Nov., 1922
T H E JOURNAL O F INDUSTRIAL A N D ENGINEERING CHEMISTRY
1035
Distribution of Methoxyl in t h e Products of Wood Di stillati on1r2r3 By L. F. Hawley4 and S . S. Aiyar FOREST PRODUCTS LABORATORY, DEPARTMENT OF AGRICULTURE, MADISON,WISCONSIN
show11 that the methanol
obtained by distillation can be increased by treating the wood with certain chemicals before distillation.6 In order to find the location of the excess methoxyl not used in forming inethanol and to determine the source of the increase in methanol when the wood is treated with chemicals before distillation, this work was undertaken. The general plan was to determine methoxyl in a sample of wood and then distil the wood, either with or without previous chemical treatment,, and determine methoxyl in the various crude products, settled tar, dissolved tar, tar-free pyroligneous acid, charcoal, and gas. It was assumed that the methane in the gas represented an equivalent amount of inethoxyl in the original wood. This assumption seems t'o be safe in view of t.he rough relationship between the amount of methoxyl in a cellulosic material and the amount of methane in the gas obt'ained on distillation.
DETERMINATION OF METHANE Several publications have given information on the amount of methane formed by the destructive distillation of wood and cellulose. Klason, von Heidenstam, and Norlin' showed that wood gave considerable amounts of methane, while cellulose from cotton, fir, and pine gave only about 0.27 per cont methane. Bantling distilled cellulose of unknown origin and obtained 0.68 per cent methane. Sarasing reported only traces of methane from cotton cellulose. These agree fairly well, but Erdmann and Schaefer'O reported 19 per cent methane in the gas from the distillat.ion of cellulose. The percentage of gas on the cellulose distilled was , not given, but even with a conservative estimate of 12 per cent gas the methane would be 2 . 3 per cent, which is very much higher than that found by others. In order t'o settle this point and to determine the amount of methane formed from celluloses of known methoxyl content, the di&illations shown in Table I were macle. It is seen that the methane is slightly greater in amount, than can be account,ed for by the methoxyl in the original 1 Presented before the Section of Cellulose Chemistry a t t h e 63rd Meeting of t h e American Chemical Society, Birmingham, Ala., April 3 t o 7, 1922. 2 Published by permission of t h e Department of Agriculture. 8 This communication is a n abstract of a thesis submitted by t h e junior author in partial fulfilment of t h e requirements for the degree of Doctor of Philosophy a t the University of Wisconsin. 4 In charge, Section of Derived Products, Forest Products Laboratory, .Madison, Wisconsin. 6 Schorger, THISJOURNAL, 9 (1917), 556. Palmer, I b i d . , 10 (1918),264; ISawley, Ibid., 14 (1922), 43. ArkivKemi. Mineral. Geol., 8(1908),1;Z.angew. Chem.,22(1909),1205. 8 .J. Gasbel., 67 (1914), 82, 55. 8 .4rch. sci. phys. nat., 141 46 (1921), 5. 10 . B e y . , 43 (1910), 2398.
ently incorrect. There is, then, a rough relation between the amount of methoxyl in a cellulosic material and the amount of methane obtained by destructive distillation, so that at least a large part of the methane must come from methoxyl. TARLE I-METHANE FORMED BY DISTILLATION OF CELLULOSES WITH K N O W N AMOUNTS OF METHOXYL
Methoxyl KIND OF CE&I.UI.OSE Content 0.225 Birch soda pulp.. , . . . . . Absorbent cotton.. . , , . . . , 0.277 Spruce sulfite pulp (bleached) 0.342
... ..
.
Methane Per cent on Original Cellulose 0.20
0.26 0.17
Equivalent of Methane in Terms of Methoxyl 0.40 0.52 0.34
The wood in the form of sawdust was distilled in a glass flask, and after condensation of the vapors the gases were passed through a wash bottle containing potassium hydroxide to remove most of the carbon dioxide, and then collected in a gasometer. Since only the methane and not the total gas was required, the removal of the carbon dioxide before measurement of the gas volume was permissible, and in this way the amount of gas to be collected and measured was considerably reduced.
