Experimental Study On Preparation Of Ketone Platform Compounds By Low Temperature Directional Pyrolysis Of Biomass

Biomass energy has obvious advantages such as abundant reserves,renewable,and less pollution.Therefore,the development and utilization of biomass energy is of great significance to the development of society.An effective strategy for using biomass feedstock is to convert it into a compound with a more unitary functional group,which is then converted into a hydrocarbon fuel component through an upgrade reaction.Ketone platform compounds are important precursors of hydrocarbon fuels,and long-chain hydrocarbon fuels can be prepared through condensation and hydrogenation reactions.Therefore,this paper proposes the idea of preparing ketone platform compounds by directional conversion of biomass,focusing on exploring the directional conversion mechanism of pyrolysis gas components,the characteristics of directional pyrolysis of biomass and the modification of directional catalysts.The specific content is as follows:The purpose of exploring the directional conversion mechanism of biomass pyrolysis gas model compounds is to clarify the ketonization characteristics of biomass pyrolysis gas components and their synergistic mechanism.Using Ce O₂ as a catalyst,the highest yields of ketones obtained by the directional conversion of acetic acid,n-butyraldehyde,n-butanol and ethyl acetate were 97.4%,47.2%,35.1%and 85.4%,respectively.Among them,the yield of ketone products obtained from ketonization of acetic acid was the highest at 360℃,and the yield of ketone products obtained from ketonization of the other three substances was the highest at 420℃.Too high a temperature will cause secondary reactions.Considering that acids are the main body of the study,it is best to choose a temperature not exceeding 420℃ when studying synergy.The water produced during ketonization of acetic acid will provide oxygen atoms to promote the ketonization of n-butyraldehyde;while furfural will adsorb on the active sites of the catalyst to inhibit the ketonization of acetic acid,resulting in a significant reduction in the yield of ketones.The gas-modeled biomass pyrolysis shows the following chain path as a whole during the directional conversion process,namely,alcohol→aldehyde→acid→ketone.On the one hand,the required oxygen comes from the lattice oxygen on the surface of the Ce O₂ catalyst,and on the other hand,it comes from water produced by the ketonization process.Explore the characteristics of the directional ketonization of biomass and the mechanism of the influence of metal ions on the process of biomass ketonization,and then realize the optimal design of pyrolysis gas components.Analyze the pyrolysis gas components of four kinds of biomass（rape straw,poplar,cypress and bagasse）by thermogravimetric-gas chromatography-mass spectrometry（TG-GC/MS）and thermogravimetric-mass spectrometry（TG-MS）Distribution,bagasse has the highest cellulose and hemicellulose content,ketones and ketoneable substances（acetone,pyruvic acid,acetic acid,glycolaldehyde,etc.）produced during the pyrolysis process were the highest,and the peak area accounts for 80.16%Therefore,it is determined that bagasse is the most suitable biomass source for ketonization.The maximum weight loss peak position temperature of bagasse was 395°C.It is determined that this temperature is the pyrolysis temperature,and the bagasse is subjected to directional pyrolysis.The optimal ketonization temperature was 380°C.At this time,the yield of ketones reaches 33.68%.The activity of acetone increases under high temperature conditions,and a secondary reaction occurs in the reactor.By increasing the metal ion content in the biomass by seawater immersion,it was found that an appropriate amount of metal ion can effectively increase the yield of ketones.The introduction of K⁺and Na⁺will cause the thermal stability of the macromolecular substances in the pyrolysis gas to deteriorate,the ring-opening reaction will generate more small molecular substances,and the formation of ketones and ketoneable substances such as glycolaldehyde and acetaldehyde will be promoted.Ca²⁺and Mg²⁺will increase the selectivity of ketones in the product,and promote the conversion of alcohols and aldehydes into acids,which are further transformed into ketones under the action of a catalyst.The red mud from the waste residue produced by the aluminum industry is used as a catalyst,and the red mud catalyst is modified to improve its directional catalytic effect.Using the original red mud as a catalyst,reasonably matching the pyrolysis temperature（395°C）and the ketonization temperature（420°C）,the overall ketone yield is only 18.66%.The main catalysts in the red mud are Fe₂O₃,Ca O,Al₂O₃ and Na₂O,etc.,which will promote the esterification of biomass pyrolysis gas at high temperature and carry out side reactions other than the ketonization reaction.The red mud catalyst was loaded with metal oxides（Ce O₂,Mn O₂,Ca O,Ti O₂,Zr O₂）.When the Ce O₂loading was 40wt%,the yield of ketones increased to 27.86%.However,when the Ce O₂ loading is 50wt%,the yield of ketones decreases relative to that when the Ce O₂ loading is 40wt%.Through TEM（Transmission Electron Microscopy）,it can be seen that too many metal oxides are supported,which is prone to agglomeration,and the specific surface area of the catalyst is reduced,which affects the activity of the catalyst.Excessive oxidation of the catalyst will result in a significant decrease in the yield of acetone.In order to control the oxidation of the catalyst,two metal oxides are supported on the red mud catalyst.Among them,the red mud catalyst loaded with Ce O₂ and Mn O2 has the best effect,and the overall yield of ketones is increased to 30.12%.