PRODUCT AND PROCESS DEVELOPMENT
Conversion of Coal to Simple Compounds Action of Aqueous Alkali on a Subbituminous Coal cat Elevated Temperatures FRANKLIN G. PARKER1, JAMES P. FUGASSI2,
AND
H. C. HOWARD3
Coal Research Laboratory, Curnegie lnstitute o f Technology, Pitfsburgh, Pa.
I
X T H E coalification process it is probable that condensation reactions involving the elimination of water are partly responsible for the changes in composition and properties u-hich are observed in the coal series in passing from the lower rank materials, such as peat, to the bituminous coals. Recent plots (12) of atomic hydrogen-carbon ratios versus oxygen-carbon ratios in the cod series emphasize the importance of such dehydration reactions over a certain part of the coalification process. Earlier studies in this laboratory on the alkaline hydrolysis of a Pittsburgh seam bituminous coal resulted in the recovery of only a small fraction of the carbon as soluble or volatile compounds, indicating the absence of any considerable amount of hydrolyzable linkages in a coal of this rank. Earlier workers (4, 6, 7, 8) have reported that lower rank coals were readily converted to brown, alkali-soluble products by fusion with caustic potash in an open dish. The failure in this early work to exclude atmospheric oxidation and the incomplete characterization of the products indicate the desirability of further investigations of the action of aqueous alkali on a subbituminous coal. I n the present work the reaction of aqueous alkali on a Wyoming subbituminous coal has been studied over the temperature range 200" to 425' C. at alkali concentrations from 1N to 662/a weight % and in an inert atmosphere. Reaction with aqueous alkali at 350' C. yielded products suitable for investigation
Materials. The coal used in this study was a sample obtained through the courtesy of G. E. Sorensen, vice-president, Kemmerer Coal Co., Frontier, Wyo. It was mine-run, subbituminous B coal, mined a t Elkol, Lincoln County, Wyo. This seam i s part of the Adaville Formation and ranges in thickness from 20 to 612 inches. There are a number of seams 6 to 25 feet thick said to total 350 feet (14). This is a predominantly bright coal, reported (15) to contain 60% anthraxylon, %yotransparent attritus, 3 % opaque attritus, and 1% fusain. The proximate and ultimate analyses (3)are shown in Table I. The atomic ratios are hydrogen/carbon = 0.7g1 oxygen/carbon = 0.15. The aqueous alkaline suspensions of the coal were made up by stirring the required amount of coal with the specified amount of reagent grade, pelleted sodium hydroxide and distilled water. Commercial, water-pumped nitrogen from a cylinder was used to flush out and pressure the vessel. Apparatus. The reactions were carried out in two types of pressure vessels-one of solid nickel, limited to a maximum internal pressure of 2300 pounds per square inch and temperatures of 370" C. and the other of stainless steel with a loose nickel liner. 1 Present address, E. I. du P o n t de Nemours & Co., Spruance P l a n t , Richmond, VB. 2 Present address, Dept. of Chemistry, Carnegie Institute of Technology, Pittsburgh, Pa. J Present address, U. 8 . Bureav of Mines, Pittsburgh, Pa.
1586
The nickel reactor was agitated by rocking. Agitation was not possible in the stainless vessel with the liner. Both were of the design described by Adkins ( 1 ) . Closure was made with a silver gasket and the assembled vessel was heated in an electric furnace; temperature control was through a Micromax controller and iron-constantan couple placed in the thermocouple well. Temperatures reported are those recorded by this thermocouple. Methods of Reaction. By preliminary experiments it was established that reaction a t 350" C. with 5N sodium hydroxide for 24 hours yielded products suitable for detailed investigation. The method employed was as follows: Seventy-five grams of minus '200-mesh Elkol coal were weighed into a beaker. The coal was transferred to the pressure vessel as quantitatively as possible by the use of three 1OO-inl. portions of 5N sodium hydroxide. The bomb was assembled, flushed three times with nitrogen, pressured to 1000 pounds per square inch gage, and allowed to remain at room temperature for one hour. If no leaks were observed the nitrogen was bled to 50 pounds per square inch gage and the rocking motor and furnace turned on. Operating temperature was reached in approximately 90 minutes. This rapid rate of heating was achieved by using initially an excess of power and then reducing the input to operating level when the thermocouple registered about 340' C. Reaction time was calculated from the time the thermocouple registered 350" C. The run was terminated automatically a t the end of 24 hours. To ohtain the amount of reaction products necessary for separation and examination 41 runs were made During this period samples of the coal were analyzed for carbon content to determine whether atmospheric oxidation was occurring, No significant reduction in carbon content was observed. Methods of Separation. After cooling, the final pressure was read. a gas sample was taken, and the vessel opened. Separation of the products was effected 8 s shown in Figure 1. PROCESB A. The reaction products were first subjected to a 3-
Table I.
