Zaher Hashisho

Effect of the adsorbate kinetic diameter on the accuracy of the Dubinin-Radushkevich equation for modeling adsorption of organic vapors on activated carbon.

This paper investigates the effect of the kinetic diameter (KD) of the reference adsorbate on the accuracy of the Dubinin-Radushkevich (D-R) equation for predicting the adsorption isotherms of organic vapors on microporous activated carbon. Adsorption isotherms for 13 organic compounds on microporous beaded activated carbon were experimentally measured, and predicted using the D-R model and affinity coefficients. The affinity coefficients calculated based on molar volumes, molecular polarizabilities, and molecular parachors were used to predict the isotherms based on four reference compounds (4.3≤KD≤6.8 Å). The results show that the affinity coefficients are independent of the calculation method if the reference and test adsorbates are from the same organic group. Choosing a reference adsorbate with a KD similar to that of the test adsorbate results in better prediction of the adsorption isotherm. The relative error between the predicted and the measured adsorption isotherms increases as the absolute difference in the kinetic diameters of the reference and test adsorbates increases. Finally, the proposed hypothesis was used to explain reports of inconsistent findings among published articles. The results from this study are important because they allow a more accurate prediction of adsorption capacities of adsorbents which allow for better design of adsorption systems.

Microbead-assisted high resolution microwave planar ring resonator for organic-vapor sensing

A microbead-assisted planar microwave resonator for organic vapor sensing applications is presented. The core of this sensor is a planar microstrip split-ring resonator, integrated with an active feedback loop to enhance the initial quality factor from 200 to ∼1 M at an operational resonance frequency of 1.42 GHz. Two different types of microbeads, beaded activated carbon (BAC) and polymer based (V503) beads, are investigated in non-contact mode for use as gas adsorbents in the gas sensing device. 2-Butoxyethanol (BE) is used in various concentrations as the target gas, and the transmitted power (S21) of the two port resonator is measured. The two main microwave parameters of resonance frequency and quality factor are extracted from S21 since these parameters are less susceptible to environmental and instrumental noise than the amplitude. Measured results demonstrate a minimum resonance frequency shift of 10 kHz for a 35 ppm concentration of BE exposure to carbon beads and 160 kHz for the polymer based ad...

Adsorption of Acid Extractable Oil Sands Tailings Organics onto Raw and Activated Oil Sands Coke

AbstractThe accumulation of organic contaminants in process-affected (PA) water represents an environmental liability for oil sands operators. Oil sands coke is a promising adsorbent for removing dissolved organic carbon (DOC), which includes toxic acid-extractable oil sands tailings organics (AEOSTO) found in PA water. The ability of raw and activated delayed and fluid coke to remove DOC and AEOSTO from PA water was assessed. Treatment with 5  g/L of activated delayed and fluid coke removed 91% of DOC and 92% of AEOSTO at levels of 36  mg/L and 60  mg/L, respectively. Heavy metal leaching of vanadium at 5.9  mg/L was observed for a 5  g/L application of activated delayed coke, representing a challenge to the approach. Microtox testing indicated that higher carbon doses of activated cokes were effective in reducing toxic the biological response caused by organic compounds; however, exposure to heavy metals increased the toxic effect with time. The proposed methodology should be coupled with an inorganic t...

The role of beaded activated carbon's pore size distribution on heel formation during cyclic adsorption/desorption of organic vapors

The effect of activated carbons pore size distribution (PSD) on heel formation during adsorption of organic vapors was investigated. Five commercially available beaded activated carbons (BAC) with varying PSDs (30-88% microporous) were investigated. Virgin samples had similar elemental compositions but different PSDs, which allowed for isolating the contribution of carbons microporosity to heel formation. Heel formation was linearly correlated (R(2)=0.91) with BAC micropore volume; heel for the BAC with the lowest micropore volume was 20% lower than the BAC with the highest micropore volume. Meanwhile, first cycle adsorption capacities and breakthrough times correlated linearly (R(2)=0.87 and 0.93, respectively) with BAC total pore volume. Micropore volume reduction for all BACs confirmed that heel accumulation takes place in the highest energy pores. Overall, these results show that a greater portion of adsorbed species are converted into heel on highly microporous adsorbents due to higher share of high energy adsorption sites in their structure. This differs from mesoporous adsorbents (low microporosity) in which large pores contribute to adsorption but not to heel formation, resulting in longer adsorbent lifetime. Thus, activated carbon with high adsorption capacity and high mesopore fraction is particularly desirable for organic vapor application involving extended adsorption/regeneration cycling.

Microporous activated carbon from pinewood and wheat straw by microwave-assisted KOH treatment for the adsorption of toluene and acetone vapors

Pinewood and wheat straw activated carbons were prepared by KOH and microwave heating, and their adsorption properties were determined. The pinewood and wheat straw activated carbons achieved total pore volumes of 0.93 and 0.60 cm3 g−1, surface areas of 2044 and 1250 m2 g−1, as well as a high contribution of micropores of 75% and 76%, respectively, at a KOH/char ratio of 3.0, in less than 30 min at 600 W and in the presence of humidity. The adsorption properties of the activated carbons were quantified using toluene and acetone adsorption at 200 ppm and adsorption isotherms. Equilibrium isotherm data were fitted using the Dubinin–Radushkevich model.

