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

Article pubs.acs.org/jced

Adsorption Isotherms of Propan-2-ol, Methylbenzene, and Tetrachloromethane on Selected Activated Carbons Józef Nastaj,* Bogdan Ambrozė k, Konrad Witkiewicz, and Joanna Rudnicka 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 propan-2-ol, methylbenzene, and tetrachloromethane vapors on commercial activated adsorbents: Norit RB4, Sorbonorit 3, and Sorbonorit 4. The adsorption isotherms were measured at 293.15, 323.15, 355.15, 373.15, 393.15, and 413.15 K and pressures up to component saturation pressures at 293.15 K. The isotherms were measured using the dynamic gravimetric method. The data obtained from experiments were correlated with following multitemperature adsorption isotherms equations: Toth, Langmuir−Freundlich, and Dubinin−Astakhov.

1. INTRODUCTION

2. EXPERIMENTAL SECTION 2.1. Materials. Three commercial adsorbents, Norit RB4, Sorbonorit 3, and Sorbonorit 4 (Norit, The Netherlands), were used in this study. Table 1 presents the basic physical and chemical properties of the used adsorbents.8−11

Adsorption processes are commonly used for volatile organic compound (VOC) removal and recovery from bulk gas streams.1 The main advantages of the adsorption processes are low operation costs, even for very low VOC concentrations (even less than 10−6 kg·kg−1), and simplicity of the industrial adsorption equipment. 1 For purposes of modeling the adsorption processes, equilibrium data over a wide range of temperatures and pressures must be avalable.2 The current state of the art does not allow the theoretical prediction of thesinglecomponent adsorption equilibrium for any adsorbent.2 Therefore, for each particular adsorbate−adsorbent pair, it is necessary to measure adequate data.3−6 In the subject literature, there is a large amount of experimental data concerning the adsorption equilibrium of various pairs of adsorbate−adsorbent. However, the adsorption capacities of a particular component on the given adsorbent bed (e.g., activated carbons) may vary significantly according to adsorbent preparation method. Adsorption equilibrium of propylene and ethylene on 15 commercial activated carbons was presented in studies by Ye et al.7 The authors stated that differences in the adsorption capacity of particular adsorbents were large, up to 300% between the lowest and the highest values.7 Therefore, it is necessary to use experimental equilibrium data for a particular adsorbentcomponent system.7 The paper presents data concerning adsorption equilibria of selected VOCs, propan-2-ol (isopropanol), methylbenzene (toluene), and tetrachloromethane (carbon tetrachloride) vapors, on three adsorbents, Norit RB4, Sorbonorit 3, and Sorbonorit 4 activated carbons. These compounds represent three groups of air pollutants: halogen derivatives, aliphatic alcohols, and aromatic hydrocarbons. Three selected equilibrium models, Toth, Langmuir−Freundlich, and Dubinin-Astakhov, were fitted to experimental equilibrium data. © XXXX American Chemical Society

Table 1. Physical and Chemical Properties of Used Carbonaceous Adsorbents property −1

a, (m ·g ) ρb,b (kg·m−3) r,c (nm) V1,d (cm3 g−1) V2,e (cm3·g−1) V3,f (cm3·g−1) a

2

Norit RB 4

Sorbonorit 3

Sorbonorit 4

1100 445 1.48 0.407 0.060 0.002

1472 410 1.52 0.515 0.255 0.015

1400 400 1.52 0.47 0.10 0.47

a BET surface area. bBulk density. cAverage pore radius. dMicropore volume. eMesopore volume. fMacropore volume.

Table 2. Source and Purity of Chemicals Used chemical name

source

volume fraction purity

propan-2-ol methylbenzene tetrachloromethane

Chempur (Poland) Chempur (Poland) Chempur (Poland)

≥0.997 ≥0.997 ≥0.990

As adsorbed component, three VOCs, propan-2-ol, methylbenzene, and tetrachloromethane, were used. Table 2 provides information about the source and the purity of the chemicals used. 2.2. Apparatus and Procedure. The pure component adsorption equilibria of propan-2-ol, methylbenzene, and Received: June 13, 2016 Accepted: August 23, 2016

A

DOI: 10.1021/acs.jced.6b00488 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Figure 1. Sketch of apparatus to study adsorption equilibrium of pure components by dynamic gravimetric method: 1a, 1b, needle valve; 2a, 2b, rotameters; 3, saturator with liquid component to be adsorbed; 4a, thermostat; 4b, thermostat/heating oven; 5, static mixer; 6, adsorbent bed in glass adsorption column; 7, analytical balance; 8, protective column.

Table 3. Experimental Isotherm Data for Propan-2-ol on Norit RB4 Activated Carbona p (Pa)

q (mol·kg−1)

p (Pa)

16.5 22.0 32.9 65.4 142.7

2.9237 3.2548 3.6342 4.3381 4.6858

284.9 441.7 662.6 883.5 1325.2

16.5 22.0 32.9 65.4 142.7

0.9818 1.0999 1.3279 1.8787 2.4211

16.5 22.0 32.9 65.4 142.7

0.3611 0.4177 0.4809 0.6956 0.9202

65.4 142.7 284.9 441.7

0.5025 0.6756 0.8803 1.0500

65.4 142.7 284.9 441.7

0.2063 0.3378 0.4809 0.5857

65.4 142.7 284.9 441.7

0.0832 0.1597 0.2579 0.3428

q (mol·kg−1)

293.15 K 4.9388 5.0536 5.1401 5.1917 5.2766 323.15 K 284.9 3.2232 441.7 3.7790 662.6 4.1800 883.5 4.3880 1325.2 4.6725 355.15 K 284.9 1.3162 441.7 1.6540 662.6 1.9885 883.5 2.2697 1325.2 2.7023 373.15 K 662.6 1.2713 883.5 1.4161 1325.2 1.7156 1767.0 1.9485 393.15 K 662.6 0.7188 883.5 0.8287 1325.2 0.9917 1767.0 1.1515 413.15 K 662.6 0.4343 883.5 0.5125 1325.2 0.6340 1767.0 0.7488

