Desorption Of Toluene Research Articles

Electrical Transport in “Few-Layer Graphene” Film Prepared by the Hot-Spray Technique: The Effect of Thermal Treatment

We investigate charge transport of a randomly stacked few-layer graphene (FLG) film supported on quartz plate, as-prepared and after annealing treatment. The film is prepared by a simple, cheap and rapid hot spray technique from a FLG suspension, while FLG was obtained in our previous report by high yield mechanical exfoliation of pencil lead. According to Hall Effect measurements, the annealing process has strong impact on the conductivity of the FLG film, despite its low oxygen/defect content as confirmed by X-ray photoelectron spectroscopy (XPS), Raman, and photoluminescense spectroscopy. The nonohmic behavior along with a sheet resistance (R□) decreases from a few tens to a few kilo-ohms is observed for the FLG film, whereas after thermal treatment, a constant R□ of 0.7 kΩ is recorded. The improvement of conductivity in the FLG film is attributed mainly to desorption of toluene from the FLG surface according to the TPD-MS analysis and not only to the oxygen decrease as generally reported.

Adsorption and Desorption of Low-Content Toluene–Ethyl Acetate Gas Mixtures on Fixed-Bed Activated Carbon for Removal and Concentration by TSA

Adsorption and Desorption of Low-Content Toluene–Ethyl Acetate Gas Mixtures on Fixed-Bed Activated Carbon for Removal and Concentration by TSA

Kinetics of Desorption of Water, Ethanol, Ethyl Acetate, and Toluene from a Montmorillonite

AbstractDesorption processes of low-molecular-weight compounds from the surface of smectites into the gas phase determine a number of processes, e.g. those involved in drug delivery and the release of herbicides. The desorption has not been investigated thoroughly and is not well understood. The present study was undertaken in order to understand better the factors influencing these desorption mechanisms. Starting with a very pure standard (Na+-rich) montmorillonite (Kunipia-F), which was exchanged against cations with different hydration properties (Ca2+, Li+, phenyltrimethylammonium, hexyltrimethyl-ammonium), the experiments explored the rate of desorption of volatiles with different chemical functionalities (water, ethanol, ethyl acetate, and toluene). The desorption was monitored by thermogravimetry and differential scanning calorimetry under isothermal conditions, and by ramping the temperature at a constant rate. The experiments were compared with numerical calculations based on finite-element methods and with analytical models. These data point to a two-step mechanism where the desorption follows the curve of the equilibrium desorption isotherms of those molecules on the montmorillonite. The bulk-like volatiles (i.e. volatiles with release kinetics close to that of the bulk liquids) were desorbed in a first step. With a decrease in the degree of coverage of the volatile on the montmorillonite, the desorption was increasingly dominated by the strength of interaction between the volatile and the interlayer cations of the montmorillonite.

Adsorption and desorption of toluene on nanoporous TiO2/SiO2 prepared by atomic layer deposition (ALD): influence of TiO2 thin film thickness and humidity

Adsorption and desorption of toluene on bare and TiO2-coated silica with a mean pore size of 15 nm under dry and humid conditions were studied using toluene breakthrough curves and temperature programmed desorption (TPD) of toluene and CO2. Two TiO2/silica samples (either partially or fully covered with TiO2) were prepared with 50 and 200 cycles of TiO2 atomic layer deposition (ALD), respectively. The capacity of silica to adsorb toluene improved significantly with TiO2-thin film coating under dry conditions. However, toluene desorption from the surface due to displacement by water was more pronounced for TiO2-coated samples than bare samples under humid conditions. In TPD experiments, silica with a thinner TiO2 film (50-ALD cycled) had the highest reactivity for toluene oxidation to CO2 both in the absence and presence of water. Toluene adsorption and oxidation reactivity of silica can be controlled by modifying the silica surface with small amount of TiO2 using ALD.

