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
684
In t h e Oklahoma fields it is t h e common practice t o treat t h e emulsified oils with water, the temperature of which is maintained a t 80 t o 125' F., depending upon t h e quality of t h e oil a n d t h e weather conditions. This t r e a t m e n t is conducted in a t a n k (Fig. V I ) , placed between t h e flow t a n k and t h e stock tanks. I t is simply one unit in addition t o t h e usual
Vol. 8, No. 8
pansion causes t h e breaking of the oil film; then the fine particles of salt are dissolved by t h e extra water present and carried t o t h e bottom of t h e stock t a n k within a short time after t h e treated oil is delivered there. Some salt is removed b y t h e water during the t r e a t m e n t , consequently t h e water in t h e treating t a n k should be renewed occasionally or it may become saturated with t h e salt and have no action on t h e oil being passed through it. OKLAHOMA AORICTILTURALA N D MZCHANICAL COLLBOB STILLWATER
THE DECOMPOSITION OF HYDROCARBONS AND THE INFLUENCE OF HYDROGEN IN CARBURETED WATER GAS MANUFACTURE By M. C. WHITAXERA N D E. H. LHs~la Received June I , 1916
(Conduded from our previous issue) T H E DECOMPOSITION O F P A R A F F I N H Y D R O C A R B O N S
equipment on a lease. T h e illustration indicates all the essential features of this method. T h e flow of oil is continuous, being controlled so t h a t a constant stream is distributed upward through t h e warm water, passing o u t t o t h e stock tanks. Many samples of crude oil from t h e Cushing field, which have been examined here, have h a d an initial boiling point of 130' F.; hence this t r e a t m e n t , even
n
54s
r 4
. II
I
I
lL-=lO!===-
.
I
I
L Fie. V I - T a a r n r ; ~ T ~ v wFOE B M U L S I P IO C n~
when conducted a t the higher temperature, should not seriously affect t h e gravity of the oil. There is a large quantity of salt in some wells in t h e Cushing pool. and it is this substance, as noted above, which is mainly t h e cause of t h e emulsified oils. In the warm water treatment, the slight ex-
Figs, g to 14 indicate t h e proportions of t h e various components obtained when t h e oil was decomposed alone. Fig. 9 shows t h a t at 621' C. t h e gases are composed of about I O per cent hydrogen a t all oil rates above 5 cc. per minute. T h e reactions which contribute t o t h e formation of this hydrogen, named in order of their probable importance, are: (I) CiHs CpH, H, (2) C,H, T ,C2Ha H* (3) CHd -+ C 2H2 ( 4 ) C2H2 --+ Z C H? T h e conditions are those' which are known t o he favorable t o t h e condensation of acetylene. T h e methods for t h e determination of acetylene are so unsatisfactory t h a t n o effort was made t o determine t h e proportion of acetylene in t h e gases formed. Other investigators have found the amount small in similar experiments. T h e rapid increase in t h e proportion of hydrogen with decreasing oil rates below 5 cc. per minute is thought t o he due t o a marked increase in t h e extent t o which reactions (3) and ( 4 ) t a k e place. A t 7 2 3 ' C. only a slightly larger proportion of hydrogen is formed t h a n a t 621O C., indicating t h a t reactions ( 3 ) and ( 4 ) do n o t become rapid u p to.this temperature. A very marked increase in the hydrogen production takes place when t h e temperature is elevated t o 825' C., chiefly due t o a n increase in reactions (3) and ( 4 ) . a s is evidenced by t h e very larae amount of free carbon which was iiberated and which tended t o stop t h e furnace tube. N o trouble was occasioned by this carbon deposition a t 621 or 7 2 3 ' C. Fig. 1 1 shows t h e proportion of illuminants, or components removed b y 2 0 per cent fuming sulfuric acid, in t h e oil gases made a t t h e three temperatures. T h e percentage of illuminants is highest in t h e gases made a t 621' C. a t all oil rates, and remains practically constant a t 5 2 per cent a t all oil rates above I O cc. per minute. T h e proportion of illuminants formed a t 7 2 3 ' C. is higher t h a n a t 825' C. except possibly a t high oil rates. I t is thought, however, t h a t t h e proportion of illuminants a t high oil rates would not he greatly different a t a n y of these temperatures.
+ + + +
T H E J O r R N A L 0 F I LVD I;'S T RI A L A Y D E Y G I N E E RING C H E &!IS T R 'E
Aug., 1916
T h e fact t h a t t h e proportion of illuminants is lower, t h e higher t h e temperature a t moderate t o low oil rates, is due t o t h e secondary reactions of these hydrocarbons. Ethylene is decomposed into carbon a n d methane t o some extent. Condensation t o naphthenes takes place. At these low oil rates t h e proportion of hydrogen present is considerable, a n d t h e higher t h e temperature t h e higher this percentage. Hence i t
Oil R a t e
-
cc. p e r
1
I
I
I
I
minute I
-
FIG.^
I
I
io
I
+
faster speeds of such reactions as CzH4+ C CH4 a n d C2H6 HP I_ 2CH4. It might reasonably be expected t h a t t h e percentage of saturateds in t h e gases would be greater a t 82 j C. t h a n a t 7 2 3 ' C., b u t it can be seen from Fig. I O t h a t this is not t h e case. At lorn oil rates t h e proportion of saturateds is lower a t 825' C. t h a n at 7 2 3 ' C. This is chiefly due t o t h e fact t h a t t h e reaction
+
Oil I
Rate
I
-
cc.
p e r minufe
-
c
ING. I 3
I
723
1
1
Oil R a t e
-
C.C. I
68 j
~
1
1
i
1
-
p e r minute I
FIG. I t
NG. I 4
825'C
GO--
I
t 0
$20
0
,
6."
