Evaluation of Phase Separation Models and Miscibility Behavior of Diol-Based Additives in Gasoline
Bakir ELOUARET, Asiah Nusaibah MASRI, Hasrinah HASBULLAH, Izni Mariah IBRAHIM
Abstract. This study investigates the miscibility and phase separation behavior of diol-based oxygenated additives in gasoline through a combination of experimental and thermodynamic modeling approaches. Binary (methanol/hexane) and ternary (methanol/hexane/ethylene glycol) systems were experimentally tested to validate three thermodynamic models—Non-Random Two-Liquid (NRTL), UNIQUAC Functional-group Activity Coefficients (UNIFAC), and WILSON—using Aspen Plus simulations. Among them, the NRTL model demonstrated the highest accuracy, with percentage errors generally below 10%, confirming its suitability for predicting liquid–liquid equilibrium (LLE) in polar–nonpolar systems. The validated NRTL model was then applied to evaluate the miscibility of 23 diols with gasoline, including linear, branched, and unsaturated structures. Results demonstrated that miscibility is critically influenced by hydroxyl group positioning, carbon chain architecture, and the presence of unsaturation. Specifically, diols with vicinal or internal OH groups exhibited superior compatibility compared to those with terminal OH groups. Branching (e.g., 2-methyl-1,3-propanediol) and unsaturation (e.g., trans-2-butene-1,4-diol) further enhanced miscibility by reducing polarity and strengthening hydrocarbon interactions. In contrast, increasing carbon chain length alone provided only a modest improvement. Crucially, to provide direct design guidelines for fuel formulation, this study establishes a definitive structural ranking for diol–gasoline miscibility: Unsaturated diols > Vicinal diols > Branched diols > Longer-chain linear diols. These findings establish NRTL as a reliable predictive tool and provide design insights for developing diol-based additives that are fully compatible with hydrocarbon fuels.
Keywords
Diol Additives, Gasoline Miscibility, Phase Separation, NRTL Model, Fuel Blending
Published online 5/10/2026, 17 pages
Copyright © 2026 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA
Citation: Bakir ELOUARET, Asiah Nusaibah MASRI, Hasrinah HASBULLAH, Izni Mariah IBRAHIM, Evaluation of Phase Separation Models and Miscibility Behavior of Diol-Based Additives in Gasoline, Materials Research Proceedings, Vol. 66, pp 98-114, 2026
DOI: https://doi.org/10.21741/9781644904152-10
The article was published as article 10 of the book Advanced Materials and Sustainable Energy Technologies
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
References
[1] Q. Wang, J. Ni, R. Huang, The potential of oxygenated fuels (n-octanol, methylal, and dimethyl carbonate) as an alternative fuel for compression ignition engines with different load conditions, Fuel 309 (2022) https://doi.org/10.1016/j.fuel.2021.122129
[2] D. Jesu Godwin, V. Edwin Geo, S. Thiyagarajan, M. Leenus Jesu Martin, T. Maiyalagan, C.G. Saravanan, F. Aloui, Effect of hydroxyl (OH) group position in alcohol on performance, emission and combustion characteristics of SI engine, Energy Conversion and Management 189 (2019) 195-201. https://doi.org/10.1016/j.enconman.2019.03.063
[3] Suyatno, H. Riupassa, S. Marianingsih, H.Y. Nanlohy, Characteristics of SI engine fueled with BE50-Isooctane blends with different ignition timings, Heliyon 9 (2023) e12922. https://doi.org/10.1016/j.heliyon.2023.e12922
