Environ. Sci. Technol. 2010, 44, 7070–7075
Capture and Recovery of Isobutane by Electrothermal Swing Adsorption with Post-Desorption Liquefaction KAITLIN E. MALLOUK, DAVID L. JOHNSEN, AND MARK J. ROOD* Department of Civil and Environmental Engineering, University of Illinois, Urbana, Illinois 61801
Received May 4, 2010. Revised manuscript received August 6, 2010. Accepted August 6, 2010.
A bench-scale capture and recovery system to convert a low concentration organic gas to a liquid is described here. Adsorption of isobutane onto activated carbon fiber cloth (ACFC) followed by electrothermal desorption and subsequent liquefaction is demonstrated. Experimental conditions to condense desorbed isobutane were determined based on Dalton’s law and Antoine’s equation. Breakthrough curves for a gas stream containing 2000 ppmv isobutane in air adsorbing onto ACFC-15 demonstrate an adsorption capacity of 0.094 ( 0.017 g of isobutane/g of ACFC with >98% capture efficiency. The system described here utilizes two adsorbers, which operate cyclically to allow for continuous treatment of the isobutane. Adsorption followed by electrothermal desorption provided a concentration ratio of 240, which facilitates condensation of the isobutane after compression and cooling and is an order of magnitude greater than what has been previously demonstrated.
activated carbon fiber cloth (ACFC). Isobutane is an organic gas that is used in industry and disposed of by thermal oxidation. Its molecular weight, normal boiling point, critical temperature, and critical pressure are 58.12 g/mol, -11.7 °C, 134.9 °C, and 36.5 bar, respectively. ACFC is an attractive adsorbent for recovering low concentration organic gases because of its high adsorption capacity, low ash content, rapid heat and mass transfer properties, shapeability, and electrical resistance, which allows adsorbate desorption through electrothermal desorption (Joule heating) (7-10). Electrothermal desorption has several advantages over vacuum or steam regeneration, such as higher energy efficiency and independent control of the adsorbent heating and the purge gas flow rate (8, 11). Capture and recovery for reuse of low concentration organic vapors (e.g., toluene, methyl ethyl ketone, and acetone) from waste streams using ACFC and electrothermal swing adsorption (ACFC-ESA) has been demonstrated at the bench- and pilot-scale (11-14). Extensive characterization of this system has occurred, including material and energy balances (11, 14) and cost estimates (12, 15). In contrast to the work cited in refs 11-15, this work demonstrates the use of ACFC-ESA with ancillary cooling and compression that separates dilute concentrations of organic gas (not organic vapor, as required in refs 11-15) and provides the gas as a liquid for reuse. Such capability is not possible with the systems described in refs 11-15. The objective of this work is to develop an ACFC-ESA system to demonstrate the capture and recovery of a low concentration organic gas as a reusable liquid. This objective has been made possible by implementing controlled desorption cycles and providing temperature and pressure control of the gas stream generated during these cycles.
Experimental Section Introduction Several industries (e.g., foam packaging manufacturing) produce waste gas streams that contain low-concentration organic gases. An organic gas has a normal boiling point (Tbp) below 20 °C. Examples include propane, isobutane, and n-butane, which have normal boiling points of -42.1, -11.7, and -0.5 °C, respectively (1). Facilities commonly use thermal/catalytic oxidation to remove organic gases from flue gas streams rather than recover the compounds for reuse. The organic gases previously mentioned have lower explosive limits from 16 000 to 50 000 ppmv (2), so low concentration (90% removal efficiency for organic gases with molecular weights >45 g/mol and concentrations >500 ppmv (6). This research focuses on capture and recovery for reuse of isobutane (C4H10) at 2000 ppmv in air using adsorption on * Corresponding author phone: (217) 333-6963; fax: (217) 3336968; e-mail:
[email protected]. 7070
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The ACFC-ESA system used to capture organic gases consisted of a gas generation system, two ACFC adsorption vessels with electrothermal regeneration capability, a postdesorption temperature and pressure control system, and a data acquisition and control system (Figure 1). The adsorption/desorption vessels (Figure 2) each consisted of an aluminum or stainless steel cylinder (height ) 27 cm) and conical base (height ) 6 cm) with a Teflon top plate (height ) 2 cm). Each vessel’s external diameter was 15.2 cm with a 0.95 cm wall thickness, which provided 3.5 L of empty internal volume. The two vessels were used to provide continuous treatment of the gas stream. Each vessel held two vertical annular cartridges, each with 91.7 ( 0.6 g of ACFC-15 (Kynol ACC5092-15). ACFC-15 is a novoloid-based fiber. It has a BET surface area of 1335 m2/g, an average pore width of 0.76 nm, and 96.6% of the pore volume is provided by micropores (16). The ACFC annular cartridges were 20 cm in height with an outer diameter of 4.9 cm and an inner diameter of 1.9 cm. The length of the adsorption bed, L, is 1.5 cm for this system. Temperature of the ACFC was measured using 0.081 cm diameter Type K thermocouples (Omega Inc.). During the adsorption cycle, pressurized air passed through a high efficiency particulate air (HEPA) filter and silica gel to remove particulate matter and water vapor, respectively. The air was then combined with the isobutane, which was obtained from a pressurized cylinder (Aeropres Corp., 97.8% isobutane, vapor withdrawal) at a controlled flow rate. All gas flow rates were controlled with mass flow controllers (air: Aalborg, model GFC571S. isobutane and 10.1021/es101516c
2010 American Chemical Society
Published on Web 08/19/2010
FIGURE 1. Experimental apparatus. Solid and dashed lines represent the flow path for adsorption and desorption cycles, respectively.
