HEAT OF REACTION OF H.M.WEIR’ AND G. L. EATON2 The Atlantic Refining Company, Philadelphia, Pa.
An experimental study, made in 1931, of the heat of reaction of cracking two different types of virgin gas oil and one refractory recycle stock is reported in part in this paper. A continuous calorimetric method was employed, in which the heat required for the cracking reaction was added in the interior of an isothermal reaction chamber. Somewhat extended ranges of temperature, pressure, and amount of cracking were covered, and several new concepts are reached. The results indicate that temperature is not of prime importance in its effect on the heat of reaction when weight
T
HE petroleum cracking capacity of refineries in the United States in August, 1933, has been reported as slightly more than 2 million barrels per day (as recalculated by Egloff and Levinson, 1,to include both raw and rerun stocks). The investments in existing and discarded cracking equipment are probably of the order of a billion dollars. Larger and more complicated cracking plants are now under construction, and in all quarters there is evident the effort to build them on the basis of rational design rather than to rely on the cut-and-try method. I n view of these facts the dearth of studies on the heat of cracking reactions is surprising, and it is believed that this paper will help to bridge a gap which has existed in the literature. The commercial cracking operation, as applied for the production of gasoline, involves a large and undetermined number of simultaneous and consecutive reactions in which both decomposition and polymerization occur. The chemistry of these operations is so complex that it is doubtful if they will ever be completely described in terms of the separate reactions. However, interest centers in the net result. In this paper the term “heat of the cracking reaction” refers to the net heat effect of the many simultaneous and consecutive reactions which occur. Leslie and Potthoff (a) earlier attempted to measure the heat of reaction of cracking, but the static method they employed gave results whose value is open to question in calculations involving industrial equipment. Furthermore, as these authors themselves clearly pointed out, the accuracy of their determinations is problematical since small experimental errors were present in magnified proportions in their final results. The method employed in this work for the determinations of the heat of the cracking reaction consisted in continuously and rapidly heating the charge stock to a previously selected temperature. The heated hydrocarbon stream was then passed through an isoCI thermal reaction chamber equipped so that 3 the chosen temperature c o u l d b e maintained s constant by the addition of measured quantities of heat to the reactants. After a period of time which could be determined relatively by the rate of flow and the previously adjusted volume of the chamber, the reaction products were reduced to atmosp h e r i c pressure and temperature. Determinations were made 1 Present address, Americsn Express Company, 3 Unter den Linden, Berlin, Germany. * Present address, Gulf 011 Corporation, Pittsburgh, Pa.
of the weight, volume, and composition of the charge stock, the material being introduced to the reaction chamber and the products taken from the chamber. The knowledge thus gained of the net results of the reactions occurring in the reaction chamber, the time required for these changes to take place, and the rate of heat input necessary to maintain the selected temperature in the chamber permitted the calculation of the over-all isothermal heat effects of cracking.
Apparatus and Procedure
The apparatus consisted essentially of a means for pumping a measured quantity of oil through a preheating section, where the oil was brought to the cracking temperature; an isothermal reaction chamber, in which the major portion of the cracking took place; a means for measuring the heat necessary to hold the oil a t constant temperature in the reaction chamber; and apparatus for condensing products, s e p a r a t i n g gas and liquid, and measuring them. Figure 1 shows the general features of the equipment : Oil was measured in charge tank A and withdrawn c o n t i n u o us 1y by a H i l l s - M c C a n n a plunger pump, B, which could be set for rates intermediate between 3 and 16 gallons per hour. It was then condvoted to preheating furnace E where it passed throu h C, a 30-foot length of 17,inch extra heavy pipe size KAnS seamless steel t u b i n g . The furnace was heated by eighteen G Io - b & r heating elem e n t s , D (E/* X 12 inches), connected two in series across 110 volts d. c., s u p p l i e d b y a 40-horsepower m o t o r FIQURE 1. ARRANQEEMENT OF APPARATUS 346
CRACKING PETROLEUM of gas and naphtha produced is taken as the measure of the reaction. I t appears that pressure and depth of cracking are of far greater significance. When attention is focused on the molecular bonds broken, and the heat of reaction is expressed as B. t . u. per pound mole of new material produced, the pressure factor drops out, leaving only charge stock and depth of cracking as important variables. The application of the experimental results to plant data has led to considerable confidence in their general utility for design purposes, heat balances on operating units, etc.
by the thermocouple in the outlet pipe extending to the same distance from the end of the pipe as did the inlet thermocou le. In no case was a correction to the heat of reaction calculate$ to account for the always small temperature change in the oil entering and leaving the chamber. Relief valve K was screwed to the outlet pipe, and the outlet from this vaIve was directly connected to cooler M (Figure 1). The relief valve contained two passages, each having its own spindle closure so that in case one passage coked the other could be brought into use. The end of each spindle was chisel shaped so that a turn on the stem served to scour the passage free of coke. The Glo-bar well was integral with the head of the bomb. In it were set four Glo-bar heating elements, two in series across 110 volts a. c. Uniform pressure was brought to bear on each Glo-bar unit by means of a yoke and saddle arrangement, which was acted on by rod C (Figure 2) screwed through metal shell D. The electrical circuit was properly insulated from the reaction chamber. Figure 3 is a photograph of the assembled reaction chamber. The chamber itself was 17 inches in diameter and 24 inches high. Inlet and outlet pipes were 1-inch double extra heavy pipe size tubing. In order to withstand pressure under the high temperatures which it was desired to use, the bomb was fabricated of 18-8 chrome-nickel steel. Outside walls were ll/a inches thick. The chamber was thus amply safe for operation at 200 pounds per square inch at 1350" F., or 1200 pounds per square inch at 1000" F. Figure 3 shows clearly the opening into the Glo-bar well.
