November, 1932
I N D U S T R I h L A N D E N GI N E E R I N G C €I E M I S T R Y
illustration the experiment may be cited where the octane number was increased from 33 to 58, with 0.84 mole of oxygen per mole of naphtha, a tube temperature of 700" C., a time of reaction of 0.56 second, and a yield of 55 per cent. Cracking this same raw material in the same furnace a t a temperature of 700" C. gave a material with quite similar yield and octane number, but the time required was three times as long. This does not mean that the output would be only one-third that, of the oxidation process, because of the volume of inert nitrogen in the former case. The reactions of this naphtha occurring in the presence of oxygen seem t o be similar in over-all effect, as shown by the knock rating, to those occurring in the absence of oxygen. The rate of the reaction with air is much more rapid than cracking below 790" C., so that the oxidation process may be considered from one angle as a method of accelerating the rate of reaction a t the lower temperatures. The amount of gas formed in these tests by either oxidation or cracking processes a t atmospheric pressure is a function of the time and temperature employed, and the knock rating is a function of the amount of gas formed. It appears that a given octane number may be obtained by a long-time lowtemperature or a short-time high-temperature treatment. These conclusions apply only to a single pass process. I n cases where air is used, the assumption is made that the oxygen concentration is constant in the cases compared. d comparison of the present data a t atmospheric pressure with a few results obtained by others a t higher pressures indicates that a distinct advantage is gained by operatting a t high pressures, since less gas is formed a t the higher pressures for the same antiknock equivalent of the fuel. The velocity constants for the cracking reaction and for the reaction of naphtha in the presence of air have been calculated from the experimental data as if they were monomolecular reactions. These calculated values have been used in
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predicting yields, gas formed by the reaction, and knock values of the modified naphthas. The calculated results agree quite closely with the experimental figures. Equations which express the velocity of the reaction in terms of the absolute wall temperature of the reaction tube have been formulated both for the reaction of this Pennsylvania naphtha with a restricted quantity of air, and for cracking. An increase in oxygen concentration increases the velocity of the reaction of naphtha with air if the temperature of the reaction tube is the same in each case. The reaction between naphtha and air occurs so rapidly that, under the conditions prevailing in these tests, the temperature of the gases rises to be higher than the wall temperature before the gases have progressed more than one-third through the tube. The maximum gas temperature attained in cracking is in all cases lower than the wall temperature. The temperature coefficient of the reaction velocity is greater for cracking than for the oxidation of naphtha in the presence of air, but the actual velocity of the cracking reaction is not as great as when air is present until the wall temperature reaches 790" C. When the separate cuts which were obtained by fractional distillation of the 300-400" F. (149-204" C.) naphtha reacted in the presence of air under similar conditions of tube temperature, time of reaction, and oxygen concentration, the velocity of the reaction increased with increase in molecular weight of the cuts undergoing reaction.
LITERATURE CITED (1) Brown, G. G., Univ. Mich., Eng. Research E d . , 7 (1927). (2) DeFlorez, Bull. Am. Inst. Petroleum Inst., 11, GO (1930). (3) Geniesse and Reuter, IXD.ESG.CHEM.,22, 1275 (1930) (4) Hurd and Spence, J. Am. Chem. SOC.,51, 3581 (1929).
RECEIVED February 19, 1932.
