264
INDUSTRIAL AND ENGINEERING CHEMISTRY
degree of accuracy as obtainable when applied to the ordinary run of absorption oils or naphthas. Indications of inconsistent deviations from Raoult’s law in previous investigations can be explained by the fact that the composition of the original sample determines the vaporization characteristics. In most cases the number of different samples used was insufficient to bring out this point and conclusions were drawn on results obtained from similar mixtures. Conclusions Deviations from Raoult’s law as applied to complex mixtures are dependent upon the relative composition of a mixture Of substances as as upon the or dissimilarity of the components in the mixture. For engineering calculations, when an accuracy of j to 15 per cent is considered satisfactory, Raoult’s law may be used with fairly satisfactory results. When greater accuracy is desired, little confidence can be placed in results calculated by means of this law.
VOl. 22, No. 3
Literature Cited (1) Brown and Caine, Trans. A m . Inst. Chem. Eng., P i , 21 (1928). (2) Calingaert and Hitchcock, J . A m . Chem. Soc., 49, 750 (1927). (3) Coats and Brown, Dept. of Engineering Research, University of Mich., Circ. P (December, 1928). (4) Davis, Proc. 5th Annual Convention Assocn. Natural Gasoline M f r s . , p. 37 (1926). ( 5 ) Findlay, “Practical Physical Chemistry,” Chapt. VII, p. 112, Longmans. (6) Kallam and Coulthurst, Oil Gas J . , 28, 50 (November 21, 1929). (7) Leslie and Good, IND.ENQ.CHEM.,19, 453 (1927). ( 8 ) Maxson, Proc. 4th Annual Convention Assocn. Natural Gasoline Mfrs., p. 25 (1925). (9) McLouth, Null. Petroleum X e u s , 20, No, 32, 54 (1928). Peters, IND, CHEM,,18, 6g (1926), (11) Piroomov and Beiswenger, Am. Petroleum Inst., Bull. 10, No. 2, 52 (January 3, 1929). (12) Podbielniak, Relrner A’atural Gasoline Mfr., 8, NO. 3, 55 (1929); oil Gas J . , 27, No. 35, 38 (January 17, 1929). (13) Podbielniak and Brown, IND.END.CHRM.,21, 7 i 3 (1929). (14) Weissenberger, Pelroleum, 1817 (1925). (15) wilson and ~ ~ ~ , 7 (1923). ciH E M~. ,1 6 , 9 4 (16) Wilson and IYylde, I b i d . , 16, 801 (1923).
The Cooking Process I-Role of Water in the Cooking of Wood1 S. I. Aronovsky2 and Ross Aiken Gortner
The cooking of wood as practiced in the industry for the production of cellulose involves the use of cooking liquors containing various chemicals in various concentrations. The exact effect of the individual constituents upon the cooking process is largely unknown. This paper reports the first of a projected series of studies designed to ascertain t h e role of each constituent of the cooking liquor. Since water comprises the main bulk of the liquor, cooking with water only was selected for the first study. I t is shown t h a t cooking with water a t different temperatures for varying lengths of time has a profound effect upon the various constituents of the wood. Pentoses and
pentosans are rapidly destroyed, resulting in the production of appreciable quantities of furfural; lignin, although apparently the most stable constituent, undergoes partial depolymerization; and the celluloses are broken down to water-soluble constituents and to gaseous products. Approximately 37 per cent of the total celluloses and 46 per cent of the alpha-cellulose were destroyed in the 12-hour (186” C.) cooks. A t the longer times and higher temperatures the rate of destruction of the alpha-cellulose was faster than was t h a t of the total celluloses, indicating a conversion of alpha-cellulose to hydrocelluloses. Water can, therefore, be looked upon as avery active reagent in the cooking process.
HE cooking process in the pulp industry is based more upon practical experience than upon the knowledge of the chemical reactions taking place in the digester. This is due partly to the limited knowledge of the chemical composition of the woods used, and partly to the lack of exact data on the action of the various cooking chemicals on the components of the wood. Empirical studies on the pulping of wood have been, and are being, carried out in various industrial and technological laboratories. Such studies, however, as a rule involve the use of cooking liquors which contain several different cheniicals in various concentrations. The composition of these
cooking liquors has, in general, been arrived a t in part by tradition, and in part by random experimentation, one composition after another having been used or varied until more or less satisfactory results were obtained. There is thus available little or no information as to the exact role which any particular component of the cooking liquor plays in the cooking process. The problem of the nature of the cooking process is further complicated by the fact that wood is a biological product of more or less uncertain and variable composition, and accordingly the various constituents of the cooking liquor probably react differently toward the various organic compounds present in the wood. Following this line of thought, it seemed desirable that a series of fundamental investigations of the cooking process should be carried out by starting with a simple substance as the cooking agent and then adding other reagents, one by one, until the composition of the cooking liquors in the present-day commercial processes was reached. This series of investigations should lead to a better understanding of the reactions taking place in the digester, and might
T
Published with t h e approval of the 1 Received November 11, 1929. Director a s Paper No. 900, Journal Series, Minnesota Agricultural Experiment Station. Presented under the title “The Chemistry of t h e Cooking Process. I-Cooking Aspen with Water” before t h e Division of Cellulose Chemistry a t the 78th Meeting of the American Chemical Society, Minneapolis, Minn., September 9 t o 13, 1929. * Cloquet Wood Products Fellow, University of Minnesota. This study was conducted under a n industrial fellowship grant from the Cloquet wood products companies of Cloquet, Minn. Thanks are especially due t o various representatives of the Northwest Paper Company, who have cooperated in this study.
March, 1930
I S D U S T R I A L A N D ENGIXEERIR'G CHEMISTRY
provide a basis for obtaining a more nearly theoretical yield of cellulose than is possible with the present methods of cooking. Water, which makes up the greatest bulk in the digester charge, 'RW considered to be the logical reagent for the first of this series of investigations.
265
not produced by cooking a t atmospheric pressure even in the presence of formic and acetic acids. Franck (?), upon steaming wood, obtained a condensate water consisting mainly of methanol, furfural, humus substance, sugars, and volatile organic acids, largely acetic. A recent patent taken out by Vickers, Ltd., and Lucas (sa)described the manufacture of furfural from straw by heating the latter with Rater at 180" C. In attempting to determine the nature of wood and woody substances, Singer (27) cooked wood with water a t atmospheric pressure 10 hours a day for 90 days. He found that the extract, as well as the extracted wood, gave all the color reactions of the original wood with phloroglucinol, aniline, resorcinol, and indol. He further states that lignin appears to be a mixture of a number of chemical individuals. Tauss (31) believed that the color reactions used by Singer were not satisfactory. He ran a series of cooks on Swedish filter paper and fine wood shavings a t various pressures, using glass flasks a t atmospheric pressure and an autoclave a t the higher pressures. The solutions separated from the residue were always clear and more or less yellow. They slowly became brown on exposure to the air, and gaw, on evaporation, black, resin-like substances n hich n-ere soluble in alkali. The maximum yields of dry matter and reducing sugars in the water extracts were found at 5 atniospliere (153" C.). At 20 atmospheres (213" C.) the celluloFe bccame gelatinous and could be powdered after it was dried. Gelatinization of the cellulose in the wood could not be detected eT-en a t this pressure. The rewlts of Tawq's n-oik are given in Table I. Table I-Yields of Dry Matter and Reducing Sugars on Heating Cellulose a n d Wood with Water at Pressures Up to 20 Atmospheres (2133 C.).