generator set. The temperature of the oil leaving the furnace could be controlled within 2' F. by control of resistances in the field of the generator, which changed the power input to the heating elements. Oil temperatures would react within 15 seconds to an adjustment of the power. The temperature of the oil leaving the furnace was measured by a pencil-type iron-constantan thermocouple set in steel block F a t the entrance to transfer line G. The reaction chamber J was placed as close to the furnace as possible so that the transfer line could be short. To maintain the oil a t a constant temperature, this line was wound with resistance elements not shown in the drawing) controlled by rheostats. Oil entere the reaction chamber through line H , in which was laced a 6/18 x 13 inch pencil-type iron-constantan thermocoup?e. After passing through the reaction chamber, the oil was released at valve K to atmospheric pressure and cooled immediately in double pipe exchanger M to a temperature where no further cracking could take place. Separation of liquid and gas took place in receivers N in which the synthetic crude was measured. Liquid samples were withdrawn from the running line at P . Gas was passed through mist removers Q, packed with steel wool. Liquids removed from the gas were withdrawn from Q at eriodic intervals. g a s was in most cases measured in meter R of 600 cubic feet per hour capacity, which had been calibrated and found to read correctly within *3 per cent. De ending on the rate of gas production, orifice meter S or gas holser T could be used in place of the gas meter. Gas samples were taken at outlet V in cubicfoot conta,iners. They were obtained by withdrawing calcium chloride solution from the container in portions allocated over the run period.
Nich ro me He a f ing KE/ernenfs
flc
d
te-filled 3-in. Pipe E
Reaction Chamber Assembly Fraom 2. REACTION CHAMBER ASSEMBLY
The heat of reaction was determined by holding the reaction chamber under isothermal conditions and supplying a measured quantity of heat to the interior of the chamber to hold the oil vapors at constant temperature. Figure 2 details the essentials of this apparatus:
The chamber was supported by E (Figure 2 ) which was itself thermally insulated from the bomb by several layers of asbestos paper in the top flange. The outer heating elements, G, were supported by iron shell D made of '/a-inch metal which was heavy enough to maintain relatively uniform temperatures over its surface. This shell was in two sections; one was raised up over the bomb from below and supported by a pin through E, and the other was laid on the top of the bomb as a bonnet. The space of approximately 2 inches between the bomb and shell was filled with powdered asbestos. There were eight thermocouples, F, attached to the outer surface of the bomb in different positions, and opposite each one of these was a thermocouple on the shell. The intention in each run was to regulate the heat in the outside resistance elements, G, so as to maintain the shell at the same temperature as the bomb.
Oil entered through line H,in which its temperature was measured as just described. It then passed down into chamber space J and under Glo-bar well A , up the other side, and into outlet . Vapors were revented from by-passing the Glo-bar well PGBpartition (not slown in the drawing) which fitted snugly against the sides of the well on each side. Six one-inch fins were welded to the sides of the well from the bottom extending to about one inch below the inlet and outlet pipes. These were for the purpose of increasing the rate of heat transfer to the vapors undergoing cracking. Outlet oil temperatures were measured 347
INDUSTRIAL AND ENGINEERING CHEMISTRY
348
VOL. 29. NO. 3
Under these conditions, with no temperature differential. the heat flow between the bomb and its surroundinctsshould be zero. Surrounaing the outer heating elements were light metal sheik eontainine maenesia insulating boards; and-around these in turn was placed a second layer of insulation. When assembled the insulation was free of sny slight cracks or crevices through which heat dissipation could occur. The outside heating elements were in four different circuits which could be independently controlled. Earlyin the experimentalwork it was found necessarv to enclose thermocouples F' in thin copper t,ubing to prevent their deterioration when in o o n t a c t with the insulating material. The Glo-bar heating elements inside the reaction chamber were powemd by 440- to 110-volt, 10-kw. transformer in the sew ondarv circuit of which were the
but the chamber itself wrs risi n g steadily in temperature, thus undoubtedly accounting for much of the balance. T h e conclusion that the chamber was not sensitive to substantial temperature drops across the insulation is justified. It should be noted that in the oil runs the At was seldom more than 2" F. In addition, the heat effects in cracking were large in comparison to those noted in the steam runs. The experiments were made on three different charge stocks, the characteristics of which am given in Table 11. The virgin gas oils from East Texas Crude and from Barbers Hill Crude received the most attention, though a few determinations were made with refractory recycle gas oil from a commercial higli-temperature cracking brated. The &ccurac this unit. The range of experiinstrument w m judgeBto be el mental variables was: temper cent. The power input to perature, 930" to 1250' F.; the Glo-bar units was controlled by viriation of the volta e to the pressure, 0 to 750 pounds per primary coil of the trans?ormer. PIGURE3. RE.GTIONCH.AMBER square inch gage; relative reacPreanures in t h e r e a c t i o n tion time. 12 to 330 seconds. chamber were measured by a All experiments were carried out with tiie same equipment nressure E ~ E + ?a t the relief valve and another at the transfer line hiock, F ( ~ 7 g uI). l~ so that the resnlts are beiieved directly comprahle. Prehester outlet, reaction chamber inlet, and reaction chamber One unavoidable drawback exists in the coiitinuoi~scalorioutlet temperatures were recorded on a four-point Lee& & metric method adopted for this work in that some decompoNorthmp recording potentiometer; this instrument iv.y&scheeked sition of the charge stock occurs in bringing it to the cracking at the start and finish of each run against a standard portable potentiometer. Insulatios thermocouple temperatures were temperature desired. Although the preheater employed was taken by a sideen-point Leeds & Northrup recorder. All designed to reduce this preliminary decomposition to a minithermocouples were repeatedly calibrated by comparison wit,h an mum, a correction to the total cracking had to he made to esaccurate standard.
