The semiconductor gas sensors used for xylene gas detection in real time has been restricted by the inadequate sensitivity and selectivity.Constructing a bilayer cascade sensor with the catalysis-gas sensitivity syner...The semiconductor gas sensors used for xylene gas detection in real time has been restricted by the inadequate sensitivity and selectivity.Constructing a bilayer cascade sensor with the catalysis-gas sensitivity synergistic is considered as an effective solution.Herein,the Ag@CeO_(2)nanosheets are synthesized by heat treating the Ag@Ce-MOF,which synthesized via solvothermal method.The morphological evolution of cerium metalorganic framework(Ce-MOF),regulated by Ag ions,is investigated,and the transformation mechanism is proposed.The bilayer sensors were constructed by using WO_(3)nanofibers,prepared via the electrospinning method,as the sensitive layer and the Ag@CeO_(2)nanosheets as the catalytic layer,respectively.The bilayer sensors exhibit remarkable performance in response to xylene.The response value(R_(a)/R_(g))of WO_(3)/Ag@CeO_(2)sensor to10 ppm xylene gas reaches 32.13 at the operating temperature of 160℃.Additionally,the sensor displays an exceptional response to even trace amounts of xylene,as low as parts per billion(ppb).The catalysis-gas sensitivity synergistic mechanism was elucidated by capturing catalytic intermediates using online mass spectrometry.These findings provide a novel strategy for benzene series(BTEX)sensor and offer a novel approach to prepare twodimensional Ce-MOF and its derived materials with tailored properties.展开更多
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...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.展开更多
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,...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.展开更多
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 s...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.展开更多
The effect of pretreatment on Pd/Al2O3 catalysts for the catalytic oxidation of o-xylene at low temperature was studied by changing the pretreatment and testing conditions. The fresh and pretreated Pd/Al2O3 catalysts ...The effect of pretreatment on Pd/Al2O3 catalysts for the catalytic oxidation of o-xylene at low temperature was studied by changing the pretreatment and testing conditions. The fresh and pretreated Pd/Al2O3 catalysts were characterized by transmission electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS） and X-ray diffraction （XRD）. The results showed that the pretreatment dramatically changed the Pd/PdO ratio and then significantly affected the Pd/Al2O3 activity; while the pretreatment had not much influence on Pd particle size. The Pd/Al2O3 pre-reduced at 300~C/400~C, which has fully reduced Pd species, showed the highest activity; while the fresh Pd/Al2O3, which has fully oxidized Pd species, presented the worst performance, indicating the Pd chemical state plays an important role in the catalytic activity for the o-xylene oxidation. It is concluded that metallic Pd is the active species on the Pd/Al2O3 catalyst for the catalytic oxidation of o-xylene at low temperature.展开更多
A bimetal-exchanged NaY zeolite(Cu(Ⅰ)-Y(Ⅲ)-Y)with a desirable adsorptive desulfurization(ADS)performance was prepared and characterized by means of X-ray diffraction,specific surface area measurements,X-ray fluoresc...A bimetal-exchanged NaY zeolite(Cu(Ⅰ)-Y(Ⅲ)-Y)with a desirable adsorptive desulfurization(ADS)performance was prepared and characterized by means of X-ray diffraction,specific surface area measurements,X-ray fluorescence spectrometer,X-ray photoelectron spectroscopy,thermal gravity analysis and Fourier transform infrared spectroscopy.The effect of Y(Ⅲ)ions on ADS in the presence of the xylenes was investigated.Results indicated that the ADS performance of Y(Ⅲ)-Y is higher than that of most reported CeY.The Y(Ⅲ)-based Cu(Ⅰ)-Y(Ⅲ)-Y demonstrated the higher breakthrough loading than those of reported Ce(Ⅲ)/Ce(Ⅳ)-based transition metal Y zeolites,showing that Y(Ⅲ)ions play a promoting role in improving the ADS selectivity.For Cu(Ⅰ)-Y(Ⅲ)-Y,a new strong S-M interaction(S stands for sulfur,while M stands for metal)active site was formed,which might be caused by the synergistic effect between Cu(Ⅰ)and Y(Ⅲ).The Cu(Ⅰ)-Y(Ⅲ)-Y,which combined the advantages of Cu(I)-Y and Y(Ⅲ)-Y,is a kind of promising adsorbent.The breakthrough loading decreased in the order of Cu(Ⅰ)-Y(Ⅲ)-Y>Y(Ⅲ)-Y>Cu(Ⅰ)-Y,and the effect of xylene isomers on the sulfur removal was in the order of ortho-xylene>meta-xylene>para-xylene,which exhibited the same trend with the bond order of xylenes.展开更多
