Low temperature formation of aromatic hydrocarbon from pyrolysis of cellulosic materials

The major chemical pathways for production of aromatic hydrocarbons in the pyrolysis and subsequent flaming combustion of biomass materials are high temperature secondary reactions of the primary pyrolysis products. The second and less explored route is the evolution of aromatics from the solid substrate in the temperature range of 400–600°C. Primary chars that form around 300–400°C, depending on the starting material, continue to undergo pyrolysis up to temperatures of 600°C and higher. In this work, the formation of aromatic hydrocarbons from the second route was investigated for cellulosic materials. Experimental work was performed primarily using TG/DSC/MS. In order to reduce the formation of hydrocarbons from secondary reactions of the primary pyrolysis products, small sample size, i.e., 2 –10 mg, and a high helium flow rate of 150 ml/min, were used. Heating rates of less than 60°C /Min were used to ensure uniform sample temperature. Py/GC/MS confirmed the identities and relative quantities of masses detected by TG/DSC/MS. Under slow heating conditions, which are typical of thermogravimetric analyzers, simple hydrocarbon products begin to evolve above 350°C, where the primary decomposition of cellulosic materials has completed and the remaining char has begun the carbonization/aromatization process. Most aromatic products such as benzene, toluene, naphthalene, anthracene are detected between 400 to 600°C. Detectable products formed at temperatures above 600°C are methane, benzene, and hydrogen, and carbon monoxide. Some kinetic parameters for the formation of hydrocarbon products are deduced from the experimental findings and discussed in this presentation.