of
Heat Losses from Chamber To determine the heat losses from the chamber a series of runs was made using superlieated steam at temperature of 1000" to l05O0 F. The temperature differences normally read on the outside and inside of the lagging were purposely exaggerated by manipulation of the proper heating elements. Readings of steam temperature change from inlet to outlet of the reaction chamber were translated to heat quantities exchanged under these unusual temperature dfiermces. Table I reports four of these runs. In the first case the insulation was held at a slightly higher level than the bomb. The temperature of the steam did not change. In the second and third cases the insulation was cooler and a small drop in the temperature of the steam was noted, I n the fourth run a substantial drop across the insulation was maintained, and the internal heating elements were supplied with a minimum amount of energy. The rise in steam temperature accounted for part of the heat input, OF HEATLOSSE~ Faox TABLE I. DETERMINATION
THE
REAC-
TION C K A M B E H
Ruq
Steam
Hest
Durstion Charaed Input Hr. Lb./N?. U . I . u./hF. 21 0 21 7 0 0 8 19 2 1Y 1300
Temp.. tern^. Drop Change ~n from Bomb to Stsam Insulatloo F. F. 0 5 (rise) 0 (drop) -17 14 (drop) - 5 +38 30 (drop)
Hont Loss from
steam E . I . u./hr.
0
170 46
340 (pain)
FIGURE 4. HEATOF REACTION "8. D E ~ ~OF I I CRACKING FOR BARBERB HILLGAYOIL
MARCH, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
349
timate the transformation takTABLE11. INSPECTIONS OF CHARGE STOCKS ing place in the chamber alone. This correction was, in general, Gas Oil Barbers Recycle East Gas Oil Barbers Recycle -East TexasHill Texas Hill less than 10 per cent of the Gravity, A. P. I. 33.5 15.1 35.9 Av. mol. wt. 189 172" 220 total reaction and was directly Fractional distn. of A. S. T. M. distn.. F.: charge stocks, F.: measured in a series of tests Over 390 400 468 Over 163 310 194 148b using the preheater alone. It 1 1 410 416 504 327 400 419 215b 3 3 514 424 430 414 b 247 388 482 should be borne in mind, how5 5 431 440 518 408 436 493 203b 10 443 10 526 450 424 446 ever, that in these data the 284b 505 20 455 20 534 468 446 465 526 3006 measured total energy i n p u t 30 461 30 541 476 462 475 304b 540 40 467 40 547 490 471 484 308b 645 was applied to t h e c h a r g e 50 473 50 552 501 554 478 493 309b 60 478 512 60 557 stock after a small amount of 313b 486 510 683 70 484 539 70 563 572 493 526 320 a d e c om po s i t i o n had taken 80 492 80 568 571 604 556 683 328b 90 90 503 624 580 640 527 ... 345: place. 95 95 516 700 ... 700 589 ... 3691 ... 524 600 . . . ... 474" In the present state of the Recovery, yo 97 95 98 Bottoms, % 9:i 4.0 19.5 0 art it is impossible to define Loss % 0.3 1.0 0.5 1.4 Naphtha, %: accurately the true composi50% at 284' F. 1.1 0.7 1.6 410 F. end tion of such liquid hydrocarbon point 5.2 2.8 a Calculated. 0.8 mixtures as gas oil, gasoline, 385' F. end b Distilled at 10 mm. Hg absolute pressure. point 2.8 1.8 Distillation of 5 . 4 0 / , bottoms at 10 mm. 0.7 or tar. The gases produced in these exDeriments were anal y z e d Gy fractionation in a standard Podbielniak column, but unfortunately these data weight per cent of Barbers Hill gas oil which emerged from cannot be included in this paper, although interesting relathe chamber as gas and gasoline. If these data were taken tions were established. by themselves, there would be no justification for the lines Seldom does a single definition of a gasoline meet all needs drawn through data taken a t 50, 100, and 760 pounds per for purposes of calculation and, although with one exception square inch pressure. However, in view of the results obgraphs are based on gasoline with a 410" F. end point, yield tained with East Texas gas oil discussed later, i t appears that data are given in the tables for gasolines with a 410" F. end these lines have some justification. point, with a 385" F. end point, and with 50 per cent over The point indicating the result at 150 pounds per square a t 284' F. The gasoline was not actually stabilized, but inch and 1250"F. which is below the zero ordinate is especially estimaterr based on the laboratory fractional analyses of both interesting. I t s location indicates that the reaction was exogaseous and liquid products from each run are believed to thermic. The exact position of the ordinate below the zero line have yieIded as accurate results as if small-scale stabilization is fictitious, however, since the apparatus was not equipped had been attempted. As stated above, gases were analyzed for measured cooling of the reaction. It is interesting to for individual components by standard Podbielniak prodetail the behavior of the system under exothermic conditions. cedure, while all liquid samples were carefully fractionated The experimental run was made by first adjusting the temin a laboratory packed column which was properly insulated perature of the flowing stream of hydrocarbons t o 1200O F. and in which sufficient reflux for good fractionation was proIt was then intended to raise the pressure from substantially vided. ;In addition, synthetic crudes were partially distilled atmospheric to 40 pounds per square inch. After some 4 hours in