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ETHANOL AND DISTILLATE BLENDS: A THERMODYNAMIC APPROACH TO MISCIBILITY ISSUES

机译：乙醇和蒸馏混合物：混溶性问题的热力学方法

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In the recent years, the quest for an ever wider cluster of sustainable primary energies has prompted an increasing number of attempts to combine the emission sobriety of bio fuels with the energy density advantage of fossil fuels.A number of compositions incorporating hydrocarbons, ethanol and in some cases limited amounts of water have been proposed, especially in the forms of micro emulsions, with a variable success. Indeed due to markedly different physical and chemical properties, ethanol and gasoil are able to blend and form homogeneous solutions only in limited proportion ranges. Indeed, such mixtures often give rise to liquid-liquid equilibrium. A key parameter is thus the Minimum Miscibility Temperature (MMT), i.e. the temperature above which ethanol and gasoil become completely miscible.In fact, commercial gasoils do not constitute a monolithic product but display in the contrary a large span of compositions that influence the stability of these blends. In this context, the LRGP laboratory (Laboratoire Reactions et Genie des Procedes) has undertaken an investigation program intended to understand the factors underlying the stability of ethanol/gasoil blends.The approach is based on the calculation of the liquid-liquid phase diagrams formed by anhydrous ethanol and a mixture of various hydrocarbons representative of the diesel oil pool using the group contribution concept. Indeed, for correlating thermodynamic properties, it is often convenient to regard a molecule as an aggregate of functional groups; as a result, somethermodynamic properties (heat of mixing, activity coefficients) can be calculated by summing group contributions. In this study, the universal quasichemical functional group activity coefficient (UNIFAC) method has been employed as it appears to be particularly useful for making reasonable estimates for the studied non ideal mixtures for which data are sparse or totally absent. In any group-contribution method, the basic idea is that whereas there are thousands of chemical compounds of interest in chemical technology, the number of functional groups that constitute these compounds is much smaller. Therefore, if we assume that a physical property of a fluid is the sum of contributions made by the molecule's functional groups, we obtain a possible technique for correlating the properties of a very large number of fluids in terms of a much smaller number of parameters that characterize the contributions of individual groups.This paper shows the large influence exerted by the paraffinic, aromatic and naphthenic character of the gasoil but also the sulfur content of the fossil fraction on the shape of the liquid-liquid phase diagram and on the value of the minimum miscibility temperature.
机译：近年来，对更广泛的可持续一次能源集群的追求促使越来越多的尝试将生物燃料的清醒性与化石燃料的能量密度优势相结合。 已经提出了许多结合了烃，乙醇以及在某些情况下有限量的水的组合物，特别是以微乳状液的形式，并取得了不同的成功。实际上，由于物理和化学性质的显着不同，乙醇和粗柴油只能在有限的比例范围内混合并形成均质溶液。实际上，这种混合物常常引起液-液平衡。因此，关键参数是最低混溶温度（MMT），即乙醇和粗柴油完全混溶的温度。 实际上，市售瓦斯油并不构成整体产品，相反却显示出影响这些共混物稳定性的大量组合物。在这种情况下，LRGP实验室（Laboratoire Reactions et Genie des Procedes）采取了一项调查计划，旨在了解乙醇/粗柴油混合物稳定性的基础因素。 该方法基于使用基团贡献概念计算由无水乙醇和代表柴油池的各种碳氢化合物的混合物形成的液相图。实际上，为了关联热力学性质，将分子视为官能团的集合通常很方便。结果，一些 热力学性质（混合热，活度系数）可通过将基团贡献相加得出。在这项研究中，已使用通用准化学官能团活度系数（UNIFAC）方法，因为它对于为稀疏或完全缺乏数据的研究非理想混合物做出合理的估计似乎特别有用。在任何基团贡献方法中，基本思想是，尽管化学技术中有成千上万的目标化合物，但构成这些化合物的官能团的数量要少得多。因此，如果我们假设流体的物理性质是分子的官能团做出的贡献的总和，那么我们将获得一种可能的技术，该技术可以根据数量非常少的参数来关联大量流体的性质，描述各个群体的贡献。 本文显示了瓦斯油的链烷烃，芳烃和环烷烃特性以及化石馏分的硫含量对液-液相图的形状以及最低混溶温度的值具有很大的影响。

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