Oil Rate
6-"
- cc. per minute
-
would be expected t h a t hydrogenation reactions such 2CHa as CzH4 H2 C2H6 a n d C2H4 zHz would t a k e place. T h e relation between t h e proportions of s a t u r a t e d hydrocarbons formed a t different temperatures is shown in Fig. I O . It can be seen t h a t t h e proportion of saturateds in t h e gas is higher a t 7 2 3 ' C. t h a n a t 621' C. a t all oil rates. This no doubt is d u e t o t h e
+
Jr
+
IO 1
0
5
io
Oil R a t e
+
15
-
I
I
20
CC.
zs
I
30
I
35
per minute
I
40
1
45
I
so
CHa + C 2H2 has a n appreciable velocity a t this temperature. As t h e oil rate increases it would be reasonable t o expect t h a t t h e effect of this reaction would be less a n d less. However, t h e divergence between t h e 8 2 j ' C. curve a n d t h e 7 2 3 ' C. curve becomes greater t h e faster t h e oil rate. This s t a t e of affairs is apparently due t o t h e superimposed effect of another reaction. When t h e high paraffin hydro-
686
T H E JOURiVlilL O F I A l r D C S T R I A L A X D E-VGILVEERIATGCHE,MISTRY
carbons first break down under these conditions t h e chief products are low molecular weight paraffin hydrocarbons and high molecular weight olefins. At 621 and 7 2 3 ' C. a considerable proportion of the high molecuiar weight olefins formed pass on through the tube into the tar. The tars were larger in amount the lower the temperature. and when the t a r curves are studied it will be seen t h a t there is not a marked difference between the t a r formation a t 6 2 1 and 7 2 3 ' C. but t h a t a considerable difference is found a t 8 2 5 ' C. These lo^ temperature tars were treated with concentrated sulfuric acid in the cold, and it was found t h a t 2 0 t o 2 j per cent by volume was removable in this fashion. t h e greater portion of which was doubtless olefins of high molecular weight. At 82 j o C. the effect of the heat is sufficient t o break down these higher olefins almost completely. In t h e process ethylene and propylene are formed in large quantity with the result t h a t t h e percentage of saturated hydrocarbons drops. The proportion of illuminants and saturated hydrocarbons present in the gases a t 8 2 j " C. is greatly lowered on account of the high percentage of hydrogen present in these gases. Figs. 1 2 , 13 and 14 show t h e relations between the component illuminants, saturateds, and hydrogen a t t h e temperatures 6 2 1 , 7 2 3 and 825' C., respectiyely. Of all the proportions of these components those a t the high oil rates a t 621' C. most nearly represent the products of the primary decomposition of the oil. The hydrogen is largely the result of secondary reactions. If the illuminants and saturateds are calculated t o a I O O per cent basis t h e proportion is 58 per cent illuminants and 4 2 per cent saturateds. Such a ratio as this would be expected in t h e reaction if the primary decomposition of t h e paraffin was:
Vol. 8, S o . 8
cent out of the 1 8 per cent increase in methane which should have been found, had the ethylene reacted entirely with formation of carbon and methane. would be accounted for. Hence the ethylene must be removed in other x a y s , for example. by the condensation t o naphthenes. It is not probable t h a t the 6 per cent increase in t h e hydrogen is entirely due t o the decomposition of methane. Dehydrogenation of naphthenes. dissociation of ethylene and ethane, etc.! may give rise t o hydrogen. Then. too, not all t h e methane formed comes f r o m the decomposition of ethylene. Decomposition of higher olefins in such a manner as CH3.CH?.CH2.CH=CH,
--j
+ CH,=CH-CH=CHq olefins, C2H4+ zH2 If 2CHI, CH,
and hydrogenation of may contribute. A similar argument may be worked out for the relation between t h e illuminants, saturateds, and hydrogen a t 7 2 3 and 8 z j " C. The marked decrease in illuminants with decreasing oil rates a t 8 2 j" C. is notable. No corresponding increase in saturateds takes place. I t is apparent from the high percentage of hydrogen t h a t methane is decomposing extensively into carbon and hydrogen. PROPORTIOX O F ILLUXINAXTS A N D SATURATED HYDROCARBOXS
I n order t h a t the effect of hydrogen on t h e composition of the gases as regards illuminants and saturated hydrocarbons may be seen, Figs. I S . 16. 1 7 , 18 and 19 are shown. These curves were drawn b y calculating the illuminants and saturated hydrocarbons t o a basis of 100per cent. I n this manner the proportions of t h e two classes of compounds can be seen. - i H z~2 CH, CnH~lt+ 2 -----) I t might be expected t h a t hydrogenation reactions Paraffin Olefin would play an important part and t h a t the proportion and if then, the high moiecular weight olefins in part of saturated hydrocarbons would be higher in the oilgas-hydrogen runs t h a n in t h e straight oil-gas runs. broke down t o lower olefins. The mechanism of the reactions a t work can be I t will be shown later in this paper t h a t hydrogenation judged somem-hat from a consideration of the relations does take place t o a considerable extent. I t should be noticed t h a t a t low temperatures the between the curves for the percentages of illuminants, saturateds, and hydrogen. Thus. in Fig. 1 2 . if it is presence of the hydrogen has no influence on t h e assumed t h a t the illuminants are chiefly ethylene and relati\.-e amounts of illuminants and saturated hydrothe saturateds largely methane. it can be seen t h a t t h e carbons a t high oil rates: i. e . . its presence has little normal formation of ethyiene is j z , t h a t of methane effect on t h e mechanism of t h e pl-imary decomposition and the early stages of the secondary decomposition. 3 9 , and t h a t of hydrogen I O per cent. Consider the proportions in che gas a t an oil rate But a t low oil rates where the gases are exposed t o the of 2 . 5 cc. per minute. They are ethylene 34. methane effect of heat for a longer time, and where extensive j o , and hydrogen 16 per cent. The decrease in secondary and tertiary changes take place, the hydrogen ethylene has been 18 per cent on the basis of the total has a considerable iafluence a t temperatures of 7 2 3 gas. If this had been due t o the reaction C2H4 --+ and 8 2 j ' C . At 6 2 1 ' C. the influence of the hydrogen C CH, the methane should have increased 18 per is not marked. I t will be remembered t h a t the first reaction undercent on the basis of the total gas. In fact it increases gone by a paraffin hydrocarbon when it is thermally only I I per cent. The hydrogen increases 6 per cent on the total gas decomposed is t h a t which gives rise t o a high molecular basis. If this were due t o the reaction CHd+ C zH2 weight olefin and a low molecular weight paraffin. a 3 per cent decrease in the methane should have taken I t is probable t h a t the higher the molecular weight of place. B u t a s has been seen, other reactions also give an olefin she more readily it is hydrogenated. If the high molecular weight olefins are hydrorise t o hydrogec. .kssuming, however, t h a t the above reactioc was t k e :ole change of this sort, on1)- 14 per genated, paraffins n-ould be formed. These would
+
+
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T H E JOrR.L'A L O F I - V D C S T R I A L
Aug., 1916
again decompose into long chain olefins and low molecular weight paraffins. This sequence of reactionslrnay be represented as follows: CxH2x+~C ~ - I H ~ ~ - ZCH, Paraffin Olefin Cx-IHz~--2 Hz + C x - ~ H z n Olefin Paraffin
+
+
+
Cw- I H Z-~-f Cx-2H2x-4 CH4 Paraffin Olefin The net result of such a sequence of reactions would be a n increase in the proportion of paraffins in t h e
I
lo
9
GO
v,
4
50
*;
?3 40 \ 9
30
%
20
zH2 : r Gas (Figs. 1 7 and IS), the proportion of saturated hydrocarbons is greater in the hydrogen-oilgas runs. It is probable, therefore, t h a t t h e above reactions take place in all cases but t h a t the effect of the hydrogen a t low oil rates on the extensive secondary changes is so great t h a t t h e result of t h e hydrogenation is masked. Apparently t h e low molecular weight olefins are not hydrogenated t o a large extent, for were this t h e case the proportion of saturated hydrocarbons present would be greatly increased. This is not t h e case. The increase in the proportion of olefins in the hydrogen-oil-gas runs a t low rates of oil feed may be accounted for in t w o ways: (I)-The effect of t h e hydrogen may be t o increase those reactions which give rise t o olefins. (>)-The effect of the hydrogen may be t o retard those reactions which tend t o remove or destroy t h e olefins. The largest proportion of the ethylene and propylene present comes from the direct splitting u p of high
F 10
b
k 0
Oil Rate
- cc.
