Elsevier

Fluid Phase Equilibria

Volume 338, 25 January 2013, Pages 265-268
Fluid Phase Equilibria

Solid–liquid equilibrium of 1-hydroxyethane-1,1-diphosphonic acid in different solvents

https://doi.org/10.1016/j.fluid.2012.11.001Get rights and content

Abstract

The solubilities of 1-hydroxyethane-1,1-diphosphonic acid in five different solvents including ethanol, isopropyl alcohol, n-propyl alcohol, acetone and acetic acid were determined at temperatures ranging from 288.45 to 327.95 K at atmospheric pressure using a gravimetric method. Van’t Hoff equation was used to correlate the experimental solubility data. The calculated values of van’t Hoff equation were found to be in good agreement with the experimental data. Further, the dissolution enthalpy and entropy of HEDP in the corresponding solvents were predicted.

Introduction

The solubility of materials is a thermodynamic variable that depends on their chemical composition and with temperature. Most solutes exhibit increasing solubility with increasing temperature, although the rate of the increase varies widely from compound to compound [1]. Solubility is also affected by the pH, by the presence of additional species in the solution, and by the use of different solvents. Especially when dealing with organic species (or inorganics in nonaqueous solvents) a wide variety of solvents and solvent mixtures can usually be employed. Although the solubility of many binary and ternary systems in aqueous solution can be found in various Refs. [2], [3], [4], [5], many more combinations of solvent and solute remain to be investigated. This is because the measurement of solubility using the current experimental method is time consuming and usually require large amount of pure solute which are often unavailable or can be very expensive.

1-Hydroxyethane-1,1-diphosphonic acid (HEDP, molecular weight 206.02) is a strong chelating agent and has been found to bind to numerous metal ions with high stability. In consequence of its powerful metal-binding ability, this simple diphosphoric acid and its derivatives are used widely in water purification and treatment [6], metal ion extraction [7] and pharmaceutical industry [8]. The chemical name of this compound is 1-hydroxyethane-1,1-diphosphonic acid. Fig. 1 shows the chemical structure of HEDP. In industrial manufacturing, HEDP is often refined through crystallization from solution. The determination of its solubility in different solvents is then crucial to choose the proper solvent and to optimize the crystallization process. A literature survey on available solubility data of HEDP in different solvents reveals no systematic study [9]. The present papers relating to HEDP are mainly concerned with synthesis and chelation except for one paper on solubility of HEDP in aqueous acetic acid mixtures reported by our group recently [10]. However, to ascertain the suitable solvent, a systematic determination of the solubility of HEDP in potential solvents is necessary.

In the present work, experimental solubility data for HEDP in five different solvents, ethanol, isopropyl alcohol, n-propyl alcohol, acetone and acetic acid, were determined at temperatures ranging from 288.45 to 327.95 K at atmospheric pressure using a gravimetric method. The dissolution enthalpy and entropy of HEDP were predicted from the solubility data using van’t Hoff equation.

Section snippets

Materials

HEDP (supplied by Jiangsu Jianghai Chemical Co., Ltd., China) was recrystallized one time from water by cooling crystallization. Its purity was analyzed by an automatic titration system and the mass fraction purity is >99.5%. The ethanol, isopropyl alcohol, n-propyl alcohol, acetone and acetic acid used for experiments were of analytical reagent grade, all supplied by Tianjin Chemical Reagent Co., China and used without further purification for experiments. Their mass fraction purities are

Results and discussions

The measured HEDP solubilities in different solvents are represented in Table 2. For real solution, the van’t Hoff equation relates the logarithm of mole fraction of a solute as a linear function of the reciprocal of the absolute temperature [9]:lnx1=ΔHdRT+ΔSdRwhere T is solution temperature (K), ΔHd and ΔSd are the dissolution enthalpy and entropy, respectively. R is the gas constant (8.314 J mol−1 K−1). The calculated solubility data and values of dissolution enthalpy and entropy of HEDP in

Conclusions

The solubility of HEDP in ethanol, isopropyl alcohol, n-propyl alcohol, acetone and acetic acid were determined at temperatures ranging from 288.45 to 327.95 K at atmospheric pressure using gravimetric method. The experimental solubility data were correlate using van’t Hoff equation. The results show that, for all examined solvents, the solubility of HEDP increases with increasing temperature. The increase rate of solubility with temperature is in the order: n-propyl alcohol > isopropyl alcohol > 

List of symbols

    x1

    solubility of the solute, mol mol−1

    m1

    the mass of the solute, g

    m2

    the mass of the solvent, g

    M1

    the corresponding molecular mass of the solute, g mol−1

    M2

    the corresponding molecular mass of the solvent, g mol−1

    T

    absolute temperature, K

    R2

    coefficient of correlation

    R

    gas constant, J mol−1 K−1

    ΔGd

    Gibbs energy, kJ mol−1

    ΔHd

    dissolution enthalpy, kJ mol−1

    ΔHm

    the enthalpy of melting of HEDP, kJ mol−1

    ΔHmix

    enthalpy of mixing, kJ mol−1

    ΔSd

    dissolution entropy J mol−1 K−1

    Tm

    the melting temperature, K

    x1exp

    experimental solubility

Acknowledgments

We thank the financial support by the Doctoral Fund of Ministry of Education of China (2011M500511) Tianjin Municipal Natural Science Foundation (11JCYBJC 04600) and the Seed Foundation of Tianjin University for their financial assistances in this project.

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