The Study On Higher Alcohols Synthesis Over CuZnAl Catalyst Under High Heat Treatment Pressure

In recent years,with the increasing pressure of global energy and environment,every country in the world have done lots of work on the production of liquid fuels from non-oil routes.Higher alcohols have a high octane number and can be used not only as a fuel additive,but also as a direct substitute for traditional liquid fuels.At present,there are many problems of the catalyst for the direct conversion of syngas into higher alcohols,such as the high price,the low activity,the harsh reaction conditions,the excessive product types and the excessive methanol,etc.,which all limit its industrial application.In view of the characteristics of the slurry bed reactor,our group proposed a new catalyst preparation method,named as complete liquid-phase method.When the methanol synthesis process was carried out using the CuZnAl catalyst prepared by the complete liquid-phase method,it was unexpectedly found that the ethanol was appeared in products.However,the structure of the catalyst was sensitive,thus the stability and repeatability of the catalyst were poor.Therefore,a more in-depth research should be conducted.This paper first studied the effects of different heat treatment pressure and heat treatment time on the structure and properties of catalysts.In order to reduce the formation of alkanes and CO₂,the effects of different heat treatment N₂atmosphere flow rates and different additives under high heat treatment pressure were also investigated.The catalysts were characterized by XPS,XRD,H₂-TPR,NH₃-TPD and N₂ adsorption-desorption.The main conclusions were as follows:1.When the catalyst was heat treated under high pressure,the more spinel phase was formed,and the amount of Cu⁺species was decreased.What’s more,the surface acid amount was changed,and the pore volume and pore size became larger.The catalyst exhibited the best catalytic performance when heat treated under 1.0 Mpa.2.Prolonging the heat treatment time of catalysts under high pressure enhanced the interaction between the various species,and the more spinel phase was formed.Moreover,the amount of Cu⁺species and the surface acidity of catalysts were reduced,but the pore volume and pore size became larger.When catalyst was heat treated under a proper time（7 h）,the higher alcohols mass fraction in total alcohols was the highest.3.The more Al content in catalyst increased the acid amount on catalyst surface,which improved the selectivity of alkane.Reducing the Al content in catalyst could effectively decrease the hydrocarbon products formation,but the higher alcohols mass fraction in total alcohols was also dreased.4.Increasing the N₂ atmosphere flow rate under high heat treatment pressure had little effect on the structure and performance of the catalyst,and it did not decrease the selectivity of hydrocarbons.5.The addition of carbon nanotube did not inhibit the water gas reaction,instead the catalyst performance was reduced.The addition of Sn suppressed the water gas reaction,and the higher alcohols mass fraction in total alcohols was at a high value.However,the activity of the catalyst decreased significantly.6.The alcohols chain growth ability of CuZnAl catalyst prepared by the complete liquid-phase method would be greatly influenced by changing the process conditions.In catalyst,an appropriate amount of Cu⁺species could enhance the synergistic effect of Cu⁺-Cu⁰ sites,thus the higher alcohols mass fraction in total alcohols was improved.In addition,a small proportion of weak acid in total acid amount,the large pore volume and pore size were favorable for higher alcohols synthesis.