Distribution Characteristics And Regulation Of Polycyclic Aromatic Hydrocarbons In Biomass Pyrolysis Oil

The non-renewability of fossil energy such as coal and petroleum seriously restricts the rapid,healthy and sustainable development of China's economy.Biomass is a cheap and readily available renewable energy source with the potential to replace fossil fuels.Therefore,countries around the world have paid close attention to the development and utilization of biomass.Pyrolysis of biomass,that is,pyrolysis of biomass in the absence of oxygen or anoxic conditions,the products of which are coke,syngas and pyrolysis oil.Among them,pyrolysis oil is considered to be a promising liquid fuel,which has higher energy density than biomass materials,and is convenient for storage and transportation.However,some small molecule compounds formed by thermal depolymerization of biomass macromolecules are prone to secondary reactions,forming a highly toxic polycyclic aromatic hydrocarbon?PAHs?contaminant through aromatization,oligomerization,etc.As the result,the environmental health risks of its subsequent application are seriously aggravated.In view of this,in this paper,the tube furnace reactor and the detailed PAHs pretreatment extraction technology were used to qualitatively and quantitatively analyze the PAHs of 16preferentially managed PAHs in biomass pyrolysis oil under different pyrolysis conditions.The main influencing factors of the characteristics were explored.The results showed that the reaction temperature had a significant effect on the distribution of PAHs in pyrolysis oil,and the total content of PAHs increased with the increase of reaction temperature.At lower reaction temperature?400-600??,the PAHs in biomass pyrolysis oil are mainly medium and low rings?2⁴ rings?,and the total content of PAHs is 389.60?400??and 2242.71?500??.And 7410.64?600???g/g,the toxicity equivalent?TEQ?is less than 1;at 700°C,high ring?5-6 rings?PAHs appear,and the total content of PAHs reaches 105435.12?g/g,the oil toxicity was dramatically increased?TEQ=6.43?.At the same time,the type and content of PAHs in pyrolysis oil decrease with the increase of carrier gas flow rate;while the addition of a certain proportion of CO₂ in the traditional inert pyrolysis atmosphere?N₂?is beneficial to the reduction of PAHs pollutants in pyrolysis oil.In addition,this paper uses the surface response method to optimize the parameters of the biomass pyrolysis process for the pyrolysis oil yield.The results showed that when the reaction temperature was 511?,the residence time of the material was 12.7 min,and the ratio of CO₂/N₂ in the pyrolysis atmosphere was 88/12,the yield of pyrolysis oil reached the maximum.Finally,CO₂ was used as the pyrolysis atmosphere,and the transition metal modified molecular sieve HZSM-5 such as Fe and Co was used to regulate the quality of biomass pyrolysis oil and the type and content of PAHs pollutants in pyrolysis oil.The results show that CO₂ atmosphere synergistic with HZSM-5and Fe/HZSM-5 molecular sieve catalyst can promote the formation of high-value monocyclic aromatic hydrocarbons?MAHs?such as benzene,toluene and xylene,and reduce PAHs pollutants in pyrolysis oil.The content reduces the toxicity of pyrolysis oil.