Study On The Formation Characteristics And Mechanism Of High-concentration Limonene In The Pyrolysis Process Of Waste Tires

With the increase in global production of waste tires,it has become a kind of"black pollution"that is difficult to degrade.Compared with developed countries,the conversion of high value-added from waste tires in China is still in its infancy.As an important product from tire derived oil（TDO）,limonene is widely used in industries such as food,medicine,and perfume industries.Research on the formation characteristics of limonene during the pyrolysis process of waste tires and increasing the yield of limonene have become a research hotspot.This study aimed to investigate the formation characteristics of limonene using the process of pressurized pyrolysis and concentrating photothermal pyrolysis of truck tire（TT）powder.Based on Spearman correlation analysis and GC-MS results,the mechanisms of limonene conversion in pressurized pyrolysis were studied.The method of concentrating photothermal pyrolysis of waste tires was proposed and used to improve limonene concentration in TDO and its yield.The study conducted relevant research as follows:Study the characteristics of limonene precipitation during pressure pyrolysis of waste tires.Limonene was easily decomposed into xylene,tri-methyl-benzene and other aromatic components under high temperature conditions,and its content in TDO decreased with increasing temperature.When the final pyrolysis temperature was 500℃,the volatile components of the sample basically completed the precipitation process,in which the yields of pyrolysis oil and limonene were highest.When the mass flow rate of N₂ was constant,the limonene yield decreased and then increased with increasing pressure at a range of 0.1-1.5MPa.Analysis to determine the decomposition mechanism of limonene in the process of pressurized pyrolysis.The shorter residence time inhibited the secondary reaction of limonene and improved the yield of limonene.At 500℃,When the residence time was constant at 15/30s,as the pressure increased from 0.1 MPa to 1.0 MPa,the yield of limonene also increased from5.37/4.16wt%to 7.74/7.20wt%.C₇-C₉ aromatic hydrocarbons such as toluene and xylene were the main products of limonene decomposition during the pyrolysis of waste tires in fixed bed reactor（XBR）,while high-molecular polyenes had similar formation mechanisms to limonene.The influence of pressure on the precipitation of limonene during pyrolysis is not limited to changing the residence time,but the obstructive effect of inert gas also had a significant effect under a certain pressure.Adoption of concentrating photothermal reactor（CPR）to avoid the secondary reaction in the pyrolysis process of waste tires by promoting the yield and concentration of limonene.When the temperature was 600-700℃,the content of limonene in TDO was generally 56.6-70.1%higher than that in conventional pyrolysis oil.The change of carrier gas flow had no obvious effect on the composition of TDO.When the output voltage was 12V,the total reaction time was 5min,the peak area of limonene in the pyrolysis oil was as high as 43.99%.Compared to the 97 components that can be detected in conventional pyrolysis tar,the number of components in concentrating photothermal pyrolysis oil was reduced to 58.The boiling points of the main components were quite different,which was conducive to the separation and purification of limonene.