OCt.,
I917
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
927
ORIGINAL PAPERS COAL DISTILLATION UNDER PRESSURE B y J. 15. CAPPS A N D G. A. HULETT Received M a y 14, 1917
T h e many uses of coal may be roughly classified under two general heads. It is burned directly as a fuel, or i t is destructively distilled (or “carbonized”). Coal is most frequently carbonized with either gas or coke in view a s t h e primary product of manufacture. Coke ovens and gas retorts subject t h e coal t o widely different conditions as regards rate of heating, duration of heating, etc., because t h e conditions which produce the maximum yield of the best coke are differe n t from those that, produce the highest possible yield of gas. Certain other conditions, however, such as pressure and maximum temperature attained are practically the same in either case. I n making gas or coke, t h e retort or oven which contains t h e coal is subjected t o a temperature of about 9 5 0 t o 1 0 0 0 ~ C . while most of the volatile matter is driven off before t h e coal itself reaches 600’. During the distillation the different layers of coal from t h e retort walls t o t h e center vary not only in temperature but also in rate a t which they are distilled. Tn general, t h e vapors, after leaving t h e coal, enter regions where they are subjected t o decidedly higher temperatures than t h a t of their origin, so t h a t secondary and uncontrolled “cracking” takes place, forming, again, decomposition products, together with carbon residues which separate in t h e form of flakes or droplets and float along with the vapors until mechanically caught with t h e condensing oils and water t o form the t a r . It is evident, therefore, t h a t the technical distillation of coal is a most complicated process from the standpoint of both t h e chemical and physical changes which take place. The present work is a preliminary attempt t o get information about the products which may be obtained from a given type of coal and how these products vary with t h e teniperature, pressure and time or rate of distillation. Our apparatus was designed with a view t o avoiding the secondary “cracking” of the vapors after they leave the coal and also with a view t o heating the whole mass of coal as uniformly, as t o time and temperature, as possible. If the first layer of coal is heated rapidly, the second layer a t a different rate, and so on, i t is obvious t h a t t h e first products of decomposition and distillation of one layer will be mixed with the later products of outer layers in a hopeless manner. This situation may be improved somewhat by heating slowly t o a given temperature which is maintained until t h e reactions for t h a t temperature are completed, then heating t o a higher temperature and holding it until the reactions for this new temperature are over, and so on. However, with a slow rate of heating we undoubtedly get different reactions and T-apor mixtures t h a n when the coal is heated rapidly. We aimed t o heat uniformly and still a t a fair rate. Practically all the work done on the carbonization of coal has been a t atmospheric pressure, save some work under diminished pressure,’ so t h a t our knowl1
Bureau oi Mines. Technzcal Pafier 140.
edge as t o the pressure factor is restricted t o a small range of from a few millimeters t o one atmosphere. We first attempted t o find out something about t h e variations with pressure up t o twenty atmospheres. After much experimentation and many failures we evolved the apparatus described below. APPARATUS
The retort used in this work was a steel cylinder of 1 . 9 liters capacity (Fig. I , A ) into which was sealed
(cemented) t h e neck B of a ‘/Bin. walled 3/4 in. steel tube. Into this were brazed a brass side tube of 1/4 in. inside diam. and 2 in. long, a t E , and a small copper tube, a t F , which led t o the pressure gauge G and could be disconnected a t the union T . The “first trap” C (see detail) was made from a seamless, spun-bottomed steel tube of I’/B in. inside diam. and in. walls. The brass inlet and outlet tubes (1/4 in. diam.) were brazed in with silver. T h e tube X was let down through the cap t o prevent the spurting of condensed liquids across the t r a p and into t h e outlet. The seat of the cap was bedded with lead, which sealed the tube X into the cap and very effectively and conveniently sealed the t r a p itself when t h e top was screwed into place. This joint withstood temperatures u p t o 2 2 0 ’ and pressures as high as 2 0 atmospheres very satisfactorily. The “second trap” D was of glass blown in our laboratory. I n the side tube t o the left, condensation of t h e light oils took place, whence they flowed into t h e main (receiver) part of the t r a p . The uncondensed gases passed out through the stopcock H t o be measured and sampled for analysis. The Liebig gas washing bulbs J were made in the laboratory t o contain a standard acid solution which would collect the ammonia from the gas as it bubbled through. T h e question of ammonia, however, was dropped because sufficient information could be obtained from the analyses of the coal and resulting coke. Also the analyses of our cokes showed t h a t a great part of t h e nitrogen was still retained after low temperature carbonization. The top of the neck B was sealed by a n ordinary cast-iron cap through the top of which a hole had been drilled for t h e introduction of the “internal condensation tube” K . This was practically a reflux condenser and its object was t o condense and return the heavier volatile products t o the coal mass where they would have further chance of cracking. If we had attempted t o cool the neck of the retort, these constituents --odd have flon-ed down the hot sides of the retort where cracking would have occurred with a deposition of carbon residue, while, by the arrangement employed, the oil was returned directly onto the coal where cracking took place on and a t the temperature of the coal. K i t h gases issuing a t a rapid rate during the period in which t h e condensable products were given off, the cooling surface exposed t o them by our internal condensation tube was undoubtedly too small and its temperature also was probably higher t h a n the boiling
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C E E M I S T R Y
928
point of the liquid inside, so t h a t t h e condensations were not as complete as are possible a t t h e indicated temper a t ures. I n view of this inefficiency and of t h e results of some subsequent work in this laboratory which have not yet been published, we disregard, in this paper, our d a t a o n t h e effect of this reflux condensation. The heater used, L , was a n electric resistance furnace of which t h e heating element was a single spiral of nichrome “flattened wire.” This coil was cemented in place with a mixture of kieselguhr and cement and
VOL 9 , No.
