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Benzene, mostly produced from fossil fuel sources, is an essential chemical to many modern industries. Alternatively to non-renewable methods currently used, the present work explores using fast pyrolysis biomass-derived bio-oils to furnish this valuable platform molecule. Notably, we report for the first time the impact of different operational parameters on the highly selective continuous catalytic hydrodeoxygenation of guaiacol, a bio-oil model compound, into benzene using a Mo2C/CNF-based catalyst. The parametric study includes a first evaluation of the effect of the hydrogen pressure (25, 50 and 75 bar), temperature (300, 325 and 350 °C) and weight hourly space velocity (4 and 10 gorg gcat−1 h−1) on the guaiacol conversion and product distribution, and a subsequent long-term evaluation (30 h on stream) of the catalyst under appropriate processing conditions The experimental results revelated that our Mo2C/CNF was able to achieve a conversion of 90–98% with a relative amount of benzene in the liquid product up to 81% for at least 30 h without any sign of deactivation at 75 bar of H2 and 350 °C, which is a landmark achievement in the conversion of bio-oil derived molecules into platform chemicals.

This study explores the co-hydrothermal treatment (co-HTT) of almond hulls and Chlorella Vulgaris using seawater as an alternative HTT medium. The influence of the feedstock (individual biomass and all the possible binary mixtures) was systematically evaluated under different conditions (reaction temperatures and times). The feedstock mixture and hydrothermal conditions significantly influenced the overall product distribution: gas (1–5%), hydrochar (6–56%), biocrude (6–55%), and aqueous fraction (33–52%), along with the most representative physicochemical and fuel properties of these products. Notably, the biocrude had a calorific value of 24–31 MJ/kg, whereas the hydrochar shifted between 3 and 26 MJ/kg. The degradation of abundant polysaccharides in almond hulls produced acidic species, promoting the degradation of proteins to N-containing species in biocrude. The synergies between microalgae and almond hulls favored the deamination of amino acid and repolymerization of formed monomers. Process optimization revealed that the best biocrude production (59% yield and HHV = 28 MJ/kg) was obtained by treating C. Vulgaris at 268 °C for 180 min. Contrarily, the HTT of almond hulls under optimum processing conditions (300 °C and 112 min) also produced an energy-dense biocrude (29 MJ/kg) but with a much lesser yield (16%). However, such a low biocrude production can be synergistically increased up to 33 %, maintaining the HHV (31 MJ/kg), including up to 61 wt% of C.Vulgaris into the feedstock, with a feedstock energy recovery of 75%. Holistically, the co-HTT of 40 wt% C. Vulgaris and 60 wt% almond hulls at 300 °C for 180 min produced energy-dense liquid (23% yield and HHV = 32 MJ/kg) and solid (29% yield and HHV = 25 MJ/kg) biofuels simultaneously, with a feedstock energy recovery of 80%. Given these excellent prospects, this strategy provides timely and new insights into developing synergetic strategies to utilize microalgal and lignocellulosic biomasses more efficiently

The proximate analysis of algae and almond hulls were analyzed by thermogravimetric analysis (ISO-18134:2016, ISO-18122:2016 and ISO-18123:2016). The elemental composition of the feedstocks was determined using an elemental analyzer. The biochemical composition of almond hulls was determined by chemical titration according to Hu et al, whereas biochemical composition was provided by the supplier.-- Table S1: Properties and composition of seawater. Table S2: Characterization results of C. vulgaris and almond hulls. Table S3: Processing conditions and experimental results for the co-HTT of C. vulgaris and almond hulls. Table S4: Relative influence of feedstock composition and processing conditions and interactions based on ANOVA analyses and cause-effect Pareto principle. Table S5: Detailed GC-MS peak area for biocrude (area%). Table S6: Process Optimization: Theoretical values vs. Experimental values.