Table 4. Experimental Isotherm Data for Propan-2-ol on Sorbonorit 3 Activated Carbona

p (Pa)

q (mol·kg−1)

p (Pa)

q (mol·kg−1)

p (Pa)

1767.0 2208.7 3136.4 3975.7 4417.4

5.3331 5.3930 5.4912 5.5894 5.6460

16.5 22.0 32.9 65.4 142.7

2.6142 2.9603 3.4545 4.3780 4.9987

284.9 441.7 662.6 883.5 1325.2

1767.0 2208.7 3136.4 3975.7 4417.4

4.7707 4.8872 4.9854 5.0919 5.1135

16.5 22.0 32.9 65.4 142.7

0.7471 0.8836 1.0517 1.5525 2.0966

1767.0 2208.7 3136.4 3975.7 4417.4

3.0335 3.3230 3.7473 4.0236 4.0984

16.5 22.0 32.9 65.4 142.7

0.1481 0.1964 0.2396 0.4376 0.6024

2208.7 3136.4 3975.7 4417.4

2.1615 2.4677 2.6757 2.8005

65.4 142.7 284.9 441.7

0.2346 0.4110 0.6140 0.7788

2208.7 3136.4 3975.7 4417.4

1.2996 1.5392 1.7505 1.8587

65.4 142.7 284.9 441.7

0.0982 0.1947 0.3212 0.4360

2208.7 3136.4 3975.7 4417.4

0.8553 1.0217 1.1448 1.2314

65.4 142.7 284.9 441.7

0.0133 0.0366 0.1165 0.1797

a Standard uncertainty is u(T) = 0.1 K. Combined expanded uncertainties are Uc(p) = 14.3 Pa and Uc(q) = 0.0013 mol·kg−1 (level of confidence = 0.95).

q (mol·kg−1)

293.15 K 5.6260 5.9288 6.1452 6.2783 6.4630 323.15 K 284.9 2.8870 441.7 3.5543 662.6 4.1284 883.5 4.5560 1325.2 5.1900 355.15 K 284.9 0.9368 441.7 1.2380 662.6 1.5708 883.5 1.9036 1325.2 2.4228 373.15 K 662.6 0.9718 883.5 1.1432 1325.2 1.4294 1767.0 1.7372 393.15 K 662.6 0.5558 883.5 0.6540 1325.2 0.8337 1767.0 0.9884 413.15 K 662.6 0.2529 883.5 0.3078 1325.2 0.4210 1767.0 0.5275

p (Pa)

q (mol·kg−1)

1767.0 2208.7 3136.4 3975.7 4417.4

6.6111 6.7525 6.9605 7.1985 7.3416

1767.0 2208.7 3136.4 3975.7 4417.4

5.5012 5.7025 5.9788 6.1552 6.2550

1767.0 2208.7 3136.4 3975.7 4417.4

2.9054 3.2265 3.7756 4.1084 4.2299

2208.7 3136.4 3975.7 4417.4

1.9752 2.4461 2.7806 2.9203

2208.7 3136.4 3975.7 4417.4

1.1282 1.3828 1.5841 1.7455

2208.7 3136.4 3975.7 4417.4

0.5940 0.7621 0.9135 0.9768

a

Standard uncertainty is u(T) = 0.1 K. Combined expanded uncertainties are Uc(p) = 14.3 Pa and Uc(q) = 0.0013 mol·kg−1 (level of confidence = 0.95). B



Article

Table 5. Experimental Isotherm Data for Propan-2-ol on Sorbonorit 4 Activated Carbona p (Pa)

q (mol·kg−1)

p (Pa)

16.5 22.0 32.9 65.4 142.7

2.7822 3.1167 3.4628 4.3431 4.9770

284.9 441.7 662.6 883.5 1325.2

16.5 22.0 32.9 65.4 142.7

0.7788 0.9135 1.0899 1.4677 2.2181

16.5 22.0 32.9 65.4 142.7

0.1964 0.2479 0.3078 0.4559 0.6573

65.4 142.7 284.9 441.7

0.2346 0.3994 0.5757 0.7355

65.4 142.7 284.9 441.7

0.0549 0.1364 0.2513 0.3461

65.4 142.7 284.9 441.7

0.0100 0.0499 0.1082 0.1697

q (mol·kg−1)

293.15 K 5.6560 6.0021 6.2367 6.3681 6.5761 323.15 K 284.9 2.8504 441.7 3.4428 662.6 4.0635 883.5 4.5278 1325.2 5.1551 355.15 K 284.9 0.9485 441.7 1.2247 662.6 1.5409 883.5 1.8287 1325.2 2.3612 373.15 K 662.6 0.9302 883.5 1.0783 1325.2 1.3528 1767.0 1.5925 393.15 K 662.6 0.4609 883.5 0.5458 1325.2 0.7188 1767.0 0.8586 413.15 K 662.6 0.2363 883.5 0.3078 1325.2 0.4243 1767.0 0.5292

Table 6. Experimental Isotherm Data for Methylbenzene on Norit RB4 Activated Carbona

p (Pa)

q (mol·kg−1)

p (Pa)

q (mol·kg−1)