IO
nichrome resistance ribbon t o maintain t h e desired temperature within t h e heater. We made only one separation of t h e liquid distillate a n d found it best t o have our first condensation a t such temperature t h a t no water would remain with t h e heavy oils in t h e first trap. For this purpose, this heater kept the temperature of the first t r a p about 20’ above t h e boiling point of water a t t h e pressure used. The cold water jacket N facilitated t h e liquefaction of t h e vapors as they passed t o t h e second t r a p and also prevented t h e conduction of heat along
K
I
-
-
N .,
0
n
t
D c
+ 0 00
around i t was wound sheet asbestos t o a thickness of in. was left and then two l / p in. An air space of layers of “corrugated” asbestos were wound around this. Several wrappings of thick asbestos felt completed t h e insulation. I n t h e bottom of t h e furnace the resistance ribbon was wound into a flat spiral. in. hole permitted Through t h e center of t h e floor a a stream of illuminating gas t o be led in, in order t o keep a reducing atmosphere around t h e hot steel retort during a run. T h e outside heater M was constructed of heavy asbestos cement board with a double glass window in front. Strung upon t h e floor were four coils of small
FIG. I-PLAN
OF
APPARATUSUSED
IN
COAL DISTILLATION EXPERIMENTS
the brass tube from t h e heater M t o t h e cement joint a t 0. The glass t u b e jacket P, containing boiling water, served t h e double purpose of keeping t h e lead bedding in t h e cap below its melting point and of acting as a condenser for t h e vapors of thymol or aniline in t h e internal condensation tube. Temperature was read outside t h e retort by t h e P t - P t R d couple Q, insulated in a glass tube and placed next t o t h e steel retort, b u t separated from t h e heating coil by sheet asbestos. PROCEDURE
The charge of coal was introduced into t h e retort through t h e neck, and t h e cap S screwed firmly into
OCt.,
1917
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
place. Then t h e short arm of t h e first t r a p was fastened t o the side t u b e a t E , by soldering with lead. The retort was then set in place in t h e furnace, t h e outside couple adjusted and the heating box M p u t in its place. The second t r a p was now connected t o t h e first t r a p by sealing with Khotinsky cement a t 0. The next step was t o displace the air in t h e apparatus with illuminating gas by alternately evacuating a t t h e cock H , a n d admitting t h e gas a t t h e union T . The connection a t T was then made with t h e pressure gauge, t h e stopcock was closed and t h e outfit was ready for a “run.” T h e electric current was from t h e A. C. lighting circuit and between 600 and 1000 watts were used, according t o t h e temperature of t h e furnace and t o t h e rate a t which t h e temperature was t o be raised. Current was regulated by a water-cooled sliding resistance in series. The temperature was raised a t t h e rate of about 4 or 5’ per minute from room temperature t o about 450’ C. (reading of couple, Q) and from 450 t o 600’ it was advanced a t the rate of practically I’ per minute. Under these conditions later experiments with this apparatus showed t h a t t h e temperature in the center of t h e coal followed t h e temperature outside t h e retort fairly uniformly a t about 50’ lower, except a t t h e stage where t h e exothermic reactions are most pronounced. Pressure in t h e retort was built up simply by confining t h e gases liberated from t h e coal. When t h e desired pressure was reached, t h e cock was opened enough t o let out gas as fast as it formed. At Io-minute intervals, readings were recorded of temperature, current through furnace, pressure, volume of water and of light oil in second trap. R a t e of flow of gas (cc. per min.), and t h e total gas volume were also known. Samples of t h e gas were taken for analysis a t t h e following temperatures: 450 ’, joo’, 5 5 0 ’ ~ and 600’ C. If t h e rate of evolution of gas be plotted against temperature of t h e coal, t h e temperatures indicated above lie on t h e curve, respectively, a t t h e points where it first begins t o rise, where i t shows t h e highest rate of evolution, where i t begins t o decline and further down t h e slope a t t h e end of t h e run. When t h e thermocouple indicated 600 t h e current was shut off and t h e pressure let down t o atmospheric, all gases being measured as usual. Then t h e t o p of t h e second t r a p was broken off with a file scratch a n d t h e water a n d oil withdrawn b y means of a siphon pipette: these were weighed separately and t h e oil sealed in glass tubes t o await analysis. The first t r a p was next disconnected, opened and emptied and t h e heavy oil weighed a n d sealed in a tube. When t h e retort had cooled i t was opened a t S by removal of t h e cap. T h e coke within was in a single brittle cake which had t o be broken into small enough bits for removal. This was done by pounding t h e cake with a n iron rod and shaking out t h e broken coke which was then weighed, sampled for analysis a n d bottled.
