FEBHUAIIY, 1940
INDUSTKIA4L 4 U D E U G I U E E H I \ G CHEZIISTKI
represent a yield in excess of 99 per cent and the product will be over 99 per cent pure. Since thiodiglycol possesses both a military arid potential synthetic significance, the object of this investigat'ion ha5 been to determine whether a distinct operation exists in this recently discovered reaction whereby thiodiglycol can be synthesized commercially. The hIeyer method has been prohibitively expensive for the last fifty years, particularly by comparison with the method outlined here which operates a t a small fraction of the former raw material, process, and equipment costs.
Acknowledgment The authors acknowledge to K. ?VI. Malisoff of the Polytechnic Institute of Brooklyn his suggestion of this subject
169
for investigation. They are also appreciative of the assistance on kinetic theory given them by C. E. ITaring of the Institute.
Literature Cited (11 Chichibabin, -1.E., French Patent 769,216 (1934). ( 2 ) Meyer. V., Ber., 19, 3259 (1886). (3) Nenitzescu, C. D.,and Scarlatescu, N.,A n t i g a z (Bucharest), 9, S o . 9 10, 12-21: Yo. 11 12, :3-11 (1935). (4) Othmer, D. F., ISD, Esc,. CHEM.. 21, 576 (1929). (5) Taylor. "Treatise on Physical Chemistry". 1934: Hinshelwood "Kinetics of Chemical Change in Gaseous Systems", 1934. ( 8 ) K h i t m a n and Keats, .J. I N D .ESG. CHEM..14, 185 (1922).
HYDROLYSIS OF PEANUT HULLS FRANK C. VILBRANDT, C. B. MATHER, AND R . S. DICKS
The action of water and dilutions of sulfuric acid on finely ground peanut hulls was studied at 20". SO", 80", and 100" C. with liquid to solid ratios of 10 to 1 and 8 to 1. For the series of concentrations of 0.2. 1.03, 2.15. 1..47. and 7.1i N a t 20". 50". and 80" C., a modified reactor was used which consisted of a dryer to recirculate the saturated air and ceramic crocks to hold the masses. The highest yields of reducing sugars produced under the conditions inwestigated occurred at 80" C. with 8 hours of treatment and a t 4.17 V concentration. Calculated as dextrose, this is a Field of 29.3 per cent of the weight of the dry hulls. Higher concentration of acid resulted in decomposition of the peanut hulls and hydrolysis products. Temperature showed a marked increase in hydroljsis. For the 100' C. series. hydrolysis at 0. 0.2, and 0 . 4 was studied ower a 18-hour period in a closed jacheted kettle. Results showed that thr carbohydrate portions of the peanut hulls form into pentoses and some other reducing sugars. Ower a long period of time ewen the 0.4 V concentration produced decomposition. a\
A
CCORDISG to Lloyd and Palmer ( 7 ) , "the term hy-
drolysis is applied to reactions of both organic and inorganic chemistry wherein water affects a double decomposition with another compound, hydrogen going to one component, hydroxyl to the other". Much of the work on the chemical transformation of pentosic-cellulosic-lignosic materials has been done with a view to producing either a cellulose pulp or pentose sugars and their derivatives. It has been shown that the pentosan and cellulose portions of these materials are hydrolyzed by the action of dilute acids to form pentose and hexose sugars and their further hydrolytic products.
Virginia Pol) technic Institute, Blacksburg, Va.
