Chemicals obtained from wood
- Resin acids.
- Fatty acids.
- Hydrolysis and fermentation.
- The sacchari?cation of wood.
- The disadvantage.
- Another product of fermentation processes.
- Thermal degradation.
A wide array of both commodity and specialty chemicals can be derived from wood, either as a primary product or by-product of another process. The technologies in which chemicals are the primary products include thermal degradation, hydrolysis/ fermentation, direct collection, and extraction methods. Chemicals collected as by-products generally come from ï¬ber-producing processes, including pulp and paper and steam explosion. While cellulose, lignin, and derivatives thereof could be classiï¬ed as chemicals derived from wood, the current review will be limited to low-molecular-weight chemicals from wood. The synthesis and utilization of various chemicals from renewable resources have received considerable recent attention through research efforts in green chemistry. Perhaps the oldest of the chemicals produced from wood are those derived from the extractives. The term 'naval stores' provides a clue to the water-prooï¬ng applications for which these chemicals were originally used. The extractives can broadly be divided into terpenes, resin acids, and fatty acids.
[...] Natural rubber (cis-1, 4-polyisoprene) comes from Hevea brasiliensis, and is still collected by tapping living trees and collecting the latex sap. Resin Acids The resin acids, the main components of rosin, are diterpenoids such as abietic acid, neoabietic acid, palustric acid, pimaric acid, and isopimaric acid. Rosins can be isolated from directly collected oleoresins, but are now more commonly separated from tall oil as a by-product of the kraft, black liquor recovery process. Metallic salts and esters of resin acids are used as additives to printing inks to improve gloss, mechanical stability and resistance to chemicals. [...]
[...] Thermal Degradation The production of chemicals from wood by the action of heat includes a broad continuum of processes, varying with respect to conditions and products. In general, these methods are done in the absence of air or other oxidizing agents, such that the substrate is thermally degraded, rather than combusted. The general terms used to describe this process include pyrolysis, liquefaction, and gasi?cation, the latter two selectively producing liquid and gas, respectively, while pyrolysis results in a mixture of all three, the relative amounts of which are a function of the conditions. [...]
[...] Hydrolysis and Fermentation The sacchari?cation of wood for the production of monomeric sugars can be accomplished by several methods, including concentrated acid hydrolysis, dilute acid hydrolysis, and enzymatic hydrolysis. Concentrated acid hydrolysis employs mineral acids (mainly hydrochloric or sulfuric acid) at percentages as high as such that relatively low reaction temperatures (20?251C) can be used. The drawbacks to this process involve corrosion of equipment due to the acidic environment, neutralization of the product stream, and recovery of the acid. In the dilute acid process, a two-step reaction is used to maximize the sugar recovery from both cellulose and the hemi-celluloses. [...]