929
Four typical coals’ were investigated with this appmatus: a West Virginia steam coal (New River) Pittsburgh bituminous, Illinois soft coal, and a Wyoming sub-bituminous coal. With the Xew River and Pittsburgh coals twelve runs each were made-four a t each of three different condensation temperatures. For instance, with aniline (b. p. 184’) in t h e internal condenser, runs were made a t I , j, I O and 20 atmospheres pressure, all conditions except pressure being kept as nearly as possible t h e same for t h e series. Then another such series was made with thymol (b. p. 230’) boiling in t h e condenser and finally a series in which there was nothing in t h e condenser. I n t h e case of t h e Illinois coal only two series were made (eight runs in all), one series with aniline condensation and another with no condensation. Only six runs were made on t h e Wyoming coal, one series with no condensation and two runs (I, and 2 0 atmospheres) with aniline boiling in t h e condenser. ~
OILS
We were most interested in t h e oils. The most obvious d a t a .on these are t h e variations in their amounts due t o changes of pressure. The yields of light and heavy oils (as percentage by weight of t h e original coal), when plotted against pressure, bring out certain marked tendencies, as shown in the following table which sums up t h e curves in Fig. 11. TABLE I-EFFECTS O F PRESSURE INCRBASE FROM 1 TO 20 ATMOSPHERES COAL HEAVYOIL New River Decrease from 4 . 8 7 to 0.4% Pittnburgh Decrease from 8.8 to 1.6% Decrease from 5 . 2 g t o 1.5%
{
Wyoming
Decrease from 5.2% to 1.1%
LIGHTOIL Increase from 1.3cJ t o 2 . 4 7 Increase from 3.75% to 4.8% Increase at no condensation Decrease at 184O
The term “heavy oil” is applied above t o t h a t fraction which condensed during t h e run in t h e first trap. The temperature of this t r a p was slightly above t h a t a t which water boils under t h e pressure of t h e experiment. “Light oil” refers t o t h a t fraction which did not condense a t t h e above temperature, b u t did condense with t h e water a t room temperature and was retained in t h e second trap. The decrease in heavy oils is a better indication of t h e extent t o which cracking has taken place t h a n is t h e increase in light oils, because t h e latter represent only a part of t h e products of cracking of t h e heavy oils, t h e other products being gases and carbon residue. Also t h e increase in light oil yield is due t o other factors besides cracking of heavy hydrocarbons. For instance, t h e partial pressure of each of t h e constituent gases in t h e mixture passing over t h e condensed oils in T r a p 2 , is increased as t h e total gas pressure increases. Of these gases which do not condense from such a mixture a t ordinary pressures, t h e less volatile will condense when their partial pressures are sufficiently increased. Also we must consider t h e solubility of these a n d other gases present in t h e condensed oils and water as following Henry’s Law a n d t h e weight of these gases dissolved a t high pressures 1 These coals were collected and sampled by Engineers of the U. S. Bureau of Mines and were preserved In air-tight containers until used
Vol. 9, No.