1767.0 2208.7 3136.4 3975.7 4417.4

6.7841 6.8973 7.1735 7.4081 7.4448

10.9 14.5 21.7 43.1 94.0

3.2917 3.4339 3.5359 3.7898 3.9396

1767.0 2208.7 3136.4 3975.7 4417.4

5.5761 5.8922 6.3249 6.5928 6.7425

10.9 14.5 21.7 43.1 94.0

2.5352 2.6232 2.7534 3.0030 3.3232

1767.0 2208.7 3136.4 3975.7 4417.4

2.7539 3.1050 3.6991 4.0801 4.2499

10.9 14.5 21.7 43.1 94.0

1.4510 1.5563 1.6974 2.0371 2.3529

2208.7 3136.4 3975.7 4417.4

1.7855 2.1399 2.3729 2.4877

43.1 94.0 187.7 291.1

1.7028 1.9177 2.2086 2.3963

2208.7 3136.4 3975.7 4417.4

0.9934 1.2314 1.4394 1.5409

43.1 94.0 187.7 291.1

1.2535 1.5042 1.7755 1.9611

2208.7 3136.4 3975.7 4417.4

0.6190 0.7821 0.9185 0.9851

43.1 94.0 187.7 291.1

0.9561 1.1493 1.3566 1.5053


p (Pa)

q (mol·kg−1)

293.15 K 4.0395 4.1002 4.1426 4.1632 4.2033 323.15 K 187.7 3.5012 291.1 3.6097 436.6 3.6889 582.1 3.7312 873.2 3.7855 355.15 K 187.7 2.6915 291.1 2.8858 436.6 3.0421 582.1 3.1430 873.2 3.2787 373.15 K 436.6 2.5515 582.1 2.6590 873.2 2.7892 1164.2 2.9064 393.15 K 436.6 2.1163 582.1 2.2357 873.2 2.3985 1164.2 2.4994 413.15 K 436.6 1.6779 582.1 1.8222 873.2 1.9828 1164.2 2.1152 187.7 291.1 436.6 582.1 873.2

p (Pa)

q (mol·kg−1)

1164.2 1455.3 2066.5 2619.5 2910.6

4.2272 4.2565 4.2934 4.3249 4.3325

1164.2 1455.3 2066.5 2619.5 2910.6

3.8267 3.8517 3.9147 3.9288 3.9396

1164.2 1455.3 2066.5 2619.5 2910.6

3.3753 3.4339 3.5120 3.5815 3.5945

1455.3 2066.5 2619.5 2910.6

2.9683 3.1137 3.1843 3.2179

1455.3 2066.5 2619.5 2910.6

2.6047 2.7523 2.8489 2.8934

1455.3 2066.5 2619.5 2910.6

2.2086 2.3681 2.4680 2.5092

a

Standard uncertainty is u(T) = 0.1 K. Combined expanded uncertainties are Uc(p) = 12.0 Pa and Uc(q) = 0.0009 mol·kg−1 (level of confidence = 0.95).

3. ADSORPTION EQUILIBRIUM MODELS To correlate equilibrium models with the experimental data, the following multitemperature adsorption isotherm equations were used: Toth, Langmuir−Freundlich, and Dubinin−Astakhov. Detailed description of the adsorption equilibrium models is available in literature.16−18 The multitemperature Toth adsorption isotherm equation is16 mp q= 1/ n nΔH ⎡ n⎤ b exp − + p 0 ⎣ ⎦ RT (1)

tetrachloromethane were determined by dynamic gravimetric method using the apparatus shown schematically in Figure 1.12−14 Before adsorption isotherm measurement, the activated carbon sample was dried at temperature 413.15 K for 12 h. An adsorbent sample (about 6 mg) was placed in a glass adsorption column kept at constant temperature. A stream of dry air was mixed at proper ratio with a second stream saturated with the organic component and delivered to the adsorption column. Adsorption capacity of the adsorbent was determined on the basis of periodic measurements of sample weight with a resolution of 0.1 mg and uncertainty of ±0.1 mg.12 The measurements were carried out until no increment of sample weight was observed. The temperature of ambient equaled 293 K and was maintained constant within ±1 K. The repeatability of isotherms is better than ±1%.12−14 Uncertainty analysis of individual measurement (weight, temperature) leads to statement that the overall measurement uncertainty is very small. The adsorption column was thermostated, which ensured good accuracy of measurements.12−14 The uncertainties of the adsorption capacity measurement were ±0.0013 mol·kg−1 for propan-2-ol, ±0.0009 mol·kg−1 for methylbenzene, and ±0.0006 mol·kg−1 for tetrachloromethane.15

(

)

where q (mol·kg−1) is equilibrium adsorption capacity, p (Pa) is the partial pressure of the adsorbate, T (K) is the temperature, ΔH (J·mol−1) is the heat of adsorption, R is the universal gas constant (J·mol−1·K−1), and b0 (Pan), m (mol·kg−1), and n are the isotherm parameters. The multitemperature Langmuir−Freundlich adsorption isotherm equation is17 q = q0

bpn 1 + bpn

(2) −n

where q0 (mol/kg), b (Pa ), and n are the isotherm parameters. C



Article

Table 7. Experimental Isotherm Data for Methylbenzene on Sorbonorit 3 Activated Carbona p (Pa)

q (mol·kg−1)

10.9 14.5 21.7 43.1 94.0

3.5467 3.7812 3.9114 4.1263 4.3520

10.9 14.5 21.7 43.1 94.0

2.3019 2.3909 2.5515 2.9140 3.3101

10.9 14.5 21.7 43.1 94.0

1.2665 1.4141 1.6323 1.9318 2.2693

43.1 94.0 187.7 291.1

1.7050 1.9796 2.2379 2.4213

43.1 94.0 187.7 291.1

1.3132 1.5075 1.7137 1.9014

43.1 94.0 187.7 291.1

0.8791 1.0744 1.2806 1.4619

p (Pa)

q (mol·kg−1)

