Sukh Sidhu

The homogeneous, gas-phase formation of chlorinated and brominated dibenzo-p-dioxin from 2,4,6-trichloro- and 2,4,6-tribromophenols☆

Abstract The homogeneous, gas-phase formation of polychlorinated dibenzo-p-dioxins (PCDD) and polybrominated dibenzo-p-dioxins (PBDD) has been observed from the high-temperature thermal decomposition of 2,4,6-trichlorophenol (2,4,6-TCP) and 2,4,6-tribromophenol (2,4,6-TBP), respectively. Experiments were conducted in a 1.0-cm-i.d. flow reactor over a temperature range of 300°–800°C with reactant concentrations of ∼ 3.0 × 10−7 mol/L in a reaction atmosphere of dry air. The 1,3,6,8- and 1,3,7,9-tetra chlorinated isomers were the dominant PCDDs observed from the thermal oxidation of 2,4,6-TCP with maximum yields of 0.05% each. The corresponding tetrabrominated isomers were observed from the thermal oxidation of 2,4,6-TBP; however, the maximum yields were approximately 500 times higher. The observed PCDD/PBDD yields and the temperature of their formation can be readily accounted for using a modified form of the original gas-phase formation model of Shaub and Tsang, if the activation energy for the formation of diphenyl ether by displacement of Cl Br from halophenol by phenoxy is decreased from 26 to 19.5 and 8.8 kcal/mol, for the chlorinated and brominated systems, respectively. This suggests that gas-phase formation reactions make a significant contribution to observed dioxin and furan yields in full-scale incinerator.

Fast pyrolysis of microalgae remnants in a fluidized bed reactor for bio-oil and biochar production

In this study, pyrolysis of microalgal remnants was investigated for recovery of energy and nutrients. Chlorella vulgaris biomass was first solvent-extracted for lipid recovery then the remnants were used as the feedstock for fast pyrolysis experiments using a fluidized bed reactor at 500 °C. Yields of bio-oil, biochar, and gas were 53, 31, and 10 wt.%, respectively. Bio-oil from C. vulgaris remnants was a complex mixture of aromatics and straight-chain hydrocarbons, amides, amines, carboxylic acids, phenols, and other compounds with molecular weights ranging from 70 to 1200 Da. Structure and surface topography of the biochar were analyzed. The high inorganic content (potassium, phosphorous, and nitrogen) of the biochar suggests it may be suitable to provide nutrients for crop production. The bio-oil and biochar represented 57% and 36% of the energy content of the microalgae remnant feedstock, respectively.

Semi-volatile and particulate emissions from the combustion of alternative diesel fuels

Motor vehicle emissions are a major anthropogenic source of air pollution and contribute to the deterioration of urban air quality. In this paper, we report results of a laboratory investigation of particle formation from four different alternative diesel fuels, namely, compressed natural gas (CNG), dimethyl ether (DME), biodiesel, and diesel, under fuel-rich conditions in the temperature range of 800-1200 degrees C at pressures of approximately 24 atm. A single pulse shock tube was used to simulate compression ignition (CI) combustion conditions. Gaseous fuels (CNG and DME) were exposed premixed in air while liquid fuels (diesel and biodiesel) were injected using a high-pressure liquid injector. The results of surface analysis using a scanning electron microscope showed that the particles formed from combustion of all four of the above-mentioned fuels had a mean diameter less than 0.1 microm. From results of gravimetric analysis and fuel injection size it was found that under the test conditions described above the relative particulate yields from CNG, DME, biodiesel, and diesel were 0.30%. 0.026%, 0.52%, and 0.51%, respectively. Chemical analysis of particles showed that DME combustion particles had the highest soluble organic fraction (SOF) at 71%, followed by biodiesel (66%), CNG (38%) and diesel (20%). This illustrates that in case of both gaseous and liquid fuels, oxygenated fuels have a higher SOF than non-oxygenated fuels.

