Recycling Recovery Ethanol Of Aspen Ethanol Pulping And Effect On Pulp Properties

Nowdays the mainstreams of paper making industry are kraft pulping and soda pulping, but they hold many disadvantages, such as severe air pollution, huge investment for alkali recycling, waste of outgrowth lignin etc. So organic solvent pulping has been attracting great attention. And ethanol pulping has become its mainstream recently because of the recyclable use of ethanol and usability of the lignin as new resource from waste liquor.High cooking temperature (205℃-210℃)for the aspen auto-catalyzed ethanol pulping and the low boiling of ethanol lead to cooking pressure to be very high (3.0MPa upwards) which demands higher requirement for cooking equipment. So it is significant and practical to further improve the ethanol pulping and do research on the method of reducing cooking temperature without lowering pulp quality by reusing the recycled ethanol and using organic acid in which to catalysis pulping.This paper uses the released organic acid in the pulping process as catalyst, reuses the recycled ethanol from waste liquor, discusses the content of organic acid in cooking liquor, improves the condition of the aspen auto-catalyzed ethanol pulping so as to upgrade cooking conditions, reduce temperature and pressure included. Finally, the goal to lower the requirement of cooking equipment could be achieved.The experiment is on the basis of the conditions of aspen auto-catalyzed ethanol pulping(liquid ratio1:10; the cooking concentration of ethanol60%(volume fraction); maximum cooking temperature205℃; holding time150min), reuses a certain volume recycled ethanol and organic acid in which from waste liquor to prepare cooking liquor. With the number of cooking increasing, organic acid of the cooking liquor is gradually accumulated, strengthens catalytic action, and then pulping yield decreases gradually. On the basis of ensuring higher yield, we are in search of the best amount of organic acid of auto-catalyzed ethanol pulping cooking liquor; on the basis of the best amount of organic acid, we achieve that the pulp yield gradually rebounds by lowering the boiling temperature and then rises to the level of auto-catalyzed ethanol pulping.The results show that from the third cooking experiment to the fourth cooking experiment, fine pulp yield decreases from47.28%to46.34%, a drop of0.94percentage points, coarse pulp yield decreases from48.47%to48.20%, a drop of0.27percentage points, but kappa value decreases from18.14to18.13, only a drop of0.01units, so we select the best amount of organic acid is the amount of organic acid of the third cooking experiment, that the content of recycling organic acid is0.3458mol/(kg dry wood). On the basis of the best amount of organic acid, we do cooling simulation cooking experiment, when the holding temperature is195℃, fine pulp yield is highest, kappa value is lower and the performance of pulp is better. So we select195℃is the best cooking temperature and the other cooking conditions remain. The cooking temperature drops from205℃to195℃while cooking pressure drops from2.34MPa to1.47MPa, having depressed0.87MPa, comparing with the auto-catalyzed ethanol pulping. Also, coarse pulp yield is50.22%, fine pulp yield is50.08%, Kappa value is22.99, which are close to those of the auto-catalyzed ethanol pulping (coarse pulp yield is49.43%, fine pulp yield is47.95%, Kappa value is20.59). The cooking condition has been greatly reduced and part of the theoretical basis has been supplied to the industrialization of ethanol pulp. And also by testing the two pulp physical properties, we find the physical properties of aspen acid catalytic ethanol pulp are generally better than that of aspen auto-catalyzed ethanol pulp.The results show that delignification reaction of aspen acid catalytic ethanol pulping follows first order reaction. Delignification reaction occurs during two phases, principal delignification phase (from beginning of heat reservation to90min) and residual delignification phase(from90min to the end of heat reservation). Under the optimal cooking conditions, to principal delignification phase, reaction velosity constant is0.0136min-1, activation energy is68.2003KJ/mol; To residual delignification phase, reaction velosity constant is0.0047mm-1, activation energy is89.7745KJ/mol. This activation energy is higher than aspen auto-catalyzed ethanol pulping (activation energy of principal delignification phase is47.9980KJ/mol, activation energy of residual delignification phase is78.7751KJ/mol), which shows that delignification during aspen acid catalytic ethanol pulping is harder than aspen auto-catalyzed ethanol pulping. So aspen is a certain adaptive to acid catalytic ethanol pulping.