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
930
-
TABLE11-EFFECT OF PRESSURE ON COMPOSITION OF THE OILS PERCENTLIGHTOIL SOLUBLE IN N a O H WYOMING PER CENTLIGHTOILBOILINGBELOW 170‘ C. Pressure In atmospheres 1 5 10 20
a
No con. 9.7 38.2 42.1 Lost
NEW RIVER COAL
b
230’ con. 22.4 38.2 48.3 34.8
c
184’ con. 17.8 38.6 44.2 49.2
d
No con. 15.4 29.5 25.2 35.2
PITTSBURGH COAL
e 230’ con. 12.6 19.8 30.0 29.4
f g 184‘ Aromatic con. from d Lost 6.6 25.1 7.5 22.7 9.7 39.1 14.7
NEW RIVER h 230’ 1384” con. con. Lost Lost 31.6 34.1 27.4 22.5 20.8 25.8
is consequently correspondingly greater t h a n a t low pressures. OIL COMPOSITION
T h e analysis of these oils presented a great many difficulties. A scheme was worked out b y which t h e oils were first subjected t o fractional distillation, t h e colors, densities a n d weights of all oils a n d fractions being recorded. Cuts were made at (I) 170’ C., (2) 230°, (3) 270’ a n d (4)above 270’. Fractions (I) a n d (2) were then analyzed as follows: Bases, pyridine, etc., were extracted with 2 0 per cent HzS04; acids a n d phenols, with I O per cent N a O H ; unsaturated substances with concentrated HzS04a n d t h e aromatic hydrocarbons by washing with dimethyl sulfate or liquid SOz. Fractions (3) a n d ( I ) were allowed t o s t a n d several days t o allow a n y anthracene present t o crystallize. This was t h e n separated by filtering with suction i n a Gooch crucible, washed with pyridine a n d weighed. T h e filtrates from this separation were t h e n analyzed a s Fractions ( I ) a n d (2). Everything not extracted by these various processes was called “paraffin hydrocarbons. ’’ A tabulation of some of t h e figures so obtained in Table I1 shows something of t h e effect of pressure o n t h e composition of t h e oils. These d a t a are plotted in Fig. 111. Columns a, b, c, d , e, f a n d n show t h e increase in percentage of more volatile components in t h e light oils with increasing pressure. Column g shows t h e increase in cracking t h e heavier paraffin a n d unsaturated hydrocarbons with increasing pressure. Columns h, j , k , I , m a n d o show how pressure decreases t h e amounts of phenols a n d “tar acids” in t h e oilsalthough it is not clear t o what this tendency can be due. I n regard t o t h e oil analysis d a t a , those on t h e fractional distillation a n d on t h e “per cent soluble in NaOH” are probably t h e most trustworthy because t h e largest obtainable samples were worked with a n d these were t h e first values determined in each oil.
-ILLINOIS Per cent Boiling PITTSBURGH COAL n o below 150’ k 1 m Per cent Per cent p r No 230’ 184‘ boiling Soluble in No 184‘ con. con. con. below 150’ N a O H con. con. 25.0 39.2 37.5 8.75 28.0 9.7 13.3 28.2 36.0 33.6 5.7 24.0 18.7 19.7 36.2 32.4 25.1 12.35 9.0 21.0 25.0 23.8 27.4 24.3 Lost Lost 22.1 17.0 C --O , AL-
COALPer cent Soluble in N a O H
s No con. 25:l 47.0 43.2
COKE
The amount of coke residue left in t h e retort after this partial carbonization is notably increased b y pressure, as t h e curves in Fig. IV show. Ordinates are percentages of t h e original coal. It is t o be noticed, especially in t h e curves for New River and Pittsburgh coals, t h a t practically all of this increase is brought about by t h e first I O atmospheres and most of i t by t h e first 5 atmospheres. COKE COMPOSITION
The analyses of these cokes gave percentages of “fixed carbon,” nitrogen, oxygen, sulfur, volatile matter a n d hydrogen a n d also t h e calorific value in B.t. u. These percentages (on moisture and ash-free basis) were plotted against pressure. These curves in Fig. V are summed u p in Table I11 in a tabulation of t h e tendencies apparent from them. I n t h e second column opposite “fixed carbon” is I per cent” which means t h a t increase of found ‘ I + pressure from I atmosphere u p t o 2 0 atmospheres is shown t o affect a n increase in t h e percentage of fixed
...............
......... ........... ...............
N
............... ...
0. ......
s.. . . . . . . . . . . . . .
......... ...........
Volatile B.t.u H
...............
+
f1.5 -0.05 -0.30 -0.10 -1.2
-o:io
+1.0 -0.10 -1.0 -0.10 -1.3 +60
+o.io
CHANGESIN No CONDENSATION SERIESALONE FixedC . . . . . . . . . f 1 . 6 +3.5 N ............... 2.0 -0.10 -1.5 -to:; 0. -15.0 .. .. s . . . . . . . . . . . . . . . -19.0 -3.5 Volatile. . . . . . . . . -17.0 +2300 +80’ B . t . u ........... ... .. H............... - 3.0
..
.
..
1814’ con. 21.1 46.4 42.4 46.2
All oil samples lose so much from simple manipulation in tubes, pipettes, a n d pycnometers by adhesion to t h e walls a n d b y solution in t h e wash liquids t h a t , with t h e (small) samples available, such a series of operations made considerable error in t h e results but these results are of value from t h e standpoint of relative changes due t o pressure. I n considering t h e d a t a so far obtained i t seemed best t o fall back on t h e following simple scheme with t h e oils of t h e Illinois coal: We took t h e densities a n d weights of t h e light oils, washed out t h e phenols a n d t a r acids with 13 per cent NaOH a n d weighed t h e residues. The residual oil was then fractionally distilled, cuts being made a t 7 5 , 100,125, 150, 175, 200, 250 a n d 300’ C. Weights and densities of each of t h e fractions were recorded. T h e s u m of t h e fractions boiling below I jo’ was called motor fuel. Curves 9 , r , s and t in Fig. I11 s u m u p t h e d a t a on t h e fractional distillation and t h e phenols and t a r acids of t h e Illinois coal oils.
