Microwave-assisted Desorption Research Articles

Graphene oxide enhances thermal stability and microwave absorption/regeneration of a porous polymer

Microwave regeneration of adsorbents offers several advantages over conventional regeneration methods; however, its application for microwave transparent adsorbents such as polymers is challenging. In this study, hypercrosslinked polymer/graphene oxide (GO) nanocomposites with large surface area and enhanced microwave absorption ability were synthesized. Polymers of 4, 4´-bis ((chloromethyl)-1, 1´-biphenyl- benzyl chloride) were hypercrosslinked through the Friedel-Crafts reactions. GO sheets were synthesized through the Hummer’s method. Nanocomposites with different GO contents (1–8 wt%) were synthesized by solution mixing method. Thermogravimetry analysis revealed a large enhancement in the thermal stability of GO-filled nanocomposites compared to pristine polymer. N2 adsorption isotherm analysis showed 7% and 10% reduction in BET surface area and total pore volume of the nanocomposite with 8 wt% GO. Compared to the pristine polymer, the dielectric constant and dielectric loss factor increased from 5 to 17 and 0.05–1.6, respectively, for the nanocomposites with 8 wt% GO. Microwave-assisted desorption of toluene from samples revealed more than 160 ºC and 4 times improvement in the desorption temperature and desorption efficiency, respectively, by addition of 4 wt% GO to the polymer. This study showed the important role of GO addition for efficient microwave-assisted regeneration of polymer adsorbents.

Porous carbon black-polymer composites for volatile organic compound adsorption and efficient microwave-assisted desorption

Adsorbents with high surface area, thermal stability and microwave absorption ability are highly desired for cyclic adsorption and microwave regeneration processes. However, most polymeric adsorbents are transparent to microwaves. Herein, porous hyper-crosslinked polymers (HCP) of (4,4′-bis((chloromethyl)-1,1′-biphenyl-benzyl chloride)) with different carbon black (CB) contents were synthesized via the Friedel-Crafts reaction. CB was selected as the filler due to its low cost and high dielectric loss and was embedded inside the polymer structure during polymerization. CB-containing composites showed enhanced thermal stability at elevated temperatures, and more than a 90-times increase in the dielectric loss factor, which is favorable for microwave regeneration. Nitrogen physisorption analysis by the Bruner-Emmett-Teller isotherms demonstrated that CB presence in the polymer structure nonlinearly decreases the surface area and total pore volume (by 38% and 26%, respectively at the highest CB load). Based on the characterization testing, 4 wt% of CB was found to be an optimum filler content, having the highest MW absorption and minimal effect on the adsorbent porosity. HCP with 4 wt% CB allowed a substantial increase in the desorption temperature and yielded more than a 450% enhancement in the desorption efficiency compared to HCP without CB.

Modeling of Microwave-Assisted Regeneration of Selected Adsorbents Loaded with Water or Toluene

In this work, the microwave-assisted desorption of water or toluene from Sorbonorit 4 activated carbon and zeolite HiSiv 3000 has been studied. The nonequilibrium, nonisothermal, and nonadiabatic process described by a mathematical model for the microwave-assisted desorption including the internal heat source capacity is formulated and solved numerically by means of a numerical method of lines. The adsorption equilibrium of water–Sorbonorit 4 is described by a multitemperature Qi-LeVan isotherm, water–HiSiv 3000 by a multitemperature Langmuir-Freundlich isotherm, and toluene–Sorbonorit 4 and toluene–HiSiv 3000 by a multitemperature Toth isotherm. Computed results show that heat and mass transport mechanisms occurring during the microwave-assisted desorption process are properly incorporated into the proposed model. Such a comprehensive mathematical modeling of microwave-assisted desorption has not previously been discussed in the literature.

Sulfonation of a hypercrosslinked polymer adsorbent for microwave-assisted desorption of adsorbed benzene

Optipore V503, a commercial hypercrosslinked hydrophobic polymer adsorbent, was sulfonated to become hydrophilic to allow more efficient microwave-assisted desorption of adsorbed nonpolar volatile organic compounds (VOCs) such as benzene under humidified conditions. Compared to Optipore V503, the hydrophilic adsorbents showed reduced adsorption capacities towards benzene, but significantly improved microwave-assisted desorption efficiencies under a semi-continuous 600W microwave irradiation process. The increased desorption efficiency was mainly attributed to adsorbed water, which indirectly allowed heating of the polymer adsorbents to higher temperatures upon irradiation by microwaves.

Preparation of highly porous hypercrosslinked polystyrene adsorbents: Effects of hydrophilicity on the adsorption and microwave-assisted desorption behavior toward benzene

In this study, highly porous hypercrosslinked polystyrene adsorbents were synthesized and subsequently sulfonated so as to make them more hydrophilic. All of the adsorbents were predominantly microporous and partially mesoporous. After sulfonation, the specific surface area and pore volume decreased to some degree, but were still within an acceptable range. The adsorption and microwave-assisted desorption behavior of the adsorbents toward benzene was investigated under humidified conditions. Compared to the as-synthesized adsorbents, the sulfonated adsorbents showed reduced adsorption capacities, but improved desorption efficiencies during a semi-continuous 600W microwave irradiation process. The increased desorption efficiency was mainly attributed to a larger amount of adsorbed water, which indirectly allowed heating of the polymer adsorbents to higher temperatures upon microwave irradiation.

