Increasing demand for fuels and chemicals, driven by factors including over-population, the threat of global warming and the scarcity of fossil resources, strains our resource system and necessitates the development of sustainable and innovative strategies for the chemical industry. Our society is currently experiencing constraints imposed by our resource system, which drives industry to increase its overall efficiency by improving existing processes or finding new uses for waste. Food supply chain waste emerged as a resource with a significant potential to be employed as a raw material for the production of fuels and chemicals given the abundant volumes globally generated, its contained diversity of functionalised chemical components and the opportunity to be utilised for higher value applications. The present manuscript is aimed to provide a general overview of the current and most innovative uses of food supply chain waste, providing a range of worldwide case-studies from around the globe. These studies will focus on examples illustrating the use of citrus peel, waste cooking oil and cashew shell nut liquid in countries such as China, the UK, Tanzania, Spain, Greece or Morocco. This work emphasises 2nd generation food waste valorisation and re-use strategies for the production of higher value and marketable products rather than conventional food waste processing (incineration for energy recovery, feed or composting) while highlighting issues linked to the use of food waste as a sustainable raw material. The influence of food regulations on food supply chain waste valorisation will also be addressed as well as our society's behavior towards food supply chain waste. “There was no ways of dealing with it that have not been known for thousands of years. These ways are essentially four: dumping it, burning it, converting it into something that can be used again, and minimizing the volume of material goods – future garbage – that is produced in the first place.” William Rathje on waste (1945–2012) – Director of the Tucson Garbage project.

Food waste as a valuable resource for the production of chemicals, materials and fuels. Current situation and global perspective

Along more than a decade, R&D on supercritical fluid extraction (SFE) of vegetable matrices has been increasingly reported in the literature. Aiming at portraying the current state of this field and its evolution in terms of raw materials, products, modes of operation, optimization, modeling techniques, and closeness to industrial application, a large compilation of almost 600 essays from 2000 to 2013 has been deeply analyzed in order to unveil those indicators and their trends. Furthermore, strengths and weaknesses are identified, and some remarks that may drive upcoming research are provided. Globally, more than 300 species are reported in the literature, with prevalence of the extraction of seeds (28% of works) and leaves (17%). The main families of extracted compounds, cosolvents and operating conditions adopted are critically examined, being possible to conclude that researchers investigate many times working regions far from the optimum due to practical limitations or absence of experimental optimization. Current phenomenological, statistical and semi-empirical approaches are reviewed, along with scale-up studies, and economic analysis. In the whole, the most comprehensive picture over SFE of vegetable matrices is provided in this review, highlighting pertinent aspects and opportunities that may further consolidate the convincing route of this technology for the next years.

Supercritical fluid extraction of vegetable matrices: Applications, trends and future perspectives of a convincing green technology

The extraction of essential oil from peppermint leaves with supercritical carbon dioxide was studied in a semibatch-flow extraction apparatus. The extraction rates of the major components, l-menthol and menthone, were measured at various conditions: 313–353 K, 8.83–19.6 MPa. The exit concentration of l-menthol extracted from peppermint leaves was much smaller than the solubility of l-menthol. The extraction curves at various flow rates coincide in the plot of yield versus quantity of CO2 consumed. A mathematical model based on the local adsorption equilibrium of essential oil on lipid in leaves and mass transfer well described the extraction results. The adsorption equilibrium constant determined by filling the theoretical extraction curve to the experimental data increased with temperature and decreased with pressure.

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Extraction of Peppermint Oil by Supercritical Carbon Dioxide

Olive husk oil was extracted from olive husk under pressures of 12.0 to 18.0 MPa and temperatures of 308 to 330 K with supercritical carbon dioxide. Olive husk was supplied by an olive oil factory. The effects of pressure, temperature, extractor capacity and superficial velocity on the extraction rate of olive husk oil were studied. Extraction curves were evaluated by an empirical model, a ‘hot sphere’ model and by the extended Lack's plug-flow model and the relative merits of the models are demonstrated. The results are compared with those obtained in the literature. Good agreement between the extended Lack's plug-flow model and our experimental measurements was obtained. The empirical model (in which only one adjustable parameter varied with extraction conditions) also fitted the data well. The ‘hot sphere’ model, as currently applied, gave acceptable results at the higher superficial velocities studied but gave a very poor fit at the lowest velocities. The effects on the parameters in this model of allowing rapid equilibration to occur between the pore fluid and adjacent adsorbed solute are examined and discussed in the light of the experimental findings.

Mathematical models for supercritical extraction of olive husk oil

The supercritical fluid extraction (SFE) of liquids and solid materials is gaining increasing interest and commercial application in last decades, most particularly under the recent concept of green chemistry and biorefinery. Hence, it is fundamental to provide adequate modeling of the SFE, in order to optimize operating conditions and simulate the global process. This work intends to review the most significant and physically sound models published in the literature for countercurrent liquid-supercritical fluid extraction and SFE of solid matrices, such as the linear driving force, shrinking core, broken and intact cells, and the combination of BIC and shrinking core models. The main assumptions and mass transfer expressions are presented and discussed.

Review of kinetic models for supercritical fluid extraction

The extraction of caffeine from whole coffee beans with supercritical carbon dioxide was studied in a continuous-flow extraction apparatus. Decaffeination rates were determined as a function of CO2 flow rate, temperature and pressure by continuously monitoring the caffeine in the effluent with a flame ionization detector. Soaking the raw beans in water prior to decaffeination enhanced the rate of extraction, which increased markedly with water content. Using CO2 saturated with water also increased the rate of extraction. The rate of decaffeination increased with pressure and temperature and was influenced by both intraparticle diffusion in the water-soaked beans and external mass transfer. A mathematical model based on a linear-driving-force approximation of mass transfer and partitioning of caffeine between the water and the supercritical CO2 describes the time-dependent process. The partition coefficient for caffeine distributed between water and supercritical CO2, the only parameter determined from the dynamic extraction rate data, increases with temperature and pressure.

Hulya Peker

Papers

Caffeine extraction rates from coffee beans with supercritical carbon dioxide