Conversion Of Aromatic Compounds Research Articles

Simultaneous ammonia and organics degradation from municipal landfill leachate by electrochemical oxidation

ABSTRACT The two primary issues for wide implementation of the electrochemical oxidation of wastewater are the significant cost of electrode and high energy consumption. On the other side, conventional biological processes and membrane technology have several drawbacks for recalcitrant landfill leachate (LL) treatment. To address these issues, graphite/PbO2 anode was used to treat medium to mature age (biodegradability index, 5-day biochemical oxygen demand/chemical oxygen demand: 0.25) LL. To reduce the cost of the oxidation process and maximize the efficiency, operating conditions were optimized. The optimum parameter values were obtained as 24.7 mA cm−2, 180 ± 3 rpm, and 1.9 cm of current density, stirring rate, and electrode gap, respectively. Dissolved organic carbon (DOC), chemical oxygen demand (COD), and ammonia-N removal efficiencies of 55 ± 1.4%, 81 ± 1.9%, and 56 ± 3% were obtained after 8 h of degradation at optimum conditions. The decrease in aromatic substances and ultraviolet (UV) quenching materials were evaluated by UV-Visible spectroscopy and Specific UV absorbance. The conversion of aromatic compounds into simpler molecule compounds was also verified by Fourier-transform infrared spectroscopy analysis. The lab-scale anode synthesis cost was evaluated as 0.42 USD.

Mechanism Insight into the Conversion between H2S and Thiophene during Coal Pyrolysis: A Theoretical Study.

Clean coal technology is the important thrust to the achievement of "carbon neutralization"; clearing the transformation mechanism of thiophene, the dominant organic sulfur species in coal, is conducive to promoting the development of sulfur removal technology. DFT calculations were performed, and 28 reaction paths were proposed in this research, clarifying the decomposition mechanism of thiophene and the fixation mechanism of H2S. Thiophene is pyrolyzed mainly through the hydrogen-transfer reaction, which occurs at above 2000 K rather than 800 K. The hydrogen transfer between the C-C bond rather than the C-S bond causes the ring opening. Hydrogen promotes the decomposition of thiophene, which happens at 800 K, with a molar ratio of hydrogen to thiophene of 5. Therefore, thiophene is decomposed at 800 K mainly through the hydrogenation reaction that occurs at para carbons and the C-S bond, the H2S elimination reaction, and the generation of ethane. Furthermore, H2S can be converted into thiophene through the addition reaction with unsaturated hydrocarbon, or the dehydration reaction with hydroxyl or carboxyl groups. The combination between H2S and the aliphatic compound occurs at 800 K, which is mainly influenced by the species of the functional group rather than the composition and morphology of the carbon chain. Meanwhile, the conversion of aromatic compounds tends to the generation of aryl mercaptan rather than thiophene at around 800 K.

Lignin bioconversion into valuable products: fractionation, depolymerization, aromatic compound conversion, and bioproduct formation

Lignin fractionation and depolymerization generates heterogeneous streams of aromatic compounds and conversion of aromatic compounds into valuable products, but it is not efficient. Many microbes in nature have evolved metabolic pathways to convert complex lignin polymers into aromatic compounds and transform these aromatic compounds into central intermediates for bioproduct synthesis. The objective of this paper is to review the recent process development of lignin bioconversion into aromatic compounds and bioproducts. Lignin structural and molecular changes during fractionation and depolymerization are presented. Subsequent lignin conversion into aromatic compounds by upper pathways and further converted into central metabolites and bioproducts via lower pathways are emphasized. In particular, enzymes and mediator systems to enhance lignin conversion and key intermediates in lignin catabolic pathways are discussed. Strategies to enhance bioproduct formation through lignin valorization are summarized.

Control of the Al Distribution in the Framework of ZSM-5 Zeolite and Its Evaluation by Solid-State NMR Technique and Catalytic Properties

The effects of the organic structure-directing agents (OSDAs) and Na cations for the synthesis of ZSM-5 on the location of Al atom in the framework as well as the acidic and catalytic properties were investigated. To achieve these purposes, ZSM-5 zeolites were synthesized by using four kinds of OSDAs including tetrapropylammonium hydroxide cations, dipropylamine, cyclohexylamine, and hexamethylenimine with or without Na cations. In situ FT-IR spectroscopy using CO as probe molecule was applied to the evaluation of the acid property of the ZSM-5 zeolites. The location of Al atoms was examined by high resolution 27Al MAS and MQMAS NMR techniques. The constraint index (CI) has also been used to estimate the distribution of acid sites in the micropores. The location of acid sites was investigated based on the difference in the transition-state shape-selectivity through the cracking of n-hexane and 3-methylpentane. Furthermore, the cracking of various types of paraffins and the conversion of aromatic compounds were conducted to clarify the acid site distributions.

Thermal Decomposition of Coal-related Aromatic Compounds in Hydrogen-donating Solvent

Abstract In order to elucidate the reaction mechanism of coal dissolution in the hydrogen-donating solvent, twenty aromatic compounds related to coal were treated at 450 °C in the presence of tetralin. Diphenylmethane and bibenzyl slowly decomposed giving alkylbenzenes almost quantitatively. Diphenylmethanol and benzophenone were hydrogenated to diphenylmethane, and benzyl phenyl ketone to a mixture of diphenylmethane and bibenzyl. Diphenyl ether and dibenzofuran are very stable, di-2-naphthyl ether decomposing slowly and benzyl phenyl ether or dibenzyl ether very rapidly. The conversion of aromatic compounds by thermolysis can be correlated as a function of bond dissociation energy. The bond rupture of coal-related polynuclear aromatic compounds at 450 °C was concluded to occur mainly at methylene or ether structures. Addition of phenolic compounds or quinoline is very effective for the decomposition of di-2-naphthyl ether. The effect of phenolic compounds and quinoline on the thermal decomposition of aromatic ether was discussed on the basis of stabilization of transition state due to solvation.