the Pcdbielniak column to obtain the quantity of normally of steady temperature operation, the pressure was slowly gaseous hydrocarbons they contained. The latter samples raised to the intended level. The temperature of the outlet were obtained in pressure containers to eliminate the possicouple immediately began to increase a t a rate which could not bility of weathering off dissolved gases. be compensated for by reducing, and finally by eliminating I n Table I11 are presented the more important items of the power input to the reaction chamber heater. All of the some of the data and calculations referring to the heat of coils which served to overcome radiation from the chamber r e a c t i o n for East Texas were then cut out, but only after the shell had dropped to gas oil. Detailed discussion TOP some 1050" F. did the reaction chamber outlet oil temperaRECYCLE GAS OIL of methods of calculation ture begin to subside from the approximate 1300' F. which NAPHTHA J O X B eea- F. and experimental technic it had attained, despite the efforts described. The plotted are included in the extenpoint for 1250" F. and 150 pounds per square inch pressure, sive notes w h i c h s h o u l d therefore, is properly placed only in so far as its location inmake i t self-explanatory. dicates an exothermic reaction. The temperature and presFor the sake of brevity, sure noted are averages of the extremely variable conditions tabulations of data obtained encountered during the period described and must be taken as on the less extensively incrude approximations. vestigated Barbers Hill and Figure 5 shows the few data obtained with recycle gas oil as recycle gas oils have been charging stock. The order of the heat of reaction with 10 omitted. H o w e v e r , t h e per cent gasoline plus gas emerging from the reaction chamber more interesting results are was about the same as with the virgin Barbers Hill gas oil. presented in graphical Conditions for an exothermic reaction were also attained in form . this case, although the average amount of gasoline plus gae was only about 36 per cent as compared to the figure of some Discussion of Data 60 per cent for the Barbers Hill gas oil. The general beF i g u r e 4 r e l a t e s the havior of the system during the operation in this case of exoheat input per pound of thermicity was much like that already described. gas plus gasoline (410' F. The most complete heat of reaction data were obtained with FIQURE5. HEATOF REACe n d p o i n t ) formed in the The results TION us. DEPTH OF CRACKING the virgin East Texas gas oil as charge stock. r e a c t i o ri chamber to the FOR RECYCLE GASOIL are presented in Figure 6, in which the abscissa and ordinates, ~~
O
C
INDUSTRIAL AND ENGINEERING CHEMISTRY
350
VOL. 29, NO. 3
*
TABLE 111. DATAON HEATOF REACTION FOR EAST TEXAS GABOIL R u n No. Temp., O F.l Pressure, Ibs./sq. in. gage2 Reaction time, 5ec.a (see 88) Run duration hr.4 Reaction chakber vol cu. in.6 Corhhargerate, gal./g;. at 60 a F.6 Cor. dharge rate, lb./hr.? Temp., O F.: Charges Prbhbater outlet9 R ddtion chamber inletlo R aqtion chamber outlet11 Se aratorll Insulation: Reaction chamber head ' (av. of 3)1' Tdp bonnet (av. of 3118 Rehction ahamber body (av. of 5)lS Lower bonnet (av. of 5)" Av. A t into reaction chamber14 Running yields, wt. %: Gas16
nthetic crude16 P oke and 10ss17 Cor. yields, wt. %:
Gas" Motor stock: 5 0 7 at 284O F 19 E n 8 point 410; F . 2 0 End point 385O F.11 Coke22 Lb hr qntering reaction chamber: Motor atocka' Lbdhr. made in reaction chamber: -rims
+
P238
P208
P207
P209
110 d 3(:
155 "(191
75 (13121'
165 (13fJ
260' (13Fi
650 6.73 47.4
650 10.25 72.2
650 14.05 98.8
1460 3.48 24.5
1460 6.61 46.5
60 928 931 930 65
60 930 929 931 68
928 930 932 69
60
78 929 93 1 930 72
939 939
942 943
958 956
927 927 0
920 921 +1
2.0 98.3 -0.3
P2JO
P236
360 (1342
610 (13A :
(119j
(1:32
(1:92
(2201
(2252
1460 10.04 70.7
1466 13.98 98.3
650 10.05 70.7
656 12.83 90.3
650 12.5 88.0
660 9.27 65.2
650 6.29 44.3
656 6.15 43.3
75 930 931 930 73
76 930 931 930 80
75 931 930 931 72
60 929 929 93 1 64
64 931 930 930 63
66 930 930 930 70
930 930 932 64
71 76 944 (92O-k) 931 930 929 930 62 75
915 916
921 923
921 918
940 941
979 979
937 936
956 943
966 962
924 922
915 907
925 926 0
903 903
+1
901 903 +2
892 895
903 906 +2
923 923 0
898 903 +3
908 917 0
915 921 +2
906 908
+1
908 905 -4
1.5 98.1 0.4
2.9 97.2 -0.1
5.7 94.3 0
6.3 93.6 0.1
5.8 94.3 -0.1
5.6 94.4
6.3 93.3 0.4
8.1 91.7 0.2
8.6 90.1 1.3
9.7 89.8 0.5
11.9 85.8 2.3
13.6 82.8 3.6
2.4
2.0
3.6
6.9
6.5
5.5
5.8
7.4
8.5
8.5
10.2
13.1
13.9
6.3 6.3 5.5
6.7 6.3 5.4
9.5 8.6 7.7
12.8 11.8 9.6
17.7 15.3 13.7
19.4 16.6 15.2
21.5 18.9 16.5
25.4 21.8 19.7
...
30.7 26.0 24.0 0.2
29.0 25.0 22.5 0.1
33.6 28.3 26.2 0.2
39.9 30.8 28.4 0.2
38.0 30.4 28.0 0.2
0.03 0.36
0.02 0.58
0.01 0.92
0.02 0.20
0.06 0.42
0.04 0.74
0.02 1.40
0.06 1.60
0.02 2.45
0.02 2.40
0.07 1.90
0.17 1.89
0.11 1.27
1.10
1.40
3.62
1.43
2.98
3.86
5.70
5.19
7.70
7.49
6.55
5.62
6.89
2.63 2.63 2.24
4.26 3.98 3.32
8.50 7.60 6.72
2.93 2.70 2.16
7.90 6.70 5.96
12.97 10.99 10 * 0 1
19.74 17.21 14.79
16.37 13.80 12.29
25.24 21.02 19.24
23.13 19.56 17.42
19.99 16.56 15.14
15.78 11.77 10.68
15.15
...
%;,ai
~
P243
65 (33
...........................................
