| Under carbon emission reduction targets,the use of renewable and environmentally friendly biomass resources to produce liquid fuels and chemicals has significant potential for application.Regarding the preparation of high-value nitrogen-containing chemicals(such as pyrrole,pyridine,indole,pyrazine,and other organic platform compounds)through nitrogen-rich biomass pyrolysis,the presence of alkali and alkaline earth metals(AAEMs)has a significant impact on the product distribution.In the constructed tubular furnace pyrolysis reaction device,the study systematically investigated the influence mechanism of AAEMs on the nitrogen-rich pyrolysis characteristics and product distribution.Typical biomass and model compounds were co-pyrolyzed with urea,and the pyrolysis products were characterized using instruments such as GC-MS,TGA,ICP-OES,XPS,XRD,FTIR,BET,and SEM.The study investigated the nitrogen-rich pyrolysis characteristics and product formation mechanism of wood cellulose under the influence of AAEMs,and obtained the coupling influence mechanism of AAEMs on the directional generation and conversion of nitrogen-rich pyrolysis products under specific proportions of the three components.The main research content:(i)The effect of loading alkaline earth metal Ca and alkali metal K on the nitrogen-rich cellulose pyrolysis characteristics was investigated.It was observed that the addition of both Ca and K was beneficial for the production of pyridine,while K was conducive to the production of pyrrole and pyrazole,and Ca was more favorable for the production of pyrazine.The influence of Ca on the composition of the bio-oil fraction was significantly greater than that of alkali metal K.Ca significantly reduced the activation energy of cellulose pyrolysis.The highest nitrogen-containing compound yield in the bio-oil was obtained when 0.5 wt.% Ca was loaded,reaching 77.98%.The relative content of nitrogen-containing heterocyclic compounds(NHCs)was significantly higher in the samples loaded with Ca(37.98%)compared to those without metal loading(27.75%).K promoted the enrichment of nitrogen elements and nitrogen-functional groups in biochar,with higher graphitization degree and stability.Ca increased the H/C value of biochar and accelerated the conversion of char-N to oil-N.(ii)The coupling mechanism of the coupling effects of different three component ratios of biomass on the directional formation and conversion of products during nitrogen-rich pyrolysis was studied.It was found that the influence of AAEMs on the homogeneous mixture of the three components during the nitrogen-rich pyrolysis was not merely the superposition of the effects of individual components.Under different mixing ratios of the three components,the same type and loading of AAEMs showed different impact effects.In the case of a mixture ratio of 5:2:2,the loading of AAEMs,especially K,was more likely to obtain high-performance nitrogen-rich biochar.(iii)The effects of pretreatment with different organic acid solutions on the nitrogen-rich pyrolysis characteristics and product distribution of typical biomass corncobs were studied.Organic acid washing pretreatment not only removed some of the AAEMs in the sample but also changed the internal structure of the sample,altering its thermal degradation characteristics.The removal of AAEMs resulted in a significant decrease in the water content and acidity of the bio-oil produced by nitrogen-rich pyrolysis.Further reduction in the variety of chemical compounds in the bio-oil could lower the refining and application costs of the liquid product.The research results of this paper have guiding significance for in-depth understanding of the role of AAEMs in the nitrogen-rich pyrolysis process,and achieving the targeted production of high value nitrogen-rich target products from lignocellulosic biomass. |
PDF Full Text Request