293.15 K 4.6863 4.8523 5.0531 5.1551 5.2734 323.15 K 187.7 3.6954 291.1 3.9667 436.6 4.1502 582.1 4.2695 873.2 4.4258 355.15 K 187.7 2.6774 291.1 2.9509 436.6 3.2060 582.1 3.3481 873.2 3.5912 373.15 K 436.6 2.5928 582.1 2.7523 873.2 2.9520 1164.2 3.0855 393.15 K 436.6 2.0729 582.1 2.2324 873.2 2.4213 1164.2 2.5700 413.15 K 436.6 1.6323 582.1 1.7799 873.2 1.9861 1164.2 2.1391 187.7 291.1 436.6 582.1 873.2

Table 8. Experimental Isotherm Data for Methylbenzene on Sorbonorit 4 Activated Carbona

p (Pa)

q (mol·kg−1)

p (Pa)

q (mol·kg−1)

1164.2 1455.3 2066.5 2619.5 2910.6

5.3418 5.4286 5.5600 5.6641 5.7076

10.9 14.5 21.7 43.1 94.0

2.9227 3.0497 3.2201 3.6672 4.0416

1164.2 1455.3 2066.5 2619.5 2910.6

4.5224 4.6158 4.7634 4.8610 4.9283

10.9 14.5 21.7 43.1 94.0

2.1695 2.3627 2.5385 2.7024 3.0367

1164.2 1455.3 2066.5 2619.5 2910.6

3.7573 3.8843 4.0677 4.2099 4.3075

10.9 14.5 21.7 43.1 94.0

1.0603 1.2611 1.4825 1.7625 2.1066

1455.3 2066.5 2619.5 2910.6

3.2070 3.4132 3.5218 3.5760

43.1 94.0 187.7 291.1

1.5791 1.8157 2.0838 2.2911

1455.3 2066.5 2619.5 2910.6

2.6894 2.8652 2.9965 3.0638

43.1 94.0 187.7 291.1

1.2296 1.4272 1.6746 1.8580

1455.3 2066.5 2619.5 2910.6

2.2552 2.4680 2.5928 2.6514

43.1 94.0 187.7 291.1

0.8606 1.0744 1.2828 1.4337


Parameters of eq 2 are temperature dependent. a a q0 = a0 + 1 + 22 T T

(3)

⎛ b b ⎞ b = exp⎜b0 + 1 + 22 ⎟ ⎝ T T ⎠

(4)

293.15 K 4.3238 4.4757 4.6201 4.7156 4.8328 323.15 K 187.7 3.4241 291.1 3.6455 436.6 3.7898 582.1 3.9353 873.2 4.0818 355.15 K 187.7 2.3811 291.1 2.6232 436.6 2.8532 582.1 2.9998 873.2 3.1864 373.15 K 436.6 2.4810 582.1 2.6405 873.2 2.8196 1164.2 2.9477 393.15 K 436.6 2.0404 582.1 2.1532 873.2 2.3410 1164.2 2.4745 413.15 K 436.6 1.5976 582.1 1.7452 873.2 1.9405 1164.2 2.1022 187.7 291.1 436.6 582.1 873.2

p (Pa)

q (mol·kg−1)

1164.2 1455.3 2066.5 2619.5 2910.6

4.9088 4.9511 5.0488 5.1020 5.1551

1164.2 1455.3 2066.5 2619.5 2910.6

4.1903 4.2706 4.4030 4.5018 4.5615

1164.2 1455.3 2066.5 2619.5 2910.6

3.3405 3.4339 3.6249 3.7844 3.8767

1455.3 2066.5 2619.5 2910.6

3.0399 3.2027 3.3297 3.4132

1455.3 2066.5 2619.5 2910.6

2.6047 2.7718 2.9042 2.9629

1455.3 2066.5 2619.5 2910.6

2.2140 2.3876 2.5168 2.5841


ps (Pa) is the saturated vapor pressure, and E (J·mol−1) is the characteristic energy of adsorption. Characteristic energy of adsorption can be expressed as E = βE0, where E0 is the characteristic energy of adsorption for the standard substance, and β is the affinity coefficient.3,4 The parameters of selected equilibrium models were obtained using Levenberg−Marquardt nonlinear regression algorithm. The average relative percentage error, δ, which is a measure of accuracy of the model fitting to the experimental data, was calculated as

n1 (5) T where a0, a1, a2, b0, b1, b2, n0, and n1 are regression constants. The multitemperature Dubinin−Astakhov adsorption isotherm equation is18

δ=

100 N

N

∑ i=1

qexpt − qcalcd qexpt

(8)

where qexpt is the experimental adsorption capacity, qcalcd is the calculated adsorption capacity, and N is the number of experimental points.

(6)

where ⎛p⎞ ε = RT ln⎜ s ⎟ ⎝ p⎠

q (mol·kg−1)

a

n = n0 +

⎡ ⎛ ε ⎞n ⎤ q = V0ρa (T ) exp⎢ −⎜ ⎟ ⎥ ⎣ ⎝E⎠ ⎦

p (Pa)

4. RESULTS AND DISCUSION The experimental adsorption isotherms of nine adsorbate− adsorbent systems were obtained. The adsorption isotherms were measured at 293.15, 323.15, 355.15, 373.15, 393.15, and 413.15 K

(7)

and V0 (m3·kg−1) is the volume of adsorptive space, ρa (mol·m−3) is the molar density of liquid, ε (J·mol−1) is adsorption potential, D



Article

Table 9. Experimental Isotherm Data for Tetrachloromethane on Norit RB4 Activated Carbona p (Pa)

q (mol·kg−1)

p (Pa)

