Ultrasound-Assisted Mineralization of 2,4-Dinitrotoluene in Industrial Wastewater Using Persulfate Coupled with Semiconductors.

Oxidative degradation of 2,4-dinitrotoluenes in aqueous solution was executed using persulfate combined with semiconductors motivated by ultrasound (probe type, 20 kHz). Batch-mode experiments were performed to elucidate the effects of diverse operation variables on the sono-catalytic performance, including the ultrasonic power intensity, dosage of persulfate anions, and semiconductors. Owing to pronounced scavenging behaviors caused by benzene, ethanol, and methanol, the chief oxidants were presumed to be sulfate radicals which originated from persulfate anions, motivated via either the ultrasound or sono-catalysis of semiconductors. With regard to semiconductors, the increment of 2,4-dinitrotoluene removal efficiency was inversely proportional to the band gap energy of semiconductors. Based on the outcomes indicated in a gas chromatograph-mass spectrometer, it was sensibly postulated that the preliminary step for 2,4-dinitrotoluene removal was denitrated into o-mononitrotoluene or p-mononitrotoluene, followed by decarboxylation to nitrobenzene. Subsequently, nitrobenzene was decomposed to hydroxycyclohexadienyl radicals and converted into 2-nitrophenol, 3-nitrophenol, and 4-nitrophenol individually. Nitrophenol compounds with the cleavage of nitro groups synthesized phenol, which was sequentially transformed into hydroquinone and p-benzoquinone.

Ultrasound-assisted desalination of crude oil: The influence of mixing extent, crude oil species, chemical demulsifier and operation variables.

Coalescence of water droplets in crude oil has been effectively promoted by chemical demulsifiers integrated with ultrasound. Temporary images of water droplets in W/O emulsions were directly monitored using a metallurgical microscope. Water droplets achieved expansion of 118% at 40 min ultrasonic irradiation time under well mixing conditions. However, water droplets in heavy crude oil undergo less aggregation than those in light crude oil, due to resistance of mobility in highly viscous fluid. In the absence of chemical demulsifiers, water droplets enveloped by native surfactants appeared to aggregate arduously because of occurrence of interfacial tension gradients. Influential significance analyses have been executed by a factorial design method on operation variables, including acoustic power intensity, operation temperature, ultrasonic irradiation time and chemical demulsifier dosages. In this work, the outcomes indicate that the optimal operating conditions for desalination of crude oil assisted by ultrasound were as follows: acoustic power intensity = 300 W, operation temperature = 90℃, ultrasonic irradiation time = 75 min and chemical demulsifier dosages = 54 mg/L. Besides, it was found that the most influential importance of operation parameter was temperature, followed with acoustic power intensity, ultrasonic irradiation time and chemical demulsifier dosages.

Photocatalytic degradation of nitrobenzene in wastewater by persulfate integrated with Ag/Pb3O4 semiconductor under visible light irradiation.

Nitrobenzene oxidation was executed utilizing an innovative method, in which Ag/Pb3O4 semiconductors irradiated by visible light were used for activation of persulfate into sulfate radicals. Batch mode experiments were accomplished to elucidate the effect of persulfate concentrations and Ag/Pb3O4 dosages on the nitrobenzene oxidation behaviors. The physicochemical properties of original and reacted Ag/Pb3O4 were illustrated by X-ray diffraction analyses, UV-Vis diffuse reflectance spectra, FE-SEM images, EDS analyses, photoluminescence spectra and X-ray photoelectron spectra, respectively. The main oxidant was hypothesized to be sulfate radicals, induced from persulfate caused by photocatalysis of Ag/Pb3O4. It was clearly reflected on the scavenging experiments with addition of benzene, ethanol and methanol individually. As far as degradation pathways concerned, nitrobenzene was essentially transformed into hydroxycyclohexadienyl radicals, and sequentially converted to 2-nitrophenol, 3-nitrophenol or 4-nitrophenol simultaneously. Denitration of nitrophenols gave rise to synthesis of phenol, followed with generation of hydroquinone and p-benzoquinone.

Mineralization of aniline in aqueous solution by sono-activated peroxydisulfate enhanced with PbO semiconductor.

