Sustainable Microwave-Assisted Aerobic Oxidation of Tomato Plant Waste into Bioaromatics and Organic Acids

Abstract

Lignin is the second most abundant polymer in lignocellulosic biomass. A biorefinery approach to lignin valorisation, as an alternative to the use of heating, can produce bioaromatics, and this idea is attracting ever more interest. However, the isolation of lignin for further processing is really quite challenging, making the valorisation of native lignin (i.e., lignin in raw biomass) crucially important. An analysis of vanillin yields in relation to total reaction feedstock weight shows that the economic viability of the process depends on the valorisation of all biomass components. This paper reports a microwave-assisted, catalyst-free aerobic oxidation process for biomass. The protocol yields bioaromatics (mainly vanillin and syringaldehyde, with traces of p-hydroxybenzaldehyde and acetovanillone) and organic acids (38.4 wt % maximum total yield) in only 30 min. Vanillin is the most valuable of the aromatic compounds to be produced by lignin oxidation, accounting for 8.7 wt % of the initial lignin. The use of biomass as the starting material means that no pretreatment is needed for component separation. Furthermore, the use of air as the oxidant and the catalyst-free nature of the protocol render the process environmentally sustainable and scalable, as the energy consumption is counterbalanced by the clean production of high market value products.

Technology and Process Design for Phenols Recovery from Industrial Chicory (Chicorium intybus) Leftovers

“…This fact combined to the negative cost of chicory leftovers, the use of water as solvent and the consequent reduction of industrial by-products make the process here described attractive for the industry. A midsized industrial plant for a MW-assisted batch treatment of tomato waste was presented by Tabasso et al in 2019 [44]. The lab-scale aerobic oxidation of biomass was carried out in the same MW professional reactor (SynthWAVE, Milestone), at a temperature of 170 °C for 30 min.…”

“…The results of our work may become the basis for the future development of the MAE and UAE methods, which are known to be extremely versatile and suitable for easy scale-up design [44,45].…”

Environmental Sustainability Analysis of Case Studies of Agriculture Residue Exploitation

“…Several articles carried out a comparison between traditional products on the market (produced by conventional manufacturing chain, from raw materials different from byproducts) and bio-based alternatives from organic residues, identifying as the most common benefit the use of low value residual biomass available in huge quantities, for example wheat, rice, and maize [16,[20][21][22][23][24]. A common goal of the processes presented by the scientific literature about organic residue exploitation is the green production, meaning low energy consumption and nontoxic agent applications [15,19,23,25].…”

Weak Bonds Joint Effects Catalyze the Cleavage of Strong C−C Bond of Lignin‐Inspired Compounds and Lignin in Air by Ionic Liquids

“…Recent studies have reported microwave-assisted catalyst-free oxidation of lignin in air at elevated temperature (170 or 180°C), and the valuable products like vanillin could be obtained effectively. [6] In spite of the encouraging results, relatively harsh conditions are needed to cleave inert lignin bonds. Obviously, current oxidation of lignin in air is generally associated with metalbased catalysts and/or relatively harsh conditions, where free radicals could be formed to oxidize lignin.…”

“…Hence, the exploration of metal‐free oxidative routes using air as an oxidant is necessary. Recent studies have reported microwave‐assisted catalyst‐free oxidation of lignin in air at elevated temperature (170 or 180 °C), and the valuable products like vanillin could be obtained effectively [6] . In spite of the encouraging results, relatively harsh conditions are needed to cleave inert lignin bonds.…”