Isolation of cellulose fibres from agricultural waste. Production of dissolving-grade pulp from oat husk and wheat straw
Typ
Examensarbete för masterexamen
Program
Innovative and sustainable chemical engineering (MPISC), MSc
Publicerad
2022
Författare
Sjöstedt, Niclas
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Recent decades have seen an increase in environmental awareness about the impact of
everyday products. Cellulose is the most abundant natural polymer in the world and
has long been used for production of films and textiles. The cellulose has traditionally
been isolated from wood as a dissolving-grade pulp and then further processed into the
desired product. Dissolving-grade pulps have narrow molecular weight distribution and
contain high levels of cellulose, low hemicellulose and low amounts of lignin and ash and
can be turned into a wide range of products. However, due to a future expected shortage
of fibres, finding new raw materials is a must. One alternative source of cellulose could
be to isolate cellulose from agricultural waste.
This project has been evaluating the suitability of using oat husk and wheat straw as alternative
raw materials for the production of dissolving-grade pulp. These raw materials
were chosen because of their abundance in Sweden, their low value and relatively high
cellulose content. The process chosen was the prehydrolysis-soda pulping process, where
a prehydrolysis step is used to remove hemicelluloses and facilitate delignification, and
soda pulping is used as the main delignifying step.
An acid prehydrolysis-soda pulping process followed by a total chlorine-free (TCF) bleaching
sequence was proven to be suitable for oat husk. The produced pulps had uniform
molecular weights, high cellulose content, low hemicellulose content and little to no lignin
content. The acid prehydrolysis was efficient in removing hemicelluloses and facilitating
delignification in the soda pulping step.
With a higher liquid to solid ratio in the acid pretreatment and higher concentrations
of NaOH during cooking, wheat straw exhibited similar properties regarding molecular
weight distribution, cellulose and hemicellulose contents. However, ash and lignin removal
was difficult. When the leaves were removed from the wheat straw, nearly all
requirements for use as dissolving-grade pulp were met but the lignin levels.
Both of the raw materials assessed in this project show great potential to be used as raw
materials for dissolving-grade pulps while also requiring milder process conditions than
wood. Even though more research is needed to fully assess the suitability of the raw
materials for dissolving-grade pulp production, the door of possibilities is wide open.
Beskrivning
Ämne/nyckelord
Dissolving-grade pulp , cellulose fibres , soda pulping , acid pretreatment , utohydrolysis , hot water extraction , wheat straw , oat husk , agricultural waste , spruce