Figure 1-Details
of Steam-Jacketed Autoclave Used in Pressure Cooks
Historical
PRESSrRE
.~tmos-
.i number of investigators, with various objectives, have heated wood or some of its constituents with water in the course of their investigations. I n studying the formation of humus substances, Hoppe-Seyler ( I S . 14) and Slunk (18) heated filter paper Kith water and obtained dark brown, brittle, solid matter and liquids containing formic acid, pyrocatechol, and furfural. Stein (29), on heating wood with water to 290" C., obtained a black carbonaceous mas;. Schwalbe and Robinoff (25) found that pure cellulose, when heated with water, was only slightly attacked even at teniperatures of about 200" C., but that modified cellulose, such as filter paper or bleached cellulose, gave increaqed copper numbers. Bergius (1) heated cellulose, lignin, and wood in the presence of water l o 340" C., converting them into products similar to coal. Berl and Schmidt (4) heated cotton linters with water to 350" C. S o change was noticed in the cotton a t 150" C., but the fiber structure was entirely destroyed a t 225" C., at which temperature copious gas production, consisting of carbon dioxide, carbon monoxide, hydrogen, methane, rind the lower hydrocarbons, began. The residual liquid contained formic acid and a brown amorphous substance resembling "huinalid' acid. Greville Williams (35) was the first to show that furfural n-as obtained by the action of steam uponwood. Zachariac (36), in treating wood for mechanical wood pulp, showed that formic and acetic acids were produced. Bergstriini (2, 3) found that heating wood and cellulose with water under pressure led to the formation of methanol and formic and acetic acids. Heuser (11, 12) found that cooking wood with water under pressure will produce furfural, but the latter is
bheres
10 20
I 1
(Data of Tauss)
FILTER PAPER Dry matter
Reducing sugars
Per cent Per cent
1.39 o:i2 13.48 5.49 Gelatinized
I 1
BEECHWOOD
SPRUCE WOOD
SHAVINGS Dry
matter
Reducing sugars
Per cent 7.25 26.75 18.41
Per Cenl 2.37 11.90 5 31 1.41
3.34
SH.4VINGS
Dry
matter
I
!
Per ccnt Per
1.18 19.18 16.10
...
-
Reducing sugars CCnl
0.18 9.08 4.25
..
These results represent the t o t a l of three succesive cook> u-mg the idme material b u t fresh water each time The figures were calculated on t h e basis of the original wood. a
Tauss found that the sugar extracted from the wood vas not all dextrose. A dextrin-like substance could be precipitated from the aqueous solution with alcohol. Ether extracted a brown decomposition product from all the water solutions. Potter (20) and Spaulding (28) showed that treating wood nith TTater a t 100-120° C. caused partial delignification of these woods. Grafe ( 9 ) treated wood with water a t 180" C. aiid obtained coniferin, vanillin, methyl furfural, and pyrocatechol. He concluded that these components make up the lignin and that they are held to the cellulose of the membrane by an ether linkage. Fromherz (8) and Koch I 1.5) cooked purified aspen and spruce lignocellulose with n ater and determined the effects of this process on the sugars produced. Khnig and Sutthoff (16) showed that part of the lignin in nitrogen-free feedstuffs is soluble in hot TTater under pressure. TVichelhaus and Lange (33) treated wood n-ith superheated steam a t 180" C., and found that the ether extract of the aqueous distillate gave, upon treatment with phloroglucinol and hydrochloric acid, a color comparable to that which wood gives with these reagents. Schmitz (22) autoclaved Douglas fir and western hemlock sawdust with water, and found that the reducing properties and total
March, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
valve, which was then closed. This procedure removed the air from the sawdust and autoclave. The relief valve was kept tightly closed during the remainder of the cooking period. The temperature and pressure in the autoclave were closely followed. Every 30 minutes the quick-opening blow valve ( F , Figure 2) was closed, and the autoclave was rotated twenty times in order to mix the contents thoroughly. Following the mixing the valve was re-opened. The variation in boiler pressure during the cooking periods did not exceed 3 to 5 pounds (0.2 to 0.35 kg. per sq. cm.). The pressure and temperature in the autoclave do not corresponds to those of saturated steam because of the formation of gases during the cooking process. I n this paper the word "pressure" denotes, unless otherwise specified, that gage pressure, taken from the "saturated steam tables," which corresponds to the temperature desired. At the end of the cooking period the steam valve was closed and the pressure in the jacket of the autoclave was reduced by opening the valve connected to the steamcondensate outlet pipe (E, Figure 1). The condenser was then connected to the relief valve and the latter slowly opened, so as to collect all the condensable vapors in the receiving flask. The autoclave cover was removed and any wood adhering to its inner surface washed into the main wood mass. The residual wood mass was filtered through a small, stout canvas bag and then heavily pressed by means of a large screw press, the liquor being, of course, preserved for analysis. The residual wood in the bag was loosened and thoroughly washed by stirring x i t h a liter of boiling water, filtering, and pressing. This washing procedure was repeated four times, the washings being added to the original liquor, which was subsequently filtered and was then ready for evaporation. The washed residual wood was dried, weighed, and set aside for analysis The digester condensate (totaling 800 to 1000 cc.) obtained when the pressure was relieved from the autoclave was light yellow, and oily droplets formed on the sides of the flask above the surface of the liquid. This oily portion was subsequently found to be furfural. This condensate was redistilled a t atmospheric pressure, and the first 500 cc. were collected and placed in a flask for further analysis. The residue in the distilling flask was then added to the bulk of the cooking liquor prior to its evaporation. The residual wood from the pressure cooks was much darker and more pliant than that obtained from cookins a t atmospheric pressure. When the product of the higher pressure cooks was separated from the liquor by means of the screw press, it packed almost a-s compactly as commercial wood pulp. The dry residual wood had an agreeable caramel odor, the intensity of which increased with the time and temperature of digestion. The cooking liquors of the cooks run a t 50 pounds pressure (148" C.) up to 4 hours were somewhat darker than those obtained a t atmospheric pressure, which were a light orange. Beginning with the %hour, 50-pound (148' C.) cook, however, the color changed to orange-red. The liquors obtained from the cooks a t 100 pounds (170" C.) and 150 pounds (186" C.) were wine-red and clear when hot, and light brown and opaque when the liquid was cooled. This color darkened somewhat upon standing. The turbidity of all the cooking liquors increased with the time and temperature of digestion. Preparation of Cooking Liquors for Analysis
CONCENTRATION OF COOKINGLIQuoRs-The cooking liquors were concentrated by means of the vacuum evaporator ahown in Figure 3, which was patterned after the apparatus
267
described by Brewster (6). The heating coil was of monel metal. This apparatus was found to be very efficient, evaporating 1.5 to 2 liters per hour when aqueous solutions were used and 2.5 to 3 liters from alcohol solutions. The temperature of the liquid in the evaporator was kept a t 2530' C. for aqueous solutions and a t 1 5 2 0 " C. when alcoholic liquors were used. The concentrated liquors were much darker than before evaporation, and contained a considerable amount of suspended matter which settled in 2 to 3 hours.
FURTHER TREATMEKT OF LIQUORPRIORTO ANALYSISThe concentrated liquors of all the normal pressure cooks, and also the liquors of the 2-hour and 4-hour cooks of the 50-pound (148" C.) series, were evaporated on a hot plate to about 200 cc. This second evaporation caused some of the suspended matter to settle out. After cooling, enough 95 per cent alcohol was added to these solutions to make a final concentration of 70 per cent alcohol. The liquors of the 8-hour and 12-hour cooks of the 50-pound (148" C.) series were evaporated to 500 cc., while those of the remaining
I
,
Figure 3-Laboratory
7
1
Vacuum Evaporator
cooks were evaporated only to 700-800 cc. before treating with alcohol. If concentration was carried too far a small amount of a very dark, gummy substance settled out on the sides, as well as on the bottom, of the container. This substance dissolved very easily in 70 per cent alcohol. On addition of the alcohol, all the solutions became winered and a brown flocculent precipitate, which settled readily, was formed. The solutions were left to settle for 24 hours. They were then filtered by suction through tared, hardened filter paper in Brichner funnels and washed with 70 per cent alcohol. The residue on the filter paper was then washed with acetone, in which it was insoluble, thus providing for a rapid drying of the precipitate. The precipitate and filter paper were dried to constant weight at 102-105" C. and
I-VDUXTRIAL A N D ENGINEERING CHEMISTRY
288
weighed. The precipitate was then brushed from the paper, ground, and set aside for analysis. The color of the dried residue varied from a light grayish brown to brown. The alcohol was removed from the filtrate by distillation under reduced pressure, following which the solutions containing the soluble extractives were diluted to a definite ITolume and preserved by toluene for subsequent analysis. T a b l e 111-Effect of T i m e and T e m p e r a t u r e on Yield of R e s i d u a l Wood a n d Dry M a t t e r in A q u e o u s E x t r a c t wood) (All . .DercentaPes calculated on basis of 89.8 arams oven-dry. original -
COOKTIME TEMP
RESIDUAL WOOD
1
D R Y MATTER IN
EXTRACT
feight o & ~ ~ Weight l
Hours
C.
