In this work, the density, viscosity, thermal conductivity, and isobaric heat capacity of mixtures of 2-ethylhexanoic acid (EHA) and p-xylene, as well as self-diffusion co- efficients of both components were measured at 101.3 kPa and temperatures between 293.15 and 353.15 K. Furthermore, vapor-liquid equilibria of this system were studied at 10 and 20 kPa. Parameters for correlations of all properties are reported together with the data in this work to facilitate the application of the results in modeling and simulation of spray flame synthesis. 1 Introduction 2-Ethylhexanoic acid (EHA) and xylene are commonly used solvents in spray flame synthesis ofnanoparticles. Mixturesofthesecomponentsaresuitablesolventsforvariousprecursors.1–7 Moreover, when studying spray flame processes with numerical techniques, mixtures of EHA andxylenecanbeusedasasimpler, surrogatemodelsystemforthefrequentlyusedprecursor solutions containing metal 2-ethylhexanoates and xylene.8–11In the mentioned applications, all three isomers of xylene, i.e., o-xylene, m-xylene, and p-xylene, occur. However, the influence of the choice of the isomer on the overall spray flame process is expected to be marginal. The p-xylene isomer is studied in this work to maintain consistence with previous work.12 Despite their relevance especially in the field of spray flame synthesis, to the best of our knowledge, no data on the properties of mixtures of EHA and xylene are available in the literature. Due to its use as an industrial solvent and intermediate,13data on the properties of purep-xylene are sufficiently available. The properties of pure EHA were extensively studied in our previous work on mixtures of EHA and ethanol.14 In this work, the density, the viscosity, the thermal conductivity, and the isobaric heat capacity of mixtures of EHA and p-xylene, as well as the self-diffusion coefficients of both componentsweremeasuredattemperaturesbetween293.15Kand353.15Kandatmospheric pressure over the entire composition range. Additionally, vapor-liquid equilibria (VLE) were investigated at 10 kPa and 20 kPa. 2 Experimental Chemicals and Sample Preparation Table 1 lists the CAS registry numbers, suppliers, and purities of the chemicals used in this work. Table 1: Chemicals CAS reg. no. supplier mole fraction puritya 2-ethylhexanoic acid (EHA) 149-57-5 Sigma-Aldrich 0.998 p-xylene 106-42-3 Thermo Fischer Scientific 0.997 1,4-dioxane 123-91-1 Sigma-Aldrich 0.9993 aAs specified by supplier Smallsamples(samplemass<50g)wereneededfortheself-diffusioncoefficientmeasure- mentsandwerepreparedgravimetricallyusingaMettler-Toledolaboratorybalance(specified standard uncertainty u(m) = 0 .0001 g). Larger samples were needed for the density and viscosity measurements as well as the thermal conductivity and isobaric heat capacity mea- surementsandwerepreparedusingaMettler-ToledoPR2003Comparatorlaboratorybalance (specified standard uncertainty u(m) = 0 .001 g). The combined expanded uncertainty of the composition of the samples is U(xXyl) = 0 .001 mol mol−1(k= 2). For the VLE measurements, about 100 – 200 ml of feed mixture were needed for each run. The equilibrium compositions of the vapor and liquid phase depend on the temperature, the pressure, and the local composition in the apparatus. Therefore, their dependence on the feed composition is fuzzy and, for simplicity, the feed for the VLE measurements was prepared volumetrically. Measurements The measurement methods for the density, viscosity, thermal conductivity, isobaric heat capacity, and self-diffusion coefficients were the same as in our previous work.12,14–16In 3 these