INDUSTRIAL AND ENGINEERING CHEMISTRY
184
which oxidizes the Dolvsulfides and the thiosulfate with the liberation of free sulrur: 3-The products Of the between hydroxide in alcoholic solution and mercaptans dissolved in naphtha are sodium mercaptide and water. On keeping the pimipitate in contactwith naphtha some of the mercaptansare returned to the oil owing to partial hydrolysis of the sodium mercaptide.
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KO.2
Literature Cited (1) A. S. T.M.Tentative Standard, 1929, D90-29T, p. 409. 22, 245 (1930). (2) Borgstrom, Dietz, and Reid, IND. END.CHEM,, (3) Bovle, “SceDtical Chemist.” Oxford. 1680. (4) Davis and Hill, J. A m . Ckem. Soc., 49 3114 (1927). (5) Mellor, “Inorganic and Theoretical Chemistry,” Vol. 11, p. 630 (1922). (6) Mellor, I b i d . , p. 639. ),( Pomeranz, z. Farbe* Chem., 392 (1905). (8) Wilson, Canadian Patent 278,381 (March 6, 1928).
Effect of Mild Heat Treatments on the Chemical Composition of Wood’ L. F. Hawley and Jan Wiertelak2 FORESTPRODUCTS LABORATORY, MADISON,WIS.
HE many studies of the
T
decomposition of wood by heat have been concerned almost entirely with the exothe,rmic r e a c t i o n occurring at about 275” C. during which the main chemical copstituents of the wood are completely decomposed. It has been noted that much lower temperatures affect the color and strength of wood and that thefse p h y s i c a l changes were p r o b a b l y acc o m p a n i e d by chemic a1 changes, but at the time the analyses reported here were undertaken there were no q u a n t i t a t i v e data on the subject.*
Analyses are recorded of white ash and Sitka spruce wood before and after heat treatments in a closed iron tube at 138” C. for 2,4, and 8 days. In both woods the losses are largely in the carbohydrate constituents and there are also gains in the lignin and the alcoholbenzene soluble. In both woods the methoxyl content remains practically constant. In the ash wood the carbohydrates lost are entirely pentosans, but in the spruce wood they are largely hexosans and even the stable (not readily hydrolyzed) cellulose is decomposed. In the ash wood the acetic acid by hydrolysis is rapidly decreased to a minimum at the fourth day. The changes in composition are discussed in the light of the empirical analytical methods used in determining the changes in composition. The indications of a change from carbohydrates to a lignin-like substance are so important that a special investigation of the change has been started.
Experimental Procedure
Samples of white ash and Sitka spruce that had been subjected to different temperatures for various periods of time were available together with well-matched specimens of unheated wood for comparison. For the present work those samples were selected that had been heated to 138” C. for 2, 4, and 8 days. The details of the heat treatments can be found in the articles describing the effect of the treatment on various physical properties of the wood (4, 5 ) . The wood was heated in sealed iron tubes contained in a small steam retort, the temperature being regulated by the steam pressure. The wood was previously dried to about 10 per cent moisture content so that it was not in contact with a large amount of water during the heating period. The samples were analyzed according to the methods in use a t the Forest Products Laboratory. These methods as described by Bray (1) were modified only in that alcoholbenzene was used instead of ether for the extractions previous to the lignin determination. Additional determinations were made of the methoxyl content of the isolated lignin and of the hydrolysis number (3)of the isolated cellulose. The complete analytical results are shown in Table I, 1 Received November 4, 1930. Presented before the Division of Cellulose Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 t o 11, 1930. 2 Research Fellow from Poland. 8 Campbell and Booth have recently published an article bearing upon this subject (2).
