Direct Synthesis Of Aromatic Formations From Syngas

Aromatic hydrocarbons are important chemical raw materials,which are used mainly for the production of plymers such as polystyrene,phenolic resins,nylon,polyurethane,and polythylene terphthalate fibers resins,and films.The world-wide demand for benzene derivatives,polyester fibers and resins is growing faster than 6%each year.In the current chemical industry,the production of aromatics heavily relies on petroleum resource.Approximately 70%of the global supply of Benzene,toluene,and xylenes?BTX?comes from the catalytic reforming of petroleumbased naphtha.The depletion of petroleum and the gap between supply and demand calls for a new strategy for the synthesis of aromatics.The approach to produce aromatic hydrocarbons from syngas?CO+H₂?derived from coal,shale gas and biomass has been one of the promising technologies to relieve the dependence of petroleum feedstock nowadays.In this article,direct synthesis of aromatics from syngas?CO+H₂?has been tested over a hybrid catalyst system composed of Fe-based FTS catalyst and HZSM-5 zeolite.The obtained aromatics were highly selective in the liquid hydrocarbon phase with a common content greater than 95%and the remained gaseous hydrocarons were close to the component of LPG which could be used as fuel.1.FeMn-HZSM-5 used as a model catalyst at varied reaction conditions including temperature,pressure,space velocity,H₂/CO ratio and weight ratio of HZSM-5 to FeMn catalyst were investigated for evaluating their effect on the catalyst activity,selectivity to aromatics and their content in liquid phase.Over the FeMn-HZSM-5?Si/Al=12.5?hybrid catalyst system at 593K,1.0MPa,2220mL/g/h and a H₂/CO ratio of 1.0,CO conversion was observed to be much stable and reached 69.9%,the total aromatic content in C₅₊hydrocarbon was 94.6%.2.Increasing weight ratio of HZSM-5 to FeMn catalyst from 0.5 to 5,the average CO conversion decreased from 81.9%to only 1.9%.Designed experiment of pre-carburized FeMn catalysts and obtained H₂-TPR profiles of hybrid catalysts,the result of which suggested that excess acidic environment suppressed the adsorption of CO on Fe carbides and,especially,the reduced Fe species,resulting in a remarkably lower CO conversion.3.Reactions operated over FeMn-HZSM-5 catalyst system at lower temperature 553K or high pressure 3MPa led to an easier deactivation of HZSM-5 mainly from coke deposition.The results showed that migration of alkaline K promoter of Fe-based FTS catalyst to zeolite in high temperature or extraction of framework Al by in situ formed H₂O and CO₂ could be ignorable in the study.Compared with the Fe Mn-HZSM-5,FeK-HZSM-5 deactivated seriously at same conditions probably due to heavier and olefinic primary hydrocarbons over the FeK catalyst.4.Different Fe-based FTS catalysts were prepared through precipitation and incipient-wetness methods,they were 96Fe4Mn,100Fe?the oleffins to paraffins ratio of obtained liquid product O/P=0.92?,99.2Fe0.8K?O/P=4.3?and 10Fe/TiO₂?obtained liquid product mainly composed of paraffins?and they showed originally different olefins'and paraffins'distribution.The obtained aromatic distributions were much similar probably due to the secondary reations?hydrocracking and hydro-isomerization,for example?of FTS product to produce similar intermediates for subsequent aromatization over HZSM-5 zeolite with higher Br?nsted acidity.