I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
September, 1930
975
Consumption of Nitric Acid in the Oxidation of X ylos elsz G. M. Kline and S. F. Acree BUREALOF STANDARDS. WASHINGTON, D. C.
The loss of nitric acid versus sugar acid production was studied. The effects of varying the quantities of sugar and nitric acid, the concentration of nitric acid, and the time of oxidation were determined. The molar quantity of nitric acid lost became greater with increasing amounts of sugar and nitric acid and longer oxidation periods. On the other hand, the yield of organic acids increased with larger amounts of sugar for a given amount of nitric acid, but was not greatly affected by increasing the amount of nitric acid with a given amount of sugar or prolonging the oxidation period. Variation of t h e concentration of nitric acid between 22.5 and 45 per cent had no appreciable effect on the loss of nitric acid or yield of organic acids other than t h a t due to the larger amount of nitric acid.
When the proportion of sugar to nitric acid approached the theoretical ratio 1:2, the loss of nitric acid after 1 hour was approximately 15 per cent and after 2 hours, 20 per cent. The quantities of nitric acid driven out of the oxidation vessel after the initial vigorous reaction had taken place were found to be almost entirely unrecoverable. The most efficient operating conditions for the oxidation have been indicated to be a 1:2 molar ratio of sugar to nitric acid and a minimum oxidation period. The acids produced from the sugars were roughly differentiated into monobasic and dibasic acids by the use of two indicators, bromophenol blue and phenolphthalein.
....... . OTTONSEED-HULL bran, a waste product of the cotton industry, has been found to be capable of yielding xylose cheaply ( 3 ) . Inasmuch as large quantities of this bran are readily available at the cottonseed-oil plants, a rich potential source of this sugar is opened. Studies designed to develop commercial uses for xylose are, therefore, in order. A study of the formation of sugar acids by the action of nitric acid on xylose and the potential recovery of the nitric acid and oxides of nitrogen is the object of this investigation.
C
General Description of Process
It has long been laboratory practice (6) to use nitric acid to oxidize aldose sugars into the corresponding dibasic acids for purposes of research and identification of the sugars. The reduction of nitric acid can take place by several different mechanisms, and in the oxidation of a sugar by nitric acid there is probably an equilbrium between the various reduction products. One possibility is the reaction of 1 mol of sugar with 1 mol of nitric acid to form the monobasic acid: CH20H-(CHOH),--CHO "03 + CHzOH-(CHOH), -COOH HNOz (1) followed by the conversion of the monobasic to the dibasic acid by the action of 2 mols of nitric acid: CH2OH-(CHOH),-COOH 2HN03 + COOH(CHOH),-COOH + 2HN02 Hz0 (2) The 3 mols of nitrous acid so formed react to form 1 mol of nitric acid, 2 mols of nitric oxide, and 1 mol of water: 3"Oz +"03 2N0 HzO (3) Theoretically, then, only 2 mols of nitric acid are needed to supply the 3 atoms of oxygen required to oxidize the sugar to the dibasic acid, and the equation may be simplified as follows: 2"03 --+ 2N0 HzO 30 (4) The oxidation of the sugar is undoubtedly accompanied by side reactions involving the splitting of the carbon chain
+
+
+
+
+
+
+
+
1 Received April 29, 1930. Presented under the title "Oxidation of Xylose with Nitric Acid" before the Division of Sugar Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 to 11, 1930. 2 Publication approved by the Director of the Bureau of Standards of the U.S. Department OS Commerce.
