Composition of Tar from Low-Temperature Carbonization of Utah Coal

This is the third in a series of cooperative studies of the composition of tars obtained from Mesa Verde. (Utah) coal when carbonized with steam super...
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INDUSTRIAL AND ELVGINEERING CHEMISTRY

234

1,335,000, or about 4 per cent, are actually absorbed in the clinkering zone. Although these figures cannot lay claim to any high degree of absolute accuracy, they do show an enormous surplus of

Vol. 21, No. 3

heat in the clinkering zone, and it may be concluded that, no matter what fuel economies are effected in the rotary kiln, it is unlikely that availability of heat in the clinkering zone will have t o be considered as a limiting factor in design.

Composition of Tar from Low-Temperature Carbonization of Utah Coal 11-Heavy

PortionslJ

Ralph L. Brown3and Robert N. Pollock4 PITTSBURGR EXPERIMENT STATION, U. S. BUREAUOR MINES,PITTSBURGH. PA.

This is the third in a series of cooperative studies of HE low-temperature This report presents the the composition of tars obtained from Mesa Verde carbonization of Utah results of (1) the analysis of (Utah) coal when carbonized with steam superheated coal c a r r i e d o u t i n tar I1 i n t o i t s c h e m i c a l to about 700" C. This investigation includes an analy1924-25 b y K a r r i c k w i t h classes; (2) the analysis of sis of tars I1 and 111; resolution into oil, wax, and resin superheated steam, resulted t a r I11 i n t o i t s c h e m i c a l of the neutral portion of these tars; a study of the classes; (3) t h e resolution in the formation of coke gas, composite neutral portion from all three tars as comlight oils, and three separate into oil, wax, and resin of the pared with crude petroleums, and of the liquid hydrotar fractions. The examinaneutral portion of tar 11; (4) carbons of this composite neutral portion and their tion of these fractions and the resolution into oil, wax, variation with their boiling temperatures. their resolution into chemical and resin of the neutral portion of tar 111: 5 ) the studv classes have formed the basis , (~, of a series of fellowships. The first5 dealt with the character of the nature of the composite neutral portion from all of the light oils obtained when this coal was distilled a t 700" three tars in comparison with crude petroleums; and (6) C. with superheated steam, and collected in a liquid-air-cooled the nature of the chemical classes constituting the liquid hycondenser. The liquid tar portion which collected in the drocarbons of the composite neutral portion and their variwater-cooled condenser and the aqueous condensate resulting ation with their boiling temperatures. from the steam employed in the carbonization were examined Analytical Method Used by Brown and BrantingG in the second study. In the school year of 1927-28 an investigation has been made of the In order to furnish an analysis and to permit an examinaheavier portions of this tar which collected in the air-cooled tion of its constituents, the tar was separated into classes of condenser and separated of its own accord into two portions chemical compounds. The "wet" method of analysis was because of their difference in specific gravity. The tar por- chosen as giving a more thorough separation, as well as tion that was lighter than the condensed steam is designated avoiding much of the decomposition and polymerization henceforth as tar I1without further explanation. The heavier effects' which accompany any method that involves direct portion is correspondingly known as tar 111. The relative distillation of the tar. I n its outlines the method followed proportions of the three tar fractions are summarized in Table that of Brittain, Rowe, and Sinnatt.8 I. The details of the carbonization and of the collection of the samples, as well as the analysis of the coal, have been Analysis of Tar I1 given in the earlier publications of this series. Samples of tar I1 weighing 200 grams in ether solution Table I-Distribution of Tar were analyzed according t o the method outlined in previous As As PER A s PER publications. PER CENT C E N T CEWT OF WEIGHT OF COAL OF TAR TOTALTAR^ TARPORTION The insoluble matter, after thorough drying, consisted of a Kg. dark brown powder made up of small amounts of tar, larger 12.70 3.91 28.85 27.94 I Medium oil quantities of ash, and coal in all stages of carbonization. Heavy tar: I1 Sp. gr. < water 17.75 5.46 40.35 39.05 The carboxylic acids mere noncrystalline, resinous solids. 13.55 4.17 30.80 29.82 111 Sp. gr. > water __ --__ --The average of two determinations gave a value of 1.85 44.00 13.54 100 00 96.81 Total tar per cent for that soluble in sulfuric ether, and 0.4 per cent for IV Material in aqueous 1.45 0.446 .... 3.19 condensate the insoluble portion. _-----The alkali-soluble material in tar I1 amounted to 9.6 per Grand total 45.45 13.99 . .. . 100.00 a Recalculated to include that material recovered from the aqueous cent ether-soluble and 5.4 per cent ether-insoluble. In apcondensate. pearance both portions were highly viscous black solids. The nitrogen bases were extracted as in the previous paper. 1 Presented before the Division of Gas and Fuel Chemistry at the 76th During this procedure a heavy black solid was thrown out of Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14,1928. solution and adhered to the walls of the vessel. From its 2 Printed by permission of the Director, U. S . Bureau of Mines, the solubility in sodium hydroxide this material was classified as Carnegie Institute of Technology, and the Mining Advisory Board. (Not composed of phenols and consequently was added t o them. subject to copyright.) A similar material was noted by Morgan' and interpreted by a Organic chemist, Pittsburgh Experiment Station, U. S . Bureau of Mines. him as being the product of hydrolysis of salts or esters origi-