Effect of Textural Properties on the Adsorption and Desorption of Toluene on the Metal-Organic Frameworks HKUST-1 and MIL-101

The adsorption and desorption of toluene on metal-organic frameworks HKUST-1 and MIL-101 were studied. The adsorption isotherms and kinetic curves of toluene on HKUST-1 and MIL-101 were separately measured by gravimetric method. Temperature-programmed desorption experiments were carried out for estimating the interaction of toluene with the surfaces of HKUST-1 and MIL-101. Our experimental results showed that the isotherms of toluene on the adsorbents were well fitted by the Langmuir-Freundlich equation. The maximum amount of toluene adsorbed on MIL-101 was 15.1 mmol/g, which was much higher than that adsorbed on HKUST-1 (6.6 mmol/g). The high adsorption capacity of MIL-101 can be attributed to its higher surface area. However, the isotherm of toluene at P/P0 < 0.09 on HKUST-1 was much higher than that on MIL-101 owing to the smaller pore size of HKUST-1. It is suggested that HKUST-1 had better adsorption performance than MIL-101 at low concentration of volatile organic compounds. The desorption activatio...

Dynamic Adsorption and Desorption of Toluene on Carbon Nanotubes Grafted Activated Carbon Fibers

Activated carbon fibers (ACFs) are widely used adsorbents due to their small fiber diameter, uniform pore size distribution and rapid adsorption/desorption rate. In addition, carbon nanotubes (CNTs) have received much attention recently because of their excellent mechanical and electrical properties and being candidates for adsorption. Thus, it should be highly interested as grafting CNTs onto ACFs to form a hybrid adsorbent. Therefore, the objective of this paper is to investigate the physicochemical properties of ACFs grafted with nitrogen-doped CNTs (CNs) and determine the adsorption and desorption performance of toluene vapor on this hybrid adsorbent. The chemical vapor deposition method was used for growth of CNs directly onto ACFs. The resulting materials were characterized by several techniques. Next, the adsorption breakthrough behaviors of toluene on the samples were measured in a continuous flow-type fixed-bed system. And then the temperature programmed desorption system was utilized to observe the desorption characteristics of toluene from the samples. Results show that the CNs have been grafted homogeneously onto the ACFs. The attachment of CNs on ACFs was believed to block part of the active surface area, causing the decrease in specific surface area and pore volume, but lead to the increase in microporosity. The adsorption of toluene on ACFs or the hybrid adsorbent was physical adsorption. At higher adsorption temperatures, the hybrid adsorbent could maintain high enough capacities of toluene and even exceed the performance of ACFs. Moreover, toluene could be desorbed completely from ACFs and the hybrid adsorbent up to 400 oC with the highest desorption efficiency at about 180 oC.

Characterization of Novel Structured Packings for CO2 Capture

Structured packing is widely being considered for post-combustion CO2 capture because of its high mass transfer per unit of pressure drop. The hydraulic and mass transfer performances of structured packings with different corrugation angles were measured. The effective mass transfer area was measured by absorption of CO2 with 0.1 gmol/L NaOH. The liquid film mass transfer coefficient was measured by desorption of toluene into air. The gas film mass transfer coefficient was measured by absorption of SO2 from air into 0.1 gmol/L NaOH. The effective area and the liquid film mass transfer coefficient are dependent on liquid velocity while the gas film mass transfer coefficient is a function of gas velocity. Increasing the corrugation angle from 45° to 60° (Mellapak 250Y to Mellapak 250X) resulted in (1) a 54% decrease in pressure drop, (2) a 6% decrease in effective area, (3) a 17% decrease in kG, and (4) a 18% decrease in kL. Increasing the corrugation angle from 45° to 70°, a larger difference was found in pressure drop, kG and kL. However, the impact of corrugation angle on effective area is not significant. In conclusion, increasing the corrugation angle will have a benefit on pressure drop with a negative impact on mass transfer properties. Future work will be focused on economic analysis between operation costs (related to pressure drop) and capital costs (related to mass transfer properties) to determine the optimum corrugation angle for a particular separation task.

