Fast Pyrolysis of Heartwood, Sapwood, and Bark: A Complementary Application of Online Photoionization Mass Spectrometry and Conventional Pyrolysis Gas Chromatography/Mass Spectrometry

Wood offers important potential for biofuel or chemical production by fast pyrolysis but exhibits variable chemical composition that impacts pyrolysis product composition. Here, fast pyrolysis of heartwood, sapwood, and bark isolated from Douglas fir (softwood) and oak (hardwood) was studied by a microfluidized bed reactor (MFBR) combined with single photoionization mass spectrometry (SPI-MS) to provide insights into the wood zone effects on the composition of pyrolysis volatiles. The difference in pyrolysis volatile composition has been clearly unraveled by principle component analysis (PCA) based on the major ions detected by SPI-MS. Some specific product markers have been defined for each wood zone (heartwood, sapwood, and bark) and related to the chemical composition of wood samples (lignin, carbohydrates, and minerals). The catalytic effect of minerals (notably potassium) has a higher impact on carbohydrate decomposition than on lignin decomposition for a given wood type. Therefore, sapwood and heartwood (for both oak and Douglas fir) can be clearly discriminated by specific markers mainly from carbohydrate pyrolysis. Interestingly, our results show that the wood cylinders exhibit a more marked wood zone effect on product compositions compared to fine powders. SPI-MS results were further compared to those of, pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), and many of them are consistent. MFBR combined with SPI-MS is a selective analytical technique to figure out the effect of wood composition on pyrolysis volatiles.