THE COOKING PROCESS X. Pulping W o o d with Alcoholic Nitric Acid Solutions' S. I. ARONOVSKY* AND ROSS AIKEN GORTNER Minnesota Agricultural Experiment S t a t i o n , St. Paul, Minn.
hama, Onishi, and Takemura (3, 4), Lynch and Goss (IO), and Payne (11) showed that yields of 35-40 per cent of high a-cellulose pulp, with low copper numbers and ash contents, could be obtained from sugar cane bagasse by the nitric acid process. Relatively high yields of good pulp were obtained from cornstalks by Horvjth and fiber (6) and Suida, Sadler, and Noss (18, 19). Suida and Sadler (17) and Shimoda (16) obtained good pulp by cooking cereal straws with nitric acid. The effects of this acid on woods were studied by Routala and Sev6n ( I d ) , Schaarschmidt and Nowak ( I S ) , Shimoda ( I d ) , Solechnik ( I @ , and Suida and Sadler (17). They obtained 40-50 per cent yields of pulps with low copper numbers and ash contents and high a-cellulose contents. These pulping experiments were carried out by steeping the raw material in aqueous nitric acid solutions of various concentrations and temperatures for definite time intervals, and then heating t h e resultant product in hot alkalies. An analytical method for the determination of the cellulose content of fibrous plant material was recently given by Kurschner and Hoffer (9). This method consists of repeated extraction of the plant material with a solution of nitric acid in ethanol. Aronovsky and Gortner (1) and Kleinert and Tayenthal (7) showed that fairly high yields of good pulp could be obtained by using alcohols as the pulping agents. It was therefore thought t h a t high yields of pulp with desirable properties might be obtained by using a combination of these methods-i. e., treatment of the fibrous raw material with alcoholic nitric acid followed by extraction with dilute alkalies.
A series of cooks was made on aspen and jack pine sawdust and chips by refluxing with aqueous and alcoholic (ethyl and nbutyl) solutions of nitric acid, followed by boiling the acid-treated wood with dilute sodium hydroxide solutions. The concentrations of the acid and alkali as well as the duration of the treatment were varied. A number of cooks were also run with mixtures of aqueous and alcoholic nitric acid and with alcoholic solutions of sulfur dioxide and lithium bisulfite. The alcoholic nitric acid solutions gave much higher yields of good pulp than were obtained with the aqueous acid under similar pulping conditions. Increasing the concentration of the acid resulted in lower total yields but gave larger yields of screened pulp. Dilution of the alcoholic solutions with water had but little effect on the yields of pulp. Jack pine did not pulp as readily as the aspen. Soda ash was not as efficient as sodium hydroxide in removing the compounds formed by the action of nitric acid o n wood. Sulfur dioxide and bisulfites in alcohol were not efficient pulping agents.
Experimental Procedure
T
Aspen and jack pine wood, both in chip and sawdust form, were used in these experiments. Ethyl and n-butyl alcohols and c. P. nitric acid and sodium hydroxide were used as the pulping agents. A number of cooks were made on jack pine wood in which sulfur dioxide and lithium bisulfite were used in place of the nitric acid as pulping agents. The procedure was as follows:
1 Previous papers in this series appeared in INDUSTRIAL AND ENGINEERINQ CHEMISTRY in 1930, 1933, 1934, 1935, and 1936. 2 Present address, Agricultural By-products Laboratory, Industrial Farm Products Research Division, Bureau of Chemistry and Soils, U. S. Department of Agriculture, Ames, Iowa.
