July, 1923
I N D U S T R I A L A N D ENGINEERIS(: CHEMISTRY
sponding";th the percentage of uniaturated plus aromatic hydrocarbons (determined by 98 per cent sulfuric acid) in the neutral oils of this fraction. Since blank runs show the mercuric acetate to be without effect on aromatics such as xylene under the conditions of the experiment, this extrapolation may be taken as confirmatory evidence of the great preponderance of unsaturated over aromatic hydrocarbons in t h e low-boiling fractions of low-temperature tars. Two observations cast some doubt on the exactness of the mercuric acetate method. I n the first place, slight polymerization is indicated by the shape of the upper half of the curve and by the fact that the decrease in density is less than would be expected from so great a reduction in the iodine number. Furthermore, the mercuric acetate seems to remove from the oil small amounts of saturated components. This is indicated by low iodine numbers of the "unsaturated" hydrocarbons recovered b y acidifying the residual addition compound and steam-distilling. These two factors are opposite in effeci,, the first tending to shift the curve slightly to the left and the second to the right, and apparently they almost balance each other. RECOVERYO F UKSATURATED HYDROCA4RBONS LOW-TEMPERATURE TAR
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A convenient method for recovering the unsaturated (and aromatic) hydrocarbons comparatively free from naphthenes and paraffins is extraction with liquid sulfur dioxide. It has been pointed out above that the hydrocarbon Fraction 2OC'-173" C. of a low-temperature tar proved miscible with this solvent in all proportions a t -35" C., but further investigation reveals the fact that the separations accomplished are more specific in mixtures of higher average molecular weight. Kevertheless, some doubt must be cast on the purity of the hydrocarbons thus extracted from a sample of the entire series of compounds in a lorn-temperature tar, in view of the variation in the effect of the solvent throughout the wide range of compounds involved. I n particular, it is to be expected that the lower fractions will be found admixed with a portion of naphthene and paraffin hydrocarbons.
The Methoxyl in Wood Charcoal' By L. F. Hawley FOREST PRODUCTS LABORATORY, U. S . FOREST SERVICE,MADISON,WIS.
I n a former article2 it was concluded that wood charcoal contains a small proportion of methoxyl groups which respond to the Zeisel method of analysis, and probably a much larger proportion which form methane when the charcoal is heated from 450" to 900" C. It was also determined that about one-third of the methoxyl groups in the original wood were left in the charcoal after the ordinary destructive distillation process was finished. This note is a report of attempts t o recover this methoxyl in the form of methanol instead of methane. Following the line of attack used in previous work on increasing yields of methanol from various chemicals were added to the charcoal and the mixture was distilled a t high temperatures (maximum about 850" C.). Since the amount of liquid products obtained from charcoal in this 1 Presented before t h e Division of Cellulose Chemistry a t t h e 65th Meeting of t h e American Chemical Society, N e w Haven, Conn., April 2 t o 7, 1923 2 Hawley and Aiyar, THISJOURNAL, 1 4 (19229, 1055. 8 Hawley, I b i d . , 14, (1922), 43.
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In most low-temperature tars the proportion of aromatics is so small that the sulfur dioxide extract is composed almost entirely of the cyclic unsaturated hydrocarbons. These compounds may be further investigated, as indicated in an earlier paper.ls A study of the various designs of apparatus and methods of procedurelg in the use of liquid sulfur dioxide points to the scheme devised by Bowrey20 as the most effective and convenient. This method does away with freezing mixtures and accomplishes effective cooling and agitation simultaneously by boiling the mixture of oil and solvent in a vacuum bottle under greatly reduced pressure. Temperatures of -35" C. are readily obtained. After the layers have separated, the reaction mixture is siphoned into a separatory funnel connected with a water vacuum pump, and the sulfur dioxide allowed to evaporate off slowly. Working with a mixture of all the fractions of a low-temperature tar distillate, a good separation of layers was accomplished by this siphoning process alone. The top layer, consisting principally of a mixture of naphthenes and paraffins, proved too viscous a t -35" C. to pass through the small-bore siphon tube, and remained behind in the vacuum bottle. After studying the effectiveness of various separations made with oil and solvent in different proportions, a ratio of three parts by volume of the hydrocarbons to five parts of the sulfur dioxide was found most practicable. It has been pointed out21 that naphthenes of low molecular weight are increasingly soluble in excesses of liquid sulfur dioxide, but this solubility was not evident in the mixture examined. The density of the extract continued to increase with greater excesses of solvent, and a practical limit to the most effective ratio of solvent to oil was reached only because the elimination from the extract of a large excess of sulfur dioxide involved considerable loss by evaporation of the more volatile hydrocarbons. Morgan and Soule, Chem. Met E n g . , 26 (1922), 980 See Footnotes 28 and 29 in P a r t I. 2 0 Bowrey, J . Inst. Petroleum Tech., 3 (1917), 287; Chem. Tvade J , 60 (1917). 426. 2 1 Moore, Morrell, and Egloff, Met. Chem. Eng., 18 (1918), 396. 18
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manner is very small and the amount of gas very large, i t is necessary to scrub the gas in large quantities of water in order to recover so volatile a product as methanol. I n blank distillations without the addition of any chemical about 0.3 per cent of methanol on the weight of the charcoal used was recovered, less than one-third of this coming off below 730" C. This is the first time that methanol has been reported as a product of the distillation of charcoal a t temperatures above those used in the normal wood distillation process. Sodium carbonate, lime, phosphoric acid, calcium carbonate, sodium sulfate, magnesium carbonate, and potassium permanganate were used for treating the charcoal in attempts to increase this yield of methanol, Only in the case of lime and of calcium carbonate was there any increase in the amount of methanol and this increase was only slight, the total methanol yield being only 0.5 per cent. Charcoal was also distilled in slow currents of carbon dioxide, air, steam, and various mixtures of these, but only in the carbon dioxide was any appreciable increase in yield obtained. When the charcoal was heated in a slow current of carbon dioxide the yield of methanol was 0.5 per cent. The increase in yields obtained was so small and the apparent chances for further increases so poor that the work was discontinued a t this stage.