Toluene methylation with methanol on H‐ZSM‐5(Z5)zeolite for the directional transformation of toluene to xylene has been industrialized.However,great challenges remain because of the high energy barrier of methanol ...Toluene methylation with methanol on H‐ZSM‐5(Z5)zeolite for the directional transformation of toluene to xylene has been industrialized.However,great challenges remain because of the high energy barrier of methanol deprotonation to the methoxy group,the side reaction of methanol to olefins,coke formation,and the deactivation of zeolites.Herein,we report the toluene methylation coupled with CO hydrogenation to showcase an enhancement in para‐xylene(PX)selectivity by employing a bifunctional catalyst composed of ZnZrO_(x)(ZZO)and modified Z5.The results showed that a PX selectivity of up to 81.8%in xylene and xylene selectivity of 64.8%in hydrocarbons at 10.3%toluene conversion can be realized over the bifunctional catalyst on a fixed‐bed reactor.The selectivity of gaseous hydrocarbons decreased to 10.9%,and approximately half of that was observed in methanol reagent route where the PX selectivity in xylene was 38.8%.We observed that the acid strength,the quantity ratio of Brönsted and Lewis acid sites,and the pore size of zeolites were essential for the PX selectivity.The investigation of the H_(2)/D_(2) kinetic isotope effect revealed that the newborn methyl group in xylene resulted from the hydrogenation of CO rather than toluene disproportionation.Furthermore,the catalyst showed no evident deactivation within the 100 h stability test.The findings offer a promising route for the production of value‐added PX with high selectivity via toluene methylation coupled with syngas conversion.展开更多
Desilication accompanied with minimum loss of crystallinity effect of a high alumina ZSM-5 zeolite on the isomerization reaction of ethylbenzene/xylene mixtures has been considered.Desilication was assessed through XR...Desilication accompanied with minimum loss of crystallinity effect of a high alumina ZSM-5 zeolite on the isomerization reaction of ethylbenzene/xylene mixtures has been considered.Desilication was assessed through XRF,XRD,FTIR,TEM,nitrogen adsorption/desorption,NH_3-TPD,^(29)Si and^(27)Al MAS NMR analytical techniques.Desilication was accompanied with the creation of super acid sites.There exists a limit(Si/Al molar ratio of9.67)for keeping high crystallinity and obtaining improved catalytic performance.Desilication promotes ethylbenzene conversion by disproportionation and trans-alkylation reactions while the same reactions are limited for the xylene isomers.The p-xylene approach to equilibrium improves by more than 7% at 400℃ and a WHSV of 2 h^(-1)for the optimum sample with respect to the parent zeolite.At the same conditions,the optimum sample exhibits the maximum ethylbenzene conversion of 89%,i.e.more than 40%w.r.t.of the parent zeolite.However,the xylene yield decreases only 3%.展开更多
The alkylation of toluene with methanol for the selective formation of p-xylene was systematically studied. Very few studies have been reported on the use of superacids such as heteropolyacids on cheap supports, such ...The alkylation of toluene with methanol for the selective formation of p-xylene was systematically studied. Very few studies have been reported on the use of superacids such as heteropolyacids on cheap supports, such as clay. This article deals with the use of different heteropoly acids （HPAs）, viz, Dodeca-Tungstophosphoric acid [H3PO4.12WO3.xH2O] （TPA）, Dodeca-Molyhdo phosphoric acid ammonium salt hydrate [H12Mo12N3O40P＋aq] （DMAA）, Dodeca-Molyhdo Phosphoric acid （PMA） on clay （MontmoriUonite, K-10） and as such plain clay. This comparative study reveals that 20%PMA/Clay shows 62% toluene conversion and 100% selectivity toward p-xylene.展开更多
