International Journal of Greenhouse Gas Control 42 (2015) 494–501 Contents lists available at ScienceDirect International Journal of Greenhouse Gas Control j ourna l ho me page: www.elsevier.com/locate/ijggc An excess Gibbs free energy based model to calculate viscosity of multicomponent liquid mixtures Diego D.D. Pinto a,∗ , Hallvard F. Svendsen b a PROCEDE Group B.V., PO Box 328, 7500 AH Enschede, The Netherlands b Department of Chemical Engineering, Norwegian University of Science and Technology, N-7491 Trondheim, Norway a r t i c l e i n f o Article history: Received 20 July 2015 Received in revised form 31 August 2015 Accepted 2 September 2015 Keywords: Viscosity Excess Gibbs Liquid NRTL CO2 capture a b s t r a c t Solution densities and viscosities are important parameters for the design and simulation of absorption processes. Accurate models are needed and in this work, a new model for calculating the liquid viscosity of mixtures is presented. The model uses an analogy to excess Gibbs energy models to account for the deviation from a simple mixing rule based on the pure component viscosities. In this work, we chose the functional form of the NRTL model to represent the excess Gibbs energy and the resulting model is referred to as NRTL-DVIS. Eleven systems (eight binaries and three ternary) were chosen for testing the accuracy of the model. The ternary systems were built from the optimized binaries and pure component systems. With few adjustable parameters, the NRTL-DVIS model represented the tested systems with good accuracy. With few exceptions the calculated total deviation (AARD) was within 3.5%. The NRTL-DVIS model shows better accuracy than other models proposed in the literature. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Densities and viscosities of solutions are especially important when designing and simulating processes. In particular viscosity is important in processes where mass transfer is involved (e.g., absorbers and desorbers). Moreover, equipments such as pumps and heat exchangers are better modeled when the physical proper- ties of the system are accurately calculated (Fu et al., 2012; Weiland et al., 1998). Several properties of a system can be directly correlated to its viscosity. For instance, Versteeg et al. (1996) show that the dif- fusivity of alkanolamines can be estimated from viscosity with a modified Stokes–Einstein relation. Hence, a good representation of the viscosity of the solution is crucial. Proposed correlations for liquid viscosity available in the literature, unfortunately, do not share the same theoretical basis as for gas viscosity (Poling et al., 2000). Therefore, it is desirable to estimate the liquid viscosity from experimental data whenever available. Many correlations are available in the literature to calculate the viscosity of both pure liquids and mixtures of liquid components. A number of proposed models use the pure liquid viscosity as a starting point and apply a mixing rule to calculate the viscosity ∗ Corresponding author. E-mail address: DiegoPinto@Procede.nl (D.D.D. Pinto). of the mixture. In these cases, it is required that pure component liquid viscosities are known at given temperatures and pressures. However, for solutions where the viscosity of at least one of the components is not known, the applicability of these types of equa- tions is not straightforward. Aqueous solutions of hydroxide salts are examples of solutions where the liquid viscosity of one com- ponent (in this case, the hydroxide) is not known for a wide range of temperatures. These solutions are of interest for CO 2 capture processes (see Yoo et al., 2013; Mahmoudkhani and Keith, 2009; Stolaroff et al., 2008). When the pure viscosity of one (or more components) is not available, models which use a reference viscosity are usually applied (see, for instance, Först et al., 2002; Mathlouthi and Reiser, 1994; Vand, 1948). An extensive review on this type of viscosity models is found in Longinotti and Corti (2008). Alternatively, one can still use models which require the pure viscosity of the compo- nents by, for instance, setting the unknown viscosity to a constant value. In this work, a new model for calculating the viscosity of multi- component liquid mixtures is presented. The model is based on the fact that excess viscosities show similar behaviour as that observed for excess Gibbs energy. Hence, the functional forms of the many existing models capable of representing excess Gibbs energy can be used for representing excess viscosities. In particular, the func- tional form of the NRTL model was chosen in this work. By setting few binary interaction parameters, the model is able to accurately represent the viscosity of liquid mixtures. Eight binary systems and http://dx.doi.org/10.1016/j.ijggc.2015.09.003 1750-5836/© 2015 Elsevier Ltd. All rights reserved.