| Due to the low energy density of biomass,high viscosity and low PH value of biomass pyrolysis oil,as well as the defects caused by direct combustion,such as accumulation and slagging,biomass is usually pretreated in order to improve the utilization efficiency of biomass and improve the quality of thermal conversion products.In this paper,thermogravimetric,pyrolysis-gas chromatography/mass spectrometry analyses and atomic absorption spectroscopy,were used to analyzed the effect acid washing concentration,acid washing temperature and acid washing time on the combustion properties,product distribution of corn straw and Triarrhena.The effects of different organic acid pretreatment conditions on the content of alkali metal in biomass were studied by atomic absorption spectroscopy.The experimental results show that the highest content of alkali metal in biomass is K+,and acid pretreatment can effectively remove most of K+,with the increase of acid washing concentration,acid washing temperatureand acid washing time,the removal efficiency of K+is higher.Among the three acid washing conditions,the increase of acid washing time had the most significant effect on the K+content of com straw and Triarrhena.The K+ content of corn straw and Triarrhena sample reached a minimum of 32.73 mg·kg-1 and 8.41 mg·kg-1 when the acid washing time was 3 hours.Thermogravimetric analyzer was used to study the effect of pretreatment of organic acids on pyrolysis of biomass.The results reveal that when organic acid washing pretreatment were made under different conditions,the TG and DTG curves of pretreated corn straw and Triarrhena moved to a high temperature range,the thermal stability increased,the maximum pyrolysis rate increased significantly,and the maximum pyrolysis rate of corn straw samples reached 15.49%/min at 75℃,the maximum pyrolysis rate of Triarrhena samples reached 19.63%/min at 1 hours.The carbon yield was decreased under different acid washing conditions.The carbon yield of corn straw samples reached the minimum of 18.79%when the acid washing concentration was 3%,and that of Triarrhena samples reached the minimum of 14.57%when the acid washing time was 3 hours.At the same time,the pyrolysis kinetics results show that,the activation energy and the pre-exponential factor of the sample increased after pretreatment,but the excessive acid washing time is not conducive to the improvement of the thermal stability of the sample.PY-GC/MS was used to conduct the fast pyrolysis experiment of the samples,and the influence of organic acid pretreatment on the pyrolysis products of biomass was studied.The results showed that the main pyrolysis products of corn straw were phenols,furans and ketones,while the main pyrolysis products of Triarrhena were phenols,furans,ketones,acids and aldehydes.Organic acid pretreatment reduced the yield of furans and ketones in the pyrolysis products of corn straw and phenols,furans,ketones,acids and aldehydes in the pyrolysis products of Triarrhena,with increased the yield of phenols in the pyrolysis products of corn straw.Among them,the yield of furans in the pyrolysis products of corn straw was the most significant,from 42.94%of the original sample to 7.13%when the acid washing concentration was 7%.The yield of ketones in the pyrolysis products of Triarrhena was the most significant,from 15.09%of the original sample to 1.07%of the acid washing time of 3 hours.Comparison experiments using inorganic acids showed that the effect of inorganic acid pretreatment on the pyrolysis characteristics of biomass was similar to that of organic acids.After pretreatment with inorganic acid,the minimum K+contents of corn straw and Triarrhena were 1.36 mg-kg-1 and 2.95mg·kg-1,respectively.The maximum pyrolysis rate and carbon yield of corn straw were 17.51%/min and 19.75%,while that of Triarrhena was 20.44%/min and 14.56%.In terms of pyrolysis products,the yield of furans in the pyrolysis products of com straw showed the most significant change,from 42.94%of the original sample to 14.75%when the pickling time was 3 hours.The yield of ketones in the pyrolysis products of Triarrhena was the most significant,from 13.16%of the original sample to 0.64%when the pickling temperature was 50℃. |