MIL-125 is a metal-organic framework with great potential for the adsorption and separation of xylene isomers.However,MIL-125 is usually synthesized under anhydrous and anaerobic conditions.In this study,homogeneously...MIL-125 is a metal-organic framework with great potential for the adsorption and separation of xylene isomers.However,MIL-125 is usually synthesized under anhydrous and anaerobic conditions.In this study,homogeneously shaped and highly crystalline MIL-125 was synthesized by introducing water-resistant titanium-containing oligomers into the synthesis process.With the assistance of the novel oligomers,MIL-125 can be synthesized in the presence of water,which meets batch-production requirements.The adsorption separation performance of the obtained highly crystalline MIL-125 was also significantly enhanced.The para-xylene/meta-xylene selectivity can reach 13.5 in mesitylene,which is higher than the selectivity values of most previously reported para-selective adsorbents.The MIL-125 xylene separation performance was verified using both batch adsorption and breakthrough experiments in the liquid phase.In addition,the influence of the solvent effect was evaluated through microcalorimetric experiments,liquid-phase adsorption experiments,and theoretical calculations.展开更多
A combination of photochlorination ofp-xylene and succedent Friedel-Crafts alkylation polymerization was firstly used in the preparation of the hypercrosslinked adsorptive resin. The data of GC-MS and GC showed that a...A combination of photochlorination ofp-xylene and succedent Friedel-Crafts alkylation polymerization was firstly used in the preparation of the hypercrosslinked adsorptive resin. The data of GC-MS and GC showed that a series of chlorizates were produced when p-xylene was photochlorinated. Hypercrosslinked resins could be synthesized by copolymerization, self-polymerization of chlorizates or post crosslinking reaction. The chemical structure and micromorphology of the porous resins were characterized by BET, FF-IR, SEM and elementary analysis （EA）. The results showed that the novel adsorptive resins possess high BET surface near to 1038 m^2/g and large pore volumes range from 0.5 to 1.2 cm^3/g.展开更多
The alkylation of toluene with methanol to selective formation of p-xylene has been systematically studied. ZSM-12 （MTW）/ZSM-5 co-crystalline zeolite in 40：60 proportions have been synthesized by the same molar gel...The alkylation of toluene with methanol to selective formation of p-xylene has been systematically studied. ZSM-12 （MTW）/ZSM-5 co-crystalline zeolite in 40：60 proportions have been synthesized by the same molar gel composition, but at different temperatures and periods than that of ZSM-12 and ZSM-5, separately. All the prepared samples are characterized by XRD, SEM, BET, and XRF. The activity of toluene alkylation was investigated with a mixture of toluene and methanol as a feed over the ZSM-12, ZSM-12/ZSM-5 co-crystalline, ZSM-5, and physical mixture of ZSM-12/ZSM-5. From characterization, it is observed that the ZSM-12/ZSM-5 co-crystalline material is different from that of ZSM-12, ZSM-5, and their physical mixture. Further, the ZSM-12/ZSM-5 co-crystalline zeolite produces the highest content of xylene and has better selectivity for p-xylene than ZSM-12, ZSM-5, and their physical mixture.展开更多
Sulfur dioxide（SO_2） and benzene homologs are frequently present in the off-gas during the process of sewage sludge drying. A laboratory scale biofilter was set up to co-treat SO_2 and o-xylene in the present study....Sulfur dioxide（SO_2） and benzene homologs are frequently present in the off-gas during the process of sewage sludge drying. A laboratory scale biofilter was set up to co-treat SO_2 and o-xylene in the present study. SO_2 and o-xylene could be removed simultaneously in a single biofilter. Their concentration ratio in the inlet stream influenced the removal efficiencies. It is worth noting that the removal of SO_2 could be enhanced when low concentrations of o-xylene were introduced into the biofilter. Pseudomonas sp., Paenibacillus sp., and Bacillus sp. were the main functional bacteria groups in the biofilter. Sulfur-oxidizing bacteria（SOB） and o-xylene-degrading bacteria（XB） thrived in the biofilter and their counts as well as their growth rate increased with the increase in amount of SO2 and o-xylene supplied. The microbial populations differed in counts and species due to the properties and components of the compounds being treated in the biofilter. The presence of mixed substrates enhanced the diversity of the microbial population. During the treatment process, bioaerosols including potentially pathogenic bacteria, e.g., Acinetobacter lwoffii and Aeromonas sp., were emitted from the biofilter. Further investigation is needed to focus on the potential hazards caused by the bioaerosols emitted from waste gas treatment bioreactors.展开更多