T

~

Research fellow, Carnegie Institute of Technology, 1927-28. Brown and Cooper, IND. END.CHEM.,19, 26 (1927). 6 Brown and Branting, Ibid., 20, 392 (1928).

4

6

7 8

Morgan and Soule, C h m Met. En&, 16, 923, 977 (1922). Brittain, Rowe, and Slnnatt, Fuel. 4, 263, 299, 337 (1925).

I N D USTRIAL AND ENGINEERING CHEMISTRY

March, 1929

nally formed by the combination of nitrogen bases and (acid) phenols. The neutral portion of tar I1 amounted to 80 per cent of the total. Note-For the present investigation the term "neutral portion" has been applied to the tar from which the carboxylic acids, phenols, and nitrogen bases have been extracted. In the literature this is more commonly called "neutral oil," but the latter term has been reserved in this work for a certain part of the neutral portion-namely, the oil which remains after the wax and resin are largely removed.

It was a semisolid, owing to the large amount of paraffin wax present. At 35" C. i t was a homogeneous liquid, but it caked rapidly on cooling below that temperature. Table I1 gives the results of the analysis of tar 11. Table 11-Components

of Tar 11, b y Classes

Insoluble in sulfuric ether Carboxylic acids: Sulfuric-ether soluble Sulfuric-ether insoluble Phenols (alkali-soluble material) : Sulfuric-ether soluble Sulfuric-ether insoluble Tar bases: Sulfuric-ether soluble Sulfuric-ether insoluble h'eutral portion

1.85 0.40 9.6 5.4

Per cent 0.85 2.25 15.0 1.55

1.40 0.15

80.0

Analysis of Tar 111

hhTHoD-The resolution of tar 111into its chemical classes was made according to the general method already outlined. However, some variations were met in successive analyses, probably because of the high resin content of this tar portion, which was highly insoluble and amounted t o 7.5 to 9.7 per cent of the tar. This can be largely accounted for by the tendency of the complex resins to form colloidal solutions in ether. I n this tar the insoluble matter divided itself roughly into two types. The fine resinous particles, which formed the suspension with the sulfuric ether, were, when collected on a filter paper, similar t o the resinous mass from tar 11. This tar I11 was richer in ash particles than was tar 11. I n addition, the insoluble matter of tar I11 contained about 1.75 per cent of a mixture of coal particles in all stages of carbonization. The total ether-insoluble was about 9.5 per cent. Of the carboxylic acids the ether-soluble portion amounted t o 1.5 per cent of the tar and the ether-insoluble, 1.0 per cent. Both were dark brown gummy masses, and showed no evidence of crystalline structure. The large quantity of the alkali-soluble in tar I11 required the use of five 150-cc. portions of reagent (10 per cent NaOH solution) t o insure its complete removal. I n this case no separate determination was made to find the percentage of sulfuric-ether soluble and insoluble. The total was 40 per cent. It was a black, plastic solid and smelled only faintly of phenol. The tar bases amounted t o 3.0 per cent of the tar; 2.75 per cent was soluble in sulfuric ether and 0.25 was insoluble. The neutral portion of tar I11 was a dark-colored semisolid and amounted to about 44.5 per cent. Table I11 summarizes the approximate analysis in classes. Composition of Tar 111 APPROXIMATE A B AVERAGE Per cent Per cent Per cent

