Optimizing support acidity of NiMo catalysts for increasing the yield of benzene, toluene and xylene in tetralin hydrocracking

To enhance the yields of benzene,toluene,and xylene in tetralin hydrocracking,the effect of the support acid properties of NiMo catalysts on hydrocracking performance of tetralin were investigated in this study.NaY zeolites were modified by hydrothermal treatment to form USY zeolites at different temperatures and adjust the type and amount of acid.In addition,H-Beta was loaded into the USY to further adjust the acidic properties of the catalysts.The result shows that when the total B acid content of the catalyst is maintained between 150 and 200μmol·g^(-1),the total acid amount is maintained between 1.7 and 1.9 mmol·g^(-1),and the L/B(L and B acids)ratio is maintained between 1.5 and 2,the catalysts have favorable performances on tetralin hydrocracking.Under this condition,the catalysts have a yield of benzene,toluene,and xylene higher than 30 wt%and a selectivity for benzene,toluene,and xylene higher than 35%.The tetralin conversion is greater than 85 wt%.The AB6 catalyst obtains the best hydrocracking effect with the conversion of tetralin reaching 90.24 wt%,the yields of benzene,toluene,and xylene reaching 33.58 wt%,and the selectivity of benzene,toluene,and xylene reaching 37.21%,respectively.

Bio-removal of mixture of benzene,toluene,ethylbenzene,and xylenes/total petroleum hydrocarbons/trichloroethylene from contaminated water

Four pure cultures were isolated from soil samples potentially contaminated with gasoline compounds either at a construction site near a gas station in Fai Chi Kei,Macao SAR or in the northern parts of China（Beijing,and Hebei and Shandong）.The effects of different concentrations of benzene,toluene,ethylbenzene,and three isomers（ortho-,meta-,and para-） of xylene（BTEX）,total petroleum hydrocarbons（TPH）,and trichloroethylene（TCE）,when they were present in mixtures,on the bio-removal effciencies of microbial isolates were investigated,together with their interactions during the bio-removal process.When the isolates were tested for the BTEX（50-350 mg/L）/TPH（2000 mg/L） mixture,BTEoX in BTEoX/TPH mixture was shown with higher bio-removal effciencies,while BTEmX in BTEmX/TPH mixture was shown with the lowest,regardless of isolates.The TPH in BTEmX/TPH mixture,on the other hand,were generally shown with higher bio-removal effciencies compared to when TPH mixed with BTEoX and BTEpX.When these BTEX mixtures（at 350 mg/L） were present with TCE（5-50 mg/L）,the stimulatory effect of TCE toward BTEoX bio-removal was observed for BTEoX/TCE mixture,while the inhibitory effect of TCE toward BTEmX for BTEmX/TCE mixture.The bio-removal effciency for TPH was shown lower in TPH（2000 mg/L）/TCE（5-50 mg/L） mixtures compared to TPH present alone,implying the inhibitory effect of TCE toward TPH bio-removal.For the mixture of BTEX（417 mg/L）,TPH（2000 mg/L） along with TCE（5- 50 mg/L）,TCE was shown co-metabolically removed more effciently at 15 mg/L,probably utilizing BTEX and/or TPH as primary substrates.

Occupational Health Risk Assessment of Benzene,Toluene,and Xylene in Shanghai

Objective This study was designed to conduct a retrospective and systematic occupational health risk assessment(OHRA)of enterprises that used benzene,toluene,and xylene(BTX)in Shanghai,China.Methods All data for the study were obtained from 1,705 occupational health examination and evaluation reports from 2013 to 2017,and a semiquantitative model following Chinese OHRA guidelines(GBZ/T 298-2017)was applied for the assessment.Results The selected enterprises using BTX were mainly involved in manufacturing of products.Using the exposure level method,health risk levels associated with exposure to BTX were classified as medium,negligible,or low.However,the risk levels associated with benzene and toluene were significantly different according to job types,with gluers and inkers exhibiting greater health risks.For the same job type,the health risk levels assessed using the comprehensive index method were higher than those using the exposure level method.Conclusion Our OHRA reveals that workers who are exposed to BTX still face excessive health risk.Additionally,the risk level varied depending on job categories and exposure to specific chemicals.Therefore,additional control measures recommended by OHRA guidelines are essential to reduce worker exposure levels.

