Continuous Catalytic Hydrogenation of Polyaromatic Hydrocarbon Compounds in Hydrogen−Supercritical Carbon Dioxide

Abstract

A continuous hydrogenation device was evaluated for the detoxification of selected tri-, tetra-, or pentacyclic polyaromatic hydrocarbon (PAH) compounds {anthracene, phenanthrene, chrysene, and benzo[a]pyrene (B[a]P)} by hydrogenation. A substrate stream in hexane, 0.05-1.0% (w/v), was mixed with hydrogen-carbon dioxide (H2-CO2, 5-30% v/v) and delivered to a heated reactor column (25 cm x 1 cm) containing palladium supported on gamma alumina (Pd0/gamma-Al2O3) that was terminated with a capillary restrictor. The flow rate from the reactor, approximately 800 mL min(-1) decompressed gas, corresponded to 4 mL min(-1) fluid under the operating conditions of the trials. Reaction products were recovered by passing the reactor effluent through hexane. At 90 degrees C, the anthracene or phenanthrene substrate was hydrogenated only partially to octahydro and dodecahydro species and contained only a minor quantity of totally hydrogenated products. For substrates with increasing numbers of fused aromatic rings, the hydrogenation efficiency was decreased further. However, at an increasing temperature (90-150 degrees C) and increasing mobile phase flow rate (20.68 MPa corresponding to 2100 mL min(-1) decompressed gas), B[a]P and chrysene were hydrogenated, virtuallytotally, to their corresponding perhydro analogues (eicosahydrobenzo[a]pyrenes and octadecahydrochrysenes), respectively. That this approach might be useful for decontaminating soil extracts was supported by companion in vitro trials in which the substrate and products were assayed for mutagenic activity with five bacterial strains that are auxotrophic for histidine (Salmonella typhimurium TA98, TA100, TA1535, and TA1537) or tryptophan (Escherichia coliWP2 uvrA), using the bacterial reverse mutation assay (modified Ames test). Generally, substantial increases in revertant colony counts were not observed with any of the strains following exposure to the hydrogenation products in the absence or presence of the 10 or 30% S9 mix, which is consistent with the loss of mutagenic activity from these hydrogenation products.

Heterogeneous Catalytic Hydrogenation Reactions in Continuous‐Flow Reactors

“…[167] "Real-time" switching to any of the products can be achieved rapidly by simply changing the reactor conditions. While Marshall and co-workers [168] used scCO 2 for the continuous catalytic hydrogenation of polyaromatic compounds, the Recasens group applied supercritical dimethyl ether as reaction solvent for the partial hydrogenation of sunflower oil. [169] Similarly, the Tacke [170] and Härrçd groups [171] reported on the supercritical hydrogenations of fats, relevant to the food industry.…”

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

“…Triple dosage (90 mg of Mg powder + 180 μL glacial acetic acid) did not show any improvement of PAH degradation (Figures 6 and 7; Table 4). The reduction of PAHs using activated Mg and anhydrous ethanol is selective because only anthracene (9) and fluoranthene (14) in the coal tar were reduced with high removal %. The main products from anthracene and fluoranthene are 9,10-dihydroanthracene and 2,3-dihydrofluoranthene, respectively.…”

“…Catalytic reduction is one of the methods used for PAHs degradation. , For example, transition metals (e.g., rhodium, ruthenium, palladium, etc.) have been successfully used as catalysts in degrading PAHs through hydrogenation, − but the procedure requires high temperature and pressure of hydrogen to obtain relatively small nontoxic products.…”

Catalytic hydrogenation of polyaromatic hydrocarbon (PAH) compounds in supercritical carbon dioxide over supported palladium

“…Moreover, partially hydrogenated products, 14H-B[a]P or 12H-Cry, that retained one benzene ring intact, were also without perceptible mutagenic activity in the Ames bacterial reverse mutation assay. 19 The regioselectivity of partial hydrogenations over a carbon-supported Pd vs. Pt catalyst coupled with the deep hydrogenation activities of noble metal catalysts suggested that this initial survey be restricted to a comparison of the hydrogenation activities of supported Pd catalysts.…”

“…To address the toxicity of the mobilized PAH contaminants in the washing solution and to recycle the surfactant, 18 a backextraction into hexane was optimized to transfer lipophilic toxicants from the aqueous surfactant soil wash to an organic carrier (hexane) that was subsequently detoxified at line by continuous catalytic de-aromatization (hydrogenation). 19 Hydrogenation over transition metal catalyst(s) to reduce PAHs has been broadly investigated by several researchers. [20][21][22][23][24] Frequently, these hydrogenation reactions have been carried out under elevated temperature and high H 2 pressure.…”