Table 111-Approximate

Insoluble in sulfuric-ether resins Coal particles, etc. Carboxylic acids: Soluble in sulfuric ether Insoluble in sulfuric ether Alkali-soluble (Dhenols) Tar bases: Soluble in sulfuric ether Insoluble in sulfuric ether Neutral portion

5

9.25

9.7 {7.g5 1.75 2.55 2.45 1.45 1.50 1.10 0.95 40.6 39.8 3.0 3.0 2.75 2.80 0.25 0.20 44.4 45.0

9.5 2.5 40.0 3.0 45.0

1.5 1.0 2.75 0.25

235

Summary of Composition of Tar Portions, with Comparisons

The values of the amounts of the various classes obtained in the present investigation when combined with those obtained by Brown and Branting for tar I allow a calculation t o be made of the relative amounts of the classes in the total tar distillate. Included in this calculation and given in column 5 of Table IV are the figures calculated from the tar content of the aqueous condensate. of Classes of Compounds in Utah Tar CLASSES RECALCULATED TO INCLUDE AQUEOUS CLASSES OF COMPOUNDS TARI TARI1 TAR111 CONDENSATE Per cent Per cent Per cent Per cent Insoluble (in sulfuric ether) 1.0 0.85 9.5 3.46 Carboxylic acids 0.25 2.25 2.5 2.14 Alkali-soluble (DhenOlS) 23.4 15.0 40.0 26.89 Tar bases 1.55 3.0 1.7 2.07 63.21 h-eutral portion 80.0 45.0 66.0 Working loss 7.6 0.35 0.0 2.27 1 0 0 . 0 0 100.00 100.00 100.00 Totals Table IV-Distribution

'-

A comparison of Utah tar with other low-temperature tars is made in Table V, which lists several typical lowtemperature tars that have been analyzed with sulfuric ether as the solvent. WeindelQ also has made analyses of lowtemperature tar in this manner, but his solvent was benzine. Edwards'o made use of alcohol as a solvent in analyzing four types of low-temperature tars. Parrish and Rowell have also studied low-temperature tars in this manner,. Table V-Sulfuric-Ether Analyses of Various Low-Temperature Tars. According t o Different Investigators Brown Brittain Brittain, A. Parrish and InvestiCooper Rowe and Rowe, F. M. Rowe gators Branting Sinnatt Sinnatt, F. S. and Pollock Pooley Hall Source of Ca ;: Gate Old Silkstone Clay Cross, 50% Indefinite Warwickshire coal Derbyshire, 50% [Utah Temperature of carbonization 700' C. 650' C. 650' C. 600' C.