VAPOR-LIQUID EQUILIBRIUM FOR TERNARY MIXTURES OF BENZENE,TOLUENE,AND p-XYLENE

Vapor-liquid equilibrium composition and temperature were measured for binary andternary mixtures of benzene,toluene and p-xylene at 101.33 kPa The equilibrium cell of Boubliketal.was modified for the present study.The experimental vapor-liquid equilibrium data were corre-lated with the Wilson equation.

Adsorption-Desorption of BTX (Benzene, Toluene and O-xylene) on Fe, Fe-Al Pillared Clay

The studies are conducted in laboratory to determine the adsorption-desorption behavior of BTX (benzene, toluene and o-xylene) in gas phase on Fe, Fe-Al pillared clays adsorbents. In experimental conditions of constant atmospheric pressure, initial concentrations with an increasing volume (0.5 - 2 ml) injected benzene (2.25), toluene (1.89) and o-xylene (1.66) μmol/L at T (40℃, 60℃ and 80℃), and the adsorption increases with increase of temperature, indicating that the adsorption process would be a chemical adsorption rather than physical one. The results are shown that the BTX adsorption data fitted very well (R2 > 0.999) to the both equations Langmuire and Elovitch for the three samples: bentonite (B), Fe-bentonite () and Fe-Al/bentonite (). At 80℃, the BTX adsorption capacity increased in the following order: . The maximum adsorption capacity () at 80℃ is 175.13, 171.84 and 171.81 μg/g respectively for benzene, toluene and o-xylene for;the last is a good adsorbent of BTX removal. The benzene diffuses faster than toluene and o-xylene. Thermodynamic parameters, such as ,and are also discussed and the results suggested that the BTX adsorption on all samples used is a spontaneous and endothermic process. Desorption studies show that BTX is very easily desorbed with .

Benzene and Toluene Levels Measured with DOAS During Vehicular Restrictions in Beijing

Measurements of atmospheric benzene and toluene were carried out continuously using dif- ferential optical absorption spectroscopy from August 7 to August 28 in Beijing during the period of vehicular restrictions. The correlations between traffic flows and totals of benzene and toluene were studied during the period of vehicular traffic restrictions from August 17 to August 20 and non-traffic restrictions on August 16 and August 21. The correlation coef- ficient was 0.8 between benzene and toluene. And the calculated daily mean value ratios of benzene to toluene were 0.43-0.50. During the period of vehicular restrictions, traffic flows were reduced about 11.8% and the levels of benzene and toluene were reduced by 11.4% and 12.8%, respectively. The vehicle emissions were recognized as the major sources for atmospheric benzene and toluene in Beijing.

Distribution Coefficient of Caprolactam and Methyl Caprolactam Using Benzene or Toluene as Extractants： Experiments and Prediction

To get high purity caprolactam is a challenging task in the chemical fiber industry. To date, reports on the prediction of the distribution of caprolactam and its derivative chemicals have been few. In this study, the extraction of caprolactam with toluene as the extractant and N-methyl caprolactam with benzene and toluene as theextractants has been camed out. By defining new UNIFAC groups and calibrating related interaction parameters, aUNIFAC method was introduced to predict the equilibrium concentration of caprolactam and methyl caprolactam intoluene or benzene extraction processes. The calculated results fit very well With the experimental data. Using theUNIFAC model, the selectivity of extractants can be predicted.

Solid-Liquid Equilibria of Musk Ketone, Musk Xylene and 1,3-Dimethyl-2,4-Dinitro-5-Tert-Butyl Benzene

The solid-liquid equilibria of musk ketone + musk xylene, musk xylene +l,3-dimethyl-2,4-dinitro-5-tert-butyl benzene are measured by differential scanning calorimeter (DSC), these systems are proved to be simple eutectics. Moreover the melting points and the fusion enthalpies of musk ketone, musk xylene and 1,3-dimethyl-2,4-dinitro-5-tert-butyl benzene are also measured by the DSC. These solid-liquid equilibrium data and the heats of fusion are reported for the first time. Then UNIFAC model is used to correlate the sofid-liquid equilibrium data. It is shown that the solid-liquid equilibria of musk systems can be predicted by the UNIFAC model.

