Pines
Pines are trees in the genus Pinus in the family Pineaceae, and there are about 115 species of pine. These are evergreen, resinous trees
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Table 3.21 The detailed composition analysis of a typical pine species, Pinus radiata [226].
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or, rarely, shrubs growing 3-80 meters tall. Pines are native to the Northern Hemisphere and are among the most commercially important of trees, valued for their timber and wood pulp throughout the world. In temperate and tropical regions they are fast growing, able to grow in relatively dense stands; their acidic decaying needles inhibit the sprouting of competing hardwoods. The composition analysis of a typical pine species, Pinus radiata, is shown in Table 3.21.
Most of the common pretreatments, saccharification and fermentation methods have been tested on pine. Some of the recent studies used sulfuric acid-SO2 [227], acid catalysis with steam [228], alkali [229], steam explosion [230], organosolv [231, 232], and ionic liquid [233] pretreatments.
In one study, three processes were compared for pine wood: concentrated hydrochloric acid process, a two-step dilute acid process with sulfur dioxide in the first and hydrochloric acid in the second hydrolysis step, and an enzymatic hydrolysis process, including steam pretreatment. The ethanol production costs for three processes were evaluated by von Sivers and coworkers [234] as 2-43, 1-89 and 1-80 SEK/L, respectively, when capital costs were excluded. Furthermore, ethanol production costs were 422, 429 and 4-03 SEK/L, (6 SEK, Swedish Kroner = 1US$), respectively, for three processes when capital costs were included in the analysis.
In a more recent technical and economic feasibility study using loblolly pines, Frederick et al. reported that at current feedstock prices, ethanol produced from loblolly pine would be competitive with ethanol produced from corn [235]. In the process evaluated, pre-hydrolysis with dilute sulfuric acid was employed to produce hemicellulose and make the cellulose more accessible to hydrolysis by enzymes. Residual biomass from hydrolysis and extraction of carbohydrates was to be burned to generate power and to produce process steam. Their analysis indicates that ethanol can be produced at a cost of US $1.53/gal, based on a delivered wood cost of US $63.80/dry metric tonne and 75% conversion of the carbohydrates in wood to sugars for ethanol production. Furthermore, Frederick et al. noted that improving the conversion of wood carbohydrates to sugars to 95% would reduce the production cost to $1.29/gal.
The inhibitors produced in the pretreatment step is a serious factor in pine, as in the case of willow feedstock. Several researchers have looked at the ways of removing these inhibitors, as well as improving the enzymes to tolerate the inhibitors. In a recent study, Tian and Zhu reported ethanol yield of 270 L/ton wood from lodge pole pine pretreated with sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL), and using an adapted strain, Saccharomyces cerevisiae Y5, without detoxification [236]. The enzymatic hydro — lyzate produced from pretreated cellulosic solid substrate was combined with pretreatment hydrolyzate before fermentation. Detoxification of the pretreatment hydrolyzate using over-liming or XAD-4 resin before being combined with enzymatic hydrolyzate improved ethanol productivity in the first 4 h of fermentation and overall fermentation efficiency. However, detoxification did not improve final ethanol yield because of sugar losses. Furthermore, in this example, Saccharomyces cerevisiae Y5 strain showed excellent ethanol productivities of 2.0 and 0.8 g/L/h averaged over a period of 4 and 24 h, respectively, in the undetoxified run [236].