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
484
been collected from t h e literature a n d are given in Tables I1 a n d 111. CONCLUSIoixS
I-The striking differences between t h e constituents of a n aliphatic oil a n d its derived t a r are made evident b y t h e characteristic differences between volatilitygravity, volatility-refractive index, a n d volatilitysurface tension relations. 11-The experiments reported herewith again verify t h e well-known information t h a t aromatic hydrocaribons can be formed from t h e aliphatic hydrocarbons occurring i n petroleum. 111-The various physical constants of typical gas oils a n d derived t a r s have been measured a n d tabulated. T h e experimental work connected with t h e determinations reported in this paper was carried out i n t h e laboratories of t h e Departments of Physical Chemistry a n d Industrial Chemistry of Columbia University, New York. CHEMICAL SECTION O F PETROLEUM
U.s. BUREAUO F
DIVISION
M I N E S , PITTSBURGH
Vol. 7 , No. 6
T h e concentration factor above is considered in t h e sense of changes involved in t h e admixing of other substances with t h e initial material, such as t h e decomposition of oil in a n atmosphere of hydrogen, carbon monoxide, etc. THEORETICAL
,According t o chemical kinetics, a reaction tending toward a s t a t e of equilibrium will require time t o reach such a state. -4 reversible reaction m a y be represented t h u s : nlAl I Z ~ A ~ ~ - P Z ~nz’A2‘. ’ A ~ ’. .
+
+
Such a n equation represents two reverse reactions, each with a separate reaction velocity: T h e difference between these t w o velocities a t a n y moment of time under constant conditions will give a certain change per unit of time i n one direction or t h e other toward equilibrium. This change per .increment of time,
dx
- ~ -
dt
’
is commonly shpwn as follows:
THE TIME FACTOR IN MAKING OIL GAS BY M. c. WHITAKER AND C. M. ALEXANDER Received April 1, 1915
T h e production of oil gas is dependent upon certain chemical laws which relate t o gas reactions in general a n d which embody t h e principles of both thermodynamics a n d chemical kinetics. I n a n .investigation on t h e effect of t h e variables, temperature, pressure, a n d concentration on t h e t h e r m a l decomposition of petroleum a n d petroleum distillates, Whitaker a n d R i t t m a n ’ have carefully considered t h e theoretical principles of thermodynamics a s applied t o gas reactions. Their experimental results verified their theoretical conclusions a n d showed t h a t t h e principles of thermodynamics apply t o t h e decomposition of petroleum hydrocarbons a s well as t o more simple reactions. I n t h e above work, however, conclusions were drawn o n t h e assumption t h a t chemical equilibrium was a t t a i n e d under t h e experimental conditions adopted. It t h e n became a question whether or not equilibrium was reached. Undoubtedly this question could be answered b y t h e application of t h e principles of chemical kinetics, which introduced t h e time factor. I n t h e present s t u d y of oil gas production, therefore, four variables-time, temperature, pressure a n d concentrat i o n-are recognized . Difficulties were foreseen, however, in t h e accurate adlustment of t h e above variables in commercial plants a n d a basis for control was sought which would fall within t h e range of engineering requirements. Under constant temperature a n d pressure conditions, t h e time factor, which can be controlled b y variation of t h e r a t e of oil feed, offers t h e most available means for t h e s t u d y of t h e thermal decomposition of petroleum a n d petroleum distillates on t h e basis of t h e principles of chemical kinetics. Design of a p p a r a t u s is fixed for a n y one construction a n d hence remains a constant factor while t h e variables are controllable within certain‘ operating limits. 1
THISJOURNAL. 6 (1914), 383, 472.
in which k a n d k‘ are t h e velocity constants of t h e two reverse reactions, (A1), (A2),etc., are t h e concentrations of t h e reacting substances, a n d n l , ? t 2 , etc., their respective molecular exponents as obtained from a properly balanced equation. T h e above velocity constants v a r y with temperature’ a n d as a result temperature has a very marked effect upon t h e reaction velocities of t h e t w o reverse reactions. T h e effect of temperature on a number of gas reactions has been very carefully studied b y Bodenstein2 a n d t h e fundamental equations applied mathematically t o t h e experimental results. At equilibrium, t h e velocities of t h e opposing reactions are equal a n d hence t h e change per increment of time,
d x = u-u‘ at -- -
ax -
dt
’
must become zero.
= k(Al)n1(A2)n2, . . -k’(Al’)n1’(A2’)nz’. . . = o
Hence,
k -
k’
(A~’)“(AP’)~’’.. . (Al)n1(A2)nP. . - K,
= ____
where K is t h e equilibrium constant. T h u s chemical equilibrium deals only with t h e end s t a t e of a reaction a n d time is not a factor. Where time is not considered t h e relations between t h e s t a t e of equilibrium a n d t h e thermal values of a reaction can be worked o u t b y t h e application of thermodynamics. Such relations have been developed b y X e r n ~ t ,3layer ~ a n d A l t m a ~ e r ,a~n d others6 a n d expressed i n terms of mathematical formulas from which equilibrium compositions can be calculated: e. g., t h e Nernst approximate formula: 1 Trautz. Z . Eleklrochem., 18 (1912), 513; Z. physik. Chem.. 68 (19091, 295; 74 (1910). 747; Zellinek, 2. anorg. Chem., 49 (1906), 229. 2 Bodenstein, 2 . physik. Chem.. 29 (1899). 147, 295, 315, 429, 665; Bodenstein and Wolgast, Ibid., 61 (1908), 422. a W. Nernst, “Theoretische Chemie.” 4 hlayer and Altmayer, Ber., 40 (1907). 2134. 5 H. von Wartenberg, 2. physik. C h e m . , 61 (1907). 366.
J u n e , ~ gj r
T H E J O U R N A L O F I N D U S T R I A L A N D ENGIllrEERING C H E M I S T R Y plinl’p2in2’
...
log KO = log ____pln’p2nz.
-
*’
..
