INDUSTRIAL AND ENGINEERING CHEMISTRY
678 100
Vol. 33, No. 5
The thermal conductivities a t 32” F. of mixtures of hydrogen and carbon dioxide, hydrogen and nitrous oxide, and hydrogen and nitrogen are related to the percentage of hydrogen, 2, by the expression, look+-
where b and c depend upon the components. The equation was developed in connection with Figure 4, where the broken line indicates that a mixture of hydrogen and nitrous oxide testing 21 per cent hydrogen has a thermal conductivity of 0.0173 (B. t. u.) (foot)/(hour)(square foot)(O F.) at 32” F. Figure 4 yields values correct to about 2 per cent. Table I lists the values of the various constants in the four equations and enables construction of full-scale charta. Equations for rlasws T and II are given by McAdams ( 2 ) .
/
/ /
/
Mixtures of H., and
/
/ / /
/
/ d
at 32 *F
/
/
/ /
/
0.246 = b x + c 100 k )
/
’0
Literature Cited ( I ) McAdams, “Heat Transmission”, New York. McGraw-Hill Book Co., 1933. (2) l h i d . , p. 323.
Q
Nitration of Woodv Tissues EDWIN C. JAHN AND SYDNEY COPPICK New
York State College of Forestry at Syracuse University, Syracuse, N . Y.
HE action of nitric acid on cellulose and lignin has received much study, but woody tissues as a whole have had comparatively little attention. Most of the investigations on woody tissue have utilized the oxidizing and degradative action of dilute nitric acid on the lignin component for the purpose of obtaining a cellulose pulp (1). Kurschner and others (6) obtained a n alcohol-soluble “nitrolignin” by treating wood with alcoholic solutions of nitric acid. The action of strong nitrating acids on woody tissues has not received more attention because the reaction often becomes vigorous with a rapid rise in temperature and generatjion of nitrogen oxide fumes, accompanied by severe degradation of the material, and because the isolated product is often unstable. Two rather recent papers (3, 4) describe the nitration of wood (pine in one case and spruce and red beech in the other) with fuming nitric acid (specific gravity 1.52), alone or mixed with sulfuric acid (specific gravity 1.84) or with other concentrated acids. The action of fuming nitric acid on spruce caused over 60 per cent (4) of the material to pass into the nitrating acid, and nitric acid mixed with sulfuric acid also
T
caused severe degradation, a 55 per cent yield of nitrated pine being obtained ( 3 ) . However, Friese and Furst were able to obtain high yields of nitrated pine wood (10.2 per cent ester nitrogen in the highest case) by using fuming nitric acid (specific gravity 1.52) with phosphoric acid (specific gravity 1.88) or with a mixture of glacial acetic acid and acetic anhydride. They report that their product is soluble in acetone to the extent of only 6 per cent, that it is not easily stabilized since a faint odor of nitrogen oxide arises, but that i t is otherwise stable. The importance of the cellulose nitrate industry has led to numerous studies of conditions for nitrating purified cellulose. It seemed of importance to apply similar studies directly to woody tissues and incompletely delignified pulps to determine whether or not woody tissues in general may be similarly nitrated t o yield products of possible scientific or practical value.
Materials and IMethods The different types of woody tissues nitrated are listed in I. None of the wood or straw samples were extracted or
Table
INDUSTRIAL AND ENGINEERING CHEMISTRY
May, 1941
13I I-
9$13.
z
I I. 9-.
H20 0
- EXTRACTED
,.