Oxidative degradation of aniline in aqueous solution was performed by the sono-activated peroxydisulfate coupled with PbO process, wherein a dramatic synergistic effect was found. Experiments were carried out in the batch-wise mode to investigate the influence of various operation parameters on the sonocatalytic behavior, such as ultrasonic power intensity, peroxydisulfate anion concentrations and PbO dosages. According to the scavenging effect of ethanol, methanol and tert-butyl alcohol, the principal oxidizing agents were presumed to be sulfate radicals descended from peroxydisulfate anions, activated via ultrasound or sonocatalysis of PbO. Based on the results attained from gas chromatograph-mass spectrometer, it was hypothesized that aniline was initially oxidized into iminobenzene radicals, followed with formation of nitrosobenzene, p-benzoquinonimine and nitrobenzene respectively. Condensation of nitrosobenzene with aniline generated azobenzene. Phenol was detected as one of degradation intermediates, which was sequentially converted into hydroquinone and p-benzoquinone.

Mineralization of dinitrotoluenes in aqueous solution by sono-activated persulfate enhanced with electrolytes.

Oxidative degradation of dinitrotoluenes (DNTs) in industrial wastewater was conducted by sono-activated persulfate process assisted with electrolytes. Experiments were carried out to elucidate the influence of various operating parameters on the sonolytic behavior, such as species and concentrations of electrolytes, ultrasonic power intensity, reaction temperature, dosage of oxygen and persulfate anions. The outcomes indicate that sulfate radicals serve as main oxidants in the sono-activated persulfate process, wherein MgSO4 electrolyte obviously inhibits microbubble coalescence, leading to enhancement of cavitation strength and DNTs removal percentage. On addition of electrolytes, the increment of DNTs removal percentages was proportional to ionic strength of electrolytes. According to the results obtained from gas chromatograph-mass spectrometer (GC-MS), it is postulated that DNTs initially undergo denitration pathway with cleavage of nitro group into o-mononitrotoluene (MNT) or oxidation of methyl group followed with decarboxylation procedure into 1,3-dinitrobenzene (DNB), respectively. Due to electrolytes observed commonly in wastewater, the sono-activated persulfate process coupled with electrolytes is potentially applied to dispose wastewater effluent from toluene nitration processes.

Mineralization of aniline in aqueous solution by electrochemical activation of persulfate.

Oxidative degradation of aniline in aqueous solution was carried out by coupling electrolysis with persulfate oxidation, in which a synergistic effect occurred. Experiments were performed under a batch-wise mode to evaluate the influence of various operation parameters on the electrolytic behavior, such as acidity of aqueous solution, temperature, electrode potential, persulfate anion concentration and nitrogen/oxygen gas dosage. The aniline pollutants could be almost entirely mineralized by means of electro-activated persulfate oxidation, wherein sulfate radicals were presumed to be principal oxidizing agents. Besides, electrogenerated hydrogen peroxide originated from cathodic reduction of oxygen, supplied chiefly by anodic oxidation of water, would contribute partially for decomposition of aniline. On the whole, the electro-activated persulfate process is a very promising method for treatment of aniline in wastewater.

Decomposition of nitrotoluenes in wastewater by sonoelectrochemical and sonoelectro-Fenton oxidation.

Oxidative degradation of dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using electrochemical and electro-Fenton processes respectively, combined with ultrasonic irradiation, wherein a synergistic effect is observed. Experiments were carried out to elucidate the influence of various operating variables on the sonoelectrolytic behavior, such as electrode potential, sonoelectrolytic temperature, acidity of wastewater, oxygen dosage, and dosage of ferrous ions. It deserves to note that the nitrotoluene contaminants could be completely decomposed by sonoelectro-Fenton method, wherein hydrogen peroxide was in situ generated from cathodic reduction of oxygen, supplied partially by anodic oxidation of water. During the sonoelectrolytic process, in spite of existence of degassing phenomenon, the high yield of hydrogen peroxide was produced due to the significantly enhanced mass transfer rate of oxygen toward the cathode, caused by ultrasonic irradiation. Because higher removal efficiency of DNTs and TNT obtained at ambient conditions, it is believed that the sonoelectrolytic method is potentially applied to dispose wastewater from toluene nitration processes.

Removal of dinitrotoluenes in wastewater by sono-activated persulfate.