Heat Transfer during Microwave-Assisted Desorption of Water Vapor from Zeolite Packed Bed

This study attempted to quantify the effect of microwave-assisted desorption of water vapor from a zeolite packed bed. Specifically, an experiment was carried out comparing water vapor desorption using hot air and microwave heating. In the experiment, the temperature in the zeolite packed bed and humidity at the inlet and outlet of the adsorption column were measured.Then, the heat transfer behavior was quantified by calculating the heat balance of a zeolite packed bed, and the effect of microwave irradiation was examined. The results showed that microwave heating is effective for desorption at the beginning.

Evaluation of an alternate microwave-assisted thermal desorption technique: compatibility with charcoal active and passive sampling for BTX exposure assessment in workplace atmospheres

A microwave-assisted alternate thermal desorption technique has been optimized and discussed concerning the compatibility with the occupational exposure assessment of organic pollution both by activated charcoal active and passive sampling. This technique applied to aromatic compounds (benzene, toluene and m-xylene) has shown a good efficiency by pumped sampling directly made on the ceramic desorption tubes. The optimal desorption recovery has been obtained with 50 mg of activated charcoal previously thermally treated, and when sampling was performed at low flow rates (<100 cm3). But, the low quantity of activated charcoal in the ceramic sampling/desorption tubes, and consequently the limited trapping capacity, could be an issue especially in highly polluted areas. The passive sampling technique, whose diffusive sampling flow rates are usually smaller than regular active sampling ones, seemed to be a better alternative in that case. A preliminary evaluation of the diffusion sampling rates Ui by the direct use of the ceramic desorption tubes as passive samplers has been undertaken using a controlled gas test facility (Ubenzene = 0.13 cm3 min−1, Utoluene = 0.11 cm3 min−1, Uxylene = 0.11 cm3 min−1). The microwave thermal desorption technique, coupled to passive sampling, could be an appropriate and efficient analytical method for the assessment of workplace organic pollutions.

Synthesis of 4-vinylpyridine–divinylbenzene copolymer adsorbents for microwave-assisted desorption of benzene

Reports on the development of polymer adsorbents for microwave-assisted desorption of nonpolar volatile organic compounds (VOCs) are rare. In this study, we synthesized macroporous polymeric adsorbents with hydrophilic methyl pyridinium units for microwave-assisted desorption of nonpolar VOCs. The benzene adsorption and desorption properties of the adsorbents were investigated under both dry and humid conditions. Under humid conditions, as the content of the hydrophilic methyl pyridinium units in the adsorbents increased from 0 to 20%, the adsorption capacity of benzene decreased from about 21 to 7mg/g, while the desorption efficiency of benzene increased significantly from 48 to 87%. The maximum concentration of desorbate also increased significantly as the content of the hydrophilic units was increased under humid conditions. We attributed the enhanced desorption efficiency mainly to more adsorbed moisture, which indirectly allowed heating of the polymer adsorbents to higher temperatures upon irradiation with 600W microwaves.

Synthesis of Hydroxylated Macroporous Polymer Beads for Microwave-Assisted Desorption of Nonpolar Volatile Organic Compounds

Opperman and Brown reported a microwave-assisted volatile organic compounds (VOCs) recovery system with polymer bead adsorbents, with emphasis on significant advantages over the conventional granulated activated carbon-based systems in terms of cost and energy efficiency, but details on their experimental results were not included.

Intensification of desorption processes by use of microwaves—An overview of possible applications and industrial perspectives

This review presents the state of the art regarding the possible intensification of desorption processes by use of microwave irradiation. The most important experimental and modeling results reported in the literature on the laboratory scale as well as on the industrial scale were collected in this paper. It follows from the review that microwave heating is a powerful novel method proving many advantages when utilized for regeneration of loaded adsorbents. In general, a short penetration depth could be a drawback of this very efficient heating method. Hence, it seems that the fluidized bed adsorbers are better choice than the fixed-bed ones when the microwave-assisted desorption step is carried out because more homogenous temperature distribution would be guaranteed.