%
%tor Stoc * 5 0 7 a t 2 h 0 F.26 En$ pojnt 410° F.27 End point 3 8 5 O F.a Ratio gas/motor atock (end point 410' F.)* Lb. mole leaving reaction chamber/hr."J Lb. mole entering reaction chamber/hr.al Lb. mole made in reaction chamber/hr 82 Heat of k c t i o n , , B. t. uJhr.88 B. t. u./lb. gas motor stock: 5 0 7 at.284O F.84 E n 8 point 410' F.a End point 385O F.36 B. t. u./lb. mole made in reaction ohamberm True reaction time, sec.a Reaation velocity constant Kas
P237
...
...
...
. I .
0
...
P273 P199 P200 P274 P198 ........................................... 740 740 740 740 740
-"
60
11.90 10.86
0.42
0.35
0.46
0.53
0.44
0.35
0.33
0.38
0.37
0.38
0.40
0.48
0.49
0.265
0,396
0.591
0.166
0.326
0.488
0.688
0.527
0.713
0.691
0.546
0.397
0.397
0.216
0.329
0.452
0.112
0.214
0.325
0.457
0.338
0.437
0.426
0.317
0.226
0.212
0.049 1450
0.067 2250
0.139 4770
0.054 1805
0.112 3540
0.163 5660
0.231 8440
0.189
6000
0.276 7900
0.265 9460
0.229 7140
0.171 3880
0.185 4130
389 389 434
398 418 477
397 429 466
414 437 503
328 366 396
336 381 408
332 369 412
278 316 343
240 275 293
309 350 380
269 309 329
181 223 238
196 232 247
22,300 29,800 33,400 34,300 33,300 31,500 34,800 36,500 31,700 28,600 35,700 31,200 22,700 327 333 33 36 37 143 164 196 208 216 194 201 250 0.00253 0,00219 0.00327 0.00130 0.00144 0.00122 0.00130 0.00149 0.00204 0.00189 0.00182 0.00162 0.00166
Attempted temperature for this run. Average pressure in the reaction chamber. reaction time calculated assuming the perfect gas laws to hold anti using the average moles in the reaction chamber obtained from items 80 and 81. The reaction time corrected for deviations from the gaa laws is given in item as. 4 Run duration waa the time in which conditions were uniform and was the period oyer which composite samples were take?. 6 Measured by filling the chamber with water and draining into graduates. 6 The charge rate which was equivalent to item 7. 1 The charge rate whioh was equivalent to the measured products. T o obtain the actually measured charge rate correct for the gain or loss show-n-in item 17. (E. g., run P237: deasured charge rate = 47.4 x = 47.3.) LU" 8 Temperature in charge tank. 9 Thermocouple a t outlet of electric preheater in the vapor stream entering the transfer line to the reaction chamber. 10 13-inch iron = constantan pencil-type couple, 6/16 inch 0. d. 11 16-inch iron = constantan pencil-type couple, 6/10 inch 0. d.; occuoies the same relative position in the reaction chamber outlet as io*does in the inlet pipe. Average temperpture for the ryn. 1% Temperature of gas-liquid mixture entering the synthetic crude separators. Temperatures 18 Average temperatures during the run period. at the top of the chamber are always higher than those a t the bottom, because the internal heating elements were in the head of the chamber. By suit.ably regulating the ener y t o the outer heating elements, the temDerature dlfference between %omb and insulation was maintained at, a minimum as is indicated in item 14. 14 When the drop in temperature is towards the reaction chamber, This figure is the average of eight the sinn is and vice versa for readings each one of which represents the difference in temperature between'the surface of the reaction chamber and the corresponding inner surface of the metal shell surrounding the chamber. 16 Gas measured by. calibrated dry meter at the cracking unit and converted t o a weight basis, using the denslty figure calculated from the fractional gm analysis. Yield based OF measured charge. 16 Synthetic crude measured in calibrated recelver and the based on the measured charge. After measurement, synt&t crude samples were taken for analysis and determination of the percentage naphtha. 1 f
* The
Yz
+,
...
+1
. . .Y ? I U . . . . .
-.
