Thermal Stabilitv of Furfural J A. P. DUNLOP AND FREDUS N. PETERS, JR. The Quaker Oats Company, Chicago, Ill.
The data presented show that, under the specific conditions of these experiments, refined furfural is quite stable. The rate of decomposition at 230' C. is so slow that from an industrial standpoint furfural is thermally stable. No commercial process is known wherein furfural is subjected to temperatures of the magnitude of 230275' C. for more than a few minutes, and the data presented show that it is a matter of hours before a change in the properties of furfural can be detected.
liquid in the tube was only slightly larger than that necessary to allow for liquid expansion on heating. The sealed glass tube waa enclosed in a bomb of iron pi e (Figure I) and then immersed in a vertical position in an oil batg maintained at the desired temperature. To keep a uniform tem rature throughout the bath, the bombs were supported on a racpwhich was rotated continuously through the oil. For the study of the effect of metals, a constant ratio of 0.76 s cm. of metal er cc. of furfural (ratio available in 2-inch pip3 was obtained Ey adding the calculated length of 18-gage wire to the furfural in the glass tube. Preliminary experiments showed that changes in the furfural were so slight after heating for a few hours as to be immeasurable by the ordinary methods of analysis. It was found necessary to heat the samples for extended periods in order to produce changes of measurable magnitude. The data were then plotted and extrapolated t o zero time for the purpose of estimating the changes occurring in furfural during short intervals of heating.
Analytical Methods
T
Samples were cooled immediately on withdrawal from the HE scarcity of information pertaining to the physical oil bath and were analyzed as soon as possible. I n some inand chemical changes involved when furfural is exposed stances, however, analysis was delayed, and some variation to elevated temperatures has led to considerable specumay have been introduced into the data as a result of this lation regarding the thermal stability of this solvent. There circumstance, are numerous processes involving the use of large quantities The difference in furfural content of the DECOMPOSITION. of furfural, sometimes at comparatively high temperatures; initial furfural and of a sample after heating is reported as hence it seems desirable to have quantitative data relating the amount of furfural which decomposed. Analyses were to this subject. The data presented in this paper were obmade by the Hughes-Acree method (4) and checked by the tained about five or six years ago but are now being offered bisulfite-iodine method (3). The results were in close agreebecause of the increasing industrial interest in the stability ment, and indicated that any furan compounds of furfural. which might have been formed by the decomposition The experiments carried out in this study were 1-IN.IRON PIPE 7 of furfural did not interfere with the analysis. I n designed to show the rate of decomposition of furthe event that furan or any other highly volatile fural. They may be divided into two main classes on the basis of the conditions adhered to for the compound was formed, it was undoubtedly lost since purpose of obtaining: a comparison of the stability the heated tubes (especiallyafter prolonged heating) of furfural at 140', 180", and 230" C.; and a were invariably found to be under superatmospheric pressure which was released on opening the tube. measure of the effect of various metals on the staRESINFORMATION. The resin formed on heating bility of furfural a t 230" C. furfural was insoluble in hydrocarbons such as Materials and Preparation of Samples toluene and xylene. The amount of resin in the The furfural used in this work was the refined heated samples was determined in the following rade which has been sold in this country for a nummanner: The treated furfural was shaken vigorer of years. This grade was chosen because in inously, and an aliquot was taken and weighed. The dustrial practice the recovery of furfural results in its refinement. For instance, in solvent refining E aliquot was filtered through a Gooch crucible packed processes, furfural is recovered in a highly purified with asbestos fiber which had been previously heated state after having been once circulated through the a t 105' C. to constant weight. The residue left in plant. The following table shows the properties of the crucible was washed with hot xylene until the the refined furfural under discussion: filtrate ran colorless; then the crucible was heated to Furfural by Hughes-Acree method ( 4 ) , % 99.6 constant weight a t 105' C. Blanks were run using Specific gravity, dzg 1.161 Acidity, moles/liter 8 8 acetic acid 0.025 resin-free furfural, and from the values obtained the Ash % 0 0017 Moihure ( I ) , % 0.24 amount of resin formed was determined. Distillation of 100 00. The samples found to contain 8-12 per cent resin Temp. a t end of 1st drop: ' C. 147 Temp. a t end of 1st cc., C. 153 appeared quite solid. This confirms the finding of Max. temp. a t dry point, C. 162 Berthelot and Rivals (2) when working with old, Recovery, % 99.0 Loss % 0.57 solidified samples of furfural. These workers found Resihue, % 0.43 that only about one tenth of such samples of furfural The furfural supply was stored in sealed bottles in a were nonvolatile, and from a carbon-hydrogen cool dark room. A fresh bottle was opened and anaanalysis of the resin they assumed it to be formed lyzed at the beginning of each series of experiments, FIGURE 1. CROSS by the condensation of three molecules of furfural which accounts for the slight discre ancy between the SE c T I o N o F values for the initial densities a n f acidities of each with the elimination of one molecule of water. series. B O M B A N D ACIDITY. Ten cubic centimeters of the heated In each case approximately 40 cc. of furfural were SEALED TUBE added to a Pyrex glass tube and sealed under a vacuum USED IN Exwere pipetted~into 2oo cc* Of disPERIMENTS tilled water, and the mixture was shaken vigorof 45-50 mm. of mercury. The gas space above the
E
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 32, NO. 12
Discussion /5 x-AT23O"C. 0 - " 1800C. A140°C.
