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.
Understanding the reaction pathways of cellulose hydrolysis in hot-compressed water (HCW) is crucial for the optimization of fermentable sugar and chemical production. Advanced analytical strategies are required to better assess the wide range of products from cellulose conversion in HCW. In this work, cellulose conversion in HCW was conducted in an autoclave with sampling upon the reaction time under isothermal conditions (180, 220, and 260 °C from 0 to 120 min). Total water-soluble carbohydrates were quantified (phenol/sulfuric acid method). These products were first characterized by size-exclusion chromatography coupled to evaporative light scattering detection and mass spectrometry (SEC–ELSD–MS). SEC is useful for screening the molecular weight distribution of soluble products. Then, the chemical structure of water solubles has been attributed by hydrophilic interaction liquid chromatography coupled to a linear trap quadrupole Orbitrap mass spectrometer (HILIC–LTQ–Orbitrap–MS). This method notably provides evidence of the formation of a cellobiose conformer under some HCW conditions. A specific high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC–PAD) method has been developed. This method allows for a selective separation of 5-hydroxymethylfurfural (5-HMF), glucose, fructose, mannose, and oligomers up to cellopentaose. Carboxylic acids were quantified by high-performance liquid chromatography with ultraviolet detection (HPLC–UV). Solid residues obtained after HCW conversion were characterized by X-ray diffraction (XRD) and permanent gas by micro-gas chromatography. The global reaction mechanism of cellulose liquefaction in HCW is rationalized on the basis of these complementary methods. Cellulose conversion first proceeds with heterogeneous hydrolysis (fiber surface) to produce soluble oligomers in competition with pyrolysis (inner fibers with limited mass transfer of water), producing levoglucosan (promoted at a higher temperature). Soluble oligomers produce glucose and isomers by homogeneous hydrolysis (liquid phase). C6 sugars can then undergo further conversion to produce notably 5-HMF and erythrose.
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