En un contexto de biorrefinería y desarrollo sostenible, la síntesis de materiales, productos químicos y energía a partir de recursos renovables es una tarea prioritaria. Para asegurar la viabilidad económica y medioambiental de estos procesos, sin embargo, es necesario incluir la recuperación de corrientes secundarias en la estrategia de valorización global. En esta línea, el presente trabajo describe una propuesta de biorrefinería basada en el proceso de defibrilación de celulosa a partir de pericarpios de almendra, en la que varias tecnologías de hidrotratamiento (hidrogenación y desoxigenación) fueron interconectadas con las etapas adecuadas de separación y extracción para la obtención simultánea de azúcares alcohólicos (sorbitol y xilitol) y una fase orgánica útil como fuente adicional de productos químicos y/o energía.

The acid-free hydrothermal microwave–assisted selective scissoring (Hymass concept) of cellulosic substrates is gaining keen interest in the field of materials science. Besides, implementing catalytic methodologies to upgrade side streams produced during this process could contribute to better, holistic utilisation of the starting feedstock. This work depicts a zero-waste biorefinery concept based on cellulose defibrillation from almond hulls using various hydrotreatment technologies (hydrogenation and hydrodeoxygenation) for downstream processing on a ruthenium catalyst. Therein, the hemicellulose separated from the biomass preconditioning step was converted into sugar alcohols and/or marketable polyols with a relatively high yield (47.4%) by hydrolytic hydrogenation (437 K, 3h, 5.0 MPa H2). Meanwhile, a family of bioactive compounds (3-hydroxypyridines) could be directly extracted from the hydrolysate stream derived from microwave digestion, along with an energy carrier that was chemically stabilised (503 K, 60 min, 4.0 MPa H2) to obtain fuel additives (diethyl succinic acid, DES) and/or fuel intermediates.

The synthesis of sorbitol from cellulose over Ni catalysts is a promising valorisation route in the biorefinery scenario, applying relatively simple preparation methods and earth-abundant metals. The overall selectivity, however, depends on the kinetic control of a complex reaction network, involving the hydrolysis of cellulose to monosaccharides via cello-oligomers, glucose hydrogenation into sorbitol and hydrogenolysis side-reactions of sugars and sorbitol to low molecular weight polyols. Therein, subtle changes in the catalyst composition and process conditions might have a strong impact on the final product distribution. Driven by these challenges, this work first-time provides novel insights into the hydrothermal hydrogenation of cellulose over a carbon nanofibre supported Ni catalyst (Ni/CNF). Firstly, the impact of the duration of a ball-milling pre-treatment step and the influences of the hydrothermal time and temperature were thoroughly analysed. The experimental results obtained highlighted the importance of process control to promote the first transformation of cellulose to glucose and its subsequent hydrogenation to sorbitol to minimise the extension of side reactions. Finally, an additional study was conducted to palliate the recalcitrant nature of cellulose by decreasing mass transfer limitations to a minimum extent. This was achieved by including an additional mix-milling of the amorphous cellulose produced in the first pre-treatment with the catalyst and increasing the H2 pressure of the hydrothermal hydrogenation process. This allowed attaining a sorbitol yield as high as 62% at 190 ºC using an initial H2 pressure of 8 MPa for 26 h, which is one of the best results reported in the literature.

Carbon nanostructures provide a unique platform for the synthesis of novel catalysts for biomass conversion. In this work, a set of graphene oxide (GO)-based materials (nanofibers (GONF), sheets of few-layers (FLGO), and quantum dots (GOQD)), differing structurally in morphology and size, was prepared from fishbone-carbon nanofibers (CNF) and their catalytic behavior was compared on the hydrolysis of amorphous cellulose under microwave (MW) radiation. First, the influence of the reaction temperature (135–180 ºC), holding time (0–120 min), catalyst morphology and cellulose/water ratio (0.25–2.0 wt%) was thoroughly screened and compared with conventional heating mode. The use of GO morphologies in concert with MW energy showed the potential to achieve similar kinetic profiles than previously reported sulfonated carbons (110 kJ/mol) but using considerably less amount of catalyst (cellulose-to-catalyst ratio 12-fold lower). Overall, the reactivity of the GO-catalyst was related to their degree of oxidation/exfoliation, decreasing as follows: GOQD > FLGO > GONF. Compared with conventional heating, MW-technology enabled higher loadings of cellulose (2.0 vs. 0.25 wt%) to be processed in a shorter time (20 min instead of 24 h), which is a landmark achievement toward process intensification.