FIGURE 2. Adsorption/desorption vessel with two annular ACFC cartridges. Solid and dashed arrows represent the flow path for adsorption and desorption cycles, respectively. nitrogen: Tylan Inc.). The isobutane and air stream entered the side of one vessel, passed from the outside to the inside of the annular ACFC cartridges in parallel where the isobutane was adsorbed, and the air and any nonadsorbed isobutane exited through two ports at the top of the vessel. The organic gas concentration was monitored downstream of the adsorption vessel with a photoionization detector (PID, RAE Systems Inc., PDM-10A), which can measure isobutane
concentrations up to 10 000 ppmv. The PID was calibrated with select concentrations of isobutane from 0 to 2500 ppmv. The desorption cycle of the second vessel occurred concurrently with the adsorption cycle of the first vessel. Nitrogen entered the top of the desorbing vessel, passed from the inside to the outside of the heated annular ACFC cartridges in parallel carrying desorbed isobutane with it, and then exited through the bottom of the vessel. ACFC heating was achieved by controlling the root mean square voltage applied to the cloth with a silicon controlled rectifier (SCR, Robicon, model 440 102.10). During desorption, the maximum voltage applied to the ACFC was 29.5 V and the maximum current experienced by the ACFC was 22 A. Isobutane concentration in the desorption gas stream was measured with a flame ionization detector (FID, MSA Inc., Series 8800), which can measure isobutane concentrations up to 100% by volume. The FID was calibrated using mixtures of isobutane (0-100% by volume) and N2. After the isobutane was desorbed from the ACFC it entered a compression module consisting of a compressor (Air Dimensions Inc. R272-BT-EA1) capable of producing pressures up to 13.1 bar gauge (190 psig), a custom copper tubing heat exchanger (outer diameter 1.59 cm, inner diameter 1.38 cm, length 3.4 m), and a polycarbonate pressure vessel (1 L, >10.3 bar gauge pressure rating). Pressure was monitored with a pressure transducer (Dwyer, IS626-12-GH-P1-E1-S1). This ESA system is fully automated. The control system consists of National Instruments Fieldpoint hardware connected to a personal computer with LabView 6.1 software. The control system monitors and records values for gas concentrations, ACFC temperatures, pressure, and power output. The LabView program maintains a user-defined ACFC temperature during desorption by controlling the power applied to the ACFC with a feedback controller. It determines when the ACFC that is undergoing an adsorption cycle is saturated based on user-defined parameters and automatically switches that vessel to a desorption cycle while simultaneously beginning the reciprocal adsorption cycle. This ensures that the organic gas/air stream is treated continuously by adsorption. VOL. 44, NO. 18, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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Determination of Experimental Conditions to Condense Isobutane. The relationship between temperature, total pressure, and isobutane concentration determines when isobutane condensation occurs during desorption. To condense isobutane, the isobutane’s concentration must exceed its saturation concentration. The relationship between temperature, pressure, and isobutane concentration was determined using Dalton’s law (eq 1) and Antoine’s equation (eq 2). The gas stream that is generated during desorption cycles was assumed to be a binary mixture of isobutane and N2 that obeyed the ideal gas law. Additionally, the maximum pressure in the pressure vessel was maintained e10.3 bar gauge (150 psig) based on the manufacturer’s specifications, and the minimum temperature achievable with the custom heat exchanger was assumed to be 20 °C, because the heat sink for the exchanger was ambient air. Pi ) yiPtot