Biodegradation of Benzene and Toluene under Enhanced Denitrifying Conditions

Abstract The biodegradation of benzene and toluene was studied by aquifer material microcosm experiment in laboratory under enhanced denitrifying conditions. Based on analyses and contrast of the experiment results, the following important conclusions were obtained. Microorganisms can utilize nitrate as the electron acceptor to degrade benzene and toluene under enhanced denitrifying conditions. The denitrifiers come from the aquifer material. The macro-nutrient that microorganisms need is provided by benzene, toluene and nitrate, and the trace elements come from the aquifer material. Environmental conditions have great effects on the biodegradation of benzene and toluene, and the pH values strongly inhibit the biodegradation when they are too high or too low.

Surface Modification of Commercial Activated Carbon (CAG) for the Adsorption of Benzene and Toluene

In this work, we determined the surface characteristics of natural (CA-1) and HNO3 treated (CA-2) CAG. Equilibrium, kinetics and breakthrough for adsorption of benzene and toluene by CA-1 and CA-2 were studied. Concentrations of benzene and toluene (mg/L) were determined by gas chromatography with headspace extraction. The data of adsorption kinetic and equilibrium were best fitted by pseudo-second order model and Langmuir isotherm, respectively. The best results of benzene and toluene adsorption from fixed bed were obtained at volumetric flow rate (Q1 = 70 mL/min) using adsorbent CA-2. The study of inferential statistics revealed that CA-1 and CA-2 adsorbents are statistically different at a 5% significance level.

Benzene, toluene and xylenes levels in new and used vehicles of the same model

The aim of this work was to determine the level of benzene, toluene, o-xylene and m, p-xylene （BTX） in air samples collected from the cabins of new and used vehicles of the same model. Ten new vehicles were examined in order to check interior emission from materials used to equip the passenger compartment. In order to compare and define the impact of exhaust gases, air samples were also collected from two used cars, at different mileages （up to 20,000 kin）. All vehicles tested were of the same type. Samples were collected onto Carbograph 1TD sorbent, thermally desorbed and examined with the use of gas chromatography with flame ionisation and mass spectrometry detectors. All results obtained were referred to Polish and German requirements for indoor air quality （both in public buildings and in workspace environments）. Average benzene, toluene, o-xylene and m, p-xylene concentrations in new cars were determined at the level of 11.8 μg/m^3, 82.7 μg/m^3, 21.2 μg/m^3 and 89.5 μg/m^3, respectively. In the used cars, BTX concentration increased with increasing vehicle mileage. The most significant increase of BTX concentration was observed above 11,000 km mileage.

Optimization of the reflux ratio of benzene-toluene stage distillation columns by the Cuckoo algorithm

In this study, an enthalpy-concentration method was applied in order to model a steady state continuous benzene-toluene mixture distillation column. For a distillation tower such as the benzene- toluene splitter, there are relatively few degrees of freedom that can be manipulated in order to minimize the total annualized cost. The reflux ratio can influence the steady-state operating point and therefore influence the total annualized cost. The trade-offs between reflux ratios and total annualized cost were discussed. The Cuckoo optimization algorithm was applied to obtain a correlation for the optimum value of the reflux ratio as a power function of the economic parameters of energy price and capital cost. The results show that, at low energy price or high capital cost, the optimum reflux factor is high.

Study on the Effectiveness of Circulation Well for Remediation of Benzene and Toluene Contaminated Silt Sand Aquifer

In order to investigate the remediation effect of groundwater circulation well on benzene and toluene contaminated silt sand aquifer,a simulation remediation experiment was conducted in the laboratory using a two-dimensional simulation tank.The results showed that in the silt sand aquifer,the concentrations of benzene and toluene decreased from 179.210 mg/L and 327.520 mg/L to below the detection limit after 24 h of operation of the circulation well.The closer to the circulation well in the horizontal direction,the faster the removal efficiency of benzene and toluene.The study has shown that circulating wells have good remediation effects on both benzene-and toluene-contaminated chalk sand aquifers.