Oxidative degradation of dinitrotoluenes (DNTs) in wastewater was performed using persulfate anions combined with ultrasonic irradiation, wherein a synergistic effect is observed. The batch-wise experiments were carried out to elucidate the influence of various operating parameters on sono-activated persulfate oxidation, including ultrasonic power intensity, persulfate anion concentration, reaction temperature and acidity of wastewater. It is noteworthy that the nitrotoluene contaminants could be almost completely eliminated by virtue of sono-activated persulfate oxidation, wherein sulfate radicals serve as principal oxidants, of which amounts are significantly enhanced via addition of sodium sulfate. Based on the results given by gas chromatograph-mass spectrometer (GC-MS), it is postulated that the methyl group of DNTs preliminarily underwent oxidation pathway into dinitrobenzoic acid, followed by decarboxylation to form 1,3-dinitrobenzene (DNB). In sum, the sono-activated persulfate oxidation is a promising method for treatment of nitrotoluenes in wastewater.

Removal of dinitrotoluenes and trinitrotoluene from industrial wastewater by ultrasound enhanced with titanium dioxide.

Oxidative degradation of dinitrotoluenes (DNTs) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using ultrasonic irradiation combined with titanium dioxide (TiO(2)). The batch-wise experiments were carried out to elucidate the influence of various operating parameters on the sonolytic behavior, including power intensity, TiO(2) dosage, acidity of wastewater, reaction temperature and oxygen dosage. It is worthy to note that the nitrotoluene contaminants could be almost completely eliminated by sonochemical oxidation enhanced significantly with the addition of TiO(2) due to the supply of adsorbent and/or excess nuclei. High destruction rate of nitrotoluenes could be achieved by increasing the acidity of wastewater and decreasing the reaction temperature. According to the result given by pyrolysis/gas chromatograph-mass spectrometer (Pyrolysis/GC-MS), it is postulated that DNTs adsorbed on TiO(2) preliminarily undergo denitration pathway to o-mononitrotoluene (MNT) or oxidation pathway to 1,3-dinitrobenzene (DNB), respectively. Further, based on the spectra obtained from GC-MS, it is proposed that DNTs dissolved in wastewater proceed with similar reaction pathways as those adsorbed on TiO(2). Besides, oxidative degradation of 2,4,6-TNT results in the formation of 1,3,5-trinitrobenzene (TNB). Apparently, the sonolytic technique established is promising for direct treatment of wastewater from TNT manufacturing process.

Sonochemical decomposition of dinitrotoluenes and trinitrotoluene in wastewater.

Mineralization of dinitrotoluenes (DNT) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted under ultrasonic irradiation. The batch-wise experiments were carried out to elucidate the influence of various operating parameters on the sonolytic behavior, including power intensity, acidity of wastewater, reaction temperature and oxygen dosage. It is remarkable that the nitrotoluenes contained could be almost completely decomposed by the sonochemical oxidation method, wherein the pyrolytic reaction was responsible for the destruction of organic compounds. During the sonication tests, the influence of reaction temperature on the degradation of nitrotoluenes is the most significant, followed by power intensity, acidity of wastewater and oxygen dosage. Based on the spectra obtained from gas chromatograph/mass spectrometer (GC/MS), it is suggested that 2,4,6-TNT is preliminarily denitrated to 2,6-DNT. The denitration of 2,6-DNT and/or 2,4-DNT results in the formation of o-mononitrotoluene, which proceeds with the cleavage of nitro group into toluene, followed by oxidation of methyl group and decarboxylation. In this study, it is believed that the sonolytic technique established is promising for wastewater disposal in toluene nitration processes.

Destruction of nitrotoluenes in wastewater by Electro-Fenton oxidation.

