Cobalt catalysts supported on silica nanotubes for Fischer-Tropsch synthesis

Silica nanotubes(SNT) have been synthesized using carbon nanotubes(CNT) as a template.Silica-coated carbon nanotubes(SNT-CNT) and SNT were loaded with a cobalt catalyst for use in Fischer-Tropsch synthesis(FTS).The catalysts were prepared by incipient wetness impregnation and characterized by N2 physisorption,X-ray diffraction(XRD),hydrogen temperature programmed reduction(H2-TPR) and transmission electron microscopy(TEM).FTS performance was evaluated in a fixed-bed reactor at 493 K and 1.0 MPa.Co/CNT and Co/SNT catalysts showed higher activity than Co/SNT-CNT in FTS because of the smaller cobalt particle size,higher dispersion and stronger reducibility.The results also showed that structure of the support affects the product selectivity in FTS.The synergistic effects of cobalt particle size,catalytic activity and diffusion limitations as a consequence of its small average pore size lead to medium selectivity to C5+ hydrocarbons and CH4 over Co/SNT-CNT.On the other hand,the Co/CNT showed higher CH4 selectivity and lower C5+ selectivity than Co/SNT,due to its smaller average pore size and cobalt particle size.     

Thermal decomposition and cobalt species transformation of carbon nanotubes supported cobalt catalyst for Fischer-Tropsch synthesis

The effect of calcination condition on the cobalt species and Fischer-Tropsch synthesis (FTS) was studied. It was found that higher calcination temperature resulted in decreased FTS activities because CNTs were consumed by oxidation in air at temperature higher than 230°C. Cobalt species went through transformation from Co3O4 to metallic Co in Ar by autoreduction at temperature over 500°C. The autoreduction route might be Co3O4→CoO→Co or Co3O4→Co2C→Co. Reduction at temperature higher than 500°C also resulted in decreased FTS activities due to the methanation of CNTs in hydrogen.     

Effects of ceria addition and pre-calcination temperature on performance of cobalt catalysts for Fischer-Tropsch synthesis

Summary The effect of ceria addition on the performance of 10 wt.% Co catalysts supported on SiO2 and Al2O3 for Fischer-Tropsch synthesis has been investigated. The catalysts were prepared by impregnation method and characterized by X-ray diffraction technique. The catalytic tests (P = 1 atm, T = 488 K, H2/CO = 2, GHSV=1800 h-1) indicate that with addition of ceria, significant changes in CO conversion and hydrocarbon selectivities are observed. Also, the experiments show that the performance of 10 wt.% Co-CeO2/Al2O3 depends on the ceria concentration as well as on the pre-calcination temperature.     

在超临界正己烷介质中的F-T合成反应行为

在固定床反应器中,以正己烷为超临界介质,研究了三种Co催化剂（浸渍、喷雾干燥、双模催化剂）上的F-T合成反应行为。在相同的Co质量分数下,喷雾干燥催化剂和双模催化剂的活性接近,都高于浸渍催化剂。在喷雾干燥催化剂上CO的转化率显著高于浸渍催化剂。喷雾干燥催化剂F-T产物中具有高的低碳选择性和低的1-烯烃质量分数,然而在相近的CO转化率下,喷雾干燥和浸渍催化剂具有类似的1-烯烃质量分数。对于浸渍催化剂,当Co质量分数从5％增加到15％,CO转化率从8.3％增加到43.6％。含Co5％的催化剂比质量分数为10％、15％、20％催化剂的甲烷选择性低2.0%～3.0%,但产物中1-烯烃的质量分数明显要高。     

Activation pressure studies with an iron-based catalyst for slurry Fischer-Tropsch synthesis

Fischer-Tropsch synthesis (FTS) was carried out with an industrial iron-based catalyst (100Fe/5Cu/6K/16SiO2, by weight) under the baseline conditions in a stirred tank slurry reactor (STSR). The effects of activation pressure on the catalyst activity and selectivity were investigated. It was found that iron phase compositions, textural properties, and FTS performances of the catalysts were strongly dependent on activation pressure. The high activation pressure retards the carburization. Møssbauer effect spectroscopy (MES) results indicated that the contents of the iron carbides clearly decrease with the increase of activation pressure, especially for the activation pressure increasing from 1.0 MPa to 1.5 MPa, and the reverse trend is observed for superparamagnetic Fe3+ (spm). The higher content of Fe3+ (spm) results in the higher amount of CO2 in tail gas when the catalyst is reduced at higher pressure. The catalyst activity decreases with the increase of activation pressure. The high quantity of iron carbides is necessary to obtain high FTS activity. However, the activity of the catalyst activated in syngas can not be predicted solely from the fraction of the carbides. It is concluded that activation with syngas at the lower pressure would be the most desirable for the better activity and stability on the iron-based catalyst.     