45.4 60.5 90.4 179.8 392.4

3.5860 3.6958 3.8272 4.0300 4.1711

783.6 1214.9 1822.3 2429.8 3644.7

45.4 60.5 90.4 179.8 392.4

2.4106 2.5842 2.8312 3.1380 3.3610

783.6 1214.9 1822.3 2429.8 3644.7

45.4 60.5 90.4 179.8 392.4

1.3867 1.5082 1.6870 2.1466 2.5406

783.6 1214.9 1822.3 2429.8 3644.7

179.8 392.4 783.6 1214.9

1.5928 1.9581 2.3020 2.5360

1822.3 2429.8 3644.7 4859.6

179.8 392.4 783.6 1214.9

1.2046 1.4946 1.8014 2.0426

1822.3 2429.8 3644.7 4859.6

179.8 392.4 783.6 1214.9

0.9238 1.1578 1.4107 1.6285

1822.3 2429.8 3644.7 4859.6

q (mol·kg−1)

p (Pa)

q (mol·kg−1)

4.2907 4.3563 4.4051 4.4402 4.4981

4859.6 6074.5 8625.8 10934.0 12149.0

4.5403 4.5657 4.6534 4.7321 4.7919

3.5905 3.7166 3.8233 3.8785 3.9481

4859.6 6074.5 8625.8 10934.0 12149.0

3.9936 4.0222 4.0833 4.1555 4.1984

2.9450 3.1627 3.3292 3.4189 3.5424

4859.6 6074.5 8625.8 10934.0 12149.0

3.5996 3.6341 3.6913 3.7712 3.8076

2.7233 2.8377 2.9840 3.0561

6074.5 8625.8 10934.0 12149.0

3.1146 3.2291 3.3168 3.3877

2.2429 2.3930 2.5302 2.6433

6074.5 8625.8 10934.0 12149.0

2.7207 2.8240 2.9242 2.9931

1.8073 1.9555 2.1252 2.2116

6074.5 8625.8 10934.0 12149.0

2.3046 2.4379 2.5386 2.5939

293.15 K

323.15 K

355.15 K

373.15 K

393.15 K

413.15 K

a


Table 10. Experimental Isotherm Data for Tetrachloromethane on Sorbonorit 3 Activated Carbona p (Pa)

q (mol·kg−1)

p (Pa)

45.4 60.5 90.4 179.8 392.4

3.4969 3.6588 3.8675 4.1516 4.6060

783.6 1214.9 1822.3 2429.8 3644.7

45.4 60.5 90.4 179.8 392.4

2.2936 2.4450 2.7577 3.1809 3.5892

783.6 1214.9 1822.3 2429.8 3644.7

45.4 60.5 90.4 179.8 392.4

1.2196 1.3451 1.4939 1.9516 2.3898

783.6 1214.9 1822.3 2429.8 3644.7

179.8 392.4 783.6 1214.9

1.5492 1.9705 2.3735 2.6836

1822.3 2429.8 3644.7 4859.6

q (mol·kg−1)

p (Pa)

q (mol·kg−1)

4.8868 5.0942 5.2762 5.3711 5.5083

4859.6 6074.5 8625.8 10934.0 12149.0

5.6364 5.7241 5.8347 5.9322 6.0030

4.0105 4.2718 4.4747 4.6034 4.8147

4859.6 6074.5 8625.8 10934.0 12149.0

4.9466 4.9889 5.1079 5.1885 5.2392

2.9586 3.2661 3.5541 3.7465 3.9975

4859.6 6074.5 8625.8 10934.0 12149.0

4.2016 4.3134 4.4291 4.5267 4.5891

2.9482 3.1406 3.4039 3.5574

6074.5 8625.8 10934.0 12149.0

3.6926 3.8993 4.0111 4.0943

293.15 K

323.15 K

355.15 K

373.15 K

E



Article

Table 10. continued p (Pa)

q (mol·kg−1)

p (Pa)

179.8 392.4 783.6 1214.9

1.0551 1.4010 1.7618 2.0283

1822.3 2429.8 3644.7 4859.6

179.8 392.4 783.6 1214.9

0.7353 1.0077 1.3067 1.5290

1822.3 2429.8 3644.7 4859.6

q (mol·kg−1)

p (Pa)

q (mol·kg−1)

2.2968 2.4769 2.7402 2.9404

6074.5 8625.8 10934.0 12149.0

3.0815 3.2986 3.4273 3.5093

1.7813 1.9451 2.1915 2.3657

6074.5 8625.8 10934.0 12149.0

2.5159 2.7233 2.8832 2.9937

393.15 K

413.15 K

a


Table 11. Experimental Isotherm Data for Tetrachloromethane on Sorbonorit 4 Activated Carbona p (Pa)

q (mol·kg−1)

p (Pa)

45.4 60.5 90.4 179.8 392.4

3.4579 3.6627 3.9175 4.0885 4.4994

783.6 1214.9 1822.3 2429.8 3644.7

45.4 60.5 90.4 179.8 392.4

2.0888 2.2689 2.4684 2.8800 3.2759

783.6 1214.9 1822.3 2429.8 3644.7

45.4 60.5 90.4 179.8 392.4

1.1045 1.1507 1.3412 1.7559 2.3111

783.6 1214.9 1822.3 2429.8 3644.7

179.8 392.4 783.6 1214.9

1.5628 1.9412 2.2780 2.5569

1822.3 2429.8 3644.7 4859.6

179.8 392.4 783.6 1214.9

1.1403 1.3945 1.6922 1.9269

1822.3 2429.8 3644.7 4859.6

179.8 392.4 783.6 1214.9

0.7314 0.9765 1.2436 1.4647

1822.3 2429.8 3644.7 4859.6

q (mol·kg−1)

p (Pa)

q (mol·kg−1)

