Study On The Supercritical Ammonia Pulping Process

Combined with the gradual development of supercritical fluid extraction technology recent year and in reference to the previous experience, wheat straw was chose as raw material and ammonia was selected as the supercritical fluid in supercritical ammonia pulping process.The critical temperature of ammonia is 132.3℃, critical pressure is 11.28MPa. In this paper, the condition that reached the critical temperature of ammonia was firstly discussed. The effects of the factors such as m (ammonia) / m (wheat straw), cooking temperature and holding time on the pulp yield, pulp hardness and pulp strength were discussed and come to the conclusion that under the condition m (ammonia) / m (wheat straw) = 1.25, cooking temperature of 130℃, heat 2 ~ 3h, liquor-to-wood ratio of 7:1, supercritical ammonia pulping can get a better pulp yield and higher pulp strength. Followed the cooking under a fully supercritical state condition was discussed. The effects of the temperature and pressure on cooking were discussed. We found that as the temperature and pressure rose higher, lignin extraction efficiency gone better, but at the same time fiber damage gone larger, pulp yield gone lower and the strength also decreased significantly, but the pulp strength could still meet the needs of ordinary paper.By use of the Scanning Electron Microscopy (SEM) and Energy Disperse Spectroscopy (EDS) on the pulp and black liquor, analysis revealed that the method achieves the aim to remove lignin and disperse the fibers. The fiber damages will be tiny under low-pressure and under high pressure can get better fiber dispersion. Both the bleached pulp brightness can reach 70% ISO or more, and the strength of bleached pulp improved. The method was applied to soft wood, bamboo and secondary fiber pulping and found that it is able to meet better cooking results. After cooking the excess ammonia can be recycled easily. The black liquor rich in lignin and ammonia can be used as organic nitrogen fertilizer. The ammonia in the black liquor was easily to be separated to get lignin for other use.