ozg:'a,
? ~ O APPARENTLY D DESTROYED Weight
Grams
70
Grams
70
Grams
87.7 87.5 87.6 87.4 86.9 86.9 86.9
97.66 97.44 97.55 97.33 96.77 96.77 96.77
2.07 2.14 2.21 2.51 2.73 2.93 3.20
2.30 2.38 2.46 2.75 3.04 3.27 3.56
0.03 0.16 +0.01 +O.ll 0.17 +0.03 +0.30
2:Lal 0.03 0.18 +0.01 +0.12 0.19 +0.03 +0.33
8 9 10 12 11
2 2 4 8 12
148 148 148 148 148
75.2 74.2 70.5 68.1 66.8
83.74 82.63 78.51 75.S4 74.39
12.6 14.0 16.3 16.7 15.6
14.03 15.59 18.15 18.60 17.37
2 0 1 6 3 0 5 0 7.4
223 1.78 3.34 5.57 8.24
13 14 15 16
2 4 8 12
170 170 170 170
63.7 63.9 63.3 61.8
70.94 71.16 70.49 68.82
17.9 14.0 12.5 12.5
19.93 15.59 13.92 13.92
8.2 11.9 14.0 15.5
9.13 13.25 15.59 17.26
17 20
2 4
18
6'/e 8
186 186 186 186 186
61.6 61.0 57.1 56.3 54.5
68.60 67.93 63.59 62.70 60.69
12.8 12.8 12.4 13.3 13.9
14.25 14.25 13.81 14.81 15 48
15.4 16.0 20.3 20.2 21.4
17.15 17.82 22.61 22.49 23.83
19 ~~
21
12
Methods of Analysis
XLCOHOGSOLUBLE PORTION OF LrQuoR-Total Solids were determined on 25-cc aliquots. Reducing sugars before and after hydrolysis-T~~enty-five cubic centimeter aliquots were clarified with the dry lead acetate, deleaded with dry disodium phosphate, and the reducing sugars were then determined colorimetrically by the Willaman and Davison (34) modification of the picric acid method.' Similar analyses were conducted on aliquots in which possible disaccharides or polysaccharides were hydrolyzed by boiling for 2 hours with 2 per cent hydrochloric acid following which the sugars were estimated as noted above. Disaccharides and trisaccharides-The total sugars in the liquors-i. e., the mono-, di-, and tri-saccharides-were also determined by the Willaman and Davison (34) modification of the picric acid method. The differences found between the reducing and total sugars were practically within the limits of experimental error. It was therefore concluded that no carbohydrates other than monosaccharides and polysaccharides were present in the aqueous wood extracts. Pentoses-Furfural was distilled from 25-cc. aliquots of the aqueous wood extract according to the method of Perrier and Gortner (19). The furfural in the distillate was determined by Powell and Whittaker's (21) bromine titration method. The xylidine and acetic acid method, which according to Suminokura and Nakahara (30) is specific for furfural only, was used qualitatively. The xylidine test was positive for all the solutions except those obtained 1 I t was found in this analysis t h a t a very small quantity of a Eocculent precipitate was formed. This amount of precipitate, mainly ferric hydroxide, aithough too small t o be weighed, was large enough t o produce a small error in t h e sugar determination. In order t o eliminate this source of error, the solution was centrifuged for a few minutes before the clear liquid was placed in the colorimeter cups for comparison.
Vol. 22, No. 3
from cooking a t 150 pounds pressure (186" C.). In the latter solutions the formation of the red color on the interaction of xylidine, acetic acid, and furfural was so slight as to be indefinite, Lignin-Twenty-five cubic centimeter aliquots of the extract were evaporated to dryness in a porcelain crucible, and 10 cc. of 72 per cent (by weight) sulfuric acid were added to the residue. The two were triturated with a glass rod and left for 16 hours, with occasional stirring, in a desiccator containing 72 per cent sulfuric acid. At the end of 18 hours the contents of the crucible was poured into B 500-cc. Erlenmeyer flask, and enough water was added to make a total of 390 cc., thus producing a 3 per cent sulfuric acid solution. The solution was boiled for 2 hours and filtered through a tared alundum crucible. The precipitate was washed with about 200 cc. of hot distilled water, dried to constant weight a t 105" C., and weighed. Solubility in ether-Twenty-five cubic centimeter aliquots of the aqueous wood extract were extracted four times with an equal volume of ether in a separatory funnel. The ether extract was filtered, evaporated, dried, and weighed. The residue was reddish brown and dried to a solid, shiny mass. Qualitative tests f o r tannins (IO),proteins, and amino acids showed that tannins were absent and that a t the most only traces of proteins and amino acids were present. ALCOHOL-INSOLUBLE PORTION OF LIQUOR-Reducing sugars after hydrolysis, pentosans, and lignin were determined on this fraction, following essentially the methods noted above. The factor 1.375, used for the conversion of furfural to pentosans, was obtained by assigning the formula (CsHs04), to the pentosans. of A q u e o u s Wood E x t r a c t s for R e d u c i n g S u g a r s and Dry M a t t e r (All figures based on use of 89.8 grams oven-dr sawdust in each cook)
T a b l e IV-Analysis
REDUCING SUGARS A S GLUCOSE TOTALDRY MATTER
COOKTIMETEMP.
ALCOHOL-
SOLUBLE
Before After hy- hydrply rolysis SIS
6 1 7 4 2 5 3
Hours 2 4 4 8 12 16 24
2 2 4
Grams Gram
::$::-
~
Alcoholinsolu- Total ble
C. 100 100 100 100 100 100 100
Grams Gvams
1.84 3.52 2.27 4.33 3.41 7.25 6 . 2 8 9.31 6.17 8.16
3.48 7.00 4.44 8.77 4.73 1 1 . 9 s 1 . 9 0 11.21 0.93 9.09
7.87 8.61 10.56 13.62 13.00
4.72 5.43 5.73 3.08 2.62
12.59 14.04 16.28 16.70 15.62
0.08 11.34 0.05 5 . 2 4 0.06 2.50 0.05 2.31
17.22 13.52 11.71 11.65
0.66 0.52 0.81 0.88
17.88 14.04 12.52 12.53
0.02 0.02 0.02 0.03 0.05
12.35 12.33 11.98 12.54 13.06
0.45 0.50 0.43 0.71 0.83
12.80 12.83 12.41 13.25 13.89
0.21 0.16 0.23 0.22 0.28 0.30 0.34
0.34 0.31 0.39 0.41 0.45 0.48 0.55
8 9 10 12 11
12
148 148 148 148 148
13 14 15 16
2 4 8 12
170 170 170 170
10.50 11.26 5 . 8 2 5.19 2.78 2.44 2 . 3 0 2.26
17 20 18 19 21
2 4 6*/2 8 12
186 186 186 186 186
4.45 4.03 2.78 2.79 2.27 2 . 3 1 2.46 2 . 4 7 2.78 2.56
S
ilcohol nsolu- Tota! ble
0.28 0.33 0.30 0.42 0.46 0.45 0.53
Grams
Grams Grams
0.62 0.64 0.69 0.83 0.91 0.93 1.08
4.05 2.81 2.33 2.50 2.61
liquets of the reDIGESTERC NDENSATE-PUTf llral. distilled digester condensate were diluted a i d acidified with hydrochloric acid to a 12 per cent acid concentration. The furfural phloroglucide was then precipitated by the addition of phloroglucinol in hydrochloric acid (11 grams of phloroglucinol dissolved in 1500 cc. of 12 per cent hydrochloric acid). The solution was allowed to settle for 18 hours in the dark and then filtered through a tared Gooch crucible with an asbestos mat. The residue was washed with 150 cc. of distilled
March, 1930
ISDUSTRIilL AND E,VGIA7EERIiYG CHEXISTRY
