Analysis of Softwood
BackgroundTrees are classified as softwoods (gymnosperms) and hardwoods (angiosperms). Globally, there are about 30 000 hardwoods and 520 softwood tree species known. However, in Europe there are only 51 and 10, respectively, of these species that exist naturally. The species of most interest for biorefining are those that can be obtained reasonably cheaply whether directly (i.e. specifically grown) or indirectly (as wastes or residues). Such feedstocks include the short-rotation coppice crops willow, poplar, and robina (hardwoods) and residues from the forestry industry (which includes the softwoods Sitka spruce, Norway spruce, and several pine varieties).
Celignis founder Daniel Hayes has considerable experience in the chemical and near-infrared analysis of softwoods and has characterised samples from a number of different species, incuding pines, spruces, willows, poplars, and eucalyptus.
Analysis of Softwood at Celignis
Celignis Analytical can determine the following properties of Softwood samples:
Sugar Alcohols and Uronic Acids
Lignin and Extractives
- Ash (Acid Insoluble)
- Volatile Matter
- Fixed Carbon
- Gross Calorific Value
- Net Calorific Value
- Ash Shrinkage Starting Temperature (Oxidising)
- Ash Deformation Temperature (Oxidising)
- Ash Hemisphere Temperature (Oxidising)
- Ash Flow Temperature (Oxidising)
- Ash Shrinkage Starting Temperature (Reducing)
- Ash Deformation Temperature (Reducing)
- Ash Hemisphere Temperature (Reducing)
- Ash Flow Temperature (Reducing)
Major and Minor Elements
Cellulose Content of SoftwoodA detailed compilation of the polysaccharide and ligneous composition of wood was carried out by (Fengel and Grosser, 1975). By tabulating the data from more than 350 references in 153 temperate species it was found that, on average, stem wood in softwoods contains 40-45% cellulose.
Click here to see the Celignis Analysis Packages that determine cellulose content.
Hemicellulose Content of SoftwoodThere are characteristic differences between hardwoods and softwoods with regard to the composition and structure of the hemicelluloses.
In softwoods, O-acetyl-galactoglucomannan is the principal hemicellulose component. The glucose to mannose ratio is about 1:3, whereas the ratio of galactose to glucose can vary from 1:1 to 1:10. Softwood O-acetyl-galactoglucomannan has been reported to have an approximate degree of polymerization between 100 and 150, equivalent to a molecular weight around 16,000–24,000.
Softwoods also contain xylans. Specifically, softwood xylans are an arabino-(4-O-methylglucurono)xylan. The softwood xylan does not contain acetyl groups and is more highly branched and more acidic than the hardwood xylan. These side chains can be removed under mild acid conditions in which the main xylose chain remains intact). The arabinose and uronic acid substituents do stabilise the xylan chain against alkali-catalysed degradation, however.
There are other hemicelluloses that are present in minor quantities in softwoods. These are built up predominantly by units of arabinose, galactose, glucuronic and galacturonic acids. There are also small amounts of starch and pectins.
Click here to see the Celignis Analysis Packages that determine hemicellulose content.
Lignin Content of SoftwoodThe lignin fraction is generally considerably greater in temperate softwoods than in hardwoods. Covalent bonds are thought to exist between the lignins and carbohydrates in woody biomass plants.
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Starch Content of SoftwoodStarch content will vary according to the species of softwood and the conditions of its growth and harvest. Starch content is typically lower in the wood than in the foliage and bark.
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Uronic Acid Content of SoftwoodUronic acids can be present as side chains attached to the main backbone of hemicelluloses in softwoods. For example, the arabinoxylans of softwoods have partial substitution of the xylan main chain by glucuronic acid, with the ratio of xylose to uronic acids varying between 4:1 and 9:1. Other softwood hemicelluloses can also contain glucuronic acid as well as galactuornic acid.
Click here to read more about uronic acids and to see the Celignis Analysis Packages that determine uronic acid content.
Ash Content of SoftwoodThe ash of most wood produced in temperate regions is not a particularly significant fraction of the biomass. Generally, softwoods contain somewhat less ash than hardwoods.
Young trees tend to have a higher ash content than mature trees and the ash content tends to be much higher in bark and foliage.
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Heating (Calorific) Value of SoftwoodGiven that the concentrations of lignin and resins tend to be higher in softwoods than in hardwoods, softwoods tend to have slightly higher heating values. Howard (1973), when examining southern pine, found that extractive content was positively correlated with the heating value and accounted for 54% of the variation, whereas variation in the proportion of the main chemical constituents had only minor effects.
With regard to the extractives, in woods these are substances that tend to be deposited in association with the transition from sapwood to heartwood. They also tend to be present in greater concentrations in barks. Large extractive concentrations are present in woods only in exceptional cases, most of these being tropical species.
Howard (1973) also found that the heating value of mixed stem-bark samples is inversely related to stem height. This is due to a greater proportion of the lower-heating value inner bark at greater heights.
Click here to see the Celignis Analysis Packages that determine heating value.
Bulk Density of SoftwoodAt Celignis we can determine the bulk density of biomass samples, including Softwood, according to ISO standard 17828 (2015). This method requires the biomass to be in an appropriate form (chips or powder) for density determination.
Click here to see the Celignis Analysis Packages that determine bulk density.
Basic Density of SoftwoodAt Celignis we can determine the basic density of some suitable biomass samples. The method requires the biomass to be in an appropriate form (chips) for density determination.
Click here to see the Celignis Analysis Packages that determine basic density.
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