-- + 1 . f 5 ( 2 n ’ - z n ) 4.751T
log T+(zn’C’-znC)
By t h e use of such formulas t h e ultimate composition represertative of equilibrium conditions is obtained. This final composition, according t o t h e principles of chemical kinetics, represents t h e e n d point of a reaction which can be attained only through a sufficient lapse of time. As applied t o t h e production of oil gas, a progressive decomposition, in which time is a n i m p o r t a n t factor, should proceed t o a n ultimate s t a t e of equilibrium. T h e reactions taking place in t h e decomposition of Petroleum heat are and not definitely known. I n t h e industries based on these decomposition reactions. as in t h e making of oil gas, carbureting W a t e r gas, and cracking petroleum for light distillates, t h e chemical nature of only t h e initial materials a n d t h e final products are determined, ‘Ona n d this does not give a n y definite cerning t h e intermediate reactions. T h e breaking down of hydrocarbons of high molecular weights t o simp1er hydrocarbons consists in consecutive a n d concurrent reactions,l b u t their actual course from t h e initial material t o t h e final products Even i n the absence Of has not been such knowledge, t h e theoretical principles of chemical kinetics which apply t o single reactions should also hold in t h e case of t h e numerous reactions involT-ed in t h e thermal decompositions of petroleum hydrocarbons. T h e importance of t h e variable time in a few related decompositions has been shown by a number of investigators. Lewes2 finds t h a t t h e decomposition of ethylene is dependent n o t only upon temperature a n d pressure b u t also on r a t e of flow. Clement3 has shown t h e importance of t h e time factor in t h e manufacture of producer gas. Hempel’s4 experiments with gas oils a t temperatures between 7 0 0 a n d g o o 0 C. have demonstrated further t h e influence of t h e r a t e of oil feed upon t h e composition of t h e products. J . F. Tocher5 has also shown some results of a change in t h e r a t e of oil feed. A technical application of t h e time factor can be found in t h e experiments of Jones.6 I n varying t h e r a t e of oil fed into a retort or furnace for t h e production of oil gas, one varies t h e time during which a n y portion is heated a n d hence t h e time allowed for t,he reaction. With a very slow r a t e of oil feed, t h e reaction would a t t a i n a n equilibrium composition representative of t h e heating zone conditions. 1 Berthelot, Ann. c h i m phys. (1866 t o 1877); Thorpe and Young, Liebig’s A n n . , 165 (1872), 1 ; Proc. R o y . SOL.,2 1 (1873), 184; Norton and A4ndrews, A m . Chem. J , 8 (1886), 1; Armstrong and Miller, J . Chem. SGC., 49 (1886), 7 4 ; Lewes, J . S o c . Chem. I n d , 11 (1892), 584; Haber, Bcr.. 29 (18961, 2691; J . Gasbel , 34, 3-7, 435. 452; Worstall and Burwell, A m . Chem J . , 19 (189i), 815; B o n e a n d Ccward, J . Chem. sot, 93 (1908), 1197; Hempel, J . Gasbel., 1910, P. 53; Kramer and Spilker, B e y , 33 (1910), 2265; Lewes, Trans. Chem. Soc., 69 (18921, 322; PYGC. R o y . SOC.,56 (1894), 90; 67 (1905), 394, 450; Bone, J . Gnsbel., 5 1 (1908), 803; Engler, Ber., 30 (1897), 2908. ? Lewes, Proc. R o y . Soc., 66 (1894), 90; 57, 594. Clement, Bull. 30 (1909), D. of Ill. Eng. Exp. S t a . Hempel, J . Gasbel., 1910, p p . 53, 7 i , 101, 137 and I 5 5 5 5. F. Tocher, J . SOC. Chem. I n d . , 13 (1894), 231. 8 Jones, A n i . Gaslight J . , 99 (1913), 273.
485
With increasing rates of oil feed t h e time allowed for reaction is shortened a n d t h e products obtained correspond t o a n earlier stage of t h e decomposition. T h e composition of oil gas is therefore dependent upon t h e time allowed for chemical change. Hence t h e study of the time factor in the making of oil gas should yield interesting a n d practical results. E X PE R I M E N T A L C 0 S SI D E R A T I O N S
of the reactions of gases moving through heated vessels, the method which was used in this investigation and is representative of practice in oil gas production, involves certain features of design which are dependent upon t h e theoretical considerations of reaction velocity, During the passage of any heating-zone-composition through t h e cooling zone, there will be a certain change in composition due t o a reversal of reactions.l The extent of this reversal m-ill depend on t h e tirne required in t h e cooling t o arrest t h e reactions. Hence t h e more quickly these gases are cooled after leaving the heating zone, t h e more nearly will t h e product obtained be representative of the heating conditions. The effi,, study
ciency of the cooling in arresting the of reactions is materially increased in some of t h e decomposition reactions b y t h e separation of carbon in t h e solid phase, making it possible to obtain as the product a gas mixture which very closely approximates t h e composition of the mixture in the heating zone. It is thus evident that reaction velocity is important not only in the heating zone, but also i n the cooling zone. Further essential considerations in t h e attainment of a product representative of heating zone conditions are those of convection a n d diffusion. As shown by Langmuir,2 diffusion a n d convection act in a way t h a t is equivalent t o decreasing t h e reaction velocity. Convection currents m a y be set u p by differences in temperatures or irregularities in design, t h e results of which mill t e n d t o shorten t h e time of contact for some of t h e molecules i n t h e heating zone. T h e effect of diffusion increases with temperature as t h e coefficient of diffusion varies approximately with t h e square of t h e absolute temperature. Considering t h e heating zone or cooling zone separately, raising t h e temperature increases t h e diffusion effect a n d is in a sense equivalent t o shortening t h e time of contact. This effect m a y be a material consideration in t h e heating zone b u t ~ 7 0 u l dbe almost negligible in t h e cooling zone. On t h e other h a n d , when one considers t h e mutual effect of t h e t w o zones, diffusion offers an advantage, due t o t h e differences in t h e partial pressures of t h e reacting substances. Differences in partial messures cause those substances whose DroDortions increase with rise i n temperature t o diffuse from t h e heating zone t o t h e Cooling zone a n d nice versa those substances whose proportions decrease with rise in temperature diffuse in the Opposite direction. Hence, this effect aids also in obtaining products more nearly corresponding t o t h e heating-zone-composition. *
2
S e r n s t , Z . anorg. Chem.. 49 (1906). 213. Langmuir. J . A m . Chem. Soc., 30 (1908), 1742.
A
T H E JOIJRNAL OF I N D U S T R I A L A N D ENGINEERISG CHEMISTRY
486
OIL G A S A P P A R A T U S
T h e design a n d construction of a n a p p a r a t u s suitable for carrying out t h e s t u d y of t h e behavior of hydrocarbon vapors u n d e r t h e conditions outlined in t h e foregoing theoretical discussion involved m a n y important considerations. In such a n a p p a r a t u s i t was desired t o provide for working with constant t e m p e r a -
c
Elecfrode Ho/der
v01. j ,
S O .6
nace, illustrated in Fig. I, was constructed. T h i s furnace embodies t h e use of a carbon t u b e resistor held b y water-jacketed electrode holders a n d surrounded b y heat-insulating material enclosed b y a n iron furnace body which is provided with suitable accessory mechanisms for electrical a n d water-cooling connections, feed a n d discharge apparatus, a n d observation of t e m p e r a t u r e s a n d pressures. T h e carbon tube' resistor (A) is 4 6 in. long, I in. inside diameter, with 0.2j in. wall. Deducting t h e electrode holder contact length, a b o u t 4 in. a t each end, this gives a heating zone of 3 8 . j linear inches with 1 2 0 sq. in. heating surface a n d a volume equal t o 30.5 cu. in. or a b o u t j o o cc. This t u b e is copper plated externally a t each e n d t o give a suitable contact surface of 18 sq. in. with each electrode holder.
.'... Pgrornefer Sigh f Tube
FIG. 11-ELECTRODEHOLDER
FIG.I-RESISTANCE F U R N A C E
tures u p t o 2300' C . ; for pressures lbs. t o I O O lbs. gauge per sq. i n . ; of oil feed over a large range; for collecting t h e resultant products; other requirements.
ranging from -15 for constant rates suitable means of a n d for numerous
THE F U R K A C E
An electrically heated carbon t u b e resistance fur-
T h e electrode holders ( B B ) are integral bronze castings with cored water jackets a n d with flanges for bolting t o t h e furnace heads. T h e construction is shown in some detail i n Fig. 11. I n t o t h e main b o d y of t h e holder outside of t h e flanges, are drilled a n d t a p p e d t h e water-jacket connections a n d binding posts for t h e electric leads. T h e outside ends are further provided with carefully insulated stuffing boxes a n d caps in order t o separate t h e heating element, electrically, f r o m t h e feed a n d discharge mechanisms of t h e assembled a p p a r a t u s , T h e flanges, bolts, a n d n u t s are insulated with sheet mica t o isolate t h e heating element f r o m t h e furnace casing. T h e resistor t u b e is surrounded by a large concentric 1
Carbon tubes were obtained from the National Carbon
eo.
