Saturated Fluorocarbons Research Articles

The “green” use of fluorocarbons in Cherenkov detectors and silicon tracker cooling systems: challenges and opportunities in an unfolding era of alternatives

Saturated fluorocarbons (SFCs) of form CnF(2n+2) are chosen for their optical properties as Cherenkov radiators, with C4F10 and CF4 currently used at CERN in the COMPASS and LHCb ring imaging Cherenkov detectors. Their non-conductivity, non-flammability and radiation-resistance also make SFCs ideal coolants: C6F14 liquid cooling is used in all LHC experiments, while C3F8 is used for the evaporative cooling of TOTEM and the ATLAS silicon tracker. These fluids, however, have high global warming potentials (5000–10000*GWPCO2), and represented around 36% of CERN’s CO2-equivalent emissions in 2018. There is thus an impetus to reduce their use, losses in purification and wastage through leaks, through improved monitoring and closed circulation system design. Newer spur-oxygenated fluoro-ketones, for example from the 3 M NOVEC® range, with CnF2nO structures, can offer similar performance to SFCs with but with very low, or zero GWP. Although these fluids do not yet exist in large quantities over the full CnF2 “matrix” the radiation tolerance and thermal performance of NOVEC 649 (C6F12O) was sufficiently promising for it to be chosen as a C6F14 replacement for cooling silicon photomultipliers. Additionally, subject to optical testing, NOVEC 5110 (C5F10O) could (if blended with nitrogen) replace both C4F10 and CF4 in Cherenkov detectors. Lighter molecules (for example C2F4O, with similar thermodynamics to C2F6)—if and when available in industrial quantities—might allow lower temperature operation than evaporative CO2 in future silicon trackers operated at very high luminosity. Ultrasonic gas mixture analysis is very sensitive to concentration changes of a heavy vapour in a light carrier, and is used—in the only such fluorocarbon coolant leak monitoring system operating at LHC—for real-time monitoring of C3F8 coolant leaks from the ATLAS pixel and SCT silicon trackers into their nitrogen-flushed environmental volumes. A typical C3F8 sensitivity of better than 10−5 is achieved. Advanced new ultrasonic algorithms allow measurement of the concentrations of a pair of gases of particular interest on top of a varying known baseline of other gases. The technique is thus of considerable value in leak monitoring and could be used to blend fluoro-ketones with nitrogen or argon to reduce the GWP “load” of large volume atmospheric pressure gas Cherenkov radiators without the recourse to higher-pressure noble gas approaches. This paper outlines an approach to GWP reduction with fluoro-ketone fluids and the blending of heritage SFCs or fluoro-ketones with lighter gases using ultrasonic monitoring and control. Possible avenues for the use of fluoro-ketones in liquid phase and evaporative cooling of silicon trackers are discussed.

Controlling refractive index and reducing the Global Warming Potential of Cerenkov gas radiators: a challenge in the era of diminishing fluorocarbon availability

Saturated fluorocarbons (SFCs) of the form CnF(2n+2) are chosen for their optical properties (high transparency in the near UV, adapted refractive index and low chromatic dispersion over wavelength ranges of interest) for use as Cherenkov radiators. The COMPASS and LHCb experiments currently use C4F10 and CF4 gas radiators. SFCs have high Global Warming Potentials (GWPs), however (in the range 5000–9000). There is thus an impetus to reduce their use and wastage through leaks in existing installations.Newer fluids of the form CnF2nO, including the 3M NOVEC® range, can offer similar optical performance to SFCs of the same order, n, but with GWPs equivalent to CO2. These GWPs are, however, geometry-specific: closed molecular rings having an oxygen atom as a link can have GWPs as high as those of SFCs, and should be avoided.While the optical constraints of RICH detectors can motivate a “special case” argument to retain the use of preferred SFCs, legislation and external market forces will limit their future availability, leaving “holes” in the CnFx spectrum that might not be filled by NOVEC equivalents. This situation might require the blending of low molar concentrations of heritage-stock higher-order SFCs and NOVEC vapours with transparent light gases such as nitrogen, and is the subject of this paper.While continuous optical measurement of refractive index in dynamically changing gas mixtures is very demanding, the monitoring of sound velocity has been historically shown to provide simple, reliable and continuous real time mixture information. Indeed the speed of sound is, in itself, a monitor of the speed of light and the Cherenkov threshold in a gas radiator.This ultrasonic (“sonar”) technique was first used for controlling the real-time blending C5F12 with N2 in the SLD CRID at the SLAC linear collider. The technique could become important again in future operation to meet the optical and low GWP constraints of future Cherenkov gas radiators. Some examples are explored in this paper.

