Extraction of hemicelluloses prior to kraft cooking: a
step for an integrated biorefinery in the pulp mill

Authors*: Cátia Vanessa Teixeira Mendes1,2
Jorge Manuel Santos Rocha1
Belinda Isabel Gomes Soares2
Gabriel Duarte Almeida Sousa2
Maria Graça Videira Sousa Carvalho1

ABSTRACT
Two treatments, an induced autohydrolysis and an acid hydrolysis,
were applied to Eucalyptus globulus wood chips prior to the
cooking stage to extract the hemicellulosic fraction that otherwise
would be dissolved in the black liquor and burnt in the recovery
boiler. The obtained hydrolysates, rich in xylose, were detoxified by
overliming and used for ethanolic fermentation. Impacts of each
wood pretreatment on the kraft cooking process and on the quality
of the produced pulp were evaluated. Both pretreatments promoted
an increase in the cooking rate, but had a negative effect on pulp
quality and overall yield. Autohydrolysis showed a less negative
influence. However, autohydrolysates led to lower values of ethanol
concentration, productivity and yield compared to the fermentation
of acid hydrolysates. To get more profit from the autohydrolysates
they were also submitted to secondary acid hydrolysis and vacuum
evaporation processes. Overliming followed by evaporation (with
a concentration factor of 3) gave better results than the inverse
method. This procedure raised the fermentable sugar content and
led to the production of ethanol with a concentration of ~10 geth L-1
(productivity of 0.23 geth L-1 h-1 and yield of 0.50 geth gxyl eq
-1) which
compares well with the results obtained with the fermentation of
acid hydrolysates.

Authors’ references:
1. CIEPQPF, Department of Chemical Engineering, University of Coimbra, R. Sílvio Lima, 3030-790 Coimbra, Portugal; phone +351.239798700; fax +351.239798703.
E-mails: cvtmendes@gmail.com; jrocha@eq.uc.pt; mgc@eq.uc.pt
2. RAIZ, Research Institute of Forestry and Paper, Qta. São Francisco, Apartado 15, 3801-501 Eixo, Portugal. – E-mail: gabriel.sousa@portucelsoporcel.com
Corresponding author: Cátia Vanessa Teixeira Mendes – E-mail: cvtmendes@gmail.com

O PAPEL vol. 72, num. 9, pp. 79 - 83 SEP 2011