Table S1 The properties and composition of deionized water and seawater. Table S2 Relative influence of operating conditions and interactions on the experimental results according to the ANOVA and cause-effect Pareto analyses. Table S3 Detailed GC-MS peak area for biocrude (area%). Table S4 Summary of C. vulgaris HTT for biocrude and hydrochar production.

To get rid of the chrome pollution faced by the leather industry, we explored a novel engineering high-quality eco-leather technology based on the synergistic interactions between biomass-based aldehydes and Al(III). Firstly, dialdehyde xanthan gum (DXG) was prepared to covalently crosslink with the collagen fibers (CFs) via Schiff-base linkages under alkaline conditions, endowing the leather with a shrinkage temperature (Ts) of 80 °C and opening channels for the subsequent penetration of Al species (AL). Secondly, and for this latter purpose, the DXG-tanned leather was acidified to release part of the DXG from the leather according to the dynamic nature of the Schiff-base. Containing suitable oxygen-containing groups (OGs) with excellent complexation capabilities, the released DXG served as masking agents for AL, facilitating the penetration of AL into the inner CFs network for further complexation crosslinking. Consequently, a denser crosslinking network was constructed in the leather, and the crust leather exhibited higher Ts (82.2 °C), improved mechanical (tensile strength: 13.4 N/mm2, tear strength: 53.3 N/mm) and organoleptic properties than those of the DXG crust or AL crust leathers. This demonstrates that this synergistic covalence and complexation bridging strategy is a sustainable option to substitute highly restricted chrome tanning agent for eco-leather production.

Engineering high-performance chrome-free colored leather is currently a tough challenge in the leather industry. Herein, we report on a novel tanning–dyeing integration strategy based on converting natural cochineal carmine (Car) into an effective tanning agent (DCar) without losing its dyeing capabilities via periodate oxidation. Initially, DCar was used as a tanning–dyeing agent, leading to tanned-dyed leather with well-dispersed and fixed collagen fibers (CFs) and a shrinkage temperature (Ts) of ca. 70 °C. Subsequently, this leather was filled and fatliquored to be prepared for the subsequent aluminum fixation of the CFs matrix, which was facilitated by the excellent metal complexation capabilities of DCar. This dual integrative process resulted in successful simultaneous leather tanning and dyeing. Consequently, the resultant crust leather had a Ts of ca. 80 °C with an outstandingly dispersed and fixed CFs network and excellent softness, fullness, and commercializable mechanical strength (tensile strength: 13 N/mm2; tear strength: 54 N/mm). Besides, it also had a highly marketable brown color, a smooth grain surface, and excellent coloring uniformity and fastness. These results open the door for a new paradigm, i.e., providing natural pigments and dyes with tanning properties to develop novel and benign dual tanning–dyeing agents for the leather industry.

The direct transformation of cellulose into sugar alcohols (one-pot conversion) over supported nickel catalysts represents an attractive chemical route for biomass valorization, allowing the use of subcritical water in the hydrolysis step. The effectiveness of this process is substantially conditioned by the hydrogenation ability of the catalyst, determined by design parameters such as the active phase loading and particle size. Herein, mechanistic insights into catalyst design to produce superior activity were outlined using the hydrolytic hydrogenation of cellobiose as a model reaction. Variations in the impregnation technique (precipitation in basic media, incipient wetness impregnation, and the use of colloidal-deposition approaches) endowed carbon-nanofiber-supported catalysts within a wide range of Ni crystal sizes (5.8–20.4 nm) and loadings (5–14 wt%). The link between the properties of these catalysts and their reactivity has been established using characterization techniques such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma-optical emission spectroscopy (ICP-OES). A fair compromise was found between the Ni surface area (3.89 m2/g) and its resistance against oxidation for intermediate crystallite sizes (∼11.3 nm) loaded at 10.7 wt%, affording the hydrogenation of 81.2% cellobiose to sorbitol after 3 h reaction at 190°C and 4.0 MPa H2 (measured at room temperature). The facile oxidation of smaller Ni particle sizes impeded the use of highly dispersed catalysts to reduce the metal content requirements.