(
Pi,s ) exp A1 +
(1)
A2 + A3 ln(T) + A4TA5 T
)
(2)
where Pi ) partial pressure of component i (Pa), yi ) concentration of component i (mole fraction), Ptot ) total pressure (Pa), Pi,s ) saturation vapor pressure of component i (Pa), An ) constants for Antoine’s equation (17), and T ) temperature (K). Dalton’s law assumes the gas mixture behaves as an ideal gas. The ideality of isobutane in the temperature range between its normal boiling temperature (261 K) and critical temperature (408 K) and up to 11 bar was confirmed by calculating the pressure exerted by one mole of isobutane at a known temperature using the ideal gas law and the Redlich-Kwong equation of state. The Redlich-Kwong equation is derived from the van der Waals equation and is a function of critical temperature and pressure and is more accurate than the ideal gas law (18). The values predicted by these two methods are within 3%, so the use of the ideal gas law and Dalton’s law is justified for isobutane in this temperature range. Determination of ACFC Adsorption Capacity. The adsorption capacity of ACFC was determined with individual breakthrough curves and during adsorption/desorption cycling. For individual breakthrough curves, the ACFC was initially heated to 200 °C in N2 at ambient pressure for ten minutes to desorb previously adsorbed compounds. After cooling the ACFC, a feed gas was generated at 100 or 50 SLPM with an isobutane concentration of 2000 ppmv. The inlet gas concentration was stable before passing the gas through the vessels containing the ACFC. The isobutane concentration at the outlet of the vessel was monitored until it returned to 2000 ppmv to determine the ACFC’s adsorption capacity. The mass of isobutane adsorbed at any time, tj, during adsorption is Mtj (eq 3), where the subscript j represents the percent of the inlet isobutane concentration reached by the outlet concentration. Breakthrough occurred when the isobutane concentration at the vessel’s outlet reached 10% of the inlet concentration, corresponding to t10 and Mt10. The adsorption capacity of the ACFC is then determined by dividing M10 by the total ACFC mass (19). Mtj )
PtotMwQg RT
∫
t)tj
t)0
(
)
yout yin dt 1 - yin 1 - yout
(3)
where Mtj ) mass of adsorbate desorbed at time tj (g), Mw ) molecular weight of the adsorbate (g/mol), R ) ideal gas constant (Pa L/mol K), Qg ) total volumetric flow rate of the gas (LPM), t ) time, tj ) time when the outlet isobutane concentration is j % of the inlet isobutane concentration 7072
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TABLE 1. Initial Operating Conditions for Capture and Recovery of Isobutane for Reuse operating parameter
condition
inlet air flow rate (SLPM) isobutane inlet concentration (ppmv) nitrogen flow rate during desorption (SLPM) maximum ACFC temperature during desorption (°C) threshold concentration (% by volume)
100 2000 1.0 200 1.5
(min), yin ) concentration of the adsorbate in the inlet gas stream (mole fraction), and yout ) concentration of the adsorbate in the outlet gas stream (mole fraction). Adsorption Properties from Breakthrough Curves. Breakthrough curves were also used to evaluate the throughput ratio (TPR), length of unused bed (LUB), and fractional LUB (fLUB). TPR characterizes the slope of the breakthrough curve (eq 4) (13). As TPR approaches unity, the time to develop the mass transfer zone becomes negligible compared to the adsorbent’s saturation time. LUB is a measure of the unused length of bed at 5% breakthrough (eq 5) and fLUB is the fractional unused length of bed at 5% breakthrough normalized to the adsorbent bed length (13, 20). For the system described here, the adsorbent length parallel to the gas flow is 1.5 cm. TPR )
t5 t50
(4)
where t5 ) the time at which the breakthrough curve has reached 5% breakthrough and t50 ) the time at which the breakthrough curve has reached 50% breakthrough.