Application of microwave-assisted desorption/headspace solid-phase microextraction as pretreatment step in the gas chromatographic determination of 1-naphthylamine in silica gel adsorbent

Pretreatment of silica gel sample containing 1-naphthylamine by microwave-assisted desorption (MAD) coupled to in situ headspace solid phase microextraction (HS-SPME) has been investigated as a possible alternative to conventional methods prior to gas chromatographic (GC) analysis. The 1-naphthylamine desorbs from silica gel to headspace under microwave irradiation, and directly absorbs onto a SPME fiber located in a controlled-temperature headspace area. After being collected on the SPME fiber, and desorbed in the GC injection port, 1-naphthylamine is analyzed by GC-FID. Parameters that influence the extraction efficiency of the MAD/HS-SPME, such as the extraction media and its pH, the microwave irradiation power and irradiation time as well as desorption conditions of the GC injector, have been investigated. Experimental results indicate that the extraction of a 150 mg silica gel sample by using 0.8 ml of 1.0 M NaOH solution and a PDMS/DVB fiber under high-powered irradiation (477 W) for 5 min maximizes the extraction efficiency. Desorption of 1-naphthylamine from the SPME fiber in GC injector is optimal at 250 °C held for 3 min. The detection limit of method is 8.30 ng. The detected quantity of 1-naphthylamine obtained by the proposed method is 33.3 times of that obtained by the conventional solvent extraction method for the silica gel sample containing 100 ng of 1-naphthylamine. It provides a simple, fast, sensitive and organic-solvent-free pretreatment procedure prior to the analysis of 1-naphthylamine collected on a silica gel adsorbent.

Separation of 20( S)-protopanaxdiol type ginsenosides and 20( S)-protopanaxtriol type ginsenosides with the help of macroporous resin adsorption and microwave assisted desorption

A novel method combining macroporous resin adsorption with microwave assisted desorption (MAD) for separation of 20( S)-protopanaxtriol type ginsenosides and 20( S)-protopanaxdiol type ginsenosides was developed. After all of the crude saponins in ginseng root extract (GRE) was adsorbed on macroporous adsorption resin, the separation of 20( S)-protopanaxtriol type and 20( S)-protopanaxdiol type ginsenosides from the resin can be completed using different solvents and power by MAD. The conditions of MAD were investigated by response surface methodology (RSM). The desorption efficiencies of 20( S)-protopanaxtriol type ginsenosides and 20( S)-protopanaxdiol type ginsenosides were both more than 90%, and that contents in the products reached 83% and 51%, respectively. Comparing with conventional methods such as ultrasonic assisted process (UAP) and reflux assisted process (RAP), this method has more merits such as using less solvents, less separation time and higher separation efficiency.

Advanced method using microwaves and solid-phase microextraction coupled with gas chromatography–mass spectrometry for the determination of pyrethroid residues in strawberries

A microwave-assisted desorption method was developed and coupled with solid-phase microextraction and GC–MS for the analysis of pyrethroid residues in strawberries. In the first step, pyrethroid analytes were desorbed from the whole fruits in an aqueous acetonitrile solution at 50% under microwave assistance, so preventing these compounds to be captured with strong matrix effects by endogenous constituents. Then, the 100 μm poly(dimethylsiloxane)-coated fibre was exposed for 30 min in the obtained extracting solution. Calibration curves, realised from blank strawberries spiked at different concentrations with standards, showed a linear range between 1 μg/kg and 250 μg/kg with r 2>0.992 and variation coefficients below 15%. Limits of detection and quantitation were found lower than 14 μg/kg and 40 μg/kg, respectively. Observed analysis results by using this method and relative to field incurred strawberry samples were also compared to those obtained by two accredited trading laboratories using traditional methods.

Determination of aniline in silica gel sorbent by one-step in situ microwave-assisted desorption coupled to headspace solid-phase microextraction and GC–FID

Microwave-assisted desorption (MAD) coupled to in situ headspace solid-phase microextraction (HS–SPME) was first proposed as a possible alternative pretreatment of samples in absorbent collected from workplace monitoring. Aniline collected on silica gel was investigated. Under microwave irradiation, the aniline was desorbed from silica gel and directly absorbed onto the SPME fiber in the headspace. Having been sampled on the SPME fiber, and desorbed in the GC injection port, aniline was analyzed using a GC–FID system. Parameters that affect the proposed extraction efficiency, including the extraction media and its pH, the microwave irradiation power and the irradiation time as well as desorption parameters of the GC injector, were investigated. Experimental results revealed that the extraction of a 150-mg silica gel sample using a 0.8-ml aqueous solution (pH 12) and a PDMS/DVB fiber under medium-high-powered irradiation (345W) for 3min maximized the efficiency of extraction. Desorption of aniline from the SPME fiber was optimal at 230°C held for 3min. The detection limit was 0.09ng. The proposed method provided a simple, fast, and organic solvent-free procedure to analyze aniline from a silica gel matrix.

Computerized model for accurate determination of ethylene oxide diffusion in sterilized medical supplies

A computerized numerical model is described which is shown to be more generally applicable than analytical methods in the determination of ethylene oxide diffusion in polymeric material. Diffusion coefficients of ethylene oxide in poly(vinyl chloride) were determined from the rates of desorption both for conventional aeration with warm air and for microwave-assisted desorption and found to be concentration dependent. The model takes account of device geometry and concentration dependence of diffusion coefficient and its predictions are in agreement with experimental results for desorption. The model is also used to simulate the whole sterilization process with a view to a planned diminution of EO residuals after sterilization.