Mechanistic Breakage of Cellulose During Media Milling and its Modeling
Date Issued
2007
Date
2007
Author(s)
Huang, Jen-Yi
DOI
zh-TW
Abstract
In this research, the breakage mechanism and its modeling of cellulose during media milling is investigated. The breakage mechanism of raw cotton cellulose is identified by comparing volume and number particle size distribution (PSD) of product at various time and their SEM photographs. The PSD is described by combining multiple beta distribution and the population balance equation is used to model the breakage kinetics of cellulose. This model can be used to simulate the PSD of various product, which the initial PSD are different.
The volume and number PSD of cellulose are convert into bimodal distribution and the fine sub-population and coarse sub-population are divided by 1 um after 15 min milling. The volume percentage of particle smaller than 1 um is 2.67 and the number percentage is 99.96 , it represent that there are a large number of fine particle after milling and the total volume increase with time. The same results are obtained by SEM photographs. Additionally, the standard deviation of coarse sub-population is decreased and the shape of distribution is narrowed. According to the results above, the breakage mechanism of cellulose is characterized in terms of surface-erosion during media milling.
Bimodal PSD was described by combining multiple beta distribution and all the correlation coefficient are larger than 0.975. Assuming specific breakage rate and breakage distribution function obey power-form and substituting all the functions into population balance equation, the partial integro-differential equation is transferred into ordinary differential equations and the breakage kinetics is then modeled. In order approach the milling process to quasi-steady state, the volume of feed is enlarge to 3000 mL and the breakage model is applied to experimental data available from various PSD of feed milling during on space time, the maximum error is less than 20%. The simulation results indicate that cellulose produce a great quantity of fine particle after breakage and it can be used to confirm the surface-erosion mechanism indirectly.
Subjects
雙峰分布
表面侵蝕
準穩態
beta分布
粒數平衡
破碎速率函數
破碎分布函數
Bimodal distribution
Surface erosion
Quasi-steady state
Beta distribution
Population balance
Specific breakage rate
Breakage distribution function
Type
thesis
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