Separation and Purification Technology 73 (2010) 106–113 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Kinetics of reactive absorption of propylene in RTIL-Ag + media Alfredo Ortiz a , Lara María Galán b , Daniel Gorri a , André B. de Haan b,∗ , Inmaculada Ortiz a,∗∗ a Advanced Separation Processes – Dep. Chemical Engineering & Inorganic Chemistry University of Cantabria, Spain b Process System Engineering Group- Dep. Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands article info Article history: Received 11 January 2010 Received in revised form 10 March 2010 Accepted 11 March 2010 Keywords: Propylene Silver BMImBF4 Reactive absorption Kinetics abstract In the present work the kinetics of absorption of propylene in Ag + -BMImBF 4 medium have been analysed, discriminating the kinetic regime and determining the expression and parameters of the rate of reactive absorption as a function of the concentration of both reagents. A stirred cell reactor was used to obtain the kinetic information by loading pure absorption gas and recording the total pressure decrease at different silver salt concentrations [AgBF 4 = 0–1 M] at 288–308 K. The experimental values of the enhancement factors (E A ) due to the presence of the chemical reaction indicate that for concentrations equal to or higher than 0.25 M of Ag + in BMImBF 4 it is possible to assume instantaneous chemical reaction between propylene and silver ions. Therefore, the rate of absorption in this case is governed by the rate at which dissolved C 3 H 6 and Ag + diffuse to the reaction plane from the G–L interface and liquid bulk, respectively. Physico-chemical parameters necessary to predict the absorption rate have been experimentally deter- mined in this work. The liquid mass transfer coefficient (k L ) was obtained in a non-reactive BMImBF 4 medium as a function of stirring speed and temperature, showing a significant increase from 1.61 × 10 -6 to 17.9 × 10 -6 ms -1 when the temperature increased from 288 to 308 K at 500 rpm. Experimental vis- cosity measurements for the reactive system Ag + -BMImBF 4 are reported in order to predict the diffusion coefficient of propylene in the absorptive media. Diffusivity of the silver ions in BMImBF 4 has been determined by the chronoamperometry technique, showing a concentration dependency in the range of AgBF 4 = [0.05–0.25 M]. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The separation of olefins and paraffins is of primary impor- tance in the chemical industry. Gas streams with extremely high purity (>99.9%) olefin-content are required in the production of polymers and many other chemicals as propylene oxide. Tradi- tional systems, like low-temperature distillation, are expensive, energy-consuming and voluminous process equipment due to the similarity in boiling points of olefins and their correspond- ing paraffin [1–3]. Therefore, alternative, less-expensive separation methods are required. In a previous work, Ortiz et al. [4] pro- posed as an attractive alternative to the classical separation of gaseous mixtures propane/propylene the reactive absorption combining the formation of reversible complexes olefin-silver in room temperature ionic liquids (RTILs) as efficient reaction media. The separation is based on the ability of silver ions to reversibly complexate olefins [2]. The advantage of chemical complexation is that the bonds formed are stronger than those formed by van der ∗ Corresponding author. Tel.: +31 40 247 5259; fax: +31 40 246 3966. ∗∗ Corresponding author. Tel.: +34 942201585; fax: +34 942201591. E-mail addresses: a.b.dehaan@tue.nl (A.B. de Haan), ortizi@unican.es (I. Ortiz). Waals forces alone, so it is possible to achieve high selectivity and high capacity for the component to be bounded. At the same time, the bonds are still weak enough to be broken by using simple engi- neering operations such as raising the temperature or decreasing the pressure [5]. Solvents with high olefin-capacity, selectivity and resistance to contaminants and process conditions are still needed. Room temperature ionic liquids (RTILs) can be used as reactive absorp- tion solvents for olefin/paraffin separations because of their ionic and organic character together with its renowned and remarkable properties. Among other properties, RTILs are non-volatile and can be considered as designer solvents [6,7]. In this work, 1-butyl-3- methylimidazolium tetrafluoroborate, BMImBF 4 , has been selected because of its absorption selectivity for propylene over propane and its ability to dissolve a suitable silver salt (silver tetrafluorob- orate, AgBF 4 ), allowing to absorb propylene due to the reversible complexation of silver ions with unsaturated olefinic double bonds [4,8]. The knowledge of the physico-chemical characteristics of the system, kinetic and equilibrium data of the complexation reac- tion between propylene and silver are required to design industrial separation processes. Several works have analysed the reaction of complexation between olefins and transition metals in aqueous and organic 1383-5866/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2010.03.008