This work first-time addresses the synergetic hydrothermal co-valorisation of almond hulls (an unavoidable food waste) and FFP2 face masks (a common plastic material) using seawater (a sustainable reaction medium). The effects of the feedstock composition (each material alone and all possible binary combinations) and the reaction medium (deionised water, seawater and all possible binary mixtures) have been evaluated at 350 °C and 170 bar over a wide range of reaction times (20–180 min). Bilateral biomass-plastic synergistic and antagonistic interactions between both feedstocks, combined with several promoting and inhibiting effects displayed by seawater, ruled the distribution of the reaction products and their most important physicochemical and fuel properties. Process optimisation revealed that the formation of an energy-dense (32 MJ/kg) liquid biofuel was maximised (26% biocrude yield) by conducting the process with almond hulls in deionised water for 115 min. At the same time, face masks promoted solid biofuel formation (83% hydrochar yield, 46 MJ/kg) by coprocessing an almond hulls/disposable face masks mixture (8:92 wt%) in salted (seawater/deionised water mixture with 37471 ppm salinity) water for 180 min. Conducting the process with seawater (44608 ppm salinity) for 180 min allowed coprocessing of both materials (22/78 wt% almond hulls/face masks) efficiently to maximise biofuels production (13% biocrude yield, HHV = 33 MJ/kg and 67% hydrochar yield, HHV = 49 MJ/kg). These results are a breakthrough in developing season-free and flexible biorefineries, which contribute to reducing pollution and bringing out the hidden value of human activity common residues.

Developing chrome-free and sustainable tanning agents is extremely important to the sustainability of the leather industry. Herein, we have synthesized an Al-Zr-oligosaccharides tanning agent via a simultaneous degradation and oxidation of cellulose in waste paper. The influence of the temperature and the concentrations of AlCl3 and H2O2 during the synthesis were thoroughly investigated on the properties of the tanning agent and the leather produced. The synthesis temperature and the concentration of AlCl3 were the factors primarily affecting the effective depolymerization of cellulose. They controlled the conversion of waste paper into oligosaccharides with an appropriate molecular weight to efficiently penetrate the leather matrix. In parallel, the H2O2 concentration substantially influenced the tanning performance of the Al-Zr-oligosaccharides, diminishing the chromaticity of the tanning liquid via oxidation and promoting the conversion of C2/C3/C6-OH moieties into -CHO/-COOH. These functional groups increased the surface charge of the oligosaccharides allowing more effective coordination with Al/Zr, which facilitated the penetration of Al/Zr species into the leather matrix. Once inside the leather matrix, Al and Zr were released and reacted with the collagen fibers in leather, which resulted in effective leather tanning. The process optimization revealed that up to 57% of waste paper could be converted into a low-chromaticity (4350 AU) liquid hydrolysate with the synthesis conducted at 177 °C in a system comprising 47 mM AlCl3 and 5 vol% H2O2. The application of this liquid for tanning provided leather with a shrinkage temperature (86.5 °C) sufficiently high for commercial applications. These excellent results, combined with the intrinsic green nature of our approach, exemplify a step forward to simultaneously reduce pollution and hazards in leather industries giving a second life to waste paper.

La creciente demanda de combustible ha promovido la búsqueda de fuentes de origen renovable alternativas al petróleo. Mediante la pirólisis de biomasa lignocelulósica es posible obtener un aceite pirolítico (bio-oil) con múltiples aplicaciones. No obstante, su alto contenido en oxígeno limita sustancialmente su uso como combustible, haciendo necesaria una etapa previa de desoxigenación. En este sentido, el proceso de hidrodesoxigenación (HDO) catalítica permite obtener un líquido orgánico con propiedades combustibles mejoradas. En este trabajo se presentan los resultados obtenidos durante la HDO de líquidos de pirólisis de biomasa utilizando un catalizador de carburo de molibdeno soportado en nanofibras de carbono (Mo2C/CNF). Inicialmente, se abordó el efecto de las condiciones de operación utilizando guayacol como compuesto modelo del líquido de pirólisis. Posteriormente, se analizó la actividad catalítica del catalizador utilizando una alimentación real consistente en la fracción lignínica de un líquido procedente de la pirólisis de biomasa lignocelulósica (lignin-oil). Estos estudios permitieron evaluar la posibilidad de utilizar los líquidos de pirólisis de biomasa como combustible.