4.8264 4.9967 5.1495 5.2541 5.3997

4859.6 6074.5 8625.8 10934.0 12149.0

5.5155 5.6383 5.8308 6.0121 6.1285

3.5730 3.7595 3.9435 4.0547 4.1880

4859.6 6074.5 8625.8 10934.0 12149.0

4.2874 4.3862 4.5520 4.7113 4.8283

2.7597 3.0015 3.2882 3.4358 3.6614

4859.6 6074.5 8625.8 10934.0 12149.0

3.7738 3.8720 4.0625 4.1678 4.2835

2.7753 2.9157 3.1341 3.2843

6074.5 8625.8 10934.0 12149.0

3.3818 3.5782 3.7387 3.8460

2.1746 2.3547 2.5913 2.7330

6074.5 8625.8 10934.0 12149.0

2.8552 3.0587 3.2388 3.3233

1.7052 1.8898 2.1310 2.2845

6074.5 8625.8 10934.0 12149.0

2.4086 2.6134 2.7974 2.8871

293.15 K

323.15 K

355.15 K

373.15 K

393.15 K

413.15 K

a


Based on the Dubinin−Astakhov model, the temperatureindependent characteristic curves were obtained, and the values of limiting adsorption volumes were calculated. For a given adsorbate−adsorbent system, the relationship between adsorption potential ε and adsorbate volume adsorbed by unit mass of adsorbent V (V = q/ρa, where ρa is adsorbate molar density) is characteristic curve:

and pressures up to component saturation pressures at 293.15 K. The equilibrium experimental data are shown in Tables 3−11. The multitemperature adsorption isotherms, Toth, Langmuir− Freundlich and Dubinin−Astakhov, were fitted to the experimental data. The obtained parameters of adsorption isotherms and average relative percentage errors are shown in Tables 12−14. The experimental and correlated isotherms for each adsorbate−adsorbent pair at various temperatures are presented in Figures 2−4.

V = f (ε) F

(9) DOI: 10.1021/acs.jced.6b00488 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


Article

Table 12. Adsorption Isotherm Parameters and Average Relative Errors for Norit RB4 model Toth

Langmuir−Freudlich

Dubinin−Astakhov

parameters and errors

propan-2-ol

methylbenzene

tetrachloromethane

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) E (J·mol−1) n δ (%)

5.77563 7.28343 × 106 5.70492 × 10−1 63974.0 11.36 79.6215 −44312.8 6.6227 × 106 −10.7862 −278.558 843785 −2.78569 × 10−2 224.728 4.87 4.26218 × 10−4 15670.6 2.41548 12.96

4.62943 486.785 2.81497 × 10−1 68322.0 1.50 3.75255 8.45325 55847.9 −11.8693 4250.93 −209502 3.99912 × 10−1 2.17527 1.30 4.51771 × 10−4 24609.9 2.07738 2.35

5.00143 695.217 2.84132 × 10−1 66181.0 2.21 3.18644 −88.1166 155147 −13.2381 4677.01 −305158 3.77055 × 10−1 38.6443 1.79 4.39910 × 10−4 22528.0 2.01104 3.85

Table 13. Adsorption Isotherm Parameters and Average Relative Errors for Sorbonorit 3 model Toth


Dubinin−Astakhov


propan-2-ol

methylbenzene

tetrachloromethane


7.45682 1.23832 × 107 0.597934 60025.8 10.33 52.5444 −25113.5 3.49862 × 106 −32.1148 11553.0 −815169 1.27841 −207.259 8.30 5.35038 × 10−4 13367.2 2.19569 12.49

6.95278 77.9704 0.22472 60759.9 2.21 −29.3906 21290.5 −3.0368e6 −8.20922 1958.57 73888.8 0.972518 −226.167 2.13 588501 × 10−4 20759.9 1.58822 2.34

6.60522 611.311 0.309617 53340.3 1.84 −6.60701 6459.35 −734969 −22.7056 10242.9 −1.15575 × 106 1.12943 −236.994 1.41 5.5463 × 10−4 19320.2 1.85205 1.96

with Sorbonorit 4 and Sorbonorit 3 activated carbons have similar values, 5.52833 × 10−4 and 5.32732 × 10−4 m3·kg−1, respectively. However, the V0 for Norit RB4 activated carbon is somewhat lower: 4.35663 × 10−4 m3·kg−1. The adsorption isotherm was used to determine the isosteric heat of adsorption by the Clausius−Clapeyron equation:13,14

Characteristic curves for different species on the same activated carbon could be brought into coincidence by using affinity coefficients for the adsorbates: ⎛ε⎞ V = f⎜ ⎟ ⎝β⎠

(10)

⎛ ∂ln p ⎞ RT 2 ⎛ ∂p ⎞ ⎜ ⎟ ⎟ = −ΔH = RT 2⎜ ⎝ ∂T ⎠q p ⎝ ∂T ⎠q

In this study, tetrachloromethane was chosen as the reference vapor. The affinity coefficient values for the used substances, calculated from definition β = V0/V0ref (where V0 is the saturated liquid molar volume and V0ref is the saturated liquid molar volume of the reference vapor), are 1.0, 0.78, and 1.10 for tetrachloromethane, propan-2-ol, and methylbenzene, respectively.12−14 For all studied adsorbent−adsorbate systems, characteristic curves (eq 9), developed from the experimental data, are shown in Figures 5−7. The values of the parameters of the characteristic curves are given in Table 15. It results from analysis of the Figures 5−7 that characteristic curves, for various components on given adsorbent, are arranged nearly on single curve. Adsorptive space volumes, V0, for systems

(11)

For the calculation of the pressure derivative in the above equation, the relationship between pressure and temperature was described using the Dubinin−Astakhov model (eq 6). Isosteric heat of adsorption of studied VOCs onto Sorbonorit 4 activated carbon is presented in Figure 8. Then, isosteric heat of adsorption of methylbenzene onto three examined activated carbons is shown in Figure 9. Values of isosteric heat of adsorption decrease with adsorbate loading in the solid phase for all systems investigated (Figures 8 and 9). G