The effects of three types of electrically-inert fillers, calcium carbonate （CaCO_3）, talc and glass fiber （GF）, on electrical resistivity, crystallization behavior and dynamic mechanical properties of poly（m-xyl...The effects of three types of electrically-inert fillers, calcium carbonate （CaCO_3）, talc and glass fiber （GF）, on electrical resistivity, crystallization behavior and dynamic mechanical properties of poly（m-xylene adipamide） （MXD6）/multiwalled carbon nanotube （MWCNT） composites are investigated. The electrical resistivity of MXD6/MWCNT composites is significantly reduced with the addition of inert fillers due to the volume-exclusion effect that leads to increased effective concentration of MWCNTs in MXD6 matrix and also due to improved MWCNT dispersion. The crystallization temperature of MXD6 increases with the addition of MWCNTs, indicating that MWCNTs can act as nucleating agent and induce crystallization of MXD6. The incorporation of inert fillers has no further effect on crystallization behavior of MXD6, but significantly improves the storage modulus of MXD6/MWCNT composite, demonstrating that CaCO_3, talc and GF filled MXD6/MWCNT composites are very promising materials with not only improved electrical property but also excellent mechanical properties.展开更多
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 eutec...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.展开更多
The activities of CeO2 nanocubes calcined at different temperatures were tested for catalytic oxidation of o-xylene. Using CeO2 nanocubes as catalysts, complete catalytic oxidation of o-xylene was achieved below 210℃...The activities of CeO2 nanocubes calcined at different temperatures were tested for catalytic oxidation of o-xylene. Using CeO2 nanocubes as catalysts, complete catalytic oxidation of o-xylene was achieved below 210℃. The CeO2 nanomaterials were characterized by means of BET, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and high-resolution transmission electron microscopy （HRTEM）. From the TEM images, all CeO2 nanocubes displayed cubic morphology irrespective of calcination temperature. The HRTEM images revealed that these nanocubes were enclosed by reactive {001} planes, which may contribute to the intrinsically catalytic property of o-xylene oxidation. The higher activity of CeO2 nanocubes calcined at 550℃ than those calcined at above 550℃ was attributed to their smaller crystallite size and larger surface area. The influences of reaction conditions were also studied, which found that a higher reaction temperature was necessary for complete catalytic oxidation of o-xylene at higher weight hourly space velocity （WHSV） and o-xylene concentration.展开更多
Density functional theory（DFT） quantum chemical method was used to study the process of meta-xylene Fenton oxidation. The EHOMO energies of meta-xylene molecules are higher, so they have better ability to provide el...Density functional theory（DFT） quantum chemical method was used to study the process of meta-xylene Fenton oxidation. The EHOMO energies of meta-xylene molecules are higher, so they have better ability to provide electron and prone to the nucleophilic reaction. M-xylene mainly reacts with OH free radical in addition reactions. And the position of C（6） is most likely to react with the OH free radical, rather than the C（3）, which is the most difficult to occur. According to all the above results, the most likely reaction mechanism of advanced oxidation degradation of meta-xylene is determined.展开更多
