(318g) Development and Application of Solid-Phase Microextraction for Pyrolysis and Syngas Analysis

Thermochemical conversion is a well-established approach to converting biomass and waste into valuable products.  New developments in technologies such as gasification and pyrolysis are making these techniques increasingly viable as a source of renewable fuels and chemical production.  As these processes become more complex and demanding, the ability to characterize product streams becomes more important.  Rapid and reliable quantification of key compounds is essential to continuing process development and ensuring optimal performance of commercialized installations.   

The primary goal of this work is to develop and demonstrate a new technique for analyzing process gas streams at elevated temperatures.  A recently developed technique using solid-phase microextraction (SPME) is extended from the proof-of-concept stage to application in pilot scale gasification and pyrolysis processes. SPME is a sample extraction and preparation technique that is growing in popularity because it eliminates several complicated and costly stages of conventional sample analysis.  Using a small needle coated with an extraction phase, sample extraction and preparation are combined into a single step using one device. [i]  Directly injecting this coated needle (a.k.a. fiber) directly into the analytical equipment facilitates rapid sample analysis using gas chromatography mass spectrometry (GC-MS) or flame ionization detection (GC-FID). 

This work applies the SPME technique for the first time to the quantification of trace tar compounds in a 20kg/h biomass gasification and gas cleaning system.  Raw syngas produced from gasification contains numerous contaminants that must be largely removed before it can be used as a fuel or chemical feedstock.  Particularly problematic are tars derived from incomplete thermochemical conversion, which condense as syngas cools and cause fouling of pipes and equipment.  Conventional tar analysis, which is based on exhaustive extraction and gravimetric measurements, requires many hours to collect and analyze a single sample.  This method is also inadequate for analyzing lower tar concentrations that exist downstream of cleaning devices, which may still be problematic to downstream processes like catalysis.  After calibrating the SPME technique on a lab scale model-tar/syngas system, its performance was evaluated on a pilot scale for determining trace tar concentrations downstream of an oil-based tar scrubber.

The SPME method is also applied in this work to directly measure vapor compounds during pyrolysis.  The liquid bio-oil product created via pyrolysis is composed of hundreds of compounds.  Many of these compounds experience rapid changes during the conversion process and when condensed into bio-oil, making them difficult to collect and analyze.  The SPME technique makes it possible to capture these compounds at different stages of the pyrolysis reaction and directly analyze them using GC-MS or GC-FID.  This work has been focused on the detection of levoglucosan, a prominent sugar product from pyrolysis.  Measuring the different levels of levoglucosan and other intermediate vapor compounds provides strong indicators of process reaction chemistry and the ability to optimize the process for desired products.