Electrolytic degradation of dinitrotoluenes (DNTs) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted by Electro-Fenton's reagents. The batch-wise experiments were carried out to elucidate the influence of various operating variables on the electrolytic behavior, including electrode potential, oxygen dosage, electrolytic temperature, acidity of wastewater and dosage of ferrous ions. It deserves to note that the nitrotoluenes contained could be completely decomposed by Electro-Fenton's reagents, wherein hydrogen peroxide was in situ generated from cathodic reduction of oxygen, supplied mainly by anodic oxidation of water. During the electrochemical process, the influence of electrolytic temperature on the degradation of nitrotoluenes is the most significant, followed by electrode potential, acidity of wastewater and oxygen dosage. Based on the spectra analyzed by gas chromatograph/mass spectrometer (GC/MS), it is proposed that initial denitration of 2,4-DNT and/or 2,6-DNT gives rise to formation of o-mononitrotoluene, which undergoes the cleavage of nitro group into toluene, followed by oxidation of methyl group to benzoic acid and subsequent decarboxylation. It is believed that the electrolytic method established is potentially applied to dispose wastewater from toluene nitration processes in practice.

Electrochemical destruction of dinitrotoluene isomers and 2,4,6-trinitrotoluene in spent acid from toluene nitration process.

Mineralization of dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) in spent acid was conducted by in situ electrogenerated hydrogen peroxide. The electrolytic experiments were carried out to elucidate the influence of various operating parameters on the performance of mineralization of total organic compounds (TOC) in spent acid, including electrode potential, reaction temperature, oxygen dosage and concentration of sulfuric acid. It is worth noting that organic compounds could be completely mineralized by hydrogen peroxide obtained from cathodic reduction of oxygen, which was mainly supplied by anodic oxidation of water. Based on the spectra identified by gas chromatograph/mass spectrometer (GC/MS), it is proposed that oxidative degradation of 2,4-DNT and/or 2,6-DNT, 2,4,6-TNT results in o-mononitrotoluene (MNT) and 1,3,5-trinitrobenzene, respectively. Due to the removal of TOC and some amount of water, the electrolytic method established is promising for industrial application to regeneration of spent acid from toluene nitration process.

Ultrasound-assisted crystallization of high purity of 2,4-dinitrotoluene from spent acid.

The high purity crystal of 2,4-dinitrotoluene (DNT) could be successfully recovered from spent acid in a short period through diluting method assisted with ultrasonic irradiation. The sonication tests were carried out to elucidate the influence of various ultrasonic powers on the performance of crystallization of 2,4-DNT. It is remarkable that under the supersaturated condition ultrasonic irradiation could significantly accelerate the crystal formation, in which the purity of 2,4-DNT reaches to approximate 98.9 wt%. Based on the particle size distribution of crystals, it is proposed that the enhancement on recovery rate of 2,4-DNT crystals by ultrasound is mainly ascribed to the elevation of mass transfer rate for crystal growth. According to the spectra examined by field emission scanning electron microscope (FESEM), the above hypothesis is further verified by the appearance of smoother surface of crystals. Furthermore, the results of metallurgical microscope measurements show that ultrasound has also an abrasive effect on 2,4-DNT crystals under high ultrasonic power inputs.

Decomposition of nitrotoluenes from trinitrotoluene manufacturing process by Electro-Fenton oxidation.

Oxidative degradation of dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) in spent acid was conducted by Electro-Fenton's reagents. The electrolytic experiments were carried out to elucidate the influence of various operating parameters on the performance of mineralization of total organic compounds (TOC) in spent acid, including reaction temperature, dosage of oxygen, sulfuric acid concentration and dosage of ferrous ions. It deserves to note that organic compounds could be completely destructed by Electro-Fenton's reagent with in situ electrogenerated hydrogen peroxide obtained from cathodic reduction of oxygen, which was mainly supplied by anodic oxidation of water. Based on the spectra analyzed by gas chromatograph/mass spectrometer, it is proposed that initial denitration of 2,4,6-TNT gives rise to formation of 2,4-DNT and/or 2,6-DNT, which undergo the cleavage of nitro group into o-mononitrotoluene, followed by denitration to toluene and subsequent oxidation of the methyl group. Owing to the removal of both TOC and partial amounts of water simultaneously, the electrolytic method established is potentially applied to regenerate spent acid from toluene nitration processes in practice.

Recovery of nitrotoluenes from wastewater by solvent extraction enhanced with salting-out effect.

