Adsorption Isotherms of Water, Propan-2-ol, and Methylbenzene

Article pubs.acs.org/jced

Adsorption Isotherms of Water, Propan-2-ol, and Methylbenzene Vapors on Grade 03 Silica Gel, Sorbonorit 4 Activated Carbon, and HiSiv 3000 Zeolite Józef Nastaj and Tomasz Aleksandrzak* Department of Chemical Engineering and Environmental Protection Processes, West Pomeranian University of Technology, Szczecin Aleja Piastów 42, 71-065 Szczecin, Poland ABSTRACT: This work reports adsorption isotherms of water, propan-2-ol, and methylbenzene vapors on three commercial adsorbents: grade 03 silica gel, Sorbonorit 4 activated carbon, and HiSiv 3000 zeolite. The adsorption isotherms were measured at (293.15, 313.15, 333.15, 348.15, 373.15, 393.15, and 413.15) K and pressures up to 2340 Pa for water, 4460 Pa for propan-2-ol, and 2910 Pa for methylbenzene. Additionally measurements for the water vapor−Sorbonorit 4 system at (293.15, 303.15, 313.15, and 323.15) K and relative humidity up to 95% (at 323.15 K up to 70%) were made because of different type of adsorption isotherm. The measurements were carried out by intelligent gravimetric analyzer. The data obtained from measurements were correlated with selected multitemperature adsorption isotherms equations: Toth, Langmuir−Freundlich, and Dubinin−Astakhov. the highest adsorption capacity.5 Therefore, it is necessary to use equilibrium data for a particular adsorbent, not for the type.5 This work presents data concerning adsorption equilibria of water and selected VOC (propan-2-ol and methylbenzene) vapors on three adsorbents: grade 03 silica gel, Sorbonorit 4 activated carbon, and HiSiv 3000 zeolite. Measurements were made by intelligent gravimetric analyzer (IGA). Three selected equilibrium modelsToth, Langmuir−Freundlich, and DubininAstakhovwere fitted to experimental equilibrium data.

1. INTRODUCTION The fast development of industry in the last few decades is main reason for the considerable growth of atmospheric air pollution. Volatile organic compounds (VOCs) are recognized as the most common group of polluting substances.1 Pollution of the atmosphere by VOCs may have negative effects on the health of humans and animals as well as plants.2 The harmfulness of VOCs was noticed by many governments which introduced regulations to limit VOC emissions into the atmosphere.1 Adsorption processes are common ways to remove and recover VOCs from bulk gas streams.1 The main advantages of the adsorption processes are low operation costs, even for very low VOCs concentrations (below 10−6 kg·kg−1), and simplicity of the industrial adsorption systems.1 An important problem during purifying of industrial gases is the presence of water vapor in almost all gas streams.3 The presence of water vapor significantly influences the adsorption capacity of the adsorbents.3 For modeling of the adsorption processes, the equilibrium data over a wide range of temperatures and pressures must be known.4 The current state of the art modeling does not allow for the theoretical prediction of a single-component adsorption equilibrium.4 Therefore, for each pair of adsorbate−adsorbent it is necessary to determine the experimental data.4 In the literature, there is a large amount of data concerning the adsorption equilibrium of various pairs of adsorbate−adsorbent. However, the adsorption capacity of the adsorbents of the same type (for example, activated carbons) may vary significantly. Ye et al.5 presented study on the adsorption equilibrium of propylene and ethylene on fifteen commercial activated carbons. Differences in the adsorption capacity of particular adsorbents were large, equaled approximately 300% between the lowest and © 2013 American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Materials. Three commercial adsorbentsgrade 03 silica gel (Grace Davison, USA), Sorbonorit 4 activated carbon (Norit, The Netherlands), and HiSiv 3000 high silica zeolite (UOP, USA)were used in this study. Table 1 shows the basic Table 1. Physical and Chemical Properties of Used Adsorbents3,6,7 property

Grade 03

Sorbonorit 4

HiSiv 3000

aa/m2·g−1 ρbb/kg·m−3 dc/nm chemical composition

780 720 0.22 SiO2 (purity 99.6 %)

1400 410 0.59

282 700 1.52 SiO2/Al2O3 (ratio >1000)

a

BET surface area. bBulk density. cAverage pore diameter.

physical and chemical properties of the used adsorbents (data provided by manufacturer). Received: May 29, 2013 Accepted: July 9, 2013 Published: August 1, 2013 2629

dx.doi.org/10.1021/je400517c | J. Chem. Eng. Data 2013, 58, 2629−2641

Journal of Chemical & Engineering Data

Article

As adsorbate two VOCs (propan-2-ol and methylbenzene) and water were used. Table 2 provides information about the source and the purity of the chemicals used. Table 2. Source and Purity Information chemical name

source

volume fraction purity

propan-2-ol methylbenzene

Chempur (Poland) Chempur (Poland)

≥0.997 ≥0.995

2.2. Apparatus and Procedure. Studies of adsorption isotherms were carried out using the system IGA-002, Hiden Isochema (United Kingdom). Fully automated isothermal data acquisition, based on the static gravimetric method, guaranteed high accuracy. The main element of the IGA system is a precise microbalance with a resolution of 0.1 μg and an uncertainty of ± 1 μg.8−10 An adsorbent was put in a stainless steel sieve, which was suspended to the balance by means of a gold chain and a tungsten wire. The sample mass was approximately 75 mg. The sample was placed in a metal reactor, which allowed an ultrahigh vacuum to be achieved. A circulating water bath GR 150 (Grant Instruments, United Kingdom) or electric furnace Cryofurnace (Hiden Isochema, United Kingdom) was used interchangeably as thermostat. The sample temperature was measured by a platinum resistance thermometer (Pt100), which was placed in the vicinity of the sample. The platinum resistance thermometer

Figure 1. Experimental and correlated (Langmuir−Freundlich equation) isotherms for water adsorption onto grade 03 silica gel at various temperatures: +, ―, 293.15 K; Δ, · · ·, 313.15 K; × ,  ·, 333.15 K; ◇,  , 348.15 K; □,  · ·, 373.15 K; ○, − − ·, 393.15 K; right-pointing triangle, − · · ·, 413.15 K.

has a resolution of 0.01 K and uncertainty of ± 0.1 K. The pressure in the reactor was measured using the manometer with a

Table 3. Experimental Isotherm Data for Water on Grade 03 Silica Gela

a

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

6.0 16.8 26.2 47.0 69.1 94.2 115.2

0.30082 0.37364 0.61021 1.23361 1.56749 1.94382 2.20648

143.8 162.8 191.1 209.6 233.8 350.6 467.5

5.3 11.0 27.1 44.0 77.1 91.3 116.1 138.2

0.08685 0.12762 0.19574 0.39275 0.53842 0.67849 0.81643 0.91799

164.0 187.4 216.4 234.5 350.8 468.6 709.0

293.15 K 2.51439 2.84247 3.12174 3.42511 3.71206 5.05590 6.42096 313.15 K 1.04590 1.15001 1.22191 1.35375 1.79610 2.21885 2.99376

