Victor Haber Perez

The growing global demand for sustainable biotechnological routes for bioenergy production has paved the way for Brazil to position itself as a strategic leader due to its vast agricultural production and, consequently, agricultural residues, among which rice husk stands out. Although rice husk is widely used for energy cogeneration, its potential for producing high-value platform chemicals remains underexplored. This study aims to evaluate the production of value-added pyrolytic derivatives from rice husk by investigating the synergy between acid pretreatments and fast pyrolysis temperatures (350–600 °C). Thus, the experimental strategy involved intensifying the production of target compounds in the condensable fraction (bio-oil) from pyrolysis gases using different biomass pretreatments before fast pyrolysis according to the following conditions: (i) acid washing using acetic acid (10%), (ii) acid washing using nitric acid (0.1%) followed by impregnation using sulfuric acid (0.1–0.3%), and (iii) impregnation using sulfuric acid alone (0.1–0.3%). Fast pyrolysis was carried out over a temperature range of 350–600 °C using a pyroprobe microreactor coupled to a mass spectrometer (GC/MS). The best results, regarding overall volatile fraction, were observed when impregnation with 0.3% sulfuric acid was used prior to pyrolysis at 600 °C, resulting in around an 8.88-fold increase compared with untreated biomass. Nevertheless, the experimental conditions that favored the formation of our main chemical targets, such as levoglucosan, furfural and some phenols, were different. For instance, levoglucosan, furfural and eugenol increased by 21-, 10- and 22-fold, respectively, for biomass treated with HNO₃ (0.1%)/H₂SO₄ (0.2%) at 450 °C, whereas phenol and 4-vinylphenol increased by 35- and 14-fold at 500 °C. These findings can be considered satisfactory, highlighting the potential of the thermochemical conversion process as a valuable tool for the production of high-value chemicals from agricultural waste like rice husk.

The novelty of this study lies in the integration of fermentation in a magnetically stabilized fluidized bed bioreactor with S. cerevisiae supported on calcium alginate with magnetic particles and using levoglucosan, a pyrolytic sugar from sugarcane bagasse, as a substrate for bioethanol production. Sugarcane bagasse was pretreated with acetic acid to remove alkali/alkaline earth metals (AAEMs) aiming to intensify levoglucosan production in the bio-oil prior pyrolysis at 400 °C in an Auger reactor. Subsequently, the levoglucosan extracted from the bio-oil was hydrolyzed with H₂SO₄ and partially detoxified to use the resulting extract as substrate. Fermentations were carried out in the bioreactor operating in magnetically stabilized bed mode with axial magnetic field lines at 12 kA/m. The fermentation kinetics were monitored by substrate consumption and ethanol production over 8h under anaerobic conditions. When glucose was used as substrate (control experiments), the results revealed that the magnetic field induced a higher sugar consumption rate and bioethanol productivity of 5.8 gL ⁻¹ h ⁻¹ , achieving a fermentative efficiency of 97.44%, since the fermentation time was reduced by approximately 2h compared to fermentations without the application of a magnetic field. However, when hydrolyzed levoglucosan extract was evaluated, the fermentative efficiency was 91.57%, approximately 6.5% lower when compared to the control experiment. This could occur due to the presence in the fermentation medium of traces of pyrolytic derivatives, which are known inhibitors of cellular activity. Furthermore, the stimulatory effect of the magnetic field on process productivity is consistent with data previously reported in studies with yeast cells during alcoholic fermentations, thus corroborating the potential of this technology as an alternative process for bioethanol production on a bench scale.

Levoglucosan is an anhydrosugar from biomass that has important applications as a platform for obtaining many value-added derivatives with high demand in the chemical industry and bioproducts by fermentation, including biofuels, among others. Thus, the experimental strategy was to intensify the levoglucosan production in the condensable fraction (bio-oil) from pyrolysis gases using different biomass pretreatments before fast pyrolysis according to the following conditions: (a) biomass washing with 10% acetic acid; (b) biomass washing with 0.1% HNO₃, followed by impregnation with 0.1% H₂SO₄; and (c) biomass impregnation with 0.1% H₂SO₄. The pyrolysis was carried out in a pyroprobe reactor, coupled to GC/MS to verify the progress of the chemicals formed at 400, 500, and 600 °C. Although levoglucosan was the main target, the programs showed more than 200 pyrolytic compounds of which more than 40 were identified, including organic acids, ketones, aldehydes, furans, and phenols. Then, principal component analysis (PCA) allowed for the discrimination of the simultaneous effect of biomass acid treatment and pyrolysis temperature on the formation of the pyrolytic products. All treated biomasses with acids resulted in a levoglucosan yield increase, but the best result was achieved with acetic acid at 500 °C which resulted from 7-fold higher levoglucosan production with changes in the profiles by-products formed concerning untreated biomass. This result was attributed to the alkali and alkaline earth metals reduction and partial removal of lignin content and extractives by acid washing, increasing the cellulose and hemicellulose relative content in the treated biomass. This hypothesis was also confirmed by scanning electron microscope (SEM) and Fourier transform infrared (FTIR) qualitative analysis. Thus, the results achieved in this work show the potential of this biomass for levoglucosan production and other pyrolytic products, thereby being able to mitigate the environmental impact of this agricultural residue and contribute to the development of the coffee agro-industrial chain and the production of bioenergy from lignocellulosic biomass.

A novel magnetic catalyst with hollow cylinder shape based on K₂CO₃/γ-Al₂O₃/Sepiolite/CoFe₂O₄ was prepared to convert macroalgae oil (Fucus vesiculosus) into biodiesel in an unconventional reactor assisted by magnetic field. Catalysts were formulated by the extrusion and characterized satisfactorily by physicochemical (mechanical strength, XRD, TG/DTG, FTIR and TPD-CO₂), magnetic (VSM and EPR), morphological (SEM) and textural properties (BET). While their catalytic performance was also evaluated at 70 °C, oil: ethanol molar ratio 1:12 and 6 wt.% of catalyst using two different reaction systems for comparative purposes: (a) conventional stirred reactor and (b) fluidized bed reactor assisted by a magnetic field. The attained biodiesel presents properties in accordance with the standard limits (ASTM and EN) and total conversion (>99%) was observed in both cases after 2 h of reaction without significant differences between the two reactors. However, the magnetic properties of these catalysts allowed stabilization of the bed under a magnetic field and easy magnetic catalyst separation/recovery at the reaction end, showing their great potential for biodiesel production with regard to conventional process and thus, transforming it into a more sustainable technology.