i/

3.5 Insoluble 2.1 Carboxylic acids Phenols 26.9 2.1 Tar bases Neutral portion 6 3 . 1

Per cent of chemical classes 0.31 8.85 O.O+ 0.05 26.6 30.6 4.1 2.45 66.1 54.5

2.08 0.31 33.84 2.66 54.72

Study of Neutral Portion of Tar I1

A considerable quantity of neutral resin in addition t o the oil and wax was known t o be present in the neutral portion of tar 11. In order to avoid complications from its cracking, it was considered advisable to remove i t before distillational analysis was begun for the purpose of studying the neutral portion. For a rough preliminary separation, the neutral portion was dissolved under refluxing in petroleum ether, in which the solubility of the resin is limited. It was found in previous analyses that the amount of resin dissolved depended to a large extent upon the boiling range of the solvent. Thus 6 volumes of petroleum ether with a boiling range 40" to 60" C. removed 17 per cent out of a total of 18.5 per cent of resins from this tar. On the other hand, 6 volumes of light gasoline with a boiling range of 40" to 100' C. removed only 12 per cent of resins. As the removal of resins was incomplete and in order to avoid decomposition in general, a further rough separation of the three components was effected by means of steam distillation, which yielded three portions-one largely oil, a second of wax and oil, and a residue largely composed of resin plus some oil and a little wax. Weindel, Brennstof-Chem., 4, 321 (1923). Edwards, J . Sac. Chem. I n d . , I S , 143 (1924). 11 Parrish and Rowe, Ibid., 46, 99 (1926). 10

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236

hfETHoD-The procedure consisted in steam-distilling the oil, first with the oil maintained in a bath a t 200" C. until oil had almost ceased to come over. This gave fraction I, an oil. The bath temperature was then raised to 300" C., when a mixture of oil and wax (fraction 11) distilled over. The residue or fraction 111 consisted of a black pitchlike resin containing the small amounts of oil and wax; these were then separated and determined as given below. The oil (fraction I) was brown and distilled completely between 87" and 340" C. without any evidence of decomposition. Its Saybolt viscosity a t 38" C. (100" F.) as determined by a calibrated pipet12 was 65 seconds; d i 0 was 0.906, which corresponds to an A. P. I. gravity of 24.2 degrees a t 15.5" C. (60" F.), and n': was 1.5108. This corresponds t o a medium gas-oil fraction from a petroleum. Fraction I1 consisted of oil and wax. The wax was separated from the mixture by chilling the solution and filtering off the paraffin crystals which came out of solution. The wax after recrystallization had a melting point of 52" C.; this compares favorably with a standard petroleum wax, which had a melting point of 47.5" C. The oil from fraction 11, which amounted to two-thirds of the material distilling a t 300" C., was dark red and had the following physical properties: d;' = 0.9540; A. P. I. gravity = 16.4" C. (60" F.); n2 = 1.4950; Saybolt viscosity = 170 seconds (100" F.). I n addition t o these fractions, the small amounts of wax and oil in the residue were extracted with light petroleum ether. The soluble portion consisted of oil and wax, and after evaporating off the ether the wax was crystallized from acetone as in fraction 11. From two determinations the percentages of oil, wax, and resin in the neutral portion were calculated and are given in Table VI. I n column 4 are the values obtained by Brown and Branting by a similar determination on fhe same neutral portion. Table VI-Oil,

Wax, a n d Resin in Neutral Portion of Tar I1 RUN ( a ) Per cent 56.0 24.6 19.2

Oil Wax Resin

RUN ( b ) Per cent 58,4 23.6 18.1

PRELIMINARY B Y BROWNAID WEIGHTED BRANTING AVERAGE

Per cent 57.6 22.9 19.5

Per cenl 57.3 24.1 18 5

FRAC-CONSTITTION

UENT

OIL

Per rent

R

A. p, 1,60 VISCOSITY 60

1OO'F. Seconds

MELTISG

';

POINT OF W A X

c.