709.1 942.5 1175.6 1408.1 1646.2 1884.7

9.29460 12.02866 14.50331 16.18772 16.73810 17.06252

99.7 119.6 138.9

0.13727 0.17640 0.20422

466.1 707.8

938.1 1172.0 1407.7 1649.4 1881.9 2109.0 2344.4

3.79051 4.61132 5.42801 6.27220 7.16864 8.10643 9.06322

0.00457 0.02402 0.04357 0.07124 0.09709 0.11923 0.13878 0.15706

333.15 K 0.42815 0.47650 0.50493 0.54650 0.73941 0.91621 1.22638

934.3 1169.1 1402.6 1637.5 1870.9 2105.4 2340.0

1.52459 1.81250 2.09404 2.37291 2.65046 2.92914 3.20775

6.6 14.5 26.1 51.1 74.8 97.2 119.7 143.7 393.15 K 10.2 14.4 27.3 50.5 71.3 94.1 119.9 147.3

4.1 17.1 23.0 44.2 70.4 95.2 118.6 148.2

0.01917 0.04385 0.08561 0.14253 0.22146 0.27839 0.33005 0.36437

166.3 190.9 218.0 241.6 353.7 472.4 700.8

348.15 K 0.22290 0.24859 0.27147 0.29452 0.39438

940.8 1176.4 1410.8 1644.7 1879.8

0.83989 1.00227 1.16407 1.32017 1.46454

6.7 12.8 27.9 50.2 73.6 95.9 120.5 148.1

5.5 13.0 22.7 47.1 70.0

0.01308 0.02831 0.04806 0.08104 0.11109

168.3 186.9 210.0 233.9 349.1

q/mol·kg−1

p/Pa

q/mol·kg−1

348.15 K 0.49065 0.66346

2111.5 2349.5

1.62065 1.75958

165.2 188.7 212.6 235.5 353.0 468.8 699.3

373.15 K 0.17123 0.18185 0.19217 0.20241 0.24207 0.27943 0.34858

943.7 1178.2 1412.5 1647.2 1881.0 2115.0 2349.8

0.41559 0.48059 0.54554 0.60968 0.67242 0.73492 0.79668

0.00462 0.00956 0.01529 0.02575 0.03528 0.04407 0.05278 0.06106

163.8 196.2 217.3 236.1 359.1 470.2 702.7

0.06705 0.07532 0.08145 0.08723 0.10584 0.12485 0.15698

936.1 1170.4 1404.1 1638.2 1873.3 2106.9 2341.5

0.18870 0.21996 0.25173 0.28317 0.31385 0.34418 0.37401

0.00715 0.00647 0.00767 0.01471 0.02190 0.02821 0.03416 0.03969

165.2 196.2 214.2 235.1 356.0 472.2 705.8

413.15 K 0.04391 0.04876 0.05272 0.05633 0.06866 0.08047 0.09593

938.5 1171.9 1405.1 1640.2 1873.6 2110.0 2343.6

0.11158 0.12706 0.14324 0.15931 0.17491 0.19017 0.20518

Standard uncertainties are u(T) = 0.1 K, and u(p) = 0.003p Pa. Combined expanded uncertainty is Uc(q) = 0.00276 mol·kg−1 (level of confidence = 0.95). 2630



Article

Table 4. Experimental Isotherm Data for Propan-2-ol on Grade 03 Silica Gela

a

p/Pa

q/mol·kg−1

5.8 21.6 44.9 88.0 132.9 179.3 223.3

0.28985 1.25248 1.79745 2.05629 2.15445 2.23063 2.28277

5.1 22.8 42.3 88.4 137.3 178.5 228.6 272.2

0.61948 1.18519 1.44889 1.69316 1.80792 1.88084 1.94521 1.99330

4.1 21.7 41.8 89.4 134.2 182.3 224.6 270.6

0.18460 0.63437 0.88567 1.14918 1.28798 1.39566 1.47807 1.54013

316.4 363.1 405.8 452.7 673.5 890.5 1335.0

5.7 21.0 46.9 92.7 136.4

0.12345 0.35662 0.55183 0.76014 0.89076

318.2 358.5 409.1 452.2 671.6

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

1335.6 1784.4 2232.7 2676.8 3123.0 3568.6 4013.2

3.18273 3.43727 3.55033 3.59384 3.61984 3.64093 3.66065

182.0 227.8 269.8

0.99614 1.08120 1.14925

890.7 1341.3

1780.6 2233.7 2679.3 3124.3 3568.1 4014.9 4460.6

2.48225 2.57680 2.67440 2.77343 2.87890 2.98145 3.07973

10.5 24.5 45.5 96.4 136.5 180.8 225.3 268.9

0.06166 0.17733 0.25468 0.37397 0.47460 0.55249 0.61735 0.67562

333.15 K 1.59329 1.63562 1.67378 1.70782 1.81864 1.89708 2.00445

1781.4 2228.9 2675.9 3121.9 3567.2 4012.8 4458.9

2.07963 2.13700 2.18480 2.22530 2.26284 2.29705 2.32927

7.7 25.1 46.1 90.9 136.7 180.9 221.3 270.3

348.15 K 1.20968 1.25958 1.30519 1.34529 1.48177

1781.8 2228.5 2676.2 3121.6 3568.0

1.79675 1.86176 1.91375 1.95654 1.99294

6.3 24.6 45.7 91.4 134.9 179.5 225.0 269.8

293.15 K 2.33773 2.37984 2.41672 2.45257 2.48976 2.65738 2.83156 313.15 K 317.6 2.02863 359.9 2.06326 406.5 2.09237 448.9 2.11750 671.4 2.20624 891.5 2.27851 1342.5 2.38630 267.8 314.2 357.5 402.7 445.4 669.7 890.8

q/mol·kg−1

p/Pa

q/mol·kg−1

348.15 K 1.57714 1.70987

4013.2 4459.7

2.02479 2.05355

319.0 357.6 404.6 446.8 670.1 892.7 1339.2

373.15 K 0.71819 0.76526 0.81152 0.84875 0.99444 1.10426 1.26108

1786.7 2232.7 2679.5 3124.8 3569.5 4016.2 4461.9

1.37317 1.45892 1.52548 1.57962 1.62547 1.66586 1.70131

0.04213 0.09743 0.15050 0.23022 0.29995 0.35615 0.40488 0.44762

312.8 358.0 402.8 448.1 671.7 892.9 1340.5

393.15 K 0.48053 0.51620 0.54978 0.58117 0.70486 0.80513 0.95621

1786.7 2233.3 2679.5 3124.8 3570.9 4016.5 4461.9

1.07105 1.16300 1.23664 1.29960 1.35432 1.40231 1.44401

0.02363 0.05145 0.07547 0.11384 0.14599 0.17512 0.20186 0.22456

314.5 359.3 403.6 447.9 672.3 896.9 1341.8

413.15 K 0.24674 0.26822 0.28777 0.30579 0.38180 0.44709 0.55072

1787.1 2232.2 2679.1 3124.4 3570.9 4016.8 4461.8

0.63601 0.70867 0.77163 0.82674 0.87647 0.92103 0.96199

Standard uncertainties are u(T) = 0.1 K and u(p) = 0.003p Pa. Combined expanded uncertainty is Uc(q) = 0.00079 mol·kg−1 (level of confidence = 0.95).

Figure 2. Experimental and correlated (Langmuir−Freundlich equation) isotherms for propan-2-ol adsorption onto grade 03 silica gel at various temperatures: +, ―, 293.15 K; Δ, · · ·, 313.15 K; × ,  ·, 333.15 K; ◇,  , 348.15 K; □,  · ·, 373.15 K; ○, − − ·, 393.15 K; right-pointing triangle, − · · ·, 413.15 K.

Figure 3. Experimental and correlated (Langmuir−Freundlich equation) isotherms for methylbenzene adsorption onto grade 03 silica gel at various temperatures: +, ―, 293.15 K; Δ, · · ·, 313.15 K; × ,  ·, 333.15 K; ◇,  , 348.15 K; □,  · ·, 373.15 K; ○, − − ·, 393.15 K; right-pointing triangle, − · · ·, 413.15 K. 2631



Article

Table 5. Experimental Isotherm Data for Methylbenzene on Grade 03 Silica Gela p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

