tropsch process

A physical mixture of alkali-promoted iron catalyst with binder based on Fischer-Tropsch synthesis and an acidic co-catalyst （HZSM5） for syngas conversion to hydrocarbons was studied in a fixed bed micro reactor. Deactivation data were obtained during the synthesis over a 1400 h period. The deactivation studies on iron catalyst showed that this trend followed the phase transformation Fe2.2C （ ε′） → Fe5C2 （χ） → Fe3C （θ）, and the final predominant phase of the catalyst was Fe3C （θ）. Deactivation of zeolite component in bifunctional catalyst may be caused by coking over the zeolitic component, dealumination of zeolite crystals, and migration of alkali promoters from iron catalyst under synthesis conditions. The deactivation rate of iron catalyst was also obtained.     

焙烧温度对铁基催化剂催化浆态床F-T合成反应性能的影响

 采用连续共沉淀与喷雾干燥成型技术相结合的方法制备了微球形Fe-Cu-K-SiO2催化剂,并考察了焙烧温度对催化剂的结构和织构性质的影响. 结果表明,催化剂具有较好的织构和结构热稳定性,粘结剂SiO2起到了分散和稳定α-Fe2O3晶相的作用. 随着焙烧温度的升高,催化剂的比表面积逐渐减小,α-Fe2O3晶粒逐渐增大,催化剂体相中的Cu和K原子向表面富集,且Cu向表面的迁移更明显; 同时,催化剂中的α-Fe2O3和CuO相发生了一定程度的离析,Cu的助剂作用减弱,使催化剂在合成气气氛下难于还原碳化. 催化剂在n(H2)/n(CO)=0.67,GHSV=2.0 L/(g·h),p=1.5 MPa和θ=250 ℃下的浆态床F-T合成反应评价结果表明,升高焙烧温度,催化剂的初活性和最高活性下降,但运行稳定性提高,而且有效地抑制了CH4的生成,明显促进了烃产物向高碳数方向移动. 反应600 h后卸载下的催化剂的形貌观测表明,催化剂的磨损主要是由化学磨损引起的,提高焙烧温度可明显改善其抗磨损性能,焙烧温度高于400 ℃时,催化剂具有较好的抗磨损性能.     

Studies on product distribution of alkali promoted iron catalyst in Fischer-Tropsch synthesis

The dependencies of hydrocarbon product distributions of alkali promoted iron catalyst in Fischer-Tropsch synthesis have been studied. The concept of two superimposed Anderson-Schulz-Flory distributions has been applied for the representation of the effects of Mg, La and Ca promoters on product distributions. The FTS performance of the catalysts was tested in a fixed bed reactor under the conditions 563 K, 1.7 MPa, H2/CO = 1 and space velocities 4.86 and 13.28 nl h-1 gFe-1 . The results indicate that approp...     

Kinetics of the water-gas shift reaction in Fischer-Tropsch synthesis over a nano-structured iron catalyst

Based on formate and direct oxidation mechanisms, three Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models of the water-gasshift (WGS) reaction over a nano-structured iron catalyst under Fischer-Tropsch synthesis (FTS) reaction conditions were derived and compared with those over the conventional catalyst. The conventional and nanostructured Fe/Cu/La/Si catalysts were prepared by co-precipitation of Fe and Cu nitrates in aqueous media and water-oil micro-emulsion, respectively. The WGS kinetic data were measured by experiments over a wide range of reaction conditions and comparisons were also made for various rate equations. WGS rate expressions based on the formate mechanism with the assumption that the formation of formate is rate determining step were found to be the best.