Aqueous phase reforming of lignin-rich hydrothermal liquefaction by-products: A study on catalyst deactivation

Valorisation of the residual aqueous phase from hydrothermally liquefied black liquor by persulphate-based advanced oxidation

Hydrothermal liquefaction of Kraft black liquor is a promising method for the production of valuable organic chemicals. However, the separation of the biochar and biocrude leaves a residual aqueous phase in large volumes, which needs to be properly managed to make the process profitable. In this work, the persulphate-based advanced oxidation was assessed, for the first time ever, as a pretreatment of this aqueous phase to reduce its content of phenolic compounds and alcohols, which hinder further valorisation strategies. Results revealed that the phenolic compounds and the alcohols were oxidised in presence of low persulphate anion concentrations (<50 mM), mainly to quinone-like compounds and organic acids. At higher oxidant concentrations, these intermediates were subsequently oxidised to valuable acetic acid. When Fe (II) was added as the catalyst, low concentrations (<9 mM) enhanced the degradation of both phenolic compounds and alcohols due to the increase of the sulphate radicals, consequently reducing persulphate requirements for their removal. Nevertheless, higher Fe (II) doses produced the sequestration of sulphate radicals, thus decreasing the oxidation performance and generating undesired parallel reactions.

Hydrothermal conversion of biomass to fuels, chemicals and materials: A review holistically connecting product properties and marketable applications

Biomass is a renewable and carbon-neutral resource with good features for producing biofuels, biochemicals, and biomaterials. Among the different technologies developed to date to convert biomass into such commodities, hydrothermal conversion (HC) is a very appealing and sustainable option, affording marketable gaseous (primarily containing H₂, CO, CH₄, and CO₂), liquid (biofuels, aqueous phase carbohydrates, and inorganics), and solid products (energy-dense biofuels (up to 30 MJ/kg) with excellent functionality and strength). Given these prospects, this publication first-time puts together essential information on the HC of lignocellulosic and algal biomasses covering all the steps involved. Particularly, this work reports and comments on the most important properties (e.g., physiochemical and fuel properties) of all these products from a holistic and practical perspective. It also gathers vital information addressing selecting and using different downstream/upgrading processes to convert HC reaction products into marketable biofuels (HHV up to 46 MJ/kg), biochemicals (yield >90 %), and biomaterials (great functionality and surface area up to 3600 m²/g). As a result of this practical vision, this work not only comments on and summarizes the most important properties of these products but also analyzes and discusses present and future applications, establishing an invaluable link between product properties and market needs to push HC technologies transition from the laboratory to the industry. Such a practical and pioneering approach paves the way for the future development, commercialization and industrialization of HC technologies to develop holistic and zero-waste biorefinery processes.

Biomass Novel Adsorbents for Phenol and Mercury Removal

This paper reports the use of activated carbons made from novel agriculture and industrial wastes, namely sunflower, vine shoots, and coffee endocarp, to remove two high-priority contaminants: phenol and mercury species (under different forms) from aqueous solutions. The activated carbons were used as prepared and also modified with nitric acid and triethylenediamine in order to explore additional adsorption mechanisms. The results showed an interesting potential of the materials to be used for water decontamination as indicated by the mercury uptake up to 1104 mg/g for Hg2+, 771 mg/g for [HgCl4]2-, 966 mg/g for HgCl2 and the maximum phenol adsorption capacity of 190 mg/g. The modification with triethylenediamine led to a significant increase in the phenol and mercury adsorption reaching an increment of 85% for phenol and 250% for Hg2+.

Bio-Crude Production through Recycling of Pretreated Aqueous Phase via Activated Carbon

The management and optimization of the aqueous phase are the major challenges that hinder the promotion of hydrothermal liquefaction (HTL) technology on a commercial scale. Recently, many studies reported about the accumulation of the N-content in the bio-crude with continuous recycling of the aqueous phase from high protein-containing biomass. In the present study, sewage sludge was processed at 350 °C in an autoclave. The produced aqueous phase was treated with activated carbon, and its subsequent recycling effect on the properties of the bio-crude and aqueous phase was investigated. By contacting the aqueous phase with activated carbon, 38–43% of the total nitrogen was removed from the aqueous phase. After applying the treated aqueous phase recycling, the energy recovery of the bio-crude increased from 50 to 61% after three rounds of recycling. From overall carbon/nitrogen recoveries, 50 to 56% of the carbon was transferred to the bio-crude phase and more than 50% of the nitrogen remained in the aqueous phase. The aqueous phase contained mostly of N&O-heterocyclic compounds, small chain organic acids, and amides. ICP-AES analysis showed that more than 80% of the inorganic elements were concentrated into the solid phase.