THE COOKING PROCESS Butanol Cooking of Hardwoods and Softwoods’ Six hardwoods and six softwoods were cooked with aqueous butanol. Analyses of original woods and residual pulps were made for Cross and Bevan cellulose, alpha-cellulose, pentosans, lignin, and ash. The hardwoods were all pulped satisfactorily, but the softwoods were only partially pulped. The softwoods have a much greater proportion of lignin resistant to butanol delignification than do the hardwoods. Birch and basswood are more efficiently delignified and balsam is less efficiently delignified than other woods in their respective classes. Aspen cellulose is recovered in higher yields than is the case with other hardwoods. The pulping action is so similar on all the hardwoods that they might well be cooked together in varying mixtures. A11 of the hardwoods yield pulps which, in so far as the analyses are concerned, would be satisfactory commercial pulp. None of the softwoods yielded pulps with analyses which would be satisfactory commercially. Whether or not these observations indicate constant chemical differences in the woods of these great botanical classes is a problem which merits further exploration.
JOHN M. McMILLEN, ROSS AIKEN GORTNER, HENRY SCHMITZ, AND A. J. BAILEY Minnesota Agricultural Experiment Station, St. Paul, Minn.
present series of experiments was undertaken to compare the effects of butanol cooking on six softwoods and six hardwoods.
Experimental Procedure
I
N A STUDY of cooking wood with alcohols and other
organic reagents Aronovsky and Gortner (3) and Aronovsky ( 1 ) found that aspen can be successfully pulped with aqueous n-butanol. The liquor from the cook separated into two layers, the upper alcoholic layer containing the lignin and the aqueous layer the sugars and acids. Other preliminary work in this laboratory indicated that jack pine, spruce, and balsam fir could not be satisfactorily delignified with butanol cooking. This difference in the response of hardwoods and softwoods to n-butanol suggested that there might be a fundamental difference in the lignin-cellulose complex in these two groups of woods. (The term “hardwoods” is used in this paper to designate woods of the Angiospermae, the term “8oftwoods” to designate woods of the Gymnospermae.) I n view of these results and other known differences between hardwoods and softwoods, and in view of known differences between aspen and other hardwoods (7, l a ) , the 1 This is the eleventh in the series on “The Cooking Process.” Previoua papers appeared in INDUBTRIAL AND ENGINEERING CHEWIBTRY in 1930, 1933, 1934, 1935, 1936, and 1937.
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The hardwoods cooked were aspen (Populus tremuloides Michaux),silver maple ( h e r saccharinum Linneaus), basswood (Tilia glabra Ventenat), white oak (Quercus alba Linneaus), red oak (Q. borealis Michaux f.), and paper birch (Betula papyrifera Marshall) ; the softwoods were jack pine (Pinus banksiana Lambert), red pine (P. resinosa Solander), tamarack [Larix laricina (Du Roi) Koch], white spruce [Picea glauca (Moench) Voss], black spruce [P. mariana (Miller) Britton, Sterns, and Poggenberg], and balsam fir [Abies balsamea (Linneaus) Miller]. With the exception of the aspen, which was previously described (@),all wood was gathered in the green condition and was a natural mixture of the heartwood and sapwood occurring in bolts of pulpwood size or slightly larger. The wood was reduced to sawdust, air-dried to a moisture content of between 6.10 and 9.40 per cent, based on the air-dry weight of the wood, and ground in a Wiley mill. Practically all the wood so prepared passed through a 20-mesh screen, and 50 to 80 per cent was retained by a 60-mesh screen. The remainder passed the 100-mesh screen. The cooking liquor was a mixture of equal volumes of distilled water and technical grade n-butanol or of equal volumes of the alcohol and water which were recovered by the distillation of the liquors from previous cooks. The use of recovered liquors made no difference in the observed pressure-temperature relation, nor in the cooking behavior. All cooks were made in a 2-liter autoclave with a hammered copper kettle bottom and a phosphor bronze head equipped with a thermometer well and a combination pressure gage and constant-temperature regulator. Cooks 8 to 15, inclusive, were made after the autoclave had been reconditioned by metallizing the interior of the kettle with Monel metal. The cooking procedure was as follows: One hundred grams of air-dry sawdust were placed in the autoclave, and 800 cc. water and 800 cc. butanol were added. The mixture was stirred and the autoclave closed. Heating was started with two burners. In half an hour the temperature reached about 158” C . and the gage pressure about 151 pounds per square inch. The pressure was held for 6 hours by means of the automatically regulated burner. At the end of the cook the autoclave was allowed to cool t o 60” without the release of gases. Cooling required about 1 hour, the warm contents were then poured on a Biichner funnel, and the liquor was drawn off by suction. The residual wood was washed successively with buta-
