Carolina Mónica Mendieta

The production of second-generation bioethanol from lignocellulosic biomass requires efficient enzymatic hydrolysis and fermentation processes that remain effective at industrially relevant solids loadings. In this study, bleached Pinus taeda kraft pulp was evaluated as a model substrate for bioethanol production at bench scale (4 L reactor) under high-consistency conditions (12.5–13.9% solids). Three process configurations were compared: separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), and pre-hydrolysis followed by simultaneous saccharification and fermentation (pSSF). Enzymatic hydrolysis in the SHF and SSF configurations stabilized between 54% and 58%, indicating that hydrolysis was the main process bottleneck under the evaluated conditions. In contrast, Saccharomyces cerevisiae efficiently fermented the available glucose, achieving nearly complete conversion of glucose. Among the evaluated strategies, pSSF showed the highest ethanol yield and volumetric productivity, achieving an ethanol yield of 61.8% and a productivity of 0.61 g L⁻¹ h⁻¹. While laboratory-scale SSF experiments conducted at 2% solids achieved complete conversion, the ethanol yield decreased to approximately 58% at the bench scale, highlighting the impact of high-solids operation on process performance. The lower performance observed at high solids may be associated with factors commonly reported during scale-up, including increased slurry viscosity, reduced mixing efficiency, limited enzyme accessibility, and mass-transfer constraints. Overall, the results manifest the need to enhance hydrolysis performance through improved reactor design, more effective mixing strategies, and optimized high-solids processing to facilitate the scale-up of lignocellulosic bioethanol production.

Producing second-generation (2G) bioethylene through the dehydration of 2G bioethanol is a challenge, requiring the effective use of catalysts as an alternative to fossil-based ethylene production. This work evaluates the production of bioethylene from the catalytic dehydration of 2G bioethanol [from pine sawdust produced via a simultaneous saccharification and fermentation SSF process (53%)] using γ-Al2O3; ZSM-5, NH₄⁺Y, H-ZSM-5, and H-Y zeolite as catalysts. Yields of 94.6% (at 372 °C) and 85.5% (at 473 °C) of 2G bioethylene were obtained when using H-ZSM-5 and H-Y zeolite, respectively. These results demonstrate that the H-ZSM-5 zeolite showed the best performance for 2G bioethanol dehydration, producing high 2G bioethanol conversion and 2G bioethylene selectivity at a lower reaction temperature. Ethylene production from the catalytic dehydration of commercial (96%) and diluted (53%) ethanol was evaluated as a reference, along with the effects of the weight hourly space velocity (WHSV) and ethanol concentration. Varying the WHSV from 2.37 to 4.73 h⁻¹ at 312 °C and using commercial ethanol at 96%, produced similar ethanol conversion of 100% and ethylene yield of 100%. At 290 °C, with a WHSV of 2.37 h⁻¹ and 53% diluted commercial ethanol, H-ZSM-5 converted 76.83% of the ethanol and produced a 75.8% ethylene yield. A study based on density functional theory (DFT) has shown that diethyl ether is a key intermediate in the conversion mechanism on H-ZSM-5, proceeding through an ethoxide intermediate in the rate-determining step, with an apparent activation energy of 25.4 kcal mol⁻¹.

There is a global trend to replace the production of conventional recyclable plastics with biobased ones, allowing a sustainable alternative adapted to the current concept of a circular bioeconomy. Forest-industrial and agricultural biomass wastes (lignocellulosic biomass waste, LCBW) produce severe problems in some developing countries because they are improperly disposed of or burned in the open air. Such wastes are attractive as a raw material to produce bioplastics due to their low cost. Furthermore, low-pollution processes can complete an economical and environmentally friendly approach. This review focuses on bio-polyethylene furanoate (PEF) production from LCBW as an alternative for polyethylene terephthalate (PET), one of the most widely used fossil-based plastic. The standpoint is based on the replacement of fossil-based monomers for the manufacture of PET, terephthalic acid (TPA), and ethylene glycol by two bio-based monomers, namely 2,5-furandicarboxylic acid (FDCA) and bio-ethylene glycol (Bio-MEG). This study describes the processes to obtain each bio-monomer, as well as the resulting polymers’ performance aspects, biodegradability, environmental and economic considerations, and recycling.

The decline in world oil reserves evidences the need to diversify the sources of equivalent raw materials. The use of biomass is one of the most explored alternatives. This work evaluates the second-generation bioethanol (2G) production from a pine sawdust soda- ethanol pulp by simultaneous hydrolysis and fermentation (SSF) to obtain the best conditions for scaling up the process. Experimental designs have been used to find mathematical models that define the complex situation jointly varying time with other variables (enzyme load and temperature). Time periods in the full model varied from 0 h to 72 h. Given the results (curve shape differences), it was decided to split the design in two, covering periods from 0 h to 24 h (Model I) and from 24 to 72 h (Model II). The pulp chemical composition was 80.2% glucans, 7.2% xylans, 0.3% galactans, 8.4% mannans, 3.7% lignin. Cellic^® Ctec2 cellulolytic enzymes were used for saccharification and Saccharomyces cerevisiae IMR 1181 (SC 1181) yeast for fermentation. The best conditions found in the two designs were 30 FPU g⁻¹ glucans, 39 °C, 24 h for Model I, and 30 FPU g⁻¹ glucans, 35 °C, 72 h for Model II. Fermentation optimal values were 63.23 and 81.93 for Models I and II, respectively.

Bio-based ethylene produced by bioethanol dehydration is an environmentally friendly substitute for oil-based ethylene. It is a low-pollution raw material that can be used to produce high-value bio-based materials. Currently, some industrial plants use first-generation (1G) bioethanol to produce bio-ethylene. However, second-generation (2G) bioethanol is not currently used to produce bio-ethylene because the manufacturing processes are not optimized. The conversion of lignocellulosic biomass to bio-ethylene involves pretreatment, enzymatic hydrolysis of carbohydrates, the fermentation of sugars to ethanol, ethanol recovery by distillation, and ethanol dehydration to ethylene. This work presents a review of second-generation (2G) bio-ethylene production, analyzing the stages of the process, possible derivatives, uses, and applications. This review also contains technical, economic, and environmental considerations in the possible installation of a biorefinery in the northeast region of Argentina (NEA).

Sustainable development is the common goal of the current concepts of bioeconomy and circular economy. In this sense, the biorefineries platforms are a strategic factor to increase the bioeconomy in the economic balance. The incorporation of renewable sources to produce fuels, chemicals, and energy, includes sustainability, reduction of greenhouse gases (GHG), and creating more manufacturing jobs fostering the advancement of regional and social systems by implementing the comprehensive use of available biomass, due to its low costs and high availability. This paper describes the emerging biorefinery strategies to produce fuels (bio-ethanol and γ-valerolactone) and energy (pellets and steam), compared with the currently established biorefineries designed for fuels, pellets, and steam. The focus is on the state of the art of biofuels and energy production and environmental factors, as well as a discussion about the main conversion technologies, production strategies, and barriers. Through the implementation of biorefineries platforms and the evaluation of low environmental impact technologies and processes, new sustainable production strategies for biofuels and energy can be established, making these biobased industries into more competitive alternatives, and improving the economy of the current value chains.