超临界和近临界条件下Fischer Tropsch合成研究：溶剂的影响

研究了超临界和近临界条件下费托合成过程中溶剂对反应行为的影响。反应在固定床反应器中进行，催化剂为Co/SiO2，所选择的溶剂有两类：纯溶剂（正戊烷和正己烷）和混和溶剂（由正己烷和少量的C5~10烃组成）。结果表明,正己烷分压对CO转化率影响很小，但是产物中1 烯烃含量随正己烷分压增加而增加，超临界条件下1 烯烃含量明显高于非临界条件下。溶剂的种类对CO转化率、CH4和CO2选择性以及产物炭分布影响不大。这一结果表明为了减少溶剂用量，对含有适量轻组分（C5~10）的正己烷溶剂进行循环使用是可行的。结果同时表明与正己烷相比，混和溶剂（25%正己烷和75%正葵烷）具有较高的1 烯烃选择性。     

费-托合成Co/ZrO2-Al2O3催化剂反应性能的研究

以ZrOCl2·6H2O和AlCl3为原料,采用共沉淀方法制得一系列不同ZrO2质量分数的ZrO2-Al2O3混合氧化物载体;并以该混合氧化物为载体,采用初湿浸渍法制得钴质量分数为12％的Co/ZrO2-Al2O3催化剂。XRD、NH3-TPD、TPR和原位IR等表征结果表明,随着混合载体中ZrO2质量分数的增加,载体比表面积先增加后减少,混合载体的平均孔径则小于单一氧化物ZrO2和Al2O3的平均孔径。ZrO2和Al2O3载体混合后会导致氧化物的比表面积和酸性增大并且有新的物相生成。当混合氧化物用作载体时,能够抑制载体表面金属钴的分散,改变催化剂的还原行为,降低催化剂对CO物种的吸附能力。CO加氢反应表明,与单一金属氧化物相比,钴负载ZrO2-Al2O3混合氧化物催化剂的加氢活性和重质烃选择性有所降低。     

Correlation between hydrocarbon distribution and water-hydrocarbon ratio in Fischer-Tropsch synthesis

In order to shorten the evaluation cycle of cobalt catalyst before the optimized catalyst is fixed on, a mathematical method is proposed to calculate weight percentage of C5+ hydrocarbons. Based on the carbide polymerization mechanism and the main hydrocarbons being linear alkanes and α-olefins, the correlation between hydrocarbon distribution and the molecular mass ratio of water to hydrocarbons is discussed. The result shows the ratio was within the range of 1.125-1.286 and the lower the ratio, the more gaseous hydrocarbons were obtained. Moreover, a linear equation between the weight percentage of C5+ hydrocarbons and the weight ratio of C5+ hydrocarbons to the total water is established. These results are validated by corresponding experiments. The weight percentage of C5+ hydrocarbons could be immediately calculated by this linear equation without detailed gas chromatography (GC) analysis of them.     

Effect of catalyst confinement and pore size on Fischer-Tropsch synthesis over cobalt supported on carbon nanotubes

This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes(CNT) on the activity and product selectivity of Fischer-Tropsch synthesis(FTS) reaction.Three types of CNT with average pore sizes of 5,11,and 17 nm were used as the supports.The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT.The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT,and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing.The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT.Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.     

SBA-15的疏水改性及其对钴基催化剂费-托合成催化性能的影响

利用甲硅烷基化作用制得了不同疏水基团(甲基、二甲基和三甲基)改性SBA-15载体,采用等体积浸渍法制备了质量分数为5%的一系列负载型钴催化剂。结合BET、FT-IR、29Si CP MAS NMR、XRD和H2-TPR等表征手段,考察了SBA-15疏水改性对钴基催化剂物相结构、还原行为以及费-托合成催化性能的影响。催化剂在固定床反应器中在p=2.0 MPa,t=200~250℃,H2和CO体积比为2和GHSV=1 000 h-1的条件下进行评价。结果表明,相对于未改性SBA-15负载钴催化剂,疏水基团改性SBA-15负载钴催化剂的还原度增加,CO转化率提高;Co3O4晶粒粒径增大,难还原钴物种减少,CH4选择性降低,C5+烃选择性增加。     

Development of niobium-promoted cobalt catalysts on carbon nanotubes for Fischer-Tropsch synthesis

Cobalt-based catalysts were prepared by a wet impregnation method on carbon nanotubes (CNTs) support and promoted with niobium.Samples were characterized by nitrogen adsorption,TEM,XRD,TPR,TPO and H2-TPD.Addition of niobium increased the dispersion of cobalt but decreased the catalysts reducibility.Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed microreactor at 543 K,1 atm and H2/CO=2 for 5 h.Addition of niobium enhanced the C5+ hydrocarbons selectivity by 39% and reduced methane selectivity by 59%.These effects were more pronounced for 0.04%Nb/Co/CNTs catalyst,compared with those observed for other niobium compositions.     