INDUSTRIAL AND EKGINEERING CHEMISTRY
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nol, dilute alkali, water, dilute acid, water, water containing 10 drops of concentrated ammonium hydroxide per liter, and finally TABLE11. ANALYSES OF RESIDUAL PULPAFTER COOKINQ with cold water. Subsequent benzene-alcohol extraction showed Components b that this washing removed all dissolved material that might have -Cellulose-been redeposited upon the fibers. The residual woods were Cross dried, weighed, and ground in a Wiley mill until practically all Cook and PentoNo. Wood Yielda Lignin Bevan Alpha Bans Ash passed a 60-mesh screen. The analyses of the original woods were made upon the ground 15 Paperbirch 45.3 3.4 96.1 79.0 8.6 0.12 7 Basswood 43.6C 4 . 4 9 4 . 5 7 7 . 3 5 . 5 0 .20 wood used in the cooking, except that the cellulose determina14 Aspen 54.2 4.8 94.2 78.3 5.2 0.11 8 Red oak 45.4 4.7 94.6 78.1 6.4 0.38 tions were made upon the 60- t o SO-mesh fractions. The analyses of the residual woods were made upon the 60- to SO-mesh fractions, 3 Whiteoak 43.1 4.9 94.1 75.1 7.0 1.28 5 Silvermaple 46.3 4.9 93.8 76.1 6.0 0.18 except that the white oak pentosan determinations were made upon 9 Red pine 58.3 17.2 81.6 67.0 2.9 0.20 13 Jack pine 59.5 17.5 80.3 67.1 3.3 0.10 the 80- to 100-mesh fractions. The following determinations were made: 11 Blackspruce 58.4 17.5 81.3 65.6 3.9 0.18 4 Whitespruce 6 0 . 0 1 9 . 8 7 8 . 3 6 3 . 0 3 . 4 0 .12 MOISTURE.Four-gram samples were dried in an oven at 10 Tamarack 57.2 21.6 75.6. 61.2 2.2 0.14 105’ C. for 3.5 to 4 hours. 12 Balsam fir 68.4 22.9 73.7 56.0 3.1 0.07 ASH. Two-four gram samples in porcelain crucibles were a Percentage based on oven-dry weight of original wood. ignited in an electric muffle furnace at 550” C. b Percentage based on oven-dry weight of residual wood. CROSSAND BEVANCELLULOSE.The Sieber and Walter proThe actual yield was somewhat greater than this since a small amount cedure (11) with Jena crucibles was used for the original woods. was accidentally lost. The Forest Products Laboratory method described by Bray (6) was used for the residual woods. ALPHA-CELLULOSE. The method of Gortner and TABLE 111. ORIGINAL COMPONENTS REMAINING I N RESIDUlL P U L P McNair (6) was used. Cross and Bevan AlphaPENTOSANS. The method of Bailey (4) was used Cellulose Cellulose Lignin Pentosans except that for the original hardwoods the furfural ,--Basis Basis Basis Basis in the dist’illate was estimated by the Powell and Basis original Basis original Basis orlglnal Basis original Whittaker method (8). Cook original C. & B. original C. & B. original ligoriginal pentoLIGNIN. The method of Ritter, Seborg, and NO. Wood wood cellulose wood cellulose wood nin wood sans Mitchell (IO)was used, except that the modification % % % % % % % % of Ritter and Barbour. (9)Was used for the original 15 paperbirch 4 3 . 5 69.2 8.4 3.g 19.0 35.8 87.0 1.6 oak woods. 3 Whiteoak 40.6 72.3 32.4 80.6 2.1 9.6 3.0 19.2 76.1 35.2 87.7 2.3 10.3 2.8 16.4 EXTRACTIVES. The residues, after all the extrac5 Silver maple 4 3 . 4 76.3 43.0 8 Redoak 35.5 90.0 2.1 11.2 2.9 17.3 tions demanded by the above lignin procedures, were 7 Basswood 41.2 67.5 33.7 80.5 1.9 11.5 2.4 16.3 oven-dried, and the extractives were obtained by 14 Aspen 51.1 42.4 92.9 81.3 13.3 2.8 18.0 2.6 11 Blackspruce 4 7 . 5 76.6 85.5 10.2 38.3 37.8 2.3 30.2 difference. 9 Red pine 47.6 76.3 39.1 84.8 10.0 39.9 1.7 52.8 86.2 10.4 76.9 39.9 40.1 2.0 27.8 47.8 The yields and analytical data are given in 13 Jack plne 89.2 11.9 4 Whitespruce 4 7 . 