(
LUB ) 1 -
Mt5 Mtsat
) ( ) L) 1-
t5 L tsat
(5)
where Mt5 ) mass of adsorbate adsorbed at time t5, Mtsat ) mass of adsorbate adsorbed at time tsat, tsat ) time at which the breakthrough curve has reached 100% breakthrough, and L ) length of adsorbent perpendicular to the adsorbate flow. As the value of fLUB approaches 0, the amount of ACFC that is being utilized during adsorption approaches 100%, which means that the ACFC is being used to its full potential. Achieving fLUB and TPR values e0.3 and g0.7, respectively, are guidelines used to evaluate if the vessels were designed appropariately for the inlet gas stream (19). Adsorption/Desorption Cycling. Automated ESA cycles were completed to determine the operating conditions that resulted in condensation of isobutane after compression and cooling of the desorbed gas stream. Initial conditions are described in Table 1. Post-desorption gas treatment (cooling and compression) occurred when a user-specified threshold concentration of isobutane was exceeded. The isobutane concentration during desorption was monitored during each test and process modifications were made to increase the desorption concentration, as described below. The N2 flow rate, maximum ACFC temperature during desorption, and user-defined threshold isobutane concentration were process conditions that were controlled to increase the isobutane concentration during desorption cycles to increase liquid recovery of isobutane. Independent control of the carrier gas flow rate and adsorbent temperature to reduce the carrier gas flow rate while increasing the ACFC temperature was used to increase the adsorbate concentration during desorption cycles (21). Performance Measures for Adsorption/Desorption Cycling. Isobutane capture efficiency achieved by the ACFC and concentration ratio were used to assess the effectiveness
FIGURE 3. Isobutane saturation vapor pressure and required concentration for condensation as a function of temperature assuming a total pressure of 10.3 bar gauge. of the adsorption/desorption cycles. Capture efficiency describes the amount of captured adsorbate relative to the inlet amount (eq 6). capture efficiency )
Mtads MW Qy t RT g in ads
× 100%
(6)
where Mtads ) mass adsorbed when ti ) tads (eq 3) and tads ) duration of adsorption cycle. Concentration ratio describes the average adsorbate concentration during post-desorption treatment (i.e., when the desorbed isobutane concentration exceeded the userdefined threshold concentration) relative to the inlet concentration during adsorption (eq 7). concentration ratio )
yjout yin
FIGURE 4. Typical breakthrough curve for isobutane on ACFC-15. The inlet gas was 100 SLPM air with 2000 ppmv isobutane, 22 °C, and ambient pressure. The mass of ACFC was 183.3 g per adsorption/desorption vessel.
TABLE 2. TPR, fLUB, and LUB Values from Breakthrough Curves Generated with 2000 ppmv Isobutane and ACFC-15 (Mean ± Standard Deviation) vessel number 1 2 average of 1 and 2
0.86 ( 0.03 0.86 ( 0.03 0.86 ( 0.03
0.29 ( 0.03 0.30 ( 0.04 0.29 ( 0.03
LUB (cm) 0.44 ( 0.04 0.45 ( 0.06 0.44 ( 0.04
TABLE 3. Adsorption Capacities for Vessels 1 and 2 during Cycling (Mean ± Standard Deviation)a vessel 1 adsorption capacity
(7)
where yjout ) time-averaged outlet adsorbate concentration during one desoption cycle (mole fraction).
TPR (unitless) fLUB (unitless)
vessel 2 adsorption capacity
average adsorption capacity of vessels 1 and 2
Figure 5 data 0.097 0.091 0.093 ( 0.007 Figure 6 data 0.094 ( 0.002 0.100 ( 0.005 0.097 ( 0.007 overall 0.095 ( 0.002 0.097 ( 0.007 0.096 ( 0.006 a
All capacities are reported in g of isobutane/g of ACFC.