Analyses of Elkol Coal
As Received.
%
Moisturefree,
%
Moistureand Ash-free,
"70
Proximatea Moisture Volatile matter Fixed carbon Ash
16.8 36.1 44.3
2.8
,..
43.5 53.1 3.4
...
45.0 55.0
...
__
__
100.0
100.0
27.6 .5 2.8
5.3 74.3 1.2 15.2 .6 3.4
5.4 76.9 1.2 15.9 .6
100.0 10870
100.0 13070
100.0 13520
100.0
Ultimate Hydrogen Carbon Nitrogen Oxygen Sulfur Ash
Q
6.3 61.8
1 .o
B.t.u./lb. Determined by modified A.S.T.M. method.
INDUSTRIAL AND ENGINEERING CHEMISTRY
...
Vol. 47, No. 8
PRODUCT AND PROCESS DEVELOPMENT LIQUID AND SOLID REACTION PRODUCT (350",5 N NoOH, 24 Hrs.)
I Dljtillation
@ Steam
Q
Q Residue
Distillate
I
bqueous Layer
I
I
I
I
Acid 8 Alkali Wosh
CzI
Ether Extroction
z
I
I
Extract A2
I Roffinot Extract
Acid 8'Alkali Wosh
II I
Physical Properties
I
I
I
@ Benzene Extraction
I Distiilotion
1
Solids
Solution
1
IBosic I I Acid 1 I N e u t d 7 36 Fractions 1 A 2 B I I A2A I l A 2 N 1
I
Pentane Froctionofin
Acid R Alkoli Wosh
Flosh Distillotioh
I Ether :xtroction
G I
I
Roffinote
Extroct I
Figure 1 .
Method of separation
hour steam distillation. The distillate consisted of two phasesan oil layer, designated Al, and an aqueous layer. After it had been determined that the oil layer consisted of components boiling over 100' C., the material was diluted with pentane to avoid handling losses and given an alkali and an acid wash. PROCESS A2. Aliquots of the aqueous layer were analyzed for total carbon and basic nitrogen. The carbon content of the aqueous distillate was determined by wet oxidation with a chromic-sulfuric acid mixture followed by absorption of the liberated carbon dioxide in a weighed adsorption tube filled with Ascarite. The basic nitrogen content was determined by titration with standard acid. Separate batches of the aqueous layer were then extracted with ether in a continuous extractor for 72 hours per batch a t a rate of 350 ml. per hour. The extract was designated A2. The recovered, extracted oils, A2, were redissolved in ether and given an alkali and an acid wash. PROCESS B. The reaction products remaining after steam distillation were further separated by first screening out the coarse pitchlike solids and then centrifuging the alkaline solutions. The coarse residues were crushed and digested three times with distilled water on a steam bath. These washings, as well as the washings from the centrifuged solids, were added t o the supernatant liquid and designated Solution B1. The solids were designated Solids B2. Although some insoluble materials were present and suspended in the liquid phase, it was advantageous to determine carbon balances before the subsequent separations by extraction with organic reagents. Accordingly, aliquots of the alkaline solution were analyzed for total carbon as previously described. The carbonate carbon was determined by liberation of the carbon dioxide with mineral acid and absorption in a weighed tube by Ascarite. The carbon content of the residue was similarly determined by the wet oxidation method. Since it was observed that hydrophobic materials were still present in both Solution €31 and Solids B2, the next separation August 1955
Distil lotion
@ Ether Extraction I
I
Extract E2
Roffinate E2
I
DistillTtion
--Physicol Properties I 51 Fractions
-!""':l""i I
@ Methyl Ethyl Ketone Extraction
1
was achieved by extracting both substances with benzene; these processes are designated in Figure 1 as C and C', respectively. PROCESS C. The alkaline solution wasextracted in a continuous extractor with benzene for 48 hours per batch a t a benzene rate of 300 ml. per hour. The benzene-soluble materials, C1, were filtered and washed with distilled water. The washings were returned to the rafhnate. PROCESS C'. The Solids B2 were placed in a Soxhlet extractor and extracted for 120 hours with benzene. The extracted residue was then digested on a steam bath three times with distilled water and added to the alkaline raffinate. The residue was dried a t 105' C. The benzene extract, C'l, was filtered and washed with water. PROCESS D. Presumably the C1 raffinate was composed of the sodium salts of phenolic and carboxylic compounds. The solution was saturated with carbon dioxide; this resulted in the separation of a flocculent brown precipitate which was filtered from the solution and thoroughly washed. It was designated Dl. Subsequent investigation showed that the carbon dioxide precipitated materials contained inorganic impurities; the residue
INDUSTRIAL AND ENGINEERING CHEMISTRY
1587
PRODUCT AND PROCESS DEVELOPMENT
SIMPLE USEFUL PRODUCTS m a y be o b t a i n e d f r o m subbituminous coal b y reactions
...with aqueous alkali .. .at moderate temperatures and pressures .. .with l o w cost reagents
on ignition was 18.5 to 23%. The ash content of these materials was reduced to 0.6y0 with a 91.3% recovery of the carbon, by the following procedure: 1. The solid residue was digested and washed with hydrochloric acid; then dried a t 105' C. 2. The resultant solid mas then extracted with warm, dilute, aqueous sodium hydroxide. The insoluble solids were filtered from the solution. 3. The alkali-soluble ninterials were then precipitated by the addition of hydrochloric acid, washed, and dried a t 105" C.
