Continuous catalytic hydrogenation of polyaromatic hydrocarbon compounds in hydrogen-supercritical carbon dioxide

Smoke Chemistry, In Vitro Cytotoxicity, and Genotoxicity Demonstrates Enhanced Toxicity of Cigarillos Compared With Cigarettes

There has been limited toxicity testing of cigarillos, including comparison to cigarettes. This study compared the smoke chemistry and the cytotoxic and genotoxic potential of 10 conventional cigarettes and 10 cigarillos based on the greatest market share. Whole smoke and total particulate matter (TPM) were generated using the Canadian Intense and International Organization for Standardization puffing protocols. Tobacco-specific nitrosamines, carbonyls, and polycyclic aromatic hydrocarbons were measured using gas chromatography-mass spectrometry. TPM smoke extracts were used for the in vitro assays. Cytotoxicity was assessed in human bronchial epithelial continuously cultured cell line cells using the neutral red uptake assay. Genotoxic potential was assessed using the micronucleus (human lung adenocarcinoma continuously cultured cell line cells), Ames, and thymidine kinase assays. TPM from all cigarillos tested was more cytotoxic than cigarettes. Micronucleus formation was significantly greater for cigarillos compared with cigarettes at the highest dose of TPM, with or without rat liver S9 fraction. In the Ames test +S9, both tobacco products exhibited significant dose-dependent increases in mutation frequency, indicating metabolic activation is required for genotoxicity. In the thymidine kinase assay +S9, cigarillos showed a significantly enhanced mutation frequency although both tobacco products were positive. The levels of all measured polycyclic aromatic hydrocarbons, tobacco-specific nitrosamines, and carbonyls (except acrolein) were significantly greater in cigarillos than cigarettes. The Canadian Intense puffing protocol demonstrated increased smoke constituent levels compared with International Organization for Standardization. Even though the gas vapor phase was not tested, the results of this study showed that under the tested conditions the investigated cigarillos showed greater toxicity than comparator cigarettes. This study found that there is significantly greater toxicity in the tested U.S. marketed cigarillos than cigarettes for tobacco constituent levels, cytotoxicity, and genotoxicity. These findings are important for understanding the human health toxicity from the use of cigarillos relative to cigarettes and for building upon knowledge regarding harm from cigarillos to inform risk mitigation strategies.

Optimizing Reductive Degradation of PAHs Using Anhydrous Ethanol with Magnesium Catalyzed by Glacial Acetic Acid

Targeted degradation of individual polycyclic aromatic hydrocarbon (PAH) constituents like anthracene, may offer cost effective and efficient cleaning of coal tar-contaminated sites. Thus, a reductive degradation procedure of anthracene using activated magnesium with anhydrous ethanol at room temperature was developed and optimized. To determine the optimum conditions for anthracene, such as effective magnesium concentrations, glacial acetic acid volumes, and exposure time for the anthracene reduction, the experiments were designed using the response surface methodology based on the central composite design. The design also minimized the number of experiments. The main product from anthracene reduction is 9,10-dihyrdoanthracene. Optimum conditions for 98% degradation capacity of anthracene (2.80 × 10^-3 mmol) were 30 mg of Mg powder (1.20 mmol), 60 μL of glacial acetic acid (1.05 mmol), and 30 min exposure time. When the optimized method was tested on the coal tar specimen, twice as many reagents (i.e., Mg and glacial acetic acid) were required to obtain a 90% degradation of anthracene and fluoranthene from the coal tar. This method of using activated Mg and anhydrous ethanol selectively reduces PAHs in coal tar; in particular anthracene and fluoranthene are most efficiently removed.

Metal complexes supported on activated carbon as catalysts for the hydrogenation of anthracene

In this work, the catalytic activity was investigated in the hydrogenation of anthracene by BaSO3 and Cu(II), Zn(II) and Ni(II) complexes that contain the ligand bis(3,5-dimethyl-1-pyrazolyl) methane (L). The compounds were supported on activated carbon (AC) and studied as catalysts for the hydrogenation of anthracene over different temperatures and reaction times. The supported catalysts (Cat/AC) were prepared by direct impregnation on the support and characterized by surface area determination, FTIR spectroscopy, and X-ray powder diffraction and pore size distribution analysis. The results showed high conversions and selectivity toward hydrogenated products, where the highest value was obtained using LNiCl2/AC and the lowest with BaSO3/AC. It was established that the selectivity for Tetrahydroanthracene was more highest quantity as a product of hydrogenation using Cat/AC which is dependent of the temperature, reaching a peak at 450 °C. At this temperature and with very short reaction times, the catalytic activity is influenced mainly by the chemical characteristics of the metal in the complexes and the AC support.

