Yulan Zhang

Design of Carbon-Encapsulated Fe3O4 Nanocatalyst with Enhanced Performance for Fischer–Tropsch Synthesis

Fischer–Tropsch synthesis (FTS), an important process for the production of liquid fuels and chemicals from syngas derived from coal and biomass, is receiving renewed interest for both industrial and academic applications. Adjusting the product distribution of hydrocarbons is the focus of research in this field. Herein, a novel carbon‐encapsulated Fe3O4 nanocatalyst was synthesized by a simple one‐step solvothermal method without calcination. The catalyst exhibited excellent catalytic activity and higher selectivity for C5–12 hydrocarbons (gasoline range products) than the traditional Fe2O3 catalyst. A 45.25 % C5–12 selectivity was obtained for Fe3O4@C, which is close to the maximum value from the Anderson–Schulz–Flory distribution.

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K 2 CrO 4 and Fe 2 O 3 , increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.

Effects of Ag on morphology and catalytic performance of iron catalysts for Fischer–Tropsch synthesis

Fe3O4 nanoparticles with pore size of 12.4 nm were synthesized and employed as catalyst for Fischer–Tropsch (FT) synthesis. The as-prepared Fe3O4 catalyst achieved a CO conversion of 98.3% while yielding higher than 50 wt% gasoline range (C5–C11) hydrocarbons after FT reaction for 48 h. Furthermore, highly activated Ag-doped composites were designed through a one-pot solvothermal method, and then porous core/shell materials were obtained. Interestingly, active metal oxide (Fe3O4) nanoparticles were interspersed on the surface of the Ag promoter. Importantly, pores could enhance the dispersion of metal particles and facilitate heat and mass transfer. The addition of Ag promoter decreased the selectivity to CH4 and enhanced the yield of C2–C4 olefins. In particular, 0.8Ag/Fe3O4 displayed high CO conversion (96.4%) and optimum selectivity to C2–C4 olefins (28.3 wt%) while yielding a low selectivity to CH4 (12.1 wt%), as well as a good selectivity to C5–C11. More importantly, 0.8Ag/Fe3O4 showed the highest catalytic activity (>1.6 × 10−4 molco gFe−1 s−1) and the best total hydrocarbon yield (5.25 × 10−3 gHC gFe−1 s−1).

Highly activated Ag-doped Fe-based catalysts designed for Fischer–Tropsch synthesis

Ag-doped Fe-based microspheres were synthesized via a one-pot solvothermal method, and displayed excellent mechanical stability and catalytic activity. Especially, the catalyst at Ag/Fe = 1 showed the lowest selectivity to CH4 (12.6 wt%) and the highest to C2–4 olefins (29.0 wt%), as well as a good selectivity to gasoline-range (C5–11) fraction products (45.7 wt%). In addition, the catalytic activity and product selectivity of Ag/Fe measured at 280 °C was superior to that at 270 °C and 260 °C.

Preparation of hierarchical porous-structured Fe3O4 microspheres for Fischer–Tropsch synthesis

Hierarchical porous-structured Fe3O4 microspheres for use in Fischer–Tropsch (FT) synthesis were fabricated via a solvothermal reaction mediated by ethylene glycol. Each microsphere was observed to consist of primary nanoparticles that served as active oxides for the FT synthesis reaction. Without additional porous support, the pore structure was well constructed through the self-assembly of the Fe3O4 nanoparticles. Compared to the previously reported Fe catalyst, the current synthesized porous structure appeared to have improved the interparticle connectivity and promote the dispersion of active metal, and hence enhance the selectivity for C5+ hydrocarbons. In particular, 1PFe with an average pore size of 3.71 nm and Fe dispersion of 13.9% exhibited the best selectivity for C5+ (59.0 wt%) combined with the lowest CH4 product fraction (11.3 wt%), as well as a high CO conversion of 93.2%.

PREDICTION OF CARBON CONCENTRATION AND FERRITE VOLUME FRACTION OF HOT-ROLLED STEEL STRIP DURING LAMINAR COOLING

A phase transformation model was presented for predicting the phase fraction transformed and the carbon concentration in austenite for austenite to ferrite transformation during laminar cooling on run-out table in hot rolling strip mill. In this model, the parameter k in Avrami equation was developed for carbon steels. The wide range of chemical composition, the primary austenite grain size, and the retained strain were taken into account. It can be used to predict the ferrite volume fraction and the carbon concentration in austenite of hot-rolled steel strip during laminar cooling on run-out table. The coiling temperature controlling model was also presented to calculate the temperature of steel strip. The transformation kinetics of austenite to ferrite and the evolution of carbon concentration in austenite at different temperatures during cooling were investigated in the hot rolled Q235B strip for thickness of 9.35. 6.4, and 3.2mm. The ferrite volume fraction along the length of the strip was also calculated. The calculated ferrite volume fraction was compared with the log data from hot strip mill and the calculated results were in agreement with the experimental ones. The present study is a part of the prediction of the mechanical properties of hot-rolled steel strip, and it has already been used on-line and off-line in the hot strip mill.

Mesoporous Fe-based spindles designed as catalysts for the Fischer–Tropsch synthesis of C5+ hydrocarbons

Conventional mesoporous catalysts are generally obtained through the dispersion of active phases on porous supports to enhance catalytic performance. However, metal-support interactions can suppress the activation of iron oxides, and this can lead to lower catalytic activity. Moreover, the effects of supports on catalytic performance are complicated for Fischer–Tropsch (FT) synthesis. Herein, we developed novel mesoporous Fe-based spindles and the pores are self-assembled via active phases. This unique structure effectively avoids metal-support interactions during activation and FT synthesis, thus improving the FT activity. More importantly, the selectivity for C5+ hydrocarbons is found to be correlated with the pore size. It is identified that Fe/2CTAB, which has the largest pore volume among the three mesoporous spindles (Fe, Fe/CTAB, and Fe/2CTAB), affords the optimum C5+ selectivity, up to 65 wt%. This value is much higher than those for traditional co-precipitation catalysts and supported Fe-based catalysts. Moreover, FT synthesis over Fe/2CTAB leads to the lowest CH4 selectivity.