together with the losses in weight observed during the heat treatments. General Changes Common to Hardwood and Softwood
The solubility of the wood in cold water, alcohol-benzene, and 1 per cent caustic soda after different periods of h e a t i n g v a r i e d in the same manner. The solubilities were increased at first and later decreased, in some instances becoming a little less than those of the original wood. I n both the hardwood and the softwood the general effects of the h e a t i n g are a decrease in the carbohydrate components and an increase in lignin. The increase in lignin may be only a p parent, since the Forest Products Laboratory method for determining lignin is based on its insolubility in 72 per cent H&Oc and in other characteristics the “lignin” formed by heating may be different from the lignin present in the unheated wood. The isolated lignins from the heated and unheated samples were analyzed for methoxyl content as shown in Table I. There was always a lower percentage of methoxyl in the isolated lignin from the heated samples than from the corresponding unheated samples, indicating that, in this characteristic a t least, there is a difference. In another (qualitative) characteristic, however, the isolated lignins were similar. It was found that they could all be put into solution by the treatment used in the analytical method for isolating cellulose-namely, chlorination followed by treatment with sulfites. Although it is not maintained that by this heat treatment carbohydrates have been transformed into lignin, yet certain carbohydrates have lost some of their carbohydrate characteristics and have been transformed into a material that possesses some of the characteristics of lignin. These indications of the transformation of carbohydrate to lignin by long-continued low-temperature heating are, however, so important in the field of the relationships between the carbohydrates and lignin in wood that further experiments are now under way in the similar heat treatments of pure wood carbohydrates. The variations in the figures for methoxyl in Table I are
INDUSTRIAL AAVDENGINEERING CHEMISTRY
February, 1931
within the limit of error of the determination or a t least within the limit of variation of matched samples, so that it can be safely concluded that the methoxyl remained constant throughout the heating periods. C o m p o s i t i o n of Wood H e a t e d a t 1 3 5 O C. for 2, 4, a n d 8 Days (All figures in percentages of dry unheated wood unless otherwise noted)
T a b l e I-Chemical
- WHITEASH
CONSTITUEXT Not heated
%
Loss in weight on heating (3) Ash Cold-water soluble Hot-water solublea Solubleb in 1 per cent PiaOH Ether soluble Alcohol - benzene soluble Acetic acid by hydrolysis Lignin Cross and Bevan cellulose Total pentosans Pentosans in cellulose Pentosans not in cellulose Total methoxyl Methoxyl in lignin Methoxyl in lignin (on basis lignin) Readily hydrolyzed cellulosec Stable cellulosec
...
0.41 3.6 1,2
SITKA SPRCCE
Days heated
2
% 5.0 0.64 6.9 1.4
4
8
Not .eated
%
%
Days heated 2
4
8
“0
%
%
%
5.8 7.7 1.31 0.9: 5.7 4.6 1.1 0 . 9
0 2:
1.6 0.14 6.9
1.3 0.47 5.4 1.0
5.6 0.25 2.9 1.4
18.2 0.9
10 2 0 9
11.2 0.5
11.8 0.7
3 1 3 1
1.0
14.3 0.9
19.4 0.6
20.1 0.4
3 9
10.9
10 1
8.5
3 7
7.4
6.3
3.8
3.6
27.0
2.2 27.0
0.5 31.0
0.5 32.6
0 6 28 5
0 4 33.6
0.5
37.3
0.8 38.4
55.9 22.6
51.1 10.8
48.0 5.4
48.0 4.5
56 8 7 0
51.0 4.7
50.4 4.2
48.1 3.6
11.0 1.7
11.0
6.2
3.1
3.1
2 4
2.3
2.0
1.5
11.6 6.9 5.2
4.7 6.9 4.1
2.2 7.1 4.5
1.5 7.0 4.1
4 7 5 3 4 0
2.5 5.3 4 2
2 1 5 1 4 5
2 0 5.4 4.3
19.4
15.2
14.6
12.5
14 0
12 7
12 2
11.2
12.8 43.1
7.9 43.2
4.9 43.1
4.6 43.4
9 6 47 2
7.0 44.0
7.2 43.2
6.4 41.7
-
a After subtracting cold-water soluble. b After subtracting hot- and cold-water soluble. C Calculated from hydrolysis number determination made on the Cross and Bevan cellulose.
