Toluene Nitration Process Research Articles

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.

Statistical optimization of removal of nitro-body compounds from spent acid of toluene nitration process

Statistical optimization of removal of nitro-body compounds from spent acid of toluene nitration process

Mineralization of dinitrotoluenes in industrial wastewater by electro-activated persulfate oxidation

Abstract Decomposition of dinitrotoluenes (DNTs) in wastewater was conducted using electrolysis coupled with persulfate oxidation, wherein a synergistic effect was found. Experiments under batch-wise mode were performed to investigate the influence of various operation variables on the electrolytic behavior, such as electrode potential, electrolytic temperature, nitrogen/oxygen dosage, acidity of wastewater and persulfate anion concentration. It is remarkable that the dinitrotoluene pollutants could be nearly completely eliminated by means of electro-activated persulfate oxidation, in which sulfate radicals offer as principal oxidizing agents, of which amounts are significantly enhanced via injection of nitrogen gas. Additionally, electrogenerated hydrogen peroxide derived from cathodic reduction of oxygen, furnished mainly by anodic oxidation of water, would make minor contribution for elimination of DNTs. It is believed that the electro-activated persulfate process is potentially applied to deal with wastewater from toluene nitration processes.

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.

Recovery of high purity sulfuric acid from the waste acid in toluene nitration process by rectification

Waste sulfuric acid is a byproduct generated from numerous industrial chemical processes. It is essential to remove the impurities and recover the sulfuric acid from the waste acid. In this study the rectification method was introduced to recover high purity sulfuric acid from the waste acid generated in toluene nitration process by using rectification column. The waste acid quality before and after rectification were evaluated using UV–Vis spectroscopy, GC/MS, HPLC and other physical and chemical analysis. It was shown that five nitro aromatic compounds in the waste acid were substantially removed and high purity sulfuric acid was also recovered in the rectification process at the same time. The COD was removed by 94% and the chrominance was reduced from 1000° to 1°. The recovered sulfuric acid with the concentration reaching 98.2wt% had a comparable quality with commercial sulfuric acid and could be recycled back into the toluene nitration process, which could avoid waste of resources and reduce the environmental impact and pollution.

Identification of semi-parametric hybrid process models

Hybrid models are mathematical models that comprise both mechanistic and black-box or data-driven components. Typically, the parameters in the mechanistic part of a hybrid model (if any) are assumed to be known. However in this research, a two-level approach is proposed for the identification of hybrid models where some parameters in the mechanistic part of the model are unknown. At the first level, the black-box component is identified using a regularization method with given values for the regularization and mechanistic parameters. At the second level, the regularization and mechanistic parameters are determined simultaneously and optimized according to a specific criterion placed on the predictive performance of the hybrid model. This approach is tested through the modelling of a toluene nitration process, where a support vector machine (SVM) model is used to represent the chemical kinetics, with the mass transfer-related mechanistic parameters being estimated simultaneously. The case study shows that good results can be obtained in terms of both the prediction of the process variables of interest and the estimates of the mechanistic parameters, when the measurement error in the training data is small whilst when the magnitude of the measurement error increases, the accuracy of the estimates of the mechanistic parameters decreases. However, the predictive performance of the resulting hybrid model in the latter case is still acceptable, and can be much better than that attained from the application of a pure black-box model under certain extrapolation conditions.

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.

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.

Determination of Operating Regimes for Chemical Reactors Using Incomplete Mechanistic Knowledge and a Mutual Information-Based Dependency Test

A chemical process that involves the interplay between chemical reaction(s) and transport phenomena may be operated in one of several possible operating regimes. In the development of such a process, the operating regime which yields desirable performance at a smaller scale should be identified to help realize successful scale-up of the process. In the past, experimental procedures for identifying operating regimes have been proposed, which utilize the qualitative trends of the response of a process to changes in operating conditions. In this study, an alternative approach which utilizes both experimental data and mathematical modeling is explored. The rationale behind this approach is that an incorrect assumption with regard to an operating regime may result in a false dependency between particular process variables. On the basis of this hypothesis, operating regime determination can be formulated around a dependency test. In this paper, the computation of a dependency measure is based on the mutual information approach as defined in information theory. The methodology proposed is able to handle the situation where mechanistic knowledge such as chemical reaction kinetics is missing. In practice, this information is often not available during the early stages of process development. The proposed methodology is tested and compared with alternative approaches on a simulated toluene nitration process. Its potential in terms of achieving a reliable discrimination between different assumptions with regard to the operating regime with fewer constraints on the experimental requirements is demonstrated.

