Study On The Reaction Process Of Catalytic Cracking Dry Gas Aromatization

At present,the catalytic cracking process is an important means of China's petroleum refining process.Thecatalytic cracking process is by-product about 3%⁵% of catalytic dry gas,each year,China's refinery can produces nearly 8.03×106t catalytic dry gas,catalyticdrygas resources are mainly used as fuel gas,and even some surpluscatalytic dry gasget into the torch system burned,resulting in a huge waste of resource,the aromatization reaction of catalytic dry gas to produce aromatics,can make full use of a large number of cheap catalyticdry gas resource,turning waste into treasure andimprove the economic benefits of refinery.ZSM-5 molecular sieve with its unique microporous pore structure and acid properties is considered to be one of the most effective catalyst carrier for aromatization reaction,however,the traditional template synthesis method of ZSM-5 molecular sieve is costly and polluted.Because the template-free ZSM-5 molecular sieve synthesis process does not use the template agentthus the synthesis process is more environmentally friendly and low cost,Therefore,it is of great significance to study the synthesis of ZSM-5 molecular sieve without template.In this paper,the ZSM-5 molecular sieve was synthesized by using silica sol as the silicon source and sodium aluminate as the aluminum sourceunder the condition of hydrothermal system,and the sample were characterized by XRD,N2adsorption/desorption,Py-IR,SEMetcetera.The optimum conditions for the synthesis of ZSM-5 zeolite were: n?SiO2?: n?Al2O3?: n?Na2O?: n?H2O?=100: 2.5: 11: 2700,the crystallization temperature of the molecular sieve was 170? and the crystallization time was 36 h.The results show that the synthesized sample had typical characteristics of ZSM-5 molecular sieve,the BET specific surface area of the sample was up to 389m2/g,the sample particles show regular hexahedral structure,the sample had good crystal morphology and thermal stability,meanwhile,the sample had more Bacidity and a small amount of L acidity on the sample.The synthesized HZSM-5 was used as a catalyst carrier,and the active metal component was loaded to prepare aromatization reaction catalyst.It was found that the activity of the catalyst was closely related to its acid type and acidity strengthdistribution.After the catalyst addition of Ga,the concentration of B acid in the HZSM-5 zeolite catalyst was decreased,the concentration of L acid was increased and the ratio of Lacid/Bacid was increased,it can promote methane and ethylene dehydrogenation,oligomerization,cyclization and then takes place aromatization reaction.The conversion of methane was 32.6%,the conversion of ethylene was over 90% and the yield of aromatic hydrocarbon was 45.9% on the 2wt % Ga/HZSM-5 catalyst at reaction temperature was 550?with methane,ethylene and nitrogen as simulatecatalytic dry gas,the catalyst exhibits high reactivity.The conversion of methane was significantly increased and the activation temperature was significantly decreased.For the reaction on the Ga/HZSM-5 catalyst,the higher reaction temperature,the lower molar ratio of CH4/C2H4 and the reaction space velocity are favorable to improved feed conversion and product selectivity to aromatics.The optimum reaction conditions were as follows: reaction temperature 550?,CH4/C2H4 molar ratio 0.7,reaction volume space velocity 1000h^-1.The activity of simulated catalyticdry gas on Ga/HZSM-5 catalyst modified by rare earth metal was higher than that of Ga/HZSM-5 catalyst,especially in the Gd-Ga/HZSM-5 catalystmethane conversion reached 34.8% ang the yield of aromatics reached 55.8%,while the life of the catalyst was also increased from 8 h on Ga/HZSM-5 catalyst to 36 h.