Experimental Study On The Mechanism Of Pyrolysis Of Lignin And Interactions Between Its Components

Biomass energy is an important renewable energy in the form of carbon-containing organic matter.The development of its pyrolysis oil production technology has the dual meaning of environmental protection and energy efficiency.Lignin is a polymer with an amorphous complex aromatic ring,and its pyrolysis behavior can greatly affect the pyrolysis process of biomass.In order to minimize the serious second reactions,this work used a wire mesh reactor to carry out relevant experimental studies on three aspects of the pyrolysis characteristics of raw lignin,different components of raw lignin and the biomass composed of cellulose and lignin.The pyrolysis characteristics of raw lignin under different heating rates(fast pyrolysis:1000 K/s and slow pyrolysis: 1 K/s)were comprehensively studied on a wire mesh reactor.It was found that fast pyrolysis promoted the conversion of solid samples to pyrolysis oil and significantly increased the molecular weight of the oil,while slow pyrolysis tended to generate equal amounts of oil and gas.The study also found that the decomposition of lignin mainly occurred at 375 to 450°C,and the temperature below 525°C helped the formation of monomes.At this stage,lignin mainly produced free radical molecules to form stable compounds through the breaking of ether bond and some C-C bonds.When the temperature was higher than 525 °C,the content of dimer compounds increased significantly.Secondly,the fast pyrolysis experiments of heavy and light molecular lignin extracted from raw lignin with THF were carried out.The results showed that light molecular lignin is the main source of oil at low temperature,while heavy molecular lignin tended to generate more char.Subsequent comparative analysis results showed that there is strong interaction between the two components during fast pyrolysis,which reduced the yield of char and increased the yield of oil.At the same time,it promoted the dehydrogenation reaction of homogeneous free radical molecules and promoted the the coupling reaction of homosplitting free radical molecules with carbonyl structure forms an oligomer,which leadedto an increase in the relative content of phenols,alcohols,and dimer compounds in the oil and a decrease in the relative content of aldehyde compounds.Finally,this paper also carried out a study on the pyrolysis characteristics of woody biomass.The results showed that the cellulose components in biomass is the main source of oil.The main products of pyrolysis were L-glucose,furans,cyclic ketones and other small molecule compounds.The lignin component tended to generate more char.The major components of the oil differed greatly in the product category from the previous pyrolysis of the lignin sample alone.Combining the difference between the theoretical and experimental values of the pyrolysis product yield distribution,it was found that interactions between cellulose and lignin are not obvious at low temperature(325°C),and strong interaction occurs at elevated temperature(450,525°C).The porous structure of the actual biomass promotes the release of volatiles,and the spray effect is enhanced,which makes the pyrolysis oil production has increased.