Thermal desorption of toluene from Vanadium-containing catalysts coated onto various carriers

Thermal desorption of toluene from Vanadium-containing catalysts coated onto various carriers

The oxidation of toluene sorbed on activated carbon in the presence of H2O2 and manganese oxide

We investigated the oxidation of toluene sorbed on activated carbon (AC) in the presence of hydrogen peroxide (H(2)O(2)) and pyrolusite (MnO(2)). Sorbed toluene was prepared by reacting a toluene-saturated solution and AC. The amounts of sorbed toluene (mg of toluene/g of AC) decreased as the amounts of AC were increased. The reaction was conducted in a gas-purging (GP) reactor and the gas flow at the outlet of a GP reactor was carefully maintained. As a result, the percentage of toluene captured by ORBO tube was 28% in the control system with pure water. When H(2)O(2) was catalyzed by AC (i.e. this forms a hydroxyl radical by electron transfer), approximately 17% of the desorbed toluene was oxidized and 68% of toluene remained on AC which was similar to the control system. However, when pyrolusite (650 mg/L) was added together with H(2)O(2) (10,000 mg/L), only 5% of toluene was captured by the ORBO tube and 55% of toluene remained on AC, which indicated that both desorbed and sorbed toluene was oxidized. Moreover, toluene oxidation increased when concentrations of pyrolusite and H(2)O(2) were increased. It was suggested that superoxide anion, which is generated by the reaction of H(2)O(2) and pyrolusite, might stimulate toluene desorption and then toluene in the aqueous phase could be oxidized by hydroxyl radical.

Optimized ionic liquids for toluene absorption

Conductor‐like‐screening model for real solvents (COSMO‐RS) method was used to analyze the solute‐solvent interactions and to screen Henry's law constant of toluene over 272 ionic liquids (ILs), to select high‐capacity absorbents. Thermogravimetric experiments were carried out to evaluate the toluene absorption by selected ILs at different temperatures and atmospheric pressure. Experimental equilibrium data were found in good agreement with COSMO‐RS predictions. Complete desorption of toluene by N2 stripping was achieved, indicating an easy regeneration. The kinetic curves were described by a phenomenological diffusion model, obtaining effective diffusivities in reasonable concordance with those calculated by Wilke–Chang correlation. The separation process with selected ILs was modeled by Aspen Plus and a comparison with organic absorbents was carried out. Equilibrium‐ and rate‐based simulations were used to analyze the importance of thermodynamics and kinetics in toluene absorption by ILs. Current computational‐experimental research allowed selecting a set of suitable ILs for toluene absorption. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1648–1656, 2013

Trends in the condensation/evaporation and adsorption enthalpies of volatile organic compounds on mesoporous silica materials

The adsorption–desorption of toluene, methylcyclohexane, neopentane and n-pentane was measured at temperatures between 258 and 308 K on mesoporous silica materials with different pore structures and pore sizes (MCM-41, SBA-15, SBA-16, LPC and MCF). It was found that the change in the width of the hysteresis cycles with temperature is similar for MCM-41, SBA-15 and MCF but distinct for the materials having pores accessible through very narrow openings (SBA-16 and LPC). A comparison between the plots of V ads vs. potential for SBA-16, LPC and MCF suggested that the differences are a consequence of the non equilibrium evaporation mechanism of the organics from the pores of SBA-16 and LPC. The isosteric enthalpies of adsorption indicated that the strength of the gas–solid interactions for toluene is superior to those corresponding to neopentane, methylcyclohexane or n-pentane. The isosteric enthalpies associated with capillary condensation are higher than the molar condensation enthalpies for the materials with narrower mesopores. As the size of the pores increases, the difference gradually decreases and the isosteric enthalpies are identical to the molar condensation enthalpies for the materials with pores larger than ∼20 nm. The apparent evaporation enthalpies were found to be higher than the apparent condensation enthalpies when the hydrocarbons isotherms exhibited developed hysteresis, except in the case of the MCF silica, for which the values of both enthalpies were similar.