0 81.6 42.2 2.0 29.5 37.6 88.7 12.3 43.2 79.3 35.0 49.0 1.2 21.9 Tables I and 11. The analytical figures are the 10 Tamarack 50.4 Balsam fir 82.2 38.3 85.9 15.7 55.2 2.1 41.9 mean of two or mbre closelyagreeingdetermina12 tions. Table I11compares the major components of the pulps with those of the original woods. The species are arranged in the order of increasing amounts The woods in the hardwood group strikingly conform to one another both in the yield and in the lignin content of the of lignin in the pulps, expressed as a percentage of the original residue. The softwoods also resemble one another. The lignin. I n no other component is the same order approached, nor does arranging the woods in the same order as in Tables I . pulping action of butanol on hardwoods is SO similar that probably all could be satisfactorily pulped together in any and I1 reveal any apparent relations although the removal of mixture using one schedule. The fact that waste wood from pentosans some.cYhat parallels the removal of lignin. It weed tree species could be pulped in the same cook with aspen should be recognized, however, that the “pentosans” include all furfural-yielding compounds, including uronic acids and and birch should make the process well suited for the pulping of thinnings and other small wood products from the Lake uronides as well as true pentosans, so that no theoretical instates region. It is obvious that the process needs further terpretation can be given t o the trend in “pentosan” changes. modification to be suitable for any of the softwoods, though, if suitable modifications were developed, it is possible that WOODSBEFORE COOKING varying mixtures of spruce and pine might be cooked by the TABLE I. ANALYSESOF ORIGINAL Componentsa same schedule. Still other modifications might give more --Cellulosesatisfactory results in cooking tamarack and balsam fir. Cross Cook and PentoExtracThe woods from the two main botanical classes show, No. Wood Lignin Bevan Alpha sans Ash tives within each class, marked similarity in cooking response and 15 Paperbirch 18.4 62.9 41.1 20.6b 0.22 4.6 marked differences between classes. Whether or not these 7 Basswood 16.7 61.0 41.9 14.8b 0.37 8.8 14 Aspen 19 8 ., 4 9 62 5 6 ., 83 49 3 5 . 47 1 65,.75a‘ ~ o0 ,. 5 31 7 4 ., 63 7 different responses reflect characteristic taxonomic differ8 Red oak 3 Whiteoak 21.8 56.1 40.1 15.8b 0.83 7.0 ences of a chemical nature is an interesting problem which, it 5 Silver maple 22.2 57.0 40.2 16.9b 0.30 3.8 is hoped, will be explored later on a larger series of samples. 0.23 4.4 3.2 62.4 46.1 25.1 9 Red pine 13 Jack pine 25.9 62.2 46.3 7.0 0.12 4.8 The paper birch pulp was low in lignin and high in cellulose 2.7 7.5 0.34 62.0 44.8 11 Blackspruce 27.1 4 White spruce 28.2 57.6 42.4 6.8 0.25 2.6 content. The lignin content of “original” basswood is sig0.26 10.9 5.8 39.5 25.2 54.5 10 Tamarack nificantly lower than that of the other hardwoods, but this is 12 Balsamfir 28.4 61.4 44.6 5.0 0.89 4.2 Peroentage based on oven-dry weight of original wood. not reflected in the resulting pulp. Aspen gave a high yield B By Powell and Whittaker method. of pulp with a relatively low lignin content. It accordingly has a high cellulose recovery as was indicated by the earlier study (3). The amount of basswood pulp that was acciDiscussion dentally lost was a t least enough to bring its yield up within the range of most of the hardwoods. I n Tables I and I1 the woods are arranged in the order of Whether the low yield of white oak is real or experimental the completeness of pulping as indicated by the amount of is problematical. A considerable part of the original sample lignin in the residues. All of the hardwoods were much was fine wood flour, a fact that would contribute to a low better pulped than were any of the softwoods. The softyield. This likewise is true of the tamarack sample, but the woods have a much larger percentage of lignin resistant to presence in this wood of a water-extractable galactan would butanol cooking than do the hardwoods. 7
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INDUSTRIAL AND ENGINEERING CHEMISTRY
also contribute to a low yield. Balsam fir gave a high yield of pulp which was high both in lignin and cellulose, expressed as a percentage of the original wood. The high yield of balsam agrees with earlier unpublished work by Aronovsky in this laboratory. The yield of white oak probably should be reduced to correct for an abnormally high ash content. This high ash content probably originated through corrosion of the digester. While the ash content of the original white oak is somewhat higher than that of most of the other woods, the ash content of the pulp is abnormally high. During the first three cooks the corrosion of the copper kettle appeared to be excessive, and apparently the white oak cook caused the most damage. The same kettle had been used many times for butanol pulping of aspen without noticeable corrosion. The corrosion in the case of the oak was possibly due to the formation of a comdex between the alcohol-soluble tannins and the comer. no further high'ash Of the Monel AftC& the pulps were obtained.
