186
IND USTRIAL AND ENGINEERIXG CHEMISTRY
This has been done with the figures in Table I1 adding the losses in the Cross and Bevan cellulose and in the pentosans not in cellulose and adding the gains in lignin (corrected for methoxyl) and in alcohol-benzene soluble. With the ash wood the differences between the observed and calculated losses are not consistently of the same sign, but they are perhaps within the limit of error of the sums of determinations involved. With the spruce wood, however, the observed loss is always greater than the calculated and this difference is consistently greater with longer time of heating. It is probable, therefore, that certain substances in the heattreated spruce were isolated and weighed in more than one determination. For instance, it is readily conceivable that a partly degraded cellulose might resist the action of the chemicals used in isolating both the lignin and the cellulose. The changes in “acetic acid by hydrolysis” in the ash wood are of interest in connection with the obscure origin of this product. If the “acetic acid by hydrolysis” comes from acetyl groups that are not isolated with the cellulose or lignin, then the losses in this constituent due to heating should be included in the calculated losses of Table 11. When such losses are included, the calculated losses become 5.0, 9.5, and 9.8 per cent instead of 3.6, 6.4, and 6.7 per cent, and are further from the observed losses of 5.0, 5.8, and 7.7 per cent, respectively, for the three periods of heating. Furthermore, the differences between the observed and calculated losses are of opposite sign from those of the softwood. (The changes in “acetic acid by hydrolysis” in the softwood are negligible.) It seems likely, therefore, that the acetic acid by hydrolysis is formed from some other constituent determined by the analytical methods used and decreases along with that constituent. Since in the ash wood the pentosans are the only constituents that decrease, the indications are
Vol. 23, KO.2
that acetic acid by hydrolysis has its origin in the pentosans, There is shown in Table I a certain amount of parallelism between the figures for pentosans in cellulose and those for acetic acid by hydrolysis. I n the ash wood they both decrease during the first two periods and then remain constant during the third period. In the spruce the changes in both of these constituents are very slight. The experiments recently reported by Campbell and Booth (2) on the analysis of green, air-dried, kiln-dried, and ovendried oak were primarily for the purpose of showing the differences between the green and the dried wood, but there were also differences between the air-dried and the artificially dried samples that might be ascribed to the higher temperatures accompanying the latter treatments. The heat effects on lignin and pentosans were naturally much less than those reported here on account of the lower temperatures used by them, but in these constituents there are no inconsistencies between the higher and lower temperature treatments. I n the case of the methoxyl, however, the results are apparently inconsistent. Even at the low temperatures used they obtained a marked reduction of methoxyl, whereas in the present higher temperature treatments the methosyl remained practically constant. This can perhaps be explained by the different conditions under which the heating took place. Campbell and Booth heated their wood in the open air, whereas the mood used in the present analyses was heated in a sealed tube. Literature Cited ( 1 ) Bray, Paper Trade J . , 81, No. 2 5 , 59 (1928). (2) Campbell and Booth, Biochem. J . , 24, 641 (1930). (3) Hawley and Fleck, IND. ENG. CHEM.,19, 850 (1927). (4) Koehler and Pillow, Southern Lumberman, Dec. 19, 1923. ( 5 ) Pillow, W o o d W o r k i n g I d . , Oct., 1929.
Study of W a x from Low-Temperature Tar’ Joseph D. Davis2 and Kenneth > I . Irey3 PITTSBVRGH EXPBRIMENT STATIOK, U. S. B U R E AOF~ MIXES,PITTSBURGH, PA.