5.2 15.5 30.4 57.2 89.3 113 151.7

0.56402 0.92622 1.30689 1.67312 1.96918 2.12978 2.34382

174.2 206.5 237.2 269.5 296.4 441.7 589.4

4.9 15.1 30.1 58.7 89.8 115.9 149.9 170.9

0.17435 0.46115 0.67211 0.93849 1.14058 1.27056 1.41940 1.49251

206.6 237.7 269.1 296.3 441.6 588.3 903.0

2.44680 2.57904 2.68920 2.79094 2.86255 3.15431 3.30984 313.15 K 1.61631 1.70872 1.77689 1.85499 2.15126 2.37313 2.73167

905.0 1166.7 1428.4 1711.4 2083.3 2360.8

3.45025 3.48835 3.51251 3.53360 3.55631 3.57056

1162.9 1426.5 1827.8 2085.4 2362.8 2659.1 2912.0

2.94140 3.09420 3.23890 3.29669 3.33823 3.36730 3.38381

5.7 15.2 30.3 57.9 92.7 113.5 152.5 172.6

0.11607 0.22163 0.33870 0.48178 0.61853 0.68608 0.80305 0.85025

208.5 235.1 266.0 296.2 445.1 584.5 906.0

333.15 K 0.93713 0.98845 1.04898 1.10444 1.33477 1.50395 1.81015

1163.8 1426.1 1824.2 2083.7 2361.5 2658.8 2911.3

2.00243 2.16712 2.37440 2.49125 2.60308 2.70849 2.78886

7.5 17.6 31.2 62.0 86.7

0.07120 0.11357 0.19167 0.29667 0.35599

204.1 235.1 266.0 296.9 442.6

348.15 K 0.58100 0.62743 0.67154 0.71230 0.87816

1166.8 1429.3 1826.0 2085.2 2362.7

1.41620 1.55455 1.73296 1.83561 1.93582

p/Pa

q/mol·kg−1

p/Pa

293.15 K

a

q/mol·kg−1

p/Pa

q/mol·kg−1

293.15 K 114.0 153.7 173.9

0.41692 0.50051 0.53193

587.1 902.2

348.15 K 1.01507 1.25249

2659.3 2911.8

2.03241 2.10928

6.9 16.0 31.7 58.8 87.7 115.4 149.8 174.2

0.02299 0.04665 0.07885 0.12056 0.16166 0.19050 0.22746 0.25176

205.7 235.9 268.0 299.6 445.2 589.4 905.1

373.15 K 0.28064 0.30636 0.33132 0.35545 0.45283 0.53577 0.68508

1167.8 1429.4 1828.9 2085.1 2364.1 2657.7 2912.3

0.79044 0.88350 1.00926 1.09598 1.16942 1.24408 1.30032

8.3 17.5 34.2 59.4 89.1 117.1 149.9 175.4

0.01152 0.02075 0.03749 0.05658 0.07886 0.09829 0.11820 0.13288

206.8 237.6 268.3 299.8 446.3 590.0 906.4

393.15 K 0.14916 0.16497 0.17970 0.19375 0.25270 0.30408 0.39918

1169.0 1430.5 1830.3 2087.1 2364.1 2661.3 2911.1

0.46862 0.53022 0.61550 0.66601 0.71672 0.76776 0.80813

7.6 18.0 33.8 56.6 87.9 116.6 151.0 175.8

0.00406 0.00936 0.01691 0.02928 0.03855 0.04887 0.06028 0.06855

208.3 237.4 269.0 299.4 447.1 589.7 906.9

413.15 K 0.07841 0.08686 0.09560 0.10382 0.13927 0.17062 0.23080

1170.3 1430.1 1830.2 2087.3 2364.4 2661.0 2912.3

0.27548 0.31549 0.37199 0.40533 0.43930 0.47379 0.50188


Figure 4. Experimental and correlated (Dubinin-Astakhov equation) isotherms for water (Table 5) adsorption onto Sorbonorit 4 activated carbon at various temperatures: +, ―, 293.15 K; △, · · ·, 313.15 K; × ,  ·, 333.15 K; ◇,  , 348.15 K; □,  · ·, 373.15 K; ○, − − ·, 393.15 K; right-pointing triangle, − · · ·, 413.15 K.

Figure 5. Experimental and correlated (Langmuir−Freundlich equation) isotherms for water (Table 6) adsorption onto Sorbonorit 4 activated carbon at various temperatures: +, ―, 293.15 K; △, · · ·, 303.15 K; × ,  ·, 313.15 K; ◇,  , 323.15 K. 2632



Article

Table 6. Experimental Isotherm Data for Water on Sorbonorit 4 Activated Carbona

a

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

5.5 11.0 22.1 44.3 68.2 92.6 117.7

0.14728 0.17924 0.21295 0.26521 0.30970 0.35011 0.38933

142.4 167.2 190.0 213.1 237.8 348.7 472.2

8.9 11.4 21.6 44.6 67.7 92.2 116.6 141.3

0.15250 0.17876 0.20492 0.24956 0.28412 0.31370 0.33900 0.36210

166.9 190.5 214.0 237.8 356.1 469.0 701.6

293.15 K 0.42499 0.46003 0.49304 0.52479 0.55832 0.71842 0.91159 313.15 K 0.38360 0.40291 0.42023 0.43683 0.49567 0.56555 0.68516

698.9 941.0 1169.8 1400.8 1641.1 1872.6 2108.6

1.60430 3.47243 6.84255 10.29944 16.06353 18.31361 19.21222

95.7 120.0 143.0

0.12941 0.14168 0.15197

473.5 708.8

933.1 1165.0 1411.6 1640.9 1872.0 2110.1 2347.5

0.80320 0.93022 1.07023 1.23905 1.43881 1.70519 2.06096

5.8 13.7 22.1 47.9 70.8 95.1 120.8 143.9

0.03415 0.04392 0.05126 0.06115 0.07186 0.07989 0.08719 0.09324

333.15 K 0.20626 0.21842 0.22945 0.23979 0.27456 0.31213 0.36740

938.6 1177.3 1410.8 1644.8 1874.4 2114.2 2347.2

0.42337 0.46510 0.50960 0.55369 0.60110 0.63908 0.67911

7.7 14.2 24.0 48.1 72.1 98.2 116.3 139.1

6.8 12.1 23.8 47.0 70.8 94.4 119.0 143.1

0.06208 0.07481 0.09427 0.12262 0.14489 0.16291 0.17881 0.19322

167.1 192.2 214.7 238.9 348.3 471.0 707.5

348.15 K 0.16178 0.17046 0.17840 0.18597 0.21044

943.0 1177.0 1411.7 1645.0 1880.0

0.31067 0.34041 0.36986 0.39509 0.42131

7.7 14.2 24.0 48.1 72.1 98.2 116.3 139.1

8.6 12.7 25.2 47.8 72.1

0.03704 0.06159 0.07619 0.09799 0.11536

168.5 191.3 215.5 239.0 348.4

q/mol·kg−1

p/Pa

q/mol·kg−1

348.15 K 0.23556 0.27309

2114.1 2348.6

0.44537 0.46626

163.2 191.8 214.8 239.2 354.3 470.6 702.6

373.15 K 0.09789 0.10340 0.10794 0.11240 0.12683 0.13988 0.15797

936.5 1170.3 1405.0 1638.7 1873.1 2108.1 2342.1

0.17592 0.19225 0.20724 0.22184 0.23288 0.24677 0.25841

0.02839 0.03834 0.04810 0.05840 0.06756 0.07561 0.08174 0.08754

170.0 185.1 218.6 240.0 348.0 469.4 701.1

393.15 K 0.09305 0.09568 0.09840 0.10005 0.10629 0.11260 0.12286

936.2 1169.4 1405.0 1637.5 1873.3 2107.3 2341.4

0.13212 0.14033 0.14796 0.15506 0.16151 0.16760 0.17322

0.02839 0.03834 0.04810 0.05840 0.06756 0.07561 0.08174 0.08754

170.0 185.1 218.6 240.0 348.0 469.4 701.1

413.15 K 0.09305 0.09568 0.09840 0.10005 0.10629 0.11260 0.12286

936.2 1169.4 1405.0 1637.5 1873.3 2107.3 2341.4

0.13212 0.14033 0.14796 0.15506 0.16151 0.16760 0.17322


Figure 6. Experimental and correlated (Langmuir−Freundlich equation) isotherms for propan-2-ol adsorption onto Sorbonorit 4 activated carbon at various temperatures: +, ―, 293.15 K; △, · · ·, 313.15 K; × ,  ·, 333.15 K; ◇,  , 348.15 K; □,  · ·, 373.15 K; ○, − − ·, 393.15 K; right-pointing triangle, − · · ·, 413.15 K.

