Adsorption Characteristics of Pentane, Hexane, and Heptane

Article pubs.acs.org/jced

Adsorption Characteristics of Pentane, Hexane, and Heptane: Comparison of Hydrophobic Hypercrosslinked Polymeric Adsorbent with Activated Carbon Jian Wu,†,‡ Liang Zhang,† Chao Long,*,† and Quanxing Zhang*,† †

State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, 163 Xianlin Road, Nanjing 210046, China ‡ Jiangsu Provincial Academy of Environmental Science, 241 Fenghuang West Road, Nanjing, 210036, China ABSTRACT: The adsorption isotherm data of light hydrocarbons (C5's−C7’s, pentane, hexane, and heptane), which are the main composition of gasoline vapor, onto hydrophobic hypercrosslinked polymeric adsorbent (HY-1) were measured at temperatures ranging from (293 to 323) K and pressures up to 60 kPa and compared with granular activated carbon (NucharWV-A 1100). The experimental data were fitted to the Langmuir, Freundlich, and Dubinin−Astakhov (DA) equations, respectively. The DA isotherms correlated with the experimental data within 1.85 % root-mean-square deviation (rmsd) and presented a better fitting than Langmuir and Freundlich equations. The experimental results indicated that HY-1 had good adsorption capacities for three hydrocarbon VOCs, which were about 85 % of those of NucharWV-A 1100. The average adsorption heats of three hydrocarbon VOCs onto HY-1 were smaller than those of NucharWV-A 1100, implying three hydrocarbon VOCs were adsorbed onto HY-1 more weakly and HY-1 could be regenerated more easily. Taken together, the hydrophobic hypercrosslinked polymeric adsorbent (HY-1) would be a potential alternative to activated carbon adsorbent for the recovery of gasoline vapor.

1. INTRODUCTION Gasoline is an important energy widely used in manufacturing and our lives, but it is likely to be volatile and cause serious loss during production, storage, transportation, and use. The emission of gasoline vapor into the atmosphere not only pollutes the air but also results in significant economic losses.1−3 In China, more than 200 million tons of crude oil was produced in 2010. It was estimated that the emission of gasoline vapor reached more than 600 thousand tons, which was equal to the output of a medium oil field. Therefore, the recovery and reuse of evaporated gasoline from loading, unloading, and other handling processes are of significant importance from both economic and environmental points of view. Gasoline is a mixture of hydrocarbons with chains containing 4−12 carbons, and its vapor mostly consists of light hydrocarbons (C4’s−C7’s).4−8 It is well-known that adsorption is one of the most practical methods for separating and recovering volatile organic compounds (VOCs) from industrial waste gas. In order to recover and reuse the mentioned light hydrocarbons gas above, lots of attempts had been made to remove these VOCs using a carbonaceous adsorbent. However, it has been recognized that carbonaceous adsorbent adsorption always encounters some problems such as poor regenerability,9−11 sharp rise of bed temperature,12,13 low mechanical strength, and the influence of water vapor.14−17 Hence, efforts have been made focusing on finding alternative adsorbents to separate and recover VOCs from polluted air streams. Hypercrosslinked polymeric resin, which is produced by cross-linking polymers of macroporous resin in a good © 2012 American Chemical Society

solvent, represents a class of predominantly microporous organic materials with high surface areas and high micropore volume.18,19 It has emerged as a potential alternative to activated carbon for removing the organic pollutants from streams due to its controllable pore structure, stable physical and chemical properties, and regenerability on site. Some investigators including our research group have found that hypercrosslinked polymeric adsorbent has a significant sorption capacity for VOCs.20−25 Recently, we synthesized a novel hypercrosslinked polymeric adsorbent (HY-1) with high surface area and specific bimodal pore size distribution in the regions of micropore (0.5−2.0 nm) and meso-macropore (30−70 nm).26 In comparison with microporous activated carbon, HY-1 possessed higher adsorption capacities for benzene and methyl ethyl ketone at the higher relative pressure. Moreover, it had an extremely hydrophobic surface and the lower water vapor uptakes at the range of lower relative pressure than a commercial activated carbon and activated carbon fiber. Our previous study has shown that the effect of the water vapor on the adsorption of the benzene on HY-1 was weaker than commercial activated carbon and activated carbon fiber,27 which is advantageous for HY-1 to adsorb VOCs from humid gas streams. Therefore, HY-1 will be a particularly efficient and competitive adsorbent for VOCs recovery from polluted vapor streams. Received: May 18, 2012 Accepted: October 24, 2012 Published: November 7, 2012 3426

dx.doi.org/10.1021/je300550x | J. Chem. Eng. Data 2012, 57, 3426−3433

Journal of Chemical & Engineering Data

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Table 1. Salient Properties of HY-1 and NucharWV-A 1100 parameters