The wood (50 grams) and the liquor were placed in a 1-liter Erlenmeyer flask and boiled gently under reflux. The concentration of acid, volume of liquor, and time of refluxing were varied. After the desired boiling period had elapsed, the contents of the flask were poured into a large Buchner funnel fitted with a filter paper, and the excess liquor was removed by suction. The residue in the funnel was washed three or four times with 800-cc. portions of water and then replaced in the flask, covered with water, and allowed to stand overnight. The water was then decanted from the residual wood, a dilute solution of sodium hydroxide was added, and the mixture was again boiled under reflux, varying the volume and concentration of the sodium hydroxide solution and the time of boiling. The contents of the flask were then poured into a set of laboratory screens (top screen, 0.065-inch or 1.65-mm. openings; bottom screen, Four-
IIE use of nitric acid as a pulping agent has received considerable attention in recent years. Although the pulping qualities of this acid were known as early as 1861 (2) and possibly earlier, its high cost prevented it from competing with the common cheap pulping agents used in the sulfite, soda, and kraft processes. The present relatively low cost of nitric acid and the search for a n efficient, economical method of pulping fibrous plant material other than wood are probably the main reasons for the revival of this pulping method. Brief reviews of recent research and patent literature on this process were given by Klein (6) and K'rais (8). Hachi-
1431
1432
INDUSTRIAL AND ENGINEERING CHEMISTRY
Concenfrutioion of N/tvicAcid- Mume Percent FIGURE 1. EFFECT OB NITRIC ACID CONCENTRATION ON YIELDSOF TOTAL AND SCREENED PULP
drinier wire) where the residue was washed and screened, if possible, to separate the pulp from the unpulped portion. The Pulps and UnPdPed Portions were then dried to constant weight in order to determine the yields obtained under the various experimental conditions. The data obtained are given in Tables I and 11and Figures 1 to 4.
Aspen The first striking feature of the results on aspen (Table I> can be seen by comparing the yields obtained with ethanol and water, the other conditions remaining constant. This is shown particularly by cooks 154 and 156. The yield obtained by using alcoholic nitric acid was 1.7 times that produced by the aqueous nitric acid liquor. This result may be due to the action of the alcohol in hindering the hydrolytic effects of the acid upon the cellulosic constituents of the wood. When water was used in these cooks, the brown fumes of nitric oxide were given off from the top of the reflux condenser, indicating decomposition of the nitric acid. This effect was not noticed when alcoholic nitric acid was used as the cooking agent. As shown in Figure 1and by cooks 159 and 163 (Table I), the concentration of nitric acid in the liquor, whether water or ethanol, should be greater than 2 volume per cent in order to obtain pulped material. This may not hold true under conditions of cooking other than t h o s e e m p l o y e d here. In the experiments conducted on aspen sawdust, the concentration of nitric acid was kept constant at 3 volume per cent. The total volume of liquor used was varied in cooks 170 to 177 (Table I), thus varying the actual quantities of nitric acid present in these cooks. The results show that the yields of screened pulp decreased and the screenings and total yields increased with the decrease in quantities of nitric acid and the ratios of total liquor to wood. This effect was more noticeable with alcohol than with water
VOL. 29, NO. 12
(Figure 2). Apparently the nitric acid delignifies the wood more readily in aqueous than in alcoholic solution, but the degradation of cellulose also takes place to a greater extent in water. Considerably lower yields were obtained with sawdust than with chips. This may have been due to the greater ease of impregnation 60 and consequently more drastic cooking of the sawdust, under similar cooking conditions. The use of mixtures of water and ethanol gave r e s u l t s i n t e r mediate between those obtained with aqueous and with a l c o h o l i c 8 nitric acid solutions, as shown in Table I and Figure 3. Eighty per \r, cent ethanol and 20 per cent water gave nearly the same yield as was g obtained with 100 per cent (cook 170)* t o Wood - cc./gFam The substitution Of 2o FIGURE 2. EFFECT OF RATIOOF per cent of the water by TOTAL LIQUOR TO WOOD ON YIELDS ethanol (cook 181)gave OF TOTAL AKD SCREENED PULP a considerably larger yield than was obtained with 100 per cent water (cook 174), thus indicating that a relatively small amount of alcohol tends to inhibit the degrading effect of nitric acid on the cellulose. It was also noticed in these four cooks that no nitric oxide fumes were formed during the refluxing. Using aqueous nitric acid solutions, varying the time of refluxing with these liquors, and keeping the other cooking conditions constant, the yields tended to decrease with increas-
T A B LI.~ COOKING DATAAND YIELDSOF PULP OBTAINEDFROM ASPEN -Acid
Vol.
Cook
No.
Treatment-
Liquor
"Os Vol. %
155 158 159 160
161
156 167
153 162 163 164 165 154 170 171 172 173 174 175 176 177 178 179 180 181 184 186 186 187 188 189 190 191
HnO
Total vol. Cc.