TABLE 111-COKE INFLUENCES OF PRESSUR@ AVERAGE CHANGES FOR ALL CONDENSATION TEMPERATURES B-PERCENTAGE OF CONSTITUENTS A-PERCENTAGE OF COKE N. R. Pgh. 111. wyo. N. R. Pgh. 111. F i x e d C ......... +1.0 +l.O +1.2 -0.5 FixedC . . . . . . . . . f 1 . 1 0 +1.1 +1.4 N ............... -0.05 -0.05 -0.10 N ............... -2.0 -2.0 -4.5 0 -0.25 -0.5 -0.5 +0:5 0 . . . . . . . . . . . . . . . -12.0 -12.0 -10.0 s ............... -0.10 -0.10 .. .. Volatile -1.0 -1.0 -1.25 +0:5 -10.0 - 9.0 -10.0 B. t. u +50 +60 +1100 ,. 3:o H -0.10 .. +o.io +o:io F i x e d C .........
IO
-
+ ] . I
- 4.0 -25.0 -10.0 -11.0
+ 3:o
4-4.0
-
4.5 -30.0
..
....
-28.0
WYO.
-0.6 +i:0 +3:0
+3:0
.. +li:O
..
..
.. ..
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
OCt., I 9 1 7
carbon in t h e coke t o t h e extent of about I per cent of t h e coke, etc. Blank spaces indicate t h a t t h e corresponding curves shorn no marked increase or decrease. It must be borne in mind t h a t t h e absolute values of some of these constituents are quite small so t h a t a large percentage of change in the constituent would s h o w as a very small change in percentage of t h e coke. I n Table I11 arrangement B shows t h e interpretation of these same curves in percentages of t h e respective
P e r c e n t of
in e
P e r c e n t of
Liqht
Oil
boil in^ below
Liohf O i l 3oluble in
constituents. Thus, in arrangement A , pressure causes a decrease of sulfur amounting t o 0.1 per cent of t h e coke of New River coal. Since however, t h e total amount of sulfur present is only about 0.8 per cent of t h e coke, t h e effect of pressure is t o drive away about I Z per cent of t h e total sulfur. Thus in Table 111 t h e figures under B are more significant t h a n those under A . T h e general though slight increase in percentage of “fixed carbon” in t h e coke indicates t h a t a t higher HEAVY
170’ G.
below
170’ C .
NAOH
;D
0
I
ri 0
F:! 7;r
Percent Ligh’
Oil
Boiling below 15O’C.
0
m
--
-
m
c1 0
1 Percent
Soluble
in
NAOH
17
Percent Soluble in NaOH
93 1
01L5
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
93 2 Per Cent
of
I .I
COAL
COKES
RESIDUAL
NEW RlVER
Per cent
g a COKE O f
X
a
w 5 U
PITTSBURGH
ILLINOIS
per Gent Of
of COKL
Per
cent
89.5
90
COKE 05.5
91.5
89.0
89
85.0
91.0
88.5
88
04.5
on c, "_.-
LIB
87
840 2.30
COKE
z
2 0
2.00
2.0
e.e
e c_
'1.35
1.9
2.1
2.25
t o
2.20
4.0
'6
7.0
2.5
3.5
5
6.5
2.0
3.0
4
5.0
1.5 a. 9
2.5
3
5.5
1.0
0.8
'.on
0.8
0.9
0.8
0.9
0.7
os
0.7
0.8
I
0.7
0.C
0.7
A
I2
It
15
71
II
II
I+
70
IO
IO
IS
63
9
9
le .-
3.45
3.4
3.6
3.45
3.35
3.3
3.4
3.35
3.25
3.2
3.2
3.25
I
81
I
I
z
I
I 5
1.90
0
73
I2 v)
d
z 1 J
z rJ
g
IO
WYOM 1 N G
OF
92.0
V
c3
Rr tent
Vol. g, No.
,,
1
0:
3.15
io
FIQ. IV-RESIDUAL COKES
OBTAINED
pressures more of t h e volatile products of distillation have undergone cracking, in contact with t h e coke residue t h a n a t lower pressures. It is t o be noticed t h a t t h e effect of pressure on Wyoming coal is t o decrease t h e fixed carbon. It has been shown t h a t t h e cracking processes are time reactions. So, t h e effect of higher pressure is t o hold back t h e volatile products in contact with t h e coke for a longer time, thus enabling t h e cracking t o take place t o a greater extent t h a n a t lower pressures. Also i t increases t h e partial pressure of t h e heavier vapors, i. e., their mass law concentrations, thus increasing t h e rate of cracking, This effect of pressure is also shown by t h e increase (2 t o 4.5 per cent) in t h e percentage of t h e coal which is left as coke residue inasmuch as carbon is one of t h e products of t h e cracking reactions. It has been shown' t h a t by passing hydrogen through heated coke, much of t h e nitrogen therein can be removed as ammonia. T h e general decrease in nitrogen in t h e cokes may be accounted for as due t o t h e increased partial pressure of hydrogen in contact with t h e coke. A study of these curves brings out some interesting tendencies. 1
J . Gas Lighting, 186, 329-31.