PROCESS D2. The weakly acidic, water-soluble materials were now exhaustively extracted (48 hours) in approximately 3.5-liter batches with ether a t a rate of 300 ml. per hour. The ethereal solution was washed with water and the ether distilled. The extract was designated D 2 and was separated into 18 fractions by distillation a t reduced pressures with a column of 10 theoretical plates. PROCESS E. The ethereal raffinate was now acidified with sulfuric acid to a p H of 3. A hydrophobic, dark brown solid, El, separated on the surface of the liquid, but was not investigated further since it represented less than 1% of the coal. PROCESS E2. The acidified filtrate, El, was extracted with ether in a continuous extractor as described for the carbonated solution. The ethereal solution was washed with water and the ether susequently separated by flash distillation. Three such distillations were found necessary. This ether extract was designated E2. These acidic materials were separated in 51 fractions by distillation a t atmospheric and reduced pressures in a column of 10 theoretical plates. The lower boiling fractions smelled strongly of acetic acid. PRocEss F. Methyl ethyl ketone is an effective solvent for extracting polyfunctional water-soluble acids from an aqueous ,solution. Hence, the raffinate, E2, was extracted in a batchwiee manner in a continuous extractor as before. The solvent was removed from the ketone solution a t reduced pressure. The resultant black sirupy mass was designated F1.
Table II.
Concentration 1N 1N 5N 5N 5N 14.5N 14.5N 14.5N 6Ga/s%
Temp.,
c.
~ i Hr.
Products were gases, an oily layer, an aqueous layer, and a solid
The results of preliminary work in which the general course of the reaction was studied are shown in Table 11. Temperatures from 250" to 425" C. and alkali concentrations from 1N (about 4%) to 662/8% were investigated. At a constant reaction time of 12 hours the maximum conversion of coal to alkali-soluble products was obtained a t 250' C. with 5N caustic. However, dark field microscopic investigations of these solubles showed that there was present a very great number of particles in the 0.5- to 2-micron range and negligible amounts of these solutions could be migrated through parchment diaphragms. Thus, a t this temperature the reaction appears to be largely a peptization of the coal, accompanied perhaps by the rupture of certain weak bonds The peptized product purified by electrodialysis showed a significantly higher percentage of methylatable hydroxyl groups than the original coal. These groups may have resulted from hydrolysis of either inter- or intramolecular carbon-oxygen bonds. At temperatures higher than 250" C. and with increased alkali concentrations, the fraction G f the carbon appearing in the alkalisoluble form decreases very markedly. There seems no doubt this is due to further chemical degradation of the initially-formed, hydrophilic colloid particles to insoluble and gaseous compounds. Comparison of the data for 250" and 350" C. experiments, at identical alkali concentrations and reaction times, shows a severalfold increase in total gaseous products, in carbonate carbon, and in benzene-soluble carbon. I n this study, we were concerned primarily with the determination of the nature of the degradation products formed by alkaline hydrolysis. The reaction conditions chosen, 350" C. and 5 N alkali, represent a compromise; less drastic conditions would have resulted in higher yields of products which would have reflected the original coal structure more accurately, but which would have been very difficult to characterize. The data of Table 11 show that in the temperature range 300' t o 350" C. degradation of the primary peptized products to simpler compounds starts in about 6 hours. It appeared to be near completion in 12, but a 24-hour reaction period did produce somewhat higher yields and was employed in the preparation work. Approximately 2000 grams of coal were reacted under these conditons in 75-gram batches. The higher than initial pressure observed when the bomb was cooled to room temperature a t the conclusion of a run showed that gaseous products were being formed. The final pressures were reproducible and the analyses of the gases showed little variation in composition from run to run. The average analysis of 7 samples taken a t regular intervals over 41 runs is shown in Table 111. The odor of ammonia was noted in all experiments when the vessel was opened. I n addition to the gases the reaction products consisted oi three phases-an oily layer, an aqueous layer, and a solid.