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 2SO 4, K 2SO 4 and MgSO 4, 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 2SO 4 > K 2SO 4 > MgSO 4 > 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/O 3 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 12 min 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/H 2O 2 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 H 2O 2 dosage. It is remarkable that organic compounds were completely mineralized by Fenton oxidation, of which removal efficiency is superior to that of UV/H 2O 2. 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.

Recovery of dinitrotoluenes and trinitrotoluene from spent acid of toluene nitration process by solvent extraction

Extraction using hexane or heptane solvent was employed to recover dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) from spent acid after toluene nitration process. Multiple stages experiments were conducted to elucidate the influence of various operating variables on the performance of removal of organic compounds from spent acid, including extracting temperature, volume ratio of solvent versus acid, spent sulfuric acid concentration and organic compounds content of the feedstock. It was found that organic compounds extracted reached nearly 78%, of which solubility in spent acid depends strongly upon the sulfuric acid concentration. In both cases of hexane and heptane, the extracting priority of organic compounds is in the following order: 2,3-DNT > 2,6-DNT > 3,4-DNT > 2,4-DNT > 2,4,6-TNT. Furthermore, this method established is promising for regeneration of spent acid preliminarily.

Recovery of high purity 2,4-dinitrotoluene from spent mixed acid in toluene nitration process

Two easy practical methods for recovery of high purity 2,4-dinitrotoluene (DNT) from spent mixed acid in toluene nitration process are established. One is the dilution manner which produces high purity crystal of 2,4-DNT (>99 wt.%) by addition of proper amounts of deionized water into the spent mixed acid. The other is a refrigeration method which also evaluates high purity crystal of 2,4-DNT (>98 wt.%) by means of simply cooling down spent mixed acid below 283 K. According to the analysis of gas chromatograph–mass spectrometer (GC–MS), the ingredients of crystals were identified. Further, the influence of dilution procedure, refrigeration treatment, and adjustment of pH value on the performance of abatement of total organic compounds (TOC) were elucidated in this research. It was found that the organic compounds dissolving in aqueous spent mixed acid are in equilibrium with the organic phase of dinitrotoluene isomers. Besides, the solubility of each organic component in spent acid depends upon the concentration of spent sulfuric acid.

An infrared study on the MoO 3/SiO 2 catalytic system employed in toluene nitration

The 15% MoO 3/SiO 2 catalyst obtained by calcination of the (NH 4) 6Mo 7O 24·4H 2O/SiO 2 system at various temperatures, as well as upon its use in the reaction of toluene nitration using 65 or 100% HNO 3, was studied by IR spectroscopy. The calcination process conducted at 240, 300, or 550 °C proceeds first through the formation of the Keggin structures, silicomolybdic acid, then, of molybdenum trioxide. All the molybdenum phases on the silica support obtained were found to be active in the toluene nitration process.

An Experimental Study of Worst Case Scenarios of Nitric Acid Decomposition in a Toluene Nitration Process

Several worst case scenarios were carried out for safety evaluation of an existing nitration process. Heterogeneous nitric acid decomposition is observed to be the worst credible scenario in the toluene nitration process. Fire or explosion may subsequently develop due to temperature or pressure runaway from the undesired reaction. Gassy nitric acid decomposition can easily be triggered by process derivation from the desired reaction. In this study, a heat-flux calorimeter (C80–II) and an adiabatic calorimeter (VSP2) were used to measure the thermokinetics and determine the runaway characteristics for assessing worst credible scenarios. The heat of reaction of toluene mononitration is measured to be 190.9±6 3.6/(kJ mol −1 ). The calculated Arrhenius parameters are Ea (kJ mol −1 ) = 30.9±2.1 and A (mol −1.5 l 1.5 s −1 ) = (1.38 ± 0.07) × 10 −2 . The ‘worst case’ scenarios were chosen at the following conditions: loss of cooling, stirrer failure, batch-wise charging, and decomposition of reactants. The experimentally determined worst case was found to be a combination of a loss of cooling with batch-wise charging coupled with decomposition of nitric acid with full mixing. Adiabatic temperature rise, self-heat rate, final pressure and non-condensable gas quantity in the VSP2 experiment were used to assess thermal explosion in a nitration reactor. Unstable and critical onset temperature to runaway is determined as about 140°C for the process in this study.