La despolimerización de la celulosa en azúcares simples representa uno de los principales obstáculos del aprovechamiento de la biomasa lignocelulósica. Las características supramoleculares de este biopolímero, impuestas principalmente por su arreglo cristalino, cobran especial relevancia en reacciones heterogéneas, donde se ve impedido el acceso de los enlaces glucosídicos más internos a los sitios ácidos de un catalizador granular. En este contexto, las nanoestructuras de carbono ofrecen una serie de posibilidades de diseño muy interesantes, con morfologías que van de 3D a 0D y grupos químicos superficiales que se pueden incorporar a través de numerosas metodologías de funcionalización y relacionarse específicamente con su tamaño. Como ejemplo ilustrativo de este potencial, el presente trabajo compara la actividad catalítica de tres morfologías de óxido de grafeno: nanofibras (GONF), láminas de pocas capas (FLGO) y puntos cuánticos (GOQD), en la hidrólisis de celulosa amorfa. Además, se emplearon diferentes fuentes de calentamiento, incluyendo el procedimiento convencional y el asistido por microondas.

High-profile chrome (Cr) pollution from tanning and potential health hazards from released leather dyes and pigments from leather products restrict the sustainable development of the leather industry. Herein, we report on a novel ‘Two Birds with One Stone’ strategy to simultaneously eliminate Cr and colorant pollutions using a Cr-free tanning agent with an in situ dyeing ability. Sucralose, containing an electron-withdrawing group (–Cl), was employed to fabricate a biomass-derived aldehyde tanning agent with in situ dyeing properties (BAT-iDP). This agent formed Schiff-base crosslinks between its aldehyde groups and the amino groups of collagen fibers (CFs), which efficiently dispersed and fixed the CFs, producing tanned leather with sufficient thermal stability (80.2 °C of shrinkage temperature) to meet commercial requirements. Simultaneously, the presence of an auxochrome (–Cl) in the structure of the Schiff-bases formed endowed the tanned leather with a brown color characteristic of leather. As a result, the tanned leather produced with our ‘Two Birds with One Stone’ strategy had excellent dyeing uniformity, color fastness to dry-wet rubbing and favorable mechanical strengths (14.7 N mm−2 of tensile strength and 46.3 N mm−1 of tear strength). This novel approach provides new insights for designing and developing multifunctional sustainable materials towards a greener and carbon-neutral leather industry.

The chemical transformation of natural oils provides alternatives to limited fossil fuels and produces compounds with added value for the chemical industries. The selective deoxygenation of natural oils to diesel-ranged hydrocarbons, bio-jet fuels, or fatty alcohols with controllable selectivity is especially attractive in natural oil feedstock biorefineries. This review presents recent progress in catalytic deoxygenation of natural oils or related model compounds (e.g., fatty acids) to renewable liquid fuels (green diesel and bio-jet fuels) and valuable fatty alcohols (unsaturated and saturated fatty alcohols). Besides, it discusses and compares the existing and potential strategies to control the product selectivity over heterogeneous catalysts. Most research conducted and reviewed has only addressed the production of one category; therefore, a new integrative vision exploring how to direct the process toward fuel and/or chemicals is urgently needed. Thus, work conducted to date addressing the development of new catalysts and studying the influence of the reaction parameters (e.g., temperature, time and hydrogen pressure) is summarized and critically discussed from a green and sustainable perspective using efficiency indicators (e.g., yields, selectivity, turnover frequencies and catalysts lifetime). Special attention has been given to the chemical transformations occurring to identify key descriptors to tune the selectivity toward target products by manipulating the reaction conditions and the structures of the catalysts. Finally, the challenges and future research goals to develop novel and holistic natural oil biorefineries are proposed. As a result, this critical review provides the readership with appropriate information to selectively control the transformation of natural oils into either biofuels and/or value-added chemicals. This new flexible vision can help pave the wave to suit the present and future market needs., This review presents the recent progress achieved in the catalytic deoxygenation of natural oils or related model compounds (e.g., fatty acids) to renewable liquid fuels (green diesel and bio-jet fuels) and valuable fatty alcohols (unsaturated and saturated fatty alcohols).