None 750 750 1 2 750 3 750 4 750 5 750 Undiluted spent liquor from cook 156 Ethanol Xone 750 Ethanol 1 750 Ethanol 2 750 Ethanol 3 750 Ethanol 4 750 Ethanol 5 750
HzO HzO Ha0 Hz0 HzO
7 750 7 750 7 750 7 750 7 750 7 750 Aspen Sawdust 750 7 600 500 7 600 400 7 600 300 7 600 750 7 600 500 7 600 400 7 600 300 7 600 750 7 600 750 7 600 750 7 600 750 7 600 750 1 600 750 2 600 750 4 600 750 6 600 750 2 600 750 2 600 750 2 600 750 2 600
3 3 3 3 Hz0 3 Hg0 3 HzO 3 nzo 3 8A-2Wb 3 6A-4W 3 4A-6W 3 28-8W 3 nso 3 HzO 3 3 Hs0 Ha0 3 HzO 3 Ha0 3 HzO 3 Hz0 3 oven-dried wood. On b A = parts alcohol; T ! = parts water.
~
Ethanol Ethanol Ethanol Ethanol
-Alkaline-. Treatment pulp Yieldsa---.. Time Time Unpulped of.bol1- Vol. 2 9 of Screened wood or ins NnOIf) boiling pulp soreenings Hr. Cc. Hr. % % Aspen Chips 7 750 6 .. 79 2 7 750 6 58.1 7 750 6 56.6 7 760 6 3i.4 2 2 7 750 6 30.8 0.7 7 750 6 28 9 7 750 6 21 7 lQ:?
..
6 6 6 6 6 6
6
6 6 6 6 6 6 6
6 6 6 6 6 6 6 6 1 2 3 4
.. ,.
41:6 43.8 45 1 39.6 37 0 33 0 30 8 25.0 28 6 28.6 26 6 38.2 34 0 36 0 31 6 28.6 27.6 28 4 26 8 32.0 30 0 27.8 30.2
82.0 75 3 66 2 12 0 6 1 4 8
0'6 16.4 22.0
i'6 2.4 2 8 0 6 0.6 0.4 10 12 0.4 0 4 014 0.4 0.4 0.4
Total
% 79 2 58.1 56 6 33 6 31 5 28 9 41 4 82 75 66 63 49 49
0 3 2 6 9 9
39.6 43 6 49 4 52 8 25 0 30 2 31 0 29 4 38 8 34 6 36 4 32.6 29 8 28 0 28 8 26 8 32 4 30 4 28 2 80 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
DECEMBER, 1937
TABLE 11.
1433
COOKING DATA AND YIELDS OF P U L P OBT.4INED FROM JACK P I X E P u l p Yield@Unpulped wood or screenmgs
c -
Acid T i e a t m e n t Total HNOa vol.
7
Cook
Liquor
NO.
Vol. %
cc.
7 -
T i m e of boiling
Alkali
HT
Alkaline T r e a t m e n t Concn.
Volume
%
Cc
301 302 303 304 305 306 307 308 309 310 329 330 331 332
H20 Ethanol Ethanol %-Butanol %-Butanol Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol
4 4 4 4 4 4 3 4 5 6 3 3 6 6
500 500 500 500 500 500 500 500 500 500 750 750 750 750
2 4 2 4 2 2 6 6 6 6 7 7 6 6
Jack Pine Chips NaOH 4 NaOH 2 NaOH 4 NaOH 2 NaOH 2 NaOH 2 NeOH 2 NaOH 2 NaOH 2 NaOH‘ 2 NaOH 2 Na2COa 2.65 NaOH 2 Na2C03 2.65
323 324 325 326 327 328
Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol
3 4 5 6 3 3
500 500 500 500 750 750
6 6 6 6 7 7
J a c k Pine Sawdust NaOH 2 NaOH 2 NaOH 2 NaOH 2 NaOH 2 NanCOa 2 65
a
Hz0
.
500 500 500 500 500 500 500 500 500 500 750 750 750 750 500 500 500 500 600 600
T i m e of boiling
Screened pulp
Hr.
%
2 2 2 2 2 2 5
25.6 16.8
3:0 5.8 4.4 2.4 5.6 29.6 38.6 6.4 2.8 34.0 33.2
5 5 5 6 6 5 5 5 5
5 6
44 4 43 4
6 6
’
%
Total
% 8 6 2 8 8 0 6 2 8 0 6 2 2 2
15.2 23.8 73.2 64.8 66.0 67.6 68.2 59.6 26.2 11.4 58.2 71.4 19.2 29.0
40 40 73 67 71 72 70 65 55 50 64 74 53 62
66.0 58.4 3.8 0.8 58 2 69 4
65.0 58 4 48 2 44 2 58 2 69 4
On basis of oven-dried wood.
