Tuning Lignin Characteristics by Fractionation: A Versatile Approach Based on Solvent Extraction and Membrane-Assisted Ultrafiltration

Abstract

Technical lignins, typically obtained from the biorefining of lignocellulosic raw materials, represent a highly abundant natural aromatic feedstock with high potential in a sustainable economy scenario, especially considering the huge primary production volumes and the inherently renewable nature of this resource. One of the main drawbacks in their full exploitation is their high variability and heterogeneity in terms of chemical composition and molecular weight distribution. Within this context, the availability of effective and robust fractionation processes represents a key requirement for the effective valorization of lignin. In the present work, a multistep fractionation of two different well known technical lignins obtained from two distinct delignification processes (soda vs. kraft pulping) was described. A comprehensive approach combining solvent extraction in organic or aqueous medium with membrane-assisted ultrafiltration was developed in order to maximize the process versatility. The obtained lignin fractions were thoroughly characterized in terms of their chemical, physical, thermal, and structural properties, highlighting the ability of the proposed approach to deliver consistent and reproducible fractions of well-controlled and predictable characteristics, irrespective of their biomass origin. The results of this study demonstrate the versatility and the reliability of this integrated multistep fractionation method, which can be easily adapted to different solvent media using the same ultrafiltration membrane set up, thereby enhancing the potential applicability of this approach in an industrial scale-up perspective for a large variety of starting raw lignins.

Fractionation of Raw and Parboiled Rice Husks with Deep Eutectic Solvents and Characterization of the Extracted Lignins towards a Circular Economy Perspective

“…Lignins derived from the complete fractionation process (using DES 2) of both raw and parboiled rice husks (rRH-Lignin and pRH-Lignin, respectively) were subjected to an extensive characterization to evaluate their properties and potential differences. A well-known commercial soda lignin (Protobind 1000, indicated from now on as Protobind) was used as the reference [44].…”

Preparation and Characterization of Size-Controlled Lignin Nanoparticles with Deep Eutectic Solvents by Nanoprecipitation

“…Lignin is the second most abundant natural biopolymer after cellulose and constitutes one of the major aromatic polymer resources available to mankind [ 1 , 2 ]. Its sustainability and biodegradability coupled with rich functional groups aid significantly in the design and development of a variety of products, e.g., micro- to nano-carriers of bioactive compounds [ 3 , 4 ]. Its limited solubility, however, in organic solvents along with heterogeneous characteristics and random microstructure preclude the downstream processing and valorization [ 5 ].…”

Use of sodium alginate biopolymer as an extracting agent of methylene blue in the polymer‐enhanced ultrafiltration technique

“…18 It is easy to implement, and it realizes high removal efficiency, low energetic cost, high availability of soluble polymers and low environmental impact. 16,19,20 The PEUF technique consists of the interaction of a functional water-soluble polymer (WSP) with low molecular weight species (e.g., heavy metals and dissolved organic compounds). 16,[21][22][23][24][25] For use in PEUF, a WSP must satisfy three general requirements: high content of functional groups that can interact with the contaminating species (such as amino, carboxylic and sulfonic acid groups), sufficient solubility in aqueous solutions and a higher molecular weight than the molecular weight cut-off (MWCO) of the ultrafiltration membranes.…”