Article

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


Dubinin−Astakhov


propan-2-ol

methylbenzene

tetrachloromethane


7.70930 1.49320 × 107 5.89205 × 10−1 61806.9 12.49 162.615 −86422.5 1.20553 × 107 −31.4273 10769.5 −630855 1.14376 −187.508 10.80 5.54556 × 10−4 12934.6 2.14458 15.18

6.58340 47.0612 2.20394 × 10−1 55381.0 2.08 3.85705 720.313 −21394.1 −11.7356 4486.39 −372903 4.88754 × 10−1 −51.1064 1.99 5.37083 × 10−4 21349.2 1.55844 2.41

7.29240 95.6482 2.35332 × 10−1 54251.6 3.51 71.7499 −42922.0 7.01860 × 106 −25.1922 12470.8 −1.59588 × 106 0.569877 −77.1094 2.77 5.46144 × 10−4 19061.6 1.581 3.99

Figure 2. Experimental and correlated (Langmuir−Freundlich equation) isotherms for propan-2-ol adsorption onto selected activated carbons at various temperatures: (a) Norit RB4 (Table 3); (b) Sorbonorit 3 (Table 4); (c) Sorbonorit 4 (Table 5); (+, ) 293.15 K; (△, ···) 323.15 K; (×,  ) 355.15 K; (◇,−) 373.15 K; (□, ··) 393.15 K; (○, ·) 413.15 K.

Figure 3. Experimental and correlated (Langmuir−Freundlich equation) isotherms for methylbenzene adsorption onto selected activated carbons at various temperatures: (a) Norit RB4 (Table 6); (b) Sorbonorit 3 (Table 7); (c) Sorbonorit 4 (Table 8); (+, ) 293.15 K; (△, ···) 323.15 K; (×, −·−) 355.15 K; (◇, −−−) 373.15 K; (□, −··), 393.15 K; (○, −−·) 413.15 K. H



Article

Figure 4. Experimental and correlated (Langmuir−Freundlich equation) isotherms for tetrachloromethane adsorption onto selected activated carbons at various temperatures: (a) Norit RB4 (Table 9); (b) Sorbonorit 3 (Table 10); (c) Sorbonorit 4 (Table 11); (+, ) 293.15 K; (△, ···) 323.15 K; (×, −·−) 355.15 K; (◇, −−−) 373.15 K; (□, −··) 393.15 K; (○, −−·) 413.15 K.

Figure 5. Characteristic curve for Norit RB4 activated carbon, based on experimental isotherms for propan-2-ol (Table 3), methylbenzene (Table 4), and tetrachloromethane (Table 5) adsorption onto activated carbon at various temperatures: (+) propan-2-ol; (△) methylbenzene; (×) tetrachloromethane; () correlated curve.

Figure 6. Characteristic curve for Sorbonorit 3 activated carbon, based on experimental isotherms for propan-2-ol (Table 3), methylbenzene (Table 4), and tetrachloromethane (Table 5) adsorption onto activated carbon at various temperatures: (+) propan-2-ol; (△) methylbenzene; (×) tetrachloromethane; () correlated curve.

Using Toth isotherm parameters, the average isosteric heat of adsorption was determined for all examined systems. The average isosteric heat of adsorption for propan-2-ol, methylbenzene, and tetrachloromethane on Norit RB4 activated carbons were 63974.0, 68322.0, and 66181.0 J·mol−1 (Table 12), respectively. For propan-2-ol, methylbenzene, and tetrachloromethane on Sorbonorit 3 activated carbon, average isosteric enthalpies of adsorption were found to be 60025.8, 60759.9, and 53340.3 J·mol−1 (Table 13), respectively. Finally, for propan-2-ol, methylbenzene, and tetrachloromethane on Sorbonorit 4 activated carbon, average isosteric enthalpies of adsorption were found to be 61806.9, 55381.0, and 54251.0 J·mol−1 (Table 14), respectively. The heats of evaporation at averaged temperature 353 K are 40073.1, 35417.3, and 29729.2 J/mol for propan-2-ol, methylbenzene, and tetrachloromethane, respectively.

In comparison with above heats of adsorption, these values are lower as it can be expected. Exemplary ratios of the heat of adsorption to that of vaporization for Sorbonorit 4 activated carbon are approximately 1.5, 1.6, and 1.8 for 1propan-2-ol, methylbenzene, and tetrachloromethane, respectively. The lowest variability of isosteric heat of adsorption on Sorbonorit 4 activated carbon was observed for propan-2-ol in comparison to methylbenzene and tetrachloromethane (Figure 8). As can be seen from Figure 9, the differences of the isosteric heat of adsorption of methylbenzene are not high for all adsorbents examined. The results show that the adsorbate−adsorbent interaction highly dominates the system. An energetically heterogeneous surface of microporous activated carbons was noted from the variation of isosteric heat of adsorption along with the surface I



Article

Figure 7. Characteristic curve for Sorbonorit 4 activated carbon, based on experimental isotherms for propan-2-ol (Table 3), methylbenzene (Table 4), and tetrachloromethane (Table 5) adsorption onto activated carbon at various temperatures: (+) propan-2-ol; (△) methylbenzene; (×) tetrachloromethane; () correlated curve.