to produce acids of smaller molecular weight such as oxalic acid, carbon dioxide, and water. Only in the case of the manufacture of mucic acid from galactose (1) has an extensive investigation been made of the nitric acid oxidation of a sugar on a plant scale. But mucic acid is very insoluble and precipitates, whereas xylotrihydroxyglutaric acid remains in solution in the mother liquors. The recovery of nitric acid and the oxides of nitrogen with the exception of nitrogen monoxide may be carried out efficiently and economically in the recovery towers in vogue today. Any portion of the nitric acid converted to nitrous oxide or nitrogen is unavoidably lost. The higher oxides formed during sugar oxidation are recovered in water or alkaline solution by the following typical series of reactions: 2N0 0 2 +2N02 (3 NO 2"Os +3NOz f HzO (6) 2N02 HzO +HNOa HNOz (7) NO NO2 2NaOH +HzO 2NaN02 (8) 2NaNOz H&04 ----f 2HN02 Na2SO4 (9)
+ ++ + ++
+ + +
The nitrous acid formed during these reactions is unstable and reacts according to Equation 3 to form nitric acid and nitric oxide vapors. I n the present study caustic soda solution was used in all the recovery towers in order to obtain the maximum recovery of the nitric oxides and consequently to determine the unavoidable losses of nitric acid during the oxidation of xylose. Standardization of Equipment and Procedure The first phase of the study of the oxidation of xylose with nitric acid consisted of devising and checking apparatus and analytical procedures to follow the recovery of the nitric acid. The decomposition of sodium nitrite by acid, Equations 9 and 3, was selected as a simple reaction involving the liberation of nitric oxides which could be used to test the efficiency of the recovery system. The apparatus as finally standardized is shown in Figure 1. An ordinary distilling flask, A , was closed by a two-holed rubber stopper through which were run a small dropping funnel for the introduction of acid and glass tubing leading from a cylinder of oxygen to the bottom of the distilling flask. This flask was connected through a water-jacketed condenser to a small suction flask, B. The side ann of the suction flask was joined to a special
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
970
Figure 1-Nitric
Acid Recovery S y s t e m
washing tower, C, containing approximately 150 ml. of 5 per cent sodium hydroxide. The outlet of this washing tower was connected to a 5-gallon (18.9-liter) bottle, D. This bottle was filled with oxygen previous to each experiment. A small dropping funnel permitted the addition of water or alkali to absorb the oxides of nitrogen present after the period of oxidation. The bottle D was connected with a train of four scrubbers, E , F , G, and H , similar to C and containing 5 per cent sodium hydroxide. The outlet of the final scrubbing tower was connected to a vacuum line by means of which the flow of the gases through the system could be regulated. I n order to ascertain the efficiency of the apparatus for the recovery of nitric acid and oxides of nitrogen, a weighed amount of sodium nitrite was first introduced into the distilling flask. An accurately pipetted portion of nitric acid solution of known strength was run into the dropping funnel. After starting a slow stream of oxygen through the system and regulating the flow of gas by suction applied at the end of the chain, the nitric acid was slowly added to the sodium nitrite. When the vigorous reaction subsided, the contents of the flask were heated to 95-100" C. for 15 minutes. The passage of the oxygen was continued for a period long enough to insure complete absorption of the oxides, usually about 1 hour. The solutions from the various units of the system were then carefully poured into volumetric flasks, the units washed with water, and these wash waters added to the respective flasks. The solutions from the last three scrubbers were combined for analysis. Water was added to the volumetric flasks to bring the volume to the standardization mark, and the solutions mixed well. Aliquots of the soluTable I-Nitrogen WEIGHT ACID NaNOn USED
OF
Grams 9.995 9.995 17.990 19.523
HNOa HNOa His04 HiSol
5'01. 22, No. 9
If we consider only that portion of the nitrogen which is converted into oxides and then recovered a better test of the efficiency of the apparatus will be obtained. It was assumed, therefore, that the nitrogen in the added nitric acid remained in the mother liquor in the oxidation vessel, A, as sodium nitrate and unused acid, and that only the nitrogen from the sodium nitrite is converted to the oxides. This is not entirely correct as some of the nitric oxide may react with nitric acid and convert it to the peroxide, Equation 6. Accordingly, the percentage of the nitrogen from sodium nitrite which remained in A was obtained by subtracting the nitrogen added as nitric acid from the total amount present at the end of the reaction. The nitrogen present in the other parts of the system was considered as set free from the sodium nitrite. On this basis the recovery of the evolved nitrogen was 98.44 per cent, distributed as shown in the second row of figures in Table I. The next experiment was carried out with a larger amount of sodium nitrite and sulfuric acid instead of nitric acid. The substitution of sulfuric acid eliminated the necessity of distinguishing between added nitrogen and evolved nitrogen. I n this experiment 96.26 per cent of the nitrogen was recovered. The oxidation tower, D,in these two preliminary experiments was connected directly to the distillate vessel, B, and the five scrubbing towers were in line following it. Thereafter one of the scrubbers, C, preceded the oxidation tower with the object of removing the soluble gases as quickly as possible and thus eliminating chances of loss and also giving the oxygen more opportunity to combine with the insoluble nitric oxide. With this set-up a repetition of experiment 2 gave a 97.22 per cent recoveIy, a 1 per cent increase in efficiency.
