Measurement of Bleaching Yield by Carbohydrate Analysis.

Transcription

1 Measrement of Bleaching Yield by Carbohydrate Analysis

2 Yield Measrement by Carbohydrate Analysis Use of celllose yield as a basis for plp yield measrement first proposed by Rydholm (1970) Method frther developed by Easty and Malcolm [Tappi J. 65(12): (1982)] Use for plping yield measrement is based on the observation that yield of celllose in kraft plping is constant after the initial phase Celllose yield mst be determined by species

3 Plping Yield Measrement by Carbohydrate Analysis Bleaching PlpingYield Yield = = g celllose g celllose 100 g wood g plp = g celllose g plp g plp g wood = g celllose g wood

4 Nomenclatre Y cell = yield of celllose, assmed to be constant after the initial phase of kraft plping (36.0% for loblolly pine) C = weight fraction celllose in plp H = weight fraction lignin in plp L = weight fraction lignin in plp O = weight fraction other components in plp

5 Plping Yield Measrement by Carbohydrate Analysis Bleaching PlpingYield Yield = = gcelllose 100g wood g plp = gcelllose Y cell C+ H+ L+ O C

6 Plping Yield Measrement by Carbohydrate Analysis Y Y cell cell Bleaching PlpingYield = C + H + L+ O C C + C H L + Y cell C

7 Lignin-Carbohydrate Method vs. Celllose Method Celllose content of plp is sbject to analytical errors that will affect yield estimates calclated directly from celllose content This difficlty is gotten arond by sing the second form of the eqation on the previos slide to calclate yield from the ratio (C + H)/C, in which the errors in C in the nmerator and denominator compensate

8 Plping Yield Measrement Assmptions Y cell, the yield of celllose, is constant over the range of degrees of delignification for which yield estimates are desired The yields of plp components other than celllose, hemicelllose and lignin are negligible in comparison to the yields of these major components

9 Bleaching Yield Measrement by Carbohydrate Analysis BleachingYield = g celllose g celllose 100 g. plp g b. plp = g celllose g b plp g b plp g plp. = g celllose g. p.

10 Bleaching Yield Measrement by Carbohydrate Analysis BleachingYield = g celllose 100 g. plp gb. plp = gcelllose 100 C C+ H+ L+ O C+ H+ L+ O C b

11 Bleaching Yield Measrement by Carbohydrate Analysis BleachingYield = = 100 C C+ H+ L+ O 100 C C+ H+ L+ O = C C + H C b b

12 Bleaching Yield Measrement by Carbohydrate Analysis C C C + H C = C = C+ H+ L+ O C+ H = C+ H+ L+ O C ( 1 L O) + H

13 Bleaching Yield Measrement by Carbohydrate Analysis Final Eqation Bleaching Yield C C H ( 1 L A E) C+ H C b = Bleaching Yield = in which A and E are wt. fractions of ash and extractives

14 Bleaching Yield Measrement Assmptions No celllose is lost dring bleaching Bleached plp contains only celllose and hemicelllose Unbleached plp contains only celllose, hemicelllose, lignin, ash and extractives

15 Example of Data Needed for Bleaching Yield Estimation Unbleached Bleached Components, % o.d.p. Total Carbohydrates Celllose Lignin Ash Extractives Celllose, % of total carbohydrates

16 Sample Calclation of Bleaching Yield C BleachingYield = = C H ( L A E) C H + C = b ( ) = 96. 6%

17 Conclsions Carbohydrate analysis, previosly shown to be sefl for estimating digester yields, is even more applicable to the estimation of yield losses-shrinkage in bleaching. The necessary assmptions concerning the compositions of the plp before and after bleaching and celllose stability dring bleaching appear reasonable.

18 Conclsions Application of the method in the laboratory to several different plps has given yield estimates which are consistent with experience in every case. The method will be particlarly sefl for monitoring yield loss in mills, either dring rotine operation or dring mill experiments.