Figure 7. Experimental and correlated (Toth equation) isotherms for methylbenzene adsorption onto Sorbonorit 4 activated carbon at various temperatures: +, ―, 293.15 K; △, · · ·, 313.15 K; × ,  ·, 333.15 K; ◇,  , 348.15 K; □,  · ·, 373.15 K; ○, − − ·, 393.15 K; right-pointing triangle, − · · ·, 413.15 K. 2633



Article

Table 7. Experimental Isotherm Data for Water on Sorbonorit 4 Activated Carbona RHb/%

p/Pa

20 30 35 40 45 50 55 60

471.5 698.8 818.6 940.6 1057.9 1168.2 1293.7 1406.3

20 30 35 40 45 50 55 60

847.3 1271.8 1483.8 1696.6 1912.6 2121.7 2331.2 2547.0

20 30 35 40 45 50 55 60

1479.7 2213.2 2578.4 2944.2 3311.3 3681.6 4051.9 4425.0

20 30 35 40 45

2456.6 3689.9 4304.8 4918.2 5539.7

q/mol·kg−1

RHb/%

293.15 K 1.02086 65 1.86410 70 2.70444 75 3.98497 80 5.75653 85 7.44942 90 9.58713 95 12.70926 303.15 K 1.04330 65 1.80706 70 2.58218 75 3.84804 80 5.63438 85 7.43523 90 9.62819 95 12.1328 313.15 K 0.99451 65 1.68889 70 2.56174 75 3.72356 80 5.55453 85 7.37599 90 9.60060 95 12.9699 323.15 K 1.00599 50 1.67961 55 2.34326 60 3.47318 65 5.26354 70

p/Pa

q/mol·kg−1

1521.4 1640.3 1759.2 1871.5 1991.3 2105.7 2222.6

15.20298 16.95501 18.03941 18.84340 19.44027 19.90382 20.40201

2757.5 2973.5 3179.7 3397.0 3610.8 3818.0 4030.2

15.31469 17.08749 18.12342 18.86708 19.42721 19.8990 20.49194

4790.2 5158.7 5532.7 5893.6 6261.2 6628.3 7000.1

15.47255 16.99177 17.97457 18.71312 19.27817 19.72751 20.20488

6150.8 6768.2 7382.7 8048.5 8637.4

7.20849 9.52251 12.96755 15.57543 17.0882

Figure 8. Experimental and correlated (Langmuir−Freundlich equation) isotherms for water adsorption onto HiSiv 3000 zeolite at various temperatures: +, ―, 293.15 K; △, · · ·, 313.15 K; × ,  ·, 333.15 K; ◇,  , 348.15 K; □,  · ·, 373.15 K; ○, − − ·, 393.15 K; rightpointing triangle, − · · ·, 413.15 K.

a

Standard uncertainties are u(T) = 0.1 K and u(p) = 0.003p Pa. Combined expanded uncertainty is Uc(q) = 0.00276 mol·kg−1 (level of confidence = 0.95). bRelative humidity.

resolution of 0.1 Pa and uncertainty of ± 0.3 % of measured value. The repeatability of isotherms is better than ± 1 %.8−10 Uncertainty analysis of individual measurement (weight, temperature and pressure) leads to statement that the overall measurement uncertainty is very small. All measurement instruments in the IGA system were thermostatted what ensured very small uncertainty.8−10 Before each measurement, the sample was outgassed “in situ” at 453.15 K under vacuum (10−6 Pa) for 2 h. This ultrahigh vacuum was achieved using a system of two vacuum pumps: diaphragm pump MD 1 (Vacuumbrand, Germany) and turbomolecular pump TMU 071 P (Pfiffer Vacuum Technology, Germany). After degassing, measurement was made for selected values of temperature and various pressures. Adsorbed compounds in the liquid phase was used as source of vapor, and was placed in thermostatted vessel at 328.15 K.8−10 The IGA system based on measurements of pressure inside the chamber automatically controlled the input and output valves in order to achieve the set point of pressure. For the each set point of pressure and temperature the real time processor (RTP) enabled automatic recording of the changes in sample mass due to adsorption. The IGA system based on measurements of mass

Figure 9. Experimental and correlated (Langmuir−Freundlich equation) isotherms for propan-2-ol adsorption onto HiSiv 3000 zeolite at various temperatures: +, ―, 293.15 K; △, · · ·, 313.15 K; × ,  ·, 333.15 K; ◇,  , 348.15 K; □,  · ·, 373.15 K; ○, − − ·, 393.15 K; right-pointing triangle, − · · ·, 413.15 K.

and the built-in algorithm of calculations enabled prediction of the asymptotic adsorption value. After reaching 99 % of the estimated mass value, the IGA system passed to the next point of isotherm (next the set point of pressure). Adsorption capacity was calculated from the equation q=

(msam − mads) madsMi

(1)

where q is the adsorption capacity, msam is the sample mass with adsorbed phase, mads is the sample mass after degassing, and Mi is the molar mass of adsorbate i. The uncertainties of the adsorption capacity measurement were ± 0.00276 mol·kg−1 for 2634



Article

Table 8. Experimental Isotherm Data for Propan-2-ol on Sorbonorit 4 Activated Carbona

a

p/Pa

q/mol·kg−1

4.3 19.9 40.6 89.1 133.8 177.0 224.0

1.24080 2.22344 3.19096 3.86358 4.10487 4.23837 4.33728

5.0 21.0 44.2 86.1 133.0 176.5 223.1 267.0

0.61145 1.26526 1.86110 2.45980 2.86837 3.13646 3.35272 3.49984

4.3 18.6 42.5 88.3 131.6 179.4 220.8 273.2

0.34534 0.64825 0.99007 1.39132 1.66539 1.91014 2.08693 2.24749

310.1 355.1 401.0 448.3 669.4 887.1 1332.8

4.9 20.6 43.5 88.5 136.0

0.23142 0.44685 0.63979 0.89389 1.10130

312.3 358.2 396.8 446.1 671.9

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

1339.3 1785.2 2229.0 2675.6 3119.8 3564.3

4.90227 4.98206 5.05194 5.10819 5.16514 5.23237

176.4 221.6 266.9

1.24810 1.38823 1.51029

887.4 1332.4

1784.3 2229.6 2675.7 3120.9 3565.6 4011.2 4457.5

4.49319 4.56886 4.62743 4.67852 4.72000 4.75810 4.79002

6.2 24.1 44.1 88.2 134.6 181.2 226.6 271.9

0.16428 0.26529 0.34734 0.48180 0.59091 0.68304 0.76133 0.83140

316.1 361.0 401.3 447.0 671.0 893.7 1339.6 316.1

333.15 K 2.39477 2.52489 2.64027 2.74781 3.12144 3.36988 3.68922

1782.3 2229.2 2675.2 3120.3 3565.5 4010.1 4456.6

3.88357 4.01322 4.10539 4.18071 4.24079 4.29009 4.33150

7.9 21.8 45.7 91.2 136.9 182.9 227.3 267.1

0.09916 0.16351 0.22763 0.31525 0.38429 0.44372 0.49451 0.53164

312.4 357.1 401.2 446.5 673.6 896.3 1342.4 312.4

348.15 K 1.62730 1.73309 1.80962 1.90876 2.26152

1780.0 2226.7 2673.6 3118.7 3564.8

3.17269 3.36793 3.51591 3.63359 3.72803

5.1 23.9 47.4 93.5 138.0 179.5 223.2 268.2

0.07003 0.11551 0.15262 0.20877 0.25042 0.28242 0.31545 0.34592

312.9 357.4 401.8 446.5 666.3 889.2 1334.4

293.15 K 4.41226 4.45446 4.51080 4.54332 4.57547 4.70440 4.78920 313.15 K 311.8 3.62492 358.2 3.72866 403.5 3.80939 448.9 3.88089 667.3 4.10002 893.0 4.23203 1338.8 4.39183 271.5 309.3 360.2 399.8 443.0 670.2 893.9