Cook “0s “ 0 3 “03 ing time of boiling but the differences so obtained were very No. Added Recovered Consumed slight. These data are given by cooks 184 to 187 (Table I ) % % % and Figure 4. I n cooks 188 t o 191 the conditions of acid 184 42.4 33.4 9.0 185 42.4 29.6 ’ 12.8 treatment were held constant while the time of boiling with ’ 27.0 15.4 186 42.4 187 42.4 23 6 18 8 alkali was varied. The results showed that there was a slight decrease in yield with increasing time of alkali treatment The amounts of nitric acid recovered, on the basis of thg (Figure4). These data seem to show that, under the conoriginal nitric acid used, were approximately 79, 70, 64, and ditions used in these experiments, it is possible to obtain a 57 per cent for cooks 184, 185, 186, and 187, respectively, good pulp of fair yield by refluxing for 1 to 2 hours with 3 decreasing with the increased duration of the cooking period. volume per cent aqueous nitric acid solution, followed by Although t h e percentage recovery of acid in cook 184 can be a 1-hour treatment with 1.5 t o 2 per cent sodium hydroxide considered fairly good, it must be pointed out that these solution. The pulps obtained with aqueous nitric acid solutions were very light in color, approximating that of sulfite pulp; the X - Nitric Acid Treatment alcohol-treated woods yielded pulps which were only slightly darker. After the acid treatment the residual woods mere orange to orange-red in color; the residual liquors were orange-red to red. The residual alkali liquors were black in bulk. The screenings were dark brown and generally fairly soft, although some hard cores were found occasionally. It was noticed, in boiling with the alkali solution, that the liquor foamed profusely. Time o f Boir’ing -Hours
1
1
FIGURE 4. EFFECTOF DURATION OF ACID AND ALKALINE TREATMENTS ON YIELDSOF TOTAL AND SCREENED PULP
’‘/O
results were obtained by titration of the residual liquors and wash liquors with standard alkali; and any other acids, such as acetic, formic, and oxalic, formed by t h e oxidizing action of the nitric acid on the wood, would be calculated in this manner as nitric acid.
I 80
0
60
40
20
0 Alcohol
20 40 60 80 /OOWater Composition o f Pulping Liquor-Per t e n t
FIGURE 3. EFFECTOF DILUTING ALCOHOLIC NITRICACID WITH WATERON YIELDSOF TOTAL AND SCREENED PULP
That the nitric acid is not completely used up in this cooking process is shown in the case of cook 157, in which the undiluted residual liquor of cook 156 was used as the cooking agent. A check on the nitric acid consumption, based on the oven-dry weight of the original wood, was attempted in cooks 184 t o 187:
Jack Pine The data on pulping jack pine wood are given in Table, 11. These results indicate that, in order t o obtain a pulp fr6m jack pine under the conditions used in these experiments, the concentration of nitric acid, whether in alcoholic or aqueous solution, should be a t least 6 volume per cent. Increasing the concentration of the acid resulted in increased yields of screened pulp and decreased total yields, similar to the results obtained with aspen. n-Butanol-nitric acid mixtures and ethanol-nitric acid solutions had approximately equal effects on the yields of pulp. Lower total yields but higher yieldsaf
screened pulp were obtained from jack pine sawdust than from the chips. It is apparent from these data that jack pine is not pulped as readi1y.m is aspen by the nitric acid process. The substitution of sodium carbonate for the sodium hydroxide in the alkaline treatment had a deleterious effect on the resultant pulps, as shown in Table 11. Apparently the reaction products from the action of alcoholic nitric acid on wood are not as soluble in sodium carbonate as in the sodium hydroxide solution. When sulfur dioxide and lithium bisulfite were substituted for the nitric acid in both ethyl and n-butyl alcohols, no pulped residues were obtained after the sodium hydroxide treatment. This indicates that the nitric acid acts as an oxidizing rather than as a hydrolyzing agent.