Changes in Certain Constituents
For a more detailed study of the changes in certain components and for a ready comparison of the hardwood and softwood, Table I1 has been prepared. I n this table certain data from Table I have been calculated in terms of decreases or increases a t the different stages of heating.
185
soluble) together with some volatile decomposition products corresponding to the loss in weight, it is impossible to tell which products are formed from each of the constituents decomposed. Since, however, the constituents decomposed are all pentosans, although of two different types, it can be stated that the pentosans decompose to form volatile products, alcohol-benzene soluble-products, and a substance that has some of the characteristics of lignin. The alcoholbenzene soluble material is apparently an intermediate product between the pentosans and one or both of the final products because it increases rapidly during the first period of heating and then decreases. Although there is no apparent increase in lignin during the first 2 days’ heating a closer examination of Table I shows that there must have been some formation of a ligninlike product because there had been a decrease in a lignin constituent and yet the total lignin was the same. I n the figures showing the percentage of methoxyl (on the basis of the original wood) in the isolated lignin (Table I) it is seen that 5.2 per cent methoxyl was in the lignin isolated from the original wood, but only 4.1 per cent in the lignin from the wood heated for 2 days. Therefore the lignin determination should have shown 1.1 per cent less lignin on the 2-day sample. Since the lignin remained constant there must have been 1.1 per cent of lignin-like material formed to take the place of the 1.1 per cent less methoxyl in the lignin. The figures in Table I1 showing the increases in lignin as calculated from the lignin determination should therefore be corrected for the differences in methoxyl content from those of the original woods. This has been done in line 3. ~
in C e r t a i n C o n s t i t u e n t s on H e a t i n g Wood for 2, 4, and 8 Days (All figures in percentage of dry unheated wood: increase, decrease)
T a b l e 11-Changes
+
1 CONSTITUENT
WHITEASH
I
Days heated 2
1 1
-
SITKASPRUCE Days heated
4
% % % % % % With the hardwood the decreases in Cross and Bevan celluLignin +O $4.0 $5.6 f5.1 4-8.6 +9,9 lose correspond almost exactly with the decreases in pentosan Lignin (cor.) +1.1 +4.7 +6.7 $4.9 4-8.3 +9.S soluble +7.0 + 6 . 2 +4.6 +3.7 4-2.6 + 0 . 1 in cellulose and with the decreases in unstable cellulose, which Alcohol-benzene Cross and Bevan cellulose - 4 . 8 -7.9 -7.9 -5.8 -6.4 -8.7 Pentosans not in cellulose -6.9 -9.4 -10.1 -2.2 -2.6 -2.7 indicates that the unstable cellulose is composed entirely of -4.8 Pentosans in cellulose -7.9 -7.9 -0.1 -0.4 -0.9 pentosans in cellulose. The stable cellulose, as calculated Readily hydrolyzed cellu -4.9 -S.2 2.6 -2.4 -7.9 lose -3.2 from the hydrolysis number determination, remains practi- Stable cellulose +0.1 0 f0.3 -3.2 -4.0 -5.5 cally constant. I n the softwood the amount of decomposi- Loss in weight: Ca1cd.a 3.6 6.4 6 7 0.6 1.9 1.7 tion of Cross and Bevan cellulose is about the same, but the am) (gain) (loss) 5.0 5.8 7.7 (g1’.6 1.3 5.6 Obsd. decomposed cellulosic material is made up of different conObsd. minus calcd. +1.4 -0.6 +1.0 $2.2 4-3.2 $ 3 . 9 stituents. There is not only much less pentosan in cellulose a From sum of losses in cellulose and pentosans not in cellulose and in the softwood than in the hardwood (2.4 and 11 per cent, sum of gains in alcohol-benzene soluble and lignin (corrected). respectively) but even the small amount present is relatively While the decomposed products in ash wood are entirely more resistant to the effects of heat. After 8 days’ heating the 2.4 per cent in the softwood has been reduced only to 1.5 pentosans, in spruce wood they consist largely of hexosans, per cent, a 37 per cent decrease, while the 11.0 per cent in so that differences in the products of decomposition may be the hardwood has been reduced to 3.1 per cent, a 72 per cent reasonably attributed to the presence of hexosan decomposidecrease. The decomposition of the softwood Cross and tion products. The main differences between the decomposiBevan cellulose is seen to occur almost entirely in the hexosan tion products of spruce and ash are the greater increases constituents, and even more in the stable cellulose than in in lignin and the lesser increases in alcohol-benzene soluble the unstable cellulose. in the case of spruce. There is also considerably less loss of The pentosans not in cellulose decrease rapidly and con- weight (formation of volatile products) with spruce. It might tinuously in both woods, but the proportion