Plants need to be protected against pests and diseases, so as to assure an adequate production, and therefore to contribute to food security. However, some of the used pesticides are harmful compounds, and thus the right balance between the need to increase food production with the need to ensure the safety of people, food and the environment must be struck. In particular, when dealing with fruit and vegetable wastes, their content in agrochemicals should be monitored, especially in peel and skins, and eventually minimized before or during further processing to separate or concentrate bioactive compounds from it. The general objective of this review is to investigate initial levels of pesticide residues and their potential reduction through further processing for some of the most contaminated fruit and vegetable wastes. Focus will be placed on extraction and drying processes being amid the main processing steps used in the recuperation of bioactive compounds from fruit and vegetable wastes.

Fate of Residual Pesticides in Fruit and Vegetable Waste (FVW) Processing.

Liquid-liquid extraction is one of the most important unit operations with a broad field of applications. During the past few years, research activities have been increasing in the area of microextraction due to the evident advantages of microchannel equipment. While there is a sweeping number of publications on the topic of the procedure of microextraction using cocurrent flow, there are still some difficulties in accomplishing multistage processes as the countercurrent extraction, such as mixer-settler arrangements. This is due to the fact that it is difficult to achieve a continuous stable phase separation with high throughput. Additionally, it is also challenging to balance the pressure loss with micropumps after every stage. Both of these processes are essential for the countercurrent extraction and, therefore, at the current state of affairs, they pose a bottleneck. This field of research bears a high development potential in order to improve these processes using microchannel equipment and to realize a multistage countercurrent extraction with high effectiveness. In this paper, different phase separation devices and their particular separation principles are presented whereas the focus lies on the continuous separation. Additionally, some experimental as well as theoretical concepts for the conduct of a multistage countercurrent extraction are outlined.

Counter-Current Extraction in Microchannel Flow: Current Status and Perspectives

Drying of porous materials containing binary mixtures changes the composition of the moisture to a certain extent. Generally the more volatile component is removed preferentially, especially when the drying rate is low. At sufficiently high drying rates the moisture always evaporates with constant composition; the drying is nonselective. This effect is due to the liquid-side mass transfer resistance. Nonselective drying is also obtained when the moisture has a pseudo-azeotropic composition; this depends on the relative volatility, the gas-side mass transfer and the residence time of the gas in the dryer. If such a pseudo-azeotropic composition does exist, then even the less volatile component may be removed preferentially, provided the initial composition is above the pseudo-azeotropic one. The selectivity of the drying process also depends on the size of the drying sample as well as upon whether the drying process is run continuously or intermittently. The complex interactions of phase equilibria, gas- and liquid-side mass transfer and capillary flow for given drying conditions were analyzed first for the case of evaporation of binary mixtures from a free liquid surface and second for the case of drying single porous bodies containing binary mixtures. In both cases experimental results were obtained with mixtures of isopropyl alcohol and water. They confirm the phenomena and tendencies as predicted from theoretical considerations.

Progress towards understanding the drying of porous materials wetted with binary mixtures

The article contains sections titled:



1.	Theoretical Fundamentals of the Drying Process	
1.1.	Concepts, Definitions	
1.2.	Characteristics of Moist Solids	
1.3.	Drying Rate Curves for ConvectionDrying	
1.4.	Drying Rate Curves for Contact Drying	
1.5.	Drying Rate and Moisture-Composition Curves for Solids Wetted by LiquidMixtures	
2.	Drying Methodsand Dryer Types	
2.1.	ConvectionDrying	
2.1.1.	Flowing Gas	
2.1.2.	The Solid is Aerated	
2.1.3.	Large-Scale Agitation of the Solid	
2.1.4.	The Solid Moves in the Drying Agent	
2.1.5.	The Material is Sprayed	
2.2.	ContactDrying	
2.2.1.	Flat and Strip Materials	
2.2.2.	Low-Viscosity Materials	
2.2.3.	Pasty Materials	
2.2.4.	Granular Materials	
2.3.	Radiant Heat or Infrared Drying	
2.4.	DielectricHeating	
2.5.	Vacuum and Freeze Drying	
3.	Selecting, Sizing, and Energy Requirements of Dryers	
3.1.	Choosing the Type of Dryer	
3.1.1.	The Role of the Material Properties of the Solid	
3.1.2.	Production Rate	
3.1.3.	Dryer Ventilation	
3.2.	Sizing the Dryer	
3.2.1.	Batch Dryers	
3.2.2.	Continuous Dryers	
3.3.	Heat and Driving Power Requirements

Drying of Solid Materials

Propylene is separated from the methanol present as a solvent in a crude olefin epoxidation product by means of an extractive distillation wherein a relatively heavy polar solvent having hydroxy groups such as water or propylene glycol is used as the extractive solvent. The method is also useful for removing water and impurities such as acetaldehyde from the propylene oxide.

Separation of methanol and propylene oxide from a reaction mixture

Destillation, Absorption, Extraktion

Etude experimentale de la cinetique de perte de masse et de la variation dans le temps des teneurs en produit evapore dans l'effluent au cours de sechage de differents materiaux impregnes d'un melange d'isopropanol et d'eau

Selektivität bei der Konvektionstrocknung von Gütern bei Beladung mit binären Gemischen

The estimation of the size of a dryer requires the knowledge of the drying rate as a function of the moisture content, called drying curve. In addition to that, for the drying of materials containing mixtures it is important to know the composition of the moisture as a function of the moisture content, called composition curve.

Convective Drying of Porous Materials Containing Binary Mixtures

When binary mixtures are evaporated, a wet-bulb temperature does exist, provided that the evaporation is non-selective. The wet-bulb temperature can be calculated based on the energy balance, the kinetic equations for heat and mass transfer and the thermodynamic equilibrium. The calculated wet-bulb temperatures were found to be in good agreement with the experimental ones, obtained with mixtures of isopropyl alcohol and water.

Franz Thurner

Papers

Progress towards understanding the drying of porous materials wetted with binary mixtures

Destillation, Absorption, Extraktion

Selektivität bei der Konvektionstrocknung von Gütern bei Beladung mit binären Gemischen

Convective Drying of Porous Materials Containing Binary Mixtures

Wet-bulb temperature of binary mixtures