Action of Alkali
on Elkol Coal
(Initial pressure 100 lb./sq. inch gage nitrogen) Distribution of "Coal Carbon"o in Products, % Pressure, ~________ ~ Lb./Sq. ~ Inch , Gage AlkaliCarbonate Hydrocarbon Maximum Final Residue soluble carbon gases .. 2.3 49.0 33.9 101 710 ,. 2.5 49.0 30.6 102 730 .. 68.4 4.6 22.3 100 740 6.9 26.5 55.0 1100 120 2:0 10.7 35.0 43.8 2350 170 .. 4.6 46.2 48.0 110 470 48.0 33.3 7.8 900 130 2:3 6.9 29.5 36.3 1590 188 2.3 17.2 29.2 15.3 470 1870 6.8 20.5 22.7 6.8 660 2830 13.2 24.0 20.0 2.7 730 3930
12 250 250 221/a 12 250 12 300 12 350 12 250 300 12 12 350 12 375 400 12 12 425 * Refers to fraction of original oqal represented b y particular product. b From benzene extraction of residue.
%%
1588
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
tars b
..
2:6 8.1 8.5
..
25:o 23.8 28.1 34.6
Vol. 47, No. 8
PRODUCT AND PROCESS DEVELOPMENT On the basis of preliminary work 300 the separation method shown in Fig!a m ure 1 was developed. Physical meth;i 250 ods of separation and identification were employed as much as possible; chemical derivatives were used as a final PO0 means of characterization when ward ranted. Y The liquid and solid reaction prod4 150 ucts were first subjected to an exhaustive steam distillation directly from the pressure vessel. The distillate and residue were treated as shown in Figure 1.54 1. The yields, the carbon distribution, I and ultimate analyses of the composite 1.52 products are shown in Table VIII. 0 15 16 Of the products recovered from the I J - 5 distillate, only the fractions designated :'1.50 I A1N constituted a significant part of Ad. the carbon of the coal. These amounted 1.48 I to 2.9% and were separated into a number of fractions by distillation. Data 1.46 are shown in Table I V and Figure 2. The 0 10 40 30 40 50 60 70 infrared spectra show peaks common to CUMULATIVE WT. % O F CHARGE trisubstituted benzenes and substituted Figure 2. Data from vacuum distillation of steam volatile neutral oils (AIN) naphthalenes. Plots of optical density versus ultraviolet wave lengths indicated alkylated naphthalene or tetralin types. which was found to contain about 20y0 inorganic material. Analyses of aliquots from the aqueous layer of the distillate The ash-free product, which was recovered by evaporation to showed the presence of a total of 1.5% of the coal carbon and dryness with excess hydrochloric acid, followed by ether extrac39.5y0 of the coal nitrogen. A large fraction of the nitrogen was tion, proved to be almost nondistillable to temperatures of 250" C. present as ammonia. Exhaustive ether extraction of this and 1 micron, and was not examined further. aqueous layer resulted in the recovery of only small amounts The filtrate, Dl, in Figure 1 was exhaustively extracted with of material. The properties of the basic components, A2B, ether and the extract was found to represent 2.8Sy0 of the coal rorresponded to methylpyridines. carbon (Table VI, Figure 3). This material was then fractionated Benzene extraction of the liquid phase from the residue in a column of 10 theoretical plates a t pressures from 22 to 4 mm.; (see Figure I) resulted in the recovery of a viscous tar. The the first 25y0 of the distillate was a crystalline solid melting a t neutral fraction of these tars constituted 3.1y0of the coal carbon 38" C. and forming tribromo- and aryloxyacetic acid derivatives and was separated broadly in two fractions, one boiling under of the proper melting point for phenol. Infrared spectra 250" C. a t 1 mm. and the other above 250' a t the same pressure. were in good agreement for phenol. Analytical data are given Analytical data for the composite and for the fractions are given in Table VII. in Table V. The data point of partially hydrogenated or alkylComparisons of the infrared spectra with authentic samples of ated condensed cyclic compounds. certain phenols indicate that 3,5-dimethylphenol, o-ethylphenol, Raffinate from the benzene extraction of the solution, B1, in and m-ethylphenol are probably present, while p-ethylphenol. Figure 1 contained the sodium salts of carboxylic acids and of 2,6-dimethylphenol, and 2,5-dimethylphenol are probably absent. phenols. Saturation of the alkaline solution with carbon dioxide The raffinate, D2, in Figure 1,from which the phenols had been t o liberate the phenols resulted in a flocculent brown precipitate extracted, following acidification with sulfuric acid and separation of a small precipitate, was exhaustively extracted with ether. The carboxylic acids so recovered amounted to 333 grains and represented 8.45% of the carbon of the coal. Table 111. Camposition and Distribution of Gaseous Fractionation was accomplished in a distillation column of 10 Products theoretical plates; the distillation was started a t atmospheric pressure and completed a t about 10 mm. A plot of the physical Volume Yo, Moles, Coal CarCoal S i t i o :as as Analyzed .we ban, % wn, % properties of the fractions versus the weight per cent distilled is 0.06 0.48 0.051 coz shown in Figure 4. The melting points of the derivatives of 1.64 0.27 0 2 ... 0.30 NHa ... 1.78 fractions 12 and 23, 113' C. for the anilide and 150' C. for the
2
4
Hz
48.75
CO C H4 C2H6 Na
8.12 0.10 0.34 1.68
0.61
2.05 10.09 34.60
0 : 065 0.217 2.142
...