/O
Figure 2 shows the data presented in Table I. It is of the utmost significance that refined furfural shows a decomposition of only 0.28 per cent after 280 hours of heating a t 140" C., and of 0.33 per cent after 185 hours a t 180' C .
5
T ~ B I.L ~EFFECTOF HEATON FURFURAL IN CONTACT WITH
GLASS
0
Temp., C. 140
180
I
aoq-
1 pI
ACIDITY CHANGE 230
61570
HOURS OF HEATING
FIGURE2. EFFECT OF HEATON FURFURAL IN CONTACT WITH GLASS
ously. Phenolphthalein (10 drops) was added, and the mixture was titrated with 0.1 N sodium hydroxide. In many cases the end point was obscured by the dark color of the samples, and it was found advisable to add an excess of sodium hydroxide and then back-titrate with 0.1 N sulfuric acid. The results were calculated as moIes of acetic acid per liter, DENSITY.The density was obtained with 25-ml. gravity bulbs in a constant-temperature bath regulated a t 25' C. OTHERDETERMINATIONS. We planned to include datk on color, refractive index, and viscosity, but it was found impractical to make these determinations. The color darkened rapidly on heating and soon became practically the same for all samples. This color also precluded the possibility of determining refractive indices accurately. Small particles of resin, in suspension in the heated furfural, were responsible for erratic viscosity determinations in an Ostwald type viscometer. The small quantity of furfural available from each sample made it difficult to attempt any other method of determining viscosity. An attempt was made to ascertain the amount of metal corrosion, if any. This was done by weighing the metal before and after treatment, but the difference was very low. A gain or loss in weight of less than 0.015 per cent was observed. A sulfated ash determination on the furfural in a number of cases gave a maximum of 0.02 per cent, of which an estimated one half t o two thirds was metal.
Time,
Decomposition, % 0.00 0.00 30.00 -0.87 70.50 -0.12 121.50 0.03 167.00 -0.04 239.00 0.08 280.00 0.28 0.00 0.00 24.00 0.53 48.00 72.00 -0:k7 97.00 0.09 141.00 -0.02 185.50 0.32 0.00 0.00 0.39 20.00 40.00 0.40 2.54 58.50 59.67 3:96 72.00 5.00 75.00 5.12 79.25 88.25 5.84 15.36 101.00 Hours
Resin Formed,
%
Acidity &a Acetio Mole/Litdr
Density, d:f
0.00 0.00 0.00 0.01
0:01 0.01 0.00 0.01 0:Ol 0.01 0.02 0.01 0.00 0.01 0.03 0:05 0.09
o:i1 2.78 11.93
0.026
...
:
1.1578 1.1579 1.1578 1.1582 1.1583 1.1584 1.1586 1.1576 1.1584 1.1598
0 027 0.027 0.028 0.028 0.025 0.027 0.041 0.031 0.039 0.042
1: iiis 1.1628
0 : hi7 0.049
1.1646 1.1656
...
....
....
The demand for greatest stability is in solvent extraction processes where residual furfural is sometimes flashed off at 275" C., although a maximum of 230" C. is usually recommended. The curves shown for 230" C. are decidedly steeper than those a t 140" and 180" C., and indicate less stability. It will be seen, however, that even a t 230" C. any change in the physical properties of furfural during the short interval required for flashing off is so small as to be undetectable. Any change in the rate of decomposition of furfural due to contact with metals would be expected to be greater a t higher temperatures. For this reason the effect of metals was TABLE 11. EFFECT OF METALSON FURFURAL AT 230" C. Time, Hours 0.00 20.00 58.50 72.00 79.25 88.25 101.00 Polished iron 20.00 40.00 58.50 72.00 79.25 88.25 101.00 20.00 Copper 40.00 58.50 72.00 79.25 88.25 101.00 Nickel 20.00 58.50 72.00 79.25 88.25 101.00 Aluminum 20.00 58.50 72.00 79.25 88.25 101.00 Metal None Black iron
Decomposition,
Resin Formed,
0.00 0.70 2.54 3.29 5.46
0.00 0.01 0.10 0.11 0.18 2.24 10.35 0.02 0.03 0.10 0.12
%
1i:74 0.14 0.74 3.04 3.31 5.38 7.22 17.29 0.34 0.54 3.04 3.61 5.20 5.20 13.59 0.01 2.43 4.22 +:87 17.42 0.01
2.67 3.28 5.90 6.44 16.19
%
4:31 12.39 0.02 0.03 0.09 0.09 0.21 0.16 9.09 0.01 0.06 0.11
...
3.94 12.44 0.02 0.10 0.11
...
3.94 12.57
Acidity as Acetic Mole/Lite(r 0.025 0.027 0.045 0.043 0.048
... ...