Recovery after Treatment of S o d i u m Nitrite w i t h Acid
NITROGEN RECOVERED IN: OF NITROGEN TIM^ OF ACID CONCN. ACID CONTENTOXIDATION Oxidation Distillate 1st scrubber Oxidation 2nd scrubber 3rd, 4th, and 5th ADDED vessel ( A ) vessel (€3 (C) tower (D) (E) scrubbers ( F . G . HI
MI.
Per cent
Grams
Hours
37.7 37.7 50 50
33.6 33.6 25 25
5.427 2.028b 3.650 3.961
0.25 0.25 0.25 0.25
I I l
Pcr cent
Per cenl
Per cent
Per cent
Per cent
Per cent
P n cent
78.60 42.73
10.65 28.50 42.22 51.13
7.73" 20.67= 25.72' 39.74
1.67 4.46 25.28 4.69
0.35 0.93 1.88 1.19
0.43 1.15 1.15 0.46
99.42 98.44 96.26 97.21
c e
a
In these runs the oxidation tower was connected immediately to the distillate vessel and the five scrubbers followed in line after it.
c
The residual liquors in the oxidation vessel ( A ) and the distillate in vessel ( B ) were combined for analysis in these experiments.
b Same experiment as one above it, but calculated on basis of nitrite nitrogen only.
tions were taken which contained convenient amounts of nitrogen for determination by the Kjeldahl method, modified to include nitrates by the use of Devarda metal. The distilled ammonia was fixed by 5 per cent boric acid and the ammonium borate titrated with N/14.01 sulfuric acid by using bromophenol blue as an indicator (4). I n the first experiment 10 grams of sodium nitrite were decomposed with nitric acid. The recovery of nitrogen as shown in Table I amounted to 99.42 per cent, calculated on the basis of the total nitrogen originally present.
The sodium nitrite used in these experiments was dried on a steam bath and then over concentrated sulfuric acid. It was
analyzed by the Devarda method and found to have a nitrogen content equivalent to 100 per cent sodium nitrite. The loss of nitrogen noted in these experiments is probably due to failure to oxidize all of the nitric oxide gas. Oxidation of Xylose
RECOVERY OF NITRIC Acm-The effects of varying the amount of xylose, the amount of nitric acid, the concentration
ILVDCXTRIAL A N D Eh'GINEERING CHEMISTRY
September, 1930
Table 11-Kitric
Acid Recovery after Oxidation of Xylose
-I
-_
(377
1
~VITRIC ACIDRECOVERRD IN:
APPROXCONCV. OF U X T n .
? ,.
p s e l ( A ) vessel ( B
*.LY=Y
~~
Grams 10 10 12 12 12 12 12 12 20 20 40 40
MI. 60 60 100 50 50 100 100 100 60 60 60 60
Per cent 33.6 33.6 22.5 36.6 45 45 45 45 33.6 33.6 33.6 33.6
Grams 24.316 24.316 28.807 22,445 28.807 57.165 57.165 57.165 24.316 24.316 24,316 24.316
Table 111-Oxidation
Hours 1 2 2 1 1 0.5 1 2 1 2 1 2
I
of Xylose:
Per cent 55.97 55.29 60.31 42.89 33.64 58.78 55.73 48.47 31.74 28.17 14.11 10.08
Mol
Mol
Percent 33.6 33.6 22.5 36.6 45 45 45 45 33.6 33.6 33.6 33.6
Hours
Mol
Per cent 13.06 10.65 4.67 18.OS 26.74 17.57 18.45 13.03 19.23 25.60 26.17 29.00
Per cent 0.12 0.19 0.09 0.11 0.12 0.08 0.16 0.32 0.16 1.91 0.21 6.50
Per cent 0.02 0.08 0.04 0.05 0.05 0.02 0.03 0.08 0.03 0.73 0.07 3.06
Per cent Per cent 0.03 91.45 89.82 0.0s 83.23 0.03 89.08 0.03 88.40 0.02 91.24 0.01 0.01 88.50 81.39 0.04 86.18 0.03 81.23 0.26 0.04 83.75 79.46 0.73
Per cenl 21
Per cenl 34
15 18 20 29 28 25 12 14 4 4
30 39 35 51 45 53 37 16 36 15
..
