Liquid-liquid equilibria, solubility and critical states in the system propionic acid – 1-propanol – n-propyl propionate – water at 303.15 K

Highlights

• LLE for the propionic acid – propanol – propyl propionate – water have been determined at 303.15 K.

• LLE compositions were correlated by NRTL model.

• Solubility and compositions of critical points have been obtained at 303.15 K.

• The critical surface in quaternary system was considered.

Abstract

New experimental data on liquid-liquid equilibria (LLE), solubility and critical states in quaternary system propionic acid – 1-propanol – n-propyl propionate – water at 303.15 K and atmospheric pressure are presented. LLE was studied by Gas Chromatography (GC). Solubility and critical (plait) points were investigated by “cloud-point technique” method. Binodal curves and surfaces are presented in concentration tetrahedron. The critical curve is presented in 3d concentration space. A comparative analysis of the results obtained in the work with literature data is carried out. The experimental data are correlated by NRTL model. Standart deviation σ for quaternary mixture does not exceed 0.344%.

Introduction

Nowadays organic compounds play a huge role not only in the area of organic chemistry and synthesis but also in such sections as industrial production, medicine and pharmaceuticals are inconceivable without their participation. At the same time, researchers and engineers often face challenges which are not connected with the search for new options for the synthesis of various organic substances, but with the selection of more convenient conditions for existing methods. Mainly optimization is a decisive part of the design and development of technological processes of both the synthesis itself and its final stages like the separation of the resulting component and its subsequent analysis. The interrelation of the mentioned methods is very important, since obtaining the most pure organic product with the highest yield is the goal of any synthesis both in production and in scientific research. It is obvious that for this it is necessary to select the optimal conditions for the extraction of this organic product from a solution. Completeness of extraction is largely determined by the right selected solvent (extractant), the choice of which is not always in its selectivity. Essential factors of its choice are availability and cost, a number of physicochemical properties (for example, the degree of immiscibility with the components of the mixture), toxicity. In this case, the classic example of extractants are relatively safe esters of carboxylic acids and alcohols.

This question is particularly important because, for example, 1-propanol contained in the object of this study, can serve as a fuel additive [1], [2], [3], [4]. Analysis of the results of recent years presented in the world literature shows that the attention of researchers, in general, is focused on the physico-chemical study of model systems, including alcohols, promising for use as a biofuel. Considered in this paper, due to its low cost and the dissolving ability of a wide range of substances, n-propyl propionate sometimes can be used instead butyl acrylate [5]. N-propyl propionate is widely used in industry as a solvent for acrylic resins with high solids content. The esterification product of propionic acid and 1-propanol is non-toxic [6], and therefore extremely relevant in industrial areas: paint and varnish production, pharmaceutical production, coatings [7], [8]. Through its pleasant smell n-propyl propionate is an indispensable component in the food and perfume industry.

The main goal of this work is to study phase equilibrium in liquid multicomponent systems formed by propionic acid, 1-propanol, n-propyl propionate and water. Despite the above practical significance of n-propyl propionate in technological processes, primarily as a solvent and extractant, data on liquid–liquid equilibria in systems with its participation are almost absent in the scientific literature [9]. Basically, the literature contains data on the vapor–liquid equilibrium [10], [11], [12], [13] and a lot of works devoted to the reactive distillation [14], [15], [7], [16], [17], [18], [19].

First results of study the solubility of n-propyl propionate in water had been presented by Hemptinne in 1894 [20] at 298 K and in the thesis by Rayman in 1906 [21] at 273.15 – 303.15 K and 101.325 KPa. LLE in this binary system was investigated in [22] in temperarure range 273–363 K and atmospheric pressure. The isothermal (293 K) titration method was used to obtain mutual solubility data for the binary system n-propyl propionate – water by Mozzhukhin et al. [13]. The same method was applied to get the these solubility results in [23] at 293.15 – 353.15 K and 101.325 KPa. The recommended data by Getzen, Hefter and Maczynski on solubility for this two-component system are also collected in [24].

It should be noted that there are a limited number of papers corresponding to the study of LLE in ternaries subsystems: 1-propanol – n-propyl propionate – water and propionic acid – n-propyl propionate – water. There is a solubility data obtained by titration method for the ternary system with alcohol [13] at 293 K and [10] at 288.15 K. Articles devoted to the study of LLE in the system propionic acid – n-propyl propionate – water are completely absent. The only paper we published earlier [25] contains detailed information on LLE not only for the binary and ternary subsystems mentioned above, but also data for the quaternary system propionic acid – 1-propanol – n-propyl propionate – water at 293.15, 313.15 and 333.15 K.

The main goal of this work is to present new data for intermediate temperature 303.15 K not only on liquid–liquid phase equilibrium, but also on solubility, and especially on critical compositions for the quaternary system. For the first time the critical curve for this system in isothermal-isobaric conditions in the concentration are presented.