water, dried, and weighed. The furfural was calculated from Krober's formulas (24, p. 536). Volatile reducing substances other than fuyfural. The reducing value of furfural was determined by treating a known quantity of furfural in solution, according to the hfunson and Walker method for reducing sugars (17). The m-eight of furfural multiplied by the factor 1.345 gives the Iveight of cuprous oxide produced. The reducing value of aliquots of the digester condensate was obtained by the Munson and Walker method. The difference between the weights of cuprous oxide determined by this method and those calculated from the furfural content of the digester condensate gave the cuprous oxide formed by the volatile reducing substances other than furfural. I'olatile acids as acetic acid. A volatile acid determination was made upon a mixture of aliquots from both the cooking liquor and digester condensate. Twenty-five Icubic centimeter portions of the alcohol-soluble liquid and an equivalent solume of the digester condensate liquor (depending upon the original volume of the alcohol-soluble portion) were placed in a 500-cc. Kjeldahl flask, marked a t 50 and 100 cc., and 10 cc. of phosphoric acid (sp. gr. 1.7) were added. The solution was then diluted with carbon dioxide-free water to the 100-cc. mark. The flask mas equipped with a dropping funnel and then connected to a Liebig condenser and a receiving flask. The solution was distilled gently until the 50-cc. mark was reached. Then 70 cc. of carbon dioxidefree water were added slowly, keeping the level in the flask constant. The distillation was continued until only about 25 cc. remained in the flask. The distillate mas titrated immediately with 0. LO S sodium hydroxide, using phenolphthalein as indicator. The quantity of acid found was calculated as acetic acid. RESIDUAL WooD--Beating tests. h weighed quantity of the residual wood from the pressure cooks (40.0 grams ovendry) and 960 grams of water were placed in a 1400-cc. pebble jar containing 1000 grams of smooth white pebbles 1 and 2 cm. in diameter, using approximately equal weights of each size. After rotating for 3 hours at 60 r. p. m., the contents were screened by washing through a perforated screen [holes 0.065 inch (0.16mm.) in diameter] onto a 70-mesh wire. The stock remaining on this wire was made into hand sheets and the remainder discarded. About 50 per cent of the pulp from the 2-hour, 50-pound (148" C.) cook remained on the perforated screen. This amount decreased gradually with the increase in time of cooking, about 10 per cent of the pulp, from the 2-hour cook of the 100-pound (170" C.) series, remaining on the perforated screen, R-hile that from the 12-hour cook was washed completely through the screen. After beating none of the pulps from the 150-pound (186' C.) series of cooks remained on the perforated screen. These pulps were slimy to the touch, and seemed to have become gelatiriized. The remainder of the wood, after the quantity required for the beating tests had been taken out, was ground to pass a 40-mesh sieve, for subsequent analysis. Cellulose. The cellulose in the residual wood was estimated by the chlorination method outlined by Bray (5). The duration of the first chlorination was 4 minutes, while the succeeding chlorinations were carried out for 2 minutes each. Four chlorinations were used on all of the samples except those of the 150-pound (186' C.) cooks, which required five. Alpha-cellulose. The alpha-cellulose mas determined on the cellulose, obtained by the chlorination procedure according to the gravimetric method given by Bray (5). It was found difficult to separate the alpha- and beta-celluloses by filtration in the case of the celluloses from the cooks of the
269
150-pound (186" C.) series. The separation and washing of these samples were accomplished by centrifuging. A considerably larger quantity of beta-cellulose was observed in the treatment of celluloses from the higher pressure cooks. Lignin. The lignin in the residual woods was determined according to the method used a t the United States Forest Products Laboratory (5), but omitting the extraction of the wood with ether prior to the addition of the 72 per cent sulfuric acid. This omission was decided upon after it was found that there was little difference in the yield of lignin from the ether-extracted and non-extracted wood (26.21 to 26.37 and 26.48 to 26.52 per cent, respectively), and that the previous extraction with ether did not speed up the rate of settling and filtration of the lignin. Pentosans, The furfural was obtained by the steam distillation method of Pervier and Gortner (IQ), and estimated according to Powell and Whittaker's (21) method. The factor used for converting the furfural to pentosans was 1.375, obtained by using ( C S H ~ O as ~)~ the empirical formula for pentosan5 of T i m e a n d Temperature on Pentoses a n d Pentos a n s i n Aqueous Wood Extract (All figures are based on the use of 89.8 grams oven-dry wood in each cook)
Table V-Effect
ALCOHOL-
.k.COHOl,-
SOLUBLE
7urfural Pentoses
Pentoses+ Fur- Pento- hrfural pentosans calcd. as fural sans pentosans
C. 100 100 100 100 100 100 100
Grams
Grams
G w m s Grams
Grams
Grams
0.041 0.045 0.043 0.048 0.052 0.055 0.067
0.064 0.070 0.067 0.075 0,081 0.086 0.105
0.100 0,112 0.114 0.182 0.197 0,212 0.224
0.138 0.154 0.157 0.250 0.271 0.292 0.308
0.141 0.157 0.157 0.230 0.249 0.267 0.291
0.194 0.216 0.216 0.316 0.342 0.367 0.400
2 2 4 8 12
148 148 148 148 148
0.941 0.956 1.907 3.518 3.144
1.470 1.494 2.980 5.497 4.913
1.162 1.295 1.746 0.583 0.221
1.598 1.781 2.401 0.802 0.304
2.103 2.251 3.6;s 4.101 3.365
2.892 3.095 5.023 5.639 4.627
2
COOKTrva T E M P .
6 1
7 4 2 5 3 8
9 10 12 , 11
TOTAL
INSO1,l~BLE
Hours 2 4 4 8 12 16 24
O
13 14 15 16
4 8 12
170 170 170 170
3.720 1.107 0.221 0.433
5.813 1.730 0.345 0.677
0.003 0,010 0.011 0.003
0.004 0.014 0.015 0.004
3.723 1 117 0.232 0.436
5.119 1.536 0.319 0.600
17 20 18 19 21
2 4 6'/2 8 12
186 186 186 186 186
0.541 0.221 0,221 0.221 0.384
0.845 0.345 0.345 0.345 0.600
0.005 0.006 0.005 0.007 0.005
0.007 0.008 0.007 0.010 0.007
0.546 0.227 0.226 0.228 0.389
0.761 0.312 0.311 0.314 0.535
Table VI-Effect of T i m e a n d Temperature on Solubility of Lignin i n Water a n d on Ether Extractives of Aqueous Wood Extract (.411 figures based on use of 89.8 grams oven-dry wood in cook) /ETHER EXTRACTIVES
LICNIKI N : COOKTIME TEMP
0.147 0.230 0.233 0,347 0,333 0,390 0 491
Grams Trace Trace Trace Trace Trace Trace Trace
3.48 4.18 5.00 4.75
0.83 0.72 0.42 0.29
4.31 4 90 5 42 5 04
1.165 1.461 1.488 1.716
Trace Trace Trace Trace
170 170 170 170
5.74 4.98 4.64 4.24
0.03 0.03 0.05 0.05
5.77 5.01 4.69 4.29
2.316 3,156 3.304 3.524
Trace Trace Trace Trace
186 186 186 186 186
4.93
0.02 0.03 0.01 0.04 0.07
4.95 5.09 4.85 5.12 5,lO
3.664 3.880 4.064 4.068 4.144
Trace Trace Trace Trace Trace
4 4 8 12 16 24
9 10 12 11
2 2 4 8 12
148 148 148 148 148
13 14 15 16
2 4 8 12
4
5
3 8
17 20 18 19 21
2 4 6'/2 8 12
Alcoholinsoluble
Grams
C. 100 100 100 100 100 100 100
-a1
Alcoholsoluble
Grams Gram Grams Very small quantity not weighed Very small quantity not weighed Very small quantity not weighed Very small quantity not weighed Very small quantity not weighed Very small quantity not weighed Very small quantity not weighed
Hours 2
6
1
Alcohol- Alcoholsoluble insoluble
O
5.06
4.84 5.08 5.03
INDUSTRIAL AND ENGINEERING CHEMISTRY
270
Table VII-Effect of T i m e a n d Temperature on Formation of Furfural, Volatile Reducing Substances Other t h a n Furfural, a n d Volatile Acids in Cooking Process (All figures based on use of 89.8grams oven-dry wood in each cook) COPPER-REDUCTION VALUE OF DIGESTER CONDENSATE, AS Cur0
FuRaURAL
COOKTIMETEMP.
