Microwave enhanced non-alkaline bleaching of mechanical pulps: A new solution to an old problem

Since the granting of our first US patent on microwave induced catalytic decomposition of PCBs some 18 years ago, microwave technology has slowly begun to attract some industrial attention in the last few years. There was no doubt that microwaves had been applied to facilitate the conventional bleaching process of wood pulps in the past but with little or no success. The myth that microwaves can be regarded and manipulated as a rapid heat source probably caused most of the failures of unsuccessful microwave applications. It is therefore necessary to understand the real potential of microwaves as an energy source and to identify the many critical electromagnetic properties of the load (chemical systems), before a final choice of a proper microwave system be designed and installed. In this preliminary report, we demonstrate the real potential of pulsed microwave radiation for non-alkaline bleaching of mechanical pulps. Typically, very high consistency TMP up to 93% can be treated by pulsed microwave in the order of 90 seconds with an average increase of 20 to 25 points in brightness.