Hazardous air pollutants formation from reactions of raw meal organics in cement kilns

Thermally induced chlorination, condensation, and formation reactions of raw meal organic surrogates were investigated on different types of surfaces. The System for Thermal Diagnostic Studies provided a powerful tool to study these reactions under defined reaction conditions, which were related to typical conditions in the preheater zone of cement kiln. Experiments were conducted with benzene and benzene/myristic acid (C6H6/C13H27COOH) mixtures in a quartz reactor containing different chlorinating catalysts/reagents over a temperature range of 300-500 degrees C. Reaction products were trapped in-line and analyzed by GC-MS. A mixture of chlorides of calcium, potassium, aluminium and iron was highly effective for chlorination/condensation reactions of benzene and benzene/myristic acid mix at temperatures above 300 degrees C. The same behavior was observed only when calcium chloride and potassium chloride were used as chlorinating catalyst/reagent. This result showed that transition metal chlorides like FeCl3 are not necessary for chlorination/condensation of organics under post-combustion conditions. Methylene chloride was the major chlorinated product followed by chloroform and various other C1, C2 and C6 chlorinated products. Yields of chlorinated aliphatics were highest at 400 degrees C for both benzene and benzene/myristic acid mix. C6 products were mainly mono- to hexa-chlorinated benzenes with trace amounts of chlorinated phenols. The major chlorinated products observed in this study (i.e., methylene chloride, chloroform, chloroethanes and monochlorobenzene) were also present as major chlorinated hydrocarbons in the cement kiln field emission data.

Evidence for a unified pathway of dioxin formation from aliphatic hydrocarbons

Acetylene is readily converted to perchlorinated gas-phase intermediates including hexachlorobenzene, hexachlorobutadiene, and tetrachloroethylene and heavier perchlorinated species via heterogeneous gas-solid reactions with HCl and cupric oxide on borosilicate under postcombustion conditions. Experiments were conducted using an integrated gas-solid flow-reactor and analytical system at temperatures ranging from 150 to 500°C for gas-phase residence times of 2.0 s and total reaction times of 60 min. Chlorine addition and chlorine net substitution mechanisms mediated by the conversion of Cu(II)Cl2 to Cu(I)Cl are proposed to account for the observed or inferred C2 reaction products including tetrachloroethylene, trichloroethylene, and dichloroacetylene. The formation of condensation products including tetrachlorovinylacetylene, hexachlorobutadiene, and hexachlorobenzene are proposed to be catalyzed by copper chloride species and involve the following steps: (1) chemisorption of a chlorinated ethylene or acetylene by HCl elimination or 1,2-Cu−Cl addition, respectively: (2) physisorption of additional chlorimated ethylenes or acetylenes followed by cis-insertions: and (3) carbon-to-copper chlorine transfer followed by desorption of the molecular growth product. The mechanism accounts for product isomer distributions and branching desorption of the higher molecular weight products, and regeneration of the copper chloride catalyst.

Formation and inhibition of chloroaromatic micropollutants formed in incineration processes

The formation pathways for chlorinated aliphatic and chlorinated aromatic compounds in technical incineration processes are reviewed. It is shown that acetylene is converted to chloroaromatic compounds including PCDD/F in a special flow reactor by catalytic activity of CuCl2 in the temperature regime of a post-combustion zone of technical incinerators. Mechanistic pathways begin with chlorination of acetylene. Dichloroacetylene is further condensed to C-4 and C-6 units. Hexachlorobenzene is the dominant aromatic compound and a likely precursor to chlorinated phenols and PCDD/F. Two specific mechanisms of formation of chlorinated aromatic compounds including PCDD/F have been advanced. Both mechanisms begin with the formation of dichloroacetylene from flame pyrolysis products like acetylene. Condensation of dichloroacetylene is mediated by copper species via metallacyclic intermediates and/or a catalytic cycle involving copper stabilized trichlorovinyl radicals. The final pathways of conversion of chlorinated benzenes to PCDD/F via chlorophenols are under active investigation.