Results and Discussion Determination of Operating Conditions. The minimum average isobutane concentration during a regeneration cycle to allow condensation in the pressure vessel was determined using Antoine’s equation and Dalton’s law. Figure 3 describes the dependence of isobutane’s saturation vapor pressure on temperature at a total pressure of 10.3 bar gauge, which is the pressure achieved in the pressurized vessel. In order to condense the desorbed isobutane, its average vapor phase concentration must exceed the saturation concentration for a given temperature shown in Figure 3. Points A and B describe saturation isobutane concentrations of 27% and 36% at 20 and 30 °C, respectively, which correspond to the heat exchanger’s temperature range. This required range of desorption isobutane concentrations in the compression module sets a metric for analyzing the desorption cycles. The 27-36% target concentration could be lowered by decreasing the gas stream’s temperature below 20-30 °C and/or increasing its pressure above 10.3 bar gauge. Breakthrough Curve Analyses. Three breakthrough curves (e.g., Figure 4) were generated for each vessel for an inlet air stream containing 2000 ppmv isobutane passing through 183.3 g of ACFC-15 at ambient temperature (22-24 °C) and 1 atm. The average adsorption capacity calculated from the
six breakthrough curves was 0.094 g of isobutane/g of ACFC with a standard deviation of 0.017 g of isobutane/g of ACFC. The adsorption capacity of ACFC-15 for 2000 ppmv isobutane in air is reasonable when compared to results for 2000 ppmv n-butane on ACFC-15 reported by Foster et al., who determined an adsorption capacity of 0.13 g of nbutane/g of ACFC (22). Previous work has shown that adsorption capacity of activated carbon for light hydrocarbons increases with increasing adsorbate boiling point (23). n-Butane is an isomer of isobutane and has a normal boiling point of -0.5 °C, 11.2 °C greater than isobutane’s, so a higher adsorption capacity for n-butane is expected. Table 2 lists the values for TPR, LUB, and fLUB that were obtained from the breakthrough tests. These results are in the acceptable range of fLUB values (e0.3) and TPR values (g0.7) (19). Adsorption Capacity During Cycling. The adsorption capacity of the ACFC was measured during adsorption/ desorption cycling to assess any changes in the performance of the adsorbent and to ensure that the ACFC was sufficiently regenerated during desorption. Table 3 shows the adsorption capacities during cycling for vessels 1 and 2 for the experiments shown in Figures 5 and 6. VOL. 44, NO. 18, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 5. Vessel outlet concentrations of isobutane during adsorption (A) and desorption (B) cycles. Adsorption inlet conditions: 100 SLPM dry air with 2000 ppmv isobutane. Desorption conditions: 1.0 SLPM N2, maximum ACFC temperature 200 °C.
FIGURE 6. Vessel outlet concentrations of isobutane during adsorption (A) and desorption (B) cycles. Adsorption inlet conditions: 100 SLPM dry air with 2000 ppmv isobutane. Desorption conditions: 0.5 SLPM N2, maximum ACFC temperature 225 °C. The data reported in Table 3 indicate that the adsorption capacity for the ACFC is consistent between cycles, with a relative standard deviation of 98% capture efficiency for isobutane during the adsorption cycles of the experiment. There were a total of five adsorptions during this experiment with an average adsorption time of 37.8 ( 1.3 min. Figure 6B shows the isobutane concentration at the outlet of the vessels during desorption cycles with concentration peaks at 94% by volume, with an average outlet isobutane concentration of 48%, corresponding to a concentration ratio of
240. Other methods of organic gas capture such as treatment with polymer membranes (24) and dual reflux pressure swing adsorption (25) have achieved concentration ratios of 5 and 91, respectively, making the ACFC adsorption with electrothermal regeneration an encouraging gas pretreatment system to achieve large concentration ratios. As discussed above, the minimum isobutane concentration that is required to achieve isobutane condensation is 27-36% for conditions tested here. Because the resulting desorption stream in the experiment shown in Figure 6 exceeded this minimum concentration, condensation of isobutane was achieved during the experiment. Formation of liquid isobutane during adsorption/desorption cycling provides the proof of concept result for capturing and recovering low concentration isobutane gas using ACFC and electrothermal desorption followed by compression/cooling. Key parameters that affected the ability to achieve isobutane condensation were ACFC temperature during desorption, N2 flow rate during desorption, and the pressure and temperature of the pressure vessel. These results demonstrate that this new gas recovery system is able to adsorb dilute isobutane from air and provide liquid isobutane for reuse. The system uses ACFC as an adsorbent and electrothermal heating for desorbing the isobutane. After desorption the high-concentration isobutane stream is compressed and cooled to produce liquid isobutane. This is the first time that a dilute gas, with a boiling point below ambient temperature, was captured and recovered with a concentration ratio as high as 240, compared to 91 (25), and then was successfully chilled and compressed to provide a liquefied organic stream for reuse. This technology shows promise as a means to capture and recover dilute organic gases as liquids for reuse instead of disposing of them with thermal oxidation.
Acknowledgments Financial support is acknowledged from the University of Illinois Technology Research, Education, and Commercialization Center; Pregis Corporation; the University of Illinois Department of Civil & Environmental Engineering Graduate Assistance in Areas of National Need Fellowships; the National Science Foundation Graduate Research Fellowship; and the Air & Waste Management Association Scholarship Program.
Note Added after ASAP Publication There was an error in Figure 3 in the version published ASAP August 19, 2010; the corrected version was published ASAP August 23, 2010.