I
June,
191j
T H E J O U R N A L O F I N D C S T R I A L A Y D ENGIiYEERILVG C H E M I S T R Y
carbon t u b e ( C ) , 3 in. inside diameter a n d 0 . j o in. wall, which is insulated from t h e electrode holders by asbestos disks. T h i s construction leaves a n annular dead gas space of o.;j in. around t h e resistor. Between this large carbon t u b e a n d t h e furnace casing powdered petroleum coke is packed for h e a t insulation. T h e furnace b o d y ( D ) is made from extra h e a v y wrought iron pipe with screwed a n d peened flanges a t each end. T o these are bolted blank companion flanges centrally bored t o receive t h e bodies of t h e electrode holders a n d faced t o seat t h e flanges. T h e electrode holders are each held in position b y six 0.5 in. stud bolts drilled a n d t a p p e d into t h e furnace heads. As above s t a t e d t h e mountings of t h c electrode holders are mica-insulated from a n y contact points with t h e furnace casing. T h r e e solid bosses,
P O W E R , KILOWATTS FIG.111-POWERCOXSCMPTION CURVEFOR RESISTANCE FURNACE
3 in. diameter b y 0.j i n . thick. are autogenously welded o n t h e outside walls of t h e furnace casing and are drilled a n d t a p p e d for I in. brass extensions which serve as sight tui-jes (EE’E”). These extension t u b e s register mith a n d support carbon side tubes (FF’F”), o.;j in. ihside diameter a n d 0 . 1 2 j in. wall, which connect t h e sight tubes with t h e annular space around t h e resistor. T h e outer ends of t h e sight tubes are provided mith glass windows 0.2 j in. thick. This combination gil-es a straight way view i n t o t h e resistor chamber at three points along i t s length. T h e water-cooling system for t h e furnace casing consists of a perforated yoke of water pipe (G) a t t h e t o p for spray cooling a n d an annular catch basin ( H ) a t t h e bottom.
487
OPERATION AND TEST O F F U R S A C E
T h e power required t o h e a t t h e furnace is derived from a single phase, 60 cycle, j o k v . alternating current generator, having a range of j t o IOO volts which can be regulated within narrow limits by a switchboard a n d rheostat combination. T h u s t h e temperature of t h e furnace can be readily controlled. Power was measured b y t h e use of a portable X e s t o n ammeter. voltmeter, a n d wattmeter placed in close proximity t o t h e furnace. T h e readings from these three instruments made it possible for t h e operator t o determine t h e power consumption of t h e furnace and t o check t h e proper working of t h e apparatus. Ordinarily i t required about an hour t o heat t h e furnace t o a constant temperature after t h e power had been t u r n e d on. T h e high temperatures are measured b y sighting through t h e observation t u b e windows with a Wanner optical pyrometer no temperature corrections arc necessary. T h e low temperatures are nieasured b y replacing t h e glass n-indows b y small stuffing boxes through which pyrods are inserted. T h e power used for t h e various temperatures is shown in Fig. 111. This furnace has been tested a t various temperatures ranging from j o o t o 2 3 0 0 ’ C. a n d held constant a t such temperatures for several hours a t a time. I n these tests t h e readings a t t h e three different observation points agreed. I n one of t h e tests t h e furnace was held a t 1600’ C. for four hours without requiring a n y regulation of t h e power. X hydrostatic pressure test t o 2 0 0 lbs. per s y . in. was made on t h e assembled furnace mith the feed a n d discharge mechanisms a t tached. FIG. Iv-PHEVAPORIZER T h e carbon resistor is t h e only p a r t of t h e furnace mhich requires renelvral. X-et a single t u b e hqs been used for fifty runs a t various temperatures. Whenever it is necessary t o renew t h e resistor, t h e electrode holders are removed a n d a new t u b e fitted. PRE\ APORIZLR
T h e object of t h e prevaporizer is t o vaporize the oil before i t enters t h e heating zone of t h e furnace. T h e prevaporizer. Fig. I\-, consists in 2% 8 in. brass pipe IS in. long, containing a bundle of iron wire for spreading t h e oil, I t is electrically heated from t h e outside b y 8 t u r n s t o t h e inch of No. 18 B.& S. nichrome resistance wire properly insulated f r o m t h e t u b e b y four wrappings of asbestos paper. For heat conservation t h e whole is surrounded b y s t a n d a r d 8 j per cent
488
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
magnesia pipe covering. T h e power required for heating t h e prevaporizer is furnished from a separate direct current line a n d regulated b y t h e use of a lamp bank. Prevaporization was found t o be a n essential feature as experiments showed t h a t even when t h e heating zone temperature of t h e furnace was 1400' C. a n d t h e r a t e of'oil feed j o drops per minute, t h e oil dropped directly through t h e heated carbon t u b e a n d came out a t a n equal r a t e with very little vaporization; this result was apparently due t o spheroidal effect a n d lack of contact with t h e heated surface. With a solid or vapor passing through t h e t u b e under t h e s a m e conditions,
Stu t i c Head Requhfor
Vol. 7 , No. 6
gauge glass, B, a n d a screw cap, C, which may be removed for internal adjustment. T h e inside mechanism consists of a cork float, D, which operates a needle valve, E. This constant level regulator i s also connected with t h e oil supply t a n k , t h e feed mechanism, t h e pressure equalizer pipe, a n d t h e pressure gauge. Valve F is a stop-valve t o be closed when t h e a p p a r a t u s is not in use. The sight feed regulator H is constructed from a brass casting provided with t w o glass windows, 11', a n d a n angle needle valve, J , t o regulate t h e r a t e of oil feed. Connections are made from this with t h e static head regulator, prevaporizer, a n d pressure equalizer a n d admixture pipes as shown in Fig. T'. A constant head of oil is necessary in order t h a t a fixed opening of t h e feed valve J m a y give a definite a n d uniform rate of oil feed. This is accomplished b y t h e cork float D operating t h e needle valve E , which admits oil from t h e storage t a n k a t a r a t e equal t o t h e r a t e of feed. I n order t o insure t h e proper working of this mechanism, a gauge glass, B, is provided, which registers t h e oil level. This level has been found t o vary not more t h a n ' 1 8 in. regardless of t h e level in t h e oil supply t a n k . T h e oil feed is regulated t o t h e desired r a t e by adjusting t h e needle valve J , according t o observations made through t h e windows I. Table I contains d a t a taken from some of t h e experimental runs a n d serves t o show t h e range of accuracy of oil feed obtained b y this mechanism: TABLEI-RANGE OF ACCURACY OF OIL FEED R a t e of feed per minute Period of test Variation 3 hrs. h-one 1.. , . . , . , . . . . . . , 8 drops 2.......... 100 drops 2 hrs. 1 drop 3............... 5.4cc. 1 hr. i-ione 4 ...... , ... , , . , , 1 5 . 8 cc. 30 min. 0 . 5 cc. 8 min. None 5 . . . . . . . , , . . . . . . 6 9 . 0 cc.