Food waste worldwide has been threatening the environment and resulting in high carbon emissions. Although anaerobic fermentation is a potential solution transforming food waste into valuable chemicals, a large amount of the fermentation residue remains as solid waste. For closing the circular economy loop for food waste valorization, we proposed a thermo-chemical activation of a fermentation residue produced from a mixture of food waste and sludge to prepare a nitrogen-enriched, advanced carbon material. This could be used as a support to synthesize Pd/C, Pt/C and Au/C catalysts for the aqueous-phase hydrogenation of vanillin to vanillyl alcohol at mild reaction conditions. The produced alcohol increased sixfold the commercial value of the original aldehyde. The catalytic performance (based on the vanillin conversion and vanillyl alcohol yield) followed the order of Pd/C > Pt/C > Au/C. The Pd/C catalyst showed an excellent catalytic activity (>99% vanillin conversion and > 99% vanillyl alcohol selectivity) at optimized reaction conditions (i.e., 30 °C and 0.7 MPa H2 for 90 min, with 2 mmol vanillin/10 mg catalyst), along with high reusability and stability (up to four consecutive runs). These catalytic features outperformed those of a commercial Pd/C catalyst owing to: (i) high reduction degree and stabilization of the Pd particles on the carbon support, which accommodated a higher proportion of pyridinic than pyrrolic nitrogen, and (ii) rapid adsorption of the aldehyde group on the catalyst combined with rapid desorption of the newly formed hydroxymethyl group. This exceptional catalytic behavior was corroborated by efficient hydrogenation of other lignin-derived aromatic aldehydes, including p-hydroxybenzaldehyde and syringaldehyde, to their respective alcohols. Our results can bring a novel use for food waste in catalysis and represent a sustainable and efficient conversion of biomass into value-added chemicals and advanced materials.

The almond industry leaves behind substantial amounts of by-products, with almond hulls being the primary residue generated. Given that one way to improve food security is by decreasing waste to reduce environmental impacts, developing sustainable processes to manage this by-product is necessary. Herein, we report on the hydrothermal hydrogenation of almond hulls over a carbon-neutral Ru supported on carbon nanofibres (Ru/CNF) catalyst, addressing the temperature, H2 pressure, time and catalyst loading. These variables controlled the distribution of the reaction products: gas (0–5%), liquid (49–82%) and solid (13–51%), and ruled the composition of the liquid effluent. This aqueous fraction comprised oligomers (46–81 wt%), saccharides (2–7 wt%), sugar alcohols (2–15 wt%), polyhydric alcohols (1–8 wt%) and carboxylic acids (7–31 wt%). The temperature and reaction time influenced the extension of hydrolysis, depolymerisation, deamination, hydrolysis, hydrogenation and dehydration reactions. Additionally, the initial H2 pressure and catalyst loading kinetically promoted these transformations, whose extensions were ruled by the amount of H2 effectively dissolved in the reaction medium and the prevalence of hydrogenations over dehydration/decarboxylation reactions or vice versa depending on the catalyst loading. Process optimisation revealed that it is feasible to convert up to 67% of almond hulls into merchantable oligomers at 230 °C, 35 bar initial H2, using 1 g catalyst/g biomass (0.4 g Ru/g biomass) for 360 min. Additionally, decreasing the temperature to 187 °C without modifying the other parameters could convert this material into oligomers (31 wt%) and small oxygenates (17 wt% carboxylic acids, 11 wt% sugar alcohols and 6 wt% polyhydric alcohols) concurrently. The theoretical energy assessment revealed that the total and partial combustion of the spent solid material could provide the required energy for the process and allow catalyst recovery and reutilisation. Th