Synthesis and characterization of multiwall carbon nanotubes/alumina nanohybrid-supported cobalt catalyst in Fischer-Tropsch synthesis

Multiwall carbon nanotubes (MWNTs) and alumina are combined to give a new type of nanohybrid for Fisher-Tropsch synthesis (FTS) catalyst support. Alumina nano-particles (10 wt%) were introduced directly on functionalized MWNTs by a modified sol-gel method. Microstructure observations show that alumina particles were homogeneously dispersed on the inside and outside of modified MWNTs surfaces. 15 wt% cobalt loading catalysts were prepared with this nanohybrid and γ-alumina as a reference, using a sol-gel technique and wet impregnation method respectively. These catalysts were characterized by TEM, XRD, N₂-adsorption, H₂ chemisorption and TPR. The deposition of cobalt nanoparticles synthesized by sol-gel technique on the MWNTs nanohybrid shift the reduction peaks to a low temperature, indicating higher reducibility for uniform cobalt particles. Nanohybrid also aided in high dispersion of metal clusters and high stability and performance of catalyst. The proposed MWNTs nanohybrid-supported cobalt catalysts showed the improved FTS rate (g_HC/(g_cat·min)), CO conversion (%), and water gas shift rate (WGS)(g_CO2/(g_cat·h)) of 0.012, 52, and 30E-3, respectively, as compared to those of 0.007, 25, and 18E-3, respectively, on the γ-alumina-supported cobalt catalysts with the same Co loading.     

浸渍钠对铁基催化剂F-T合成浆态床反应性能的影响

以FeCuK/Si O2为母体催化剂,通过乙酸钠浸渍得到一组不同Na含量的费托合成铁基催化剂.采用原子发射光谱、低温N2吸附、程序升温还原和M ssbauer谱等技术对催化剂进行了表征.在H2/CO摩尔比为0.67,空速为2 000 h-1,压力为1.5 MPa和温度为250℃的条件下进行了浆态床F-T合成反应性能评价实验.结果表明,浸渍少量Na能提高催化剂的比表面积,促进铁物相的分散,而浸渍大量Na却大大降低了催化剂的比表面积,使催化剂中的铁物相聚集形成较大的颗粒;浸渍Na抑制了催化剂在H2中的第一步还原,但促进了催化剂在CO中的碳化;在原位合成气还原过程中,浸渍Na有利于催化剂的碳化.在500 h的运行实验中,浸渍Na的催化剂均表现出不同程度的失活现象.反应结果表明,浸渍Na对水煤气变换反应活性影响不大,对费托合成反应活性和烃产物选择性有较大的影响.在铁基催化剂上浸渍Na有利于C12 重质烃和低碳烯烃的生成.     

Effect of preparation method on halloysite supported cobalt catalysts for Fischer-Tropsch synthesis

Novel cobalt Fischer-Tropsch synthesis(FTS) catalysts were prepared from natural halloysite nanotubes(HNT) by double-solvent and wetimpregnation methods,and characterized by TEM,XRD,TPR and N2 adsorption-desorption.Comparing with the catalyst prepared by wetimpregnation method,the catalyst prepared by double-solvent method reduces Co3O4 particle migration and agglomeration due to size-induced effect,thus showing higher catalytic activity for Fischer-Tropsch synthesis.     

Kinetics and product distribution studies on ruthenium-promoted cobalt/alumina Fischer-Tropsch synthesis catalysts

Hydrocarbon production rates and distributions on ruthenium promoted alumina supported cobalt Fischer-Tropsch synthesis (FTS) catalysts were studied by the concept of two superimposed Anderson-Schulz-Flory (ASF) distributions. The results indicated that the characterizing growth probabilities α1 and α2 were strongly dependent on reaction conditions. By increasing the H2/CO partial pressure ratios and reaction temperatures, deviation from normal ASF distribution decreases and the double-α-ASF distribution changes into a straight line. Based on the concept of double-α-ASF distribution, a useful rate equation for the production of hydrocarbons under industrial reaction conditions is obtained.     

