Preparation Of Aromatic Compounds From Bamboo Lignin And Oils By Microwave-assisted Catalytic Pyrolysis

China is rich in bamboo resources,and 85% of the world's bamboos grow in the south of the Yangtze River.According to the statistics of the State Forestry Administration,China's bamboo output in 2017 was 2.72 billion,of which 1.61 billion were moso bamboo?phyllostachys pubescens?,and the output value of bamboo industry reached 234.6 billion yuan.As the most widely used bamboo species in bamboo plants,moso bamboo is closely related to people's daily life and plays an important role in clothing,food,housing,transportation,view and decoration.However,in the process of processing and utilization of bamboo products,a large number of processing wastes have been produced,such as the discharge of black liquor from papermaking and the processing waste of bamboo-related food.Most of the wastes can not be properly treated because of the high output,time-consuming treatment and lack of high-value utilization channels.The production of a large number of bamboo processing wastes is not only a waste of resources,but also a serious environmental pollution problem caused by the mildew of the wastes.The raw materials of bamboo products are mainly composed of cellulose,hemicellulose and lignin.Among them,the research on cellulose and hemicellulose is relatively perfect.However,due to the complex structure of lignin and the difficulty of degradation,the research on lignin is still imperfect.But researchers have also found that lignin,as the second abundant component of lignocellulose biomass,is the only non-petroleum resource that can provide aromatic compounds in nature.Therefore,finding a suitable method to degrade bamboo lignin and turn it into a treasure will not only help to deal with the waste disposal problem in bamboo processing industry,but also help to improve the economic,social and environmental benefits of the bamboo industry in China.In this paper,the microwave catalytic pyrolysis technology,which combines the advantages of microwave technology and catalytic technology,is used to explore the relevant conditions in the pyrolysis process of bamboo lignin.The aim is to provide theoretical basis for finding the best catalyst and reaction conditions in the process of preparing aromatic compounds by microwave catalytic pyrolysis of lignin.1.Microwave-assisted metal chloride catalytic depolymerization of lignin in hydrochloric Acid-Formic acid systemIn order to understand the properties of lignin and its depolymerization products,we first chose to depolymerize lignin in mild liquid phase to prepare aromatic compounds monomers.With the help of microwave-assisted catalysis,the effects of different catalysts on lignin depolymerization to prepare phenolic compounds under mild conditions were investigated in hydrochloric Acid-Formic acid system.The results showed that different catalysts played different catalytic roles in the process of lignin depolymerization.The catalytic effect was not only reflected in the content of products,but also in the types of products.Transitional metal chlorides such as FeCl₃,ZnCl₂ and MnCl₂ can catalyze lignin depolymerization to produce a large number of products,while alkaline earth metal chlorides such as MgCl₂ and AlCl₃ play a better role in promoting lignin depolymerization to produce a specific compound.Under this experimental condition,lignin produced the most vanillin when catalyzed by MnCl₂,and its yield was 2.78%.The catalytic abilities of different metal chlorides were as follows: no catalyst < MgCl₂ < AlCl₃ < FeCl₃ < ZnCl₂ < MnCl₂.Among them,MnCl₂ had the best catalytic effect.The highest yield of total monophenol products is 48.7%,with about 23.0% G-type monophenols,11.9% S-type monophenols and 14.8% H-type monophenols were found.2.Preparation and characterization of composite catalyst ZSM-5/MCM-41Microwave-assisted catalytic fast pyrolysis?MACFP?technology,which combines the advantages of rapid pyrolysis and product shape selection,has been widely used in industrial fields in recent years.Among many factors affecting the reaction?reaction temperature,reaction time,catalyst selection,etc.?,an excellent catalyst can not only increase the reaction efficiency,but also improve the economic benefits of lignin pyrolysis.Therefore,in this part,we prepared ZSM-5/MCM-41 composite molecular sieve catalyst by hydrothermal high-temperature synthesis method.The catalysts were characterized by SEM,TEM,N₂-BET and the catalytic effect of the catalyst was tested by preliminary experiments.The results showed that the catalyst had good catalytic effect.Under the catalysis,the oil yield of lignin and oils increased by 15.8% and 14.2%,respectively.And the yield of monocyclic aromatic hydrocarbons of lignin increased by 22.70%,while the highest yield of aromatic hydrocarbons in oils was 61.75%.3.Microwave-assisted co-pyrolysis of lignin and oils to aromatics compounds over ZSM-5/MCM-41 catalystAs a kind of biomass material with low H/Ceff?hydrogen/carbon efficiency?,lignin produces a large amount of coke during pyrolysis,which prevents its further pyrolysis into bio-oil.Therefore,in this part,oils with high H/Ceff was introduced as hydrogen supplying material to pyrolysis with lignin.Under these conditions,the optimum reaction conditions?catalytic temperature,material ratio,catalyst to oils ratio?were discussed from three aspects?bio-oil yield,ratio of oxygenated compounds and selectivity of monocyclic aromatic hydrocarbons?.The experimental results show that catalytic co-pyrolysis is a complex reaction process,and many reaction conditions would affect the final reaction results.Considering comprehensively,the optimum reaction conditions are as follows: the catalytic temperature was 500 degree C,the ratio of raw material to catalyst was 10:1,and the ratio of lignin to oils was 2:1.Under these conditions,the conversion rate of raw materials can reach 76.00%,and the oil yield was higher than that of lignin alone?20.00%?by about 20%.The ratio of aromatics was 50.31%,and the selectivity of monocyclic aromatics was 42.83%,both of which were greatly improved compared with the use of lignin alone.4.Problems to be solvedAlthough two pyrolysis methods were used to catalyze the pyrolysis of lignin and oils to produce aromatic compounds.There are still some problems to be solved in the process of experiment,such as the lack of deep discussion on pyrolysis mechanism,the time-consuming of catalyst synthesis,and the gap between laboratory conditions and actual industrial production,which need to be solved in the future.Microwave catalytic pyrolysis combines the advantages of microwave technology and catalytic technology.It is helpful for the high value utilization of lignin and oils under suitable catalytic conditions and reaction conditions In this paper,composite catalysts were synthesized and microwave-assisted catalytic pyrolysis of lignin and oils to prepare aromatic compounds was used to study the related problems in the reaction process.