URING the years 1924 I t has been shown t h a t the wax from Utah coal is a tar 11, and 30.80 per cent and 1925, a primary paraffin hydrocarbon wax containing a small percentage tar 111. Table I gives the or 1on:temperature of unsaturates. This wax is of a superior grade as cornd i s t r i b u t i o n of chemical tar was produced in quantity pared with commercial petroleum wax, as it has a higher groups in tars I, 11, and 111, by continuous carbonization melting point, and is a relatively dry wax. and Table I1 shows the disof Mesa Verda (Utah) coal tribution of oils, waxes, and The bituminous coals are found to Yield a tar of low at 700” C. in superheated wax content as compared with t h a t of the Utah coal resins in the neutral oils from steam. The composi$ion and the sub-bituminous coals. Carbonization with these tars, It was noted that of this tar (1, 2, 3) and of the wax content of all these superheated steam tends to increase the yield of wax the gas (6) and light oil as in a tar, but it is not required to obtain an appreciable tar portions was higher than \yell have been s u b j e c t s amount of wax from a coal high in wax-producing conthat reported in the literafor p r e v i o u s investigation. stituentsture; it is seen, for example, This tar c o n s i s t e d of an in Table I1 that the amount oily portion, liquid a t ordinary temperatures, and two solid of wax in the combined portions exceeds 10 per cent of the portions, one lighter and one .heavier than water. These total tar. On considering this and the fact that the wax was have been termed tars I, 11, and 111, respectively, by the of high melting point (54” C.), further investigation seemed previous investigators. worth while for possible industrial utilization of this conThe tar consisted of 28.85 per cent tar I, 40.35 per cent stituent of low-temperature tar. Accordingly, the work described mas undertaken. Received November 24, 1930. Presented before the Division of Gas Enough T ~ a x recovered from tar 11 for purification, and Fuel Chemistry a t the 80th Meeting of the American Chemical Society, determination Of physical and approximate ‘OnCincinnati, Ohio, September 8 to 12, 1930. This paper presents the results StitutiOn Of the purified wax. It was found to consist mainly of work done under a cooperative agreement between the u. S. Bureau of Mines, t h e Carnegie Institute of Technology, and the Mining Advisory of pentacosane (melting point 54” C.) and heptacosane Board. Published by permission of the director, U. S. Bureau of Mines. (melting point 600 c,), j$raxes mere then recovered from (Not subject t o copyright.) tars of several bituminous and sub-bituminous coals, listed in Fuels chemist, U. S. Bureau of Mines. Table V, which were carbonized a t low temperatures in a Research Fellow, Carnegie Institute of Technology.
D
I S D USTRIAL A K D ENGINEERING CHEMISTRY
February, 1931
laboratory apparatus, and melting points of the waxes were determined. In no case was enough wax available for complete investigation, but the melting points were within the range of those obtained from the Utah coal tar. The inference is that they were similar in composition. Tars from bituminous coals did not yield more than 2 per cent wax; those from the sub-bituminous coals yielded 4.5 to 8.6 per cent. Three lom-temperature tars made on a large experimental (semi-commercial) scale from bituminous coals were examined for wax content and found to contain only a fraction of 1 per cent of wax. T a b l e I-Distribution
CLASSESIS TOTAL TIR INCLCDINC
TARI1
% Insoluble (in sulfuric ether) Carboxylic acids Alkali-soluble (phenols) Tar bases Neutral portion lvorkinn loss
1.0 0.3 23.4 1 7 66 0 7.6
T a b l e 11-Oil,
Oil
\Vax Resin Resin present in insoluble matter Neutral Dortion as' per cent of fraction Total a
So K E . 85 7 . 1 2 10 0 . 8 4 5 0.42
grams too high, as a certain amount of substitution takes place, probably occurring in the end carbon atom, as explained by Johansen ( 8 ) . The acid and ester value, as determined according to Holde ( 7 ) , was 1.1 for acid and 5.6 for ester value, the total, 6.7, being the number of milligrams of potassium hydroxide required to saponify 1 gram of wax. The physical constants of the crude lvax were as follows: dE Melting point, C Iodine value plus substitution value Acid value Ester value
0 9211 55 23 1 1 5 6
of Classes of C o m p o u n d s i n U t a h Coal T a r
CLASSESOF COMPOUNDS TARI
T A R~a
187
1
T A R111
CONDEKSATE
%
% 0.85 2.25 15.0 1.55 80.0 0 33
AQUEOUS
%
9.5 2 5 40 0 3.0 45.0 0.0
3 46 2.14 26.85 2.07 63.21 2 27
As there p a s considerable resin in the original neutral oil (see Table II), it was thought possible that the crude wax might contain some resin. As this is but very slightly soluble in petroleum ether (boiling point 40" to 60" C.) and the wax is completely soluble, some of the wax was dissolved in petroleum ether and filtered. There was no measurable amount of resin left on the filter paper, although this was colored slightly. The petroleum ether solution was then treated with 80 per cent sulfuric acid to remove unsaturates. This
Wax, a n d R e s i n i n T o t a l Tar TAR110
%
Kg. 8.12 3.42 18.6 2 . 6 4
37.2 24.1
1
TAR1115
%
TOTAL
&?.
