WOOD ENERGY AND EXTRACTIVES

ENERGY AND CHEMICALS FROM WOOD

1. WOOD ENERGY AND EXTRACTIVES

2. Woody biomass is the accumulated mass, above and below ground, of the roots, wood, bark, and leaves of living and dead woody shrubs and trees. Traditionally, the portion of the forest related biomass not used in the manufacture of wood products has been referred to as residue. Mill residues Woods or logging residues

3. Urban and municipal waste wood Yard trimmings Storm damage Construction and demolition waste Land-clearing debris Forestry residues Thinning for forest health, wildfire risk reduction Branches from harvesting Processing residue

4. WOOD ENERGY Wood energy is one of the oldest forms of energy used for heating and processes. The energy for commercial and industrial applications are similar except the technology and types of wood fuel are slightly more advanced. It is sourced from local forestry and utilized by efficient clean burning boilers to produce heat or hot water for processing by commercial and industrial businesses.

5. Wood is considered humankind’s very first source of energy. Today it is still the most important single source of renewable energy providing about 6% of the global total primary energy supply. More than two billion people depend on wood energy for cooking and/or heating, particularly in households in developing countries. 

6. It represents the only domestically available and affordable source of energy. Private households cooking and heating with wood fuels represents one third of the global renewable energy consumption, making wood the most decentralized energy in the world. Wood fuels arise from multiple sources including forests, other wooded land and trees outside forests, co-products from wood processing, post-consumer recovered wood and processed wood-based fuels.

7. Wood energy is also an important emergency backup fuel. Societies at any socio-economic level will switch easily back to wood energy when encountering economic difficulties, natural disasters, conflict situations or fossil energy supply shortages

8. Gasification Gasification is a thermochemical process in which biomass at high heat is turned directly from a solid into a gaseous fuel called syngas (a mixture of carbon monoxide, hydrogen and some methane).

9. Feedstock Wood biomass are generally used for gasification of wood Wood pellets Chips from wood residues Waste wood Pelletization is desirable (handling/transport/storage, consistency of the fuel, moisture, energy density, etc.

10. Processes involved in gasification of wood

11. 1. Drying The dehydration or drying process occurs at around 100 °C . B y using heat (supplied by burning some of the wood), water evaporates from the wood. Typically the resulting steam is mixed into the gas flow and may be involved with subsequent chemical reactions, notably the water-gas reaction if the temperature is sufficiently high .

12. 2. Pyrolysis Pyrolysis is the thermal degradation of organic components in biomass in the absence of oxygen. Major products are oil, gas, and char. The pyrolysis (or devolatilization ) process occurs at around 200-300 °C . Above 270°C (heat supplied by burning some of the wood) the wood structure breaks apart chemically. Long molecules are made smaller. Charcoal/char and tar-oil gases are created

13. Volatiles are released and char is produced, resulting in up to 70% weight loss for coal. The process is dependent on the properties of the wood and determines the structure and composition of the char, which will then undergo gasification reactions.

14. 3. Combustion The combustion process occurs as the volatile products and some of the char react with oxygen to primarily form carbon dioxide and small amounts of carbon monoxide , which provides heat for the subsequent gasification reactions . Under supply of a measured quantity of air, a part of carbon oxidizes (burns) to carbon dioxide and hydrogen oxidizes to water

15. 4. Reduction In the reduction area several key conversions take place, and these require significant heat Carbon (char) reacts with CO 2 and converts it to carbon monoxide (CO). Carbon also reacts with H 2 O , “stealing” an oxygen atom producing carbon monoxide and hydrogen gases . Some of the char also binds with H to create methane , and some CO reacts with H to form methane + water.

16. Aerobic Digestion Aerobic digestion is a process in which bacteria use oxygen to convert organic material into carbon dioxide . Products include nutrient-rich fertilizers and composts.

17. Anaerobic Digestion Anaerobic Digestion is the decomposition of biomass by bacteria in the absence of oxygen . Biogas, or methane, is the primary product produced.

18. Fermentation Fermentation is a biological process in which enzymes produced by microorganisms cause chemical reactions to occur. Products include ethanol, commercial levels of therapeutic and research enzymes, antibiotics, and specialty chemicals.

19. Types of Gasifires Several types of gasifies are currently available for commercial use: Counter-current fixed bed (updraft) Co-current fixed bed (downdraft) Fluidized bed Entrained flow

20. What is wood gas? Typically woodgas consists of: 22% carbon monoxide (CO) 8% hydrogen (H 2 ) 3% methane (CH 4 ) 6% carbon dioxide (CO 2 ) 51% nitrogen (N 2 )

21. Yield of products Charcoal :33 – 50 % Wood tar :7- 11% Acetic acid :4.5-5 % Methyl alcohol :2 %

22. Softwood distillation products Gas Wood alcohol Acetic acid Acetone Methyl acetone Tar oil Pitch Charcoal Wood tar Charcoal Turpentine Pine tar Tar oils Pitch Hardwood distillation products

23. Extractives Extractives are obtained by extraction wood with organic solvents or water or steam distillation , and some are obtained as exudates from wounded trees . The amounts of extractives is small, generally up to 5-10% in the wood in the temperate zone. However, in some tropical woods relatively high amounts of extractives are found.

24. Although the extractives are low in concentration compared with those of the cell wall polymers, this fraction characterizes each wood species chemically . Most component of wood extractives are classified as secondary metabolites , and the distribution of specific compounds in certain wood species. This feature provide the basis of chemotaxonomy of woody plants.

25. Individual compounds are often found in specific tissues of individual trees, and their amounts can vary from season even in the same tissue. Extractives are the predominant contributors to wood color, fragrance, and durability . Extractives also influence the pulping, drying, adhesion, hygroscopicity, and acoustic properties of wood.

