In Situ Atmospheric Pressure Photoionization Mass Spectrometric Monitoring of Initial Pyrolysis Products of Biomass in Real Time

Abstract

Knowledge on the initial and intermediate pyrolysis products of biomass is essential for the mechanistic investigation of biomass pyrolysis and further optimization of upgrading processes. The conventional method can only detect the final products, which do not resemble the initial or intermediate pyrolysis products. Here, we introduce a direct orifice sampling combined with atmospheric pressure photoionization mass spectrometry (APPI-MS) for in situ online analysis of the evolved volatile initial products from the pyrolysis of biomass. Pyrolysis experiments of both dimeric model compound (guaiacylglycerol-β-guaiacyl ether, GGGE) and poplar wood were carried out to validate the generality of the method. Generally, secondary reactions can be reduced by shortening the distance between the sample and sampling orifice. Large molecular-weight initial products up to trimers were detected during the pyrolysis of poplar wood, and no initial products larger than trimers were detected. It is inferred that in situ APPI immediately after sample extraction ensures efficient and effective product detection. Furthermore, the present work offers a promising feasible method for online tracing of reaction intermediates not only in pyrolysis but also in various reactive processes (e.g., catalytic reaction, oxidation) under operando conditions.

Determination of absolute photoionization cross‐sections of some aromatic hydrocarbons

“…Vacuum ultraviolet (VUV) light, produced by discharge lamps, 8 lasers, 9–11 and tunable synchrotron radiation, 3 is an elegant ionization source for mass spectrometry. As a soft ionization process, VUV photoionization can facilitate selective identifications of species to avoid interference from fragmentation 12–15 . The photoionization cross‐section (PICS) is thus the key parameter to quantify the concentration of organic compounds.…”

Chemical Reaction Monitoring by Ambient Mass Spectrometry

“…Kauppila et al (2016) investigated the nucleophilic aromatic substitution between halogenated benzene dopants and nucleophiles. Zhou et al reported real-time APPI-MS monitoring of initial pyrolysis products of biomass, which revealed the mechanism of biomass pyrolysis (Chen et al, 2020).…”

Evidence of a Phenolic Pool as a Key Intermediate for Zeolite‐Catalyzed Lignin Pyrolysis

“…TG/MS experiments [28, 29] indicate that the formation of phenolic pool is favorable at moderate temperatures (Figures S2 and S3). The phenolic pool‐related oligomers during catalytic pyrolysis of GGGE over HZSM‐5 were probed in gas phase by in situ atmospheric pressure photoionization high‐resolution mass spectrometer (APPI HRMS) combined with a fixed‐bed reactor under isothermal mode [30] . Low volatility of phenolic pool‐related oligomers lead to low concentrations in gas phase while the high oxygen content makes them thermally labile, resulting in a high propensity to lose during the sampling process with traditional technologies.…”

“…The phenolic pool-related oligomers during catalytic pyrolysis of GGGE over HZSM-5 were probed in gas phase by in situ atmospheric pressure photoionization high-resolution mass spectrometer (APPI HRMS) combined with a fixed-bed reactor under isothermal mode. [30] Low volatility of phenolic pool-related oligomers lead to low concentrations in gas phase while the high oxygen content makes them thermally labile, resulting in a high propensity to lose during the sampling process with traditional technologies. The in situ APPI HRMS method used in current work (inserted sketch in Figure 1 a) proceeds without any sample collection and pre-treatment, and the combination of "direct orifice sampling" and in situ APPI method avoids condensation during sampling process and secondary reactions, ensuring the effective detection of reactive intermediates.…”

“…The in situ APPI HRMS method used in current work (inserted sketch in Figure 1 a) proceeds without any sample collection and pre-treatment, and the combination of "direct orifice sampling" and in situ APPI method avoids condensation during sampling process and secondary reactions, ensuring the effective detection of reactive intermediates. [30] Figure 1 a exhibits the comparison of pyrolysis of GGGE with and without HZSM-5. Remarkably, oligomers with a mass distribution ranging from 200 to 1000 Da were detected during catalytic pyrolysis of GGGE over HZSM-5 while no detectable oligomers except for cracking fragments was observed in the case of thermal pyrolysis process (Figure 1 a).…”