Hydrolysis of Cellulose According to Schorger (14), dilute acids a t the boiling point, or when allowed to dry on t'he fibers of cellulose, produce chiefly hydrocellulose which may be converted into glucose by the action of dilute acids under pressure (15). Groggins (8),however, states that the glucose resulting from the hydrolysis is partly decomposed if left in contact with the acid a t high temperature and pressure. He states that cellulose can also be hydrolyzed to cellobiose by its own specific enzyme, cellulase. Minor ( l a ) , in explaining the mechanism of hydrolysis of cellulose, reports that a mucilaginous, soluble dextrin is first formed which is adsorbed by the remaining cellulose to form a reactive insoluble mass known as hydrocellulose. Like Schorger, Minor concludes t,liat the complete hydrolysis of cellulose leaves only soluble dextrins. Spurlin (16) states that structure of the fiber and degree of swelling have no detectable influence on the type of reaction when the degradation of cellulose is accomplished by t)he action of dilute acids. H e also states that the rate of reaction is not dependent on the fiber structure or degree of swelling since the hydrolysis does not depend on the diffusion of any s u b st'ance.
Hydrolysis of Pentosans Pentosans constitute the major portion of that part of' cellulosic material known as hemicellulose, a polysaccharide soluble in dilute alkalies and convertible into simple sugars by heating with dilute acids under pressure ( I S ) . According to Holleman (IO), pentosans are polyoses of the pentose sugars such as xylose, arabinose, and mannose. On heating xibh dilute acids, the pentose sugars are deconiposed to form furfural. The quantitative determination of pentoses or pentosans is based on the quantitative conversion of pentoses to furfural by 12 per cent hydrochloric acid ( 3 ) .
INDUSTRIAL ,4SD ENGINEERING CHEMISTRY
170
Composition of Peanut Hulls Peanut hulls and other cellulosic agricultural waste products are composed chiefly of a carbohydrate portion and a ligneous portion. The carbohydrate portion consists essentially of pentosans and cellulose. Hydrolysis of pentosans yields pentose sugars, and cellulose may be hydrolyzed to yield dextrose. The ligneous portion is not subject to hydrolysis, concentrated acid having no effect. Lignin, however, may be extracted by the use of hot strong alkali solution. The following table illustrates the relation between peanut hulls and other agricultural wastes: Material
Cellulose %
Peanut hulls ( 1 1 ) 44.9-46.5 Cornstalks (18) 38.4 Oat hull8 (6) 36.04* Cereal straws (1.9) 38-43 a Reported a8 crude fiber. b Reported as xylose.
Pentosans % 18.5-19.4
27.6 39.lb 25-30
Lignin %
Ash
33.4-33.7 34 3 20.69 24-28
1.6-1.9
%
...
7.32 3.80
Hall, Slater, and Acree (9) investigated the hydrolysis of the pentosan portion of peanut hulls as a source for the pentose sugar xylans. They found that peanut hulls contained 17 to 20 per cent of furfural-yielding materials which they considered to be mainly xylose. I n preliminary tests they found that 0.2 N sulfuric acid extraction of hulls originally yielding 10.8 to 10.9 per cent furfural, reduced the furfural yield of the residue t o 5.1 per cent; likewise, extraction with cold 42 per cent hydrochloric acid reduced the furfural yield of the residue to 6.5 per cent. Treatment with 2 per cent sodium hydroxide for one hour at 100" C. increased the furfural yield of the residue to 11.1per cent. Battery extraction with 0.2 N sulfuric acid reduced the hulls from 34 to 40 per cent in weight when treated for one hour a t 10 pounds per square inch (0.7 kg. per sq. cm.) steam pressure. Increasing the concentration of the acid from 0.16 to 0.35 N had little effect on the extraction. Fred, Peterson, and Anderson (6) hydrolyzed peanut hulls n-ith 2 per cent sulfuric acid and obtained a yield of 7.6 per cent reducing sugars which, upon fermentation, produced 2.6 per cent acetone, 2.4 per cent ethyl alcohol, and 2.5 per cent volatile acids, calculated as acetic. Holleman (IO) stated that the pentoses cannot be fermented and that the degree of fermentation is a measure of hexose formation. De Belsunce (4) treated 8 kg. of peanut hulls with 7 kg. of dilute sulfuric acid (strength not given) according to the bleunier process and obtained 21.8 per cent reducing sugars (completely fermentable), 4.38 per cent alcohol, 2.66 per cent furfural, and 0.47 per cent acetone with one hour of treatment.
