Kinetics

854 views
767 views

Published on

Project from Chemical Reaction Engineering

Published in: Education
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
854
On SlideShare
0
From Embeds
0
Number of Embeds
5
Actions
Shares
0
Downloads
16
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Kinetics

  1. 1. Kraft Process <ul><li>Jennifer Pratt </li></ul><ul><li>Chemical Reaction Engineering </li></ul><ul><li>5/1/06 </li></ul>
  2. 2. Outline <ul><li>Intro </li></ul><ul><li>Overview </li></ul><ul><li>Theory </li></ul><ul><li>Applications </li></ul><ul><li>Conclusions </li></ul>
  3. 3. Introduction <ul><li>Paper making began in China 2000 years ago </li></ul><ul><li>-originally used old rags  fibers </li></ul><ul><li>Today: trees/ recycled materials  fibers by pulping </li></ul><ul><li>Kraft process is main chemical method for tree  pulp </li></ul><ul><li>“ Kraft”=strong in German. Strong paper is made from Kraft pulped paper </li></ul><ul><li>Also “Sulfate Process” because sulfates are produced as a byproduct </li></ul><ul><li>Goal = remove lignin from the wood and obtain individual fibers </li></ul><ul><li>Lignin=strong polymer in plant cell walls for support and structure </li></ul>
  4. 4. Paper Making Process
  5. 5. Source: http://www.epa.gov/ttn/chief/ap42/ch10/final/c10s02.pdf
  6. 6. Overview <ul><li>Begins in Digester </li></ul><ul><ul><li>White liquor= Na 2 s+NaOH </li></ul></ul><ul><ul><li>Chips=logs chopped up into cornflake sized pieces </li></ul></ul><ul><li>Reaction of White liquor and chips </li></ul><ul><ul><li>Yields Black Liquor/Pulp mixture </li></ul></ul><ul><li>Blow Tank then Filter </li></ul><ul><ul><li>Contents separated into Black Liquor and Pulp Slurry </li></ul></ul><ul><ul><li>Pulp eventually becomes paper </li></ul></ul><ul><li>Chemical Recovery </li></ul><ul><ul><li>Black Liquor diluted and burned  energy and smelt </li></ul></ul><ul><ul><li>Smelt diluted  Green Liquor </li></ul></ul><ul><ul><li>Green Liquor converted back to White Liquor with Calcium Oxide </li></ul></ul>
  7. 7. Theory <ul><li>In the Digester </li></ul><ul><ul><li>Na 2 S + NaOH + wood chips —>Na 2 SO 4 + Na 2 CO 3 + pulp </li></ul></ul><ul><li>Five steps in Digester </li></ul><ul><ul><li>transportation of liquor ions to wood surface </li></ul></ul><ul><ul><li>diffusion of the ions into the wood fibers </li></ul></ul><ul><ul><li>chemical reaction between the wood and the ions </li></ul></ul><ul><ul><li>diffusion of the products back to the surface of the wood fibers </li></ul></ul><ul><ul><li>movement of the products into the bulk liquor. </li></ul></ul>
  8. 8. Theory <ul><li>Residence time is important </li></ul><ul><ul><li>More time=more lignin removal </li></ul></ul><ul><ul><li>Too much time=cellulose in fibers breaks down </li></ul></ul><ul><li>Kappa Number </li></ul><ul><ul><li>Degree of Lignification </li></ul></ul><ul><ul><li>Goal=maximize Kappa Number with least amount of chemicals </li></ul></ul>
  9. 9. Theory <ul><li>Rate of Delignification </li></ul><ul><ul><li>Initial-extraction of low MW lignin, turpentine and tall oil </li></ul></ul><ul><ul><li>Bulk-most lignin removed </li></ul></ul><ul><ul><li>Residual-last remnants of lignin removed </li></ul></ul>
  10. 10. Bulk Delignification Kinetics <ul><ul><li>-dL/dt=k 1 (OH - )(L) </li></ul></ul><ul><ul><li>Constant white liquor input  ln(Lo/L)=(k o )(t) </li></ul></ul><ul><ul><li>k o =Ae (-Ea/RT) </li></ul></ul><ul><ul><li>Activation energy for each wood is ultimately determined from experiment </li></ul></ul>
  11. 11. Conclusion <ul><li>Industry needs to know activation energy for pulp reaction to optimize process </li></ul><ul><li>Different parts of tree have different lignin content and uses </li></ul><ul><li>Trees from different geographical regions have different lignin content </li></ul><ul><li>Wood type chosen based on paper product produced, wood’s resistivity to delignification, & integrity of wood fibers produced in pulping </li></ul>
  12. 12. References <ul><li>Andersson, N., Wilson, D., and Germgard, U. (2002). Validating Continuous Kraft Digester Kinetic Models with Online NIR Measurements. Anchorage, AK. Proceedings for the American Control Conference. </li></ul><ul><li>Helm, R. (2000). Kraft Pulping . Retrieved April 25, 2006, from http://dwb.unl.edu/Teacher/NSF/C06 /C06Links /www.chem.vt.edu/chem- dept/helm/3434WOOD/notes2/kraft.html. </li></ul><ul><li>Wong, B.M., Deka, G.C., and Roy, D.N. (1995). Bulk Delignification Kinetics at Selected Vertical Heights With Jack Pine Plus Trees. Wood Science and Technology, 29, 11-18. </li></ul>
  13. 13. Questions?

×