마이크로파조사를 위한 개질화 활성탄의 톨루엔 탈착

Toluene desorption of modified activated carbon for microwave irradiation was evaluated. As a virgin GAC reacted from microwave energy, it created an "arcing" between GAC particles in desorption process. The arcing became more and more vigorous and achieved a red flame of GAC. The silica coated GAC(Si/GAC) was developed to prevent arcing phenomenon and temperature control problem. The result shows virgin GAC with 5wt%, 10wt% and 20wt% silica had no arcing and could control temperature very well. However, the adsorption rate of Si/GAC was decreased by coated silica amount due to decreasing surface area of GAC. The 5wt% Si/GAC adsorption rate was quite similar to virgin GAC adsorption rate. After adsorption, the toluene-loaded GAC and Si/GAC was reactivated by 2450MHz MW irradiation with 300W for 5 min. Quantitative desorption of the toluene was achieved at MW irradiation at 300W with desorption efficiencies as high as 98.59% to 84.65%% after four cycles.

Titanium alkoxo oximates, with surfactant-like properties of the oximate ligands, as precursors for porous TiO2 and mixed oxide sol–gel films

Titanium alkoxo oximates with long-chain alkyl groups were used as sol–gel precursors for simultaneous deceleration of the reaction rates of Ti(OR)4 and creation of porosity upon calcination due to surfactant-like properties. Both titania and hybrid silica–titania films with high surface areas were obtained. Extraction studies showed that only part of the employed oxime is coordinated, but both coordinated and non-coordinated oxim(at)e contribute to pore formation upon heat treatment. Sorption properties of silica–titania hybrid materials were studied by investigating temperature-programmed desorption of toluene.

Factors Controlling Alkylbenzene and Tetrachloroethene Desorption from Municipal Solid Waste Components

Desorption rates of toluene, o-xylene and tetrachloroethene from individual municipal solid waste components [high-density polyethylene (HDPE); poly(vinyl chloride) (PVC); office paper; newsprint; and rabbit food, a model food and yard waste] were determined. Effects of sorbent and sorbate properties, solvent composition (ultrapure water, acidogenic and methanogenic leachates), and contact time ("aging") on desorption rates were evaluated. Hydrophobic organic contaminant (HOC) desorption from PVC and HDPE could be described with a single-parameter polymer diffusion model. In contrast, a three-parameter, biphasic polymer diffusion model was required to describe HOC desorption rates from biopolymer composites. In general, HOC desorption rates from plastics were rapid for HDPE (D = 10(-10) cm(2)/s), a rubbery polymer, but slower for PVC (D = 10(-13)-10(-14) cm(2)/s), a glassy polymer. For biopolymer composites, a large fraction of sorbed HOCs was rapidly released (D(r) = 10(-9)-10(-10) cm(2)/s) while the remaining fraction desorbed slowly (D(s) = 10(-11)-10(-16) cm(2)/s). The toluene desorption rate from PVC was 1 order of magnitude faster in acidogenic leachate than in either ultrapure water or methanogenic leachate, a result that was primarily attributed to the plasticizing effect of volatile fatty acids in acidogenic leachate. For biopolymer composites, small increases in the slowly desorbing HOC fraction were observed with increasing aging time.

