Abstract
The conditions for promoting the joint conversion of CO2 and syngas in the direct synthesis of light olefins have been studied. In addition, given the relevance for the viability of the process, the stability of the In2O3–ZrO2/SAPO-34 (InZr/S34) catalyst has also been pursued. The CO+CO2 (COx) hydrogenation experimental runs were conducted in a packed bed isothermal reactor under the following conditions: 375–425 °C; 20–40 bar; space time, 1.25–20 gcatalyst h molC–1; H2/(COx) ratio in the feed, 1–3; CO2/(COx) ratio in the feed, 0.5; time on stream (TOS), up to 24 h. Analyzing the reaction indices (CO2 and COx conversions, yield and selectivity of olefins and paraffins, and stability), the following have been established as suitable conditions: 400 °C, 30 bar, 5–10 gcat h molC–1, CO2/COx = 0.5, and H2/COx = 3. Under these conditions, the catalyst is stable (after an initial period of deactivation by coke), and olefin yield and selectivity surpass 4 and 70%, respectively, with light paraffins as byproducts. Produced olefin yields follow propylene > ethylene > butenes. The conditions of the process (low pressure and low H2/COx ratio) may facilitate the integration of sustainable H2 production with PEM electrolyzers and the covalorization of CO2 and syngas obtained from biomass.
Highlights
It is well established that replacing fossil sources for renewable energies is the solution to reverse the climate change caused by greenhouse gas emissions.[1]
With similar studies in the literature, as CO2+CO mixtures are used as carbon source in our case, unlike the pure CO2 feedstocks used in the literature. These results show that CO2+CO mixtures in the feedstock do not hamper CO2 conversion, meaning that the approach presented in the work, of considering H2+CO+CO2 feedstocks feasible for the process, is viable, as similar values were obtained by other authors within the 360−400 °C range with H2+CO2 feedstocks over In2O3/SAPO-3465 and In2O3−ZrO2/ SAPO-3448 catalysts
The direct synthesis of light olefins from CO2 and syngas mixture hydrogenation is an attractive alternative to the twostage process, because it can be carried out under low H2 pressure conditions and a moderate H2/CO2 mixture (COx) ratio, facilitating the valorization of syngas obtained from biomass or wastes and
Summary
It is well established that replacing fossil sources for renewable energies is the solution to reverse the climate change caused by greenhouse gas emissions (in particular by CO2).[1]. The technological development of efficient routes for the large-scale conversion of CO2 into value-added products is imperative (to offset the cost of its capture and storage) to facilitate the viability of CCU strategies. This requires activating the stable structure of CO2 generating C−C, C− H, C−O, and C−N bonds.[4] In addition, biomass gasification and pyrolysis derivatives (syngas and bio-oil, respectively) offer good prospects to replace fossil sources, helping to reduce CO2 emissions. The synthesis of methanol is an ideal process to be integrated with CO2 capture in conventional cement
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