Serious environmental concerns regarding the use of fossil-based fuels have raised awareness regarding the necessity of alternative clean fuels and energy carriers. Biodiesel is considered a clean, biodegradable, and non-toxic diesel substitute produced via the transesterification of triglycerides with an alcohol in the presence of a proper catalyst. After initial separation of the by-product (glycerol), the crude biodiesel needs to be purified to meet the standard specifications prior to marketing. The presence of impurities in the biodiesel not only significantly affects its engine performance but also complicates its handling and storage. Therefore, biodiesel purification is an essential step prior to marketing. Biodiesel purification methods can be classified based on the nature of the process into equilibrium-based, affinity-based, membrane-based, reaction-based, and solid-liquid separation processes. The main adverse properties of biodiesel – namely moisture absorption, corrosiveness, and high viscosity – primarily arise from the presence of oxygen. To address these issues, several upgrading techniques have been proposed, among which catalytic (hydro)deoxygenation using conventional hydrotreating catalysts, supported metallic materials, and most recently transition metals in various forms appear promising. Nevertheless, catalyst deactivation (via coking) and/or inadequacy of product yields necessitate further research. This paper provides a comprehensive overview on the techniques and methods used for biodiesel purification and upgrading.

Dimethyl ether (DME) is a promising multisource and multipurpose clean fuel and value-added chemical synthesized from syngas. This process can be either performed in a single stage (direct...

Supercritical fractionation of lignocellulosic biomass enhances the production of lignin-derived hydrocarbons and boosts the digestibility of the cellulose-rich pulp.

The integration of microbial and electrochemical conversions in hybrid processes broadens the portfolio of products accessible from biomass. For instance, sugars and lignin monomers can be biologically converted to cis,cis-muconic acid (ccMA), a bioprivileged intermediate, and further electrochemically upgraded to trans-3-hexenedioic acid (t3HDA). This novel monounsaturated monomer is gaining increasing attention as it can substitute adipic acid in Nylon 6,6 to introduce desired properties and yield polyamides with performance advantages. The implementation of t3HDA for advanced polymer production is, however, hampered by the low productivities achieved to date, in the order of milligrams per hour per cm². Here, we report on new synergies between microbial and electrochemical conversions and present a simple strategy to enhance the productivity of t3HDA by over 50 times. Specifically, we show that the broth composition has a dramatic role on the subsequent electrochemical step. Broth with neutral pH and high ccMA titer obtained from bacteria was found to enhance the electrochemical hydrogenation while impeding the parasitic hydrogen evolution reaction. As a result, high productivities were achieved under industrially-relevant current densities (200–400 mA cm⁻²). The effect of other parameters that are key for scale up and continuous operation, namely reactor configuration, potentiostatic/galvanostatic operation mode, and cathode material are also discussed. The experimental results served as input parameters for a detailed technoeconomic analysis and the blueprint of a hybrid microbial electrosynthesis process for t3HDA production.