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			EFPG DAYS 2003			cerig.efpg.inpg.fr

You are here : Home > Training > EFPG Days > 5- Reasons for yield loss in kraft cooking (slides 1-10)

Last update : August 05, 2003

			Second Session : The yield issue
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					V - Reasons for yield losses during kraft cooking. Possible strategies for yield increase D. Lachenal (EFPG)

A - Origin of yield loss (slides 1-10)

	1 - Chemical composition of plant materials Plant Softwood Hardwood Monocotyledons Cellulose 43% 45% 42% Hemicellulose 28% 34% 40% Glucomannans 16 5 0 Xylans 9 25 33 Lignin 29% 21% 17%				2 - Chemical pulping Chemical pulping consists in removing most of the lignin in wood or annual plant, in order to get individual fibers of high flexibility and in most cases ready to be fully bleached. Theoretical yield should be 70 to 80% if lignin removal were selective. Yield figures are 45-48% for softwood and 47-50% for hardwood in the case of bleachable grades. WHY is that ??

	3 - Origin of yield loss The origin of yield loss is carbohydrate (hemicellulose and cellulose) degradation during kraft cooking. Two mechanisms affect carbohydrates during a kraft cook: -- peeling, which starts at low temperature and goes very fast already at 100°C -- alkaline hydrolysis, which starts around 140°C				4 - Cellulose molecule Partial chemical structure of O-acetyl-galactoglucomannan from softwood

	5 - Peeling mechanism (1)

	6 - Peeling mechanism (2)

	7 - Peeling mechanism (3)

	8 - Peeling mechanism (4)

	9 - Peeling mechanism (5)

	10 - Peeling mechanism (6)

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