q/mol·kg−1

p/Pa

q/mol·kg−1

348.15 K 2.52044 2.90499

4009.7 4455.9

3.80753 3.87259

373.15 K 0.89357 0.95212 0.99834 1.05010 1.27109 1.45262 1.74739

1785.1 2232.0 2677.7 3122.9 3569.5 4014.7 4461.4

1.98241 2.17806 2.34504 2.48573 2.60997 2.71806 2.81526

393.15 K 0.57324 0.61168 0.64741 0.68199 0.82972 0.95486 1.15190

1788.5 2234.0 2680.0 3125.4 3570.2 4016.3 4461.8

1.32161 1.46498 1.59346 1.70813 1.81283 1.90972 1.99733

413.15 K 0.37391 0.39980 0.42451 0.44768 0.54477 0.62867 0.76709

1780.6 2226.6 2672.1 3117.7 3563.1 4008.9 4455.0

0.88425 0.98588 1.07658 1.16020 1.23602 1.30627 1.37311


Figure 10. Experimental and correlated (Langmuir−Freundlich equation) isotherms for methylbenzene adsorption onto HiSiv 3000 zeolite at various temperatures: +, ―, 293.15 K; △, · · ·, 313.15 K; × ,  ·, 333.15 K; ◇,  , 348.15 K; □,  · ·, 373.15 K; ○, − − ·, 393.15 K; right-pointing triangle, − · · ·, 413.15 K.

Figure 11. Comparison of adsorption capacity at 293.15 K of water on: +, grade 03silica gel; ○, Sorbonorit 4 activated carbon; □, HiSiv 3000 zeolite. 2635



Article

Table 9. Experimental Isotherm Data for Methylbenzene on Sorbonorit 4 Activated Carbona

a

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

5.6 14.6 30.6 62.3 88.9 116.6 150.4

2.87727 3.15818 3.34702 3.48546 3.54229 3.58517 3.62337

176.0 207.8 238.0 269.2 300.1 448.3 591.0

7.0 15.6 31.2 60.3 91.9 116.0 151.0 175.9

2.30476 2.58908 2.83463 3.04289 3.15938 3.21807 3.27441 3.30658

209.3 239.8 271.5 302.7 448.7 585.1 901.8

293.15 K 3.64770 3.67275 3.69354 3.71193 3.72832 3.78534 3.82361 313.15 K 3.34050 3.36612 3.38680 3.40567 3.47379 3.51142 3.58065

907.5 1170.2 1431.0 1829.6 2086.5 2364.9 907.5

3.88488 3.92334 3.95389 3.99654 4.02734 4.06719 3.88488

114.4 154.1 175.6

2.49204 2.60269 2.64448

591.2 901.3

1164.5 1425.3 1825.3 2081.8 2359.2 2655.5 2908.7

3.61927 3.65100 3.68809 3.70925 3.72915 3.74808 3.76239

4.5 14.4 30.6 57.3 89.2 118.5 147.8 177.6

0.71600 1.13579 1.40749 1.62926 1.79104 1.89644 1.98025 2.04833

333.15 K 3.05154 3.08271 3.11676 3.14747 3.24938 3.31200 3.39381

1171.6 1433.2 1831.6 2087.9 2365.6 2661.9 2915.1

3.43900 3.47439 3.51622 3.53865 3.56007 3.58027 3.59534

4.9 13.2 30.5 58.7 85.7 117.2 147.7 177.5

4.5 14.7 32.3 61.5 87.9 119.2 153.8 172.9

1.59677 2.09594 2.41608 2.63853 2.76353 2.86599 2.95515 2.98753

212.3 237.2 267.5 298.7 447.5 592.7 909.5

348.15 K 2.70179 2.74865 2.79050 2.82626 2.95793

1163.6 1425.0 1824.9 2081.4 2359.1

3.20795 3.25190 3.30155 3.32675 3.35034

5.6 15.1 30.0 54.8 90.4 119.8 145.0 174.2

4.9 14.6 30.2 60.4 91.7

1.16016 1.68820 2.00087 2.26433 2.41266

207.2 237.3 268.7 299.5 448.0

q/mol·kg−1

p/Pa

q/mol·kg−1

348.15 K 3.03913 3.14694

2655.6 2908.3

3.37211 3.38827

207.1 237.9 261.1 290.4 440.2 586.5 879.2

373.15 K 2.10470 2.14416 2.18788 2.22727 2.37872 2.48112 2.61969

1169.9 1461.5 1752.0 2043.2 2334.2 2626.0 2916.9

2.71232 2.78105 2.83498 2.87835 2.91325 2.94488 2.97019

0.61512 0.82692 1.08393 1.29995 1.43017 1.54225 1.62941 1.69596

206.9 237.6 267.2 291.1 440.9 587.8 878.4

393.15 K 1.75537 1.80750 1.83979 1.88083 2.03818 2.14507 2.29227

1170.4 1461.8 1754.1 2044.3 2335.1 2624.7 2917.2

2.39572 2.47559 2.53878 2.59052 2.63459 2.67356 2.70723

0.07691 0.18983 0.36715 0.65274 0.85393 0.99454 1.10715 1.19940

204.9 235.1 264.1 293.9 435.1 583.1 874.5

413.15 K 1.29443 1.35692 1.40782 1.45574 1.63305 1.76460 1.94234

1165.5 1456.7 1748.4 2039.8 2330.5 2621.1 2913.9

2.06439 2.15705 2.23111 2.29301 2.34538 2.39141 2.43336


Figure 12. Comparison of adsorption capacity at 293.15 K of propan-2ol on: +, grade 03silica gel; ○, Sorbonorit 4 activated carbon; □, HiSiv 3000 zeolite.

Figure 13. Comparison of adsorption capacity at 293.15 K of methylbenzene on: +, grade 03 silica gel; ○, Sorbonorit 4 activated carbon; □, HiSiv 3000 zeolite. 2636