Influence of toluene contamination at the hydrogen Pt/C anode in a proton exchange membrane fuel cell

For fuel cells run on hydrogen reformate, traces of hydrocarbon contaminants in the hydrogen gas may be a concern for the performance and lifetime of the fuel cell. This study focuses on the influence of low concentrations of toluene on the adsorption and deactivation chemistry in a proton exchange membrane (PEM) fuel cell. For this purpose cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques were employed. Results from adsorption and desorption (by oxidation or reduction) experiments performed in a humidified nitrogen or hydrogen flow in a fuel cell test cell with a mass spectrometer system connected to the outlet are presented. The influence of adsorption potential, temperature, and humidity are discussed. The results show that toluene adsorbs on the catalyst surface in a broad potential window, up to at least 0.85 V versus RHE at 80 °C. Adsorbed toluene oxidizes to CO 2 with peak potentials above 1.0 V for temperatures below 95 °C. Some desorption of toluene (or reduced products) may take place at potentials below 0 V. In a hydrogen flow, toluene contamination in per mille concentrations leads to a continuous growth of the charge transfer resistance, while a 10-fold dilution of the toluene concentration resulted in a low and constant charge transfer resistance even for longer exposures. This indicates that a competition between toluene and hydrogen may take place on the active platinum surface at the anode.

Synthesis and characterization of aluminium containing CIT-1 and their structure–property relationship to hydrocarbon trap performance

The present work focuses on the synthesis of Al-CIT-1 by various post-modification procedures of B-CIT-1 and their structure–property relation to hydrocarbon trap performance. Al substitution in B-CIT-1 was carried out by three different post-modification procedures, viz., direct exchange (Al-CIT-1_DEX), insertion (Al-CIT-1_INS), and impregnation (Al-CIT-1_IMP), and characterized in detail by various physico-chemical techniques such as XRD, N 2 adsorption, SEM, NH 3-TPD, XPS, and solid state 27Al and 29Si MAS NMR. The Al-CIT-1 samples were tested for their adsorption–desorption characteristics of toluene, and 2,2,4-trimethylpentane (2,2,4-TMP) to understand the Al distribution in CIT-1 as well as the efficacy of these materials as hydrocarbon traps. The Al distribution in Al-CIT-1 plays a critical role in the adsorption–desorption characteristics of toluene and 2,2,4-TMP. Al-CIT-1 with high relative proportion of framework Al and less extraframework Al (Al-CIT-1_DEX) showed maximum toluene and 2,2,4-TMP adsorption capacity. The presence of finely distributed extraframework Al 2O 3 species in Al-CIT-1_INS modify the pores and causes a slow release of toluene during desorption. Al-CIT-1_IMP with less Al content and acidity showed the lowest toluene desorption temperature. Large amount of surface Al species hinder a relatively bulky molecule 2,2,4-TMP to access the available active sites of tetrahedral Al and the associated Brϕnsted sites in the zeolite, and as a result, Al-CIT-1_INS showed hardly any adsorption towards 2,2,4-TMP. Thus, by varying the post-modification method and treatment condition, it is possible to tune the performance of Al incorporated CIT-1 as a useful material for hydrocarbon trap.

Absorption and desorption of gaseous toluene by an absorbent microcapsules column

Heavy solvents absorption appears to be very attractive in recovering of volatile organic compounds (VOCs) from industrial tail gas. Their high viscosities make good dispersion required but difficult to reduce mass transfer resistance. Microencapsulation techniques provide a candidate solution. In this paper, vapor pressures for toluene+poly(dimethylsiloxane) (PDMS) mixtures were measured at temperature ranging from 273.2K to 343.2K. Polyacrylonitrile (PAN) hollow microspheres, prepared by orifice dispersion plus solvent extraction method, was used to immobilize PDMS. The capacity was adjusted from 2.3g to 9.3g PDMS/g PAN by addition of cyclohexane in PDMS during solvent impregnation. The breakthrough curves of column packed with PDMS/PAN microcapsules were determined, indicating shapes close to ideality, high absorption efficiencies and considerable absorption capacities before breakthrough. The influence of operational temperature, concentration of feed and gas feed flow rate on the absorption process were investigated as well. A mathematical model, suitable for dilute gas absorption process, was used to simulate the breakthrough curves. This model has proved to be useful to fit curves and analyze the absorption kinetics of PDMS/PAN microcapsules column. After absorption, the column can be regenerated completely by gas stripping. Enrichment of toluene was founded by increasing desorption temperature. Through absorption and desorption by turns, the stability of PDMS/PAN microcapsules column was verified.