CL02- BLEACHED
FIGURE 1. RELATIONOF ESTER NITROGEN CONTENTOF NITRATED PRODUCTS TO HOT WATER SOLUBILITY OF ORIGINAL CRUDENITRATED MATERIAL
pulps were prepared b v c o o k i n mechanical pufp according t o t h e sulfate process (sodium h droxide and s u l d e ) for short periods. The a l k a l i - d i g e st e d bagame was prepared by digestin hammer-mille$
showed that the Yield and content of the Product depend Won t h e species a n d Dhvsical character bf ihe woody tissue and also upon the nitratin conditions. The usual oellulose nitrating conditions when ap$ied to lignified woody tissues result in vigorous exothermic decomposition. Lower temperatures and longer time periods overcome this difficult and permit a good deof nitration without temperature rise luring the reaction. The ollowing conditions were found satisfactory and were standardized in order to compare the products of various woody tissues. An acid mixture weighing 500 grams and of the followin percentage composition by weight was used: Sulfuric aci3, 72; nitric acid, 17.2; water 10.8. This acid was cooled 40 10" C. and then poured with stirring on 10 grams of air-dried finely divided woody tissue. The mixture was kept a t 10" C. by an ice water bath for 5 hours. After the excess acid was removed on a lass suction filter funnel, the nitrated tissue was at once intro8uced with stirring into 500 cc. of cold water, stirred thoroughly, filtered, and washed with cold water until neutral to litmus. The product was then air-dried. ANALYTICAL METHODS.The hot water solubility was l4-.*... determined by ex.. t r a c t i n g 1-gram samples of the nia-0 I 2 trated tissues in a Z Soxhlet extractor for 12 hours. 0 The nitrated tissues were bleached by two methods. ( a ) The 6 + nitrated sample was 0 1 0 M 3 0 4 0 s u s p e n d e d for 3 H20 SOLUBILITY 4/, days at room temp e r a t u r e i n an FIGURE2. RELATIONOF ESTER aqueous solution of NITROGEN CONTENT OF HYPOchlorine dioxide (0.5 CHLORITE-BLEACHED MATERIAL TO gram cloz Per gram HOTWATERSOLUBILITY OF ORIGINAL of sample) buffered NITRATEDPRODUCT with pyridine as in Schmidt's method (e) of isolating the total carbohydrate fraction of wood. (a) Unextracted nitrated material was also bleached with calcium hypochlorite at 11.2 for 12 hours at 40' C., employing 23.0 per cent of avails!: chlorine. The permanganate numbers of the nitrated products were determined according to standard procedure (7). The permanganate number is the number of cubic centimeters of 0.1 N
6179
Natural unextracted ground woody tissues of ten different species, two groundwood pulps, and three partially deligniiied pulps were nitrated under suitable conditions with appropriate mixtures of nitric and sulfuric acids. Yellow or orange products, otherwise similar in physical appearance to the original material, are formed. If thoroughly washed with water, the products are stable. The ' yield depends upon the nitrating conditions and materials used, but under the same conditions the hardwoods and straws give lower yields than the softwoods. For example, average yields for a given set of conditions were 112 and 122 per cent, respectively. Nitration of tissues which have been partially deligniiied results in higher yields. The ester nitrogen content of the nitrated natural woody tissues is about 11 per cent. The nitrated tissues are about 20-30 per cent soluble in hot water and about 93 per cent soluble in acetone. There is a correlation between the hot water solubility and the content of readily oxidizable material in the nitrated product. By fractional precipitation from acetone solution, it is possible to divide the nitrated wood into several rather clearly defined fractions.
0 10 20 30 40 number determination. Acetone solutions of H20 SOLUBILITY % the unextracted nitrated FIGURE 3. RELATIONOF PERproducts were prepared by swelling 2 . 0 - g r a MANGANATE NUMBER TO HOT s a m ~ l e ~ i n s m ~ l l ~ o u nWATSR ts SOLUBILITY OF ORIGINAL of acetone. The volume NITRATEDPRODUCT was then brought up to 250 cc., which meant 1 per cent solutions by weight (0.8 per cent solution based on volume of the acetone). The vimosity of the resulting cloudy solution was determined by using a calibrated capillary tube viscometer. Upon standing, the insoluble material gradually separated out, and by evaporation of an aiquot portion of the clear solution and weighing the oven-dried residue, the percentage solubility in acetone was determined. The viscosity of the clear solution was then measured. The amount of material precipitated from the acetone solutions by water w~ determined by slowly adding 50 cc. of the clear acetone solution t o 250 cc. of cold water with vigorous stirring, allowing to stand overnight, filtering, washing, air drying, and weighing the residue. Nitrated raw sulfate white pine pulp (16.7 er cent lignin) was fractionated by adding 10-cc. portions of t f e clear acetone solution to 25-cc. portions of various acetone-water mixtures. After standing at least 24 hours, the precipitates were filtered, washed with cold water, and dried over P*O,, and the yields were determined. The percenta e of ester nitrogen in the various materials was determined by &e Schultz-Tiemann method (0).
