440 / 2018-09-01 17:03:13

Photoionisation Mass Spectrometry: a Powerful Tool to Study Biomass Pyrolysis

全体主题 > 平台科技

Many analytical methods (mass spectrometry, nuclear magnetic resonance, infrared, etc.) have been used in order to understand the chemical mechanisms occurring during biomass pyrolysis. Despite all these studies, the understanding of chemical mechanisms remains a major challenge to optimise thermochemical bio-refineries. It is essential to describe the evolution of volatiles release as a function of the process conditions in order to predict products composition and design reactors.
In this context, the real time analysis of volatiles from pyrolytic reactors appears to be a promising solution to give new insights, because it has the ability to analyse the volatiles directly from their reactive environment avoiding sampling/storage steps. Besides, soft photoionization (PI) mass spectrometry (MS) method allows monitoring the evolution of tars as a function of time. It also improves the mass spectrometric analysis of biomass volatiles, because most of them are very fragile and the lower ionization energy of PI can reduce fragmentation of pyrolysis products and efficiently simplify the final mass spectra.
In this talk, we will present the development conducted in our groups on PI−MS analysis of biomass pyrolysis volatiles by (1) synchrotron light PI−MS [1] and (2) various commercial PI−MS techniques [2-5] (vaccum ultra violet lamp, laser Xe cell, developed by Photonion GmbH). On-line PI-MS analysis has been combined on different reactors in Nancy (fixed bed and micro-fluidized bed). Slow pyrolysis of different biomasses (miscanthus, douglas and oak) was conducted in a fixed bed combined with on-line analysis of the vapors by PI-MS and quantitative off-line analysis of condensed vapors by GC*GC/MS-FID [2]. The combination of on-line PI/MS and off-line GC/MS is a powerful approach for the assignment of the chemical structure of main m/z markers. Their formation profiles are plotted as function of temperature helping to understand the chemical mechanisms occurring during pyrolysis.
The influence of several parameters i.e. sizes, shapes (powder, lamella and cylinder) and composition of biomass particles were investigated for fast pyrolysis into a micro-fluidized bed [3-5]. The combination with Principal Component Analysis reveals some interesting “fingerprints” for different pyrolytic regimes [3] and biomass initial compositions (carbohydrates structures, minerals content). These experimental results were also compared with predictions of a pyrolysis model [4] that combines external and internal heat transfers in biomass particles and recently published detailed kinetics [6]. Experimental and simulation results are mostly in agreement, but more detailed kinetic mechanisms still need to be developed to capture the complex phenomenon of biomass pyrolysis [4]. PI-MS has been also applied on catalytic pyrolysis of biomass with different zeolites [7] in order to study 1) the dynamics of volatiles (in real time) produced during the catalytic pyrolysis of wood in a fluidized bed of zeolite and 2) the deactivation of zeolites. We will conclude this talk on the high potential of PI-MS to study various processes (pyrolysis, gasification and combustion) and mechanisms.