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(4) Jiang, X.; Ding, J.; Kumar, A. Polyurethane-poly(vinylidene fluoride) (PU-PVDF) thin film composite membranes for gas separation. J. Membr. Sci. 2008, 323 (2), 371–378. (5) Baker, R. W.; Wijmans, J. G. Membrane Separation of Organic Vapors from Gas Streams; CRC Press: Boca Raton, FL, 1994. (6) Noll, K. E. Fundamentals of Air Quality Systems; American Academy of Environmental Engineers: 1999. (7) Subrenat, A.; Le Cloirec, P. Thermal behavior of activated carbon cloths heated by Joule effect. J. Environ. Eng. 2003, 129 (12), 1077–1084. (8) Petkovska, M.; Tondeur, D.; Grevillot, G.; Granger, J.; Mitroviæ, M. Temperature-swing gas separation with electrothermal desorption step. Sep. Sci. Technol. 1991, 26 (3), 425–444. (9) Baudu, M.; LeCloirec, P.; Martin, G. Thermal regeneration by Joule effect of activated carbon for air treatment. Environ. Technol. 1992, 13 (5), 423–435. (10) Lordgooei, M.; Carmichael, K. R.; Kelly, T. W.; Rood, M. J.; Larson, S. M. Activated carbon cloth adsorption-cryogenic system to recover toxic volatile organic compounds. Gas Sep. Purif. 1996, 10 (2), 123–130. (11) Sullivan, P. D.; Rood, M. J.; Grevillot, G.; Wander, J. D.; Hay, K. J. Activated carbon fiber cloth electrothermal swing adsorption system. Environ. Sci. Technol. 2004, 38 (18), 4865–4877. (12) Sullivan, P. D.; Rood, M. J.; Dombrowski, K. D.; Hay, K. J. Capture of organic vapors using adsorption and electrothermal regeneration. J. Environ. Eng. 2004, 130 (3), 258–267. (13) Dombrowski, K. D.; Lehmann, C. M. B.; Sullivan, P. D.; Ramirez, D.; Rood, M. J.; Hay, K. J. Organic vapor recovery and energy efficiency during electric regeneration of an activated carbon fiber cloth adsorber. J. Environ. Eng. 2004, 130 (3), 268–275. (14) Emamipour, H.; Hashisho, Z.; Cevallos, D.; Rood, M. J.; Thurston, D. L.; Hay, K. J.; Kim, B. J.; Sullivan, P. D. Steady-state and dynamic desorption of organic vapor from activated carbon with electrothermal swing adsorption. Environ. Sci. Technol. 2007, 41 (14), 5063–5069. (15) Kaldate, A.; Thurston, D.; Emamipour, H.; Rood, M. Engineering parameter selection for design optimization during preliminary design. J. Eng. Des. 2006, 17 (4), 291–310. (16) Sullivan, P. D.; Stone, B. R.; Hashisho, Z.; Rood, M. J. Water adsorption with hysteresis effect onto microporous activated carbon fabrics. Adsorption 2007, 13, 173–189. (17) Perry, R. H.; Green, D. W. Perry’s Chemical Engineers’ Handbook, 7th ed.; McGraw Hill: New York, 1997. (18) Murdock, J. W. Fundamental Fluid Mechanics for the Practicing Engineer; CRC Press: Boca Raton, FL, 1993; pp 25-27. (19) Sullivan, P. D.; Rood, M. J.; Hay, K. J.; Qi, S. Adsorption and electrothermal desorption of hazardous organic vapors. J. Environ. Eng. 2001, 127 (3), 217–223. (20) Ruthven, D. M. Principles of Adsorption and Adsorption Processes. Wiley: New York, 1984; pp 270-271. (21) Subrenat, A.; Le Cloirec, P. Adsorption onto activated carbon cloths and electrothermal regeneration: its potential industrial applications. J. Environ. Eng. 2004, 130 (3), 249–256. (22) Foster, K. L.; Fuerman, R. G.; Economy, J.; Larson, S. M.; Rood, M. J. Adsorption characteristics of trace volatile organic compounds in gas streams onto activated carbon fibers. Chem. Mater. 1992, 4 (5), 1068–1073. (23) Ruthven, D. M., Ed. Encyclopedia or Separation Technology;: John Wiley & Sons: New York, 1997; Vol. 1. (24) Nitsche, V.; Ohlrogge, K.; Sturken, K. Separation of organic vapors by means of membranes. Chem. Eng. Technol. 1998, 21 (12), 925–935. (25) McIntyre, J. A.; Halland, C. E.; Ritter, J. A. High enrichment and recovery of dilute hydrocarbons by dual-reflux pressure-swing adsorption. Ind. Chem. Eng. Res. 2002, 41, 3499–3504.
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