5.15
3.0
14650
15000
15000
FIQ.V-ANALYSES
LO
14000
14600
1300b
I4550
IZOQb
i
5
IO
20
OP RESIDUAL COKBS
Pressure increases t h e fixed carbon in all cokes except those of Wyoming coal in which fixed carbon is decreased. It decreases oxygen and volatile matter in all except Wyoming cokes b u t in these oxygen and volatile are increased. Hydrogen is decreased in New River and increased in Illinois and Wyoming cokes. GAS
Pressure causes marked increase in t h e amount of gas liberated, particularly in t h e case of the Pittsburgh coal. With New River .coal t h e effect is less pronounced, With both Wyoming and Illinois coals it increases t h e gas markedly when there is no internal condensation, while with 184' condensation there is a slight decrease in gas yield from I t o 2 0 atmospheres. The curves in Fig. VI illustrate these tendencies. GAS C O M P O S I T I O N
Gas samples, as mentioned before, were taken for analysis a t about 450°, ~oo', 550' and 600' from each run, except with high pressure runs, in which cases t h e desired pressure was not attained until t h e first of t h e above sampling temperatures had been passed. With each of t h e coals studied, the building up of a pressure of 2 0 atmospheres was not accomplished until t h e temperature of t h e retort registered between
OCt., I 9 1 7
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y so04 G A S
I
I
I
/
O
I I
I
550° G A S
933
G O O 0 GAS
I
I
c
'
40 th i I
e a
I
42
20
I
41
40
10
I
I
39
0
3 8'
J
6
48 47
50
4G
40
44
30
0 0 45
-
2
43
f
42
-I
41
1
20 10
40 39
0
38
I/
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I
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46 45
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44 43 42
30
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20
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39
20
FIG.VI GASESEVOLVED
0
unont:
Fro. VI1 ANALYSSSOF GASESLIBERATED DURING DISTILLATION OF VARIOUS COALS
EO
934
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
450' and joo', a n d with such runs t h e first gas sample was taken at 500'. Gas analyses gave per cent by volume of COz, C2H4, 02, CO, CH4, C2H8, H2 and "2. Something was learned of t h e effect of pressure on t h e gases evolved from t h e coal b y plotting t h e values of each of these constituents against pressure-the coal, condensation temperature and temperature of sampling being t h e same. With four coals, two or three series of runs for each coal, four (or three) samples taken for each r u n and eight constituents determined in each sample, t h e number of curves necessary t o cover t h e whole gas field is so great t h a t they cannot all possibly be given herewith. T h e curves for hydrogen, unsaturated hydrocarbons, ethane and methane, which were deemed t h e most significant, must suffice. They are shown in Fig. VII. Here t h e percentages of H2, C2H4, etc., C2He a n d CHI are ordinates a n d t h e pressures, abcissae. Each graph represents gas samples taken a t a single temperature from t h e various runs. I n t h e 500' gases, pressure increases t h e hydrogen, with some irregularities, in all cases except t h a t of t h e Pittsburgh coal, where i t causes no marked change. Unsaturated compounds, in all coals except S e w River, are somewhat decreased by pressure. E t h a n e shows (in general) a decrease, and methane no pronounced general effect. I n t h e gases taken a t jjo', hydrogen decreases markedly with pressures. The effect seems t o be more pronounced as t h e age of t h e coal increases. Unsaturated hydrocarbons show, if anything, a slight decrease. E t h a n e shows a general increase, nearly corresponding t o t h e decrease in hydrogen. Methane 'shows (as a t 500') no general effect. At 6 0 0 ° , hydrogen decreases more sharply. Unsaturated bodies are not perceptibly affected, except b y a slight increase with Illinois and Wyoming coals. Ethane ,is generally, though irregularly, increased. Except with Wyoming, and possibly Pittsburgh coals, t h e striking rise in methane corresponds roughly with t h e decrease of hydrogen as t h e result of pressure. Of t h e above curves those on t h e change in per cent of hydrogen with pressure are particularly significant. With high-pressure runs t h e partial pressure of -hydrogen is necessarily much higher t h a n with low pressures. T h e high hydrogen concentration undoubtedly affects t h e composition of t h e oils of t h e coke. T h e decrease in nitrogen content of,t h e coke with pressure is undoubtedly due t o this factor.' We find t h e hydrogen percentage decreasing as pressure increases in spite of t h e fact t h a t t h e increased cracking which takes place a t higher pressures liberates more hydrogen t h a n a t low pressures. The hydrogen, therefore, must be used u p in liberating nitrogen as ammonia from t h e coke as well as in saturating olefine a n d acetylene compounds present. This conclusion is borne out in t h e observed decrease of nitrogen in t h e cokes (Fig. V). T h e increase of ethane at 5 j o o a n d of ethane and methane at 600' may be regarded as a rough measure 1Loc. cit.