per minute
-
Oil Rate - c c . per minute
Oil
t
Rate
- cc. per
rninufe
-
-
70
v)
Z 60
4
c: 50
6
.
40
I
30 -+-
C
g0 2 0
5QI O L,
b 0
-
-
O i l Rate c c . p e r minute gas. But as can be seen in t h e figures, t h e proportion of paraffins is less in the cases of the hydrogen-oil gases. However, a t high oil rates where secondary reactions are not so important, and in t h e series of runs a t 82;' C. where the concentration ratio was
0' 5 10 O i l Rate
1
15
-
CC.
20
per
25
30
minute
35
I
40
----
45
3
molecular weight olefins. If a n olefin of fairly high molecular weight may be used t o illustrate, this reaction may be represented: C H ~ C H ~ C H Z C H = C H ~ + C H ~ C H = C H Z CHz=CHs I t will be noticed t h a t the result is an increase in
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T H E J O U R N A L O F I N D C ' S T R I A L d Y D E./TGINEERISG C H E M I S T R Y
688
volume. The equilibrium point of the reaction would therefore be shifted by a diminution of pressure in such direction as t o favor t h e production of ethylene and. propylene. The introduction of hydrogen has t h e same effect as a reduction in pressure, and would therefore have a similar effect on t h e equilibrium. Chief among the reactions which remove olefins
as t h e influence of volume relationships on the equilibrium point is concerned, would not be affected. 'Il'hether the displacement of the equilibrium points in any of these reactions is sufficient t o be worthy of mention can not be said. In no case is the equilibrium condition attained, b u t t h e speeds of the various reactions would depend on t h e difference between the actual condition of the system and the equilibrium condition; hence any displacement of the equilibrium point would be important. The increase in the proportion of olefins may be looked upon from another angle. When hydrogen is introduced along with t h e gas t h e time of contact of the gas with the heated tube is diminished, due t o t h e increase in the total volume passing in unit time. If it is the case t h a t the reactions which give rise t o t h e olefins ethylene and propylene are fairly rapid, while those which destroy t h e m are slower, the summational effect of an increased gas rate would be an increased proportion of olefins. T h a t the speed of the reactions which produce olefins is fairly great can be seen by reference t o Fig. 2 2 , which shows the mean molecular weight of the olefins formed a t 8 2 j o C. The mean molecular weight lies between 30 and 34. The molecular weight of ethylene is 2 8 . while t h a t of propylene is 4 2 . The proportion of olefins higher t h a n propylene cannot be great? therefore, and it would seem t h a t they break down largely t o ethylene and propylene. T h a t the reactions which cause a removal or destruction of ethylene are only moderate in speed has been seen under t h e discussion of t h e reactions of ethylene in t h e first part of this paper. This latter explanation appears more probable t h a n the one concerning the displacement of t h e equilibrium points of reactions; however, both of these effects may be concerned in the production of t h e results observed. I t will be noticed t h a t the two different hydrogen concentrations produce similar results a t j 2 3 O C. b u t t h a t a t 8 2 5 " C. t h e proportion of olefins is much higher when the concentration ratio is 2H2 : I Gas. The rather large difference in this last case indicates t h a t the chief effect of the hydrogen is due t o its cutting down the time of heating. for a t 8 2 j " C. t h e decomposition of the higher olefins t o ethylene is doubtless very rapid, and takes place extensively in spite of the reduced time of heating in t h e hydrogenoil-gas runs THE A B S O R P T I O K
011
R a t e - cc. p e r m i n u t e
-
such as ethylene and propylene are condensatlon and decomposition. These reactions may be represented as 3C2H4 + CSHE and C2H4 -+- C CH4. The presence of the hydrogen mould displace the equilibrium point of t h e first of these reactions in favor of the ethylene. The latter reaction, in so f a r
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T'ol. 8, SO.8
OF HYDROG€S
Calculations from t h e analytical d a t a show t h a t a considerable absorption of hydrogen takes place when the oil is cracked in an atmosphere of this gas. Haber was of the opinion t h a t the oil produced no hydrogen by its own decomposition when it was cracked in an atmosphere of hydrogen. On t h e other hand, it might be assumed t h a t there would be as much hydrogen produced under these conditions as when the oil \vas cracked alone. These tn-0 assumptions offer two bases on m-hich the absorption of hydrogen may be calculated. (I)-If no hydrogen is produced b y the cracking of the oil, the hydrogen absorption per cc. of oil would
Aug., s 9 s 6
T H E J O r R S . I L O F I S D C ' S T R I I L A,VD ELVGIAVEERIAVGC H E i M I S T R Y
be equal t o t h e difference between the hydrogen added and t h a t present in the final gas divided b y the total number of cc. of oil. (11)-If t h e oil produces as much hydrogen as when cracked alone, t h e difference between the hydrogen added plus t h a t normally produced from t h e oil a t t h e particular oil rate a n d t h e hydrogen in t h e final gas represents t h e absorption. This divided b y the total number of cc. of oil gives t h e absorption in cc. per cc. of oil. Fig. 2 s shows t h e absorption per cc. of oil calculated on basis ( I ) for t h e several temperatures and concentrations. Fig. 2 2 shows these absorptions calculated on basis (11). I t will be seen t h a t t h e curves of Fig. 2 2 are much smoother and more regular t h a n those of Fig. 2 1 , not because t h e y are drawn more smoothly, b u t because the points fall on smoother curves. The general form of t h e curves, too, in Fig. 2 2 is t h a t which would be expected from a consideration of t h e curves for the hydrocarbon components formed per cc. of oil. The curves of Fig. 2 1 show no general similarity t o each other, while those of Fig. 2 2 show similar