..
Table V. Table IV. Fraction A1N 18 AlN24 AIN29
AlNR
August 1955
Ultimate Composition of A l N Fractions
C, %
H, % '
X,
%
5, %
0 (Diff.) %
C/H
88.15 87.24 88.53 87.43
10.31 11.20 10.18 9.95
0.85 0.28 0.22 0.96
0.3 0.3 0.3 0.3
0.69 1.28 1.07 1.66
0.711 0.648 0.724 0.732
Coinponent C1A C1B C1P ClNl ClNH
Analytical Data for Composite and Fractions of C1 Extract Coal U t i i n a t e Analysis, % Amount, Grams
Carbon,
Yo
C
II
19.9 1.7 12.1 28.6 39.5
0.870 0.075 0.515 1.310 1.830
80.11 82.80 80.21 88.46 87.38
7.96 7.83 626 9.29 7.32
INDUSTRIAL AND ENGINEERING CHEMISTRY
N
S Ash 0.3 0 . 3 0.66 7 . 5 3 0 . 3 1.24 2.00 0 . 3 2.58 0.75 0 . 3 0.66 1 . 0 7 0 . 3 1.53
0
(diff.) 11.26 0.90 8.95 2.94 2.73
1589
PRODUCT A N D PROCESS DEVELOPMENT 300
d
n-butyric, isocaproic, and lauric acids. Acetic, propionic, and n-butyric acids were definitely shown to be present in certain fractions. Water extraction of an ether solution of the residual acids resulted in the recovery of a white, solid acid with an equivalent weight of 60, forming an anhydride melting a t 118" to 119' C . and an imide melting a t 124' t o 125'. The corresponding figures for succinic acid are 59", 120', and 126" C. It is probable that other dicarboxylic acids were present, but succinic was the only one definitely characterized. The summation of the carbon found in the products represents 88.6% of that in the original coal and it is probable that the losses were fairly evenly distributed over all of the products. A comparison of the elemental balances of the products obtained in this reaction with those for the coal used shows that the elements of hydrogen and oxygen were added to the products in approximately the ratio _.
.'T I
d- 260 m
0 PPO
'
I4
(Y
I
180
2
3
4
FRACTIONS 1-5 SOLIDS
5
.'
___---- /-12
IO
V
/-L*-----
6
6
7
-
-
1.54
d
1 0
0
/I -
,
~
I'
.
-
I3
14
~
15
-
16
3 e 1.52 1.50
1 .OS 1.06
2104
1
1.04
'D
.
I I
@
F R 4 C T I O N NUMBER FRPCTION NUMBER
I1
-12 - 13
I
17
I
+ INFRARE
1.OP
drogen, equivalent to reaction with water. Figure 3. Distillation data on phenols (D2) The reaction was carried out in a closed system with the reactants coal, sodium hydroxide, water, and nitrogen. p-toluidide, were close to those for acetic acid, 114" C. for the Addition of the elements hydrogen and oxygen t o the original anilide and 153' C. for the p-toluidide. Fraction 34 appeared to coal, assuming the nitrogen to have been inert, could take place contain both acetic and propionic acids since the anilide melted by either of the following reactions: a t 78' to 79' C. and these acids are known to a form a eutectic. Since it was impossible t o prepare satisfactory derivatives in all Coal OH' or Coal HzO instances, infrared spectra were obtained on a number of fractions and compared with authentic samples of acetic, propionic, The enrichment of the products in oxygen and hydrogen will be in the ratio of 16 to 1, if the reaction took place according to the former, and 8 to 1, if according to the latter. The yields of the products, their elemental composition, the Table VI. Distillation Data of Phenols, D2 weight of the element in each fraction, and the percentage of that Charge: 63.18 grams element in the coal are shown in Table VIII. These data show Pressure 22 t o 4 mm. Hg that the total oxygen in the products amounted t o 708.6 grams Weight, Gram B.P. a t and that in the coal was 342 grams so that the excess oxygen in 740 Mm., Mol. FracCumulan 'g tion Actual tive d: QCQ Wt. b the products over that in the coal is 366.6 grams. By a similar 1 3.260 3.260 solid solid 183 93.1 calculation it can be shown that the excess hydrogen is 41.1 2 2.442 5.702 solid .. ... solid 3 1.880 7.582 ,.. solid solid .. grams. Thus, excess oxygen and hydrogen are found in the 4 1.945 9.527 solid .. ,.. solid ratio 8.93 to 1, and the over-all result of the reaction is ap5 1.260 10.787 ... solid solid .. proximately the addition of oxygen and hydrogen in the pro6 1.740 12.527 1,5468 1.078 183 ... 7 1.840 14.367 1.5468 1.076 ... portions in which they are contained in water. ... 8 1.380 15.747 1.5442 1.060 187 The following reactions could conceivably have taken place: 9 2.440 18.187 1.5411 1,055 CUMULATIVE WT.