I
..
Effect of Various Factors on Nitric Acid Loss a n d Organic Acid Yield
HNOI CONCN. OF TIMEOR HNOs LEFTI N "01 OXIDATION MOTHER LIQUOR
0.066 0.066 o.os0 0.080 0,080 0.080 0.080 0.080 0.133 0.133 0.267 0.267
Per cenl 22.25 23.53 18.10 27.91 27.82 14.78 14.19 19.46 35.00 24.56 43.16 30.08
TITEROF ORGANIC MONORASIC ACID IN IN LIOUOR MOTHER LIQUOR
~ ~ ~ $"PG $o"?%,i~ %" ~ "IDsrN ~ LIOUOR & Mol 0.170 0.173 0.181 0.203 0.303 0.377 0.405 0.471 0.263 0.277 0.332 0.347
of nitric acid, and the duration of heating upon the recovery of nitric acid were investigated. Drastic conditions of operation, tending to cause over-oxidation, were studied in order to indicate the maximum loss of nitric acid which might be expected. The weighed quantity of sugar was placed in the oxidation vessel, A , which was kept a t 90-95' C. in a water bath, and the nitric acid was added to it froin the dropping funnel. Oxygen was passed through the system just as in the above experiments with sodium nitrite. Aliquot portions of the mother liquors and liquors from the various units of the recovery system were analyzed for nitrogen by the Devarda method. The calculated percentages of the nitric acid found in each vessel and the total percentage of the nitric acid remaining in the system are given in Table 11. PRODUCTION OF ORGAXIC ACIDS-TO obtain a rough indication of the yield of monobasic and dibasic acids, it was assumed that the only acids present in the mother liquors were nitric acid and the monobasic and dibasic sugar acids. One acid group of the dibasic acid is stronger than the other and also stronger than the single group of the monobasic acid. Bromophenol blue, which becomes definitely green at about pH 3.5, was chosen to titrate this first acid group of the dibasic acid. The amount of nitric acid present in the sample can be calculated from the determination of nitrogen by the Devarda method. Subtraction of the titer due to the nitric acid from the titer obtained with bromophenol blue gives the amount of alkali required to neutralize the first group of the dibasic acid. Titration with phenolphthalein, end point pH 8.0, would include the nitric acid, the monobasic acid, and the two groups of the dibasic acid. However, the bromophenol blue titration has indicated the titer due to the nitric acid and the first group of the dibasic acid. Subtracting this from the phenolphthalein value gives the amount of alkali required to neutralize the monobasic acid and the second group of the dibasic acid. If the titer due to the second group of the dibasic acid, which would be the same as that for the first group found above, is subtracted from the difference in the titers with phenolphthalein and bromophenol blue, the amount of alkali required for the monobasic acid is obtained. Therefore, in order to determine the sugar acids present in
Mol 0.033 0.039 0.077 0.039 0.053 0.080 0.105 0.170 0.053 0.072 0.063 0.079
Per cent 8.55 10.18 16.77 10.92 11.60 8.76 11.44 18.61 13.82 18.77 16.25 20.54
MI. 10 N N a O H 10.34 10.82 14.21 12.45 13.78 16.87 17.28 24.42 18.15 18.44 27.68 27.53
Md 0.063 0.060 0.041 0.055 0.053 0.043 0.039
Md 0.020 0.024 0.051 0.035 0.042 0.063 0.067
o:ii3 0.083 0.107 0.109
0:035 0.051 0.085 0.083
the mother liquors after oxidation, separate aliquot portions were titrated with standard alkali by using two indicators, bromophenol blue and phenolphthalein. The end point with bromophenol blue was taken as the change from the yellow of the acid sample to a distinct green color. This change is not sharply defined, as the sugar acids act as buffers in this p H zone (pH 3.0 to 4.6) and accordingly the calculations based on this titration serve only as a rough approximation. The end point with phenolphthalein fades out very rapidly a t first and finally very slowly. This is due to the presence of the acid lactone and its slow change to the sugar acid which neutralizes the alkali. The usual procedure adopted in the titrations was to add an excess of alkali, let the sample stand overnight, and titrate back with standard acid. The molar yields of monobasic and dibasic acid were calculated from these determinations. The data are presented in Table 111. Distribution of Nitric Acid after Oxidation
A study of the distribution of the nitric acid through the system after oxidation enables one (1) to estimate the importance of recovering the nitric acid in the mother liquor, (2) to obtain data on the effect of dilution of nitric acid on the oxidation, and (3) better to estimate the efficiency of the recovery system. The per cent of the nitric acid remaining in the oxidation vessel is to a great extent determined by t h e amount of sugar and nitric acid taken and by the period of oxidation. Table 11,sixth column, reveals, however, that, even in the presence of excess sugar and after 2 hours' oxidation, 10 per cent of the acid remained in the mother liquors. The problem of recovery of this nitric acid cannot, therefore, be neglected in plant operation. The nitric acid in the mother liquors may be judged to be still active in solution down to 4 per cent strength. The data in this table reveal, also, that in most cases more than 50 per cent of the oxides driven from the oxidation vessel were found in the distillate collected in vessel B. The last column shows that in general the concentration of the nitric acid recovered in this way is greater than the initial concentration of the acid in the oxidation vessel. The scrubber, C, immediately following the distillate receiver, B , serves to fix the greater portion of the remaining oxides.