Figure 8. Isosteric heat of adsorption of various VOCs onto Sorbonorit 4 activated carbon: () methylbenzene; (−−−) tetrachloromethane; (···) propan-2-ol.

loading for each adsorbate. From the adsorbent regeneration viewpoint, understanding the thermal desorption behavior of adsorbates from an adsorbent is important. For nine pairs of adsorbate−adsorbent examined systems, adsorption isotherms are type I of BDDT classification.19 The increase in temperature causes a decrease in the adsorption capacity. As may be seen, from analysis of the Figures 2−4, the temperature dependence of adsorption capacity is fairly linear. In this work, three equilibrium adsorption models, Toth, Langmuir−Freundlich, and Dubinin−Astakhov, were correlated with experimental data. The equilibrium models had four, eight, and three adjustable parameters, respectively. For the all adsorbate−adsorbent pairs, the Langmuir−Freundlich model gave the best fit to the multitemperature experimental data, so it can be concluded that the number of parameters have a great impact on the fit quality. The lowest errors were obtained for methylbenzene on all adsorbents studied (1.3% on Norit RB4, 1.99% on Sorbonorit 4, and 2.13% on Sorbonorit 3). For tetrachloromethane on these adsorbents, the fitting errors were not much larger (1.41% on Sorbonorit 3, 1.79% on Norit RB4, and 2.77% on Sorbonorit 4). For propan-2-ol, the fitting errors were significantly larger but still acceptable (4.87% on Norit RB4, 8.30% on Sorbonorit 3, and 10.80% on Sorbonorit 4). The larger errors were caused by poor fitting of the isotherm at 293.15 K, where some kind of capillary condensation phenomenon may occur at near saturation pressures. Toth and Dubinin−Astakhov models also show a fairly good fit for most pairs of adsorbent−adsorbate. In addition, the Toth equation can provide the mean value of the heat of adsorption,

Figure 9. Isosteric heat of adsorption of methylbenzene onto various activated carbons: () Norit RB4; (−−−) Sorbonorit 3; (···) Sorbonorit 4.

and the Dubinin−Astakhov equation can provide the total adsorbent micropore volume. From the comparison of adsorption isotherms for each component at 293.15 K (Figures 2, 3, and 4) it can be concluded

Table 15. Parameters and Average Relative Errors for Characteristic Curves (Figures 5−7) model


Norit RB4

Sorbonorit 3

Sorbonorit 4

characteristic curve

V0 (m3·kg−1) E0 (J·mol−1) n δ (%)

4.35663 × 10−4 21163.7 2.39190 8.62

5.52833 × 10−4 18252.7 2.03630 12.65

5.32732 × 10−4 18086.7 1.92471 15.59

J



Article

Impregnated Activated Carbons. Ind. Eng. Chem. Res. 2002, 41, 672− 679. (12) Rudnicka, J. Modelowanie usuwania lotnych związ ków organicznych ze strumieni gazowych metodą adsorpcji zmiennotemperaturowej prózṅ iowej VTSA, (in Polish) [Modeling of VOCs removal from gas streans using Vacuun Temperature Swing Adsorption VTSA]. Ph.D. Thesis, Technical University of Szczecin, Szczecin, 2007. (13) Nastaj, J. Modelowanie wybranych procesów adsorpcyjnych i biosorpcyjnych w ochronie s ́rodowiska [Modeling of selected of adsorption and biosorption processes in environmental protection] (in Polish); BEL Studio Sp. zo.o.: Szczecin, 2013. (14) Ambrożek, B. Modelowanie procesu odzyskiwania lotnych związków organicznych w cyklicznym układzie TSA z zamkniet̨ ym obiegiem gazu podczas regeneracji złoża adsorbentu [Modeling of volatile organic recovery in cyclic TSA system with closed gas recycle during adsorbent bed regeneration] (in Polish); . West Pomeranian University of Technology Publishing House: Szczecin, 2010; 257 pp. (15) Pendleton, P.; Badalyan, A. Gas adsorption data uncertainty and propagation analyses. Adsorption 2005, 11, 61−66. (16) Toth, J. Adsorption: Theory, Modelling, and Analysis; Marcel Dekker: Basel, 2001. (17) Do, D. D. Adsorption Analysis: Equilibria and Kinetics; Imperial College Press: London, 1998. (18) Dubinin, M. M. The potential theory of adsorption of gases and vapors for adsorbents with energetically nonuniform surfaces. Chem. Rev. 1960, 60, 235−241. (19) Brunauer, S.; Deming, L. S.; Deming, W. E.; Teller, E. On a theory of the van der Waals adsorption and gases. J. Am. Chem. Soc. 1940, 62, 1723−1732.

that both Sorbonorit 4 and Sorbonorit 3 activated carbons have similar equilibrium adsorption loading. However, adsorption isotherms for each component at 293.15 K (Figures 2a, 3a, and 4a) on Norit RB4 show significantly lower adsorption capacity, which is caused by its lower BET surface area (Table 1). The obtained results indicate that Sorbonorit 4 activated carbon has the highest adsorption capacity for VOCs (propan-2-ol, methylbenzene, and tetrachloromethane).

5. CONCLUSIONS The adsorption isotherms of propan-2-ol, methylbenzene, and tetrachloromethane vapors on three commercial adsorbents, Norit RB4, Sorbonorit 3 and Sorbonorit 4 activated carbons, were measured at 293.15, 323.15, 355.15, 373.15, 393.15, and 413.15 K and pressures up to particular component saturation pressures at 293.15 K. The selected equilibrium models, Toth, Langmuir−Freundlich, and Dubinin−Astakhov, were correlated with the experimental equilibrium data. The lowest average relative errors of models fitting to experimental data were obtained for Langmuir−Freundlich isotherm equation. It can be the basis for modeling of the multicomponent adsorption equilibrium using interpolative models. The experimental and computed data obtained in this study can be used for modeling of cyclic adsorption processes such as temperature swing adsorption (TSA), pressure swing adsorption (PSA), or pressure and temperature swing adsorption (PTSA).

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AUTHOR INFORMATION

Corresponding Author

*E-mail address: [email protected]. Notes

The authors declare no competing financial interest.

■

REFERENCES

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

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