Convertion Of Isobutanol Into Olefins And Aromatics On Zeolites: Product Distribution Control And Reaction Mechanism Study

Low-carbon olefins and light aromatic hydrocarbons are the most basic chemical raw materials,and their industrial development has an important impact on the chemical industry.At present,low-carbon olefins and light aromatic hydrocarbons are mainly obtained through traditional petrochemical and coal chemical industries.With the shortage of traditional fossil energy and the growing market demand,the development and utilization of biomass has become the current research hotspot.Biological isobutanol is a new generation of biomass energy produced through biomass fermentation.The production of low-carbon olefins and light aromatic hydrocarbons using biological isobutanol as a raw material is a very promising new process route that does not depend on traditional fossil energy sources.ZSM-5 is a common aromatization catalyst.One-step conversion of biological isobutanol to lower olefins and light aromatics can be achieved with its acidity and shape-selective catalytic properties.However,the conversion behavior of biological isobutanol is complicated and dozens of products are involved.Therefore,the research on the biological isobutanol conversion pathway is of great significance for understanding the reaction mechanism and improving the selectivity of the target product.The activity of catalytic biological isobutanol conversion on ZSM-5 was affected by experimental conditions such as temperature and W/F.Besides,the strength and density of Br?nsted acid active sites have an important influence on the product distribution.Stronger Br?nsted acid and higher acid density favor the aromatization reaction,but too strong Br?nsted acid and too high acid density may lead to carbon deposition and cracking reactions.The literature reports that Ga active species can replace H⁺on Br?nsted acid sites on ZSM-5 zeolite to form BAS-Ga structure and regulate the acid properties of the catalyst.On the other hand,Ga metal sites having a catalytic direct dehydrogenation reaction is formed,thereby changing the reaction path and promoting the formation of aromatics products.This dissertation mainly studies the effects of different temperature,W/F,and Si/Al conditions on the distribution of biological isobutanol conversion products on ZSM-5,and forms a preliminary understanding of the biological isobutanol conversion pathway.The distribution of Ga-modified control acid sites was loaded on ZSM-5 by incipient wetness impregnation method,and the selectivity of the products was investigated and analyzed.Combined with the literature analysis,the conversion pathway of biological isobutanol was proposed.In addition,the effect of the matching relationship between the Ga active species and the Br?nsted acid in the biological isobutanol conversion reaction on the product selectivity has also been studied in this paper.Main conclusion as below:1.Br?nsted acid sites are active center for the formation of aromatics from biological isobutanol.This dissertation investigates the products distribution at different Si/Al ratios?25-150?,temperatures?300-550°C?,W/F?0.05-0.8h?and products are divided into alkanes,olefins and aromatics.The olefins are mainly ethylene,propylene and butylene isomers,and the aromatics are mainly benzene,toluene and xylene.Decreasing the Si/Al ratios and increasing W/F value promote the selectivity of aromatics.The selectivity of olefins varies with Si/Al ratios,W/F,and temperature is in contrast to aromatic hydrocarbons.2.Biological isobutanol is first dehydrated to form isobutylene on ZSM-5,and isobutylene is in the acid position.The isobutene is produced by the isomerization reaction,and a high carbon number olefin is produced by the polymerization reaction?C₆⁼-C₉⁼?.High-carbon olefins are cracked to produce lower olefins?C₂⁼-C₄⁼?.Polymeric cracking reactions are reversible reactions.High-carbon olefins are converted to aromatics and alkanes through a hydrogen transfer route.3.The Ga metal modification can significantly improve the aromatics selectivity on ZSM-5.The Ga active species replace the H⁺on the Br?nsted acid at surface of the zeolite,forming BAS-Ga structure and promote the dehydrogenation aromatization reaction through the synergy effect.The reduction treatment at high temperature 500°C facilitates the migration of Ga active species in the ZSM-5 pore channel,replaces H⁺on the Br?nsted acid sites and further enhances the aromatics selectivity.4.Water may inhibit the dehydrogenation aromatization activity of isobutylene on Ga-modified ZSM-5 by competitive adsorption or changing the structure of active sites.