Study on iron-manganese catalysts for Fischer-Tropsch synthesis

Iron-manganese catalysts were prepared by co-precipitation method.Characterization of catalysts was carried out by using X-ray diffraction(XRD),scanning electron microscopy(SEM),temperature program reduction(TPR),N2 adsorption-desorption measurements.The results from catalytic performance tests in Fischer-Tropsch synthesis showed that the iron-manganese catalysts are supersensitive to catalyst composition and materials source.It was found that C2~4 light olefins increased while CH4 and CO2 decreased by using iron-manganese catalyst prepared from iron(II) sulfate(A catalyst).The activity and selectivity of A catalyst was studied in different operational conditions.The results showed that the best operational conditions for C2~4 light olefins production were H2/CO=1/1(GHSV=2400h-1) at 260℃ under 0.3MPa total pressure.     

Conversion enhancement of tubular fixed-bed reactor for Fischer-Tropsch synthesis using static mixer

Recently,Fischer-Tropsch synthesis(FTS) has become an interesting technology because of its potential role in producing biofuels via Biomassto-Liquids(BTL) processes.In Fischer-Tropsch(FT) section,biomass-derived syngas,mainly composed of a mixture of carbon monoxide(CO) and hydrogen(H2),is converted into various forms of hydrocarbon products over a catalyst at specified temperature and pressure.Fixed-bed reactors are typically used for these processes as conventional FT reactors.The fixed-bed or packed-bed type reactor has its drawbacks,which are heat transfer limitation,i.e.a hot spot problem involved highly exothermic characteristics of FT reaction,and mass transfer limitation due to the condensation of liquid hydrocarbon products occurred on catalyst surface.This work is initiated to develop a new chemical reactor design in which a better distribution of gaseous reactants and hydrocarbon products could be achieved,and led to higher throughput and conversion.The main goal of the research is the enhancement of a fixed-bed reactor,focusing on the application of KenicsTM static mixer insertion in the tubular packed-bed reactor.Two FTS experiments were carried out using two reactors i.e.,with and without static mixer insertion within catalytic beds.The modeled syngas used was a mixed gas composed of H2/CO in 2:1 molar ratio that was fed at the rate of 30mL(STP)min1(GHSV≈136mL g1 cat h1) into the fixed Ru supported aluminum catalyst bed of weight 13.3g.The reaction was carried out at 180℃ and atmospheric pressure continuously for 36h for both experiments.Both transient and steady-state conversions(in terms of time on stream) were reported.The results revealed that the steady-state CO conversion for the case using the static mixer was approximately 3.5 times higher than that of the case without static mixer.In both cases,the values of chain growth probability of hydrocarbon products(α) for Fischer-Tropsch synthesis were 0.92 and 0.89 for the case with and without static mixer,respectively.     

费托合成鼓泡浆态床反应器模型化研究

建立了费托合成鼓泡浆态床反应器双泡模型,通过模型对比的方法模拟讨论了多个反应器模型,双泡模型、全混模型以及多级串联模型,对比模拟讨论了费托合成反应各模型的适用性。模拟结果说明,全混模型适用于费托合成动力学行为的考察模拟;多级串联模型在一定的级数下能够近似模拟鼓泡浆态床中费托合成反应结果,更适用于探讨返混对费托合成反应行为的影响;双泡模型能够描述鼓泡浆态床中流体力学对反应的影响。     

Fischer-Tropsch synthesis over cobalt catalysts supported on modified SiO2 with mesoporous silica

SiO₂ was modified by hexagonal mesoporous silica to form a mixture with meso-/macroporous sizes and used as support of Co catalysts for Fischer-Tropsch synthesis in a slurry phase. A synergistic effect on the activity of Co catalyst was found. The catalytic properties are related to the state of surface Co and the character of support.     

Study of activated carbon supported iron catalysts for the Fischer-Tropsch synthesis

Summary Characterization (BET and TPD) and reaction studies were conducted with activated carbon supported iron catalysts (Fe/AC) used for the Fischer-Tropsch synthesis (FTS). The TPD study showed that there existed interactions between metals and the AC surface. Greater association of Cu and K promoters with the AC surface resulted in stronger promoter to surface interaction, which enhanced the H₂ desorption ability of the Cu and K promoted Fe/AC catalyst prepared under vacuum impregnation (VI). Catalytic behavior of a Fe/AC catalyst (VI-15 Fe/2 Cu/2 K/81 AC, in parts per weight) was studied in a 1-liter slurry phase continuous stirred tank reactor. The catalyst presented moderate syngas conversion (44.3-60.6%) and high gaseous selectivity (CH₄, 12.8-15.1% and C₂-C₄, 42.4-46.1%) under 304^oC, 3.0 MPa, 1.1 L(STP)/g-cat/h, and H₂/CO = 2.0 during 166 h of testing. Detectable hydrocarbons up to C₁₈ were formed on the Fe/AC catalyst.