general characteristics. T h e curves representing t h e formation of all t h e other components of t h e gases show regular variations, and i t would be expected t h a t this regularity would extend t o t h e curves for hydrogen absorption. I n general, therefore, it seems t h a t the basis on which t h e curves of Fig. 2 2 are calculated is more nearly correct t h a n t h e basis which assumes t h a t no hydrogen is produced from t h e oil when it is decomposed in hydrogen. This view is strengthened b y the fact t h a t in t h e case of t h e 8 2 5 ' C. gases with ~ 2 Gas, the absorption hydrogen concentrates I H : curve in Fig. 2 1 falls below t h e 0.0 line, i. e., hydrogen must have been formed from t h e oil since there was more hydrogen in t h e final gas t h a n was added through the meter. It is probable t h a t t h e t r u e value for the hydrogen absorptions for a n y set of conditions falls between t h e two values as calculated from t h e two limiting assumptions. It is thought t h a t t h e true values are slightly less t h a n t h e values of t h e absorptions as t h e y would be read from t h e curves in Fig. 2 2 . T h e curves of Fig. 2 2 show t h e interesting fact t h a t a t a n y particular temperature t h e hydrogen absorption per cc. of oil decreases with increasing oil rate. T h e great importance of t h e time factor is well brought out here. At constant oil rate, and approximately t h e same hydrogen concentration t h e absorption per cc. of oil is greater the higher t h e temperature. There would, however, be an upper limit t o this on account of t h e excessive decomposition of all hydrocarbons a t elevated temperatures. T h e effect of increasing the concentration of hydrogen is clearly shown in Fig. 2 2 for the curve for t h e HZ : I Gas runs is above t h e curve for t h e I H :~ 2 Gas runs a t both 7 2 3 and 82.5' C. T h e speed of hydrogenation reactions is greater the higher t h e concentration of hydrogen. I t is interesting t o note t h a t t h e curve for t h e
689
I H : ~ 2 Gas runs a t 8 2 5 ' C. falls below the curve for the 2 H Z : I Gas runs a t 7 2 3 ' C. This shows t h a t the increasing temperature is tending t o cause dehydrogenation reactions or hydrocarbon dissociations t o a marked degree a t 82.5' C. T h e effect of hydrogen in greater concentration in reversing these dissociations is clearly brought out when t h e position of the 2 H 2 : I Gas curve for 8 2 j ' C. is considered in its relation t o the I H : ~ 2 Gas curve a t this same temperature. MEAN JIOLECULAR W E I G H T O F T H E OLEFIKS
I n Fig. 2 3 the mean molecular weight of the olefin hydrocarbons in gases made a t 8 2 5 " C. in oil-gas runs and in hydrogen-oil-gas runs with the concentra~ 2 Gas can be seen. tion ratio I H : I t should be kept in mind t h a t t h e molecular weight of ethylene is 2 8 and t h a t of propylene is 4 2 . From the position of the curves it can be seen t h a t approximately one-third of the olefins is propylene. The curves lie very close together, and it is impossible t o say just what t h e influence of t h e hydrogen is on the formation of t h e olefins. If t h e method of calculation of t h e molecular weight of t h e olefins, as explained under the discussion of the analytical methods, ,is considered, it is apparent t h a t all t h e h a l y t i c a l ' e r r o r s pile up and are brought out in this calculation. This no doubt accounts for t h e irregularity in the curve, and also for the f a c t t h a t there is no consistent difference in t h e position for the oil-gas runs and t h e hydrogen-oil-gas runs. It was thought t h a t certain differences might be brought t o light b y the curves for t h e mean molecular weights of the olefins. If the higher olefins were more easily hydrogenated t h a n ethylene t h e curve for the mean molecular weight of t h e olefins in t h e hydrogenoil-gas runs would fall below t h a t of t h e oil runs. If, on t h e other hand, t h e presence of t h e hydrogen, on account of its causing a more rapid passage of the gas through t h e tube, resulted in a less extensive decomposition of t h e higher olefins, t h e curve for the hydrogen-oil-gas runs would lie above t h a t for the oilgas runs. It may be thought t h a t these two effects are balancing each other with t h e result t h a t the curves are practically t h e same. I t would have been desirable t o have carried out a similar series of runs with a high concentration of hydrogen, b u t t h e calculation of t h e mean molecular weight of t h e olefins can be made oniy when t h e per cent of benzene in the gas is known, and, as has been noted, t h e method for t h e determination of benzene was found only as this experimental work was drawing t o a close. T H E F O R M A T I O N O F AROMATIC HYDROCARBOKS
Fig. 24 shows t h e percentage of aromatic hydrocarbons present in t h e gases made a t 8 2 5 ' C. when oil is cracked alone or in hydrogen when t h e concentration ratio is I H : ~ 2 (Oil Gas Tar Gas). The method of determining these percentages has been described under t h e analytical methods. T h e percentage of aromatics appears t o increase slightly with increase in oil rate. Whether this is
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T H E J O C R S A L OF I S D C S T R I l L A N D E S G I N E E R I S C C H E M I S T R Y
690
actually the case or not cannot be definitely stated. The exact opposite would be expected. I t is thought t h a t t h e apparent increase may be due t o the freezing out of high molecular weight hydrocarbons of other types t h a n t h e aromatic compounds. High molecular weight paraffins and olefins are present in greater 70-
I
I
1'01"8, NO. 8
This is possibly due t o the retarding eflect which t h e presence of hydrogen would have on the formation of aromatics or hydroaromatics by condensation reactions. Less gas is formed from the oil a t high oil rates t h a n a i low oil rates, and as a consequence t h e concentration of hydrogen is greater a t high oil rates t h a n a t lo^ oi! rates. TARS
-
Oil Rate
cc. per
minute.
