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
With the shape selective zeolite catalyst,toluene alkylation with methanol to para-xylene(MTPX)technology could produce highly pure para-xylene(PX)in one step.The lower feedstock cost and less energy consumption in pr...With the shape selective zeolite catalyst,toluene alkylation with methanol to para-xylene(MTPX)technology could produce highly pure para-xylene(PX)in one step.The lower feedstock cost and less energy consumption in products separation make it more competitive compared to the current toluene disproportionation route.Thus,MTPX is regarded as the most reasonable production route for PX production.This article reviews the strategies that applied to the preparation of high-performance catalysts for MTPX,with special focus on the precise control of pore dimension and acid sites distribution in zeolite to achieve the highest selectivity to PX.The outlook of the MTPX catalyst is also proposed to guide the catalyst development in the field.展开更多
Para-xylene was chosen as the probe molecule to study adsorption thermodynamics and diffusion kinetics on NaY zeolite and composite structured NaY zeolite synthesized by in-situ crystallization from kaolin microsphere...Para-xylene was chosen as the probe molecule to study adsorption thermodynamics and diffusion kinetics on NaY zeolite and composite structured NaY zeolite synthesized by in-situ crystallization from kaolin microsphere(designated as Na Y/kaolin composites) separately, using a high precision intelligent gravimetric analyzer(IGA). The adsorption isotherms showed normal Langmuir type-Ⅰ behaviors. The increased adsorption heat with an increasing p-xylene coverage supported a mechanism of phase transition, diffusion and re-arrangement of p-xylene molecules during the adsorption process. The rearrangement seemed to be most pronounced at an adsorption loading of 2.13 and 2.29 mmol/g for Na Y zeolite and Na Y/kaolin composites respectively. Compared with Na Y zeolite, a 2—3 times higher in the diffusion coefficient of p-xylene was observed on Na Y/kaolin composites when the pressure was more than 50 Pa. Temperature-programmed desorption(TPD) of p-xylene on two samples from room temperature to 450 ℃ at a special loading has also been investigated by IGA. Results showed only single desorption peak appeared for Na Y zeolite, indicating that adsorption can only occur in the super-cage structure. Comparably, there were two different peaks for in-situ synthesized Na Y zeolite, corresponding to the two thermo desorption processes in both super-cage structure and the channels provided by kaolin, respectively.Key words:展开更多
The application of X zeolite in the areas for producing para-xylene by adsorptive separation, N_2/O_2 separation,etc., was reviewed, and the framework SiO_2/Al_2 O_3 molar ratio, the cations and the water content of X...The application of X zeolite in the areas for producing para-xylene by adsorptive separation, N_2/O_2 separation,etc., was reviewed, and the framework SiO_2/Al_2 O_3 molar ratio, the cations and the water content of X zeolite significantly affected its selectivity and capacity. As the active component of para-xylene adsorbent, the X zeolite with a framework SiO_2/Al_2 O_3 molar ratio of 2.2—2.4 coupled with cations of Ba^(2+) and K^+, as well as a water content of 4.0%—5.0% exhibited higher para-xylene selectivity. For N_2/O_2 separation, higher N_2 capacity and N_2/O_2 separation factor were achieved when the X zeolite had a framework SiO_2/Al_2 O_3 molar ratio of 2.0 coupled with Li^+ cations. The introduction of another cation in X zeolite could further increase the N_2/O_2 separation factor, while the adsorption of water, however, could lead to a remarkable decrease of N_2 capacity. Besides, the X zeolite could be used in adsorptive separation of highly pure He and selective adsorption of CO_2, CO, CH_4, N_2, Ar,and H_2.展开更多
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the funding support(Project No.:CF9300172922)from National Institute of Clean-and-low-carbon Energy.
文摘With the shape selective zeolite catalyst,toluene alkylation with methanol to para-xylene(MTPX)technology could produce highly pure para-xylene(PX)in one step.The lower feedstock cost and less energy consumption in products separation make it more competitive compared to the current toluene disproportionation route.Thus,MTPX is regarded as the most reasonable production route for PX production.This article reviews the strategies that applied to the preparation of high-performance catalysts for MTPX,with special focus on the precise control of pore dimension and acid sites distribution in zeolite to achieve the highest selectivity to PX.The outlook of the MTPX catalyst is also proposed to guide the catalyst development in the field.
基金financial support from the National Natural Science Foundation of China(20976077,21076100)the National 973 Foundation of China(2007CB216403)
文摘Para-xylene was chosen as the probe molecule to study adsorption thermodynamics and diffusion kinetics on NaY zeolite and composite structured NaY zeolite synthesized by in-situ crystallization from kaolin microsphere(designated as Na Y/kaolin composites) separately, using a high precision intelligent gravimetric analyzer(IGA). The adsorption isotherms showed normal Langmuir type-Ⅰ behaviors. The increased adsorption heat with an increasing p-xylene coverage supported a mechanism of phase transition, diffusion and re-arrangement of p-xylene molecules during the adsorption process. The rearrangement seemed to be most pronounced at an adsorption loading of 2.13 and 2.29 mmol/g for Na Y zeolite and Na Y/kaolin composites respectively. Compared with Na Y zeolite, a 2—3 times higher in the diffusion coefficient of p-xylene was observed on Na Y/kaolin composites when the pressure was more than 50 Pa. Temperature-programmed desorption(TPD) of p-xylene on two samples from room temperature to 450 ℃ at a special loading has also been investigated by IGA. Results showed only single desorption peak appeared for Na Y zeolite, indicating that adsorption can only occur in the super-cage structure. Comparably, there were two different peaks for in-situ synthesized Na Y zeolite, corresponding to the two thermo desorption processes in both super-cage structure and the channels provided by kaolin, respectively.Key words:
文摘The application of X zeolite in the areas for producing para-xylene by adsorptive separation, N_2/O_2 separation,etc., was reviewed, and the framework SiO_2/Al_2 O_3 molar ratio, the cations and the water content of X zeolite significantly affected its selectivity and capacity. As the active component of para-xylene adsorbent, the X zeolite with a framework SiO_2/Al_2 O_3 molar ratio of 2.2—2.4 coupled with cations of Ba^(2+) and K^+, as well as a water content of 4.0%—5.0% exhibited higher para-xylene selectivity. For N_2/O_2 separation, higher N_2 capacity and N_2/O_2 separation factor were achieved when the X zeolite had a framework SiO_2/Al_2 O_3 molar ratio of 2.0 coupled with Li^+ cations. The introduction of another cation in X zeolite could further increase the N_2/O_2 separation factor, while the adsorption of water, however, could lead to a remarkable decrease of N_2 capacity. Besides, the X zeolite could be used in adsorptive separation of highly pure He and selective adsorption of CO_2, CO, CH_4, N_2, Ar,and H_2.