The role of beaded activated carbon’s surface oxygen groups on irreversible adsorption of organic vapors

The objective of this study is to determine the contribution of surface oxygen groups to irreversible adsorption (aka heel formation) during cyclic adsorption/regeneration of organic vapors commonly found in industrial systems, including vehicle-painting operations. For this purpose, three chemically modified activated carbon samples, including two oxygen-deficient (hydrogen-treated and heat-treated) and one oxygen-rich sample (nitric acid-treated) were prepared. The samples were tested for 5 adsorption/regeneration cycles using a mixture of nine organic compounds. For the different samples, mass balance cumulative heel was 14 and 20% higher for oxygen functionalized and hydrogen-treated samples, respectively, relative to heat-treated sample. Thermal analysis results showed heel formation due to physisorption for the oxygen-deficient samples, and weakened physisorption combined with chemisorption for the oxygen-rich sample. Chemisorption was attributed to consumption of surface oxygen groups by adsorbed species, resulting in formation of high boiling point oxidation byproducts or bonding between the adsorbates and the surface groups. Pore size distributions indicated that different pore sizes contributed to heel formation - narrow micropores (<7Å) in the oxygen-deficient samples and midsize micropores (7-12Å) in the oxygen-rich sample. The results from this study help explain the heel formation mechanism and how it relates to chemically tailored adsorbent materials.

A Microwave Ring Resonator Sensor for Early Detection of Breaches in Pipeline Coatings

A planar microwave resonator sensor is designed, customized, and fabricated to detect coating breaches in industrial steel pipelines. The sensor, which utilizes a ring-shaped resonator to maximize the sensitivity at its core, is tuned to 2.5 GHz with a quality factor of 280. In the setup, the sensor is grounded to a piece of steel pipeline with an Epoxy-100 coating, which provides the substrate beneath the microstrip structure. It is demonstrated that any change in the gap height between the substrate layer and the pipeline, from 0 to 3.5 mm, produces a significant resonant frequency variation and bandwidth change in the sensors response. The sensor structure demonstrates sensitivity and selectivity to air and water penetration to the breach. The sensor structure described in this work is a compact, low-cost solution and has potential for further miniaturization in mobile applications which may serve as a method for pipeline breach detection.

Flexible coupled microwave ring resonators for contactless microbead assisted volatile organic compound detection

In this paper, a new microwave contactless sensor is presented to monitor the level of volatile organic compound (VOC) in a dry gas stream. The platform is based on two passive ring resonators, which are magnetically coupled where the sensing tag is implemented on a flexible RF substrate. The wireless coupling between the reader and the tag, enables contactless as well as sensitive sensing. The microwave sensor operates at 4 GHz while the distance between the reader and the tag can be extended up to 1.5 cm. To increase the sensitivity of the sensor, VOC polymeric adsorbent beads (V503) are used inside a cylindrical quartz reactor and the tag monitors the adsorption on the V503 bed directly. Various concentrations of Methyl Ethyl Ke-tone (MEK) and Cyclohexane in the range of 250 to 1000 ppm are detected distinctively. The sensor demonstrates a sensitivity of 40 kHz/ppm for MEK and 2 kHz/ppm for Cyclohexane operating as a real-time detector.

Adsorption of volatile organic compounds onto natural porous minerals

The abundance of natural porous minerals and their low cost make them the potential adsorbents for VOCs (volatile organic compounds). In this paper, three natural minerals (diatomite, stellerite and vitric tuff) and their corresponding acid-treated minerals were used as adsorbents. The adsorption performances of minerals were investigated by the adsorption breakthrough curves of VOCs. The results indicated that the properties of organic compounds such as boiling point and polarity and the surface area and pore volume of minerals had obvious effects on the adsorption of VOCs over minerals. Increasing adsorption temperature and relative humidity would have negative effects on the VOC adsorption of minerals. The adsorption capacity of 2-heptanone over acid stellerite decreased by 7.2% as the temperature rose from 25°C to 45°C. The adsorption capacity of acid stellerite for 2-heptanone reduced by 60.9% when relative humidity increased from 0% to 75%. Minerals were tested for five adsorption-regeneration cycles to study the reusability. Better fittings of Thomas model, pseudo-first order kinetics model, and Freundlich model were showed in fitting the adsorption. Overall, porous minerals with high specific surface area and pore volume have promising prospect in VOCs adsorption.

Tailoring the electrical resistivity of zeolite Y by carbon addition to allow resistive heating

Resistive heating or electrothermal regeneration is a valuable alternative to conventional adsorbent regeneration methods because of cost, energy, and time efficiency; however, it only works for electrically conductive adsorbents such as activated carbon. Zeolites are widely used adsorbents for gas separation; however their high resistivity prevents their regeneration with resistive heating. This paper describes a proof of concept study assessing the feasibility and performance of multiple carbon loading techniques to decrease zeolite resistivity and allow its resistive heating without sacrificing its adsorption properties. Carbon was added to zeolite by physical mixing, chemical vapor deposition of ethanol and benzene, carbon nanotube growth via catalytic CH4 decomposition, and thermal decomposition of polyvinyl-alcohol. Similar thermal conditions were applied (2 hours at 600 °C) for all carbon deposition methods to avoid the impact of multiple variables. Elemental analyses and scanning electron micrographs confirmed the addition of carbon, and resistivity decreased by up to 8 orders of magnitude. Resistivity decrease was greatest when carbon was added directly to the zeolites surface compared to physical mixing with zeolite. Carbon nanotube growth decreased zeolite resistivity from >107 Ω m to 0.7 Ω m, but caused partial loss of adsorption capacity. The reduction in zeolite resistivity, however, allowed resistive heating of zeolite at a heating rate as high as 120 °C min−1. This work presents CNT-addition as a potential method to allow resistive heating for zeolite adsorbent regeneration. By considering multiple carbon addition methods and identifying CNT-addition as preferred, these findings inform future research efforts that will focus on optimization and application testing.