Application of a magnesium/co-solvent system for the degradation of polycyclic aromatic hydrocarbons and their oxygenated derivatives in a spiked soil

This study evaluates the capability, efficacy and practicality of a combined approach based on solvent extraction and chemical reduction to simultaneously degrade polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (OPAHs) in spiked soil. The spiked soil was washed using a composite organic solvent consisting of ethanol and ethyl lactate (1:1, v/v) and then degradation of the extracted contaminants using zero-valent magnesium. The extraction conditions were optimized at 25 °C with solvent-soil ratio of 2:1 (v/w) and the ensuing degradation efficiency ranged from 79% to 88% for the OPAHs, and 66% to 87% for the PAHs after 24 h of reaction at pH of 6.1. The reductive degradation of the spiked contaminants followed pseudo-first-order kinetics; however, comparing the kinetic results of this study to soil-free studies, the degradation rates are significantly reduced. It can be inferred that extracted organic or inorganic components from the soil medium hinder the degradation process, possibly by reducing the reactivity of the activated metal. Furthermore, to our understanding, this study is the first report on the simultaneous degradation of these priority pollutants and their oxygenated derivatives. The experimental results encourage the application of this magnesium/co-solvent system for future pilot-scale remediation studies.

Multivariate evaluation and optimization of an activated-magnesium/co-solvent system for the reductive degradation of polycyclic aromatic hydrocarbons

The present study evaluates the capability of an activated-magnesium metal and protic co-solvents to promote the reductive degradation of three different polycyclic aromatic hydrocarbons, specifically pyrene, benzo[k]fluoranthene and benzo[g,h,i]perylene. Multivariate analyses demonstrated that the kinetics of degradation was affected by several experimental factors such as magnesium loading, acid addition and solubility of the compounds. It was determined that an acid activator is needed for the degradation reaction to proceed and it is also noted that the use of a 1:1 ethanol/ethyl lactate co-solvent is ideal for the complete dissolution of all three compounds with concentrations varying from 200 to 275mgL(-1). The experimental results also indicate that, at room temperature conditions, only 0.05-0.1g of magnesium is required in order to achieve greater than 93% degradation efficiency after 24h of reaction. This methodology is attractive and may allow for the development of an economic and environmentally friendly field application for the remediation of other polycyclic aromatic hydrocarbons.

Reduction of benzo[a]pyrene with acid-activated magnesium metal in ethanol: a possible application for environmental remediation

Persistent organic pollutants (POPs) are a well-known threat to the environment. Substances such as polycyclic aromatic hydrocarbons (PAHs) in contaminated soils and sediments can have severe and long-term effects on human and environmental health. There is an urgent need for the development of safe technologies for their effective degradation. Here we present a new technique using ball-milled magnesium powder and ethanol solvent as a convenient electron transfer/proton source for the partial reduction of PAHs under ambient conditions. The rates of degradation were determined while evaluating the influences of acetic acid and type of ball-milled magnesium added to the reaction mixture. The results of these triplicate studies indicate that with the use of acetic acid as an activator and ball-milled magnesium carbon (Mg/C), this reducing system (Mg-EtOH) is able to achieve a 94% conversion of 250 μg/mL of toxic benzo[a]pyrene into a mixture of less toxic and partially hydrogenated polycyclic compounds within 24h. This methodology can be used as a combined process involving ethanol washing followed by reduction reaction and it can also be considered as an easy handling and efficient alternative process to the catalytic hydrogenation of PAHs.

Simultaneous mobilization of macro- and trace elements (MTEs) and polycyclic aromatic hydrocarbon (PAH) compounds from soil with a nonionic surfactant and [S,S]-ethylenediaminedisuccinic acid (EDDS) in admixture: PAH compounds