-
The tars TTere collected from t h e tar drip and t h e volume measured. This volume divided b y t h e volume of the total oil used and multiplied by I O O giT7es the percentages of t a r formed. Figs. 2 j t o 2 9 shorn these tar percentages for both oil-gas a n d hydrogen-oil-gas runs plotted against the oil rate a t t h e temperatures indicated. I t should be mentioned t h a t a t low oil rates these percentages are not accurate. The low-oil-rate tars are heavy and viscous, and as a result do not run down through the condenser a s easily as the lighter high-oil-rate tars. AS far as can be judged from the curves in Figs. 2 j : 2 6 , and 2 7 , for temperatures of 6 2 1 and 7 2 3 ' C., there is no marked regular difference between t h e t a r formation in the oil-gas runs and t h e hydrogen-oilgas runs. A t 8 2 j ' C. the percentage of t a r in the oil-hydrogen runs is consistently less t h a n in the oil runs except a t low oil rates where, as has been mentioned, t h e 'tar percentages as shown mean little, This difference is more marked in the curves of Fig. 2 7 where the concentration ratio was 2 Hydrogen : I (Oil Gas Tar G a s ) t h a n in the curves of Fig. 28. I n general, two classes of compounds are contained in the t a r : ( I ) unchanged or partially changed oil; ( 2 ) synthetic hydrocarbons which are the products of extensive change. I t may be thought t h a t hydrogen, on account of its decreasing t h e time of contact of the hydrocarbon r a p o r s with the heated t u b e , would tend t o increase the proportion of tar since t h e decrease in t h e time of heating would cause a less extensive decomposition of t h e oil vapors. On t h e other hand, this decrease in the time of heating would also diminish t h e extent t o which synthetic reactions resulting in the formation of tarry products would take place. Also the percentages of the hydrogen would retard these reactions, since they are all reactions which result in decrease of volume. Apparently these effects are balanced a t temperatures of j 2 3 O C. or below. At 825' C.: however, the percentage of t a r is less. This leads t o the belief t h a t synthetic reactions are responsible for a considerable proportion of the tars a t temperatures in the neighborhood of 8 2 j " C. Fig. 3 0 shows clearly t h e effect of temperature o n t a r formation, and also the effect of increase of oil rate a t constant temperature, The proportion of t a r increases with increasing oil rate and most markedly so, a t temperatures of 6 2 1 and 7 2 3 ' C. The largest proportion of these tars a t moderate t o high oil rates is undecomposed oil, as shown by distillation and treatment with concentrated sulfuric acid. This is also indicated by t h e fact t h a t a temperature change from 6 2 1 t o j 2 3 O C. produces no great difference
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I
5
I
li?
OiJ R a t e
I
-'
L O 2 5 3b J k cc. p e r mlnuie.
l!5
-
70
40
1
45
I
50
GO 50 40
30 i.
2
20 IO
6\0 0
Oil
Rate
-
CC.
per
minute
-
proportion in the gases made a t high oil rates t h a n in those made a t low oil rates. T h e smaller proportion of aromatic hydrocarbons present in t h e gases made a t lorn oil rates may possibly be due t o the removal of benzene t o form compounds such as diphenyl, naphthalene and anthracene. which pass largely into t h e tars. The hydrogen apparently has little effect on the formation of aromatics a t low oil rates. b u t decreases t h e aromatic formation somewhat a t higher oil rates.
Aug., 1916
T H E J O U R N A L O F I N D l r S T R I A L AAVD E N G I N E E R I N G C H E M I S T R Y
in t a r formation, and also b y t h e fact of t h e very rapid increase in the percentage of t a r with increasing oil rate. A t 8 2 j C. the proportion of t a r does not increase greatly with increasing oil rate, indicating t h a t these tars are largely composed of synthetic products, O
ai/ Rate
- cc. p e r m i n u i e
-
which is further substantiated b y other physical characteristics, such as distinct aromatic odor and their reactions with concentrated sulfuric acid. All t h e tars were strongly fluorescent. FORLIATION
O F ILLUMINANTS,
METHANE, AliD ETHANE,
OB P A R T I C U L A R E N D - P R O D UCTS F R O M A P A R A F F I N HYDROCARBON OIL
AND
THE
OBTAINING
I n Figs. 3 1 t o 3 j t h e cc. of illuminants, methane and ethane formed from I cc. of oil are shown plotted against the oil rate a t t h e temperatures and hydrogen-
691
gas concentration ratios indicated. It can be seen from Fig. 31 t h a t a t 621 ' C., with t h e exception of t h e illuminants in t h e case of t h e straight oil-gas runs, the number of cc. of all these hydrocarbons formed from I cc. of oil increases with decreasing oil rate. There would be a limit t o this, however, for, were the oil rate
OI/
R a t e - cc.