HY-1

WV-A 1100

SBET (m2·g−1) micropore volume (cm3·g−1) mesopore volume (cm3·g−1) total pore volume (cm3·g−1) average pore diameter (nm) wear-resisting ratea (%) wear-resisting rateb (%)

1244.42 0.541 0.305 0.907 2.35 93.3 94.2

1644.9 0.742 0.628 1.141 2.77 15.3 37.5

a By the measuring method of GB/T12598-2001, in Chinese. bby the measuring method of GB/T12496.6-1999, in Chinese.

Figure 1. Pore size distributions of HY-1 and NucharWV-A 1100.

In this study, pentane, hexane, and heptane were used as representatives of gasoline vapor. The adsorption of the above three VOCs on HY-1 was investigated and compared with a commercial activated carbon (NucharWV-A 1100). The experimental data at three different temperatures ((293, 308, and 323) K) were correlated with Langmuir, Freundlich, and Dubinin−Astakov (DA) adsorption models. Moreover, the isosteric enthalpies of adsorption on two adsorbents were calculated. Such a basic experimental investigation of pentane, hexane, and heptane adsorption onto HY-1 and NucharWV-A 1100 is essential for the application of hypercrosslinked polymeric resin to recovering gasoline vapor and designing an efficient system as well. Figure 3. Adsorption isotherms of three hydrocarbon VOCs on HY-1 and NucharWV-A 1100 fitting by DA model at (293, 308, and 323) K: (a) pentane, (b) hexane, and (c) heptane.

2. EXPERIMENTAL SECTION 2.1. Materials. The hypercrosslinked polymeric adsorbent (HY-1) was prepared via a post-crosslinking step of low-crosslinked macroporous poly(styrene−divinylbenzene); the synthetic process had been described in detail in a previous paper.26

The granular activated carbon (NucharWV-A 1100) is commercially available (MeadWestvaco, USA), which is especially designed

Figure 2. Schematic diagram of the experimental apparatus. 3427



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Table 2. Experimental Adsorption Equilibrium Data of Pentane, Hexane, and Heptane on HY-1 and NucharWV-A 1100 293 K

308 K q/mg·g−1

323 K q/mg·g−1

q/mg·g−1

adsorbate

P/kPa

HY-1

WV-A 1100

P/kPa

HY-1

WV-A 1100

P/kPa

HY-1

WV-A 1100

pentane

2.057 4.114 8.229 12.857 17.143 25.715 34.286 51.429 0.559 1.119 2.237 3.496 4.661 6.992 9.323 13.984 0.121 0.243 0.486 0.759 1.012 1.518 2.025 3.037

276.8 309.5 363.0 402.8 417.0 438.2 451.5 484.6 276.4 332.9 379.3 405.1 420.8 442.0 454.8 466.1 303.4 358.6 415.1 449.4 464.0 483.1 494.7 510.7

352.1 388.2 435.7 472.1 489.8 528.9 557.6 598.9 354.0 409.5 443.6 474.2 498.9 542.8 577.0 597.6 373.7 406.5 458.3 489.9 510.2 535.0 561.1 602.9

2.402 4.803 9.607 15.010 20.014 30.020 40.027 60.041 0.730 1.460 2.921 4.563 6.084 9.127 12.169 18.253 0.145 0.290 0.580 0.906 1.208 1.812 2.416 3.624

268.6 317.0 362.0 389.4 403.2 417.5 433.5 450.3 271.6 321.9 366.8 392.6 411.2 431.1 445.7 470.1 295.1 343.0 386.0 409.6 424.3 442.6 455.9 466.0

318.9 355.8 395.5 421.4 429.4 457.7 477.9 505.0 328.6 364.1 401.3 426.5 450.0 483.4 513.3 550.4 341.5 356.0 408.3 440.8 460.9 491.5 511.2 536.5

2.402 4.803 9.607 15.010 20.014 30.020 40.027 60.041 0.730 1.460 2.921 4.563 6.084 9.127 12.169 18.253 0.145 0.290 0.580 0.906 1.208 1.812 2.416 3.624

