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Prediction of Filter Performances against Organic Vapours: Statistical Analysis of Breakthrough Times as a Basis for a Simple Prediction Model
The prediction of the protection efficiency of NBC-respiratory filters against organic vapours is often very difficult, especially when strong physical interactions or chemisorption processes are invoved. The presented statistical analysis is an attempt to develop a simple, but reliable, prediction model for breakthrough times. In over 70 experiments run under conditions of the EN 141 guidelines the breakthrough times of 39 organic compounds including alkanes, cyclo-alkanes, alkenes, alcohols, ketones and carboxylic acids have been measured for a given filter type. A linear regression model is then postulated to relate the breakthrough time to the adsorptive properties. For the model, each adsorptive molecule has been considered to be composed of a chemical functional group and a chain radical, resulting in a two dimensional structural code. The number of carbon atoms in the radical-chain and physical properties has been considered as an additional model parameter. General Linear Model (GLM) analysis was run to estimate model performances. We found out, that a simple linear model with only four regressors (two dimensional structural code, number of C atoms in the radical-chain and the saturation pressure) yields satisfactory breakthrough time predictions. Therefore, this study shows that, for a given filter type and well defined testing conditions, satisfactory predictions of breakthrough times of organic vapours are feasible.
Dynamic adsorption, in active carbon beds, of vapour mixtures corresponding to miscible and immiscible liquids
It is shown that the combined Myers–Prausnitz–Dubinin theory (MPD) can be extended to the adsorption of ternary mixtures from an air stream. When combined with a computer model developed for dynamic adsorption, it provides a satisfactory agreement with the experimental breakthrough curves in active carbon beds. On the other hand, as illustrated by a mixture of water and 2-chloropropane vapours, MPD is no longer valid when the corresponding liquids are not miscible. In this case, binary adsorption can be described with a relatively good precision by assuming independent co-adsorption of the vapours. This, in turn, leads to satisfactory previsions for dynamic adsorption.
Binary Adsorption of Vapours in Active Carbons Described by the Combined Theories of Myers-Prausnitz and Dubinin (II)
The Myers–Prausnitz–Dubinin Theory and Non-ideal Adsorption in Microporous Solids
The adsorption of vapour and liquid mixtures of benzene + 1,2-dichloroethane, chlorobenzene + carbon tetrachloride, chlorobenzene + cyclohexane and 1-bromo,2-chloroethane + 1,2-dichloroethane on two activated carbons and on two zeolites (UC13X and ZSM-5) was examined near room temperature. It was shown that the combination of the recent Myers–Prausnitz–Dubinin (MPD) theory with the activity coefficients of the corresponding solid-liquid equilibrium leads to a good correlation between the calculated and the experimental mole fractions for binary vapour adsorption by microporous solids. This confirms that the approach based on an ideal adsorbed state (IAS) can be improved by using these activity coefficients as a first and good approximation.
Adsorption of Vapour Mixtures in Active Carbons described by the Myers-Prausnitz-Dubinin Method
Binary Adsorption of Vapours in Active Carbons Described by the Dubinin Equation
Static Adsorption, by activated Carbons, of vapour Mixtures corresponding to immiscible Liquids
Dynamic adsorption of vapour mixtures in active carbon beds described by the Myers-Prausnitz and dubinin theories
The adsorption of binary vapour mixtures from air by active carbon beds can be predicted with a good accuracy by adapting a model developed earlier for single vapours. This model is based on a semi-implicit finite difference scheme. Multiple adsorption of vapours is described by the combined theories of Myers-Prausnitz and of Dubinin (MPD), which have already been applied successfully to static adsorption. A good agreement is found between the predicted and the experimental breakthrough curves of the systems 2-chloropropane + chlorobenzene and carbon tetrachloride + chlorobenzene on two activated carbons at 298 K and under different experimental conditions.
Determination of the Surface Fractal Dimension of Active Carbons by Mercury Porosimetry
Mercury porosimetry has been used to characterize the macroporosity of several carbon materials activated by steam or carbon dioxide and their surface fractal dimension is determined. The first part is devoted to the analysis of the differential volume versus pressure curves in order to distinguish between mechanical effects resulting from the mercury pressure and true pore filling. It is shown, in the second part, that the macropore volume is not strongly affected by the activation process, but it depends mainly on the initial texture of the carbon. On the other hand, the fractal dimension varies largely with the activation conditions and burn-off. The experimental results suggest that the fractal dimension tends to increase with the degree of burn-off in steam, whereas the opposite occurs during activation by carbon dioxide. These observations are discussed in relation to the mechanisms of activation.