Article

Table 10. Experimental Isotherm Data for Water on HiSiv 3000 Zeolitea

a

p/Pa

q/mol·kg−1

p/Pa

5.0 11.1 23.1 46.6 69.0 91.7 115.1

0.14251 0.18309 0.23775 0.32026 0.38537 0.43459 0.48173

138.5 162.3 186.8 209.7 233.0 349.5

8.5 11.6 25.6 49.6 70.4 93.8 118.0 140.5

0.06838 0.09112 0.11544 0.14946 0.17655 0.20442 0.22987 0.25250

6.6 12.4 21.9 49.7 69.7 92.3 116.4 139.9 4.7 13.1 26.1 50.2 66.4

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

293.15 K 0.52580 0.56828 0.60902 0.64668 0.68433 0.85030

466.9 700.2 935.3 1168.4 1406.0 1637.7

0.98723 1.20731 1.37394 1.52486 1.65164 1.77500

91.0 122.5 139.3

0.16027 0.17211 0.17967

474.2 709.2

164.6 189.0 212.5 236.3 357.0 473.6 707.9

313.15 K 0.27478 0.29550 0.31457 0.33320 0.40270 0.47272 0.59121

937.8 1171.7 1407.0 1641.3 1878.7 2113.3 2346.4

0.70754 0.81814 0.92052 1.01043 1.09711 1.17779 1.25054

6.5 14.6 22.9 49.9 69.0 93.1 118.3 144.2

0.03184 0.05115 0.05771 0.07100 0.08010 0.08912 0.09728 0.10371

0.06875 0.08394 0.09925 0.11818 0.13189 0.14531 0.15799 0.17007

164.0 188.0 210.7 230.6 357.5 475.3 709.1

333.15 K 0.18211 0.19385 0.20501 0.21694 0.29528 0.33111 0.39273

943.2 1178.0 1413.0 1647.3 1881.6 2111.6 2351.1

0.44968 0.50218 0.55429 0.60291 0.65010 0.69989 0.74011

4.0 11.3 24.5 47.8 69.5 90.1 113.1 140.9

0.05285 0.07106 0.08441 0.10306 0.13814

164.2 186.6 211.3 235.2 358.0

348.15 K 0.18897 0.19786 0.20571 0.21203 0.23321

943.5 1178.5 1412.4 1646.7 1881.4

0.33093 0.36592 0.40062 0.43126 0.46203

4.1 13.7 24.2 48.2 71.6 90.3 116.2 139.6

q/mol·kg−1

p/Pa

q/mol·kg−1

348.15 K 0.25440 0.29380

2116.5 2351.9

0.49123 0.51971

168.7 185.5 211.0 233.2 353.4 472.4 701.7

373.15 K 0.11064 0.11565 0.12130 0.12562 0.13790 0.14875 0.16451

935.6 1169.7 1405.4 1639.6 1872.6 2107.5 2340.8

0.17916 0.19201 0.20442 0.21683 0.22780 0.23800 0.24860

0.02883 0.03810 0.04576 0.07937 0.09930 0.11234 0.12554 0.13696

164.9 185.9 209.4 232.7 349.8 468.7 699.9

393.15 K 0.14311 0.14741 0.15111 0.15453 0.16259 0.17175 0.18334

935.0 1168.3 1409.6 1637.4 1872.8 2104.4 2342.6

0.19336 0.20219 0.21136 0.21919 0.22647 0.23382 0.24169

0.01830 0.02852 0.03377 0.04504 0.05626 0.06540 0.07505 0.08303

164.8 187.4 211.5 235.7 352.5 469.9 698.6

413.15 K 0.09032 0.09791 0.10467 0.10964 0.11988 0.12890 0.14066

933.5 1167.7 1403.4 1638.9 1871.8 2106.3 2341.7

0.15014 0.15881 0.16670 0.17327 0.18002 0.18610 0.19147


water, ± 0.00079 mol·kg−1 for propan-2-ol, and ± 0.00055 mol·kg−1 for methylbenzene. The measurement was carried out until all pressure set points were finished. Next, the sample was degassed, and measurements were made for next temperature.8−10

(

(( (

nΔHi RT

))

+ pn

⎛ ⎛⎛ RT ln(p (T )) ⎞⎞n⎞ s ⎟⎟⎟⎟ ⎟ q = V0ρa (T ) exp⎜⎜ −⎜⎜⎜⎜ βE 0 ⎠⎠ ⎟⎠ ⎝ ⎝⎝

T

)

(4)

where V0 is the volume of adsorptive space, ρa is the molar density of liquid, ps is the saturated vapor pressure, β is the affinity coefficient, and E0 is the characteristic energy of adsorption for the standard substance (benzene). The affinity coefficient values for the used substances, calculated from definition, are 0.063, 0.860, and 1.253 for water vapor, propan-2-ol, and methylbenzene, respectively.3 The parameters of selected equilibrium models were obtained by nonlinear regression using Statistica 10 (Statsoft). The average relative error δ, which is a measure of model fitting accuracy to the experimental data, was calculated as follows:

1/ n

)

)

where a0, a1, a2, b1, b2, n0, and n1 are the isotherm parameters. The mathematical form of multitemperature Dubinin− Astakhov adsorption isotherm is

mp b0 −

b

(3)

3. ADSORPTION EQUILIBRIUM MODELS To enable practical application of investigated adsorption isotherms, it must be presented in the form of mathematical equations.11 To correlate equilibrium models with the experimental data, the multitemperature adsorption isotherm equations of Toth, Langmuir−Freundlich, and Dubinin− Astakhov were selected. More detailed description of used adsorption equilibrium models is available in the literature.12−14 The mathematical form of multitemperature Toth adsorption isotherm is q=

b

(

(n0 + n1/ T ) 1 2 ⎛ a1 a 2 ⎞ exp b0 + T + T 2 p q = ⎜a 0 + + 2⎟ ⎝ T T ⎠ 1 + exp b + b1 + b22 p(n0 + n1/ T ) 0 T

(2)

where p is the partial pressure of the adsorbate, T is the temperature, ΔH is the heat of adsorption, R is the universal gas constant, and b0, m, and n are the isotherm parameters. The mathematical form of multitemperature Langmuir− Freundlich adsorption isotherm is 2637



Article

Table 11. Experimental Isotherm Data for Propan-2-ol on HiSiv 3000 Zeolitea

a

p/Pa

q/mol·kg−1

5.8 23.7 44.6 86.8 137.3 183.6 222.6

0.50472 0.94752 1.19927 1.38733 1.48334 1.54189 1.57229

5.3 25.5 42.9 91.9 135.0 181.7 229.2 267.1

0.35104 0.53891 0.66222 0.92652 1.06975 1.17395 1.23128 1.28267

6.1 22.9 47.1 93.0 138.2 177 228.2 268.2

0.26543 0.35284 0.43220 0.55029 0.64272 0.70997 0.79343 0.84486

316.8 355.6 400.0 444.4 672.7 896.3 1341.1

6.4 23.6 47.3 93.7 138.9

0.20756 0.27815 0.33275 0.40683 0.46278

312.1 356.1 399.9 445.2 673.6

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

1341.1 1786.1 2232.0 2676.9 3121.9 3567.0

1.74231 1.76273 1.77622 1.78486 1.79286 1.80592

177.5 222.7 267.7

0.50161 0.54693 0.58884

890.0 1332.3

1786.1 2231.6 2677.0 3122.0 3566.4 4011.6 4456.5

1.61206 1.64193 1.66530 1.68373 1.69778 1.70953 1.71940

6.7 23.5 48 90.1 134.3 178.5 224.1 269.6

0.10866 0.14584 0.17596 0.21083 0.23991 0.26510 0.28833 0.30949

333.15 K 0.90432 0.94290 0.98283 1.01915 1.15079 1.23212 1.32959

1786.1 2223.9 2669.3 3114.1 3559.3 4004.5 4450.0

1.38841 1.42986 1.46124 1.48538 1.50494 1.52152 1.53646

4.6 24.6 48.3 90.4 134.9 178.3 223.1 267.9

348.15 K 0.62609 0.66125 0.69462 0.72588 0.85401

1778.2 2223.3 2669.2 3114.2 3559.0

1.16117 1.22167 1.26759 1.30340 1.33336

5.2 24.6 48.3 90.2 134 178.8 223.3 269.7

293.15 K 1.60031 1.62067 1.63692 1.65033 1.66105 1.69562 1.71644 313.15 K 312.4 1.32191 356.5 1.35357 400.7 1.37918 445.5 1.40082 673.6 1.47392 896.0 1.51780 1341.4 1.57383 267.1 312.1 357.1 401.6 446.3 673.5 892.5