$7 Percentage difference between the total synthetic crude gaa and the measured charge. When products totaled more the charge. a minus sign is shown. 18 The-gas as measured a t the cracking unit was corrected for the naphtha which it contained by subtracting the weight of material heavier than butane shown by the fractional gas analysis. Where no analysis of the gas was available an estimated correction based on other factors was applied. T o ' t h e corrected figure was then added the gas obtained in the fractional distillation of the synthetic crude. Thus, in effect, the gas reported here shpuld include all compounds up to and including butane. The yield is based on total measured products. 19 The motor stock, defined as 50'% over on the A. S. T. M. distillation at 284O F., was obtained by .multiplying the measured svnthetic crude bv the Dercentaze of this material reDorted in the iiboratory. The -deteriination ;of the percentage moaor stock was by fractional distillation of the synthetic crude in a laboratory packed column. To the resulting. figure was added the heavier than butane in the gas, obtained as indicated under 18. 20 This figure was obtained i n a manner exactly similar t o 1) exce t that the percentage of 410° F. end point naphtha in th: syntEetic crude was obtained b.y plotting the fractional distillation of the synthetic crude and readmg tee per cent off a t 410" F. This figure should include all material bolling between butane and 410° F. 21 Similar t o 20, except that the per cent off a t 385O F. on the fractional distillation is w e d for determining the amount of naphtha in the synthetic crude. 2% In certain cases this is an estimated figure because sometimas two or three runs were made between shutdowns to clean coke. 28 These figures were obtained from runs made with the preheater alone in order to determine the amount of cracking taking place up t o the entrance t o the reaction chamber. For every run with the reaction chamber there was a corresponding run made with the preheater. In these runs the preheater outlet was brought up t o run temperature and the transfer-line heating coils were turned on as in the cricking runs. The oil was quenched immediately after passing through the transfer line. Products were measured and anal zed as in runs with the reaction chamber. The figurea include tEe gas dissolved in the synthetic crude. 2:These figures were obtained from the preheater runs as described under item 28. Whether the naphtha was defined 88 50% at 284O F., 410' F. end point, or 385O F. end point, made little
MARCH, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
351 1
TABLE111. DATAON HEATOF REACTION FOR EASTTEXAS GASOIL(Continued) Run No. Temp., F.1 Pressure lbs./sq. in. gage2 Reactio; time sec.8 (see 88) Run duration 'hr.4 Reaction chaAber vol cu. in.8 Cor. chargerate,gal./c;. a t 6 0 O F.8 Cor. charge rate, lb./hr.v Temp., a F.: Charge' Preheater. outlet9 Reaction chamber inlet10 Reaction chamber outlet11 Beparator12 Insulation: Reaction chamber head (av. of 3)la Top bonnet (av. of 3)la Reaction chamber body (av. of 5)18 Lower bonnet (av. of 5)la Av. At into reaction chamber" Running yields, wt. Yo: fin* IS
%%thetic crude's oke and loss17 Cor. yields, wt. %: GEd8 Motor stock: 5 0 7 a t 284' F.j@ E n 8 point 410° F.10 .E n d point 385O F.*l Coke22 Lb. hr. entoring reaction chamber:
. Motor stock24
c/as28
Lb. hr. made in reaction chamber: d a s zs Motor stock: 5 0 7 at 284' F 28 E n 8 p o i n t 410' F.n E n d point 385O F . 2 8 Ratio gas/motor stock (end point 410° F.)" Lb. mole leaving reaction chamber/hr.*o Lb. mole entering reaction chamber/hr.aI Lb. mole made in reaction chamber/hr.a* Heat of reaction, B. t. u./hr.aa B. t. u./lb. gas motor stock: 5 0 7 at 284O F *4 E n 8 point 410; F.*6 E n d point 385O F.8 B. t. u./lb. mole made in reaction chambers) True reaction time, sec.8 Reaction velocity constant Kat
+
P205
P206
P267
.........9411 5 0 . . ...... 411 40 ( 3
P229
P271
2 (25
23 (2:J
75 (264
'2B
146; 6.88 48.4
656 6.60 46.4
650 6.75 47.5
650 10.41 73.3
650 14.07 98.9
1460 3.56 25.06
P240 P239 .............1000 .... . . P241 . . . . . . . i30. .....l.7.0. 75 (2161
P212 ,1000. 90
P232R P233 . .............. 180 295
'IO?]
(106)
6 1460 6.78 47.7
(128; 1460 10.27 72.2
1460 13.96 98.2
1460 6.74 47.4
6.66
46.8
1466 3.60 25.3
69 950 953 951 78
74 949 951 950 72
60 951 950 950 60
75 999 1001 1000 74
76 1000 999 1000 66
50 1005 1001 1000 57
65 999 998 1000 63
60 1000 999 1000 64
50 1001 999 1001 63
71 1000 999 1000 58
60 1001 1000 999 63
1010 1000 1001 69
950 949
948 948
949 951
IO16 1015
1007
1006
1002 1001
1033 1033
1049 1047
1065 1064
1000 1000
1007 1007
1014 1019
934 935 0
933 933 0
935 935
994 996
985 984
988 987
999 999 0
1000 1002
-1
0
1000 1001 0
970 971 0
967 968 0
969 980 +8
2.3 97.3 0.4
3.8 96.2 0
3.4 96.6 0
10.8 89.2 0
7.9 91.9 0.2
9.1 91.0 -0.1
10.3 89.7 0
19.5 81.3 -0.8
19.1 81.5 -0.6
20.8 79.1 0.1
2.5
3.9
4.1
6.4
7.0
11.5
8.3
9.3
10.1
18.7
17.7
18.5
6.0 4.3 4.0
8.6 8.2 7.2
9.3 7.9 7.1
10.8 9.9 8.3
11.7 11.2 9.5
20.8 16.7 15.3
14.2 13.2 11.7
16.9 14.5 13.4
17.7 15.4 13.9
29.6 23.5 21.5
33.2 26.7 26.0
...
37.2 30.1 27.9 0.2
0.02 0.78
0.04 0.38
0.04 0.38
0.03 0.20
0.06 0.40
0.14 0.54
0.13 0.52
0.14 0.91
0.09 1.22
0.12 0.35
0.21 0.88
0.24 2.17
...
...
1460
P211
+1
...
-1
+1
6.4 94.0 -0.4
...
6.6 94.6 -1.2
...
...
...
...
...
...