Experimental Work on Peanut Hulls The hulls were obtained from the peanut products plant a t Suffolk, Va., where approximately 59,000,000 pounds of
hulls are available annually. These hulls were ground in a "Cnique" attrition mill. size S o . 13, to 95 per cent passing the 20-mesh U.S. standard screen. The chemical analysis of the original ground hulls is as follows, in per cent on a dry basis : Moisture Ash Ether extract
Q
c.
1
80
2 3
SO SO
4 5
80 80 80 50
6 7 8 a
Water
93.2% Sulfuric Acid
Grams
Grams
2999 2990 2920 2860 2740 2560 2740 2740
0.0 31.6 162.0 333.0 716,O 1160.0 716 0 716.0
Temp.
,
20
O n basis of dry hulls.
b
Pentosans Reducing sugars (actual) Cellulose
4.6Y 3.16 3.22
PROCEDURE. Hydrolysis runs using solutions of high concentrations and a t loiv temperatures were made in ceramic crocks as reaction vessels, using a Proctor and Swartz tray dryer for a constant temperature vessel. I t i v y possible to maintain the temperature in this equipment at 80 * 2" C. Saturated conditions of humidity were maintained by evaporation pans and recirculated air. The reaction masses were agitated every 15 minutes with a glass rod. Hydrolysis runs at approximately 100" C. and at low concentrations were made in porcelain jars in a steam-jacketed copper kettle viith mechanical agitation. A steam-jacketed, copper vacuum still, manufactured by the F. J. Stokes Machine Company, serial S o . A6630, was modified for use as a reaction kettle. The condenser, ordinarily attached to the still, was cut off from it by the insertion of a copper plate into the flange connecting the entrance to the condenser and the vapor tube from the still. In order to secure some refluxing of vapors, an air-cooled condenser consisting of a coil of standard half-inch copper tubing wxs connected, in place of the trap, between the entrainment eliminator in the vapor line and the still proper. To maintain uniform steam-jacket temperatures during the course of a run, a pilot-type diaphragm steam-pressure-regulating valve was used. rlgitation of the liquid and hulls mixture in the vessel was accomplished hy a small "Lightnin" mixer, model C-3. The shaft and propeller of the mixer were introduced into the still by removing one of the sight glasses from the top of the still and sealing the lower bearing of the mixer into the sight glass opening with a strip of sponge rubber. The tdmperature of the liquid and hull mixture was measured by an electric resistance thermometer type-A resistance bulb which was suspended with a length of iron pipe, threaded into the thermometer opening on the top of the still. The temperature of the reacting mixtures was checked a t one hour or shorter intervals. Samples of the material in the vessels were taken at regular intervals. A t the same time the samples were taken, the kettle pressure and temperature and the pressure of the jacket steam were noted, recorded, and controlled to uniformity. The samples were immediately filtered and analyzed for total reducing sugars and pentoses.
ACID O S
HYDROLYSIS O F 286.5-GRAM PORTION8
Normality Acid/U~ater/Hulls 0 0 /10.6/1.0 0.10/10.4/1.0 0.52/10.2/1.0 1.08/10.0/1.0 2.32/ 9.7/1.0 3.741 9 . 2 / 1 . 0 2.32/ 9.7/1.0 2.32/ 9 . 7 / 1 . 0
Time of hydrolysis in hours.
16.03 1.63 50 to 60
The moisture content of the original ground hulls was determined by drying weighed samples to constant xeight a t 105" C. Ash was determined by heating weighed samples of the ground hulls a t a medium red heat for 12 hours in an electric muffle. The determination of ether extract was carried out as directed by the official A. 0. A. C. method ( 2 ) . Total reducing sugars were determined by the method of Quisumbing and Thomas (1). The total reducing sugars mere calculated as dextrose by the tables of Quisumbing and Thomas. The pentosan content of the original hulls It-as obtained from the official ii. 0. A. C. method of Krober ( 3 ) . The cellulose content of the original hulls was estimated by the Sieber and Walter method as given by Schorger (17).
