Development of pretreatment processes with ionic liquids and deep eutectic solvents for the valorization of rice straw into biobutanol
- Autores: Helena Poy Andreu
- Directores de la Tesis: Carmen Gabaldón García (dir. tes.), Sonia Loras Gimenez (codir. tes.), Estela Lladosa lópez (codir. tes.)
- Lectura: En la Universitat de València ( España ) en 2024
- Idioma: inglés
- Número de páginas: 462
- Tribunal Calificador de la Tesis: F. J. Álvarez-Hornos (presid.), Aloia Romaní Pérez (secret.), Carlos Martín Medina (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Química, Ambiental y de Procesos por la Universitat de València (Estudi General)
- Materias:
- Enlaces
- Tesis en acceso abierto en: RODERIC
- Resumen
One of the main strategies in the fight against climate change lies in the decarbonization of society, promoting the transition to an economy based on the exploitation of renewable resources. In this context, the use of lignocellulosic wastes is gaining importance due to their high availability and low cost. The major challenge in the valorization of these wastes resides in their recalcitrant nature that hinders their conversion, thus requiring a pretreatment step to fractionate their main components (polysaccharides and lignin) and enable their efficient processing. However, the conventional pretreatments often involve the use of harmful reagents and severe operational conditions, compromising the sustainability of the process. Among the alternative methods proposed, the use of ionic liquids (ILs) and deep eutectic solvents (DES) has recently been praised for their remarkable properties, highlighting their low volatility and tunability.
The general aim of this doctoral thesis is the development of alternative fractionation approaches, based on the use of ILs and DES, for the pretreatment of rice straw. Particularly, this doctoral thesis deals with the valorization of the polysaccharides contained in rice straw through enzymatic hydrolysis, as well as the further acetone-ethanol-butanol (ABE) fermentation for the production of biobutanol as proof of concept. The selection of rice straw as feedstock is based on the environmental threat posed by its current management practices, as well as the abundance of the cereal in the Valencian region, which concentrates the 15% of the Spanish rice production in the Albufera Natural Park (Valencia, Spain).
In the case of the study of the pretreatment of rice straw with ILs, an aprotic IL (AIL) based on the acetate anion (1-ethyl-3-methylimidazolium acetate) as well as two families of protic ILs (PILs) based on acetate and hydrogen sulfate anions were used. Both AIL and acetate-based PILs showed high selectivity for extracting lignin from rice straw without significantly affecting the sugar fraction. Particularly, the PIL composed of ethanolamine and acetic acid (2-hydroxyethylammonium acetate) provided excellent selectivity for extracting lignin from rice straw (98%) along with the preservation of 90% of the polysaccharides. Consequently, after pretreatment with acetate-based ILs, high sugar yields could be obtained in the enzymatic hydrolysis step, even reaching the complete saccharification of the pretreated material (98% saccharification yield). In contrast, the high acidity of hydrogen sulfate-based PILs promoted the degradation of a significant portion of the polysaccharides present in rice straw, leading to reduced saccharification yields.
The pretreatment of rice straw with DES was evaluated using two families of these solvents based on lactic acid (LA) and p-toluenesulfonic acid (pTSA). Among the formulations studied, the use of the DES composed of cholinium chloride, LA and ethylene glycol (ChCl:LA:EG) provided excellent saccharification of both glucan (89% saccharification yield) and xylan (54% saccharification yield), despite the lower degree of delignification obtained (39%) compared to other pretreatment approaches developed. In this sense, it was shown that, in the case of rice straw, the preservation of polysaccharides after efficient disruption of the material plays a key role in maximizing their subsequent saccharification, while high delignification degrees are not required for this purpose.
In terms of biobutanol production, the selected PIL and DES pretreatments were postulated as alternative approaches as effective as conventional pretreatments, resulting in similar or even higher butanol yields (75.0-95.6 g butanol/kg rice straw). In addition, the recyclability of the selected PILs and DES was evaluated, demonstrating the suitability of these solvents in the biorefinery framework. In this regard, pretreatment with PIL showed similar performances in terms of saccharification and butanol production after six uses, while DES showed good recyclability in terms of saccharification after three uses. Finally, it was shown the possibility of reducing the energy consumption by integrating microwave irradiation in DES pretreatment from 62 to 17 kJ/g biomass, demonstrating the potential of using this technology in the search for cost-effective pretreatments.