26. DIFFERENT TYPES OF EXTRACTIVES ARE NECESSARY TO MAINTAIN THE DIVERSIFIED BIOLOGICAL FUNCTIONS OF THE TREE. Exudates Exudates are formed by the tree through secondary metabolism after mechanical damage or attack by insect or fungi. Resins Resin is often used as a collective name for the lipophilic extractives soluble in non polar organic solvents but insoluble in water. Gums a viscous secretion of some trees and shrubs that hardens on drying but is soluble in water, and from which adhesives and other products are made

27. Tannins Extractive compounds found largely in the bark of certain species. Used primarily in the leather tanning industry, these compounds are becoming important in the wood adhesives industry Fats : The energy source of the wood cells. Lower terpenoids, resin acids, phenolic substances : Protection the wood against microbiological damage or insect attacks. Metal ions : Catalyst of enzyme for biosynthesis.

28. Terpenoids and Steroids . Monoterpenoids and especially resin acids (diterpenoids) are dominant and commercially important oleoresin constituent. The softwood resin canals are filled with oleoresin. The parenchyma resin of both softwoods and hardwoods contains triterpenoids and steroids, main occurring as fatty acid esters .

29. Terpenoids and steroids are formally derived from isoprene units and are sometimes called isoprenoids . The name terpene was given to hydrocarbons which were detected in turpentine oil. Terpenes are known as the large group of hydrocarbons made up of isoprene units.

30. Their respective derivatives with hydroxyl, carbonyl, and carboxyl functions are not hydrocarbons but strictly speaking terpenoids. It has been proposed to call both the terpene hydrocarbons and their derivatives collectively terpenoids. Steroids are structurally related to terpenoids, but some pathways in their biosynthesis have resulted in their structural characteristics and biological function.

31. Terpenoids can be divided into subgroups according to the number of isoprene units . Isoprene itself had been characterized as a decomposition product from various natural cyclic hydrocarbons, and was suggested as the fundamental building block for isoprenoids .

32. Isoprene is produced naturally but is not involved in the formation of these compounds (terpenoids), and the biochemically active isoprene units were identified as the DMAPP ( dimethylallyl diphosphate ) and IPP ( isopentenyl diphosphate ) .

33. Monoterpenoids are dominant in the volatile terpenoids fraction (essential oil) as turpentine from different parts of the tree by steam distillation. They can be divided into acylic, monocyclic, bicyclic, and tricyclic structural types. They are derived from geranyl pyrophosphate (GPP) Tropolones , a seven- membered ring compounds, are belong to monoterpenes.

34. Sesquiterpenoids More than 10000 sesquiterpenoids have been identified, representing a wide variety compounds of different skeletal types from acyclic to tetra cyclic systems.

35. Diterpenoids Diterpenoids constitute a major part of oleoresin . This group can be divided into acylic, bicyclic, tricyclic, tetracyclic, and macrocyclic structural types. Diterpenoids are present either as hydrocarbons or as derivatives with hydroxyl, carbonyl, or carboxyl groups.

36. The resin acids are dominant constituents in pine wood oleoresin and in commercially important rosin. The most common resin acids in softwood are tricyclic terpenoids, and they are classified into pimarane and abietane types .

37. Triterpenoids Compounds belonging to this group are widely distributed in plants. The most common steroid in wood and higher plants is sitosterol . Campesterol is a structurally similar monoenolic steroid but is less abundant than sitosterol . Citrostadienol is a dienolic sterol having a 4α-methyl group.

38. Betulinol ( betulin ) is a pentacyclic triterpenoid occuring in large amounts in free from in the outer bark of birch. Serratenediol present in the bark of pines , is a member of a small pentacyclic triterpenoid subgroup so-called serratanes , having a seven membered C-ring.

39. Triterpenoids and steroids occur mainly as wax and as glycosides , but also in the free form. Hydrophobic compounds – causing problems in pulping and papermaking process. Sitosterol and betulinol are potential raw materials for making wood chemicals.

40. Polyterpenoids Acyclic primary alcohols of polyisoprenoids , so-called polyprenols , are abundant in high plants, especially in the leaves, but in wood. A special type of polyprenols , called betulaprenols , occur as fatty acid esters in silver birch. Betulaprenols are built up 6-9 isoprene units, which double bonds have cis and trans configuration.

41. Fats and Wax Fats and wax are the predominating constituents of the lipophilic material encapsulated in parenchyma cells . The fats are glycerol esters of fatty acids occurring in wood predominantly as triglycerides. In fresh wood free fatty acids are present practically only in heartwood.

42. Fatty acids are partially liberated from triglycerides during wood storage . More than 30 fatty acids, both saturated and unsaturated, have been identified in softwoods and hardwoods. Waxes are esters of higher fatty alcohols, terpene alcohols, or sterols. Fats and waxes (esters) are hydrolyzed during kraft pulping. The fatty acids, which are liberated, can be recovered together with resin acids as soap skimming from the black liquor.

43. Phenolic Constituents Heartwood and bark contain a large variety of complex aromatic extractives. Most of them are phenolic compounds, and many are derived from the phenylpropanoid structure .

44. Inorganic Components Wood contains only rather low amounts of inorganic components, measured as ash seldom exceeding 1% the dry wood weight . Ash content of needles, leaves, and bark can be much higher. Typical deposits in the cell walls are various meta salts, such as carbonates, silicates, oxalates, and phosphates .

45. The most abundant metal component is calcium followed by potassium and magnesium . A spectrum of other metals is also present, amounting up to 100 ppm for iron and manganese whereas most of the other metals usually occur only as traces or at least below the 10 ppm .

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