Literature Cited (1)
VOL. 29, NO. 12
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1434
(5) Horvhth, E., and fiber, G., Cellulosechem., 12, 85 (1931). (6) Klein, A. S., Papier-Fabr., 27, 325 (1929). (7) Kleinert, T., and Tayenthal, K., 2. angew. Chem., 44, 788 (1931). (8) Krais, P., Papier-Fabr., 29, Fest- u. Auslands-Heft, 71 (1931). (9) Kiirschner, K., and Hoffer, A., Tech. Chem. Papier u. ZellstofFabr., 26, 125 (1929); Chem.-Ztg., 55, 161, 182 (1931). (10) Lynch, D. F. J., and Goss, M. J., IND.ENQ.CHEM., 24, 1249 (1932). (11) Payne, J. H., Ibid., 26, 1339 (1934). (12) Routala, O., and Sev6n, J . , Cellulosechem., 7, 113 (1926). (13) Schaarschmidt,A., and Nowak, P., Ibid., 13, 143 (1932). (14) Shimoda, I., Cellulose Ind., 12, 13 (1936). (15) Ibid., 12, 71 (1936). (16) Solechnik, N. Y., Bumazhnaua Prom., 14, No. 4, 30 (1935).
(17) Suida, H., and Sadler, H., Papier-Fabr., 25, Fest- u. AuslandsHeft. 93 (1927). (18) Suide, H., Sadler, H., and Noss, F., Ibid., 27, Fest- u. AuslandsHeft, 71 (1929). (19) Ibid., 28, 363 (1930).
Aronovsky, S.I., and Gortner, R. A., IND.ENQ.CHEM., 28, 1270
(1936). (2) B a d , E. H., and Blondel, C. M. J., British Patent 391 (Feb. 16, 1861). (3) Hachihama, H., Onishi, M., and Takemura, W., J . SOC.Chem. Ind., Japan, 38, suppl. binding, 690 (1935). (4) Ibiu., 39, suppl. binding, 239 (1936).
RECEIVED August 12, 1937. Presented before the Division of Cellulose Chemistry at the 94th Meeting of the American Chemioal Society, Rochester, N. Y . . September 6 to 10, 1937. Paper No. 1528, Journal Series, Minnesota Agricultural Experiment Station. S. I. Aronovsky was Cloquet Wood Products Fellow, Vniversity of Minnesota; the fellowship was established by the Northwest Paper Company of Cloquet, Minn.
Calculation of the N u m b e r of Theoretical Plates for a Rectifying Column BARNETT F. DODGE Yale University, New Haven, Conn.,
JOHN R. HUFFMAN‘ Columbia University, New York, N. Y.
T
HE usual means of estimating the number of theoreti-
cal plates for a given separation of two liquids is the McCabe-Thiele graphical method. When the number of plates is very large, as is the case with certain hydrocarbon separations and especially with isotopes, this method is tedious and a p t to be inaccurate if carried out with the usual, smallscale diagram. The purpose of this paper is to call attention to the method proposed by Lewis (S) some years ago which has been completely supplanted by the later method of but which has distinct advantages in McCabe and Thiele (4, the case of a large number of plates. This method was given in the first edition of Walker, Lewis, and McAdams’ book (7) but was omitted from the second. The usual material balance on a rectifying column, coupled with the assumption of constant heat content of the vapor and liquid streams throughout the column, leads to the following equation for rectification above the feed level:
Y,
+ jj 1
xn+l
(%e
- yn)
1 Present address, Department of Chemical Engineering, New York University, University Heights, New York, N. Y.
Subtracting xn from both sides, xn+ 1
- x,
=
yn
- x*
-
B1
(2,
- Yn)
(2)
x n + l - xn is the enrichment per plate and may be written Ax/ An. When the number of steps is large, Ax/An = dx/dn very closely. Finally we may write : dn
z=
~n
- xn
1 - B1
(2,
-~
n )
(3)
Similarly for the section below the feed level: dm dy =
Ym
- Xm
1 -+P0 (Ym -F F __
- 2),
(4)
Equations 3 and 4 can be rearranged to 5 and 6, respectively: An =
lxc lxfYn
dX 1
- xn. - E
(2,
(5)
- Yn)
dx
Am =
- zn
~ r n
- FF~- P
- xw)
( ~ m
(6)
I n the originaI application of these equations, as given by Lewis (S), and in the text by Walker, Lewis, and McAdams (‘ithey ‘),were integrated graphically; but in the case of an