Potential Reducing Numbers of Lignin and of Carbohydrates of Wood GEO. J. RITTER,R. L. MITCHELL, AND R. A I . SEBORG,Forest Products Laboratory, Madison, Wis. erties in Fehling's solution. I n a n investigation a t the Forest Products Laboratory, the authors of this paper observed that from wood, whereas others are not. For example, some lignin isolated by the sulfuric acid method also reduced of the methoxyl groups are removed when lignin is separated, Fehling's solution, and moreover, that the reducing number of the percentage so removed, depending upon the severity of such lignin is increased several times by solution and hythe method of isolation. Further, if change in color is a true drolysis. This finding indicated that the material has potential reducing groups similar indication of chemical change, to the groups in cellulose that then lignin is altered chemically during such isolation, for the The poteniial reducing properties of lignin and require chemical treatment to carbohydrates in wood are studied to determine render them reactive. color darkens c o n s i d e r a b l y . whether they are affected by the treatments emWith cellulose the situation On the other hand, the reacis p a r a l l e l . For instance, the tion of lignin with chlorine is ployed to isolate the lignin and the cellu~ose, It si m i 1a r whether the substance solubility of t h i s s u b s t a n c e Of 'pruce and is found in cuprammonium solution is has been isolated or is still in the wood, and the s o l u b i l i t i e s catalpa lignins have reducing numbers which are affected markedly by the pro29.5 and 38.6 per cent, respectively, of that of cedure for isolating it from wood. of the two chlorinated products Isolated cellulose in solid form in sodium sulfite solution are glucose. The treatnlent employedfor isolating the lignin dissolves in t h i s s o l v e n t with similar also. I n addition, lignin ease, whereas cellulose in wood "Iated either a caustic and the cellulose has no effect on the potential redissolves w i t h e x t r e m e difsoda digestion (4) or the concentrated hydrochloric acidmethod ducing Properties Of the lignin and the carboficulty. I n a d d i t i o n , s o m e ( 3 ) e x h i b i t s r e d u c i n g prophydrates. investigators (2) contend that
OME properties of both lignin and cellulose are modifled by treatments for separating these two constituents
S
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Cross and Bevan cellulose residue differs chemically from the cellulose in the wood, asserting that some of it is oxidized to a substance resembling uronic acids by the hypochlorous acid formed during the chlorination step in the process of isolation. On the other hand, when others (6) attempted t o determine the extent to which this residue might be so modified under such conditions, their study showed that little if any oxidation takes place during such isolation. Further, the solubility of cellulose in 7 2 per cent sulfuric acid is virtually the same, regardless of whether the substance is dissolved directly from wood or after isolation in the solid state. Along similar lines, investigators may contend that the potential reducing properties of lignin and cellulose isolated by the sulfuric acid and the chlorination methods, respectively, are not necessarily a n indication of the chemical constitution of the lignin and the cellulose existing in the wood or separated from it by other means. Only a quantitative comparison will disclose the facts. The means chosen by the authors for such comparison was selected to determine also the reducing properties of the two constituents after they had been dissolved directly from the wood. I n such a solution it was necessary to consider also the potential reducing property of a third type of material-namely, carbohydrates not in cellulose, which dissolve in both lignin and cellulose solvents. I n the first procedure of this investigation these carbohydrates are dissolved with the cellulose; in the second they are dissolved with the lignin. I n other words, the total carbohydrates are dissolved, leaving lignin as a solid in one method, whereas the lignin and the noncellulose carbohydrates are dissolved, leaving cellulose as a solid in the other method. The purpose of this report is to show that the potential reducing numbers of both the lignin and the carbohydrates are unchanged, whether the lignin and the cellulose are separated from wood in the solid state or in solution.
EXPERIMENTAL PROCEDURE MATERIALS USED. Sawdust passed by a screen of 60 meshes to the inch and retained on one of 80 meshes was thoroughly extracted with alcohol-benzene solutions to remove resins, fats, waxes, etc., was washed with alcohol, digested in boiling water to remove the water extractives, rewashed several times, and then air-dried. The materials were analyzed for lignin and cellulose by the methods described in the text for the isolation of the lignin and the cellulose, and for pentosans by Tollens' method (8). Results of a partial analysis of the materials prepared from spruce and catalpa heartwood are recorded in Table I TABLE I.