INDUSTRIAL AND ENGINEERING CHEMISTRY
978
Only 0.1 to 0.4 per cent of the nitric acid was retained in the oxidation bottle and four succeeding scrubbers except when the reaction proceeded very vigorously and forced the gases rapidly through the system. This occurred in most of the experiments in which an excess of sugar was present and brought the total nitric acid recovered in the latter part of the apparatus to more than 10 per cent. For most of the experiments, therefore, the potential recovery capacity of these latter scrubbers was far in excess of the acid actually recovered in them, and the losses of nitric acid found by the experiments are due to the formation of unrecoverable gases
Vol. 22. No. 9
EFFECTOF VARYING QUANTITY OF Xnos~--Lossof nitric acid is related to the amount of sugar added to a given amount of nitric acid. The data in Table I11 show that both the per cent loss and the absolute loss of nitric acid increase with increasing quantities of xylose. It is further evident that when 0.267 mol of xylose was oxidized with 0.386 mol of nitric acid there was insufficient acid to cause complete oxidation, resulting in a flattening of the curves in Figure 4. However, an increase in the quantity of sugar taken per mol of nitric acid also results in a larger yield of acids until the molar ratio of sugar to nitric acid becomes approximately 1:2. This is shown in Figure 4 in which the number of mols of xylose is plotted against titer of organic acids produced, the quantity of nitric acid being constant. The increased loss of nitric acid occurring with larger portions of xylose is therefore offset by the higher yields of organic acid. EFFECTOF VARYING THE QUANTITY OF NITRICAcm-The amount of nitric acid present also has its effect on the loss of this acid. The continuous lines in Figure 2 show that the percentage of nitric acid lost does not change greatly with increasing quantities of nitric acid and that, therefore, the absolute loss does increase, as shown by the continuous lines in Figure 3. On the other hand, it will be observed that a great excess of nitric acid does not markedly increase the yield of organic acids. For example, the molar ratios of loss Nofe-The high titer obtained for the 2-hour time period with 0.915 mol of nitric acid is undoubtedly caused by overoxidation during the extended oxidation and may be discounted for the present consideration. Further evidence will be presented which indicates t h a t this value is high.
IO
12 14 16 I6 20 22 24 26 28 30 Titer of orqonic acids produced (ml. 10N NOOH)
Figure 2-Relation of Titer of Organic Acids Produced to Per C e n t Loss of Nitric Acid
such as nitrous oxide and nitrogen during the oxidations, except for a possible loss of nitric oxide up to 3 per cent as indicated above by the sodium nitrite data. I n addition to the rapid movement of the gases in the presence of excess sugar, it should be pointed out that more nitric oxide would be formed under these conditions which would not be collected with nitrogen peroxide in the first alkali scrubber (Equation 8), but would later be oxidized to nitrogen peroxide in the oxidation tower and retained in the succeeding scrubbers. The amounts of nitrous oxide, nitrogen peroxide, and nitric acid vapors which are present a t any particular stage of the reaction are not known (2). This phase of the nitric acid recovery problem, as well as the identification of the nitrogen-containing gases that escape fixation, should be investigated further. Relation of Loss of Nitric Acid to Yield of Organic Acid
12 14 16 18 20 E2 24 26 28 30 Titer o f o r q o n i c acids produced Irnl. 10N NOOH) Figure 3-Relation of Titer of Organic Acids Produced t o Molar Loas of Nitric Acid
It is necessary to compare loss of nitric acid with gain in yield of organic acids in order to arrive a t the best operating conditions for the oxidation of xylose. Figures 2 and 3 summarize the data that have been obtained regarding the effect of certain variables on this reaction. I n Figure 2 the per cent loss of nitric acid is plotted against the titer of organic acids produced; Figure 3 presents the same losses of nitric acid plotted as molar or actual losses. The broken lines give a comparison between the loss of nitric acid and the amount of organic acids formed by the action of a given &mount of nitric acid upon increasing amounts of xylose; the continuous lines represent the data for increasing quantities of nitric acid in the presence of a given amount of xylose. The effect of time on the reaction is obtained by using different symbols for each time period and plotting the separate curves.