[4] M.D. Bohon, M.J. Al Rashidi, S.M. Sarathy, W.L. Roberts, Experiments and simulations of NOx formation in the combustion of hydroxylated fuels, Combustion and Flame 162 (2015) 2322-2336. https://doi.org/10.1016/j.combustflame.2015.01.022
[5] J. Zhu, R. Li, Z. Wang, S. Liu, H. Lv, Decoupled analysis of the effect of hydroxyl functional groups on delay of ignition with fictitious hydroxyl, Process Safety and Environmental Protection 161 (2022) 285-294. https://doi.org/10.1016/j.psep.2022.03.028
[6] O.I. Awad, R. Mamat, T.K. Ibrahim, A.T. Hammid, I.M. Yusri, M.A. Hamidi, A.M. Humada, A.F. Yusop, Overview of the oxygenated fuels in spark ignition engine: Environmental and performance, Renewable and Sustainable Energy Reviews 91 (2018) 394-408. https://doi.org/https://doi.org/10.1016/j.rser.2018.03.107
[7] J.K.A. Bezerra, R.R. da Silva, E.L. de Barros Neto, G.G. de Medeiros, L.J.N. Duarte, H.N.M. de Oliveira, Evaluation of the Effect of Ethyl Alcohol Content In A Ternary Ethanol/Biodiesel/Diesel System, International Journal of Thermodynamics 27 (2024) 19-26. https://doi.org/10.5541/ijot.1372558
[8] M.V. Kirillov, A.A. Sizova, V.V. Sizov, Octanediols in confined hydrocarbon/water systems: A molecular simulation study of aggregation phenomena and liquid–liquid interface morphology, Journal of Molecular Liquids 428 (2025) 127503. https://doi.org/https://doi.org/10.1016/j.molliq.2025.127503
[9] C. Jin, X. Zhang, X. Wang, Y. Xiang, X. Cui, Z. Yin, X. Sun, J. Ji, G. Wang, H. Liu, Effects of polyoxymethylene dimethyl ethers on the solubility of ethanol/diesel and hydrous ethanol/diesel fuel blends, Energy Science & Engineering 7 (2019) 2855-2865. https://doi.org/https://doi.org/10.1002/ese3.466
[10] N. Ali, The Effect of Compositions (PIONA) on the Octane Numbers of Environmental Gasolines of Reformate, Isomerate and Hydrocracked Naphtha Blends by Using GC, International Journal of Oil, Gas and Coal Engineering 5 (2017) 167. https://doi.org/10.11648/j.ogce.20170506.17
[11] J.A. Labarta, M.M. Olaya, A.F. Marcilla, What does the NRTL model look like? Determination of boundaries for different fluid phase equilibrium regions, AIChE Journal 68 (2022) e17805. https://doi.org/https://doi.org/10.1002/aic.17805
[12] M. Rakhatkyzy, B. Suleimenova, M. Shaimardan, D. Shah, N. Nuraje, Modeling Solubility of Acetylsalicylic Acid in Aspen Plus, Engineered Science 26 (2023) 987. https://doi.org/10.30919/es987
[13] E. Sheikholeslamzadeh, S. Rohani, Solubility prediction of pharmaceutical and chemical compounds in pure and mixed solvents using predictive models, Industrial and Engineering Chemistry Research 51 (2012) 464-473. https://doi.org/10.1021/ie201344k
[14] H. Tun, Y. Hao, M. Haddix, C.C. Chen, Thermodynamic solubility modeling of 2, 2ʹ, 4, 4ʹ, 6, 6ʹ – hexanitrostilbene (HNS), Fluid Phase Equilibria 565 (2023) https://doi.org/10.1016/j.fluid.2022.113627
[15] Z.A. Hamamah, T. Grützner, Measurement and thermodynamic correlation of liquid–liquid equilibria of water + n-propanol + toluene at 20°C and atmospheric pressure, Discover Chemical Engineering 4 (2024) 20. https://doi.org/10.1007/s43938-024-00057-6
[16] M. Neagu, P. Rosca, R.E. Dragomir, O. Mihai. The effect of bioalcohol on the water solubility in reformulated gasoline. in Chemical Engineering Transactions. 2010.
[17] X. Li, L. Hou, C. Chai, S. He, Y. Huang, A New Molecular Insight in Effects of Alcohol Co-Solvents on Miscibility of Anhydrous Ethanol/Diesel Blends, Journal of Energy Resources Technology, Transactions of the ASME 145 (2023) https://doi.org/10.1115/1.4056115