PARTIAL ANALYSIS O F
the solution, the sensitive aniline acetate test was employed. I t indicated a faint trace of furfural, after which the phloroglucinol and the Fehling's solution tests showed positively that the amount was too slight for quantitative determination. The moist lignin residue was dissolved by treating it alternately with chlorine gas and hot 2 per cent sodium sulfite solution. At this stage the solution reduced Fehling's solution slightly. After heating with sulfuric acid to destroy the sulfite and then hydrolyzing in 4 per cent sulfuric acid solution for 4 hours, its reducing capacity was increased. This solution was designated B. PROCEDURE 2 (SOLUTIONS C ASD D ) . Two grams of the extracted air-dry sawdust were treated alternately with chlorine gas and hot 2 per cent sodium sulfite solution to dissolve the lignin and the carbohydrates not in the cellulose. The filtrate, acidified to a 4 per cent concentration of sulfuric acid and boiled for 4 hours, was designated solution C. The cellulose residue was then treated with 7 2 per cent sulfuric acid for 4 hours at approximately 20" C., diluted with water to a 4 per cent concentration, and then boiled for 4 hours to convert the dissolved cellulose to sugar. This solution was designated D.
REDUCIKG CAPACITY The reducing numbers of the four solutions were determined by the precipitation of cuprous oxide from Fehling's solution in accordance with standard procedure (6). The cuprous oxide, in turn, was dissolved in nitric acid solution from which the copper was recovered electrolytically, weighed, and calculated in terms of glucose. The results are recorded in Table 11. The glucose equivalents of the four solutions offer a common basis for comparison of the potential reducing numbers of both the lignin and the Carbohydrates, after the materials have been separated from wood by the different methods. TABLE11. REDVCIXQ NCMBERSOF HYDROLYZED SPRUCEAND CATALPA LIGXIN AND CARBOHYDRATE SOLUTIOSSa PROCEDCRE 1 (LIQXISISOLATED)
SAMPLE
1 7
3 -1: 5
6
k
9 10 11 12
hIETHOD
SPRCCE KOOD MIXATIOX % % 15.0 26.7 Lienin (7) 57.8 ... 57.0 Linnin-free cellulose 58.3 58.1 Cellulose as isolated (6) 23.5 11.8 Pentosans (8) 16.4 6.1 Pentosans i n cellulose 6.8 5.4 Pentosans not in cellulose Slight trace Slight trace ... Pentosans in lignin residue I n terms of weight of original sawdust when oven-dry.
Total oarbohydrates ( s o h R)
Cellulose (soln. D )
70
%
70
8.i 6i.l 67.7 8.8 68.6 8.4 68.7 7.8 67.6 8.8 67.5 7.6 68.2 7.4 68.6 7.8 68.1 7.2 67.3 7.8 7.1 .. 7.5 Average 7.9 67.9 Total 7.9 67.9 = 75.8
..
+
62.2 13.8 14.2 60.8 15.6 60.3 13.8 61.6 14.8 62.2 14.4 61.8 60.5 14.5 62.2 14.3 61.4 14.8 60.4 14.3 61.5 15.3 60.9 15.8 14.6 61.3 14.6 61.3 = 75.9
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CATALPA H E A R T W O O D
... ...
PROCEDURE 1 (SOLUTIOSS A - 4 x B~ ) . To isolate the lignin in the solid state, a 2-gram sample of extracted air-dry sawdust was treated for 4 hours a t approximately 20" C. with 20 cc. of 7 2 per cent sulfuric acid. The acid-sawdust mixture mas diluted with distilled water to a 4 per cent acid concentration, boiled for 4 hours, and filtered The residue consisted of lignin; the filtrate, which was designated solution B, contained chiefly sugars resulting from a hydrolysis of the total carbohydrates. To investigate the possibility of conversion of pentoses to furfural under the conditions of preparation of
PROCEDURE 2 (CELLULOSE ISOLATED)
Lignin and carbohvdrates not in cellulose (soln. C )
SPRUCE
HEART-OF DETER-
a
Lignin (aoln. A )
40
EXTRACTED S.4wDCST4 CATALP.4
Vol. 24, No. 11
60.3 13.9 67.7 59.8 14.0 67.6 60.5 14.0 68.1 3 59.2 14.8 68.1 4 59.4 15.0 67.5 5 60.7 14.5 68.3 6 60.8 14.0 68.1 60.6 14.8 69.1 b 60.8 14.4 68.4 9 59.3 13.9 67.5 10 Average 5.8 68.0 14.3 60.1 Total 5.8 68.0 = 73.8 14.3 +60.l= 74.4 Based on t h e original oven-dry sawdust and calculated as glucose. 1
2
6.4 6.3 5.7 5.4 6.4 5.4 5.4 5.7
... ...