Test
T h e pressure of t h e whole system is equalized b y a pressure equalizing pipe, G, which communicates t h e furnace pressure through t h e sight feed t o t h e static head regulator a n d t h e oil supply t a n k . Pipe K is used for recirculating t h e gases made or for admixing other material with t h e oil. OIL SUPPLY T A N K
W FIG. V-STATIC HEADAND FEEDREGULATOR
t h e solid would become heated b y radiation a n d t h e vapor mainly b y conduction. Prevaporization was found t o be incomplete a t very high rates of oil feed, i. e . , t h e prevaporizer has a maximum capacity. As a n additional precaution, at high feed rates, t h e wire filling of t h e prevaporizer was extended into t h e heating zone of t h e furnace. STATIC HEAD AND P E E D REGULATOR
T h e object of t h e static head a n d feed regulator is t o provide for a n accurate a n d steady rate of oil feed which in t u r n controls t h e time factor. T h e static head regulator, shown i n Fig. V. is made u p of a specially designed cast brass casing, A, with a
T h e oil supply t a n k (see Fig. V I ) , with a capacity of 600 cc., is made from standard 1 . j in. brass pipe a n d fittings. ' T o this a gauge glass is connected a n d provided with a parallel meter stick carrying a sliding pointer. This arrangement is calibrated for volume a n d enables t h e operator t o verify t h e uniformity of t h e r a t e of oil flow a n d hence t h e accuracy of t h e cons t a n t head apparatus. GAS HOLDERS
The gas holders are balanced bell holders with water seal. These are calibrated a n d provided with a meter stick a n d pointer in order t o facilitate t h e recording of t h e r a t e of gas generation during a run. F E E D AND DISCHARGE MECHAKISM
Both t h e oil feed mechanism a n d t h e condensing system are carried on t h e supporting framework b y swinging arms, T h e connections t o t h e furnace at their respective ends are made through ground joint.
June, 191j
T H E JOURhTAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
unions. When cle?ning, renewals or repairs t o t h e furnace are necessary, t h e unions m a y be disconnected a n d t h e mechanism swung aside without disturbing t h e furnace. ASSEMBLY AND OPERATION
T h e arrangement of t h e complete apparatus ready for operation is sholvn in Fig. 1'1. At t h e beginning
489
oil is carried directly into t h e heating zone of t h e furnace. T h e oil gas runs were made over a range of constant temperatures from 800' t o 1600' C. Temperature observations, during a run, showed t h a t t h e feed end of t h e resistor was 50' t o 100' C. cooler t h a n t h e center a n d discharge points which remained practically t h e same. This lower temperature of t h e feed end of t h e reaction chamber is obviously due both t o t h e heating up of t h e oil vapors and t o t h e large amount of heat required for t h e endothermic reactions taking place in this part of t h e tube. Furthermore, t h e de'position of carbon here may reduce t h e resistance a n d hence lower t h e temperature. TABLE11-RECORDSOF RUKSAT DIFFERENT RATESOF OIL FEED S L O W RATEOF OIL FEED K. W. 4.0
Time 11.15 11.20 11.25 11.30 11.35 11.40 11.45 11.50 11.55 12.00 12.05
...
... ... ... ... ... 4.1 ... ...
__
,
.
I
Temp. Gauge pressure Oil rate C. Lbs. per sq. in. Cc. per min. 1010 0 2.1 .... 0 2.1 0 1000 2.0 0 .... 2.0 0 2.1 .... 1000 0 2.2 .... 0 2.0 2.1 .... 0 1010 2.2 0 0 2.1 iooo 1 2.1
__
Gas rate Litersper min.
...
2.0 1.9
1.7 1.8 1.8 1.9
1.8 1.8 1.8 l.i
-_
50 min.
105 cc. 92 liters P E R C E K T A G E GAS ANALYSIS-SLOW RATE O F FEED-MARCH 8. 1915 COr Ill. Oz CO H2 C,Hzn+2 N z (diff.) Total Carbon T a r 0.6 or
6.7 7 5
...
Time
0.8
1 . 0 54.5 29.0 7.4 100 60.5 32.0 ... 100 MODERATERATEO F OIL FEED Gauge pressure Oil rate C. Lbs. per sq. in. Cc. per min.
......
Temp.,
__
~
25 min. PERCENTAGE G A S
or
COz
Ill.
0.1
19.2
...
19.5
0 2
Trace
...........
Gas rate Liters per min.
-_
240 cc. 160 liters ANALYSIS-MODERATE RATEOF FEED-APRIL 16, 1915 CO Hz C,H2*+2 Ns (diff.) Total Carbon T a r
0.0
0.8 44.3
35.2 0.4 100 Little 125 cc. 35.7 ... 100 ....... RAPIDRATEOF OIL FEED Gauge pressure Oil r a t e , Gas rate Lbs. per sq. in. Cc. per min. Liters per min.
......
Temp. Time
Little
c.
44.8
-
__
-
11 min.
490 cc.
445 liters
PERCENTAGE GAS ANALYSIS-RAPID RATE OF FEED-APRIL 16, 1915 CO Hz C n H 2 n + 2 Nz (diff.) T o t a l Carbon T a r COr Ill. 0 2 36.0 4.8 100 Trace 245 cc. 0.0 35.0 0.6 1 8 21.8 or . . . 3 7 . 7 . . . . . . 2 3 . 5 38.8 ... ...........
FIG.VI-OIL
GAS APPARATUS
of a n experiment t h e oil t a n k is first filled-with oil; after t h e feed valve has been adjusted t o t h e desired rate of oil feed, oil-tank readings are t a k e n at definite intervals of time. T h e oil passes from t h e supply t a n k t o t h e static head regulator a n d o u t through t h e feed adjusting valve t o t h e prevaporizer. From here t h e vaporized
T h e measurement of t h e high temperatures by the optical pyrometer offered no difficulties as there were no fumes present in t h e furnace. T h e hot gases are discharged from t h e reaction chamber directly into t h e primary condenser where t h e reactions are arrested by t h e cooling. From here t h e gases go through t h e t a r drip which is followed by a secondary condenser a n d thence out t o t h e gas holders, where t h e rate of gas generation is noted a t definite intervals of time. The condensates from both t h e primary a n d secondary condensers r u n into t h e same t a r drip from which t h e y m a y be readily removed a t t h e end of each experiment. Typical records of runs are shown in Table 11.
T H E JOYRiVAL OF I N D C S T R I A L A N D ENGINEERING C H E M I S T R Y
490
GAS S A U P L I K G A N D A N A L Y S I S
T h e gas from t h e r u n s was collected in t h e balanced bell gas holders already described. Care was always t a k e n t o saturate t h e seal water with a similar gas previous t o t h e collection of t h e r u n from each experiment. Before taking a sample of gas from t h e holders for analysis, t h e product was allowed t o s t a n d a sufficient length of time for complete mixing by diffusion a n d for t h e settling out of a n y t a r or carbon t h a t might have been carried over. T h e gas samples were analyzed b y t h e standard methods’ with a few modifications t o meet special requirements. T h e Hempel equipment was used in all analyses a n d t h e order of procedure was as follows: I-Absorption of the carbon dioxide with KOH solution. 2-Absorption of the illuminants with fuming sulfuric acid ( 2 3 per cent free SOa). 3-Absorption of the oxygen by alkaline pyrogallol. 4-Absorption of the carbon monoxide by two ammoniacal cuprous chloride solutions. 5-Partial combustion of the hydrogen by passing 20 to 30 cc. of the remaining gas mixed with the proper proportion of pure oxygen over palladium black heated t o 70’ t o 80‘ C. 6-Explosion of the remaining hydrocarbon-oxygen mixture. T h e partial combustion of hydrogen in gas mixtures containing percentages above 90 per cent was difficult on account of t h e danger of explosion. I n such cases t h e mixture was exploded directly a n d calculated as hydrogen a n d methane from t h e formulas, zT.C. - 4 C 0 2 CC. of H z = ___-__~ a n d cc. of C H ? = COZ, 3 where T. C. = total contraction noted directly after t h e explosion a n d COS = contraction due t o absorption with KOH after explosion. I n t h e partial combustion of hydrogen followed by t h e explosion of t h e residual gas mixture, i t was often difficult t o obtain a n explosion b y using air as the source of oxygen. This difficulty was avoided, however, by t h e use of pure oxygen in such a n amount t h a t , after t h e removal of t h e hydrogen b y t h e palladium black t r e a t m e n t , an explosive mixture remained. F r o m t h e total contraction a n d t h e carbon dioxide found b y explosion, t h e volume of saturated hydrocarbons mas calculated b y t h e following formula:* 2T.C. - COS T‘ _____ 3
This gave t h e total volume of all t h e saturated hydrocarbons: methane, ethane, propane, etc. From t h e T’ a n d t h e C02 a mean value of IZ for t h e t y p e formula C,H,,+z was obtained, which gave a n indication of t h e nature of t h e hydrocarbons present, COS t h a t is, =
v
There is no proof t h a t t h e saturated hydrocarbons d o not contain hydrocarbons of higher molecular weight t h a n ethane. T h e t r u e percentages of each of t h e CnH2n+2 hydrocarbons can be determined only 1 2
Dennis, “Gas Analysis.” 1913. DeVolderc and DeSmet, Z a n d . C h e m . , 49 (1910). 661
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by t h e fractional distillation methods of Burrell’ a n d his associates, of t h e U. S. Bureau of Mines. I n common analytical practice, when t h e hydrogen is separated by partial combustion, t h e remaining gas is assumed t o contain only methane and ethane a n d is calculated as such. This obviously would give a n error dependent upon t h e a m o u n t of heavier hydrocarbons present. For t h e calculation of t h e respective volumes of ethane a n d methane present on t h e above assumption, t h e following formulas were used: 4 C 0 2 - -2 T. C. C C . of C2Hs = _ _ _ _ and .?
