Study On Pulping Condition Of Rice Straw With Ammonium Sulfite Method And Oxiammonolysis Modification Of The Pulping Waste Liquor

This paper studied the pulping method in which ammonium sulfite with urea as buffer agent was used for cooking rice straw. Effects of pulping conditions such as dosage of cooking liquor, maximum cooking temperature, and cooking time were discussed systematically by experiments. The optimum condition of cooking was found. The rice straw ammonium sulfite pulp was bleached under different conditions. Then its bleachability was concluded.Under the optimum condition, we could produce the rice straw pulp, whose fine pulp yield is 46.34%, potassium permanganate value is 9.13 and brightness is 35.4%ISO. It can be bleached to a brightness of 70.4%ISO with the H₈H₂P₂ procedure. As compared, the targets of paper made of this pulp had met the standard of A grade offset point paper.In the following experiment, the black liquor of ammonium sulfite of rice straw was oxiammonolysis by using oxygen. The effects of oxygen pressure, reaction time and temperature and concentration of black liquor on the contents Of nitrogen, carboxyl group and value of pH and C/o-N were discussed. It could be inferred from the results that the properly improved oxygen pressure and reaction temperature and prolonged reaction time could contribute to the oxiammonolysis. But the concentration of black liquor should not be too high.After oxiammonolysis under the optimum condition, of the modified product, 34.82% of total nitrogen was organic nitrogen. The content of carboxyl group was 9.18 mmol/g and the value of pH is 5.2. C/o-N had decreased to 5.03, which absolutely conformed to the standard of slow-released nitrogen fertilizer.Through the extract experiment, we could distinguish the ligonsulfonate from the carbohydrate of sugar, semi-cellulose in the raw black liquor. There were large amounts of ammonia nitrogen in the water phase. After the oxiammonolysis, the components in the black liquor had taken some changes. The quantity of ligonsulfonate decreased. There is about 8.12 percent of ammonia nitrogen that conversed into organic nitrogen in the water phase. In the organic phase, 44.67percent of ammonia nitrogen conversed into organic nitrogen. It was concluded that carbohydrate of sugar, semi-cellulose did also take part in the oxiammonolysis. But the ligonsulfonate still played an important role. The most organic nitrogen came from the reaction in which the ligoncarboxylic ammonia dehydrogenated.Comparing the FTIR of the structures of components in the black liquor before and after oxiammonolysis, we inferred that the branch chain of lignosulfonate and carboxylnate and some aromatic structure were partly broken and degraded because of the oxiammonolysis. This resulted in the decrease of methoxyl and phenolic hydroxyl groups and increase of carboxyl and carbonal. Most organic nitrogen in product existed as amide, amine and imide. All the facts could contribute to the conclusion that the oxiammonolysis of black liquor of ammonium sulfite of rice straw was a progress in which the carboxyl and carbonal increased and the function groups reacted with the ammonia as a covalently attached interaction and amine-organic compounds were generated.