60
2.46
1.83
1.88
1.58
3.32
5.20
3.81
6.65
9.86
4.56
8.22
13.10
5.08 3.46 3.11
3.69 3.50 3.03
3.95 3.30 2.96
2.54 2.31 1.91
5.27 5.01 4.19
9.12 7.20 6.54
6.22 5.76 5.04
11.48 9.73 8.90
16.28 13.98 12.51
7.06 5.54 5.04
14.93 11.85 11.05
24.69 19.52 17.99
0.71
0.52
0.57
0.68
0.66
0.72
0.66
0.68
0.71
0.82
0.69
0.67
0.545
0.293
0.291
0.178
0.344
0.388
0.357
0.566
0.790
0.259
0.485
0.756
0.447
0.216
0.214
0.116
0.221
0.216
0.220
0.340
0.458
0.118
0.228
0.355
0.098 3475
0.077 2650
0.077 2470
0.062 2230
0.123 4000
0.172 5660
0.137 4370
0.226 6900
0.332 10,300
0.141 3950
0.257 6680
0.401 9170
461
480 497 546
424 477 510
542 574 639
466 480 533
396 456 482
435 457 494
381 422 444
394 432 460
340 391 412
293 339 353
243 281 295
587 024
35,400 34,500 32,100 35,800 32,600 33,000 31,800 30,500 31,000 28,100 25,900 22,900 29 31 20 113 118 129 23 45 46 22 27 27 0.00270 0.00268 0.00260 0.00769 0.00710 0.01170 0.00788 0.00832 0.00938 0.00468 0.00478 0.00492
(Table I11 concluded on next page.) difference in this figure, so t h a t the same one was used for three different kinds of naphtha. No correction was made for the product heavier than butane i n the gas since it was such a small quantity. I n most cases the cracking in the preheater amounted to only 5-10% of the total cracking so t h a t small errors in these figures were not significant. 25 Obtained by subtracting item from the lb./hr. equivalent t o item 18, using the corrected charge rate as the basis. 28 Obtained by subtracting item 24 from item 19 as in item 26. 27 Subtract item 24 from item 20 as in item 26. 28 Subtract item 2 4 from item 2 1 as in item 25. 29 Obtained by dividing item 25 by 27. 80 Calculated from the fractional gas anal ses and from molecular weight determinations on the synthetic cru&. 81 Same as item 80, except that data from the preheater runs were used. 82 Obtained by subtracting item 8 1 from item 80. 8.8 Average rate of heat input t o the Glo-bar heating elements inside the reaction chamber. It was measured by a calibrated watt-hour meter and is judged to be accurate to *I%. 84 Obtained by dividing item 88 by the sum of items 25 and 28. 86 Item 88 divided by t h e sum of items 26 and 27. 86 Item divided by the sum of items 25 and 28, 87 Obtained by dividing item $1 by 82. 88 The correction, p, t o the perfect gas laws was first obtained for the gas oil (mol. wt. = 220) and na htha (mol. wt. = 115) from the ENQ.CHEM..23.887 (1931)l. article by Corm Lewis. and Weber I&=.
it was possible to extrapolate the vapor pressure t o the critical tem erature and read off t h e corresponding critical pressure. This
metgod has been found to give fair prediction of critical pressures. Since the determination of true vapor volumes is only a n approximation a constant molecular weight of 115 was taken for the naphtha, an'd a constant molecular weight of 220 for the material boiling above 410' F. The average value of p for the material leaving the chamber was then determined from items 18 and 20 and assuming the
balance t o be recycle. The gas was assumed not t o deviate from the gas laws appreciably. The average value for p of the vapors entering the chamber was obtained i n a similar manner from items 28 and 24, I n this manner a n average molecular volume for the vapors in the chamber was calculated. This was compared with the molecular volume calculated using the same molecular weights and with the assumption that the gas laws do hold. The reaction time from item a was then multiplied by the ratio of these two molecular volumes to give the reaction time of item 8s. This general method of obtaining true reaction times was described by Keith Ward, and Rubin (Proc. Am. Petrqleum Inst., 1933, Sect. 111, 54): Althou h these corrected reaction times are undoubtedly nearer the truth t f a n the reaction times calcu!ated with the gas lays, it should be remembered t h a t they are still only approximations due to meager fundamental data and may be in error up t o possibly 100%. This is es ecially true in the high pressure-low temperature region (e. g 930' F 740 lb./sq. in.). $he e q u d i o n for a first order reaction is: *@
where
a
-
a
-
l
n
a = Kt
4 - x
initial quantity of reacting material X = amount of reacting material left after t sec.
I n these calculations a was assumed to be the material boiling X ) the material above 410° F. entering the reaction chamber (a boiling above 410O.F. leaving the reaction chaAber, and t the reaction time as listed in item 88. The figures of item 19 are the values of K solved for in the above equation. Any error in the Calculated reaction time would cause B proportional error in these figures. 10 I n run P272 the heat input was arbitrarily fined at halt t h a t reqmred t o hold the outlet temperature at the same level as the inlet temperature as i n run P271. I n run P271D the heat input WBS double this requirement. I n calculating the heat of cracking it was thus necessary t o correct for the sensible heat involved in the temerature drop through the chamber in one case and rise in the other. &he figure in brackets repfesents the calculated quantity of heat, which may be assigned t o cracking. Heats of reaction listed i n items * ( I ab and 88 for these runs are calculated from the corrected heat input and are seen t o be closely comparable.