per
minufe
-
made low enough, a very extensive decomposition of the hydrocarbons would set in. Fig. 3 1 shows t h a t t h e illuminants are the most easily decomposed of the gaseous hydrocarbons. T h e curve for t h e illuminants in t h e straight oil-gas runs has a maximum due t o the fact t h a t though t h e longer time of contact of t h e oil vapors with t h e heated tube a t low oil rates causes a more extensive formation of ethvlene and other illuminants, a n oil rate is reached where extensive decomposition of these
69 2
T H E J O I ' R S A L O F I A J T D r S T R I A L. l T D E S G I A V E E R I N G C H E M I S T R Y
hydrocarbons takes place, which more t h a n overcomes the more rapid illuminants formation a t low oil rates. Condensation and hydrogenation, which are more extensive a t low oil rates. are important in this connection also. N o maximum is observed in the illuminants curve for the hydrogen runs, doubtless because t h e time of contact of t h e oil vapors with the heated t u b e is less a t any particular oil rate t h a n in t h e case of the oilgas runs. The curve for the illuminants in the hydrogen-oil-gas runs. for this reason also, is always below t h a t for the illuminants in t h e oil-gas runs, except a t low oil rates. Less methane is formed per cc. of oil in t h e hydrogen-oil-gas runs t h a n in the straight oil-gas runs except a t low oil rates. T h a t t h e time of contact here is sufficient so , t h a t extensive hydrogenation takes place is clearly brought out from a consideration of Fig. 2 2 in connection with Fig. 31. d t all oil rates t h e decreased time of contact of the gases with t h e heated furnace tube, on account of t h e absorption of hydrogen, results in a lower formation of methane. The relationships for ethane are much t h e same as for methane, and for t h e same reasons. Figs. 32 and 33 show t h e relationships between the hydrocarbons a t 7 2 3 C. at hydrogen concentration ratios of r H 2 : 2 Gas and 2 H z : I Gas, respectively. N o r e of each of the components is formed per cc. of oil a t 723' C. t h a n a t 621' C. T h e maximum in the illuminants curve falls a t a higher oil rate t h a n a t 621' C. as would be expected, since the higher temperature would cause a more rapid decomposition, condensation, and hydrogenation of t h e illuminants t o take place. At 723' C. the maximum on t h e illuminants curve for t h e hydrogen runs can be seen clearly. It is interesting t o note t h a t this falls t o the left of t h e maximum on t h e curve for t h e oil-gas runs. T h e decreased time of heating on account of the hydrogenation admixture is responsible for this. T h e effect on t h e illuminants of increasing t h e concentration of hydrogen is clearly brought out in Figs. 3 2 and 33. The maximum on t h e curve for t h e illuminants in the hydrogen-oil-gas runs a t the higher hydrogen concentration falls a t a slightly lower oil rate t h a n the maximum on the curve for t h e lower hydrogen concentration. The divergence between t h e il!uminants curves for t h e oil-gas runs and the hydrogen-oil-gas runs is greater both a t low and high oil rates a t t h e higher hydrogen concentration t h a n a t t h e lower hydrogen concentration on t h e time of contact of the gases with the heated tube surfaces. The relationships in t h e case of the methane and ethane are exceedingly interesting. The formation of methane is less in the hydrogen-oil-gas runs t h a n in t h e oil-gas runs a t moderate t o high oil rates, due t o the decreased time of contact of t h e gases with t h e heated surfaces, and this effect is more pronounced a t the higher hydrogen concentrations, as m-ould be expected. As t h e oil rate decreases t h e hydrogenation effect becomes important and the proportion of methane formed from I cc. of oil is greatest in the case of t h e hydrogen-oil-gas runs. The curve for O
Yol. 8 . No. 5
methane in the hydrogen-oil-gas runs crosses t h e methane curve for the oil-gas runs. This crossing is a t a higher oil rate with t h e higher hydrogen concentration, showing clearly the effect of t h e increase of concentration of hydrogen on the hydrogenation reactions. The formation of methane is slightly greater in the hydrogen-oil-gas runs t h a n in t h e straight oil-gas runs when t h e hydrogen concentration ratio is I H ? : z Gas. This difference is slightly greater a t low oil ra-tes t h a n a t high oil rates. When the hydrogen concentration ratio is z H 2 : I Gas the ethane formation per cc. of oil is less in t h e hydrogen-oil-gas runs t h a n in the oil-gas runs a t high oil rates. This is the effect of the decreased time of contact due to t h e admixture of a larger volume of hydrogen. But a t low oil rates the formation of ethane is much greater in the hydrogen-oil-gas runs as can be seen ir, Fig. 33. The ethane curve has a maximurn, too, which is interesting because i t shows t h a t a t lorn oil rates t h e reactions of the hydrocarbon ethane itself have a n important part t o play. Figs. 34 and 3 j show the relationships between these hydrocarbons a t 8 2 5 ' C. X much less pronounced decrease in the formation of illuminants with increasing oil rate is due t o the fact t h a t t h e temperature of 8 2 5 " C. is sufficient t o promote actively t h e formation of illuminants. The maxima on the illuminants curves for the oil-gas runs fall a t t h e higher oil rates, as would be expected when t h e higher temperature is taken into consideration. The illuminants curves for t h e hydrogen-oil-gas runs are entirely above t h e illuminants curves for the oil-gas runs. This is again a result of t h e decreased time of heating when hydrogen is admixed. The effect is most marked when the higher concentration of hydrogen is used. T h e curves for methane in the hydrogen-oil-gas runs fall above the curves for methane in the oil-gas runs a t all oil rates a t 82;' C. This is due t o two effects: $first, t h e less extensive decomposition of t h e methane into carbon and hydrogen due t o the decreased time of heating in t h e hydrogen-oil-gas runs; second, t h e increased rate of hydrogenation reactions such as zHz 2CH4. The effect of hydrogen in CzH4 reversing t h e reaction C H 4 C zH2 is probably not important, as has been brought out in t h e discussion of the methane equilibrium and the reactions of methane in the first part of this paper. The effect of t h e greater concentration of hydrogen on methane production can be seen clearly by comparing Figs. 34 and 3 j . The divergence between t h e hydrogen-oil-gas and the oil-gas methane curves is greatest when the hydrogen concentration ratio is z H ? : r Gas, and this is practically true a t low oil rates v h e r e hydrogenation reactions are most important. LIore ethane is formed when hydrogen is mixed with the vapors of the oil t h a n when i t is not added. This is doubtless due t o the combined influence of the hydrogen in diminishing the decomposition of the ethane and t o its effect in hydrogenating the olefins. These effects are particularly marked when the concentration ratio is 2H2 : I Gas.
+
+
; i
I t may have been noticed t h a t t h e curves for t h e oil-gas runs made a t t h e same temperature do not coincide exactly, since the carbon t u b e used carbonizes somewhat and becomes of smaller internal diameter, t h u s decreasing t h e time of contact of t h e gas with t h e t u b e and consequently altering t h e composition somewhat. The effect of temperature on t h e hydrocarbon products of decomposition of a n oil can be seen very
011 R a t e - c c . p e r minute
D E X GI S E E RI S G CH E M I S T R Y
693
higher temperatures in promoting the decomposition of t h e long chain olefins t o ethylene and propylene. I t is interesting t o note the position of t h e maxima of t h e curves for t h e illurninants a t t h e several temperatures. These maxima indicate where t h e balance between the reactions of formation and t h e reactions of decomposition falls. Within t h e temperature range studied, t h e formation of methane is gr,eater t h e higher t h e temperature, At low oil rates the difference in the methane produced b y a Iooo-temperature rise is greater in t h e range from 621 t o 723' C. t h a n from 723 t o 8 2 j 0 C.r since a t low oil rates 7 2 3 ' C. is a sufficiently high temperature t o break down t h e original oil extensively.