Toluene extraction enhanced by salting-out effect was employed to recover dinitrotoluene isomers and 2,4,6-trinitrotoluene (2,4,6-TNT) from wastewater of toluene nitration processes (e.g. dinitration or trinitration). The batchwise experiments were conducted to elucidate the influence of various operating variables on the extracting performance, including concentrations and species of inorganic salts, such as NaCl, KCl, Na(2)SO(4), K(2)SO(4) and MgSO4, acidity of wastewater, volume ratios of solvent versus wastewater and extraction stages in existence of inorganic salts. It was found that recovery of total organic compounds (TOC) was significantly elevated with increasing concentrations of salts, whose promoting effects were in the following order: NaCl>Na(2)SO(4)>K(2)SO(4)>MgSO4>KCl on the weight basis of wastewater. Besides, high volume ratio of toluene/wastewater (ca. 2.0) was more suitable for recovery of TOC from wastewater with or without addition of NaCl, of which extractable priority was as follows: 2,6-DNT>2,4-DNT>2,4,6-TNT. It is remarkable that TOC in wastewater would be almost completely recovered by sequential four stages toluene extraction, promoted continuously by salting-out effect.

Decomposition of dinitrotoluene isomers and 2,4,6-trinitrotoluene in spent acid from toluene nitration process by ozonation and photo-ozonation.

Ozone and UV/O3 were employed to mineralize dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) in spent acid from toluene nitration process. The oxidative degradation tests were carried out to elucidate the influence of various operating variables on the performance of mineralization of total organic compounds (TOC) in spent acid, including reaction temperature, intensity of UV (254 nm) irradiation, dosage of ozone and concentration of sulfuric acid. It is remarkable that the nearly complete mineralization of organic compounds can be achieved by ozonation combined with UV irradiation. Nevertheless, the hydroxyl radicals (*OH) would not be generated by either ozone decomposition or photolysis of ozone under the experimental condition of this study. According to the spectra identified by gas chromatograph/mass spectrometer (GC/MS) and further confirmed by gas chromatograph/flame ionization detector (GC/FID), the multiple oxidation pathways of DNT isomers are given, which include o-, m-, p-mononitrotoluene (MNT) and 1,3-dinitrobenzene, respectively. In addition, oxidative degradation of 2,4,6-TNT leads to a 1,3,5-trinitrobenzene intermediate.

Recovery of nitrotoluenes in wastewater by solvent extraction.

Toluene extraction was utilized to recover 2,4-dinitrotoluene (DNT), 2,6-DNT, and 2,4,6-trinitrotoluene (TNT) from wastewater of toluene nitration process. The batch-wise experiments were performed to elucidate the influence of various operating variables on the extracting behavior, including extracting temperature, volume ratios of solvent versus wastewater, agitation time, acidity of wastewater, and extraction stages. It was found that recovery of total organic compounds (TOC) was significantly elevated with increasing extraction temperature. Besides, high volume ratio of toluene/wastewater (2.0) and wastewater acidified to lower pH value enhanced the recovery percentage of TOC, in which extractable tendency was as follows: 2,6-DNT>2,4-DNT>2,4,6-TNT. It is worth noting that the nitrotoluenes in wastewater would be almost completely recovered using three sequential stages toluene extraction at the agitation time of 12min and pH 3.0. It is apparent that this established method is promising for the treatment of wastewater from toluene nitration processed industrially.

Mineralization of dinitrotoluenes and trinitrotoluene of spent acid in toluene nitration process by Fenton oxidation.

Fenton's reagent, UV/H2O2 and UV/Fenton's reagent were employed to mineralize dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) of spent acid in toluene nitration process. The bench-scale experiments were conducted to elucidate the influence of various operating variables on the performance of removal of total organic compounds (TOC) from spent acid, including reaction temperature, concentration of ferrous ion and H2O2 dosage. It is remarkable that organic compounds were completely mineralized by Fenton oxidation, of which removal efficiency is superior to that of UV/H2O2. Nevertheless, it makes slight difference between Fenton oxidation and UV/Fenton oxidation. According to the spectra identified by gas chromatograph/mass spectrometer (GC/MS), it is proposed that oxidative degradation of DNT isomers leads to o-, m-, p-mononitrotoluene (MNT) and 1,3-dinitrobenzene respectively. Besides, the oxidation of 2,4,6-TNT gives the 1,3,5-trinitrobenzene intermediate. Apparently, Fenton oxidation is promising for purification of spent acid industrially.