Studies on the Sulphite Cooking (Part 9)
Improvement of Pulping Results of Larch Heart Wood Chip by Ca-Base Sulphite Cooking Accompanied with Various Techniques Promoting Penetration
1957 Volume 11 Issue 2 Pages 116-121
Details
1957 Volume 11 Issue 2 Pages 116-121
In Ca-base sulphite cooking of larch (Larix leptolepsis Murray) heart wood chip, it has been investigated how various techniques promoting penetration of cooking liquor improve the cooking results.The results obtained are as follows.
1.Effect of high concentration cooking liquors.Relating to the concentration of combined acid, its effect was investigated within the range from 1.0 to 1.7% at the same concentration of free acid (7%) and liquor to wood ratio of 6.Comparatively great improvement was found by increase of the acid from 1.0 to 1.2%, but increase over 1.2 % had not any improvement in the results.Increase of free acid brouht noticeable improvement.Under the concentration used in this study, the best pulping results was obtained with the liquor of 6.5 ro free acid and 1.5 ro bombined acid (Screenins/pulp : 20.1%, Cl2 consumption : 7.7%, see Table I)
2.Effects of steeping chips in water, presteaming or Va-purge pretreatment.These pretreatments showed substantial improvement.Presteaming (for 4 mins.by 2.5 kg/cm2 steam) and Va-purge pretreatment (3 times for 1.5 mins.by 2.5 kg/cm2 steam) showed identical results that screensngs/pulp was ca.10% and Cl2 consump.7.5%.Under the conditions used, the better next to the above pretreatments was steeping chips in water under reduced pressure (screenings/pulp : 12.1%, Cl2 consump. : 8.74%) followed by vacumimpregnation of cooking liquor (screenings/ pulp : 16.4% Cl2 consump.7.25%).Steeping chips in water without evacuation showed little improvement compared with regular pulping. (see Table I andIII)
3.Although the above techniques brought considerable improvement in the pulping results, they were much inferior to the use of soluble bases such as Na and NH3 by which sceernings was only about 2 % of screened pulp and Cl2 consumption of the pulp ca.4%.
4, From curves of delignification and thiosulfate and sulfate formation during cooking, it has been deduced that, besides the decomposition of cooking liquor by taxifolin, slowness of delignification in sulphite cooking of larch heart wood is another substantial cause of difficult pulping of the wood.The slower delignification may be caused by difficult penetration of the wood.