METHOXYL DETERMINATIONS The methoxyl determinations were made by the Zeisel method, which has been used for all the analyses of wood and wood products made at the Forest Products Laboratory. According to Klason'l this method may give too high results when used with wood, on account of the formation of ethyl iodide from the -CH&H2OH group in lignin, but this error amounts to very little and does not affect the conclusions to be drawn from this work. It is also possible that some methoxyl is formed from methyl groups like those in the methyl pentosans. In the gas analysis care was taken to remove all carbon monoxide before determining the methane by the explosion method. Two cuprous chloride pipets were used, the second of which always contained a fresh solution, which had been used only for removing the last traces of carbon monoxide not absorbed by the first pipet. Table I1 gives the results of such distillations and analyses on three different species, both without treatment and after trcatment with different amounts of sodium carbonate or phosphoric acid. All the results rue the averages of a t least two distillations. The blank runs show the nornial distribution of methoxyl groups in the products of distillation. In the case of maple the largest, amount of methoxyl in any one product is found in the pyroligneous acid, and this represents very closely the methanol formed. The next 1%"Papperstidning,"
19a0, p. 319,
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 14, No. 11
TABLE 11-DISTRIBUTIONOF METHOXYL IN PRODUCTS OB WOODDISTILLATION (All figures in percentages of dry weight of wood distilled)
---
PRODUCTS Pyroligneoug acid (tar free) Dissolved tar Settled tar , Charcoal ......... . ,., Gas (calc. from C H I ) . . Total methoxyl recovered..
....... . .. .. . ..,..... .. . .. . ....
.. . .
Hard maple(6.09per cent -0CHs) NazCOs Blank 0.5% 1% 1.62 1.73 1.92 0.34 0.23 0.21 0.52 0.60 0.59 0.28 0.06 0.04 1.31 1.23 1.47 4.07 3.85 4.23
- ---
1.5% 1.91 0.22 0.59 0.04 1.34 4.10
largest amount of methoxyl is represented by the methane in t h e gas, and the other three products contain only small amounts of methoxyl. The total methoxyl found in the products is only about two-thirds that in the original wood and it seemed a t first impossible to account for the other one-third. The slight error in the methoxyl determination in the original wood1' might be the cause of an apparent loss of this kind, but such an error would amount to only a few tenths of a per cent. After the experimental work was all finished, a probable explanation of this apparent loss was discovered. I n "Om Tralrolning," by Bergstrom and Wesslh (Stockholm, 19181, is shown the composition of the gas given off when commercial charcoal is heated to temperatures above those a t which it was originally produced from the wood. Large quantities of gas are given off from 450" to 900" C., and a large proportion of this gas is methane. Comparative figures are not available to show whether this methane is produced in just the right amount to account for the difference between the methoxyl in the original wood and in the distillation products aR shown in Table I, but it is as near as could be expected with different species of wood and different methods of distillation, being about 2 . 1 per cent of the weight of the wood from which the charcoal was produced. If this methane is formed from methoxyl groups in the charcoal, some explanation is required of the small amount of methoxyl found in the charcoal by analysis. It may be that the charcoal is so complex and most of the methoxyl so condensed that only a small part of the possible methyl iodide is formed by the action of hydriodic acid. This is the assumption made in the further discussions, and when "methoxyl in the charcoal" is mentioned only the methoxyl determined by the method of analysis is included. MArm-When the maple sawdust was treated with sodium carbonate solution before distillation, the total methoxyl recovered was not greatly changed but the distribution was different. The pyroligneous acid contained more methoxyl (increase in methanol), and this increase is about equal to