Research Article pubs.acs.org/journal/ascecg
Pyrrolidinium-Based Ionic Liquids as Sustainable Media in HeatTransfer Processes Małgorzata Musiał,† Katarzyna Malarz,†,‡ Anna Mrozek-Wilczkiewicz,‡,§ Robert Musiol,† Edward Zorębski,† and Marzena Dzida*,† †
University of Silesia in Katowice, Institute of Chemistry, Szkolna 9, 40-006 Katowice, Poland Silesian Center for Education and Interdisciplinary Research, University of Silesia in Katowice, 75 Pułku Piechoty 1A, 41-500 Chorzów, Poland § University of Silesia in Katowice, Institute of Physics, Uniwersytecka 4, 40-007 Katowice, Poland Downloaded via NEW MEXICO STATE UNIV on July 5, 2018 at 23:11:22 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
‡
S Supporting Information *
ABSTRACT: Ionic liquids are viewed as green media for many engineering applications and exhibit exceptional properties, including negligible vapor pressure, null flammability, wide liquid range, and high thermal and chemical stabilities. We present new thermophysical properties of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imides ([CnC1pyr][NTf2] with n = 3, 4) for future application them as heat-transfer media. The speed of sound was measured at pressures up to 100 MPa and at temperatures from 293 K to 318 K. The pρT, pCpT data, and derived thermophysical properties were determined using the acoustic method. TGA of [CnC1pyr][NTf2] and cytotoxicity of [CnC1pyr][NTf2] and their imidazolium counterparts ([CnC1im][NTf2]) are investigated. The physicochemical properties of [CnC1pyr][NTf2] are compared with those of [CnC1im][NTf2] and commercial heat-transfer fluids (Therminol VP-1, Therminol 66, Marlotherm SH). [C3C1pyr][NTf2] and [C4C1pyr][NTf2] have a wide liquid range of ∼480 K and high decomposition onset temperatures of 771 and 776 K, respectively. [CnC1pyr][NTf2] exhibit high energy storage density of ∼1.98 MJ m−3 K−1, which is slightly dependent on temperature and pressure. The thermal conductivity of [CnC1pyr][NTf2] is comparable to that of commercial heat-transfer fluids. [CnC1pyr][NTf2] have lower toxicity for normal human dermal fibroblast cells than [CnC1im][NTf2]. Thus, [CnC1pyr][NTf2] are promising heat-transfer fluid candidates. KEYWORDS: Pyrrolidinium-based ionic liquids, Green media, Energy storage density, Sustainable heat transfer fluids, Cytotoxicity, High pressure
■
INTRODUCTION The sustainability of our energy supply has become one of the greatest challenges in the present time. The development of a modern energy sector requires the search for alternative energy sources, the optimization of used technologies, and the search for innovative working fluids, which would reduce energy consumption. The applications of heat-transfer fluids include low-temperature refrigeration systems, as well as solar energy collection and thermal storage at high temperatures.1,2 The currently used heat-transfer fluids are primarily organic solvents, such as Therminol 66, Therminol VP-1, and Marlotherm SH; these fluids have a relatively high vapor pressure in the desired temperature range. Moreover, as an example, the decomposition of Therminol VP-1 generates hydrogen, which must be trapped, and thus causes an energy loss.3 ILs are currently the subject of intensive research as environmentally friendly engineering liquids in a variety of industrial applications, including solvents in separation processes and chemical reactions, lubricants, heat-transfer fluids and more. Some important features that distinguish ionic © 2017 American Chemical Society
liquids (ILs) from other compounds are good chemical and thermal stability, nonflammability, a wide range of liquidity, and an exceptionally low saturated vapor pressure at high temperatures, which makes them nonvolatile, nonexplosive, and especially attractive as heat-transfer fluids. To date, studies on ILs as heat-transfer fluids were focused on imidazoliumbased ILs with the [BF4]−, [PF6]−, or [NTf2]− anion.4−9 Tenney et al.10 analyzed the possibility of applying nine different ILs as heat-transfer fluids such as imidazolium- and pyridinium-based ILs with the [DEP]−, [C1SO4]−, [TFO]−, [SCN]− or [NTf2]− anion. Chernikova et al.11 compared the thermophysical properties of 25 imidazolium, pyrrolidinium, pyridinium, phosphonium, and ammonium derivatives with anions as above with the properties of some commercial heattransfer fluids, and they found that the substituted imidazolium and pyrrolidinium bis(trifluoromethyl sulfonyl)imides are bestReceived: August 22, 2017 Revised: October 5, 2017 Published: October 9, 2017 11024
DOI: 10.1021/acssuschemeng.7b02918 ACS Sustainable Chem. Eng. 2017, 5, 11024−11033
Research Article
ACS Sustainable Chemistry & Engineering
Table 1. Name, Acronym, CAS Number, Molar Mass, Purity, Water Content, and Halides Content of the Ionic Liquids Studied in This Work
a
name
acronym
CAS number
M (g mol )
mass fraction puritya
1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide
[C3C1pyr][NTf2] [C4C1pyr][NTf2]
223437-05-6 223437-11-4
408.38 422.41
>0.99 >0.99
−1
water content (ppm)
halides
100a/46b 100a/370b
