Article pubs.acs.org/IECR
Experimental and Theoretical Thermodynamic Study of Distillable Ionic Liquid 1,5-Diazabicyclo[4.3.0]non-5-enium Acetate Alexandr Ostonen,*,† Justine Bervas,† Petri Uusi-Kyyny,† Ville Alopaeus,† Dzmitry H. Zaitsau,‡ Vladimir N. Emel’yanenko,‡ Christoph Schick,§ Alistair W. T. King,∥ Jussi Helminen,∥ Ilkka Kilpelaï nen,∥ Artashes A. Khachatrian,⊥ Mikhail A. Varfolomeev,⊥ and Sergey P. Verevkin*,‡ †
Department of Biotechnology and Chemical Technology, Aalto University, Kemistintie 1, FI-00076 P.O. Box 16100, Espoo, Finland Institut für Chemie, Physikalische Chemie, Universität Rostock, Dr-Lorenz-Weg 1, 18059 Rostock, Germany § Institut für Physik, Polymerphysik, Universität Rostock, Albert-Einstein-Str. 23-24, 18051 Rostock, Germany ∥ Department of Chemistry, University of Helsinki, A.I. Virtasen Aukio 1, FI-00014 P.O. Box 55, Helsinki, Finland ⊥ Department of Physical Chemistry, Kazan Federal University, Kremlevskaya str. 18, 420008 Kazan, Russia ‡
S Supporting Information *
ABSTRACT: A thermochemical study of the protic ionic liquid 1,5diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]), a prospective cellulose solvent considered for the Ioncell-F process, was carried out. The heat capacities of 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and [DBNH][OAc] were measured by differential scanning calorimetry (DSC) at 223− 323 and 273−373 K temperature ranges, respectively. The enthalpies of fusion and synthesis reaction of [DBNH][OAc] were measured by DSC and reaction calorimetry, respectively. The gas-, liquid-, and solid-phase enthalpies of formation of [DBNH][OAc] and DBN were determined using calorimetric and computational methods. The enthalpy of vaporization of [DBNH][OAc] was estimated from the formation enthalpies. The activity coefficients at infinite dilution of 17 and the enthalpies of solution at infinite dilution of 25 organic solutes in [DBNH][OAc] were measured by gas chromatography and solution calorimetry methods, respectively. The obtained data will be used in the design and optimization of the Ioncell-F process.
1. INTRODUCTION In the near future, the demand for textile fibers will increase rapidly while increasing cotton production will be challenging because of its high consumption of land area and water. Thus, an increased demand for the production of cellulose fibers with properties similar to those of cotton fiber is expected.1 Currently, cellulose fibers are produced commercially either via derivatization (Viscose process) or direct dissolution (Lyocell process). However, both processes have considerable disadvantages. The solvent N-methylmorpholine N-oxide (NMMO) used nowadays in the Lyocell process is unstable and flammable and requires high temperatures during cellulose dissolution and spinning. The Viscose process, on the other hand, produces lower-quality fibers and uses hazardous carbon disulfide as a solvent. Therefore, novel solvents are required to address these intrinsic problems and enable the environmentally friendly and feasible production of the cellulose fibers.2,3 Within the last decade, solvation properties of protic and aprotic ionic liquids have been studied intensively.4 From the group of protic ionic liquids, a new subclass of distillable ionic liquids was presented first by King et al.5 The reported distillable ionic liquids consisted of a superbase cation and a carboxylic acid anion. In addition to their recyclability via distillation, some of these ionic liquids were reported to effectively dissolve cellulose.5,6 From this subclass, the ionic © 2016 American Chemical Society
liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]; see Figure 1) first reported by Parviainen et al.6 was
Figure 1. Reaction of the ionic liquid ([DBNH][OAc]) synthesis from the precursors DBN and acetic acid.
