ular weight of the ether-insoluble fraction, and higher yield of distillable phenols. Also, a purer lignin fraction is obtained-the refractive index range of the distillable liquid is that of the pure identified phenols and a portion of the distillate crystallizes readily. Adkins has similarly reported that in hydrogenolysis, products obtained from soda lignin are far more complex than those from lignin extracted under milder conditions (7). Furthermore, lignin recovery on exhaustive chloroform extractions is near theoretical but that from the hydrogenated soda liquor is much higher, probably because of contamination with carbohydrate residues. The soda lignin itself contains a surprisingly high proportion of distillable phenols which seemingly have not been reported. The data of Table I were obtained on hydrogenation of birch chips. Thus, the catalyst is distant from the locus of reaction for lignin with alkali, yet yield of monomeric phenols is equal to that reported by Pepper or that found in comparable runs on wood meal in this laboratory. In hydrogenation where a low ratio of liquor to wood meal was used and catalyst layered on top, diffusion was slow; the pulp and liquor near the catalyst were light colored while that more distant was the usual color expected in soda pulping. The lifetime of reactive intermediates which are stabilized and degraded by hydrogenation is sufficiently long to permit some separation of catalyst and pulp. Two effective methods were found for isolating pulp produced in this process. Either the nickel catalyst and wood were mixed for thecook and separated magnetically, or a small chamber of fine screening was used to hold a tableted catalyst separate from the wood. Because the cooks were carried out in a shaking hydrogenation bomb without facilities for forced circulation of liquor through the catalyst, runs using the catalyst in a separate container were generally carried out at higher than customary liquorwood ratios to increase contact with the catalyst. Results (Table 11) confirmed the statement made previously that this was a soda pulping process with simultaneous
I
Alkaline Hydrogenation Pulping
H Y D R O G E N A T I O N of wood and lignin has a lengthy history (Z),but little information is available on quality of pulp thus produced; nor is it clear if hydrogenation used in conjunction with a pulping process offers advantages over either conventional pulping or hydrogenation of an isolated commercial lignin. Hydrogenation has been described as a pulping method (8),but, actually, lignin solution occurs below pyrolytic temperatures only if acid- or alkalicatalyzed degradation occurs (4, 7). Hydrogenation merely stabilizes or degrades previously dissolved wood components. Pepper and Hibbert (7) and Pepper, Brounstein, and Shearer (5) have reported a method of wood hydrogenation using alkali, aqueous dioxane, and Raney nickel at a hydrogen pressure of 3000 pounds per square inch. This yielded a lignin-free hardwood pulp in 25 to 5070 yield, depending on time of cooking, which they freed from catalyst by acid washes, but apparently investigated no further. Three pure monomeric phenols accounted for one fourth of the lignin-most of the remainder was a chloroform- and alkali-soluble resin of apparently low molecular weight. Two per cent of the wood appeared as methanol. Conditions used by these authors can be modified to approximate those used in alkaline pulping. A pure aqueous alkaline liquor can be used in lieu of 5070 dioxane. Dioxane is not a good solvent for lignin salts; its elimination caused no observable change in the lignin fraction. Ratios of liquor and alkali to wood can be decreased to commercial ratios and chips can be used instead of wood meal. Initial hydrogen pressure can be decreased from 3000 to 400 to 600 pounds per square inch (cf. 6) with the distillable fraction of lignin remaining near 40%. This fraction is completely monomeric and corresponds to that portion distilling
below bath temperature of 250" C. at 1- to 3-mm. pressure. T h e total lignin fraction isolated from the liquors is a viscous phenolic oil. When the monomers are removed, the nondistillable fraction is a thermoplastic resin, lighter in color than commercial lignins, which can be melted repeatedly to a clear brown liquid over a temperature range of 90" to 150' C. Countercurrent distribution studies of the distillable material indicated guaiacylpropanol and syringylpropanol (cf. 3) in addition to 4-ethylguaiacol, 4-ethylsyringol, and 4-~-hydroxyethylsyringolpreviously reported. Table I compares lignin fractions obtained from a typical soda cook, for the same soda liquor hydrogenated, and from simultaneous hydrogenation and alkaline pulping. White birch, a/,-inch chips were cooked in 8.34% sodium hydroxide with 1-hour heating to temperature and 3-hour cooking a t 165" to 170" C. Initial hydrogen pressure was 400 to 600 pounds per square inch (column 2 and 3), and catalyst was mixed with chips (column 3 ) . The most notable difference obtained by simultaneous pulping and hydrogenation is in the small molecular size of the lignin. This is indicated by low yield of ether-insoluble material, lower molec-
Table 1.
Comparison of Soda and Hydrogenated Lignins
% mason Lignin from Soda pulping
Chloroform-ethanol soluble Ether insoluble Ether soluble Ether soluble, distillable up to bath temp. of 250' C.
110 70
Ether insoluble, molecular wt. Ether soluble, NL5
940
Hvdroaenated " sAa liquor
Directlv hydrogenated wood
36
132 68 61
105 25 71
13
25
37
...
VOL. 49, NO. 9
...
1.483
690 1.518
SEPTEMBER 1957
1399
Table II.