Density, d;; 1.1576 1.1588 1.1612 1.1626 1.1649
.... ....
0.029 0.035 0.045 0.042 0.048 0.052
1.1585 1.1598 1.1615 1.1629
...
1.1642
0.027 0.035 0.041 0.042 0.046 0.044
1.1585 1.1603 1.1607 1.1621
...
0.025 0.042 0.045 0.039 0.042
...
0.028 0.041 0.044 0.046 0.049
...
....
....
.... .... 1,1584 .... 1.1622 1.1633 .... .... 1.1635
1.1585 1,1620 1.1626
....
1.1653
....
DECEMBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
studied only at the highest temperature employed-namely, 230" C. The results of this study are shown in Table 11; i t is interesting to note that the curves for furfural in contact with glass a t 230" C. (Figure 2) are the approximate mean of the data on the effect of metals. However, with the possible exception of black iron and copper, the decomposition of furfural a t 230" C. appears to be slightly accelerated after approximately 80 hours owing to the presence of the various metals employed. If there is any initial effect due to the metals, the present analytical methods are not sufficiently refined to show it. Additional work which has not been completed indicates that, when the moisture content of refined furfural is increased, the rate of decomposition a t 230" C. is increased. At
1641
180' C., however, this acceleration is not noticeable, even after prolonged treatment.
Acknowledgment The collaboration of J. Pokorny of G. S. Blakeslee and Company, Chicago, is gratefully acknowledged.
Literature Cited (1) Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 3rd. ed., p. 277 (1930). (2) Berthelot and Rivals, Compt. rend., 120, 1086 (1895).
(3) Dunlop, A. P.,and Trimble, Floyd, IND. ENQ. CHEW, Anal. Ed., 11, 602 (1939). (4) Hughes, E. E., and Acree, S. F., Ibid.,6,123 (1934).
Cellulose Derivatives as Basic Materials for Plastics EMIL OTT Hercules Powder Company, Wilmington, Del.
Cellulose derivatives are adaptable for use in plastics because of their inherent properties. Cellulose is a long-chain molecule whose chemical and physical nature may be changed by different degrees and kinds of substitution. By proper adjustment of the composition of its derivatives, moldability and compatibility with solvents and plasticizers may be altered to conform to diversified plastic specifications. The chainlilie structure of cellulose and cellulose derivatives, the high molecular weight of these chains, and the relatively uniform distribution of the size of such chains contribute to its outstanding strength, toughness, flexibility, and other important physical characteristics. Because of these inherent properties, cellulose products have enjoyed and will continue to enjoy an important place in the plastics industry and related fields.
A
T A TIME when plastics which claim synthesis from basic raw materials such as coal, air, water, coke, limestone, and other similar basic materials have been so widely publicized, it may appear old-fashioned to review chemical products such as cellulose derivatives which cannot claim similar creation in the laboratory and chemical plant. However, in nature's own laboratory, cellulose and hence its derivatives are synthesized similarly from the combustion product of carbon (carbon dioxide) and water, aided by the energy of sunlight and the catalyst chlorophyll in the living plant. Thus, a yearly recurring crop is produced in the form of cotton, linters, or wood cellulose in abundant quantities.
Through this genesis these polymers possess certain inherent properties, only difficultly reproduced by chemical manufacture alone, which make them eminently suitable for use in plastics. The story of the discovery of nitrocellulose about a hundred years ago and of other cellulose derivatives has been adequately told by Sproxton (49),Conaway (3),and others (69, 60, 62). The industrial utilization of the first cellulose derivative, nitrocellulose (19,WO, 36,47, SI),in plastics matured only after the development, during fifty years, of suitable solvents and plasticizers (SO, 31, 41, 48,56). The springboard for the present-day industrial success of cellulose acetate was the discovery, forty years after the first successful acetylation of cellulose (11,44,4-5,64), that partial hydrolysis of the triacetate produced a secondary acetate with profoundly altered properties (34). Commercial production of cellulose acetate began with the demand for airplane dopes during the World War and was further increased by its introduction into plastics in 1926 (15). Recently the production has been accelerated because of its utility in injection molding. The stories of the mixed cellulose esters and of the ethers (6, 8,27, 6.3)are newer but similar, all illustrating the necessity of exact, expensive, and long-time research and plant development work.
Economics and Trends A graphic picture of the growth of the nitrocellulose and cellulose acetate plastics industry is shown in Figure 1. No official figures are available on the newest cellulose ester, cellulose acetate butyrate ( S Y ) , to be adopted by the plastics industry. The introduction of cellulose ethers, particularly ethylcellulose, into plastics is a still more recent development (68). Steadily declining trends in prices of nitrocellulose, cellulose acetate, and ethylcellulose are shown in Figure 2. The abundance and continuous formation of cellulosic raw materials and the ready availability of other important ingredients, such as nitric acid, acetic anhydride, and ethyl chloride, make it obvious that the raw materials for the cellulosederivative plastics industry are of satisfactory supply and relatively low cost.
