The Chemistry of Extractives

Softwood species Volume % of wood Ray cells Parenchyma cells (%) Mean pit size of parenchyma cells (Atm) 

The hardwood resin is located in the ray parenchyma cells which are connected with the vessels. It consists of fats, waxes, and sterols. The accessibility of the resin depends on the pore dimensions as well as on the mechanical stability of the ray parenchyma cells. Considerable variations occur among different wood species (Table 5-3). For instance, the accessibility of the resin in birch is much lower than in aspen. 

The content of extractives and their composition vary greatly among different wood species and also within the different parts of the same tree (cf. Appendix). Wood extractives can be divided into three subgroups aliphatic compounds (mainly fats and waxes), terpenes and terpenoids, and phenolic compounds. Parenchyma resin is rich in aliphatic components and the oleoresin is mainly composed of terpenoids. Characteristic of the heartwood is the accumulation of phenolic compounds. 

Genus or species Ray parenchyma cells Vertical parenchyma cells Average pit size (pm) Amount in pulps (weight %) Reason for heartwood formation 

Populus tremula (aspen) 10-11 Very little 8-10 2 Tylose 

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Extraction, a unit operation, is a complex and rapidly developing subject area (1,2). The chemistry of extraction and extractants has been comprehensively described (3,4). The main advantage of solvent extraction as an industrial process Hes in its versatiHty because of the enormous potential choice of solvents and extractants. The industrial appHcation of solvent extraction, including equipment design and operation, is a subject in itself (5). The fundamentals and technology of metal extraction processes have been described (6,7), as has the role of solvent extraction in relation to the overall development and feasibiHty of processes (8). The control of extraction columns has also been discussed (9). 

In contrast to the chemistry of extraction of uranium(VI) by organophosphorus acids, that of uranium(IV) has not been widely studied. It is known,135 however, that the extraction of U4+ by mono(2-ethylhexyl)phosphoric acid (2-ethylhexyl dihydrogen phosphate), for example, exceeds that of U022+ by a factor of 105. This clearly provides the basis for the strong extraction of uranium(IV) from phosphoric acid solutions by extractants containing monoalkyl phosphates. The existence of a synergistic effect in the extraction of uranium(IV) by mixtures of mono(2-ethylhexyl)phosphoric acid and neutral organophosphorus compounds was also reported recently.136... 

LIX 64N hes been used to separate nickal ions as well as copper.20 22 The chemistry of extraction in the two cases is the same [see Eqs. (19.4-3) and (19.4-4)]. However, data on transport throngh supported liquid membranes suggest that the copper flux across the membrane to fonr times that of nickal and selective extraction of copper can be achieved.22 The compound di-Q-elhylhexyl) phosphoric acid also has besn proposed for die essraciion of nickel II using liquid membranes,35... 

The simultaneous extraction of trivalent chromium, hexavalent chromium, and zinc from cooling lower blowdown water was studied in detail by Fuller and Li. They investigated Alamine 336, an oil-solaUe tertiary amine, and Aliquat 336-S, an oil-soluble quaternary amine salt, both manufactured by General Mills, as carriers in various liquid-membrane systems. Alamine was found to be an effective extractant for Cr , Ct, and Zn. However, for Cr and Cr, a pH of 3.0 or less in the external (feed) phase was required while Zn could be extracted only at a pH > 7. Thus, a combined process could not be developed. Aliquat 336-S was more promising. The chemistry of extraction with this carrier involves the following steps ... 

Hobbs, J. J., and F. E. King The Chemistry of Extractives from Hardwoods. XXIX. Eusiderin, a Possible By-product of Lignin Synthesis in Eusideroxylon zwageri. J. Chem. Soc. (London) 1960, 4732. 

The Chemistry of Extractives from Hardwoods. XXXVII. The Synthesis of... 

King F E, Cotterill C B, Godson D H, Jurd L, King T J 1953 The chemistry of extractives from hardwoods. Part XIII. Colourless constituents of Pterocarpus species. J Chem Soc 3693-3697... 

King F E, Bottomley W 1954 The chemistry of extractives from heartwoods. Part XVII. The occurrence of a flavan-3,4-diol (melacacidin) in Acacia melanoxylon. J Chem Soc 1399-1403... 

King F E, Clark-Lewis J W, Forbes W F 1955 The chemistry of extractives from hardwoods. 25. (-)-Epiafzelechin, a new member of the catechin series. J Chem Soc 2948-2956... 

King FE, Housley JR, King TJ 1954 The chemistry of extractives from hardwoods. XVI. Coumarin derivatives of Fagara macrophylla, Zanthoxylum flavum and Chloroxylon swietenia. J Chem Soc pp. 1392... 

The chemistry of extraction frequently involves nonlinear equihbria between the raffinate and extract. This reflects the extraction chemistry, which is often more com-phcated than that for absorption or dilute distillation. The nonlinear equilibria frequently result from specific chemical reactions. For example, benzoic acid can be extracted from water into benzene. The benzoic acid in water can ionize to form a mixture of benzoic acid, benzoate anions, and protons. Benzoic acid in benzene can dimerize. The ionization and dimerization may result in an equihbrium that is nonlinear and strongly dependent on concentration, pH, and temperature. 

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