Analytical Techniques - Biomass Gasification, Pyrolysis and Torrefaction - page 454

Calcination Kinetics in CO 2 medium

-4

y = -21717x + 12.265

-6

-8

0.00078 0.0008 0.00082 0.00084 0.00086

1/T

FIGURE 13.6 Arrhenius plot to identify the reaction rate and activation energy.

13.5 PYROLYSIS-GAS CHROMATOGRAPHY/MASS
SPECTROMETRY
Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) is an analyti-
cal method to identify compounds. It involves heating the sample to high
temperatures, where they are decomposed to smaller molecules, which are
separated by gas chromatography and identified by mass spectrometry.
As described in Chapter 5, pyrolysis is a thermal decomposition of mate-
rials, which occurs at high temperatures (above 600 C) in the absence of
oxygen. Usually, the sample is contacted with a platinum fuse wire or placed
in a quartz tube. A high temperature of 600 1000 C or even hotter ambient

is employed. Heating the sample is very rapid and temperatures of 700 C are
reached in about 10 s. Resistive heating, isothermal furnace, and inductive
heating methods are commonly used in such equipment. Large molecules
breakdown (cleave) and produce more volatile fragments. A methylating
reagent sometimes aids the production of the volatile fragments. The pyroly-
sis and gas chromatography/mass spectrometry (GC/MS) could take place in
either one instrument or pyrolysis is separately performed before sending it
to a GC/MS.
Once the sample is decomposed into smaller molecules, a small fraction
of the volatile produced is injected into a GC at 300 C, along with an inert
carrier gas like helium. The molecules are then carried into a 30 m GC col-
umn. The GC column is housed in an oven that maintains a temperature of
40 320 C. The inside of the column is coated with a special polymer. The

mixture is separated depending on their volatility. Higher volatile particles
travel faster through the column and lower volatile particles travel slower.
The volatile molecules are then ionized using an electric charge. The
charged ions are then sent to an electromagnetic field that filters the ions
based on their mass. The user can define the range of mass, through the fil-
ter, which continuously scans through the range of masses. An ion detector