C.
Hours 8
9
2 2
10 12 11
12
13 14 15 16 17
148 148 148 148 148
12
20
2 4
19 21
8
12
Grams 0.81 0.85 1.38 1.66 1.65
1
Grams
Volatile reducing substances other than furfural
Grams
Grams
Gram
o:iie
o:Ok
-o:o3i
0.196 0.611 1.178
0,175 0.579 1.098
-0,021 -0.032
170 1.77 170 1.52 170 ' 1.63 170 1.58
1.332 2.966 2.888 2.446
1.792 3.990 3.886 3.291
1.760 4.120 3.916 3.464
-0,032 0,130 0.030 0,173
186 186 186 186
3 512 3.390 2.670 2.008
4.725 4.561 3.592 2.701
4.532 3.710 2.608
4.858
0.133 -0,029 0.118 -0,093
8
8
fu2;rslFound
o:o86 0.146 0.454 0.816
4
2 4
ACIDS IN AS DIGESTER Calcd. ACETIC CONDENSATE
1.34 1.96 2.07 1.60
I
-0.080
Vol. 22, No. 3
caused by the larger quantities of substance, soluble in hot and insoluble in cold water, which are removed from the wood. After standing 4 months the insoluble portions of the cooking liquors had precipitated and the mother liquor was very clear. This mother liquor was orange-red for the lower pressure cooks and cherry-red for the 150-pound (186" C.) cooks. The solution became light orange on acidification, but on the addition of alkali the original color became still darker. The paper used to filter the cooking liquor, after filtration through the canvas bag, took on a bright red color similar to that produced by the reaction of furfural with aniline acetate. This color could not be removed with ordinary washing with water. The liquors, therefore, contained a dye which also acted as an indicator. The neutrality of the cooking liquors, coupled with the increased content of iron above that expected from the materials used in the cooks, indicates that the acids formed in the cooking process were taken up by the autoclave material itself.
Table VIII-Effect of T i m e a n d Temperature o n Cellulose a n d Alpha-Cellulose of Residual Wood (All percentage figures on basis of 55.72grams cellulose and 41.27grams alpha-cellulose in original wood) U-CELLULOSE I N WOOD
CELLULOSE NOT ANALYSIS
~ C C O U N T E DFORB Y
Weight
8
9 10 12 11 13 14 15 16 17 20 18 10 21
1
12 24
100 100
2 2 4
50.81 49.84 48,49 47.43 47.07
91.19 89.45 87.03 85.12 84.48
4.91 5.88 7.23 8.29 8.65
8.81 10.55 12.97 14,8S 15.52
40
m
12
148 148 148 148 148
40 40 39 39
54 64 81 55
98.86 98 23 98 47 96 46 95 83
0.47 0.73 0.63 1.46 1.72
1.14 1.77 1.53 3.54 4.17
2
170
44.23 44,2S 43.73 42.40
79.38 79.47 78.48 76.10
11.49 11.44 11.99 13.32
20.62 20.53 21.52 23.90
37.66 37.55 37.08 34.11
91.25 90.98 89,84 82.65
3.61 3.72 4.19 7.16
8.75 9.02 10.16 17.35
42.68 41.55 37.19 37.34 34.87
76.60 74.57 66.74 67.01 62.58
13.04 14.17 18.53 18.38 20.85
23.40 25.43 33.26 32.99 37.42
35.40 32.31 21.81 26.76 22.49
85.77 78.29 52.85 64.84 54.49
5.87 8.96 19.46 14.51 18.78
14.23 21.71 47.15 35.16 45.51
2 4 8
8
4 8
12 2 4 61/1 8
12
C.
100
170 186 186 186
Per cent
1
Grams 55.88 55.75 55.75 55.80 55.87
Hours
6 7 4 2 3
100.29 100.05 100.05 100.14 100.27
Grams +0.16 +0.03 +0.03 4-0.08
+0.15
As a check on our methods it was decided to also deter.mine the furfural by the official phloroglucide method for pentosans (84, p. 535). The original sawdust, ground to pass a 40-mesh sieve, was used for this comparison. Four determinations by the official method gave yields of furfural varying from 12.25 to 12.48 per cent of the wood; eight determinations by our method gave values ranging from 12.57 to 12.96 per cent, with an average of 12.76 per cent, of the wood. The slightly larger yield of furfural obtained by the pentosan method used in this paper can probably be attributed to the fact that the furfural is not decomposed during distillation. Experimental Results
The experimental data are shown in Tables I11 to XI1 and Figures 4 to 7, inclusive. EFFECT OF TIME AND TEMPERATURE IN COOKING PROCESS
On Gross Distribution of Major Fraction
RESIDUALCOOKING LIQUOR-The changes in the appearance of the residual cooking liquors with the increase of the time and temperature of cooking have been noted under "Cooking Methods and Apparatus." The increase in turbidity, on cooling, with increasing time and temperature is
Per cent +0.29 +0.05 +0.05 +0.14 +0.27
% .of original
Grams 41.03 41.54 41.63 41.34 41.58
Grams 0.24 +0.27 +0.36 +0.07 +0.31
Per cent
99.41 100.65 100.87 100.17 100,75
Per cent
0.59 +0.65 +O.S7 + O . 17 i-0.75
DIGESTER CONDENSATE-This fraction, obtained on reducing the pressure in the autoclave by passing the steam and other condensable vapors through a condenser, showed little change in appearance, except that the color increased from almost colorless for the lower pressure cooks to a golden yellow for the high-pressure cooks. This color is due mainly to the presence of furfural. The condensate liquors of all the cooks were slightly acid to litmus. RESIDUALWoo-The appearance of the wood was not changed by cooking with water at atmospheric pressure, while a t the higher pressures the color and pliability of the residual wood were profoundly affected. The color deepened gradually from the gray-brown obtained from the 50-pound (148' C.), 2-hour cook to the dark brown of the 150-pound (186' C , ) , 12-hour cook. The pulp from the last-named cook was very soft, while that from the low-pressure cook was only a little more pliable than the wood from the normal pressure cooks. The yields of the residual wood from the various cooks are given in Table I11 and Figure 6. The change in pressure from atmospheric (100' C.) to 50 pounds (148" C.) caused a large drop in the yield of residual wood, while the subsequent increases in pressure show a more gradual decline in the quantity of residual wood obtained. The yield decreases more rapidly with increasing time at 50 and 150 pounds pressure (148" and 186" C . ) than at 100 pounds
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
March, 1930
Table IX-Effect of T i m e a n d Temperature on Distribution of Pentosans in Residual Wood a n d Aqueous Extract (All percentage on basis of 15.76 grams pentosans in original wood) . figures . PENTOSES AND PENTOSANS COOK TIME
TEMP.
PENTOSANS AQUEOUS
N I
I N WOOD
PENTOSANS
DECOMPOSED IX COOKING
EXTRACT
( C A L C D . AS PENTOSAXS)
Hours C. 2 100 4 100 8 100 12 100 24 100
%
%
Srams 15.20 15.18 15.12 14.95 14.88
96.45 96.32 95.94 94.86 94.42
Grams 0.19 0.22 0.32 0.34 0.40
1.21 1.40 2.03 2.16 2.54
Grams 0 37 0 36 0 32 0 47 0 54
2 1 3 5 8
13 14 15 16
2 4 8 12
170 170 170 170
9.13 13.25 15.59 17.26
1.01 2.52 4.24 6.47
50.06 77 60 87.37 87.31
20.62 20.53 21.52 23.90
8.73 9.02 10.16 17.35
17 20 18 19 21
2 4
186 186 186 186 186
17.15 17.82 22.61 22.49 23.83
4.83 1.85 3.99 4.12 0.59
85.34 92.45 93.27 95.11 95.30
23.40 25.43 33.26 32.99 37.42
14.23 21.71 47.15 35.16 45.51
18.34 19.67 31.85 35.79 29.38
3.00 3.57 3.83 5.78 6.92
19.04 22.65 24.30 36.68 43.91
13 14 15 16
2 4 8 12
170 170 170 170
2.75 1,9!3 1.67 1.40
17.45 12.63 10.60 8.88
5.12 1.54 0.32 0.60
32.49 9.77 2.03 3.81
7.89 12.23 13.77 13.76
50.06 77.60 87.37 87.31
17 20 18 19 21
2 4
186 186 186 186 186
1.56 0.88 0.75 0.46 0.21
9.90 5.58 4.76 2.92 1.33
0.75 0.31 0.31 0.31 0.53
4.76 1.97 1.97 1.97 3.36
13 45 14.57 14 70 14 99 15 02
85.34 92.45 93.27 95.11 95.30
of T i m e a n d Temperature on Distribution of Lignin in Residual Wood a n d in Aqueous Extract (All percentage figures on basis of 23.80 grams lignin in original wood)
Table X-Effect
COOK TIMET E M P .