221.3 263.9 310.9 339.0 354.6 372.5 384.1 399.3 220.2 264.5 313.0 342.8 360.1 382.5 397.8 416.7 193.2 260.7 315.7 349.5 369.4 389.6 402.1 414.4

265.6 302.4 340.1 365.3 377.8 398.6 409.0 426.7 278.4 322.8 362.8 387.1 403.4 427.2 445.5 461.0 298.6 317.8 355.2 397.2 412.7 431.6 446.2 467.5

hexane

heptane

was 0.1 mg. After the adsorption procedure, desorption behavior was investigated by connecting the adsorption column to a vacuum pump under vacuum at 0.098 MPa for 30 min. The amount desorbed was equal to the weight change of adsorbent before and after the desorption process. The desorption ratio was calculated by dividing the difference between the adsorption capacity and the amount desorbed by the former value. 2.3. Isotherm Models. Adsorption experimental data were correlated with three different isotherms, namely, Langmuir, Freundlich, and DA. Langmuir Equation. The well-known Langmuir isotherm can be expressed by eq 1.

for hydrocarbon vapor adsorption. The selected physiochemistry properties of HY-1 and NucharWV-A 1100 as well as wearresisting rate are listed in Table 1. The mechanical strength means the anti-damage performance of adsorbent under mechanical force and is signified by wear-resisting rate usually. As can be seen, the wear-resisting rate of HY-1 is much higher than that of NucharWV-A 1100. Pore size distributions of HY-1 and NucharWV-A 1100 are shown in Figure 1. 2.2. Adsorption−Desorption Experiments. Measurements of the adsorption equilibrium of VOCs onto HY-1 and NucharWV-A 1100 have been conducted using a gravimetric method. Figure 2 shows the schematic diagram of the experimental apparatus which basically consists of a VOC vapor generator, an adsorption column (5 mm in inner diameter and 100 mm in height) where polymeric adsorbent was held, and a gas analysis system. First, the nitrogen steam was divided into two streams using two mass flow controllers. One nitrogen flow was conducted to the bubble saturator containing pure liquid VOCs, which was held at a constant temperature by means of a thermostatic water bath. Then, the stream was diluted with another nitrogen stream to attain a given VOCs concentration. The carrier gas containing a scheduled concentration of VOCs vapor was passed through the adsorption column. At the outlet of the adsorption column, a gas chromatograph (GC, 9790, FULI, China) with a flame ionization detector (FID) and a thermal conductivity detector (TCD) was used to continuously measure the concentrations of VOCs. The adsorption equilibrium was attained when the exit concentration became equal to the inlet concentration. The equilibrium adsorption amount of VOCs onto adsorbent was equal to the weight change of adsorbent before and after the adsorption process. Here, a high precision microbalance (AL204, Mettler Toledo, China) was adopted as the weighing device, whose precision for a measurement

q = qs

bP 1 + bP

(1) −1

where q is the amount adsorbed (mg·g ), qs is the saturated amount adsorbed (mg·g−1), P is the equilibrium pressure (kPa), and b is the adsorption affinity (kPa−1) . Freundlich Equation. The Freundlich isotherm is expressed by eq 2.

q = kP n

(2) −1

where q is the amount adsorbed (mg·g ), k and n are empirical constants that are generally temperature-dependent, and P is the equilibrium pressure (kPa). The Freundlich equation is very popularly used in the description of adsorption VOCs from gas stream. DA Equation. The DA model is a commonly used isotherm model for physical adsorption of organic vapors onto microporous adsorbent. The DA model can be defined as the following equations: qv = qo exp[− (ε /E)r ] 3428

(3)



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Table 3. Fitting Parameters of Langmuir, Freundlich, and DA Models for VOCs on HY-1 pentane model

