Extraction of Natural and Artificial Coals with Solvents E. BERL AND W. KOERBER Cnrnegie Institute of Technology, Pittsburgh, Penna.
Q
UALITY and quantity of the bitumen, the material which can be extracted more or less from natural and artificial coals with solvents, determine the technical value of these fuels. Bitumen which distills off at higher temperatures without being strongly decomposed is the cause of sandy coke formation from certain bituminous coals. If decomposition of bitumen below its boiling point under formation of larger molecules takes place, then these compounds cement the residual coal particles (the nonsoluble organic part of coals) together, and hard coke is obtained. In the following study different solverits were used for the extraction of different coals. This has been done t o get some insight into the nature of those coals and of the resulting residual coals, and t o obtain some data concerning the extraction capacity of different bitumen solvents. These coals were ground to 200 mesh and extracted aa completely as possible with the following solvents: acetone, benzene, dioxane, acetophenone, acetophenone followed by extraction with benzophenone, tetrahydronaphthalene (above its boiling point under pressure), and benzophenone at different temperature and pressures. Twenty-five grams of eacli coal quality were extracted during 24 hours at room temperature or at the boiling temperature of the solvent. The extracts were separated from the residual coal by filtration over porous glass filters, the residual coals were washed with acetone, and this solution was combined with the solution containing the chief amount of bitumen. The solvents were evaporated in vacuum. Repeated boiling with water was carried out to remove these amounts of solvent which, through the formation of molecular compounds (for instance between phenols and ketones) at their boiling temperature cannot be elimi-
I. Coke of original coal A
IA,. A after citn. bitumen neetone nt
of C.3%
with
201
c.
In,. A after ID,. ID, sitcr extn. of 4.090 bl- ertn. of 22.6% turnen with meto- bitumen with uhenone at 201 C. heetoyhenonr a t 100- c.
IA?
I*, after ortn.
of 0.7% bittimen with uectone a t 68" c.
ID1. 102 after ealn. of 52.8% bitumen with scetoplrenone st 206' C.
nated from the residual coal. In this way the solvent can be removed completely. The bitumen was dried at room temperature over phosphorus pentoxide in vacuum. When benzophenone was used as a solvent, the adhering benzophenone was eliminated from the bitumen by extraction with benzene. The extractions with acetone, benzene, and dioxane were carried out in a Soxhlet extractor. The extraction temperature, therefore, was somewhat below the boiling temperature of the solvents. The amount of extracted bitumen was determined by the weight of the extract and by the amount of residual coal. Those figures checked within a difference of about 5 per cent. The bitumens of artificial coals extracted below 100" C. were solid. At higher t.emperatures very viscous oils resulted. A small amount of cracking may have taken place. Different solvents extract different components from natural coal. Extraction of Pittsburgh coal with benzophenone at 310" C. produces 12.6 per cent bitumen. The remaining residual coal gives sandy coke. The same coal extracted with tetrahyrlronaplitlialene under pressure at 300" C . yields 18.8 per cent bitumen. I n spite of the higher amount of extracted bitumen, the residual coal gives a hard coke. Polar solvents with partial valences ou their oxygen atoms (dioxane, acetone, acetophenone) have a selective affinity toward the phenolic components of bitumen. Those phenolic substances are re sponsible for the caking properties of coal. Less polar substances, such as tetrahydronaphthalene, extract more of the neutral substances of bitumen which have little to do with the caking properties of this bitumen. Acetophenone (proposed in this laboratory by Regis &ab) is the best extracting solvent at normal pressure. Ibs use
1 ~ A~niter . extn. of
V.Ul
C
Bensene I 2
20 80
zxoxsne 1
20 100
2 U
Aoetwbenone 1
20
1w
2
205
3
n. E F
c.
20 56.5
Uz extd. with benmphenone Tetrahydrooa~htheiene twiae under pre98u18 Original cos1 with ben-
rophenoae *Hard dense coke. sandy aake,
+:
-.
Pittsburgh Bituminous Coal, I Coke of Residual Coal Yo Weight Appear of art. anoe' Yield, % 0.3 c 64.4 0> 64.5 0.7 0.01 64.2 0Z .64.0 0.21 0.6 64.6 04 63.8 1.0 4.0 65.5 18.6 71.9 10.2 73.9
+
m
Aitifioial Coals OH-Cellulose Coal. I1 Coke of
c
%Weight ofert. 36.2
4.4
3
3
++
21.5
++
16.5 2.7
+ -
1 s 86.3
-1
22 0 9 6
26.0
Ern
HzO-
Re8id"al c ? ? L ~eiluiose.III. ~i n i ~IY. APPSBI% wt. of g w t : oi sno@ Yield, % e d ert. 77.2 13.3 0.8 78.6 2.1 15.4 1.4 72.0 11.9 0.04 78.2 2.0 813.9 0.12 70.2 5.3 0.0 70.7 1.9 73 0.4 71.3 6.2 O.? 79.6 2.5 1.1 81.8 11.6 0.2
-
-
e
__
-
20.3
310
0
-
74.0
0.8
-
82.5
0
3w
18.8
+
..
..
..
..
..
310
$2.6
-
73.7
59.6
-
83.3
20.8
1.5
0
.. 1.5
DECEMBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
Benzene is a poor extraction agent for natural bituminous coals compared with acetophenone and tetrahydronaphthalene. Artificial carbohydrate coals give much more soluble bitumenlike materials after extraction with any of the used solvents compared with natural bituminous coals. Artificial cellulose coals produced in weak alkaline medium show more soluble bitumen than artificial cellulose coal produced in neutral or weak acid medium. Lignin coals give very little soluble bitumen. Its results probably from the small amounts of carbohydrates which are
1607
difficult to separate from the isolated lignin. This is one more important reason why natural bituminous coals could not have been formed extensively from lignin and its derivatives. I n another publication i t will be shown that by a special treatment the amount of soluble bitumen of artificial carbohydrate coals, which for the coals described in this paper is much higher than that of natural coals, can be reduced to the amount which the latter coals show. This is due to a conversion of lower molecular phenols and phenol-carbonic acids into more complex and therefore less soluble higher phenols and phenol derivatives.
AEROGEL CATALYSTS Dehydrations and Decarboxylations' IC. I
