Study On Catalytic Materials For Direct Conversion Of Syngas Into Aromatics

Aromatics are important raw materials in the current chemical industry.With the rapid economy development and the prosperity of the manufacturing industry,the demand for aromatics is growing fast.Meanwhile,the import quantity and foreign trade dependence continue to rise.At present,aromatics mainly comes from the catalytic reforming of naphtha.There are few petroleum resources but lots of coal in our country.So the research on alternative routes using coal as raw materials could alleviate the shortage of domestic aromatics.And it’s also important for the development of the downstream industry of aromatic hydrocarbons.Syngas(CO/H2)dirives form coal is clean and efficient.The synthesis of aromatics from syngas,which be produced by coal gasification,has drawn lots of attention.The traditional synthesis of aromatics from syngas used a two-step process with low conversion and energy efficiency.In the meantime,the reaction equipment is also a bit complicated.In this study,we designed a bifunctional catalyst with Fe embedded in the HZSM-5 zeolite,named Fe@HZSM-5.It successfully combined Fischer-Tropsch synthesis with aromatization reaction and realized the direct conversion of syngas to aromatics.This thesis first explored the optimal synthesis method,crystallization time,metal loading and Si/Al ratio of Fe@HZSM-5.By analyzing the performance of the catalyst and XRD characterization results,we found that the embedded zeolite prepared by the solvent-free method has better crystallinity.And the optimal crystallization time was 72 h.In addition,when the Fe loading was 15 wt%and the Si/Al ratio of the zeolite was 40,the Fischer-Tropsch synthesis and aromatization reaction achieved the best coupling effect.The performance evaluation of embedded catalyst Fe@HZSM-5,physical mixed catalyst Fe-HZSM-5,supported catalyst Fe/HZSM-5 was carried out in fixed bed reactor.And through XRD,N2 adsorption-desorption,SEM,XPS,TG characterization,the structure,morphology,surface element composition,carbon deposits of catalyst were investigated.Analysis results showed that Fe is mainly located inside the embedded zeolite,which make it closer to acidic sites of the zeolite and promote the aromatization of intermediate.Compared with physical mixed and supported catalysts,it also has more mesoporous structure,thereby facilitating the transfer of product and bringing it excellent carbon deposition resistance.We further optimized the reaction conditions and found that Fe@HZSM-5 has the best performance at 300℃,1.0 MPa,H2:CO=1,the aromatics selectivity reached 20.46%at CO conversion of 64.79%.In order to improve the selectivity of aromatics,Zn,Mn,and Mo promoters were introduced to synthesize bimetal embed catalyst.And through the H2-TPR and NH3-TPD characterization,we explored the effects of different promoters on the reduction and surface acidity of the catalyst.Mn and Mo inhibited the reduction of Fe species,while the appropriate amount of Zn promoted the reduction of Fe.The addition of these three promoters increased acid content in zeolite surface and improved the aromatization performance of the catalyst.