68.9 4.20 10.4 0.63 19.8 1.21
19 44 4 89 4 27
67 78 17 OS 14 89
42 8 10 8 9 4 58
2 3
66
8.38
80 0
14.2
45.0 6.10 28.60
99 72
96
65.3
Neutral portion. per cent of total neutral portion from first three tar portions As per cent of total tar, including that from aqueous condensate.
b As c
9 Method of Recovery and Analysis of Wax
The neutral oil was separated from the tar in sulfuric ether solution. The tar acids were extracted with caustic soda and the bases were removed by washing with 10 per cent hydrochloric acid. The ether was then distilled from the neutral oil, leaving a semi-solid material when cooled to room temperature. The neutral oil was steam-distilled with an oil bath kept at 250" C. under the flask containing the neutral oil. This process carried over most of the light oils. The residue was then refluxed with 5 volumes of acetone and filtered a t 5" C. The residue was allowed to dry in the air and was then recrystallized from 12 volumes of acetone. Wyant and Marsh (10) used 10 volumes of acetone to recrystallize the paraffin wax they investigated, but this proved insufficient to take the wax completely from the Utah tar into solution with refluxing. The recrystallized wax was filtered at 0" C. and washed with 2 volumes of cold acetone. It was then heated on a steam bath to remove any solvent remaining. This wax had a creamy color before it was melted, but when it was fused it turned a dark brown. Repeated crystallization with acetone would not remove this color. Hereafter, this wax mill be spoken of as crude wax. The melting point, as determined by the A. S. T. R1. (5) method (using a Centigrade instead of a Fahrenheit thermometer), was 55" C. The cooling curve (Figure 1) has five distinct rest points or fusion points. This would indicate five different compounds. The iodine value was determined by the Wijs ( 7 ) method. This involves the action of iodine trichloride and iodine dissolved in acetic acid solution. The wax had an iodine value of 23, which means that 23 grams of iodine are absorbed by each 100 grams of wax. This value is approximately 8
g 54
5E 8
52
50
48
0
TIME. MINUTES
Figure 1-Cooling
Curves for Wax
sulfuric acid solution was colored, but did not indicate the removal of more than 1 or 2 per cent of substance. The solution was then treated with 95 per cent sulfuric acid, which should remove the aromatics. This formed a rather thick sludge and indicated the removal of a considerable portion of substance. It is possible that the 80 per cent sulfuric acid failed to remove the unsaturates and the larger portion of the latter sulfuric acid sludge was unsaturates. The petroleum ether solution was then washed with water and a weak solution of sodium hydroxide to remove all traces of the acid, after which it was distilled to 100" C. to remove the ether. As it v a s difficult to eliminate all the petroleum ether in this manner the wax was crj stallized from 12 volumes of acetone. An 85 per cent yield of paraffin wax resulted, and its melting point
INDUXTRIAL A N D ENGINEERING CHEiVISTRY
188
was 55.6" C. (Figure I ) . This wax has only three fusion points, which would indicate that two compounds had been removed from the original crude wax by the purification described. These three definite fusion points may indicate three different paraffin hydrocarbons present in relatively large quantities. The lower fusion point is of very short range and indicates a very slight amount of soft wax. The purified wax was a white crystalline compound before melting, but when fused it took on a brown color, but noticeably lighter than the melted crude wax. As the crude wax was so dark and of such an undesirable character, a method for decolorizing it was worked out. It was found that filtering through fuller's earth in a hot water funnel gave the best results. A white wax could be obtained by repeated filtration, changing the fuller's earth several times. As the supply of wax was limited and the fuller's earth absorbed some of it, it was not completely decolorized, but a wax slightly tinted was obtained for further examination. This was examined in a similar fashion to the crude wax. The determination of the refractive index was made with an Abbe refractometer a t a temperature of 60" C. The molecular weight was determined by the ebullioscopic method in a Beckmann apparatus, benzene being used as a solvent. Table I11 gives the results. T a b l e 111-Constants
