BUCHI KjelDigester K-449 - Manual (Page 21)

4 – 21 Operation Manual KjelDigester K-446/K-449
4 Description of function
4.3 Function
The KjelDigester is used to convert organic bound nitrogen (e.g. in proteins) in a sample into
ammonium sulfate. During the digestion process, acid fumes and reaction gases may emerge
and are handled by the Scrubber. The Scrubber is connected to the KjelDigester for neutralizing
acid fumes and adsorbing unpleasant odors.
4.3.1 Digestion process
The aluminum heating block d generates high temperatures of up to 450 °C in order to heat the
sample c up to 370 °C (boiling point). The sample is digested in constantly boiling H
2
SO
4
. Hot
acid fumes rise into the condensation zone b, condense and rinse back down to the sample
creating a constant reflux. Residual fumes which escape the condensation zone via the acid
fume outlet a are highly corrosive and must be withdrawn and efficiently neutralized (e.g. with
the Scrubber K-415).
The condensation should not take place inside the safety zone
X
in order to avoid shortening
the lifetime of the sealings. In case the condensation is too close to the suction module (e.g. due
to very high temperature settings or if too much catalyst was used) losses of nitrogen through
creating N
2
are possible and the samples can dry out.
Fig. 4.4 Function of the KjelDigester
X Safety zone c Boiling/digestion sample
a Acid fume outlet d Heating block
b Condensation zone