Oil
-
Rate
cc. per
minute
-
BOO,
011 Rute - cc. p e r m i n u t e
-
clearly from Fig. 36. Within t h e temperature range studied, t h e cc. of illuminants per cc. of oil increases with temperature, with one exception. At low oil rates there are more illuminants formed a t 723' C. t h a n a t 8 2 5 " C. The effect of the higher temperature in increasing t h e speed of t h e reactions which decompose ethylene more t h a n overcomes the effect of the
0/1 Rate
-
cc
per
minute
-
T h e methane increase between 723 and 8 2 j 0 C. is largely due t o the decomposition and hydrogenation of olefins C2H4 -+ C CH4 and CzH4 zHz 2CH4, as can be seen from a consideration of t h e illuminants curve for 82 j ' C. 4 t high oil rates a temperature of 8 2 j 0 e. is necessary t o form methane largely, as can be seen from t h e
+
+
T H E JOC'KSAL OP I S D C S T R I A L A N D E S G I S E E R I S G CHEMISTRY
694
position of the curve for methane a t 6 2 1 , 723 and 82;' C. The formation of ethane per cc. of oil is not large a t a n y temperature studied, as s h o v n in Fig. 36. The primary decomposition of the oil therefore involves chiefly a splitting off of methane rather t h a n ethane or higher paraffin. The decomposition and dissociation of ethane are clearly shown b y the falling off of the ethane curve as t h e oil rate decreases a.t a temperature of 825' C. On t h e 'other hand, a temperature of 82;' C. is necessary t o cause an extensive formation of methane and ethane per cc. of oil a t high oil rates. TOTAL HYDROCARBOKS OBTAINABLE FROM THE OIL
The greater t h e proportion of the carbon of t h e oil which can be obtained in gaseous form t h e better the utilization of the oil for gas-malting purposes. Fig. 37 shows t h e total cc. of i l l u n i i n a n f s methane +.etizaize obtainable from I cc. of oil under the varying conditions. ilt 621' C. more hydrocarbons are obtained per cc. of oil in the oil-gas runs t h a n in the hydrogen-oil-gas runs: except at lo^ oil rates where hydrogenation reactions become important. This is due t o t h e lower time of contact of t h e oil vapors with the furnace tube in the case of the hydrogen-oil-gas runs. T h e same relations hold a t 7 2 3 ' C. except t h a t the hydrogen-oil-gas curves cross t h e oil-gas curve a t a higher oil rate because of t h e greater effect of t h e higher temperature in hastening t h e hydrogenation reactions. The effect of the higher concentration of hydrogen is clearly shown. A t 8 2 ; ' C. the hydrocarbons formed per cc. of oil are of greater volume in the hydrogen-oil-gas runs a t all oil rates studied. The higher temperature promotes hydrogenation reactions a t all oil rates. The effect of the greater concentration of hydrogen can be seen. I t is interesting t o note t h a t t h e slope of t h e curve for the hydrogen-oil-gas runs a t 7 2 3 ' C. is much steeper t h a n t h e slope of these curves a t 825' C. a t low oil rates, doubtless because a t 82 j' C., and low oil rates, dehydrogenation reactions and reactions of decomposition of t h e hydrocarbons become of importance.
+
S U M 3IA R Y1
I--A
critical review of the most important work on hydrocarbon decomposition and the influence of hydrogen on the reactions involved has been given. This has concerned itself with: j r s t , t h e hydrocarbons of high molecular weight; s e c o n d , t h e products of t h e primary decomposition; and t h i r d , t h e reactions of the simpler hydrocarbons. Summaries have been included which state concisely t h e probable course of the reactions of dissociation, decomposition, and condensation inrolved. 2--The subject of the mechanism of heat transfer in gas machines has been discussed. 3-Difficulties in the measurement of t h e true temperature of a gas have been pointed out. 4-In the experimental work a paraffin oil was thermally decomposed alone and in hydrogen a t temperatures of 621, 7 2 3 and 825' C. Concentra1 Summaries
I . 2 a n d 3 refer to t h e printed dissertation.
T'ol. 5.
SO 8
tions of hydrogen approximating I H :~ z Oil Gas and 2 H 2 : I Oil Gas were those studied. I t has been shown what results may be expected in the dccomposition of a hydrocarbon oil m-lien temperature, rate of oil feed, and concentration of admixed hydrogen are carefully controlled. ;-The relationship between t h e rate of oil feed and. the rate of gas generation has been brought o u t . 6-The proportions of illuminants, saturated. hydrocarbons, and hydrogen resulting a t varying rates of oil feed, and a t temperatures of 6 2 1 , 7 2 3 and 82 j c C. have been shown graphically and discussed. 7-The effects of hydrogen on t h e reactions which give rise t o saturated hydrocarbons and illuminants have been shown graphically and discussed a t some length. Besides its effect in hydrogenating olefins and ot.her hydrocarbons, the hydrogen, since its addition causes a n increase in t h e total volume of the gas passing through the heated zone of the furnace in a given time. decreases the time of contact of the gases with t h e heated walls of the resistor tube. T h e effects of this are discussed in connection v i t h the curves showing t h e relationships between t h e components of the gas m-hen t h e oil is cracked in hydrogen. 8-The mean molecular meight of the olefins in a series of gases made a t 82 j o C. has been determined, and also the proportion of aromatic hydrocarbons in these gases. 9-The formation of t a r was studied a t the various oil rates, temperatures and concentrations of hydrogen. Io-Curves showing t h e number of cc. of illuminants, ethane and methane obtainable from I cc. of oil have been shonm. 11-In general the manner of decomposition of a paraffin hydrocarbon oil has been mapped out over a considerable rang5 of temperature, rate of oil feed, and concentration of hydrogen. 12-The results recorded in this paper may serve as a guide t o t h e obtaining of more desirable results in commercial operations involving t h e decomposition of oil for gas-making purposes.
c 0 s c L uS I 0 K s I n addition t o showing t h e proportions of products which are obtainable under a variety of conditions, which relationships have been fully set forth in t h e figures shown and which it is impossible t o briefly summarize, it has been concluded as a result of this investigation: I-That the importance of radiation insofar as it is concerned in the furnishing of the energy for the production of hydrocarbon reactions has been overestimated. 11-That effects often ascribed t o catalysis are in reality due t o effective heat transfer b y conduction and convection from the large heated surfaces exposed t o the gases. 111-That t h e equilibrium condition is not attained in a hydrocarbon system when an oil is decomposed by heat under conditions analogous t o those of carbureted water-gas manufacture. IV-That the course of the changes involved in the breaking down of a hydrocarbon oil may be roughly traced.
