计算机流程模拟技术已成为当今石油化工技术研发、设计和生产优化的有效手段,其核心基础是建立数学模型,利用数学模型模拟复杂工业过程。利用Aspen Plus V12稳态模拟软件对工业对二甲苯(PX)工艺流程中二甲苯塔进行模拟设计,使设计工作...计算机流程模拟技术已成为当今石油化工技术研发、设计和生产优化的有效手段,其核心基础是建立数学模型,利用数学模型模拟复杂工业过程。利用Aspen Plus V12稳态模拟软件对工业对二甲苯(PX)工艺流程中二甲苯塔进行模拟设计,使设计工作更加可靠、高效、节能,在Aspen Plus软件中先后使用简捷塔模块DSTWU、严格精馏塔模块RadFrac、灵敏度分析、可视化水力学分析工具探讨流程模拟软件对精馏塔设计的指导意义。结果表明:软件模拟结果与某厂PX工艺装置设计数据吻合良好,另外通过灵敏度分析,找到了更优的精馏塔进料位置,降低了回流比和塔顶塔釜热负荷,达到了节能降耗的目的,优化了原有设计。同时也利用RadFrac模块内置的塔内件数据讨论了可视化水力学分析在精馏塔设计中的应用,可以很准确地计算塔径,这些都对指导设计工作具有一定的参考价值。展开更多
Two-step conversion of methanol to aromatics via light hydrocarbons can significantly improve the conversion stability compared with direct aromatization of methanol,but it remains a challenge to achieve a high p-xyle...Two-step conversion of methanol to aromatics via light hydrocarbons can significantly improve the conversion stability compared with direct aromatization of methanol,but it remains a challenge to achieve a high p-xylene(PX)selectivity.Herein,silica coating was firstly used to passivate external acid sites of ZSM-5 catalyst for the aromatization of light hydrocarbons by the chemical liquid deposition method.With the increase of SiO_(2) deposition,the density of the external acid sites of the catalyst was decreased from 0.1 to 0.03 mmol·g^(-1),which inhibited the surface secondary reactions and increased the PX/X from 34.6% to 60.0%.In view of the fact that the aromatization process in the second step was partly inhibited as methanol was consumed in advance in the upper methanol-to-light hydrocarbons catalyst layer,part of methanol was directly introduced into the lower aromatization catalyst layer to promote the alkylation process during the aromatization,which decreased the toluene selectivity from 34.5% to 14.3% but increased the xylene selectivity from 40.0%to 55.3%.It was also found that an appropriate external acid density was needed for aromatization catalyst to strengthen the alkylation process and improve the selectivity of xylene under the conditions of methanol introduction.展开更多
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
文摘计算机流程模拟技术已成为当今石油化工技术研发、设计和生产优化的有效手段,其核心基础是建立数学模型,利用数学模型模拟复杂工业过程。利用Aspen Plus V12稳态模拟软件对工业对二甲苯(PX)工艺流程中二甲苯塔进行模拟设计,使设计工作更加可靠、高效、节能,在Aspen Plus软件中先后使用简捷塔模块DSTWU、严格精馏塔模块RadFrac、灵敏度分析、可视化水力学分析工具探讨流程模拟软件对精馏塔设计的指导意义。结果表明:软件模拟结果与某厂PX工艺装置设计数据吻合良好,另外通过灵敏度分析,找到了更优的精馏塔进料位置,降低了回流比和塔顶塔釜热负荷,达到了节能降耗的目的,优化了原有设计。同时也利用RadFrac模块内置的塔内件数据讨论了可视化水力学分析在精馏塔设计中的应用,可以很准确地计算塔径,这些都对指导设计工作具有一定的参考价值。
基金financial support from the National Natural Science Foundation of China(21978191 and 22278292)Key Research and Development Project of Shanxi Province(International Science and Technology Cooperation Program)(201803D421011)。
文摘Two-step conversion of methanol to aromatics via light hydrocarbons can significantly improve the conversion stability compared with direct aromatization of methanol,but it remains a challenge to achieve a high p-xylene(PX)selectivity.Herein,silica coating was firstly used to passivate external acid sites of ZSM-5 catalyst for the aromatization of light hydrocarbons by the chemical liquid deposition method.With the increase of SiO_(2) deposition,the density of the external acid sites of the catalyst was decreased from 0.1 to 0.03 mmol·g^(-1),which inhibited the surface secondary reactions and increased the PX/X from 34.6% to 60.0%.In view of the fact that the aromatization process in the second step was partly inhibited as methanol was consumed in advance in the upper methanol-to-light hydrocarbons catalyst layer,part of methanol was directly introduced into the lower aromatization catalyst layer to promote the alkylation process during the aromatization,which decreased the toluene selectivity from 34.5% to 14.3% but increased the xylene selectivity from 40.0%to 55.3%.It was also found that an appropriate external acid density was needed for aromatization catalyst to strengthen the alkylation process and improve the selectivity of xylene under the conditions of methanol introduction.
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.