CC.
of CH4
COS -
2
C2HG.
T H E TIME FACTOR
T h e experimental values found in this investigation are considered on t h e assumption t h a t t h e t r u e time factor is a function of t h e r a t e of oil feed. As stated above, t h e t r u e time factor, which represents t h e interval of time in which t h e reactions progress, is dependent upon t h e theoretical considerations of reaction velocity. It is substantially a function indirectly proportional t o t h e rates of oil feed; i. e . , a n increase i n t h e r a t e of oil feed decreases t h e time of reaction. On t h e other hand, t h e r a t e of gas production might be considered as a means of obtaining a better a p proximation of t h e t r u e time factor. This would necessitate t h e calculation of t h e volumes of t h e gases t o t h e reaction zone conditions. Furthermore, t a r s would have t o be considered, in case of their formation. Such a method, even if both t a r s a n d gases were considered, would not give a value approximating t h e t r u e time factor, as t h e original oil vapors occupy a much smaller volume t h a n their decomposition products; in fact decomposition in t h e reaction zone proceeds with a continuous increase in volume. It is apparent t h e n t h a t this basis of a time factor would be impractical either for experimental s t u d y or for technical purposes. For these reasons t h e time factor as based on t h e r a t e of oil feed was selected for this investigation as i t offers a comparative value for theoreticalconsiderationsand is a n easily measured quantity, as well as a readily controllable variable for practical work. EXPERIMEKTAL
X water-white kerosene, boiling between I jo--290’ C., was used in all experimental runs. ,411 runs were made a t atmospheric pressure, a n y variation of which was indicated by t h e pressure gauge. The complete gas analyses always showed varying percentages of carbon dioxide, carbon monoxide, a n d air ( e . g., see Analyses in Table 11), so t h a t t h e figures for illuminants, hydrogen, a n d saturated hydrocarbons did not present these constituents in their proper relationships. This difficulty was overcome b y recalculating t h e analyses t o t h e illuminanthydrogen-saturated hydrocarbon basis (see Analyses in Table 11) a n d all subsequent d a t a are presented from this view point 1 Burrell a n d Seibert, J A m Chem S O C ,36 (1914), 1537, Burrell and Robertson, THISJOERNAI., I (1915), 17, 210
J u n e , 191j
T H E J O U R N A L O F I N D U S T R I A L A N D ENGILTTEERINGC H E M I S T R Y
E F F E C T O F RECIRCULATIOS O F GASEOUS PRODUCTS
I n this investigation i t was necessary first t o prove t h a t i n t h e production of oil gas, chemical equilibria are n o t obtained, for if such were not t h e case, a s t u d y of t h e t i m e factor would be valueless. T h i s point was proved b y r u n s a t slow rates of oil feed, so a s t o allow a considerable t i m e for reaction, a n d subsequent recirculations of t h e products. Slow rates of oil feed were selected because, if equilibria were not established a t such rates, i t is self-evident t h a t t h e y would n o t be established a t higher rates with correspondingly less time for reaction. I n experiihental d a t a given i n Table I11 three different rates of oil feed a t t h e same temperature, 1200' C . , were selected a n d t h e recirculations ( a a n d b ) made at rates equal t o their respective rates of gas TABLE111-GAS
GENERATIOX AND Oil r a t e Gas r a t e KO.Cc. per min. Liters per min 1.25 1 1.1 1.25 la ... 2 2.4 2.4 2a ... 2.4 2.4 2b 3 6.0 5.3 30 ... 5.3 3b .. 5.3
Run
...
RECIRCULATION AT 1200" C. GAS ANALYSES(PERCENTAGES) Illum. H? CnH2n+2 0.0 92.5 7.5 0.0 94.0 6.0 1.1 90.5 8.4 0.0 92.8 7.2 0.0 93.2 6.8 88.2 10.3 1.5 88.9 10.1 0 5 90.5 9.5 0.0
generation. R a t e s t h a t gave practically n o t a r were selected; this mas necessary because t a r s , if present, undoubtedly t a k e p a r t i n t h e reactions i n t h e heating zone. A consideration of t h e general velocity equation in conjunction with t h e above d a t a will show some inter e sting relations bet ween re action \-el o ci t y a n d gas recirculation
Here t h e r a t e of change is dependent upon t h e respective velocity constants of t h e reverse reactions a n d t h e concentrations of t h e reacting substances. F o r a n y one t e m p e r a t u r e t h e velocity constants have a fixed value. Should t h e decomposition reactions have completed themselves or come t o equilibrium, d x / d t would have been equal t o zero, b u t t h e above d a t a shows t h a t this was not t h e case, a n d hence equilibrium As t h e reactions approach equiwas not attained. librium, t h e respective velocities of t h e t w o reverse reactions become more nearly equal, i. e., t h e r a t e of change, d x l d t , is a decreasing function as equilibrium is approached. T h e results i n Table I11 show t h i s effect quite conclusively, a s t h e change i n t h e second recirculation is less t h a n t h a t i n t h e first. I n case one considers t h e reactions t o proceed t o completion i n one direction only, t h e same theoretical conclusions hold. I n t h e above gas mixtures, with no illuminants present, t h e s a t u r a t e d hydrocarbon percentages were found t o consist entirely of methane. T h e reaction involved a t such a stage of t h e decomposition consists only i n t h e decomposition of m e t h a n e i n t o carbon a n d hydrogen. T h e equilibrium composition of this reaction a t 1200' C. (calculated according t o t h e formulas of Nernst o r M a y e r a n d Altmayer) should show n o t
19 *
