• Energy Research

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.

Planet Earth is under severe stress from several inter-linked factors mainly associated with rising global population, linear resource consumption, security of resources, unsurmountable waste generation, and social inequality, which unabated will lead to an unsustainable 21st Century. The traditional way products are designed promotes a linear economy that discards recoverable resources and creates negative environmental and social impacts. Here, we suggest multi-disciplinary approaches encompassing chemistry, process engineering and sustainability science, and sustainable solutions in “game changer” challenges in three intersecting arenas of food: Sustainable diet, valorisation of unavoidable food supply chain wastes, and circularity of food value chain systems aligning with the United Nations’ seventeen Sustainable Development Goals. In the arena of sustainable diet, comprehensive life cycle assessment using the global life cycle inventory datasets and recommended daily servings is conducted to rank food choices, covering all food groups from fresh fruits/vegetables, lentils/pulses and grains to livestock, with regard to health and the environment, to emphasise the essence of plant-based diet, especially plant-based sources of protein, for holistic systemic sustainability and stability of the earth system. In the arena of unavoidable food supply chain wastes, economically feasible and synergistically (energy and material) integrated innovative biorefinery systems are suggested to transform unavoidable food waste into functional and platform chemical productions alongside energy vectors: Fuel or combined heat and power generation. In the arena of circularity of food value chain systems, novel materials and methods for plant-based protein functionalisation for food/nutraceutical applications are investigated using regenerative bio-surfactants from unavoidable food waste. This circular economy or industrial symbiosis example thus combines the other two arenas, i.e., plant-based protein sourcing and unavoidable food waste valorisation. The multi-disciplinary analysis here will eventually impact on policies for dietary change, but also contribute knowledge needed by industry and policy makers and raise awareness amongst the population at large for making a better approach to the circular economy of food.

Food waste is a global problem, causing significant environmental harm and resulting in substantial economic losses globally.

This critical review summarises and analyses all the work conducted to date on the use of microwave-assisted hydrothermal processes for the conversion of biomass into hydrochar, bio-crude (bio-oil) and valuable chemicals.

This work addresses a novel and green process for the co-production of lignin and oligosaccharides from rapeseed meal, examining the effects of the temperature (150–210 °C), reaction time (0–60 min) and catalyst amount (1–4 mol/L, CH3COOH) on the process. The yields to gas, liquid and solid varied by 0–18%, 22–64% and 34–74%, respectively. The solid consisted of high purity lignin (26–88 wt.%) together with unreacted cellulose (0–28 wt.%), hemicellulose (0–28 wt.%) and proteins (11–28 wt.%). Increasing the temperature and/or reaction time produced an increase in the liquid yield and a decrease in the solid yield due to the solubilisation of the cellulosic and hemicellulosic contents of the feedstock. Acetic acid exerted a positive catalytic effect, promoting the solubilisation of cellulose and hemicellulose and preventing humins formation. The relative amounts (wt.%) of C, H, O and N in the solid fraction shifted between 46–63, 5.8–6.4, 28–42 and 2–6, respectively. Py-GC/MS analysis revealed that the solid decomposed into phenols (1–19%), sugars (0–15%), N-compounds (0–31%), carboxylic acids (37–75%), hydrocarbons (4–20%) and furans (1–8%). The liquid phase comprised oligo- and mono/di-saccharides (33–51 C-wt.%, 0–3 C-wt.% and 0–6 C-wt.%) and carboxylic acids (40–62 C-wt.%). The progressive solubilisation of cellulose and hemicellulose produced an increase in the proportion of C together with a decrease in the amounts of H and O in the solid product, which also accounted for the increase and decrease observed in the proportions of phenols and sugars, respectively. An optimum was found at 186 °C using an acid concentration of 1 mol/L and a total reaction time of 2 min. These conditions maximise the solubilisation of cellulose and hemicellulose without altering the lignin content of the solid; thus allowing the selective and simultaneous production of high purity (85 wt.%) lignin together with a rich oligossacharide (51 C-wt.%) solution. The acid can be recovered from the sugar mixture, which not only improves the efficiency of the process but also allows the production of a pure saccharide (92 C-wt.%) product.

2 Figuras.-- Información suplementaria disponible en línea en la web del editor. Xylooligosaccharides (XOS) produced from biomass offer a plethora of excellent physicochemical and physiological properties to be used as natural prebiotic nutraceuticals. Herein, this work first addresses and optimizes a novel one-pot, additive-free, microwave-assisted process to produce high purity XOS from beech wood hemicellulose, studying the influence of the temperature, reaction time, and solid loading. These variables exerted a significant influence, allowing the transformation of hemicellulose into a gas (0–19%), an XOS-rich liquid product (9–80%) and a spent solid material (17–90%). The liquid phase consisted of a mixture of XOS with a degree of polymerization (DP) DP > 6 (75–100 C-wt %) and DP 3–6 (0–10 C-wt %), together with mono/disaccharides (0–1 C-wt %), carboxylic acids (0–5 C-wt %), ketones (0–12 C-wt %) and furans (0–12 C-wt %). A good compromise between the liquid yield (81%) and XOS purity (96 C-wt %) was achieved at 172 °C using a solid loading of 5 wt % for 47 min. This time could be reduced (33 min) and the solid loading increased (25 wt %) without substantially altering the XOS (98 C-wt %) purity, although the liquid yield was reduced. The liquid yield could be increased up to 97% at the expenses of XOS purity (90 C-wt %) at 177 °C using a 5 wt % solid loading for 60 min. For these optima, the microwave production costs shifted between 1.42 and 6.50 €/kg XOS, which is substantially lower than the XOS market price, thus highlighting the high potential of this emerging technology. The authors acknowledge the Industrial Biotechnology Catalyst (Grants Innovate U.K., BBSRC, EPSRC, and EP/N013522/1) and EPSRC research grant number EP/K014773/1 for financial support. In addition, J.R.N. would like to express his gratitude to the Spanish Ministry of Science, Innovation and Universities for the Juan de la Cierva fellowship (FJCI-2016-30847) awarded. Peer reviewed