LIGNINNOT
AQUEOUS
EXTRACT
LCCOUNTED FOR BY
-
ANALYSIS
%.of original Hours 6 2 7 4 4 8 2 12 3 24 2 2
C.
%
yo
100 100 100 100 100
Trams 23.22 23.30 23.15 22.91 23.05
97.56 97.90 97.39 96.53 96.86
Grams Trace, not Trace not Trace' not Trace: not Trace, not
19.29 19.06 18.50 18.02 17.79
81.05 80.08 77.73 75.71 74.75
4.16 4.31 4.90 5.42 5.04
17.48 18.11 20.59 22.77 21.18
a
weighed weighed weighed weighed weighed
% '
;rams 0 58 0 50 0 65 0 89 0 75
2 44 2.10 2.61 3 47 3 14
0 0 0 0
35 43 40 36 0 97
1.47 1.81 1.68 1.51 4.07
9 10 12 11
8 12
148 148 148 148 148
13 14 15 16
2 4 8 12
170 170 170 170
17.79 18.18 18.10 17.97
74.75 76.39 76.05 75.50
5.77 5.01 4.69 4.29
24.24 21.05 19.71 18.03
0 24 0 60 101 154
1.01 2.52 4.24 6.47
17 ~. 20 18 19 21
2 -
I_R_ R _
17.70 18.27 18.02 17.70 18.56
74.37 76.77 75.71 74.37 77.98
4.95 5.09 4.85 5.12 5.10
20.80 21.39 20.38 21.51 21.43
1 15 0 44 0 95 0 98 0 14
4 83 1.85 3 99 4.12 0.59
8
4
4 6'/2
8 12
186 186 186 186
Table XI-Relation between Benzene-Alcohol Extractives a n d Chlorine Consumption of Wood (All figures based on weiaht of wood used for analysis) ~ H L O R I N ECONSUMPTION IN
COOK
TIME
TEMP.
CELLULOSE DEID. ALCOHOL Total
8 9 10 12 11 13 14
16 l5
Chlorineforming HCI
100 100 100 100 100
I 2.66 1.80 1.84 1.87 1.47 1.50
26.15 26.49 26.23 25.33 24.38 25.42
16.19 16.53 16.53 16.28 16.03 16.81
2 2 4 8 12
148 148 148 148 148
2.65 3.32 4.37 5.94 6.07
22.77 22.12 20.40 18.92 20.80
15.39 15.36
2 4 8 12
170 170 170 170
8.82 10.69 11.52 10.93
20.09 19.52 19.01 19.32
13.25 12.09 11.57 11.81
186 186
11.48 14.32 14.07 14.04 13:71
18.39 17.31 19.20 18.31 20.46
11.49 11.48
Hours Original wood 6 2 7 4 4 8 2 12 3 24
17 20 18
2 4
21 l9
12
6'/1 8
e
C.
...
186
186 186
I _
%
7n 0.59
148 148 148 148 148
2.89 3.10 5.02 5.64 4.63
LIGNINI N
7" +0.29
2 2 4 8 12
62.63 57.68 43.84 27.54 26.71
I
9% ."
8 9 10 12 11
9.87 9.09 6.91 4.34 4.21
WOOD
% .2.44 2.10 2.61 3.47 3.14
a-CELLuLODE
35 28 03 98 43
148 148 148 148 148
LIGNINI N
9% .-
'::::-","O"s","-
None None $0.07 O,l5 +0.37
2 2 4 8 12
8 12
WOOD LIGNIN
C. 100 100 100 100 100
8 9 10 12 11
6'/2
COOKTIME TEMP. Hours 2 4 8 12 24
% 2 2 2 2 3
Table XII-Main Components of Wood Ap arently Destroyed in Cooking Process, Not Accounted For in )Ana&sia of Residual Wood a n d Cooking Liquors (All figures on basis of quantities of these components in original wood)
6 7 4 2 3
-
%.of Neight o ~ i $ , l Weight original
6 7 4 2 3
271
%
13:23 14.13
ii:is
13.07
61/2
8 12
23 78 34 57 24
1 1 1 1 4
47 81 68 51 07
2.35 2.28 2.03 2.98 3.43 19 22 24 36 43
04 65 30 68 91
I "
+0.05
$0.05 +0.14 $0.27 8 81
10 12 14 15
55 97 88 52
,I
+0.65
4-0.87 +0.17 +O 75 1 14
1 1 3 4
77 53 54 17
(170" C,). At 148" C. (50 pounds pressure) the drop in yield is greatest between 2 and 4 hours' cooking, while a t 186" C. (150 pounds) the largest decrease occurs between the 4- and &hour periods. The fact that the wood lost 39.31 per cent of its original weight (cook 21, Table 111) through cooking with water for 12 hours a t 150 pounds (186" C.) shows that the combination of water and high temperature has an enormous effect on the stability of the wood. It was impossible to make hand sheets from the residues of the 148" C. cooks, owing to the coarseness and porosity of the material. The sheets made from the remaining pressure cooks showed varying characteristics. Those from cooks 18, 19, and 21 (see tables for the cooking time and temperature) were very brittle and could be powdered with ease by rubbing them between the fingers. It is of interest to note in this connection that the yields of alpha-cellulose in the residual woods of these cooks (Figure 6) show a correspondingly larger drop than the yields of the cellulose. It was also noted, after screening the pulps, that the material from the above cooks had a more slimy feel-i. e., appeared to be more gelatinous-than the pulps from the other cooks. These facts show that hydrocellulose was formed at the expense of the alpha-cellulose in the high-pressure longtime cook8. On Components of Residual Cooking Liquors
TOTALDRY MAwER-The variation of the total dry matter with time and temperature is shown in Table IV and Figure 4. A large increase in the total solids of the pressure cooks above that of the normal pressure cooks is shown strikingly in Figure 4. This increase corresponds well with the decrease in the quantity of residual wood. The general trend of the curves shown for total dry matter in Figure 4 indicates that the soluble and easily hydrolyzed substances are removed from the wood a t 50 pounds (148" C.) and that these are decomposed slowly a t 100 pounds (170" C.), while a t 150 pounds (186" C.) some of the more resistant components of the wood are apparently broken down into water-soluble products. The high yield of total solids obtained by cooking for 2 hours a t 170" C. indicates that the maximum yield may be obtained by cooking a t this pressure for less than 2 hours. The quantity of the alcohol-soluble portion of the total dry matter is highest in cook 13, while the alcohol-insoluble portion has its peak in cook 10 (Table V). TOTAL SuGARsThe total sugars in the aqueous wood extracts follow the same trend as the total dry matter, as
INDUSTRIAL A X D EI1'GlNEERIh-G C H E M I S T R Y
272
shown in Figure 4. The actual weights are given in Table IV. The greatest difference between the total sugars and total solids is found in the cooks made a t 186' C. (150 pounds). I n this series the quantity of sugars decreased, while the dry matter increased slightly. The relation between the sugars of the alcohol-soluble and alcohol-insoluble fractions was about the same as that between the total solids of these
Vol. 22, No. 3
substances in the cooking liquor (Table VI and Figure 4) increased regularly with pressure. The increase with time was noticeable, but not marked. Phloroglucinol and hydrochloric acid produced no color change with these substances. The ether-soluble portion of the cooking liquor from the atmospheric cooks appeared to be softer and more oily than that obtained from the pressure cooks. On Components of Digester Condensate
The amounts of furfural found in the digester condensate are given in Table VI1 and Figure 5. I n the 50-pound (148" C.) cooks the quantity of furfural was small but increased rapidly with the time of cooking. It reached a maximum in the 100-pound (170" series a t 4 hours, A longer cooking period caused the destruction of some furfural. In the 150-pound (186" C.) cooks the highest furfuralyield was obtained in 2 hours, and longer periods destroyed this substance rapidly. Close examination of the curves in Figure 5 reveals that the furfural and pentosans are inversely related, especially in the 50- and 100-pound (148' and 170" C.) series. These curves show that, except when the temperature was high enough to decompose the furfural, the latter was formed a t the expense of the pentosans. The volatile acids in the liquor and digester condensate of the pressure cooks increased with time in the 50-pound (148" C.) series. (Table VI1 and Figure 5) The quantity of acids remained fairly constant throughout the 100-pound (170' C.) series. I n the 150-pound (186" C.) cooks the acids rose to a maximum and then decreased, indicating a probable decomposition. No attempt was made to determine the distribution of the volatile acids between the residual cooking liquor and the digester condensate.
e.)
