Assessment and comparison of thermochemical pathways for the rice residues valorization: pyrolysis and gasification.

Lignocellulosic biomass conversion applying thermochemical routes has been postulated as an alternative for generating renewable energy. This research compares energy-driven biorefineries based on two thermochemical routes addressed to upgrade rice husk and rice straw produced in the Department of Sucre-Colombia. Initially, this research analyzes the physico-chemical and structural characterization of the rice residues. Four different scenarios were proposed to compare the energy-driven biorefineries based on fast pyrolysis and gasification considering technical, economic, and environmental metrics. These biorefineries were simulated using the Aspen Plus V.14.0 software. The novelty of this research is focused on the identification of the biorefinery with the best techno-economic, energetic, and environmental performance in the Colombian context. Economic and environmental analyses were done by using economic metrics and emissions. From an economic perspective, the stand-alone gasification process did not have a positive economic margin. In contrast, the fast pyrolysis process has the best economic performance since this process has a positive profit margin. Indeed, scenario 1 (fast pyrolysis of both rice residues) presented an economic margin of 13.75% and emissions of 2170.92 kgCO2eq/kg for 10 years. However, this scenario was not energetically the best, holding second place due to the feedstock requirements, compared to gasification. The biorefinery scenario 1 has the best performance.

Fast pyrolysis as a tool for obtaining levoglucosan after pretreatment of biomass with niobium catalysts.

Levoglucosan (LGA) is a promising chemical platform derived from the pyrolysis of biomass that offers access to a variety of value-added products. We report an efficient route to produce LGA via the pretreatment of biomass with niobium compounds (oxalate, chloride and oxide) followed by fast pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC-MS) at temperatures of 350-600 °C. Catalytic pretreatment reduces the quantity of lignin in the biomass, concentrates the cellulose and enhance LGA formation during fast pyrolysis. The pretreatment also removes alkaline metals, preventing competitive side reactions. The effect of several parameters such as catalyst weight, time, temperature, and solvent, with the optimal pretreatment conditions determined to be 3 (wt.%) niobium oxalate for 1 h at 23 °C in water. Pretreatment increased the LGA yields by 6.40-fold for sugarcane bagasse, 4.15-fold for elephant grass, 4.13-fold for rice husk, 2.86-fold for coffee husk, and 1.86-fold for coconut husk as compared to the raw biomasses. These results indicate that biomass pretreatment using niobium derivates prior fast pyrolysis can be a promising technique for biomass thermochemical conversion in LGA and others important pyrolytic products.

Sustainability assessment of water hyacinth fast pyrolysis in the Upper Paraguay River basin, Brazil.

Fast pyrolysis of naturally produced water hyacinth was assessed through Emergy accounting approach. Two analyses were carried out to evaluate the influence of additional services and externalities on Emergy indicators for a pyrolysis plant unit able to process 1000 kg of dry biomass per hour. The initial approach was a traditional Emergy assessment in which financial fluxes and externalities were not considered. The second approach included taxes and fees of the Brazilian government, interests related to financing operations and assumes a reserve financial fund of 5% of the total investment as externalities cost. For the first evaluation, the renewability of 86% indicates that local and renewable resources mainly support the process and the Emergy Yield Ratio of 3.2 shows that the system has a potential contribution to the regional economy due to the local resources use. The inclusion of financial fluxes and externalities in the second evaluation reduces both renewability and Emergy Yield Ratio, whereas it increases the Emergy Investment Ratio which means a higher dependence on external resources. The second analysis allows portraying significant forces of the industrial and financial systems and the evaluation of the externalities' impact on the general system Emergy behavior. A comparison of the renewability of water hyacinth fast pyrolysis with other biofuels like soybean biodiesel and sugarcane ethanol indicates that the former is less dependent on fossil fuel resources, machinery and fertilizers. To complement the sustainability assessment provided by the Emergy method, a regular financial analysis for the second defined system was done. It shows that the system is financially attractive even with the accounting of additional costs. The results obtained in this study could be used as the maximum and minimum thresholds to subsidize regulatory policies for new economic activities in tropical wetlands involving natural resources exploitation and bio-industrial systems.