I
PARAFFIN WAX ( 9 ) From oil shale
From petroleum
0.7875 1.4362 56.0
0.7841 1.4293 55.4
% 0.7929 1.4425 M-&ing point, O C. 54.6 Iodine value 9.91 13.7 (max.) 5.63 Substitution value 0.27 Acid value 0.62 Ester value 0.70 1.10 Molecular weight 350
dii ny
The specific gravity was taken as described by Buchler and Graves (4); a 5-cc. specific gravity bottle is standardized with water a t 15" C. and the volume calculated a t 60" C. The bottle is filled with the wax and placed in an oven a t 58" C. for 2 hours; the stopper is then put in and the temperature raised to 60" C. for 1 hour. The specific gravity is slightly higher than that of the shale oil and petroleum wax (Table 111). The specific gravity and temperature a t which it was taken vary in an indirect proportion, whereas the refractive index varies in a direct proportion. With this explanation, the properties of the waxes may be considered to agree well. The melting point of the purified wax, slightly lower than that of the crude, is attributed to the fuller's earth absorbing some of the wax of a high melting point. As to the iodine value, little can be deduced, for considerable unsaturation may be present in a given unsaturated molecule; or there may be only one double bond present. If we suppose i t to be one double bond in a molecule with a molecular weight of 350, unsaturates would amount to 13.7 per cent of the wax. This would be the maximum amount of unsaturates in the wax. The percentage of acids and esters was calculated by taking a theoretical molecular weight, and from this the percentage of oxygen may be calculated. By taking the molecular weight of cimic acid (CI4Hz7COOH,melting point 55" C.) which is 242.0, the percentage of acid was calculated to be o'ooo62 X 242 X 100
=
0.268 per cent
A molecular weight of 350 was taken for the determination of the per cent of esters:
X 350 X 100
=
0.7
From the above data the calculated percentage of oxygen is 0.0668. The ultimate analysis of the decolorized wax gave 85.24 per cent carbon, 14.74 per cent hydrogen, 0.05 per cent nitrogen, and no sulfur. As the method of analysis is not accurate to better than 0.1 per cent, the calculated value of oxygen is in agreement with the results. If the wax were a pure pentacosane (G6Hsz),the theoretical percentage of carbon and hydrogen would be 85.24 and 14.76, respectively. I n conclusion, from the ultimate analysis and study of the composition of the wax with its physical properties, it may be safely classified as a paraffin wax of the hydrocarbon series. By fractional crystallization of the decolorized wax with ethylene dichloride (CHzCICHzCl) it separated largely into two major portions, as shown in Table IV. T a b l e IV-Fractional
Crystallization of Decolorized Wax
MELTING POINT
AMOUNTCRYSTALLIZED
c.
%
47.8 50.1 54.3 57.6 59.6 63.6
12.2 6.85 33.0 8.05 32.7 6.8
e
of Decolorized Wax
DECOLORIZED WAX
56
"::"
~ 0 1 23, . SO. 2
The wax is clearly composed of a series of hydrocarbons, and these data indicate a predominance of pentacosane (C25H62, melting point 54" C.) and heptacosane (CnHw, melting point 60" C.) with a small amount of soft wax. On repeated crystallization of the decolorized wax the melting point was constant, which proves it to be a wax free from oil. This indicates a superior grade of dry wax with a melting point higher than the marketable petroleum waxes. Utilization of Wax
Several crayons were molded from the decolorized wax, using suitable pigments to obtain the desired color. When these crayons were warmed in the palm of the hand and pressure was applied, they remained firm, whereas commercial crayons or those made from parawax were pliable when subjected to the same treatment. This would indicate a good raw material for candles or a good grade of wax paper and other waterproof materials. Upon analysis, the commercial crayons proved to be approximately a 1 to 1 mixture of paraffin and fatty acid. Crayons made by adding 10 per cent stearic acid to the wax from Utah tar seemed to have no more desirable characteristics than the crayon made from pure wax. Wax Content of Other Coals