Rational Design to Activate Tetrafluoromethane by Two-Coordinate Borinium.

The activation of tetrafluoromethane (CF4) is quite challenging. The current methods have a high decomposition rate but are expensive, and therefore, their widespread use is limited. Here, inspired by the successful C-F activation within saturated fluorocarbons, we have designed a rational approach based on two-coordinate borinium for activating CF4 using density functional theory (DFT) calculations. Our calculations predict that this approach is both thermodynamically and kinetically favorable.

Thermal and electrical decomposition products of C5F10O and their compatibility with Cu (1 1 1) and Al (1 1 1) surfaces

Perfluoroketone C5F10O has drawn much attention in recent years as a promising environmental-friendly gas to substitute SF6 in power equipment. In this paper, the decomposition characteristics of C5F10O and C5F10O/air mixture under pyrolysis and partial discharge conditions were explored by experiments using a gas chromatography/mass spectrometer. Besides, the compatibility of decomposition products with the copper and aluminum was evaluated based on the density functional theory calculation. We found that C5F10O has good thermal stability at 300 ℃. At 500 ℃, C5F10O starts to decompose and it produces CO, CO2, C2F6, C2F4, C3F8, C3F6, C4F10, C4F8 and CHF3, among which CO2, C3F6, and C4F10 are dominant. For C5F10O/air mixtures, the pyrolysis products are mainly saturated fluorocarbons and more CO2 is produced. Partial discharges in C5F10O/air mixture mainly produce CO2, saturated fluorocarbons and a unique compound C3F6O3. It is found that CF4, C3F6, CF2O, CHF3, and C3HF7 have good compatibility with Al (1 1 1) and Cu (1 1 1) surfaces, while the interactions between C2F6O3 and Al (1 1 1), Cu (1 1 1) surfaces are relatively strong, which are chemisorption. The identified by-products of C5F10O and C5F10O/air mixture under different conditions as well as their compatibility with metal materials is essential for online fault-diagnostic and long-term maintenance in engineering applications.

Activation of Saturated Fluorocarbons to Synthesize Spirobiindanes, Monofluoroalkenes, and Indane Derivatives.

SummaryFluorinated organic compounds are produced in abundance by the pharmaceutical and agrochemical industry, making such compounds attractive as building blocks for further functionalization. Unfortunately, activation of C(sp3)-F bond in saturated fluorocarbons, especially for aliphatic gem-difluoroalkanes, remains challenging. Here we describe the selective activation of inert C(sp3)-F bonds catalyzed by B(C6F5)3. In hexafluoro-2-propanol (HFIP), chemically robust aliphatic gem-difluorides are converted in high yields to the corresponding substituted 2,2′,3,3′-tetrahydro-1,1′-spirobiindenes via a B(C6F5)3-catalyzed intramolecular cascade Friedel-Crafts cyclization, not requiring a silicon-based trapping reagent. However, in the absence of a hydrogen-bonding donor solvent such as HFIP, the aliphatic gem-difluorides preferentially engage in a defluorination/elimination process that provides monofluorinated alkenes in good yields. Furthermore, a series of substituted 1-alkyl-2,3-dihydro-1H-indenes was obtained in high yield from the B(C6F5)3-catalyzed defluorinative cyclization of aliphatic secondary monofluorides in HFIP. The protocol could inspire development of a new class of main-group Lewis acid-catalyzed C(sp3)-F bond activation in general unactivated fluorocarbons.

B(C <sub>6</sub>F>sub>5) <sub>3</sub>-Catalyzed C(Sp <sup>3</sup>)-F Bond Activation With/Without the Cooperation of HFIP: Synthesis of Spirobiindanes, Monofluoroalkenes, and Indane Derivatives

The activation of C(sp3)-F bond in saturated fluorocarbons, especially for aliphatic gem-difluoroalkanes, remains challenging and less reported. Herein, we describe the selective activation of inert C(sp3)-F bonds catalyzed by B(C6F5)3. In hexafluoro-2-propanol (HFIP), chemically robust aliphatic gem-difluorides are converted in high yields to the corresponding substituted 2,2',3,3'-tetrahydro-1,1'-spirobiindenes via a B(C6F5)3-catalyzed intramolecular cascade Friedel-Crafts cyclization, whereby a silicon-based trapping reagent is not required. However, in the absence of a hydrogen-bonding donor solvent such as HFIP, the aliphatic gem-difluorides preferentially engage in a defluorination/elimination process that provides monofluorinated alkenes in good yields. In addition, a series of substituted 1-alkyl-2,3-dihydro-1H-indenes was obtained in high yield from the B(C6F5)3-catalyzed defluorinative cyclization of aliphatic secondary monofluorides in HFIP. The protocol could inspire the development of a new class of main-group Lewis acids-catalyzed C(sp3)-F bond activation in general unactivated fluorocarbons.