considered to be the greatest potential system for a novel dryjet wet spinning process named Ioncell-F. Several cellulose dissolution and regeneration studies performed for [DBNH][OAc] have revealed that it is less hazardous, requires lower temperature for cellulose regeneration, and produces stronger filaments than NMMO.2,3,7 Received: Revised: Accepted: Published: 10445
June 23, 2016 August 5, 2016 August 18, 2016 August 18, 2016 DOI: 10.1021/acs.iecr.6b02417 Ind. Eng. Chem. Res. 2016, 55, 10445−10454
Article
Industrial & Engineering Chemistry Research Despite its aforementioned advantages, the main criterion for the industrial application of the process is its feasibility, which highly depends on the solvent recycling efficiency. Similarly to NMMO in the Lyocell process, [DBNH][OAc] has to be almost completely (>99%) recycled.8 In addition, the energy consumption of the recycling process has to be at the same level or lower than in the Lyocell process. The recent study by Parviainen et al.9 demonstrated that the efficient recycling of [DBNH][OAc] is possible. However, the optimization of the solvent recovery via thermal separation requires thermodynamic data of [DBNH][OAc] as well as its precursors 1,5diazabicyclo[4.3.0]non-5-ene (see Figure 1) and acetic acid. Unfortunately, only a small fraction of the required data is currently available.6,10,11 The main purpose of this work was to address this issue with an extensive study of thermodynamic properties of DBN and [DBNH][OAc]. Using a combination of experimental and computational methods, we studied in this work heat capacities, enthalpy of reaction, enthalpy of solution, enthalpy of formation, as well as thermodynamics of fusion and vaporization. To test capacity of [DBNH][OAc] for industrial separation processes, activity coefficients and enthalpies of solution at infinite dilution of organic solutes in [DBNH][OAc] were measured in this work by a gas chromatographic method and by solution calorimetry. An effect of temperature on the solubility of organic compounds in [DBNH][OAc] was analyzed on the basis of the solution calorimetry results. The results obtained in this work are aimed for design and optimization of the Ioncell-F process.
Figure 3. Hydrolysis and condensation reactions of [DBNH][OAc] into [APPH][OAc] and APPAc.
around 323 K during the whole time of synthesis to keep the hydrolysis reaction rate low. The mole fraction of the hydrolysis product (APP or APPH+) was analyzed using proton nuclear magnetic resonance (1H NMR) spectroscopy. The 1H NMR samples were prepared by dissolving 20 mg of the sample in 0.7 mL of DMSO-d6. Quantitative spectra were acquired at 300 K on a Varian UNITY INOVA 600 MHz NMR spectrometer using ∼45° pulse angle and 8 transients with a recovery delay of 30 s. The analysis of the [DBNH][OAc] samples has been previously described in Parviainen et al.9 Furthermore, because the chemical shifts of ionizable species depend on the sample acidity, samples containing purified DBN with small traces of acetic acid, APP, and 1-(3-acetamidopropyl)-2-pyrrolidone (APPAc, see Figure 3) were prepared to support signal assignment and integration in such cases. Peak fitting was used for integration in difficult cases of signal overlap. The measured mole fractions of the hydrolysis products were ≤0.0001 and ≤0.0095 for DBN and [DBNH][OAc], respectively. The measured APPAc mass fraction in [DBNH][OAc] was less than 100 ppm. Because of the careful temperature management during the synthesis, the possibility of [DBNH][OAc] decomposition into APPAc (Figure 3) was minimized. The ionic liquid [DBNH][OAc] samples synthesized from the carefully purified DBN samples were white. The measured water mass fraction in the [DBNH][OAc] samples was less than 300 ppm. The purity of the produced [DBNH][OAc] sample was further analyzed using the 1H NMR. The samples used for the thermochemical measurements had purity higher than 98.9% in mass. Further purification of [DBNH][OAc] via the vacuum distillation failed because the ionic liquid [DBNH][OAc] underwent decomposition, and it was observed to evaporate as two products during the distillation. The distillation conditions of the first product were very close to that of pure DBN. The second product was distilled at considerably higher temperatures and was more viscous than pure DBN. Compositions of the distillates were analyzed using 1H NMR. The first distillate contained ≥98.9 wt % DBN, while the second distillate was a complex of acetic acid and DBN having the ratio HOAc:DBN = 5:3. The remaining bottom flask product mainly contained the same complex with small amounts of APP and APPAc (