Musk xylene（MX） is frequently used as fragrances in formulation of personal care products. Quantification of a bound 4-amino- MX（4-AMX） as cysteine adducts in trout hemoglobin（Hb） was made by gas chromatography-...Musk xylene（MX） is frequently used as fragrances in formulation of personal care products. Quantification of a bound 4-amino- MX（4-AMX） as cysteine adducts in trout hemoglobin（Hb） was made by gas chromatography-ion trap-mass spectrometry（GC/MS）. The Hb samples were collected from trout after 24 h exposure to MX at 10μg/g, and or menhaden oil（control）. The formation of cysteine-Hb adduct was observed from nitroso derivative of MX, released by alkaline hydrolysis. The released 4-AMX metabolite was extracted in n- hexane. The extract was then reduced by evaporation, and analyzed by GC/MS. When similar agreement of mass spectral features and retention time of 4-AMX were obtained in both standard and sample solutions, the presence of 4-AMX metabolite in the Hb was confirmed. The concentration of 4-AMX was found to be 3.1 × 10^-6 6.9 × 10^-6 mg/g in the Hb solution. Quantitation was made based on an internal standard, a calibration plot, and response factor. In the non-hydrolyzed and laboratory blank extracts, the 4-AMX metabolite was not detected. Additionally, coeluting and interfefing ions were observed in the biological samples.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.62471303,62071300,22176127,22301181,22406130 and 22476131)Shanghai Sailing Program(Nos.23YF1429000 and 22YF1430400)
文摘The semiconductor gas sensors used for xylene gas detection in real time has been restricted by the inadequate sensitivity and selectivity.Constructing a bilayer cascade sensor with the catalysis-gas sensitivity synergistic is considered as an effective solution.Herein,the Ag@CeO_(2)nanosheets are synthesized by heat treating the Ag@Ce-MOF,which synthesized via solvothermal method.The morphological evolution of cerium metalorganic framework(Ce-MOF),regulated by Ag ions,is investigated,and the transformation mechanism is proposed.The bilayer sensors were constructed by using WO_(3)nanofibers,prepared via the electrospinning method,as the sensitive layer and the Ag@CeO_(2)nanosheets as the catalytic layer,respectively.The bilayer sensors exhibit remarkable performance in response to xylene.The response value(R_(a)/R_(g))of WO_(3)/Ag@CeO_(2)sensor to10 ppm xylene gas reaches 32.13 at the operating temperature of 160℃.Additionally,the sensor displays an exceptional response to even trace amounts of xylene,as low as parts per billion(ppb).The catalysis-gas sensitivity synergistic mechanism was elucidated by capturing catalytic intermediates using online mass spectrometry.These findings provide a novel strategy for benzene series(BTEX)sensor and offer a novel approach to prepare twodimensional Ce-MOF and its derived materials with tailored properties.
基金Financial support from Polish Ministry of Science and Higher Education(No.N N509 480438)is gratefully acknowledged
文摘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.
基金supported by the University of Macao Research Committee and the Macao Science and Technology Development Fund
文摘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.
基金supported by research grants from the National Natural Science Foundation of China[No.81474929]。
文摘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.
基金supported by the Ministry of Science and Technology of China (No. 2012AA062702,2010AA64905)the National Natural Science Foundation of China (No. 21077117)
文摘The effect of pretreatment on Pd/Al2O3 catalysts for the catalytic oxidation of o-xylene at low temperature was studied by changing the pretreatment and testing conditions. The fresh and pretreated Pd/Al2O3 catalysts were characterized by transmission electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS） and X-ray diffraction （XRD）. The results showed that the pretreatment dramatically changed the Pd/PdO ratio and then significantly affected the Pd/Al2O3 activity; while the pretreatment had not much influence on Pd particle size. The Pd/Al2O3 pre-reduced at 300~C/400~C, which has fully reduced Pd species, showed the highest activity; while the fresh Pd/Al2O3, which has fully oxidized Pd species, presented the worst performance, indicating the Pd chemical state plays an important role in the catalytic activity for the o-xylene oxidation. It is concluded that metallic Pd is the active species on the Pd/Al2O3 catalyst for the catalytic oxidation of o-xylene at low temperature.