As there is considerable industrial interest in the wax content of tars, it was thought advisable to determine the wax content of tars from several typical coals. Enough coal was carbonized in a manner similar to that of the Utah coal (superheated steam) to determine the wax content of the resultant tar. One-hundred-gram samples of coal were carbonized by heating to 630" C., a t which temperature it was held for 1 hour. The tar was extracted with ether from the water distillate. The ether was evaporated and the tar weighed to find the percentage yield. The wax content was then determined by dissolving the tar in 5 volumes of acetone and cooling to -10" C., a t which temperature it was filtered. It was then dried in the oven a t 105" C. and weighed. Where the higher percentage of wax was found, it was dissolved in petroleum ether (boiling point 40" to 60" C.), filtered, and the
INDUSTRIAL A N D ENGINEERING CHEMISTRY
February, 1931
189
petroleum ether evaporated on the steam bath. This removed any resin present. Two of these coals were carbonized without using superheated steam to compare the relative merits of carbonization with and without steam for the production of wax in the tars. Table V gives the results. From Table V it is evident that none of the bituminous coals, except the Utah coal, yield an appreciable amount of wax. It is difficult to classify this coal; it cannot be considered a true bituminous coal. The sub-bituminous coals and the one lignite yield a tar containing considerable quantities of wax. It seems probable that these waxes are paraffin hydrocarbons similar to the wax from the Utah tar. This conclusion is based on the melting points of the waxes, as they range from 52" to 57" C., but insufficient quantities were available to prove this conclusively. I n the carbonization without superheated steam the wax content of the tar is lower, but not alarmingly so in the case of the Utah coal. From this one can conclude that carbonization with superheated steam favors a higher yield of wax in the tar. To compare these results with commercially carbonized tars, three tars which the writers investigated were analyzed for their wax content as given in Table VI. T a b l e VI-Wax
in Commercial Tars PRoCsss
COAL
TEMPRRA-WAX TURE
c. Illinois" Pjttsburgh and Sunday Creekb Pittsburehc
Parr Wisner Haves
so0 500 750
INTAR
% 0.i2 0.62 0.37
Harrisburg premium coal, No. 5 bed, Harrisburg, Saline County, Ill. b NO. 5 block bed Campbells Creek W. Va and No. 6 bed, Sunday Creek, Athens County,'Ohio, mixed in e q i a l prop&ions. C Pittsburgh, No. S bed, Panama mine, Moundsville, Marshall County, W. Va.
From these data it would seem that carbonization on a large scale tends to decrease the yield of wax in the tar. This may also be attributed to a higher temperature in the carbonization of the Parr and Hayes tars. The Wisner tar was carbonized a t a lower temperature than the laboratory prepared tars, but still the wax content is lorn. Literature Cited (1) Brown and Branting, IND. ENG.CHEM.,20, 392 (1928). (2) Brown and Cooper, I b i d . , 19, 26 (1927). (3) Brown and Pollock, I b i d . , 21, 234 (1929). (4) Buchler and Graves, I b i d . , 19, 718 (1927). (5) Federal Specifications Board, Standard Specification No. 2C, Bur. Mines, Tech. Paper 32SA, 42 (1924). ( 6 ) Frey and Yant, IND. END.CHBM.,19, 21 (1927). (7) Holde, "Examination of Hydrocarbon Oils," p. 352, Wiley, 1915. ( 8 ) Johansen, J. I m . END.CHEM.,14, 288 (1922). (9) Tanaka, Kaboyaski, and Ohno, J. Faculty Eng., T o k y o Imp. U n i v . , 17, 15 (1928). (10) Wyant and Marsh, Bur. Mines, Tech. Paper 368,26 (1925).
Y . I
3
Analysis of Color Characteristics of Paints Committee D-1 on Preservative Coatings for Structural Materials of the American Society for Testing Materials, 1315 Spruce St., Philadelphia, Pa., has adopted as standard a method of analysis for the color characteristics of paints in terms of fundamental physical units. More satisfactory analyses of colors could be obtained by means of instruments capable of measuring in terms of fundamental physical units, since these do not necessitate constant checking. The use of an apparatus of the primary type enables determination of the spectral distribution curve of the colors selectively reflected by any given sample within the limits of the visible spectrum. The proposed method consists of the characteristic spectral reflectance in terms of fundamental physical units, determined in accordance with certain stipulations, the specific description of the standard reflecting surface used, and the complete description of the character of illumination employed.
