One-step upgrading of real flue gas streams into syngas over alumina-supported catalysts

Flue gas is a major source of CO2 and the development of technologies for its utilization is of utmost interest both by environmental and industrial perspectives. Recently investigated CO2 valorization processes still face technoeconomic challenges for implementation for costs associated with different steps, including CO2 purification steps. Thus, for the first time in literature, the feasibility of the direct one-step upgrading of real untreated flue gas into syngas is investigated here. For that end, classical alumina-supported catalysts (Ni, Co and Fe) were used for concept validation. The influences of temperature (500-900 degrees C), metal load (10-15 %), residence time (GHSV = 315-1260 h-1) and the effects of flue gas impurities (NOX and SO2) are reported here. Best CO2 and H2O conversion performances (XCO2 = 53.9 %, XH2O = 67.0 %) were obtained with the nickel catalyst with 15 wt % Ni at 900 degrees C and the highest residence time (GHSV = 315 h-1). The highest H2/CO ratio of the produced syngas was 0.70 and it was obtained with the same 15 wt% Ni catalyst at T = 700 degrees C, GHSV = 630 h-1. The NOx present in the FG was completely removed as part of the one-step upgrading strategy, while SO2 did not interact with the tested catalysts. Finally, a long-term operation strategy was proposed by supplementing the flue gas with H2 (H2/CO2 = 1.0), which yielded 24 h stable operation with around 40 % CO2 conversion and a syngas with H2/CO = 1.2-1.3. The results presented here, for the first time in the literature, demonstrate the feasibility of a novel one-step process for direct valorization of flue gas. The direct upgrading of flue gas would potentially decrease the costs associated with CO2 purification and valorization.

Automated summary

The feasibility of directly upgrading untreated flue gas into syngas was investigated using nickel catalysts, achieving the best results at a temperature of 900 degrees Celsius and the highest residence time.