Catalytic methylation of toluene with methanol is an important alternative pathway for xylene production.Previous studies have indicated that methanol always undergoes several side reactions on acidic zeolites,resulti...Catalytic methylation of toluene with methanol is an important alternative pathway for xylene production.Previous studies have indicated that methanol always undergoes several side reactions on acidic zeolites,resulting in oxygencontaining byproducts such as dimethyl ethers,ketones,and carboxylic acids.Herein,the presence and distribution of the oxygenated compounds formed during toluene methylation were firstly examined by systematic chromatographic analysis.Plausible formation mechanisms for the various oxygenates are discussed.The most problematic byproduct is found to be acetic acid,which can lead to inferior product quality and damage downstream units.A feasible solution is presented for oxygenate removal after toluene methylation,in which acetic acid is eliminated by catalytic decomposition into low-boilingpoint acetone over a MgO catalyst.This process allows for all of the low-boiling-point oxygenates,including methanol,dimethyl ether,acetone,and butanone,to be removed from the aromatics phase,taking advantage of the temperature of the reaction effluent and standard distillation equipment.X-ray diffraction was used to characterize the crystal phase of the fresh and used MgO decarbonylation catalysts,while thermogravimetry/mass spectrometry and Fourier-transform infrared spectroscopy were applied to investigate the transformation mechanism of acetic acid over the decarbonylation catalyst.CO insertion and ketonization of acetic acid accounted for the formation and elimination of acetic acid,respectively.The combined methylation/decarbonylation process should enable the production of high-quality xylenes,an important industrial feedstock,by overcoming the main technical obstacles associated with the toluene methylation process.展开更多
To improve their thermal stability, La0.8Sr0.2MnO3 cordierite monoliths are washcoated with mayenite, which is a novel Al-based material with the crystal structure of 12MO 7Al2O3 （M= Ca, Sr）. The monoliths are chara...To improve their thermal stability, La0.8Sr0.2MnO3 cordierite monoliths are washcoated with mayenite, which is a novel Al-based material with the crystal structure of 12MO 7Al2O3 （M= Ca, Sr）. The monoliths are characterized by means of nitrogen adsorp- tion/desorption, scanning electron microscopy, and X-ray diffraction. Catalytic performances of the monoliths are tested for methyl methacrylate combustion. The results show that mayenite obviously improves both the physic- chemical properties and the catalytic performance of the monoliths. Because mayenite improves the dispersity of Lao.sSro.2MnO3 and also prevents the interaction between La0.8Sr0.2MnO3 and cordierite or γ-A1203, both crystal structure and surface morphology of La0.8Sr0.2MnO3 phase can thereby be stable on the mayenite surface even at high temperature up to 1050 ℃. Under the given reaction conditions, La0.8Sr0.2MnO3 monolith washcoated with 12SrO. γ-A1203 shows the best catalytic activity for methyl methacrylate combustion among all the tested monoliths.展开更多
基金We gratefully acknowledge the support from the National 973 Program of China(Grant No.2003CB615800).
文摘Catalytic methylation of toluene with methanol is an important alternative pathway for xylene production.Previous studies have indicated that methanol always undergoes several side reactions on acidic zeolites,resulting in oxygencontaining byproducts such as dimethyl ethers,ketones,and carboxylic acids.Herein,the presence and distribution of the oxygenated compounds formed during toluene methylation were firstly examined by systematic chromatographic analysis.Plausible formation mechanisms for the various oxygenates are discussed.The most problematic byproduct is found to be acetic acid,which can lead to inferior product quality and damage downstream units.A feasible solution is presented for oxygenate removal after toluene methylation,in which acetic acid is eliminated by catalytic decomposition into low-boilingpoint acetone over a MgO catalyst.This process allows for all of the low-boiling-point oxygenates,including methanol,dimethyl ether,acetone,and butanone,to be removed from the aromatics phase,taking advantage of the temperature of the reaction effluent and standard distillation equipment.X-ray diffraction was used to characterize the crystal phase of the fresh and used MgO decarbonylation catalysts,while thermogravimetry/mass spectrometry and Fourier-transform infrared spectroscopy were applied to investigate the transformation mechanism of acetic acid over the decarbonylation catalyst.CO insertion and ketonization of acetic acid accounted for the formation and elimination of acetic acid,respectively.The combined methylation/decarbonylation process should enable the production of high-quality xylenes,an important industrial feedstock,by overcoming the main technical obstacles associated with the toluene methylation process.
文摘To improve their thermal stability, La0.8Sr0.2MnO3 cordierite monoliths are washcoated with mayenite, which is a novel Al-based material with the crystal structure of 12MO 7Al2O3 （M= Ca, Sr）. The monoliths are characterized by means of nitrogen adsorp- tion/desorption, scanning electron microscopy, and X-ray diffraction. Catalytic performances of the monoliths are tested for methyl methacrylate combustion. The results show that mayenite obviously improves both the physic- chemical properties and the catalytic performance of the monoliths. Because mayenite improves the dispersity of Lao.sSro.2MnO3 and also prevents the interaction between La0.8Sr0.2MnO3 and cordierite or γ-A1203, both crystal structure and surface morphology of La0.8Sr0.2MnO3 phase can thereby be stable on the mayenite surface even at high temperature up to 1050 ℃. Under the given reaction conditions, La0.8Sr0.2MnO3 monolith washcoated with 12SrO. γ-A1203 shows the best catalytic activity for methyl methacrylate combustion among all the tested monoliths.
