| In order to cope with the worldwide increase in energy demand,the increase in the cost of fossil fuels,and global warming,the development and utilization of clean and renewable biomass energy is a high priority that needs to be addressed globally.However,the biomass components are complex,and the quality of the bio-oil produced by pyrolysis is low,which limits the development and utilization of biomass energy.The use of acid pretreatment technology can change the chemical composition and improve the characteristics of biomass.In this study,ultrasonic assisted technology was added on the basis of traditional acid pretreatment to improve the efficiency of chemical pretreatment of biomass,so as to obtain high-quality bio-oils with high value-added chemicals,and provide a theory for optimizing pretreatment process prior to fast pyrolysis.In this thesis,pine wood(Pinus tabuliformis Carr.)is used as the raw material,and three variables of different acid concentration,processing time and ultrasonic amplitude are used to pretreat the pine wood.First,Py-GC/MS was used to study the components of pyrolysis products of pine wood samples before and after ultrasonic-assisted acid pretreatment,and to explore the effect of pretreatment on the distribution of rapid thermal cracking products to optimize the pretreatment conditions of biomass raw materials;Compositional analysis,crystallinity analysis,electron microscopy,and infrared spectroscopy were used to explore the effects of ultrasonic-assisted acid pretreatment on the physicochemical properties of pine wood.Finally,thermogravimetric analysis was utilized to study the fast pyrolysis performance of pine wood.The main conclusions are as follows:(1)In order to completely crack the pine wood raw materials to produce a high content oflevoglucosan,Py-GC/MS was used to perform a pyrolysis reaction on the pine wood samples pretreated with different variables.According to the product,it was concluded that 100%amplitude ultrasound was used to assist the 1%concentration of phosphoric acid solution for30min as the best pretreatment condition for rapid pyrolysis of pine wood to obtain high anhydrosugar yield,the chromatographic peak area of levoglucosan was 21.73%.(2)Through SEM analysis,ultrasonic-assisted acid pretreatment can destroy the structure of wood cells to a certain extent,causing partial degradation of hemicellulose and cellulose polymer structures.However,the ultrasonic-assisted acid pretreatment has more significant damage to pine cell wall.(3)The ultrasonic-assisted acid pretreatment has a significant effect on the removal of inorganic metal elements in pine wood,especially Ca and Mg divalent metal elements.Through FT-IR analysis,ultrasonic-assisted acid pretreatment promoted the hydrogen bond break between cellulose molecules in pine wood samples,and some carbon chain structures in the molecule were broken.At the same time,it was found that ultrasonic-assisted acid pretreatment did not significantly change the lignin structure.(4)Through XRD analysis,the crystal structure of the pretreated cellulose did not change.The crystallinity of ultrasonic-assisted acid-treated pine wood samples increased from 42.4%(untreated raw materials)to 60.2%.(5)The rapid thermal cracking of pine wood is mainly divided into three stages:drying stage(<150?),pyrolysis stage(150?-450?),and carbonization stage(450?-750?).The DTG curve showed a shoulder-shaped side peak(mainly hemicellulose pyrolysis)and a distinct main peak(mainly cellulose pyrolysis).The ultrasonic-assisted acid pretreatment made the shoulder-side peak almost disappeared,and the initial pyrolysis temperature The T_P and T_M temperatures dropped to 260?and 365?,respectively.By analyzing the micromorphology,chemical composition,pyrolysis characteristics and pyrolysis product distribution of pine wood raw materials,it was proved that ultrasonic assisted acid pretreatment can effectively improve the pretreatment efficiency,reduce the pretreatment time,improve the biomass pyrolysis performance and obtain high-quality bio-oil.The research results can provide biomass energy enterprises with an efficient and feasible biomass pre-treatment technology,and promote the industrialization of bioenergy. |
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