7% OF CHARGE
+
10
2.310
20.497
1.5403
1.048
195
104:2
11 12 13 14
2.550 3.175 1,980 2.745 2.780
23.047 26.222 28.202 30.942 33.722
1.5387 1.5375 1.5355 1.5311 1.5311
1.038 1.038 1.037 1.025 1.031
..
...
2.280 36.002 3.880 39.854 18 3.400 43.252 19 0.620 43.872 Residue 11.91 55.782 a Micro boiling point. b Ebullioscopic in acetone.
1.5308 1.5029 1.5100 1,5190
1.043 1.037 1.045
15
16 17
Table VII.
202
Zi7
..
lis11
238
...
295
188:1
..
...
...
+ HzO NaOH RCOOH + ROH
(2)
-
0
Analytical Data for Filtrate D1 Distillate C,
H,
N,
S,
76.32 77.26 74.81
7.20 8.47 9.22
0.2 0.2 0.2
0.3 0.3 0.3
%
%
%
%
(DIG.),
R-d
%
14.48 13.27 15.97
RzCO 1590
(1)
...
n Fraction D2-28 D2-14 D2-18
-
+ HzO NaOH ROH + R'OH
R'-0-R RCOOR
+
+ H20
NaOH
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
RCOOH
+ RH
(4)
Vol. 47, No, 8
PRODUCT AND PROCESS DEVELOPMENT
Table VIII. Product Grams
...
Gases A1 A2 c1 C'1
70.7 25.0 102.0 328.2 754.0 151.5 70.4 333.3 61.7 674.0 71.4
R D1 D2 E2 F1
c02
Interfaoe
% of
Carbon,
%
Carbon, Grams
Coal Carbon
87'.89 67.33 85.05 87.64 76.06 77.63 76.39 47.78 45.41 27.27 7 6 ,a
46.54 62.14 16.83 86.75 287.63 573.49 117.61 53.78 159.25 29.01 183.80 54.66
2.47 3.29 0.89 4.60 15.26 30.42 6.24 2.85 8.45 1.48 9.75 2.90
Elemental Balances and Distributions
Hydrogen
%'
Hydrogen, Grams
10.71
28.71 7.56
{;:E 8.02
10.65 7.87 8.27 4.80 5.70 8.20
27.10 36,20 8.60 5.70 36.205 6.20b
...
5
Coal Hydrogen
Oxygen,
22.43 5.90 2.08 6.26 21,17 28.28 6.71 4.45 28.28 4.84
... 0.25 ...
...
...
... -
Total 0
% of
%
5.82 2.55 5.93 13.03 14.72
... ,..
72.7
...
Oxygen, Grams ,
..
0.20 2.30 5.90 8.4 44.7 20.0 10.4 107.0b 19.7b 490.0
...
?' & of
Coal Oxygen
...
0.06
0.67 1.72 2.45 13.07 La4 9.04 31.28 5.76 1. 4 3 . 2 0
Nitrogen,
Nitrogen, Grams
82.35 1.15
5.1 0.81 9.95a 1.08 4.26 8.82
%
..
1.06 1.30 1.17 0.91 0.49
...
.. , .
..
..
..
.. ..
..
..
..
% of
Coal Nitrogen 13.7 2.7 39.3 3.5 14.0 28.9 4.5
.. .. , .
, .
..
% of
Coal Nitrogen (Basic) 13,7 1.0
39.3 2.3 7.0
..
.. .. , .
.. ..
..
-7
169,08
Titration of aqueous layer f r o m steam distillation. Calculated from equivalent weight.