Study of Neutral Portion of Tar I11

The neutral portion of tar I11 was subjected to an analysis similar to that of tar 11. A lower wax content was expected, not only from a consideration of the specific gravity of tar 111,but also from the appearance and melting characteristics of the neutral portion, as contrasted with the similar fraction from tar 11. Whereas tar I1 showed evidence of solidifying soon after removal from a boiling water bath, the neutral portion of tar I1 was a liquid a t body temperature (37" C.), and a t room temperature (20" C.) was still a soft semisolid. As in the case of the neutral portion of tar 11, a large part of the resins (6.0 out of 19.8 per cent) were removed from a sample of the neutral portion by refluxing it with 6 volumes 12

Dean et al., Bur. Mines, Bull. 207, 44 (1922).

of Neutral Oil of Tar 111

Table VIII-Resolution

FRAC-CONSTIT-NEUTRAL d:O TION

UENT

OIL

1 2

Oil Oil Wax Oil Wax Resin

Per cent 30.5 34.8 9.2 7.3 3.0 14.7

3

MELT-

SAYBOLT A, p. 1 , 6 0 v I S c o S I T Y 60

0.9572 1.0192

15.9

100°F. Seconds 66

n?

ING

POINT OF W A X O C

1.4955 1.4958

56.4

Oil, Wax, and Resin Content of Total Tar-Summary

The data relative to oil, wax, and resin content of the three tar fractions as a whole can now be calculated by using the values5 obtained for tar I in conjunction with the two sets of values for tars I1 and 111, respectively, as in Table IX.

R

of Neutral Oil of Tar I1 SAYBOLT

NEUTRAL G

of 60" C. end-point petroleum ether. The resultant material was then subjected to steam distillation under the conditions previously outlined. Fraction I was a light oil having a specific gravity of 0.957 a t 20" C. and an index of refraction n2 of 1.4965. On direct distillation it had initial and final boiling points of 180" and 343" C. No perceptible decomposition occurred during this distillation. Fraction 11, which distilled a t a bath temperature of 300 O C., was found by treatment with acetone to yield roughly 20 per cent wax and the remainder was oil. The wax was similar to that from tar 11, and had a melting point of 56.4" C. The oil was very dark and viscous. The index of refraction, n2,0, was 1.4958, and d:' was 1.019. The high values of the latter suggested the presence of a considerable amount of naphthene hydrocarbons. Fraction 111, or the residue which remained after the distillation, contained small quantities of wax and oil. The oil, wax, and resin contents of the neutral portion of tar I11 were, respectively, 68.9, 10.4, and 19.8 per cent, and in terms of total tar I11 equaled 31.0, 4.7, and 8.9 per cent, respectively. The properties of these constituents as determined are summarized in Table VIII.

Table IX-Oil, Wax, and Resin in Total Tar NEUTRAL PORTION TARI11 -TOTAL-TARI TARI1

The properties of these constituents as determined are summarized in Table VII. Table VII-Resolution

Vol. 21, KO.3

Kg.

%

Kg.

%

Kg.

Kg.

%"

%b

6 8 . 9 4 . 2 0 19.44 6 7 . 7 8 4 2 . 8 Oil 85 7.12 57.2 8.12 Wax 10 0.84 24.1 3.42 1 0 . 4 0 . 6 3 4 . 8 9 17.05 1 0 . 8 Resin 5 0.42 18.6 2.64 1 9 . 8 1 . 2 1 4 . 2 7 14.89 9 . 4 2.3 Resin present in insoluble matter As per cent of tar fraction 6 6 . 0 8 . 3 8 80.0 14.20 4 5 . 0 6 . 1 0 Grand total 28.60 99.72 6 5 . 3 a As percentage of total neutral portion from the three tar portions. b As percentage of total tar including that from aqueous condensate.

The amount of wax in the tar from Utah coal is of interest, as it is high, even for a low-temperature tar. Most of the investigators whose work appears in the literature first subjected their tars to a fractionation to remove resins and higher phenols, in many cases carrying the distillation no higher than 300" C. As the paraffin hydrocarbons boiling a t this temperature are not solid a t ordinary temperatures, it is apparent that most of the solid paraffins will not b6 present in the neutral portion of the distillate. Morgan and Soule' carried their distillation to 326" C. Edwards,loin addition t o analyzing with alcohol as a solvent, distilled the same tars and obtained corresponding values for the distillate. However, in these cases and most of the others using solvents, the paraffin has been determined as a class with the naphthenes, which are also completely hydrogenated. Whether the low-temperature tars of the literature did not contain the important amount of wax that this tar does, or whether it was largely overlooked, it is not possible to say. However, i t is noteworthy that this tar from Utah coal does have an

