Res. Chem. Intermed.
, Vol. 27, No. 9, pp. 917–926 (2001)
Non-alkaline bleaching of wood pulp using pulsed RF
dielectric heating: comparison with pulsed microwave
JEFFREY K. S. WAN, IVAN KALATCHEV, JANUSZ DZIAK
and M. CATHERINE DEPEW
Department of Chemistry, Queen’s University, Kingston, ON, K7L 3N6, Canada
Received 30 January 2001; accepted 23 April 2001
Abstract—Non-alkalinebleaching of thermo-mechanical pulps using 40 MHz RF dielectric capacitor
heating is described. Experimental data obtained under RF irradiation are compared with non-alkaline
bleaching under pulsed microwave at 2.45 GHz. Optimal processing time is determined. Effectiveness
of non-alkaline bleaching of TMP in RF is shown to be close to that in microwave. Neither microwave
nor RF irradiation, under non-alkaline bleaching conditions, is shown to result in detriment to the
physical properties of the pulp.
Recently, we have described the bleaching of mechanical wood pulps using hydro-
gen peroxide and solid magnesium or calcium carbonate under non-alkaline con-
ditions . Although initially the process was studied using conventional heating
to temperatures of 70 –100
C, it was subsequently shown that a pulsed microwave
heating process could afford effective bleaching with brightness increases of 20– 25
points for softwood pulps readily achievable . This microwave processing had
additional advantages in that the non-alkaline bleaching could be accomplished at
high pulp consistencies (30– 90%) and in very short processing times (
with total microwave irradiation times of »90 s).
In dealing with microwave chemistry there are always questions regarding the
ef ciency of the process. Several factors may in uence this ef ciency, including
the rapid rate of heating, the uniformity or selectivity of heating and thus effects on
reaction rates, and the effects of the frequency of the electromagnetic eld.
Currently, dielectric heating in RF electromagnetic elds is being widely used
industrially for processes involving drying, melting, heating, etc. Continuous wave