SeaSolv: Multi-product biorefinery of seaweed using green solvents

Background

Deep eutectic solvents (DES), being cost-effective solvents, have attracted increasing attention in both academia and industry in recent years. Bringing together mixtures of hydrogen-bond donor(s) (HBD), such as an amide, an alcohol or a carboxylic acid and hydrogen-bond acceptor(s) (HBA) such as an ionic component with an anion like Chloride, DESs are formed, and such mixtures show substantially high melting-point depression upon mixing.

DES are produced from low cost and natural sources, together with their almost null toxicity and high biodegradability make them suitable solvents for wide range of applications such as organic synthesis, catalysis, biocatalysis, biodiesel transformation, electrochemistry, batteries and capacitors, (nano)materials and pharmaceutical.

Recently, DESs have been applied as extraction solvents for biological compounds. They have been a potential alternative to replace conventional organic solvents for the extraction of interesting metabolites (flavonoids, proteins, lipids, and polysaccharides) from different biomass such as plants, microalgae, and lignocellulosic biomass. Nevertheless, the extraction process is affected by several factors: affinity between DES and the target compounds, the water content, the mole ratio between DES’ starting molecules and their physico-chemical characteristics (polarity, viscosity, conductivity), the liquid/solid ratio between the DES and sample, and the conditions and extraction method. Moreover, the use of eutectic solvents still faces several challenges, such as difficult product recovery and solvent regeneration. This is mainly because these solvents have low volatility.

In the typical organic solvent process, these two processes were done via distillation and solvent condensation. However, applying distillation to eutectic solvents would require a tremendous amount of energy. Therefore, one of the most promising techniques is switching the solvent hydrophobicity, which approach was inspired by switchable solvents have reported the use of a switchable-hydrophilicity eutectic solvent system. When this solvent is mixed with an aqueous solution, they form hydrophilic ionic liquid made of a protonated amine and deprotonated acid (forward switching). Then, CO2 or acid could be used to protonate back the acid, thus, obtaining the hydrophobic eutectic solvent (backward switching).

With this system, both hydrophilic and hydrophobic biomolecules can be extracted and separated. However, this approach involved two additional compounds (the amine and carbon dioxide or acid) which later need to be removed further downstream. 

SeaSolv proposes another approach to tune the hydrophobicity of a semi-hydrophobic solvent, consisting of hydrophilic and hydrophobic compounds. With this approach, the eutectic solvent can have a spectrum of hydrophobicity, depending on the composition of the parental compounds. Hence, at the hydrophobic state, the solvent can be used to dissolve hydrophobic solutes, such as lipids for example. Afterwards, the lipid can be recovered by adding an excess of the hydrophilic parental compound, making the overall solvent hydrophilic. The approach will be applied to macroalgal biomass. 

Project description

The proposed research has the overall goal of developing a cost effective, environmentally and scalable multi-product biorefinery for the extraction of high-value products from seaweeds using Deep Eutectic Solvents (DES) from plant-based metabolites.

The research questions we plan to answer with the proposed project: 

1. What is the appropriate choice of DES mixture and their operating parameters for highest products yield?
2. What are the physicochemical properties of DES that may affect the extraction efficiency and give major impact on the interaction between DES and target compounds?
3. What is the effect of seaweeds pretreatments and storage on the extraction efficiency? Does silage or drying impact the biomass composition thus the product extractability and functionality?
4. How can we recover multi-products? Can switchable DES be an option or additional techniques are necessary?
5. How can we recycle DES in a sustainable way without affecting the overall economic and environmental feasibility?
6. What is the quality of seaweed products, recovered after DES extraction, with respect to desired properties (e.g. solubility, gelation, foaming)?
7. Is the process with DES economically attractive compared to current seaweed processing?
8. Are we able to recover all the products from seaweed without generating waste?

The research questions above will be answered within 6 Work Packages. Two PhDs will be appointed with the collaboration of Algaia, Kelp Blue, Hortimare and PATh_UAVR.

Throughout the project, we will focus on three macroalgae species provided by the three companies: Saccharina latissima, Laminaria digitata and Macrocystis pyrifera. These are brown macroalgae with the most abundant and representative pigment being fucoxanthin. Their cell wall consists of several components with alginates being its main ingredient (up to 40%). Proteins are present in these seaweeds with a content of 8-15% of the total biomass dry weight.

On the one hand, considering all factors influencing the biomass content, i.e. harvesting stage and storage, the process will be developed and optimized to obtain the highest products yield. This will be followed by a techno-economic evaluation and a life cycle assessment. On the other hand, we will focus on the physicochemical properties of Deep Eutectic Solvents, how they interact with the desired compound (in this project the focus is on alginates, proteins and lipids) and the way to regenerate them.