Properties of Nitrated Woody Tissues The washed and dried nitrated woody tissues retain their original particle shape and appearance, with the exception
INDUSTRIAL AND ENGINEERING CHEMISTRY
680
Vol. 33, No. 5 TABLE I. PROPERTIES OF
Crude Nitrated Woody Tissue
Material Nitrated
Yield
Nitrogen
%
%
Increase in permanganate Hot water No. by Total solubility Permanboiling permanganate No. in water ganate No. %
Hot-Water Extd. Product Yield
(B. 0. W.)*
Nitrogen
%
%
1Q19i 11.0 11.07
Hardwood Tissues (60-80 Mesh) Aspen (Populus orandidentata Michx.) Beech (Fugus mandifolia Ehrh.) Fire cherry (Prunus pennsylvanica L.) Red gum (Liquidambar styracifiua L.)
102.6 112.4 111.2 128.0
Dou las fir (Pseudotsuga tazifolia ,Britt.) soutfern pine (Pinus palustrls ~ 1 1 1 . ) Eastern spruce (Picea glauca Voas.) Idaho white pine (Pinue nonticola D. Don.)
120.0 122.5 122.8 121.6
10.8 10.27 11.1 10.8
18.8 25.8 20.8 20.5
i:5
1i:1
16:s
3.4 2.2
11.0 13.4
14.4 15.6
83.5 83.5 88.4 101.7
15.2 11.5 11.8 2.6
24.6 22.4 27.2 16.6
39.8 33.9 39.0 19.2
76.4 80.4 83.3 96.0
9.7
22.3
30.0
3:4 2.7
15: 1 8.7
Ia:5 11.4
86.7 115.2 126.0 136.6
10.9 11.43 12.11 12.12
5:3
20:5
25:s
89.1 72.4 118.5
1b:87 11.76
Softwood Tissues (60-80 Mesh) 10.0 10.0 10.3 9.7
36.2 34.5 32.2 21.0
11.05
..,
11.3
...
Mechanical and Raw Sulfate Pulps Eastern spruce mechanical Eastern white pine mechanical p n i n , 28.8%) Raw sulfate eastern white pine ( !gnin, 23.7% Raw sulfate eastern white pine (lignin, 16.7%]
129.0 136.0 146.4 152.5
...
10.9 11.55 12.1
32.8 15.3 14.0 10.5
Straw and Bagasse 113.0 102.7 152.1
Wheat straw Bagasse Alkali-digested bagasse c
-
10.15 10.3 9.9
21.0 29.6 22.1
..
..
..
B. 0. W. basis original wood or lignocellulose: b B. N. W. = basis nitrated woody tissue. 3 (viscosity oloudy visoosity alear)/viscosity clear.
Vz
-
of color which varies from bright yellow to orange-brown. Although the products are thoroughly washed with cold water, they contain an appreciable hot-water-soluble fraction which, in general, is less for hardwoods than for softwoods and is still less for partially delignified pulps (Table I). The hot-water-extracted nitrated products also retain the shape and character of the original tissue but are brown in color. The nitrated products are readily bleached with calcium hypochlorite or aqueous solutions of chlorine dioxide, and yield nearly white, light cream, or pale lemon products which still retain their original woody character and appearance. The nitrated tissues, including those bleached or extracted with hot water, are all readily combustible and burn with a quick bright flame. The crude products appear to be stable under ordinary conditions, yielding no odor of nitrogen oxide after standing for a year and a half or after heating a t 105" C. in open vessels or sealed tubes for a nuniber of hours. Heating dulls the color of the nitrated woody tissues. The crude nitrated products must be thoroughly washed with large volumes of cold water to remove all traces of "acid in order to ensure stability. All of the crude nitrated products are over 90 per c e n t s o l u b l e in acetone and form yellow or orange solutions, and the nitrated partially , , , delignified pulps 0 are 99.5 per cent 0 10 20 30 40 H20 SOLUBILITY soluble in acetone. Small amounts of FIGURE4. RELATION OF YIELDOF acetone cause the BLEACHED PRODUCT (BASIS,NITRATED TISSUE)TO HOT WATERSOLUBILITY products to swell and then to coalOF ORIGINAL NITRATED MATERIAL
q
,I
60
80
YIELD
FIGURE 5. RELATIONOF PERMANGANATE NUMBERTO YIELD (left) OF HYPOCHLORITE BLEACHED PRODUCT AND (right) OF CHLORINEDIOXIDE-BLEACHED PRODUCT (BASIS,NITRATED TISSUE)