of nitric acid to yield of organic acid in three experiments in which the quantity of nitric acid was varied, keeping the amount of xylose and time constant, were 0.039 to 0.090, 0.053 to 0.095, and 0.105 to 0.106. An excess of nitric acid, therefore, causes an increased loss of nitric acid without a comparable accompanying gain in yield of sugar acids. Furthermore, any excess of sugar would be unoxidized and the cost of this sugar or its recovery would be added to the operating expense, If the percentage yield of organic acids is plotted against the molar ratio of nitric acid to sugar, keeping the time constant, as shown in Figure 5, it is found that the optimum ratio of sugar to nitric acid is about 1:2. This is also the theoretical ratio based on Equations 1,2, and 3. Presumably enough of the reduced nitric acid is recovered in the mother liquors to offset the nitric acid which is not utilized because of dilution.
io
INDUSTRIAL A N D ENGINEERING CHEMISTRY
September, 1930
EFFECTOF VARYINGCONCENTRATION OF NITRIC ACIEThe effect of variation of the concentration of nitric acid was not studied independently, but it will be noted in Table I11 that in those experiments in which the concentration was varied between 22.5 and 45 per cent along with the quantity of nitric acid, no appreciable change was noted other than that due to the increments of nitric acid. Similarly no change in the shape of the curves in Figures 2, 3, and 5 is caused by
979
recovery system. This same relationship is found to be true for the other experiments in which the time period was varied. This fact leads one to the conclusion that there is a definite reaction taking place which gives rise to the formation of nitrous oxide or nitrogen gases which are not oxidized or absorbed in the recovery system. Moreover, examination of the data in Table I11 and the curves in Figure 4 shows that no appreciable increase in the
.06 .08
.IO .I2 .I4 .I6 .I8 .ZO 2 2 .24 .26 2 8 Mols. xylose ( H N 0 3 = 0.386 mol.) Figure 4-Effect of Quantity of Xylose and T i m e o n Titer of Mother Liquors
R a t i o of nitric acid to xylose of Nitric Acid-Xylose Ratio to Yield of Organic Acids
Figure 5-Relation
varying concentration of nitric acid. Inasmuch as the cost of manufacturing nitric acid increases with concentration, and since the starting material for sugar oxidations may often be a molasses or sirup, a low operating concentration of nitric acid is essential for commercial oxidations. These experiments show that the nitric acid may be used in concentration as low as 25 to 30 per cent. EFFECT O F VARYINQ TIMEO F OsI~A~Io~--4nother factor which strikingly affected the percentage of nitric acid recovered was the duration of the heating or the period of oxidation. Figures 2 and 3 show very clearly the increased losses of nitric acid when the heating is prolonged. When this increased loss of nitric acid is compared with the decrease of residual nitric acid in the mother liquors, a very important relationship is disclosed. I n the three experiments listed in Table I11 in which 0.080 mol xylose was oxidized with 0.915 mol of nitric acid, the decrease in residual nitric acid in the mother liquor is 0.28 mol between 0.5-hour and 1-hour heating periods and 0.66 mol between 1- and 2-hour heating periods. The increases in loss of nitric acid during these intervals are 0.25 mol and 0.65 mol, respectively. I n other words, after the first half-hour of oxidation practically all the nitric acid that disappears from the oxidation vessel escapes fixation in the
GA-
.r"o"s',' Grams 10 10 20 40
HNOs CONCN. ADDED OFHNOJ "03
MI.