more t h a n 0.3 per cent methane, as has been esperimentally proved b y m a n y investigat0rs.l T h e reason t h a t this value was not obtained i n t h e above experiments is t h a t sufficient time was n o t allowed for t h e reactions t o reach equilibrium. T h e intervals of reaction t i m e in t h e r u n s in Table I11 calculated from t h e gas rates, temperature, pressure a n d volume of heating zone, a m o u n t e d t o only a fen. secondsj, 2 l , a n d I second, respectively-for S o s I , 2 a n d 3. Equilibrium compositions could be a t t a i n e d only b y t h e lapse of m a n y minutes in t h e heating zone. This emphasizes t h e fact t h a t equilibrium compositions are n o t obtained in oil gas practice a n d further t h a t it would be impractical t o r u n a n oil gas generator a t such rates of oil feed as would even approsimate equilibrium compositions. CHANGE O F COMPOSITIOS I\ITH
R A T E O F OIL FLED AT
C0N STA i YT T E h I P I:R A T U R E
T h e changes of composition with t h e r a t e of oil feed at constant temperature are plotted from t h e experimentally determined d a t a i n Fig. V I I . I n general, these curves sho\T t h a t a decrease i n t h e oil r a t e , i. e . , a n increase in t h e time of reaction, a t a n y one constant t e m p e r a t u r e , results i n a greater degree of decomposition F o r a n y t w o temperatures t h a t can be compared with reference t o percentage of a n y one selected constituent, t h e higher temperature \\-ill result in a n equivalent degree of t h e decomposition a t a much higher r a t e of oil feed. However, t h e t o t a l compositions of t h e gases produced a t t h e different,tempEratures are n o t strictly comparable, i. e . , t h e percentages of illuminants or s a t u r a t e d hydrocarbons for equal percentages of hydrogen are n o t t h e same. This is apparently d u e t o different reactions t a k i n g place a t t h e different temperatures a n d t o t h e unequal effect of t h e different temperatures on t h e velocities of t h e various reactions. It will be noted t h a t a t low temperatures a n d a t high rates of oil feed a decrease or increase i n t h e oil r a t e has comparatively little effect on t h e percentages of hydrogen or illuminants in t h e gaseous products. This suggests t h a t there m u s t be a minimum percentage of each constituent a t these temperatures. Yet one must not conclude from these facts t h a t t h e decompositions a t t h e low temperatures proceed i n a b r u p t stages, as this phenomenon finds explanation in a more close consideration of t h e t r u e time factor. F r o m Fig. I X i t will be seen t h a t t h e rates of gas generation do not undergo material change over a considerable range of oil feed. On t h e assumption t h a t t h e volumes of t h e t a r s in t h e heating zone are a p proximately equal, t h e n t h e reaction periods for t h e high rates of oil feed are almost t h e same a n d should give gaseous products of similar compositions. I n accordance with t h e theoretical considerations, t h e maximum decomposition a t a n y one temperature c a n be a t t a i n e d only at equilibrium, which is char' B o n e and Jerdan, J . Chem. S O C , 71 (1897). 41; 79 (1901). 1042; M a y e r a n d .4ltmayer, Rer., 40 (1907). 2134; H. von Wartenberg, 2. phrsik. C h e m , 6 1 (1907), 366; Bone a n d Coward, J Chem. SOC.,93 (1908), 1197. 93 (1908). 1975; Pring, J . Chem. SOC..97 (1910). 498; Pring a n d Fairlie, Ibid.. 99 (1911). 1796; 101 (1912). 91; also THISJOURNAL. 4 (1912), 812.
T H E JOURNAL OF INDLISTRIAL A N D ENGINEERING CHEMISTRY
492
acteristic of a n extremely long t i m e for reaction. T h e curves in Fig. VI1 point t o w a r d such equilibrium compositions a t t h e slow rates of oil feed. Such compositions can in all probability be a t t a i n e d i n t h e heating zone a t extremely slow rates of oil feed b u t experimental results would not verify this o n account of t h e reversal of reactions which would t a k e place in t he cooling zone.
Vol. 7 , No. 6
temperatures a t which maximum a n d minimum percentages of t h e various constituents of t h e gas mixtures exist. T h e maxima for hydrogen a n d t h e minima for s a t u r a t e d hydrocarbons indicate t o a complete decomposition of t h e oil i n t o carbon a n d hydrogen. T h e minima for illuminants exist at a lower temperature t h a n t h e minima for s a t u r a t e d hydrocarbons at t h e same rates of oil feed, i. e . , in t h e complete t h e r m a l
100
90 80
z 70 w 0 W
E60 z >
2 50 u W E
240 30 20
10 0
10
20
30 40 50 60 70 RATE OFOILFEED-cc p e r m i n
80
90
10
20
30 40 50 60 70 RATE OF OIL FEED - cc p e r m in
80
9C
v)
z 50
s
g
40
n
>
30
5 20 cn 4 b-
5
IO
w U
e o
TEMPERATURE,DEG C
50
5
u)
-
40
3 x
2 30 z k-
Y
20
E
a w
I0
IO
20
30 40 50 60 70 R A T E O F O I L FEED-cc p e r m i n
80
90
FIG.VII-CONSTANT TEMPERATURE CURVES C H A N G E O E COMPOSITION WITH T E M P E R A T U R E AT C O N STAiYT R A T E S O F OIL F E E D
I n general, t h e constant feed curves1 i n Fig. VI11 show t h a t increase in temperature results in a greater degree of decomposition a n d t h a t there are definite 1
Plotted from values obtained b y interpolation from the curves in
Fig. VII.
TEMPERATURE.DEG C
FIG VIII- CONSTANT FEED CURVES
decomposition of hydrocarbon oils i n t o carbon a n d hydrogen. t h e illuminants disappear before t h e s a t u rated hydrocarbons. T h e curves for hydrogen a n d for illuminants seem t o indicate minima a n d maxima, respectively, a s shown b y t h e extrapolations. On t h e other h a n d , t h e percentages of s a t u r a t e d hydro-
T H E J O C R N A L OF I L V D C S T R I A L A X D ENGINEERING C H E M I S T R Y
J u n e , 1915
carbons show t r u e maxima dependent upon t h e r a t e of oil feed a n d t h e temperature. PRODUCTIOS OP HYDROGES
Table IT shows t h a t a t 1600' C., with increasing rates of oil feed. t h e percentages of hydrocarbons in t h e resulting gases decrease until a maximum of deTABLEI V - P R O D U C T I O N Run K'a.
1 2 3
2 6
Oil rate Cc. per min. 69.0 32.4 11.5 6.8 2.4 0.27 0.15
Gas r a t e Liters per rnin. 54.0 34.0 13.0 8.3 2.9
....
....
