Over the last few years the impact of products from natural sources in food, nutraceuticals, cosmetics, flavors/fragrances, and also the pharmaceutical industry has increased due to the consumer demand for nature-derived products. Meeting this demand requires that existing manufacturing processes have to be optimized and process development for a variety of new products, sometimes with short life cycles, has to be accelerated. A scientific literature review covering equipment and modeling for plant-based extractions shows an enormous demand for new approaches in process design for solvent extraction, isolation, and purification of ingredients from botanical sources and its transfer from academic research into manageable solutions for industrial use. An approach combining the design of experiments and rigorous process modeling on the one hand and an intensified collaboration between different disciplines including process engineering, botany, and analytical chemistry on the other hand seems to be the only way forward to address the current issues and shortcomings systematically and efficiently. Hence, a standard apparatus for the assessment of the governing process parameters for plant-based extraction processes is proposed.

A rigorous model supported by botanical investigations has been developed to predict percolation results. Botanical investigations provide needed modeling parameters like pore size, porosity, or target compound distributions over the particle. After determining the desorption isotherm with maceration experiments at different solvent-feed ratios, the model is validated with short residence time percolation experiments. With the aid of this validated model, percolation experiments with long residence times can be predicted and different process scenarios calculated. A combination of design of experiments and rigorous modeling together with standard equipment and experimental model parameter determination provides a fast and robust experimental design on the one hand and the precondition for a process parameter data-based learning curve on the basis of rigorous modeling in the mid-or long-term on the other hand.

In this study, the technology of membrane contactors was assessed for the liquid-liquid extraction of highly valuable oxygenated terpenes from lemon essential oil using mixtures of water and ethanol as solvents (20-66% v/v ethanol). The main expected benefit of using membrane contactors in this application was the elimination of the phase separation step, which can be difficult in these types of systems, which are characterized by a low interfacial tension and the presence of natural surfactants. A commercially available polypropylene hollow fibre contactor (Liqui-Cel ® 2.5 × 8 with X30fibres) was used in this study. Stabilizing the interface between the hydro-alcoholic solvent and lemon essential oil in membrane pores proved difficult (breakthrough pressure below 0.2 bar), even with solvents containing only 20% v/v ethanol. This problem was probably due to defects in the membrane material such as the presence of large pores (up to 4 µm in diameter). Nonetheless, the hydro-alcoholic extract remained emulsion free throughout extraction, considered to be an improvement since it eliminated the time-consuming decantation step (process intensification). High mass transfer coefficients up to 1.08 × 10 −6 m/s were obtained for the tracer of oxygenated terpenes and a solvent with 66% v/v ethanol. The membrane never represented more than 25% of the total resistance to mass transfer. We demonstrated the high potential of using membrane contactors for this application, provided that improvements were performed on membrane materials.

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