Direct production of olefins via syngas conversion over Co2C-based catalyst in slurry bed reactor

Abstract

Direct production of olefins via syngas conversion over a Co₂C-based catalyst was investigated in a slurry bed reactor (SBR). It was found that the total selectivities to olefins and oxygenates reached 88.8C% at a CO conversion of 29.5% at 250 °C, 5 bar and H₂/CO = 0.5. The hydrocarbon distribution greatly deviated from the classical Anderson-Schulz-Flory (ASF) distribution, with only 2.6C% methane selectivity was obtained. XRD and TEM characterization verified that the Co₂C nanoprisms with special exposed facts of (101) and (020) constitutes the Fischer-Tropsch to olefins (FTO) active site. The catalytic activity increased gradually with rising the reaction temperature, while the product distribution almost kept unchanged under various reaction condition in SBR. Compared to the reaction in FBR, the Co₂C-based catalyst exhibited relative better catalytic performance during FTO process in SBR. Specifically, a higher CO conversion, a lower methane selectivity and a higher total selectivities to olefins and oxygenates were achieved in SBR. In addition, the catalyst can be in situ reduced in slurry bed reactor at mild temperature (300 °C) and no obvious deactivation was found within nearly 100 h time-on-stream, which suggested a promising route for the direct production of olefins via syngas in industrial application.

Fig. 1. XRD patterns of CoMn catalysts after drying (a), calcination (b), reduction in FBR (c) and SBR (d) as well as reaction in FBR (e) and SBR (f).

Fig. 2. TEM images and particle size distribution for CoMn catalyst after dried (a–c), calcination (d–f) as well as reduction in FBR (g–i) and SBR (j–l).

Fig. 3. TEM images of the spent CoMn catalysts withdrawn from FBR (a–c) and SBR (d–f).

Fig. 4. The chain growth probability of hydrocarbons over CoMn catalyst under various reaction conditions. (a) 250 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in FBR; (b) 260 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in FBR; (c) 270 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in FBR; (d) 250 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (e) 260 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (f) 270 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (g) 250 °C, 5 bar, 1000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (h) 250 °C, 5 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (i) 250 °C, 5 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.75 in SBR; (j) 250 °C, 5 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 1 in SBR; (k) 250 °C, 7.5 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (l) 250 °C, 10 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR.

Fig. 5. The distributions of hydrocarbons on CoMn catalyst under various reaction conditions. (a) 250 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in FBR; (b) 260 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in FBR; (c) 270 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in FBR; (d) 250 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (e) 260 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (f) 270 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (g) 250 °C, 5 bar, 1000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (h) 250 °C, 5 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (i) 250 °C, 5 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.75 in SBR; (j) 250 °C, 5 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 1 in SBR; (k) 250 °C, 7.5 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR; (l) 250 °C, 10 bar, 4000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5 in SBR.

Fig. 6. Catalytic performance of CoMn catalyst in the initial stage for the FTO process in SBR. (a) CO conversion and product selectivity as a function of time-on-steam. The selectivities to CH₄, CO₂, C_2–4⁼ and C₅₊ + Oxy. were calculated based on tail gas analysis. (b) O/P ratio as a function of time-on-stream. (c) Product plots (ln(W_n/n) and n) with time-on-stream. W_n is the weight fraction of a product with n number of carbon atoms. (d) Chain growth probability (α₃) as a function of time-on-stream, obtained by fitting the results generated for chains of three to seven carbons using ASF model (reaction conditions: 250 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5).

Fig. 7. Catalytic stability of CoMn catalysts in FBR and SBR for the FTO process (reaction conditions: 250 °C, 5 bar, 2000 ml h⁻¹ g_cat⁻¹ and H₂/CO = 0.5).