基金the financial supports from the National Natural Science Foundation of China(81172204)。
文摘A bimetal-exchanged NaY zeolite(Cu(Ⅰ)-Y(Ⅲ)-Y)with a desirable adsorptive desulfurization(ADS)performance was prepared and characterized by means of X-ray diffraction,specific surface area measurements,X-ray fluorescence spectrometer,X-ray photoelectron spectroscopy,thermal gravity analysis and Fourier transform infrared spectroscopy.The effect of Y(Ⅲ)ions on ADS in the presence of the xylenes was investigated.Results indicated that the ADS performance of Y(Ⅲ)-Y is higher than that of most reported CeY.The Y(Ⅲ)-based Cu(Ⅰ)-Y(Ⅲ)-Y demonstrated the higher breakthrough loading than those of reported Ce(Ⅲ)/Ce(Ⅳ)-based transition metal Y zeolites,showing that Y(Ⅲ)ions play a promoting role in improving the ADS selectivity.For Cu(Ⅰ)-Y(Ⅲ)-Y,a new strong S-M interaction(S stands for sulfur,while M stands for metal)active site was formed,which might be caused by the synergistic effect between Cu(Ⅰ)and Y(Ⅲ).The Cu(Ⅰ)-Y(Ⅲ)-Y,which combined the advantages of Cu(I)-Y and Y(Ⅲ)-Y,is a kind of promising adsorbent.The breakthrough loading decreased in the order of Cu(Ⅰ)-Y(Ⅲ)-Y>Y(Ⅲ)-Y>Cu(Ⅰ)-Y,and the effect of xylene isomers on the sulfur removal was in the order of ortho-xylene>meta-xylene>para-xylene,which exhibited the same trend with the bond order of xylenes.
文摘Toluene methylation with methanol on H‐ZSM‐5(Z5)zeolite for the directional transformation of toluene to xylene has been industrialized.However,great challenges remain because of the high energy barrier of methanol deprotonation to the methoxy group,the side reaction of methanol to olefins,coke formation,and the deactivation of zeolites.Herein,we report the toluene methylation coupled with CO hydrogenation to showcase an enhancement in para‐xylene(PX)selectivity by employing a bifunctional catalyst composed of ZnZrO_(x)(ZZO)and modified Z5.The results showed that a PX selectivity of up to 81.8%in xylene and xylene selectivity of 64.8%in hydrocarbons at 10.3%toluene conversion can be realized over the bifunctional catalyst on a fixed‐bed reactor.The selectivity of gaseous hydrocarbons decreased to 10.9%,and approximately half of that was observed in methanol reagent route where the PX selectivity in xylene was 38.8%.We observed that the acid strength,the quantity ratio of Brönsted and Lewis acid sites,and the pore size of zeolites were essential for the PX selectivity.The investigation of the H_(2)/D_(2) kinetic isotope effect revealed that the newborn methyl group in xylene resulted from the hydrogenation of CO rather than toluene disproportionation.Furthermore,the catalyst showed no evident deactivation within the 100 h stability test.The findings offer a promising route for the production of value‐added PX with high selectivity via toluene methylation coupled with syngas conversion.
基金financed by BIPC,Mahshahr,Iran under the contract number 08-133/57665
文摘Desilication accompanied with minimum loss of crystallinity effect of a high alumina ZSM-5 zeolite on the isomerization reaction of ethylbenzene/xylene mixtures has been considered.Desilication was assessed through XRF,XRD,FTIR,TEM,nitrogen adsorption/desorption,NH_3-TPD,^(29)Si and^(27)Al MAS NMR analytical techniques.Desilication was accompanied with the creation of super acid sites.There exists a limit(Si/Al molar ratio of9.67)for keeping high crystallinity and obtaining improved catalytic performance.Desilication promotes ethylbenzene conversion by disproportionation and trans-alkylation reactions while the same reactions are limited for the xylene isomers.The p-xylene approach to equilibrium improves by more than 7% at 400℃ and a WHSV of 2 h^(-1)for the optimum sample with respect to the parent zeolite.At the same conditions,the optimum sample exhibits the maximum ethylbenzene conversion of 89%,i.e.more than 40%w.r.t.of the parent zeolite.However,the xylene yield decreases only 3%.
