Study On Self - Cleaning And High Efficiency Ozone Bleaching

As the strains on the shortage of wood resources, an abundance of annual straws just has to faced up to, as an alternative resource of wood for pulping and papermaking, though they can cause the production processes a lot of troubles It is of great importance to the propelling straw pulping industry forward how to bleach the traditional chemical straw pulp high-selectively with ozone in order to obtain the high-quality TCF bleaching pulp.In this thesis,soda-AQ wheat straw pulp was bleached with ozone in a self-made high consistency ozone bleaching device. The optimized ozone bleaching were carried out under pulp consistency of 40% with ozone flow of 0.9 kg/(odtmin) for 10 min, using oxalic acid dosage of 1.19% at pH= 1.5. traditional chemical straw pulp33.1%ISO brightness, an reduction of 58.8% Kappa number, and a drop of 185ml/g viscosity.It is indicated that the main factor influencing the ozone bleaching is the pulp consistency,the other factors such as the solution pH, bleaching time and the flow rate of ozone were less important than the pulp consistency, and the effect get weak in turn. The addition of oxalic acid to bleaching process can improve the selectivity of the ozonation significantly, which increased the viscosity of the bleached pulp to a large extent, favoring the elevation of the brightness as well. Additionally, the effect of bleaching the pulp with a large number of non-fibrous cells was better than the pulp almost without these cells.In order to measure quantitatively oxalic acid with outstanding protection of carbohydrates in ozone bleaching. We established a method for measuring oxalate in bleaching effluent and pretreatment liquid by UV spectrophotometry. On this basis, the study on recycling of bleached waste liquor in ozone bleaching process to make use of the oxalate produced from ozonation showed that the recycle had no negative effect on ozone bleaching of the straw pulp.The accumulation of the organic load in recycled waste liquor was much slower than expected, and the grow rate get extremely low after several times of the recycle.It is to be observed that BODs/CODcr of the effluent were more than 0.45,belonging to high biodegradability also more likely to system closure.Through the study on the mechanism of delignification, the degradation of carbohydrates, and the effect of non-fibrous cell existing during ozone bleaching of soda-AQ wheat straw pulp, it is cleared that:(1) The bleaching effect was poor in medium and low consistency of the pulp because of the prevailing carbohydrate degradation in ozonation.(2) Adding oxalic acid Could not improve the lignin removal, but obviously restrain the ozonation of C-H and C-OH, which would help prevent fiber from over-degradation.(3) The effect of bleaching the pulp with a large number of non-fibrous cells was better than that consisting of almost all the fibers. Non-fibrous cells would easily contact with ozone and take part in reaction, instead, which protected the fibers to some extent.