March, 1929

INDUSTRIAL AiYD ENGINEERING CHEMISTRY

237

pressure of 40 mm. of mercury. Of the five vacuum fractions the last three were solid, owing to the paraffin wax present, which emphasizes the high wax content of the tar oil. As the physical properties (specific gravity) of the fractions distilled a t atmospheric pressure approached closely those of a typical naphthenic crude, the paraffin was considered as an additional product and its removal was effected t o permit the examination of the oil proper. In Figure 1 the results from the atmospheric distillation of the composite have been compared with the same curves Assay Distillation of Composite Neutral Oil for four types of crude petroleum as given by the Bureau of In the vacuum fractions, comparison is made Xormally, except for special utilization that may be developed, lotv-temperature tar would be collected in industrial (Figure 2) of the five fractions (of which the last three have carbonization plants as a whole. With this in mind, and been dewaxed) with the vacuum fractions of the typical Tvith the view of getting a general picture of the total oil of naPhthene crude. INTERPRETATION OF RESULTS-The examination Of the Oil the 1oTv-temperature tar under exadnation, the neutral portions of tar portions I, 11, and 111 were combined so distilled a t atmospheric pressure, and the dewaxed oil in the as to give a true composite sample for examination. In the further vacuum distillation showed the composite neutral present state of industrial development in the use of liquid oil to correspond to the naPhthene type of crude Petroleum. In further comparison it may be said that this tar 0% fuels, petroleum and petroleum products are most frequently used as the basis of comparison and a guide for treatment in so far as the specific gravity, boiling characteristics, and of oils from low-temperature tar. Therefore, for further viscosity go, gives fractions similar to those obtained from information on the general character of low-temperature tar naphthene-base petroleum. A large part of the distillate oils, as well as to set u p a comparison with petroleum, the falls in the gasoline, naphtha, and gas-oil fractions, but the standard assay distillation (for crudes) of the petroleum di- higher boiling fractions are present. As stated above, there vision of the U. S. Bureau of Mines was employed as a means is much wax present and with it is some oil of high viscosity of study. as in petroleum. DISTILLATION OF SAMPLE B-The procedure for sample B Two composite samples of neutral tar oil were prepared, one consisting of the total oil and wax, and the second of oil was the same as for the preliminary sample A. The values for from which the wax was in large part removed and hence percentage of fractions and other data relative to the distillation are given in Table X. The data as plotted (Figures consisting largely of the oil proper. PREPARATION OF COMPOSITE NEUTRAL TAR-OILSAMPLES- 1 and 2) fall closely on the curve for the previous distillation Sample A (containing wax). The sample was prepared by for which the points only are indicated. combining in the proper proportionate amounts the neutral VACUUMDISTILLATION-of the five fractions collected, portion from tar I, already practically free from resin, the the last two were solid, due t o the paraffin wax which was neutral oil from tar 11, and a similar portion from tar 111. removed as before with acetone. The third fraction deposited This composite sample was a black, waxy oil having a specific crystals when cooled slowly from 20" to 15" C. I n Table gravity of approximately 0.929 a t room temperature. X and Figure 2 are given the specific gravities and viscosities Sample B (composite dewaxed). The oil resulting 6 0 Z __from the combination of the dewaxed neutral oil portions of tars I1 and I11 and the 50 entire neutral portion of tar I is called the composite dewaxed oil. I n color it was r=-T ?+-&! between red and brown and $ 4 0 ~ , X I had the fluidity of a light lubricating oil. The specific gral-ity, d;: g, was 0.952, e q u i v a l e n t to an A. P. I. gravity of 17.2 degrees (60" F.), Saybolt v i s c o s i t y a t 38" C. (100" F.) was 78 seconds. DISTILL~TION OF SAMPLE A-This oil was distilled with the standard apparatus and under the condiATMOSPHERIC DISTILLATION ("C )VACUUM DISTILLATIOX of Composite Neutral Oils A and B in Comparison with tions described in the B ~ -Figure I-Bureau of Mines Assay Distillation Types of Crude Petroleum reau of Mines bulletin.'* The first drop, which came over a t 63" C.,as well as the of the first three vacuum fractions and of the dewaxed oil succeeding distillate up to about 115" C., was colorless. from the last two. From this point to 275" C. the fractions changed progressively Chemical Nature of Composite Neutral Oil from pale yellow to deep red. These distillation data are similar to those of sample B, and the latter only will be given. The general distribution of the oil, wax, and resin in the T.-acuu&fDISTILLATION-The remainder of the oil furnished neutral portions of tars I1 and I11 has been shown. The the "vacuum" fractions, for they were distilled under a 13 Smith, B U ~ .Mines, R C ~ ~ ofrnvesicgotrons S. 2806, I (1927). important wax content. Full account for this cannot be rendered a t the present time, but it is obvious that it depends upon the composition of the coal and the favorable circumstances of the original carbonization-namely, (1) a true low-temperature distillation with no overheating; (2) the countercurrent flow of steam with respect to the incoming coal and the absence of overheating of the vapors; and (3) the high ratio of steam to coal employed favoring complete and rapid volatilization and removal.