q/mol·kg−1

p/Pa

q/mol·kg−1

348.15 K 0.94608 1.07415

4004.2 4450.0

1.35768 1.37781

313.8 358.6 403.8 448.3 672.1 895.3 1340.9

373.15 K 0.32880 0.34738 0.36493 0.38163 0.45341 0.51653 0.61995

1787.0 2232.2 2677.0 3123.1 3568.9 4014.3 4459.6

0.70149 0.76861 0.82401 0.87110 0.91121 0.94641 0.97737

0.07006 0.10201 0.12460 0.14979 0.17017 0.18683 0.20173 0.21531

312.1 357.7 403.8 449.0 670.5 890.1 1336.2

393.15 K 0.22769 0.23954 0.25076 0.26139 0.30590 0.34534 0.41269

1782.9 2230.8 2675.1 3120.9 3566.7 4010.8 4456.5

0.46943 0.51872 0.56253 0.60124 0.63658 0.66844 0.69733

0.05452 0.07728 0.09319 0.11127 0.12553 0.13750 0.14772 0.15726

314.1 359.1 404.4 448.6 667.5 889.7 1335.1

413.15 K 0.16558 0.17335 0.18065 0.18739 0.21669 0.24221 0.28592

1781.3 2227.0 2673.9 3119.8 3564.7 4009.9 4457.6

0.32333 0.35673 0.38727 0.41508 0.44083 0.46436 0.48698


1 δ= N

N

∑ i=1

qexp − qsim qexp

Adsorption isotherms of water on grade 03 silica gel are mostly linear in the experimental range. Adsorption capacity is very high and at 293.15 K reaches 17.06 mol·kg−1 for 1880 Pa. When the the temperature increases, the adsorption capacity decreases rapidly, and at 313.15 K is 7.17 mol·kg−1 for 1880 Pa, while at 333.15 K is 2.65 mol·kg−1 for 1870 Pa. For higher temperatures, decreasing of the adsorption capacity is lower and at 413.15 K is 0.17 mol·kg−1 for 1870 Pa. It can be concluded that the silica gel is an excellent adsorbent for drying gas streams. The best fit to the experimental equilibrium data for water−grade 03 silica gel pair gives the Langmuir−Freundlich model, with a relative error of 19.22 %. Adsorption isotherms of water vapor on Sorbonorit 4 activated carbon are type V of Brunauer classification. For the isotherms of this type, the highest impact has capillary condensation phenomenon, which occurs for the water relative humidity above 50 %. Basic measurements are presented in Table 5. In Table 6 additional data were presented for which better fitting was achieved. Adsorption capacity is significant, with a value of 20.4 mol·kg−1 for 2220 Pa. The Dubinin−Astakhov model best describes the data shown in Table 5, with a relative error of 31.52 %. The Langmuir−Freundlich model best describes the data showed in Table 6, with a relative error of 12.39 % For remaining seven adsorbate−adsorbent pairs examined, adsorption isotherms are type I of Brunauer classification. The increase in temperature causes a decrease in the adsorption

× 100 (4)

where qexp is the experimental adsorption capacity, qsim is the calculated adsorption capacity, and N is the number of experimental points.

4. RESULTS AND DISCUSION The experimental adsorption isotherms of nine adsorbate− adsorbent systems were obtained. The adsorption isotherms were measured at (293.15, 313.15, 333.15, 348.15, 373.15, 393.15, and 413.15) K and pressures up to 2340 Pa for water, 4460 Pa for propan-2-ol, and 2910 Pa for methylbenzene. Because of the specific nature of water adsorption on activated carbon, additional measurements were made at (293.15, 303.15, 313.15, and 323.15) K and relative humidity up to 95% (at 323.15 K up to 70%). The equilibrium experimental data are shown in Tables 3 through 12. The multitemperature adsorption isothermsToth, Langmuir−Freundlich, and Dubinin−Astakhovwere fitted to the experimental data. The obtained adsorption isotherms parameters and average relative errors are shown in Tables 13 through 15. The experimental and correlated isotherms for each pair adsorbate − adsorbent at various temperatures are presented in Figures 1 through 10. 2638



Article

Table 12. Experimental Isotherm Data for Methylbenzene on HiSiv 3000 Zeolitea

a

p/Pa

q/mol·kg−1

p/Pa

6.0 15.2 31.9 59.5 89.8 117.1 151.4

0.65034 0.70050 0.73748 0.77173 0.79715 0.81557 0.83445

175.5 208.1 239.3 269.7 300.5 446.4 590.4

5.1 16.6 32.5 59.0 90.9 116.6 151.4 176.5

0.38425 0.58727 0.64459 0.68022 0.70415 0.71788 0.73205 0.74087

207.8 239.0 270.6 301.3 449.1 592.4 909.3

4.9 17.8 35.3 58.0 89.1 117.2 152.6 175.8

0.19513 0.35756 0.48087 0.56652 0.60801 0.63042 0.64975 0.65938

207.9 238.2 270.2 300.9 441.2 584.6 901.7 207.9

4.6 16.3 30.5 62.5 88.8

0.11332 0.23925 0.33290 0.44665 0.49584

208.0 237.7 269.6 300.1 441.1

q/mol·kg−1 293.15 K 0.84716 0.86241 0.87700 0.89225 0.90899 0.97531 1.01031 313.15 K 0.75019 0.75833 0.76569 0.77221 0.79559 0.81458 0.84800 333.15 K 0.66989 0.67818 0.68544 0.69163 0.71236 0.72756 0.75131 0.66989 348.15 K 0.59441 0.60645 0.61725 0.62571 0.65302

p/Pa

q/mol·kg−1

p/Pa

q/mol·kg−1

p/Pa

907.5 1170.0 1430.7 1830.0 2086.9 2363.8 907.5

1.05089 1.07162 1.08702 1.10672 1.11923 1.13793 1.05089

115.5 150.8 175.2

0.53059 0.56152 0.57754

584.4 901.9

1171.9 1432.2 1833.0 2088.9 2366.7 2665.9 2918.6

0.87185 0.89483 0.92886 0.94820 0.96847 0.98528 0.99740

5.7 15.5 30.2 58.3 87.9 117.6 148.1 177.3

0.04127 0.07545 0.11743 0.18004 0.23036 0.27037 0.30308 0.32855

1163.5 1424.5 1824.3 2080.6 2358.2 2656.8 2909.2 1163.5

0.76543 0.77729 0.79302 0.80128 0.80978 0.81811 0.82479 0.76543

6.9 18.1 32.6 59.5 88.7 117.9 147 176.5

1163.6 1424.8 1824.4 2080.7 2358.2

0.71026 0.72113 0.73460 0.74119 0.74800

3.5 15.8 34.3 61.2 90.0 116.3 152 176.2

q/mol·kg−1

p/Pa

q/mol·kg−1

348.15 K 0.67111 0.69624

2656.8 2909.2

0.75465 0.75961

206.2 236.1 264.9 294.9 441.7 587.7 879.6

373.15 K 0.34987 0.36855 0.38387 0.39784 0.44347 0.47320 0.50908

1170.2 1461.5 1753.3 2044.2 2334.4 2625.4 2916.0

0.53066 0.54565 0.55706 0.56624 0.57399 0.58089 0.58680

0.0364 0.05246 0.07146 0.10189 0.13061 0.15613 0.17885 0.19980

206.3 235.3 263.8 293.2 440.4 587.8 877.8

393.15 K 0.21895 0.23602 0.25141 0.26603 0.32273 0.36350 0.41639

1169.0 1460.0 1751.2 2041.5 2332.5 2623.1 2913.6

0.45027 0.47445 0.49236 0.50600 0.51747 0.52681 0.53490

0.02879 0.04264 0.05780 0.07584 0.09316 0.10798 0.12697 0.13793

208.0 237.9 268.7 300.1 448.2 592.0 909.5

413.15 K 0.15237 0.16359 0.17340 0.18719 0.23448 0.27376 0.34048

1171.0 1433.1 1831.9 2088.9 2366.6 2665.3 2918.1

0.38148 0.41421 0.45258 0.47178 0.48950 0.50586 0.51815


capacity. As may be seen, from the analysis of Figures 2, 3, and 6 through 10, the temperature dependence of adsorption capacity is more or less linear. For the adsorbate−adsorbent pairs propan2-ol−grade 03, methylbenzene−grade 03, propan-2-ol−Sorbonorit 4, water−HiSiv 3000, propan-2-ol−HiSiv 3000, and methylbenzene−HiSiv 3000, the best fit to experimental data gave the Langmuir−Freundlich mode, with relative errors of 8.91 %, 10.31 %, 4.2 %, 11.35 %, 7.61 %, and 9.22 %, respectively. For the methylbenzene−Sorbonorit 4 pair, the most appropriate model was the Toth model, with a relative error of 5.06 %. In the work, three equilibrium adsorption modelsToth, Langmuir−Freundlich, and Dubinin−Astakhovwere correlated with experimental data. The Toth equation had four adjustable parameters, the Langmuir−Freundlich equation had eight adjustable parameters, and the Dubinin−Astakhov equation had three adjustable parameters. Generally, the best fit gave Langmuria− Freundlich model, so it can be concluded that the number of parameters have a great impact on the fit quality. Toth and Dubinin−Astakhov models also showed a fairly good fit for most adsorbent−adsorbate pairs. In addition, the Toth equation can provide the heat of adsorption, and the Dubinin−Astakhov equation can provide the total micropore volume of the adsorbent. In Figures 11 through 13 the comparison of adsorption capacity for each component at 293.15 K were shown. The obtained results indicate that Sorbonorit 4 activated carbon has the highest adsorption capacity for VOCs (propan-2-