A laboratory study was conducted to assess the feasibility of a washing process with nonionic surfactant in combination with EDDS for the simultaneous mobilization of MTEs and PAH compounds from a field-contaminated soil. Unit processes consisting of complexometric extraction and surfactant-assisted mobilization were combined with reagent regeneration and detoxification steps to generate innocuous products. Thirty minutes of ultrasonic mixing of the soil with a combination of 20 mL L(-1) surfactant suspension and a sparing quantity (2 mmol) of EDDS mobilized virtually all of the benzo[α] pyrene (B(a)P) and chrysene (Cry) and an appreciable portion of the burdens of Cd, Cr, Mn, Ni, Pb and Zn, lesser amounts of the As and Cu, but only small quantities of Al and Fe. Relative to individual reagents, combinations of surfactant (Brij98), with EDDS increased the recovery of B(a)P but seemingly did not influence Cry extraction efficiencies perceptibly. Nine sequential washes with the same initial dosage of mobilization aids decreased the quantities of both PAHs to levels in the soil that conformed to recommended maxima. What resulted was a soil that had been cleaned and a limited quantity of innocuous wash water.

Scaling up a treatment to simultaneously remove persistent organic pollutants and heavy metals from contaminated soils

Soil washing is a treatment process that can be used to remediate both organic and inorganic pollutants from contaminated soils, sludges, and sediments. A soil washing procedure was evaluated utilizing about 100g samples of soil that had been field-contaminated with arsenic, chromium, copper, pentachlorophenol (PCP), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The highest level of mobilization/detoxification was achieved in three soil washes with a mixture of 0.1M [S,S]-ethyelnediaminedisuccinate ([S,S]-EDDS) and 2% Brij 98 at pH 9 with 20 min of ultrasonication treatment at room temperature. This combination mobilized 70% of arsenic, 75% of chromium, 80% of copper, 90% of PCP, and 79% of PCDDs and PCDFs, so that the decontaminated soil met the maximum acceptable concentrations of the generic C-level criteria regulated by the Ministère du Développement Durable, de l'Environnement et des Parcs for the Province of Québec, Canada. The organic pollutants were back-extracted from the aqueous suspension with hexane. Heavy metals were virtually completely precipitated from the aqueous washing suspension with Mg(0) particles at room temperature. The PCP was detoxified by catalytic hydrodechlorination with a stream of 5% (v/v) H(2)-supercritical CO(2) that transported the organosoluble fraction through a reaction chamber containing 2% Pd/γ-Al(2)O(3). In toto, this soil washing procedure demonstrates that persistent organic pollutants and selected heavy metals can be co-extracted efficiently from a field-contaminated soil with three successive washes with the same soil washing solution containing [S,S]-EDDS and a non-ionic surfactant (Brij 98) in admixture. An industrial-scale ex situ soil washing procedure with a combination of a non-ionic surfactant and a complexing reagent seems to be a plausible remediation technique for this former wooden utility pole storage facility.

Heterogeneous catalytic hydrogenation reactions in continuous-flow reactors

Microreactor technology and continuous flow processing in general are key features in making organic synthesis both more economical and environmentally friendly. Heterogeneous catalytic hydrogenation reactions under continuous flow conditions offer significant benefits compared to batch processes which are related to the unique gas-liquid-solid triphasic reaction conditions present in these transformations. In this review article recent developments in continuous flow heterogeneous catalytic hydrogenation reactions using molecular hydrogen are summarized. Available flow hydrogenation techniques, reactors, commonly used catalysts and examples of synthetic applications with an emphasis on laboratory-scale flow hydrogenation reactions are presented.

Catalytic hydrogenation rate of polycyclic aromatic hydrocarbons in supercritical carbon dioxide containing polymer-stabilized palladium nanoparticles

Catalytic hydrogenation of polycyclic aromatic hydrocarbons (PAHs) with up to four fused benzene rings over high-density-polyethylene-stabilized palladium nanoparticles in supercritical carbon dioxide via in situ UV/Vis spectroscopy is presented. PAHs can be efficiently converted to saturated polycyclic hydrocarbons using this green technique under mild conditions at 20 MPa of CO₂ containing 1 MPa of H₂ at 40-50°C. Kinetic studies based on in situ UV/Vis spectra of the CO₂ phase reveal that the initial hydrogenation of a given PAH and the subsequent hydrogenations of its intermediates are pseudo-first-order. The hydrogenation rate of the latter is always much smaller than that of the former probably due to increasing steric hindrance introduced by the hydrogenated benzene rings of PAHs which impedes the adsorption process and hydrogen access to PAHs on catalyst surfaces.