+
5
For each species of wood, the total reducing numbers, given in Table 11,are approximately the same. This fact suggests that the treatments of the two procedures have a closely similar effect on the reducing property.
Sovember, 1932
I S D U S T R I A L A N D E N G I N E E R I N G C H E ;\I I S T R Y
REDUCIKG PROPERTIES OF LIGNIZ~ SOLUTION A. Based on the original oven-dry sawdust (Table I), 26.7 per cent of isolated spruce lignin is equivalent as a reducing material to 7.9 per cent (average sample) of glucose (Table 11). The reducing number of spruce lignin, therefore, is 29.6 per cent (7.9 0.267) that of glucose. On the same basis the isolated catalpa lignin is equivalent to 5.8 per cent of glucose and hence its reducing number is 38.7 per cent (5.8 - 0.15) that of glucose. SOLUTION C. The reducing number of solution C is due to hydrolyzed lignin and carbohydrates not in cellulose The reducing value of these carbohydrates is represented by the average difference between solutions B and D, which for spruce is 6.6 per cent (67.9 - 61.3) as shown in Table 11. The spruce lignin in solution C, then, has a reducing value of 8.0 per cent (14.6 - 6.6). Table I shon-s, houever, that there remained in the cellulose residue 1.1 per cent (58.1 57.0) of lignin, n-hich has a reducing value of 0.3 per cent (0.296 x l.l), making a total lignin reducing value of 8.3 per cent (8.0 0.3) in procedure 2 . Similarly, the reducing value of the catalpa carbohydrates in solution C is represented by the difference between 68.0 and 60.1 per cent, which is 7.9 per cent, leaving 6.4 per cent (14.3 - 7.9) for the lignin. Likewise 0.5 per tent lignin, with a reducing number of 0.2 per cent (0.387 K 0.5), remained in the cellulose residue, making a total of 6.6 per cent (6.4 0.2). COMPARISON OF TWOPROCEDURES. Comparison of the glucose equivalents of the hydrolyzed lignin solutions in the t n o procedures-7.9 with 8.3 per cent and 5.8 a i t h 6.6 per cent-indicates that the potential reducing value of the lignin was decreased only slightly, if a t all, by the treatment with 7 2 per cent sulfuric acid. DISCUSSIOS.-4s already mentioned, the reducing numbers of the spruce and the catalpa lignins used in this research are 29.6 and 38.7 per cent that of glucose, respectivcly. These numbers are considerably higher than that of the soda-isolated spruce lignin reported by Pori-ell and Whittaker ( 4 ) . These investigators concluded that one carbonyl group evists on a molecule of lignin having a molecular weight of 844, under which conditions the reducing number of the lignin would be approximately 21 per cent that of glucose. To show that the reducing property of solution A and also the reducing property attributed to the lignin in solution C are not due to the sulfite, blank tests were mrtde. They showed no reduction of Fehling’s solution. Further, the isolated lignin exhibited reducing properties when other solvents that are being investigated were substituted for the sodium sulfite solution. These results indicate that lignin isolated k1.y different methods has potential reducing groups, and they strongly suggest also that lignin as it exists in wood has such potential reducing groups. -4finely divided insoluble brown precipitate formed during the hydrolysis of solutions ,4 and C in 4 per cent sulfuric acid. The nature of that material will be investigated arid reported in a later publication.