Table 13. Adsorption Isotherm Parameters and Average Relative Errors for Grade 03 Silica Gel model Toth

Langmuir− Freundlich

Dubinin− Astakhov

parameters and errors

water

propan-2-ol

methylbenzene

m/mol·kg−1 b0/Pa·n−1 n ΔH/J·mol−1 δ/% a0 a1 a2 b0 b1 b2 n0 n1 δ/% V0/m3·kg−1 E0/J·mol−1 n δ/%

495.0632 292021.9 0.416800 49198.17 24.99 147821.4 −221699 −1312.36 −32.2400 5030.883 173.6723 0.875638 −14.8950 19.22 0.000514 38371.80 0.852898 25.63

4.593866 1003.337 0.273484 66370.78 11.99 −9.55159 5624.119 −436926 −31.3172 15288.82 −1919913 1.538212 −343.639 8.91 0.000277 19361.79 1.717726 14.64

4.429046 522717.7 0.538236 51604.23 10.31 8.379185 −1233.69 −7.96581 −19.1231 4722.677 30.08240 0.738360 −24.6269 6.33 0.000397 8480.636 1.806957 13.99

ol and methylbenzene). Grade 03 silica gel has highest adsorption capacity of water for lower pressures (up to 1700 Pa). For higher 2639



Article

Table 14. Adsorption Isotherm Parameters and Average Relative Errors for Sorbonorit 4 Activated Carbon model Toth

Langmuir−Freundlich

Dubinin−Astakhov


water (Table 5)

water (Table6)

propan-2-ol

methylbenzene


75731.99 7.913104 0.624156 76864.67 86.24 −171.568 −1012.14 20302863 −29.2729 1368.398 586391.6 0.320000 561.8056 86.29 0.001686 1633.304 0.368967 31.53

10813087 234612858 0.485635 45789.93 70.12 25.07614 −790.1377 62.20862 −126.7161 27236.17 221.6467 5.659907 −280.5971 12.39 0.0003611 29156.04 2.143299 14.31

5.459757 691599.3 0.536789 56710.34 11.79 7.271600 −1236.19 181926.0 −9.30321 −391.209 716065.1 0.252833 141.2876 4.2 0.000393 18484.72 2.179261 12.29

4.169556 724.9838 0.308307 64535.28 5.06 −5.85289 5807.751 −851063 −11.3601 3424.256 20.26393 0.866759 −145.447 5.88 0.000409 19748.70 2.296868 5.33

VOC adsorption onto examined adsorbents. Also fairly good agreement was stated for water adsorption. The experimental and computed data obtained in this study can be used for modeling of cyclic adsorption processes (for example, temperature swing adsorption (TSA), pressure swing adsorption (PSA), and pressure and temperature swing adsorption (PTSA)). It also can be the basis for modeling of the multicomponent adsorption equilibrium using interpolative models.

Table 15. Adsorption Isotherm Parameters and Average Relative Errors for HiSiv 3000 Zeolite model Toth

Langmuir− Freundlich

Dubinin− Astakhov


water

propan-2-ol

methylbenzene


562.4601 9.246880 0.100000 42030.17 26.39 3360954 22973750 148595.1 −14.7897 −3596.60 751896.6 −0.178966 205.6102 11.35 0.000100 14010.12 0.414892 23.36

2.030956 81779.48 0.439860 60762.08 12.33 1.896385 −1.42565 0.844577 −14.6690 3720.665 22.18401 0.291363 102.3324 7.61 0.000141 18943.20 2.099447 11.94

1.150891 1212.083 0.305445 64308.35 10.14 −3.23229 2341.450 −313941 −16.6998 5509.945 −209039 1.517377 −336.821 9.22 0.000100 15000.00 2.000000 10.28

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Funding

This study was funded by Polish Ministry of Science and Higher Education under project No. N N209 254938. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Khan, F. I.; Ghoshal, A. K. Removal of volatile organic compounds from polluted air. J. Loss Prev. Process Ind. 2000, 13, 527−545. (2) Nastaj, J.; Aleksandrzak, T. Removing and recovery of volatile organic compounds on multilayer adsorption bed by cyclic thermal pressure swing adsorption. A literature review. Przem. Chem. 2011, 90, 407−411. (3) Nastaj, J.; Chybowska, M. Adsorption equilibria of butan-1-ol, toluene and water vapour onto Sorbonorit 4 activated carbon and the co-adsorption of organic compounds and water vapour onto SKT activated carbon. Adsorpt. Sci. Technol. 2006, 24, 283−300. (4) Keller, J. U.; Staudt, R. Gas Adsorption Equilibria: Experimental Methods and Adsorptive Isotherms; Springer: Boston, 2005. (5) Ye, P.; Fang, Z.; Su, B.; Xing, H.; Yang, Y.; Su, Y.; Ren, Q. Adsorption of Propylene and Ethylene on 15 Activated Carbons. J. Chem. Eng. Data 2010, 55, 5669−5672. (6) http://catalog.adcoa.net/item/silica-gel/silica-gel-grade-03/ sg03001?; accessed May 21, 2013. (7) Bao, Z.; Yu, L.; Dou, T.; Gong, Y.; Zhang, Q.; Ren, Q.; Lu, X.; Deng, S. Adsorption Equilibria of CO2, CH4, N2, O2, and Ar on High Silica Zeolites. J. Chem. Eng. Data 2011, 56, 4017−4023. (8) IGA Systems User Manual, Hiden Isochema Limited. (9) Chen, M.; Wang, J.; Jiang, B.; Yang, Y. Diffusion Measurements of Isopentane, 1-Hexene, Cyclohexene in Polyethylene Particles by the

pressures (above 1700 Pa) Sorbonorit 4 activated carbon has the highest adsorption capacity.

5. CONCLUSIONS The adsorption isotherms of water, propan-2-ol, and methylbenzene vapors on three commercial adsorbents, grade 03 silica gel, Sorbonorit 4 activated carbon, and HiSiv 3000 zeolite, were measured at (293.15, 313.15, 333.15, 348.15, 373.15, 393.15, and 413.15) K and pressures up to 2340 Pa for water, 4460 Pa for propan-2-ol, and 2910 Pa for methylbenzene. Additionally measurements for the water−Sorbonorit 4 system at (293.15, 303.15, 313.15, and 323.15) K and relative humidity up to 95% (at 323.15 K up to 70%) were also made. The selected equilibrium models, Toth, Langmuir−Freundlich, and Dubinin− Astakhov, were correlated with the experimental equilibrium data. The computed average relative errors of models fitting to experimental data proved that good agreement was attained for 2640



Article

Intelligent Gravimetric Analyzer. J. Appl. Polym. Sci. 2013, 127, 1098− 1104. (10) O’koye, I. P.; Benham, M.; Thomas, K. M. Adsorption of Gases and Vapors on Carbon Molecular Sieves. Langmuir 1997, 13, 4054− 4059. (11) Ruy, Y. K.; Lee, H. J.; Yoo, H. K.; Lee, C. H. Adsorption Equilibria of Toluene and Gasoline Vapors on Activated Carbon. J. Chem. Eng. Data 2002, 47, 1222−1225. (12) Toth, J. Adsorption: Theory, Modelling, and Analysis; Marcel Dekker: Basel, 2001. (13) Do, D. D. Adsorption Analysis: Equilibria and Kinetics; Imperial College Press: London, 1998. (14) Dubinin, M. M. The Potential Theory of Adsorption of Gases and Vapors for Adsorbents with Energetically Nonuniform Surfaces. Chem. Rev. 1960, 60, 235−241.

2641


Adsorption Isotherms of Water, Propan-2-ol, and Methylbenzene

Recommend Documents