Fluid Phase Equilibria 356 (2013) 30–37 Contents lists available at ScienceDirect Fluid Phase Equilibria j our na l ho me pa ge: www.elsevier.com/locate/fluid Electrical conductivity of ammonium and phosphonium based deep eutectic solvents: Measurements and artificial intelligence-based prediction F.S. Ghareh Bagh a , K. Shahbaz b , F.S. Mjalli c,∗ , I.M. AlNashef d , M.A. Hashim a a Chemical Engineering Department, University of Malaya, Kuala Lumpur, Malaysia b School of Engineering, Taylor’s University, Selangor, Malaysia c Petroleum and Chemical Engineering Department, Sultan Qaboos University, Muscat, Oman d Chemical Engineering Department, King Saud University, Riyadh, Saudi Arabia a r t i c l e i n f o Article history: Received 1 March 2013 Received in revised form 2 June 2013 Accepted 4 July 2013 Available online 17 July 2013 Keywords: Deep eutectic solvents Electrical conductivity Artificial neural network Phosphonium Ammonium a b s t r a c t The evaluation of deep eutectic solvents (DESs) as a new generation of solvents for various practical appli- cation requires an insight of the main physical, chemical, and thermodynamic properties. In this study, the experimental measurements of the electrical conductivity of two classes of DESs based on ammonium and phosphonium salts at different compositions and temperatures were reported. The results revealed that electrical conductivity of DESs has temperature-dependency. In addition, molar conductivities of ammonium and phosphonium salts in DESs were obtained using DESs experimental values of electrical conductivities. The feasibility of using an artificial neural network (ANN) model to predict the electrical conductivity of ammonium and phosphonium based DESs at different temperatures and compositions was also examined. A feed-forward back propagation neural network with 8 hidden neurons was suc- cessfully developed and trained with the measured electrical conductivity data. The results indicated that among the different networks tested, the network with 8 hidden neurons had the best prediction per- formance and gave the smallest value of Normalized Mean Square Error (NMSE) (0.0010) and acceptable values of Index of Agreement (IA) (0.9999) and Regression Coefficient (R 2 ) (0.9988). The comparison of the predicted electrical conductivity of DESs by the proposed model with those obtained by experiments confirmed the reliability of the ANN model with an average absolute relative deviation (AARD%) of 4.40%. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Ionic liquids (ILs) are salts with weak ionic interaction which allows them to be liquid in ambient temperature (typically below 373.15 K). The scientific and significant importance of ILs have spanned a broad range of applications, owing to their tempting physicochemical properties, such as thermal and chemical stabil- ity, low melting point, negligible volatility, high ionic conductivity, moderate viscosity, high polarity, and solubility (affinity) with many compounds [1–5]. Their potential use in a variety of chem- ical and industrial applications as green solvents has been greatly explored [1,3]. Nevertheless, ILs are too expensive to be used in bulk applications since they cannot be well prepared at the labora- tory with one step of synthesis. Due to the multi-stage purification processes required to purify the ILs after their synthesis, their pro- duction cost is quite high. Consequently, researchers prefer to buy ∗ Corresponding author. Tel.: +968 2414 2558; fax: +968 2414 1354. E-mail address: farouqsm@yahoo.com (F.S. Mjalli). them than to synthesize them locally. This imposes a constraint on using them as a viable and practical industrial chemical ingredient [6,7]. Fortunately, a low cost alternative for ILs is available. Deep eutectic solvents (DESs) belong to a class of ionic liquids which are mixtures of a quaternary salt with a metal halide (Lewis acid), a hydrated salt, or an ordinary hydrogen bond donor (HBD) such as alcohol, amide as well as carboxylic acid as complexing agent. This results in the formation of an eutectic mixture with a melting point that is considerably lower than its original precursors. For this rea- son, this mixture is called a DES. Moreover, DESs overcome some principal disadvantages from ILs, they are easy to prepare in pure state, non-reactive with water, fairly safe (when carefully designed from benign components) and biodegradable [8–12]. Recently, few research groups reported the synthesis and use of DESs in different applications. Abbott research group was the first to report the synthesis and use of ammonium-based DESs in different promising applications [9]. They described for the first time the electrodeposition of composite materials using DESs [13]. Kareem et al. [14] reported some important physical properties of 0378-3812/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2013.07.012