of them removed be concluded, therefore, that the hexosans, in comparison is greater a t all stages in the hardwood. At the end of 8 with the pentosans under the same conditions of heat treatdays’ heating 88 per cent of the pentosans not in cellulose in ment, are transformed less into volatile products and more ash had been decomposed, but only 42 per cent of those in into lignin-like substances and that alcohol-benzene-soluble spruce. substances are not so important intermediates in these transSince there are two main constituents of the ash wood formations. that are decomposed (the pentosans in cellulose and the If the sum of the gains in the various exclusive constituents pentosans not in cellulose) and two main constituents that is subtracted from the sum of the losses, the calculated losses are increased in amount (the lignin and the alcohol-benzene may be obtained for comparison with the observed losses.
I
1
I
II
186
IND USTRIAL AND ENGINEERIXG CHEMISTRY
This has been done with the figures in Table I1 adding the losses in the Cross and Bevan cellulose and in the pentosans not in cellulose and adding the gains in lignin (corrected for methoxyl) and in alcohol-benzene soluble. With the ash wood the differences between the observed and calculated losses are not consistently of the same sign, but they are perhaps within the limit of error of the sums of determinations involved. With the spruce wood, however, the observed loss is always greater than the calculated and this difference is consistently greater with longer time of heating. It is probable, therefore, that certain substances in the heattreated spruce were isolated and weighed in more than one determination. For instance, it is readily conceivable that a partly degraded cellulose might resist the action of the chemicals used in isolating both the lignin and the cellulose. The changes in “acetic acid by hydrolysis” in the ash wood are of interest in connection with the obscure origin of this product. If the “acetic acid by hydrolysis” comes from acetyl groups that are not isolated with the cellulose or lignin, then the losses in this constituent due to heating should be included in the calculated losses of Table 11. When such losses are included, the calculated losses become 5.0, 9.5, and 9.8 per cent instead of 3.6, 6.4, and 6.7 per cent, and are further from the observed losses of 5.0, 5.8, and 7.7 per cent, respectively, for the three periods of heating. Furthermore, the differences between the observed and calculated losses are of opposite sign from those of the softwood. (The changes in “acetic acid by hydrolysis” in the softwood are negligible.) It seems likely, therefore, that the acetic acid by hydrolysis is formed from some other constituent determined by the analytical methods used and decreases along with that constituent. Since in the ash wood the pentosans are the only constituents that decrease, the indications are
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that acetic acid by hydrolysis has its origin in the pentosans, There is shown in Table I a certain amount of parallelism between the figures for pentosans in cellulose and those for acetic acid by hydrolysis. I n the ash wood they both decrease during the first two periods and then remain constant during the third period. In the spruce the changes in both of these constituents are very slight. The experiments recently reported by Campbell and Booth (2) on the analysis of green, air-dried, kiln-dried, and ovendried oak were primarily for the purpose of showing the differences between the green and the dried wood, but there were also differences between the air-dried and the artificially dried samples that might be ascribed to the higher temperatures accompanying the latter treatments. The heat effects on lignin and pentosans were naturally much less than those reported here on account of the lower temperatures used by them, but in these constituents there are no inconsistencies between the higher and lower temperature treatments. I n the case of the methoxyl, however, the results are apparently inconsistent. Even at the low temperatures used they obtained a marked reduction of methoxyl, whereas in the present higher temperature treatments the methosyl remained practically constant. This can perhaps be explained by the different conditions under which the heating took place. Campbell and Booth heated their wood in the open air, whereas the mood used in the present analyses was heated in a sealed tube. Literature Cited ( 1 ) Bray, Paper Trade J . , 81, No. 2 5 , 59 (1928). (2) Campbell and Booth, Biochem. J . , 24, 641 (1930). (3) Hawley and Fleck, IND. ENG. CHEM.,19, 850 (1927). (4) Koehler and Pillow, Southern Lumberman, Dec. 19, 1923. ( 5 ) Pillow, W o o d W o r k i n g I d . , Oct., 1929.