Typical Pulps from Alkaline Hydrogenation -___
Yield
Lignin
I
OL
KMnOi
Pentosan
DP
22.5 11.7
1248 1965
11.6
...
27.7 26.0
340 457
7Ze
0.78
4.3
664
...
10.6
700
5.1
6.3
765
7.8
NO.
3 % PTaOH at 165’ C.
White birch chips“ Sugar maple meaP Norway spruce chipsa White pine chipsQ
46.3 ca. 45 54.5 49.0
2.2
83.7 90.0 74.3
1.25 20.0 16.8
... ...
...
...
...
5% NaOH at 180’ & 5’ C. Sugar maple meal* Sitka spruce meal*
30 34
0.06 0.03
Sitka spruce meal6
36
1.25
White birch chipsa
40
0.96
White oak chipsa
37.4
0.02
86 89
1.8
...
3% NaOH at 180’ C. 92 57, NaOH at 168’ C. 93.3
77, NaOH at 165O C. a
90
Catalyst, ‘/rinch tahleted nickel on kieselguhr, Harshaw 0104T, in separate screen container. Raney nickel mixed with pulp and separated magnetically. Bromine No.
hydrogenation of dissolved components. T h e liquor to wood ratio used was 10 or 20 to 1; initial hydrogen pressure, 400 to 600 pounds per square inch with 1hour heating to temperature and 3 hours a t temperature, then rapidly cooled. Catalyst to wood weight ratio was 0.5 to 1.5. The usual pulping temperature and alkali concentration range was needed for a reasonable pulping rate without too severe carbohydrate degradation. Softwoods gave low yields of pulp having high lignin content under conditions which give hardwood pulps of the same viscosity and lignin content as commercial soda pulps. Yields and pulp viscosities decreased rapidly when the lignin content was reduced below 1%.
Table 111.
Acknowledgment This work was supported by the U. S. Army Office of Ordnance Research and by the Technical Association of the Pulp and Paper Industry.
Literature Cited (1) Pldkins, H., Frank, R. L., Bloom, E. S., J . Am. Chem. Sod. 6 3 , 5 4 9 (1 941 ). ( 2 ) Brauns, F. E., “Chemistry of Lignin,” Academic Press. New York. 1952. ( 3 ) Brewer, C. P., Cooke, L. lf.,Hibbert, H., J . .4m. Chem. Soc. 70, 57 (1948). ( 4 ) Granath, M., Schuerch, C., Ibid., 75, 707 (2954). ( 5 ) Pepper, J. M., Brounstrin, C. J . , Shearer, D. A , Ibid., 73, 3316 ,,nr,,
(IY31).
(6) Pepper, S. M., Hagerman, D. C., Can. J . Chem. 3 2 . 6 1 4 (1954). (7) Pepper, J. M., Hibbert, H., J . Am. Chem. SOC.70, 67 (1948). ( 8 ) Sherrard, E. C., Harris, E. E., U. S. Patent 2,328,749 (Sept. 7, 1943).
IGOR SOBOLEV, H. G. ARLT, Jr., and CONRAD SCHUERCH State University CoNege of Forestry at Syracuse University, Syracuse 10, N. Y.
Comparison of Soda and Hydrogenated Pulps Yield, Lignin, % %
Experimental pulps Hydrogenated 5.770 NaOH (initial 384concn.) 8.341, NaOH (initial concn.) 364Soda, 8.3% 40 NaOH Commercial soda Mixed hardwoods Mixed hardwoods, rnodified soda with 18% can. sulfidity Poplar
1400
Therefore, even though white, essentially lignin-free pulps are obtainable, final purification by bleaching would be more economical. Pulps produced under identical conditions by a conventional soda cook and by hydrogenation pulping have the same viscosity and seem to differ only in color. T h e hydrogenation pulp is somewhat lighter. For Table 111, chips, hydrogen pressure, and heating periods were the same as for Table I. Temperature was 165’ to 168’ C., liquor to wood ratio was 6 to 1, and Raney nickel catalyst was mixed with the chips.
DP
Kinetics of Gas-Liquid Reactions-Correction 1.03
966
0.80
618
1.21
648
0.93
858
As was pointed out recently by Harding Bliss of Yale University, Equation 3 of our paper, “Kinetics of Gas-Liquid Reactions” [IND.ENG.CHEM.45, 12475 3 (1953)], is incorrect. T h e last two terms on the right side should be multiplied by 2 to correspond to the stoichiometry of the chemical equation A B = 2C. T h e calculated results reported in the paper are, however, unaffected if c (Equation 6) is defined as C/2B3 and K is taken as Ko,:4, where K,, is the mass-
+
1.30
935 968
INDUSTRIAL AND ENGINEERING CHEMISTRY
action equilibrium constant, C2/AB, for the above reaction. If the chemical reaction has the stoichiometry corresponding to A -!r vR -+ but is irreversible ( K = m), all the previous results apply provided the parameter B o I A , of the paper is interpreted as
Bo/vAi. T h e two lowest lines on Figure 2 are in error. T h e corrected version is shown in Figure 153 of later editions of “Absorption and Extraction” (T. K . Sherwocd and R. L . Pigford, McGraw-Hill, New York, 1952) R. H. PERRY R.L. PICFORD