OF
HYDROGEN A T 1600' c. GAS AXALYSES( P E R C E K T A G E S ) Ilium. H2 C232nS2 11.8 73.1 15.1 1.6 96.0 2.4 0.0 99.2 0.8 0.0 100.0 0.0 0.0 100.0 0.0 0.2 98.6 1.2 0.7 96.8 2.5
composition is reached, when t h e oil is completely decomposed into carbon a n d hydrogen. * s s t a t e d above, under t h e recirculation of gas, even at I Z o o o*' the hydrocarbons be 'Omand hydrogen, but to pletely decomposed into a t t a i n such a result a t this temperature would require On the Other many minutes in the heating 'One' h a n d , this complete decomposition is realized a t I 6 O o 0 c. i n a comparatively short reaction period, due t o t h e great increase in t h e r a t e of decomposition a t t h e high temperature over that at the Derature so t h a t t h e shorter time i n t h e heating zone is sufficient for t h e complete decomposition. With a n y design of generator for t h e production of hydrogen b y t h e direct decomposition of hydrocarbon oils, t h e time i n t h e heating zone must be such as t o favor complete decomposition a t t h e desired t e m perature. This temperature has b o t h a minimum a n d a maximum value dependent upon t h e principles of thermodynamics a n d upon practical reasons, respectively. T h e minimum is t h a t lowest temperature at which equilibrium composition represents complete decomposition; i. e., about 1200' C., a t which t e m perature a long time would be necessary t o complete t h e reaction. T h e maximum is t h a t limited b y economical design a n d practical temperatures. I n R u n s 6 a n d 7, made a t very slow rates of oil feed, there are small percentages of hydrocarbons present. This is apparently due t o a reversal of reactions as i n t h e theoretical consideration i t was concluded t h a t if t h e r a t e of cooling was slow t h e reactions would reverse toward t h a t equilibrium composition corresponding t o a lower temperature. I n view of these results t h e range of complete decomposition is limited n o t only b y temperature b u t also b y definite rates of oil feed which have a maximum a n d a minimum limit. T h e maximum is t h a t r a t e a t which t h e time allowed for reaction is just sufficient for complete decomposition. T h e minimum is t h a t r a t e a t which t h e t i m e required t o arrest t h e reactions in t h e cooling zone is sufficiently long t o cause a measurable reversal of reactions. F o r a n y temperature a t which complete decomposition is possible, these limiting rates will have different values. F r o m these considerations i t seems t h a t t h e direct decomposition of hydrocarbon oils might become a f u t u r e source of large quantities of hydrogen, but difficulties mould be encountered in t h e commercial
-
493
application of such a process. These obstacles would consist mainly in t h e economical heating of t h e reacting substances t o t h e necessary high temperature a n d i n t h e purification of t h e resulting gas. Economical heating could probably be attained b y t h e use of a counter-current system. Purification woultl be necessary i n order t o remove t h e oxygen a n d sulfur compounds derived from t h e original oil. Crossleyl has reviewed t h e commercial hydrogen situation t o date, b u t has omitted reference t o t h e direct decomposition of oil as a possible source of hydrogen. h few patents2 relating t o such processes have been issued. I L L U 111 6 A N T S
Table v consists of d a t a taken from the of Fig. V I I . These d a t a show t h a t i t is possible t o obtain gases containing equal percentages of illuminants a t different temperatures by varying t h e r a t e of oil feed. At a given temperature a n d r a t e of oil feet1 a certain percentage of illurninantsis obtained. Should it be desired t o obtain a gas containing an equal percentage of illurninants at a higher temperature, it would be necessary t o increase t h e r a t e of oil f e e d ; this is strictly i n accord with the theoretical principle of reaction TABLE V-EQUAL P E R C E N T A G E S O F I L L U x I N A N T s O B T A I N E D AT DIFFERENT TEMPERATURES B Y VARYILGTHE RATE OF OIL FEED Temperatures Oil rate COMPOSITIONS OF GASES (PEKCENTAGES) C. Cc. per min. Illum. Hs CnH2n+2 40.0 18.5 41.5 800 14.0 40.0 22.0 38.0 1000 55.0 2 0 . 0 14.0 44.4 35.6 1000 1200 57.0 20.0 53.7 26.3 58 2 31.8 3.5 10.0 1000 66.5 23.5 1200 26.5 10.0 ,410 16.0 55.5 10.0 1400 31.5 1.0 5.0 63.5 1000 5 . 0 78.5 16.5 14.0 1200 35.0 5.0 85.5 9.5 1400 5 0 . 0 5 . 0 8i.0 8.0 1600
velocity t h a t increase i n temperature increases rate of decomposition a n d hence i t should be necessary t o increase t h e r a t e of oil feed (equivalent t o decreasing t h e time for reaction) in order t o obtain t h e same percentage of illuminants in t h e resulting gas. However, gases containing equal percentages of llluminants d o not necessarily contain equal percentages of t h e other constituents. This is apparently due t o unequal effects of change of temperature on t h e various reactions involved in t h e decomposition. With a desired percentage of illuminants in view, t h e n , i t would be possible t o increase materially t h e capacity of a n y oil gas generator b y increasing t h e temperature a hundred or more degrees. Experimentally i t was found t h a t a gas containing about j Z . 0 per cent illuminants could be obtained a t 800' C. a t a high r a t e of oil feed b u t a t t h e same time a large a m o u n t of t a r was produced. GAS GENERATED
Fig. I X consists of t w o sets of curves, one showing t h e gas rates a n d t h e other t h e gas yields for t h e various rates of oil feed a t constant temperature. The rates of gas generation a n d yields a t 1600' C. are not shown, as runs a t this temperature could not. be maintained for a sufficiently long time t o obtain accurate 1
Crossley, J. SOC.Chem. I n d . . 33 (1914), 1135. Frank, U. S. Pat. 1,107,926 (1914); Ellis, U. S. Pat. 1,092,903 (1914).
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
494
d a t a , on account of t h e choking of t h e furnace b y t h e large amounts of carbon formed. T h e gas r a t e curves show t h a t a t constant t e m perature a n increase i n t h e r a t e of oil feed does not result i n a proportionate increase i n t h e r a t e of gas generation b u t rather in a decreasing ratio of gas r a t e t o oil r a t e . As a result, at low temperatures a n d high rates of oil feed t h e rates of gas generation do not show a material change over a considerable range. At 800' C. a n d a t very high rates of oil feed t h e r a t e of gas generation actually becomes a decreasing func50
t h e r a t e of oil feed will result i n a n increase in t h e yield of gas t o whatever maximum is representative of t h e most complete decomposition t o be attained a t t h e given temperature. As s t a t e d previously a decrease in t h e r a t e of oil feed provides t h e longer reaction period necessary for final equilibrium. Since t h e most complete decomposition a t a n y one temperat u r e is characteristic of equilibrium composition, a maximum yield of gas can be obtained only at t h i s final stage, although such yields of gas can not be realized experimentally on account of t h e abovementioned reversal of reactions in t h e cooling zone. TARS
40
5
30
a,
-
i 4
w b-
2
.
T a r yields could not be determined with accuracy i n these runs as t h e high rates of gas generation in m a n y of t h e experiments made it impossible completely t o separate t h e t a r s from t h e gases with t h e a p p a r a t u s at hand. I n general, t h e t a r yield increased with increase i n t h e r a t e of oil feed a t a given temperature a n d with a decrease in temperature a t constant rates of oil feed. Above 1 2 0 0 ~C., a t slow rates of oil feed, no t a r s were obtained. T h e n a t u r e of t h e t a r s obtained a t t h e various temperatures has n o t been investigated.
E
% .
