Process development and environmental assessment within softwood based biorefineries

Abstract

We urgently need to
move from a fossil-based to a bio-based society. From a Swedish perspective, a
promising way forward are biorefineries with an integrated production of
materials, chemicals, and energy from the softwood species Scots pine (Pinus
sylvestris) and Norway spruce (Picea abies). A diverse set of
process routes will be necessary to produce all intermediates and commercial products. In this thesis, the
focus is the production of phenolic compounds through extraction, and
production of fermentable sugars through steam explosion pretreatment with
subsequent enzymatic hydrolysis.

Although renewable, the annual biomass
production is limited, and efficient biorefinery processes are essential. By
understanding the structural or chemical differences within the feedstock,
processes can be optimized further. In this thesis, it is shown how more
juvenile tissue, or sapwood, of Scots pine required lower severity in steam
explosion pretreatment than older tissue, heartwood, or knots for the
production of fermentable sugars. Pretreating different wood tissues of Scots
pine at different severity can thus increase the overall yield of fermentable
sugars. Bark is chemically significantly different from wood and the production
of fermentable sugars from bark is not feasible using the same processes as for
wood. In this thesis, it is shown how removing water-soluble extractives prior
to steam explosion pretreatment, and enzymatic hydrolysis can increase the
yield of glucose by 30 % and 11 % in the enzymatic hydrolysis of bark
from Norway spruce and from Scots pine, respectively.

To develop new process technologies with
favorable environmental profiles, it is essential to quantitatively assess the
potential environmental impact of different process choices through life cycle
assessment (LCA), early during process development. In this thesis, the
potential environmental impact of the production of cationized tannins from
high-pressure hot water extract of Norway spruce bark was evaluated. The
potential environmental impacts when using the three different extraction
technologies: hot water extraction, ultrasound extraction, and supercritical
extraction, for the production of phenolic compounds, were also assessed and
compared. For the production of 1 kg cationized tannins the overall
contribution to climate change was estimated to be between 1.2-4.7 kg CO₂
eq. The potential impact on climate change for the three extraction
technologies were estimated to 0.48-0.68, 5.9-11, and 5.8-6.3 kg CO₂-eq.
per kg of produced phenolic compounds for hot water extraction, ultrasound
assisted extraction, and supercritical fluid extraction, respectively. The need
for chemical solvents and reagents were identified as primary hotspots, i.e.
critical aspects to be prioritized for action, in all studied systems and for
most of the studied impact categories. Simple, water-based systems, therefore,
have substantial advantages. In addition, it will be necessary with sustainably
produced solvents and reagents to reach a sustainable biobased economy.

• author: Carlqvist, Karin
• supervisor: Gunnar Lidén; Pål Börjesson; Henrik Stålbrand
• opponent: Prof. Svanström, Magdalena, Chalmers, Sweden.
• organization: Division of Chemical Engineering
• publishing date: 2022
• type: Thesis
• publication status: published
• subject: Chemical Engineering
• keywords: sugar platform, extractives, steam explosion, pretreatment, bark, enzymatic hydrolysis, phenolic compounds, bioeconomy, LCA, Pinus sylvestris, Picea abies, pine, spruce, sockerplattform, extraktivämnen, Steam explosion (SE), förbehandling lignocellulosa, bark, enzymatisk hydrolys, fenoler, bioekonomi, LCA, Pinus sylvestris, Picea abies, tall, gran
• pages: 80 pages
• defense location: Lecture hall KC:A, Kemicentrum, Naturvetarvägen 14, Faculty of Engineering LTH, Lund University, Lund. Youtube: https://youtu.be/6ynmb9SeLR0
• defense date: 2022-03-04 09:00:00
• ISBN: 978-91-7422-859-5
• ISBN: 978-91-7422-858-8
• language: English
• LU publication?: yes
• id: b443d86a-d19f-4121-928f-57335d2191dd
• date added to LUP: 2022-02-04 10:58:41
• date last changed: 2022-02-09 13:36:42