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
352
VOL. 29, NO. 3
TABLE 111. DATAON HEATOF REACTION FOR EASTTEXAS GABOIL (Concluded) Run No; Temp., F.1 Pressure lbs./sq. in. gage2 ReaotioA time sec.8 (see 88) Run duration 'hr.4 Reaotion ohaAber vol cu. in., Cor. charge rate, gal.&. a t 60° F.6 Cor. oharge rate, lbJhr.7 Temp., F.: Chargee Preheater outlet9 Reaction chamber inletlo Resction chamber outlet11 Separator's Insulation: Reaation chamber head (av. of 3)" T o p bonnet (av. of 3)** Reaction chamber body (av. of 5)La Lower bonnet (av. of 5112 Av. At into reaction chamber" Running yields, wt. Yo: Gas16
S nthetic crude16 oke and 1055'7 Cor. yields, wt. %: Gas" Motor stock: 5 0 7 a t 284' F.10 E n 8 point 410° F . 2 0 End point 3 8 5 O F.21 Coke22 Lb hr entering reaotion chamber:
cy
dW,a Motor stock.2'
Lb hr made in reaction chamber:
&z;
Motor stock: 5 0 7 a t 284' F 20 En$ point 410' F.27 End point 385' F.28 Ratio gas/motor stock (end point 410° F.)*9 Lb. mole leaving reaction chamb&/hr.ao Lb. mole entering reaction chamber/hr.a' Lb. mole made in reaction chamber/hr.a2 Heat of reaction B. t. u./hr.aa B. t. u./lb. ga; motor stock: 5 0 7 at 284' F . 8 4 Encfp oint 410° F." End point 385O F." B. t. u./lb. mole made in reaction ohambern True reaction time, 8ec.s Reaction velocity constant K89
:
+
P203
P231
40
(1s
9 (25
1460 13.85 97.5
1460 3.67 25.8
1460 6.86 48.36
650 6.30 44.32
650 6.74 47.42
650 10.3 72.6
1460 6.68 47.1
1460 6.58 46.32
1460 13.81 97.2
1460 6.64 46.7
1460 650 6.68 6.55 47.0 46.15
P271 P271D 1000 1031 75 75 (26) (21) 7 10 650 650 6.60 6.60 46.4 46.45
73 1074 1076 1075 77
68 1075 1074 1074 59
65 1075 1072 1075 65
50 1103 1075 1076 61
63 1075 1074 1075 64
67 1090 1075 1075 67
75 1075 1076 1075 71
1077 1076 1075 59
55
69 1106 1106 1105 76
75 1108 1105 1105 72
50 1115 1105 1105 54
63 1005 1000 968 61
50 1005 1001 1000 57
55 1004 1000 1063 55
1119 1118
1081 1081
1093 1094
1094 1099
1131 1131
1135 1134
1094 1091
1088 1088
1156 1155
1130 1126
1123 1123
968 968
1002 1001
1063 1063
1046 1048 +1
1048 1048 0
1042 1040
1040 1039
1071 1071 0
1057 1057
1073 1074
1065 1069
1062 1064
-1
+1
+1
+1
961 961 0
988 987 -1
1022 1023
0
1039 1040 0
1036 1035
$1
17.8 82.1 0.1
19.1 81.6 -0.7
21.3 79.8 -1.1
25.0 74.3 -0.7
23.0 77.4 -0.4
23.0 77.6 -0.6
23.1 77.1 -0.2
20.3 78.6
24.0 75.8 0.2
32.4 67.6 0
28.7 71.1 0.2
7.3 92.3 0.4
10.8 89.2 0
19.1 80.5 0.4
16.8
18.1
19.5
23.6
21.5
20.5
21.8
19.7
22.3
30.0
26.5
8.4
11.5
19.1
21.3 17.6 15.8
23.2 19.2 17.6
24.7 21.7 18.3
30.4 23.4 21.7
27.5 21.8 20.2
28.9 22.0 21.1
26.0 21.1 19.6
27.1 21.1 19.5
23.9 20.2 18.6
27.8 22.2 20.7
31.5 24.1 22.3
15.4 13.6 12.2
20.8 16.7 15.3
28.0 21.8 20.4
0.20 1.27
0.16 0.26
0.34 0.75
1.02 2.51
0.60 1.54
0.88 3.89
0.38 0.82
0.39 0.85
0.36 1.83
0.75 1.32
0.85 1.49
0.14 0.54
0.14 0.54
0.14 0.54
8.74
21.35
13.24
11.61
3.73
6.20
8.76
11.71 21.38 8.92 17.76 8 . 2 0 16.26
11.66 9.06 8.33
13.31 9.83 9.01
6.58 5.74 5.09
9.12 7.20 6.54
12.45 9.57 8.94
...
P230
.
33 ' (23
0
'
P234 P242 P244 P204 P266 P201 1075 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ' '85 85 140 40 40 40 (2:J (23 (2;: (1;;
...
...
...
'
...
...
...
16.14
4.52
9.11
9.42
9.58
13.99
9.88
19.45 15.87 14.12
5.73 4.70 4.29
11.21 9.75 8.59
10.96 7.84 7.09
11.47 8.80 8.05
17.05 12.07 11.40
11.42 9.13 8.42
1.1
P202 P265 110 .... 40 (2g (2;;
P272 985 75 (28&
...
. . . . . . . . . . . . . . .
+1
...
1.02
0.96
0.93
1.20
1.09
1.16
1.08
0.98
1.20
1.46
1.18
0.65
0.72
0.92
0.991
0.274
0.531
0.532
0.543
0.807
0.548
0.527
1.149
0.656
0.617
0.345
0.388
0.496
0.454
0.120
0.230
0.248
0.242
0.391
0.227
0.223
0.462
0.237
0.242
0.214
0.216
0.216
0.537
0,154
0.301
0.284
0.301
0.416
0.321
0.304
0.687
0.419
0.375
16,420
4550
8610
6710
7530
8390
9090
461 513 543
444 494 517
423 456 486
329 389 406
358 410 427
270 322 331
427 478 497
30,600 29,600 14.3 22.2 0.0284 0.0203
28,600 23.4 0,0217
23,600 21.6 0.0255
25,000 22.6 0.0230
20,200 22.2 0.0219
28,300 26.4 0.0203
8000 19,900 10,970 391 453 472
466 509 529
440 492 508
0.131 0.172 0.280 (3940)4o (8500)4Q 9190 2740 5660 10,960 369 428 446
382 416 447
395 456 482
401 463 480
26,300 29,000 26,200 24,500 30,200 33,000 27.4 12.2 22.3 23.3 29 27 0.0182 0,0435 0.0310 0,0280 0.01170
30,300 22
...
...
(Footnotes are printed on the two preceding pages.)
are the same as in Figures 4 and 5. A substantial change in the heat of reaction with pressure was encountered. All attempts to make a correlation between heat of cracking and temperature were fruitless, as were the attempts to correlate reaction time and heat of cracking. Although the results in some cases appear t o deviate considerably from the average lines which
have been drawn, it is felt that the average and maximum deviation figures indicate reasonable correlation, considering the difficultnature of the operation. The data have been expressed on the basis of heat input in B. t. U. per pound mole us. the ratio of moles of products per mole of charge; Figures 7 and 8 present these results.
i