the decrease of methoxyl in the charcoal and the dissolved tar. WHITE OAK-In the case of white oak, the methoxyl in the pyroligneous acid is low corresponding with the low yield of methanol from this species, and more methoxyl is accounted for in the gas than in the pyroligneous acid. When the white oak is treated with sodium carbonate solution before distillation, the methanol is increased, but this increase is not quite equaled by the decrease in the dissolved tar and charcoal. There is with this species, however, a marked decrease in the methane in the gas due to the addition of the sodium carbonate] and this decrease is sufficient to furnish the additional methoxyl required for the methanol increase. A similar increase is found in the methanol when phosphoric acid is added to the wood before distillation. I n this case, however, the decrease in the charcoal is not so great, but the decrease is much greater in all the other products, the total recovered methoxyl being only two-
Blank 1.16 0.22 0.46 0.70 1.34 3.88
-White oak-----(5.12per cent -0CHa) NazCOa &PO4 0.5% 1% 1% 1.5% 1.61 1.84 1.67 1.76 0.21 0.16 0.11 0.08 0.66 0.60 0.12 0.13 0.52 0.13 0.57 0.76 0.90 0.78 0.40 0.40 3.80 3.51 2.87 3.13
3% 1.82 0.06 0.02 0.49 0.21 2.60
Tncensecedar ( 5 . 9 per cent -0CHa) NanCOa Blank 1% 0.97 1.45 0.10 0.07 1.04 0.84 0.46 0.12 1.60 1.17 4.16 3 70
thirds as much with 3 per cent phosphoric acid as with t h e untreated wood. The decrease of methoxyl in the settled tar is due more to a decrease in the amount of the tar1* than to a change in the composition of the tar. INCENSE CEDAR-A softwood was included in this study, since softwoods give a lower proportion of their methoxyl in the form of methanol on distillation, and the distribution of methoxyl must, therefore, be different. Incense cedar was chosen as it contains an unusually large amount of methoxyl for a softwood. With this species not only t h e gas but also the tar contains more methoxyl than the pyroligneous acid, in contrast to the hard maple which gives more methoxyl in the pyroligneous acid than in any other product. When distilled after treatment with 1 per cent sodium carbonate] the effect is very much the same as in t h e case of oak-the methoxyl is increased in the pyroligneous acid, not much changed in the dissolved tar, and decreased in the charcoal and gas. The decrease in the charcoal and gas is more than enough to account for the increase in t h e pyroligneous acid. TABLE 111-TOTAL VOLATILE ACIDS (All figures in per cent of dry weight of wood distilled) Sodium Carbonate Phosphoric Acid SPECIES Blank 0.5% 1% 1.5% 1% 1.5% 3% Maple 4.94 4.32 4.04 4.10 Whiteoak 3.88 3.93 3.81 3124 3:i5 2:i7 Incense cedar.. 2.17 1.87
......... ...... .
..
.. ..
..
..
..
The yields of total acids obtained during these distillations are given in Table 111. These acid yields, as well as the methoxyl yields in the pyroligneous acid, do not agree very well with the acid and alcohol yields, respectively, reported b y Palmer and by Hawley,6 but the conditions of distillation were different and there may have been differences in t h e samples of wood used even when the species were the same. It must also be remembered that the figures for methoxyI in the pyroligneous acid may not be the exact equivalent of the methanol as determined by specific gravity. The increase in alcohol yields due to phosphoric acid, as reported by Palmer, has been confirmed, although on another species of wood, but a decrease in acid was found contrary to Palmer's results. The increases in alcohol due to treatment with sodium carbonate are not so great as those reported previouslyI6but the acid yields for oak wood were not decreased by this treatment.
CONCLUSION The methane in wood gas is formed largely from the methoxyl groups in the original wood. Wood charcoal contains a small proportion of methoxygroups 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. Softwoods give more methoxyl in the settled tar and more methane in the gas than hardwoods, and these increases make u p for the less methoxyl in the pyroligneous acid (small yield of methanol). 12
Palmer, THIS JOURNAL, 10 (1918),264.