Per cent
60 60 60 60
33.6 33.6 33.6 33 6
Grams 24.316 24.316 24.316 24.316
GLU- "01 C O N C N . O F HS08 COSE ADDED H S O J
Grams MI. 20 60 40 60
Per cent 33.6 33.6
Fig-
TIME OF OXIDAS TION
Grams Hours 24.316 1 24.316 1
Relative Proportions of Monobasic and Dibasic Acids
It has been mentioned above that the method used to differentiate between the sugar acids is only approximate. The accuracy of the method used may be judged by inspection of' the data in Table 111. The molar sum of the monobasic and dibasic acids formed is in most cases greater than the mols of sugar taken, owing probably to breaking down of dibasic
NITRIC ACIDRECOVERED IN:
TIMEOF
Hours 1 2.3 1 1
titer of organic acids is produced by extending the time of oxidation from 1 to 2 hours. The only exception is the value obtained with 0.08 mol of xylose oxidized with 0.915 mol of nitric acid. As explained above, this anomaly is apparently due to overoxidation and is given little weight in the conclusions drawn from these experiments. It is included because its behavior is normal in regard to the nitric acid recovery. The period of oxidation, therefore, should be kept to a minimum, since further heating results in increased losses of nitric acid without material effect on organic acid production. For larger scale production, the time period will be largely dependent on the efficiency of mixing the contents of the oxidation vessel and also on the necessary control of the reaction to prevent a fume-off.
1
Oxidation vessel ( A )
Distillate vessel ( B )
Per cent 66.13 50.95 46.43 21.25
Per cent 19.53 24.29 27.99 44.35
2nd
Ist
scr$per ?t;y% Per cent 9.53 11.86 15.40 15.32
Per cent 0.17 0.23 0.21 0.63
Per cenl 0.03 0.09 0.02 0.12
NITRIC ACIDR E C O V E R E D Oxidation Distillate vessel ( A ) vessel ( B )
Per cent 28.38 10.01
Per cent 37.34 38.15
1st Oxidation scr(uCPber tower (D)
Per cenl 22.73 24.13
Per cent 0.12 10.24
APPROX.CONCN. OP
nNoaI N :
3rd, 4th, and
5tt:7zl',$y Per cenz 0.04 0.12 0.03 0.12
Per cent 95.43 87.54 90.08 81.78
IN:
2nd 3rd, 4th, and scrubber 5th scrubbers (E) ( F ,G , H )
Per cent 0.04 2.22
Per cent 0.03 0.43
liquor
Distillate
Per cent 26 24 16
Per cent 27 24 44
..
A P P R O X . C O N C N . OF HNOs I N :
Total
Per cent 88.60 85.18
?$:? Per cent 10 3
Distillate
Per cent 40 30
980
INDUSTRIAL AND ENGINEERING CHEMISTRY HNOI
GALACTOSE
Mol 0.056 0.056 0.111 0,222
Mol 0.386 0.386 0.386 0.386
_____
CONCN.OF HNOi
Per cent 33.6 33.6 33.6 33.6
Table VII-Oxidation CONCN. OF
”0s
Mol 0.111 0.222
Mol 0.386 0.388
Percent 33.6 33.6
TIME OF HNOa LEFTIN HNOs DRIVENFROM Loss OB OXIDATIONMOTIIER LIQUOR OXIDATION VESSEL HNOa
Hours
1 2.3 1 1
Mol 0.255 0.197 0.179 0.082
Mol 0.131 0.189 0.207 0.304
1 1
Mol 0.018 0.048 0.038 0.070
Loss OF
M
~
$MUCIC ~ACID ~
HNOa
Moruna T,mrrna
PPT.
Per cent 4.57 12.46 9.92 18.22
Mol 0.078
Md 0.010 0.016 0.019 0.015
0.088
0.145 0.248
of Glucose: Effect of Various Factors on Nitric Acid Loss a n d Organic Acid Yield
TIMEOF HNOa LEFTI N “Os Loss OF OXIDATIONMOTHER LIQUORF R o ~ ~ ~ ~ rHNOa l o M
Hours
Vol. 22, No. 9
of Galactose: Effect of Various Factors on Nitric Acid Loss a n d- Oreanic A r i d Yield ~.~~ _~__.~..
