Integrating a high-pressure syngas step with Fischer-Tropsch synthesis (FT) in a single vessel reduces investment and operating costs for Gas-toLiquids technology (GtL). Methane catalytic partial oxidation (CPOX) to produce syngas for FT is an economic opportunity for micro-refineries. Many metals and metal oxides selectively convert natural gas to CO and H 2 , but they also form coke, which must be removed intermittently, otherwise it deactivates the catalyst and can foul the reactor and process lines. Here, we prepared a 1 % mass fraction (0.01 g/g) Pt/Rh (Pt/Rh = 9) catalyst supported on MgO over FeCralloy woven fibre via solution combustion synthesis. At 900 • C, from 0.1-2 MPa, and with a 2:1 feed composition of CH 4 to O 2 , the reaction consumed all the oxygen and we obtained a H 2 /CO ratio of 2 (ideal for FT). At low pressure and a 0.1 s residence time the catalyst converted 90 % of the methane at 90 % CO selectivity. At 2 MPa, CO yield reached 50 % (< 80 % conversion and 57 % selectivity). Based on thermodynamic calculations, less than 5 % coke forms below 900 • C. At high pressure and short residence time (0.1 s), the coke yield (presumed to be coke crystallites) was 24 %. Increasing the residence time to 0.3 s reduced the amount of coke by 33 % because it is metastable.
Heat-treatment of spodumene concentrate at 1323 K (1050 °C) for 30 min in a rotary kiln yielded a successful decrepitation. Particle size decreased from 2 cm to less than 425 µm for 80% of the initial mass. X-ray analysis of both fractions did not reveal the presence of α-spodumene or γ-spodumene. The coarse fraction was ground to less than 425 µm with minimal mechanical energy and mixed with the finer fraction to perform lithium extraction. The lithium extraction efficiency reached 98 wt% without the need for flotation. Some aspects of the thermodynamic behavior of the spodumene system were assessed. Results show that metastable γ-spodumene may hinder the formation of β-spodumene at lower heat treatment temperatures. Some heat-treated samples presented non-negligible γ-spodumene content and lithium extraction efficiency decreases as the γ content increases. Finally, the assumed irreversibility of the transformations was studied by analyzing heat-treated samples following long controlled-storage periods. The results show that concentrate composition is not static over the studied time. This suggests that the β formation is not as irreversible as claimed. It is recommended to avoid long periods between heat-treatment and extraction to avoid the slow conversion of β-spodumene to other allotropes, which are less susceptible to lithium extraction.
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