Copper-catalyzed chlorination and condensation of acetylene and dichloroacetylene

The chlorination and condensation of acetylene at low temperatures is demonstrated using copper chlorides as chlorinated agents coated to model borosilicate surfaces. Experiments with and without both a chlorine source and borosilicate surfaces indicate the absence of gas-phase and gas-surface reactions. Chlorination and condensation occur only in the presence of the copper catalyst. C2 through C8 organic products were observed in the effluent; PCDD/F were only observed from extraction of the borosilicate surfaces. A global reaction model is proposed that is consistent with the observed product distributions. Similar experiments with dichloroacetylene indicate greater reactivity in the absence of the copper catalyst. Reaction is observed in the gas-phase and in the presence of borosilicate surfaces at low temperatures. The formation of hexachlorobenzene is only observed in the presence of a copper catalyst. PCDD/F were only observed from extraction of the borosilicate surfaces. A global reaction model is proposed for the formation of hexachlorobenzene from dichloroacetylene.

A dye binding method for measurement of total protein in microalgae.

Protein is a large component of the standing biomass of algae. The total protein content of algae is difficult to measure because of the problems encountered in extracting all of the protein from the cells. Here we modified an existing protein assay to measure total protein in microalgae cells that involves little or no extraction of protein from the cells. Aliquots of fresh or pretreated cells were spotted onto filter paper strips. After drying, the strips were stained in a 0.1% (w/v) solution of the protein stain Coomassie Brilliant Blue R-250 for 16 to 24 h and then destained. The stained protein spots were cut out from the paper, and dye was eluted in 1% (w/v) sodium dodecyl sulfate (SDS). Absorbance at 600 nm was directly proportional to protein concentration. Cells that were recalcitrant to taking up the dye could be either heated at 80°C for 10 min in 1% SDS or briefly sonicated for 3 min to facilitate penetration of the dye into the cells. Total protein measured in Chlorella vulgaris using this method compared closely with that measured using the total N method. Total protein concentrations were measured successfully in 12 algal species using this dye binding method.

Fuel Additive Effects on Soot across a Suite of Laboratory Devices, Part 1: Ethanol

The impact of a variety of non-metallic fuel additives on soot was investigated in a collaborative university, industry and government effort. The main objective of this program was to obtain fundamental understanding of the mechanisms through which blending compounds into a fuel affects soot emissions. The research team used a suite of laboratory devices that included a shock tube, a well-stirred reactor, a premixed flat flame, an opposed-jet diffusion flame, and a high pressure turbulent reactor. The work reported here focuses on the effects of ethanol addition to ethylene on soot. The addition of ethanol led to substantial reductions in soot in all of the devices except for the opposed-jet diffusion flame. Modeling of the premixed flame and opposed-jet diffusion flame was used to obtain insights into the mechanism behind the opposing effects of ethanol addition in these two flames.

FUEL ADDITIVE EFFECTS ON SOOT ACROSS A SUITE OF LABORATORY DEVICES, PART 2: NITROALKANES

This is the second in a series of papers to summarize results of the impact of nonmetallic fuel additives on soot. The research was conducted by a university, industry, and government team with the primary objective of obtaining fundamental understanding of the mechanisms through which additive compounds blended into a fuel affect soot emissions. The work involved coordinated testing across a suite of laboratory devices: a shock tube, a well-stirred reactor, a premixed flat flame, an opposed-jet diffusion flame, and a high-pressure turbulent reactor. This article summarizes results on the addition of nitroalkanes to a base fuel consisting of n-heptane and toluene as a simple surrogate for jet fuels. In these experiments, the nitroalkanes serve as chemical probes of key reactions leading to soot. The effects of nitroalkane addition on soot were found to be device and condition dependent with no simple trends across the suite of devices.