Measurement of heat transfer coefficient in two phase flows of radiation-resistant zeotropic C2F6/C3F8 blends

We have measured the flow boiling heat transfer coefficient (HTC) of saturated fluorocarbon blends in a horizontal copper-nickel tube with a diameter of 4mm. Direct (Joule) heating of the tube wall was used to obtain heat fluxes from 5 to 13.7kWm−2. Two different injection capillaries were used, permitting measurements at mass fluxes varying between 94 and 164kgm−2s−1. The evaporation pressure was approximately 0.2MPa for the mass fluxes close to 164kgm−2s−1 and 0.15MPa for the lower mass fluxes. The same tube dimensions and material are used in the on-detector cooling channels of the silicon micro-strip charged particle tracker (“SCT”) of the ATLAS experiment at the CERN Large Hadron Collider. The range of heat flux and mass flow studied encompasses the operating conditions of the tracker. When operating in the high radiation environment near to the proton beam collisions radiation tolerant coolants are essential. Saturated fluorocarbons (CnF(2n+2)) are radiation resistant and allow thermodynamic “tailoring” by blending saturated molecules of different orders. Measurements were made with pure C3F8 (R218) and zeotropic blends containing 5, 10, 15, 20 and 25% (molar) C2F6 (R116). This work is a continuation of a previous study which showed that the operating temperature of the ATLAS SCT could be reduced by around 10°C with the admixture of 25% (molar) C2F6, with no changes needed to the existing on-detector and circulatory pipework. The data analysis revealed multiple flow boiling regimes of the two-phase flow that varied as a function of coolant flow rate, heat flux, vapour quality and mixture composition. As expected, the HTC in pure C3F8 was higher than in blends with increasing C2F6 content. Nevertheless, the study confirmed that the ATLAS SCT could be operated at full power dissipation with cooling tube temperatures up to 10°C colder than in pure C3F8 with C3F8/C2F6 blends having relatively modest values of HTCs in the range 1500–4000Wm−2K−1.

Experimental study on the formation of higher fluorocarbons from CF4 by a tip–tip electrical arc discharge at very high pressure

This work presents the study of the synthesis of higher fluorocarbons from tetrafluoromethane (CF4) with a plasma process based on the generation of a tip–tip electrical discharge at very high pressure. A series of experiments were performed using a He/CF4 mixture with a ratio 60/40% at a pressure of 2MPa to investigate the effects of two modes of treatment: a continuous mode and an intermittent mode including a 30s relaxation time between two successive discharges. The study shows the production of low quantities of saturated fluorocarbons (C2F6 and C3F8) at the experimental conditions employed. It also shows the intermittent mode of treatment to be more efficient in the synthesis of the saturated C2 and C3 fluorocarbon molecules in comparison to the continuous mode. The continuous treatment mode leads to unfavorable kinetics of synthesis for a given discharge duration while the intermittent treatment mode leads to an increase of higher fluorocarbon production with the number of discharges.

ChemInform Abstract: Main‐Group Lewis Acids for C—F Bond Activation

AbstractReview: 86 refs.

Main-Group Lewis Acids for C–F Bond Activation

The significant benefits of fluorinated compounds have inspired the development of diverse techniques for the activation and subsequent (de)functionalization of rather inert C–F bonds. Although substantial progress has been made in the selective activation of C(sp2)–F bonds employing transition metal complexes, protocols that address nonactivated C(sp3)–F bonds are much less established. In this regard, the use of strong main-group Lewis acids has emerged as a powerful tool to selectively activate C(sp3)–F bonds in saturated fluorocarbons. This Perspective provides a concise overview of various cationic and neutral silicon-, boron-, and aluminum-based Lewis acids that have been identified to facilitate the heterolytic fluoride abstraction from aliphatic fluorides. The potential of these Lewis acids in hydrodefluorination as well as defluorinative C–F bond functionalization reactions is highlighted. Emphasis is placed on the underlying mechanistic principles to provide a systematic classification of the in...