AND CONCENTRATIOPI' O F SULFCRIC TABLE I. EFFECTO F TIME,TEMPERATURE, PEANUT HULLS
Run Xo.
VOL. 32, NO. 2
of
Soln. 0.0 0 20 1.03 2.15 4.47 7.47 4.47 4.47
Reducing Sugars"
0.5s
1.0
2.0
4.0
%
%
%
%
1.90 5.33 6.90 12.60 21.75 21.20 7.66 6.31
2.10 6.00 10.04 17.48
1.50 5.28 5.71
8.82 19.08 8.50 6.18 5.87
23.60 24.03 9.00 6.75
2.20 8.15 15.68 21.20 27.23 25.10 8.93 6.98
8.0
% 2.50 11.10 22.08 25.00
29.30
27.20 12.10 7.11
OF
FEBRUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
ANALYTICAL METHODS. To determine the total reducing sugar content of the solution, duplicate 25-cc. samples were measured out. The samples for analysis were first neutralized by the addition of precipitated calcium carbonate, then clarified and analyzed according to the official A. 0. A. C. method of Quisumbing and Thomas ( 1 ) . The method of direct weighing of the cuprous oxide was used. In all cases the total reducing sugars were computed as dextrose, the values being taken from the tables of Quisumbing and Thomas. Pentoses and pentosans in the filtrate were determined by the official -4. 0. A . C. method of Krober ( 3 ) . The residue left after filtration of the final sample was thoroughly washed with distilled water and dried, and the ash and pentosan content determined. The pentosan content of the final residue was found by the official A. 0. A. C. Krober method (5). The ash in the final residue was determined by heating neighed samples of the residue in porcelain crucibles at red heat in an electric muffle.
171
The dry-hulls basis was used to compensate for differences in liquid to solid ratio in the different runs; thus all runs were placed on a common basis for comparison. Percentages of the various constituents were converted from the filteredsolution basis to the dry-hulls basis by multiplying the percentages on the filtered-solution basis by the original liquid to solid ratio, or the grams of liquid originally present per gram of dry peanut hulls. The results are summarized in Tables I and 11. A uniform weight of 286.5 grams of the hulls (bone-dry basis) mere used in the tray-dryer equipment, in gallon-size jars; samples were taken after 0.5, 1, 2, 4, and 8 hours. The data ohtained in these runs are plotted in Figure 1.4 and B. Since temperatures a t 100" C. could not be maintained in the dryer equipment, the still provided the necessary closure to permit this elevated temperature. I n these cases longer periods of reaction were carried out; the samples mere taken a t 3-hour intervals during the first 12 hours and a t 6-hour intervals during the following 24 hours, and a final sample a t the end of 48 hours. The data are plotted in Figure IC.
Effect of Time and Concentration of Sulfuric Acid at 80' C. The data in runs 1 to 6, Table I, and the curves of Figure I d
I %.'
ON I
30-
i
I 2
HYDROLYSIS OF PEANUT HULLS AT
I
1
1
eo-c.
4
I
6
I
I
5
0
show the amount of reducing sugars produced as a function of the time when the temperature of the reaction is 80" C. The curves are similar in that a rather rapid change seems to take place in the first 4 hours; then the slopes are reduced with the exception of the curve for 1.03 N sulfuric acid. It is probable that this slow increase will continue until a maximum value for each is reached, which will possibly approximate 35 per cent. TABLE11. EFFECTOF TIMEAND COSCENTRATIOX OF SULFURIC ACIDAT 101-104" c. ON HYDROLYSIS OF PE.4XlJT HULLS
6.EFFECT OF TIME L TEMPERATURE ON HYDROLYSIS OF P E A N U T H U L L S WITH
4.47 N
Run No.