parameter −1

q0/mg·g b/kPa−1 R2 rmsd/% k n R2 rmsd/% q/mg·g−1 E/kJ·mol−1 r R2 rmsd/%

Langmuir

Freundlich

DA

hexane

heptane

293 K

308 K

323 K

293 K

308 K

323 K

293 K

308 K

323 K

472.5 0.533 0.9850 5.25 250.6 0.171 0.9967 2.25 484.6 12.594 1.290 0.9987 1.43

446.3 0.548 0.9943 3.01 251.4 0.149 0.9945 3.11 454.4 13.890 1.755 0.9997 0.60

400.7 0.435 0.9937 3.54 204.6 0.173 0.9925 3.68 413.3 14.298 1.998 0.9999 0.41

471.4 2.225 0.9937 2.80 324.8 0.155 0.9947 3.54 474.0 12.474 1.537 0.9995 1.03

461.1 1.668 0.9909 3.76 302 0.159 0.9966 2.56 479.1 13.995 1.537 0.9997 0.69

416.1 1.268 0.9907 4.32 249.7 0.188 0.9946 3.27 440.6 14.109 1.820 0.9999 0.23

512.9 10.446 0.9961 2.73 448.9 0.151 0.9916 3.75 513.3 12.455 1.911 0.9999 0.43

464.4 10.529 0.9950 2.76 405 0.135 0.9951 2.80 479.4 15.561 1.992 0.9999 0.23

430.1 5.249 0.9986 1.83 337.5 0.206 0.9807 7.25 429.2 14.176 2.884 0.9999 0.48

Table 4. Fitting Parameters of Langmuir, Freundlich, and DA Models for VOCs on NucharWV-A 1100 pentane

hexane

heptane

model

parameter

293 K

308 K

323 K

293 K

308 K

323 K

293 K

308 K

323 K

Langmuir

q0mg·g−1 b/kPa−1 R2 rmsd/% k n R2 rmsd/% q/mg·g−1 E/kJ·mol−1 r R2 rmsd/%

566.7 0.589 0.9707 6.68 307.3 0.168 0.9997 0.73 617.6 15.122 0.920 0.9999 0.43

484.3 0.646 0.9843 4.81 285.9 0.140 0.9997 0.80 532.0 17.513 1.124 0.9999 0.70

418.5 0.601 0.9903 3.85 242.9 0.143 0.9978 1.86 448.7 16.901 1.616 0.9999 0.22

571.1 2.301 0.9754 6.15 392.4 0.161 0.9992 1.49 615.0 15.262 0.988 0.9992 1.49

514.2 1.827 0.9727 6.78 341.5 0.158 0.9996 1.18 602.0 16.593 0.903 0.9997 0.85

452.4 1.823 0.9886 4.15 303.7 0.152 0.9980 1.84 493.7 16.623 1.557 0.9999 0.45

571 11.876 0.9776 5.68 507.7 0.149 0.9996 0.73 646.2 16.652 0.954 0.9997 0.71

515.6 9.815 0.9756 6.37 445.9 0.150 0.999 1.72 624.4 17.086 1.018 0.9990 1.83

454.1 9.825 0.9800 5.80 392.8 0.147 0.9976 1.88 547.0 18.545 1.319 0.9980 1.85

Freundlich

DA

ε = RT ln(Ps/P)

(4)

qv = q/ρ

(5)

pressure (kPa), T is the absolute temperature (K), and q is the amount adsorbed (mg·g−1).

3. RESULTS AND DISCUSSION 3.1. Adsorption Isotherms. The adsorption equilibrium data of pentane, hexane and heptane onto HY-1 and NucharWV-A 1100 at (293, 308 and 323) K are shown in Figure 3a−c, respectively. The experimental uptake of three hydrocarbon VOCs profile characteristic of type I adsorption isotherm is observed according to the IUPAC classification. The amounts of the pentane, hexane and heptane uptake drastically increased at lower pressures, and then slowly increased with the further rise of pressure. The raw data for three hydrocarbon VOCs on HY-1 and NucharWV-A 1100 are presented in Table 2, respectively. It is clearly shown in Figure 3 and Table 2 that HY-1 had comparable adsorption capacities with NucharWV-A 1100. The average adsorption capacities of HY-1 for pentane, hexane, and heptane in experimental pressure range were 87.86 %, 85.61 %, and 88.18 % of that of NucharWV-A 1100, respectively, which may be attributed to its large micropore volume and high surface area. Therefore, HY-1 would be a potential alternative to activated carbon adsorbent for the recovery of gasoline vapor. 3.2. Correlation of Isotherms. The experimental data are fitted with Langmuir, Freundlich, and DA equations. A nonlinear optimization routine is used to optimize the parameters of the models to fit the experimental data. The root-mean-square