文摘The alkylation of toluene with methanol for the selective formation of p-xylene was systematically studied. Very few studies have been reported on the use of superacids such as heteropolyacids on cheap supports, such as clay. This article deals with the use of different heteropoly acids （HPAs）, viz, Dodeca-Tungstophosphoric acid [H3PO4.12WO3.xH2O] （TPA）, Dodeca-Molyhdo phosphoric acid ammonium salt hydrate [H12Mo12N3O40P＋aq] （DMAA）, Dodeca-Molyhdo Phosphoric acid （PMA） on clay （MontmoriUonite, K-10） and as such plain clay. This comparative study reveals that 20%PMA/Clay shows 62% toluene conversion and 100% selectivity toward p-xylene.
文摘MIL-125 is a metal-organic framework with great potential for the adsorption and separation of xylene isomers.However,MIL-125 is usually synthesized under anhydrous and anaerobic conditions.In this study,homogeneously shaped and highly crystalline MIL-125 was synthesized by introducing water-resistant titanium-containing oligomers into the synthesis process.With the assistance of the novel oligomers,MIL-125 can be synthesized in the presence of water,which meets batch-production requirements.The adsorption separation performance of the obtained highly crystalline MIL-125 was also significantly enhanced.The para-xylene/meta-xylene selectivity can reach 13.5 in mesitylene,which is higher than the selectivity values of most previously reported para-selective adsorbents.The MIL-125 xylene separation performance was verified using both batch adsorption and breakthrough experiments in the liquid phase.In addition,the influence of the solvent effect was evaluated through microcalorimetric experiments,liquid-phase adsorption experiments,and theoretical calculations.
基金support of the National Natural Science Foundation of China(Nos.20574063 and 21004055)
文摘A combination of photochlorination ofp-xylene and succedent Friedel-Crafts alkylation polymerization was firstly used in the preparation of the hypercrosslinked adsorptive resin. The data of GC-MS and GC showed that a series of chlorizates were produced when p-xylene was photochlorinated. Hypercrosslinked resins could be synthesized by copolymerization, self-polymerization of chlorizates or post crosslinking reaction. The chemical structure and micromorphology of the porous resins were characterized by BET, FF-IR, SEM and elementary analysis （EA）. The results showed that the novel adsorptive resins possess high BET surface near to 1038 m^2/g and large pore volumes range from 0.5 to 1.2 cm^3/g.
文摘The alkylation of toluene with methanol to selective formation of p-xylene has been systematically studied. ZSM-12 （MTW）/ZSM-5 co-crystalline zeolite in 40：60 proportions have been synthesized by the same molar gel composition, but at different temperatures and periods than that of ZSM-12 and ZSM-5, separately. All the prepared samples are characterized by XRD, SEM, BET, and XRF. The activity of toluene alkylation was investigated with a mixture of toluene and methanol as a feed over the ZSM-12, ZSM-12/ZSM-5 co-crystalline, ZSM-5, and physical mixture of ZSM-12/ZSM-5. From characterization, it is observed that the ZSM-12/ZSM-5 co-crystalline material is different from that of ZSM-12, ZSM-5, and their physical mixture. Further, the ZSM-12/ZSM-5 co-crystalline zeolite produces the highest content of xylene and has better selectivity for p-xylene than ZSM-12, ZSM-5, and their physical mixture.
基金financially supported by the National Natural Science Foundation of China(Nos.51478456 and 51308527)
文摘Sulfur dioxide（SO_2） and benzene homologs are frequently present in the off-gas during the process of sewage sludge drying. A laboratory scale biofilter was set up to co-treat SO_2 and o-xylene in the present study. SO_2 and o-xylene could be removed simultaneously in a single biofilter. Their concentration ratio in the inlet stream influenced the removal efficiencies. It is worth noting that the removal of SO_2 could be enhanced when low concentrations of o-xylene were introduced into the biofilter. Pseudomonas sp., Paenibacillus sp., and Bacillus sp. were the main functional bacteria groups in the biofilter. Sulfur-oxidizing bacteria（SOB） and o-xylene-degrading bacteria（XB） thrived in the biofilter and their counts as well as their growth rate increased with the increase in amount of SO2 and o-xylene supplied. The microbial populations differed in counts and species due to the properties and components of the compounds being treated in the biofilter. The presence of mixed substrates enhanced the diversity of the microbial population. During the treatment process, bioaerosols including potentially pathogenic bacteria, e.g., Acinetobacter lwoffii and Aeromonas sp., were emitted from the biofilter. Further investigation is needed to focus on the potential hazards caused by the bioaerosols emitted from waste gas treatment bioreactors.