9 450 3620 0 0/8.05/1 0.0 C . 102-3
HnS04
10
.a
11
457 462 3620 3791 80.0 38 1 0 084/8 02/l.O 0 . 1 7 3 / 8 . 2 0 / 1 0 0.20 0.40 101-3 1024
Reducing sugars. % 3 0 hr. 9 . 0 hr. 1 8 . 6 hr. 3 0 . 0 hr. 4 8 . 0 hr.
I
I
I
I
I
I
I
Pentosesa, % 3 . 0 hr. 9 . 0 hr. 1 8 . 6 hr. 3 0 . 0 hr. 4 8 . 0 hr.
Final residue, % Pentosan Ash Ratio total reducing sugars to pentoses a
T I M E
IN
FIGURE 1
HOURS
2.1 2.5 3.3 4.2 4.5
7.4 11.1 19.5 26.8 25.6
10.2 15.2 18.1 20.6 21.7
0.64 1.02 1.28 2.71 2.17
4.20 6.04 10.6 13.1
5.47 8.35 12.0 12.4 13.1
17.0 2.06
10.9 1.83
5.8 1.78
2.14
1.55
1.42
...
Calculated from pentosans.
The curve on the 4.47 N acid run shows that a vigorous action takes place when the hulls are first mixed with the solution. If all the reducing sugars are calculated as dextrose, over 20 per cent of the weight of the hulls appears in the solution as reducing sugars after the first hour. The curve flattens off after 2 hours. The highest value for reducing sugars occurs in this run after 8 hours and was 29.3 per cent (based on the dry weight of peanut hulls charged).
172
INDUSTRIAL A I D EKGINEERING CHEMISTRI-
The curve for the 7.47 S solution falls below the one for the 4.47 S and indicates that possibly the reducing sugars n ere decomposed after formation. Considerable action took place as soon as the hulls were put into the 7.47 S solution. The solution blackened somewhat, and the residue, separated by filtration, showed signs of decomposition. Higher concentrations of sulfuric acid were tried, and 12 N sulfuric acid was found t o cause frothing and carbonization as soon as the hulls were mixed with it a t a temperature of 80” C. After about 4 hours the residue was a black, gelatinous mass. Lloyd and Palmer (7) comment that the wood extract in 40 per cent sulfuric acid (Scholler-Tornesch process) must be cooled immediately to prevent decomposition of the sugars present.
Effect of Temperature with 4.47 N Sulfuric Acid The data for showing the effect of temperature when other conditions are constant are given by runs 5, 7, and 8 in Table I and are plotted in Figure 1B. The curves follow the same general trend; the reducing sugars produced increase rapidly during the first hour of reaction, then the curves level off. Temperature seems to have a marked effect on the rate of hydrolysis of peanut hulls to reducing sugars. Too high temperatures appear to cause decomposition of the sugars, too low temperatures seem to retard the reaction.
