Variation in Composition of Species

The ifiain variations in composition are between the hardwoods and the softwoods. The hardwoods are generally higher in thé amount of add by hydrolysis, methoxyl groups, pentosans, and pentosans in cellulose. The ash and the potash content of the ash are also higher in the hardwoods. . Contrary tó the general opinion thé cellulose is not generally higher in softwoods and the lignin is not generally higher in hardwoods.

The high ether soluble in longleaf pine and Western yellow pine is due to the high resin content of the wood from these species. The high water soluble in Western larch is due to a gum, galactan, which occurs in unusually large quantities in this species.8 The composition of the material which furnishes the high water soluble value for mes-quite is not known. The action of 1 per cent sodium hydroxide is

3I J^1' No- 3 G^ste Experiment Station. Reported by Bateman, Cham, & Met. Eng.

greater on hardwoods than on softwoods, the average of- hardwoods from Table 4 being 21.5 per cent and the softwoods 17.6 per cent. This difference is more marked if we exclude the woods which have high water soluble or ether soluble and include only those in which the action of the alkali is mainly on the ligno-cellulose (probably on the pentosans). Excluding mesquite from the hardwoods and longleaf pine, Western yellow pine and larch from the softwoods, the average solubilities in alkali of the rest are, respectively, 20.5 per cent and 15 per cent.

Another difference between the hardwood and softwood groups which does not show in the table was studied by Schorger0 who found that all the softwoods contained mannan, some in quantities as high as 7 per cent, while the hardwoods contained none of this substance.

Effect of Composition on Value for Distillation

There are no direct and quantitative relationships known between the composition of a wood and the value for distillation, that is, chemical analysis will not give sufficient information on which to base the probable yields of distillation products. There is, however, an apparent connection between some of the values determined by analysis and the yields of methyl alcohol and acetic acid. It would naturally be expected that the methoxyl groups would be the only source of methyl alcohol and that the yield of this product by destructive distillation would, therefore, bear a relation to the amount of methoxyl in the wood. To a limited extent this is true, but unfortunately only a small and variable part of the methoxyl in the wood forms methyl alcohol on distillation. It lias been noted that the hardwoods have generally higher methoxyl values than the softwoods and it is also true that the yields of methyl alcohol are also higher from the hardwoods, but the ratio of methoxyl groups to methyl alcohol is not the same in the two classes of wood, being about 4 for certain hardwoods and about 7 for certain softwoods. There are not enough figures available to show whether these ratios hold for all species, but in the case of maple and birch, which differ in methoxyl content by about 1 per cent, there is a corresponding difference in methyl alcohol yields.

The acetic acid by hydrolysis is higher in hardwoods atjd the acetic acid by distillation is also higher, but here there is no sort of regularity in the ratios between these values. In. fact, it is unlikely that the acetic acid obtained from wood by these two methods comes from the same part of the ligno-cellulose, since cellulose yields little acetic acid by hydrolysis but considerable by distillation. Klason 10 has also shown that birch cellulose yields much more acetic acid on distillation than spruce cellulose.

•The Chemistry of Wood, IH. Jottr. Jnd. Bng1 Chtm. 9, 748' (1917).

Arbiv fSt Kimi, Min. &ch G*ol„ 1907» Z. angno Chemit as, 1205 (1909).

It is not known just what effect the various extractives may have on the yields of distillation products except in the case of very resinous woods, such as "lightwood" or stumpwood from longleaf pine where the resin is the source of the main valuable distillation products, lnis will be treated as a special case in another chapter.

It is also unknown what effect the other differences in composition between hardwoods and softwoods have on the products of distilla-

Fig. 9.—Charcoal going from First to Second Coolers.

tion. The much greater proportion of pentosans in the hardwoods must influence the distillation products in some way, but this effect has never been noticed.

When we have more comparative figures on chemical analyses and yields of distillation products not only from the same species but from the same pieces of wood it will probably be possible to find some closer connection between analyses and yields, but at present the data are too fragmentary. It may be possible sometime to determine the value of a wood for methyl alcohol production from the methoxyl content and even at present the greater value for methoxyl than for the methyl alcohol obtained by distillation is useful in showing the possibility of greater alcohol yields. ■

Yields from Various Species and Forms

As will be noted in a future section the yields of various products can be varied by the conditions of distillation and, therefore, most of the comparisons of species and forms to be given here will be from one series of tests made under as nearly as possible the same conditions. With the usual variations in the wood from the same species and with the difficulty of controlling the distillation conditions it is not to be expected that one or two test runs will give the average for the species, but only by careful selection of the wood and averaging the results from several runs can satisfactory figures be obtained. Most of the results given here are taken from the Forest Service work on this subject.11

The distillations were made in a horizontal, cylindrical retort 15" in diameter and 36" long, heated by an oil jacket. The average moisture content of the wood was determined from small blocks cut from selected portions of the charge just before going to the retort and the yields were computed on the dry weight of the wood. The acetic acid yields are die total volatile acid figures determined by distillation and titration of a portion of the pyroligneous acid. This introduces a slight error, since some formic acid is always present. The alcohol yields are determined from the specific gravity after several distillations with excess of sodium hydroxide; they, therefore, include acetone, methyl acetate and other low gravity products which may be present, but the methyl acetate would be mostly hydrolyzed by the treatment and acetone occurs only in small quantities when wood is distilled under these conditions.

Table 7 gives the yields of alcohol and acid from several forms and( species. It is seen that the species most commonly used for distillation, beech, birch and maple, are among the highest, while oak, which has only recently been used in large quantities, is lower in both acid and alcohol. Hickory, elm and ash are also high in alcohol yields.

The variation in yields between heartwood and sapwood or heart-wood and slabs (sapwood and bark) is variable both in amount and direction. The high acid yield of beech slabs is shown to be due to the sapwood, while the high alcohol yield of maple slfcbs is due to the bark. Much further work needs to be done to get'figures on heartwood, sapwood and bark for the different species.

Similar small scale experiments have recently been made on 46 species of wood from South India, Mysore and Baroda.12 None of these woods gives yields of both alcohol and acetate as high as the

"Dept. Agr. Bulls. 139 and 508. "Yields from the Destructive Distillation of Certain Hardwoods,"

"Watson una Sudborough, Jottr. Ind. Inst, Sci., Vol. a, Part VII, p. 79 <1918), and Vol. 3, Part IX, <1930).

0 0

Post a comment