文摘The effects of three types of electrically-inert fillers, calcium carbonate （CaCO_3）, talc and glass fiber （GF）, on electrical resistivity, crystallization behavior and dynamic mechanical properties of poly（m-xylene adipamide） （MXD6）/multiwalled carbon nanotube （MWCNT） composites are investigated. The electrical resistivity of MXD6/MWCNT composites is significantly reduced with the addition of inert fillers due to the volume-exclusion effect that leads to increased effective concentration of MWCNTs in MXD6 matrix and also due to improved MWCNT dispersion. The crystallization temperature of MXD6 increases with the addition of MWCNTs, indicating that MWCNTs can act as nucleating agent and induce crystallization of MXD6. The incorporation of inert fillers has no further effect on crystallization behavior of MXD6, but significantly improves the storage modulus of MXD6/MWCNT composite, demonstrating that CaCO_3, talc and GF filled MXD6/MWCNT composites are very promising materials with not only improved electrical property but also excellent mechanical properties.
文摘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.
基金supported by the National Natural Science Foundation of China (No.50921064,20973193)the Ministry of Science and Technology of China (No.2007AA061402,2010CB732304)
文摘The activities of CeO2 nanocubes calcined at different temperatures were tested for catalytic oxidation of o-xylene. Using CeO2 nanocubes as catalysts, complete catalytic oxidation of o-xylene was achieved below 210℃. The CeO2 nanomaterials were characterized by means of BET, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and high-resolution transmission electron microscopy （HRTEM）. From the TEM images, all CeO2 nanocubes displayed cubic morphology irrespective of calcination temperature. The HRTEM images revealed that these nanocubes were enclosed by reactive {001} planes, which may contribute to the intrinsically catalytic property of o-xylene oxidation. The higher activity of CeO2 nanocubes calcined at 550℃ than those calcined at above 550℃ was attributed to their smaller crystallite size and larger surface area. The influences of reaction conditions were also studied, which found that a higher reaction temperature was necessary for complete catalytic oxidation of o-xylene at higher weight hourly space velocity （WHSV） and o-xylene concentration.
基金Supported by the research and practice project of scientific and technological innovation of school enterprise cooperation in Guangdong University of Petrochemical Technology(660648)
文摘Density functional theory（DFT） quantum chemical method was used to study the process of meta-xylene Fenton oxidation. The EHOMO energies of meta-xylene molecules are higher, so they have better ability to provide electron and prone to the nucleophilic reaction. M-xylene mainly reacts with OH free radical in addition reactions. And the position of C（6） is most likely to react with the OH free radical, rather than the C（3）, which is the most difficult to occur. According to all the above results, the most likely reaction mechanism of advanced oxidation degradation of meta-xylene is determined.
文摘Musk xylene（MX） is frequently used as fragrances in formulation of personal care products. Quantification of a bound 4-amino- MX（4-AMX） as cysteine adducts in trout hemoglobin（Hb） was made by gas chromatography-ion trap-mass spectrometry（GC/MS）. The Hb samples were collected from trout after 24 h exposure to MX at 10μg/g, and or menhaden oil（control）. The formation of cysteine-Hb adduct was observed from nitroso derivative of MX, released by alkaline hydrolysis. The released 4-AMX metabolite was extracted in n- hexane. The extract was then reduced by evaporation, and analyzed by GC/MS. When similar agreement of mass spectral features and retention time of 4-AMX were obtained in both standard and sample solutions, the presence of 4-AMX metabolite in the Hb was confirmed. The concentration of 4-AMX was found to be 3.1 × 10^-6 6.9 × 10^-6 mg/g in the Hb solution. Quantitation was made based on an internal standard, a calibration plot, and response factor. In the non-hydrolyzed and laboratory blank extracts, the 4-AMX metabolite was not detected. Additionally, coeluting and interfefing ions were observed in the biological samples.