Table VI-Oxidation
Mol 0.110 0.039
Mol 0.276 0.347
sugar acid into oxalic and other acids of small molecular weight. However, fair agreement of the molar sums for each group of experiments in which the amount of xylose taken wa.s constant indicates that the relative amounts of monobasic and dibasic acids can be approximately ascertained by the procedure used. For more accurate analyses of the mother liquors the pure acids must be studied electrometrically and their ionization constants determined in order to select, if possible, indicators which will effectively reveal the respective amounts o€ monobasic and dibasic acids present. The probability of the presence of other oxidation products of these acids, such as oxalic acid, or of the original sugars must also be considered. Further experiments are under way on a study of the mother liquors from the oxidation of these sugars, particularly xylose, to include means of separating the acids and identifying them and of developing methods for control analyses on the oxidation process.
Mol 0.044 0.071
HNOa
OF
TITEROF ORGANIC ACIDS IN M~~~~~ L~~~~~
Per cent 11.40 18.42
MI. 10 N NaOH 17.55 25.13
MONOBASIC DIBASIC ACIDIN ACIDIN M~~~~~ LIQUORMOTHER LIQUOR
Mol 0.146 0.113
Md 0.015 0.069
Oxidation of Galactose and Glucose
For comparative purposes a few oxidations of crude galactose and pure glucose were carried out. The results are set forth in Tables IV, V, VI, and VII. The procedure used was the same as that of the experiments with xylose, except that in the case of galactose the dibasic acid, mucic acid, precipitated, and was separated from the mother liquor by filtration before dilution. The losses of nitric acid and the organic acids produced .are found to be dependent upon the same variables that affected the xylose oxidations. Literature Cited (1) Acree. British Patent 160,777 (March 18, 1921); C. A . , 16, 2545 (1921). (2) Burdick and Freed, J . A m . Chem. Soc., 43,518 (1921). (3) Hall, Slater, and Acree, Bur. Standards J . Research, 4, 152 (1930): Schreiber, Geib, Wingfield, and Acree, IND.ENO.CHBM.,sa, 497 (1930). (4) Markley and Hann, J . Assocn. Oficial Agr. Chcm., 8,455 (1925). (5) Tollens, “Kurzes Handbuch der Kohlenhydrate,” p. 731,Leipzig, 1914.
The Silk-Soaking Process* I-Effect of Soap and Other Alkali on Silk Sericin Ralph Hart THE HARTPRODUCTS CORPORATION, 1440 BROADWAY, ~ ‘ E WYo=, N, Y.
It was shown that, when raw silk is soaked in a solution of soap, there is a marked decrease in the concentration of fatty matter and particularly of alkali in the solution. This is due to an adsorption by the silk and to the interaction between the silk sericin and the soap-alkali. There is developed at the same time, probably as a result of the decomposition of the soap by the sericin, a large amount of free fatty acids. Consequently the treated silk, as well
as the spent liquor, contains a considerable amount of free fatty acids. The quantitative distribution of the ingredient after soaking is given and the results graphically represented. It is also indicated that a small but constant fraction of the sericin is capable of reacting with excess alkali in the cold and that ita combining weight with alkali is probably on the order of fatty acids.
.............. HE cocoon of the silkworm produces simultaneously two continuous filaments which immediately upon spinning are cemented together into a single fiber by natural gum substance called “silk gum” or “sericin.” The fiiament proper or fibroin and the sericin are proteins of practically identical ultimate composition and somewhat similar chemical properties, though they differ greatly in physical characteristics. To produce the raw silk skein of commerce a number of cocoons are heated in hot water to soften the gum, their ends joined together, and the cocoons unwound simultaneously. They are then twisted to increase the “cohesion” of the individual fibers, and finally reeled on a swift,
T
1
Received May 19, 1930.
producing a skein of strands which is stronger, heavier, and more uniform than the individual filaments. The quality and strength of the thread, however, reeled at the filature is still insufficient for the purpose of knitting or weaving, and hence is subjected to a series of mechanical operations known as “throwing,” which consist of re-winding the silk on suitable holders, cleaning and in other ways rendering the fibers more uniform, and finally of doubling and spinning, or twisting a number of threads together. As a preliminary to throwing, the yarn is nearly always treated with an emulsion of oil and soap or their equivalents, which treatment may be done either by spraying or soaking. The function of the oil seems to be entirely physical and
~
