Study On The Catalysts For Synthesis Of 1,3-butadiene From Ethanol

1,3-butadiene（BD）is an important building block in chemical industry and generally used for synthetic polymers and rubbers.BD is mainly obtained as by-product of ethylene production in the process of hydrocarbon steam cracking.While the nonrenewable resources with a single source limits its sustainable development.As the ethanol production from nonfood biomass feedstock is widely used and gradually matured,the process of ethanol conversion to BD has attracted extensive attentions in recent years.This article explores two types of catalyst systems namely Mg-Al and Zr-Si for BD conversion from ethanol.The structure and surface chemical properties of the catalysts were systematically studied.The effects of pore structure,acid-basic strength and its catalytic activities of bifunctional catalysts on the catalytic performance were systematically investigated.The structure-propertiesrelationship for the catalyst was further understood.In the meantime,the stability of the catalyst with high activity was preliminary texted.For Mg-Al catalyst systemcompared with the co-precipitation,hydrotalcite-like compounds（HTLcs）and impregnation methods,more acid sites as well as basic sites were found on the surface prepared by co-precipitation methods.The catalyst with MgO content of 35 wt%and calcination temperature at 773K shows that a relatively good BD selectivity of 20.06%.Based on the relationship between distribution of products and the catalyst properties,we may safely arrive at the conclusion that the weak acid and basic sites or a little numbers of strong basic sites should be active sites of ethanol conversion to BD.The catalysts of ZrO₂/Nano-Si O₂,ZrO₂/SBA-15,ZrO₂/MCM-41 and ZrO₂/SiO₂with 2 wt%ZrO₂ content were prepared by impregnation.The influence of different kinds of SiO₂ carrier on the BD synthesis from combined feed of ethanol and acetaldehyde was investigated.Comprehensive analysis shows that there are weak acid and basic sites on the surface of all the samples.The surface area of the catalyst using different support decreases as ZrO₂/MCM-41>ZrO₂/SBA-15>ZrO₂/Nano-SiO₂>ZrO₂/SiO₂,while the average diameter decreases as ZrO₂/Nano-SiO₂>ZrO₂/SBA-15>ZrO₂/SiO₂>ZrO₂/MCM-41.ZrO₂/Nano-SiO₂ has the best performance.The influences of the calcination temperature and ZrO₂ content are also investigated.The surface area of the catalysts decreased with the unchanged average pore,while the Lewis acidity increases with the increasing calcination temperature（723K⁹73 K）,which is still considered as weak acid site.With the increasing Zr O₂ content（1 wt%⁴ wt%）,the surface area of the catalyst samples increased,while the acidity kept unchanged.The results show that the 2 wt%ZrO₂/Nano-SiO₂ calcined at 823 K shows the best performance with the selectivity of 93.18%and conversion of 58.52%when reacted at 593 K,a WHSV of 1.8 h^-1and 3.5:1 molevolume ethanol-to-acetaldehyde in an atmospheric fixed-bed reactor.The structure and properties of the ZrO₂ and Nano-SiO₂ was investigated systematically.Compared with dry-mixed samples,the average pore diameter of the catalyst prepared by impregnation is larger.The ZrO₂ could be dispersed on the surface of Nano-SiO₂ more uniformly,while the existence mode of the catalyst is amorphous SiO₂.The interaction between ZrO₂ and Nano-SiO₂ is stronger because of the formation of Zr-O-Si bonds are formed.The investigation results of catalyst stability show that the selectivity of BD and conversion of the catalyst are barely lower after reaction for 30 h.The characterizations of BET and NH₃-TPD indicate that the BET surface areas,average pore diameter and the acid sites are almost nothing to reduce.This means that there is no carbon deposition on the surface after reaction for 30 h.