Comparison of MEA/AQ, soda and soda/AQ pulping of wheat and rye straw

• Monoethanolamine (MEA) is a highly selective organic solvent for pulping of straw.
• MEA pulping increases pulp yield by 10% compared to conventional soda pulping.
• MEA pulping can be powerfully catalyzed by AQ which allows reducing the MEA charge drastically.
• MEA straw pulps can be bleached in an environmentally friendly way to high brightness.
• Papermaking properties of MEA pulps are fully comparable to those of soda/AQ pulps.

MEA (monoethanolamine)/AQ pulping of wheat and rye straw and bleaching of the produced pulps were investigated. The delignification behaviour of wheat and rye straw using varying MEA/water and liquor/straw ratios was studied. Furthermore, the impacts of mono-, di-, tri-ethanolamine/water mixtures and addition of KOH to the cooking liquor were monitored. The best results were achieved with a MEA/water ratio of 50/50 at a liquor/straw ratio between 3:1 and 4:1. The use of the mixture of mono-, di-, tri-ethanolamine instead of MEA only was not effective for straw pulping. The effect of adding KOH to the MEA pulping liquor was negligible. The results of MEA pulping of both straw species were compared with results for production and bleaching of soda and soda/AQ reference pulps. At similar degree of delignification, the MEA pulps showed 10% higher yield (based on straw), which demonstrates the unusually high selectivity of MEA in straw pulping. The MEA straw pulps showed fairly low brightness and were more difficult to bleach than the corresponding soda pulps. Nevertheless, it is possible to bleach MEA pulps to more than 80% ISO brightness, applying an ECF bleaching sequences (O-Q-OP-DQ-P). With regard to bleachability, yield and strength properties the rye straw pulp sample performed much better than wheat straw pulp sample.