Aspects of the use of saturated fluorocarbon fluids in high energy physics

The excellent dielectric properties of saturated fluorocarbons have allowed their use in direct immersion liquid cooling of electronics, including supercomputers and as heat transfer media in vapour phase soldering and burn-in testing of electronics. Their high density, UV transparency, non-flammability, non-toxicity and radiation tolerance have led to their use as liquid and gas radiator media for RICH detectors in numerous particle physics experiments. Systems to circulate and purify saturated fluorocarbon Cherenkov radiator vapours often rely on thermodynamic evaporation–condensation cycles similar to those used in refrigeration. Their use as evaporative refrigerants was pioneered for the ATLAS silicon tracker, and they are now also used as evaporative coolants in ALICE and TOTEM and as liquid coolants in ATLAS and CMS. Ultrasonic techniques for vapour phase analysis of fluorocarbon mixtures—developed for the SLAC SLD barrel CRID radiator during the 1980s as an alternative to UV refractometry are again under development for the ATLAS tracker evaporative cooling system. Examples of fluorocarbon circulation systems, together with purification and analysis techniques for these versatile fluids are mentioned.

Properties of saturated fluorocarbons: Experimental data and modeling using perturbed-chain-SAFT

We present experimental speed of sound data for the saturated fluorocarbons used most frequently in particle detector cooling systems. Data were collected over the moderate range of pressure (≤0.4 MPa) and temperature 250–340 K. A commercial sound/density analyzer operating on the vibrating tube principle was employed for the measurements in liquid state. A dedicated sonar analyser – described in detail – was recently redesigned and developed for the speed of sound measurements in gas phase. Data for speed of sound in saturated fluorocarbons presented in previous papers [V. Vacek, G. Hallewell, S. Ilie, S. Lindsay, Fluid Phase Equilib. 174 (2000) 191–201; V. Vacek, G. Hallewell, S. Lindsay, Fluid Phase Equilib. 185 (2001) 305–314] were reanalyzed and corrected and some new measured data were added. Our experimental data were then used to validate a theoretically based equation of state application rather than the empirical or semi-empirical equations of state mostly used up to now in fluorocarbon applications.

Effect of Gas Impurities on the Throttling Process of Fluorocarbon Refrigerants: Estimation of the Henry’s Law Constant

The effect of the presence of noncondensing gases on the throttling process of a saturated fluorocarbon refrigerant was studied. Two-phase flow of the throttled refrigerant was investigated in a special divided small-diameter tube equipped with pressure and temperature sensors. Gas impurities affected the manner of onset of vaporization and consequently decreased the overall effectiveness of a vapor cooling circuit. Available literature data on three gases (O2, Xe, N2) was collected and analyzed to establish a simple temperature correlation for the Henry’s law constant of gases dissolved in saturated fluorocarbons at a low gas partial pressure around 0.1 MPa. The Peng-Robinson cubic equation of state and the perturbed-chain modification of statistical associating fluid theory (PC-SAFT) were employed to predict the temperature dependency of gas solubility in fluorinert substances.

Functionalization of Saturated Fluorocarbons with and Without Light.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Functionalization of saturated fluorocarbons with and without light

Photochemical transformation of saturated fluorocarbons into tetrabutylammonium enolates has been improved, and a method employing ketyls as reductants has been developed that accomplishes the same chemistry without light. Enolates have been isolated as enol methyl ethers, from which they can be efficiently regenerated with tetrabutylammonium iodide. In other cases, enolates have been isolated as the corresponding ketone or stable enol. Fluorocarbon LUMO energies correlate with their reactivity and serve as a guide to the choice of ketyl. Use of this chemistry for fluoropolymer surface modification is discussed.

Gas and Vapor Sorption, Permeation, and Diffusion in Poly(tetrafluoroethylene-co-perfluoromethyl vinyl ether)

Solubilities of N2, CO2, C1−C3 saturated hydrocarbons, C1−C3 saturated fluorocarbons, and normal- and cyclo-C5 and -C6 alkanes at 35 °C are reported in an amorphous, rubbery, random copolymer composed of 50.7 mol % tetrafluoroethylene and 49.3 mol % perfluoromethyl vinyl ether, TFE/PMVE49. Permeabilities of N2, O2, CO2, and C1−C3 saturated hydrocarbons in this polymer at 35 °C are also presented. Solubilities of hydrocarbon vapors in this fluoropolymer are lower than those of their corresponding fluorocarbon analogues due to less favorable interactions of the fluorinated polymer with hydrocarbon vapors than with fluorocarbon penetrants. Polymer density was measured over a wide temperature and pressure range to estimate parameters for equation-of-state modeling of gas sorption. Modeling the sorption isotherms with the Sanchez−Lacombe equation-of-state model requires a reduction of approximately 10% in the cohesive energy density of the gas−polymer mixture from that predicted by the geometric mean mixing ru...

