Properties of Carbon Dioxide Legal units of measurement and most recent technical developments Preface Consumers from all sectors are showing keen interest in carbon dioxide (CO2). This document contains data and information characterising the physical, chemical and physiological properties of carbon dioxide. It takes into account both the legal units of measurement and the latest technical developments. Ihre Messer Group GmbH 2 Gases for Life | Properties of Carbon Dioxide Contents Important data for CO2 4 Temperature-entropy diagram 6 Pressure-enthalpy diagram 8 Vapour table 10 Specific heat capacities of CO2 11 Water content as a function of dew point 12 Solubility of water in liquid CO2 14 CO2 solubility in water 14 CO2 solubility in alcohol and other organic liquids 16 Pressure conditions in CO2 cylinders as a function of temperature and filling level 18 Isochores (lines of equal density) 19 Specific volume of CO2 at different temperatures and pressures 20 Density of CO2 22 Dissociation 24 Neutralisation 25 Definitions 26 Units of measurement and conversion tables 27 Literature references 34 This publication is based on the state of technical knowledge at the time of issue. It is the responsibility of the user to check its applicability to his or her particular case and to ensure that the version in use is up to date. Neither the Messer Group GmbH nor those involved in the preparation of the publication accept any liability for its use. Gases for Life | Properties of Carbon Dioxide 3 Important data for CO2 Chemical formula CO2 (atomic bonding O = C = O) Molar mass MCO2 = 44.011 kg/kmol 3 Standard molar volume Vmn = 22.263 m /kmol Specific gas constant RCO2 = 0.1889 kJ/(kg ∙ K) 3 Standard density rn = 1.977 kg/m CO2/air density ratio under standard d = 1.529 conditions Critical temperature tcrit = 31 °C Critical pressure Pcrit = 73.83 bars 3 Critical density rcrit = 466 kg/m Sublimation point ts = -78.9 °C bei 0.981 bars Triple point tT = -56.6 °C bei 5.18 bars Decomposition temperature From about 1,200°C, for a decomposition level of about 0.032 vol% Colour in gaseous state Colourless Fire behaviour Not combustible, known as a fire-extinguishing agent Static electricity/charge When CO2 effuses into the atmosphere from the liquid phase, the dry ice particles that form give rise to an “electrostatic charge”. Reactivity under normal conditions Stable compound, employed as an inert gas at normal ambient temperatures. Combination with water CO2+H2O=H2CO3 Of the CO2 gas dissolved in water, only about 0.1% exists as the acid H2CO3. The pH value of aqueous CO2 solutions at standard pressure is 3.7. Under pressure, it falls to a limiting value of 3.3. Hence CO2 is well suited as a neutralising medium for alkaline solutions. Odour Odourless Taste Neutral Toxicity Non-toxic, legally approved for use with foodstuffs and does not require declaration OEL value 5,000 ml/m3 (ppm) as an eight-hour average Medical application Inhalation of 3 to 5% CO2 in breathing gas Experience with high Irritation of the respiratory centre at 30,000 to 50,000 ppm (3 to 5 vol%). concentrations of CO2 in breathing gas Loss of consciousness at 70,000 to 100,000 ppm (7 to 10 vol%) due to lack of oxygen. 