Vol. 9 , No.
IO
of t h e extent t o which hydrogenation of unsaturated hydrocarbons and saturated ones has been affected b y t h e high partial pressure of hydrogen. I t is somewhat doubtful whether a sample of gas taken from a high-pressure run can be compared with fairness t o one taken a t t h e same temperature from a low-pressure run. Thus, in t h e case of a I-atmosphere run, since t h e gases are allowed t o escape as rapidly as they are evolved from t h e coal, there is not much mixing of t h e gases from one stage of t h e distillation with those from another stage. I n t h e case of a 20-atmosphere run, on t h e other hand, t h e whole of t h e gases produced in t h e earlier stages of distillation are confined within t h e retort t o build u p t h e pressure t o t h e desired point, and these mix with t h e gases from later stages. I n comparing two j o o o samples, one from a I-atmosphere and one from a zo-atmosphere run, i t must be borne in mind t h a t t h e sample withdrawn from t h e system in t h e first case represents pretty accurately t h e gases which are being evolved a t t h a t temperature, while in t h e second case t h e corresponding sample comprises gases formed a t every stage of t h e distillation from its beginning t o t h e point of sampling. The degree t o which t h e latter sample is contaminated with gases from earlier stages depends, of course, upon t h e amount of gas which has been formed u p t o t h e time of sampling. I n a pressure run, t h e proportion of "earlier" gases is greatest in t h e first sample (500') a n d grows less with succeeding samples. This is because gas is allowed t o escape as fast as i t is formed when once t h e requisite pressure is established. On account of frequent breakage of t h e apparatus and occasional loss of oils, etc., a number of runs had t o be repeated. I n such cases some duplicate gas samples were obtained whose analyses furnish evidence as t o t h e reproducibility of conditions in t h e retort. Two sets of such "check" gases are given i n Table IV, one of t h e m in triplicate. TABLE 1 v - h ' ~ ~RIVERCOAL:184' COKDENSATION: 550" SAMPLES PRESSURE : 10 ATMOSPHERES 20 ATMOSPHERES Run61 Run91 Run 62 Run 92 Run 65 2.4 2.4 2.0 1.5 coz.,, . , , . . . , , . . . 1 . 1 1.6 1.6 1.9 1.2 1.8 CzH4, e t c . . . . . , . . . 1.5 0.5 0.2 0.4 0 2 ...... . . . . . . . 0.3 1.95 1.0 1.5 1.4 co ...... , , , . , .... 2 . 0 57.2 57.7 58.2 59.1 CHI... . , , , . , , . . , 6 2 . 7 24.8 22.4 21.7 21.1 CZH6.. . . , . . . , . . 1 4 . 2 12.3 12.5 6.1 14.8 Hz . . . . . . . . . ... ... . 16.1 3.15 2.6 0.0 2.7 2.4 Nz ........ . . . , . . . .
. .. . . . ..
When a r u n was finished and t h e retort registered 600'~ t h e current was shut off and t h e gas let out
until pressure within t h e apparatus was atmospheric. TABLEV -----ILLINOIS Run 101 10 5 Atm. Atm. 4.1 1.9 c o * .. . . . . . 0.4 0.8 CZH4. etc.. 0.1 1.0 0 2 . . .. .. . . co. . . . . . 6 . 6 6 . 2 73.5 38.8 CH4. . . . 0.0 7.2 &He. . . Hr . . . . 15.0 43.9 0.3 0.2 hT2.. . . . .
. . . . . .. . . ..........