Perfluorinated Cyclic Phosphazenes.

Publisher Summary This chapter discusses properties and reaction chemistry of perfluorinated cyclophosphazenes, with an emphasis on comparing their reactivity with that of the perchlorinated analogs. In contrast to chloro- and bromophosphazenes, for which a variety of synthetic methods have been reported, the only effective way of making fluorophosphazenes is by fluorinating chlorophosphazenes to per-or polyfluorinated derivatives using a variety of fluorinating reagents. Fluorination of chlorophosphazenes, especially the trimeric phosphazene, has been the subject of studies primarily to understand the mechanism and regiospecificity involved in metathetical reactions. The boiling points of the cyclic fluorophosphazenes are similar to those of saturated aliphatic fluorocarbons of comparable molecular weight. Structures of cyclic fluorophosphazenes, especially those of the smaller rings, received increased attention because these data were utilized to support theoretical studies in which participation of phosphorus d orbitals and contraction of d orbitals for effective overlap for π bonding were discussed. Reactions of a variety of monofunctional nucleophiles have been carried out with trimeric perfluorinated phosphazenes.

Functionalization of saturated fluorocarbons

A method is described for transforming perfluoroalkanes and perfluorocycloalkanes bearing tertiary fluorine into perfluoroenolates, which can be variously derivatized.

Synchrotron radiation ablative photodecomposition and production of crystalline fluoropolymer thin films

Deposition of crystalline thin films of polytetrafluoroethylene (PTFE) was carried out on Si(100) substrates by synchrotron irradiation of a PTFE target in vacuo. In situ mass spectrometric analysis of gaseous species evolved during the irradiation shows that, different from the laser ablation of PTFE for the deposition, the SR-induced reactions should be ablative photochemical decomposition (APD) rather than photothermal unzipping decomposition, yielding saturated fluorocarbons rather than monomers as the main gaseous products. Detection of a trace of CF3 in the deposited films by XPS and FTIR was consistent with our APD mechanism. In our processing, an increase in the target temperature made great improvements including considerable enhancement of the deposition rates, reduction of the CF3 component, and achievement of the crystalline features closer to the PTFE target, whereas an increase in the substrate temperature made the film surface rough.

Selective Solubility of Organometallic Complexes in Saturated Fluorocarbons. Synthesis of Cyclopentadienyl Ligands with Fluorinated Ponytails

Cyclopentadienes bearing varying length fluorinated “ponytails”, C5H5[(CH2)n(CF2)mF] ([n.m] = [0.8], [0.10], [0.12], [2.6], [2.8], and [2,10]) have been prepared by reaction of the corresponding fluoroalkyl iodides and triphenylphosphine with nickelocene. From these, the 1,1‘-bis[2.6]-, 1,1‘-bis[2.8]-, and 1,1‘-bis[2.10]-disubstituted ferrocenes and [2.10]-substituted [Mn(CO)3L], [Re(CO)3L], and [Co(CO)2L] derivatives (L = η5-C5H4[2.10]) were prepared. Although the anions of the [0.m] compounds were thermally unstable, the corresponding [0.8], [0.10], and [0.12] cobalt dicarbonyl complexes were prepared directly from the cyclopentadienes. The solubilities of these compounds in both saturated fluorocarbon (fluorous) and conventional solvents was found to depend strongly on the length of the fluoroalkyl tail and on the temperature. These compounds all dissolve in fluorous solvents, and the 1,1‘-bis[2.10]ferrocene partitions selectively into the fluorous layer of a biphasic perfluoro(methylcyclohexane)/toluene system. The oxidation potentials of the 1,1‘-, bis[2.6]-, and 1,1‘-bis[2.10]ferrocenes are only very slightly more positive than ferrocene itself, demonstrating that the C2H4 spacer effectively insulates the electron-withdrawing effect of the fluoroalkyl part of the ponytail from the metal. A similar insulating effect is noted in the carbonyl stretching frequencies of [Mn(CO)3L], [Re(CO)3L], and [Co(CO)2L] derivatives (L = η5-C5H4[2.10]), which are slightly to low energy of those in the corresponding parent cyclopentadienyl analogues. In contrast, the corresponding frequencies in [Co(CO)2L] derivatives (L = η5-C5H4[0.10]; η5-C5H4[0.12]) without the hydrocarbon spacer group are at higher energy than the parent compound.