0
4
8
1 2 0 4 8 1 2 0 4 8 1 2 TIME ,n HOURS, Figure 4-Weights of Substances Found i n Aqueous Wood Extracts
portions. The maximum yield of total sugars appeared to be produced b y cooking the wood with water between 4 and 8 hours a t 148" C. The highest quantity of actual reducing sugars may be obtained in less than 2 hours a t 100 pounds (148' C.). The sugars were more drastically decomposed, with increase in the time of cooking, than were the total solids. This was especially true in the 100-pound (148' C.) series of cooks. PENTOSES AND PENTOSANS-The curves for the pentoses and pentosans (calculated together as pentosans) are nearly identical in shape with those for total sugars. These curves are shown in Figure 5, and the data are given in Table V. The similarity of the curves for total dry matter, total sugars, and pentosans points to the fact that the other constituents of the total solids are relatively stable and are not much affected by the increase in the time and temperature of cooking. The pentosans appear to be more easily decomposed by the increase in time than any of the other constituents of the dry matter. It can be seen in Table V that large increases in the pentoses of the alcohol-soluble portions are generally accompanied by a decrease in the pentosans of the alcohol-insoluble fractions. The increase in the total pentosans between the 8- and 12-hour cooks of the 100and 150-pound (170' and 186" C.) series is very small, and so it may be attributed in part to experimental error. LIGNIN-The data and curves for the quantity of lignin (as determined by the 72 per cent sulfuric acid method) in the various wood extracts are shown in Table VI and Figure 4, respectively. The amounts of lignin obtained from the liquors of the atmospheric pressure cooks were so small that no quantitative determination was made. The quantity of lignin (or depolymerized lignin?) extracted by the water in the pressure cooks appears to be fairly constant irrespective of the pressure and duration of cooking. Some of this lignin, finely ground, was placed in a fritted-glass crucible and chlorinated and then washed with water, and treated with sulfurous acid and sodium sulfite. The beet-red lignin color was obtained a t once. The non-chlorinated product gave a very light red color with sodium sulfite only after a few hours' standing. ETHERExTmcmvEs-The quantity of ether-soluble
Figure 5-Weights of Pentoses and Pentosans (Calculated Together a s Pentosans) Found in Aqueous Wood Extracts, and Furfural and Volatile Acids (as Acetic Acid) i n Digester Condensate
On Components of Residual Wood
CELLuLosE-The weight of the cellulose in the residua! wood of the various cooks is given in Table VI11 and Figure 6. Cooking a t atmospheric pressure did not affect the cellulose. At 50 pounds (148' C.) there was a gradual decrease in the amount of cellulose with the increasing time of cooking, starting with a drop of 10.5 per cent a t 2 hours and ending with a loss of 15.5per cent a t 12 hours. The loss of cellulose in the 100-pound (170' C.) series of cooks waa more gradual. The rate of destruction of the cellulose was greatest in t h e
I?iDUXTRIAL AND ENGIAVEERIA'G CHEMISTRY
March, 1930
1,iO-pound (186" C.) series. Although part of this loss can probably be attributed to pentosans which are intimately associated with the cellulose, the largest portion is most likely decomposed to gaseous products and water. This is especially true of the cooks run a t 170' and 186' C., where the pentosans in the residual wood were very low. .iLPHA-CELLnLosE--Table VI11 and Figure 6 show that no alpha-cellulose was destroyed in cooking a t atmospheric pressure, and very little was destroyed a t 141" C. The alpha-cellulose from the residual mood of the 100-pound (170" C.) cooks showed a slight progressive decrease up t o 8 hours, with a greater loss between 8 and 12 hours of cooking;. The rate of destruction of the alpha-cellulose speeded up considerably in the 150-pound (186' C.) series of cooks. The relation between the cellulose and alpha-cellulose content of the residual wood is very well shown in Figures 6 and 7. Larger quantities of beta-cellulose were formed
G
4
8
Figure 6-Weights
8 TIME
/Z
4 8 12 4 8 /Z HOOKS of Various Components Found in Residual Wood a f t e r Cooking
/Z
4
,n
when the rate of decrease of the alpha-cellulose exceeded that of the cellulose. This was indicated in the difficulty of separating by ordinary filtration the alpha- from the betaand gamma-celluloses of the 150-pound (186' C.) cooks, due to the fact that celluloses containing a large quantity of beta-cellulose became jelly-like when treated with 17.5 per cent sodium hydroxide. It is shown in Table VI11 that as much as 45.5 per cent of the original alpha-cellulose was destroyed or altered, while the cellulose proper suffered a loss of 37.4 per cent. The low alpha-cellulose content of the residual wood from cook 18 is probably due to the increase in the ratio of wood to water caused by a steam leak in the cover of the autoclave. PExTosaNs-The pentosans of the residual wood were reduced very rapidly with increasing time and pressure. (Table I X and Figures 6 and 7) Cooking a t atmospheric pressure caused relatively little decomposition of the pentosans. However, there was a destruction of the pentosans in the 50-pound (148" C.) series, the residual mood from cook 11 showing a reduction of 73.3 per cent. I n the 12-hour, 150-pound (186" C.) cook only 1.3 per cent of the original pentosans remained in the residual wood. It appears that cooking wood with water is a more drastic treatment, in so far as its effect on the pentosans is concerned, than is the treatment with chlorine in the isolation of cellulose, for in the latter process a relatively large quantity of pentosans remains closely associated with the resulting cellulose. LIGNIN-Liccordin& to Table X the lignin, as determined
273
by the 72 per cent sulfuric acid method, shows practically no change with increasing time and pressure. Moreover, the sum of the lignin in the residual wood and the cooking liquor is practically equal to the amount in the original wood, indicating that the lignin was not destroyed in the cooking process. The data are shown graphically in Figures 6 and 7 . However, it was noticed in the cellulose determination that the quantity of materials extracted from the residual wood with the benzene-alcohol solution increased rather rapidly with temperature in the higher pressure cooks. The amounts extracted from the wood cooked at atmospheric pressure were lower than that removed from the original wood, probably because the boiling had removed some of the benzene-alcohol-soluble substances. (Table XI) This increase in the extractives of the wood from the pressure cooks was accompanied by a decrease in the quantity of chlorine necessary for the isolation of cellulose. Since the quantity of lignin remained fairly constant throughout the cooking process, it was thought that the benzene-alcohol extractives rnight be composed of lignin or its decomposition products, which were insoluble in water but readily dissolved or peptized by the extracting solution. In order to test this hypothesis, the residual wood from cook 20 was extracted with the benzene-alcohol solution, and the lignin in the extracted wood was determined in the usual way. The lignin content of the unextracted residual wood was 29.95 per cent, whereas after extraction it was only 16.54 per cent, a decrease of 13.41 per cent which was essentially equivalent to the 14.32 per cent of benzenealcohol extractives removed from the wood by the extraction procedure. This experiment substantiates the idea that the extract was composed mainly of lignin or lignin decomposition products. Lignin from the original wood was not very soluble in alcohol, so the substances in the extract were, presumably, depolymerized products of lignin. The extract residue, obtained on evaporation of the alcohol and benzene, mas easily soluble in alcohol and glacial acetic acid, but its solubility in ether and benzene was very slight. This residue dried to a dark, shiny, brittle substance, resembling the material found on hydrolysis of the aqueous wood extracts. This latter material was soluble in the same solvents as the alcohol extract, forming almost identical deep-red solutions. Addition of distilled water to the alcohol solutions resulted in the formation of a sol, red and clear to transmitted light and brown and opaque to reflected light. A voluminous, flocculent, light tan precipitate was formed when water was added to the glacial acetic acid solutions. This precipitate, after centrifuging and washing free from acid, gave acid numbers (milligrams of potassium hydroxide necessary to neutralize one gram of sample), in alcoholic solution, of 113 and 154.5 for the substances obtained from the acid hydrolysis and benzene-alcohol extract, respectively, indicating that the substances are very likely acidic in nature. On Gases Evolved in Cooking