Vol. 7 , No. 6
20
w l
a IO
CONCLUSIONS
5
IO
15
20 25 30 35 40 OILRATE-cc p e r m i n
45
50
55
60 65
0 I L RATE - c c . per rn i n . FIG.IX-GAS CURVES
tion. This is apparently due t o t h e checking of t h e course of t h e reactions by t h e insufficient time interval allowed or t o so exceeding t h e capacity of t h e furnace t h a t t h e oil vapors are not heated t o t h e temperature of t h e reaction zone. T h e gas yield curves indicate t h a t increase i n t e m perature results i n a n increase of t h e yield of gas a t a n y constant r a t e of oil feed. This is due t o t h e more complete decomposition of t h e hydrocarbons, as shown b y t h e compositions of t h e gases made at slow r a t e (Fig. V I I ) . A t constant temperature, decrease in
I-The control of t h e composition of t h e products obtained in t h e manufacture of oil gas involves not only thermodynamics b u t also chemical kinetics. 11-In practice, equilibrium is not reached in t h e thermal decomposition of petroleum hydrocarbons. This is proved b y t h e fact t h a t a recirculation of t h e products, under t h e same conditions a t which t h e y were generated, results i n a further change i n composition. 111-The time factor, which is controlled b y t h e r a t e of oil feed, is just as imporqant as are t h e other variables (temperature, pressure a n d concentration), as i t has been found t h a t t h e compositions of t h e products obtained in making oil gas vary with t h e r a t e of oil feed. Hence, from t h e standpoint of practical operation of a n oil gas plant, t h e r a t e of oil feed offers a n easily accessible means of control. IT-Maximum a n d minimum percentages of t h e various constituents in t h e products formed b y t h e decomposition of petroleum a n d petroleum distillates b y heat can be obtained b y a proper adjustment of t h e variables. V-Petroleum hydrocarbons can be completely decomposed into carbon a n d hydrogen only within well defined limits of t h e four variables. I n t h i s investigation t h e range of complete decomposition a t a definite temperature a n d pressure was limited b y definite rates of oil feed. VI-Oil gases containing equal percentages of illuminants can be produced a t different temperatures b y varying t h e r a t e of oil feed. Such gas mixtures, although t h e y have equal percentages of illurninants, do n o t i n general have equal percentages of saturated hydrocarbons a n d hydrogen, i. e., gases of equal illuminating values are n o t necessarily of equal thermal values.
J u n e , 1915
T H E J O U R N A L OF I N D C ‘ S T R I A L A X D ENGISEERI,VG C H E M I S T R Y
VII-In a n isothermal decomposition of petroleum hydrocarbons, maximum yields of gas a n d minimum yields of t a r are characteristic of equilibrium compositions. CHEMICAL ESGISEERIXG LABORATORY COLUMBIAUNIVERSITY A-EW YORK
pure salts dissolved in distilled water were used in experiments. I n canning beans, t h e y are soaked over night, washed, placed in cans a n d covered n i t h a syrup, t h e composition of which varies widely. Usually t h e s y r u p consists of water, salt, brown sugar a n d molasses. Parts per mil. Potassium, K 2.6 Sodium, K a 29.0 Ammonium. NHa 2 3 Magnesium, A f g 3 4 9 io 1 Calcium, C a Iron, F e 1.0 1.3 Aluminum, A1 0.7 N i t r a t e , pi00 Chlorine, C1 3 5 Sulfate, SO4 2.3 18.9 Silica, Si02 IONS
T H E EFFECT OF T H E MINERAL CONTENT OF WATER ON CANNED FOODS By H. L.
H L E N I h K AKD
EDNARD BARTOW
Received M a y 3, 1915
T h e quality of canned foods produced b y certain factories is always superior t o t h a t produced b y other factories. T o be convinced of this fact it is only necessary t o examine t h e product of a n u m b e r of factories. I t will become a p p a r e n t t h a t this difference is always present. I n general, t h e character of t h e products p u t o u t b y each factory is t h e same from year t o year. Canned-food brokers, who probably examine more canned food t h a n a n y other class of people, often r e m a r k upon t h e consistent difference in quality. a n d frequently raise t h e question as t o why it should exist. There are, of course. numerous causes which m a y lead t o differences i n t h e quality of canned foods, such as climate conditions, character of t h e soil, mode of handling t h e crops, factory management, character of t h e water used in t h e process, etc. T h e climatic conditions a n d t h e character of t h e soil cannot be controlled, whereas t h e others m a y be entirely corrected in a scientifically managed factory. One of t h e factors which m a y affect t h e quality of canned foods is t h e water used in processing. W a t e r is used extensively in t h e canning i n d u s t r y for washing, soaking, blanching a n d making of brines a n d syrups. T h e foods are also sterilized i n autoclaves in t h e presence of water a n d t h e action of its mineral constituents is probably greater here t h a n a t a n y other step in t h e process of canning. With t h e hop e t h a t some i m p or t a n t inform a t i o n m a y be gathered, whereby t h e quality of canned foods c a n be improved, we have begun a systematic investigation of t h e action of various salts occurring in water on canned foods. Because beans could be canned during t h e winter m o n t h s a n d also because baked beans are canned in f a r greater quantities t h a n a n y other class of soaked vegetables , t h e preliminary investigation vi as m a de with beans. Beans were canned with distilled water a n d with University of Illinois t a p water t o determine t h e effect which would be produced b y t h e presence of t h e salts in t h e water. T h e analysis of t h e CnitTersity supply is shown in t h e accompanying table. T h e beans canned with t h e University water were harder t h a n those canned with distilled water a n d their color was very much darker. This .shom-s t h a t t h e dissolved salts in t h e water affect t h e quality of canned beans. T o s t u d y t h e effect of t h e individual salts,
495
P a r t s Grains per per HYPOTHETICAL COMBIXATIONS mil. gal. Potassium n i t r a t e , KNOs 1.1 0.06 Potassium chloride, K C I 2.9 0.li Sodium chloride, N a C l 3.5 0.20 Sodium sulfate, SasSOa 3.6 0.21 Sodium carbonate, hTazC03 60.5 3.52 Ammonium carbonate, (NHa)?CO% 6 . 1 0.36 Magnesium carbonate, MgCOs 121.2 7.07 Calcium carbonate, CaC03 175.2 10.22 Iron carbonate, F e C 0 3 2.1 0.12 Alumina, A1203 2.5 0.15 Silica, Si02 18.9 1.10 TOTAL.
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397.6
23.18
h l a n y brands are p u t u p with t o m a t o ketchup. I n t h e soaking process t h e beans absorb a large a m o u n t of water. according t o their dryness. T h e beans which were used in these experiments took u p very nearly their own weight of mater. T h e beans were canned in 2 jo cc. flasks closed with cotton plugs. These containers were found very convenient for experimental work, a n d t h e method was found satisfactory. Beans canned simultaneously i n t h e flasks a n d i n regular No. z tin cans could n o t be distinguished from each other. T h e method of canning was as follows: jo g. of d r y n a v y beans were completely covered with water in a 2 5 0 cc. Florence flask a n d allowed t o soak over night ( a b o u t 1 2 hours). T h e excess water was t h e n poured off a n d t h e beans rinsed several times. T h e r e were added jo cc. of s y r u p , which was prepared a s follows: 20 g. brown sugar, 2 . j g. NaCl, j cc. New Orleans molasses a n d water t o make I O O cc. T h e flasks were plugged with cotton a n d sterilized in a n autoclave for 6 j minutes at 14 pounds pressure. T h e only variable in t h e experiments was t h e composition of t h e water which was changed in order t h a t t h e effect of t h e soluble salts could be observed. I n t h e first series we used waters containing q u a n tities of CaCl? ranging from o (distilled water) t o 1000 p a r t s per million. with differences of I O O p a r t s per million between t h e samples. T h e results showed in a very striking manner a gradation in t h e hardness of t h e beans. T h e sample which h a d been processed with t h e distilled water was very tender a n d would grade “strictly fancy.” Those processed with water containing I O O a n d with 2 0 0 p a r t s per million of CaC12 were h a r d a n d tough a n d t h e criticism would be, “underprocessed.” Beans of this character are often found on t h e market a n d are graded as “standards.” T h e remaining samples, processed with water containing from 300 t o 1000 p a r t s per million of CaCl?, were extremely h a r d a n d practically unmerchantable. T h e sample processed with 1000 p a r t s per million of CaC1: was almost as h a r d as t h e uncooked beans. These differences were so marked t h a t t h e samples could easily be placed in their proper order b y one who did not know t h e quantities of CaC12 used. T h e experiment was repeated several times with t h e same results.