INDUXTRIAL AND ENGINEERING CHEMISTRY

238

general physical properties of these materials were likewise determined. This same information for the entire neutral portion has been summarized. An assay distillation furnished a rough comparison of the composite neutral oil with typical crude petroleums. It also served as a check on the earlier determinations of wax content. It seemed desirable t o know more about the chemical nature of the liquid hydrocarbons such as occur in the gas-oiI and higher fractions. 4 o o 1 1 1 , 1, ,

l I

1

,

,, I

Vol. 21, No. 3

from the two methods indicate that up to about 260" C. the oil was 40 to 45 per cent unsaturated, containing 25 to 30 naphthenes and about 12 t o 15 per cent each of aromatics and paraffins (wax not included). Above 260" C. the percentage of unsaturation was greatly increased a t the expense of the other three classes. The method was then applied to a second sample of the same composite tar oil, the fractionation of which had been carried out entireIy a t 40 mm. Distillation of Composite Neutral Oil B (Dewaxed} GRAVITY VOLUME FRACTION VOLUME SUM A. P. I . ~ I s c o s I T r c. Cc. Per cent Per cent -125 2.4 0.8 0.8 0.7748 51.1 125- 150 8.0 2.7 0.7844 48.9 3.5 15C-175 3.1 9.4 0.8094 6.6 43.3 175-200 8.5 2.8 0.8317 9.4 38.6 200-225 3.5 13.0 0.8549 3 4 . 0 10.6 225-250 7.1 0.8781 29.6 20.1 21.4 2 50-27 5 33.2 13.1 0.9056 39.4 24.8

Table X-Assay

i l l

4;

360

0.98

VACUUM DISTILLATION AT 40 MM.

0.86 0 84

10

15

20

25

30

82

SUM, PERCENTAGE Figure 2-Vacuum Fractions of Bureau of Mines Assay Dietillation of Composite Neutral Oils A and B and a Typical Naphthene Crude