The inability to account for 100 per cent of the wood by analysis, and the excess pressure in the autoclave above that required for the observed temperature, point to the fact that non-condensable gaseous substances were formed in the cooking process. A study of this phase of the problem was not undertaken, however, because the autoclave was not equipped for quantitative work of this type, and it was not felt that the results of such a study would be commensurate with the labor involved. General Findings The quantity of material present in the aqueous extract increased at first and then decreased with the increased time
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and temperature of cooking; and the same was true of the furfural in the digester condensate. The volatile acids increctsed rather regularly throughout the series. The quantity of residual wood and all of its major constituents except lignin decreased with an increase in time and temperature of cooking. The summarized data of the destruction of the components of the residual wood are given in Table XI1 and Figure 7. It was thought that perhaps the destruction of the wood and the formation of furfural were brought about by acids formed during the cooking process-i. e., that the cooking agent may have been a dilute solution of organic acids rather than only water. In order to prove definitely whether or not the results were produced by cooking with an acid liquid, two cooks were run at 150 pounds (186” C.) for a 2-hour period, 5 grams of precipitated calcium carbonate being added to one of these charges. A considerable quantity of the original calcium carbonate still remained in the auto-
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in time and temperature to 61 per cent of the original wood in the 12-hour, 150-pound (186’ C.) cook. 7-The cellulose in the residual wood decreased progressively with increased time and temperature to 63 per cent of the original cellulose in the 12-hour, 150-pound (186’ C.) cook. 8-The alpha-cellulose decreased a t the higher pressures a t a greater rate than did the total cellulose, indicating that hydrocellulose was formed. The 12-hour, 150-pound (186O C.) cooks showed a destruction of 45.5 per cent of the alphacellulose originally present in the wood. 9-The pentosans in the residual wood decreased progessively with time and pressure, so that only 1.3 per cent of the amount present in the original wood remained after cooking for 12 hours a t 150 pounds pressure (186’ 10-The total quantity of lignin (as determined by the 72 per cent sulfuric acid method) in the wood remained practically constant, but it was found that a part of the lignin was altered so as to be soluble (peptized ?) in alcohol. This is probably due to depolymerization. 11-It was shown, by adding calcium carbonate to the autoclave charge, that the yield of total solids in the extract and of furfural in the digester condensate, in cooking for 2 hours a t 150 pounds (186’ C.), was not due to the action of acids formed in the process but only to water per se and to temperature.
e.),
Literature Cited
0
4
a i z
Figure 7-Percentage
a
4 8 I2 0 4 8 1 2 1 2 TlUEm HOURS, of Components of Uncooked W o o d Destroyed in Cooking Process
0
4
8
clave a t the end of the cooking period. The yields of residual wood, of total dry matter in the extract, and of furfural in the digester condensate were essentially the same in both cooks, so that the changes noted in the earlier tables were not brought about by cooking with an acid liquor but were due to the effect of water per se. SUMMARY OF RESULTS
(1) Bergius, NalurlL’issenschaften,16, 1 (1928). ( 2 , Bergstrom, Papier-Fabr., 8, 506, 736 (1910); cited from Schorger. “Chemistry of Cellulose and Wood, p. 362, McGraw-Hill, 1926. (3) Bergstrom, Ibid., 11, 305 (1913); cited from C. A . , 7, 2854 (1913). (4) Berl and Schmidt, Ann., 461, 192 (1928). (5) Bray, Paper Trade J . , 87, No. 25, 59 (1928). (6) Brewster, I N D .ENG.CHEM.,16, 139 (1923). (7) Franck, Pagier-Fabr., 17, 1019 (1919). (8) Fromherz. 2. physiol. Chem., 60, 209 (1906). (9) Grafe, V., Monatih., 26, 987 (1904). (IO) Haas and Hill, “Chemistry of Plant Products,” Vol. I, p. 196,Longmans, 1921. (11) Heuser, 2. angew. Chem., 27, 654 (1914). (12) Heuser, Chem.-Ztg., SS, 126 (1914). (13) Hoppe-Seyler, Ber., 4, 15 (1871). (14) Hoppe-Seyler, 2. physiof. Chem., 18, 66 (1889). (15) Koch, Dissertation Freiburg, 1909. (16) Konig and Sutthoff, Landw. Vers. Sta., 70, 343 (1909). (17) Morrow, “Biochemical Laboratory Methods,” p. 199, Wiley, 1927. (18) Munk, Z . physiol. Chem., 1, 357 (1878). (19) Pervier and Gortner, IND. END.CHRM.16, 1167 (1923). (20) Potter, A n n . Botany, 18, 121 (1904). Chem. I n d . , I S , 35T (1924). (21) Powell and Whittaker, J . SOC. Ann. Missouri Bolan. Gardens, 6, 93 (1919). (22) Schmitz, H., (23) Schorger, IND.ENO.CHSM.,16, 812 (1923). (24) Schorger, “Chemistry of Cellulose and Wood,” McGraw-Hill, 1926. (25) Schwalhe and Robinoff, 2. angew. Chem., 24, 256 (1911). (26) Sherrard and Blanco, IND. END.CHSM.,16, 611 (1923). (27) Singer, S i h b . ARad. Wiss. Wien, 86 (Abt. I), 345 (1882). (28) Spaulding, 17th Annual Report of Missouri Botanical Gardens, p.
1-The maximum yield of total solids in the cooking liquor was 19.9 per cent of the original weight of the wood obtained in a 2-hour cook at 100 pounds pressure (170’ C.). 2-The sugars, pentoses, and pentosans (furfural-yield41 (1906). ing compounds) in the liquor reached a maximum in the (29) Stein, Magyar Chem. Foly6iral, 6 , 39; cited from Chem. Zentr., 72 2-hour cook a t 100 pounds pressure (170” C.) for the sugars, (11). 950 (1901). and in 8 hours at 50 pounds pressure (148’ C.) for the pento- (30) Suminokura and Nakahara, “New Colorimetric Microdetermination of Furfural,” Trans. Toltori Soc. Agr. Sci. (Japan). 1, 158 (1928). sans, and then decreased, showing that these substances (31) Tauss, Dinglers polytech. J., 973, 276 (1889). were decomposed with increasing time and temperature of (32) Vickers, Ltd., and Lucas, British Patent 298,800 (November 29,1927); cooking. cited from C. A , , 2S, 3098 (1929). 3-Lignin (as determined by the 72 per cent sulfuric acid (33) Wichelhaus and Lange, Ber., 49, 2001 (1916). method) dissolved (depolymerization ?) to a small extent (34) Willaman and Davison, J . Agr. Research, 28, 479 (1924). (35) Williams, Greville, Chem. News, 26, 231, 293 (1872). in the water. (36) Zacharias, J . SOC.Chem. I n d . , S1, 582 (1912). &Furfural, formed in the cooking process, reached a maximum in the 2-hour cook a t 150 pounds pressure (186’ C.), and then gradually decreased with increase in time and Little danger of carbon monoxide poisoning was found to exist temperature. in multi-story garages in experimentsconducted by W. C. Randall &-A small amount of volatile acids w&sformed in the cook- and L. W. Leonhard, Detroit engineers. The greatest concening process. tration of the gas found in large garages during many tests is +The yields of residual wood decreased with increase only sufficient to cause attendants to have headaches.