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Literature Cited Aronovsky, S. I., U. 9. Patent 2,037,001 (April 14, 1936). Aronovsky, S. I., and Gortner, R. A., ISD. ENG..CHEM.,22, 264 (1930). Ibid., 28, 1270 (1936). Bailey, A. J.,IXD.ENQ.CHEJ?.,-4nal. Ed., 8, 389 (1936). Bray, M. IN., Paper Trade J . , 87, No. 25, 59 (1928). Gortner, R. A , and McNair, J. J., 1x0. ENQ.CHEhl., 25, 505 (1933). Hawkins, W. L., Wright, G. F., and Hibbert, H., J. Am. Chem. Soc., 59, 2447 (1937). Powell, W. J., and Whittaker. H., J. SOC. Chem. Ind., 43, 35T (1924). Ritter, G. J., and Barbour, J. H., IND.EKG.CHEM.,Anal. Ed., 7, 238 (1935). Ritter, G. J., Seborg, R. M., and Mitchell, R. L., Ibid., 4, 202 (1932). Sieber, R., and Walter, L. E., Papier-Fabr., 11, 1179 (1913). Van Beckum, W. G., and Ritter, G. J., Paper Trade J . , 104, No. 19, 49 (1937). R ~ c a r v July s ~ 9, 1938. Paper No. 1629, Journal Series Minnesota Agricultural Experiment Station.
Microscopy of Starch by
the Spierer Lens
T
RE Spierer lens has been found in this study to reveal certain details in microscopic structure of starch which are only suggested by the usual microscope objective. Soon after swelling begins, starch granules become transparent and difficult to bring into focus with the ordinary lens. They show little in a dark field except a fringe of light a t their edges. With the Spierer lens, however, a different effect is possible. Seifriz ( 2 , 3, 4, 6) has given complete details concerning the construction and use of the Spierer system. It operates as a dark field owing to the fact that a mirror built into the front lens of this special objective covers part of the field and a t the same time reflects back onto the surface of the specimen the light which enters vertically from below. Scattered light reaches the eye through the part of the lens not covered by the mirror. The lens was employed in this study in conjunction with a special cardioid condenser which does not stop all direct light but allows a tiny pencil of light to strike the colloidal particles from below and thus render them visible to a degree which would be impossible with dark field oblique illumination only. No papers have come to the author's attention which report the use of the Spierer lens in studying the microscopy of starch. Cellulose was observed with it by Seifriz and also by Thiessen (7) to be made up of parallel alternating light and dark lines which show a discontinuous or nodular construction. Streaming protoplasm was shown by Seifriz (f?) to exhibit similar arrangement. Some critics have contended that the "Spierer lines" on cellulose are only artifacts produced by diffraction; but Seifriz (s),in defending his view that supermicellar structure of the cellulose is indicated by such pictures, contends that there must necessarily be structure present in order for the artifact to have been produced.
Methods The Spierer oil immersion objective provided an initial magnification of 90 times and it was used here together with
SYBIL WOODRUFF University of Illinois, Urbana, Ill.
a 12.5X ocular. The ordinary oil immersion lens used magnified 92 times. At the time of taking each picture with the Spierer lens, i t was made certain that light was entering the lens through the pinhole opening in the condenser-in other words, that the field observed was typical of the lens and not of an ordinary dark field. Except for the centrifuged particles shown in Figures 17 and 18, the specimens of starch were mounted in water and protected with a sealed cover slip. Methods of swelling the starch were the same as those previously described (8,9, 10). The freezing temperature of the gels was about - 18" C. for 24 hours or longer.
Native and Swollen Starch Starch in its native or unswollen state is difficult to photograph a t the high magnifications of the Spierer lens because of marked marginal diffraction by objects which possess as much contour of surface as it does. Furthermore, when the granules are completely swollen-for example, a t 95" C. in an abundance of water-they are exceedingly transparent. They contain little structural matter in this swollen state which is dense enough to scatter the light coming through to the lens; for this reason they are too indistinct to warrant making photographs. Photomicrographs of gelatinized corn and wheat starches, taken with the usual type of objective, were previously published by the author and by Sjostrom (6). Partial hydration, obtained, for example, by pasting starch a t a temperature of 70" C., separates structural components in the granule from one another but allows them to retain sufficient density to be visible with the Spierer equipment. This effect is shown in Figures 1, 2, and 3 where three differently appearing fields of cornstarch are shown. Brightly luminous dots, single or in clusters, can be seen in these Spierer photographs, and Figure 3 shows a concentric arrangement of such units. One picture of wheat starch, also pasted a t 70" C. but taken with an ordinary oil immersion lens in a bright field, is given in Figure 4.