+ H2O
SaOH
+ R'CH2CHO 3aOH 2RCHO + HQO RCHZOH + RCOOH NaOH RCH3OH + 2HzO RCOOH + 2H2
RCHzCH = CHR'
-+
___*
RCH,
-
(5) (6)
(7)
An interesting feature of this reaction is the amount of carbon dioxide produced. This could arise from carboxyl groups already in the coal or from those formed by Equations 2, 3, 4, 6, or 7 . If the carbon dioxide came exclusively from Equations 2,3, 4,or 6 there would be no accompanying hvdrogen formation. If it came from Equations 7 or 8, there would be two moles of hydrogen per mole of carbon dioxide. Some idea of the type of reaction with which we are concerned can be obtained from the ratio of oxygen recovered as carbon dioxide to that oiiginally present in the coal. This ratio was found to be 1.4. If complete decarbos-
ylation is assumed, then in Equation 2 the ratio of oxygen in carbon dioxide formed, to that in the reactant, is I ; in Equation 3, 413; in Equation 4, 2; in Equation 6, 1, and in Equation 7 , 2. Thus, the partial occurrence of Equation 4 or 7 would account for the observed ratio. The presence of hydrogen in the gases indicates that a part of the carbon dioxide has probably resulted from a reaction in which hydrogen is formed concomitantly, but it is not possible to state on the basis of these data just what fraction of the carbon dioxide is so formed. If, however, it is assumed that the hydrogen found in hydroxyl groups, carboxyl groups, and ammonia is derived exclusively from hydrolytic reactions, then the additional hydrogen must have come from oxidation-reductions such as Equations 7 or 8. On the basis of such calculations it can be shown that approximately 60% of the excess hydrogen resulted from oxidation-reduction reactions and 40% from hydrolytic. The difference between the total hydrogen produced and the amount present in the gas phase a t the conclusion of the reaction represents that reacted. The amount so calculated corresponds to about 0.26 mole or 0.5 gram per 100 grams of coal. These data confirm the qualitative conclusions of earlier investigations that oxidation and reduction, as well as hydrolysis, occur in high temperature reactions of alkali with coal.
Origin of phenols and carboxylic acid i s not fossil I
80
I
I
I
I
I
1.45 20
1.40
5101
i
1.00
a
12 FRACTION LUMBERS NUMBER + lNFRAR€D
@ FRACTION t
A
TOTAL REFLUX REDUCED PRESSURE IY1sm B.P.1
I
0.95 0
Figure 4. August 1955
10
20
I
30 40 CUMULATIVE WT. % OF CHARGE
50
60
Distillation data on extracted carboxylic components (E2)
'O
I n order to determine whether fossil, resinous materials in the coal, were responsible for the production of the acids and phenols which were recovered in the products, a sample of the coal was exhaustively extracted with a mixture of alcohol and benzene a t 200' C. and the recovered extract subjected to the alkaline hydrolysis reaction. The extract represented 8.7% of the carbon of the coal. I n the hydrolytic reaction only the products considered to be significant were separated and analyzed. The fraction of the carbon of the whole coal appearing as phenolic materials was more than twentyfold that obtained by reaction of the resins alone, and that appearing ap carboxylic acids about fifteenfold. Thus, resins could not have been responsible for the yields of phenols and carboxylic acids obtained. Similar large
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1591
PRODUCT AND PROCESS DEVELOPMENT differences were observed when comparison was made with other components. There was, however, similarity of distribution of the products from the extract and from the whole coal. Thus, it may be concluded that the general structure of the extract was similar to that of the whole coal. A summary of the yields and balances is given in Table IX. The gases from this reaction were predominantly hydrogen and hydrocarbons. The possible origin of the hydrogen has already been discussed; the hydrocarbons may have resulted from pyrolysis of aliphatic chains, decarboxylation or, in the case of ethane, from hydrogenation. The ammonia may have come from hydrolysis of a ring-type amide or imide. One would expect nitrogen in this form to be difficult t o liberate from the coal and only 5% of the coal nitrogen was liberated a t 250’ C., 9% at 300’ C., and 39.3% at 350’ C., as determined by titration of the aqueous layer from the steam distillation. The pyridinetype bases may either have been present as heterocycles in the original coal or synthesized by reaction of ammonia and aldehydes. The production of phenols may be attributed to the cleavage of ether linkages by hydrolysis, hydrogenation, or pyrolysis. The formation of phenols by all these reactions has been reported in the literature (6,6,8,9, IS, 16). Some types of reactions which may have been responsible for the formation of fatty acids have already been discussed. I n addition to these, earlier workers (IO)have reported the formation of fatty acids by high temperature alkaline degradation of phenols. The hydrocarbons recovered probably resulted from decarboxylation or cleavage of carbon to carbon bonds in ketones, Equation 4, or cleavage adjacent t o a double bond, Equation 5.
Table IX. Products Gases Ammonia Nitrogen bases Phenols, li uid, low mol. wt. Phenols. d i d . high mol. wt.