1

The hydrocarbons generally recognized as distinct types are the paraffin, aromatic, naphthene, and unsaturated classes. This division is only approximate and is not always clear-cut. The type of side chains in a hydrocarbon with a benzene nucleus may have as much or more effect on many of the properties of the hydrocarbon than the nucleus itself contributes. The overlapping of these classes in chemical properties, and even in structure, is such that unless the mixture is one composed of simple types there are no criteria by which hard and fast divisions can be drawn. Consequently, the application of empirical chemical and physical methods of analysis to high-boiling mixtures of unknown composition is equivalent to attempting to define a point in a two- or three-dimensional system of poorly-known boundaries by one linear dimension or by reference to one axis. Based on the useful method of Morrell and Egloff" for the analysis of motor fuels in terms of classes of hydrocarbons, GrifTithl6 has proposed an adaptation of it to the class analysis of oils with boiling points above those of gasoline-namely, gas oil and hydrocarbon oils from both high and low temperature tar. Although carefully worked out as to procedure, the method involves the tacit assumption that all the oils for which it is proposed undergo no serious cracking during the primary fractionation which is carried up t o 340-380" C. To this assumption the writers could not agree, and for the oils from low-temperature tar it was contradictory to their experience not t o expect cracking to occur under 300" C. a t atmospheric pressure. Notwithstanding the limitations inherent in the method, they sought to employ i t on their tar-oil boiling between 210" and 315" C. The fraction boiling below 210" C. was analyzed by the Morrell and Egloff method. The combined results 14

10

Morrell and Egloff, IND. END.CHEM.,18, 354 (1926)l Gri5th. Chemistry Industry, 47, 21T (1928).

Up t o 2 0 0 200-225 225-260 25C-275

14.6 22.5 23.2 Oil

275-300

Oil (wax)

(wax)

4.9 7.5 7.7 6.2 (1.4) 1(1.4) 0.3

4.9 12.4 20.1 2.63

0.9263 0,9358 0.9455 0,9796

21.3 19.7 18.2 12.9

43 52 71 183

36.6

0.9980

10.3

600

The results in general show increases in the values of the paraffin, aromatic, and naphthenic hydrocarbons over those given above, and a marked decrease in the unsaturated figure. This is most manifest a t the higher temperatures; and cracking clearly accounts for the greater part of the differences. As the revised values are preliminary, further discussion of the methods is being reserved for the present, and simply an estimate given of the distribution of the classes of hydrocarbons in the composite oil-namely, unsaturated, about 35 per cent; naphthenic, 30 to 35 per cent; aromatic, about 20 per cent; and the paraffins, 15 per cent. Summary

The heavy portions of the tar obtained from Mesa Verde coal (Utah) when the latter is carbonized with steam superheated to about 700" C. have been examined. The tar was collected in two parts, one (tar 11) lighter than the aqueous condensate and the other (tar 111)heavier than water. Tar I1 was 40 per cent of the total tar and consisted of insoluble matter, 0.85; carboxylic acids, 2.25; alkali soluble (phenolic), 15.0; tar bases, 1.55; and neutral portion, 80 per cent, consisting of 18.5 parts resin, 24.1 parts wax, and 57.3 parts oil. Tar I11 amounted to 30.8 per cent of the total tar and was made up of 9.5 per cent insoluble (in ether) matter, 2.5 per cent of carboxylic acids, 40 per cent of alkali soluble (phenolic), 3 per cent of tar bases; and 45 per cent of neutral portion consisting of 69 parts of oil, 10+ parts of wax, and 20 parts of resinous matter. The composite total tar contained 3.5 per cent insoluble material-dust, coal, coke, etc.-2.15 per cent carboxylic acids, 26.9 per cent phenolic material, 2.1 per cent tar bases, and 63.3 per cent neutral portion (working loss 2.2 per cent) made up as follows: resin, 9.4; wax, 10.8; and oil, 42.8. The oil was approximately 35 per cent unsaturated, 30 per cent naphthenic, 20 per cent aromatic, and 15 per cent paraffin hydrocarbons. An outstanding fact is the large paraffinwax content of the tar. The importance of the wax content arises from the potential increase it offers in economic return from the by-products of low-temperature carbonization.

Correction In the article by W. B. Plummer and S. P. Burke under the title, "Gas Flow through Packed Columns," IND. ENG.CHEM., 20, 1196 (1928), the correct form of Equation 10 on page 1199 is P I 1 - 0.000050p V.S2/f3.