esce into clear, transparent sticky masses. When swollen with acetone, the nitrated products will dissolve almost completely in a number of other organic solvents. If a clear solution of nitrated tissue is evenly spread on a glass plate, and the solvent allowed to evaporate, a reasonably strong clear yellow or orange film is formed. Nitration of partially delignified wood results in products of higher yield and nitrogen content than are obtained from the original wood (Table I). This may be due in part to the ability of the cellulose to nitrate to a greater extent than the lignin, to greater losses of degradation products in the nitrating liquors from the uncooked wood and pulps of higher lignin content, and to the fact that delignification makes the cellulose more available for nitration. That the latter is probable is shown by the nitrogen contents of the bleached nitrated pulps; the bleached nitrocelluloses from the partially delignified pulps have a higher nitrogen content than from the mechanical pulp. The hot-water-extracted materials show the same trend (Table I).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
May, 1941
681
NITRATED WOODY TISSUES Hypochlorite-Bleached Material ClOn-Bleached Material Yield Yield Yield Yield (B. N. W . ) b (B. 0. W.)O Nitrogen (B. N. W.)b (B.0. W.10 Nitrogen
%
%
%
%
%
%
Acetone Soln. of Nitrated Crude Woody Tissues (1.0% by Wt. or O.8Y0 by Vol. Acetone) Sohbility
%
Viscosity Viscosity of cloudy of clear suspension soh. Centipoises
Yield of material pptd. by water
B. N . W.b B. 0. w.0 % %
Vd
Nitrogen in p td pr o ~ u c i
%
Hardwood Tissues (60-80 Mesh) 90 88 88
92 ... 9s
113
ii:i
10.95
90 93 87 92
92 105 97 118
58.5 71 69 84
70 87 85 102
10.5 10.75 10.5 10.3
70 83 78 90
84 102 96 109
..
11.2
11.55 11.27 11.5 11,s
93.5 94.2 90.1 93.6
31.2 14.6 64.2 32.6
Softwood Tiasues (613-80 9.5 10.23 10.85 11.4
93.7 95.0 94.5 92.1
24.0 10.0 39.6 22.6
89 117 126 138
11.0 11.7 12.5 12.4
94 ... ...
83
.. ..
11.5
... ...
77
99 ...
..
90 89
93 87 82
9.87
92.0 96.2 99.5 99.5
...
14.2
li:?55 12.9
105 89 126
Straw and Bagasse 92.1 17.5 11.63 4.25 98.3 11.07 99.0 2.96 11.77
CL02 BLEACHED
FIQURE 6.
COMPARIYIELDS OF BLEACHED AND HOTWATER EXTRACTED NITRATEDPRODUCTS (B A s I s, ORIQINAL WOODY TISSUE) SON
0
!
25 SO mB
100
75 W
~
L'-
28:Q 11.9 12.0
132 136
The yield of nitrated products is, in general, higher from softwoods than from hardwoods, despite the fact t h a t softwoods contain a greater amount of lignin. This would seem to be due t o chemical differences between the two types of lignin. The amount of hot-water-soluble material is greater in the nitrated softwoods than in the nitrated hardwoods so that there is no significant difference between the yields of hot-water-extracted material, on the basis of the original weights of wood nitrated, for either type. The nitrated softwoods evidently contain greater amounts of nitrated lignin components. This is borne out by their higher permanganate numbers and greater amounts of material removed on bleaching. Thus the higher yield of nitrated softwoods is counterbalanced by their greater content of readily oxidizable and hot-water-soluble material. The bleached products show a higher nitration of the cellulosic portion of the hardwoods and straws than of the softwoods (Table I). The ester nitrogen content of the crude nitrated tissues,
OF
-
125 0 2S do 75 YIELD % cio2 BLELDED
100 I25
I
..
75.8 64.0 75.3
12.95 12.67 12.95
...
...
Mesh)
... ...
...
57.3
68.7
ii:3 11.7
.. .. ..
0.21
55:5 56.8
68.1 67.7
l2:57
11.3 21.5 11.2 11.4
0.34 0.063 0.071
65.5 63.0 69.5 76.2
84.4 86.7 101.8 114.2
13:is
11.4 8.40 2.34
0.54 0.25 0.26
57.0 49.8 60.0
64.4 51.2 91.2
13.60 12.72 12.75
*.
Mechanical and Raw Sulfate Pulps 69 86 86 90
73.4 56.9 67.7
0.80 0.46 0.62 0.44
h o t -wa t er-extracted products, or bleached products decreases as the percentage hot water solubility of the crude nitrated material increases (Figure 1). I n t h e case of the hypochlorite-bleached material, thisrelation is a b o u t
... ...
...
100
...
12.63 12.83
- - -- -- - . - - I ; , , ~ , , - c - - - - - - - -- - -1- -8
*
E
50