Study of W a x from Low-Temperature Tar’ Joseph D. Davis2 and Kenneth > I . Irey3 PITTSBVRGH EXPBRIMENT STATIOK, U. S. B U R E AOF~ MIXES,PITTSBURGH, PA.
URING the years 1924 I t has been shown t h a t the wax from Utah coal is a tar 11, and 30.80 per cent and 1925, a primary paraffin hydrocarbon wax containing a small percentage tar 111. Table I gives the or 1on:temperature of unsaturates. This wax is of a superior grade as cornd i s t r i b u t i o n of chemical tar was produced in quantity pared with commercial petroleum wax, as it has a higher groups in tars I, 11, and 111, by continuous carbonization melting point, and is a relatively dry wax. and Table I1 shows the disof Mesa Verda (Utah) coal tribution of oils, waxes, and The bituminous coals are found to Yield a tar of low at 700” C. in superheated wax content as compared with t h a t of the Utah coal resins in the neutral oils from steam. The composi$ion and the sub-bituminous coals. Carbonization with these tars, It was noted that of this tar (1, 2, 3) and of superheated steam tends to increase the yield of wax the wax content of all these the gas (6) and light oil as in a tar, but it is not required to obtain an appreciable tar portions was higher than \yell have been s u b j e c t s amount of wax from a coal high in wax-producing conthat reported in the literafor p r e v i o u s investigation. stituentsture; it is seen, for example, This tar c o n s i s t e d of an in Table I1 that the amount oily portion, liquid a t ordinary temperatures, and two solid of wax in the combined portions exceeds 10 per cent of the portions, one lighter and one .heavier than water. These total tar. On considering this and the fact that the wax was have been termed tars I, 11, and 111, respectively, by the of high melting point (54” C.), further investigation seemed previous investigators. worth while for possible industrial utilization of this conThe tar consisted of 28.85 per cent tar I, 40.35 per cent stituent of low-temperature tar. Accordingly, the work described mas undertaken. Received November 24, 1930. Presented before the Division of Gas Enough T ~ a x recovered from tar 11 for purification, and Fuel Chemistry a t the 80th Meeting of the American Chemical Society, determination Of physical and approximate ‘OnCincinnati, Ohio, September 8 to 12, 1930. This paper presents the results StitutiOn Of the purified wax. It was found to consist mainly of work done under a cooperative agreement between the u. S. Bureau of Mines, t h e Carnegie Institute of Technology, and the Mining Advisory of pentacosane (melting point 54” C.) and heptacosane Board. Published by permission of the director, U. S. Bureau of Mines. (melting point 600 c,), j$raxes mere then recovered from (Not subject t o copyright.) tars of several bituminous and sub-bituminous coals, listed in Fuels chemist, U. S. Bureau of Mines. Table V, which were carbonized a t low temperatures in a Research Fellow, Carnegie Institute of Technology.
D