where qv is the volume adsorbed capacity (mL·g−1), q0 is the limiting micropore volume (mL·g−1), ε is the adsorption potential (kJ·mol−1) written by eq 4, E is the adsorption characteristic energy (kJ/mol), R is the gas constant (8.314 J·mol−1·K−1), T is the absolute temperature (K), Ps is the saturation vapor pressure (kPa), P is the equilibrium vapor pressure (kPa), q is the equilibrium adsorption amount (mg·g−1), and ρ is the adsorbate density in the adsorbed phase assumed to be the same as that in the liquid phase (g·mL−1). 2.4. Isosteric Heat of Adsorption. Knowledge of the thermodynamic properties of the adsorbent−adsorbate system allows for a better understanding of the adsorption process. The determination of the heat of adsorption permits measurement of the degree of energetic heterogeneity of gas−solid interactions. The Clausius−Clapeyron (C−C) equation has been widely used to estimate the isosteric heat of adsorption (ΔHst) from isotherm equations and can be expressed as ΔHst RT 2

=

⎛ ∂ln P ⎞ ⎜ ⎟ ⎝ ∂T ⎠q

(6)

where ΔHst is the isosteric heat of adsorption (kJ·mol−1), R is the gas constant (8.314 J·mol−1·K−1), P is the equilibrium 3429



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Figure 5. Adsorption characteristic curve for three hydrocarbon VOCs (pentane, hexane, and heptane) on NucharWV-A 1100 by DA equation at (293, 308, and 323) K: (a) pentane, (b) hexane, and (c) heptane.

Figure 4. Adsorption characteristic curve for three hydrocarbon VOCs (pentane, hexane, and heptane) on HY-1 by DA equation at (293, 308, and 323) K: (a) pentane, (b) hexane, and (c) heptane.

large correlation coefficient (R2 > 0.98). However, the DA equation presented a much better fit to the experimental data than Langmuir and Freundlich equations. The maximum rmsd of DA equation was found to be 1.43 %, 1.49 %, and 1.85 % for pentane, hexane and heptane adsorption on HY-1 and NucharWV-A 1100, which was smaller than those of Langmuir and Freundlich equations, respectively. From the Figure 3, it is clearly shown that the experimental data were well fitted by the DA equation. The plots of adsorbed volume (qv) versus the adsorption potential (ε) are presented in Figures 4 and 5 for the adsorption of pentane, hexane, and heptane onto HY-1 and NucharWV-A 1100, respectively. These plots are supposed to follow one

deviation (rmsd) between the calculated values (cal) and experimental data (exp) is defined as

rmsd =

⎞2 N ⎛ qexp − qcal ∑0 ⎜ q × 100⎟ ⎝ exp ⎠ N

(7)

The fitting parameters and rmsd of Langmuir, Freundlich, and DA equations for the adsorption of pentane, hexane and heptane onto HY-1 and NucharWV-A 1100 are presented in Tables 3 and 4. It is found that all of the equilibrium data were correlated by Langmuir, Freundlich and DA equations with 3430



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Table 5. Fitting Parameters of DA Model Adsorption Characteristic Curve for VOCs on HY-1 and NucharWV-A 1100 HY-1