Thermal Behaviors and Regeneration of Activated Carbon Saturated with Toluene Induced by Microwave Irradiation

Microwave irradiation is an effective way to regenerate the activated carbon after adsorption and separation of waste. In this work, activated carbon saturated with toluene was efficiently regenerated by microwave irradiation. The maximum regeneration ratio of 77.2% was obtained under the following optimal operation conditions: saturated activated carbon of 5.01 g, microwave power of 500 W, carrier gas N2 flow of 60 mL/min, and microwave irradiation time of 180 s. It was found that the higher microwave power may result in self-burning of activated carbon due to the presence of traces of oxygen, which might slightly deteriorate the pore structures of activated carbon. On the other hand, the lower microwave power cannot start desorption of toluene or might cause re-adsorption. The introduction of N2 flow during regeneration was necessary to release the desorbed toluene from activated carbon, but it might cool the adsorption system under a much higher N2 flow rate.

Regeneration of Honeycomb Zeolite by Nonthermal Plasma Desorption of Toluene

In order to develop an economical volatile organic compound (VOC) removal process, a concentration technique using nonthermal plasma combined with an adsorption process is investigated. Toluene-one of the most commonly used VOCs-is used, and the optimization of plasma desorption is investigated. The effects of toluene concentration and adsorbent regeneration are investigated by varying the plasma desorption methods: closing method, in which a carrier gas is stopped flowing during a portion of plasma desorption time, and nonclosing method. As a result, the closing method is favored with regard to parameters such as concentration, desorption efficiency, regeneration efficiency, and by-product formation. Then, the plasma desorption using closing method is investigated as a function of discharge power, closing time, a carrier gas flow rate for plasma desorption, and plasma desorption time. When a 2-L/min and 30-ppm toluene gas is employed as a target gas, a toluene concentration exceeding 30 times the original concentration is achieved with a reduction in the gas volume by 1/60. The repeatability of adsorption and plasma desorption is successfully demonstrated; these processes yield an extremely effective and practical VOC removal process.

Hydrocarbon Desorption Characteristics of Metal-impregnated Zeolite and Its Evaluation in Vehicle Test

For the purpose of heightening hydrocarbon desorption temperature for hydrocarbon adsorption-combustion catalyst, we researched about some kinds of zeolites and of hydrocarbon adsorption elements. The hydrocarbon desorption temperature for 5 type of zeolites were measured by temperature programmed desorption (TPD) with model gas which simulated engine start exhaust one. The TPD measurement showed that the beta zeolite had that the highest hydrocarbon desorption temperature and its amounts was largest among all zeolites evaluated in this study. Ag, Mg, Ni, Co, Cu, Ce and Sr addition to beta zeolite increased the toluene desorption temperature as much as 170-320°C. On the other hand, among these added elements, only Ag increased the pentane desorption temperature by 90°C. The chemical states of Ag was measured with an ultra violet visible spectrophotometer (UV-vis). UV-vis suggested that Ag+ and Ag0 (metal) increased the desorption temperature of paraffin and aromatics, respectively. After the endurance test by being exposed to an air excessive gas and a fuel excessive gas alternately at 800°C or 850°C for the catalysts, the desorption temperature of the hydrocarbon, especially of paraffin lowered. These phenomena were thought to be caused by the change of chemical state for Ag+ which existed besides the ion exchange site to Agxn+ (cluster) or Ag0 and by the sintering of Ag. The hydrocarbon desorption temperature obtained in the vehicle test was the same as the temperature predicted from the chemical state of Ag and the composition of the exhaust gas.