The alkali metal release during pyrolysis of biomass is investigated w
ith a surface ionization method. Wheat straw samples (20 mg) are pyrol
yzed in a laboratory unit under Nz atmosphere, and two characteristic
temperature intervals for alkali metal emission are identified. A smal
l fraction of the alkali metal content is released in a low-temperatur
e region (180-500 degrees C) and is attributed to a connection with th
e decomposition of the organic structure. The two most pronounced emis
sion processes below 500 degrees C are well described by a first-order
rate behavior, and the activation energies are found to be 156 +/- 11
and 178 +/- 8 kJ/mol, The major part of the alkali metal release take
s place in the high-temperature region (> 500 degrees C), and activati
on energies of alkali metal emission from the ash residues are found i
n the range 168-238 kJ/mol. A high chlorine content is found to enhanc
e the alkali metal emission from the ash, while the alkali metal relea
se in the low-temperature region cannot be correlated with the chlorin
e content.