Total
Yields and Balances Weight % of Coal AshAsh- and free moisture-free
2.85 0.56 0.70 3.02 4.97 12.95 15.60 23.86 22.09 18.50
3.63 0.71 0.88 3.85 6.31 16.46 19.83 30.31 28.08
___
... -
105.10
100.60
Coal Carbon,
% 2.47
...
0.88 3.77 6.24 9.93 21.87 33.32 9.75 ,..
__
88.23
The properties of the fractions of the steam-immiscible oils indicate that these materials contain one or more alkylated cyclic nuclei, one of which is of the benzenoid type. In the higher molecular weight fractions the rapid change of carbon-hydrogen ratios with molecular weight points to condensed cyclic structures. The solid coallike residue from this reaction is substantially lower in oxygen and hydrogen than the original coal and has a composition that places it in the bituminous region of the coal band. This is in accord with Kasehagen’s ( 1 1 ) findings that the residues from high temperature alkaline hydrolytic reactions on coal are closer in composition to coals of higher rank than they are to carbonization products. The carbon dioxide produced in this reaction appears in solution as alkaline carbonate. It probably resulted from decomposition of carboxyl groups either originally present in the coal or formed by cleavage and oxidation. As a result of this study certain speculations can be made as to the general character of this subbituminous coal. Approximately 30% of the carbon of the coal can be accounted for in condensed
1592
cyclic nuclei. These are apparently interconnected by hydrolyzable links. The hydrolysis of these results in the formation of hydroxyl and carboxyl groups that aid in the peptization of the large fragments of condensed cyclic structure so that a significant fraction of the coal becomes colloidally dispersed by reaction at temperatures not higher than 250”. At temperatures above 300’ the hydrogen derived from oxidation-reduction reactions probably aids materially in further cleavage by the rupture of stronger bonds. Summary
By preliminary experiments, the optimum conditions for degradation of a Wyoming subbituminous coal, into fragments of moderate molecular weight, were found to be 250’ C. with 5Asodium hydroxide and a 24-hour reaction period. Approximately 3 kg. of the coal were reacted in 75-gram batches under these conditions and the accumulated products separated and characterized. The products obtained in weight per cent of the ash-free coal were gases, predominantly hydrogen, methane, and ethane, 2.8%; liquid phenols, molecular weight 90 t o 180, 3.0%; solid phenols. molecular weight over 300, 5%: fatty acids, average equivalent weight 100, 13.0%; nitrogen bases. 0.7%; ammonia, 0.5%; hydrocarbons, molecular weight 100-400, 15.6%; carbonat,es, 22.0% as carbon dioxide; and an insoluble residue, 23.8%. The compounds identified were phenol, acetic, propionic, and butyric acids. The cornpounds probably present were caproic and lauric acids, cresols and xylenols, and alkylated, cyclic hydrocarbons, containing one or more condensed rings. Elemental balances show that the over-all reaction corresponds to the addition of water to the coal and, from the yield and composition of the products, the extent to which the individual reactions of hydrolysis, oxidation, and hydrogenation occur is postulated. From these facts a generalized structure for this coal is suggested. literature cited
Adltins, H., “Reactions of Hydrogen,” pp. 29-45, Univ. Wisconsin Press, Madison, Wis., 1937. Allen, I., Rfeharg, V. E., Schmidt, J. H., IND.ENG.CHEv., 26, 663 (1934). Cooper, H. M., U. S. Bur. Mines, Pittsburgh, Pa., private communication, June 27, 1950. Donath, E., and Braunlich, F., Chem.-Ztg., 36, 373-6 (1912). Dress, K., and Kowalski, G., Brennstoff-Chem., 15, 449 (1934). Fischer, F., and Gluud, W.. Ces. Abhandl. Kenntnis Kohle, 3, 75 (1918). Ibid., pp. 243-5. Fischer, F., and Schrader, H., Ibid., 5 , 332-65 (1920). Gomberg, M., and Snow, H. R., J . Am. Chem. Soc., 47, 208 (1925). Hofmann, F., Boente, L., Stech, W., and Amende, J.. .\-atu~wissenschaften, 20, 403 (1932). Kasehagen, L., IND.ENG.CHEM.,29, 600-4 (1937). Krevelen, D. W. van, Brennstoff-Chem., 33, 261-8 (1952). Kruber, O., Ber., 6 5 , 1383 (1932). Osgood, F. D., U. S. Bur. Mines, Tech. Paper 484, 115 (1931). Parks, B. C., U. S. Bur. Mines, Pittsburgh, Pa., private communication, August 15, 1950. Ungnade, H., Chem. Rec., 38, 405 (1946). RECEIVED for review November 23, 1954. .4CCEPTED April
