Influence of the chain length on the dynamic viscosity at high pressure of some 2-alkylamines: Measurements and comparative study of some models

Abstract

This work reports the dynamic viscosity data (a total of 93 points) of 2-alkylamines, which exhibit small association, consisting of 2-aminobutane, 2-aminopentane, 2-aminoheptane and 2-aminooctane at four temperatures between 293.15 K and 353.15 K (every 20 K), and pressures up to 100 MPa (every 20 MPa) which allows to study the influence of the chain length. A falling-body viscometer with an uncertainty of ±2% was used to perform these measurements. The variations of dynamic viscosity are discussed with respect to their behaviour due to chain length. Seven different models, most of them with a physical and theoretical background, are studied in order to investigate how they take the chain length effect into account through their required model parameters. The evaluated models are based on the empirical Vogel–Fulcher–Tamman (VFT) representation (combined with a Tait-like equation), the rough hard-sphere scheme, the concept of the free-volume, the friction theory, a correlation derived from molecular dynamics, a model based on Eyring’s absolute rate theory combined with cubic EoS. A scaling viscosity representation has also been considered. These models need some adjustable parameters except the molecular dynamics correlation that is entirely predictive. Overall a satisfactory representation of the viscosity of these 2-alkylamines is found for the different models within the considered T, p range taking into account their simplicity. Moreover, it has been verified that the viscosity is a unique function of TV γ where the exponent γ is generally related to the steepness of the intermolecular repulsive potential ( T: temperature and V: specific volume).