The chemical looping gasification of residual biomasses—operated in fluidized beds composed of oxygen-carriers—may allow the production of biofuels from syngas. This biomass-to-fuel chain can contribute to mitigate climate change, avoiding the accumulation of greenhouse gases in our atmosphere. The ongoing European research project Horizon2020 CLARA (G.A. 817841) investigates wheat-straw-pellets (WSP) and raw-pine-forest-residue (RPR) pellets as feedstocks for chemical looping gasification. This work presents experimental results from devolatilizations of WSP and RPR, in bubbling beds made of three different oxygen-carriers or sand (inert reference), at 700, 800, 900 °C. Devolatilization is a key step of gasification, influencing syngas quality and quantity. Tests were performed at laboratory-scale, by a quartz reactor (fluidizing agent: N2). For each pellet, collected data allowed the quantification of released gases (H2, CO, CO2, CH4, hydrocarbons) and mass balances, to obtain gas yield (ηav), carbon conversion (χavC), H2/CO ratio (λav) and syngas composition. A simplified single-first order-reaction model was adopted to kinetically analyze experimental data. WSP performed as RPR; this is a good indication, considering that RPR is similar to commercial pellets. Temperature is the dominating parameter: at 900 °C, the highest quality and quantity of syngas was obtained (WSP: ηav = 0.035–0.042 molgas gbiomass−1, χavC = 73–83%, λav = 0.8–1.0); RPR: ηav = 0.036–0.041 molgas gbiomass−1, χavC = 67–71%, λav = 0.9–1.0), and oxygen-carries generally performed better than sand. The kinetic analysis suggested that the oxygen-carrier ilmenite ensured the fastest conversion of C and H atoms into gases, at tested conditions.
The European research project CLARA (chemical looping gasification for sustainable production of biofuels, G.A. 817841) investigated chemical looping gasification of wheat straw pellets. This work focuses on pretreatments for this residual biomass, i.e., torrefaction and torrefaction-washing. Devolatilizations of individual pellets were performed in a laboratory-scale fluidized bed made of sand, at 700, 800, and 900 °C, to quantify and analyze the syngas released from differently pretreated biomasses; experimental data were assessed by integral-average parameters: gas yield, H2/CO molar ratio, and carbon conversion. A new analysis of devolatilization data was performed, based on information from instantaneous peaks of released syngas, by simple regressions with straight lines. For all biomasses, the increase of devolatilization temperature between 700 and 900 °C enhanced the thermochemical conversion in terms of gas yield, carbon conversion, and H2/CO ratio in the syngas. Regarding pretreatments, the main evidence is the general improvement of syngas quality (i.e., composition) and quantity, compared to those of untreated pellets; only slighter differentiations were observed concerning different pretreatments, mainly thanks to peak quantities, which highlighted an improvement of the H2/CO molar ratio in correlation with increased torrefaction temperature from 250 to 270 °C. The proposed methods emerged as suitable straightforward tools to investigate the behavior of biomasses and the effects of process parameters and biomass nature.
The environmental impact of traditional fuels and related greenhouse gas emissions (GHGE) has promoted policies driven towards renewable fuels. This review deals with green diesel, a biofuel obtained by catalytic deoxygenation of edible and non-edible biomasses. Green diesel, biodiesel, and petrodiesel are compared, with green diesel being the best option in terms of physical–chemical properties and reduction in GHGE. The deoxygenation process and the related types of catalysts, feedstocks, and operating conditions are presented. Reactor configurations are also discussed, summarizing the experimental studies. Several process simulations and environmental economic analyses—up to larger scales—are gathered from the literature that analyze the potential of green diesel as a substitute for petrodiesel. In addition, current industrial processes for green diesel production are introduced. Future research and development efforts should concern catalysts and the use of waste biomasses as feedstock, as well as the arrangement of national and international policies.
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