Simultaneous Measurements of Solubilities and Diﬀusion Coeﬃcients of Volatile Species in Liquids Bernd J¨ahne, Institut f¨ur Umweltphysik and HCI, Universit¨at Heidelberg Bernd.Jaehne@iwr.uni-heidelberg.de 7th SOPRAN Annual Meeting, March 25/26, 2014, Universit¨at Bremen   State of the Art • For many volatile species of environmental importance, no measured diﬀusion coeﬃcients in fresh water and sea water are available, but only theoretical estimates [6, 7] according to the Wilke and Chang relation [5]. • These estimates are associated with high uncertainties. • Most measurements do not cover full range of environmental tempera- tures, 0–40 ◦C. Solubility (partition coeﬃcient α in cm3/cm3), diﬀusion coeﬃcient D, and Schmidt number Sc in water for some gases and volatile species useful for gas exchange studies and/or of environmental importance. All values at 25 ◦C. Values marked in grey: no measurements available, only estimates. Species MG g/Mol α D, (10−5cm2/s) Sc Long-lived species 3He 3.02 0.0089 8.30 108 4He 4.00 0.0095 7.22 124 H2 2.02 0.0191 5.13 174 Ne 20, 22 0.0110 4,16 215 Kr 80–86 0.061 1.84 486 Xe 128–136 0.107 1.47 608 N2 28.01 0.0161 2.3 388 O2 32.00 0.031 2.6 344 N2O 44.01 0.591 1.92 468 CO2 44.01 0.86 1.92 468 methane (CH4) 16.04 0.0346 1.84 486 acetylene (C2H2) 26.04 0.97 1.68 532 n-hexane (C6H14) 86.18 0.0188 0.79 1131 cyclohexane (C6H12) 84.16 0.124 0.94 947 cyclohexene (C6H10) 82.15 0.54 0.92 971 benzene (C6H6) 78.11 4.4 1.10 812 Fluorocarbons CF4 88.00 0.0052 1.42 629 SF6 146.06 0.0060 1.20 745 pentaﬂuorethane 120.02 0.184 1.12 798 diﬂuoromethane (CH2F2) 52.02 2.1 1.64 545 CFC-12 (CCl2F2) 120.91 0.052 1.08 825 CFC-13 (CClF3) 104.46 0.025 1.02 880 1,4-diﬂuorobenzene (C6H4F2) 114.09 3.2 0.94 950 hexaﬂuorobenzene (C6F6) 186.05 0.1 0.86 1039 Halocarbons chloromethane (CH3Cl) 50.49 2.55 1.40 638 bromomethane (CH3Br) 94.94 4.0 1.35 662 iodomethane (CH3I) 173.84 4.6 1.29 693 dichloromethane (CH2Cl2) 84.90 8.6 1.26 709 dibromomethane (CH2Br2) 173.84 27.2 1.16 770 diiodomethane (CH2I2) 267.84 66 1.03 867 chloroform (CHCl3) 119.38 6.3 1.08 827 bromoform (CHBr3) 252.73 44 0.98 912 Oxygenated volatile organic carbons (OVOCs) methanol (CH40) 32.04 5380 1.66 538 acetonitrile (C2H3N) 41.05 1270 1.38 647 acetaldehyde (C2H40) 44.05 342 1.39 643 dimethyl ether (C2H60) 46.07 25 1.30 687 acetone (C3H60) 58.08 690 1.28 698 Sulfur containing volatiles hydrogen sulﬁde (H2S) 34.08 2.51 1.35 662 carbonyl sulﬁde (COS) 60.08 0.48 1.48 604 carbon disulﬁde (CS2) 76.14 1.41 1.31 682 dimethyl sulﬁde (C2H6S) 62.13 12.7 1.35 662 Nitrogen containing volatiles ammonia (NH3) 17.03 670 1.72 519 dimethylamine 45.08 1410 1.45 715 trimethylamine 59.11 363 1.04 519 Previous Experimental Approaches Diaphragm Method Diﬀusion through a water diaphragm gel (0.5% agarose) with thickness d supported by a 0.5 mm silicon rubber membran [1]. Evaluation by modifed Barrer method [1] Diﬀusion constant from delay: Tl = d2 6D Solubility from linear concentration increase (slope m): m = αD dheﬀ6D Works very well for inert gases with low solubility, not suitable for volatile liquids because of high surface to volume ratio of apparatus [4]. Jet Method From Petermann [3] • Short contact times • Invasion ﬂow proportional to α √ D • Evasion ﬂow proportional to √ D • Diﬃcult to handle, not suitable for automated operation. Proposed Novel Experimental Approach • Simultaneous determination of diﬀusion coeﬃcients and solubility by gas transfer measurements in gas-tight tank • Partly ﬁlled with water (Vw) and argon atmosphere (V a) • Built out of seawater-resistant aluminum, total volume 15 L; suitable for corrosive gases and liquids • Gas phase stirred by wind paddle • Temperature control by Peltier cooling/heating • Automatic measurements using computer-controlled mass ﬂow control- lers and magnetic values • Use of reference tracers with well known diﬀusivity and solubility for absolute measurements of diﬀusion coeﬃcients; candidates marked red in table on left. Tran