Screening of bimetallic heterogeneous nanoparticle catalysts for arene hydrogenation activity under ambient conditions

This study focuses on the application of a simple screening approach to prepare and test heterogeneous mono- and bimetallic nanoparticle (NP) catalysts for arene hydrogenation activity under ambient conditions in a quick and time efficient manner, as well as detailed testing and characterization of identified active catalysts. Over 90 mono- and bimetallic NP catalysts supported on alumina were efficiently screened for arene hydrogenation activity under ambient conditions using toluene as a model substrate. Through this approach, four catalysts were determined to be active: RhPt/Al(2)O(3), RuPt/Al(2)O(3), IrPt/Al(2)O(3), and IrRh/Al(2)O(3). These catalysts were further synthesized and tested in bulk, and RhPt/Al(2)O(3) was confirmed to be the catalyst with the highest observed rate of all the bimetallic combinations screened. Further studies were then performed, and the metal loading, temperature, pressure, and substrate to metal ratios were varied to determine the effects of these variables on the activity of the RhPt/Al(2)O(3) catalyst and a CS(2) poisoning study was performed on this catalyst to determine the number of active sites. From the temperature studies, the activation energy was calculated to be 30.4 kJ/mol, which is moderate when compared to other arene hydrogenation catalysts (42.0 kJ/mol for the hydrogenation of toluene with Ru NPs, (1) and 34.7 and 45.6 kJ/mol for benzene hydrogenation with cuboctahedral and cubic Pt NPs, respectively, (2) have been reported). Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) surface area measurements were used to characterize the active catalysts, where it was observed that very small zero oxidation state metal NPs were well dispersed throughout the high-surface area alumina support.

Continuous catalytic hydrodechlorination of polychlorinated biphenyls (PCBs) in transformer oil

Continuous catalytic hydrodechlorination of polychlorinated biphenyls (PCBs) in the presence of transformer oils was carried out in a fixed bed reactor using a 57.6 wt% Ni on silicon oxide-aluminum oxide (SiO(2)-Al(2)O(3)) catalyst. Reaction temperatures ranging 150-300 degrees C, PCBs concentrations ranging 50-200 ppm, and reaction times ranging 1-8 h were tested. At a higher reaction temperature or at a lower PCBs concentration, catalytic activity was higher and complete dechlorination of PCBs resulted even at long reaction time. Catalyst regeneration using hexane and 0.1 M sodium hydroxide (NaOH) was effective to restore the catalytic activity. Fresh, spent and regenerated catalysts were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. XRD analysis revealed growth of Ni crystallite size of the spent and the regenerated catalysts. XPS analysis showed that a considerable amount of chlorine and carbon species were deposited on the surface of the spent catalyst, which may play a role in the catalysts deactivation.

Recycling of transformer oil contaminated by polychlorinated biphenyls (PCBs) using catalytic hydrodechlorination

Catalytic hydrodechlorination of polychlorinated biphenyls (PCBs) in the presence of transformer oil was carried out in a batch mode to detoxify PCBs and to recycle the treated oil. Various metal supported catalysts, including 0.98 wt% Pt, 0.79 wt% Pd and 12.8 wt% Ni on gamma -alumina (gamma -Al(2)O(3)) support, and 57.6 wt% Ni on silicon oxide-aluminum oxide (SiO(2)-Al(2)O(3)) support were used for the hydrodechlorination. Metal particle size of the Pt catalyst was 2.0 nm and metal particle sizes of the Pd and Ni catalysts were in the range of 6.4-6.9 nm. Various supercritical fluids, supercritical carbon dioxide (scCO(2)), supercritical propane (scPropane), supercritical dimethyl ether (scDME) and supercritical isobutane (scIsobutane) were used as reaction media. PCBs conversion, dechlorination degree of PCBs, was measured using gas chromatograph (GC) with an electron capture detector (ECD). The hydrodechorination degree increased in the order Ni > Pd > Pt, possibly due to higher metal loading and larger metal size of the Ni catalysts. At temperatures below 175 degrees C, scCO(2) was effective as the reaction media for the catalytic hydrodechlorination of PCBs in the presence of the transformer oil. However, PCBs conversion decreased significantly when the hydrodechlorination was carried out in a homogeneous phase with using scPropane, scDME or scIsobutane as a reaction medium. This was attributed to dilution effect of the supercritical fluids. Molecular weights of the transformer oils before and after the catalytic hydrodechlorination were analyzed using high-performance size exclusion chromatography (HPSEC). The molecular weight of the treated oil with 100 % PCBs conversion did not change after the catalytic hydrodechlorination at 200 degrees C. This process has proven to be effective to detoxify PCBs containing transformer oil and to recycle the treated oil.