Study On The Process For P-xylene Production Based On The Short-process Toluene Methylation Intensification

As an indispensable chemical intermediate,paraxylene（PX）is widely used.The conventional aromatics combined process is used to produce PX.But the production capacity is far from meeting the demand of consumption.The toluene methylation process is a promising route to increase the production of high-value p-xylene from low-cost feedstocks such as toluene and methanol.However,there are still some shortcomings in the actual alkylation technology of toluene and methanol,such as low selectivity of PX and separation of xylene isomers high energy consumption.The factors influencing the para-xylene（PX）selectivity for methylation of toluene and methanol are discussed,and a short process for PX production is proposed based on the idea of PX selectivity intensification.A strategy for 99.7%PX selectivity for a toluene methylation reactor is firstly explored based on two catalytic reaction kinetics.The analysis results of the abovementioned PX selectivity influencing factors showed that the S_PX was more than99.7%at a lower residence time.The selected optimized parameter ranges（reaction temperature and pressure）were 420.0-550.0℃ and 200.0-500.0 k Pa to analyze the“trade-off”relationship between conversion rate and PX selectivity.According to the results of selective intensification,a novel short PX production process was proposed.The parameters including raw material utilization,energy consumption,and economic data,was used to evaluate the technical and economic performance of the six process.The results show that the short process using catalyst Si-Mg-P-La/ZSM-5 exhibited the highest effective utilization rates of 96.27 and 95.50%for toluene and methanol,respectively.The short process also showed a good economic value due to the multistage reactor without benzene byproducts.Thus,the obtained total annual cost（TAC）value of 8.79×10⁷（?）·year^-1was 68.9 and 87.9%of the existing processes（Case1 and Case3）.An aromatic combined PX production process integrating a short toluene methylation process was proposed to achieve the purpose of increasing PX production.The Aromatic benzene ring utilization,energy consumption,and economic data was used to evaluate the process performance.The results show that the unit energy consumption,unit production costs,and PX output of the methylation coupled process were 5.59%lower,21.75%lower,and 31.24%higher than those of the conventional aromatics combined process,respectively.Meanwhile,the effective utilization rate of benzene ring in the methylation coupled process reached the highest of 86.23%.The research results of this paper provide certain theoretical guidance value for the design of toluene and methanol alkylation process.