Process development and environmental assessment within softwood based biorefineries

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

Life cycle assessment for identification of critical aspects in emerging technologies for the extraction of phenolic compounds from spruce bark

Polyphenolic compounds in bark are resources of great interest to produce renewable chemicals and several different technologies are available or under early development for the extraction of these types of compounds. Since critical environmental effects of a product are often set during the design phase, it is important to use life cycle assessment (LCA) to identify the steps resulting in the largest environmental burdens and the overall performance of the various technologies at an early stage during technology development. In addition, for a better understanding of the environmental impact of the future system, it is needed to consider an up-scaled process already in early process development. In the current study, LCAs of three different technologies; hot water extraction (HWE), ultrasound assisted extraction (UAE), and supercritical fluid extraction (SFE) for the extraction of phenolic compounds from spruce bark were compared in a large-scale production scenario. The study includes industrially relevant heat sources and heating technologies, downstream separations, solvent recovery, and heat recovery within the processes. The LCA shows that the simpler HWE process has a lower environmental impact per amount of phenolic compound extracted than UAE and SFE unless the extraction yields of the latter are more than about 5 times that of HWE. The reason for this result is mainly the environmental burden caused by the consumption of ethanol in the UAE and SFE processes, which accounts for more than 70% of the total environmental burden in most impact categories. Even if bioethanol produced with a particularly low carbon footprint would be used, the impact from ethanol use in the extractions would be considerable. UAE and SFE were also more dependent on the use of electricity. In the base case scenario, electricity produced with a low share of fossil resources was used, and electricity was in this case not one of the main contributors to the environmental impact of the processes. However, if the production of electricity is largely fossil-based, it comes out as a significant factor. Furthermore, the heat recovery in an up-scaled process is very important and accounts for a reduction of 35–60% net heat demand. As a complement to LCAs, future studies of promising polyphenolic compound production systems should also include economic aspects and performance

Removal of Water-Soluble Extractives Improves the Enzymatic Digestibility of Steam-Pretreated Softwood Barks

Softwood bark contains a large amounts of extractives—i.e., soluble lipophilic (such as resin acids) and hydrophilic components (phenolic compounds, stilbenes). The effects of the partial removal of water-soluble extractives before acid-catalyzed steam pretreatment on enzymatic digestibility were assessed for two softwood barks—Norway spruce and Scots pine. A simple hot water extraction step removed more than half of the water-soluble extractives from the barks, which improved the enzymatic digestibility of both steam-pretreated materials. This effect was more pronounced for the spruce than the pine bark, as evidenced by the 30 and 11% glucose yield improvement, respectively, in the enzymatic digestibility. Furthermore, analysis of the chemical composition showed that the acid-insoluble lignin content of the pretreated materials decreased when water-soluble extractives were removed prior to steam pretreatment. This can be explained by a decreased formation of water-insoluble “pseudo-lignin” from water-soluble bark phenolics during the acid-catalyzed pretreatment, which otherwise results in distorted lignin analysis and may also contribute to the impaired enzymatic digestibility of the barks. Thus, this study advocates the removal of extractives as the first step in the processing of bark or bark-rich materials in a sugar platform biorefinery

SO2-catalysed steam pretreatment of quinoa stalks

BACKGROUNDQuinoa is a pseudo-cereal grown predominantly in South America. The quinoa stalks are lignocellulosic residues, which have a limited use today. The objective of the current study was to assess the potential of this material as a source of monosaccharides for fermentation purposes by means of steam pretreatment giving sugars from the hemicellulose part, and enzymatic hydrolysis of the solid fraction obtained. SO2 catalysed steam pretreatment was carried out with a holding time of 5min at temperatures between 180 and 220 degrees C. The pretreatment was carried out at two different scales, a small reactor of size 0.5L and a somewhat larger reactor of size 10L, to allow comparison of scale effects in the pretreatment. RESULTSThe highest xylose yield in the liquid phase, obtained after pretreatment at 210 degrees C, was 80%. In the smaller scale unit, longer residence times were needed. The enzymatic hydrolysis, at an enzyme loading of 15 FPU g(-1) glucan and a WIS loading of 2%, resulted in a glucose yield of 70% based on the original glucan. The overall sugar yield, including the xylan hydrolysed in the enzymatic treatment, at dilute conditions was 75%. CONCLUSIONSSO2 catalysed pretreatment of quinoa straw followed by enzymatic hydrolysis gave a relatively good sugar yield. However, the yield obtained was somewhat lower than previously reported for similar materials, such as wheat straw and sugarcane bagasse, steam pretreated with SO2. (c) 2013 Society of Chemical Industr

Implications of differences in macromolecular composition of stem fractions for processing of Scots pine

Use of wood feedstocks for sugar-based biorefineries requires suitable treatments of the various tree fractions to optimize yields. In the current study, stem wood fractions (sapwood, heartwood and knotwood) were sampled at different heights from well-documented Scots pine trees taken from two contrasting stands. The fractions were assessed in terms of chemical composition, response to SO2-catalysed steam pretreatment and enzymatic digestibility. There were significant differences in total extractive contents between the fractions, where the heartwood fractions had an extractive content 1-3 wt% higher than sapwood (corresponding to a relative increase of 20-60 %) for samples at the same height. In contrast, the differences in macromolecular carbohydrate contents between the fractions were smaller and mainly insignificant. One exception was the xylan content, which was higher in heartwood than in sapwood at the same tree height (a relative difference of 10-15 %). Steam pretreatment resulted in a clearly higher degree of hydrolysis for sapwood than for heartwood at the same conditions. However, at optimal pretreatment temperatures a higher total sugar yield was in fact obtained for heartwood, showing the importance of tuning the process conditions for the respective wood fractions

Life-cycle assessment of the production of cationized tannins from Norway spruce bark as flocculants in wastewater treatment

It will be necessary to make efficient use of our resources if our society is to be converted into a bio-based economy. Every year large side streams of bark are produced in sawmills and pulp mills. In addition to utilizing the bark for heat and electricity production, as happens today, high-value chemical components could be extracted prior to energy conversion. These components include tannins. Cationized tannins have already been indicated as promising renewable flocculants in wastewater treatment. However, today's industrial production of tannins uses species from subtropical or temperate climates, and there has so far been little attention to the use of tannins from Norway spruce (Picea abies), an important species in forestry in the subarctic climate. The present life-cycle assessment (LCA) was undertaken to understand the environmental performance of the production of cationized tannins from the bark of Norway spruce and how the environmental impact is distributed along the production system. This work was connected to the Interreg Botnia-Atlantica TanWat research project, which studies the production and use of cationized tannins from Norway spruce for wastewater treatment at a pilot scale. The present LCA shows that the main environmental impact stems from the reagents used in the cationization step. The purification step could also be a significant issue depending on the possibility of reusing the eluent (ethanol) and the lifetime of the resin. The importance of running the processes with as concentrated streams as possible to minimize the need of process water and energy was also confirme