On-Line Process Analysis of Biomass Flash Pyrolysis Gases Enabled by Soft Photoionization Mass Spectrometry

In the current discussion about future energy and fuel
supply based on regenerative energy sources, the so-called second-generation
biofuels represent a vitally important contribution for the provision
of carbon-based fuels. In this framework, at the Karlsruhe Institute
of Technology (KIT), the bioliq process has been developed, by which
biomass is flash-pyrolyzed at 500 °C for the production of so-called
biosyncrude, a suspension of the pyrolysis liquids and the remaining
biochar. However, little is known about the composition of the pyrolysis
gases in this process with regard to different biomass feedstock and
process conditions, and the influence on the subsequent steps, namely,
the gasification and subsequent production of biofuels or base materials.
Time-of-flight mass spectrometry (TOFMS) with two soft (i.e., fragmentation
free) photoionization techniques was for the first time applied for
on-line monitoring of the signature organic compounds in highly complex
pyrolysis gases at a technical pyrolysis pilot plant at the KIT. Resonance-enhanced
multiphoton ionization with TOFMS using UV laser pulses was used for
selective and sensitive detection of aromatic species. Furthermore,
single-photon ionization using VUV light supplied by an electron beam-pumped
excimer light source was used to comprehensively ionize (nearly) all
organic molecules. For the miscellaneous biomass feeds used, distinguishable
mass spectra with specific patterns could be obtained, mainly exhibiting
typical pyrolytic decomposition products of (hemi)­cellulose and lignin
(phenol derivatives), and nitrogen-containing compounds in some cases.
Certain biomasses are differentiated by their ratios of specific groups
of phenolic decomposition products. Therefore, principal component
and cluster analysis describes the varied pyrolysis gas composition
for temperature variations and particularly for different biomass
species. The results can be integrated in the optimization of the
bioliq process.