Anaerobic biodegradation of benzene series compounds by mixed cultures based on optional electronic acceptors

A series of batch experiments were performed using mixed bacterial consortia to investigate biodegradation performance of benzene, toluene, ethylbenzene and three xylene isomers （BTEX） under nitrate, sulfate and ferric iron reducing conditions. The results showed that toluene, ethylbenzene, m-xylene and o-xylene could be degraded independently by the mixed cultures coupled to nitrate, sulfate and ferric iron reduction. Under ferric iron reducing conditions the biodegradation of benzene and p-xylene could be occurred only in the presence of other alkylbenzenes. Alkylbenzenes can serve as the primary subs＇rates to stimulate the transformation of benzene and p-xylene under anaerobic conditions. Benzene and p-xylene are more toxic than toluene and ethylbenzene, under the three terminal electron acceptors conditions, the degradation rates decreased with toluene 〉 ethylbenzene 〉 m-xylene 〉 o-xylene〉 benzene 〉 p- xylene. Nitrate was a more favorable electron acceptor compared to sulfate and ferric iron. The ratio between sulfate consumed and the loss of benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene was 4.44, 4.51, 4.42, 4.32, 4.37 and 4.23, respectively; the ratio between nitrate consumed and the loss of these substrates was 7.53, 6.24, 6.49, 7.28, 7.81, 7.61, respectively; the ratio between the consumption of ferric iron and the loss of toluene, ethylbenzene, o-xylene, m-xylene was 17.99, 18.04, 18.07, 17.97, respectively.

Benzene alkylation with methanol over phosphate modified hierarchical porous ZSM-5 with tailored acidity

The acidity and acid distribution of hierarchical porous ZSM-5 were tailored via phosphate modification. The catalytic results showed that both benzene conversion and selectivity of toluene and xylene increased with the presence of appropriate amount of phosphorus. Meanwhile, side reactions such as methanol to olefins related with the formation of by-product ethylbenzene formation and isomerization of xylene to meta-xylene were suppressed efficiently. The acid strength and sites amount of Br?nsted acid of the catalyst were crucial for improving benzene conversion and yield of xylene, whereas passivation of external surface acid sites played an important role in breaking thermodynamic equilibrium distribution of xylene isomers.

Photocatalytic oxidation of gaseous benzene,toluene and xylene under UV and visible irradiation over Mn-doped TiO_(2)nanoparticles

The photocatalytic oxidation of gaseous benzene,toluene and xylene(BTX)over un-doped,0.1 and 1 wt%Mn-TiO_(2)nanoparticles under ultraviolet and visible irradiation was studied in atmosphere of synthetic air or inert gas.The photocatalytic decomposition efficiency and the oxidation products were determined using a Static Photochemical Reactor coupled with FTIR spectroscopy.BTX underwent efficient decomposition over Mn-TiO_(2)photocatalysts under UV irradiation,more with oxygen presence and less without oxygen.More important toluene and xylene went substantial decomposition over 0.1 mol%Mn-TiO_(2)under visible irradiation with oxygen presence.The main final oxidation products in the UV photocatalysis of BTX were CO_(2),CO and H2O,with CO_(2) and CO yields 4 and 2 respectively.The conversion percentage of benzene,toluene,and xylene to CO_(2) were 63.6%,56.4%,51.8%,and to CO 29%,26.5%,23.2%,respectively.In the visible photocatalysis of toluene and xylene the yields of CO were insignificant.Formation of carbon containing deposits on TiO_(2)surfaces was observed after extensive UV photocatalysis of toluene and xylene,and such by-products surface coverage may reduce the photocatalytic activity of TiO_(2)samples.Some aspects of the photocatalytic mechanism were examined.

