Influence of delignification and reaction conditions in the aqueous phase transformation of lignocellulosic biomass to platform molecules

An Innovative, Green Cascade Protocol for Grape Stalk Valorization with Process Intensification Technologies

Valorization of agri-food residues to produce bio-based platform chemicals will enhance the transition to the bio-economy era. To this end, a sustainable process has been developed for the overall valorization of grape stalks (GS) according to a circular approach, starting from the lignin fraction to further deal with the cellulose-rich residue. This non-conventional protocol fully adheres to green chemistry principles, exploiting the so-called enabling technologies—mainly ultrasound and microwaves—for energy-saving innovative processes. Firstly, ultrasound-assisted extraction (UAE, 40 kHz, 200 W) demonstrated to be an excellent technique for GS delignification combined with natural deep eutectic solvents (NaDESs). Delignification enables isolation of the pertinent lignin framework and the potential to obtain a polyphenol-rich liquid fraction, focusing on the valorization of GS as source of bioactive compounds (BACs). Among the NaDESs employed, the combination of choline chloride (ChCl) and levulinic acid (LevA) (ChLevA) presented noteworthy results, enabling a delignification higher than 70%. LevA is one of the top-value biobased platform chemicals. In this work, a flash microwave (MW)-assisted process was subsequently applied to the cellulose-rich fraction remained after delignification, yielding 85% LevA. The regeneration of this starting compound to produce ChLevA can lead to a further biomass delignification cycle, thus developing a new cascade protocol for a full valorization of GS.

Kinetics of Lignin Removal from Rice Husk Using Hydrogen Peroxide and Combined Hydrogen Peroxide–Aqueous Ammonia Pretreatments

The rice husk has the potential to be used for converting agricultural wastes into renewable energy. Therefore, this study aims to improve the hydrolysis of rice husk through Hydrogen Peroxide (HP) and Combined Hydrogen Peroxide–Aqueous Ammonia (CHPA) pretreatments. The removal of lignin from rice husks was determined using SEM–EDS examination of the samples. At a specific concentration of H2O2, (CHPA) pretreatment eliminated a significantly larger amount of lignin from biomass. The percentage of lignin removal of HP varied from 48.25 to 66.50, while CHPA ranged from 72.22 to 85.73. Hence, the use of batch kinetics of lignin removal of both pretreatments is recommended, where the kinetic parameters are determined by fitting the experimental data. Based on the results, the activation energies for HP and CHPA pretreatments were 9.96 and 7.44 kJ/mol, which showed that the24 model is appropriate for the experimental data. The increase in temperatures also led to a higher pretreatment value, indicating their positive correlation. Meanwhile, CHPA pretreatment was subjected to enzymatic hydrolysis of 6% enzyme loading for the production of 6.58 g glucose/L at 25 h.

Fermentative Lactic Acid Production From Lignocellulosic Feedstocks: From Source to Purified Product

The second (lignocellulosic biomass and industrial wastes) and third (algal biomass) generation feedstocks gained substantial interest as a source of various value-added chemicals, produced by fermentation. Lactic acid is a valuable platform chemical with both traditional and newer applications in many industries. The successful fractionation, separation, and hydrolysis of lignocellulosic biomass result in sugars’ rich raw material for lactic acid fermentation. This review paper aims to summarize the investigations and progress in the last 5 years in lactic acid production from inexpensive and renewable resources. Different aspects are discussed—the type of raw materials, pretreatment and detoxification methods, lactic acid-producers (bacteria, fungi, and yeasts), use of genetically manipulated microorganisms, separation techniques, different approaches of process organization, as well as main challenges, and possible solutions for process optimization.