Aug., 1916
T H E J O C R S d L O F I N D U S T R I A L z4.VD E N G I Y E E R I N G C H E M I S T R Y
V-That hydrogen is produced from a n oil even when the cracking takes place in hydrogen. VI-That considerable absorptions of hydrogen t a k e place when a n oil is. cracked in an atmosphere of hydrogen, and this absorption is greater t h e higher t h e concentration of hydrogen, t h e higher t h e temperature (within t h e range studied), and t h e lower t h e oil rate. VII-That propylene and higher olefins constitute approximately one-third b y volume of t h e illuminants of t h e gas. VIII-That the proportion of t a r increases with decrease in temperature, and with increasing oil rate, particularly a t the lower temperatures. IX-That no marked and consistent difference in t h e amount of tar formed when an oil is decomposed alone or in hydrogen a t temperatures of 723' C. or below is noticeable. At 8 2 j ' C. less t a r is formed when t h e oil is cracked in hydrogen. The tars formed below 7 2 3 ' C . are in large part unchanged or partly changed oil, whereas those t a r s formed above 800' C. are essentially composed of synthetic products. X-That the reactions which result in decreasing t h e proportion of illuminants are t h e most rapid. XI-That the presence of hydrogen during t h e decomposition of an oil has t h e effect of increasing largely t h e proportion of the carbon of t h e oil appearing as hydrocarbons in t h e gas. XII-That v i t h i n the temperature range studied the volume of illuminants produced per volume of oil increases with t h e temperature with one slight exception. The formation of methane is gre'ater t h e higher t h e temperature. The formation of ethane is not large a t a n y temperature and therefore t h e primary decomposition of a n oil involves chiefly a splitting off of methane rather t h a n ethane or higher homologues. XIII-That a temperature of 823 ' C.is desirable in decomposing an oil provided t h a t too great opportunity for extensive secondary and tertiary change is not given. XIV-That with correct design of apparatus, a n d proper adjustment of temperature, rate of oil feed, and concentration of hydrogen it is possible t o obtain gases of widely varying compositions. The authors wish t o extend t o Professor Floyd J. Metzger, Professor Samuel A. Tucker and Dr. Clive M. Alexander their thanks for valuable help a n d suggestions received. DEPARTMENT OF CHEMICAL ENGINEERIBG COLUMBIA UBIVERSITY, NEW YORK CITY ~~~~
STUDIES ON THE EXTRACTION OF ROSlN FROM WOOD. I-EXPERIMENTS USlNG A PETROLEUM SOLVENT By R. C. P A L Y E RA~ N D H. R . BOEHMER?
Received April 2 1, I9 16
PURPOSE O F W O R K
From a technical viewpoint, t h e process of extracting rosin from wood with chemicals offers a promising possibility for t h e utilization of "fat" stumps and 1 Chemist in Forest Products, Forest Products Laboratory, Madison, Wisconsin. 2 The data obtained in these experiments mere submitted by this author in partial fulfilment of the requirements for the degree of B.S.in Ch.E. in the University of Wisconsin.
695
other waste resinous wood. I n the simple steam distillation process only t h e volatile constituents of the wood are recovered and this method is no longer industrially feasible on this account. I n the destructive distillation process, the products are charcoal, t a r , and a turpentine more or less contaminated with products from the destructive distillation of t h e rosin and wood substance. This turpentine, a t best, does not bring as high a market price as steam-distilled wood turpentine, although the recent introduction of temperature-controlled processes has removed this objection t o a large extent. Compared with these two processes. t h e so-called solvent or extraction process affords t h e recovery of wood turpentine and pine oil comparable in quality and value with t h e oils from steam distillation and also a medium grade rosin whose market value, under normal conditions, is practically equal t o t h e combined value of charcoal and t a r from t h e destructive distillation process. However, t h e market value is less likely t o fluctuate for t a r and charcoal t h a n for rosin. Strictly speaking, t h e extraction and distillation processes are not comparable, because t h e products are quite different. These processes represent the two types which taken together cover most of the possible products t o be obtained from resinous wood. Of t h e several different processes proposed for treating wood. t h e destructive distillation method, which is b y far t h e oldest, is also a t t h e present time apparently t h e best established from t h e standpoint of profitable commercial 0peration.l The principal difficulties t h a t have been encountered in t h e extraction process have been: ( I ) an unstable market price for rosin, and ( 2 ) high cost of operation, due largely t o a n excessive loss of solvent. I n attempting a solution of these difficulties, there are then a t least two lines of attack which may give this process a better opportunity for commercial success: ( I ) obtaining another product which would not be subject t o very great market variations, and ( 2 ) decreasing the operating cost. The use of the extracted wood as a raw material for paper pulp has been suggested several times as a possible solution of the problem of obtaining another product. Extraction b y t h e usual method requires wood so finely divided (shredded wood) t o yield a high proportion of the rosin t h a t t h e extracted material is not suitable for pulp. If t h e wood is large enough for pulp, the yield of rosin is decreased. Considering the high operating costs as due largely t o t h e loss of solvent, i t would seem t h a t the problem here is largely mechanical, and its solution should not offer very great difficulties. With these ideas in mind, it was felt t h a t a careful study should be made of some of t h e fundamental operating variables of the process. The experiments were carried on a t the Forest Products Laboratory, Madison, Wisconsin. The material consisted of longleaf pine stumps from Louisiana, donated b y t h e Long-Bell Lumber Company of Kansas City, Missouri. Acknowledgment is made t o Mr. S. D. Wells, Engineer in Forest Products, of t h e section ,
1 'I'HIS
JOURN.4L.
6 (1914), 151.