NucharWV-A 1100

adsorbate

q0/mL·g−1

E/kJ·mol−1

r

R2

rmsd/%

q0/mL·g−1

E/kJ·mol−1

r

R2

rmsd/%

pentane hexane heptane

0.7425 0.7147 0.6655

14.1340 13.8922 14.5266

1.4511 1.5083 2.2845

0.9783 0.9844 0.9889

2.74 2.52 2.14

0.9758 0.9549 0.9502

15.1921 15.5533 16.9310

0.8140 0.8459 0.9397

0.9766 0.9809 0.9920

2.92 2.46 1.64

single line independent of temperature, known as the characteristic curve which is an index of good fit of the DA model and can be employed to examine whether the Polanyi theory mechanistically captures the adsorption process of compounds by adsorbent. As can be seen in Figures 4 and 5, they all fell essentially onto a single curve with large correlation coefficient (R2 > 0.9766 Table 5). According to potential theory, for the adsorption of different apolar adsorbates on a given adsorbent, it is certain that plots of adsorbed volume (qv) against the ratio of the adsorption potential to molar volume (ε/Vm) at different temperature should yield a unique curve that is independent of temperature and adsorbate.28 Therefore, to further examine whether DA equation mechanistically captures the adsorption process of compounds by adsorbent, plots of adsorbed volume (qv) vs adsorption potential density (ε/Vm) of three hydrocarbon VOCs onto HY-1 and NucharWV-A 1100 are shown in Figure 6. As the Polanyi potential theory would predict, they both fell essentially onto a single curve with correlation coefficient R2 = 0.9704 for HY-1 and R2 = 0.9663 for NucharWV-A 1100, indicating the usefulness of the DA equation to describe the adsorption of three hydrocarbon VOCs onto HY-1 and NucharWV-A 1100, and that micropore filling is the dominating mechanism for the adsorption of three hydrocarbon VOCs. This result is important because it allows the use of DA equation without introducing any additional parameters to describe the temperature effect on adsorption isotherms for three hydrocarbon VOCs. 3.3. Isosteric Heat of Adsorption. It is shown in the Figure 3 that the equilibrium amounts adsorbed of three VOCs all decreased when the temperature rose, which means the adsorption of pentane, hexane and heptane onto HY-1 and NucharWV-A 1100 is an exothermic process. Therefore, lower temperature is advantageous for the adsorption of pentane, hexane and heptane onto HY-1 and NucharWV-A 1100. The isosteric heats change accompanying adsorption can be used as a measure of the energetic heterogeneity of a solid surface.12,29 For the heterogeneous adsorption system, the isosteric heat curve varies with the surface loading. Moreover, the isosteric heat has been used to examine the molecular scale interactions between adsorbate molecules and adsorbent. In Figure 7, the isosteric heats of adsorption for three hydrocarbon VOCs were plotted as a function of equilibrium adsorption capacities. It is observed that the isosteric heats of adsorption for the three hydrocarbon VOCs were varied with equilibrium adsorption capacities. This result implies that both HY-1 and NucharWV-A 1100 have the energetically heterogeneous surface. It is noted in Figure 7 that the curves of isosteric heats for three hydrocarbon VOCs onto HY-1 have points of intersection with that of NucharWV-A 1100. In order to understand the adsorption heats of pentane, hexane, and heptane onto HY-1 and NucharWV-A 1100 more clearly, the average adsorption heat was calculated. Here, the average adsorption heat is defined as the arithmetic mean value of isosteric heats at different

Figure 6. Plots of adsorbed volume (qv) vs adsorption potential density (ε/Vm) for three hydrocarbon VOCs (pentane, hexane, and heptane) onto HY-1 and NucharWV-A 1100 at (303, 318, and 333) K.

equilibrium capacities ranged from (250 to 600) mg·g−1. According to experimental data, the average adsorption heats of pentane, hexane, and heptane onto HY-1 were (32.0, 34.5, and 40.5) kJ·mol−1, respectively, and (44.8, 45.2, and 47.6) kJ·mol−1 onto NucharWV-A 1100, respectively. We found that the average adsorption heats of three VOCs onto HY-1 were smaller than those onto NucharWV-A 1100. The larger isosteric heats imply that NucharWV-A 1100 had the stronger adsorption affinity for pentane, hexane, and heptane than HY-1; thus, it was more difficult to regenerate NucharWV-A 1100. The desorption hebavior of HY-1 and NucharWV-A 1100 will be discussed in the following section. In addition, the high exothermic heats of adsorption of pentane, hexane, and heptane onto NucharWV-A 1100 can lead to significant temperature rise during the adsorption step, which has negative impact on the performance of the adsorption unit, such as the reduce of dynamic adsorption capacity. 3.4. Desorption Behavior. The desorption efficiency was evaluated and presented in Figure 8. It is clearly shown that 3431



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Figure 8. Desorption efficiencies of three hydrocarbon VOCs on HY-1 and NucharWV-A 1100.

4. CONCLUSIONS Adsorption isotherm data of pentane, hexane, and heptane onto hypercrosslinked polymeric resin (HY-1) and activated carbon (NucharWV-A 1100) were obtained through a gravimetric technique. The adsorption uptake measurements cover the temperatures ranging from (293 to 323) K and pressures up to 60 kPa. HY-1 had a comparable sorption capacity to NucharWV-A 1100 for pentane, hexane and heptane. The adsorption capacities of pentane, hexane, and heptane onto HY-1 were about 85 % of those of NucharWV-A 1100. The equilibrium data were fitted well to DA equation, and the rmsd of DA model for VOCs onto HY-1 was found to be within 1.85 % and smaller than those of Langmuir and Freundlich models (5.25 % and 7.25 %, respectively). Plots of adsorbed volume (qv) vs adsorption potential density (ε/Vm) of three hydrocarbon VOCs onto HY-1 fell essentially onto a single curve with correlation coefficient R2 = 0.9704, indicating that micropore filling is the dominating mechanism for the adsorption of three hydrocarbon VOCs. The isosteric heats were calculated using the C−C equation. The average adsorption heats of pentane, hexane and heptane on HY-1 in the range of study were found to be (32.0, 34.5, and 40.5) kJ·mol−1, respectively, which were lower than those on NucharWV-A 1100 ((44.8, 45.2, and 47.6) kJ·mol−1, respectively).