COALRun 102 20 5 Atm. Atm. 4.2 4.7 2.5 2.0 0.0 0.2 4.8 4.0 65.8 59.2 1 0 . 7 10.7 11.3 18.2 0.1 1.3
1
Atm. 2.7 2.7 0.3 5.2 39.2 19.1 29.8 0.1
---WYOMING COAL-Run 84 Run 88 2 1 6 1 Atm. Atm. Atm. Atm. 9.7 6 . 6 11.9 9.5 5.8 7.6 3.7 2.7 0.1 0.1 0.2 0.5 6.2 5 1 . 4 4 75 . 27 4 48 . 92 3 66 . 30 10.1 12.6 1 6 . 4 25.6 1 6 . 4 2 2 . 0 10.5 13.3 2.0 2.2 1.4 3.2
During this "let down" from a high t o a low pressure, t h e light oil in t h e second t r a p was observed t o boil violently. I n several runs, a number of gas samples were taken during this boiling of t h e light oil, in order
Qct., 1917
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
t o ascertain what constituents were being vaporized so rapidly. Analyses of some of these samples are given in Table V, From t h e observed increase in t h e gas of unsaturated compounds, carbon monoxide, ethane a n d hydrogen, it was concluded t h a t these were t h e constituents which were boiling out of t h e oil when the pressure over it was released. SUMMARY
This work has shown t h e influences of pressure on t h e carbonization of coal in some striking tendencies. I-Pressures u p t o 2 0 atmospheres decrease t h e amounts of high-boiling compounds a n d increase t h e amounts of low-boiling compounds in t h e condensable vapors evolved from coal below 600' C. Also pressure causes a n increase of low-boiling aromatic bodies in these oils. These results are directly attributable t o cracking or thermal decomposition which is brought about b y subjecting t h e vapors of heavy compounds t o t e m peratures considerably higher t h a n their boiling points, as t h e increased partial pressures of these constituents retards their vaporization. Pressure also decreases, in most cases, t h e amounts of phenols and acid bodies in t h e oils. T h e reasons for this are not clear 11-Pressure increases t h e amount of coke left as residue and also t h e per cent of fixed carbon in t h e coke. These are effects of cracking oils in contact with t h e coal. The calorific value of t h e coke is increased a n d t h e nitrogen, oxygen, sulfur and volatile matter are decreased. This decrease of nitrogen, sulfur and oxygen in t h e cokes is probably due t o increased partial pressure of hydrogen in contact with t h e hot coke. 111-Pressure causes a n increase in t h e volume of gas evolved from coal below 600' C. Up t o 2 0 atmospheres i t increases t h e per cent of hydrogen in these gases at j o o o a n d decreases i t a t j j o o a n d 600'. The increase at j o o o is probably due t o cracking of heavy hydrocarbons. The decrease a t j j O o a n d 600' is attributed t o t h e action of hydrogen at high concentration on nitrogen (and sulfur a n d oxygen) in t h e coke and upon unsaturated products of cracking. Increase of ethane a n d methane in t h e gas seems t o bear out this last view. The authors wish t o acknowledge their indebtedness t o Dr. W. D. Bonner of t h e University of U t a h for valuable assistance in t h e analysis of oils a n d t o t h e Pittsburgh Station of t h e U. S. Bureau of Mines for t h e analysis of gas a n d coke samples. PRINCETON UNIVERSITY PRIKCETOS, S E W JERSEY
A NEW METHOD FOR THE RECOVERY OF SALTS OF
POTASSIUM AND ALUMINUM FROM MINERAL SILICATES' B y J. C. W. FRAZER. W. W. HOLLANDA N D
E. MILLER
A great many efforts have been made t o obtain salts of potassium from such silicates as sericite and orthoclase. These minerals are not attacked b y 1 Presented at t h e Buffalo Meeting of t h e American Institute of Chemical Engineers, June 20 t o 22, 1917.
935
acids. The feldspars occur widely distributed a n d are t h e most abundant of all minerals. Orthoclase feldspar of a sufficient degree of purity occurs in such quantities as t o make i t a possible source of supply of potassium salts. Owing t o t h e fact t h a t in normal times potassium salts can be obtained very cheaply from Germany, and, also t o t h e further fact t h a t such silicates as feldspar and sericite can be decomposed only with difficulty, any process for t h e successful treatment of such silicates must obtain by-products of value i n addition t o t h e potassium. A great many patents have been obtained on processes for t h e treatment of feldspar. Most of t h e m make use of very high temperatures a n d rely in many cases on t h e separation of t h e potash by volatilization. The greatest objection t o such processes is t h a t in addition t o being expensive i t is difficult t o separate the potash from t h e other constituents after t h e silicate has been decomposed. I wish t o call your attention t o t h e results of some experiments which were made last year in our laboratory for t h e purpose of making available t h e potassium and aluminum contained in such silicates as feldspar a n d sericite. It was soon realized t h a t for a n y such process t o be successful all t h e constituents of t h e silicate must be recovered in valuable form a n d at a minimum expenditure of energy and cost. The t r u t h of these statements is borne out b y t h e great number of unsuccessful attempts which have been made recently t o obtain potash from feldspar. On this account i t was decided t o avoid, if possible, t h e method so frequently resorted t o b y others, of bringing about complete decomposition of t h e mineral, for b y operating in this way there is avoided a resort t o high temperature, which adds t o t h e cost of operation and leads t o final products, many of which are useless or can be separated only with difficulty. The method finally adopted secures t h e transformation of feldspar b y successive states into products analogous t o certain well defined minerals occurring in nature. It is well known t h a t most of t h e "available" potash which occurs in t h e soil comes from the weathering of feldspar. This so-called weathering process takes place slowly in nature and t h e final product of this reaction is a hydrated silicate of aluminum known as kaolinite ( H4A12Si209). I n addition t o kaolinite there are certain minerals such as leucite which are intermediate in composition between feldspar and kaolinite though they probably d o not appear in t h e course of t h e weathering process. The important difference between t h e feldspars a n d leucite is, t h a t whereas feldspar is not attacked b y mineral acids, leucite is easily decomposed under these circumstances, giving salts of potassium and aluminum and liberating silica. Our experiments soon showed t h a t a n alteration of feldspar t o a substance analogous in composition t o