4 Gases for Life | Properties of Carbon Dioxide 103 Supercritical Solid Liquid 102 Critical point p,T-Diagramm 10 Pressure p, bars The regions in which the various Triple point pressure and temperature dependent 1 aggregate states of CO2 exist can be seen in the phase diagram (p,T) Gaseous 10-1 173 223 273 323 373 Temperature T, K Solid CO2 (dry ice) At p = 0.981 bars and t = -78.9°C (194.25 K) Heat of sublimation rs = 573.02 kJ/kg Refrigerating capacity when warming from -78.9°C (194.25 K) auf 0°C (273 K) qO ≈ 645 kJ/kg Gases for Life | Properties of Carbon Dioxide 5 Temperature-entropy (t,s) diagram for CO2 solid – liquid – vapour Plank and Kuprianoff Specific enthalpy h, kJ/kg Specific volume v, dm3/kg Pressure p, bar 0.9 Entropy s, kcal/(kg·K) 1.0 1.1 1.2 1.3 1.4 At 0°C [= 273.15 K] gilt: h 790 40 100 h = 418.7 kJ/kg [= 100 kcal/kg] 30 liq 413 140 90 140 780 20 413 80 15 = 5.18 10 8 6 tr sliq = 4.187 kJ/(kg ∙ K) [= 1 kcal/(kg ∙ K)] p 770 70 130 130 403 60 403 50 760 393 120 120 750 393 740 383 110 110 383 730 720 373 100 100 373 710 700 363 90 90 690 363 680 , K 670 T 353 80 80 , °C 353 t 660 650 343 70 640 70 630 343 620 610 600 60 3 60 333 590 100 5 333 Temperature 580 4 6 570 Temperature 560 8 550 110 10 50 540 90 50 323 530 323 520 15 510 80 40 500 40 313 70 313 490 70 100 31°C , K 480 tK = 150 60 , °C t v = 200 T 303 30 470 30 303 50 460 20 Temperature 40 450 50 20 20 293 440 293 30 40 430 10 30 10 283 418.68 283 s, kcal/(kg·K) 0.7 0.8 420 20 410 0 0 273 0 400 273 v = 2 390 3 263 -10 10 -10 263 380 4 370 300 600 800 5 500 15 253 -20 400 -20 360 8 253 6 350 1000 -30 243 -30 x = 0.1 243 340 8 0.4 10 0.6 6 x = 0.9 = x 0.2 0.8 330 0.7 0.3 -40 233 -40 = 5.18 233 tr 320 15 p , K 0.5 , °C T 310 t 300 20 223 -50 -50 223 Temperature 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 30 40 50 4 3 100 2 213 -60 -60 213 90 80 v = 1200 -70 203 -70 1.5 203 1.0 v = 10 70 0.8 193 -80 0.6 -80 193 60 0.4 183 -90 0.7 -90 0.5 0.8 183 50 100 0.4 0.3 x = 0.9 p = 0.2 50 200 0.2 0.6 1000 x = 0.1 500 173 -100 -100 173 2.5 3.0 3.5 4.0 4.1868 4.5 5.0 5.5 Entropy s, kJ/(kg·K) 6 Gases for Life | Properties of Carbon Dioxide 0.9 Entropy s, kcal/(kg·K) 1.0 1.1 1.2 1.3 1.4 h 790 40 100 30 413 140 90 140 780 20 413 80 15 = 5.18 10 8 6 tr p 770 70 130 130 403 60 403 50 760 393 120 120 750 393 740 383 110 110 383 730 720 373 100 100 373 710 700 363 90 90 690 363 680 , K 670 T 353 80 80 , °C 353 t 660 650 343 70 640 70 630 343 620 610 600 60 3 60 333 590 100 5 333 Temperature 580 4 6 570 Temperature 560 8 550 110 10 50 540 90 50 323 530 323 520 15 510 80 40 500 40 313 70 313 490 70 100 31°C , K 480 tK = 150 60 , °C t v = 200 T 303 30 470 30 303 50 460 20 Temperature 40 450 50 20 20 293 440 293 30 40 430 10 30 10 283 418.68 283 s, kcal/(kg·K) 0.7 0.8 420 20 410 0 0 273 0 400 273 v = 2 390 3 263 -10 10 -10 263 380 4 370 300 600 800 5 500 15 253 -20 400 -20 360 8 253 6 350 1000 -30 243 -30 x = 0.1 243 340 8 0.4 10 0.6 6 x = 0.9 = x 0.2 0.8 330 0.7 0.3 -40 233 -40 = 5.18 233 tr 320 15 p , K 0.5 , °C T 310 t 300 20 223 -50 -50 223 Temperature 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 30 40 50 4 3 100 2 213 -60 -60 213 90 80 v = 1200 -70 203 -70 1.5 203 1.0 v = 10 70 0.8 193 -80 0.6 -80 193 60 0.4 183 -90 0.7 -90 0.5 0.8 183 50 100 0.4 0.3 x = 0.9 p = 0.2 50 200 0.2 0.6 1000 x = 0.1 500 173 -100 -100 173 2.5 3.0 3.5 4.0 4.1868 4.5 5.0 5.5 Entropy s, kJ/(kg·K) Gases for Life | Properties of Carbon Dioxide 7 Pressure-enthalpy (p,h) diagram for CO2 350 400 450 500 550 600 650 700 750 solid – liquid – vapour 383 K 383 373 K 373 403 K 403 333 K 333 323 K 323 353 K 353 243 K 248 K 253 K 258 K 263 K 268 K 273 K 278 K 283 K 288 K 293 K K 313 308 K 308 233 K 298 K K 303 343 K 343 305.££‚5 K 305.££‚5 310.5 K 310.5 393 K 393 363 K 363 T = 223 K According to Plank-Kuprianoff 110 110 6 7 2 1 4. 8 5 6 2 0 .7 5 9 3 8 0 0 1 4.