■

AUTHOR INFORMATION

Corresponding Author

*Phone: +86 25 89680380. E-mail: [email protected].

Figure 7. Plots of isosteric heats (ΔHst) vs equilibrium adsorption capacities (qe) for three hydrocarbon VOCs onto HY-1 and NucharWV-A 1100: (a) pentane, (b) hexane, and (c) heptane.

Funding

This research was financially supported by National Natural Science Foundation of China (Grant No. 51078180) and Program for New Century Excellent Talents in University (Grant No NCET-11-0230). This research was also sponsored by Qing Lan Project of Jiangsu Province, Program for Changjiang Scholars Innovative Research Team in University and the Fundamental Research Funds for the Central Universities (Grant No. 1116021105).

HY-1 had higher desorption efficiencies than Nuchar WV-A 1100 whether pentane, hexane or heptane was adsorbed. The desorption efficiencies of HY-1 for pentane, hexane, and heptane were 81.1 %, 61.3 %, and 36.3 %, respectively, whereas those of Nuchar WV-A 1100 were 80 %, 56.5 %, and 22 %, respectively. This result was mainly attributed to different pore structure distributions of two adsorbents. Table 1 showed that the micropore volume of HY-1 (0.541 cm3·g−1) was smaller than Nuchar WV-A 1100 (0.742 cm3·g−1). The adsorption energy in the micropore is much larger compared to mesopore and macropore because of the overlapping of adsorption forces from the opposite walls of the micropore. Therefore, HY-1 with lower micropore volume can be regenerated more easily than Nuchar WV-A 1100.

Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Melaina, M. W. Turn of the century refueling: A review of innovations in early gasoline refueling methods and analogies for hydrogen. Energy Policy 2007, 35, 4919−4934. (2) Demirbas, A. Pyrolysis of municipal plastic wastes for recovery of gasoline-range hydrocarbons. J. Anal. Appl. Pyrol. 2004, 72, 97−102.