Adsorption of toluene, ethylbenzene and xylene isomers on multi-walled carbon nanotubes oxidized by different concentration of NaOCI

Multi-walled carbon nanotubes （MWCNTs） were fabricated and oxidized by different concentrations of sodium hypochlorite （NaOC1） solutions. The untreated MWCNTs and modified MWCNTs were employed as adsorbents to study their characterizations and adsorption performance of toluene, ethylbenzene and xylene isomers （TEX） in an aqueous solution. The physicochemical properties of MWCNTs were greatly affected after oxidation, which influences TEX adsorption capacity. The 3% NaOCl-oxidized MWCNTs shows the greatest enhancement in TEX adsorption, followed by the 30% NaOCl. More interestingly, the 15% NaOCl-oxidized MWCNTs has lower adsorption capacities than untreated MWCNTs. The adsorption mechanism of TEX on treated MWCNTs is attributed to the combined action of hydrophobic interaction, π-π bonding interaction between the aromatic ring of TEX and the oxygen-containing functional groups of MWCNTs and electrostatic interac- tion. 3% NaOCl solution could not only introduce much oxygen-containing functional groups on MWCNTs, but also lead to less damage for the pore structure. This suggests that the CNTs-3% NaOCl is efficient adsorbent for TEX and that they may possess good potential for TEX removal in wastewater treatment.

Adsorption of benzene and toluene from waste gas using activated carbon activated by ZnCl2

A series of activated carbons with high surface area were prepared from walnut shell using chemical activation with ZnCl2. In this research the carbonization stage was carried out at 500℃. The performance of the synthesized carbons evaluated in adsorption of benzene and toluene from waste gas. The influence of impregnation ratio on the characteristics of synthesized activated carbons as well as their adsorption capacity was investigated. The ratio of activation agent to walnut shell was selected in the range of 0.5-2.0 wt/wt. The synthesized activated carbons were characterized using XRD, SEM, BET and FTIR techniques. The highest activated carbon production yield was obtained at impregnation ratio of 1.5 wt/wt. The XRD analysis illustrated that peaks intensity decreased with increasing impregnation ratio showing that amorphous property of samples was increased. The SEM analysis revealed successful pore development in synthesized activated carbons obtained at high impregnation ratios. The surface area of the activated carbons increased with increasing impregnation ratio and its maximum value reached 2643 m2.g 1 at impregnation ratio of 2/1. FTIR analysis indicated that the relative amount of different acidic surface groups on synthesized carbons was a function of impregnation ratio. Experimental results for benzene and toluene adsorption showed a high potential of employing synthesized impregnated activated carbon for treatment of waste gas. Generally, the amount of VOC adsorbed on the surface was affected by physicochemical properties of synthesized activated carbons.

Soot size distribution in lightly sooting premixed flames of benzene and toluene

The evolution of particle size distribution function(PSDF)of soot in premixed flames of benzene and toluene was studied on a burner stabilized stagnation(BSS)flame platform.The cold gas velocities were changed to hold the maximum flame temperatures of different flames approximately constant.The PSDFs of all the test flames exhibited a bimodal distribution,i.e.,a small-size nucleation mode and a large-size accumulation mode.It was observed that soot nucleation and particle growth in the benzene flame were stronger than those in the toluene flame at short residence times.At longer residence times,the PSDFs of the two flames were similar,and the toluene flame showed a larger particle size distribution range and a higher particle volume fraction than the benzene flame.

Effect of benzene,toluene,xylene on the semen quality of exposed workers

Objective To examine the effects on semen and sperm quality of workers after a short and long term exposure to benzene, toluene, and xylene Methods The semen and blood of 24 married workers exposed to benzene, toluene, and xylene from shoemaking, spray painting, or paint manufacturing factories were collected The concentration of benzene, toluene, and xylene in the blood and semen was determined by using headspace chromatographic method Routine sperm test was carried out and acrosin activity detected Results The results showed that benzene, toluene, and xylene were found in the blood and semen of some ex workers in a working environment where the air concentration of benzene, toluene, and xylene exceeded the maximum allowable concentration (MAC) This result was not found in workers of the control group There were also some effects on the quality of semen in the exposed workers For example, the percentage of semen with liquefaction time exceeding 30 minutes increased The sperm vitality, motility and acrosin activity decreased At the same time, there were a positive correlation between liquefaction time and the level of toluene in semen, and a negative correlation between sperm vitality, sperm activity or acrosin activity and working history Conclusions The results suggested that the mixture could affect the quality of semen and sperm, which might be the main reason of the abnormal pregnancy outcome among the wives of workers exposed to benzene, toluene, and xylene Further studies are, however, required to confirm these findings