+
+
REDUCING PROPERTIES OF CARBOHYDRATES If the sum of the carbohydrates is multiplied by 1.1, the approximate theoretical equivalent of glucose is, obtained. Thus with spruce the percentage of pentosans plus the percentage of cellulose, taken from Table I, multiplied by 1.1 is 68.6 per cent [1.1 X (5.4 57.0)]. Similarly, with catalpa the carbohydrates are equivalent to 71.1 per cent [1.1 X (6.8 57.8)] of glucose. If the actual glucose equivalents obtained experimentally are divided by the theoretical glucose equivalents, the efficiency of conversion is the higher for
+
+
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the spruce carbohydrates. It is 99.0 per cent (67.9 i68.6) in 68.61 in proprocedure 1, and 98.5 per cent [(75.9 - 8.3) cedure 2 . With catalpa it is 95.6 per cent (68.0 + 71.1) in 71.11 in proprocedure 1, and 95.4 per cent [(74.4 - 6.6) cedure 2. These figures, obtained under the conditions of this research, indicate that the potential reducing numbers of the carbohydrates are the same in the two procedures employed. Assuming in spruce the absence of other furfural-producing material, there m-as by analysis 5.4 per cent of pentosans or 6.1 per cent (5.4 X 150l132) of pentoses in solution C. According to Bronme ( 1 ) the ratio of glucose to xylose for the same weight of reduced copper is 0.98. Then as a reducing material the pentoses in solution C are equivalent to 6.0 per cent (0.98 X 6.1) of glucose as compared with 6.6 per cent (67.9 - 61.3) of glucose for the total carbohydrates in solution C. For catalpa there mas 6.8 per cent of pentosans or 7.7 per cent (6.8 X 150/132) of pentoses in solution C. As reducing material those pentoses are equivalent to 7.5 per cent (0.98 X 7.7) of glucose, which compares with 7.9 per cent (68.0 - 60.1) of glucose for the total carbohydrates in the solution. The assumption upon which the preceding discussion is based, however, is slightly in error, since the pentosans were not the only furfural-producing material. A small amount of furfural came from the uronic acids, and consequently calculating the pentosans from the total furfural obtained is inaccurate by the percentage of furfural that the uronic acids contributed. Allowing for this inaccuracy and for experimental error, the computations indicate that the potential reducing number of the pentosans not in the cellulose accounts for the total carbohydrates that dissolve with the lignin when cellulose is isolated from wood by means of the modified Cross and Bevan method. A
SUMVARY
Investigation of the reducing properties of hydrolyzed solutions prepared from lignin and carbohydrates of wood under different conditions may be summarized as follows: 1. Lignin separated from wood by the sulfuric acid and the chlorination methods has potential reducing properties which are rendered reactive by solution and hydrolytic treatments. The potential reducing numbers of either spruce or catalpa lignins are approximately the same, whether the materials are isolated by the sulfuric acid method or separated from the n-ood by chlorination and solution in sodium sulfite. 2 . Isolated spruce lignin has a potential reducing number which is 29.6 per cent that of glucose; isolated catalpa lignin has a potential reducing number which is 38.7 per cent that of glucose. 3. The potential reducing number of the carbohydrates of wood is the same whether the cellulose is isolated as a solid or is dissolved directly from the wood. 4. The pentosans that dissolve with the lignin in the chlorination and sulfite treatments are sufficient to account for the reducing number of the carbohydrates not in cellulose. LITERATURE CITED (1) Browne, C. A , J . Am. Chem. SOC.,28, 409 (1906). (2) Heuser, E., and Casseus, H . , Papier-Fabr., 20, 800 (1922). (3) Heuser, E., and Skioldebrand, C., Z. angew. Chem., 32, 41 (1919). (4) Powell, W. J., and Whittaker, H , J . Chem. SOC.,1925, 132. (5) Ritter, G. J., ISD. ESG.C H E U . , 16, 947 (1924). (6) Ritter, G. J., and Fleck, L. C., Ibid., 20, 371 (1928). (7) Ritter, G. J., Seborg, R. XI.,and Mitchell, R. L., Ibid , Anal. Ed., 4 , 202 (1932). (8) Tollens, B., Kurses Handbuch der Kohlenhydrate, p. 137, J. A. Barth, Leipzig, 1914. (9) U. S Dept. Agr., Bur. Chem., Bull. 107 (revised), 49 (1912).
RECEIVED April 29, 1932. Pre9ented before the Division of Cellulose Chemistry a t the 83rd Meeting of t h e American Chemical Society, New Orleans. La.,March 28 t o April 1, 1932.