Comparison of 0.2 N and 0.4 ,1’Sulfuric Acid and Water as Hydrolyzing Agents Figure 1C shows the apparent conversion of peanut hulls to reducing sugars upon treatment with water and with 0.2 and 0.4 N sulfuric acid, and the variation of this conversion with time. It is evident that u p to 12 hours, 0.4 N sulfuric acid is the most efficient hydrolyzing agent. However, the difference between the action of 0.2 N sulfuric acid and water i. considerably more than the difference between 0.2 A’ and 0.4 S sulfuric acids. After 12-hour hydrolysis the curve representing hydrolysis with 0.2 sulfuric acid crosses the curve representing that with 0.4 X acid, and rises considerably above it; apparently the 0.2 S curve shows a greater amount of hydrolysis. The sugars produced apparently increase with time, but the rate of conversion slows up, and there seems to be little hydrolysis after 36 hours of treatment. Analysis of the dry final residue, tvith water and dilute sulfuric acid as hydrolyzing agents, showed that the pentosan and ash content decreased as the original acid concentration increased. It seems that within the range of acid concentrations used, the amount of hydrolysis of the pentosan portion of the hulls increased with the increase in acidity. The statement of Hall, Slater, and Acree (9) that a large portion of the ash content of peanut hulls is soluble in dilute acid is also borne out by the low ash content of the residue from the acid runs. The assertion that the amount of hydrolysis of the pentosan portion of the hulls increases with the increase in acid concentration of the original hydrolyzing solution is further borne out by the ratio of total reducing sugars to pentoses ivith the acid concentrations used. The ratios expressed in Table TV represent the averages of the total sugar to pen-
YOL. 32. NO. 2
tose ratio in the individual solution samples taken during the different runs. The ratio of total reducing sugars to pentoses decreased as the concentration of acid in the original hydrolyzing solution increased-i. e., as the acid concentration is increased. A greater portion of the reducing sugars present are pentoses, which checks rather well with the decrease in pentosan content of the residue as the acid concentration is increased.
Conclusions 1. Water hydrolyzes peanut hulls to a small extent; bubstances are produced which act as reducing sugars equal t o approximately 5 per cent of the original dry weight of the hulls in 48 hours. 2. Dilute sulfuric acid up t o 0.4 hydrolyzes peanut hulls and produces reducing sugars equal to approximately 22 per cent of the original dry weight of the hulls in 48 hours. 3 . The amount of reducing sugars in solution increases with the time of treatment. 4. The amount of reducing sugars produced from peanut hulls increases as the concentration of sulfuric acid in the original hydrolyzing solution is increased to above 4.5 ,l’. 5 . Concentration of sulfuric acid up to about 2.0 N has a marked effect on the rate of hydrolysis. 6. If the concentration of the hydrolyzing solution of sulfuric acid is above 4.5 *I reducing T,sugars are decomposed at temperatures of 80” C. or higher. 7. The proportion of the total reducing sugars which are pentoses increases as the concentration of sulfuric acid in the original hydrolyzing solution is increased up to 0.4 iV. 8. Temperature has a marked effect on the rate of hydrolyhis of peanut hulls with sulfuric acid in concentrations up to 4 . 5 S; temperatures less than 80” C. induce little action
Literature Cited .hsOc. Official Agr. Chem., Official and Tentative Methods of Analysis, 4th ed., p. 135, Washington, D. C., 1935. Ibid., p. 331. Ibid., p. 344. Belsunce. G. de, Bull. mat. grasses inst. colonial Marseille, 1926, 1-3. Bryner, L. C., Christensen. L. M., and Fulmer, E. I., IND. ESG. C H E M . 28, , 206-8 (1935). Fred, E. B., Peterson, W. H., and Anderson, J. A,, Ihid., 15, 126 (1923). Groggins. P. H., “Unit Processes in Organic Synthesis”, p. 590, New York, McGraw-Hill Book Co., 1938. Ibid., pp. 611-14. Hall, W. L., Slater, C . S.,and Acree, S.F., Bur. Standards J . Research. 4, 329-43 (1930). Holleman, A. F., “Textbook of Organic Chemistry”, p. 239, New York, John Wiley &- Sons, 1930. Lynch, D. F. J.,and Goss, M. J., IND.Eso. CHEM.,22, 903-i (1930). Minor, J. E., Ibid., 13, 131-5 (1921). Schorger, A. W., “Chemistry of Cellulose and Wood”, p. 141, New T o r k , McGraw-Hill Book Co., 1926. lbid., p. 176. lbid., p. 183. lbid., p. 335. (17) I b i d . , p. 514. (18) Webber, H . ri., h D . EXG.CHEY., 21, 270 (1929). (19) Webber, H. -4.. Iowa E x p t . S t a . , B u l l . 118 (1934).