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(3) Pakbin, P.; Ning, Z. Characterization of particle bound organic carbon from diesel vehicles equipped with advanced emission control technologies. Environ. Sci. Technol. 2009, 43, 4679−4686. (4) Lin, C. W.; Chiang, S. B. Investigation of MTBE and aromatic compound concentrations at a gas service station. Environ. Monitor. Assess. 2005, 105, 327−339. (5) Shie, J. L.; Lu, C. Y. Recovery of gasoline vapor by a combined process of two-stage dehumidification and condensation. J. Chin. Inst. Chem. Eng. 2003, 34, 605−616. (6) Liu, Y. J.; Feng, X. Separation of gasoline vapor from nitrogen by hollow fiber composite membranes for VOC emission control. J. Membr. Sci. 2006, 271, 114−124. (7) ChristensenU, C. S.; Skov, H.; Palmgren, F. C5−C8 nonmethane hydrocarbon measurements in Copenhagen concentrations, sources and emission estimates. Sci. Total Environ. 1999, 236, 163− 171. (8) Chue, K.; Park, Y. K.; Jeon, J. K. Development of adsorption buffer and pressure swing adsorption (PSA) unit for gasoline vapor recovery. Korean J. Chem. Eng. 2004, 21, 676−679. (9) Allen, J. L.; Gatz, J. L.; Eklund, P. C. Applications for activated carbons from used tires butane working capacity. Carbon 1999, 37, 1485−1489. (10) Fan, Y. J.; Zhang, S. Q.; Yao, G. F.; Zhu, W. K. Research on the preparation of activated carbon for adsorbing gasoline-vapor. J. China Univ. Mining Technol. 2005, 34, 817−820 In Chinese. (11) Huang, W. Q.; Lu, A. H.; Zhong, J. Study on activated carbon adsorpting and recovering high concentration gasoline vapor. Chin. J. Environ. Eng. 2007, 1, 73−77 In Chinese. (12) Delage, F.; Pré, P.; Cloirec, P. L. Mass transfer and warming during adsorption of high concentrations of VOCs on an activated carbon bed: experimental and theoretical analysis. Environ. Sci. Technol. 2000, 34, 4816−4821. (13) Zerbonia, R. A.; Brockmann, C. M.; Peterson, P. R.; Housley, D. Carbon bed fires and the use of carbon canisters for air emissions control on fixed-roof tanks. J. Air Waste Manage. Assoc. 2001, 51, 1617−1627. (14) Qi, N.; Appel, W. S.; LeVan, M. D. Adsorption dynamics of organic compounds and water vapor in activated carbon beds. Ind. Eng. Chem. Res. 2006, 45, 2303−2314. (15) Kaplan, D.; Nir, I.; Shmueli, L. Effects of high relative humidity on the dynamic adsorption of dimethyl methylphosphonate (DMMP) on activated carbon. Carbon 2006, 44, 3247−3254. (16) Cosnier, F.; Celzard, A.; Furdin, G.; Bégin, D.; Marêché, J. F. Influence of water on the dynamic adsorption of chlorinated VOCs on active carbon: relative humidity of the gas phase versus pre-adsorbed water. Adsorption Sci. Technol. 2006, 24, 215−228. (17) Slasli, A. M.; Jorgeb, M.; Stoeckli, F.; Seaton, N. A. Water adsorption by activated carbons in relation to their microporous structure. Carbon 2003, 41, 479−486. (18) Davankov, V. A.; Tsyurupa, M. P. Structure properties of hypercrosslinked polystyrenes: the first representative of anewclass of polymer networks. React. Funct. Polym. 1990, 13, 27−42. (19) Tsyurupa, M. P.; Davankov, V. A. Porous structure of hypercrosslinked polystyrene: state-of-the-art mini-review. React. Funct. Polym. 2006, 66, 768−779. (20) Podlesnyuk, V. V.; Hradil, J.; Králová, E. Sorption of organic vapours by macroporous and hypercrosslinked polymeric adsorbents. React. Funct. Polym. 1999, 42, 181−191. (21) Simpson, E. J.; Koros, W. J.; Schechter, R. S. An emerging class of volatile organic compound sorbents: Friedel-Crafts modified polystyrenes. 1. synthesis, characterization, and performance in aqueous- and vapor-phase applications. Ind. Eng. Chem. Res. 1996, 35, 1195−1205. (22) Simpson, E. J.; Koros, W. J.; Schechter, R. S. An emerging class of volatile organic compound sorbents: Friedel-Crafts modified polystyrenes. 2. performance comparison with commercially-available sorbents and isotherm analysis. Ind. Eng. Chem. Res. 1996, 35, 4635− 4645.

(23) Baya, M. P.; Panayotis, P. A.; Davankov, V. A. Evaluation of a hypercrosslinked polystyrene, MN-200, as a sorbent for the preconcentration of volatile organic compounds in air. J. Assoc. Official Anal. Chem. 2000, 83, 579−583. (24) Liu, P.; Long, C.; Li, Q. F.; Qian, H. M.; Li, A. M.; Zhang, Q. X. Adsorption of trichloroethylene and benzene vapors onto hypercrosslinked polymeric resin. J. Hazardous Mater. 2009, 166, 46−51. (25) Long, C.; Li, Q. F.; Li, Y.; Liu, Y.; Li, A. M.; Zhang, Q. X. Adsorption characteristics of benzene-chlorobenzene vapor on hypercrosslinked polystyrene adsorbent and a pilot-scale application study. Chem. Eng. J. 2010, 160, 723−728. (26) Long, C.; Li, Y.; Yu, W. H.; Li, A. M. Removal of benzene and methyl ethyl ketone vapor: Comparison of hypercrosslinked polymeric adsorbent with activated carbon. J. Hazardous Mater. 2012, 203−204, 251−256. (27) Long, C.; Li, Y.; Yu, W. H.; Li, A. M. Adsorption characteristics of water vapor on the hypercrosslinked polymeric adsorbent. Chem. Eng. J. 2012, 180, 106−112. (28) Wood, G. O. Affinity coefficients of the Polanyi/Dubinin adsorption isotherm equations: A review with compilations and correlations. Carbon 2001, 39, 343−356. (29) Do, D. D.; Do, H. D. A new adsorption isotherm for heterogeneous adsorbent based on the isosteric heat as a function of loading. Chem. Eng. Sci. 1997, 52, 297−310.

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Adsorption Characteristics of Pentane, Hexane, and Heptane

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